Molybdenum effect
Molybdenum in pure γ-Fe in the maximum solubility of about 3%, ω (C) ≈ 0.25% ~ 0.30%, the maximum solubility in austenite is about 8%. Molybdenum in pure α-Fe the maximum solubility of about 32%, and decreased with temperature can precipitate Fe3Mo2, to obtain an age-hardening systems. Molybdenum is a ferrite forming element, capacity equivalent to chromium. In the martensitic stainless steel, molybdenum addition to improving the corrosion resistance, but also improve the hardness and strength, and enhance the secondary hardening effect of steel. The role of the stainless steel molds and cutting tools is very beneficial, usually in the martensitic stainless steel in the ω (Mo) <1%.
Molybdenum content is too high, will lead to the formation of δ ferrite and have some adverse effects. Molybdenum can expand the scope of reduction of the passive medium, improve strength and corrosion resistance of passive film, anti-H2SO4, HCl,H3PO4, and some organic acids, resistance to pitting and crevice corrosion. Mo can improve the ability of chloride stress corrosion cracking, especially chloride ions in salt or brine case. Solid solution strengthening method using molybdenum austenitic stainless steelimproves the strength and resistance to tempering of martensitic stainless steel capacity. In addition, the molybdenum can also increase the hardenability of steel, high temperature strength and creep resistance.
Nitrogen effect
Nitrogen is an austenite stabilizing element, can increase the strength of stanless steel. In the austenitic stainless steel or austenitic – ferritic duplex stainless steel, can enhance the resistance to pitting and crevice corrosion, and reduce the ó-phase intermetallic welding at high temperature or precipitation opportunities. Meanwhile, a compound of nitrogen and manganese instead of expensive nickel alloy, as well as the advantages of improving the solubility of nitrogen. With nitrogen and manganese on behalf of low-nickel stainless steel and nickel-manganese nitrogen-free nickel-chromium stainless steel, has received applications in industry. Typical components of such steel 18Cr-5Ni-8Mn-0.15N, than 304 304L austenitic stainless steel grades with higher strength and corrosion resistance.
Source: wilsonpipeline Pipe Industry Co., Limited (www.wilsonpipeline.com)
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