Relevant bibliographies by topics / Low-temperature tempering

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  1. Journal articles
  2. Dissertations / Theses
  3. Book chapters
  4. Conference papers

Academic literature on the topic 'Low-temperature tempering'

Author: Grafiati
Published: 4 June 2021
Last updated: 4 February 2022

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Journal articles on the topic "Low-temperature tempering"

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Peet, Mathew J., Sudarsanam Suresh Babu, Mike K. Miller, and H. K. D. H. Bhadeshia. "Tempering of Low-Temperature Bainite." Metallurgical and Materials Transactions A 48, no. 7 (April 10, 2017): 3410–18. http://dx.doi.org/10.1007/s11661-017-4086-x.

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Ivanov, Yu F., and É. V. Kozlov. "Low-temperature tempering kinetics of hardened steel 38KhN3MFA." Russian Physics Journal 36, no. 2 (February 1993): 132–36. http://dx.doi.org/10.1007/bf00574093.

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Worasaen, Kaweewat, Andreas Stark, Karuna Tuchinda, and Piyada Suwanpinij. "Performance of a Matrix Type High Speed Steel after Deep Cryogenic and Low Tempering Temperature." Materials Science Forum 1016 (January 2021): 1423–29. http://dx.doi.org/10.4028/www.scientific.net/msf.1016.1423.

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A matrix type high speed steel YXR3 designed for a combination of wear resistance and toughness is investigated for its mechanical properties after hardening by deep cryogenic treatment follow by tempering. The deep cryogenic quenching carried out at -200 °C for 36 hours and the single step tempering results in an obvious improvement in wear resistance while balancing the toughness, comparing with the conventional quenching followed by a double tempering treatment. The quantitative image analysis reveals little difference in the MC carbide size distribution between tempering at different temperatures. The synchrotron high energy XRD confirms the MC type carbide with some evolution in its orientation together with tempered martensite approaching the BCC structure at higher temperatures. In contrary to the conventional quenching and tempering, the lowest tempering temperature at 200 °C yields a moderate drop in hardness with increase in surface toughness proportionally while exhibiting exceptional wear resistance. Such thermal cycle can be recommended for the industry both for the practicality and improved tool life.
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Liu, Sheng Xu, Yi Qiang Xiao, Ming Long Kang, Jian Min Zeng, Guo An Wang, Qiu Hong Meng, and Ying Zhang Deng. "Effect of Different Tempering Temperatures on Microstructure and Impact Property of 20CrMnTi Steel." Advanced Materials Research 900 (February 2014): 92–95. http://dx.doi.org/10.4028/www.scientific.net/amr.900.92.

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The effect of different tempering temperatures on microstructure and impact property of 20CrMnTi steel has been studied on Zwick/roell Amsler PKP 450 pendulum machine, SU-8020 scanning electron microscope (SEM) and optical microscope. The results shows that the impact property of 20CrMnTi steel is dramatically improved after high-temperature tempering. However, the minimum value occurs when it was tempered at 350°C because of low-temperature tempering brittlement at this degree. The SEM fracture morphology was typical dimples after high temperature tempering, and the type of fracture was ductile fracture; the type of cleavage characteristic and quasi cleavage characteristic were generated on the fracture morphology at low-temperature and medium-temperature tempering respectively, and the type of fracture was brittle.
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Wang, Ke Lu, Xin Li, and Xian Juan Dong. "Effect of Tempering Temperature on Mechanical Properties and Microstructures of 800MPa Microalloy Low Carbon Bainitic Steel." Advanced Materials Research 893 (February 2014): 406–9. http://dx.doi.org/10.4028/www.scientific.net/amr.893.406.

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The effect of tempering temperature on the microstructures and mechanical properties of a microalloy low carbon bainitic steel was investigated by microscopic analysis and testing of mechanical properties. The results show that the microstructures of the tested steel primarily consists of lath bainite, granular bainite, quasipolygonal ferrite and little acicular ferrite at different tempering temperatures. With the tempering temperature increasing, the proportion of lath bainitie decreases, while the volume of granular bainite and quasipolygonal ferrite increases. At the tempering temperatures of 550-650°C and tempering time of 1 hour, the steel was mostly composed of granular bainite, quasipolygonal ferrite and a little lath bainite, which a good combination of strength and toughness can be obtained.
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Wang, Xue Min, and Hui Zhao. "The Tempering on Microstructure and the Yield-to-Tensile Ratio of High Performance Steels." Advanced Materials Research 535-537 (June 2012): 655–58. http://dx.doi.org/10.4028/www.scientific.net/amr.535-537.655.

