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STAINLESS STEEL COMPOSITION
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 judgment 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 the type. Modifications of types are indicated by suffix letters. The series designations identify the following groups:
Stainless Steel Composition and Major Characteristics
| Stainless Steel Composition 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. |
Stainless steel couplings are widely used in petroleum, chemical, metallurgy, electric power, fertilizer, pharmaceutical, food, urban construction, sewage treatment and environmental protection industries.
