Abstract: Dynamic CCT curves of S355 low alloy structural steel was measured by Gleeble-3800 thermal simulation tester, and the effects of different rolling temperatures and cooling methods on the microstructure and mechanical properties of the S355 steel were studied by means of room temperature tensile test, low temperature impact test and microstructure observation. The results show that when the cooling rate is less than 10 ℃/s, the phase transformation products of the S355 steel are ferrite, pearlite and bainite. When the cooling rate is in the range of 10-15 ℃/s, the phase transformation products are ferrite and bainite. After rolling with water cooling, the steel has high strength and higher yield ratio, but has lower low-temperature impact property. After rolling with air cooling, the steel has lower strength and yield ratio, and higher low-temperature impact property. When the rolling temperature is 840 ℃, the comprehensive mechanical properties of the S355 steel rolled with air cooling can meet the requirements of BS EN 10225—2009 standard.

Key words: S355 steel, CCT curves, rolling process, microstructure, mechanical properties