Dissertations / Theses on the topic 'Steel fasteners'

In this project, the main research objective is intend to seek criteria for evaluating the capacity of BAC screw fasteners with mixed configuration of waterproof seal washer, sealer tape and different pre-drill holes to determine shear and tension strength values for the screws used in cold-formed steel connections. The thesis presents the design methods and test program conducted to investigate the behavior and strength of the screw connections in shear and tension test. Test results were compared with AISI design provisions to determine if new design equations will be developed for those screws used in BAC cooling tower applications. LRFD resistance factors and ASD safety factors were investigated to the proposed design equations.

Incremental step load testing was used in accordance with ASTM F1940 to rank a number coating processes used in the fastener industry for their propensity to cause internal hydrogen embrittlement. The results showed that coating permeability has a first order effect, while the quantity of hydrogen introduced by the process has a second order effect. Pure zinc electroplating processes, alkaline and acid, were found to be the most embrittling, owing to the low permeability of zinc. The least embrittling processes were zinc-nickel, alkaline and acid, owing to the high permeability of Zn-Ni coatings. Non-electrolytic processes, namely phosphating, mechanical galvanising, DacrometRTM and Magni 555RTM were found to be non-embrittling. Hot dip galvanising was found to be highly embrittling, evidently due to trapped hydrogen being released by the thermal shock of up-quenching upon immersion in molten zinc. The full effect of up-quenching on the metallurgical and mechanical properties of high strength steel requires further investigation.

The main purpose of this thesis is to investigate the ductility and application of titanium alloys, like titanium 6Al-4V, when used in aerospace fasteners compared to more conventional stainless steel aerospace fasteners such as A286. There have been concerns raised about the safe usability of titanium 6-4 in the aerospace industry due to its lack of strain hardening. However, there is a lack of data pertaining to this concern of safe usage which this thesis aims to address. Tensile tests were conducted to find the ductility indexes of these fasteners which quantify the amount of plastic to elastic elongation. From the tests conducted it was found that the two materials yield and tensile strengths were very similar, though the ductility index of A286 is on average ten times greater than that of titanium 6-4. This thesis includes joint diagram examples that analyze typical joints using both materials. It was found from joint diagram examples that the lower ductility index of the titanium alloy will only be detrimental to use at higher preloads. However, the titanium alloy can be used safely in place of A286 in most loading situations just with narrower safety margins in these controlled examples.

The use of deck fasteners as shear connectors for composite open web steel joists is studied. Results of thirty-six push-off tests are evaluated in terms of strength and behavior. Six types of deck fasteners are considered. They are: 1. #12-24 Teks/5 self-drilling, self-tapping screws. 2. 1/4-14 Teks/3 with a 1 1/4 in. stand-off sleeve. 3. 1/4-14 Teks/3 with a 1 3/4 in. stand-off sleeve. 4. 1/4-14 Teks/3 with a 2 1/4 in. stand-off sleeve. 5. 0.150 in. dia. air fired pins. 6. Puddle welds (5/8 in. and 3/4 in. diameter). All push-off tests utilize Vulcraft 1.5 VL, 22 gage, composite deck. Several modifications to the typical push-off test arrangement are made, which will permit the test to more closely model the top chord of an open web steel joist. It was found from the push-off test results that all of the deck fasteners, tested in this study, can obtain composite action for snort span open web steel joists with the exception of 0.150 in. diameter air fired pins. A description and the results of each push-off test is included.
Master of Science

