Research on the Heat-affected Zone of Flame Cutting and Machining Allowance of Alloy Steel (40CrNiMoA)

This article adopts flame cutting as the method to process large-module involute gears, with the part material being alloy steel （40CrNiMoA）. After cutting, the parts were subjected to dye penetrant inspection and hardness testing, leading to the following conclusions: the gear surface after flame cutting showed no cracks; the hardness of the gear tooth tip and tooth surface after flame cutting ranged from 30 to 37 HRC, with the tooth surface hardness slightly higher than that of the tooth tip. Through cross-sectional metallographic examination and hardness gradient testing, it was determined that the depth of coarse grains on the flame-cut surface was approximately 1.0 mm, and the heat-affected zone （HAZ） on the gear surface after flame cutting was about 4 mm. If flame cutting is used as the rough machining method for the part, leaving a unilateral allowance of 4–5 mm on the tooth surface and root, subsequent fine machining will completely remove the heat-affected zone, ensuring no adverse impact on the mechanical properties of the part.