The corosion resistance of 14 mm plate of steel 09CuPCrNi(0.09C
0.35Mn
0.09P
0.31Cu
0.45Cr
0.31Ni)and ULCB steel(0.05C
1.61Mn
0.51Cu
0. 17Cr
0.26Ni)was measured by periodic dip corrosion test and the corrosion resistance mechanism was studied by polarizing microscope
X-ray difractometer and energy dispersive spec- trum analyser.Results showed that the corrosion resistance of ULCB steel was better than that of steel 09CuPCrNi and it was found that there were dense inner rust layer consisting of a-Fe00H
B-Fe0OH and Fe
3
O₄ and loose outer rust layer consisting of a-
y-Fe0OH and Fe
3
O₄
and the copper and chromium alloy elements enriched at rust layer - steel substrate interface and in rust layer.