Study On Regional Plastic Rheology Of Single-Phase Ferrite Structure Hammering Plastic Zone

Mold production occupies a large proportion in industrial manufacturing,and has the advantages of low cost,wide range of use,and the ability to produce parts with complex shapes.Hot work molds are often exposed to rapid temperature changes and huge pressures during service to produce fatigue cracks.This kind of crack expansion is often the main cause of mold failure.The value of the mold for producing large parts can reach hundreds of thousands of dollars.If the mold surface can be treated to delay the expansion of fatigue cracks,and the life of the mold can be extended,the cost of each product can be greatly reduced.Applying pre-compression stress to the surface of the mold is an effective means to inhibit crack propagation.Under the action of precompression stress,it can effectively prevent the expansion of cracks and improve the service life of the mold.Hammering is a processing method for applying precompression stress to materials.It has the advantages of large depth,convenient operation and wide application range.In order to explore the plastic rheology and stress-strain state of the material after the hammering treatment to obtain the best strengthening effect,the DT4 material with low hardness and strength,good plasticity and single phase state is selected as the research object for hammering experiment.The single-point and double-point repeated hammering of DT4 material with a grid of0.1mm pitch was carried out by the impact hammering method,and the same experiment was repeated on the solid material at the same time.Based on the analysis of the change of the contact surface mesh and the results obtained from the finite element simulation,the plastic flow and stress distribution of the material are studied.In addition,using EBSD to conduct microscopic analysis of the deformed edge area and the boundary area of the two pits after double-point hammering,the relationship between plastic deformation and dislocation density is obtained.The results of the experiment show that:1.The size comparison and morphological analysis of the pits formed on the surface of the sample after the compression hammering method and the solid part are hammeringed,it can be seen that the impact of the existence of the compression surface on the pits is negligible.The rheological information obtained by the hit method can effectively explain the internal situation of the real material.2.The finite element simulation of the single-point hammered sample shows that the largest residual stress appears at the edge of the hammered pit,and the radial tensile stress at this point is likely to lead to crack propagation.The inside of the material under the pits is three-dimensional compressive stress,which is the best stress state desired after surface treatment.3.After single-point hammering,the mesh after the change of the compression surface is extracted and analyzed,and the strain and displacement data of each mesh in the compression surface can be obtained,and the corresponding data can be compared with the results obtained by finite element simulation.Comparing,the two are in good agreement.4.Using EBSD technology to scan the characteristic area after double-point repeated hammering,the results prove that under the same number of hammering times,the overlapping area of the double-point has a greater dislocation density than the edge of the pit.