Experimentation in the late 19th century with levels of chromium (at least 10%) and carbon (less than 0.2%) produced today’s impressive variety of stainless steel grades. There are now more than 100 grades of stainless steel. However, they all fit into one of five different types:
- Austenitic steel: Chromium-nickel alloys
- Ferritic steel: Smooth chrome steels
- Martensitic steel: Chromium and carbon
- Precipitation hardened steel: chrome-nickel
- Duplex: a mix of austenitic and ferritic
Turning a metal into something really useful often means adding alloying elements. For example, adding chromium and carbon to iron creates a stronger, more corrosion-resistant stainless steel. The various metallurgical combinations that followed were created to provide these alloys with different sets of properties and ultimately uses within industry.
austenitic steel It is a chrome-nickel alloy and non-magnetic. Contains at least 16% chromium and 6% nickel (basic grade 304 is called “18/8” which means 18% chromium, 8% nickel). Molybdenum is added to some grades to increase corrosion resistance.
There are two series of alloys that fall into this category, the 200 Series (common alloys 201, 202, 203, 204 and 205) and the 300 Series (common alloys 302, 302, 303, 304, 305, 308, 309, 310). . , 314, 316, 317, 321, 330, 347, 384).
ferritic steel it is a plain chrome steel and is magnetic. It has a chromium content in the range of 12-18% and whose structure consists largely of ferrite.
Common alloys are 405, 409, 429, 430, 434, 436, 442, 446.
martensitic steel lLike the ferritic grades, chromium is the only major alloy. It is also magnetic. Chromium is in the range of 11% to 17%. However, carbon is added in amounts from 0.10% to 0.65%, giving it very different characteristics than ferritic grades.
Common alloys are 405, 409, 429, 430, 434, 436, 442, 446.
Precipitation Hardened Steel It is chrome-nickel based. Steels acquire very high tensile strengths through precipitation hardening. Common alloys are 13-8, 15-5, 15-7, 17-4, 17-7.
Duplex It is a mixture of austenitic (stainless chrome-nickel) and ferritic (simple stainless chrome) structures. The combination originated to offer more strength than any of its respective component stainless steels. Common alloys are 329, 2205, 2304, 2507, 3RE60.
