hardening cutting edges

[Lance Takara]

Is there any way to "reharden" edges of hand tools once they are heated by welding or grinding?

Does reheating with oxy-acetylene then quenching in water work to reharden edge (I know it also makes the edge brittle)?

[75]

Heat-treating is a fairly comprehensive topic - there are 40 pages devoted to it in the Machinery's Handbook - but in a nutshell, yes the heating and quenching does harden the edges. The reason they become brittle is because they are hardened.

I'm assuming these tools were hardened to begin with since not all steels are suitable for hardening.

Again without getting too deeply into the technical/engineering details (which are over my head anyway :blush: ) one thing you can try is quenching in oil instead of water since oil will cool the steel at a slower rate than the water.

[chip hayden]

yes you can reharden but trial and error and experience play a major part when doing it in the field.
i prefer oil over water for quenching it causes less distortion and brittleness. i use atf but be carefull it can "flash over" so watch out for flames.
get the area you want to harden cherry red then dip in the atf and move it around. polish steel back to silver then apply a neutral flame towards the heel of the tool. watch the color change especially at the surface you want to remain hard. don't try this in bright light. the longer the heat is applied the softer the tool will be "drawn" or tempered. then quench a second time to "freeze" it in this state. this is where experience comes into play. light to dark straw color works well for many tools but each application is different as well as the chemistry of the steel. just think about what the tool does. do you strike it? does it take shock loads? does it have to resist abrasion? i'm sure other people can give you more info. have fun-be careful, chip.

[Lance Takara]

Thanks for the info, guys - always appreciated.

75, the edges were once hardened. They are simple digging spades, but we modify them such that I can't just go and replace them. We also use them to full capacity and beyond.

Chip, your reference to "heel" means opposite (far away?) side of hardened edge?

Is "drawn" or "tempered" basically hardened?

Thus, if I understand correctly, the longer and thus slower the heat is applied, the metal will reach its maximum potential hardness or did I misunderstand.

Lastly, stupid question, but I've never experienced auto trans fluid flaming. How do you get it under control? Obviously, it's not like a carbon material fire.

As you can see, I'm not into reinventing the wheel. I'm more than grateful to learn from you experienced guys and would be more than glad to share any info I might have to others.

[chip hayden]

by heel i mean away from the edge of the tool. about 2 inches back from the edge.
tempered means to relax or slightly soften the metal. if it's fully hardened it can shatter like glass. here's where trial and error comes into play. to hard it splinters-to soft it folds over. also this works with primarily run of the mill 1040 steel + or - a few points of carbon. as other elements are alloyed with the iron and carbon[boron, manganese,etc.] this changes the physical properties of the steel.
there is a time/temperature curve but don't be concerned with this. the slow heat is to watch the color change to know how soft[temper] the steel gets.
the atf just burns while the steel is in it, maybe. it will go out when the steel is removed. just do it in a steel pail and put a lid on it when you remove the steel.
anyone else please feel free to jump in if i misspeak[lie] or give bad info.

[75]

Chip - there ain't nothing wrong with your advice! :)

Your definitions are good too.

Lance - without getting too deeply into the science of metallurgy and related fields, in a nutshell the rate of cooling is a bigger factor in the hardness of the steel than the rate of heating. If you take two identical spades and heat them to the same temperature, then cool one quickly by quenching and let the other cool on it's own, the quenched one will be hard (and brittle) and the one that cooled down slowly will be soft (annealed)

"Drawn" and "tempered" are actually synonomous according to the Machinery's Handbook, and refer to what Chip describes: slightly softening the hardened metal to reduce the brittleness.

"Hardened" is the steel in it's heated/quenched, and thus brittle, state.

[diginahole]

OK Lance, you have piqued my interest. What do you do to your spades, and why?

[Lance Takara]

Note that my terminology might be a little different.

Here was the dilemma. For small tasks, a short handled digging spade was adequate. For larger tasks, a miniloader was necessary. However, for tasks in between, the spade was too slow and made the work difficult while the miniloader either was too much to set up for such a task or else there was no access.
In other words, the tools we were using did the job but were inefficient. In that context,

We basically made a digging spade with a long, heavier (metal pipe) handle. Also, we added a little more reinforcement in the spade section. The end result is a heavier long tool where the weight is more distributed in the spade section. It's a simple looking tool but

The benefits are many.

1. This particular tool functions as a digging spade while standing up for more leverage
2. It has the weight similar to a digging bar (we call it an o'o here) for digging in hard clay soils or rocky areas.
3. It has the feel of a pick with the weight concentrated in the head
4. Because of the reinforcement, we can use it to pry and set good sized rocks similar to an o'o
5. All tree and shrub removal in this medium range is a piece of cake when the miniloader is not available for whatever reason
6. One tool has the best features of many others so we don't have to keep switching tools - a real timesaver.

Thnough simple looking, there are many uses for this tool that are only realized once you use it.

[diginahole]

Great Idea....

I see many uses for such an impliment of destruction. It reminds me of a story from few years back. A customer was admiring my spade and I told him how much it cost ($70), he said I bet you go through a few of those. Well 5 minutes after boasting how I never broke one yet I tried to pop out a large rock, you can guess what happened...GRR. I still have the spade without the handle, I just may try to attach a nice long solid steel handle to it.

[Lance Takara]

Put a little reinforcement in the neck area, where the handle attaches to the spade head - similar to an extended wrench where the handle is thick at the wrench head and tapers to the tip. (Obviously, you don't have to reinforce the entire handle length, though)

Your toughest guy would be hard pressed to break much less bend your super duty tool now.

[rdln]

Also guys, isnt there a powder that you coat steel after heating that "case hardens" called caseite? I used it once on an ice spud a made.

[chip hayden]

yes, it's kasenit and it works quite well.

[Lance Takara]

Does kasenit work on standard digging tool steel (Sorry I don't know the technical term for this type of steel)? Also, does it work just as good as the quenching method discussed in this thread for hardening edges?

[chip hayden]

imo kasenit works really well because it case hardens even low carbon steel. what you end up with is about a .010 thick hardened shell with a soft core which can stand up to shock. it's easy to do, cheap, and safe to work with.

[Lance Takara]

Who is the manufacturer of kasenit? I am looking for a distributor.

[chip hayden]

try MSC 800-645-7270 or mscdirect.com part number is 00263012 for 1 lb. or 00263053 for for 5lb.?

[Lance Takara]

chip, backtracking a little . . .

How does this kasenit work? You mentioned a thin outer layer (of kasenit) is the hardened layer while the inner, original steel is the "soft" layer.

Does that mean that if the protective outer layer is damaged or "torn" then the tool will dull easily? If so, then would more than 1 hardened outer layer make the tool edge last longer?

[75]

I don't believe it's really feasible to have more than one "layer" of casehardening - in a nutshell, the way the process works is by increasing the carbon content on the surface of the steel so that outer "case" can then be hardened. There's a limit to how deep that increased carbon content can go.

Along the same lines, although a different approach, when doing hardsurfacing "buildup" on crusher hammers it isn't possible to add layer upon layer of hard surfacing - it will break off in chunks if that is done. My experience has been 1 to 2 layers, tops. Once those layers wear down it is OK add more material because the hardsurfacing has been worn away at this stage. Crusher buildup often ends up being a daily or every other day operation for this reason.

[chip hayden]

i couldn't explain it any better than 75 did. chip