Journal articles: 'Ultra high strenght steels'

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Kah, Paul, Markku Pirinen, Raimo Suoranta, and Jukka Martikainen. "Welding of Ultra High Strength Steels." Advanced Materials Research 849 (November 2013): 357–65. http://dx.doi.org/10.4028/www.scientific.net/amr.849.357.

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The ongoing need to reduce the weight of products while increasing strength has resulted in new generation steel manufacturing using special heat treatments to produce High Strength Steels (HSS) and Ultra High Strength Steels (UHSS) with up to 1700 MPa tensile strength. The high strength level of these steels makes it possible to produce structures with a considerable weight and cost reduction, and such steels have been adopted in the automotive industry and for mobile heavy equipment. Welding of UHSS is, however, not without its complications and welding processes for these steels need careful attention. For instance, their high susceptibility to cracking and Heat Affected Zone (HAZ) softening are risks that need to be borne in mind when choosing welding parameters. This research work discusses the difficulties and challenges of successful welding of UHSS. Common welding methods used in welding of UHSS are briefly reviewed to gain a better understanding of the effects of different welding parameters and methods. The paper finds that UHSS can be satisfactorily welded with laser welding, electron beam welding, resistance welding, and conventional arc welding methods, but the quality of the weld is dependent on appropriate control of several parameters and variables of the welding processes.

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GARCIA-MATEO, C., and F. G. CABALLERO. "Ultra-high-strength Bainitic Steels." ISIJ International 45, no. 11 (2005): 1736–40. http://dx.doi.org/10.2355/isijinternational.45.1736.

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Dahmen, Martin, Benjamin Gerhards, and Stefan Lindner. "Alloyed Ultra-High Strength Steels." Laser Technik Journal 13, no. 2 (April 2016): 48–52. http://dx.doi.org/10.1002/latj.201600009.

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Arola, Anna Maija, Kari Mäntyjärvi, and Jussi A. Karjalainen. "FEM - Modeling of Bendability of Ultra-High Strength Steel." Key Engineering Materials 549 (April 2013): 333–39. http://dx.doi.org/10.4028/www.scientific.net/kem.549.333.

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Ultra-high strength steels have been widely used in different industrial applications. It is necessary to understand the behavior of these materials in common forming processes such as air bending. It is known that the bendability of ultra-high strength steels is lower than other high-strength steels but what are yet to be discovered are the parameters that define the limits of bendability of these steels. The aim of this study was to investigate the factors affecting the bendability of ultra-high strength steel using optical strain measurements and FEM-modeling of the bending process. By using the true stress-strain relation measured by optical strain measuring system the bendability of ultra-high-strength steel was modeled fairly accurately. As a result, it was noted that the strain distribution at the bend of a steel possessing better uniform strain was more widely distributed and there were no highly localized strains. On the other hand as the failure occurred the strains were considerably smaller than the true failure strain of the material in uniaxial tension. As a conclusion it was stated that the ability to withstand the localization of deformation might describe the bendability of ultra-high-strength steel better than the values of the uniform or true failure strain in uniaxial tension test.

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Väisänen, Anu, Kari Mäntyjärvi, and Jussi A. Karjalainen. "Bendability of Ultra-High-Strength Steel." Key Engineering Materials 410-411 (March 2009): 611–20. http://dx.doi.org/10.4028/www.scientific.net/kem.410-411.611.

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Utilisation of ultra-high-strength (UHS) steels is rapidly spreading from the automotive industry into many other application areas. It is necessary to know how these materials behave in common production processes such as air bending. The bendability of UHS steels is much lower compared to normal and high-strength construction steels. In this work, experimental tests were carried out using complex phase (CP) bainitic-martensitic UHS steels (YS/TS 960/1000 and 1100/1250) and S650MC HS steel in order to inspect material bendability and possible problems in the bending process. Mechanical and geometrical damages were registered and classified. The bending method used was air bending and press brake bending with an elastic lower die. The FE analysis was used to understand the stress state at different points in the material and build-up of failure. As UHS steels cannot stand large local strains, a large radius must be used in air bending. The results show that even when a large radius is used in air bending, the strain is not evenly distributed; there is a clear high strain area in the middle of the bend. It was also possible to simulate the other phenomena occurring in experimental tests, such as losing contact with the punch and ‘nut-like’ geometry, using FE analysis. Experimental test results also show that by using an elastic lower die, it is possible to avoid unwanted phenomena and obtain an almost 50% smaller punch radius, but the required force is 50% bigger than that required in air bending.

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Chen, Meng Yang, Bo Ming Hwuang, and Jer Ren Yang. "Microstructural Characterizations of Ultra-High Strength Steel Bars." Advanced Materials Research 168-170 (December 2010): 796–804. http://dx.doi.org/10.4028/www.scientific.net/amr.168-170.796.

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Steel bars used in high-rising building were developed by the addition of V and Nb in medium carbon steels. In this study, two steel bars with different diameters (16 mm and 36 mm) were analyzed via optical and transmission electron microscopy (OM and TEM)., the microstructures of the steels studuied consist of ferrite and pearlite the same as those of the conventional steel bars, but they possess higher yield strengths (over 685 MPa) in combination of considerable elongations (above 10%). The results of transmission electron microscopy reveals that the copious nano-sized (about 20 nm) carbides were interphase-precipitated in ferrite and that the inter-lamellar spacings of pearlite were extra fine, about with a scale of 100 nm. It has been estimated that the small carbides and fine pearlite provide yield strengths, approximately 300 MPa and 800 MPa, respectively. In addition, the volume fraction of ferrite was up to 40%, which offered sufficient soft phase to experience external stress. The results of tensile tests for the steels studied demonstrat that the amount of strain can be up to 1.4% as a yield stress is reached, and the apparent yield point and plateau are present in the stress-strain curves.

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Kwon, Ohjoon, Kyoo Young Lee, Gyo Sung Kim, and Kwang Geun Chin. "New Trends in Advanced High Strength Steel Developments for Automotive Application." Materials Science Forum 638-642 (January 2010): 136–41. http://dx.doi.org/10.4028/www.scientific.net/msf.638-642.136.

