长时间水浸泡奥贝球铁的腐蚀行为及拉伸性能

研究了长时间水浸泡奥贝球铁(ADI)的腐蚀行 为和拉伸性能.浸泡中，ADI的石墨周围的基体被腐蚀，形成腐蚀凹坑；其中的针状铁素体优 先腐蚀.水附着拉伸试验中，浸泡后试样的抗拉强度和延伸率比未浸泡的低，发生明显的水 脆化.干燥使浸泡后试样的强度和延伸率恢复到较高水平，但腐蚀凹坑和表面腐蚀溶解减少 了试样的有效断面积，其抗拉强度和延伸率低于大气中的.与浸泡在离子交换水相比，自来 水加速试样腐蚀，其水脆化程度也明显.     

等温淬火温度对奥贝球铁水脆化行为的影响

研究了等温淬火温度对奥贝球铁(ADI)水脆化行为的影响，水附着条件下不同等温淬火温度处理的ADI均发生水脆化行为，抗拉强度和伸长率显著降低；但随着等温淬火温度升高，ADI的水脆化程度降低。高强度的ADI、淬火回火球铁和珠光体球铁均发生水脆化行为，而铁素体含量高的铸态球铁和铁素体球铁无明显的水脆化行为。     

表面涂层对奥贝球铁水脆化行为的影响

水附着拉伸试验中,试样表面附着的水在试样塑性变形时分解出氢使奥贝球铁(ADI)产生氢脆,抗拉强度和伸长率显著下降,发生明显的水脆化现象.试样表面镀锡使ADI的抗拉强度和伸长率下降,镀锡层不能有效防止ADI的水脆化.聚乙烯涂覆能降低ADI的水脆化程度,而环氧树脂和尼龙涂覆无防止ADI水脆化的效果.     

奥氏体化温度对等温淬火球墨铸铁摩擦磨损性能的影响

奥氏体化处理是得到高性能等温淬火球墨铸铁(Austempered ductile iron, ADI)的关键步骤，通过奥氏体化处理，铸铁基体组织向奥氏体转化，为后续的等温淬火处理过程中奥氏体向奥铁体的相变提供前驱体。对奥氏体化温度进行调控，研究了ADI微观组织的相应变化及其对力学性能、摩擦磨损性能的影响。研究发现，奥氏体化温度的提高使石墨向基体的渗碳作用增强，奥氏体碳含量增加、稳定性增强，一方面导致奥氏体在冷却转变过程中铁素体的形核驱动力降低，奥铁体组织中铁素体形态更细长，另一方面导致块状残留奥氏体增多、碳含量提高，使材料强度、硬度及断后伸长率均发生下降。较高的奥氏体化温度使ADI含有大量高碳残留奥氏体，导致其在摩擦磨损过程中难以通过应力诱发相变形成马氏体来提升耐磨性。综合力学及摩擦磨损性能，ADI的奥氏体化温度应不大于950℃。     

氢致马氏体对304不锈钢在MgCl2中应力腐蚀的影响

通过电解充氢后除气，即可在304奥氏体不锈钢中引入不同数量的氢致马氏体（ε α′，其中ε占2/3），同时并未明显改变试样的强度和位错密度，氢致马氏体使304不锈钢脆化，塑性损失随马氏体含量升高而升高，在沸腾MgCl2溶液中慢应变速率拉伸实验表明，随氢致马氏体含量升高，应力腐蚀敏感性也升高，但当马氏体总量超过10%之后，应力腐蚀敏感性逐渐趋势地一个稳定值。     

低相变点马氏体焊缝组织与高强钢焊接裂纹的关系

文章归纳了低相变点（low transformation temperature, LTT）马氏体焊缝组织与高强钢焊接裂纹的关系。结果表明，在冷裂纹影响因素中，马氏体焊缝的裂纹倾向，受控于氢的脆化与拉应力减小效果间的竞争。低相变点马氏体焊缝与高强钢焊接冷裂纹之间的关系，取决于马氏体焊缝的品质、焊缝中的应力状态与氢行为间的关系。工程上常用焊缝中残留的扩散氢含量最小化、不足以引发氢致冷裂纹的“焊缝金属低氢化”综合工艺，并获得了满意的效果。     

