低碳微合金钢中TixO-MnS型复合夹杂对焊接热影响区微观组织相变的影响

对比分析了两种低碳微合金钢中夹杂物对焊接热影响区组织相变的影响.对实验钢中夹杂物的分布和尺寸进行观察并在透射电镜下分析了夹杂物的选区衍射斑图样.采用热膨胀法结合金相分析建立了实验钢的连续冷却转变曲线(CCT曲线)和等温转变曲线(TTT曲线).研究发现,Ti脱氧钢中夹杂物以尺寸小于3μm的Ti_xO-MnS型球状复合夹杂为主,其中Ti_xO核心有两种类型(Ti₂O₃和Ti₃O₅).这类夹杂物具有诱导晶内针状铁素体形核的能力,针状铁素体优先在Ti_xO-MnS型复合夹杂界面上形核,从而导致Ti脱氧钢相对于Al脱氧钢的贝氏体相变开始温度升高,相变时间也明显提前.

Effects of TixO-MnS complex inclusions on the microstructure phase transformation of heat affected zone in the welding of low carbon microalloyed steels

The effects of inclusions in two kinds of low carbon micro-alloy steels on the phase transformation of welding heat affected zone were analyzed and compared.Inclusion distribution and size were observed and the selected area diffraction patterns(SADP) of inclusions were analyzed by transmission electron microscopy(TEM).The continuous cooling transformation curves(CCT) and isothermal cooling transformation curves(TTT) of the test steels were built by thermal expansion method and metallographic analysis.It is shown that the main inclusions in Ti-deoxidized steel are globular Ti_xO-MnS compounds with the size smaller than 3μm,and the Ti_xO cores have two types,Ti₂O₃ and Ti₃O₅.These inclusions have the effect of inducing the nucleation of intragranular acicular ferrite.The acicular ferrite prefers to nucleate on the surface of Ti_xO-MnS compounds in Ti-deoxidized steel,therefore,compared with that in Al-deoxidized steel,the bainite transformation temperature is increased and the transformation time is advanced obviously.