C-Mn-Ti-B超高强度钢焊接熔合区的形成过程及其组织转变

Mechanism of weld bond formation and its microstructures of martensite/austenite dissimilar metal welded joint

关键词:  熔合区  富奥氏体带  异种金属焊接  焊接热循环  扩散

Key words:  ld bond  austenite-rich zone  dissimilar metal welding  welding thermal cycle  diffusion

摘要:

研究了C-Mn-Ti-B超高强度钢焊接熔合区及其组织转变,发现焊接接头的最高硬度位于熔合区和富奥氏体带,而不是通常所认为的淬火区;富奥氏体带的化学成分及浓度接近于焊缝金属中的成分与浓度。考虑焊接接头所经受的热循环、元素扩散以及室温下焊接接头的组织、成分变化,提出了一种新的富奥氏体带形成机制并建立了熔合区的过程模型。该模型认为:焊接热作用下的焊接接头可划分为三个特征区域:熔化区、固液共存区和固相区;在冷却过程中,熔化区转变为富奥氏体带和焊缝混合区(α+γ组织);固液共存区转变为熔合区;固相区转变为通常意义下的纯热影响区和未发生变化的基体。根据此模型,成功地解释了熔合区类马氏体组织和含碳硼化物(Cr、Fe)₂₃(C、B)₆的转变机理。

Abstract:

In the paper,the weld bond and its microstructures of a dissimilar metal welded joint of C-Mn-Ti-B ultra strength m steel and γ-steel were investigated.It was found that microhardness (HV_0.05) in the weld bond and austenite-rich zone was larger than the one in the quenched zone near the fusion line.And the results shown that chemical compositions in austenite-rich zone were almost the same as those in composite weld metal and the formation of austenite-rich zone was dependent both on its chemical components and on its cooling rate.Considering weld thermal cycle,diffusion of alloy elements such as C、B、Cr、Ni、Fe,chemical elements distributions and microstructures of the joint,a model which can be used to explain the formation of the weld bond and its microstructures transformation was presented.According to the model,a welded joint during welding possessed three zones:liquid zone,liquid+solid coexistent zone and solid zone.During consequent cooling,the metal in liquid zone became the composite weld metal (α+γ) and austenite-rich zone,the metal in liquid+solid zone formed the weld bond,the metal in solid zone transformed into true HAZ and parent metal unaffected by welding heat.Based on the model,martensite like structure and formation of (Cr、Fe)₂₃(C、B)₆ Boride in the weld bond can be explained successfully.