Overview
Stainless steels embody good corrosion resistance and excellent mechanical properties. Hence, it is no surprise to see its ubiquitous applications in almost every walk of life, such as architecture, aerospace, and mechanical manufacture. This week we will introduce stainless steels in perspective of chemical compositions and performance testing.
Stainless Steel Series
Based on chemical compositions, stainless steels can be classified into five categories as below,
- • Cr-series (400 Series)
- • Cr-Ni Series (300 Series)
- • Cr-Mn Series (200 Series)
- • Precipitation Hardening Series (600 Series)
- • Duplex Stainless Steel Series
400 Series Stainless Steel
400 series are constituted by ferritic stainless steels and martensitic stainless steels. They are magnetic with good resistance to high temperature oxidation. Both ferritic and martensitic stainless steel can be heat treated.
| Grade | Structure | Description |
|---|---|---|
| 409 | Ferritic | the cheapest stainless steel, usually used as auto exhaust pipe. |
| 410 | Martensitic | high strength chromium steel with good wear resistance but poor corrosion resistance. |
| 416 | Martensitic | better processability (free machining) with the addition of sulfur. |
| 420 | Martensitic | blade steel, known for making surgical knives with very bright and shiny finish, similar to the earliest Brearley steel. |
| 430 | Ferritic | Good formability but poor temperature and corrosion resistance, mainly used for decoration purpose, such as automotive decorative supplies. |
| 440 | Martensitic | High-strength blade steel with higher carbon than 420. Higher yield strength with proper heat treatment. Hardness can be achieved up to 58HRC, known as the hardest stainless steel series. The most common application is razor blade. 440 Series include three common grades 440A, 440B & 440C and one free-machining grade 440F. |
300 Series Stainless Steel
300 series are also known as the Cr-Ni austenitic stainless steels that feature good formability, weldability and toughness with enhanced corrosion resistance. The series are typically represented by the most popular 8Ni18Cr stainless steel 304, and molybdenum-containing grade 316(L).
| Grade | Description |
|---|---|
| 301 | excellent ductility, readily hardenable through mechanical processing, good weldability, better wear resistance and superior fatigue resistance than 304. |
| 302 | similar to 304 in corrosion resistance, but higher strength with enhanced carbon content. |
| 303 | free machining with the addition of higher sulfur and phosphorous. |
| 304 | also known as 18/8 stainless steel with general applications, like cutlery, home appliances, handrails and medical equipment. |
| 304L | reduced carbon content in contrast with 304, more corrosion resistant and easier for heat treatment, but with poor mechanical properties, suitable for products that need welding and are difficult for heat treatment. 304N: nitrogen-strengthened 304 with enhanced strength. |
| 309 | good temperature resistance, which can withstand temperature up to 980°C. |
| 309S | great heat resistance and oxidation resistance, suitable for making heat exchangers, boiler components and jet engines. |
| 310 | excellent oxidation resistance under high temperature up to 1200°C. |
| 316 | second only to 304 in applications, mainly applied in food industry, watch and jewelry, pharmaceutical industry and surgical equipment, a special corrosion resistant structure gained from the added molybdenum. Better chloride corrosion resistance than 304, known as marine steel. Widely used in fuel recover unit where 18/10 stainless steel is also applicable. |
| 316L | reduced carbon from 316, better corrosion resistance and easier heat treatment, used for chemical processing equipment, nuclear power generators, refrigerant storage tanks and so on. |
| 317L | Higher content of chromium, nickel and molybdenum than 316L, superior corrosion resistance, especially in applications involving sulfuric acid compounds. |
| 321 | reduced exposure to corrosion resistance at the welds due to the addition of titanium element. |
| 347 | adding the stabilizing element niobium, suitable for welding aircraft parts and chemical equipment. |
200 Series Stainless Steel
200 series, known for high-manganese grades typically represented by 201 and 202 are austenitic stainless steel. The series were firstly developed in 1930s and were expanded during world war II due to worldwide nickel shortages, especially in USA. To maintain the austenitic structure, manganese, nitrogen and even copper were added to partially replace nickel.
600 Series
600 series are also called precipitation hardening stainless steels, with 630 (17-4PH) and 631 (17-7PH) widely known.
Duplex Stainless Steel Series
Duplex stainless steel series are mostly known for S31803, S32205 (2205) and S32750 (2507). These stainless steels are duplex for they simultaneously embody austenitic stainless steel structure which features good corrosion resistance and ferritic stainless steel structure which has high strength.
Stainless Steel Performance Tests
There are varied tests on stainless steel performance. We will introduce the main common tests that will matter at certain applications. These tests are categorized as below,
| Content | Tests |
|---|---|
| Physical Property | Salt Spray Test |
| Composition Detection | PMI Test |
| Chemical Properties | Intergranular Corrosion Test |
| Mechanical Properties | Flaring Test, Flange Test, Hardness Test, Reversing Flattening Test, Pneumatic Test, Hydrostatic Test |
| Non-destructive Test (NDT) | Electromagnetic Testing (ET), Radiographic Testing (X-ray Inspection), Ultrasonic Testing, Eddy Current Test, Magnetic Flux Leakage Testing, Dye Penetrant Inspection, Magnetic Particle Testing. |
Stainless Steel At CIVMATS
Contact CIVMATS for stainless steel purchasing from China. We have best quality for the same price and best price for the same quality. We are your most reliable stainless steel choice in China! Drop us an email and let us talk!
