What is the difference between stainless steel 1Cr18Ni9Ti (321) and 0Cr18Ni9 (304)

321 stainless steel and 304 stainless steel

1Cr18Ni9Ti (321 stainless steel) and 0Cr18Ni9 (304 stainless steel) belong to the 18-8 series of stainless steel types, and the difference is mainly the amount of carbon content and whether or not it contains a bowl. Their mechanical properties are basically not much difference. In the early stage of the production of stainless steel varieties, by the limitations of smelting technology, stainless steel can not be reduced in the amount of carbon, so in which a small amount of bowl to improve its corrosion resistance. With the progress of technology, the production of low carbon and ultra-low carbon stainless steel is no longer a problem, so the application of 304 stainless steel is more and more widely used, while 321 stainless steel is reduced to limit the production and not recommended varieties. But this does not mean that 321 stainless steel is not useful at all. There is a foreign stainless steel grade called 321H, which is basically equivalent to the chemical composition of 321 stainless steel, the production of this grade of stainless steel is to improve the high temperature performance of 321 stainless steel!

304 stainless steel is the U.S. standard 304, is the most commonly used stainless steel.304L is ultra-low carbon stainless steel, corrosion resistance is better.304H carbon content is higher, high-temperature strength is good.321 material has been rarely used, commonly used is 304/304L or 316/316L . Stainless steel 1Cr18Ni9Ti is a common stainless steel.

Chemical composition of 304 stainless steel

<=0.12 %

Cr: 17-19 %

Ni: 8-11 %

Ti: 5* (C%-0.02) -0.8 %

Mechanical properties of 304 stainless steel

Tensile strength (MN/m2) >=550

Yield strength (MN/m2)>=200

Elongation5 (%)>=40

Shrinkage (%)>=55

If used for 700 ° C high temperature, AISI321 stainless steel should be able to handle, because it is both austenitic stainless steel, but also widely used austenitic heat treatment steel, but it is best not to exceed 750 ° C, its heat treatment for the solution treatment, that is, heated to more than 1,000 ° C, insulation for a certain period of time after the quenching of the water, and then higher than the use of temperature of 60 ~ 100 ° C to do aging.

The difference between AISI321 stainless steel and AISI304 stainless steel

The carbon content of the two is not the same, AISI321 stainless steel is high. The content of chromium and nickel is the same, respectively 18% and 9%. In this case, due to the low carbon content of AISI304 stainless steel, the strength is lower than AISI321 stainless steel, and the corrosion resistance is better than AISI321 stainless steel. But because AISI321 stainless steel contains a mantle of grain boundary corrosion resistance, so it can be heat treated to improve its resistance to grain boundary corrosion. Normal temperature and normal conditions can be substituted.

Previously commonly used stainless steel grade AISI321 stainless steel, now commonly used grade AISI304 stainless steel (or 304L). AISI321 stainless steel carbon content is higher for about 0.1%. The carbon is supersaturated and solidly dissolved in austenite at room temperature. When AISI321 stainless steel is heated to 550800 ° C when the supersaturated carbon in the form of chromium carbides precipitated at grain boundaries. Chromium carbides on the grain boundary can easily react with acid to cause pitting corrosion and intergranular corrosion. The chromium carbide precipitation temperature just contains the vacuum interrupter brazing temperature, so the interrupter brazing will cause AISI321 stainless steel chromium carbide precipitation. This can easily lead to vacuum interrupter chamber leakage during use. AISI304 stainless steel or 304L stainless steel carbon content is less than 0.03%, which is close to the carbon content of carbon solubility in austenite, and thus heating does not cause chromium carbide precipitation, which can be exempted from intergranular corrosion and pitting corrosion. This greatly reduces the possibility of air leakage.