Molybdenum is mainly used for production of iron and steel industry in many countries, basically accounted for more than 8 of the molybdenum is added as elements of steel, but only about 2 is used to produce metal molybdenum, super alloy and special alloy, chemical products, they are used in the petroleum chemical industry, light industry, electronic and high-tech fields.
Molybdenum elements can improve the hardenability and thermal strength of stainless steel pipes. Avoid temper brittleness and improve corrosion resistance in some medium. Mo can make larger sections of stainless steel pipe parts quenching depth, quenching and tempering, improve the anti tempering stability of stainless steel material, the material can be tempered at high temperature, so as to effectively reduce or even eliminate the residual stress, enhance the plasticity in the Mo elements in carbon steel in addition to the above use, but also can reduce the the carbide forming tendency of continuous net at the grain boundary in the carburized layer, reduce the residual austenite in the carburized layer, enhance the relative wear resistance of the surface layer of the stainless steel pipe.
In 316L and 2205 stainless steel welded pipes, the molybdenum element can also guarantee the stability of the hardness of the stainless steel and enhance the resistance to deformation, cracking and wear. In the stainless steel and acid resistant steel, the molybdenum element can further enhance the corrosion resistance in various environments. In addition, the corrosion tendency of chlorine ions can be avoided.
The effect of molybdenum on Microstructure and heat treatment of stainless steel welded pipe is mainly four points. In the first Mo solid solution in stainless steel and ferrite, austenite and carbide in the pipe, which is to narrow the austenite phase elements; when the content is low, and iron and carbon composite formation of cementite, when high concentrations can generate special carbide; molybdenum can improve the hardenability of stainless steel pipe, than Cr, was less than that of manganese; molybdenum can enhance the stability of tempering steel.
Molybdenum plays a great role in the mechanical properties of stainless steel pipes. First, molybdenum has solid solution strengthening effect on ferrite, and it also increases the stability of carbides, thereby increasing the strength of stainless steel. Molybdenum also improves the ductility and toughness of stainless steel and is also beneficial to the enhancement of wear resistance. In addition because molybdenum will make deformation enhanced after softening and recrystallization temperature and recovery temperature increase, and significantly enhance the creep resistance of ferrite, can effectively inhibit the aggregation of cementite at 450-600 DEG C, promote the precipitation of special carbide, so it became an enhanced heat resistance stainless steel material is the most effective alloy elements.
The effects of molybdenum on the physical, chemical and technological properties of stainless steel pipes are also reflected in four aspects. The first is 1.5% carbon steel, 2%-3% molybdenum will improve the remanence and coercivity; can make stainless steel pipe surface passivation in reducing acid and strong oxidizing salt solution in the second, so Mo can generally improve the corrosion resistance of stainless steel materials, stainless steel in chloride solution to avoid the occurrence of pitting corrosion in liquid the third is the antioxidant; molybdenum high content of stainless steel materials will deteriorate. Finally, the stainless steel with no more than 8% molybdenum still can be forged and rolled, but when the molybdenum content is high, the stainless steel pipe has greater resistance to the deformation of the heat processing.
Source: China Stainless Steel Pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)