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.

Microstructure and properties of CGHAZ of precipitation strengthening ultra-fine grain steel

By using Gleeble 3500 thermal simulation testing machine, single pass welding thermal cycle tests were conducted on 800 MPa grade Ti-Nb micro?alloyed precipitation strengthening ultra?fine grain steel. The influence of cooling rate and cooling time t8/5 on the microstructure and properties of coarse?grained heat affected zone ( CGHAZ ) was investigated. The results show that the microstructure of CGHAZ is Bainite with the cooling rates ranging from 5 to 15℃/s. When cooling rate increases further, the microstructure of CGHAZ is Martensite. With increasing t8/5 , the grain size of the original austenite increases and the hardness decreases. With increasing t8/5 , the impact toughness increases at first and then decreases. When t8/5 ranges from 20 to120 s, the micro hardness of CGHAZ, ranging from 223 HV to 250.4 HV, is less than that of base material (270.6 HV), and softening phenomenon appears. When t8/5 is 20 s, CGHAZ has highest impact toughness of 18.2 J, which is 25.3% of the parent material. The austenite grain coarsening and the bainite microstructure appearing in CGHAZ after welding thermal cycle are the maincause of the embrittlement.