Adhesive bonding as an alternative method of joining materials together has many advantages over the more conventional joining methods such as fusion and spot welding, bolting and riveting. For example, adhesives can be used to bond dissimilar materials, adhesive joints have a high stiffness to weight ratio and the stress distribution within the joint is much improved. Stainless steels are commonly used in applications that would clearly benefit from adhesive bonding; architectural cladding, because of the large bond areas involved, and in the railway industry, due to improved acoustic insulation and greater fatigue resistance. The work presented in this thesis is concerned with adhesive bonding of stainless steels intended for structural applications. As a starting point to the investigation, a review of the literature was conducted, covering the intrinsic mechanisms of adhesion, the significance of the chemical and physical nature of the adherend surface, the types of structural adhesives, the methods of testing adhesive joints and surface characterisation techniques. The first experimental stage, involved a screening programme to evaluate a number of candidate adhesive systems and adherend surface pre-treatments. Standard single overlap shear and floating roller peel tests conducted in ambient conditions were employed in the discrimination and the degree of compatibility between adhesive and adherend, as measured by the proportion of cohesive failure on the post-fracture face, was also considered. In the second stage of the experimental work, lap shear tests were used to evaluate the affects of surface contamination on joint strength. In addition, lap shear and peel tests were considered to assess the significance of the adhesive bondline and primer thickness. In order to assess the environmental durability of adhesive joints, lap shear and peel tests were conducted after ageing in ambient and high humidity environments. To compliment the data, Boeing wedge crack extension tests were also carried out on adhesive bonded joints incorporating adherends with different surface conditions, to investigate the contribution to joint strength in ambient and adverse environments afforded by surface pre-treatment. The next stage of the experimental work was designed to evaluate the significance of the adherend type and its thickness on initial lap shear strength. Several different commercial grades and gauges of stainless steel were used in the tests, which were conducted at room temperature. The final stage of the experimental work was concentrated on the room temperature creep and dynamic fatigue performance of adhesive joints. Throughout the course of study a number of different surface analytical techniques were employed to physically and chemically characterise the surfaces of pm-bonded adherends and to identify the locus of failure on post-fracture faces. The single overlap shear and floating roller peel tests were able to differentiate between the candidate adhesives; epoxy systems, particularly the toughened variants, were considered the most suitable structural adhesives for bonding stainless steels in load bearing applications. However, these tests and subsequent tests using lap shear and peel, failed to discriminate conclusively between the different surface pre-treatments (except untreated or crudely prepared surfaces) and ageing environments. The Boeing wedge crack extension tests were found to be sensitive to the condition of the adherend surface and the environment in which the joint is located; roughening the surface of the adherend either chemically or physically was found to enhance joint durability in ambient, high humidity and sub-zero environments. The use of surface primers and coupling agents may protect the un-bonded surface and benefit joint durability, but excessively thick primer layers may reduce joint strength. The stiffness of the adherend material was found to significantly influence lap shear strength. Stiffer adherends, either thicker or inherently stronger, give higher joint strengths because they resist joint rotation and the peel stresses at the extremes of the overlap are minimised. Lap joints with low stiffness adherends will fail by peel-dominated, adherend-controlled failure and lap joints with high stiffness adherends will fail by shear-dominated, adhesive-controlled failure. Two elastic models were proposed for determining the elastic rotation and the line peel force as a function of the shear stress. The room temperature creep results showed an endurance limit of -40% mean static failure load (design load = 250 N.mni1 ). The dynamic fatigue results were favourable compared to those of spot welded and weldbonded joints and an endurance limit of 40% mean static failure load (design load = 250 N.mm-1 ) was observed. Finally, leaving the hard fillets of cured adhesive squeeze-out, intact at the extremes of the overlap, will reinforce the joint and minimise the rotation-induced peel stresses that will lead to premature failure when the adherend plastically deforms under static or dynamic loading.

Timber construction has increased in popularity in different countries in Europe thanks to a new material apparition and environmental stakes. In order to construct a timber structure we use different types of connections. The design of connections is complex since it is influenced by many different factors. However, the connection is the weak part of the structure and has high risk of collapse. Therefore the connection often determines the capacity of the structure.In 1975 the commission of the European Community decided to harmonize of technicalities and rules of design in the field of construction. The aim is to increase the competition between companies and simplify the trade of products and services within the European Union. The regulation for timber structures is Eurocode 5 (EC5).This study investigates how the EC5 can influence the design of a connection with a single shear plane for a steel-timber connection with nails or screws. This study is based on the comparison between the connection properties obtained using the EC5 and those recommended in a brochure from one of the large glulam manufacturers in Sweden based on the Swedish regulations.The outcome is that the new regulation has a strong impact on the design of the steel plates. The requirement in minimum spacing imposes a specific dimension and position of the fasteners. Moreover, the capacity of the connection is influenced by the distance between the fasteners parallel to the grain, which determines the effective number of fasteners involved in the connection.

