Fracture mechanics investigations with respect to the use of steels

The failure behaviour of cracked components can be described sufficiently precisely and assessed conservatively using fracture mechanics based methods within their limits of application. Depending on the chosen procedure rather different results can be obtained concerning the accuracy reaching from relatively rough estimations up to very exact assessments. Toughness requirements can be specified quantitatively for cracked components reversing the conventional fracture-mechanics analysis. The required toughness values depend on the component and defect geometry, the strength of the material and the safety criterion. The presented examples have revealed that for realistic defect sizes the material toughness of low-strength steels shows a much higher level than required, whereas in case of higher strength steels the margin between requirements and properties may become small.     

Optimization Evaluation Test of Strength and Toughness Parameters for Hot-Stamped High Strength Steels

Use of hot-stamped high strength steels (HSHSS) not only reduces the vehicle weight, but also improves the crash safety, therefore more and more mentioned steels are used to produce automobile parts. However, there are several problems especially the low ductility and toughness, which have restricted the application of HSHSS in automobile body. Suitable process parameters are very crucial to improve strength and toughness. In order to study the effect of austenization temperature, soaking time and start deformation temperature on strength and toughness of boron steel 22MnB5, an L9 (3⁴) orthogonal experiment which was analyzed by means of comprehensive evaluation was carried out based on Kahn tear method to obtain the value of fracture toughness. The results indicate that the excellent formability, high strength and toughness of boron steel 22MnB5 with 1.6 mm in thickness are obtained when the austenization temperature is in the range of 920 — 950 °C, the soaking time is 1 min and the start deformation temperature is in the range of 650 — 700 °C. The optimal parameters were used for typical hot stamping structural parts tests. Properties of samples such as tear strength, unit initiation energy and ratio of strength to toughness (RST) were improved by 10.91%, 20.32% and 22.17%, respectively. Toughness was increased substantially on the basis of a small decrease of strength.     

新型低密度高强高韧热轧层状钢研发

 鉴于能源短缺与高安全性要求,钢铁材料的低密度化与高强韧化成为高强钢的研发热点。大量报道证明,铝等元素合金化可以显著降低钢材密度,层状复合组织大幅度提高钢铁材料的韧性。在介绍国内外传统等轴晶粒高强韧钢、层状复合钢铁材料及低密度钢研发结果的基础上,提出了Fe-Al-Mn-C低密度双相钢的低中等合金质量分数（4%～12%）的合金化设计和高温铁素体和奥氏体的几何扁平化组织调控思路,制备出具有铁素体与马氏体相间排列的层片复合双相钢组织结构的高强韧钢研发思路。初步研究结果证明,层片双相钢的组织结构设计是可行的,实现了钢铁材料的高强度化（抗拉强度为1 000～1 500 MPa）、低密度化（6.5～7.5 g/cm3）和高韧性化（室温V型冲击韧性为200～400 J）,突破了传统等轴结构材料的强韧化机制制约,形成了新型层状复合结构强韧化的钢铁材料研发方向。强调未来需要对层片双相钢材料进行深入研究,以实现对化学成分、层片组织结构参数与材料强度、韧性和材料密度关系的定量研究,深入探讨低密度层状双相钢的层状组织调控机制及其强韧化机理,为未来高强韧金属材料研发及应用开辟出创新发展方向。     

调质工艺对Q690D钢综合力学性能及组织的影响

 以60mm厚Q690D高强度结构钢板为研究对象,在相同轧制条件下,系统地研究了淬火、回火温度对试验钢综合力学性能及显微组织的影响,并对第二相析出进行理论分析。试验结果表明：随淬火温度升高,试验钢强度升高,韧性下降;随回火温度升高,试验钢强度下降,但韧性明显升高。该钢采用930℃淬火(保温10min)650℃回火(保温40min)的调质热处理工艺具有良好的强韧性匹配,综合力学性能最佳,满足国标GB/T 16270—2009要求。     

