800 MPa级低合金钢焊接热影响区韧性的研究

利用Gkeble-1500热模拟机对弛豫-析出-控制相变(RPC)得到的低合金钢进行不同焊接工艺下的热模拟实验，研究了激光焊接条件下热影响区粗晶区(CGHAz)组织、韧性及其变化规律．结果表明，CGHAz组织为粒状贝氏体；CGHAZ韧性随800-500℃冷却时间￡8／5的增大先增大然后减小，当t8／5为3—8s时，-40℃ CGHAZ冲击吸收功远高于母材的冲击吸收功，表明在合适的激光焊接条件下，激光焊接CGHAZ可获得很好低温韧性．考虑马氏体-奥氏体(M—A)组元平均宽度、总量、分布、形态对粒状贝氏体韧性的综合影响，提出了M—A组元韧性参数的概念，并利用M—A组元韧性参数阐述了CGHAZ韧性随t8／5的变化规律．     

M-A组元对石油储罐用钢粗晶热影响区韧性的影响

利用Gleeble-3800热模拟试验机模拟粗晶热影响区(CGHAZ)焊接热循环,研究了大热输入条件下不同石油储罐用钢的粗晶区组织、韧性及其变化规律.结果表明,各钢粗晶区组织均以贝氏体为主,但由于铁素体、粒状贝氏体等组织的比例差异,韧性差别较大.同时,随着M-A组元面积分数的增加,韧性也呈下降趋势,两者均为先降之后维持较低值.另外,M-A组元的形态等也对韧性有影响,块状M-A组元对韧性的损害大于条状M-A组元.考虑多种合金元素共同作用对M-A组元形成的综合影响,利用多元线性回归的方法对M-A组元面积分数做出了预测,对粗晶区韧性评判有一定实际意义.     

Q460耐候钢焊接粗晶热影响区中M-A组元及其对韧性的影响

利用模拟试验机对Q460耐候钢不同热输入条件下的焊接粗晶热影响区进行模拟,分析粗晶热影响区中显微组织及其中马氏体-奥氏体(M-A)组元的数量、形态、分布及大小对韧性的影响。结果表明,t8/5较小时,组织由板条贝氏体和粒状贝氏体构成,M-A组元尺寸较小;t8/5为100 s时,组织中板条贝氏体量逐渐减小,粒状贝氏体含量逐渐增多,M-A呈块状,尺寸变大,有效晶粒尺寸增加,韧性降低;当t8/5达到150~200 s时,即使组织粗大,M-A组元的量有所减少,出现部分残留奥氏体,韧性也会增加。     

Ti—Nb微合金钢焊接粗晶热影响区组织及韧性

利用碳萃取复型技术研究了Ti—Nb微合金钢及其模拟粗晶区(CGHAZ)中的第二相粒子，并利用OM、TEM及系列冲击试验对Ti—Nb微合金钢焊接粗晶区的组织及韧性进行了研究。研究结果表明，Ti—Nb微合金钢中含有大量的、尺寸细小的TixNb1-x(CyN1-y)粒子，粒子中Nb的相对含量在0．25—0．82之间，形状接近球形。这些粒子具有很高的稳定性，在焊接过程中这些粒子能有效地阻止奥氏体晶粒长大、抑制粗大贝氏体的形成、促进针状铁素体析出及M-A组元的分解，从而显著善低合金高强钢焊接粗晶热影响区的韧性，t8/5越大，这种改善作用越明显。     

微钙钢焊后显微组织中的粒状贝氏体对韧性的影响

研究了焊接热模拟工艺参数t8/5对微钙钢焊接粗晶热影响区(CGHAZ)显微组织和冲击韧度的影响.利用Lepera试剂腐蚀法,采用光学金相显微镜、透射电子显微镜分析了不同t8/5条件下粒状贝氏体中MA组元的形态及分布特征.研究结果表明当冷却速度较快时,M-A组元主要以长条状、呈方向性分布;当冷却速度降低时,M-A组元逐渐变成颗粒状,并失去方向性;当t8/5＝40 s时,韧性较好.     

