CR can also form a dense oxide film on the surface of JIS G3125 SPA-H steel plate, improve the passivation ability of the steel and slow down the growth rate of rust layer. However, due to the selective oxidation of Cu, the Added Cu alone will be enriched on the surface of JIS G3125 SPA-H steel plate, which is easy to lead to hot cracks in the production process of Cu containing steel, commonly known as "copper embrittlement".
This is because Cu can delay austenite transformation. With the increase of Cu content, the brittle zone of JIS G3125 SPA-H steel plate becomes wider and the brittle temperature range increases.
Adding Ni to the steel can improve the brittle zone plasticity and minimum area shrinkage of JIS G3125 SPA-H steel plate, improve the high temperature plasticity of the steel, and Ni is also an effective element for atmospheric corrosion resistance. When Cu, Ni and C are added at the same time, the corrosion resistance of JIS G3125 SPA-H steel plate is particularly obvious. However, for the weather resistant steel plate without Ni, the occurrence of "copper embrittlement" defect can also be reduced by improving the heating time, discharge temperature and optimizing production scheduling.
