Inspection and Control of Fracture Delamination of 440 MPa Low Alloy Steel

CHEN Maobing; SUN Qian; CHENG Xinli; MENG Qian; ZHANG Weixiu; ZHANG Ruiqi

Abstract：The chemical composition,non-metallic inclusions and metallographic structure of 440 MPa low-alloy steel plate were analyzed by means of spectral inspection,metallographic observation,scanning electron microscopy and energy spectrum examination,and the specific reasons for the post-fracture delamination phenomenon in the transverse tensile fracture were analyzed.The results show that there are MnS,Al2O3 inclusions and pearlite bands in the steel matrix,and the plastic inclusions have obvious splitting effect on the steel matrix.The band structure induced by alloying element segregation induces microcracks,and the interaction and joint action of the two destroy the continuity of the base metal matrix,which is the key factor leading to the lamination of the fracture.By strengthening the pretreatment of molten iron raw materials,the purity of liquid steel is improved,and the content of harmful elements such as phosphorus and sulfur is strictly controlled.The form of sulfide inclusions is changed by means of calcium treatment,and the content of Al2O3 inclusions is reduced.Low superheat casting is adopted in the continuous casting process and the process of controlled rolling and cooling is combined to obtain the expected metallurgical structure.It can significantly reduce the occurrence rate of such defects.