冶金处理方式对高强钢粗晶热影响区组织与韧性的影响

利用热模拟技术，研究了450MPa级耐大气腐蚀钢不同焊接条件下焊接热影响区组织与性能变化，通过TEM观察不同冶金处理方式（RH精炼炉中加Ti，LF精炼炉中加Ti）第二相粒子的形貌和分布。试验结果表明，在合金成分基本相同的情况下，通过LF精炼炉加Ti的冶金处理，粗晶热影响区中的第二相粒子尺寸更细小，分布1更弥散，阻碍奥氏体晶粒长大的效果更突出。     

S355J2钢粗晶热影响区M-A组元对韧性影响的研究

通过热模拟试验研究了不同热输入条件下S355J2钢粗晶热影响区M-A组元的体积分数及形态对韧性的影响。试验结果表明,热循环峰值加热温度T_max一定,粗晶热影响区M-A组元的体积分数随冷却时间t_8/5的延长而增大,在t_8/5为60_s时M-A组元的体积分数增加的幅度最大;随着t_8/5的延长,M-A组元的形态由颗粒状向长条状和块状转变,在T_max较大、t_8/5较长时,M-A组元的形态将趋向于形成细长条状和块状;粗晶热影响区的韧性随M-A组元体积分数的增大而降低,细长条状和块状的M-A组元对韧性的影响最大     

微合金钢模拟焊接热影响区组织和韧性研究

采用焊接模拟试验方法，研究了不同峰值温度（Tmax）和不同冷却时间（t8/5），对合Ti-N、TI-NB-N两种微合金钢热影响（HAZ）显微组织、奥氏体晶粒度、冲击韧性影响。试验结果表明：Ti-N钢焊接热影响区比Ti-Nb-n钢具有更高的冲击韧性、更适用于大线能量的焊接条件。     

X80管线钢焊接热影响区的韧性分析

X80管线钢在焊接过程中,热影响区由于受到焊接过程热的作用,其组织和性能会发生较大的变化.韧性是天然气长输管线的重要性能,采用热模拟技术、现代工程测试手段和显微分析方法,分析了不同热输入参数下X80管线钢焊接热影响区粗晶区(CGHAZ)韧性(夏比冲击功和CTOD)的差异及其原因.在一定范围内,较高焊接热输入下CGHAZ的韧性比较低热输入下CGHAZ的韧性明显高,超过一定范围,随着热输入的增加韧性激剧下降.造成不同热输入下韧性差异的根本原因是由CGHAZ显微组织的差异引起的.较低的热输入下CGHAZ中产生了一定量的低碳马氏体,从而导致韧性较差.     

V - N钢焊接粗晶区的组织和韧性研究

在不同焊接工艺下对V钢、V—N钢和V—Ti—N钢三种钢的焊接粗晶热影响区的组织和韧性进行了研究。利用Gleeble3500模拟粗晶区的焊接过程，将锻后试样重新加热到峰值温度1350℃后给以不同的热输入量并以相应的t8/5冷却速度进行冷却。结果表明热输入量高时容易得到粒状贝氏体和晶界上的侧板条铁素体组织。随着热输入的降低会出现大量的多边形铁素体和晶界铁素体，并且明显长大。对于含氮量较高的V—N钢来说，容易形成马氏体-奥氏体岛，这种组织降低了粗晶区的韧性。在高氮的情况下添加另一种微合金化元素Ti，钛可以提高HAZ的相变温度，使铁素体和贝氏体连续冷却转变曲线的鼻点左移，细化奥氏体晶粒，促进铁素体和贝氏体的形核，改善粗晶区的韧性。     

含Al超细晶粒钢焊接热影响区组织转变的热模拟

为改善超细晶粒钢焊缝热影响区(HAZ)组织软化问题,对不同Al含量的Fe-Mn-Si超细晶粒钢进行了热模拟研究.结果表明,在一定冷速条件下,此类钢随Al元素添加量的变化,组织从上贝氏体转变为无碳化物贝氏体,且随Al含量的不同,无碳化物贝氏体中残留奥氏体含量及其形态存在明显变化.另一方面,适当Al含量可增加此类钢种焊接条件下贝氏铁素体的形核数量,造成晶粒细化.残留奥氏体相数量与形态变化及晶粒细化是含Al超细晶粒钢HAZ区韧性提高的根本原因.     

