Martensitic stainless steel is a type of stainless steel whose properties can be adjusted by heat treatment (quenching, tempering). In layman's terms, it is a type of hardenable stainless steel. This characteristic determines that this type of steel must meet two basic conditions: first, there must be an austenite phase region in the equilibrium phase diagram. After long-term heating within the temperature range of this region, carbides are dissolved in the steel and then quenched to form martensite, that is, the chemical composition must be controlled in the γ or γ+α phase region. Second, the alloy must form a corrosion-resistant and oxidation-resistant passivation film, and the chromium content must be above 10.5%. According to the difference in 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. This type of alloy is a single-phase ferrite alloy, and martensite cannot be produced under any heat treatment system. For this reason, austenite-forming elements must be added to the Fe-Cr binary alloy. To expand, C and N are effective elements. The addition of C and N elements allows the alloy to have a higher chromium content. In martensitic chromium stainless steel, besides chromium, C is another most important essential element. In fact, martensitic chromium stainless heat-resistant steel is a ternary alloy of iron, chromium and carbon.
SA268 TP439 Heat exchanger Tube
