Stainless steel knowledge

- Apr 30, 2020-

Stainless steel is a kind of material, with a brightness close to the mirror surface, a hard and cold touch, it is a relatively avant-garde decorative material, with excellent corrosion resistance, moldability, compatibility and strength and toughness, it is used in heavy industry and light industry , Daily necessities and building decoration industries.

stainless steel pipe 1

Stainless acid-resistant steel is called stainless steel for short. It is composed of two parts: stainless steel and acid-resistant steel. In short, the steel that can resist atmospheric corrosion is called stainless steel, and the steel that can resist chemical medium corrosion is called acid-resistant steel. Generally speaking, the steel with the content of Wcr greater than 12% has the characteristics of stainless steel. Stainless steel can be divided into five categories according to the microstructure after heat treatment: ferritic stainless steel, martensitic stainless steel, austenitic stainless steel, Austenitic-ferritic duplex stainless steel and precipitation hardening stainless steel.

There are many classification methods for stainless steel materials, the common ones are the following, and the classification according to metallographic structure is the most common.

Chemical composition classification

Basically, it can be divided into two systems: chromium series stainless steel (such as ferrite series, martensite series) and chromium nickel series stainless steel (such as austenite series, abnormal series, precipitation hardening series).

Metallographic classification

Can be divided into austenitic stainless steel, ferritic stainless steel, martensitic stainless steel, duplex stainless steel, precipitation hardening stainless steel.

Classification according to corrosion resistance

Can be divided into stress corrosion resistant stainless steel, pitting corrosion resistant stainless steel, intergranular corrosion resistant stainless steel, etc.

Classification by function

Can be divided into free-cutting stainless steel, non-magnetic stainless steel, low temperature stainless steel, high strength stainless steel.

There are nearly 100 kinds of stainless steel that have been incorporated into various standards in the world, and with the progress of science and technology and the development of industry and agriculture, new stainless steel grades are still increasing. For a known grade of stainless steel, the chromium equivalent [Cr] and nickel equivalent [Ni] can be deduced based on its chemical composition, and then the structure and properties of the steel grade can be roughly estimated by using the Schaeffler-Delong stainless steel structure chart.

stainless steel partition 26

During the manufacturing process of stainless steel equipment, there will be performance damage, defects and some substances that affect the surface, such as: dust, floating iron powder or embedded iron, thermal tempering color and other oxide layers, rust spots, abrasive burrs, arc welding marks, welding Splashes, fluxes, welding defects, oils and greases, residual adhesives and paints, chalk and marking pen marks, etc. The overwhelming majority are not paying attention or doing badly because they ignore their harmful effects. However, they are potentially harmful to oxidation protective films. Once the protective film is damaged, thinned or changed by other methods, the underlying stainless steel will begin to corrode. Corrosion is generally not over the entire surface, but at or around the defect. This kind of localized corrosion is usually pitting corrosion or crevice corrosion. These two types of corrosion will develop toward depth and breadth, and most of the surface will not be eroded.