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The effects of tempering temperature on the microstructure and mechanical properties of 600MPa grade low carbon bainitic steel were investigated. The cause for the microstructure evolution has been investigated and the best tempering process was chosen to decrease the yield ratio of the steel. The influence of tempering process on the yield-to-tensile ratio of steels has been investigated by the aid of optical microscopy, SEM and XRD. The results show that after the TMCP processing the microstructure of steels mainly consist of lath martensite and bainite. The bainite and martensite have been refined markedly after the relaxation processing, therefore the properties of steels has been improved evidently. In order to decrease the yield-to-tensile ratio the steels underwent high temperature tempering. It has been found that during the tempering with the tempering temperature increased the yield-to-tensile ratio of steels decreased. The XRD and EBSD results show tempering temperature has considerable influence on the yield strength, but the influence on the tensile strength is not considerable. With the increase in tempering temperature, the low temperature toughness of steel can be improved considerably. The yield ratio of the steel was reduced after tempering at 650 °C and higher temperatures due to reversed austenitic phase transformation.
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Liu, E., Feng Lan Wei, and Li Chun Qiu. "Orthogonal Test on Heat Treatment Parameters of Modified Low Chromium White Cast Iron." Advanced Materials Research 399-401 (November 2011): 268–72. http://dx.doi.org/10.4028/www.scientific.net/amr.399-401.268.

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The effect of austenitizing temperature, heating time and tempering temperature on hardness and impact toughness of low chromium white cast iron was studied by orthogonal test. The optical microstructure was used to analyze the reasons of changes on mechanical properties. The results showed that the hardness increases at beginning and then decreases with the increase of each parameter, high impact toughness can be obtained at high tempering temperature and high austenitizing temperature, the descending order of influence on hardness and impact toughness is austenitizing temperature, heating time, tempering temperature.
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Haiko, Oskari, Antti Kaijalainen, Sakari Pallaspuro, Jaakko Hannula, David Porter, Tommi Liimatainen, and Jukka Kömi. "The Effect of Tempering on the Microstructure and Mechanical Properties of a Novel 0.4C Press-Hardening Steel." Applied Sciences 9, no. 20 (October 10, 2019): 4231. http://dx.doi.org/10.3390/app9204231.

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In this paper, the effects of different tempering temperatures on a recently developed ultrahigh-strength steel with 0.4 wt.% carbon content were studied. The steel is designed to be used in press-hardening for different wear applications, which require high surface hardness (650 HV/58 HRC). Hot-rolled steel sheet from a hot strip mill was austenitized, water quenched and subjected to 2-h tempering at different temperatures ranging from 150 °C to 400 °C. Mechanical properties, microstructure, dislocation densities, and fracture surfaces of the steels were characterized. Tensile strength greater than 2200 MPa and hardness above 650 HV/58 HRC were measured for the as-quenched variant. Tempering decreased the tensile strength and hardness, but yield strength increased with low-temperature tempering (150 °C and 200 °C). Charpy-V impact toughness improved with low-temperature tempering, but tempered martensite embrittlement at 300 °C and 400 °C decreased the impact toughness at −40 °C. Dislocation densities as estimated using X-ray diffraction showed a linear decrease with increasing tempering temperature. Retained austenite was present in the water quenched and low-temperature tempered samples, but no retained austenite was found in samples subjected to tempering at 300 °C or higher. The substantial changes in the microstructure of the steels caused by the tempering are discussed.
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Liu, Chen Xi, Ze Sheng Yan, Zhi Zhong Dong, Yong Chang Liu, and Bao Qun Ning. "Effects of Two-Step Tempering Treatment on the Microstructural Formation of T91 Ferritic Steels." Solid State Phenomena 172-174 (June 2011): 875–80. http://dx.doi.org/10.4028/www.scientific.net/ssp.172-174.875.

