氮对钒微合金钢粗晶热影响区(CGHAZ)的组织和性能的影响

用热模拟方法研究了氮含量对钒微合金钢粗晶热影响区(CGHAZ)的组织和性能的影响。结果表明,氮含量为0.0031%或0.021%时,CGHAZ的韧性较差。氮含量0.0031%时CGHAZ中有少量的Ti(C,N),晶界铁素体(GBF)较少,晶内有大量尺寸较大的侧板条铁素体(FSP),解理裂纹沿FSP的直线扩展使其韧性较差。氮含量0.021%时在CGHAZ中生成了较为粗大的(Ti, V)(C, N)和GBF,解理裂纹沿GBF扩展使其韧性较差。氮含量为0.012%时低温韧性较好,在CGHAZ中生成了大量细小的(Ti, V)(C, N)粒子,且GBF尺寸相对较小,晶内有大量的针状铁素体(AF)。这些因素都有利于阻止裂纹扩展,使其低温韧性显著提高。     

析出强化超细晶粒钢焊接热影响区粗晶区的组织和性能

为研究焊接对800 MPa级Ti、Nb复合微合金化析出强化超细晶粒钢组织性能的影响.运用Gleeble3500热模拟试验机,对实验钢进行单道次焊接热循环试验,并研究冷却速度、冷却时间t8/5对焊接热影响区粗晶区(CGHAZ)组织、性能的影响.结果表明:冷却速度5~15℃/s,CGHAZ的组织为贝氏体,冷却速度进一步增大,会出现马氏体.随着冷却时间t8/5的增加,原奥氏体晶粒尺寸逐渐增加,硬度值逐渐降低,冲击韧性先上升后下降.t8/5为20~120 s时,CGHAZ显微硬度(223~250.4 HV)均小于母材的显微硬度(270.6 HV),出现软化现象,t8/5为20 s时,冲击吸收功最高,为18.2 J,但仅有母材的25.3%.经历焊接热循环后,奥氏体晶粒粗化以及CGHAZ出现贝氏体组织是导致脆化的主要原因.     

V、N含量和热处理对抗腐蚀油套管组织和性能的影响

研究了不同正火温度和不同V、N含量对1%Cr中碳钢的组织和力学性能的影响,结果表明,V、N含量提高,虽然增加了析出强化作用,但材料强度却随之降低,韧性大幅度提高。在950℃正火温度下较高V、N含量V3钢中的铁素体含量是较低V、N含量的V1钢中铁素体的6倍,而在850℃正火温度下V1钢中的珠光体晶粒尺寸是V3钢的3倍。随着正火温度提高,铁素体和珠光体含量均降低,贝氏体含量增加。因此可以看出增加V、N含量以及降低正火温度都有利于铁素体和珠光体组织转变。通过分析可知,未溶解的V(C,N)会阻碍奥氏体晶粒的粗化,并作为先共析铁素体的形核质点促进了铁素体转变,阻碍了贝氏体的形成,从而获得了具有良好抗腐蚀性能的铁素体+珠光体组织结构,并且使材料强度达到80ksi(552 MPa)。     

正火温度对Nb-V-Ti微合金化大截面锻材Q345E钢组织与韧性的影响

采用热膨胀法测定了Nb-V-Ti微合金化Q345E钢的相变临界温度Ac1和Ac3,使用45kW箱式电阻炉对实验钢进行了正火处理,利用光学显微镜(OM)、扫描电镜(SEM)、电子背散射衍射(EBSD)和透射电镜(TEM)观察了正火后试样的组织演变规律,分析了正火温度对组织与低温韧性的影响。结果表明,Q345E钢的Ac1约732℃、Ac3约871℃;当正火温度为820℃和850℃时,组织由针状珠光体和未发生重结晶的粗大原始铁素体构成,针状珠光体由针状奥氏体转变而来,相邻针状珠光体中的铁素体相具有相同的晶体取向特征;当正火温度不低于880℃时,组织由重结晶后的铁素体和珠光体构成,随正火温度的提高组织尺寸逐渐增大;当正火温度为820~940℃时,随正火温度的提高冲击功呈现先增加后降低的变化规律,组织类型、尺寸、形态和均匀性是影响大截面锻材Q345E低温韧性的主要因素。     

