轧制工艺对V-N-Ti钢焊接粗晶热影响区组织和韧性的影响

摘 要: 为了分析大线能量焊接下接头低温韧性的影响因素,研究轧制工艺对V-N-Ti钢粗晶热影响区(CGHAZ)组织和韧性的影响。试验结果表明,当终轧温度从950降低到800 ℃,且t_8/5(从800冷却到500 ℃的时间)为180 s时,CGHAZ中铁素体面积百分数从91.2%降低到53.9%,贝氏体面积百分数从0%增加到31.1%,-20 ℃冲击功从182降低到92 J。上述现象是由于终轧温度影响了母材中尺寸为30~70 nm的富Ti-(Ti,V)(C,N)粒子的成分。与低温终轧相比,高终轧温度条件下母材中富Ti-(Ti,V)(C,N)粒子的V元素含量较高,这使其在焊接加热过程中更易发生溶解,并在焊接冷却过程中以细小富Ti-(Ti,V)(C,N)析出,钉扎奥氏体晶界;焊接冷却过程中,富Ti-(Ti,V)(C,N)可以作为V元素的析出核心促进VN的析出,提高了其铁素体形核能力,改善了CGHAZ组织和韧性。

Effect of rolling process on microstructure and toughness of coarse grain heat affected zone of V-N-Ti steel

In order to analyze the influencing factors of low temperature toughness of joints under high heat input welding, the effect of rolling process on microstructure and toughness of coarse grain heat-affected zones (CGHAZ) of V-N-Ti steel was analyzed. The results showed that when the final rolling temperature was decreased from 950 to 800 ℃ and t_8/5(the time from 800 to 500 ℃) is 180 s, the area fraction of ferrite in CGHAZ was reduced from 91.2% to 53.9%, bainite was increased from 0 to 31.1%, and the impact energy of CGHAZ at -20 ℃ was reduced from 182 to 92 J. The reason for the change was that the final rolling temperature affected the composition of Ti-rich (Ti,V)(C,N) particles with a base material size of 30-70 nm in experimental steel. Compared with low-temperature finishing rolling, vanadium content of Ti-rich (Ti,V)(C,N) particles in the base metal under high finishing temperature conditions was higher, which made it easier to dissolve during welding heating process and re-precipitate as fine Ti-rich (Ti,V)(C,N) during cooling stage of welding to pin the austenite grain boundaries. During welding cooling process, Ti-rich (Ti,V)(C,N) can be used as the precipitation core of vanadium to promote precipitation of VN, increase the ferrite nucleation potency, and improve the CGHAZ microstructure and toughness.