Chad V. Rhen

Date of Award

8-1991

Document Type

Thesis

Degree Name

Master of Science (MS)

Abstract

The problem of this study was to investigate the effect of tempering temperature and tempering time on the hardness of a 4130 alloy steel. The objectives of this study were to determine: (a) the effect of tempering temperature on hardness, (b) the effect of tempering time on hardness, and (c) the interaction between tempering temperature and tempering time.

This study used an experimental research design method. The factorial design was the two-factor, fixed-effects model. Tempering temperature and tempering time were the predictors and hardness was the criterion. Time intervals of 15, 30, 60, 120, and 180 minutes were used. Temperature levels of 100, 150, 200, 250, and 300 °c were used.

The research design had six specimens randomly assigned to each of the 25 cells or treatment combinations for a total of 150 specimens. The specimen material was 4130 tubular alloy steel, 0.875 in. OD x 0.065 in. wall thickness x 2 in. length.

All specimens were processed identically for the hardening step of the heat treating process. The six specimens from each cell were tempered according to that cell's designated time interval and temperature level.

Data were collected by evaluating specimen hardness on the Rockwell C scale. Two-way ANOVA was the statistical method used to test the three null hypotheses. A multiple comparison, using Dunnett's test as the statistical method, was used to investigate simple effects by testing among the cell means.

The researcher concluded, based on the findings of this study, that there was: (a) a statistically significant difference in hardness among the five predetermined temperature levels, (b) a statistically significant difference in hardness among the five predetermined time intervals, (c) statistically significant interaction between tempering temperature and tempering time, and (d) an individually statistically significant difference in hardness between cell 10 (150 °c, 180 minutes) and cells 2, 4, 5, 7, 13, 14, 15, and 17 through 25.

Using omega squared (w2) as a measure of association between the independent and dependent variables, the data indicated that 47.93% of the variance of the hardness scores can be attributed to the differences in the tempering temperature levels, 2.66% can be attributed to the differences in the tempering time intervals, and 4.17% can be attributed to the interaction of the two independent variables.

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