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A round robin program was conducted to determine the hardness conversions for ferritic stainless steels. Each of six participating laboratories conducted hardness tests on specimens representing nine grades, each having varying amounts of cold reduction. Conversions were established to the Rockwell B scale from Rockwell 15T, 30T, 45T, and A scales.
In all cases, the Wilson Chart (Chart No. 52—Wilson Instruments Division, American Chain and Cable Company) conversion fits the least squares round robin data line better than does the ASTM Method E140 austenitic conversion. The Wilson Chart conversion line falls within the 95 percent confidence band of the round robin data for the conversions to Rockwell B from Rockwell 30T, 45T, and A. For the 15T to Rockwell B conversion, the Wilson line falls outside the 95 percent confidence limits for values below HRB 80.
As a result of this round robin program, a joint task group was organized under ASTM Subcommittees A-01.13 and E-28-06 to determine what changes should be made in the hardness conversion tables in ASTM Methods A 370 and E 140. The recommendations of this task group are currently being balloted.
hardness, ferritic stainless steels, mechanical tests
Senior staff metallurgist, Research and Technology, Armco Steel Corp., Middletown, Ohio