The Effect of an Encapsulated Specimen's Mounting Material on Its Rockwell Hardness Test Results

摘要

This study addresses the affect of mounting material used with an encapsulated metallographic specimen on its Rockwell hardness test results. Thirty-five specimens were sectioned from a grade i 144 medium carbon steel rod as the experimental material. Thirty of the sections were encapsulated in six different mounting materials (the test groups), and five were left unencapsu-lated (the control group). Each specimen was ground and polished using the same metallographic preparation procedure, and then hardness tests were performed using the Rockwell hardness C scale. The repeatability (r_(PB)) value, from the ASTM International tnter-Laboratory Study to Establish Precision Statements for ASTM El8, was used to compare the hardness lest results of the encapsulated test groups to the results of the unencapsulated control group. Using that study, if the average hardness of a test group fell within ± r_(PB) of the control group, there would be approximately a 95 % probability that it was equivalent to the control group. Five out of the six test groups (all except transparent thermoplastic) had average hardness values that fell within ± r_(PB) of the control group average. Four of the six test groups (all except green phenolic and transparent thermoplastic) had standard deviations that were less than r_(PB). With such results, green phenolic and transparent thermoplastic are not suitable mounting materials for Rockwell hardness testing.