Formation and Deformation Mechanism of Mountain‐Like Surface Crack on the Hot‐Rolled Thick Plate of HSLA Steel

Abstract

Mountain‐like surface cracks often appear on the thick plates of high‐strength low‐alloy (HSLA) steel after hot rolling, which have a serious impact on production efficiency. Herein, the formation cause of mountain‐like cracks is discussed using methods such as acid pickling and observations of microstructure and inclusions. The deformation behavior of microcracks is obtained by analyzing the rolling process of slab. The inclusions in the top of the crack are Type‐I inclusions with high elemental contents of K and P and Type‐II inclusions with high elemental contents of C. The inclusions in the sides of the crack are Al2O3. It is concluded that mountain‐like cracks are caused by surface microcracks containing Type‐I inclusions in the continuous casting slab. During rolling, the rapid deforming of side‐1 stretches the crack so that the unusual microstructure appears. The cracks extended in the rolling direction have Al2O3 inclusions. The mountain‐like crack with Type‐I inclusions in the top and Al2O3 in the sides eventually form. A single microcrack forms a single mountain‐like crack and multiple clustered microcracks form a continuous mountain‐like crack. To reduce mountain‐like cracks, reducing Type‐I inclusions to reduce surface defects of the slab is an effective means.

Cause Analysis of Low Tensile Plasticity in Normal Direction for Hot‐Rolled Thick Plate of HSLA Steel

“…The service environment requires that the S355 thick plate should have good mechanical properties, and the tensile plasticity in normal direction (ND) of the thick plate is one of its important mechanical properties. [1][2][3] The thick plate has three different directions, transverse direction (TD), rolling direction (RD), and ND, as shown in Figure 1. The reduction of area of the tensile fracture is the form of tensile plasticity characterization.…”