THE TEMPER-BRITTLENESS OF BAINITIC STEELS

本文系统地研究了在石氏体组织中所发生的回火脆性。下石氏体在回火过程中脆化的趋势略小于回火马氏体,上石氏体的脆化趋势略大于珠光体,而回火马氏体的回火过程的脆化趋势远大于珠光体。上石氏体的回火脆性发生温度区域是460—580℃,回火马氏体是430—630℃,两者的最大回火脆性温度都是530℃。     

石氏体的回火脆性

本文系统地研究了在石氏体组织中所发生的回火脆性。下石氏体在回火过程中脆化的趋势略小于回火马氏体,上石氏体的脆化趋势略大于珠光体,而回火马氏体的回火过程的脆化趋势远大于珠光体。上石氏体的回火脆性发生温度区域是460—580℃,回火马氏体是430—630℃,两者的最大回火脆性温度都是530℃。     

ADI的研究与应用--2002年ADI国际会议简介

介绍2002年ADI国际会议简况，ADI的发展过程以及欧洲和北美的ADI研究和生产、应用情况。ADI的研究和生产集中在三个问题：(1)对生产ADI用球铁的要求；(2)等温处理工艺；(3)ADI的性能。对这三个问题分别进行了论述。对奥氏体等温形变——等温淬火球铁(AADI)和含碳化物的ADI(CADI)的生产原理以及ADI的环境脆化(EAE)也作了叙述。     

消除应力退火处理对WB36钢粗晶区性能的影响

研究了消除应力(SR)处理对WB36钢粗晶区组织性能的影响,重点研究其SR处理脆化倾向,确定脆化敏感温度,分析了脆化机理.研究结果表明,在590～620℃进行SR处理时,WB36钢粗晶区具有较好的抗回火稳定性,组织精细结构虽然有一定变化,但仍保持较明显的板条马氏体组织形态.随着回火温度的升高,粗晶区硬度逐渐降低,没有出现二次硬化现象.粗晶区有明显的SR处理脆化倾向,韧性损失率超过66%,脆化敏感温度在590℃附近,超过620℃后脆化程度明显减轻.粗晶区SR处理脆化原因是由于高温回火脆性.     

Microstructure and cavitation behaviour of alloyed austempered ductile irons

In this paper, the study of cavitation behaviour of austempered ductile iron (ADI) alloyed with copper, as well as copper and nickel with a fully ausferritic microstructure, is presented. The ADI materials used were austenitized at 900 °C and austempered at 350 °C having an ausferrite microstructure with 16 and 19% of austenite, respectively. The experimental investigations were conducted using the ultrasonically induced cavitation test method. The results show that the cavitation damage was initiated at graphite nodules, as well as in the interface between a graphite nodule and an ausferrite matrix. The cavitation rate revealed that the ADI material alloyed with Cu + Ni austempered at 350 °C/3 h has a higher cavitation resistance in water than ADI alloyed with Cu. An increased cavitation resistance of the ADI material alloyed with Cu and Ni is due to the matrix hardening by stress assisted phase transformation of austenite into the martensite (SATRAM) phenomenon.     

Microstructure and properties of austempered ductile cast iron with refined graphite nodules

Abstract

The present study examined the influence of refinement of graphite nodules on microstructure and tensile properties of austempered ductile cast iron (ADI). A casting technique using deoxidation treatment enabled manufacture of thin walled castings made of ductile cast iron without ledebulite. The thin walled casting (t=2 mm) was subjected to extreme refinement of graphite nodules, where the number of graphite nodules was 1750 mm^?2. Decrease in graphite nodule diameter resulted in refinement of ausferrite and γ-pool structures in ADI and rapid reaction of austempering. The significant increase in the number of graphite nodules resulted in a remarkable drop in the tensile strength and elongation of ADI. These results can be explained by the graphite nodule distance.     

