论文部分内容阅读
本文用热模拟技术研究了15MnVN 调质钢板焊接热影响区的组织和韧性,探讨了焊接线能量对组织和性能的影响。用定量金相、电镜观察、X 光相分析、CCT 曲线测定等综合手段,研究了热影响区的组织和相变,用扫描电镜断口观察和断裂路径观察分析了各种显微组织的断裂特征。在△t为8～117 s 范围内,随冷却速度减小,组织从马氏体、侧板条状贝氏体过渡到细针状铁素体和岛状相,最后变为有粗大多边形铁素体析出。讨论了 B_Ⅰ、B_Ⅱ、B_Ⅲ和针状贝氏铁素体的形貌特征及形成条件。试验表明,侧板条状贝氏体不利于韧性,细针状铁素体能阻碍裂纹直线扩展而有利于韧性,粗大的铁素体晶粒也不利于韧性,这样就从组织因素的角度满意地解释了随线能量增大,韧性非单调变化的原因,这就为焊接实际提供了一个有益的启示,即改变线能量,从而控制组织百分数的合适比例,可改善韧性,减少出现裂纹的倾向性。
In this paper, the microstructure and toughness of 15MnVN quenched and tempered steel HAZ were studied by means of thermal simulation, and the influence of welding wire energy on microstructure and properties was discussed. The microstructure and transformation of the HAZ were studied by quantitative metallography, electron microscopy, X-ray phase analysis and CCT curve analysis. The fracture characteristics of various microstructures were observed by scanning electron microscopy and fracture path observation . In the range of △ t from 8 to 117 s, the microstructure changes from martensite and side-lath bainite to fine-needle ferrite and island-like phase with the decrease of cooling rate, and finally becomes coarse polygonal iron Body precipitation. The morphological features and formation conditions of B Ⅰ, B Ⅱ, B Ⅲ and acicular bainitic ferrite were discussed. Experiments show that the side strip of bainite is not conducive to toughness, fine acicular ferrite can hinder the linear expansion of the crack in favor of toughness, coarse ferrite grains are not conducive to the toughness, so from a tissue factor perspective This explains the reason for the non-monotonous change in toughness with increasing line energy, which provides a useful insight into the welding practice by changing the line energy to control the appropriate percentage of the tissue fraction to improve toughness and reduce the tendency to crack .