加热状态下的45钢内裂纹表面迁移

Surface migration of internal crack in 45 steel during heating

采用钻孔压缩法在45钢试样内部预制内裂纹,并对裂纹试样进行900℃、1000℃、1200℃加热,观察裂纹表面的组织变化。结果表明,45钢内裂纹试样加热时,裂纹表面普遍存在铁素体晶粒形核与长大,从而使裂纹表面向裂纹中心方向迁移,裂纹表面迁移有分段现象。原子扩散是物质补给方式,铁素体晶粒形核长大是内裂纹表面迁移方式。原子扩散是裂纹愈合的基本要素,为内裂纹表面迁移提供物质来源,但是铁素体晶粒形核长大能够使原子扩散速度加快,而裂纹表面无新晶粒形核长大的裂纹愈合现象,相比之下,存在铁素体晶粒形核长大现象的裂纹愈合行为中,裂纹表面迁移更迅速。

45 steel samples containing internal crack were heated at 900℃ and 1000℃ for different time to examine the evolution of microstructure near the crack during heating process.It is found that nucleation and growth of ferrite grains occurs on the surface of the crack and it is a common phenomenon.Therefore crack surface migrates inward whole or partly.Atom diffusion is the material supply mode and ferrite grain nucleation and growth is the surface migration mode.So atom diffusion is the basic factor of crack healing and it transfers materials for crack surface migration.But ferrite grain nucleation and growth could accelerate atom diffusion.Compared with the inner crack healing without ferrite grain nucleation and growth on surface,the crack healing with ferrite grain nucleation and growth finishes fast.