EFFECT OF ELECTRIC FIELD ON THE AUSTENIZATION OF A LOW CARBON STEEL

With an electric field during austenitizing, the martensite transformation of the low carbon steel was promoted, and more martensite were obtained. The electric field promotes the homogeneity of carbon, and reduces the free energy of austenite. The critical neuclus r^* and the critical driving force G^* responsible for the nucleation of proeutectoid ferrite were increased. As a result of which the diffusion controlled proeuctoid ferrite transformation was retarded and the hardenability was improved.     

EFFECT OF MICROSTRUCTURE ON CORROSION FATIGUE BEHAVIOUR OF A LOW CARBON BAINITE STEEL

The behaviour towards corrosion fatigue of low carbon bainite steel with variousmicrostructures after tempered at different temperatures has been examined. The susceptibilityof the steel to corrosion fatigue may be improved by tempering at 300℃.     

LOW CYCLE FATIGUE OF Cr-Mn-N STAINLESS STEEL

An investigation was conducted to examine the low cycle symmetric push-pull fatiguebehaviour of the Cr-Mn-N dual-phase stainless steel.Two groups of specimens,A and B,were used,they were solution treated at 1050 and 1250℃,respectively.The.fatigue life ofgroup A is almost twice as long as that of group B under the same total strain amplitude.Theenergy loss during the fatigue tests and the mophology of the fracture surfaces have been stu-died and discussed.     

EFFECT OF SUBSTRUCTURE AND RESIDUAL STRESS IN STRENGTHENED LAYER ON FATIGUE STRENGTH OF STAINLESS OR LOW CARBON STEEL

In the strengthened layer of stainless steel after shot peening,there are a great amount ofdeformation microtwins which may act as structural strengthening factor and prevent thegradual relaxation of surface residual stress during fatigue,so as to keep its rather high levelof bending fatigue strength.However,in the strengthened surface layer of low carbon steel,dislocation cell structure is so unstalbe during fatigue that its surface residual stress relaxationcannot be retarded.Therefore,the bending fatigue strength of the low carbon steel can not beimprored by shot peening.     

PHOSPHORUS SEGREGATION AND ANNEALING TEXTURE IN A LOW CARBON STEEL SHEETS

The present work is to study the effect of phosphorus on the annealing texture of a low carbonsteel at different cold rolling and annealing condition by means of pole-figure,inverse-polefigure and orientation distribution function(ODF)method.The microstructure and distribu-tion of phosphorus in steel sheet are studied by means of metallography,scanning electron mi-croscope(SEM)and electron probe microanalysis(EPMA).The results show that phos-phorus promotes the formation of the fiber texture of〈011〉parallel to the rolling direc-tion and〈111〉normal to the sheet surface.The texture was found to be affected mainlyby preannealing temperatures,promoted at 390 or 590℃,and retarded at 490℃.At thepreannealing temperature promoting the formation of texture,phosphorus segregation to theinterior of grains was observed.It seems that the formation of the fiber texture may be associ-ated with the segregation of phosphorus.     

CHARACTERISTICS OF MARTENSITE IN A HIGH CARBON FERROALLOY

Some characteristics of plate martensite in a 1.03% C ferroalloy have been studied by usingthe transmission electron microscopy.The habit plane of the plate martensite in this ferroalloywas found to be close to{224}_f.The morphology,distribution,coalescence and curving ofmartensite as well as the substructure in both martensite and austenite have been observed.The mechanism of both nucleation and growth of the martensite have been discussed.     

EXAMINATION OF CARBON DIFFUSION IN TANTALUM CLAD STEEL COMPOSITE

ＥＸＡＭＩＮＡＴＩＯＮＯＦＣＡＲＢＯＮＤＩＦＦＵＳＩＯＮＩＮＴＡＮＴＡＬＵＭＣＬＡＤＳＴＥＥＬＣＯＭＰＯＳＩＴＥ①ＸｉａＣｈａｎｇｑｉｎｇ，ＪｉｎＺｈａｎｐｅｎｇＤｅｐａｒｔｍｅｎｔｏｆＭａｔｅｒｉａｌｓＳｃｉｅｎｃｅａｎｄＥｎｇｉｎｅｒｉｎｇ，Ｃｅ...     

