How to identify stainless steel and stainless iron

by yane Yang Sales Manager

Stainless iron is a kind of stainless steel, the material mainly has 409, 410, 430, 444, which belongs to the martensitic and ferritic stainless steel, they will be attracted to a magnet. While the stainless steel can resist unity refers to the atmosphere or chemical substances such as acid corrosion of steel. But it is not stainless steel does not rust, corrosion behavior in different medium.

The common stainless steel materials can be divided into three types: martensitic stainless steel, ferritic stainless steel and austenitic stainless steel by metallographic structure.

Martensitic stainless steel

The common martensite stainless steel carbon content is 0.1-0.45%, chromium content is 12-14%, is chromium stainless steel, also commonly known as Cr13 stainless steel. Typical material models 1Cr13, 2Cr13, 3Cr13, 4Cr13 etc.. This type of stainless steel is usually used to make all kinds of valves, pumps and other parts that can withstand load and corrosion resistance, as well as some stainless steel tools.

In order to enhance corrosion resistance, the carbon content of martensitic stainless steel is controlled in very low content range, usually not more than 0.4%. The carbon content is low, the corrosion resistance of stainless steels is higher, and the higher the carbon content, carbon content in the matrix is higher, so the strength and hardness of the steel is higher, but it will form the chromium carbide content also more, so the stainless steel corrosion resistance becomes worse. So it can be seen that the strength and hardness of 4Cr13 are better than that of 1Cr13, but its corrosion resistance is worse than that of 1Cr13.

Both 1Cr13 and 2Cr13 are resistant to atmospheric and vapor corrosion, and are commonly used as corrosion resistant structural steels. In order to obtain good comprehensive performance, the tempered bainite is often obtained by quenching + high temperature tempering (600~700 C) to produce steam turbine blades and boiler tube accessories. While the 3Cr13 and 4Cr13 steel, because of high carbon content, the corrosion resistance is relatively poor, the low temperature quenching and tempering (200~300 C), are tempered martensite, with high strength and hardness (HRC 50), it is often used as tool steel, manufacturing medical equipment, cutting tools, oil pump shaft etc..

Ferritic stainless steel

The carbon content of common ferritic stainless steel is less than 0.15%, the chromium content is 12~30%, also is a kind of chromium stainless steel, the typical models are 0Cr13, 1Cr17, 1Cr17Ti, 1Cr28 and so on. Because of the decrease of carbon content, chromium content has been improved. The stainless steel is heated from room temperature to high temperature (960~1100 C), and its microstructure has been a single phase ferrite structure. The corrosion resistance, ductility, weldability than martensitic stainless steel excellent. The corrosion resistance of high chromium ferritic stainless steel is stronger than that of chromium containing stainless steel, and the corrosion resistance is further improved with the increase of chromium content.

Ferritic stainless steel can not be strengthened by heat treatment because it does not produce phase change during heating and cooling. If the grain coarsening during heating, only cold plastic deformation and recrystallization can be used to improve the microstructure and improve the properties.

If this kind of stainless steel stays at 450~550, it will cause embrittlement of stainless steel, which is called "475 degree brittleness"". By heating to about 600 DEG C and fast cooling, can eliminate embrittlement.

Austenitic stainless steel

Join 8-11% in nickel containing 18% chromium stainless steel, austenitic stainless steel becomes. For example, 1Cr18Ni9 is the most typical model. Such stainless steel expands austenite region because of the addition of nickel, and thus metastable metastable austenite can be obtained at room temperature. Because it contains higher chromium and nickel, and single-phase austenite structure, so it has higher chemical stability than chromium stainless steel, corrosion resistance is better, is now the most widely used stainless steel.

Type 18-8 stainless steel exhibited austenite and carbide microstructure in the annealed state, carbide, stainless steel on the corrosion resistance of the greater harm, so the general use of solid solution treatment, the stainless steel is heated to 1100 DEG C after cooling, the dissolution of carbide obtained under high temperature austenite, followed by rapid cooling, it obtain the austenite single-phase at room temperature.

We usually said the stainless iron is a ferritic stainless steel and martensitic stainless steel. The distinction between the good and the antirust performance of the most widely used austenitic stainless steel.

Source: China Stainless Steel Pipe Fittings Manufacturer - Yaang Pipe Industry Co., Limited (www.yaang.com)