Chromium plays a significant role in stainless steel in that it exerts effects on stainless steel microstructure and heat treatment, mechanical properties, physic-chemical properties and process performance, which will be discussed later in the article.
Background Information
Chromium comes from Greek, meaning color because chromium compounds have colors. Pure chromium looks metallic grey. Chromium was produced the following year by carbon reduction of a new mineral discovered in Siberian phoenicochroite by the French chemist L.N. Vauquelin in 1797. Chromium abundance is 0.01% in the earth's crust, ranking 17th. It is mainly found in chromite, not found free in nature.
- Item Name: Chromium
- Element symbol: Cr
- Atomic number: 24
- Atomic volume: 51.996
The Role Chromium Plays in Stainless Steel Microstructure and Heat Treatment
1. Chromium forms continuous solid solutions with iron, reducing the Austenite phase region. Chromium forms with carbon a variety of carbides and has a higher affinity for carbon than iron and manganese and lower than tungsten and molybdenum. Chromium and iron can form intermetallic compounds.
2. Chromium reduces the carbon concentration in pearlite and the limit solubility of carbon in austenite.
3. Chromium slows down the austenite decomposition rate, significantly improves steel hardenability, but also increase steel temper brittleness tendency.
The Role Chromium Plays in Stainless Steel Mechanical Properties
1. Chromium improves steel strength and hardness, which effect will be pronounced when adding other alloying elements.
2. Chromium significantly increases the brittle transition temperature of steel.
3. In high-chromium Fe-Cr alloys, if the phase precipitates, the impact toughness will drop sharply.
The Role Chromium Plays in Stainless Steel Physical and Chemical Properties
1. Chromium improves the wear resistance of steel and can produce very bright finish after grinding.
2. Chromium reduces the electrical conductivity of steel and its coefficient of resistance to temperature.
3. Chromium improves the steel coercivity and its residual magnetic induction, hence it is widely used in fabrication of permanent magnet steel
4. Chromium promotes the formation of passivation film on steel surface. A certain amount of chromium can enhance the steel corrosion (especially nitric acid) resistance significantly. If chromium carbides are precipitated, the steel corrosion resistance will get weakened.
5. Chromium improves the steel oxidation resistance.
6. It is easy to form dendritic segregation in chrome steel and reduce the steel plasticity.
7. As chromium reduces steel thermal conductivity, the steel should be slowly heated during hot working, and slowly cooled after forging.
Chromium Applications in Stainless Steel
1. Chromium is used in alloy structure steel to improve hardenability and also its wear resistance through the formation of chromium carbide on the carburized surface.
2. Chromium is used with other alloying elements in spring steel to obtain their comprehensive properties.
3. Chromium is used in bearing steel alloy to enhance wear resistance by the special carbide of chromium and also to produce bright finish through grinding.
4. Chromium is used in tool steel and high-speed steel mainly to improve the wear resistance and obtain certain tempering stability and toughness.
5. In stainless steel and heat-resistant steel, chromium is often used in combination with manganese, nitrogen, nickel, etc. When producing austenitic steel, there must be a balanced ratio between the ferrite stabilized chromium and the austenite stabilized manganese and nickel.
Related
- Functions of Microalloy Elements Nb, V and Ti in Steel
- The Role Manganese Plays in Stainless Steel
- The Role Molybdenum Plays in Stainless Steel
- The Role Nickel Plays in Stainless Steel
Contact
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