ANALYSIS ON THE BEHAVIOR OF PRECIPITATES IN ULTRA-THIN HOT STRIP OF PLAIN LOW CARBON STEEL PRODUCED BY COMPACT STRIP PRODUCTION

This paper investigated the mechanism of precipitation and its influence upon prop-erties of ultra-thin hot strips of low carbon steel produced by CSP techniques using experiment and thermodynamics theory. The experimental results show that there are lots of fine and dispersive precipitates in microstructures. By analysis, most of aluminum nitrides are in grains, while coexisted precipitates of MnS are along grain boundaries. Coexisted precipitates compose cation-vacancy type oxides such as Al2O3 in the core, while MnS is at the fringe of surface. The precipitation behavior of AlN and MnS in the hot strip is studied by thermodynamic calculation. At last, implica-tions between strengthening effect and techniques are analyzed using obtained solubility products.     

ACOUSTIC EMISSION DURING PLASTIC DEFORMATION AND MICROCRACKING PROCESS OF α-Ti

本文采用声发射能量技术研究低强度、高塑性材料α-Ti的形变、断裂特征。发现声发射总能量ΣE与长程应力场σ-σs间存在lgΣE-lg(σ-σs)的线性关系,曲线的拐点即为开裂点。因而有可能利用这种方法较精确地测定出低强度、高塑性材料的开裂点,为这类材料的断裂力学测试解决了一个难题。 α-Ti的形变、断裂过程中存在两种声发射源:位错运动引起的滑移和裂纹的徽开裂和长大。     

MODELING OF FERRITE GRAIN GROWTH OF LOW CARBON STEELS DURING HOT ROLLING

1．I尬roductlonThe dewlopment of mathematical model to predict the inal room temperature proper－ties ofhot－rolled steels hajs received consider劝ie attention over the past t侧 decades[1一31．These models contain equations to calculate the mlcrostructure     

低碳钢氢蚀后拉伸过程中的声发射特征

对氢蚀前后低碳钢拉伸过程中的声发射（AE）行为进行了研究。结果表明，氢蚀使低碳钢拉伸过程事件数明显减少，但是高幅声发射信号的振铃计数明显增多，声发射源以显微裂纹长大与连接为主。     

20G钢氢腐蚀的超声背散检测

选用20G低碳钢,经450℃和500℃,18MPa氢气中分别暴露240,480和720小时,使材料发生不同程度氢腐蚀,用背散法对氢蚀进行了超声波检测结果表明,背散法对氢蚀程度非常敏感,用杂草波平均高度与原始波高之比做为信噪比,能很好地反映氢蚀程度,论证了用背散法检测氢蚀程度的可能性.     

热塑性变形条件下碳钢氢腐蚀裂纹的愈合

采用热压愈合的实验方法，对碳钢氢腐蚀裂纹的愈合行为进行研究．结果表明，在热塑性变形条件下，经1000℃、压下率为40％、15min短时间处理，能够基本消除碳钢试样内的氢蚀裂纹，局部未修复裂纹呈现为尺寸4μm～8μm的透镜状．与单纯高温愈合处理（1000℃循环热处理10h）的实验结果相比，塑性形变可大大缩短裂纹愈合所需要的热处理时间。热塑性变形下的裂纹愈合进程及程度加大，且氢蚀裂纹内高压甲烷气体的分解不是裂纹愈合过程的控速步骤．     

热处理愈合不锈钢氢蚀裂纹实验研究

对含氢腐蚀甲烷气泡和裂纹的304不锈钢进行了600℃,6h的再热处理,SEM观察表明,氢蚀气泡和裂纹发生了完全愈合,氢蚀气泡和裂纹的愈合机制是热扩散,Fe和C在奥氏体中的快速扩散是304不锈钢中氢蚀裂纹的自愈合的必要条件,发生氢蚀裂纹愈合的动力是氢蚀气泡长大导致的塑性变形能Es,在Fe,C和H原子扩散都足够快的情况下,氢蚀气泡和裂纹的愈合条件是Es≥2r(γ为界面表面张力,r为气泡半径或裂纹半长）,氢蚀气泡或裂纹的愈合过程伴随亚晶长大,多边形化的高温回复过程甚至再结晶。     

铝合金凝固过程的声发射及氢气析出过程

采用声发射测试技术,对Al-Si和Al-Cu系合金凝固过程进行监测,证实合金在凝固过程中存在声发射现象,表现为两个声发射信号计数率峰,两个峰的总计数都随着合金中气体含量增加而增高。本文对Al-Si,Al-Cu合金系产生声发射现象的机理进行了探讨,同时,借助其它实验手段证实了声发射信号与合金凝固中气体析出有很好的对应性。第一个计数率峰与气泡在枝晶臂间形核相吻合。第二个计数率峰与凝固末期的枝晶间拉裂现象相对应,可能是氢在枝晶间析出和聚集产生高压氢导致的拉裂。     

