Investigation of Microstructure and Hardness of Tempered Fe-1C-2Si (wt.%) and Fe-1C-2Si-2Cu-1Ni (wt.%) Nanostructured Bainitic Steels

Abstract

In this study, the tempering behavior of two nanostructured bainitic steels of composition Fe-1C-2Si (Alloy1) and Fe-1C-2Si-2Cu-1Ni (Alloy2) is examined and compared. The alloys were homogenized, austenitized, and isothermally held at 300°C for 12 h and 24 h, respectively. Then they were tempered at 350-500°C for 30-240 min and investigated in terms of microstructure and hardness. It was observed that Alloy2 exhibited superior thermal stability in comparison to Alloy1. Moreover, the hardness of Alloy2 increased steadily up to a peak value under the conditions where the hardness of Alloy1 decreased gradually. The secondary hardening peaks were attributed to copper precipitation, which was evidenced by TEM investigation.