Grain Size Evolution of Test Methods ASTM E112
Methods E 2-17T was only slightly more than three pages long and had three sections: standard magnifications, lenses, and grain size. The grain size section did not actually detail the measurement methods, it merely suggested the method to apply depending on whether the grains were equiaxed (Jeffries planimetric method) or elongated (Heyn intercept method). The 1920 revision of Methods E 2 added details on performing the Jeffries planimetric measurement method.
The 1930 revision of Methods E 2 witnessed the addition of Committee E-4's first standard chart, a grain size chart (ten pictures) for brass, i.e., a twinned austenitic structure with a grain contrast etch at 75X magnification. The chart was developed by a special committee formed on June 28, 1928, which consisted of: C.H. Davis, chairman (American Brass Co.); Henry S. Rawdon (U.S. Bureau of Standards); Edgar H. Dix, Jr. (Aluminum Co. of America); and Francis F. Lucas (Bell Telephone Laboratories). Types of grain structures are shown in the sidebar on grain types.
A special subcommittee to study grain characteristics of steels was formed in 1931 with Clarence J. Tobin (General Motors Research Laboratory) as chairman. They decided to adopt the McQuaid-Ehn carburizing test for evaluating the grain growth characteristics of steel, again with the aid of a comparison chart. The proposed chart method was approved as E 19-33T, Classification of Austenite Grain Size in Steel. At that time, grain size was defined in terms of the number of grains per square inch at 100X; ASTM grain size numbers were not introduced until much later. However, this chart was criticized for being inaccurate and it was eventually dropped when ASTM E112, Test Methods for Determining the Average Grain Size, was introduced.
Oscar E. Harder took over this special subcommittee in 1936, with the idea of revising Classification E 19 and adding a non-carburizing method. The next year, Dr. Marcus A. Grossman (Carnegie-lllinois Steel Co.) took over control of this group, which became Subcommittee Vlll (Arabic numerals are now used) on Grain Size in 1938. Grossman ---famous for his work on hardenability---was chairman of Subcommittee Vlll until his death in 1952. Subcommittee Vlll formed three sections (the term task group was not used at that time), referred to as A, B, and C.
Section A was chaired by Grossman and was concerned with improving Classification E 19 on austenite grain size of steels. Section B was chaired by R. Earl Penrod (Bethlehem Steel-Johnstown Plant) and was to develop a ferrite grain size rating method and chart. Section C was chaired by Carl Samans (American Optical Co., later with Standard Oil Co. of Indiana) and was to develop charts for nonferrous metals and alloys that could not be rated by the brass chart in Methods E 2. The brass grain size chart and grain size measurement information was deleted from Methods E 2 in the 1949 revision and this information was incorporated into a new standard, E 79-49T, Methods for Estimating the Average Grain Size of Wrought Copper and Copper-Base Alloys. Two pictures were added to the chart; later when it was transferred to Test Methods E 112, two more pictures were added (14 in all). Methods E 2 was discontinued in 1984 when E 883, Guide for Metallographic Photomicrography, was introduced.
Section B produced E 89-50T, Methods for Estimating the Average Ferrite Grain Size of Low-Carbon Steel, with a chart depicting a ferritic grain structure as revealed by nital etching. This was the first chart (eight pictures) to define grain size in terms of the now familiar ASTM grain size numbers (1 to 8 in this chart). Methods E 89 also marked the first detailed description of the Heyn intercept method with equations and a conversion approach to yield ASTM grain size numbers. Earlier Methods E 2 versions only gave a general description of how to do the intercept test with no interrelationship to the result from the planimetric method. Method E 89, however, had a short life, being discontinued when Test Method E112 was adopted.
Section C produced E 91-51T, Methods for Estimating the Average Grain Size of Non-Ferrous Metals, Other Than Copper, and Their Alloys. This consisted of two charts, one for twinned alloys, the other for non-twinned alloys; both charts had 17 pictures with grain sizes from 2 to 10. Methods E 91 also had a short life, also being discontinued when Test Methods E 112 was adopted. Neither of the charts of Methods E 91 were incorporated in Test Methods E 112.
The net result was four standards (Methods E 19, E 79, E 89, and E 91) dealing with various aspects of grain size measurement. It was recognized that all four shared many common points and it was believed that they could be combined into one overall grain size standard, hence the birth of Test Methods E 112. However, the story of ASTM and grain size measurement does not end with the adoption of Test Methods E 112 in 1961. Since then, the standard has been revised nine times and is presently now under intense scrutiny for further refinement.
 ASTM E112 - 13 Standard Test Methods for Determining Average Grain Size
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