Microstructure and toughness of intercritically reheated heat affected zone in reactor pressure vessel steel weld

Abstract

This study is concerned with correlating the metallurgical factors and the toughness of the intercritically reheated coarse grained heat affected zone (ICCGHAZ) of multipass welded SA508–cl. 3 reactor pressure vessel steel. The influence on toughness was investigated by means of a simulated heat affected zone test. Toughness and other properties of the ICCGHAZ were strongly influenced by metallurgical factors such as high concentration of carbon martensitic islands (secondary phase, martensite–austenite constituents) formed along the prior austenite grain boundaries and martensite lath interfaces, and a softened matrix (tempered martensite or bainite). The characteristics (amount, hardness, and size) of the islands were found to be strongly correlated with both peak temperature and the cooling time of the previous pass. The toughness of the ICCGHAZ deteriorated with increasing amounts of martensite–austenite constituents, which were made more abundant by increasing the final peak temperature within the intercritical temperature range. Meanwhile, for the same intercritical peak temperature, toughness decreased with increased cooling time. When the cooling time was short, the dominant factor influencing toughness of the ICCGHAZ was the amount of martensitic islands. However, when the cooling time was long, the hardness difference between the martensitic islands and the softened matrix (tempered martensite) was found to be the dominant factor.     

Observation of twinned martensite in weld heat affected zone of Grade 100 low carbon microalloyed steel

Abstract

The microstructural changes caused by a low nominal heat input of 0.5 kJ mm^-1 in the coarse grained heat affected zone (CGHAZ) of Grade 100 microalloyed steel were investigated. Microhardness measurements suggested that the CGHAZ was martensite of maximum theoretical hardness for the carbon content of the steel. The bulk of the CGHAZ was lath martensite containing none of the small and few of the intermediate sized Nb precipitates responsible for strength and grain size control in the steel plate. Twinned martensite was unexpectedly observed in local areas of the CGHAZ. The formation of twins, which are normally seen in steels with a higher level of carbon, is explained by a combination of the rapid heating rates, high peak temperatures, precipitate dissolution and dispersion, and rapid cooling rates.     

焊接热循环对09MnNiDR钢热影响区低温韧性的影响

利用Gleeble-3800研究了焊接热循环对09MnNiDR钢焊接热影响区粗晶区（CGHAZ）和中间临界再热粗晶区(IRCGHAZ)低温韧性的影响. 结果表明,热输入为15 kJ/cm、层间温度为150 ℃时,CGHAZ组织形态为板条状马氏体+下贝氏体,下贝氏体的存在限制了马氏体的生长,提高了低温韧性,而IRCGHAZ继续保持了CGHAZ的组织. ?70 ℃冲击试验中,IRCGHAZ相比于CGHAZ具有较好的低温冲击韧性,热输入为15 kJ/cm、层间温度为150 ℃时,冲击吸收能量最高为65 J. 根据热模拟结果,采用焊接热输入15 ~ 22 J/cm、层间温度为150 ℃的工艺参数对09MnNiDR钢进行焊接,?70 ℃冲击试验中热影响区冲击吸收能量值为101 J,冲击断口存在大量的等轴韧窝,具有较好的低温韧性;?70 ℃拉伸试验屈服强度为477 MPa、抗拉强度607 MPa、断后伸长率为28.5%,表现出较好的强度和塑性;硬度试验结果表明母材、焊缝和热影响区硬度依次增大,且没有软化现象.     

