Study On Fracture Mechanism Of EH47 Ship Plate And Damage Evolution Analysis Under Heavy Reduction Rolling

There are many defects existed in the continuous casting billet,such as center shrinkage and porosity,and it is hard for large section products to eliminate these defects in subsequent rolling process because of the lack of compression ratio,so it will influence on the performance of the final product.The process of continuous casting billet under high temperature and heavy reduction rolling makes full use of the waste heat,decorating large pressure rolling mill in the export of the continuous casting machine,using special temperature distribution characteristics of low surface temperature and high core temperature to conduct high permeability and high pressure rolling,in order to achieve the purpose of eliminating the shrinkage and porosity defects of casting billet.In the process of high temperature and heavy reduction rolling,the temperature of billet is 900℃～1050 ℃,which near or in the brittle temperature range of the material.It will improve the core quality of casting billet,but at the same time,there is a dispute in the industry whether it will cause surface crack problems.So this paper will take EH47 ship plate steel(which has a certain crack sensitive)as the research object,combined with experimental study and numerical simulation methods to explore the problem of the surface damage and crack of continuous casting billet in high temperature and heavy reduction rolling.The main research contents and results are as follows:(1)Using Gleeble-3800 thermal simulation machine to conduct single-pass thermal simulation tensile test.Obtain the true stress-strain curve at 700～1000℃deformation temperature and 0.01 s-1,0.1s-1,1s-1,5s-1strain rate,and establish the constitutive equation under the experimental conditions,as well as carrying out the error analysis on the model.(2)Study the thermalplasticity including the reduction of area and tensile strength of EH47 ship plate steel,and the influence of temperature and strain rate.On the other hand,using scanning electron microscopy and energy dispersive spectrum and Thermo-Calc thermodynamic calculation software to study the morphology and structure defects near the fracture,and analyse the precipitation behavior of micro alloying elements and the effect of inclusions on the plasticity.(3)To study the material damage and evolution rule of EH47 ship plate steel continuous casting slab in high temperature and heavy reduction rolling,select the appropriate ductile fracture criterion to describe the damage distribution of heavy reduction process.Consider the effect of temperature and strain rate of damage evolution to derive the damage model,and determine the coefficient by multi-pass thermal simulation tensile test.Using Absoft Pro Fortran to compile the damage model into DEFORM-3D finite element simulation software for secondary development.(4)Using ABAQUS finite element simulation software to establish temperature field of continuous casting process of EH47 ship plate steel.Establish finite element model of continuous casting slab in high temperature and heavy reduction rolling by DEFORM-3D finite element simulation software based on the continuous casting slab initial temperature field,boundary conditions,constitutive equation and damage model,to study the damage distribution of upper surface,laterial surface and corner,and the influence of the reduction ratio on the damage of rolled piece.