THE EFFECT OF PACK CARBURIZING ON HARDNESS AND FATIGUE STRENGTH OF LOW CARBON STEEL

Abstract

For many engineering components such as gears, shafts and valves, it is an advantage to use steel (iron) with a hard surface (case) and a soft, tough interior (core). This is usually achieved by one of   several case hardening treatments, in which, the surface layer of the soft steel enriched with hardening alloying, usually carbon, by diffusion treatment. The main purpose of this work is to study the pack carburizing of the low carbon steel by means of three different holding times which are; 4, 6 and 8 hours at a temperature of 925˚C. Also in this paper, fatigue strength was examined for different samples under certain conditions. The combination of the carburizing mixture (carburizer) used in this study was 87.5% charcoal and 12.5% barium carbonates (carefully mixed). From the experiments, the hardness gradient and the thickness of carbon layer were highly effected by the duration of the carburizing process. The hardness range through the carburized case could be tightly correlated with the carbon content of martensite. The highest hardness value and carbon gradient recorded (layer thickness) were after carburizing treatment for eight hours. Water was used as the quenching medium in the quenching experiments. Some of the tested specimens were exposed to a tempering treatment at 200˚C and 450˚C for three different times i.e. 1⁄2 , 1 and 1 1⁄2 hours. The highest hardness value achieved was after tempering at 200˚C for 1⁄2 hour, while the lowest value was at 450˚C for 1 1⁄2hours. Mean while, the  highest fatigue strength value was monitored after tempering the carburized samples.