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As a representative type of high Cr ferritic heat-resistant steels, T91 steels (ASME SA-213 T91/P91) has been recognized as the preferable materials and widely used in high-temperature structural components such as header and main steam pipe in advanced power plants. For the service condition is tempered martensites, its corresponding microstructure and mechanical performance are mainly adjusted by the tempering treatment. After exploring the size and number of MX and M23C6precipitating particles and the width of martensitic lath as a function of tempering temperature, it is recognized that the high tempering temperature leads to an increase of secondary hardening effect, while the low tempering temperature brings a high dislocation density and a small martensitic lath. Hence, a two-step tempering treatment was developed after the traditional normalizing process, in which the T91 steels sample was firstly tempered at a low temperature in order to form some precipitates and then tempered at a high temperature. Those firstly-formed precipitates would pin the dislocations and martensitic laths on the subsequent tempering process, which finally leads to more precipitates, higher dislocation density and smaller martensitic lath width than that obtained from the traditional tempering process.
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Zuo, Long Fei, Li Li Qiu, Bin Hou, Xiao Hua Chen, Ming Wen Chen, and Zi Dong Wang. "Study of Nano-Precipitate in High Strength Low Carbon Steel during Tempering by TEM." Applied Mechanics and Materials 327 (June 2013): 123–27. http://dx.doi.org/10.4028/www.scientific.net/amm.327.123.

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The behavior of nanoprecipitates of 800Mpa grade high strength low carbon steel during tempering has been studied. Transmission electron microscope (TEM), high resolution transmission electron microscopy (HRTEM) and energy dispersive spectrometry (EDS) were used to systematically analyze the morphology of precipitates and their grain orientation with matrix at different tempering temperatures. Experimental results confirm that the composition of these nanometer sized particles in the matrix was compound carbonitrides containing Ti, V, Mo and other elements. The precipitates of the as-received steel are (Nb,Ti)(C,N) at low tempering temperature, while those at high tempering temperature are composite carbides containing a variety of elements such as Mo, V, Ti and Nb. On the other hand, as tempering temperature increases, precipitates in the steel were slowly growing up and roughening according with the typical Oswald ripening mechanism; a sharp orientation relationship exists between precipitates and matrix.
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Dissertations / Theses on the topic "Low-temperature tempering"

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Peet, Mathew James. "Transformation and tempering of low-temperature bainite." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609018.

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Bílková, Lenka. "Nízkoteplotní a kryogenní zpracování cementačních součástí." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2008. http://www.nusl.cz/ntk/nusl-228073.

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This work deals with the assessment of the influence of low-temperature treatment on the structure and properties of casehardened surface layer of parts. The objective was to assess whether low-temperature treatment is sufficient, insufficient, or unnecessary for the given purpose. Gears which form a part of Zetor tractors gear boxes were used as samples. Thirteen pairs of frozen and non-frozen samples were used; they were taken from production batches throughout 2007, their hardness was assessed and furthermore, the experiment itself, freezing casehardened and hardened samples to different temperatures reaching as low as -196°C, was carried out. A moderate increase in hardness was registered with the majority of the frozen samples, which proved the effectiveness of the low-temperature treatment.
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Pytlíčková, Kateřina. "Vliv struktury a tepelného zpracování na vlastnosti ložiskových ocelí." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2008. http://www.nusl.cz/ntk/nusl-228091.

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Heat treatment influences structure and characteristics of treatmented material. Good heat treatment of steels for bearings ensures hardness of matrix 60 - 65 HRC, whereas structure has be formed by tempered fine needle-shaped martensite with definite part of residual austenite. Carbides should be evenly dispersed, they mustn´t create carbide network and carbide lines. Quality of steels for bearings is also influenced by volume and morphology of inclusions in the matrix. In this diploma thesis various conditions of heat treatment were to be set up with the aim of choose the optimal ones. These ensures perfect martensite transformation and full hardening of all component. Quenching from 760 °C – 770 °C was quite unsatisfactory. At this temperature resulting structure was ferritic-perlitic, because martensite transformation did not pass. Too long hold on hardening temperature also had unfavourable influence on resulting structure and characteristics. In this case, structure was created by very coarse needle-shaped martensite. Coarsening of martensite needle locally exceeded maximum allowed level. In the structure there was also possible to watch partly soluted globular carbides. Optimal heat treatment is quenching from 850 °C – 870 °C followed by tempering at 220 °C. Resulting structure quite agree with above-mentioned needs. This heat treatment can be recommended for technical practise.
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Lee, Wen-Chuan, and 李文全. "The Effects of Phosphate Coating Surface on Tempering Treatment of Low Carbon Steel Carburizing Temperature." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/ezxqvt.

