直接热装轧制的X60微合金钢连铸坯红送裂纹形成机制的研究

Formation Mechanism of Hot Charging Cracks in Continuously Cast Billet of X60 Micro-alloy Steel during Direct Hot Rolling

通过对热装、热送过程中连铸坯组织转变的热模拟研究,结合凝固过程中微合金元素第二相的析出行为和热应力变化,研究了X60微合金钢红送裂纹的形成机制。结果表明,X60微合金钢连铸坯不同的热装、热送方式会导致显著不同的铸坯组织和析出物形态,从而显著影响在再加热过程中铸坯红送裂纹的产生。X60微合金钢红送裂纹是在组织转变、微合金元素第二相析出和热应力三者的共同作用下形成的。组织转变过程中沿奥氏体晶界析出的先共析铁素体膜,在降低铸坯高温塑性的同时,也促进了第二相沿奥氏体晶界的析出。再加热过程中,先共析铁素体膜的减薄与第二相在晶界的偏聚和固溶间隙,导致了铸坯高温塑性的降低,从而显著增加了形成红送裂纹的可能性。连铸坯再加热至850℃的过程中产生的峰值应力是形成红送裂纹的主要原因。

Based on the thermal simulation study on structural transformation of continuously cast billet during hot charging and hot transferring,and combined with the precipitation behavior of second phase of microalloy elements and the variation in thermal stress during solidification,the mechanism whereby the hot charging cracks formed in X60 micro-alloy steel was investigated. The results showed that the ways of hot charging and hot transferring could significantly affect the microstructure and the morphology of precipitate in the continuously cast billet of X60 micro-alloy steel,thus exhibit a significant impact on the formation of hot charging cracks in the steel billet during the reheating. The hot charging cracks in X60 micro-alloy steel were formed by the common action of structural transformation,precipitation of secondary phase of microalloy elements,and thermal stress.A proeutectoid ferrite film precipitated at austenite gain boundary during the structural transformation not only reduced high temperature plasticity but also promoted precipitation of the second phase at austenite gain boundary. When reheated,the proeutectoid ferrite film was thinned,and segregation and solid solution voids of the second phase at the grain boundary occurred,which resulted in the less high temperature plasticity of the cast billet and,therefore,in great possibilities of the formation ofhot charging cracks. The hot charging cracks stemmed primarily from a peak stress developed during the reheating to 850 ℃.