What is stainless steel?

Answer 1

*Stainless Steel is a common name for metal alloys that consist of 10.5% or more Chromium (Cr) and more than 50% Iron (Fe). Although it is called "stainless", a better term for it is "highly stain resistant". A somewhat dark metal, it looks bright because it reflects light.
*What gives stainless steel its properties?

The chromium content in stainless steel alloys is what generally prevents corrosion. Pure iron, the primary element of stainless steel, is extracted from its natural state as iron ore, it is unstable by itself, and naturally wants to corrode (rust). The chromium helps to procrastinate nature's attempts to combine the pure iron with oxygen and water to form rust.

The chromium works by reacting with oxygen to form a tough, adherent, invisible, passive layer of chromium oxide film on the steel surface. If damaged mechanically or chemically, this film is self healing as long as it has enough oxygen.

Because oxygen is necessary for the reaction, liquids and other foodstuffs stored for a prolonged time in stainless can prevent oxygen contact and thus promote corrosion, as can prolonged contact with household cleaners such as bleach.

Generally, an increase of chromium content improves the corrosion resistance of stainless steels. The addition of nickel is used to raise the general corrosion resistance required in more aggressive usage or conditions. The presence of molybdenum (Mo) improves the localized corrosion resistance, such as against pitting (scarring).

Other alloying metals are also used to improve the structure and properties of stainless steels, such as Titanium, Vanadium and Copper. Non metal additions typically include natural elements such as Carbon & Nitrogen, as well as Silicon.

High-carbon stainless steel contains a minimum of 0.3% carbon. The higher the carbon content, the less formable and the tougher the steel becomes. Its hardness makes it suitable for things such as cutting edges, and other high-wear applications like plow blades. Carbon thus helps makes the edge easier to sharpen, and helps retain a sharp edge longer.
*The three major classes of stainless steel are:
♦ Austenitic: Chromium-nickel-iron alloys with 16-26% chromium, 6-22% nickel (Ni), and low carbon content, with non-magnetic properties (if annealed - working it at low temperatures, then heated and cooled). Nickel increases corrosion resistance. Hardenable by cold-working (worked at low temperatures) as well as tempering (heated then cooled). Type 304 (S30400) or "18/8" (18% chromium 8% nickel), is the most commonly used grade or composition.

♦ Martensitic: Chromium-iron alloys with 10.5-17% chromium and carefully controlled carbon content, hardenable by quenching (quickly cooled in water or oil) and tempering (heated then cooled). It has magnetic properties. Commonly used in knives. Martensitic grades are strong and hard, but are brittle and difficult to form and weld. Type 420 (S42000) is a typical example.

♦ Ferritic: Chromium-iron alloys with 17-27% chromium and low carbon content, with magnetic properties. Cooking utensils made of this type contain the higher chromium levels. Type 430 is the most commonly used ferritic.

Two additional classes worth mentioning include Duplex (with austenitic and ferritic structures), and Precipitation Hardening stainless steel, used in certain extreme conditions.

*ss304/ss316 have 0.08% carbon, while ss304L/ss316L have 0.03% CARBON.That is why less carbon content are more corrosion resistant and removal of carbon is costly affair.

Answer 2

Steel is iron containing a small amount of carbon. Other alloying elements are optional. If a stainless steel contains no or very little carbon, it will be more correct to call it a stainless iron.

What makes steel stainless? A minimum amount of Chromium, which forms a tough oxide film immediately on exposure to an oxidising environment. Steels containing only Chromium will be ferritic stainless steels. Austenitic Stainless Steels (most of the stainless steels in use) are alloys of iron, with chromium and nickel. A typical composition is 18 % Cr and 8% Ni. Austenitic stainless steels are non-magnetic when fully annealed, are soft, easy to work and are generally corrosion resistant. IGC and IGSCC are problems but are tackled by modifying the chemical composition, heat treatment etc.

Answer 3

Stainless steel is defined as a ferrous alloy with a minimum of 10.5% chromium content. The name originates from the fact that stainless steel does not stain, corrode or rust as easily as ordinary steel. This material is also called corrosion resistant steel when it is not detailed exactly to its alloy type and grade, particularly in the aviation industry. As such, there are now different and easily accessible grades and surface finishes of stainless steel, to suit the environment to which the material will be subjected to in its lifetime. Common uses of stainless steel are the everyday cutlery and watch straps.

Stainless steels have higher resistance to oxidation (rust) and corrosion in many natural and man made environments; however, it is important to select the correct type and grade of stainless steel for the particular application.

High oxidation resistance in air at ambient temperature is normally achieved with additions of a minimum of 13% (by weight) chromium, and up to 26% is used for harsh environments. The chromium forms a passivation layer of chromium(III) oxide (Cr2O3) when exposed to oxygen. The layer is too thin to be visible, meaning the metal remains lustrous. It is, however, impervious to water and air, protecting the metal beneath. Also, this layer quickly reforms when the surface is scratched. This phenomenon is called passivation and is seen in other metals, such as aluminium and titanium. When stainless steel parts such as nuts and bolts are forced together, the oxide layer can be scraped off causing the parts to weld together. When disassembled, the welded material may be torn and pitted, an effect that is known as galling.

Nickel also contributes to passivation, as do other less commonly used ingredients such as molybdenum and vanadium.

Answer 4

In metallurgy, stainless steel is defined as a ferrous alloy with a minimum of 10.5% chromium content. The name originates from the fact that stainless steel does not stain, corrode or rust as easily as ordinary steel. This material is also called corrosion resistant steel when it is not detailed exactly to its alloy type and grade, particularly in the aviation industry. As such, there are now different and easily accessible grades and surface finishes of stainless steel, to suit the environment to which the material will be subjected to in its lifetime.

Answer 5

Stainless steel is iron alloyed with a minimum of 10.5% chromium.  Nickel is another common constituent.  The chromium oxidizes to a protective surface layer which halts most further corrosion, thus "stainless".

Stainless steels are usually low-carbon alloys.

Answer 6

Any of various steels alloyed with at least 10 percent chromium and sometimes containing other elements and that are resistant to corrosion or rusting associated with exposure to water and moist air.

Answer 7

A type of steel with nickel and chromium added to prevent rusting

Answer 8

an alloy of steel that is resident to rust

Answer 9

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