海洋平台用高强度齿条钢的研制

自升式海洋平台桩腿用厚规格A517Q高强度结构钢,要求具有高的强度及优良的低温冲击韧性。为了满足上述要求,在工艺上采用模铸、初轧及厚板轧制,并采用淬火加回火的调质工艺;在成分设计上,为得到回火后组织,保证高的强度和一定的淬透性能,主要通过Mo、B、Cr等元素的作用,同时加入一定数量的Ni。通过成分与相应的调质工艺配合,保证A517Q钢具有高的强度、高的冲击韧性及良好焊接性能。宝钢生产的127、152.4 mm厚的A517Q钢板制造的齿条已经成功应用在中海油923、924自升式海洋平台。     

Study of processing,microstructure and mechanical properties of hot rolled ultra-high strength steel

Hot rolled ultra-high strength steel with a gauge range of 3–10?mm (0.118¨–0.395¨) was developed using conventional slab caster and hot strip mill technology at Stelco Inc. (Stelco) to meet standard industry specifications along with additional unique customer requirements. The effects of chemical composition, steelmaking and hot rolling process parameters on microstructure, precipitation behaviour, and mechanical properties were studied. Both Grade 90 (620?Mpa, Stelco trademarked STELMAX^TM90) and Grade 100 (690?MPa, STELMAX^TM100) products met strength requirements in longitudinal and transverse directions. Furthermore, these ultra-high strength steels exhibited excellent ductility, impact toughness, edge stretchability and bendability. The enhanced mechanical properties are the results of chemistry design and carefully controlling austenite/ferrite grain size and precipitation behaviour at different processing stages. These newly developed steels have extensive applications in automobile safety components, light-weight construction, piping/tubing and offshore structures.     

超高强钛合金研究进展

随着新一代航空航天飞行器向着高速化、大型化、结构复杂化以及提高燃油效率等方向的跨越式发展,要求钛合金结构材料具有高比强度、高比模量、高韧性、高损伤容限、低成本以及可焊接等优良的综合性能匹配。此外,航天、兵器、船舶等武器装备各框梁类承力构件、承力螺栓等紧固件、高强度弹簧等弹性元件、航母弹射器与装甲等均对高强度钛合金、超高强度钛合金提出了明确需求。因此,超高强度钛合金成为了新一代武器装备发展的关键支撑材料之一,是钛合金开发和应用研究的重点方向,更是各国政府关注和重点发展的新型军用先进材料。介绍了国内外主要超高强度钛合金(TB8,TB-13,Ti-B19,Ti-B20,GUM,β21S和Timetal-LCB等)的发展和应用情况,指出了超高强度钛合金存在强度不断提高的同时,塑性、韧性、模量、疲劳性能以及损伤容限性能不同程度地降低,同时缺乏对合金化机制、强韧化理论和方法等基础问题的深入系统研究。最后提出了超高强度钛合金的发展方向。     

Study on Heat Treatment Process of AB/EQ56 Steel Plate

The article mainly describes the development process of AB/EQ56 steel plate for ocean engineering with thickness ≤50mm in Wuyang Iron and Steel Co.,Ltd.(Wugang),and studies the chemical analysis,metallographic structure,tensile strength and serial temperatures impact toughness of the steel plate.The results show that a good match of strength and toughness of AB/EQ56 steel plate with thickness ranging from 12mm to 95mm produced by ultra low alloying component control,controlled rolling and controlled cooling,proper quenching and tempering process,of which the properties are all conforming to the requirements of ABS rules.The steel plate has passed the certification of ABS and is qualified for production.More than 7000 tons of such steel plate have been ordered,which mainly apply for the cantilever beam of offshore oil platform.     

Ultrafine high-cobalt hard alloys. II. Connection between mechanical properties and structure

The experimental dependences of strength, plastic properties, hardness, and fracture toughness on sintering or pressing temperature for ultrafine alloy WC-41 wt.% Co are presented. The alloy densifies in solid phase and temperature varies from 950 to 1250°C. The dependences of mechanical properties are extreme, excepting fracture toughness. The properties reach their maximum values at 1050 to 1150°C depending on the type of testing. Fracture toughness continuously increases with densification temperature. The highest values of some properties are reached after additional solid-phase annealing. The mechanical properties of ultrafine high-cobalt alloy samples are assessed with the use of structural parameters and empirical equations established for standard hard WC-Co alloys sintered in liquid phase. The calculated and experimental values of properties differ: transverse rupture strength, fracture toughness, and yield strength show higher values, while hardness and compressive strength have lower values as compared with calculated ones.     

