Grades & Properties of Steel
Different grades of steel have been developed and classified over years, based on their chemical composition and physical properties by a number of standard development organizations such as SAE steel grades, British standards, International Organization for Standardization, German steel grades,
steel grades and UNS. The chemical composition of steel is a key characteristic as it determines the corrosion-resisting ability of the alloy, its physical and chemical properties as well as the microstructural balance. Steel is gaining popularity because of its versatility and it can completely be recycled. It is used in the manufacturing of various appliances and products ranging from medicine to buildings to cookware. Japan
Grading and properties of steel
There are various ways in which grading of steel is done – based on their physical and chemical properties, on the carbon content present or on the classification system used.
Grading by mechanical properties
In general, steel grading falls into categorizations based on their mechanical properties and corrosion resistance, as described below-
- Chemical Composition of steel, such as carbon type, low alloy type and stainless steel type
- Manufacturing Methods - including open hearth, electric furnace or basic oxygen process
- Finishing process (hot rolled or cold rolled products)
- Shape of the product - bar, sheet or strip
- Deoxidation process
- Microstructural phase - which may include different steel grades such as ferritic (contains 30% chromium with a crystal structure called ferritic), austenitic (consists of 0.15% carbon and 16% chromium), duplex (mix of austenite and ferrite) and martensitic (mixture of 1% carbon and 18% chromium)
- Heat treatment such as annealing, quenching and tempering
The most widely used grades of steel are ferritic Types 409 and 430 and the austentic Types 304 and 316.
Grading by percentage of carbon
Strength of the steel that is determined by the percentage of carbon present, as it decides the hardness of steel. Therefore, the higher the percentage of carbon content, the harder the steel and lower its ductility.
Steel grades are divided into three main categories based on their carbon content - low carbon steel grades, middle carbon steel grades and high carbon steel grades.
Grading type by organization
Sometimes, steel grading can vary according to different grading organizations. According to European standards of classification, steel grades are divided into following categories-
- Alloy steel grades
- Non-alloy steel grades
- Stainless steel grades
- Tool steel grades
- Steel grades for sheet and strip and
- Steel grades for electric sheet and strip
Appropriate steel grade can be selected by closely evaluating its corrosion resisting ability in the given environment and also by monitoring its mechanical properties.