<p>According to the Koistinen-Marburger model, the evolution mechanism of the hardened layer during laser quenching can be quantitatively revealed. This is of great significance for improving the laser quenching effect and optimizing the process parameters. This study thoroughly investigated the distribution of the hardened layer and the transient temperature evolution during laser quenching of the rack by numerical simulations. Under the premise of considering the angle of incidence of the laser beam, the focus is on exploring the significant influence of the laser overlap rate on the size of the tempering softening zone and the uniformity of the hardened layer. The results indicate a positive correlation between the laser beam’s incident angle and the hardened layer’s surface width, and an inverse correlation with its depth. It was found that as the laser overlap rate increases, the hardened layer distribution becomes more uniform and the tempered softening region expands. In-depth comparison shows that changes in tempering width are more pronounced than those in depth. Finally, Considering the efficiency of laser processing and the specific parameters of the gear rack, it was determined that the optimal quenching effect is achieved when the incident angle of the gear rack laser quenching is 35 ° and the overlap rate is 40%. The numerical simulation’s validity is confirmed by comparing its results with experimental data. The Koistinen-Marburger model-based numerical simulation offers substantial theoretical support for optimizing machining process parameters, significantly enhancing the rack’s service life.</p>