(4) the development of stainless steel
China is a big country in the production of stainless steel. With the production and development of stainless steel, many varieties have been developed naturally. At present, more than 50 kinds of stainless steel have been developed, which basically meet the needs of domestic production and development, and a brief description of some new varieties developed at present.
1) the initial formation of austenitic stainless steel system. Low carbon austenitic stainless steel 0Cr18Ni9 and 00Cr17Ni2Mo2 have been developed to eliminate fatigue corrosion caused by carbon element. In order to improve its special properties, Cu, Ti, Nb, Mn, Cr, Si and N elements can be added.
2) the development of nitrogen containing stainless steel. The results of nitrogen generation of carbon in stainless steel were achieved. N and C have many common characteristics in austenitic stainless steel. The effect of N stable austenite is larger than that of Ni, which is equal to that of C. The combination of N and Mn can replace the more expensive Ni.
N is also one of the most effective solid solution strengthening elements in austenite. The affinity between N and Cr is less than that of C and Cr, and austenitic steels rarely see the precipitation of Cr2N. Therefore, N can improve the strength of stainless steel without decreasing the corrosion resistance.
3) the development of super ferritic stainless steel. Ferritic stainless steel has good corrosion and oxidation resistance, and its stress corrosion resistance is better than that of austenitic stainless steel. The price is cheaper than austenitic stainless steel. However, the disadvantages of poor weldability and brittleness tend to be limited, and the production and use are limited. The weldability and brittleness of ferritic steel can be improved by reducing the content of carbon and nitrogen in steel and adding the stabilizing elements such as Ti, Nb, Zr and Ta, and adding three kinds of metal toughening elements such as Cu, AI and V.
4) the development of super austenitic steel. The content of super austenitic steel Cr, Mo and N is significantly higher than that of conventional stainless steel. The more famous one is the steel containing 6% Mo (245SMo). This kind of steel has very good local corrosion resistance. Under the condition of sea water, gas, crevice and low speed scour, it has good resistance to pitting (PI 40) and good resistance to stress corrosion. It is a substitute for Ni based alloy and titanium alloy.
5) the development of super martensitic stainless steel. The traditional martensitic stainless steel 2Cr13, 3Cr13, 4Cr13 and 1Cr17Ni2 lack sufficient ductility, and the corresponding force is very sensitive during the cold deforging process, and cold forming is difficult. In addition, the weldability of steel is relatively poor, and the application scope is limited. In order to overcome the above shortcomings of martensitic steel, an effective way has been found recently, which is to develop a new series of alloy steel super martensitic steel by reducing the content of C and Ti and increasing the content of Ni. This kind of steel has high tensile strength, good ductility and improved welding performance, so super martensitic steel is also called soft martensitic steel or weldable martensitic steel.