The knowledge of stainless steel is as follows:
Definition of stainless steel
Stainless steel is a kind of high alloy steel which can resist corrosion in air or chemical corrosive medium.Stainless steel is a kind of steel which has beautiful surface and good corrosion resistance.It does not need to be treated by surface treatment such as plating.It can make full use of the inherent surface properties of stainless steel.The representative properties include 13 chromium steel,18- chromium nickel steel and other high alloy steels.
From a metallographic point of view,because stainless steel contains the surface of the formation of a very thin tunica,this membrane isolated from the intrusion of oxygen into the steel to play a corrosion-resistant role.In order to maintain the inherent corrosion resistance of stainless steel,the steel must contain more than 12% chromium.
History of stainless steel development
The Chinese nation is the earliest country in the world to smelt iron and steel.Our ancestors mastered some techniques of smelting iron, steelmaking,casting and forging,and heat treatment as far back as 3000 years ago.They were more than 1700 years earlier than European countries and made important contributions to world civilization and human progress.
Iron and steel has become the most basic and important material for modern industrial and agricultural production,transportation, national defense and even people's lives.At present,although various new inorganic materials and organic synthetic materials have been greatly developed.But it is one of the important signs of a country's national strength from production to scale.The reason why iron and steel materials are so widely used is that iron ore deposits are concentrated,reserves are large, mining and smelting are relatively economical,and semi-finished steel products have strong cold and hot deformation capacity.The finished products have excellent mechanical properties (strength,plasticity and impact resistance) and processing properties (cutting,welding,cold deformation,etc.).But compared with silicic acid materials,polymer synthetic materials and some non-ferrous metals,its biggest drawback is:in the atmosphere or acid, alkali,salt and other media conditions,it is easy to lose weight due to corrosion,and even completely destroyed.
Types of stainless steel
Stainless steel can be broadly classified according to its use, chemical composition and metallographic structure.
Austenitic steels consist of 18% Cr - 8% Ni,and the amount of each element varies. Various kinds of steels are developed.
Classified by chemical composition:1.Cr series:ferrite series, martensite series;2.Cr-Ni series:austenite series,abnormal series, precipitation hardening series.
Classification of metallographic structure:1.Austenitic stainless steel;2.Ferritic stainless steel;3.Martensitic stainless steel;4. Duplex stainless steel;5.Precipitation hardening stainless steel.
Development of stainless steel
From 1910 to 1914,stainless steel with martensite,ferrite and austenite was formed,which mainly belonged to Fe-Cr and Fe-Cr-Ni systems.Nearly thirty years from the end of the First World War to the end of the Second World War (1919-1945).With the development of various industries,stainless steel has been differentiated to suit the working conditions,that is,on the basis of the original three kinds of structure of the two systems,many new types of stainless steel have been derived by increasing or decreasing carbon content and adding many other alloying elements.In the past 30 years from the end of World War II to the present,pitting-resistant stainless steel,stainless steel for atomic energy industry,precipitation hardening stainless steel and manganese-nitrogen Nickel-Substituted stainless steel have been developed to meet the needs of resisting seawater or salt corrosion,absorbing Y-rays and neutrons,obtaining ultra-high strength and saving nickel.
In recent years, ultra-low carbon stainless steel and ultra-pure ferritic stainless steel have been developed to solve the problems of intergranular corrosion and stress corrosion of austenitic stainless steel.At present,more than 230 kinds of stainless steel have been put into market,and there are nearly 50 kinds of stainless steel which are often used.About 80% of them are derivatives of austenitic stainless steel (18 Cr-8 Ni),while the other 20% are evolved from 13 Cr steel.The main research and development of stainless steel are concentrated on two aspects:steel.The main research and development of stainless steel are concentrated on two aspects:
The first aspect is to improve the corrosion resistance of steel.The study on intergranular corrosion of 18-8 steel not only develops steel grades,but also puts forward the technological methods to solve this problem.It also promoted the research on the purification and corrosion texture of stainless steel.
The second aspect is the development of highly stainless steel (precipitation hardened stainless steel),which was developed after World War II with advances in aerospace and rocket technology.Semi-austenitic precipitation hardening stainless steel has excellent technological properties (17-7PH class),and is easy to form after solution treatment.And the subsequent strengthening heat treatment (aging treatment) temperature is not high deformation is very small, in the United States,this steel is mostly used in aviation structures,and has been mass produced,similar steel has been put into use in various countries.
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