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The body design with light weight and enhanced safety is a key issue in the car industry. Corresponding to this trend, POSCO is developing various automotive steel products with advanced performance. Conventional advanced high strength steels such as DP and TRIP steels are now expanding their application since the steels exhibit higher strength and ductility than those of conventional solution and precipitation strengthened high strength steels. Efforts have been made to enhance the mechanical performance of these steels such as ductility, hole expansion ratio, deep drawability, etc. Current research is focused on development of extra- and ultra-AHSS. Extra-AHSS are designed to utilize nano-scale retained austenite embedded in fine bainite and martensite. Ultra-AHSS are designed to have austenite as the major phase, and the ductility is enhanced primarily by continuous strain hardening generated during forming. These steels including extra- and ultra-AHSS are believed to be the next generation automotive steels which will replace the existing high strength steels due to their extremely high strength and ductility combinations.

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Hietala, Mikko, Antti Järvenpää, Markku Keskitalo, and Kari Mäntyjärvi. "Bending Strength of Laser-Welded Sandwich Steel Panels of Ultra-High Strength Steel." Key Engineering Materials 786 (October 2018): 286–92. http://dx.doi.org/10.4028/www.scientific.net/kem.786.286.

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The study was performed to investigate the bending resistance of laser-welded sandwich panels (Vf-core). The main aim of the study was to determine the effect of the tensile strength on bending strength of the panel structures. Panels were manufactured using an ultra-high strength (UHS) and low strength (LS) steels with yield strengths of 1200 and 200 MPa, respectively. Secondly, the bending strength of the panel structures was compared with the conventional sheet steels to estimate the possibilities for weight reduction. Results showed that the UHS steel panels had significantly higher bending strength than panels of the LS steel. The bending strength in the weakest loading direction of the UHS panel was approximately four times higher than the one of LS steel panel. The panels made with UHS steel faceplates and LS steel cores had better bending strength than LS steel panels. In comparison to UHS sheet steel, 30% weight saving is estimated by using the geometry optimized UHS steel panel.

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Martinez, M. A., J. Abenojar, J. M. Mota, and R. Calabrés. "Ultra High Carbon Steels Obtained by Powder Metallurgy." Materials Science Forum 530-531 (November 2006): 328–33. http://dx.doi.org/10.4028/www.scientific.net/msf.530-531.328.

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The objective of the present work is to study the manufacturing process of steels with high carbon content (1.5–2.1wt%) obtained by powder metallurgy. The reference material was the Damascus steel, which was employed to manufacture swords named after it and has been widely known due to its very good mechanical properties. The main reasons of the success of this product are: the high carbon content of the initial steel and the thermomechanical treatment (forge and quenching) that ancient iron forgers kept secretly during centuries. Different carbon contents (2 to3 wt%) were added to the same Fe powder matrix (ASC 300), and compacted and sintered steels are heat laminated (750°C) with a reduction of 20%. For 2% carbon content, the result is a steel with yield strength of 450 MPa, Young’s Modulus of 14.3 GPa and hardness of 109 HV(30).

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Hlebová, Stanislava, and Ladislav Pešek. "Toughness of Ultra High Strength Steel Sheets ." Materials Science Forum 782 (April 2014): 57–60. http://dx.doi.org/10.4028/www.scientific.net/msf.782.57.

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Currently only few methods exist for thin steel sheet testing, especially based on fracture mechanics concept. Charpy impact test is one of the most used method for testing notch toughness and fracture behaviors because of the simplicity and the other advantages [. This article deals with toughness testing of automotive ultra high strength steel sheets (UHSS). Several standard types of toughness test that generate data for specific loading conditions and/or component design approaches exist. Two definition of toughness will be discussed: i) Charpy V-notch toughness, method includes joining of thin steel sheets to one compact unit and ii) material (tensile) toughness [. Two steels were used, DP1000 and 1400M of 1,8 mm thickness and two joining techniques: bonding with adhesives and joining with holders. Effect of material, joining technology, structural adhesives, and number of joined plates on the toughness values was quantified at the room temperature. Toughness of steels by the tensile test was added for comparison. Fracture surface was observed using scanning electron microscope analysis.

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Määttä, Antti, Kari Mäntyjärvi, and Jussi A. Karjalainen. "Incremental Bending of Ultra-High-Strength Steels." Key Engineering Materials 473 (March 2011): 53–60. http://dx.doi.org/10.4028/www.scientific.net/kem.473.53.

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Utilisation of ultra-high-strength steels (UHS) has increased, particularly in the automotive industry. By using these materials vehicle structures can be lightened. However, one of the problems of UHS is weak formability. Materials fracture easily with small bending radii and the minimum bending radii are rather large. In this study, the tested materials were complex phase (CP) bainitic-martensitic UHS steels (YS/TS 960/1000 and 1100/1250). The steels were incrementally bent with a press brake in the rolling direction and perpendicular to it, and the final bending angle was 90 degrees. The incremental bending angles were 150°, 130°, 110° and 90°. The punch was unloaded after every incremental bending step. The test materials were bent with different bending radii. The aim was to find the minimum bending radius which produces an acceptable bend. Every incremental bend was compared with a bending performed in the traditional manner. The aim of this study was to examine how well the results of incremental bending compare to roll forming. In addition, clarification studies of when the bend started to fracture were made. It is well known that steels are more efficiently bent by roll forming compared with traditional bending. The results presented in this study demonstrate that incremental bending does not produce better results than traditional bending. Nevertheless, it has been shown that the examined steels can be bent incrementally against manufacturer’s recommendations.

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Liu, Zhi Yong, Xin Lai He, Shan Wu Yang, and Qiang Xue Zhou. "Ultra-Low Carbon High Strength Weathering Steels." Advanced Materials Research 317-319 (August 2011): 236–39. http://dx.doi.org/10.4028/www.scientific.net/amr.317-319.236.

