2023-10-27
Stainless Steel is the common name of a large family of corrosion-resistant metals. There are a variety of stainless steels. For example, austenitic and tempered. However, one thing they have in common is that all contain a minimum amount of chromium, 10.5%. Once the chromium in steel is alloyed, it forms a film of protection on its surface that prevents contact with oxygen. Depending on material requirements, nickel, titanium, or molybdenum can be included to increase corrosion resistance.
There are a number of families that make up stainless steel. The three main types of stainless steel are austenitic, ferritic, and martensitic. They are named according to their characteristics. In each family you will find compositions or grades of stainless-steel. These are the 300 series and 400 series, which refer to its alloy and mechanical properties.
Austenitic alloys, primarily stainless steels of type 304, account for over 70% of the total stainless steel produced. Austenitic materials are composed of 8% and 18% nickel. Type 316, on the other hand, is composed of between 16% and 18.5% chromium as well as 11% to 14.5% nickel. This makes type 316 ideal for use in environments with high corrosion. Nickel is found in higher concentrations in austenitic stainless than in ferritic or martensitic. The steel, which is non-magnetic is hardened considerably by cold-working. Other fine mechanical properties include its corrosion resistance, formability, and weldability. Austenitic is found in grades 200 and 300 and is widely used as cookware, in food and drink equipment, in processing equipment and in the automotive, chemical, pulp and papers industries.
Ferritic Stainless Steels are classified under the 400 Series Grade and make up approximately 20% of all stainless steels. They are made of lower carbon steels with a chromium level between 10.5% to 18%. They contain no nickel. Ferritic grades are magnetic, offer good ductility and formability. However, they, like austenitic grade stainless steels, cannot be heat-treated. They offer excellent tensile stability, superior stress corrosion resistance, and better thermal fatigue and thermal conductivity. Type 430 ferritic is the most popular, with its high corrosion resistant to nitric gas, sulfur gases, organic acids and food acid. Other grades are types 405, 409 434 436 442, and 454. Ferritic materials are typically used for applications at elevated temperatures such as exhausts systems in vehicles. Ferritic stainless-steels are also used to make petrochemicals components, automotive trims or heat exchangers.
Martensitic alloys of stainless steel contain between 12% and 18% chrome, but have a relatively higher carbon content in comparison to other stainless materials. These grades of steel contain straight chromium but no nickel. The steels have high strength and good corrosion resistance. They also exhibit magnetic properties. Martensitic alloys are the best choice for applications where hardness strength and wear resistance is required. This grade belongs in the 400 Series, which includes types 410S 4141 416 420 431, 440. The general-purpose martensitic grade of stainless steel is 410. The surgical cutting tool grade 420 is made from grade 410. Martensitic alloys of stainless steel are used for cutlery as well as surgical and dental tools, springs scissors, industrial knives, aerospace components, and other general engineering parts.
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