不同t8/5条件下NM400耐磨钢焊接热影响区的组织及性能Microstructure and Properties of Welding HAZ in NM400 Wear-Resistant Steel with Different t8/5

利用Gleeble-3500型热模拟试验机, 对NM400耐磨钢在不同热循环条件下进行焊接热模拟试验, 研究了从800 ℃至500 ℃的冷却时间t8/5对焊接热影响区粗晶区和临界粗晶区组织及性能的影响。结果表明: 单次热循环时, 随着t8/5的增大, 粗晶区硬度逐渐下降, 而-20 ℃冲击吸收功先增加后下降; t8/5为10 s时, 粗晶区冲击吸收功最高(64 J), 这是因为形成了板条马氏体和下贝氏体的混合组织, 且马氏体发生了自回火; 二次热循环时, 随着t8/5的增大, 临界粗晶区硬度和冲击吸收功下降, 且均低于单次热循环粗晶区的, 这是由于不完全重结晶形成了粒状贝氏体和粗大上贝氏体组织; 此钢种焊接时, t8/5应控制在10 s左右。
The welding thermal simulation experiments for NM400 wear-resistant steel under different thermal cycle conditions were carried out on Gleeble-3500 thermal simulator to study the effect of t8/5 (cooling time from 800 ℃ to 500 ℃) on microstructure and properties of coarse grained heat-affected zone (CGHAZ) and intercritically coarse grained heat-affected zone (IC CGHAZ). The results show that with the increase of t8/5 in single-pass welding thermal cycle, the hardness decreased gradually, while the impact energy (-20 ℃) increased first and then decreased. CGHAZ had the highest impact energy (64 J) when the t8/5 was 10 s, because the structure was composed of a great quantity of lath martensite and a little lower bainite, and the martensite had self-tempered. With the increase of t8/5 in twice-pass welding thermal cycle, both the hardness and impact energy of IC CGHAZ decreased, and were lower than those of CGHAZ, because granular bainite and coarse upper bainite formed in the process of incomplete recrystallizations. The t8/5 for this steel should be controlled around 10 s during welding.