Handbook-Steels Classified

3 and to many corrosive chemicals, the 18-8 grades are both strong and ductile. They cannot be hardened by heat

treatment, and can be welded by many different processes. Not all stainless steels are ”18-8”. Stainless steel

kitchen knives will usually be made from a high-chromium steel containing little or no nickel, since such steel can be hardened by heat treatment, and will take a much better edge than an 18-8 steel. AISI and SAE Numbering Systems. Most standard steels, both carbon and alloy, are given number designations within a system originally set up by the American Iron and Steel Institute (AISI) and later adopted, with some modifications, by the Society of Automotive Engineers (SAE). In both the AISI and SAE systems, the same four- digit numbers are used to identify the compositions of carbon steels and most standard alloy steels. The first digit represents the general class of steel, based on its major alloy ingredient; the numbers for all steels classed simply as ”carbon” steels start with ”1”; the numbers for all alloy steels categorized as ”nickel” steels start with ”2”, for ”chromium” steels with ”5”, etc. The second digit gives a general indication of the percentage of the principal alloy ingredient, and the last two digits indicate the approximate amount of carbon in the composition, expressed as ”points”. (A ”point” of carbon is 0.01%.) Thus a 1013 steel (either AISI 1013 or SAE 1013) is a carbon steel containing approximately 0.13% carbon; 2511 is a nickel steel containing about 5% nickel and about 0.11% carbon. In the AISI system, most stainless steels carry three-digit numbers (such as 302, 347, etc.). The same three digits are used in the current SAE system, but are preceded by ”30”, in the case of the non-hardenable nickel- chromium alloys, or by ”50”, for the hardenable alloys. Thus ”AISI 304” refers to the same composition designated by SAE as ”30304”. ASTM Specifications AISI and SAE specification numbers always relate to the chemical composition of steels, with prefix or suffix letters used for special distinctions. (For example, the AISI system provides for prefix letters to indicate the type of furnace in which the steel is manufactured; ”B” for basic open-hearth, ”E” for electric, etc.) An entirely different series of specifications is published by the American Society for Testing and Materials (ASTM).