Cr-Al钢焊接热影响区冲击韧性研究

INVESTIGATION OF HAZ IMPACT TOUGHNESS OF A Cr-Al STEEL

本文采用模拟焊接热循环试验方法,测定了不同峰值温度下Cr-Al钢冲击韧性的变化,并对各峰温下的断口形貌、金相组织、晶粒度及析出物等进行了观察和鉴定。结果表明,随着峰值温度的提高,冲击韧性下降,断口形貌由韧窝状变成解理或准解理状。模拟热循环的峰温高于Ac_3时,随着峰温的提高,奥氏体晶粒明显长大,马氏体板条尺寸也相应增大,因此冲击韧性相应下降。模拟热循环的峰温低于Ac_3时,高温下马氏体板条内的碳进一步析出,基体软化,塑性提高;马氏体板条变得弯曲,碳化物聚集成球状,致使冲击韧性明显提高。

r By using simulated weld thermal cycle tests, the variations of HAZ Charpy impact toughness of a Cr-Al steel heated to different peak temperatures were determined. The fractographic appearance, metallographic microstructure' prior austenite grain size and precipitation behavior of the simulated HAZ were also observed and identified. The results showed that the HAZ impact toughness decreased with the increase in peak temperature and hence the fractographic appearance changed from dimple pattern to cleavage or quasi-cleavage pattern. As the peak temperature of thermal simulation, which was higher than Ac3, increased, the prior austenite grain size and the martensite lath size increased, and consequently the impact toughness depressed. When the steels thermal-simulated to the peak temperatures below Ac3, the well-performed precipitation of carbides from the martensite matrix occured, which could soften the matrix and therefore increase the ductility. Furthermore, the curvature of martensite lath boundaries and the aggregation and globurization of carbides are considered to be responsible for the improvement of HAZ impact toughness.