Legislative and market pressures are pushing automakers to achieve new fuel economy requirements in the coming years. To help achieve these goals automakers are reducing the overall weight of the vehicle by increasing the use of high-strength aluminum and advanced high-strength steels, and with this increased use comes the desire to quickly, and securely, join these materials within the vehicle. Friction bit joining is a process that lends itself well to joining these materials. This process uses consumable fasteners that need to be used in an automated production line. The geometry of these fasteners causes two main problems: the bits have a short longitudinal axis, which makes them difficult to orient, and the welding platform may be used at different angles; requiring a robust reloading system that is indifferent to its orientation.Our research explored ways that these short axis FBJ fasteners could be handled and transported using various automated methods. We tested the use of small mechanical carriages and magnetic tracks to test their viability for transporting FBJ fasteners. The two different types of fasteners that were used in the project are described. Blow feed tubes ended up being a reliable method of transportation given that the fastener has suitable geometry. The superior bit and feed system design were bench tested using a manually controlled feed system. The system was tested in various orientations to test the robustness of the system since the system was designed to be part of the end effector on a production line robot. The testing revealed that the feed tube is a reliable method of bit transportation and mechanical jaws are a suitable solution for FBJ fastener manipulation. These jaws have several key design features that dramatically increase their effectiveness. Suggestions for future work would be an optimized feed tube cross section, improved material properties in the bit jaw, and more air flow at a higher pressure through the feed tube.

A series of full-scale beam-to-column moment connection tests were completed to determine the effects of powder actuated fasteners (PAF) and puddle welds on the seismic behavior of steel moment connections.  In seismic regions, PAF are currently prohibited in the connection region (referred to as the protected zone) due to the concern of low-cycle fatigue fracture.  There is almost no information available in the literature regarding the seismic behavior of moment connections with PAF or puddle welds.
Full-scale connection testing is the most accurate way to investigate the behavior of different moment connections with common defects and fasteners applied in the protected zone.  However, it is cost prohibitive to conduct full-scale testing programs that are sufficiently comprehensive to investigate a wide range of defect types, severity, and locations.  For this reason, it is desired to develop alternative methods of investigation.  A finite element (FE) model capable of simulating both the global deformation patterns and local buckling effects in a moment connection has been developed.  Validated FE models will allow for further evaluation through numerical simulation of additional configurations.  Furthermore, alternate, more economical, test configurations to experimentally investigate the effect of defects on steel moment connections were explored.  This report discusses the full-scale test setup, results and analysis of completed experimental testing, the development of an FE connection model, and the preliminary development of alternate test configurations.

Master of Science

Este trabalho consiste numa revisão bibliográfica sobre ligações em estruturas de aço. Inicialmente são abordados os dispositivos de ligação, enfatizando os tipos e as características estruturais dos conectores, os processos de soldagem mais empregados nas estruturas de aço e suas implicações. A seguir são apresentados os aspectos mais importantes sobre o comportamento estrutural de parafusos e soldas e a avaliação da resistência com base na norma brasileira NBR 8800 e nas principais normas estrangeiras aplicáveis. Finalmente, são apresentados e discutidos os modelos teóricos clássicos usualmente empregados para a avaliação de solicitações em ligações parafusadas e soldadas.
This work gives a reference review on steel structure connections. First, connection designs are discussed, emphasizing the types of fasteners, their characteristics, the most common employed welding processes for steel structures and the technical implications. It is also presented the most important aspects regarding the structural behaviour of bolts, welds and the strength evaluation based on the Brazilian code NBR 8800, as well as on the main known foreign codes. Finally the classical theoretical analysis often adopted for the evaluation of welded and bolted connections are presented and discussed.

