Abstract: A comparison study is performed on the heat-treatment processes of a new bainitic steel containing Al used for railway crossing. Microstructures and properties obtained by air cooling, fast cooling before bainite transformation starting temperature (BS) followed by air cooling and isothermal quenching are analyzed. Results show that the microstructure obtained by isothermal quenching is the finest and possesses the best comprehensive properties. However, higher production cost is caused by isothermal quenching and it is not available in actual production limited by the large size of railway crossing. Based on the character of isothermal quenching process, a three-step cooling method is designed, which consists of fast cooling before BS point, then slow cooling in furnace between BS and martensite transformation starting temperature (MS) and eventually followed by air cooling. It is found that the microstructure, strength and toughness obtained by the three-step cooling method are almost the same as that of isothermal quenching. The cooling curves of the bulk samples close to the actual size of rail crossing under different cooling ways are measured and find that oil cooling can achieve the required cooling rate and easy to realize in actual production.

Key words: bainitic steel;heat treatment;mechanical property;microstructure;railway crossing