Effects of Intercritical Annealing on Microstructure and Mechanical Properties of Low C-Mn Steels

The present study deals with intercritical annealing (IA) and water quenching (WQ) to develop a dual-phase microstructure in two low-carbon Mn-containing steels. The microstructure of steel 1 consists of polygonal ferrite (approximate to 25 mu m) and pearlite. In contrast, steel 2 shows slightly coarser ferrite (approximate to 28 mu m) and pearlite after hot rolling and air cooling. All hot-rolled samples after IA (750 degrees C, 30 min) and WQ exhibit equiaxed ferrite (approximate to 16 mu m) and martensite islands (approximate to 4 mu m). The cold-rolled (CR) samples after IA and WQ reveal elongated ferrite, fine lath martensite, and martensite/austenite (M/A) constituent. The higher hardness (298 HV) and strength (951 MPa) of the HR + CR + IA + WQ sample than the HR + IA + WQ sample (259 HV and 872 MPa, respectively) are attributed to high dislocation density and martensite island. The three-stage work hardening has been demonstrated by the Jaoult-Crussard analysis. The fractography reveals fine dimples (10-15 mu m), flat facets, and few voids.