EN19 Shafts induction

[thejackal3]

Dear all
we manufacture rock shaft for tractors. material EN 19 with hardened n tempered with hardness 30 -35 HRC.after finishing we have to do induction hardening the splines and required case hardness 45-50 HRC depth 1 mm..Is it ok if we induction hardened these shafts in water or it should be done in oil or in polymer water.
rgds

 

[CoryPad]

Using water only as the quenchant likely will lead to distortion and cracking. It would be better to use a polymer additive with the water as your quenchant.

 

[thejackal3]

Dear all
we manufacture rock shaft for tractors. material EN 19 with hardened n tempered with hardness 30 -35 HRC.after finishing we have to do induction hardening the splines on both the ends and required case hardness 45-50 HRC depth 1 mm... recently in final inspection we found some rock shafts are having 40 hrc on one spline end.. should we anneal and again do the induction hardening?
rgds

 

[arunmrao]

I agree with corypad. There is the fear of distortion, a milder quenchant will be preferred. Any straightening is needed after induction hardening?

I'm just one step away from being rich, all I need now is money.
( read somewhere on the internet)

 

[dbooker630]

You need to find out why the one end is at 40 HRC:
- did the end get hot enough to quench?
- if it did, was the quench interrupted?
- are you still using a straight water quench instead of what CoryPad recommended?
- if the shaft heated and quenched okay but is also induction tempered, was the temper cycle interrupted?
Answering the above as well as looking at the microstructure should point you in the right direction. Certainly it is simple enough to anneal, normalize, or temper back the existing structure and induction the part again. But I would want to know why the end was soft before moving forward.

 

[redpicker]

As he is not asking questions about how to stop the cracking, I would assume he is not using water.
;^)

To answer your question

recently in final inspection we found some rock shafts are having 40 hrc on one spline end.. should we anneal and again do the induction hardening?

You should temper the shafts at or below (by about 15C) the tempering temperature used to produce the 30-35 HRC, then repeat the induction hardening operation.

There are a number of reasons that would result in soft parts after the induction cycle. If this happens often, a detailed investigation should be started to determine the cause. Without knowing the cause, you are not likely to find the solution.

 

[FennLane]

What diameter are the shafts and how do you control the heat input when you induction harden.

I assume that you temper after hardening.

Be careful with using Polymer quenching media.

I saw a problem with truck axles and cracking many years ago.(late 1970's)

A client had moved form oil to a polymer which was relatively new and a small percentage of the axles we was processing developed cracks.

It transpired that at low concentrations (circa 5%) the polymer being used increased the cooling rate to greater than iof water had been used and in fact approached that of brine. At 15% it slowed appreciably and all cracking was eliminated.

 

[thejackal3]

thanks all for the valuable information.