Effect of Tempering Temperature on the Structure and Mechanical Properties of Medium-Carbon Steel with Elevated Silicon Content

• Published in: Metal science and heat treatment Vol. 66; no. 1-2; pp. 17 - 24
• Main Authors: Borisov, S. I., Borisova, Yu. I., Tkachev, E. S., Knyazyuk, T. V., Gaidar, S. M., Kaibyshev, R. O.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01.05.2024; Springer Nature B.V
• Subjects: Boundaries; Carbon; Cemented carbides; Cementite; Characterization and Evaluation of Materials; Chemistry and Materials Science; Classical Mechanics; Composition effects; Dilatometry; Electrostatic precipitation; Engineering Thermodynamics; Heat and Mass Transfer; Impact analysis; Impact strength; Martensite; Materials Science; Mechanical properties; Medium carbon steels; Metallic Materials; Phase composition; Quenching and tempering; Residual stress; Rockwell hardness; Steels for General Engineering Purposes; Tempering; Yield strength; Yield stress; quenching and tempering; mechanical properties; martensitic structure
• ISSN: 0026-0673; 1573-8973
• DOI: 10.1007/s11041-024-01012-6

The effect of quenching and tempering on the microstructure, phase composition and mechanical properties of steel 0.33C – 1.8Si – 1.44Mn – 0.58Cr is investigated. The structure is studied using scanning and transmission electron microscopy, dilatometry and differential scanning calorimetry. Tensile and impact strength tests are performed. The Rockwell hardness is measured. The processes of formation of carbides in the steel at different temperatures are analyzed, as well as the influence of the structure on the mechanical properties. Quenching yields laths of martensite with carbon-saturated dislocation boundaries due to formation of Cottrell atmospheres. The internal stresses reach 40% of the yield strength σ 0.2 . Tempering to a temperature of 280°C causes precipitation of transition η-carbides (Fe 2 C) inside the laths, which depletes the martensite matrix of carbon by about 90%. This increases the yield strength by 16% to 1130 MPa despite the lowering of the internal stresses and growth of the width of the laths. Precipitation of cementite chains over the lath and block boundaries occurs in tempering at 500°C, which is accompanied by lowering of the yield strength to 1130 MPa. Calculations of the proportion of carbon atoms in the martensite shows that almost all of the carbon present in the steel goes to formation of cementite. The decomposition of martensite during tempering increases the toughness but has a minor effect on the strength-ductility parameter σ r × δ (MPa ∙ %).