氮含量对钒微合金钢粗晶热影响区组织和韧性的影响

采用焊接热模拟的方法,研究了氮含量对实验钢焊接粗晶热影响区(CGHAZ)显微组织和韧性的影响规律。结果表明:随着氮含量的增加,CGHAZ的组织从晶界铁素体、贝氏体和侧板条铁素体转变成针状铁素体、多边形铁素体和少量的贝氏体,且铁素体晶粒细化;CGHAZ韧脆转变温度(FATT₅₀)先降低后升高,屈服强度升高。氮含量从0.004 4%增加到0.009 4%时,有效晶粒尺寸减小,导致CGHAZ的FATT₅₀降低;氮含量从0.009 4%增加到0.019 0%时,CGHAZ中固溶氮、屈服强度增量对FATT₅₀的综合作用大于晶粒的细化作用,导致FATT₅₀升高。      

抗大变形管线钢焊接粗晶区的组织和韧性

采用Gleeble-3800模拟研究了抗大变形管线钢中不同Nb含量和不同热输入时的焊接热循环过程,并通过光学显微镜(OM)、扫描电镜(SEM)、电子背散射衍射(EBSD)及冲击载荷试验等研究了抗大变形管线钢焊接粗晶区(CGHAZ)的微观组织特征和冲击韧性。结果表明:随着热输入量的增加显微组织逐渐从板条贝氏体到粒状贝氏体过渡,M/A尺寸增大,比例提高,同时显微组织的平均有效晶粒尺寸也增大;在热输入相同的条件下,高Nb钢中原始奥氏体细化明显,组织中M/A尺寸细小,分布更加弥散;随着焊接热输入量的增加实验钢的冲击韧性急剧降低,高Nb钢的韧性急剧降低的热输入临界值约为35 k J/cm,低Nb钢韧性降低的热输入临界值约为25 k J/cm,在整个实验参数范围内,高Nb钢的冲击韧性值明显比低Nb实验钢的高。     

Zr微合金钢粗晶热影响区韧性和组织分析

为了获得大热输入焊接热影响区,利用实验室25 kg真空感应炉炼制不同Zr含量的实验用钢,在MMS-300型热模拟机上,对其试样进行热输入能量为100 kJ/cm,峰值温度1 400℃的大热输入焊接热模拟实验.借助电子探针(EPMA)等对CGHAZ中形成针状铁素体(AF)的夹杂物进行了微区分析,研究了夹杂物的化学组成和分布形态.结果表明:当Zr含量为0.003%时,焊接CGHAZ区低温冲击韧性最好,当Zr含量大于0.003%时CGHAZ的低温韧性随着Zr含量的增加呈下降趋势;CGHAZ中的奥氏体晶粒尺寸随小尺寸夹杂物数量的增加而降低;形成AF的夹杂物多以Zr的氧化物为核心表面析出MnS的复合氧化物夹杂,尺寸在0.5～3μm.     

CLAM钢焊接热影响区连续冷却过程相变规律

采用Gleeble1500热模拟机,物理模拟中国低活化马氏体(CLAM)钢焊接热影响区粗晶区(CGHAZ)的冷却过程,结合组织观察、Thermo-calc热力学软件计算和硬度测试等手段分析了冷速ωc对CGHAZ的组织演变及硬度的影响,并绘制了CLAM钢的SH-CCT图。结果表明:CLAM钢的CGHAZ中过冷奥氏体仅发生低温板条马氏体(LM)及先共析铁素体(α铁素体)转变。0.25℃/s为CGHAZ过冷奥氏体发生完全LM相变的临界冷速。当ωc>0.25℃/s时,CGHAZ的组织除LM外,还含有少量的δ铁素体,δ铁素体是δ→γ相变阶段转变不充分而残留至室温的组织,在该冷速范围内粗晶区的组织形态变化不明显。当ωc<0.25℃/s时,由于发生γ→α转变,CGHAZ的组织为α铁素体及LM的混合组织,随着冷速的降低,α铁素体含量增加;当ωc=0.04℃/s时,CGHAZ的组织已完全转变为α铁素体和碳化物的混合组织。     

