CHEMICAL COMPOSITIONS OF SAE CARBON STEELS J403_199405

In 1941, the SAE Iron and Steel Division, in collaboration with the American Iron and Steel Institute, made a major change in the method of expressing composition ranges for the SAE steels. The plan, as now applied, is based in general on narrower cast or heat analysis ranges plus certain product analysis allowances on individual samples, in place of the fixed ranges and limits without tolerances formerly provided for carbon and other elements in SAE steels. To avoid the possibility of confusion and conflict between SAE and AISI steel designations, all proposed changes in compositions or additions or deletions of numbers will be coordinated between the two organizations.

For years the variety of chemical compositions of steel has been a matter of concern in the steel industry. It was recognized that production of fewer grades of steel could result in improved deliveries and provide a better opportunity to achieve advances in technology, manufacturing practices, and quality, and thus develop more fully the possibilities of application inherent in those grades.

Comprehensive and impartial studies were directed toward determining which of the many grades being specified were the ones in most common demand, and the feasibility of combining compositions having like requirements. From these studies, the most common grades of steel have been selected and kept in current revision. The cast or heat chemical composition limits or ranges of these grades are given in Tables 1, 2, 3A, 3B, 4, and 5. These cast or heat limits or ranges are subject to standard variations for product analysis as given in SAE J409.

It is recognized that chemical compositions other than those listed in the previously mentioned tables will at times be needed for specialized applications or processing. When such a steel is required, the elements comprising the desired chemical composition are specified in one of three ways: (a) by a minimum limit, (b) by a maximum limit, or (c) by minimum and maximum limits, termed a range.

Standard cast or heat analysis limits and ranges for the various elements of carbon steels are given in Tables 6 and 7. In these tables, range is the arithmetical difference between the minimum and maximum limits (that is, 0.19 to 0.25 is a 0.06 range). These cast or heat limits and ranges are also subject to standard variations for product analysis as given in SAE J409.

It will be noted that certain grade numbers in Tables 4 and 5 have slightly wider ranges for carbon and manganese than the same grade number in Tables 1 and 2. These wider ranges are necessary when producing steel for structural shapes, plates, strip, sheets, and welded tubing because of a combination of factors involving complex problems arising from the use of larger mill equipment due generally to the larger sizes of these products. Chemical composition demands for these products are also of a different pattern and offer less flexibility of steel application. These differences are also reflected in Tables 6 and 7.

When the cast or heat analysis is requested to be reported to demonstrate conformance to the chemical limits shown in Tables 1, 2, 3A, 3B, 5, or 6 in addition to the quantities of carbon, manganese, phosphorus, and sulfur, the following elements and their quantities shall also be reported: copper, chromium, nickel, molybdenum, and silicon. When the amount of any one of these last five elements is less than 0.02% that analysis may be reported as "<0.02%."

In addition to the standard steels noted in the tables mentioned, there is group of steels which are known as Merchant Quality products. Table 8 lists the cast or heat chemical composition limits. It should be noted that these grades are produced to wider carbon and manganese ranges than standard steels and are designated by the prefix "M" as shown in Table 8. Merchant Quality "M" steels are not subject to product analysis tolerances. These hot rolled carbon steel bars are produced for a wide range of uses, such as structural and similar miscellaneous applications involving mild cold bending, mild hot forming, punching, and welding. These processes are used in the production of noncritical parts of bridges, buildings, ships, agricultural implements, road-building equipment, railway equipment, and general machinery. (A further description of these steels and products can be found in SAE J411 and the Carbon and Alloy Steel Bar and Semi-Finished Products Manual as published by the Iron and Steel Society.)