Klöckner Metal Publishes Guide to Grades Of Stainless Steel
Strategic Research Institute
Published on :
11 Nov, 2021, 4:54 am
Klöckner & Co SE’s North American subsidiary Kloeckner Metals Corporation has published a Guide to Grades of Stainless Steel. The term stainless steel refers to any of several iron-based alloys that include the element chromium as at least 10.5% of their composition. Although all stainless steel is defined by its crystalline structure, the metal comes in more than 100 grades. The American Iron and Steel Institute first developed a structure of grades for steel in the 1930s and 40s. Later, this system combined with one from the Society of Automotive Engineers International to form a more standardized numbering system. Today, steel manufacturers may use more than one numbering system, however, which can complicate matters.
The general idea behind grading the metal is that stainless steel can be divided into three broad categories austenitic, ferritic, and martensitic, based on the crystalline structure of its iron atoms. Each category is further divided into series and grades. The grades reflect the specific alloy’s durability, quality, and temperature resistance. Numbers listed after the grade refer to the item’s chemical composition, specifically to it’s chromium and nickel percentages. The 300 series of stainless steel is the most common with 304 stainless steels and 316 stainless steels being the most prevalent grades. Two other common grades are 409 stainless steels and 430 stainless steels.
300 Stainless Series Stainless Steel Grades
Stainless steel grades in the 300 series are classified as austenitic with 18-30% chromium and 6-20% nickel as their major alloying additions. It is solid iron containing face-centered cubic crystals. The composition of 300-series stainless steel grades makes it especially useful in the construction, automotive, and aerospace industries. Since it can withstand extremely high temperatures, series 300 stainless steel is hardenable only by cold working methods.
301 Stainless Series Stainless Steel Grades
Attractive and malleable, grade 301 features high strength and corrosion-resistant composition. It is highly malleable and abrasion resistant, grade 301 stainless steels often gets used for decorative structural applications.
304 Stainless Series Stainless Steel Grades
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. Its one weakness is saline, so grade 304 can pit or crevice when used near salt water.
316 Stainless Series Stainless Steel Grades
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 steels. Kloeckner Metals supplies the ultra low carbon variant of this grade stainless steel.
317 Stainless Series Stainless Steel Grades
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 steels. Due to its composition, grade 317 stainless steel is a more expensive alloy than most other 300-level grades.
400 Stainless Series Stainless Steel Grades
This series of stainless steel contains 11% chromium and 1% more manganese than 300-series grades, making it slightly magnetic. This steel also features 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 Stainless Series Stainless Steel Grades
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 steels is also commonly used in backyard barbecue grills. It is less expensive than grade 304 since it does not contain nickel. 430 stainless steel sheets are routinely stocked.
434 Stainless Series Stainless Steel Grades
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 Stainless Series Stainless Steel Grades
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 Stainless Series Stainless Steel Grades
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.
The SAE developed a four-digit grading system for carbon steel and a three-digit one for stainless steel. The first digit refers to the primary alloy element, the second and third digits to the alloy’s carbon percentage. Carbon steel needs four digits because there are more carbon steel alloys than stainless steel alloys. The ASTM developed a six-digit system for categorizing stainless steel. Composed of both letters and numbers, this classification system begins with the letter A, which stands for any ferrous material, followed by a sequential series of numbers unrelated to the metal’s properties. The letter M, standing for “metric,” follows this number series. The last two digits refer to the year the standard for the grade was adopted or last revised. Other organizations have also published grades and series of steel, including the British Standards BS, German Standard DIN, Chinese Standard GB, European Standard EN, Japanese Industrial Standards JIS and the International Organization for Standardization IOS. Each system functions entirely differently.