T91连铸坯开裂分析

Cracking analysis of T91 continuous casting ingot

通过低倍观察、金相观察和相转变分析等手段对连铸过程中产生角边裂的T91管坯进行剖析。结果表明,连铸坯合金成分Cr当量高和铸坯在零强度温度和零塑性温度区间局部冷却过快是铸坯角部产生裂纹的主要原因,在后续的奥氏体向马氏体转变的过程中,残留的δ铁素体的硬度低,在管坯应力最大的角部45°方向易于沿铁素体晶界进行裂纹二次扩展。

T91 continuous ingot in the corner of which cracking generated was analysed by macrostructure observation,microstructure observation and analysis of phase transformation. The results showed that high Cr equal content and quick cooling speed near ZST and ZDT temperature for part of the casting ingot were the main reasons of corner cracking. In the followed process of austenite to martensite phase transformation,the hardness of the remained δ ferrite was low,so the secondary cracking extension was occured at 45°corner of the casting ingot in which the inner stress was at its biggest level.