AGMA 12FTM21

Steel gears are heat treated to obtain enhanced properties andimproved service performance. Quench hardening is one of the mostimportant heat treatment processes used to increase the strengthand hardness of steel parts. Defects seen in quenched parts areoften due to high thermal and phase transformation stresses.Typical defects include excessive distortion, surfacedecarburization, quench cracks, large grain growth, and unfavorableresidual stresses. Gear geometries with large section differencesmay suffer high stress concentrations and crack during quenching.Surface decarburization before quenching may lead to high surfaceresidual tension and possible post heat treatment cracking. In thispaper, the commercial heat treatment software DANTE is used toinvestigate three examples of heat treatment defects. Improvedprocesses are suggested with the help of modeling. The firstexample is an oil quench process for a large gear. Peeling crackswere observed on the gear surface during grinding of the quenchhardened gears. Computer modeling showed that surfacedecarburization was the cause. The second example is a press quenchof a large face gear. Unexpected large axial bow distortion wasobserved in quenched gears, and computermodeling indicated that anincorrect press load and die setup were the reasons. The thirdexample is an in-process quenching crack caused by highconcentrated tensile stress from unbalanced temperature and phasetransformations in a spiral bevel pinion gear. The quenchingprocess was modified to solve the problem. This example alsoemphasizes the need for heat treatment modeling in gear design toreduce the possibility of heat treatment defects. The threeexamples illustrate how to effectively use heat treatment modelingto improve the quality of the gear products.

Edition:

12

Published:

10/01/2012

Number of Pages:

14

File Size:

1 file , 940 KB