Study on thermal stability of F40 hull structure steel

The mechanical properties of F40 hull structure steel processed by thermo-mechanical controlling process(TMCP) and reheating at 400~750 ℃ and holding for 1 h were investigated.The structure evolution and thermal stability mechanism of the steel during reheating process were studied by OM,SEM and TEM.It was found that the hardness variety decreased prior and then increased up until emerging the hardening peak.The microstructure of the steel before reheating are the quasi-polygonal and the acicular ferrite mixed structure,after the temperature rising higher than 600 ℃ for 1h the structure variety is not obvious.With the reheating temperature raising the acicular ferrite gradually disappear and at last turns to polygonal morphology.Therefore,the F40 hull structure steel hot processed at lower 600 ℃ can still hold better structure stability.