Study on the stability of retained austenite in marine steel

Abstract

The residual austenite stability in marine steel was studied by different heat treatment processes. After heat-treatment process 1 (quenching + tempering) and heat treatment process 2 (quenching + intercritical annealing + tempering), the austenite content was determined by X-ray diffraction (XRD), and the microstructure of the test steel was tested by Scanning electron microscope (SEM), Transmission electron microscope(TEM), and Electron Backscattered Diffraction (EBSD). Experimental results showed that the microstructure of the test steel consisted of martensite/ bainite + ferrite + retained austenite. The retained austenite volume fractions were 20,8 % and 18,1 %, respectively, for process 1 and process 2.The retained austenite morphology, C content, distribution, and grain size all affect a steel’s thermal and mechanical stability. Film-like residual austenite with high C content and fine grain size has the best stability.

Keywords

• marine steel
• heat treatment
• microstructure
• retained austenite
• mechanical stability