ACOUSTIC EMISSION AND HYDROGEN EVOLUTION DURING SOLIDIFICATION OF ALUMINUM ALLOYS

Study of the solidification process of both Al-Si and Al-Cu alloys proved the presence ofacoustic emission phenomena.Two peaks of count rate have been observed.The total countsof both peaks increase with the increasing hydrogen content of the alloy.The mechanism ofproducing the acoustic emission has been discussed.At the same time,results obtained by oth-er techniques strongly support the good correlation between the acoustic emission andhydrogen releasing during solidification.The bubble nucleation between dendrite arms is themain cause of the first peak,while the fracture of the bridge connecting the interdendrites atthe later stage of solidification is the main cause of the second peak.It is probably due to thehydrogen evolution and accumulation to create high pressure in the interdendritie region.     

碳钢氢腐蚀裂纹愈合的TEM观察

对含氢腐蚀裂纹的碳钢进行1000℃、10h的再热循环处理后，SEM和TEM观察表明，氢蚀裂纹发生完全愈合．Fe和C在γ-Fe中的快速扩散是碳钢中氢蚀裂纹愈合的必要条件．氢蚀裂纹愈合的动力是氢蚀气泡长大导致的塑性变形能Es，在Fe、C和氢原子扩散都足够快的情况下，氢蚀裂纹的愈合条件是Es≥2γ／r(γ为界面表面张力，r为裂纹半长)．TEM观察表明，氢蚀裂纹形成使晶界发生严重的塑性变形，位错密度高且相互缠绕，氢蚀裂纹的愈合过程伴随着亚晶长大、晶界滑动的高温回复过程甚至再结晶，位错回复低密度、整齐排列的低能态，片层状珠光体的出现也表明基体组织发生修复。     

15CrMo钢氢蚀激活能测定及焊头氢蚀分析

选用１５Ｃｒ－Ｍｏ钢，分别在３００，３５０，４００，４５０，５００℃和１８ＭＰａ下氢蚀不同时间，分析其高温高压氢中脱碳激活能和氢蚀激活能。结果表明，氢蚀脱碳激活能与氢蚀激活能接近，说明其氢蚀初期，氢蚀过程由碳的扩散速率控制．焊接热影响区的氢蚀程度大于基体．     

高强度低碳贝氏体钢的工艺与组织细化

在超低碳贝氏体钢中，采用弛豫-析出-控制相变(RPC)技术可得到细化的中温转变组织，组织类型为细化的板条贝氏体及少量不规则粒状贝氏体或针状铁素体，与一般控轧空冷和调质处理组织比较，除细化外，所得贝氏体类型及形貌均有所不同，通过这种工艺细化的低碳贝氏体钢板其强度比控轧后空冷或轧后再加热-淬火(调质处理)钢有明显提高。在采用RPC工艺时，轧后弛豫时间长短对最终组织细化程度和形貌也有明显影响，从而造成性能有所差别，终轧后弛豫阶段形成并被应变诱导析出物钉扎的位错胞状组织或亚晶结构是细化相变组织、阻碍贝氏体生长的主要原因，冷却过程中，在贝氏体相变前形成的不规则粒状贝氏体或针状铁索体，分割了压扁的原奥氏体晶粒，同样限制了贝氏体板条柬的长度和宽度。     

超高强度钢37SiMnCrNiMoV应力腐蚀过程中声发射信号的研究

采用AE技术对超高强度钢37SiMnCrNiMoV在3.5%NaCl 溶液中的SCC行为进行研究.证明在裂纹的稳定扩展区内,裂纹是间歇,跳跃式的扩展.发现 腐蚀裂纹尖端的应力强度因子处于0.7KIC和0.23KIC时,平均每次声发射事件 对应的裂纹扩展量相近;应力强度因子处于035 KIC时,平均每次声发射事件对应 的裂纹扩展量较大;声发射事件的发生频率随应力水平的增加,有很大的增加.腐蚀裂纹扩 展的全过程存在两种不同的声发射信号.还证明了37SiMnCrNiMoV的应力腐蚀裂纹扩展过程 中,氢脆起着主要的作用.提出了计算腐蚀裂纹稳定扩展区内声发射事件累积数的公式.