Giving a mild steel bar a hard point.

[rjimmer]

The old man next door had a round bar that was used for making starter holes for fence posts. It was about 4-5 feet long with a formed 'mushroom' head and a squared section about 8-9 inches long near the point, which was very hard. The bar appeared to be soft iron/mild steel. My father explained that the hard point was achieved by splitting the end of the bar into 4 quadrants, inserting part of a rat tail file in the middle and forging the 4 quadrants around it. The temperature at which the job was quenched in water was critical, he told me. As the forged point cooled down the correct time was when a certain colour reached the point. I think it was orange! Any one ever done this?

[Eddie Mullins]

I am not familiar with this exact application,but what you are describing is very similar to the insertion of a higher carbon bit into a lower carbon body of an axe.

[VaughnT]

No.

 

Sounds like you're describing a star drill.  It might have a high-carbon cutting edge welded into it, but it wouldn't have been quenched in water because that's too fast a quenchant and would shatter the carbon steel.  Tempering the hardened steel does rely on color to guide you, but that's it.

[ThomasPowers]

If it was old enough the high carbon insert may have been a water quenching steel.  Putting a steel piece to make a cutting, pounding, etc end was a fairly common task for the old smiths as even as late as the American Civil War high carbon  steel could be 6 times the cost of iron. So it once was common to forge weld higher carbon steel for the working ends of axes, picks, adzes, hammers, drills, chisels, knives, etc.  If the steeled end/edge wore out you would take it back and the smith could weld another on.

 

 

As for the temperature to quench at it sounds like he is trying to describe a one step hardening and tempering.  The temperature you quench a steel at depends on the alloy, quenchent, intended use, skill of the heat treater, etc.  In bladesmithing we try to quench on a rising heat rather than a falling heat as over heating steel is bad for it.  However if they are quenching right after forge welding it would be a falling heat and quenching it one high enough to harden it but not so high as to make it crack would be a skilled judgement call.

 

Nowadays we have such an abundance of cheap high carbon steel available to use we tend not to steel ends of low carbon items save for stuffy purists getting historical replica work done---and are willing to pay the greater price for the extra work.

[John B]

 

As for the temperature to quench at it sounds like he is trying to describe a one step hardening and tempering.  

 

 

Hi Thomas, Is that the same as what I would term a "Double Dip" technique?

 

I.E. Weld is consolidated, then item is quenched at high end heat (30 to 50 degrees C above the Upper critical point)  to induce hardening, then removed from quenchant at a suitable temperature, and then the residual heat allowed to get workpiece to the required tempering colour, then catch it at that temperature by dipping into quenchant again.

 

Takes some practise and experience, but one way to produce the desired effect.

[ThomasPowers]

Yup the old term "tempering" was often used to cover both hardening and drawing temper on a piece whereas today we split them apart into hardening and tempering (and many are quite fussy in the terminology...I myself haven't had any luck with the double dip technique when working on claviers....)

[Frank Turley]

I made a digging bar by upsetting and forging a cleft scarf (bird's mouth) on the long, mild steel bar. The square, water hardening high carbon steel was tapered to fit inside the cleft and was overly long, so we could start the weld by end-hammering while both pieces were still in the fire. We used a sweating heat, which is a welding heat with no sparks. Our method required two men. Once the weld was cohering, we carried the weld to the anvil and double-struck it. Then it was heated and hot cut to size using hardie, hot-cut and sledge hammer. Another two welding heats were taken to insure a good weld and to smooth the forging, trying to get rid of shuts.

 

John B. talked about the one heat method of hardening and tempering which Francis Whitaker called "the reserve heat method." This takes practice depending on the size of stock and length of heat. You quench out part of the cherry red hardening heat, vertically and with agitation. I usually quench at least half or more of the heat length. Then you quickly abrade the end to bare metal and watch for surface tempering colors. I took my cutting edge to a full blue, about 560F. Requench to hold the temper. Don't allow any more colors to chase down.

[Eddie Mullins]

John B. talked about the one heat method of hardening and tempering which Francis Whitaker called "the reserve heat method." This takes practice depending on the size of stock and length of heat. You quench out part of the cherry red hardening heat, vertically and with agitation. I usually quench at least half or more of the heat length. Then you quickly abrade the end to bare metal and watch for surface tempering colors. I took my cutting edge to a full blue, about 560F. Requench to hold the temper. Don't allow any more colors to chase down.

 

Not the method I am ready to attempt with knife making, but did this yesterday when making a small scribe. Heated to critical, quenched the lower half with some vertical movement so there was no defined quench line , quick touch to sand paper and waited until I got a dark straw color back, quenched fully.

[John B]

Not the method I am ready to attempt with knife making, but did this yesterday when making a small scribe. Heated to critical, quenched the lower half with some vertical movement so there was no defined quench line , quick touch to sand paper and waited until I got a dark straw color back, quenched fully.

 

and the result ????

[Eddie Mullins]

and the result ????

 

 Successful by my measure, it will scribe/mark mild steel and the point remains intact. It was 5160 BTW.

[Bob Menard]

The original post seems to have been a little bit hijacked. As it has been I'll add a few comments of my own.

Another method of making a hard point on a digging bar is to case harden the end. It is amazing how effective this technique is for improving mild steel. The downsides are if you have to dress the point you can grind the hard shell right off. Another problem, case hardening only effects the surface so if you are banging your digging bar on a rock you can drive to point back into itself because the softer mild steel core is not strong enough to support the hard point. I will use case hardening for tools like top and bottom swages and fullers that don't get dressed.

Francis Whitaker had a few comments regarding tool making. He said you should use known tool steels, preferably new. Then you always know what it is you are working with. He also suggested you should get comfortable with a few grades of tool steel and become proficient with them. Your tool making will be more consistent and you will have a better result in the long run.

Much of my tool making has been influenced by Mark Aspery as evidenced by the tools shown here. I use 4140 regularly and I am comfortable with the techniques of hardening and tempering it. I have to buy it new. Apparently in places in the US where there is oil drilling 4140 lays about in piles and is known as sucker rod. No oil in New England so no sucker rod. Anyhow...

The technique to making hand tools with this material is to forge it to form, bring it above the critical temp, generally orange, and bury in vermiculite to cool very slowly. I find it takes all day to cool with this method so I just leave it in overnight. The next morning it is dead soft, like mild steel dead soft. This is where I do any filing or grinding to final shape. Then the tool is heated back above the critical temp. Not the whole tool but more like 4"-5" of the performance end. The struck end is on its own at this point. I then quench the end 1" or so in water dipping it up and down until water stays on the working end. For me this is a major selling point for 4140, water quench. I then abrade the end of the tool looking for the colors (purple to straw) which are generally an 1 1/2" away from the end. I watch for them to run toward the end, aiming for straw at the working end, and repeat the quench technique again. I re-abrade the end and let the colors run again. The tempering heat is supplied by the residual heat stored in the body of the tool. I will run the colors as often as the tool has heat for which for a chisel or punch is usually 3 times. I did make a hardy hot cut recently that ran the colors 7 times but the body of the tool was stocky.

I don't ever quench the entire tool. It is made harder by quenching the tip and air cooling the rest but it is not made too hard, which would risk the tool cracking during use or making it harder than my hammer, which would be bad for the hammer.

I have had good success with this method and my hot cut chisels work just as well as a cold chisel. I have yet to have a working end fail or a struck end crack.

[ThomasPowers]

Just saw a full stick of 1" diameter sucker rod at the scrap yard Saturday...20 cents a pound.