Study On Inner Folding Of 2Cr13 Steel In Rotary Tube Piercing Process

Inner folding is one of the most common quality defects in rotary piercing process of hot-rolled seamless steel tube,and cannot be completely eliminated in the subsequent production process,which in turn causes the steel tube to be degraded and used or scrapped,which seriously affects the batch production,product quality and economic benefits of the enterprise.Therefore,it is of great theoretical and practical significance to systematically study the influence of different process parameters and adjustment parameters on the tendency of inner folding and stalled rolling in the rotary piercing process of 2Cr13 steel,and to propose technical measures to reduce or prevent inner folding and the optimization scheme of process and adjustment parameters.In this paper,on the basis of measuring the rheological stress,tensile strength and thermoplasticity of 2Cr13 steel,a three-dimensional elastoplastic finite element simulation of the existing process of the typical specification 2Cr13 steel rotary tube piercing process with the help of finite element software Simufact was constructed,and the stress strain distribution,damage field,temperature field,force energy parameters and tendency of inner folding defects of pierced shell during the rotary piercing process were analyzed.The critical reduction ratio range of 2Cr13 steel was predicted by Oyane ductile fracture damage field simulation,and the influence of the roll inlet cone friction coefficient on the rolling force and the axial speed of the round bar center was analyzed,and on this basis,the influence of different rotary piercing process parameters and adjustment parameters on the inner folding and stalled rolling tendency was studied,and the main conclusions are as follows:(1)In the current rotary piercing process,at about 80 mm away from the front end of the pierced shell,the three-direction normal stresses at the center point of the pierced shell are tensile stresses and reach the maximum value at the same time,and the maximum transverse,radial and axial tensile stresses are 87.3 MPa,12.39 MPa and 53.38 MPa,respectively;the internal tear occurs in the center of the pierced shell at above area and its vicinity,which results in the inner folding defect.(2)The distribution of equivalent plastic strain of the pierced shell is:"W" shape in the feed region,"2U" shape in the working region,and "inverted(?)"shape in the reeling region in rotary piercing process,which indicates that the deformation of 2Cr13 steel is more difficult to penetrate.(3)The critical reduction ratio range of 2Cr13 steel is between 6%and 6.5%,and the reduction rate range before plug is narrow which does not occur inner folding and the second bite is smoothly,so the process adjustment range is small.(4)As the friction coefficient of the roll inlet cone increases,the drag force of the pierced shell increases,the axial slip decreases,and the rolling times in the feed region decreases,which is beneficial to the secondary bite of the perforation,and reduces roll wear and the occurrence of inner folding.Therefore,in actual production,grooves or knurls should be used to increase the coefficient of friction of the roll inlet cone.(5)The reduction ratio before plug is adjusted from 6.39%of the original process to 5.75%,and the internal tear phenomenon does not occur in the center of pierced shell during the rotary piercing process,and the inner folding defect is not generated.The optimized adjustment parameters are:the distance between two roll high points BCK=133.6 mm,the distance of the front end of plug b=89 mm.