Effect of Molybdenum on the Properties of Stainless Steel

Like tungsten, molybdenum is a refractory rare metal with a melting point of 2620 ° C. The bonding force between atoms is extremely strong, and the coefficient of expansion is small, the conductivity is large, and the thermal conductivity is good. The effect of molybdenum on the properties of stainless steel is as follows.

The oxidation of molybdenum to stainless steel is not significant. Therefore, when chromium-nickel stainless steel maintains a single austenite structure and no metal precipitates, the addition of molybdenum has little effect on the mechanical properties at room temperature, but with the increase of molybdenum content, steel The high-temperature strength is improved, such as long-lasting, creep and other properties are greatly improved, therefore, molybdenum-containing stainless steel is also often used at high temperatures.

The addition of molybdenum increases the high temperature deformation resistance of the steel. In addition, a small amount of ferrite is often present in the steel. Therefore, the kneading process of the molybdenum-containing stainless steel is inferior to that of the non-molybdenum steel, and the higher the molybdenum content, the worse the hot workability. In addition, it is easy to precipitate one million κ phase in molybdenum-containing stainless steel, which will significantly deteriorate the plasticity and toughness of steel. Therefore, in the production and application of molybdenum-containing stainless steel, care should be taken to prevent the formation of intermetallic phases in steel.

The main role of molybdenum in stainless steel is to improve the corrosion resistance of steel and the resistance to pitting corrosion and crevice corrosion. The effect of molybdenum on the corrosion resistance of chromium-nickel stainless steel in nitric acid, sulfuric acid, acetic acid, phosphoric acid and urea, except for the oxidizing medium HNO3, the effect of molybdenum is beneficial. Therefore, the molybdenum-containing stainless steel is generally It is not necessary to resist the corrosion of nitric acid.

Although the role of molybdenum as an alloying element in the reduction of stainless steel and the effects of pitting corrosion and crevice corrosion is still not fully understood, a large number of experiments have indicated that the corrosion resistance of molybdenum is only equivalent to the case where the steel contains a relatively high amount of chromium. Effectively, molybdenum is mainly used to strengthen the corrosion resistance of chromium in steel. At the same time, the corrosion inhibition effect of molybdenum formation has also been confirmed by experiments. In terms of stress corrosion resistance of high-concentration chloride solution, although molybdenum is an alloying element for stainless steel resistant to reducing medium, the causes of pitting corrosion and crevice corrosion are not fully understood.

In terms of stress corrosion resistance to high-concentration chloride sinking, although this experiment is the same. Molybdenum-containing chrome-nickel-molybdenum stainless steels have better resistance to chloride stress corrosion in practical applications than in non-molybdenum steels due to their high pitting corrosion resistance.