TMCP工艺在船板生产中的应用

以E36为例介绍了采用TMCP工艺生产A32～E36系列高强度船用结构钢的成分设计和工艺设计。该钢种化学成分符合GB712及DNV、LR等六国船级社标准的要求。采用TMCP工艺，通过晶粒细化和析出强化保证钢材的强韧性。工业试制所生产的钢板采用连铸板坯，钢板最大厚度可达60mm，各项力学性能完全符合船规要求。     

铌对9%Ni钢用镍基焊条熔敷金属组织和性能的影响

研制9%Ni钢用镍基焊条的难点在于满足熔敷金属强度和塑性指标的前提下提高其低温韧性.在力学性能分析的基础上,采用彩色金相分析、扫描电镜及能谱分析、X射线衍射分析技术研究了铌对9%Ni钢用镍基焊条熔敷金属组织和性能的影响.试验结果表明,熔敷金属中铌的加入能明显提高其强度和塑性.但铌的质量分数达到3.5%后,虽然熔敷金属的强度进一步提高,但形成了脆性的金属间化合物Laves相,导致熔敷金属低温韧性下降.     

采用TMCP工艺生产40kg级高强度船用钢板的研究

介绍了采用TMCP工艺生产A40、D40、E40系列高强度船体用结构钢的成分设计和工艺设计的情况.该钢种化学成分符合GB712及DNV、LR等九国船级社标准的要求.采用TMCP工艺,靠晶粒细化和析出强化保证了钢材的强韧性.工业试制所生产的钢板采用连铸板坯,最大钢板厚度可达80mm,各项力学性能完全符合要求.     

Development of SA-533 Type B CL.1 + SA-240 Type 304L roll-bonded clad steel plate for safety injection tank of CAP1400 nuclear power plant

Aiming to meet the demand of the country' s nuclear demonstration project on the CAP1400 nuclear power plant,Baosteel uses the roll-bonding technology and develops the SA-533 Type B CL.1 + SA-240 Type 304L high-strength and high-toughness clad steel plate with a shear strength of over 310 MPa for the nuclear power plant' s safety injection tank.The properties of the quenched and tempered and the simulated post-weld heat treatment states are systematically studied herein through a comprehensive inspection and evaluation of the composition,microstructure,and properties of the clad steel plate.The results show that the bonding interface has high shear strength and that the base metal has high strength and good toughness at low temperatures.Hence,the performance fully meets the technical requirements of the CAP1400 nuclear power plant' s safety injection tank in the country' s nuclear demonstration project.The roll-bonded clad steel plate can be used to manufacture the safety injection tank of the CAP1400 nuclear power plant.     

High Performance Structural Steels for Shipbuilding and Offshore Structures

Recently,there have been the increase of ship size and the development of oil and gas in arctic region.These trends have led to the requirements such as high strength,good toughness at low temperature and good weldability.The high performance structural steels for shipbuilding and arctic offshore structure have been developed by our own micro-alloying and TMCP technologies.M-A constituent was precisely controlled in the both HAZ and base metal to get high toughness at low temperature.Also,the grain growth of austenite at HAZ was effectively suppressed by thermally stable TiN particles,leading to a good HAZ toughness.On the other hand,there has been the key issue of crack arrestability in large size container ship.The effect of joint design on crack arrestability was investigated to prevent a catastrophic failure along the block joint of hatch side coaming.A brittle crack arrest technique was developed without block joint shift,using an arrest weld in the end of hatch side coaming weld line.     

