C is an effective element for strengthening steel. With the increase of C content, the strength and hardness of the steel increase, but the plasticity, toughness and weatherability of the steel decrease. So the content of C for SPA-H steel plate is 0.08 to 0.11%.
Cu is the most important and widely used alloy element in weathering steel to improve the atmospheric corrosion resistance, and the atmospheric corrosion resistance of Cu is better when combined with other elements (such as P, Cr). When the content of Cu is 0.25%, the steel has good weathering resistance. When the content of Cu exceeds 0.30%, the corrosion resistance is improved slowly, and the effect of increasing Cu is not obvious. At the same time, the steel containing Cu is sensitive to hot working and easy to produce reticulate cracks. Therefore, in order to improve the atmospheric corrosion resistance and prevent the SPA-H steel plate from cracking, the content of Cu in SPA-H steel plate is designed to be 0.25-0.35%.
P is the most effective element to improve the atmospheric corrosion resistance of alloy elements, generally not used alone, and the combined use of Cu, Cr will be better. When the P content increases from 0.01% to 0.08%, the atmospheric corrosion resistance of steel plate is greatly improved, but when the P content exceeds 0.08%, the atmospheric corrosion resistance is not improved significantly. At the same time, excessive addition will reduce the toughness and toughness of steel. Therefore, the content of P for SPA-H steel plate is designed from 0.07 to 0.09%.
Ni is a relatively stable element. The higher the content of Ni in steel, the stronger the atmospheric corrosion resistance. At the same time, Ni and Cu can form a copper alloy with a higher melting point in steel, which reduces the crack sensitivity of copper-containing steel. The content of Ni is generally more than half of the content of copper. Therefore, the designed Ni content for SPA-H steel plate is 0.15-0.25%.
Cr and Cu composite use can improve the weatherability of steel, in order to reduce costs, Cr content for SPA-H steel plate is set at 0.40-0.50%.
The S has great harm to the atmospheric corrosion resistance of steel, so the lower the S in SPA-H steel plate, the better.
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