Steel grades can be distinguished based on:

Chemical composition, such as carbon, low-alloy or stainless steel grades
Manufacturing methods, such as open hearth, basic oxygen process, or electric furnace methods
Finishing process, such as steel grades for hot rolled or cold rolled products
Product form, for example bar plate, sheet, strip, tubing or structural shape
Deoxidation practice, such as killed, semi-killed, capped or rimmed steel grades
Microstructure, such as ferritic, pearlitic and martensitic steel grades
Required strength level, for example steel grade A240 Grade C specified in ASTM standards has the tensile stress value between 515 and 655 MPa
Heat treatment performed, such as annealing, quenching and tempering, and thermomechanical processing.

Carbon Steel and Alloy Steel.

Carbon steels and alloy steels are designated by a four digit number, where the first digit indicates the main alloying element(s), the second digit indicates the secondary alloying element(s), and the last two digits indicate the amount of carbon, in hundredths of a percent (basis points) by weight. For example, a 1060 steel is a plain-carbon steel containing 0.60% C

An “H” suffix can be added to any designation to denote hardenability is a major requirement. The chemical requirements are loosened but hardness values defined for various distances on a Jominy test.

Grade SAPH440-Structural Automobile Steel.

The Chemical Composition of SAPH440 Steels: JIS G 3113 defines the chemical composition of SAPH440 steels as under:

Carbon (C) is not identified in the standard.

Manganese (Mn) is not identified in the standard.

Maximum percentage of Phosphorous (P) is 0.040 percent.

Maximum percentage of Sulphur (S) is 0.040 percent.

Remaining is iron (Fe) percentage and with few negligible impurities.

Mechanical Properties of SAPH440 Steels: The tensile strength of the SAPH440 Steels is expressed in Newton per millimeters and it must be at-least 440 N/mm2 (MPa). The yield strength is minimum 275 to minimum 305 N/mm2 (MPa) depending on the thickness. The elongation property of SAPH440 steel varies with the ranges of thickness. The minimum percentage ranges for elongation is 29 to 34 minimum. Only over 6.5 mm thickness requires 22 minimum percentage elongations. Higher thickness gauges usually show higher elongation than lower gauges.

Some other hot rolled commercial quality materials are also used in industrial applications, SPHC steel comparison with this grade of SAPH440 material will show how structural automobile hot rolled steel differs with commercial quality SPHC steel in chemical composition & mechanical properties.

Alloy Steel.

Steel is considered to be an alloy steel when either (1) the maximum of the range given for the content of alloying elements exceeds one or more of the following percentages: manganese 1.65, silicon 0.60, copper 0.60; or (2) a definite range or definite minimum quantity of those elements considered alloys is specified. For example, chromium, molybdenum and nickel.

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