石油储罐钢焊接热影响区模拟研究

采用焊接热模拟技术,研究不同焊接热输入条件下焊接热循环对石油储罐钢焊接热影响区粗晶区(CGHAZ)的组织和性能的影响.结果表明:实验钢在80～100kJ/cm的大热输入下,热影响区仍能够保持良好的低温韧性;随着焊接热输入的增加,实验钢CGHAZ组织变粗大,低温冲击功下降;钢中弥散分布着大量细小TiN粒子,在焊接热循环中...     

两次淬火对HSLA钢组织和冲击韧性的影响

研究了两次淬火+回火和传统的一次淬火+回火热处理对HSAL钢的显微组织和力学性能的影响。结果表明,在不显著降低强度的条件下,两次淬火使实验钢的冲击功明显提高,还改善了低温韧性和稳定性。两次淬火回火热处理可细化钢的组织,使原始奥氏体晶粒的尺寸和有效晶粒尺寸减小、大角度界面的密度和解离裂纹的扩展偏折频率提高。组织的细化和大角度晶界的增多抑制了裂纹的扩展,使韧性大幅度提高。     

Correlation of microstructures and low temperature toughness in low carbon Mn–Mo–Nb pipeline steel

Abstract

By adjusting thermomechanical controlled processing parameters, different microstructures were obtained in a low carbon Mn–Mo–Nb pipeline steel. The microstructural characteristic and its effect on low temperature toughness were investigated. The results show that under higher reduction in austenite non-recrystallisation region and faster cooling rate during accelerated cooling, the microstructure is dominated by acicular ferrite (AF) accompanied by a small amount of fine martensite/austenite (M/A) islands. In contrast, lower reduction and slower cooling rate lead to a predominantly quasi-polygonal ferrite microstructure with coarse M/A islands. The fine effective grain size (EGS) and the high fraction of high angle grain boundaries (HAGBs) make the cleavage crack propagation direction deflect frequently. The coarse M/A islands can lead to cleavage microcracks at the M–A/ferrite matrix interfaces. Compared with the microstructure mainly consisting of quasi-polygonal ferrite, the microstructure dominated by AF exhibits excellent low temperature toughness because of fine EGS, high fraction of HAGBs and fine M/A islands.     

Effect of Cu addition on microstructure and impact toughness in the simulated coarse-grained heat-affected zone of high-strength low-alloy steels

The effects of Cu content on microstructure and impact toughness in the simulated coarse-grained heat-affected zone (CGHAZ) of high-strength low-alloy steels were investigated. It has been observed that the microstructure in the simulated CGHAZ of Cu-free steel is dominated by a small proportion of acicular ferrite and predominantly bainite with martensite–austenite constituent. Whereas, in the 0.45 and 1.01% Cu-containing steels, the acicular ferrite increased significantly due to the effective nucleation on intragranular inclusions with outer layer of MnS and CuS. The formation of acicular ferrite is attributed to superior high heat-affected zone impact toughness in the 0.45% Cu-containing steel. Furthermore, the increasing martensite–austenite constituent and ε-Cu precipitates in the simulated CGHAZ of 1.01% Cu-containing steel caused degradation in impact toughness.     