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碩士
高苑科技大學
機械與自動化工程研究所
102
The influence of metal surface state on phosphatizing quality are great, even on the same phosphatizing, formulations, or in different parts phosphatizing of the same piece may also be difference, because the surface state of the piece are difference. This difference to the screw is about carburizing of heat treatment before phosphating, the quality of formation on the phosphatizing has a decisive influence. This article is to explore the impact that different tempering of gas carburizing demonstrated mechanical properties to phosphatizing. The experiment focused on material wire of SAE 1022 AK-KILLED (MQ) that drywall screws be carburizing heat treatment, in heat treatment taken furnace to general carburizing heat treatment, then carburizing heat treatment by carburizing temperature of 820 ℃ it to 900 ℃, holding temperature of 40 minutes, controlling carbon potential of 1.1% in the furnace gas, and quench cooling oil to temperature is 75 ℃, then carry on the gas carburizing heat treatment and at different temperatures by tempering. The results showed that by carburizing then different tempering of variables, then after plating that the showing no difference in color; but there are significant differences in the color of the surface phosphate treatment, so by observe the microstructure Test phase diagram, and know the tempering treatment of work-piece affects the surface of phosphate coating to diffusion adsorption, and resulting the surface color of phosphide be difference and change.
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Book chapters on the topic "Low-temperature tempering"

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Zhang, Z. C., L. X. Zhou, L. H. Ruan, J. A. Qiu, and K. M. Wu. "Effect of Tempering Temperature on the Low Temperature Toughness of the Cr-Mo Alloyed Pressure Vessel Steels." In Energy Materials 2014, 839–44. Cham: Springer International Publishing, 2014. http://dx.doi.org/10.1007/978-3-319-48765-6_103.

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Zhang, Z. C., L. X. Zhou, L. H. Ruan, J. A. Qiu, and K. M. Wu. "Effect of Tempering Temperature on the Low Temperature Toughness of the Cr-Mo Alloyed Pressure Vessel Steels." In Energy Materials 2014, 839–44. Hoboken, NJ, USA: John Wiley & Sons, Inc., 2015. http://dx.doi.org/10.1002/9781119027973.ch103.

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Tekeli, Süleyman, Ahmet Güral, and Metin Gürü. "Influence of Tempering Temperature and Microstructure on Wear Properties of Low Alloy PM Steel with 1-2 % Ni Addition." In Progress in Powder Metallurgy, 629–32. Stafa: Trans Tech Publications Ltd., 2007. http://dx.doi.org/10.4028/0-87849-419-7.629.

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Jena, Pradipta Kumar, K. Siva Kumar, and A. K. Singh. "Effect of Tempering Temperature on Microstructure, Texture and Mechanical Properties of a High Strength Steel." In Materials Science and Engineering, 1690–702. IGI Global, 2017. http://dx.doi.org/10.4018/978-1-5225-1798-6.ch069.

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This work describes the microstructure, texture and anisotropy in mechanical behavior of a high strength steel in various tempered conditions. The microstructures and mechanical properties change considerably with varying tempering temperatures. The material exhibits low in-plane anisotropy and low anisotropic index in terms of yield strength and elongation with increase in tempering temperature. The anisotropy of the material displays similar behavior to that of the yield strength.
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Conference papers on the topic "Low-temperature tempering"

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Shmatov, Alexander A. "Low-Temperature and High-Temperature Thermochemical Hardening Technologies for Hard Alloys." In ASME 8th Biennial Conference on Engineering Systems Design and Analysis. ASMEDC, 2006. http://dx.doi.org/10.1115/esda2006-95092.

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The new surface hardening methods for hard alloys are developed: (1) high-temperature process for producing multicomponent carbide coatings by thermochemical heat treatment of hard alloys at 1050 °C and (2) low-temperature process for producing thin-film coatings by chemical treatment of hard alloys in specially prepared aqueous suspensions of nanosized hard refractory compounds and subsequent tempering (minimal temperature is 130°C). The structure and properties of the obtained coatings are examined. The coatings permit improving substantially the service life of cutting tools.
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Pillot, Sylvain, Mikihiro Sakata, Lionel Coudreuse, and Valéry Ngomo. "Consideration on Tempering and PWHT Temperatures of C-Mn and Low Alloy Steels Used for the Fabrication of Pressure Vessels: Smart Tuning of Heat Treatment Parameters." In ASME 2018 Pressure Vessels and Piping Conference. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/pvp2018-84004.

