加热温度对热成形中锰钢氢脆敏感性的影响

对0.1C–5Mn中锰钢在不同温度(850、950和1000℃)加热后进行热成形处理,利用电化学预充氢、慢应变速率拉伸及氢渗透实验等研究了加热温度对其氢脆敏感性的影响.结果表明,试验钢在不同温度加热后进行热成形处理,其组织全部为马氏体,同时因自回火而生成一定量的ε-碳化物,且随着加热温度的升高,原奥氏体晶粒尺寸增加,而试验钢的强度和塑性逐渐降低.当加热温度为850℃时获得了较好的强度与塑性配合,强塑积为22 GPa·%.随着加热温度升高,充氢样中的可扩散氢含量明显降低而非可扩散氢含量有所增加,而以相对缺口抗拉强度损失表征的氢脆敏感性指数及有效氢扩散系数呈现先升高后显著降低的变化趋势,当加热温度为1000℃时,氢脆敏感性最低.进一步断口分析表明,试验钢充氢断口起裂区均为沿着原奥氏晶界的沿晶断裂.试验钢的这种氢脆断裂行为主要与热成形中锰钢的强度水平及自回火析出的ε-碳化物有关.与常用的传统热成形钢22MnB5相比,试验钢的氢脆敏感性较高,这主要与其M_s点(马氏体转变开始温度)较低而使得自回火程度较低等有关.     

L245管线钢环焊缝在4 MPa氢气环境中的氢脆敏感性探讨

一般认为低钢级钢管受到的氢损伤较小，是输氢管道实际铺设的首选，但是环焊缝的组织变化和冶金缺陷有可能使氢脆敏感性显著增加。通过光滑和缺口试样慢拉伸试验对比研究了正火态L245管线钢环焊缝在空气和4 MPa氢气中的氢脆敏感性，并采用金相显微镜、扫描电子显微镜(SEM)和电子探针显微镜(EPMA)对显微组织和断口形貌进行了系统表征与分析。结果表明，当组织中存在应力集中时，L245管线钢环焊缝在4 MPa氢气环境中的氢脆敏感性会显著增加造成氢损伤，使得慢拉伸断裂方式从韧性断裂转变成准解理+韧性断裂，并且在缺口边缘伴随有大量的环向裂纹。L245环焊缝组织中的铁素体/针状铁素体相界面作为氢陷阱会加速氢的渗入，同时碳偏析的存在也会促进氢富集，导致慢拉伸断口表面出现了大量裂纹。     

热处理工艺对3.5Ni钢组织和性能的影响

通过拉伸和冲击试验以及OM和SEM的组织观察,研究了不同热处理工艺对3.5Ni低温钢显微组织和力学性能的影响。结果表明:3.5Ni钢正火(Normalizing)态及正火+回火(Normalizing+tempering)态的组织均为铁素体基体加珠光体。冲击韧性随正火温度的升高先增加后降低,正火温度为860℃时,低温韧性最佳;回火后3.5Ni钢塑性和低温韧性明显提高。随着回火温度的升高,带状组织减弱,冲击功增加,当回火温度达到两相区的650℃时,冲击功降低,最佳的回火温度为590~630℃。     

动态充氢电流密度对BG110S油井管力学性能的影响

利用 MTS-810材料试验机测量了BG110S油井管在动态拉伸(边充氢边拉伸)实验中的力学性能,并利用扫描电镜观察分析了拉伸断口形貌,研究了动态充氢电流密度对油井管力学性能的作用,讨论了氢原子浓度对油井管氢脆敏感性的影响。实验结果表明：随着充氢电流密度的增加,BG110S试样的屈服强度和抗拉强度先增大后减小;试样的伸长率、断面收缩率及拉伸韧性连续降低;试样的拉伸断口形貌由韧性断裂特征向脆性断裂特征转变;试样的氢脆敏感性连续增加。当动态充氢电流密度i＜30 mA/cm2时,氢原子在 BG110S试样中呈现固溶强化作用,而当i≥30 mA/cm2后,氢原子在BG110S试样中则呈现氢致脆化作用。     

阴极极化对10Ni9CrMoV高强钢氢脆敏感性的影响

采用电化学测试﹑慢应变速率拉伸实验(SSRT)并结合断口形貌观察,研究了海水环境中阴极极化对10Ni9CrMoV钢氢脆敏感性的影响。结果表明:随阴极极化程度加强,阴极反应控制步骤逐步由氧的去极化反应转变为氢的去极化反应;随阴极极化电位负移,10Ni9CrMoV钢的强度没有明显变化,但其断面收缩率和伸长率均减小,断口形貌由韧窝型韧性断裂向解理断裂转变,氢脆敏感性提高;当极化电位为-926 mV时,氢脆系数达到25%,说明10Ni9CrMoV钢在海水中的最高保护电位为-926 mV。     

