Isothermal normalizing technology of carburized gears steel forging

Abstract

The invention discloses an isothermal normalizing process of a carburized gear steel forging stock, which relates to the technical field of metal heat treatment. The process is carried out on a bright isothermal normalizing production line under a preevacuated and fully electrically heated roller bottom protective atmosphere. The heating, heat preservation, fast cooling, isothermy and water cooling in the protective atmosphere are automatically completed by a PLC control. The normalizing heating temperature of the forging stock is Ac3 plus (100-150) DEG C, and the temperature is kept for 36-45min, and the forging stock is quickly cooled to 560-600 DEG C within 10min by high-purity nitrogen gas blown by an electric fan. The normalizing process has the advantages of normative operation, high production efficiency, and can ensure that the forging stock is not oxidized and decarburized in the heat treatment process, and austenite crystals in the forging stock are evenly distributed, which avoids the appearance of banded structures and causes the forging stock to have good and stable quality with small hardness fluctuation.

Description

technical field [0001] The invention relates to a metal heat treatment method, in particular to an isothermal normalizing process for a gear forging blank made of carburized gear steel. Background technique [0002] According to the definition of normalizing in GB7232 and GB / T16923: normalizing (including ordinary normalizing, two-stage normalizing and isothermal normalizing) is to heat the steel to 30-50°C above Ac3, keep it for a proper time, and then leave it at rest Or cooling in flowing air (two-stage normalizing cooling to Ar1 and then slow cooling, isothermal normalizing for fast cooling to a certain temperature in the pearlite transformation zone, so as to obtain pearlite structure and then air cooling) process. [0003] The main purpose of normalizing is to normalize steel parts with abnormal microstructure and obtain a relatively stable and normal microstructure. Due to the different types and shapes of processing objects and abnormal microstructures, the requirem...

AI Technical Summary

Problems solved by technology

[0007] (3) Uneven hardness and low pass rate

[0009] At present, normalizing heat treatment in my country's normalizing production line (including isothermal normalizing) inevitably produces oxidative decarburization. If machining is performed after normalizing, oxidative decarburization can be eliminated in subsequent machining, but Jiangsu Pacific Precision Forging Co., Ltd. adopts the most advanced cold precision forging forming technology. The gear tooth surface formed by precision forging is no longer processed. In addition, in order to facilitate cold precision forging before cold precision forging, spheroidizing annealing technology is used, which is beneficial to the subsequent The machining is not good