Since stainless steel is aesthetically pleasing and corrosion-resistant, it is frequently used to produce cookware, kitchen sinks, and automobiles. The term stainless steel refers to any of several iron-based alloys that contain at least 10.5% chromium.
Although the crystalline structure of all stainless steel defines it, the metal is available in over 100 grades. In the 1930s and 1940s, the American Iron and Steel Institute established a steel-grade structure. This system was later combined with one developed by the Society of Automotive Engineers (SAE) International to create a more standardized numbering system. However, steel manufacturers may now use multiple numbering systems, which can complicate matters.
The general idea behind grading stainless steel is that it can be divided into three broad categories based on the crystalline structure of its iron atoms: austenitic, ferritic, and martensitic. Each category is subdivided further into series and grades. The grades reflect the specific alloy’s durability, quality, and temperature resistance. The numbers listed after the grade refer to the item’s chemical composition, specifically the percentages of chromium and nickel.
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What are the Different Grading Systems?
3-Digit System of the Society of Automotive Engineers
The SAE created a four-digit carbon steel grading system and a three-digit stainless steel grading system. The first digit represents the primary alloy element, while the second and third digits represent the carbon percentage of the alloy. Carbon steel requires four digits because there are more carbon steel alloys than stainless steel alloys.
6-Digit System of the American Society for Testing and Materials (ASTM)
The ASTM developed a six-digit classification system for stainless steel. This classification system, made up of letters and numbers, begins with the letter “A,” which stands for any ferrous material, and is followed by a series of numbers that have nothing to do with the metal’s properties. This number series is followed by the letter M, which stands for “metric.” The last two digits indicate the year the grade standard was adopted or last revised.
Other organizations, such as the British Standards (BS), German Standards (DIN), Chinese Standards (GB), European Standards (EN), Japanese Industrial Standards (JIS), and the International Organization for Standardization, have also published steel grades and series (IOS).
Each system works in a completely different way. For example, SAE grade 304 steel is graded as follows:
- UNS: S30400
- X5CrNi18-9, X5CrNi18-10, X5CrNi19-9 DIN
- 1.4305 is the EN number.
- X8CrNiN18-9 in English
- SUS 304, SUS 304-CSP (JIS)
- En58E BS: 304S 15, 304S 16, 304S 18, 304S 25
The specific alloy must meet the composition standards the system’s governing agency sets, regardless of its classification number. Let’s look at some of the most common grades of stainless steel using the SAE system to keep things as simple as possible.
Most popular series, and what distinguishes each grade?
Each stainless steel grade has a slightly different chemical composition and, as a result, a distinct physical appearance.
The 300 series of stainless steel is the most common, with the most common grades being 304 stainless steel and 316 stainless steel. 409 stainless steel and 430 stainless steel are two other common grades.
300 Series Stainless Steel.
Stainless steel grades in the 300 series are austenitic, with major alloying additions of 18–30% chromium and 6-20% nickel. It is made of solid iron with face-centred cubic crystals.
The 300-series stainless steel grades’ composition makes them particularly useful in the construction, automotive, and aerospace industries. Series 300 stainless steel can only be hardened by cold working methods because it can withstand extremely high temperatures.
Grade 301 is attractive and malleable, with high strength and a corrosion-resistant composition. Grade 301 stainless steel is frequently used for decorative structural applications due to its high malleability and abrasion resistance. 301 stainless steel sheet is available from Kloeckner Metals.
Grade 304 accounts for 50% of all steel produced globally. Grade 304 contains 18% chromium and 8% nickel, making it aesthetically pleasing and durable. Because of its saline sensitivity, grade 304 can pit or crevice when used near salt water. 304 stainless steel sheet, 304 stainless steel plate, 304 stainless steel bar, and 304 stainless steel tube are all available from us. 316
The second most common steel contains 2–3% molybdenum. As a result, it is more resistant to saline and thus better suited to coastal environments. Many surgical supplies are also made from 316 stainless steel. The ultra-low carbon variant of this grade of stainless steel is available from Kloeckner Metals. It comes in the following forms: 316L stainless steel sheet, 316L stainless steel plate, 316L stainless steel bar, and 316L stainless steel tube.
This grade has a high tensile strength at high temperatures. It is more corrosion and pitting resistant than either grade 304 or grade 316 stainless steel. Grade 317 stainless steel is a more expensive alloy due to its composition than most 300-level grades.
400 Series Stainless Steel.
This stainless steel series has 11% more chromium and 1% more manganese than the 300-series grades, making it slightly magnetic. This steel has a higher carbon content as well. As a result, 400-series stainless steel has greater strength and wear resistance than 300-series grades, but it is also more easily corroded. Hardened 400-series stainless steel is hardened by heat treatment.
Grade 430 ferritic steel forms easily but does not withstand high temperatures or corrosion well. It’s frequently used as a decorative material, such as automotive trim. In addition, grade 430 stainless steel is commonly used in backyard barbecue grills. Because it does not contain nickel, it is less expensive than grade 304. 430 stainless steel sheet is frequently in stock.
Grade 434 is the most commonly used ferritic steel because it is highly corrosion and oxidation resistant. It can also withstand temperatures as high as 1500°F. Grade 434 stainless steel cannot be hardened by heat treatment and is typically cold-formed in the same way that low-carbon steel is. It is commonly used in automotive trim.
Stainless Steel Grade 420 is very bright steel and one of the first carbon/iron alloys. This steel grade is highly corrosion-resistant due to its 12% chromium content. Because it is frequently used to make surgical instruments, it is often called “blade-grade steel.”
Stainless Steel 904L
904L grade products are non-stabilized austenitic stainless steels with copper as part of the alloy. As a result, this grade of steel is resistant to many acids. Due to the high cost of this grade of stainless steel, many manufacturers have turned to the lower-cost duplex stainless steel 2205 as an alternative.
Stainless steel is available in a variety of series and grades. Selecting the appropriate stainless steel for your product in your environment is critical. Visit our website to learn more about stainless steel.