Heat Treat Before or After Grinding?

[TIZWIN]

Hello guys. I'm not a knifemaker, but I'm fascinated by the process. Can anyone give their opinion on when it's best to heat treat a blade? I presume that it's done after the initial shaping of the blade, but is it best done before grinding the bevels, or after?

Will it do any good to heat treat a blade that had already been ground and sharpened?

I ask because I recently got a blade blank made of EN45 steel, which has been roughly ground, and I'm wondering if it would improve the blade by having a real whiz-bang heat treating.

Thanks in advance for any thoughts on this.

 

[Barker]

Depends on the complexity of the grind for me. I like to heat treat first before grinding double edge and complex grinds to avoid warpage. Otherwise I grind first, heat treat and then finish grinding at the higher grits. I usually go up to 220 grit and sometimes 400 grit before heat treat on simple grinds.
-John

 

[David Wesner]

As a new maker I found it easier to do all or most of my work prior to HT. Much easier to bench a soft blade than one @ 60 HRC. As my grinding skills improved I started to grind my blades to almost finished then finish grinding the bevels after HT. I couldn't imagine doing it any other way now. I think it was Don Hanson who finally hit me over the head with a board (actually it was his response to a post of almost the exact same question )thereby knocking a little bit of sense into my pea brain . It has changed the way and the speed with which I now finish my knives, all for the better. Like I said, now I couldn't imagine doing it any other way :thumbup: :thumbup:

I'm not familier with EN45 so I can't help in that respect

 

[Barkes Knife Shop]

It totally depends on the kind of steel you are using. I personally like to rough cut my blades out and stamp, drill holes, Spanish notch, before I heat treatment my knives. This way I can reduce the possibilities of warpage of my blades. When I am finished with the heat treat and tempering process I then place my knives on the surface grinder and removed the black/gray bar from the steel. By doing this I also know for sure everything is absolutely flat. But you can grind before doing all of that. Is just opens up all the other possibilities. And yes you will use more belts in doing so, but what is more important a $ 3.65 belt or a $300.00 and up knife. Heat treating steels can be a tricky thing, til you get on to doing it. There are formulas for doing the process correctly, and there are steps to follow in a precise procedure to achieve the best results. And you learn by doing it. Most knife makers will tell you there way. But it isn't the only way. That something you will learned for yourself, and that comes by doing it. I hope this was of help to you. Have safe one out there. :thumbup: Just to add, my knives come out on the Rockwell 59 to 62 Rc. with a temper Line. Steels are 1095-1084-52100.

 

[Bufford]

My knives are nearly complete prior to HT. After HT I put the final finish on the blade and handle it up. I could not imagine trying it any other way. Grinding a blade out of hardened steel would take forever, and it would be hard to keep the blade cool enough to avoid ruining the temper during grinding.

 

[heatride]

John Fraps , A.T. Barr and several other well known makers grind after the heat treat and love it. John told me he would not do it any other way. I am very seriously thinking of trying it myself. With thats said I grind my profile , hollow grind the blade with 50 or 80 grit belts ,leave about .050 to .080 on edge heat treat then finish grind after.

 

[silver_pilate]

I've always ground to near completion and drill all holes, perform all filework prior to heat treat. If you are using an oil quenching steel, you'll have to remove some "scale" discoloration and any decarb that has developed during heat treat. I've recently started doing my work down to basically finished at 220 grit, and then hand sanding the blades at 220 to remove all the deep scratches left from the grinder before heat treating. I found that it just takes forever after heat treat to hand sand the deeper marks out. Then when I get the knife out of the tempering oven, I use a 400 grit belt to remove decarb/scale and then hand sand again from 220 and up. Makes the final hand sanding process much quicker when you've got it smooth and uniform prior to heat treat.

As far as heat treating a sharpened blade, you may run into problems with the edge warping or rolling during heating or quenching. If you've got a blade that you don't think is heat treated properly, and it doesn't have handles or hardware (basically a blank), it can sure help to redo the heat treat, but it's gonna be hit and miss (more likely miss) with a sharpned edge.

Most heat treatments are pretty standard. You will find steels that develop an extra degree of hardness if a cryo treatment is used (such as 440C), but as far as a fancy form of heat treatment, it's basically all the same within a given steel to produce the best qualities in the finished product. However, it can be done wrong, or it can be done right.

--nathan

 

[Rob!]

We get lots of blades finished to 800 grit or so before heat treat.

AS for HT before grinding, properly hardened and cryo'd 154 is darn near impossible to get below RHC60. We temper it at 500F normally. You'd have to be really careless to get it that hot - although - is there any one of us that hasn't seen a cherry red tip from time to time?

My vote is to grind first and HT when almost done.

Rob!

 

[Stacy E. Apelt - Bladesmith]

EN45 is basicly a silicon alloy steel similar to 5160, but with about 2% silicon. Unless the HT was bad the first time, there is no reason to redo it.
Stacy

 

[TIZWIN]

Thank you all. How can I judge the quality (or lack thereof) of the original heat treat?

Furthermore, how can I judge the quality of the original grind?

Is there any other way--a regrind perhaps--to get the most out of this hunk of steel?

 

[Nathan the Machinist]

"Thank you all. How can I judge the quality (or lack thereof) of the original heat treat?"

Well, a Rockwell hardness test is a start. However, many steels can be heat treated to a particular Rockwell hardness, but perform differently depending on heat treat. An extreme example would be a blade in the as quenched condition that was cooled too slow to get under the TTT nose, so was full of pearlite. This blade would be too weak to take or hold an edge. A more common example would be a blade with retained austenite. Or quenched from a non-optimal temperature. Or baked at too high a temp for too long, causing grain growth....

The short answer:
If the knife takes and holds an edge well, it was heat treated right.

"Furthermore, how can I judge the quality of the original grind? "

Look at it.

"Is there any other way--a regrind perhaps--to get the most out of this hunk of steel?"

You can heat treat a sharpened blade, it won't roll. The problem is the thin section at the edge can lose it's carbon to the furnace atmosphere as CO2. Or burn up if using a forge. I use argon or foil in a electric furnace when I HT to prevent these problems. Count on a few good sharpening to get down to virgin metal again.