不同t8/5條件下NM400耐磨鋼焊接熱影響區(qū)的組織及性能Microstructure and Properties of Welding HAZ in NM400 Wear-Resistant Steel with Different t8/5

利用Gleeble-3500型熱模擬試驗機, 對NM400耐磨鋼在不同熱循環(huán)條件下進行焊接熱模擬試驗, 研究了從800 ℃至500 ℃的冷卻時間t8/5對焊接熱影響區(qū)粗晶區(qū)和臨界粗晶區(qū)組織及性能的影響。結果表明: 單次熱循環(huán)時, 隨著t8/5的增大, 粗晶區(qū)硬度逐漸下降, 而-20 ℃沖擊吸收功先增加后下降; t8/5為10 s時, 粗晶區(qū)沖擊吸收功最高(64 J), 這是因為形成了板條馬氏體和下貝氏體的混合組織, 且馬氏體發(fā)生了自回火; 二次熱循環(huán)時, 隨著t8/5的增大, 臨界粗晶區(qū)硬度和沖擊吸收功下降, 且均低于單次熱循環(huán)粗晶區(qū)的, 這是由于不完全重結晶形成了粒狀貝氏體和粗大上貝氏體組織; 此鋼種焊接時, t8/5應控制在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.