Study On Microstructure Evolution And Mechanical Properties Of 55SiCr Spring Steel

55SiCr spring steel is a high-grade steel for automotive suspension,providing shock absorption and cushioning protection for the car.Due to its decarburization and subsequent heat treatment and the uneven cooling of material during the spring steel production process will result its performance and lifetime decreasing dramatically.Therefore it is necessary to study 55SiCr steel production to develop a high-quality spring steel.Taking a 55SiCr steel spring steel as material,the evolution and the mechanical properties of the experimental billet were researched,thesis research results are as follows.(1)The experimental steel decarburization behavior at different heating temperatures and different holding times were studied by thermal gravimetric analysis and optical microscopy.The results showed that the heating temperature reaching 1150℃,the decarburized layer will reach the peak and the partial decarburization depth is deepening with increasing temperature.Decarburization depth will be the minimum when the temperature reaches 1050℃,so the heating temperature of 55SiCr spring steel is 1050 ℃.Decarburization and partial decarburization depth will deepen with time increasing.Heating effect of temperature on depth of decarburization is more obvious than holding time effect.(2)Single pass compression test of the experimental steel shows that dynamic recrystallization likely occur at high temperature and low speed.And the dynamic recrystallization activation energy Qa is 239.6kJ/mol.And we get the relationship of peak stress and the Z parameter,and the model of deformation stress.(3)CCT curve were measured by thermal expansion test combined with optical microscopy.It is easy to produce a uniform fine pearlite at high cooling termination temperature through the simulated cooling process.(4)Using different cooling temperatures,different cooling speed and final cooling temperature,experimental steel was rolled under laboratory conditions.And then quenching and tempering was adopted to the experimental steel.Compared mechanical properties after rolling and rolling after heat treatment and microstructure,the results showed that:water cooling process after spinning via heat treatment has good microstructure performance providing a reference to producing 55SiCr spring steel at site.(5)By the conclusion of rolling in laboratory situation,55SiCr spring steel was test-rolled at Anshan Iron and Steel Wire Plant.Explore the impact of cooling speed and spinning temperature mechanical properties of the wire at different spinning temperature and different fan RPM.The results show that:in the actual production,it will not produce a decarburization and the partial decarburization depth is very shallow.In the cooling process,the pearlite transformation area,the greater cooling speed,the better mechanical properties are.It proves that it is feasible to add water cooling after spinning.