440C Stainless Drilling Problem

[TeccBoxx]

I am having some problems with drilling some 440C Stainless Steel. We just got a new shipment in and this stuff is harder then normal. We are drilling 1/8" holes and normally we got around 60-75 holes before they dulled or broke. However this new stuff we are lucky to get 5 holes drilled. We checked the hardness and get Rockwell hardness of around 60 before heat treating. Normally it is around 30-35. I am not a metallurgical type guy so I was wondering if anyone had any suggestions on how I might fix this problem? I was thinking of trying to normalize it with heating up up but I cannot find a normalizing temp. for 440c. So does anyone have any suggestions on how I can get around this problem? Also does anyone know why this batch is harder than normal?

[Mike Whitten CAD/CAM Contractors]

-How deep are the holes?

-Is this the only issue that you are having? IOW, once this issue is fixed are you good to go?

 

Mike

[TeccBoxx]

Thanks for the quick reply the holes are 1/4" deep. Yes, we are good to go once the holes are drilled.

[robk]

Are you machining a flat machined surface and not a casting? If so give Mitsubishi MZS solid carbide, coolant through drills a shot. Do not spot drill, and you shouldn't have any problems.

[Müřlıń®]

Sounds like it has already been tempered. Someone got the lots mixxed up or sumpthin'

Heat treaters screw up all the time.

[Mike Whitten CAD/CAM Contractors]

Tazzer,

 

I think that you only have one choice. You must use a very short, high quality, coated carbide drill. Alway play with a scrap pice or drop if you can. 60rc is very hard but carbide should drill it.

 

 

Thanks,

Mike

[Tim Johnson]

quote:

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We checked the hardness and get Rockwell hardness of around 60 before heat treating. Normally it is around 30-35.

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Send it back and demand the right material.

[Mike Whitten CAD/CAM Contractors]

This is of-course the first choice.

quote:

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Send it back and demand the right material.

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[Jack Mitchell]

quote:

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Send it back and demand the right material.

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Excellent advice, otherwise be prepared to expense four times the tooling cost and four times the machining quote.

 

 

Regards, Jack

[CAM-mando]

Rc 60 has been Hardened ant tempered.

 

Annealed 440C will range in the low to mid 20's Rc.

 

Annealing at 1350/1400°F and Air cooling will get you about Rc 25 or 26.

 

If you have time though I als recomend returning the material from whence it came and have whoever screwed up fix the problem.

[Kevangel]

I use a fair amount of 420 F SS which comes with a RC of 33-37...I would not substitute different rockwell material without written permission from customer as harder material may be more prone to crack and break althouth It may be more wear resistant. Most mold steels can be re- heat treated to proper RC. Sometimes they have to take it all the way back to annealled and start all over. Talk to your heat treater(talk to a good one)

[Kevangel]

Ooops, if this is the steel suppliers fault, talk to them first...( if you ordered the right spec. and they supplied the wrong one)

[connormac]

I agree with all the above. send it back to the supplier.

[chris m]

Material hardness is often crucial to the application of the component being machined; send it back

 

C