Reasons for non-compliance of fracture of DH36 steel plate

The main factors leading to the fracture failure of DH36 steel plate are the serious center segregation and center porosity of the slab, and the presence of abnormal bainite structure and elongated MnS inclusions in the DH36 steel plate with fracture delamination to varying degrees.

The main mechanism of center segregation and porosity formation is the theory of precipitation and enrichment of easily segregated solute elements in DH36 molten steel, that is, during the crystallization process from the shell to the center of the billet, the solute elements in DH36 molten steel have dissolution equilibrium shifts, C, Mn, S, P and other easily segregated elements are precipitated as columnar grains and discharged into the unsolidified DH36 molten steel. As the crystallization continues, these easily segregated elements are enriched in the center of the slab or solidified end zone, resulting in central segregation and central porosity.

Sulfur segregation will cause MnS segregation, the increase of manganese content will enhance the stability of austenite, and severe manganese segregation will prevent austenite from pyrolysis even in the process of slow cooling, resulting in martensite, bainite, etc. The medium and low temperature transforms the structure, so the abnormal structure on the DH36 steel plate and the reasons for the formation of long strips of MnS inclusions are essentially the same, and they are all caused by the segregation of the DH36 steel slab.

Long strips of MnS inclusions often coexist with abnormal structures, which split the continuity of the matrix. At the same time, due to their different expansion coefficients from the DH36 steel matrix, holes will be generated at the interface between the tip of the inclusion and the matrix during the cooling process. During stretching, a large stress concentration occurs in the matrix around the hole, which subsequently expands into a lamellar fracture in the abnormal tissue.