Nb在低温高强度船体结构钢EH36中的应用

本文介绍了Nb在低温高强度船本结构钢板EH36中的实际应用，通过试验对比，总结出用Nb作为微合金元素生产的EH36钢板组织均匀、晶粒细化，具有良好的强度、低温冲击韧性和厚度方向性能。实物质量进一步证明控制轧制加正火工艺是生产HE36低温高强度船体结构钢板获得理想强韧性指标的最佳工艺。     

低合金高强度结构钢A572Gr.50的研制

本文介绍了低合金高强度结构钢A572 Gr.50不同正火温度下的机械性能、低温系列冲击、奥氏体晶粒粗化试验,并检验分析了该钢的显微组织、夹杂物与晶粒度.结果表明:我厂生产的A572Gr.50钢板的各项性能均满足技术标准要求.特别是低温冲击韧性较好.     

大厚度严要求14Cr1MoR钢最佳热处理制度探究

简要分析了大厚度14Cr1MoR钢板强度/低温冲击韧性匹配性差的原因,在此基础上研究了系列热处理制度对钢板组织和性能的影响,进一步探究了最佳的热处理制度.结果表明,导致大厚度14Cr1MoR钢板强度/低温冲击韧性匹配性差的根本原因是轧制或淬火过程中形成的大块状非均匀性组织,以及晶界及基体处含铬/钼碳化物的不规则聚集长大...     

高性能Q460耐火耐候结构用钢的研发

以低C- Mn为基体,辅以钼、铜、铬、镍等元素合金化,采用实验室冶炼及轧制,配合合理的控轧控冷工艺,研发了Q460级别耐火耐候抗震结构用钢。对试制的钢板进行了力学性能、高温耐火性能及耐大气腐蚀性能检验,并进行分析。结果表明,Q460钢韧性和塑性优异,屈强比低,具有较好的抗震性,600 ℃保温3 h耐火及耐大气腐蚀性能良好,完全满足高性能建筑结构钢的要求。     

Interpretation of the Effects of High Austenitizing Temperature on Toughness Behavior in a Low Alloy,High Strength Steel

An experimental investigation into the effects of high temperature austenitizing treatment (h.t.a.) on the microstructure and the mechanical properties, and micromechanisms of fracture in a variety of test conditions has been carried out on a Ni-Cr high strength steel. H.t.a. increased the fracture toughness, but decreased the tensile ductilities and notch toughness of this steel with a slight reduction in strength in the condition of strain-controlled fracture mode. However, the fracture toughness and notch toughness of steel were simultaneously improved by h.t.a. in the condition of stress-controlled fracture mode. This behavior of ductility and notch toughness is because the micro structural variations arising from h.t.a. have different roles in different fracture modes. It appears that the general effect of microstructural changes is beneficial to stress-controlled fracture, but the reverse is true to straincontrolled fracture. The fracture toughness behavior was greatly affected by the change in characteristic distance with austenitizing temperature, but the characteristic distance obtained from the best fitting of experimental results does not have clear physical meaning. It is observed that the application of macroscopic fracture stress or strain in analyzing local failure behavior ahead of the crack tip can be justified if the characteristic distance is consistent with the microstructural parameters related to the fracture process. The improvement in fracture toughness for stress controlled fracture mainly results from the large characteristic distance; whereas in the case of strain controlled fracture, this is caused by the much higher local fracture strain ahead of the crack tip of h.t.a. structure compared to that observed in structures produced by conventional austenitizing.     

Fracture toughness of 12Cr2Mo1R steel at elevated temperature

The microstructure,tensile properties,and fracture toughness of 12Cr2Mo1R steel were studied. The results indicate that this steel is characterized by a bainite microstructure,in which several types of carbides precipitate along the ferrite laths. As the temperature increases from room temperature to 375 ℃,the strength of the steel increases slightly and the fracture toughness clearly decreases. However,when the temperature continues to increase up to 500 ℃,the strength decreases and the fracture toughness increases. At all the temperatures investigated,the strength and toughness of the developed 12Cr2Mo1R steel were capable of meeting the design requirements of a high-temperature gas-cooled reactor. The fracture of 12Cr2Mo1R steel at high temperature typically occurs in the ductile mode.