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The ultra-low carbon high strength weathering steel was trial manufactured. By Optical micrographs observation, scanning electronic microscope (SEM), transmission electronic microscope (TEM), accelerated corrosion test, the corrosion resistant performance of test steel and CortenB steel were studied. The results showed that yield strength, tensile strength, elongation and -40 °C impact energy of test steel reached 510MPa, 600MPa, 22% and 115J, respectively. Corrosion resistance of test steel was superior to that of CortenB. The microstructure of ferrite and bainite, quickly forming adhesive dense rust layers to improve the corrosion resistance of test steel.

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Hazra, S. K., P. Efthymiadis, A. Alamoudi, R. L. V. Kumar, B. Shollock, and R. Dashwood. "The Bendability of Ultra High strength Steels." Journal of Physics: Conference Series 734 (August 2016): 032097. http://dx.doi.org/10.1088/1742-6596/734/3/032097.

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Restrepo Garcés, G., P. Verrier, O. Glaise, and S. Boidin. "Laser welding of ultra high strength steels." Revue de Métallurgie 100, no. 10 (October 2003): 1015–22. http://dx.doi.org/10.1051/metal:2003119.

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Amraei, Mohsen, Lingjia Zong, Antti Ahola, and Timo Björk. "Bonded CFRP to high strength steels." Rakenteiden Mekaniikka 52, no. 4 (December 31, 2019): 222–35. http://dx.doi.org/10.23998/rm.76267.

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Research on the bond performance of CFRP-strengthened steel have been done for the past years, but it has mainly focused on lower grades of steel. The performance of the bond between ultra-high modulus (UHM) CFRP and high/ultra-high strength steel (HSS/UHSS) is investigated in this paper. A series of experiments have been conducted, with single/double side-strengthened (SSS/DSS) HSS/UHSS with CFRP laminates using Araldite adhesive. It was found that strengthening up to the ultimate strength of the DSS specimens is feasible. However, debonding happens at the ultimate strength of SSS specimens.

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Järvenpää, Antti, Pentti Karjalainen, and Kari Mäntyjärvi. "Passive Laser Assisted Bending of Ultra-High Strength Steels." Advanced Materials Research 418-420 (December 2011): 1542–47. http://dx.doi.org/10.4028/www.scientific.net/amr.418-420.1542.

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Formability of ultra-high strength steels is poor causing problems in bending and stretch forming. The target of this work was to improve the formability of ultra-high strength steel sheets by controlled local laser heat treatments. Three steel grades, a bainitic-martensitic 4 mm DQ960 and two martensitic WR500 with 6 mm and 10 mm thicknesses were heated by controlled thermal cycles using a 4 kW Yb:Yag –laser, followed by self-cooling. Sheets with the thicknesses of 4 and 6 mm were treated on one side only by heating up to the austenitizing temperature. The 10 mm thick WR500 sheet was heat treated separately on the both surfaces by heating to a lower temperature range to produce a shallow tempered layers. The tensile and bendability tests as well as hardness measurements indicated that laser heat treatment can be used to highly improve the bendability locally without significant strength losses.

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Garrison, Warren M. "Cobalt and the Toughness of Steel." Materials Science Forum 710 (January 2012): 3–10. http://dx.doi.org/10.4028/www.scientific.net/msf.710.3.

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In developing compositions for new ultra-high strength steels it is important to understand the effects of alloying additions on the microstructure, strength and fracture resistance. Cobalt has been widely used in the development of high toughness ultra-high strength steels and the effects of cobalt on the strength of steels has been studied extensively but there is remarkably little known about how cobalt influences toughness. In this article are reviewed the effects of cobalt on the toughness of steel. The literature suggests that cobalt in solid solution will act to raise the ductile-to-brittle transition temperature but that it can act to increase the upper-shelf toughness of steel.

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Ghosh, A., Brajendra Mishra, and Subrata Chatterjee. "Development of Low Carbon Microalloyed Ultra High Strength Steels." Materials Science Forum 500-501 (November 2005): 551–58. http://dx.doi.org/10.4028/www.scientific.net/msf.500-501.551.

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In the present study HSLA steels of varying carbon concentrations, alloyed with Mn, Ni, Cr, Mo, Cu and micro-alloyed with Nb and Ti were subjected to different finish rolling temperatures from 850oC to 750oC in steps of 50oC. The microstructure of the steel predominantly shows martensite. Fine twins, strain induced precipitates in the martensite lath along with e-Cu precipitates are observed in the microstructure. With an increase in carbon content the strength value increases from 1200MPa UTS to 1700MPa UTS with a negligible reduction in elongation. Impact toughness values of 20-26 joules at room temperature and −40oC were obtained in sub-size samples.

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Homberg, Werner, and Tim Rostek. "Thermo-Mechanical Hardening of Ultra High-Strength Steels." Key Engineering Materials 549 (April 2013): 133–40. http://dx.doi.org/10.4028/www.scientific.net/kem.549.133.

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nnovative ultra high-strength steels have excellent mechanical properties which commonly relate to the materials martensitic microstructure. As thermal heat treatments are state-of-the-art for obtaining the desired microstructure, innovative thermo-mechanical treatments are likely to give rise to even better material qualities. This article highlights various aspects of innovative thermo-mechanical hardening strategies for the processing of ultra high-strength steels, involving both press hardening and friction spinning operations.

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Sugimoto, Koh Ichi, Junji Tsuruta, and Sung Moo Song. "Fatigue Strength of Formable Ultra High-Strength TRIP-Aided Steels with Bainitic Ferrite Matrix." Key Engineering Materials 345-346 (August 2007): 247–50. http://dx.doi.org/10.4028/www.scientific.net/kem.345-346.247.

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Formable ultra high-strength TRIP-aided steel with bainitic ferrite matrix structure (TBF steel) contributes to a drastic weight reduction and an improvement of crash safety of automobile. In this study, fatigue strength of 0.2%C-1.5%Si-1.5%Mn TBF steels was investigated. High fatigue limit was achieved in TBF steels austempered at 400-450oC, containing a large amount of stable retained austenite. The fatigue limit was linearly related with mobile dislocation density, as well as TRIP effect of retained austenite. When compared to conventional martensitic steel, the TBF steel exhibited lower notch-sensitivity or higher notched fatigue performance. Complex additions of 0.5%Al, 0.05%Nb and 0.2%Mo considerably improved the notched fatigue performance, as well as the smooth fatigue strength. This was associated with the stabilized retained austenite and refined microstructure which suppress fatigue crack initiation and/or propagation.