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For many years, process licensors and/or end-users have frequently specified that the tempering temperature of C-Mn alloys and low alloy steels (i.e. Cr-Mo, Mn-Mo-Ni alloys) should be greater than the post-weld heat treatments (PWHT). Most of the time, tempering temperature is then required as much as 30°C (54°F) above the PWHT temperature, making it very difficult for steelmakers to be able to supply compliant materials, especially for heavy wall components. Application of rules in the applicable codes often leads steelmakers to request for deviations in cases where they become not compatible with material capabilities. This report is intended to illustrate the combined effect of tempering and PWHT on materials properties and to provide recommendations on how to tune smart the tempering treatment with the aim of proposing the most efficient complete heat treatment sequence. Data provided within this paper for C-Mn steels and low alloy grades (Cr-Mo and Mn-Mo-Ni alloys) prove that tempering can be performed at temperatures below, at or above one of PWHT without any adverse effect. Data from actual mill production records show that stringent material specifications can be met by steelmakers when they are allowed to tune smartly the heat treatment parameters (tempering temperature) in accordance with applicable construction codes. The data also demonstrate that limiting the tempering temperature in the lower range of allowed temperatures may be beneficial to customers as it gives more safety margins for fabrication and maintenance (i.e. potential repairs/modifications) of pressure vessels. It permits either to consider more cycles for PWHT or to perform PWHT at higher temperatures or for longer durations, while on the opposite, current trend imposing high tempering temperatures limits flexibility.
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Li, Defa, Feng Huang, Shisen Wang, Yuzhang Xiong, and Shuqing Xing. "Effect of tempering temperature on microstructures and properties of niobium and titanium microalloying low carbon bainite steel." In 2nd International Conference on Electronic and Mechanical Engineering and Information Technology. Paris, France: Atlantis Press, 2012. http://dx.doi.org/10.2991/emeit.2012.342.

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Jang, Eun, Jeffrey Stewart, Yuxiang Luo, Shijie Qu, Boian Alexandrov, Steven L. McCracken, Jonathan Tatman, Darren Barborak, and Jorge A. Penso. "Tempering Efficiency Evaluation for Dissimilar Weld Overlays." In ASME 2020 Pressure Vessels & Piping Conference. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/pvp2020-21708.

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Abstract The objective of this work was to develop a procedure for evaluation and quantification of the tempering efficiency of corrosion resistant weld overlays used in the power generation and oil and gas industries. Three two-layer weld overlays of Alloy 625 on Grade 22 steel plates were produced using GTAW cold wire procedures. Typical welding parameters corresponding to low, medium, and high heat input were utilized. The overlays consisted of nine beads on the first layer and five to seven beads on the second layer. The weld thermal histories experienced in the coarse-grained heat affected zone (CGHAZ) were measured with Type K thermocouples and recorded with a 55 Hz sampling rate. Two rows of seven thermocouples were used in each overlay: one row located in a mid-bead position beneath the center bead of the overlay and the other row located in the nearest bead overlap position. Additionally, one Type C thermocouple was plunged into the weld pool of a second layer weld bead. The acquired thermal histories and the CGHAZ hardness at the thermocouple locations were evaluated to quantify the tempering efficiency in each welding procedure. The weld thermal histories with peak temperatures between 500°C, assumed as the minimum tempering temperature, and the base metal AC1 temperature were considered as tempering thermal cycles. The number of tempering thermal cycles and the sum of tempering cycle’s peak temperatures in each thermocouple location, as well as the corresponding hardness were used to quantify the tempering response efficiency for each of the three welding procedures. The results of this study will be used for validation of a computational model-based approach for prediction of tempering response and optimization of temper bead welding procedures.
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Wei, D. Q., J. Lu, and R. Wang. "The effect on the properties of low alloyed bainite ductile iron in oil quenching and isothermal tempering temperature." In 5th International Conference on Information Engineering for Mechanics and Materials. Paris, France: Atlantis Press, 2015. http://dx.doi.org/10.2991/icimm-15.2015.298.

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Toribio, J., D. Vergara, M. Lorenzo, and J. J. Marti´n. "Role of Residual Stresses and Strains Fields Generated by Heat Treatments on the Hydrogen Embrittlement of a Nuclear Reactor Pressure Vessel." In ASME 2011 Small Modular Reactors Symposium. ASMEDC, 2011. http://dx.doi.org/10.1115/smr2011-6537.

