Stainless Steel Composition 101

Updated: December 25, 2023

The American Iron and Steel Institute has simplified these compositions into “standard types” based on metallurgical judgment, engineering counsel, specification writing bodies, and the needs of the armed services. These types use a simple numbering system to identify several groups, with the first digit indicating the series or group, the last two digits indicating the type, and suffix letters indicating any modifications.

The table below will show you unique information about stainless steel composition.

TypeCrNiCmaxOther ElementsFamilyMajor PropertiesApplication
30317.00-19.008.00-10.000.15S 0.15 minAustenitic. Non-Hardenable by heat treatmentEasily machinable.
Free-machining modification of Type 302
Applications that require extensive machining operations.
303 Se17.00-19.008.00-10.000.15Se 0.15 minAustenitic. Non-Hardenable by heat treatment Free-machining version of Type 302.
Produces better surface finish than Type 303.
Aerospace components
Pump and valve
Threaded machine products.
30418.00-20.008.00-10.000.08Austenitic. Non-Hardenable by heat treatmentLow carbon variation of Type 302. Minimizes carbide precipitation during weldingFood processing equipment and utensils
Kitchen appliances
Chemical containers and equipment
304L18.00-20.008.00-10.000.03Austenitic. Non-Hardenable by heat treatmentExtra-low carbon content eliminates harmful carbide precipitation due to weldingFood processing equipment and utensils
Kitchen appliances
Chemical containers and equipment
30922.00-24.0012.00-15.000.2Austenitic. Non-Hardenable by heat treatmentHigh strength and resistance to scaling at high temperaturesHeating elements
Aircraft and jet engine parts
Heat exchangers
31024.00-26.0019.00-22.000.2Austenitic. Non-Hardenable by heat treatmentHigher alloy content improves basic characteristics of Type 309Industrial furnaces
Steam boilers
Thermocouple protection tubes
31616.00-18.0010.00-14.000.08Mo 2.00-3.00Austenitic. Non-Hardenable by heat treatmentMo improves general corrosion and pitting resistance and high temperature strength over that of Type 302Marine environments
Chemical processing
Medical implants
316L16.00-18.0010.00-14.000.2Mo 2.00-3.00Austenitic. Non-Hardenable by heat treatmentExtra-low carbon version of Type 316. Eliminates harmful carbide precipitation due to weldingChemical and petrochemical industry
Medical equipment
Food and beverage industry
31718.00-20.0011.00-15.000.08Mo 3.00-4.00Austenitic. Non-Hardenable by heat treatmentHigher alloy content improves basic advantages of Type 316Offshore oil rigs
Chemical storage tanks
Food processing plants
32117.00-19.009.00-12.000.08Ti 5 x C. minAustenitic. Non-Hardenable by heat treatmentStabilized to permit use in 800-1500°F temperature range without harmful carbide precipitationHeat Exchangers
Aircraft Components
Kiln Linings
34717.00-19.009.00-13.000.008Cb + Ta 10 x C. minAustenitic. Non-Hardenable by heat treatmentCharacteristics similar to Type 321. Stabilized by Cb and Ta.Collector Rings
Annealing Box Covers
Aircraft Exhaust Stacks
34817.00-19.009.00-13.000.08Ta 0.10 max Cb 0.20 max
 Cb + Ta 10 x C min
Austenitic. Non-Hardenable by heat treatment† Similar to Type 347 but Ta reduced for atomic energy applicationsHeat Exchangers
Jet Engine Parts
Chemical Processing Equipment
41011.50-13.500.15Martensitic. HardenableLowest cost general purpose stainless steel. Wide use where corrosion is not severe.Cutlery and Kitchenware
Surgical and Dental Instruments
Firearms Components
41612.00-14.000.15S 0.15 minMartensitic. HardenableFree-machining version of Type 410.Automotive and Aerospace
Tooling and Equipment
Pump and Valve Components
42012.00-14.000.15 minMartensitic. HardenableSimilar variation of Type 410 but higher carbon produces higher strength and hardness.Cutlery
Surgical Instruments
Needle Valves
43014.00-18.000.12Feretic. Non-HardenableMost popular of the chromium types. Combines good corrosion and heat resistance and mechanical properties.Architectural Applications
Industrial Equipment
Cutlery and Kitchenware
430 F14.00-18.000.12S 0.15 minFeretic. Non-HardenableFree-machining version of Type 430.Machined Components
Fasteners and Bolts
Pump Shafts
440A16.00-18.000.60-0.75Martensitic. HardenableSeries of high carbon types. Some basic composition with varying carbon content. Higher carbon produces higher strength and hardness but lower toughness. All Type 440 versions are corrosion resistant only in the hardened condition.Valve Components
Ball Bearings
Surgical Instruments
High-Quality Knife Blades
44623.00-27.000.2Feretic. Non-HardenableSimilar to Type 442 but Cr increased to provide maximum resistance to scaling.Heat Exchangers
Combustion Chambers
Gas Burner Components
15-5 PH14.00-15.503.50-5.500.07Cu 2.50-4.50Martensitic. Precipitation hardenedSimilar in properties and characteristics to 17-4 PH but has superior transverse ductility and toughness.Aerospace Components
Nuclear Applications
Oil and Gas Industry
PH 15-7 Mo14.00-16.006.50-7.750.09Mo 2.00-3.00
Al 0.75-1.50
Semi-Austenitic. Precipitation hardenedSpecial type similar to 17-7 PH but with higher strength.Aerospace Components
Springs and Fasteners
Marine Applications
17-4 PH15.50-17.503.00-5.000.07Cu 3.00-5.00Martensitic. Precipitation hardenedSpecial type that combines excellent corrosion resistance…high strength and hardness… low temperature hardening and good fabrication characteristics.Aerospace Components
Medical and Dental Instruments
Oil and Gas Industry
17-7 PH16.00-18.006.50-7.750.09AL 0.75-1.25Semi-Austenitic. Precipitation hardenedSpecial ultra-high strength type with good formability and excellent fabricating characteristics.Aerospace Components
Springs and Fasteners
Automotive Industry


Feretic: Non-Hardenable
Austenitic: Non-Hardenable by heat treatment
Martensitic: Hardenable
Martensitic: Precipitation hardened
Semi-Austenitic: Precipitation hardened


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