Effect of Double-Step and Strain-Assisted Tempering on Properties of Medium-Carbon Steel

The present work aimed to study the properties of medium-carbon steel during tempering treatment and to present the strength increase of medium-carbon spring steels by strain-assisted tempering (SAT). The effect of double-step tempering and double-step tempering with rotary swaging, also known as SAT, on the mechanical properties and microstructure was investigated. The main goal was to achieve a further enhancement of the strength of medium-carbon steels using SAT treatment. The microstructure consists of tempered martensite with transition carbides in both cases. The yield strength of the DT sample is 1656 MPa, while that of the SAT sample is about 400 MPa higher. On the contrary, plastic properties such as the elongation and reduction in area have lower values after SAT processing, about 3% and 7%, respectively, compared to the DT treatment. Grain boundary strengthening from low-angle grain boundaries can be attributed to the increase in strength. Based on X-ray diffraction analysis, a lower dislocation strengthening contribution was determined for the SAT sample compared to the double-step tempered sample.

Automated summary

The present study aimed to investigate the properties of medium-carbon steel during tempering treatment and to enhance the strength of medium-carbon spring steels using strain-assisted tempering (SAT). The effects of double-step tempering and double-step tempering with rotary swaging (SAT) on mechanical properties and microstructure were examined. The results showed that SAT treatment significantly increased the yield strength of the medium-carbon steel samples, while reducing the plastic properties such as elongation and reduction in area compared to the double-step tempering treatment. Grain boundary strengthening and lower dislocation strengthening contribution were observed in the SAT samples.