Basic Research On Composite Forming Of 30CrMnSiNi2A Steel Slide Part By Die Forging And Wire Arc Additive Manufacturing

High-strength steel is widely used in manufacturing important components in the aviation,aerospace,nuclear power and other fields,its large and complex high-quality forgings are an important symbol to measure the level of national industrial science and comprehensive national power.The complex geometry structure of large high-strength steel forgings,especially the local features represented by boss and ribs,significantly increases the complexity of the forging process,which leads to a significant increase in production cycle and production costs.As a near-net forming technology,wire+arc additive manufacturing technology has the advantages of high forming efficiency,low cost and high flexibility.In this study,combining the geometrical characteristics of large high-strength steel forgings and the advantages of wire+arc additive manufacturing technology,it is proposed to first form the main part of the slide part through forging,and then form the process boss on the slide part through the wire arc additive manufacturing technology.This research carried out the basic research of this composite forming process,the microstructure and properties evolution of the heat affected zone and the additive manufacturing area during the forming process were studied,the main research contents and conclusions are as follows:The hot deformation characteristics of 30Cr Mn Si Ni2A steel under different deformation parameters were studied by hot compression test.The influence of deformation parameters on the dislocation substructure and microstructure evolution of 30Cr Mn Si Ni2A steel was analyzed by optical microscopy and transmission electron microscopy.It was found that the dynamic recrystallization nucleation mechanism was mainly composed of discontinuous dynamic recrystallization under different deformation parameters.The Arrhenius constitutive model and hot processing maps were established.The Arrhenius constitutive model has high prediction accuracy and can well predict the constitutive relations of materials.According to the predicted results of hot processing maps,the material has higher power dissipation efficiency factor and better formability at low strain rate,and the deform instability is prone to occur at high strain rate.The Arrhenius constitutive model was imported into the finite element simulation software DEFORM,and the die forging process of the slide part without process boss was simulated by finite element method.The single-track single-layer wire+arc additive manufacturing experiments using custom high-strength steel flux-cored wire were conducted to study the influence of additive manufacturing parameters on the morphology of the formed parts.It was found that when the wire feed speed was 5 m/min and the welding speed was 7 mm/s,the welding bead had good morphology,the maximum aspect ratio and no obvious internal defects,which was determined as the best additive manufacturing parameters.Based on this results,further single-track multi-layer additive manufacturing experiments and heat treatment experiments were conducted,the effects of different areas and heat treatment on the microstructure and comprehensive mechanical properties of single-track multi-layer parts were investigated.The mechanical properties of the as deposited material is excellent,but the plasticity is poor.After heat treatment,the microstructure transformed from martensite and lower bainite into tempered martensite,the plastic deformation capacity and the anisotropy of the material had been improved.The segregation of carbon elements and carbide M₇C₃ in heat affected zone were investigated by scanning electron microscope,X-ray powder diffractometer and electron probe microanalysis.It was found that when the reheating temperature was between 600°C and 700°C,the carbon elements in the martensite gradually deviated to the grain boundaries.During the cooling process,the carbon elements were precipitated at the grain boundaries in the form of carbide.The change in reheating crack susceptibility of the heat affected zone during partial additive manufacturing process was studied by high temperature slow tensile test,and it was found that the fracture mode was mainly intergranular fracture under different peak temperatures,and the recrystallization could reduce the reheating crack susceptibility of material.