Heat treatment process of reducer gear
Generally, the blank materials used to make reducer gears need to be forged to eliminate carbide segregation in steel, which is conducive to obtaining qualified metallographic structure and properties and ensuring the strength and impact toughness required for reducer gears to work under complex loads. The general process is: shearing blanking forging normalizing or tempering turning outer circle and drawing hole stress relief annealing finishing (drawing, inserting, milling, planing, etc.) carburizing Low temperature nitrocarburizing.
The preparatory heat treatment of gear reducer refers to the most commonly used heat treatment of formed gear blanks, namely annealing or normalizing treatment and quenching and tempering treatment. Normalizing or annealing is generally arranged after casting or forging, that is, before rough machining, in order to obtain good machinability, eliminate the residual stress generated during steel forging, refine the grain and improve the structure, and reduce the tendency of deformation and cracking during quenching. The normalizing temperature is 900~970 ℃, and the hardness is 156-269HBW. The purpose of quenching and tempering treatment is also to refine the grain and homogenize the structure. As tempered sorbite structure is obtained, the toughness of gear blank is higher. This process is generally arranged after rough machining (such as low-carbon steel). In addition, the stress relief treatment of some reducer gears can stabilize the structure and reduce the deformation.
For carburized gears, the usual heat treatment process is: cleaning the part surface - charging - carburizing, quenching - intermediate inspection - cleaning - tempering - spline hole correction.
Generally, the gear of the quenching and tempering reducer is characterized by large size and weight, easy design, processing and heat treatment, easy running in in the working process, high tooth root strength and strong impact resistance. Therefore, this type of gear has a relatively large proportion in heavy gear transmission with less strict requirements. Common quenched and tempered gear materials and heat treatment processes are as follows:
1. Pre heat treatment: after the blank of the quenched and tempered reducer gear is deformed by hot working, pre heat treatment is required to reduce the hardness, improve the machinability and the coarse and banded grain structure caused by improper forging, rolling, etc., eliminate the structural defects caused by hot working and refine the grain, so as to prepare for the final heat treatment of the reducer gear.
Generally, the preparatory heat treatment includes normalizing or annealing treatment. For carbon steel and low alloy steel, normalizing or annealing treatment is adopted; For alloy steel or steel with high hardenability, normalizing+high temperature tempering or normalizing+high temperature annealing shall be adopted.
2. Final heat treatment - quenching and tempering treatment: in order to obtain the required structure and properties, the quenching and tempering reducer gear needs to be quenched+high temperature tempered to obtain sorbite structure with good comprehensive mechanical properties. After the gear is heated, the hardenability, deformation and cracking tendency of the steel shall be considered, and the best quenching cooling medium shall be selected on the premise of ensuring the hardenability, effectively controlling deformation and avoiding cracking.
The second type of temper brittleness of steel shall be considered during high temperature tempering. For carbon steel without such brittleness, high cooling shall be adopted, while for alloy steel gear, it shall be cooled rapidly in water or oil after tempering.
3. Precautions for heat treatment of reducer gear
3.1 Gear normalizing of reducer is a necessary and key process. Reducing the hardness of gear blanks after hot working, improving the structure and eliminating defects are good foundations for subsequent machining and quenching and tempering.
3.2 The basic requirements for gear quenching and tempering of the reducer are that the metallographic structure, hardness and deformation meet the requirements. Therefore, when preparing the heat treatment process, a series of process parameters should be verified according to the selected heat treatment equipment performance, heating temperature, cooling medium, cooling mode, etc. to find the best process parameters.
3.3 Pre cooling quenching or dual medium quenching is an important measure to reduce the thermal stress generated during quenching, which can effectively reduce deformation and cracking; In addition, the sub temperature quenching method is a method to obtain better strength and toughness effect for gears, and has also been widely used.