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The wall of a nuclear reactor pressure vessel can undergo a reduction of its mechanical properties due to the presence of hydrogen, a process known as hydrogen embrittlement (HE). A numerical model of hydrogen diffusion assisted by stress and strain was used in this paper to evaluate the HE process in the wall of a real nuclear reactor pressure vessel, formed by a bimaterial (stainless steel and low carbon steel). In this sense, a quantitative analysis was carried out of the influence of tempering heat treatments conditions applied to these two steels on hydrogen concentration accumulated in the nuclear reactor vessel during its operation time. To this end, the most relevant parameters of these heat treatments were considered: (i) tempering temperature and (ii) tempering time.
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Kusunoki, Takuya, Boian Alexandrov, Benjamin Lawson, Jorge Penso, and Joe Bundy. "Tempering Response in Type 410 Stainless Steel Welds for Petrochemical Application." In ASME 2020 Pressure Vessels & Piping Conference. American Society of Mechanical Engineers, 2020. http://dx.doi.org/10.1115/pvp2020-21753.

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Abstract Type 410 martensitic stainless steel is typically used in highly corrosive environments within petrochemical installations due to its resistance to halide stress corrosion cracking, hardenability, and low cost compared to austenitic stainless steel. However, the industry has experienced difficulties in meeting the ASME toughness, and NACE hardness requirements for wet sour services of Type 410 steel welds. Recent studies have shown that these problems are related to the wide compositional ranges of Type 410 base metals and welding consumables, leading to exceeding the A1 temperature during postweld heat treatment (PWHT) and formation of fresh martensite, and to retention of significant amount of delta ferrite in the final weld metal and heat affected zone microstructures. These studies have identified two Type 410 optimized weld metal compositions that met the specified hardness and toughness requirements. The objective of this work was to quantify the tempering response in one of the optimized welding consumables and in two Type 410 base metals. Samples of these materials were subjected to a series of PWHTs at temperatures corresponding to the lower and upper limits of the ASME code recommended temperature range (760 C and 800 °C) and at 10 °C below the A1 temperature of each material. The PWHT durations were 5 and 30 minutes, and 1, 2, and 4 hours. The hardness values related to all PWHTs performed below the corresponding A1 temperatures were used to generate Holloman–Jaffe type equations for all tested materials. As expected, the PWHTs performed above the A1 temperatures resulted in the formation of fresh martensite.
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Koripelli, Rama S., and David N. French. "Issues Related to Creep-Strength-Enhanced Ferritic (CSEF) Steels." In ASME 2014 Power Conference. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/power2014-32027.

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T-91 and P-91 are the oldest of a new class of creep-strength-enhanced ferritic steels (CSEF) approved for use in boilers and pressure vessels. These newer alloys develop high strength through heat treatment, a rapid cooling or quenching to form martensite, followed by a temper to improve ductility. As a result, these alloys offer a much higher allowable stress which means thinner sections provide adequate strength for high-temperature service. Most of the applications thus far have been a substitute for P-22/T-22. The primary advantages of T91 materials over conventional low-alloy steels are: higher allowable stresses for a given temperature, improved oxidation, corrosion, creep and fatigue resistance. T23 is also considered as a member of the family of CSEF steels. The alloying elements such as tungsten, vanadium, boron, titanium and niobium and heat treatment separate this alloy from the well defined T22 steel. Although, T23 is designated for tubing application, its piping counterpart P23 has a strong potential in header applications due to superior strength compared to P22 headers. Now that T-91 and P-91 have been in service for nearly 30 years, some shortcomings have become apparent. A perusal of the allowable stress values for T-91 shows a drop off in tensile strength above about 1150°F. Thus, start-up conditions where superheaters, and especially reheaters, may experience metal temperatures above 1200°F, lead to over-tempering and loss of creep strength. During welding, the temperature varies from above the melting point of the steel to room temperature. The heat-affected zone (HAZ) is defined as the zone next to the fusion line at the edge of the weld metal that has been heated high enough to form austenite, i.e., above the lower critical transformation temperature. On cooling, the austenite transforms to martensite. Next to this region of microstructural transformation, there is an area heated to just below the austenite formation temperature, but above the tempering temperature of the tube/pipe when manufactured. This region has been, in effect, over-tempered by the welding and subsequent post-weld heat treatment (PWHT). Over-tempering softens the tempered martensite with the associated loss of both tensile and creep strength. This region of low strength is subject to failure during service. Creep strength of T91 steel is obtained via a quenching process followed by controlled tempering treatment. Elements such as niobium and vanadium in the steel precipitate at defect sites as carbides; this is known as the ‘pinning effect’. Any subsequent welding/cold working requires a precise PWHT. Inappropriate and/or lack of PWHT can destroy the ‘pinning effect’ resulting in loss of creep strength and premature failures. Several case studies will be presented with the problems associated with T91/T23 materials. Case studies will be presented, with the results of optical microscopy, scanning electron microscopy, hardness measurements and energy dispersive spectroscopy analysis. One case study will discuss how the over-tempering caused a reduced creep strength, resulting in premature creep failure in a finishing superheater tube. A second case presents the carburization of a heat recovery steam generator (HRSG) superheater tube, resulting in reduced corrosion/oxidation resistance. A case study demonstrates how a short-term overheating excursion led to reheat cracking in T23 tubing. Another case will present creep degradation in T91 reheater steel tube due to high temperature exposures (over-tempering).
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So¨zbir, Nedim, and Shi-Chune Yao. "Experimental Studies of Using Water Mist Cooling for the Tempering of Glass." In ASME 2002 International Mechanical Engineering Congress and Exposition. ASMEDC, 2002. http://dx.doi.org/10.1115/imece2002-32524.

