Research On Effect Of Si Content And Heat Treatment Process On Microstructure And Properties Of Strength Steels

In order to find the best heat treatment process and the optimal element ratio,40 SiMnCrMo high-strength wear-resistant steel is used to explore the relationship between the microstructure and macroscopic mechanical properties of the sample during the experiment.Carry out different heat treatment process experiments,observe the microstructure,test the macroscopic mechanical properties,determine the optimal heat treatment process parameters;adjust the silicon content of the alloy elements under the optimal heat treatment conditions,explore the best performance and composition relationship,determine the appropriate silicon content It conducts performance tests to find the best ingredients,and performs experiments under different quenching cooling rates to find the best quenching cooling rate based on finding the best ingredients.The test content and conclusions of this paper are as follows:The test steel was subjected to a 20 kg vacuum induction furnace smelting-ingot-forging process to obtain a sheet having a thickness of 30 mm.After the sheet is annealed by a reduced hardness,it is cut into an impact sample and a metal phase observation sample.The CCT curve and critical point of the test steel were determined by the expansion method and the metallographic method.Ac3 = 918.9℃,Ac1 = 715.5℃,Ms = 317℃.As the cooling rate increases,the structural transformation changes from ferrite to bainite transformation to martensite transformation.The test steel was austenitized at 950℃ for 30 min,then directly quenched to room temperature,and then tempered,the tempering temperatures were 220℃,240℃,260℃,280℃,300℃,and the tempering time was 6 h.The test results show that the test steel has the best toughness and the highest hardness when the tempering temperature is 240 °C.The impact absorption work was 61.7 J and the hardness value was 55.3 HRC.Through metallographic observation and fracture scanning,it is found that the microstructure is mostly acicular martensite bainite structure,and the fracture property is ductile fracture.The test steel composition was adjusted to mainly adjust the Si element content.The heat treatment process still selected oil quenching and 240 ℃ tempering process.The test results showed that the test steel had the best toughness and the highest hardness when the Si content was 2.0%.It is measured in the previous article.The heat treatment process of the test steel was further adjusted,and the test was carried out by changing the quenching cooling rate.The experimental results showed that the test steel had the best hardness and toughness matching value when the air pressure was cooled by 4 atmospheres,and the impact absorption work was 99.75 J.The value is 44.3HRC.t was found by Zeiss microscope that there was a large amount of acicular bainite under this condition,which made the test steel tough.Through the fracture scanning comparison,it was found that the maximum number of dimples and the deep dimples were obtained when the blast was cooled by 4 atmospheres,so the toughness of the test steel was the best.