AISI 304 Stainless Steel Properties: Tensile Yield Strength and Hardness
AISI 304 stainless steel (UNS S30400) is the most widely used stainless steel, containing 18-20% Cr and 8-10.5% Ni, also known as 18-8 stainless steel. SS 304 is non-magnetic under annealing conditions, but after cold working (such as stamping, drawing, bending, rolling), part of the austenite structure may transform into martensite, so it has weak magnetism. Type 304 has good resistance to atmospheric corrosion and oxidation. The high nickel-chromium alloy content gives it excellent corrosion resistance and is widely used in the food industry as standard food-grade stainless steel.
There are several variations of grade 304 stainless steel, such as the ultra-low carbon version 304L, the nitrogen-containing version 304N, 304H with improved creep properties and the higher carbon content type 302. The second most widely used grade 316 stainless steel, compared with AISI 304, has reduced chromium content, increased nickel content, and added 2-3% molybdenum. The addition of molybdenum increases resistance to pitting and crevice corrosion caused by chlorides. Therefore, 316 SS is widely used in marine applications.
강화
Conventional austenitic stainless steels such as AISI 304 cannot be hardened by heat treatment because they do not change their lattice structure when heated, so they can only be hardened by cold working. Cold working will transform part of the austenite into martensite. As the amount of martensite in steel increases, its strength increases and its plasticity decreases.
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The reason why SS 304 material does not rust is because the Cr and Fe in it are oxidized to form a dense passivation film to prevent further corrosion.
AISI 304 stainless steel has excellent corrosion resistance in mild atmosphere and fresh water, and even the surface will not rust. However, it is not resistant to corrosion by halides (such as chloride, fluoride, etc.), because halides can easily penetrate the passivation film and make stainless steel lose its resistance.
Welding of AISI Grade 304 Stainless Steel
Type 304 stainless steel has excellent weldability and does not require preheating. Post-weld heat treatment is generally not required unless large sections are welded, in which case weld decay may occur.
To prevent weld corrosion, please refer to Heat Treatment - Stress Relief, or it is recommended to use ultra-low carbon stainless steel such as 304L, or stabilized stainless steel 321, 347.
Filler metals for welding AISI 304 materials: E308, E309. E308L can be used when the service temperature is 370 degree (700 degree F).
AISI 304 stainless steel is widely used in the food industry, home appliances and consumer electronics, medical equipment, architectural decoration, hardware tools, automobile industry, petrochemical industry, water treatment plants, aerospace, etc. The following table lists typical uses by industry:
- Electronic appliances: SS 304 liner, washing machine drum, watch and mobile phone case, microwave oven, range hood hood, control cabinet, water pump casing, etc.
- 석유 화학 산업 % 3A 여과 장비 % 2C 오일 및 가스 파이프 라인.