影响高速钢韧性的因素

 分析了化学成分、冶炼方法、钢中碳化物和热处理工艺等因素对高速钢韧性的影响。结果表明：纯净度高、杂质元素含量低和夹杂物少的钢韧性较高；同一钢种随碳含量升高其韧性降低；在同一类型钢种中，通常W Mo系钢的韧性优于W系钢；碳化物分布均匀、颗粒尺寸细小的钢韧性高，而碳化物分布不均匀、粗大角状碳化物多的钢韧性差；粉末高速钢的韧性显著优于常规方法生产的高速钢。热处理是影响高速钢韧性的另一个重要因素：随淬火温度升高，钢的韧性下降；回火温度较低和回火程度不充分时，也会显著降低钢的韧性。     

碳和硅对Mn系空冷贝氏体钢回火韧性的影响

研究了碳的质量分数低于0.3%、不同硅含量的Mn系贝氏体钢的冲击韧性随回火温度的变化,结果表明,随着Si含量的提高,低温回火阶段出现韧性峰值的温度由220℃提高至340℃,韧性出现低谷的温度由340℃提高至520℃,这与Si抑制碳化物析出、稳定残余奥氏体有关。低Si钢一般适合高温回火后使用,高Si钢一般适合低温回火后使用;但碳的质量分数低于0.08%时,无论Si含量如何,低温或高温回火均适用,若碳含量过高,回火改善韧性的作用不明显。     

固溶温度对403Nb钢组织和性能的影响

研究了固溶温度（940℃-1180℃）对403Nb组织和性能的影响,结果表明：随固溶温度升高,固溶强化和回火过程合金元素碳化物析出起主要强化作用,虽然晶粒长大,但钢的强度提高;断口类型由韧性断裂转变为脆性断裂。     

轧辊用高碳高速钢系合金的KIC及力学性能

研究了新开发的轧辊用高碳高速钢系合金的ＫⅠｃ值、弯曲强度、压缩强度。结果表明，这类合金具有优良的力学性能和ＫⅠｃ值，同高铬铸铁相比ＫⅠｃ值高约４０％－２００％。随碳量增加，ＫⅠｃ值、弯曲强度明显下降，压缩强度下降不明显；钒含量增加上述性能均增加。回火温度升高、压缩强度下降，ＫⅠｃ值升高；回火次数增加，弯曲强度下降，ＫⅠｃ值升高，压缩强度几乎不变。材料的断裂属脆性断裂，碳含量低时为准解理断裂；碳含量     

晶粒尺寸对高锰奥氏体TWIP钢氢脆行为的影响

主要研究了晶粒尺寸对Fe- 17Mn- 1Al- 0.6C TWIP钢的氢脆行为的影响。原始材料经过不同的热处理制度,得到晶粒尺寸为17和45μm的材料。通过慢拉伸试验研究氢质量分数在0～0.001%材料的氢脆敏感性。试验结果表明,充氢后的试验材料比未充氢试验材料易发生氢脆,充氢后的试验材料断裂强度和断裂应变均降低。随着晶粒尺寸的增大,试验材料的氢脆敏感性增强。在氢质量分数为0.001%,晶粒尺寸增加到45μm时,应变损失率为17%,随着晶粒尺寸的增大,氢脆敏感性增加的原因是晶粒尺寸较大的材料孪晶较早出现,孪晶密度较大,同时单位晶界氢质量分数增加。     

Influence of nitrogen alloying on hydrogen embrittlement in AISI 304-type stainless steels

Hydrogen embrittlement of AISI 304-type austenitic stainless steels has been studied with special emphasis on the effects of the nitrogen content of the steels. Hydrogen charging was found to degrade the mechanical properties of all the steels studied, as measured by a tensile test. The fracture surfaces of hydrogen charged specimens were brittle cleavage-like whereas the uncharged specimens showed ductile, dimpled fracture. In sensitized materials transgranular cleavage mode of fracture was replaced by an intergranular mode of fracture and the losses of mechanical properties were higher. Nitrogen alloying decreased the hydrogen-induced losses of mechanical properties by increasing the stability of austenite. In sensitized steels the stability of austenite and nitrogen content were found to have only a minor effect on hydrogen embrittlement, except when sensitization had causedα′-martensite transformation at the grain boundaries. Formerly with Helsinki University of Technology, Laboratory of Physical Metallurgy, SF-02150 Espoo 15, Finland.     

Effects of chromium on the temper embrittlement and wear resistance of 0.25% C low-alloy cast steel

The effects of additions of 0.6 to 2.0% Cr on the temper embrittlement behaviour of 0.25 C–1.0 Si–1.3 Mn cast steel under several hardening conditions were studied. The susceptibility to temper embrittlement, transgranular and intergranular fracture were increased as the chromium content increased when the steels were tempered at 350°C and slowly cooled from 550°C. The impact toughness and abrasion resistance of the steels were found to depend to a great extent on the Cr-content and tempering temperature.     

