Abstract
A method for controlling the high-frequency current hardening (HFH) process for internal gears made of 20KhGNM case-hardening steel was developed using multiphysics finite element modeling. All components were pre-hardened at 920-950°C for 4-8 hours in an endogas environment with a carbon potential controlled at 0.9-1.1%, ensuring a carbon distribution from 0.8-1.0% on the surface to 0.2% at a depth of 1.0-1.5 mm. Durability is understood as a complex indicator that includes: contact fatigue (N ≥ 10⁷ cycles at σH = 1200 MPa), bending fatigue (σF ≥ 450 MPa according to GOST 21354-87), hardened layer depth (1.8-2.2 mm with a hardness ≥ 550 HV), residual compressive stresses on the surface (≤ –800 MPa). Experimental verification on one gear size (modulus 3 mm, z = 55) confirmed the accuracy of the hardness distribution prediction (MAE = 2.8 HV, RMSE = 3.5 HV, R² = 0.96) and residual stresses (deviation 2.9%). A comparative analysis showed the advantage of the proposed FEM approach over traditional empirical methods: a reduction in the development time of modes from 8-12 hours to 1.5-2 hours, a decrease in the forecast error from ±15-25% to ±5-7%, a reduction in cost by 12-15%, and a reduction in defects from 8-12% to 2-3%. The estimated service life of optimized parts increases by 25-30% due to the formation of a favorable distribution of residual stresses (–1020±45 MPa on the surface) and the optimal depth of the hardened layer.