The strength of stainless steel is affected by various factors, and the most important and basic is the chemical elements added to the chemical composition. Therefore, the strength of the ferrite, martensite and austenitic stainless steel is different because of the differences in their chemical composition.
Martensitic stainless steel has the characteristics of hardening by quenching, so it can obtain good mechanical properties by selecting the brand and heat treatment conditions.
Martensitic stainless steel from the point of view, is Fe-Cr-C stainless steel. Then it can be divided into martensitic chromium stainless steel and martensitic chromium nickel stainless steel.
In the quenching and tempering conditions of martensitic chromium stainless steel, the increase of chromium content will increase the content of ferrite, so the hardness and tensile strength will be reduced. In the annealing environment, low carbon martensitic chromium stainless steel increases slightly when the chromium content is increased, while the elongation will decrease slightly. Under the established conditions of chromium content, the increase of carbon content will lead to the increase of hardness and the decrease of the plasticity of the stainless steel. The purpose of adding molybdenum elements is to increase the strength, hardness and two hardening effects of stainless steel. After the low temperature quenching, the addition effect of molybdenum element is very obvious.
In martensitic chromium nickel stainless steel, the content of delta ferrite in stainless steel can be reduced by a certain amount of nickel element, and the hardness of the material is maximized.
In the ferritic stainless steel, when the chromium content in the composition of less than 25% ferrite will inhibit the formation of martensite, so as to enhance the material strength of the chromium content will gradually decrease; chromium content is greater than 25% because of the effect of solid solution strengthening, stainless steel material strength to be improved. The increase of molybdenum content can make it easier to obtain ferrite, which can promote the precipitation of alpha phase, sigma phase and X phase, and enhance its strength after solid solution strengthening. But at the same time, the sensitivity of the material notch will be enhanced to reduce the toughness.
After increasing carbon content in austenitic stainless steel, the strength of the material will be improved because of its solid solution strengthening. The chemical composition of austenitic stainless steel is the addition of molybdenum, tungsten, niobium and titanium on the basis of chromium and nickel. Because the metallographic structure is a face centered cubic structure, it will have high strength and creep strength at high temperature. And because the linear expansion coefficient is high, so the thermal fatigue strength is weaker than that of ferrite stainless steel.
Source: China Stainless Steel Pipe Fittings Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)