水附着状态下奥贝球铁的拉伸性能及断裂机制

研究结果表明，水附着状态下，奥贝球铁的抗拉强度和伸长率显著降低，发生明显的脆化现象。特别是在工艺窗口内等温淬火处理的试样脆化更显著。经断口分析发现，这种脆化现象是水附着拉伸试样在塑性交形初期。表面附近产生了脆性断裂区域，作为试样破坏的起点，导致试样早期断裂而造成的。     

Hydrogen embrittlement behavior induced by dynamic martensite transformation of Ni–Ti superelastic alloy

The hydrogen embrittlement behavior induced by the martensite transformation of Ni–Ti superelastic alloy subjected to a dynamic cyclic tensile test with hydrogen cathodic charging has been investigated by hydrogen thermal desorption analysis. The critical stress for the martensite transformation steeply decreases with increasing number of deformation cycles, whereas the critical stress for the reverse transformation only slightly changes. The dynamic stress-induced martensite transformation markedly enhances hydrogen absorption, compared with that of the martensite phase itself. The hydrogen concentration at the surface layer of the specimen is evaluated to be above 3500 mass ppm; nevertheless, no fracture associated with the stress-induced martensite transformation occurs. In addition, no hardening is observed at the surface layer of the specimen despite the formation of the hydride and hydrogen enrichment. The hydrogen thermally desorbed at a low temperature markedly increases, indicating that the hydrogen states are changed by the dynamic martensite transformation. Note that interactions between hydrogen and the phase transformation are probably irreversible, although the phase transformation is reversible. The present study shows, for the first time, that the hydrogen embrittlement behavior of the alloy strongly depends on the dynamic change of the hydrogen states accompanied by the martensite transformation.     

FATIGUE PROPERTIES OF AUSTEMPERED DUCTILE IRON （ADI） IN WATER ENVIRONMENT

The acicular ferrite in austempered ductile iron (ADI) matrix around graphite was corroded preferentially in wet condition, promoting crack origination and propagation and resulting in the disappearance of ADI fatigue limit. ADI fatigue strength was gradually reduced with increasing the time of test and was reduced by 50% in wet condition at 10^7 cycles compared with the fatigue limit in dry condition.The fatigue strength variation of ferritic ductile iron in wet condition was similar to that of ADI.The ferritic ductile iron, however, has better corrosion resistance so that the fatigue strength was lowered only by 10^7 in wet condition at 10^7 cycles compared with the fatigue limit in dry condition. On the other hand, the fatigue limits of ADI and ferritic ductile iron were dropped by 32% and 25% in tap water dipping 480h/dry condition respectively compared with those in dry condition.The reduction of fatigue limit was attributed to corrosion pits formation correlated with stress concentration, resulting in origination and propagation of fatigue crack.     

DUCTILE FRACTURE OF FERRITE NODULAR GRAPHITE CAST IRON UNDER MULTIAXIAL TENSILE STRESS

为研究多轴应力下铁素体球铁延性断裂机制,采用三种不同曲率半径(ρ=2,4,10mm)的缺口圆柱试样进行拉伸试验,并用大弹塑性变形有限元分析法计算试样缺口部位的应力、应变分布。在中断拉伸试样上进行金相观察,跟踪石墨球与基体界面处微空洞的形核和长大。研究结果表明,当石墨球与基体界面处的应力到达650MPa时,微空洞形核,空洞长大和聚合导致延性断裂。     

A comparison of hydrogen embrittlement susceptibility of two austenitic stainless steel welds

Slow displacement rate tensile tests were carried out to assess the effect of hydrogen embrittlement on notched tensile strength (NTS) and fracture characteristics of AISI 316L and 254 SMO stainless steel (SS) plates and welds. 254 SMO generally exhibited a better resistance to hydrogen embrittlement than 316L. The strain-induced transformation of austenite to martensite in the 316L SS was responsible for the high hydrogen embrittlement susceptibility of the alloy and weld. Sensitized 254 SMO (i.e., heat-treated at 1000 °C/40 min) base plate and weld comprised of dense precipitates along grain boundaries. Interfacial separation along solidified boundaries was observed with the tensile fracture of 254 SMO weld, especially the sensitized one. Dense grain boundary precipitates not only reduced the ductility but also raised the susceptibility to sulfide stress corrosion cracking of the sensitized 254 SMO plate and weld.