Pack-Boronizing of AISI 4140 Steel: Boronizing Mechanism and the Role of Container Design

In this study, pack-boronizing of AISI 4140 steel was done. Three mild-steel containers with different size, namely, small-size container (SC), medium-size container (MC), and big-size container (BC) were used. Steel specimens were boronized at 950 degrees C for 2 or 3 h. Preconditioning of the containers was observed to be essential before doing final pack-boronizing of steel. MC was found suitable for the formation of monophase Fe2B layer while BC produced unwanted FeB phase along with Fe2B layer. Fe2B phase showed the columnar morphology. Continuous decrease in the hardness from surface to nonboronized core was observed. Maximum surface hardness of about 1367 HV0.1 was obtained (hardness of nonboronized core was about 252 HV0.1) for the boronized steel. As compared to the normalized and hardened-tempered (HT) AISI 4140 steel pins, boronized steel pin showed the lowest specific wear rate'' (0.89 x 10(-6) mm(3)/Nm) and coefficient of friction (COF) (0.55).