Molybdenum is mainly used in iron and steel industry, generally more than 80% is added to the molybdenum in steel, only about 20% to produce metal molybdenum, molybdenum alloy, super alloy and special chemical products, they are mainly used in petroleum chemical industry, light industry, electronics and other high-tech fields.
Molybdenum in stainless steel welded pipe may enhance hardenability and thermal strength, avoid temper brittleness, and improve the corrosion resistance of stainless steel in some media. Molybdenum can make stainless steel parts quenching large section deep, hardenability, improve the resistance to tempering or tempering stability, so that it can be tempered at high temperature, so as to effectively reduce or eliminate the residual stress of stainless steel materials, reinforced plastic. In the carburizing steel in molybdenum in addition to the above effect, but also can reduce the carbides in the carburized layer tended to form continuous net at the grain boundaries, reduce the residual austenite in the carburized layer, the relative increase in wear resistance of the surface layer.
In 316L and 2205 stainless steel welded pipe, molybdenum also makes stainless steel material to form a relatively stable hardness, and enhance the resistance to deformation, cracking and wear. In stainless acid resistant steel, molybdenum can further improve the corrosion resistance of organic acids and hydrogen peroxide, sulfuric acid, sulfurous acid, sulfate, acid dyes, bleaching powder, etc.. In particular, because of the addition of molybdenum, it can effectively avoid the point corrosion tendency due to the existence of chloride ion.
Below introduce some under the effect of molybdenum on the stainless steel welded pipe.
The stainless steel welded pipe and the effect of heat treatment on Microstructure
Because molybdenum can dissolved in ferrite, austenite and carbide in stainless steel, so it can reduce the austenite phase elements, another is when the Mo content in stainless steel is low, and the formation of cementite iron and carbon composite, special carbon compounds and high content can be formed of stainless steel, is third to improve the hardenability of stainless steel, it is more than a strong and slightly inferior to chromium manganese molybdenum is fourth points, can enhance the tempering stability of stainless steel, as there is a single alloy element, increase the temper embrittlement of stainless steel, chromium, manganese and other elements when they coexist, Mo also reduce or suppress brittleness caused by other elements.
Effect of stainless steel welded pipe on mechanical properties
First of all, Mo element has a solid solution strengthening effect on ferrite in stainless steel, and it also improves the stability of carbide, thus improving the strength of stainless steel. The molybdenum stainless steel can improve the ductility and toughness and wear resistance. The third point is that the softening and recovery temperature, recrystallization temperature and the creep resistance of ferrite can be effectively improved by molybdenum, which can effectively restrain the aggregation of cementite at 450-600 oc. To promote the precipitation of special carbides, so the most effective alloying elements improve heat resistance of stainless steel.
The physical, chemical and process properties of stainless steel welded pipe
The first is in the 1.5% carbon steel, 2%-3% molybdenum enhanced remanence and coercivity, can make stainless steel surface passivation in reducing acid and strong oxidizing salt solution in the second, so Mo can generally improve the corrosion resistance of stainless steel, stainless steel to avoid pitting corrosion in chloride solution. The second is the high content of molybdenum (>3%) when the deterioration of the oxidation resistance of stainless steel. In addition, the stainless steel with molybdenum content of no more than 8% can still be forged and rolled, but when the content is high, the deformation resistance of the steel to hot working is enhanced.
Because chromium can form a thin and protective passivation film naturally on the steel surface, the stainless steel welded pipe has corrosion resistance. Molybdenum can make this passivation film more robust, and can be destroyed in the chloride passivation film to the rapid regeneration. The increase of Mo content can improve the corrosion resistance of stainless steel pitting and crack.
Source: China stainless steel welded pipe Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)