12CrNi5MoV锻钢焊接热影响区组织与性能研究

采用热模拟技术研究了12CrNi5MoV锻钢焊接热影响区粗晶区的组织与性能。结果表明,经历一次焊接热循环后,材料粗晶区的抗拉强度与原始态试样相比显著升高,而冲击韧性明显降低;冷却过程中冷却速度加快引起材料组织中孪晶马氏体与残余奥氏体含量的增加是其粗晶区力学性能变化的主要原因。     

原位观察稀土镧对低合金高强度钢焊接热影响区晶粒细化的影响

使用高温激光共聚焦扫描显微镜原位观察了含0.016％(质量分数,下同)的La和不含La的低合金高强钢模拟焊接热影响区中高温阶段奥氏体的长大和组织转变行为,并使用光学显微镜和电子扫描显微镜对比分析了添加0.016％的La对粗晶热影响区晶粒细化的影响.结果 表明:添加0.016％的La使低合金高强钢中的夹杂物由Al-Mg-...     

Effect of austenite transformation degree on microstructure and fracture toughness of high-strain pipeline steel

In order to clarify the relationships among austenite transformation degree, microstructure and fracture toughness, the simulated inter-critical heat-affected zones (ICHAZ) of high-strain pipeline steel were prepared with five different austenitizing degrees (0%, 20%, 50%, 80% and 100%). The microstructure and the fracture toughness of simulated ICHAZ specimens were investigated. It was found that the microstructure evolution and fracture toughness of ICHAZ were closely related to the austenite transformation degree. In partially austenitized ICHAZ, the fresh bainite and ferrite could break the original structure and decreased effective grain size. The fine grains with disorderly arranged M–A constituents could improve fracture toughness of partially austenitized ICHAZ. In contrast, the linearly aligned M–A constituents in 0%-austenitized region and the chain-distributed ones in 100%-austenitized region could lead to deterioration of fracture toughness. Furthermore, the excellent fracture toughness of partially austenitized ICHAZ was related to the high density of high-angle grain boundaries (HAGBs), homogeneous distribution of local strain as well as the high percentage of small-deformed grains (SDGs).

     

回火温度对两相区退火海工钢组织和性能的影响

对690 MPa级海工钢进行“淬火+两相区退火+回火”三步热处理,研究了回火温度对其组织和性能的影响、分析了力学性能变化与组织演变和残余奥氏体体积分数之间的关系。结果表明：回火后实验钢的显微组织为回火贝氏体/马氏体、临界铁素体和残余奥氏体的混合组织。随着回火温度的提高贝氏体/马氏体和临界铁素体逐渐分解成小尺寸晶粒,而残余奥氏体的体积分数逐渐增加;屈服强度由787 MPa降低到716 MPa,塑性和低温韧性明显增强,断后伸长率由20.30%增至29.24%,-40℃下的冲击功由77 J提升至150 J。残余奥氏体体积分数的增加引起裂纹扩展功增大,是低温韧性提高的主要原因。贝氏体/马氏体的分解和残余奥氏体的生成,引起组织细化、晶粒内低KAM值位错的比例逐渐提高和小角度晶界峰值的频率增大,使材料的塑性和韧性显著提高。     

HAZ microstructure simulation in welding of a ultra fine grain steel

In the present work the evolution of grain structure in the weld HAZ (heat affected zone) under welding thermal cycle was simulated. Especially the grain growth in the HAZ of a SS400 ultra fine grain steel was investigated. An integrated 3-D Monte Carlo (MC) simulation system for grain growth of the weld HAZ was developed based on Microsoft Windows. The results indicate that MC simulation is an effective way to investigate the grain growth in weld HAZ. The method not only simulates the non-isothermal dynamics process of the grain growth in the weld HAZ, but also visualizes the austenite grains realistically. Moreover, the thermal pinning effect can be easily included in the simulation process. The grain sizes of the CGHAZ (coarse grain heat affected zone) obtained from MC simulation are basically in agreement with the experimental measurement of the real welded joints under different heat input. Furthermore, the simulation indicates that the grain growth degree is higher for the SS400 ultra fine grain steel compared to conventional steel. With the increase in the heat input, the grain growth of the CGHAZ rapidly increases. Because the activation energy of the grain growth is lower for the SS400 ultra fine grain steel, austenite grains can grow at a relatively lower temperature, hence the range of the CGHAZ becomes wider.