Stainless Steel
Stainless steel is the name of a family of iron-based alloys known for their corrosion and heat resistance. One of the main characteristics of stainless steel is its minimum chromium content of 10.5%, which gives it its superior resistance to corrosion in comparison to other types of steels. Like other steels, stainless steel is composed primarily from iron and carbon, but with the addition of several other alloying elements, the most prominent being chromium. Other common alloys found in stainless steel are nickel, magnesium, molybdenum, and nitrogen.
Properties of Stainless Steel
Stainless steel has many desirable properties that contribute greatly to its widespread application in the making of parts and components across many industrial sectors. Above all, because of its chromium content, it is extremely resistant to corrosion. The 10.5% minimum content makes steel approximately 200 times more resistant to corrosion than steels without chromium. Other favorable properties for consumers are its high strength and durability, its high and low temperature resistance, increased formability and easy fabrication, low maintenance, long-lasting, attractive appearance and it is environmentally friendly and recyclable. Once stainless steel is put into service, it does not need to be treated, coated or painted.
- Corrosion resistant
- High tensile strength
- Very durable
- Temperature resistant
- Easy formability and fabrication
- Low-maintenance (long lasting)
- Attractive appearance
- Environmentally friendly (recyclable)
Grading Systems for Stainless Steel
There are many numerical grading systems for stainless steel, designated
according to their composition, physical properties, and applications. Each type of
stainless steel is classified by its series number and then assigned a numerical
grade. The most popular series numbers are 200, 300, 400, 600, and 2000. The most
common grades are type 304 and 316 that consist of austenitic chromium-nickel
alloys. Cutlery grade stainless steels are found in the 400 Series, which is derived
from ferritic and martensitic chromium alloys. Type 420 is known as surgical steel,
and type 440 is known as razor blade steel.
Stainless Steel Classifications
The family of stainless steels is primarily classified into four main categories based upon their crystal microstructure.
Ferritic
Ferritic steels are the 400 Grade stainless steels noted for their high chromium content, which can range from 10.5% to 27%. They have magnetic properties, too, offers good ductility, tensile-property stability, and resistance to corrosion, thermal fatigue, and stress-corrosion cracking.
Austenitic
Perhaps the most common category of stainless steel, austenitic grade steels are high in chromium, with varying amounts of nickel, manganese, nitrogen, and some carbon. Austenitic steels are divided into the 300 series and 200 series subcategories, which are determined by which alloys are used. The austenitic structure of the 300 series is distinguished via the addition of nickel. The 200 series primarily uses the addition of manganese and nitrogen. Grade 304 is the most common stainless steel.
Martensitic
Martensitic stainless steels are in the 400 Grade series of stainless steels. They have a low to high carbon content, and contain 12% to 15% chromium and up to 1% molybdenum. It’s used whenever corrosion resistance and-or oxidation resistance are required along with either high strength at low temperatures or creep resistance at elevated temperatures. Martensitic steels are also magnetic and possess relatively high ductility and toughness, which make them easier to form.
Duplex
As the name implies, duplex stainless steels possess a mixed microstructure of ferrite and austenite. The chromium and molybdenum content is high, with 22% to 25%, and up to 5%, respectively, with very low nickel content. The duplex structure gives the stainless steel many desirable properties. For starters, it offers double the strength of ordinary austenitic or ferritic stainless steels, with excellent corrosion resistance and toughness.
301
Attractive and malleable, grade 301 features high strength and corrosion-resistant composition. Since it is highly malleable and abrasion resistant, grade 301 stainless steel often gets used for decorative structural applications. Kloeckner Metals supplies 301 stainless steel sheet.
304
Grade 304 represents 50% of the steel produced around the world. Grade 304 contains 18% chromium and 8% nickel, which makes it aesthetically pleasing as well as durable. It’s one weakness is saline, so grade 304 can pit or crevice when used near salt water. We stock 304 stainless steel sheet, 304 stainless steel plate, 304 stainless steel bar, and 304 stainless steel tube.
316
The second most commonly produced steel, grade 316 contains 2-3% molybdenum. Consequently, it’s more resistant to saline and thus better for coastal environments. Many surgical supplies also get made from grade 316 stainless steel. Kloeckner Metals supplies the ultra low carbon variant of this grade stainless steel. It is available in 316L stainless steel sheet, 316L stainless steel plate, 316L stainless steel bar, and 316L stainless steel tube.
317
This grade provides high tensile strength at elevated temperatures. It is more resistant to corrosion and pitting than either grade 304 or grade 316 stainless steel. Due to its composition, grade 317 stainless steel is a more expensive alloy than most other 300-level grades.
400
This series of stainless steel contains 11% chromium and 1% more manganese than 300-series grades, making it slightly magnetic. This steel also features a higher carbon content. As a result, 400-series stainless steel offers higher strength and more wear resistance, but it is also more easily corroded than 300-series grades. Heat-treating hardens 400-series stainless steel.
430
A ferritic steel, grade 430 forms easily but does not resist extreme temperatures or corrosion well. It’s often used for decorative purposes such as automotive trim. Grade 430 stainless steel is also commonly used in backyard barbecue grills. It is less expensive than grade 304 since it does not contain nickel. 430 stainless steel sheet is routinely stocked.
434
Among the most widely used ferritic steels, grade 434 is highly corrosion and oxidation resistant. It can also resist temperatures of up to 1500°F. Grade 434 stainless steel cannot be hardened by heat treatment and is generally cold formed like low carbon steel. It is typically used for automotive trim.
420
Grade 420 stainless steel is a very bright steel and one of the earliest carbon/iron alloys. Containing 12% chromium, this grade of steel is highly corrosion resistant. It is often called “blade grade steel” since manufacturers frequently use it to make surgical instruments.
904L
A non-stabilized austenitic stainless steel, 904L grade products contain copper as part of the alloy. As a result, this grade of steel can resist corrosion from many acids. The high cost of this grade of stainless steel, however, has caused many manufacturers to turn to the lower-cost duplex stainless steel 2205 as an alternative.