In situ observation of pearlite phase transition in high-carbon steel under different holding temperatures and cooling rates using confocal laser scanning microscope

Abstract

The pearlite phase transition behavior of the high-carbon steel (0.82% C) under different holding temperatures (1050 °C and 1450 °C) and cooling rates (60, 300 and 600 °C/min）were investigated using a confocal laser scanning microscope (CLSM). The phase diagram of the researched steel in an equilibrium state was calculated by JMatPro software, and the identifications of the pearlite lamellar spacing and dislocation density were conducted by SEM and TEM analysis, respectively. The in situ observation showed that the pearlite formed at the grain boundary and grew into austenite grains. As the cooling rate increased, the beginning and finishing temperature of pearlite transition moved in a lower direction as a whole. Compared with the normal heat treatment of 1050 °C, the pearlite formation temperature increased by 30 °C with a holding temperature of 1450 °C at the same cooling rate of 60 °C/min, which was contributed to the enhancement of dislocation density along the grain boundary. In addition, the liner relationship between average phase transition temperature and reciprocal of pearlite lamellar spacing was obtained.

Keywords

• High-carbon steel
• CLSM
• Holding temperature
• Cooling rate
• Pearlite phase transition