This research introduces a proposed model for predicting tilting angle and limit states of single-fastened cold-formed steel-to-steel shear connections. Predictions are validated through an experimental study considering ply configuration and a single Hex #10 -washer head fastener, centered in a 102 mm by 102 mm three boundary window. The fastener tilting angle is captured using an automated, optical non-contact measurement procedure. The results are used to identify cold-formed steel shear connection deformation as load progresses, including tilting, bearing, and combined tilting bearing at the plies and thread tension, shear and bearing fastener failure. Results shows that fastener tilting plays a kinematic affect for the connection. Fastener tilting is predicted in function of ply thickness and fastener pitch. Local ply bending deformation is reported to be the main deformation of the connection during fastener tilting. While fastener bending and shear failure occurred if the fastener does not tilt.
Master of Science

Selection of steels for industrial purposes usually means choosing a type of steel to make a part or a product. The steel that is chosen must meet all the designer requirements. A quantitative selection procedure has been used to analyze the large amount of data involved in this selection process so that a complete and systematic evaluation can be made. The designer is responsible for the selection of steel, and this selection requires the designer to find data and information on the mechanical properties required, and also learns ways to improve these properties through different heat treatment processes. When a large number of steels and a large number of specified mechanical properties are being evaluated for selection, the weighed properties method can require a large number of tedious and time-consuming calculations. In such cases a computer program could greatly facilitate the selection process. This thesis reports the selection of steels for gears, shafts, fasteners and springs where the steps involved in the weighted properties method which is written in the form of a simple computer program to select steels from a data bank. This program also includes the digital logic method to help in determining weighing factors. The steels are ranked according to standard designation; BS, AISI, and DIN. It has been found that alloyed steels hardened and tempered at 2050C are most suitable for gears, shafts, fasteners, and springs when higher mechanical properties required, and carbon and low alloyed steels when cost is the main consideration.

Thesis (M.S.)--Missouri University of Science and Technology, 2010.
Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed July 26, 2010) Includes bibliographical references (p. 58-59).

Master of Science
Department of Civil Engineering
Hani Melhem
The combination of cold formed steel (CFS) with structural wood panels exhibits a degree of partial composite action behavior. In the current design and construction codes, CFS and wood sheathing systems are considered separate, in a non-composite manner, due to the absence of sufficient supporting experimental and research data. The problem with previous research is the lack of information to fully define the composite action between CFS and wood sheathing. The scope of this study is to check fundamental information provided in previous research. The approach adopted to solve the problem follows previous experimental procedures conducted at Kansas State University. The objective of the research is to determine the slip modulus with various fastener spacing. Additional results obtained in this study are compared to previous research results.

The objectives of this research were to determine if mechanically-fastened steel built-up axially-loaded tension members are resistant to complete cross-sectional fracture when a single component suddenly fractures and if so, to develop simplified methods of analysis for post-fracture load redistribution behavior for calculation of remaining fatigue life. The ability to resist complete member failure and perform at a predetermined level of reliability with a failed component is referred to as internal member redundancy (IMR). The experimental program included seven full-scale tests; five were extremely demanding fracture tests, including one specimen with a tack weld placed in the path of a running fracture, and the other two were full-scale specimens removed from a 1940’s era built-up riveted deck truss, which were partially failed and tested to calibrate finite element models. Comprehensive finite element model-based parametric studies were carried out investigating the post-fracture load redistribution behavior and resulting stress amplification for multi-component, angle-only, and two-channel type axial members. Simplified closed-form solutions were developed for members of any geometry that fall within these broad categories of built-up axially-loaded tension members.

