Induction hardening distortion 6

[MarkQA]

Hello,
We have had some trouble with one of our spindle shafts.
1. I was hoping to learn how to estimate how much distortion/ dimensional growth I should expect after induction hardening a shaft (drawing attached). Material is 4140. Could someone provide a number, or means to calculate?
2. I would like to improve our drawing callout for heat treat. All we say now is induction harden, min. 45 HRc, and the location to be hardened. Could someone provide pointers, or reference material for specifying?

Thanks,
Mark

 

[TemperedMartensite]

Hello Mark,

Distortion will be tough to create a specific formula, since there are many factors that contribute... processing history, heat-up rate, quench rate...

As far as you call-out - you need to add a minimum temper say 300- 350F just to make sure you don't have a surface of virgin martensite. Most heat treaters will do this automatically.... but it is better to be safe-than-sorry. Other consideration...if you are concerned with distortion you may want to mandate an oil quench (or even warm oil).

 

[redpicker]

As has been mentioned above, there are too many variables that contribute to the distortion to be able to accurately predict how much you will get (or even if it will be a growth or a shrinkage). The best you can do is be aware that distoriton will occur and either adjust your tolerances to allow for it or plan on finishing after heat treatment.

I don't like the practice of specifying the tempering temperature in this case. The problem with specifiying a tempering temperature is if there is a problem, at least part of the blame could be put on the tempering temperature that was specified. If you tell the baker how to make the cake, you can't complain about how it tastes.

Rather than specify a minimum temper, I would suggest you change the callout from just "induction harden" to "induction harden and temper", and then give a hardness range instead of just a minimum. That is, your note could say, Induction harden and temper to 45-50 HRC. Personally, I think 50 HRC is a bit high for 4140, but if you have too narrow of a hardness range, the heat treater will not be able to hit it. If you could accpet 42 HRC as a minimum, I'd be more comfortable with 42-47 HRC than 45-50. If you just have to maintain the 45 HRC minimum, I'd suggest a talk with your heat treater to see how narrow of a range he would be comfortable with.

rp

 

[israelkk]

To my experience this part should be heat treated all over before (final) machining/grinding. It will be cheaper and you will save the induction treatment and distortion.

 

[tbuelna]

MarkQA,

I'd agree with israelkk's comments. If all you need in that flange area is Rc45, rough machining and then a full oil quench and 800degF temper, followed by finish machine operations on the part would be more cost effective.

An induction heating and quenching of the flange area would leave you with a very hard and brittle material condition (>Rc55) unless it was subsequently tempered. Quenching the flange area with those small holes and sharp edges may also result in cracking.

Good luck.
riff_raff