Heat treat question

Matt Rochester

Matt Rochester

Joined
Nov 28, 2014
Messages
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Cpm154. Equalize at 1400 for 15 mins. 1950 for 30-45. Plate quench. Subzero for 2 hours. Temper at 420 twice for an hour. Blades tested between 62-66. Tempered again at 475 and got the same readings. Any suggestions? Try another tester?
 
Sounds like the tester might be off. After tempering at 475 you should have a significantly different hardness
 
154CM-TC.gif
 
Sometimes there is a bit of surface oxidation or mill scale that adds variability and sometimes increases the hardness reading. Grind down to clean steel and see how it tests.
 
The Rc 62-66 hardness sounds odd. They should all be the same, and all should be about Rc 61/62 as quenched according to my charts.

Shane's chart is slightly different ( higher) than mine , but the general curve is close to the same. I have the hardness at 420F temper dropping about two points to Rc 59/60, and it might only drop a single point between that and 475F. The hardness curve bottoms out at Rc 56 around 600F, and is almost flat ( Rc 57/56) between 500F and 900F until it rises at the higher temper points in the 1000F area, where it tops out at Rc60.

Check you tester and the procedures you used ... and make sure things are right. You should not be getting an Rc 66 on any CPM 154 steel....or on most any stainless knife steel.
 
Jason, I will clean them up and check them again.

Stacy, I am a little confused by some of the charts. The one Shane posted is the same one I used from crucibles site. Last time I tempered at 425 and got 61.5 so its either the tester or needs cleaned up. Thanks fellas.
 
Matt,
If the as-quenched on that knife was around 62.5 after cryo, then the hardness at 425F could well be 61.5. It only drops about one point by 400-425F.

I have noticed that the newer steel seems to harden a bit more than the old stuff. My ISM chart is older, and is about a point lower than Shane's.

The biggest difference in getting higher than the charts is the difference between sub-zero ( as the OP said) and cryo. With cryo you can sometimes get a 2 point gain over a standard chart that isn't cryo specific..
 
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