Edge Hardening with Torch??

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Dt_Trainer

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I had a knife maker advised me that I could heat treat my 1084/1095/ and 5160 blades with my oxygen/acetylene torch and not have to temper them. I have been heat treating my blades with my oxygen/acetylene torch using the process I have read in numerous magazines and books how to heat treat blades with a torch. I have always heated the blade to non-magnetic and then quenched tip down in medium oil. With this process I usually get a pretty heavy scale that I have to grind a way or shine up and then get the blades in the oven to temper them. The knife makers treats the back of the edge toward the guard area and uses that area to draw the red heat to the rear of the edge as he works the torch up and back on the blade from the tip to the guard area. He heats about ½ inch up the edge bevel and once he has a good medium red color he quenches tip down in a good quenching oil. I had 4 1095 blades read to treat so I stopped by his place last night and we treated them. We checked the blade with a file and sure enough we got a uniform hardness on all 4 of the blades and there was very little scale on the blades. Here’s the question the knife maker has been making knives for quite some time and makes beautiful hard working knives, so I am not questioning his methods they sure have worked for him all theses years. I guess I just wonder why I haven’t heard of this process if it will actually save me the time of tempering the knives. He told me tempering the blade really isn’t needed because the back of the blade didn’t get that hot. Does this create any stress in the blade that needs relieving/ tempering? I have definitely heard of differential heat treating and drawing the back of the blade with a torch, could this just be a different form of differential heat-treating I have overlooked.

Again, I want to emphasize that I am not criticizing the way this gentleman does his heat-treating. I am very appreciative of all guidance and training I have received from all the knife makers I have met who have invited me into their homes and opened their shops to me. I am still in the quest for further knowledge.

Any help would be appreciated,


Jim Bunker
 
I've tried it and a bunch of other edge quenching methods. I have found and others may well disagree, that if you do not temper the edge will be so brittle that it is useless.
I do edge quench but still temper each blade. The scale that forms can be removed in a number of ways including soaking in vinegar.
 
Tempering isn't for the back of the blade that was left soft but to relieve sress that builds up in the hardened portion of the blade caused by the transformation of austenite into martensite. I don't think many well known knife makers would leave any knife they made from a 10xx series steel untempered.
 
As the previous posts said...
Wayne Goddard talks about various types of edge hardening (he favors the edge quench) in his books. He says you still have to temper the blade as usual.
 
You have to temper 1095 after treating but then again you said your quenching medium was oil,since 1095 is a water hardening steel oil may reduce the hardness somewhat. I know when I quench with water the steel is extremely hard and brittle. Unless you are trying to get a japanese style temperline,the easy way I found is to heat up the steel and dip the part/edge in the water till cooled much of the way than let the rest air cool. Than I temper till a light straw color comes up. I've worked alot with 1095 and I just hate it. It warps too much its seems my only safe bet is to treat after profiling the blade. O1 is the way to go in my book. But you won't get a dramatic temper line as in the 10 series. Just my 2 cents.
 
Jim,

I won't critize anyway another maker performs his techiques, for we all have our own ways for what we do and expect from our knives. But I would suggest, you perform the brass rod test on your blades to make sure you have achived the right hardness for any particular steel you heat treat yourself. I was told my a mastersmith several years ago that steel loves heat and if kept at the right tempertures for long peroids ( 3 - 1 to 2 Hour peroids when tempering), you will increase the performance of your high carbon steels dramatically. All I can say is, test your blades and destroy a few, after heat treating with different techiques, that will give you the answers you need.

Hope this helps ;)

Bill
 
The method you describe is the way I learned to harden and temper chisels in high school. The heat from the spine of the blade takes the edge back to a tempering heat. It might well work for a man who has practiced it for many years on knife blades.

I do not have that kind of skill to make it work the same all the time. That is why I use the edge quench, then temper.

Bill you are absolutely correct, time at tempering temperature (for lack of a better word) matures at about 2 hours and a slow cool down time for 5160, 52100 and maybe some others. I repeat tempering circles for a total of three cycles, 24 hours in between. It all happens very slowly when done right. Every little bit helps.
 
Yea I kinda thought this would be the case but like I said I don't have the amount of experience that this gentleman has. I really try to read as much as I can and I will continue to temper my blades.

The positive side of this is that I have a really great source of assets here and this knife makers like 5 others in the area have been true wealth of knowledge and have been supremely courteous in allowing me to come to their shops. I have always been able to take the good and disregard the bad. In this case I just learned some good info on edge hardening and thanks to all of you I will continue to temper the same way I have in the past.

Mr. Fowler I would like to note that before I stepped foot in one knife makers shop I re-read your article about etiquette while visiting a knife makers shop so I would make sure not to offend and ask intelligent questions.

Jim Bunker
 
I think I need to apologize for my earlier post as I may have misunderstood how this knifemaker is doing this. I must say I'm still a little confused.

I am familiar with the process Ed talked about. It is also how I've watched some local blacksmiths heat treat and temper hammer faces. The hammer head is heated to non-magnetic and then only the faces are quenched. The faces are then quickly hit on a sander and the heat from the body of the hammer head flows back to the face and the whole hammer is then quenched when the proper tempering color is reached on the face. This does require quick work and a practiced eye.

I didn't quite understand this as the method that was used however. Jim, did you say that the knifemaker in question heated the edge and 1/2" up the edge bevel to an even red and then quenched point first, (which means the whole blade is quenched and cooled at the same time)and then there is no further tempering process involved? If only the edge is heated and the whole blade is quenched then there is no heat left from the spine to flow back to the edge. Does this knifemaker then reheat the spine and watch the colors develop on the edge?

Again I would like to apologize for my earlier post that sounds (as Bill's post reminded me) critical and dismisive. I am actually very intrigued as you say he makes good hard use knives and I'd like to be very clear on the process involved. I feel I am very lucky as several local knifemkers have seen fit to share there knowledge freely with me just as your friend has helped you.
 
No need to apologize Guy, I have always taken this forums to be a friendly place for us to share others views no matter if they are exactly the way we would do it.

You were right I re-read Ed Fowlers response and I understand what he is saying however the maker does it just like you explained he only heats the edge of the blade. He starts at the rear of the blade edge around the ricasso (Sp) and then goes up and down the edge on both sides until he gets a good medium red heat. He then quenches tip first the whole blade until it is cool enough to touch and then does no further tempering as we discussed earlier.

Jim Bunker
 
Thanks Jim for clarifying that. I'd be really interested in hearing how the edges of those knives hold up. I think you ought to do as someone suggested earlier and sharpen one of your knives and see if it chips out at all either in use or using the brass rod test. Hell, the last knife I made from 1084 chipped out just from the pressure of sharpening after a 385 degree temper. I moved the temper up to 400 degrees and probably should have gone up to 420 degrees or so.
 
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