The IRM evaluation process is intended to combine the concepts related to probability of detection (POD) of fatigue cracks on steel bridges with the fatigue damage tolerance of mechanically-fastened built-up members. Preliminary results from ongoing POD research at Purdue University suggests that the steel bridge industry has unknowingly been relying on internal redundancy of mechanically-fastened built-up members. In other words, due to the difficulty of finding small cracks in components of built-up members, it is more likely that traditional arms-length inspections of fracture-critical members will find broken components instead. More candidly stated, this research provides the industry with quantitative analysis for the purpose of establishing rational inspection intervals for built-up axial members that are realistic about what can be reliably found during inspections and for what duration undiscovered damage can be safely tolerated due to internal member redundancy of the mechanically-fastened built-up member.

Master of Science
Civil Engineering
Hani G. Melhem
Bill Zhang
Composite action is the joint behavior of two elements connected or bonded together. It is a phenomenon that is utilized in several applications throughout engineering. Previous studies have shown that cold formed steel (CFS) sheathed with structural wood panels exhibits a degree of partial composite action behavior. However currently in the design process, CFS and wood sheathing systems are considered separately in a non-composite manner due to the absence of sufficient supporting data. These systems can include the floors, roofs, and walls of a building. In order to determine the level of composite action present, the slip modulus is needed. The slip modulus describes the relationship between the shear force and the displacement exhibited by two elements in a composite system. The scope of this research is to determine the influence of fastener spacing on the slip modulus and provide a foundation of information to fully define the composite action between CFS and wood sheathing.

This thesis introduces an approach for modeling the monotonic and cyclic response of cold-formed steel framing screw-fastened connections in commercial finite element programs. The model proposed and verified herein lays the groundwork for seismic modeling of cold-formed steel (CFS) framing including shear walls, gravity walls, floor and roof diaphragms, and eventually whole building seismic analysis considering individual fastener behavior and CFS structural components modeled with thin-shell elements. An ABAQUS user element (UEL) is written and verified for a nonlinear hysteretic model that can simulate pinching and strength and stiffness degradation consistent with CFS screw-fastened connections. The user element is verified at the connection level, including complex cyclic deformation paths, by comparing to OpenSees connection simulation results. The connection model is employed in ABAQUS shear wall simulations of recent monotonic and cyclic experiments where each screw-fastened connection is represented as a UEL. The experimental and simulation results are consistent for shear wall load-deformation response and cyclic strength and stiffness degradation, confirming the validity of the UEL element and demonstrating that light steel framing performance can be directly studied with simulations as an alternative to experiments.
Master of Science

The topic of my diploma thesis is a design of a construction of a multipurpose building. The floor plan is of irregular shape with a maximal span of 35 metres. There are two buildings in shape of a hexagon, to which another building in shape of a half of a hexagon is connected. Part of the building is designed as a two-storey building and all parts are different in height. The hight of the designed building in its highest point is 13,5 metres. The load-bearing structure consists of glued laminated wood elements and raised wood with steel elements used as fasteners. The construction is designed alternatively from wood and steel. The static solution was made using the RFEM software.

The objective of this study was to investigate the monotonic and cyclic behaviour of different kinds of slender dowel-type fasteners. To accomplish this, four types of fasteners were tested in a series of 73 monotonic and cyclic tests. All tests used either one or two slotted-in steel plates in PARALLAM®, a Parallel Strand Lumber (PSL) product. The fastener types were a) plain shank steel dowel of 6.35 mm diameter (SH), b) plain shank steel dowel of 6.35 mm diameter with threads on both ends to allow for nuts and washers to be attached (SHT), and c) two types of a new commercially available self-drilling dowel of 7 and 5 mm diameter which feature a threaded end on one side and a cutting bit on the other (SFS WS-T7 and -T5). In addition to the test regimen, the monotonic and cyclic behaviour of the fasteners was modeled using a finite element program based on the theory of an elasto-plastic beam on a nonlinear foundation. The existing program was extended to include fastener head behaviour, hole tolerances and fastener material fatigue. Testing results illustrated a direct influence of the head type on the monotonic as well as cyclic load-deformation behaviour of the tested fasteners. Strength and stiffness increases were observed with increasing head resistance. In the cyclic tests, it was found that this head restraint was influenced by permanent elongation of the fasteners. In addition, cyclic test results were influenced by slack in the connection due to oversized holes as well as fastener material fatigue. The analytical model yielded good representations of the monotonic as well as the cyclic load-displacement behaviour of the tested fasteners. Inclusion of hole tolerances, fastener fatigue and fastener head behaviour was found to be essential to correctly approximate real fastener behaviour.

