Stainless Steel Composition 101

At Eagle, we not only provide our clients with the highest quality stainless steel tube, we are happy to offer helpful information and resources. Our clients often ask us about the unique stainless steel compositions, and we’re glad to explain!

The American Iron and Steel Institute has conducted in-depth studies resulting in a simplified list of stainless steel composition types. This list is known as “standard types”. These types were selected on the basis of metallurgical judgement after considering many factors such as the counsel of engineering and specification writing bodies, as well as the needs of the armed services. This method of standardization has led to identification by types according to several groups, using a simple system of numbers and sometimes letters. In a 3 digit number, the first digit indicates the series or group, and the last two digits indicate type. Modifications of types are indicated by suffix letters. The series designations identify the following groups:

Chemical Compositions and Major Characteristics
TypeCrNiCmaxOther ElementsMajor Characteristics
30317.00-19.008.00-10.000.15 S 0.15 min† Free-machining modification of Type 302
303 Se17.00-19.008.00-10.000.15Se 0.15 min† Free-machining version of Type 302. Produces better surface finish than Type 303.
30418.00-20.008.00-10.000.08† Low carbon variation of Type 302. Minimizes carbide precipitation during welding
304L18.00-20.008.00-10.000.03† Extra-low carbon content eliminates harmful carbide precipitation due to welding
30922.00-24.0012.00-15.000.20† High strength and resistance to scaling at high temperatures
31024.00-26.0019.00-22.000.20† Higher alloy content improves basic characteristics of Type 309
31616.00-18.0010.00-14.000.08Mo 2.00-3.00† Mo improves general corrosion and pitting resistance and high temperature strength over that of Type 302
316L16.00-18.0010.00-14.000.20Mo 2.00-3.00† Extra-low carbon version of Type 316. Eliminates harmful carbide precipitation due to welding
31718.00-20.0011.00-15.000.08Mo 3.00-4.00† Higher alloy content improves basic advantages of Type 316
32117.00-19.009.00-12.000.08Ti 5 x C. min† Stabilized to permit use in 800-1500°F temperature range without harmful carbide precipitation
34717.00-19.009.00-13.00.008Cb + Ta 10 x C. min† Characteristics similar to Type 321. Stabilized by Cb and Ta.
34817.00-19.009.00-13.000.08Ta 0.10 max Cb 0.20 max
Cb + Ta 10 x C min
† Similar to Type 347 but Ta reduced for atomic energy applications
41011.50-13.50-0.15-¥ Lowest cost general purpose stainless steel. Wide use where corrosion is not severe.
41612.00-14.00-0.15S 0.15 min¥ Free-machining version of Type 410.
42012.00-14.00-0.15 min-¥ Similar variation of Type 410 but higher carbon produces higher strength and hardness.
43014.00-18.00-0.12-* Most popular of the chromium types. Combines good corrosion and heat resistance and mechanical properties.
430 F14.00-18.00-0.12S 0.15 min* Free-machining version of Type 430.
-¥ Series 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.
44623.00-27.00-0.20-* Similar to Type 442 but Cr increased to provide maximum resistance to scaling.
15-5 PH14.00-15.503.50-5.500.07Cu 2.50-4.50• Similar in properties and characteristics to 17-4 PH but has superior transverse ductility and toughness.
PH 15-7 Mo14.00-16.006.50-7.750.09Mo 2.00-3.00
Al 0.75-1.50
•• Special type similar to 17-7 PH but with higher strength.
17-4 PH15.50-17.503.00-5.000.07Cu 3.00-5.00• Special type that combines excellent corrosion resistance…high strength and hardness… low temperature hardening and good fabrication characteristics.
17-7 PH16.00-18.006.50-7.750.09AL 0.75-1.25•• Special ultra-high strength type with good formability and excellent fabricating characteristics.
* Feretic. Non-Hardenable
† Austenitic. Non-Hardenable by heat treatment
¥ Martensitic. Hardenable
• Martensitic. Precipitation hardened
•• Semi-Austenitic. Precipitation hardened