Investigation on Formation of Delayed Cracks of Abrasion-resistant Steel

Abstract

To the problem of delayed cracking of the high strength low alloy abrasion-resistant steel plate NM360, the fracture, surface cracks and microstructure were investigated by optical microscopy, electron scanning microscopy and energy spectroscopy, and the residual stress was tested by X ray. The main results were as follows: The fracture source was in the center of the thickness of the steel plate and there were obvious central segregation in the mid-depth of the plate. Microstructure was not uniform in the surface, 1/4 depth and mid-depth of the steel, changed form lath martensite to martensite+granular bainite+ferrite. The steel showed the characteristics of the typical stress crack, there were different degree of resiual stree from edge to center, the impact of various residual stresses generating during heat treatment and the flame cutting on the defective areas was the main reason for the formation of the delayed crack.