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.

309 STAINLESS STEEL

Type 309 (UNS S30900)
Description
Type 309 is a high temperature chromium nickel austenitic stainless steel that resists oxidation at temperatures up to 1900˚F in dry air at constant temperature. Under thermal cycling conditions this grade resists oxidation up to a temperature of approximately 1850˚F. Type 309 has good sulfidation resistance but low resistance to carburization and should not be used in highly carburizing atmospheres. Type 309 is non-magnetic in the annealed and cold worked conditions and is as resistant to corrosion as Type 304/304L.
Chemical Composition
Chemical Composition (wt%) limits as specified in ASTM A167** Maximum, unless range is indicated
Mechanical Properties
Mechanical property requirements for annealed product as specified in ASTM A167.Physical Properties
Physical properties for Type 309 stainless steelFeatures

• Corrosion Resistance: 309 stainless stands-up excellently in a range of atmospheric environments even when exposed to corrosive elements.
• Heat Resistance: Can be hot worked at 1177C and then can be quenched rapidly.
• Easy to weld by using fusion or resistance welding methods (preferably not oxyacetylene though).
• Can be headed, upset, drawn, and stamped even though it has high work hardening rate.

Applications
The 309 can be applied to a range of applications including a variety of accessories and equipment such as boiler baffles, furnace components, oven linings, fire box sheets, and other high temperature containers.

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

AISI316L SUS316L 1.4404 TP316L 2B cold rolled stainless steel coil