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Very high velocity air jet impingement has been applied during the cooling process of glass tempering. In order to reduce the usage of high-pressure air in the process, it is intended to demonstrate the feasibility of using water mist to enhance the air-cooling. The multiple jet experiments were performed using air jet velocities between 40 and 90 m/sec containing low mass flux of water mist that was varied from 0 up to 0.145 kg/m2sec for each jet. The experiments include different glass thickness. The optimal tempering conditions were explored. The mechanisms of mist cooling are revealed from the experiments of a single water mist jet impinging on hot stainless steel plates. Since the droplets are small, on the order of 20 micron, heat transfer distribution of the water mist has a similar form as the air jet cooling. The total heat transfer coefficient can be viewed as two separable effects: the summation of the heat transfer coefficient of the convective air and of the impinging water flux, respectively. The heat transfer of multiple water mist jets on larger glass is studied. When the liquid flux is too high or when the surface temperature falls below the Leidenfrost temperature, excessive local thermal stress will occur, which leads to cracking of glass. It is possible to reach the optimal tempering with a moderate amount of water applied on the glass surface for a short duration of time. The mist cooling demonstrates a definitive saving on the use of high-pressure air. When using mist cooling, the energy requirements of the system are significantly lowered. The mist cooling creates more refined fracturing in the punching tests of tempered glass. For glass thicker than 3 mm, the particle counts due to water mist improve about 121%. For 2 mm glass, the improvement is about 38%. The mist cooling of the thinnest glass is still not able to give the desired particle counts. But definitive improvement toward this objective is shown. Further studies of other alternatives may give a chance to achieve this goal.
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Liu, Yu, Tao Han, Yezheng Li, Zhanghua Yin, Peng Zhu, Lijun Yan, and Qiang Li. "Development of Large Diameter Heavy Wall Seamless Tee Fitting of WPHY-80 Grade for Low Temperature Pipeline Station Application." In 2018 12th International Pipeline Conference. American Society of Mechanical Engineers, 2018. http://dx.doi.org/10.1115/ipc2018-78748.

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Abstract:
This paper describes the development of large diameter heavy wall seamless tee fitting of WPHY-80 grade for low temperature pipeline station application. Steel tees with thicker wall generally tend to have low fracture toughness either in pipe body or in weld joint and low weldability. Therefore, improvement of fracture toughness and weldability are particularly important with respect to development of higher strength and thicker wall seamless tee fittings. For the requirement of the China-Russia Eastern Gas Pipeline Project, WPHY-80 large diameter, seamless heavy wall reducing outlet tees were developed, with DN1400 × DN1200 and 57mm wall thickness. The billet steel production process was electroslag remelting (ESR), and the tee fitting production process used a forging and hot extrusion combination. Finally, quenching and tempering were carried out. In this paper, the mechanical properties and microstructure of WPHY-80 seamless tee were studied. The results of mechanical testing showed that the tensile yield strength of the tee body was more than 590 MPa and also provided excellent low temperature toughness (CVN > 200 J at −45°C), which met the requirements of the specification for fittings applied in the China-Russia Eastern Gas Pipeline Project. In addition, the results of welding procedure qualification showed that the welding performance of the WPHY-80 seamless tee was excellent.
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