Can one fairly easily harden/toughen steel?

[Chris Green]

I have a couple of weed forks which have flat tines. These are much easier than the round or square ones on ordinary forks to push into hard ground to extract weeds.

However some of them (not all) don't have tough enough tines, they bend when you try to lever out weeds with them.

Is there any straightforward sort of heat treatment I can apply to try and make the tines stiffer? These are just steel, not stainless. If it doesn't work then I've not lost anything really as they're not very useful as they are.

[Harry Bloomfield, Esq.]

Chris Green laid this down on his screen :

Get the steel cheery red, then quench it rapidly in water or oil.

[Roger Hayter]

Unless you want them to snap off instead of bending, a little tempering might be in order. Outside my experience, so I am not advising how!

[Fredxx]

I would say no. If mild steel with very little carbon content it is very difficult to harden by the typical tempering of heating and quenching.

However it might be worth trying, as even mild steel has some carbon content. Some say you can:

You should be able to test with a file before and after to see if the surface shows any indication of hardening.

[Andrew]

Think laterally. Soak the soil around the weed with a hosepipe and this will loosen the soil, requiring less effort to extract the weed.

[Chris Green]

Given that there's 7 acres to manage this might use rather a lot of water! :-)

[Fredxx]

It's also a lot of ground to fork!

[Max Demian]

The Vikings found that heating to red heat and quenching in the urine of a red headed boy to be effective (if you have such a thing handy).

[Tim Lamb]

I have a very vague recollection that an idea of the carbon content can be found by observing the sparks produced by grinding the material.

Mild steel sparks simply fade as the heat dissipates. Carbon steel sparks *burn* producing tiny radial spikes.

[John Rumm]

Much depends on the type of steel. If it's just a mild steel, then you won't get much if any hardening. A carbon steel will harden - although it's quite tricky to control the amount. You will typically want a cycle or two of tempering after hardening to draw back the hardness a bit, so you get a tool that is hard and tough, but not so "glass" hard that it shatters (potentially very dangerously) the first time you put any bend on it.

Normally heating to cherry red (or just beyond the curie point), then quenching in oil will give a decent hardness. Then temper in an oven for a couple of hours at a high oven temperature to stress relieve and anneal it slightly. Let it cool fully, then repeat.

You will probably need a forge of some kind[2] in order to get it all the parts of it up to quenching temperature at the same time though.

(or possibly some fire bricks and some big F'off blow torches).

[Tricky Dicky]

The forks are most likely mild steel which cannot be effectively hardened or tempered, the best you can do is case harden by enriching the surface with carbon but all that will produce is harder wearing surfaces but with a malleable interior so will not prevent the bending you are experiencing. Only medium and high carbon steels can be hardened and tempered.

Richard

[newshound]

+1

Certainly some forks are made from reasonably high carbon steel, but cheaper ones are not. You only need to do heat and quench to find out, followed by a file test. Unless they come out unfileable you should not need to temper.

I'd expect to be able to harden tines one at a time, by heating with a good gas torch (ideally propane) while having something like a brick either side and one underneath. Proper firebrick or vermiculite slabs as used in woodburners would be even better. Although each successive tine will tend to soften the cross-piece and the adjacent tines.

[Brian Gaff (Sofa]

You need to heat them up so they glow then quench them fast in cold water. How successful this is seems pretty variable, we did it in metalwork back in school in the 60s. Brian

[Brian Gaff (Sofa]

Yes, it really depends on the steel in question, and clobbering it a bit is a help, but we are into blacksmith territory here, so find one locally and see what they say, Its probably safer anyway! Brian

[nightjar]

On 26/07/2021 14:57, John Rumm wrote: ...

The latter always worked well for me.

[Fredxx]

Something I wasn't aware of:

And in practice

[John Rumm]

My 36kW output roofing torch would probably do a fairly decent job if you can avoid setting your trousers on fire!

[newshound]

The trouble with flat tines is that they are going to have more of a tendency to bend than symmetric ones with the same amount of metal.

[newshound]

That would do the whole fork in one go, handle and all, if you contained it a bit!

[Chris Green]

Absolutely, however since it's well nigh impossible to force round or square tines into our soil when it's a dry as it is at the moment I don't have much choice.

I do have two weeding forks whose tines are tough enough so it is possible.

To deal with really big weeds I have to use a 'normal' fork but that involves driving it into the ground several times to get it under the weed and that's not a particularly accurate process and takes quite a while.