Forging Breakup - M50 Tool / Bearing Steel

[Jeff37]

Hi All,

I was wondering if anyone can help me understand a problem I'm experiencing. I'm trying to produce a small scale hammer forging from M50 and having trouble with break-up. I know that these grades can have issue with liquation causing breakup but the temperature we're using (1120°C) is the same temperature the bar stock was forged at, so I can't see why it would be an issue now if it wasn't when originally forged. It has been spheroidised since then - could this lower the forging temperature enevolope? As far as I know, this is within recommended forging temperature ranges, if a little towards the top end.

Thanks for amy help.

 

[btrueblood]

Sounds like you might be hot tearing - the data sheets for M50 steels state quite clearly "do not forge below 1800 F" - that's only 250 F below your value, and the part may cool rapidly enough that it's approaching 1800 even on the first few hits?

 

[Maui]

An image that illustrates the condition would help here. Can you provide one?

http://www.EngineeringMetallurgy.com

 

[tbuelna]

Here is Latrobe's recommendation for forging M50:
"Preheat at 1400-1500°F (760-816°C) and hold until uniformly heated; then heat rapidly to 2025-2100°F (1107-1149°C) and again hold until parts are uniformly heated. Do not forge below 1700°F(927°C). Parts should be slow cooled after forging by furnace cooling or by burying in an insulating medium. A full annealing treatment should always follow forging.

Here's Latrobe's datasheet for M50.

As btrueblood pointed out, the problem may be due to the small preform mass losing too much heat at its extremities and hot tearing. Also, you mentioned this is a hammer forging operation on a "small scale". Is the forging process performed manually or is it automated?

Hope that helps.
Terry