Comparative Analysis of Factors Affecting Gas Carburization Optimization in Chromium and Chromium Molybdenum Alloy Steels

Abstract

Background/Objectives: We analyzed the optimal factors affecting the surface hardening properties of chromium alloy steel and chromium molybdenum alloy steel heat treated by propane gas carburization.
Methods/Statistical analysis: The heat treatment conditions were optimized using a simulation program. Simulation results were applied to control the atmosphere in the carburizing furnace. Control factors were temperature, time and carbon potential in the furnace. The effect on the surface properties of heat treated alloy steels was analyzed. Mechanical properties of the carburized layer were compared by measuring the Energy Dispersive X-Ray Spectroscopy, Scanning Electron Microscope, X-ray diffraction, Electron Probe Micro Analyzer and micro-Vickers hardness.
Findings: The carburizing temperature of 0.2 wt.% C chromium alloy steel for automobile parts was 930?. The carburizing time was 10hr at carbon potential 0.90 wt.%. And the diffusion time was 3hr at the carbon potential 0.75 wt.%. The carburizing temperature of 0.2% C chromium molybdenum alloy steel was 930?. The carburizing time was 2hr 10min. at the carbon potential 0.90 wt.%. The diffusion time was 1hr at carbon potential 0.75 wt.%. The surface hardness depth of alloy steels increased with decreasing carbon content. The surface structure of the alloy steels were a mixture of ferrite and pearlite, the martensitic structure decreased and the hardness decreased from the surface to the inside. In alloy steels, surface hardness seems to have a significant effect on the amount of martensitic structure. These results were consistent with EDS, XRD and EPMA analysis. Chromium alloy steel and chromium molybdenum alloy steel showed similar tendency in carburizing behavior.
Improvements/Applications: These results may be applicable to the study on the carburizing optimization of chromium and chromium molybdenum alloy steels used in automobile parts. In order to apply it to materials used in automobile driving parts, research related to durability will be conducted in the future.