回火时间对低焊接裂纹敏感性压力容器用钢组织性能的影响

Effect of tempering time on microstructure and properties of low welding crack sensitivity pressure vessel steel

采用金相显微镜、扫描电镜、透射电镜镜、拉伸试验机、冲击试验机、硬度计等研究回火时间对低焊接裂纹敏感性压力容器用钢组织性能的影响。所设计化学成分的试验钢轧后进行950℃淬火,610℃回火12、23、45和180 min的调质热处理。结果表明,调质后显微组织主要由回火索氏体组成;随着回火时间的延长,晶内位错密度降低,生成不同取向的板条状晶粒,并且沿着晶界有碳化物析出,保证了钢板具有良好的低焊接裂纹敏感性。随着回火温度的升高,强度受晶内位错密度和Nb、V元素的碳化物影响呈先降低后升高趋势,冲击性能和硬度受碳化物M23C6析出的影响基本呈下降趋势。

Effect of tempering time on the microstructure and properties of a low welding crack sensitivity pressure vessel steel with designed chemical composition was studied using metallographic microscope,scanning electron microscope,transmission electron microscope,tensile testing machine,impact testing machine and hardness tester,etc.The tested steel was quenched at 950℃after rolling and tempered at 610℃for 12,23,45 and 180 min,respectively.The results indicate that the microstructure after quenching and tempering is mainly composed of tempered sorbite.With the increase of tempering time,the intragranular dislocation density decreases,and lath grains with different orientations are generated,and carbides are precipitated along the grain boundary,which ensures that the steel plate has a good low welding crack sensitivity.As the tempering temperature increases,the strength decreases first and then increases due to the influence of intragranular dislocation density and carbides of Nb and V elements,while the impact property and hardness are basically decreasing due to the precipitation of carbides M23 C6.