塑性损伤对焊接接头热影响区韧性的影响

基于小冲杆试验法对25Cr2Ni2Mo V百万千瓦级核电汽轮机焊接转子深窄间隙埋弧焊接头热影响区进行了力学性能评估。通过有限元方法模拟得到焊接转子接头的残余应力分布及塑性应变的演变过程,并引进非线性塑性损伤理论进行汽轮机转子接头韧性分析。小冲杆试验结果表明,埋弧焊热影响区断裂韧性沿着深度方向存在差异,断裂韧性呈现为"中间高两端低"分布特征。由于焊接过程中塑性应变累积,热影响区塑性损伤程度不同,材料塑性储备能变化导致接头热影响区韧性差异。     

Effect of fast cooling on microstructure and toughness of heat affected zone in high strength offshore steel

E690 is a newly developed high strength high toughness steel for offshore structures. The effect of different cooling modes on the microstructure and toughness of the heat affected zone in E690 weldment were investigated in this work. The outcome of microstructural examinations and mechanical tests showed that fast cooling immediately after submerged welding can reduce the width of heat affected and coarse grained zones, as well as improving the low temperature impact toughness. It was also shown that reduction in the grain size of the parent austenite and having lower amounts of retained austenite within bainitic structure are the main causes of the observed improvement.     

Effect of nickel with chromium on microstructure and toughness of heat affected zone in low carbon steel

Abstract

In the present work, the effects of nickel with chromium and of varying heat input on the microstructure and toughness of the grain coarsened heat affected zone (GCHAZ) of a low carbon steel were investigated. In the welding experiments, low carbon steel specimens having five different combinations of nickel and chromium content (0·9Ni–0·3Cr, 1·9Ni–0·8Cr, 2·8Ni–1·3Cr, 3·8 Ni–1·7Cr, and 4·9Ni–2·1Cr, all wt%) were welded using a submerged arc welding process with heat inputs of 0·5, 1, and 2 kJ mm^-1. Following welding, the microstructure, hardness, and toughness of the GCHAZs were investigated. From the results, attempts were made to establish a relationship between heat input, nickel and chromium contents, microstructure, hardness, and toughness of the GCHAZ. Charpy impact testing and microstructural observation showed that, for a heat input of 0·5 kJ mm^-1, nickel plus chromium contents in the range 1·9Ni–0·8Cr to 4·9Ni–2·1Cr promoted the formation of martensite, thereby producing lower toughness values. It was subsequently found that, taking into consideration the microstructure, hardness, and toughness of the GCHAZ, an intermediate heat input (1 kJ mm^-1) gave higher toughness values for all nickel and chromium contents. However, it was observed that satisfactory toughness values could not be obtained by varying the heat input for the 3·8Ni–1·7Cr and 4·9Ni–2·1Cr steels.     

微合金钢焊接热影响区的再热脆化问题

采用金相显微镜、扫描电镜和透射电镜及焊接热模拟技术研究了焊后热处理温度对Nb、V、Ti微合金钢焊接热影响区粗晶区(CGHAZ)组织和性能的影响.结果表明,Nb、V、Ti微合金钢的CGHAZ经焊后热处理后存在再热脆化的现象,为了改善热影响区的韧性,应该选取较低的焊后热处理温度.焊后热处理过程对冲击性能的影响主要与钢中的析出粒子有关.     

含铜时效钢焊接粗晶区组织与韧性分析

研究了含铜时效钢焊接粗晶区的组织与韧性,并测定了含铜时效钢焊接粗晶区连续冷却转变曲线(SHCCT曲线).结果表明,冷却速度对含铜时效钢焊接粗晶区的组织和韧性有显著影响.随着冷却速度的增加,粗晶区的组织由粗大的粒状贝氏体转变为细小的板条贝氏体;当t8/5≤40s时,焊接粗晶区无塑性转变温度低于-50℃,可获得良好的低温韧性.当t8/5＞40s时,焊接粗晶区冲击韧度显著降低,大尺寸M-A组元的增多是导致含铜时效钢韧性恶化的重要原因.