Effect of oxygen and nitrogen on 42CrMo4 steel plate

Gas in steel is a general term for gases such as oxygen, nitrogen, and hydrogen in the medium absorbed by steel during smelting, welding, or chemical and electrochemical reactions on the steel surface. The gas in the steel has adverse effects on the performance of 42CrMo4 steel, and its content should be strictly controlled.

Oxygen in steel
Steelmaking itself is an oxidation process. Although deoxidizers such as ferromanganese, ferrosilicon, and aluminum are added in the later stage of steelmaking, part of the oxygen is still dissolved in 42CrMo4 steel. Oxygen generally dissolves in ferrite, or forms oxides such as FeO, SiO2, MnO, Al2O3 (that is, non-metallic inclusions in steel), which reduces the tensile strength, plasticity and toughness of 42CrMo4 steel. Especially when inclusions exist, the fatigue strength of 42CrMo4 steel decreases, and the hot and cold workability becomes poor. Therefore, oxygen control technologies such as VD deoxidation must be strictly adopted to keep the oxygen content of 42CrMo4 steel below 20ppm or even lower.

Nitrogen in steel
During steelmaking, molten steel absorbs nitrogen from the air. Part dissolves in ferrite, and part becomes non-metallic inclusions. When 42CrMo4 steel does not contain Al, Ti, Zr and other elements, most of the nitrogen and iron form needle-like compounds Fe4N. Although the presence of Fe4N increases the strength of 42CrMo4 steel, it greatly reduces its plasticity and toughness. By preventing LF nitrogen absorption technology and increasing VD denitrification rate, these two methods can effectively reduce nitrogen content, and can effectively control nitrogen content below 90ppm.

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