碩士
國立中山大學
企業管理學系研究所
89
Abstract Taiwan has won the good name of “the Kingdom of Fasteners” for years. With the dedication by the whole industry the exporting volume of fasteners products kept significantly growing every year in Taiwan and the production scale has become the leading position worldwide as well. However, due to the unlimited investment along with large expansion of production capacity made in the past decade, the market situation tends to be oversupplied. Price war emerges whenever business gets slow, as a result, the exporting price keeps dropping year by year and Taiwan is likely to be the target of foreign anti-dumping suits. As a matter of fact, Taiwan fastener industry has encountered several anti-dumping suits before. Among all the cases, the European anti-dumping suit on import of stainless steel fasteners has resulted in a considerable impact to the industry that the exporting volume of fasteners products has significantly decreased since 1988 and many companies were forced to seek for other markets, downscale their operation or even move the factories to overseas. The Agreement on Implementation of Article VI of the General Agreement on Tariffs and Trade 1994 exercises multilateral agreement to sanction the dumping activities based on non-discrimination principle and adopts necessary measure to restrict the dumping activities. As a result, to avoid any negative impact caused by the free trade and protect the benefit of local industries, every country is allowed to bring the anti-dumping law into their trading policy. However, we noted from the evolution of the trading policy that the mechanism of protection measure has been shift from tariff barrier to be non-tariff barrier, and from non-tariff barrier to the abuse or misuse of WTO regulation, the discretion of the administration has even become one of the mechanisms. This paper is intended to emphasize the impact to the free trade by anti-dumping measure and the impropriety of the European anti-dumping system. This paper includes six chapters: Chapter 1 - General introduction; Chapter 2 – The development of Taiwan fasteners industry; Chapter 3 – The illustration of the European anti-dumping system and suit case; Chapter 4 – The initial and definitive determinations of suit case; Chapter 5 – The disputes of legal procedure and substance; Chapter 6 – Conclusion and suggestion.

碩士
義守大學
機械與自動化工程學系碩士班
93
The research is utilized the thread shape mold dental plate surface coatings to let the dental plate surface of friction coefficient reduce, abrasion resistance and its use life increase while dental plate rolling the thread. The first phase uses SS304 stainless steel to explore coating TiN, TiCN,CrN and then finding the best adhesive coatings. The second phase uses SKD11 of dental plate sputtering suitable coating to test and to raise dental plate using life. After previews coating by abrasive test we know, The friction coefficient of TiN,TiCN,CrN are o.3174,0.094 and 0.1526 respectively. The lower friction coefficient is the better for abrasion, The TiCN coating possess the higher bonding strength as well as lower friction coefficient compare with that of TiN or CrN coating, We selected TiCN coating to farther evaluate the life time and failure mechanisms, accordingly. The TiCN coated and uncoated molds were evaluated under mild steel production process, and life time was 456 hours and 360 hours, respectively. After long periods operation, No any interdiffusion between coating and steel substrate was detected under SEM Mapping. The failure mechanisms is possibly due to the cohesion loss fatigue in TiCN coating.

