Study On The Influence Of Preparation Method On The Structure And Performance Of Ultra Low Carbon Low Density Steel

The production of traditional low-density steel usually requires a long process,and there are problems such as low material utilization and difficulty in processing when dealing with specific parts with complex shapes.In order to explore and expand the application field of this type of low-density steel,this article takes the ultra-low carbon low-density steel prepared by two different preparation methods as the research object,through the analysis means such as SEM,EBSD,TEM,etc.The structure and properties of carbon low density steel were studied.The main research contents and results are as follows:(1)The Gleeble-3500 thermal simulation test machine was used to perform hot compression test on the test steel,and the high temperature deformation behavior and hot working diagram of the test steel were studied.The results show that dynamic recrystallization is more likely at high temperature and low strain rate.According to the thermal processing drawing of the test steel drawn by the Prasad instability criterion,the optimal deformation process parameters of the test steel at high temperature were determined:the temperature was 1000?1100?,and the strain rate was 0.01?0.1 s^-1.(2)Using SEM,EBSD,TEM and other methods to study the microstructure and properties of the smelted low-density steel after hot rolling and heat treatment and its toughening mechanism.The hot-rolled test steel is mainly composed of ferrite,austenite and carbide.After solid solution,the average grain diameter decreases from 12.5?m to 9.8?m.As the aging temperature increases,the austenite content gradually decreases.The tensile test showed that after aging at 510?for 8 hours,the tensile strength of the test steel reached841 MPa,brittle fracture occurred during the tensile process of the test steel,and the fracture mode was cleavage fracture.Fe₃C and Ti C are precipitated in the heat treatment of the test steel,and the cutting effect of Fe₃C and dislocations makes the strength of the test steel after aging increase,and the analysis of the inclusions in the test steel shows that there are irregularly shaped large-particle silicate inclusions,oxide inclusions,and carbide aggregation in the test steel,which can also have a fatal effect on the toughness of the test steel.(3)To study the structure and properties of SPS sintered low-density steel before and after heat treatment.The results show that the main alloy elements are fully diffused and distributed relatively uniformly,and the structure is mainly composed of ferrite+austenite solid solution.The pores of the sintered samples before and after heat treatment have obvious differences.After heat treatment,the number of pores decreases,the strength increases significantly,but the elongation decreases.Before and after heat treatment,C is enriched in the vicinity of the pores,and the content of C after heat treatment is significantly increased compared with that before heat treatment,making cracks easier to nucleate in the vicinity,resulting in a decrease in the toughness of the material.(4)The relationship between the structure and properties of the materials under different preparation methods is compared and analyzed.The results are as follows:the original structure of the rolled state of the smelting test steel is composed of two phases of ferrite+austenite,and the distribution of ferrite has obvious directionality(along The rolling direction is distributed in strips),while the original structure of the sintered state is a uniform fine structure mainly composed of ferrite.The sintered sintered sample eliminates the coarse and uneven structure,and the hardness and tensile elongation are significantly improved compared to the smelted low-density steel.The smelting test steel precipitates Fe₃C and Ti C after heat treatment,and the bypass effect of the precipitated phase and dislocation is its main deformation mechanism.Unlike the smelting test steel,the heat treatment process of the sintering test steel is accompanied by a significant difference in the pores.The enrichment of C near the pores affects the aggregation of the material pores,resulting in a different plastic toughness from the smelting test steel.