Stainless steel is an alloy developed in the early 1900’s after metallurgists discovered that chromium added iron alloys displayed superior corrosion resistance to carbon steel alloys. The first products using stainless steel were produced in 1908 and the first patents were granted in 1912. Stainless Steel is a highly durable alloy containing the following major ingredients:
The corrosion resistance that is unique to stainless steel is the result of a transparent passive film of chromium oxide forms on the surface of the steel and protects it from oxidation. Higher chromium levels increase the corrosion resistance of the steel, but it creases the brittleness of the metal, making it hard to work with. There are different categories and types stainless steels. To know more please refer to -
Alloy Steel is an iron based mixture containing manganese greater than 1.65%, silicon over 0.5%, copper above 0.6%, or other minimum quantities of different alloying elements such as chromium, nickel, molybdenum, or tungsten are present, each of which imparts different properties to alloy steel. Alloy Steels are made by combining elements during the smelting process when the iron is still molten. Chromium is added in smaller amounts (0.5-2%) to increase hardenability and larger amounts (4-18%) to increase corrosion resistance. Molybdenum is added in amounts of 0.25-0.40% to increase the strength of the steel. Nickel is added in smaller amounts (2-5%) to increase toughness and in larger amounts (12-20%) to increase corrosion resistance. Silicon is added to steel in smaller amounts (0.2-0.7%) to increase strength and in larger amounts (>2%) to improve its magnetic properties while addition of Sulfur or Lead is done to increase the weldability.
Composition of 1%-2.1% carbon. Its high carbon content makes it an extremely strong material. Due to its brittleness, this grade requires special handling. However, ultra high carbon steels can be tempered to great hardness and are used for specialized products such as knives, axles etc. Tighter carbon content control for more consistent heat treatment. Steels with carbon content above 2% are considered to be cast iron.
Composition of 0.55%-0.99% carbon, with 0.30%-0.90% manganese. It is very strong and holds shape memory well, making it ideal for springs and high-strength wires.
Composition of 0.29%-0.54% carbon, with 0.60%-1.65% manganese. Medium carbon steel is ductile, strong and has good wear resistance. Because of the above properties, they find use in forging, heavy industries, and automotive components.
Composition of 0.05%-0.29% carbon and up to 0.4% manganese. They are the most common form of steel commonly known as mild steel, a relatively low-cost material, easy to shape (malleable). Low carbon steels provide material properties that are acceptable for many applications.
Carbon steels are the base metals widely used in manufacturing in nearly every industry, including aerospace, aircraft, automotive, chemical, defense, and precision. Carbon steel’s strength is due to its crystalline structure. Groups of iron and carbon atoms are arranged in a lattice, with the carbon atoms preventing the iron atoms from slipping over each other, which imparts the steel more rigidity.
The addition of an alloy such as titanium or manganese strengthens this structure by adding different atomic sizes to the lattice. This reinforces steel's rigidity by further impeding molecular movement when the metal is subjected to stresses. There are four types of carbon steel based on the amount of carbon present in the alloy.
The basic difference between stainless steel, conventional alloy steel and carbon steel is that Stainless Steel contains a very high percentage of chromium (11 – 26 percent) and nickel (3.5 – 22 percent). Through varying chromium content and by addition, substitution of other alloying elements like nickel, molybdenum, copper, titanium, aluminium, silicon, niobium, sulfur, selenium etc., resistance to corrosion, oxidation, abrasion, hardness and a variety of other distinct properties are either created or enhanced.
On the other hand, steel that contains carbon up to about 1.7 percent as an essential alloying constituent and has properties and structure made up mostly of the element carbon is better known as Carbon Steel. Most of the steel produced in the world is carbon steel. Unprotected carbon steel rusts when exposed to air or moisture but stainless steel is almost immune to rusting and ordinary corrosion.