cracking occured in en 19 shafts after induction hardening

[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 case depth 2-3 mm..After induction hardening we are getting 55 to 57 hrc quench hardness.Recently we found cracking occurred in some shafts immediate after induction hardening.does adding polymer 5% will solve this problem?
regards

 

[CoryPad]

Are you currently using water only as the quenchant? Adding polymer will help reduce cracking.

 

[arunmrao]

A search performed has listed some good discussions. Link is provided below. Hope it is useful.

http://www.eng-tips.com/search.cfm?...ening&t=&h=&searchSite=1&searchArea=1&d=1&s=1

"Even,if you are a minority of one, truth is the truth."

Mahatma Gandhi.

 

[redpicker]

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 case depth 2-3 mm..After induction hardening we are getting 55 to 57 hrc quench hardness.Recently we found cracking occurred in some shafts immediate after induction hardening.does adding polymer 5% will solve this problem?

If you are quenching with water, that is most definitely contributing to the cracking. As to whether or not a 5% polymer will solve it is questionable. You should discuss this with your quenchant vendor. They are very good at providing exactly the guidance you are looking for. A lot is going to depend on the type of polymer, your quench system design, as well as operating temperatures.

Another issue that is often overlooked is the temperature of the part after it leaves the quench. Cooling below 175C does not improve the hardness, but does increase the cracking tendency. Most of the quench systems are set-up with timers. If so, when determining the process parameters for each part size, pay attention to the post-quench temperature and if it is close to room temperature, adjust the quench time to target 150C or so. You will also find you get less drag-out of the quenchant since it will drain faster off a hotter piece of material.

 

[dbooker630]

Typically 5% polymer works OK with carbon steels, but I suggest at least 12-15% since you are induction hardening an alloy steel. If you have some sharp diameter transitions or snap rings in your shaft you may need to go even higher, toward 20%. You should not have a problem attaining as-quenched hardness around 60 HRC that you can temper back to your spec.

 

[thejackal3]

thanks alot for you valuable advice..

 

[thejackal3]

dear all
of lately we are having this problem .picture attached for ur ref.. we have 10 to 15% polymer added.earlier we were not facing this problem.. out of 200pcs lot 10 pcs break from the exact position..
regards

 

[CoryPad]

Is that a crack at the spline transition? Have you checked material from different batches? Chemical composition, hardenability, microstructure, etc.?

 

[dbooker630]

The spline roots appear to have very sharp corners and it looks like the crack is initiating at this point. If you cannot refine the spline profile you will need to go higher in quench concentration as I noted earlier. It looks like you have a hobbed spline, perhaps you can change the hob profile to include a small radius in the corners.

 

[redpicker]

As I mentioned above, you need to make sure you are watching the temperature of the part as it leaves the quench. Also, the temperature of the quenchant is very important. The polymer has an inverse solubility with temperature in water, meaning if the quenchant is too hot, it is almost just like spraying water on the part. You need to keep the temperature of the quenchant below 40C, preferably below 35C.