How to Choose the Steel for Stainless Steel Fasteners?
How to choose the steel for stainless steel fasteners? The requirement for the selection of stainless steel fasteners is that the main material is stainless steel. Stainless steel is steel that is not easy to rust. In fact, some stainless steels have both rust resistance and acid resistance (corrosion resistance). The rust and corrosion resistance of stainless steel is due to the formation of a chromium-rich oxide film (passivation film) on its surface. This rust resistance and corrosion resistance are relative. Tests show that the corrosion resistance of steel in weak media such as atmosphere and water and in oxidizing media such as nitric acid increases with the increase of chromium water content in steel. When the chromium content reaches a certain percentage, the corrosion resistance of steel occurs. Mutation, that is, from easy to rust to not easy to rust, from corrosion-resistant to corrosion-resistant.
There are many ways to classify stainless steel. According to the structure at room temperature, there are martensitic, austenitic, ferritic and duplex stainless steels; according to the main chemical components, they can be basically divided into two major systems: chromium stainless steel and chromium-nickel stainless steel; There are nitric acid-resistant stainless steel, sulfuric acid-resistant stainless steel, seawater-resistant stainless steel standard parts, etc., which can be divided into pitting corrosion-resistant stainless steel, stress corrosion-resistant stainless steel, intergranular corrosion-resistant stainless steel, etc. according to the type of corrosion resistance; For non-magnetic stainless steel, free cutting stainless steel, low temperature stainless steel, high strength stainless steel and so on. Due to its excellent corrosion resistance, formability, compatibility and toughness in a wide temperature range, stainless steel has been widely used in heavy industry, light industry, daily necessities industry and building decoration industries. .
Austenitic stainless steel, one of the materials for stainless steel fasteners
Stainless steel with austenitic structure at normal temperature. When the steel contains about 18% Cr, 8%~10% Ni, and about 0.1% C, it has a stable austenite structure. Austenitic chromium-nickel stainless steel includes the well-known 18Cr-8Ni steel and high Cr-Ni series steel developed on this basis by increasing the content of Cr and Ni and adding Mo, Cu, Si, Nb, Ti and other elements. Austenitic stainless steel is non-magnetic and has high toughness and plasticity, but its strength is low, it is impossible to strengthen it through phase transformation, and it can only be strengthened through cold working. Such as adding S, Ca, Se, Te and other elements, it has good machinability. In addition to the corrosion resistance of oxidizing acid medium, this type of steel can also resist the corrosion of sulfuric acid, phosphoric acid, formic acid, acetic acid, urea, etc. if it contains elements such as Mo and Cu. If the carbon content in this type of steel is less than 0.03% or contains Ti and Ni, its resistance to intergranular corrosion can be significantly improved. High-silicon austenitic stainless steel with concentrated nitric acid has good corrosion resistance. Due to the comprehensive and good comprehensive properties of austenitic stainless steel, it has been widely used in various industries.
Two ferritic stainless steels for stainless steel fasteners
Stainless steel mainly composed of ferrite in the use state. The chromium content is between 11% and 30%, and it has a body-centered cubic crystal structure. This type of steel generally does not contain nickel, and sometimes contains a small amount of Mo, Ti, Nb and other elements. This type of steel has the characteristics of large thermal conductivity, small expansion coefficient, good oxidation resistance, and excellent stress corrosion resistance. It is mostly used in the manufacture of atmospheric resistance. , Parts corroded by water vapor, water and oxidizing acid. This type of steel has disadvantages such as poor plasticity, significantly reduced post-weld plasticity and corrosion resistance, which limits its application. The application of out-of-furnace refining technology (AOD or VOD) can greatly reduce interstitial elements such as carbon and nitrogen, and stainless steel standard parts therefore make this type of steel widely used.