The structure of tempered martensite and its susceptibility to hydrogen stress cracking

A series of 4130 steels modified with 0.50 pct Mo and 0.75 pct Mo were tempered at temperatures between 300 and 700 °C for one hour. The changes in the carbide dispersion and matrix substructure produced by tempering were measured by transmission electron microscopy. These measurements were correlated with resistance to hydrogen stress cracking produced by cathodic charging of specimens in three-point bending. Scanning electron microscopy showed that specimens tempered between 300 and 500 °C failed by intergranular cracking while those tempered at higher temperatures failed by a transgranular fracture mode. Auger electron spectroscopy showed that the intergranular fracture was associated with hydrogen interaction with P segregation and carbide formation at prior austenite grain boundaries. Transgranular cracking was initiated at inclusion particles from which cracks propagated to produce flat fracture zones extending over several prior austenite grains. The 4130 steels modified with higher Mo content resisted tempering and showed better hydrogen stress cracking resistance than did the unmodified 4130 steel. The transition in fracture mode is attributed to a decohesion mechanism in the low temperature tempered samples and a pressure mechanism in the highly tempered samples.     

Hydrogen embrittlement of dual-phase steels

Reversible hydrogen embrittlement (HE) is usually only found in quenched and tempered steels with yield stresses in excess of 1035 MPa (150 ksi). A study of the HE phenomena in two dual-phase steels with tensile strengths of about 690 MPa (100 ksi) has shown that these steels are susceptible to the presence of hydrogen. HE results in a reduction in fracture strength, although no preyield failures are observed, and a change in fracture mode from ductile dimpling to transgranular cleavage. After prestraining and HE, it is found that the greater the prestrain the higher is the fracture stress. It is concluded that the presence of the 15 to 20 pct high carbon (0.6 pct C) high strength martensite in the dual-phase steels is responsible for the HE; tempering studies give results consistent with this idea. Delayed failure tests on notched specimens showed that for the as-received condition, the run-out stress (stress for no failures in 50 to 100 h) to be above the macroscopic flow stress. A condition for HE failure in dual-phase steels appears to be considerable macroscopic deformation.     

数据清洗对热轧微合金钢性能预报模型的改进

摘要：对热轧0.1C-5Mn中锰钢进行了3种不同的处理制度：在两相区分别进行5min(TG7样)和30min退火(TG8样)，随后将一部分TG8样再500℃回火60min(TG8-500样)，其余TG8样则拉伸预变形5%(TG8-5%样)，然后利用电化学充氢和慢应变速率拉伸实验研究了3种试样的氢脆敏感性。结果表明，3种试样的奥氏体体积分数均约为12%，然而其氢含量和氢脆敏感性却不同，其中TG8-500样几乎不呈现氢脆敏感性，而TG7和TG8-5%样的氢脆敏感性指数分别为56%和67%。扫描电镜断口分析表明，充氢的TG7和TG8-5%样的拉伸断口呈现穿晶+沿晶的混合断裂机制，而充氢的TG8-500样则呈现韧窝韧性断裂，且存在较多的二次裂纹。3种实验钢氢脆敏感性的这种差异主要与其微观组织特征特别是原奥氏体晶界的逆转变奥氏体有关。     

不同处理状态下0.1C-5Mn中锰钢的氢脆敏感性

摘要：对热轧0.1C-5Mn中锰钢进行了3种不同的处理制度：在两相区分别进行5min(TG7样)和30min退火(TG8样)，随后将一部分TG8样再500℃回火60min(TG8-500样)，其余TG8样则拉伸预变形5%(TG8-5%样)，然后利用电化学充氢和慢应变速率拉伸实验研究了3种试样的氢脆敏感性。结果表明，3种试样的奥氏体体积分数均约为12%，然而其氢含量和氢脆敏感性却不同，其中TG8-500样几乎不呈现氢脆敏感性，而TG7和TG8-5%样的氢脆敏感性指数分别为56%和67%。扫描电镜断口分析表明，充氢的TG7和TG8-5%样的拉伸断口呈现穿晶+沿晶的混合断裂机制，而充氢的TG8-500样则呈现韧窝韧性断裂，且存在较多的二次裂纹。3种实验钢氢脆敏感性的这种差异主要与其微观组织特征特别是原奥氏体晶界的逆转变奥氏体有关。     

Retained Austenite and Tempered Martensite Embrittlement in Medium Carbon Steels

Electron microscopy, diffraction and microanalysis, X-ray diffraction, and auger spectroscopy have been used to study quenched and quenched and tempered 0.3 pct carbon low alloy steels. Some in situ fracture studies were also carried out in a high voltage electron microscope. Tempered martensite embrittlement (TME) is shown to arise primarily as a microstructural constraint associated with decomposition of interlath retained austenite into M₃C films upon tempering in the range of 250 °C to 400 °C. In addition, intralath Widmanstätten Fe₃C forms from epsilon carbide. The fracture is transgranular with respect to prior austenite. The situation is analogous to that in upper bainite. This TME failure is different from temper embrittlement (TE) which occurs at higher tempering temperatures (approximately 500 °C), and is not a microstructural effect but rather due to impurity segregation (principally sulfur in the present work) to prior austenite grain boundaries leading to intergranular fracture along those boundaries. Both failures can occur in the same steels, depending on the tempering conditions.     

