Effect of Tempering Temperature on the Microstructure and Hardness of a Super-bainitic Steel Containing Co and Al

Abstract

The effect of tempering temperature, within the range of 400 to 700°C, on the microstructure and hardness of two super-bainitic steels, one as the control parent sample and the other with added Co & Al was investigated. Post-tempering examinations of the super-bainitic samples showed that low temperature tempering cycles (400-500°C) resulted in carbides formation, and some increases in the hardness possibly due to precipitation strengthening in the Co & Al contained steel. Once the tempering temperature increased to 600°C, the hardness plummeted in both steels due to the concurrent coarsening of the bainitic ferrite plates and more precipitation of carbides. At the higher tempering temperature of 700°C, further reduction in the hardness occurred because of the accelerated recovery of ferrite and spheroidization of carbides. This work clearly showed that the super-bainitic steel containing Co & Al had a superior tempering resistance particularly at low tempering temperatures (<500°C) due to reduced carbide precipitation in the presence of Co & Al.

A comparative study of the thermal and mechanical cutting influence on the cut-edge hardness of structural steels S355 and S1100

“…In essence, the microstructure of BM and SCHAZ is tempered martensite, while the tempering temperature and the endurance of tempering are different between BM and SCHAZ. Many research showed that the hardness decreases with tempering temperature overall [31]. From point D to point E, the magnitude of hardness increases due to the weakening tempering effect back to the level of the base material.…”

Controlling the Thermal Stability of a Bainitic Structure by Alloy Design and Isothermal Heat Treatment

“…Then, at higher tempering temperatures, a hardness drop was revealed, and at 650 • C, the hardness was 418 ± 5 HV1. In contrast, many investigations indicate a continuous decrease in the hardness of bainitic steels [27,[49][50][51]. Based on the microstructural approach (Figure 14), designed steel during the tempering processes was characterized by a comparable morphology of structure up to a temperature of 500 °C (not presented here) in relation to the austempering process (Figure 14a).…”