Study On Reheating And Semi-solid Forming Properties Of Rolled SKD61 Die Steel

The different uses of the mold require that the materials used to make the mold have different characteristics,but the basic requirements are high hardness,high strength,and high toughness.The coarse dendrite structure of the casting mold steel will reduce its mechanical properties.Therefore,in the traditional mold manufacturing,the multi-pass rolling method is usually used to refine the grain,improve the structure,and improve the mechanical properties.However,the multi-pass rolling method is more time-consuming and energy consuming.Due to the characteristic microstructure of metals in the semi-solid state,the semi-solid technology can be used as one of the methods for refining grains.In order to study the microstructure and formability of SKD61 die steel in the semi-solid state,this paper carried out reheating experiments and semi-solid hot compression experiments on the rolled SKD61 die steel material through multi-pass thermal simulation compressor.The main parameter of the experiment is temperature.The microscopic structure was observed and photographed by optical microscope.Combined with the real stress-strain curve obtained during the hot compression process,the evolution of the microstructure at different temperatures and the different deformation behaviors of the semi-solid compression process are analyzed and discussed.Through the research in this article,the following conclusions are obtained:(1)Partial melting occurred in the reheating process of the alloy.When the temperature is low,the liquid phase content is small and discontinuous;when the temperature is high,the liquid phase increases and interconnects.When the heating temperature is 1405 ?,solid phase grains without dendrites uniformly surrounded by the liquid phase are obtained.(2)In the hot compression experiment,with the increase of heating temperature under the same strain,due to the different solid and liquid content of the rolled SKD61 material at different temperatures,the deformation method under the action of compressive force is also different.When thermally compressed at a lower temperature,the material's deformation mode is mainly the plastic deformation of the solid particles;when the temperature is slightly higher,the material's deformation mode is mainly the sliding of the solid particles along the liquid phase and the plastic deformation of the solid phase;When the temperature is higher,the deformation mode of the material is mainly the outflow of the liquid phase from the central area.During this temperature increase process,due to the different deformation methods,the deformation resistance of the material gradually decreases,showing that the flow stress decreases with increasing temperature.(3)In the semi-solid billet,during the hot compression experiment,when the temperature is low,the liquid phase content is small,and the liquid phase cannot flow freely,so the liquid phase content of the sample center area and the edge area is almost the same;A complete liquid phase flow channel can be formed,and the liquid phase can smoothly flow from the center of the sample to the edge under pressure,causing the liquid content in the edge area to be higher than the center area,resulting in liquid phase segregation.