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Hietala, Mikko, Markku Keskitalo, and Antti Järvenpää. "The Comparison between Mechanical Properties of Laser-Welded Ultra-High-Strength Austenitic and Martensitic Steels." Key Engineering Materials 841 (May 2020): 132–37. http://dx.doi.org/10.4028/www.scientific.net/kem.841.132.

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The paper investigates experimentally the usability of ultra-high-strength stainless steel and abrasion resistant steel in laser-welded sandwich structures. The fatigue and shear strength of laser joints were investigated using lap joints that were welded using two very different energy inputs. Also the effect of multiple weld tracks was investigated. The properties of separate laser welds were characterized by hardness testing and optical microscopy. Results of the hardness measurements showed that there was softened area at heat-affected-zone and weld metal of the ultra-high-strength stainless steel welds. AR steels weld metal was harder than base metal and there was softened zone in heat-affected-zone of the weld. The shear strength of tested single weld joints of the ultra-high-strength stainless steel was higher compared abrasion resistant steel single weld joints, but stronger joint can be made with multiple weld seams for abrasion resistant steel. Fatigue strength of investigated ultra-high-strength stainless steel lap joint was lower than fatigue strength of abrasion resistant steel lap joint in the low-cycle regime, but there was no practical difference in fatigue limit (10e7 cycles).

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NAGAI, Kotobu, and Saburo MATSUOKA. "R & D on High Strength in steels"Ultra-Steels Project"." Journal of the Society of Materials Science, Japan 48, no. 7 (1999): 723–32. http://dx.doi.org/10.2472/jsms.48.723.

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Esterl, R., M. Sonnleitner, M. Stadler, G. Wölger, and R. Schnitzer. "Microstructural Characterization of Ultra-High Strength Martensitic Steels." Practical Metallography 55, no. 4 (April 16, 2018): 203–22. http://dx.doi.org/10.3139/147.110491.

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Chen, Xinping, Haoming Jiang, Zhenxiang Cui, Changwei Lian, and Chao Lu. "Hole Expansion Characteristics of Ultra High Strength Steels." Procedia Engineering 81 (2014): 718–23. http://dx.doi.org/10.1016/j.proeng.2014.10.066.

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Afkhami, Shahriar, Timo Björk, and Jari Larkiola. "Weldability of cold-formed high strength and ultra-high strength steels." Journal of Constructional Steel Research 158 (July 2019): 86–98. http://dx.doi.org/10.1016/j.jcsr.2019.03.017.

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Li, Qing Shan, Mei Zhang, Chao Bin Huang, Ru Yi Wu, Xue Zhao, Yong Zhong, and Lin Li. "Hot Ductility Behavior of 800MPa Ultra High Strength Niobium Containing Steels." Advanced Materials Research 690-693 (May 2013): 227–32. http://dx.doi.org/10.4028/www.scientific.net/amr.690-693.227.

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The hot ductility behavior of 800MPa ultra high strength niobium containing steels has been investigated with Gleeble3500 hot simulator. Tensile test was carried out at 650°C1300°C at a constant true strain rate of 0.001 s1. Experimental results showed that steel A has quite well ductility, and the brittle zone is narrow. Due to pro-eutectoid ferrite film formation along the prior austenite grain boundary at 650°C-750°C, samples showed a loss of hot ductility, and the fracture morphology of the specimens was brittle intercrystalline fracture, indicating the third brittle zone of the steel. However, the third brittle zone can be avoided during continuous casting, if the temperature of straightening could be kept over 800°C.

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Suikkanen, Pasi, and J. I. Kömi. "Microstructure, Properties and Design of Direct Quenched Structural Steels." Materials Science Forum 783-786 (May 2014): 246–51. http://dx.doi.org/10.4028/www.scientific.net/msf.783-786.246.

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Direct quenching (DQ) is one of the latest process routes in production of ultra-high strength, high performance steels and Ruukki one of the pioneering companies in the utilization of direct quenching. Ruukki has applied direct quenching for the production of ultra-high-strength structural steels in the form of hot-rolled strip and plate. The paper briefly summarizes the physical metallurgy fundamental of direct steels and shows some selected examples of the microstructures and properties of steels produced by direct quenching. In addition, a brief review on the usability properties and design rules of ultra-high strength structural steels is made.

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Adachi, Yoshitaka, and Kaneaki Tsuzaki. "Ultra Rapid Softening of High Strength Structural Steels by Thermomechanical Treatment." Materials Science Forum 539-543 (March 2007): 4807–12. http://dx.doi.org/10.4028/www.scientific.net/msf.539-543.4807.

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This study aims to shorten the softening treatment period as possible in high strength structural steels. The steel used is SCM440 steel. As an initial microstructure, martensite, bainite, pearlite and complicated microstructure consisting of ultrafine polygonal, martensite and equiaxed cementite were extensively examined to understand their softening process on aging at 973K. These initial microstructures were prepared by heat or thermomechanical treatment. Their initial Vickers hardness (Hv(10kgf)) were 634, 281, 219 and 238, respectively. It is noteworthy that within five minutes on aging hardness of the complicated microstructure reached lower than Hv200, while it took more than several hours for other initial microstructures. A quantitative evaluation of microstructures appears to help in understanding the mechanism of the softening kinetics.

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Caballero, Francisca García, J. Chao, J. Cornide, Carlos García-Mateo, Maria Jesus Santofimia, and Carlos Capdevila. "Toughness of Advanced High Strength Bainitic Steels." Materials Science Forum 638-642 (January 2010): 118–23. http://dx.doi.org/10.4028/www.scientific.net/msf.638-642.118.