Cold-formed steel connections are commonly fastened using self-tapping self-drilling screws. The behavior of these connections can differ based on the screw manufacturer or the cold-formed steel product used, both of which have a large selection available for use in industry. Because of their popularity and the many possible variations of these connections, researchers have frequently tested screw connections to characterize their behavior. However, repeatedly conducting this type of experiment is time consuming and expensive. Therefore, the purpose of this work was to create finite element models that can successfully predict the behavior of single lap shear screw connections, a common connection type used in cold-formed steel framing. These models were created using the finite element program Abaqus/CAE. To validate these models, test results from Pham and Moen (2015) were used to compare the stiffness, strength, and failure mode of multiple connections. A parametric study is also conducted to determine the influence of contact parameters on the behavior of the model. The results showed that all models consistently had good agreement with the connection stiffness and that most of the models also had good agreement with the peak load and failure mode of the v tests. These results were also compared to the design equations available for screw connections from the American Iron and Steel Institute (AISI). This comparison revealed that the models are more successful at predicting screw connection behavior than AISI, and thus work is required to improve the accuracy of AISI’s design equations. The eventual goal of this work is to develop a procedure to build and validate models without requiring test data. This work continuing in the future can lead to recommendations to improve AISI’s design equations and to implement the behavior of the connections into large cold-formed steel framing models such as diaphragms or shear walls.

碩士
義守大學
材料科學與工程學系碩士班
98
Bolts and nuts, made by medium carbon steels and low alloyed steels, are the mainly export-oriented steel products in Taiwan. However, the medium carbon and low-alloy steels are featured with scattered and laminated-structured pearlite, which generally causes serious deformation cracking along steel outer fringe area during cold working. Therefore, before the cold working, such steels usually go through spheroidization treatment to enhance the continuity of ferrite, and reduce the hardness and ductility, thus benefiting for avoiding the cold forging fractures. The three main factors affecting spheroidization rate are temperature, holding time, and cooling rate. The purpose of this research mainly focuses on the effect of various holding time on the spheroidization rate. The influence of the change of carbon, chromium, and molybdenum content, and the holding time of austenitization are also investigated. The spheroidization features were observed by using optical microscope and scan electrical microscope. The hardness and tensile properties were measured using hardness instrument and tensile test machines, respectively.The experimental results show that sphericity increases with increasing holding time. Sphericity was significantly increased when the steels were soaked for 2hr, thus causing the decrease of yield strength and tensile strength. A trivial change of spehericity was obtained when the steels were soaked over 2hr. Concerning the effect of carbon content, the variation of the hardness value becomes more apparent when the carbon content was increased. The spheroidization time for steels with higher carbon contents was shorter compared with that for steels with lower carbon contents. A better spheroidization thus leads to a better ductility for higher carbon steels.

碩士
國立高雄大學
化學工程及材料工程學系碩士班
103
In this experiment, we used the wire of 40ACR chromium steel material that has been once spheroidizing treatment and drawing. After the twice spheroidizing treatment of different temperatures and holding time, we observed microstructure, patterns of carbide analysis and calculation of the rate of the sphericity. After that we did the hardness test and tensile test to investigate the mechanical properties. And we comprehend the effect of microstructure, the different carbide type, sphericity and mechanical properties by different twice spheroidizing treatment. In the research, it was found the lamellar structure without the twice spheroidizing treatment. After twice spheroidizing treatment at 700 ℃, 720 ℃ and 740 ℃, all of the sphericity are higher than 99 %. Since 760 ℃ is the temperature above anstenitizing, the microstructure of 760 ℃ cooling to room temperature has appeared lamellar structure and the sphericity is less than 99%. From the mechanical properties we can found that the tensile strength of twice spheroidizing treatment at 700 ℃, 720 ℃ and 740 ℃ is slightly decreased by raised holding temperature. But the hardness and the tensile strength after twice spheroidizing treatment at 760 ℃ are higher than other parameter. The reason is the appearance of the lamellar structure and the chromium in carbides took place solid solution, so that the tensile strength rised. The material with twice spheroidizing treatment of 740 ℃ holding temperature and 6 hours holding time is the best one for forging industry because the properties of the lowest hardness, lowest tensile strength and the highest elongation.