齿轮传动轴用钢ML45n2的冷镦开裂原因分析

Analysis on cold-heading-cracking reason of ML45Mn2 steel for gear transmission shaft

齿轮传动轴用钢ML45Mn2在冷镦成形过程中出现冷镦开裂问题,对开裂样品宏观形貌、化学成分、气体含量及显微组织进行了分析。结果表明,原工艺(670℃×2 h→730℃×6 h→680℃×7 h→缓冷到500℃出炉)退火后,截面上碳化物分布很不均匀,表层呈现沿晶分布的网状碳化物;碳化物的形状也不规则,是引起开裂的主要原因。改进球化退火工艺(670℃×2 h→740℃×6 h→(13℃/h)670℃×7 h缓冷→500℃出炉)后,碳化物的形态和分布得到明显改善,满足冷镦成形要求。其冷镦开裂率由100%下降到2%以内。

ML45Mn2 Steel for gear transmission shaft was cracking in cold heading process. The macro-morphology,chemical composition,gas content and microstructure of cracking samples were analyzed. The results show that after annealing by original process（ 670 ℃ × 2 h→730 ℃ × 6 h→680 ℃ × 7 h→furnace cooling to 500 ℃,tapping）,the distribution of the carbides on the whole section of the sample is very uneven,the network carbides in surface layer along the grain boundary appears,and the shapes of the carbides are not regular,which are the main reason caused cold heading cracking. After improving the spheroidization annealing process（ 670 ℃ × 2 h→740 ℃ × 6 h→（ 13 ℃ / h）670 ℃ × 7 h→furnace cooling to 500 ℃,tapping）,the morphology and distribution of the carbides are obviously improved which can meet the requirement of cold heading process. The cold heading cracking rate can decline from 100% to less than 2%.