Small gear - 8620 core hardness concerns warranted?
Small gear - 8620 core hardness concerns warranted?
(OP)
Have run into a rash of gear failures on a small gear (.06 tooth thickness approx.) that for years did not have any issues.
Current spec is 89-91 R15N effective depth of .008-.014. Core hardness 35-45 Rc. Measure at pitch line.
The gears are currently always coming on the high end on the core hardness. I am checking to see if this was always the case. Regardless, is this the right investigative road to travel down?
Also, isn't the core hard hardness just a by-product of the temper before the carbururuzing process or are there significant controls with the process that dictate the final core hardness.
Not a metallurgist ... just a guy with way to many metallurgy issues. Thanks for any comment.
BCK
Current spec is 89-91 R15N effective depth of .008-.014. Core hardness 35-45 Rc. Measure at pitch line.
The gears are currently always coming on the high end on the core hardness. I am checking to see if this was always the case. Regardless, is this the right investigative road to travel down?
Also, isn't the core hard hardness just a by-product of the temper before the carbururuzing process or are there significant controls with the process that dictate the final core hardness.
Not a metallurgist ... just a guy with way to many metallurgy issues. Thanks for any comment.
BCK





RE: Small gear - 8620 core hardness concerns warranted?
Gear tooth pitchline core hardness is associated with carbon content/overall chemistry, hardenability, temperature prior to quenching, quench media, quench temperature, and draw (tempering) temperature.
I would start with the material though. See if you can write an internal spec for a restricted hardenability 8620H with the near surface hardness properties (J1 and J2 jominy hardenability position) below 45 HRC.
RE: Small gear - 8620 core hardness concerns warranted?
RE: Small gear - 8620 core hardness concerns warranted?
But the met analysis will tell you if it was an overload, instantaneous, or fatigue type of fracture; it may also point out irregularities in machining or finishing. I've seen many gears that met specs yet did not perform in service. The metallurgist's conclusion will tell you what data you have to gather.