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Carbide free bainite has achieved the highest strength and toughness combinations to date for bainitic steels in as-rolled conditions. By alloying designing and with the help of phase transformation theory, it was possible to improve simultaneously the strength and toughness because of the ultra-fine grain size of the bainitic ferrite plates. Ultimate tensile strengths ranging from 1600 MPa to 1800 MPa were achieved while keeping a total elongation higher than 10 %. Their toughness at room temperature matches tempered martensitic steels, known to be the best-in-class regarding this property. However, it has been observed that the presence of coalesced bainite leads to a dramatic deterioration in toughness in these novel high strength bainitic steels.

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Arlazarov, Artem, Jean-Christophe Hell, Carla Oberbillig, and Frédéric Kegel. "High Strength High Ductility Low Alloyed Steel." Materials Science Forum 941 (December 2018): 100–105. http://dx.doi.org/10.4028/www.scientific.net/msf.941.100.

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Annealed Martensite Matrix (AMM) concept was studied on two steel grades with low alloyed base composition of Fe-C-Mn-Si and two levels of Nb. Conditions for the thermal treatments were selected based on the experimental dilatometry tests and thermodynamic calculations. Annealing trials with short austempering holding were performed in the laboratory salt pots. Mechanical properties of heat treated steels have been investigated by tensile tests. Associated microstructures have been analyzed using Scanning Electron Microscopy as well as magnetization saturation method for measuring retained austenite fractions. Excellent strength-ductility balance was obtained due to the ultra-fine multiphase structure and high amount of stable retained austenite.

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Määttä, Antti, Antti Järvenpää, Matias Jaskari, Kari Mäntyjärvi, and Jussi A. Karjalainen. "Influence of Predetermined Surface Defect to the Bendability of Ultra-High-Strength Steel." Key Engineering Materials 504-506 (February 2012): 901–6. http://dx.doi.org/10.4028/www.scientific.net/kem.504-506.901.

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The use of ultra-high-strength steels (UHS) has become more and more popular within last decade. Higher strength levels provide lighter and more robust steel structures, but UHS-steels are also more sensitive to surface defects (e.g. scratches). Practically this means that the critical crack size decreases when the strength increases. The aim of the study was to study if the formula of critical crack size is valid on forming processes of UHS-steels. Surface cracks with different depths were created by scratching the surface of the sheet by machining center. Effect of the scratch depth was determined by bending the specimens to 90 degrees. Bents were then visually compared and classified by the minimum achieved bending radius. Test materials used were direct quenched (DQ) bainitic-martensitic UHS steels (YS/TS 960/1000 and 1100/1250). Results from the bending tests were compared to the calculated values given by the formula of critical crack size.

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Hwang, Byoung Chul, Chang Gil Lee, and Sung Hak Lee. "Microstructure and Mechanical Properties of Ultra-High Strength Steel Plates with High Deformability." Materials Science Forum 638-642 (January 2010): 3266–71. http://dx.doi.org/10.4028/www.scientific.net/msf.638-642.3266.

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High deformability has been considered as a critical factor of ultra-high strength steel plates subjected to compressive, tensile, and bending deformation induced by large ground movements. In this paper, various dual phase microstructures consisting of soft ferrite and strong low-temperature transformation phases without deformation in the (austenite + ferrite) two-phase temperature region after controlled rolling were introduced and then the mechanical properties were discussed with emphasis on deformability such as yield ratio and uniform elongation. Ultra-high strength steel plates fabricated by a modified thermo-mechanical control process showed lower yield ratio of under 0.75 and higher uniform elongation of 5% as a minimum, as compared to commercial API X100 and X120 grade pipeline steels, without much sacrifice of Charpy impact properties because of an appropriate formation of soft ferrite and strong low-temperature transformation phases.

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Lu, Qi, Wei Xu, and Sybrand van der Zwaag. "A Material Genomic Design of Advanced High Performance, Non-Corroding Steels for Ambient and High Temperature Applications." Materials Science Forum 783-786 (May 2014): 1201–6. http://dx.doi.org/10.4028/www.scientific.net/msf.783-786.1201.

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This work presents an artificial intelligence based design of a series of novel advanced high performance steels for ambient and high temperature applications, following the principle of the materials genome initiative, using an integrated thermodynamics/kinetics based model in combination with a genetic algorithm optimization routine. Novel steel compositions and associated key heat treatment parameters are designed both for applications at the room temperature (ultra-high strength maraging stainless steel) and at high temperatures (ferritic, martensitic and austenitic creep resistant steels). The strength of existing high end alloys of aforementioned four types are calculated according to the corresponding design criteria. The model validation studies suggest that the newly designed alloys have great potential in outperforming existing grades.

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Haferkamp, H., O. Meier, and K. Harley. "Laser Beam Welding of New High Strength Steels for Auto Body Construction." Key Engineering Materials 344 (July 2007): 723–30. http://dx.doi.org/10.4028/www.scientific.net/kem.344.723.

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With the regard to the development of modern car bodies the focus lies on low production costs, environmental sustainability and high security standards. In order to meet these requirements the weight of modern car bodies has to be reduced consistently. Amongst other things, this becomes possible by the use of new high and ultra high strength steels. These materials are characterised by their high strength, good ductility and a high absorption capacity. In addition they have a lower density in comparison to other steels. TRIP and TWIP steel belong to these high and ultra high strength steels as well as iron-manganese steel. The development of new materials also puts new demands on the joining technologies used for producing semi finished products and parts of car bodies. Due to its high flexibility, its good automation and the minor influence on the work piece, laser beam welding is an established procedure in the automotive series production. The high cooling rates in combination with a carbon equivalent of the new materials which is usually higher then 0.4% lead to a martensitic solidification of the weld seam. Martensite is characterized by its low ductility and thus affects the forming capability as well as the absorption capacity of the welded parts. In order to avoid this effect a new process has been developed within the scope of the collaborative research program 362 (SFB 362, 1993-2005) at the Laser Zentrum Hannover. Using that process the weld seam structure is inductively annealed directly after the welding process. Experiments with high strength steel like TRIP700 and H320LA have shown that the tempering leads to an increase of ductility. The process is suitable for butt joints and overlap joints and is to be transferred into industrial usage within the scope of the project “Laser Beam Welding of Car Body Parts Made of High and Ultra High Strength Steel”. Based on the results obtained in the SFB 362 continuous investigations will be made in order to qualify the process for boron alloyed steel and iron-manganese steel.

