Cold Bending Cracking Characteristics And Mechanism Analysis Of Low Alloy High Strength Steel Plate For Engineering Structure

This paper takes the low-alloy high-strength steel plate for Q345 B engineering structure as the research object,and analyzes the characteristics and causes of cracking during the cold bending process.The characteristics,causes,the main corresponding relationship between cracking degree and microstructure and the cracking mechanism of cold bending deformation of this kind of plate were analyzed using OM,SEM,EDS,ASPEX,EBSD and finite element simulation analysis.The method of combining orthogonal experimental design and finite element simulation is used to analyze the cold bending process cracking of this type of steel plate,which is caused by the bulge or sag of the residual oxidized iron sheet pressed into the surface of the steel plate.Therefore,the experimental and theoretical basis is provided to control the cracking of cold bending deformation of this kind of steel plate from the point of view of hot rolling technology.The main conclusions of this paper are as follows:(1)In the process of cold bending deformation of Q345 B steel plate,there are mainly three types of cracking features such as lower surface cracking,complete fracture and surface cracking of cold-formed parts when they are welded into a cylinder after cold bending deformation,and the cracking direction is perpendicular to the rolling direction.(2)The results of orthogonal experiments to study the control of the iron oxide properties show that in the temperature range of 1100?1200?,in the holding time of180?300 min,in the range of 5%?21% oxygen content,when it is controlled by the combination of heating temperature of 1100?,holding time of 180 min and oxygen content of 10% process,it is expected to make the furnace raw iron oxide with loose porous easy to rise and crack off components,thus making it easy to be removed by high-pressure water descaling,which helps to reduce the cold bending deformation cracking caused by the residual iron oxide pressed into it.(3)For cold-bending deformed steel plates with F and P banding characteristics where the influence of the non-metallic inclusions is not considered,cracks are induced at weak areas between the F and P bands and the band interface when the banding organization is greater than or equal to level 4,under the action of the applied stress.organization is greater than or equal to level 4,under the action of the applied stress.As the applied stress increases,the crack expands laterally along the weaker mechanical properties and extends slightly along the interface between the F and P bands,with a jagged crack.(4)For the cold-bending deformed steel plates with F and P banding characteristics where the influence of the non-metallic inclusions is considered,stress concentrations around the non-metallic inclusions induce cracking under the effect of applied stresses,with cracking extending along the vertical banding direction.The large size of the nonmetallic inclusions reduces the small size of it from 4 to 3 levels,which corresponds to cracking.The non-metallic inclusions are the cause of cold bending cracking in steel plates,and larger sized non-metallic inclusions contribute to cracking.(5)When there is the oxide scale pressed into the surface of the steel plate,hard and brittle oxide scale can induce the formation of cracks in the subsequent cold bending deformation process of the oxide scale pressed into the surface of the steel plate,and the surface of the steel plate presents the cracks with the cold bending deformation.