Effect of Manganese content on tool steel performance?

[coreman73]

I have a couple of broaches made from M2 tool steel, which have catastrophically fractured prematurely while in service. I've analyzed the chemical composition and everything meets ASM specification for M2 except for Manganese. The spec calls for 0.15-0.40% and I am getting around 0.57% for both broaches so it's definitely high.

Hardness meets internal specification of 63-68 HRC for each sample (measured roughly 65 HRC). Structure doesn't show anything out of the ordinary.

Is it possible that the out of spec Manganese content could have directly contributed to the failures?

 

[saberblue]

I can't help with the question as written but I would be looking a the material being broached - is it harder or softer than "normal" and where and what kind of failure you have having.

 

[coreman73]

I do not know what type of material was being broached but will try and find out. Good point.

The failure mode is fatigue. The initiation site is at the end of broach where impact is first made. However, the initiation site was nowhere near the "teeth" but about halfway down the end cross section at an area that does not take any direct impact.

 

[saberblue]

If what you are seeing is fatigue failure at the point of initiation you need to check a few other things as well:
1- how much stock are you taking off -- in other words are all the parts the same size at the point you are cutting both now and in the past
2- are the good broaches ground the same way as the bad? What is your QC on the broaches -- do they all come from the same source -- are there any "regrinds" in the mix? If so how do they preform in relation to the new broaches?
3- check the machine it's self is there any "play" in the slide? Is the feed rate the same throughout the cut (it is amazing what a little air in a hydraulic system do)?
4-get out your copy of the Machinist Handbook and run thru the broaching check list

Good luck




A.R. "Andy" Nelson
Engineering Consultant
anelson@arnengineering.com

 

[coreman73]

Thanks Saberblue. I will try and get more of this information from our cold forming technicians.