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

Abstract

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.

Quench and Tempered Embrittlement of Ultra-High-Strength Steels with Transition Carbides

“…Sufficient ductility and fracture toughness is attained in these steels by vacuum arc remelting, the use of modified heat treatment routes, and/or alloying the steels with ≥1.5 wt.%Si [1,[7][8][9][10][11]. Additions of Si ≥ 1.5 wt.% reduce significantly the precipitation of cementite which enhances the strength and toughness of UHSS [1,4,10,[12][13][14][15][16]. The microstructure of Si-enriched UHSS consists of lath martensite with transition carbides located in the matrix and film-like retained austenite (RA) located at lath and block boundaries [1,14,17].…”