The role of nitrogen in the embrittlement of steel

Nitrogen is one of the most common impurity elements to be found in steels. Previous work has shown that it is a potential grain boundary embrittler. In this paper we examine its role in both tempered martensite embrittlement and temper embrittlement. The basic composition of the steel used for this study was, in wt pct, 3.5 Ni, 1.7 Cr, 0.3 C, and 0.01 N. It was found that nitrogen could be very detrimental to mechanical properties but not as a grain boundary embrittler in the typical sense that P, Sn, and Sb are. Rather, nitrogen is almost always precipitated as nitrides and these second phase particles can induce low energy ductile fracture. The distribution of nitrides in the solid and the type of nitride present is dependent on the heat treatment. If a low austenitizing temperature is used, the nitrides in the steel dissolve and considerable nitrogen segregates to the grain boundaries. During an oil quench it reprecipitates at the boundaries, primarily as Cr₂N. These nitrides cause low energy, ductile intergranular fracture. If a high austenitizing temperature is used, much less nitrogen segregrates so fewer nitrides precipitate during the quench. However, upon tempering the nitrogen does reprecipitate. At low tempering temperatures, small nitrides form both within the grains and along the grain boundaries. When these nitrides become sufficiently large, voids form around them as well as around the carbides during fracture. These small voids help link the large voids that form around oxide and sulfide particles and lower the energy for ductile fracture. After high temperature tempering treatments large nitrides and carbides form at the grain boundaries. These produce low energy, intergranular ductile fracture. These large grain boundary precipitates can also aid in brittle intergranular fracture by providing many more sites for nucleation of intergranular cracks when the boundary is weakened by another impurity element.     

The Fracture Behavior of Quenched and Tempered Manganese Steels

Manganese is present in all commercial low alloy steels, but its various effects on fracture are not completely understood. In this paper we report a study of the fracture behavior of quenched and tempered manganese steels. The steels were austenitized, quenched, and then tempered at temperatures between 150 °C and 500 °C. If the steel contained phosphorous, the fracture energy after all tempering treatments was very low and the fracture was intergranular. Tempering at temperatures near 350 °C produced especially low fracture energies because of the occurrence of intergranular tempered martensite embrittlement. Manganese does not increase the amount of phosphorous segregation during austenitization or tempering. However, it may increase the embrittling potency of phosphorous. If the steel did not contain a sufficient concentration of a grain boundary embrittling element such as phosphorous, the fracture mode was ductile microvoid coalescence. In this case manganese can be very important because it scavenges all of the residual sulfur in the alloy to form MnS precipitates. These are the initial sites of microvoid formation during ductile fracture, and their presence, especially in the form of elongated stringers, can lead to a reduced fracture energy.     

The effect of hydrogen on the fracture toughness of alloy X-750

The effect of hydrogen on the fracture toughness behavior of a nickel-base superalloy, Alloy X-750, in the solutionized and aged condition was investigated. Notched bend specimens were tested to determine if the fracture process was stress or strain controlled. The fracture was observed to initiate at a distance between the location of maximum stress and maximum strain, suggesting that fracture required both a critical stress and strain. The effect of hydrogen was further investigated and modeled using fracture toughness testing and fractographic examination. The fracture toughness of the non-charged specimen was 147 MPa√m. Charging with hydrogen decreased the fracture toughness, K _Ic , to 52 MPa√m at a rapid loading rate and further decreased the toughness to 42 MPa√m for a slow loading rate. This is consistent with the rate-limiting step for the embrittlement process being hydrogen diffusion. The fracture morphology for the hydrogen-charged specimens was intergranular ductile dimple, while the fracture morphology of noncharged specimens was a mixture of large transgranular dimples and fine intergranular dimples. The intergranular failure mechanism in Alloy X-750 was a microvoid initiation process at grain boundary carbides followed by void growth and coalescence. One role of hydrogen was to reduce the void initiation strain for the fine intergranular carbides. Hydrogen may have also increased the rate of void growth. The conditions ahead of a crack satisfy the critical stress criterion at a much lower applied stress intensity factor than for the critical fracture strain criterion. A model based on a critical fracture strain criterion is shown to predict the fracture behavior.