The Properties of Martensitic Stainless Steel
Martensitic stainless steel can be welded in the state of annealing, hardening and tempering. Regardless of the original state of the steel, a hardened martensite zone is produced adjacent to the weld bead after welding. The hardness of the heat affected zone is mainly Depending on the carbon content of the base metal. As the hardness increases, the toughness decreases, and this area becomes more prone to cracking. Preheating and controlling the temperature between layers is the most effective way to avoid cracking. For best properties, post-weld heat treatment is required.
Martensitic stainless steel is a type of stainless steel that can be adjusted by heat treatment (quenching, tempering). In layman's terms, it is a type of hardenable stainless steel. This property determines that the steel must have two basic conditions: First, there must be an austenite phase region in the equilibrium phase diagram. After a long time of heating in the temperature range of the region, the carbide is solid-dissolved into the steel, and then quenched to form martensite. That is, the chemical composition must be controlled in the γ or γ + α phase region, and the second is to make the alloy form a passivation film resistant to corrosion and oxidation, and the chromium content must be above 10.5%. According to the difference of alloying 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. If Cr is greater than 13%, there is no gamma phase, and such alloys are called single phase ferritic alloys. It does not produce martensite under any heat treatment regime. For this purpose, austenite forming elements must be added to the inner Fe-Cr binary alloy. In terms of expansion, C and N are effective elements, and their addition allows the alloy to allow a higher chromium content. In martensitic chromium stainless steel, in addition to chromium, C is another most important essential element. In fact, martensitic chromium stainless steel is a class of iron, chromium and carbon ternary alloys. Of course, there are other elements. Using these elements, the approximate organization can be determined from the Schaeffler diagram.