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Gao, Yu Kui, Xue Ren Wu, Feng Lu, Mei Yao, and Qingxian Yan. "Influence of Shot Peening on Fatigue Properties in Ultra-High Strength Steels." Materials Science Forum 490-491 (July 2005): 448–53. http://dx.doi.org/10.4028/www.scientific.net/msf.490-491.448.

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The characteristics of compressive residual stress fields induced by shot peening in 40CrNi2Si2MoVA, 16Co14Ni10Cr2Mo, 30CrMnSiNi2A and 0Cr13Ni8Mo2Al ultra-high strength steels, which are used widely in aeronautical industry were investigated, and the change of surface integrity including surface residual stress, surface roughness as well as its effects on fatigue properties were investigated. The results show that the fatigue limits of ultra-high strength steels can be increased by shot peening because the surface integrity can be ameliorated by shot peening, and that for a given steel there is a appropriate peening intensity under which the fatigue property of this steel is optimum. Finally, a judgement for the optimization condition of shot peening process is proposed based on a theory of micro-meso processes of fatigue crack initiation and experimental results. The technique should be considered to be optimum, if the fatigue crack source of shot peened specimen has been moved to the internal matrix metal region beneath the hardened layer; and its apparent fatigue limit has been improved and got to a value, which is near to that predicted according to the concept of surface/internal fatigue limit.

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Cherubini, Antonello, Linda Bacchi, Serena Corsinovi, Marco Beghini, and Renzo Valentini. "Hydrogen Embrittlement in Advanced High Strength Steels and Ultra High Strength Steels: a new investigation approach." Procedia Structural Integrity 13 (2018): 753–62. http://dx.doi.org/10.1016/j.prostr.2018.12.125.

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37

Jiang, Han, Yanlin He, Li Lin, Rendong Liu, Yu Zhang, Weisen Zheng, and Lin Li. "Microstructures and Properties of Auto-Tempering Ultra-High Strength Automotive Steel under Different Thermal-Processing Conditions." Metals 11, no. 7 (July 14, 2021): 1121. http://dx.doi.org/10.3390/met11071121.

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Automotive steels with ultra-high strength and low alloy content under different heating and cooling processes were investigated. It was shown that those processes exhibited a great influence on the performance of the investigated steels due to the different auto-tempering effects. Compared with the steels under water quenching, there was approximately a 70% increase in the strength and elongation of steels under air cooling, in which the martensite was well-tempered. Although the elongation of the steel with a microstructure composed of ferrite, well-tempered martensite and less-tempered martensite could exceed 15%, the hole expansion ratio was still lower because of the undesirable hardness distribution between the hard phases and the soft phases. It followed from the calculation results based on SEM, TEM and XRD analyses, that for the steel under air cooling, the strengthening mechanism was dominated by the solid solution strengthening and the elongation was determined by the auto-tempering of martensite. Experiments and analyses aimed to explore the strengthening and plasticity mechanisms of auto-tempering steels under the special process of flash heating.

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38

Chatterjee, Subrata, S. K. Ghosh, and P. S. Bandyopadhyay. "Thermo-Mechanically Controlled Processed Ultrahigh Strength Steels." Materials Science Forum 783-786 (May 2014): 685–91. http://dx.doi.org/10.4028/www.scientific.net/msf.783-786.685.

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A low-carbon, titanium and niobium (Ti-Nb) bearing and a low-carbon titanium, niobium and copper (Ti-Nb-Cu) bearing ultra high strength steel have been thermo-mechanically processed on a laboratory scale unit. Evolution of microstructure and mechanical properties of the above air cooled steels have been studied at different finish rolling temperatures (FRTs). Microstructural characterization reveals largely a mixture of granular bainite and bainitic ferrite along with the precipitation of microalloying carbide/carbonitride particles and/or Cu-rich precipitates. (Ti-Nb) bearing steel yields higher yield strength (1114-1143 MPa) along with higher tensile strength (1591-1688 MPa) and moderate ductility (12-13%) as compared to (Ti-Nb-Cu) bearing steel having yield strength (934-996 MPa) combined with tensile strength (1434-1464 MPa) and similar ductility (13%) for the selected range of 850-750°C FRT. Due to higher strength-ductility combinations, these present investigated steels can be regarded as the replacement material for ballistic applications as well as other sectors like defense, pipeline, cars, pressure vessels, ships, offshore platforms, aircraft undercarriages and rocket motor casings etc. Key words: Thermo-mechanical controlled processing, ultra high strength steel, microstructure, mechanical properties.

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Tohgo, Keiichiro, Tomoya Ohguma, Yoshinobu Shimamura, and Yoshifumi Ojima. "Influence of Strength Level of Steels on Fatigue Strength and Fracture Morphology of Spot Welded Joints." Key Engineering Materials 462-463 (January 2011): 94–99. http://dx.doi.org/10.4028/www.scientific.net/kem.462-463.94.

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In this paper, fatigue tests and finite element analyses are carried out on spot welded joints of mild steel (270MPa class) and ultra-high strength steel (980MPa class) in order to investigate the influence of strength level of base steels on fatigue strength and fracture morphology of spot welded joints. From the fatigue tests the following results are obtained: (1) Fatigue limit of spot welded joints is almost the same in both steels. (2) Fatigue fracture morphology of spot welded joints depends on the load level in the ultra-high strength steel, but not in the mild steel. From discussion based on the finite element analyses the following results are obtained: (3) The fatigue limit of spot welded joints can be predicted by stress intensity factors for a nugget edge, fracture criterion for a mixed mode crack and threshold value for fatigue crack growth in base steel. (4) Plastic deformation around a nugget in spot welded joints strongly affects the fatigue fracture morphology.

