Tests of fatigue crack propagation behavior of 19Mn5 steel and its weldment were carried out in air and in salt environment by using MTS salt fog chamber. The results show that the da/dn of weld metal is higher than that of 19Mn5 base metal under both air and salt fog environments and at room temperature. For both 19Mn5 base metal and its weld metal on lower Ak region the da/dn in salt fog environment and at 32鈩?is lower than that in air environment and at room trmperature

but in higher Ak region the result is to the contrary. This is because that the corrosion matter leads to the closure and block-up in crack tip.