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The reason of affecting the quality of the metal shaft

  • Time:2020-04-10
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The reason of affecting the quality of the metal shaft
Some of the raw materials of the metal rotating shaft are standard martensitic stainless steel, i.e. 403, 410, 414, 416, 416 (SE), 420, 431, 440A, 440b and 440C. The corrosion resistance of these steels comes from "chromium", whose scale is from 11.5 to 18%. The steel with higher chromium content needs higher carbon content to ensure the composition of martensite during heat treatment. The above three types of 440 stainless steel are rarely considered As an application requiring welding, the 440 type composition of the filler metal is not easy to obtain.
The improvement of standard martensitic steel contains elements like nickel, molybdenum and vanadium, which are mainly used to increase the limited allowable working temperature of standard steel to higher than 1100k. When these elements are increased, the carbon content also increases. With the increase of carbon content, the problem of preventing cracking in the heat affected zone of hardening of weldment becomes more serious.
Martensitic stainless steel can be welded in annealing, hardening, hardening and tempering state. No matter what the original state of the steel is, a hardened martensitic zone will occur at the nearby weld bead after welding. The hardness of the heat affected zone mainly depends on the carbon content of the base metal. When the hardness increases, the resistance will be reduced, and the zone will become more prone to cracking, preheating and control layer Temperature, is the most useful way to prevent cracking, in order to get the best properties, post weld heat treatment is required.  Martensitic stainless steel is a kind of stainless steel whose properties can be adjusted by heat treatment (quenching and tempering). Generally speaking, it is a kind of hardenable stainless steel.
There are two basic conditions for this kind of steel: first, it is necessary to have austenite phase zone in the equilibrium phase diagram. After long-term heating in the temperature scale of this zone, the carbide is dissolved in the steel and then quenched to form martensite. That is to say, the chemical composition must be controlled in the γ or γ + α phase region. Second, it is necessary to make the alloy form corrosion resistance and oxygen resistance  It is necessary that the chromium content of passivated film should be more than 10.5%.
According to different alloy elements, it can be divided into martensitic chromium stainless steel and martensitic chromium nickel stainless steel.  The main alloying elements of martensitic chromium stainless steel are iron, chromium and carbon. For example, when Cr is more than 13%, there is no γ phase in the phase diagram of Fe Cr system. This kind of alloy is a single-phase ferrite alloy, and martensite can not occur under any heat treatment criterion. Therefore, it is necessary to participate in the austenite constituent elements in the Fe Cr binary alloy to expand the γ phase region. For the martensitic chromium stainless steel, C and N are useful elements. The increase of C and n elements makes the alloy more promising High chromium content. In addition to chromium, C is the most important element in martensitic chromium stainless steel. In fact, martensitic chromium stainless steel is a kind of ternary alloy of iron, chromium and carbon. Of course, there are other elements that can be used to confirm the general organization according to Schaeffler diagram. The martensitic stainless steel for metal shaft is mainly low carbon or high carbon steel with chromium content in the range of 12% - 18%.

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