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Zeng, Yan Ping, Hong Mei Fan, Xi Shu Wang, and Xi Shan Xie. "Study on Micro-Mechanism of Crack Initiation and Propagation Induced by Inclusion in Ultra-High Strength Steel." Key Engineering Materials 353-358 (September 2007): 1185–90. http://dx.doi.org/10.4028/www.scientific.net/kem.353-358.1185.

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Specially designed SEM in-situ tensile and fatigue tests have been conducted to trace the entire process of crack initiation and propagation till fracture in an ultra-high strength steel MA250. TiN is a typical inclusion and its average size is in the range of 8~10μm in MA250 steel. The micro-mechanism of the effect of TiN inclusion on crack initiation and propagation at tensile and fatigue tests both have been studied in detail. Experimental results show the harmful effect of TiN on tensile and fatigue properties both. This work is helpful to establish the practical life prediction model for the characteristic inclusion parameters in ultra-high strength steel components. It also enlightens us to eliminate TiN in the further development of ultra-high strength steels.

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Hojo, Tomohiko, Junya Kobayashi, Koh-ichi Sugimoto, Akihiko Nagasaka, and Eiji Akiyama. "Effects of Alloying Elements Addition on Delayed Fracture Properties of Ultra High-Strength TRIP-Aided Martensitic Steels." Metals 10, no. 1 (December 19, 2019): 6. http://dx.doi.org/10.3390/met10010006.

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To develop ultra high-strength cold stamping steels for automobile frame parts, the effects of alloying elements on hydrogen embrittlement properties of ultra high-strength low alloy transformation induced plasticity (TRIP)-aided steels with a martensite matrix (TM steels) were investigated using the four-point bending test and conventional strain rate tensile test (CSRT). Hydrogen embrittlement properties of the TM steels were improved by the alloying addition. Particularly, 1.0 mass% chromium added TM steel indicated excellent hydrogen embrittlement resistance. This effect was attributed to (1) the decrease in the diffusible hydrogen concentration at the uniform and fine prior austenite grain and packet, block, and lath boundaries; (2) the suppression of hydrogen trapping at martensite matrix/cementite interfaces owing to the suppression of precipitation of cementite at the coarse martensite lath matrix; and (3) the suppression of the hydrogen diffusion to the crack initiation sites owing to the high stability of retained austenite because of the existence of retained austenite in a large amount of the martensite–austenite constituent (M–A) phase in the TM steels containing 1.0 mass% chromium.

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42

Hannula, Jaakko, David Porter, Antti Kaijalainen, Mahesh Somani, and Jukka Kömi. "Mechanical Properties of Direct-Quenched Ultra-High-Strength Steel Alloyed with Molybdenum and Niobium." Metals 9, no. 3 (March 19, 2019): 350. http://dx.doi.org/10.3390/met9030350.

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The direct quenching process is an energy- and resource-efficient process for making high-strength structural steels with good toughness, weldability, and bendability. This paper presents the results of an investigation into the effect of molybdenum and niobium on the microstructures and mechanical properties of laboratory rolled and direct-quenched 11 mm thick steel plates containing 0.16 wt.% C. Three of the studied compositions were niobium-free, having molybdenum contents of 0 wt.%, 0.25 wt.%, and 0.5 wt.%. In addition, a composition containing 0.25 wt.% molybdenum and 0.04 wt.% niobium was studied. Prior to direct quenching, finish rolling temperatures (FRTs) of about 800 °C and 900 °C were used to obtain different levels of austenite pancaking. The final direct-quenched microstructures were martensitic and yield strengths varied in the range of 766–1119 MPa. Mo and Nb additions led to a refined martensitic microstructure that resulted in a good combination of strength and toughness. Furthermore, Mo and Nb alloying significantly reduced the amount of strain-induced ferrite in the microstructure at lower FRTs (800 °C). The steel with 0.5 wt.% Mo exhibited a high yield strength of 1119 MPa combined with very low 28 J transition temperature of −95 °C in the as-quenched condition. Improved mechanical properties of Mo and Mo–Nb steels can be attributed to the improved boron protection. Also, the crystallographic texture of the investigated steels showed that Nb and Nb–Mo alloying increased the amount of {112}<131> and {554}<225> texture components. The 0Mo steel also contained the texture components of {110}<110> and {011}<100>, which can be considered to be detrimental for impact toughness properties.

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NAGASAKA, Akihiko, Toshio MURAKAMI, and Katsuhiro NAKABAYASHI. "1116 Burring of Ultra High Strength TRIP Sheet Steels." Proceedings of Conference of Hokuriku-Shinetsu Branch 2010.47 (2010): 419–20. http://dx.doi.org/10.1299/jsmehs.2010.47.419.

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44

Polak, P., and S. Rajec. "Welded joints in thermomechanically treated ultra high strength steels." Welding International 4, no. 1 (January 1990): 58–61. http://dx.doi.org/10.1080/09507119009446697.

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45

Golovashchenko, Sergey F., Alan J. Gillard, Alexander V. Mamutov, John F. Bonnen, and Zejun Tang. "Electrohydraulic trimming of advanced and ultra high strength steels." Journal of Materials Processing Technology 214, no. 4 (April 2014): 1027–43. http://dx.doi.org/10.1016/j.jmatprotec.2013.09.003.

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46

Laitinen, Risto O., David A. Porter, L. Pentti Karjalainen, Pasi Leiviskä, and Jukka Kömi. "Physical Simulation for Evaluating Heat-Affected Zone Toughness of High and Ultra-High Strength Steels." Materials Science Forum 762 (July 2013): 711–16. http://dx.doi.org/10.4028/www.scientific.net/msf.762.711.

