Stainless steels are a family of iron based alloys that contain a minimum of 10.5% chromium (CR). The presence of chromium creates an invisible surface film that resists oxidation and makes the material passive or corrosion resistant (stainless). There are multiple families of stainless steel which are designed for various applications and uses. Stainless grades can be further modified to meet various processing, corrosion, temperature and strength conditions.

300 series grade. 

300 Series stainless steels are classified as austenitic, and are hardenable only by cold working methods. These grades of stainless have chromium (approx. 18 to 30%) and nickel (approx. 6 to 20%) as their major alloying additions. Type 304 is the most widely used alloy of all stainless steels. 300 Series Stainless steel alloys resist corrosion, maintain their strength at high temperatures and are easy to maintain.
 

Stainless steel 321/321H grade.

Alloy 321 (UNS S32100) is a titanium stabilized austenitic stainless steel with good general corrosion resistance. It has excellent resistance to intergranular corrosion after exposure to temperatures in the chromium carbide precipitation range of 800 - 1500°F (427 - 816°C). The alloy resists oxidation to 1500°F (816°C) and has higher creep and stress rupture properties than alloys 304 and 304L. It also possesses good low temperature toughness.

Alloy 321H (UNS S 32109) is the higher carbon (0.04 - 0.10) version of the alloy. It was developed for enhanced creep resistance and for higher strength at temperatures above 1000oF (537°C). In most instances, the carbon content of the plate enables dual certification.

Alloy 321 cannot be hardened by heat treatment, only by cold working. It can be easily welded and processed by standard shop fabrication practices.

Stainless steel 309 309S 310 310S grade:

The 309 stainless steel has a higher corrosion resistance and strength compared to 304 stainless steel. This product is versatile and known for its high heat treatment capabilities.

Great ductility, weldability, and high-temperature properties make 310 Stainless Steel the ideal choice for projects that require service at temperatures up to 1150 degrees Celsius. Grade 310 resists oxidation and is also used at temperatures up to 1040 degrees Celsius intermittently. Similar to other austenitic steel grades, toughness down to cryogenic temperatures is another feature of 310.

Stainless steel 347 grade:

Alloy 347 is a stabilized, austenitic, chromium steel containing columbium which allows for the elimination of carbide precipitation, and, consequently, intergranualr corrosion. Alloy 347 is stabilized by the additions of chromium and tantalum and offers higher creep and stress rupture properties than alloy 304 and 304L which may also be used for exposures where sensitization and intergranualr corrosion are of concern. The addition of columbium also allows Alloy 347 to have excellent corrosion resistance, even superior to that of alloy 321. 347H is the higher carbon composition form of Alloy 347 and demonstrates improved high temperature and creep properties.

Other common 300series grade 
Stainless steel 304/304L Grade : 

Type 304/304L is the modern version of "18-8" stainless steel containing approximately 18% chromium and 8% nickel and is the most commonly specified stainless steel used throughout the world. Type 304/304L is a versatile, general purpose stainless steel with good resistance to atmospheric corrosion, and to many chemicals and food and beverages. These grades can be specified in the annealed condition where they have very good formability. Higher nickel versions can be specified to enhance multi-stage deep drawing characteristics. Higher strength, cold-worked conditions can also be specified for Type 304/304L for spring type applications. Type 304/304L is non-magnetic in the annealed condition but may become slightly magnetic as a result of cold working.

Type 304L can be dual certified as 304 when the composition meets the lower carbon limit of 304L and the slightly higher strength levels of 304. Type 304L should be specified for welded applications as the low carbon version eliminates chromium carbide precipitation and enhances the corrosion resistance in the as-welded condition.

Another common material Stainless steel 316/316L Grade : 

Alloy 316/316L is molybdenum-bearing austenitic stainless steel. The higher nickel and molybdenum content in this grade allows it to demonstrate better overall corrosion resistant properties than 304, especially with regard to pitting and crevice corrosion in chloride environments. In addition, Alloy 316/ 316L provides excellent elevated temperature tensile, creep and stress-rupture strengths, as well as outstanding formability and weldability. 316L is the lower carbon version of 316 and is immune from sensitization; therefore, it is very frequently used in heavy gauge welded components.
Specifications: UNS S31600 / S31603

Chemical Composition&Mechanical Properties

Chemical Composition (wt%) limits as specified in ASTM A240 and ASME SA240*

Mechanical property requirements for annealed product as specified in ASTM A240 and ASME SA240

Other common Specification for stainless steel sheet

AISI321 TP321 4X8 5X10 5X20 stainless steel plate price