Microstructural Changes in Crankshaft Steel After Exposure to Boriding

Abstract

This study investigates microstructural and mechanical changes in automotive steel after a boriding process. Extended thermal exposure was analyzed to study the development of carbon diffusion zones (CDZs) and the resulting mechanical properties. Experimental results reveal the relationship between treatment conditions and carbon enrichment beneath the Fe2B phase. First, cylindrical samples were obtained from an automotive crankshaft. The samples were exposed to the boriding process at 900, 950, 1000, and 1050 °C for 2, 4, and 6 h. The results indicate a clear influence from the treatment conditions (temperature and time) on both the material microstructure and mechanical properties. Additionally, the carbon content of the steel was redistributed across the samples, reaching a maximum of 0.79% in the CDZ and a minimum of 0.55% in the core of the samples at short times and low temperatures. In contrast, at long times and high temperatures, the carbon concentration was homogeneous across the sample. Finally, the material microstructure and hardness exhibited behavior consistent with the carbon content as a function of the treatment conditions.