Effectiveness evaluation of thermochemical treatment of carbonitriding in motorcycle gears

ABSTRACT

The objective of this study is to evaluate the effectiveness of the thermochemical treatment of carbonitriding employed in motorcycle gears for the replacement of a medium carbon steel to a low carbon steel. For this, the chemical composition of the material was determined, the microstructure analyzed, traced the microhardness profile and verified the conformity of the tests. As the gears used in the thermochemical treatment were produced with SAE 1015 steel, such as those that were subjected to austenitization at a temperature of 880 ° C for 6 hours, using a controlled atmosphere with 1% carbon potential and low NH₃ volume, cooled in oil and tempered at 180 ° for 1 hour. A presented microstructure of the ferrite and perlite core and a high hardness nitrided carbonitride layer and high carbon martensite associated with the austenite retention volume. The x-ray diffraction technique confirmed the presence of austenite retained on the sample surface. A maximum depth reached was 949 HV_0.1 and a carbonitride layer depth of 0.8 mm. Thereby, the use of low carbon and unalloyed steel could be a manufacturing route for gears when using carbonitride thermochemical treatment. The presence of very high carbon potential is favorable for austenite retina formation.

Keywords
XRD; microhardness profile; thermochemical treatment