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
Type Cr Ni Cmax Other Elements Major Characteristics
303 17.00-19.00 8.00-10.00 0.15 S 0.15 min † Free-machining modification of Type 302
303 Se 17.00-19.00 8.00-10.00 0.15 Se 0.15 min † Free-machining version of Type 302. Produces better surface finish than Type 303.
304 18.00-20.00 8.00-10.00 0.08 † Low carbon variation of Type 302. Minimizes carbide precipitation during welding
304L 18.00-20.00 8.00-10.00 0.03 † Extra-low carbon content eliminates harmful carbide precipitation due to welding
309 22.00-24.00 12.00-15.00 0.20 † High strength and resistance to scaling at high temperatures
310 24.00-26.00 19.00-22.00 0.20 † Higher alloy content improves basic characteristics of Type 309
316 16.00-18.00 10.00-14.00 0.08 Mo 2.00-3.00 † Mo improves general corrosion and pitting resistance and high temperature strength over that of Type 302
316L 16.00-18.00 10.00-14.00 0.20 Mo 2.00-3.00 † Extra-low carbon version of Type 316. Eliminates harmful carbide precipitation due to welding
317 18.00-20.00 11.00-15.00 0.08 Mo 3.00-4.00 † Higher alloy content improves basic advantages of Type 316
321 17.00-19.00 9.00-12.00 0.08 Ti 5 x C. min † Stabilized to permit use in 800-1500°F temperature range without harmful carbide precipitation
347 17.00-19.00 9.00-13.00 .008 Cb + Ta 10 x C. min † Characteristics similar to Type 321. Stabilized by Cb and Ta.
348 17.00-19.00 9.00-13.00 0.08 Ta 0.10 max Cb 0.20 max
Cb + Ta 10 x C min
† Similar to Type 347 but Ta reduced for atomic energy applications
410 11.50-13.50 - 0.15 - ¥ Lowest cost general purpose stainless steel. Wide use where corrosion is not severe.
416 12.00-14.00 - 0.15 S 0.15 min ¥ Free-machining version of Type 410.
420 12.00-14.00 - 0.15 min - ¥ Similar variation of Type 410 but higher carbon produces higher strength and hardness.
430 14.00-18.00 - 0.12 - * Most popular of the chromium types. Combines good corrosion and heat resistance and mechanical properties.
430 F 14.00-18.00 - 0.12 S 0.15 min * Free-machining version of Type 430.
440A
440B
440C
16.00-18.00
16.00-18.00
16.00-18.00
- 0.60-0.75
0.75-0.95
0.95-1.20
- ¥ 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.
446 23.00-27.00 - 0.20 - * Similar to Type 442 but Cr increased to provide maximum resistance to scaling.
15-5 PH 14.00-15.50 3.50-5.50 0.07 Cu 2.50-4.50 • Similar in properties and characteristics to 17-4 PH but has superior transverse ductility and toughness.
PH 15-7 Mo 14.00-16.00 6.50-7.75 0.09 Mo 2.00-3.00
Al 0.75-1.50
•• Special type similar to 17-7 PH but with higher strength.
17-4 PH 15.50-17.50 3.00-5.00 0.07 Cu 3.00-5.00 • Special type that combines excellent corrosion resistance…high strength and hardness… low temperature hardening and good fabrication characteristics.
17-7 PH 16.00-18.00 6.50-7.75 0.09 AL 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