Strange experience with 154CM

[Don Robinson]

I had an experience yesterday and today that is hard for me to believe.

I've been involved one way or another over 50 years with the heat treatment of tool steels. This one is a totally new experience for me.

I hope Mete is out there somewhere and can help me understand this. Here's what happened:

I made a blade and backspacer out of 2 different pieces of as-rolled 154CM for a button lock folder and started heat treating them yesterday. The backspacer has to be .010" thicker than the blade. That's why I used two different pieces from my stock.

Both bars were marked clearly with a paint stick 154CM. The marking was placed there by the mill, the distributer, or whoever I purchased the bars from. I've had these bars on hand for a few years.

Now for the nitty gritty.

I wrapped both pieces separately and heat treated them separately. Same formula I've used before with fine results. 1950f for 30 minutes, unwrap and plate quench as always.

Flash tempered at 350f for two hours.

At this point, I always cryo, but there was no dry ice in town and my LN dewar is empty, so I decided to go ahead and temper without cryo.

Tempered both pieces together at 775f for two hrs. to avoid the 800 to 1100 range as Crucible recommends. I usually get 60 to 61Rc with cryo and three 2-hr. tempers using 154CM with this recipe.

At this point I checked the hardness of the backspacer only to avoid marking the blade. Surprise!!!! It measured only 57Rc instead of around 60Rc as usual.

I decided to see if a higher tempering temp. would bring it up in hardness, so I tempered both pieces again at 1000f for two more hours.

Checked the hardness of the backspacer only again and believe it or not, it went up to 63Rc!!!!

I had no idea why or how this could happen, so I decided to check the blade. Remember, it was made from a different bar of as-rolled 154CM.

The blade checked 61Rc, right where I wanted it. But the backspacer was 63Rc.?????

I tempered the backspacer again for one hour at 1050f and it came out 57Rc, which is fine for that.

It's a mystery to me how one piece but not both pieces of 154CM could get 5 points harder after tempering, especially since I was using Crucible's chart and following their recommendations.

I'm guessing that the one bar of steel is mis-marked, but even so I've never heard of this happening before, no matter what kind of alloy it is.

There is nothing wrong with my hardness tester and it's calibrated to less than one Rc point.

Has anybody ever seen or heard of this kind of thing before?

[GHNorfleet]

Don, I have not but I would like to follow along on this thread to see any new posts about this.

[mete]

First there is always a chance of mismarked steel. This alloy has a good percentage of Mo which along with V and W will give secondary hardening at about 1000 F temper as the Crucible chart shows. Other problems such as decarb might be there. Did you try a spark test to see if they are different ?

[Don Robinson]

No, I haven't spark tested but I will, and post again tomorrow.

I'm amazed that any steel, even with secondary hardening, could gain 5 points of hardness between 775f and 1000f, as this did.It went from 57Rc to 63Rc after a flash quench at 350f and a 2 hr. temper at 775f, then finally up to 1000f for 2 hours.

I think I'll offer to sell this mystery steel to a science fiction buff.

Thanks, Mete.

[Don Robinson]

I've been out all day at the Dr's. I'll spark test tomorrow.

In the meantime, it's strangely quiet around here. Nobody except Mete have anything to say about this?

Mete, I forgot to answer one of your questions. No decarb evident. Just the normal foil wrap colors.

I sanded both surfaces as usual before hardness testing. Tested 3 spots each time to settle the tester down.

[Don Robinson]

Originally Posted by mete

Did you try a spark test to see if they are different ?

Mete, I apologize for taking so long to answer your question. My old mind is very forgetful.

I did spark test.

It takes considerable pressure against a new 100 grit belt to produce any spark. I got the same result from both pieces.

Medium length light red or orange sparks with a burst at the ends using flourescent lighting.

Very sparse amount of sparks with lots of separation.

Since the spark test came out the same on both pieces, I'm assuming they are both the same type of steel from different mill heats. The actual chemistry must vary quite a bit between the 2 pieces.

As I said before, I've never seen anything like the heat treat results in the piece I used for the back spacer.

[mete]

Very strange unless you've missed some detail .

[Don Robinson]

Yep, very strange.