Views:12 Author:Site Editor Publish Time: 2020-09-17 Origin:Site
Molybdenum, like tungsten, is a refractory rare metal with a melting point of 2620°C, strong interatomic bonding, small expansion coefficient, high electrical conductivity and good thermal conductivity. The influence of molybdenum on the properties of stainless steel is as follows.
The oxidation effect of molybdenum on stainless steel is not significant. Therefore, when the chromium-nickel stainless steel maintains a single austenite structure and no intermetallic precipitation, the addition of molybdenum has little effect on its room temperature mechanical properties, but as the content of molybdenum increases, the steel The high-temperature strength of the steel is improved, such as durability, creep and other properties have been greatly improved. Therefore, molybdenum-containing stainless steel is often used at high temperatures.
The addition of molybdenum increases the high-temperature deformation resistance of steel, and there is often a small amount of ferrite in the steel, so the hot workability of molybdenum-containing stainless steel is worse than that of molybdenum-free steel, and the higher the molybdenum content, the worse the hot workability. In addition, it is easy to precipitate one million κ phases in molybdenum-containing stainless steel, which will significantly deteriorate the plasticity and toughness of steel. Therefore, in the production and equipment manufacturing and application of molybdenum-containing stainless steel, attention should be paid to prevent the formation of intermetallic phases in steel.
The main role of molybdenum in stainless steel is to improve the corrosion resistance of the steel against reducing media, pitting corrosion resistance, and crevice corrosion resistance. They are the influence of molybdenum on the corrosion resistance of chromium-nickel stainless steel in nitric acid, sulfuric acid, acetic acid, phosphoric acid and urea. Except in the oxidizing medium HNO3, the role of molybdenum is beneficial. Therefore, stainless steel containing molybdenum is generally No need to resist the corrosion of nitric acid.
Although the role of molybdenum as an alloying element on the resistance of stainless steel to reducing media, as well as the reasons for surface pitting corrosion and crevice corrosion are still not fully understood, a large number of experiments have pointed out that the corrosion resistance of molybdenum is only equivalent to that of steel containing a higher amount of chromium. Molybdenum is mainly used to strengthen the corrosion resistance of chromium in steel. At the same time, the corrosion inhibition effect of molybdenum after forming acid salt has also been confirmed by experiments. In terms of resistance to stress corrosion in highly concentrated chloride solutions, although molybdenum, as an alloying element, is resistant to reducing media for stainless steel, the reasons for its resistance to pitting and crevice corrosion are not fully understood.
In terms of resistance to stress corrosion caused by high concentration of chloride, although this experiment refers to the same. Because of the high pitting corrosion resistance of molybdenum-containing chromium-nickel-molybdenum stainless steel, it often has better chloride stress corrosion resistance than molybdenum-free steel in practical applications.