ASTM specifications represent a consensus among producers, specifiers, fabricators, and users of steel mill products. In many cases, the dimensions, tolerances, limits, and restrictions in the ASTM specifications are similar to or the same as the corresponding items in the standard practices contained in the AISI Steel Products Manuals.
Many of the ASTM specifications have been adopted by the American Society of Mechanical Engineers (ASME) with little or no modification; ASME uses the prefix S and the ASTM designation for these specifications. For example, ASME-SA213 and ASTM A 213 are identical.
ASTM’s designation system for metals consists of a letter (A for ferrous materials) followed by an arbitrary sequentially assigned number. These designations often apply to specific products, for example A548 is applicable to cold-heading quality carbon steel wire for tapping or sheet metal screws. Metric ASTM standards have a suffix letter M.
Examples of the ASTM ferrous metal designation system, describing its use of specification numbers and letters, are shown below:
Example - ASTM A 582/A 582M-95b (2000), Grade 303Se-Free-Machining Stainless Steel Bars:
‘A’ describes a ferrous metal, but does not sub classify it as cast iron, carbon steel, alloy steel, tool steel, or stainless steel;
582 is a sequential number without any relationship to the metal’s properties;
M indicates that the standard A582M is written in rationalized SI units (the M comes from the word Metric), hence together 582/A582M includes both inch-pound and SI units;
95 indicates the year of adoption or last revision and a letter b following the year indicates the third revision of the standard in1995;
(2000), a number in parentheses, indicates the year of last re-approval;
Grade 300Se indicates the grade of the steel, and in this case, it has a Se (selenium) addition.
Within the steel industry, the terms Grade, Type, and Class are generally defined as follows: Grade is used to describe chemical composition; Type is used to define the deoxidation practice; and Class is used to indicate other characteristics such as strength level or surface finish. However, within the ASTM standards, these terms were adopted and used to identify a particular metal within a metal standard and used without any strict definition. Although there are differences between the ASTM and traditional definitions of these terms ASTM have applied some loose rules to the use of this terminology in their designation system :
Example 1 - ASTM A 106-02a Grade A, Grade B, Grade C - Seamless Carbon Steel Pipe for High-Temperature Service:
Typically an increase in alphabet (such as letters A, B, C) results in higher tensile or yield strength steels, and if it’s an unalloyed carbon steel, an increase in carbon content;
In this case: Grade A:0.25%C (max), 48 ksi tensile strength (min); Grade B: 0.30%C (max), 60 ksi tensile strength (min); Grade C 0.35%C (max), 70 ksi tensile strength (min).
Example 2 - ASTM A 276-03, Type 304, 316, 410 – Stainless and Heat Resisting Steel Bars and Shapes:
Types 304, 316, 410 and others are based on the SAE designation system for stainless steels (see SAE and former AISI description that follows).
Another use of ASTM grade designators is found in pipe, tube, and forging products, where the first letter P refers to pipe, T refers to tube, TP may refer to tube or pipe, and F refers to forging.
Examples are found in the following ASTM specifications:
AISI (American Iron and Steel Institute)
ASTM (American Society for Testing and Materials)
UNS (Unified Numbering System)
These three systems are US-based and supported by one or other standards body. Some decades ago, AISI and ASTM developed three-digit designations for stainless steels. This system defines three series:
200 series – austenitic chromium manganese stainless steels
300 series – austenitic chromium nickel stainless steels (the most often used steel series)
400 series – ferritic and martensitic chromium stainless steels
The system proved inadequate with the development of new grades so ASTM and SAE (Society of Automotive Engineers) introduced a new system – the Unified Numbering System (UNS). UNS designations use the three-digit system as a starting point, adding two more digits to further define the steel. For example, S30400 is 304. A single letter before the number indicates the alloy family: S stands for stainless steel (N means nickel alloy).