The standard martensitic stainless steels are: 403、410、414、416、416 (Se), 420、431、440、A440B and 440C, the corrosion resistance of these steels comes from "chromium" and ranges from 11.5 to 18.The higher the chromium content, the higher the carbon content. To ensure the formation of martensite during heat treatment, the above three types of 440 stainless steels are rarely considered for applications requiring welding, and type 440 molten metals are not easy to obtain.
Martensitic stainless steel is a kind of stainless steel which can be adjusted by heat treatment (quenching, tempering). This property determines that this kind of steel must have two basic conditions: first, the austenitic phase region must exist in the equilibrium phase diagram, and the carbide must be heated for a long time in the temperature range of the region, so that the carbides can be solid dissolved in the steel. Martensite is formed by quenching, that is, the chemical composition must be controlled in the γ or γ α phase region, and the passivation film resistant to corrosion and oxidation must be formed, and the chromium content must be more than 10.5%. It can be divided into martensite according to the difference of alloying elements. Chromium stainless steel and martensite chromium nickel stainless steel.
Martensitic stainless steel can be welded in the state of annealing, hardening and tempering, regardless of the original state of the steel, and a hardened martensite zone is produced near the weld track, regardless of the original state of the steel. The hardness of the HAZ mainly depends on the carbon content of the base metal. When the hardness increases, the toughness decreases, and the region becomes prone to crack. Preheating and controlling the interlaminar temperature are the most effective methods to avoid the cracking. In order to obtain the best properties, post-welding heat treatment is required.
The main alloying elements of martensitic chromium stainless steel are iron, chromium and carbon. Figure 1-4 shows the iron rich part of the Fe-Cr phase diagram. If Cr is greater than 13, there is no γ phase. This type of alloy is a single-phase ferrite alloy and cannot produce martensite under any heat treatment system. For this reason, austenitic forming elements must be added to Fe-Cr binary alloys in order to expand the γ phase region. For martensite chromium stainless steel, Con N is an effective element, and the addition of Con N makes the alloy allow higher chromium content. In martensitic chromium stainless steel, in addition to chromium, C is another of the most important essential elements, in fact, martensite chromium rust resistance Hot steel is a class of iron, chromium, carbon ternary alloys. Of course, there are other elements that can be used to determine the approximate organization based on the Schaeffler diagram.
Similar to ferrite stainless steel, other alloying elements can be added to martensitic stainless steel to improve other properties: 1. Add 0.07S or Se to improve cutting performance, such as 1Cr13S or 4Cr13Se2. The wear resistance and corrosion resistance of 9Cr18 steel can be increased by adding about 1%Mo and 0.1% V. The thermal strength of 1Cr13 and 2Cr13 steels can be improved by adding about 1Mo-1W-0.2V.
Martensitic stainless steel can be used for quenching, tempering and annealing, just as for modulated steel. The mechanical properties of the steel are similar to that of the modified steel: when the hardness increases, the tensile strength and yield strength increase, while the elongation, the cross section shrinkage and the impact energy decrease with the increase of hardness.
The corrosion resistance of martensitic stainless steel mainly depends on the content of chromium, while the carbon in the steel has an indirect effect on the corrosion resistance of the steel because of the formation of stable chromium carbide with chromium. Therefore, the lower the carbon content in 13%Cr steel, the higher the corrosion resistance. The corrosion resistance of 1Cr13Cr2Cr133Cr13 and 4Cr13 steel is in the opposite order of strength and corrosion resistance.
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