Tech Steel & Materials
Stainless Steel
Tech Steel & Materials offers stainless steel alloys in a variety of shapes and parts – rod, bar, wire, sheet, plate, strip, coil, tubing, forging and casting – for use in the applications demanding both the diverse properties of steel along with corrosion resistance.
About 150 grades of stainless steel alloys are currently in use, although only 15 different types are commercially available.
Properties
Stainless steel alloys are fairly low maintenance with a shiny, high-luster finish. They are easily welded and tolerate high temperatures. In addition, stainless steel alloys are corrosion-resistant, antibacterial and 100% recyclable. Stainless steel alloy finishes are not prone to flaking, peeling or wear from continuous friction.
However, stainless steel alloys are not good conductors of electricity.
What makes stainless steel alloys different from carbon steel is their higher level of chromium. Because carbon steel contains less chromium, it tends to rust when exposed to air and moisture if left unprotected. Stainless steel alloys contain higher amounts of chromium, which form a protective coating of chromium oxide, preventing further surface corrosion as well as protecting its inner layer.
Those stainless steel alloys that contain 13%-26% chromium by weight are also highly resistance to oxidation. When exposed to oxygen, chromium forms a layer of chromium oxide that makes the alloy’s surface impervious to water and air, protecting the metal’s inner layer. This layer immediately reforms when its surface is scratched – a process known as passivation.
When stainless steel alloys are forced together (commonly seen in the pairing of nuts and bolts), the chromium oxide layer can be scraped off, allowing the parts to be welded together.
Stainless steel alloys are classified by their crystalline structure. There are six classifications:
- Austenitic. Also known as 200 and 300 series, these stainless steel alloys have an austenitic crystalline structure (face-centered cubic crystal) as their primary phase. They make up more than 70% of all stainless steel alloys and contain a maximum of .15% carbon, a minimum of 16% chromium and sufficient levels of nickel and/or manganese.
- Superaustenitic. These stainless steel alloys exhibit great resistance to chloride pitting and crevice corrosion because of a high concentration of molybdenum. They offer better stress-corrosion resistance cracking compared to the 300 series. Low-carbon versions of this alloy are used to avoid corrosion problems caused by welding.
- Ferritic. With a ferrite (body-centered cubic crystal) as their main phase, these stainless steel alloys have better engineering properties than austenitic grades but are less corrosion resistant because of lower nickel and chromium levels. They usually contain between 10.5- 27% chromium and very little nickel, if any. Most alloys of this type contain molybdenum, aluminum or titanium.
- Martensitic. These low carbon steels present a characteristic orthorhombic martensite microstructure. They are even less corrosion resistant than ferritic stainless steel alloys. However, they are extremely strong and tough, highly machinable and magnetic and can be further tempered and hardened by heat. They contain 12-14% chromium, .2-1% molybdenum, less than 2% nickel and about .1-1% carbon.
- Precipitation-hardening Martensitic. Offering corrosion resistance comparable to austenitic varieties, this alloy can be precipitation hardened to even higher strengths than other martensitic grades. The most common type, 17-4PH, contains 17% chromium and 4% nickel.
- Duplex. This type of stainless steel alloy is a mixed microstructure of austenite and ferrite; the goal ratio is a 50/50 mix, although commercial alloys contain a ratio of 40/60. Duplex stainless steel alloys are twice as strong as austenitic stainless steel alloys and are more resistant to localized corrosion and stress corrosion cracking. They contain high chromium contents of 19-32% and up to 5% molybdenum, with lower nickel content than austenitic stainless steel alloys. Duplex stainless steels can be further divided into lean duplex, standard duplex, super duplex and hyper duplex grades.
Applications
Stainless steel alloys are often used in automotive and aerospace structural applications due to their ability to withstand high levels of friction. Their corrosion resistance makes stainless steel alloys ideal for use in harsh environments, while their shiny appearance makes them the alloy of choice for aesthetic reasons.
No matter what shape, size or weight, Tech Steel & Materials can customize your stainless steel alloys’ order to your exacting specifications. Simply complete the Request a Quote form, and we’ll take it from there.
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