Formation of Medium Carbon TRIP Steel Microstructure During Annealing in the Intercritical Temperature Range

Abstract

Abstract The paper presents the results of research conducted on austenite formation in the microstructure of 41MnSi6-5 TRIP steel during annealing in the intercritical temperature range. The influence of the annealing temperature on the volume fraction of retained austenite in the microstructure of the investigated steel after water quenching was also determined.Based on the results of a dilatometric analysis and metallographic investigation it was noted that the pearlite-to-austenite transformation does not occur at a constant temperature, which is referred to as Ac1, but rather within some, possible to determine, temperature range which is bounded by the values Ac1s and Ac1f.Moreover, through X-ray analysis, it was stated that the largest amount of retained austenite remained in the samples which were annealed at the lowest temperatures in the Ac1s-Ac1f range prior to quenching. Increasing the annealing temperature to a two-phase a+g (ferrite + austenite) range, resulted in a decrease of the volume fraction of retained austenite.It was also found that during annealing in Ac1s÷Ac1f temperature range, austenite is also formed from ferrite simultaneously. This could be the reason for the decrease the carbon content in the formed austenite and consequently the decrease in the volume fraction of retained austenite in the microstructure of the investigated steel, which was quenched after having reached temperatures higher than Ac1s + 30°C.