Effect of Precarburization on Growth Kinetics and Mechanical Properties of Borided Low-Carbon Steel

Abstract

Boriding is a thermochemical process employed widely for increasing the resistance of ferrous materials to wear and corrosion. In this work, the influence of precarburization on microstructure, boride layer thickness, microhardness, growth kinetics, and mechanical properties of untreated and borocarburized AISI 1015 steel is studied. The thickness of boride layer ranges from 205.9 to 215.9 µm for borocarburized specimens to a maximum of 247.7 µm for borided AISI 1015 steel. The carbon content in the case improves the microstructure by the formation of single-phase iron boride mainly on the surface. Boride layer thickness decreases with increase in carbon content of the case. Activation energy for the borided AISI 1015 steel is 119.22 KJ/mol. The activation energies are 174.4 and 194.7 KJ/mol for borocarburized AISI 1015 steel having 0.30% C and 0.45% C, respectively. The activation energy increases with increase in carbon content due to precarburization. Empirical relations have been developed to predict boride layer thickness and are well correlated with experimental values for the process temperature and time. Tensile strength ranges from 421 to 599 N/mm2. Impact strength of borided specimens varies between 386.7 and 493.3 N-m while for borocarburized specimens it ranges between 103.7 N-m and 183.3 N-m. Fracture behavior of borided and borocarburized specimens under tensile and impact tests has been analyzed.