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Physical simulation of the most critical sub-zones of the heat-affected zone is a useful tool for the evaluation of the toughness of welded joints in high-strength and ultra-high-strength steels. In two high-strength offshore steels with the yield strength of 500 MPa, the coarse grained, intercritical and intercritically reheated coarse grained zones were simulated using the cooling times from 800 to 500 °C (t8/5) 5 s and 30 s. Impact and CTOD tests as well as microstructural investigations were carried out in order to evaluate the weldability of the steels without the need for expensive welding tests. The test results showed that the intercritically reheated coarse grained zone with the longer cooling time t8/5=30 s was the most critical sub-zone in the HAZ due to the M-A constituents and coarse ferritic-bainitic microstructure. In 6 mm thick ultra-high-strength steel Optim 960 QC, the coarse grained and intercritically reheated coarse grained zones were simulated using the cooling times t8/5 of 5, 10, 15 and 20s and the intercritical zone using the cooling times t8/5 of 5 and 10 s in order to select the suitable heat input for welding. The impact test results from the simulated zones fulfilled the impact energy requirement of 14 J (5x10 mm specimen) at -40 °C for the cooling times, t8/5, from 5 to 15 s, which correspond to the heat input range 0.4-0.7 kJ/mm (for a 6 mm thickness).

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47

Hietala, Mikko, Atef Hamada, Markku Keskitalo, Matias Jaskari, Jani Kumpula, and Antti Järvenpää. "Microstructural Evolution and Tensile Strength of Laser-Welded Butt Joints of Ultra-High Strength Steels: Low and High Alloy Steels." Key Engineering Materials 883 (April 2021): 250–57. http://dx.doi.org/10.4028/www.scientific.net/kem.883.250.

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The present study is focused on joining two ultra-high strength steels plates of 3 mm thickness using laser-welding. Abrasion resistant steel with martensitic structure, tensile strength (Rm) ≥ 2 GPa, and cold-deformed austenitic stainless steel, Rm 1.3 GPa, were used for the dissimilar butt joints. Two different laser energy inputs, 160 and 320 J/mm, were presented during welding. The weld morphology and microstructural evolution of the fusion zone were recorded using optical microscopy and electron back scattering diffraction (EBSD), respectively. The mechanical properties of the dissimilar joints were evaluated by hardness measurements and tensile tests. It was found that fusion zone has undergone a change in morphology and microstructure during welding depending upon the energy input. Analysis of the microstructural evolution in the fusion zone by EBSD examination showed that the presence of a mixture of small austenite grains in a matrix of martensite. The changes in hardness profiles and tensile strength under the experimental parameters were further reported.

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48

Berg, Jörn, and Natalie Stranghöner. "Fatigue behaviour of high frequency hammer peened ultra high strength steels." International Journal of Fatigue 82 (January 2016): 35–48. http://dx.doi.org/10.1016/j.ijfatigue.2015.08.012.

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49

Liu, Yong Ning, Jie Wu Zhu, and Yan Xu. "Microstructure and Mechanical Properties of A 1.4%C Ultra High Carbon Steel." Key Engineering Materials 297-300 (November 2005): 1178–82. http://dx.doi.org/10.4028/www.scientific.net/kem.297-300.1178.

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1.4 %C ultra high carbon steel (UHCS) was prepared in order to study the structure of martensite transformation and mechanical properties. Ultra-fine spherical carbide and ultra-fine austenite grain size were obtained. A great deal of lath martensite was observed after quenching. The phenomenon does not agree with the traditional knowledge that the lath martensite would disappear when carbon content is in excess of 0.8% in austenite. The strength, fatigue properties and fracture toughness have been measured. A good combination of strength, toughness and fatigue properties come from fine and uniform distributed carbide particles and ultra-fine austenite grain size. Fracture strength increases by 48%, yield strength increases by 15% and plasticity keep the same comparing with that of hardened and tempered 40CrNiMo. The carbon content of ultrahigh carbon steels (UHCS) is in the range of 1.0-2.1% [1, 2]. Traditional heat treatments for normal steels will cause the microstructure of UHCS to be coarse and do not produce optimal properties. With controlled rolling and special heat treatment, UHCS can be in ferrite, pearlite, bainnite or martensite structures, which all have different mechanical properties. The yield stress of a 1.8%C, 1.6%Al ferrite UHCS can reach 1500MPa, which is much higher than that of high strength and plain alloy steels [3]. The tensile strength of a 1.25%C-1.5%Cr pearlite UHCS can reach 1810Mpa and its elongation can be 18%. When it is treated into martensite, its compression strength reached to 4690Mpa and compression strain reached to 26% [1, 4], which is comparable to WC-12Co. Such good mechanical properties can be ascribed to the ultra fine grain sizes because of the undissolved carbide particles which resist growth of austenite grain during heating. Another reason could be the lath martensite structures. O.D.Sherby [4] had reported that there was a lot of lath martensite in quenched UHCS. The UHCS was considered not only as tool steels but also as good structure materials. Fracture and fatigue properties are important for structure materials. However, they have rarely been studied. The present paper is going to study the martensite structure and mechanical properties of a prepared 1.4% C UHCS.

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Kutuniva, Kari, Jussi A. Karjalainen, and Kari Mäntyjärvi. "Effect of Convex Sheared Punch Geometry on Cutting Force of Ultra-High-Strength Steel." Key Engineering Materials 504-506 (February 2012): 1359–64. http://dx.doi.org/10.4028/www.scientific.net/kem.504-506.1359.

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Extremely high strength of the ultra-high-strength steels leads to increased load factors on the tooling machines and punching tools. This experimental study examines how much convex punch geometry affects cutting forces when punching ultra-high-strength steels. Tools used in punching tests were four different convex sheared rooftop punches and one conventional flat end punch, to which rooftop punches were compared to. The material in punching tests was ultra-high-strength steel Ruukki Optim 960 QC, with a thickness of 4 mm. The test material in punching tests was sheared with rooftop punches and a flat end punch and occurred cutting forces were measured. The qualities of punched holes were evaluated visually and the roundness measurements were also performed. The results show that the cutting forces of Optim 960 QC can be reduced radically with optimal convex punch geometry. With using 14-degree shear angle of the punch end, the cutting forces reduced up to 57 % compared to forces of the conventional flat end tool. However, largest tested shear angles caused several negative effects on the cutting quality of the holes and therefore they are not suitable in all applications. Punching tests proved that the cutting clearance had no appreciable effect on cutting forces when punching ultra-high-strength steel. Instead there was a noticeable effect on the quality of the punched hole, especially when large shear angles were used.

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Journal articles on the topic 'Ultra high strenght steels'

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