I made a Burke Bar

[Alaskan Bladesmith]

On 11/17/2021 at 7:01 AM, Merlin05 said:

Speaking of welding on spring steel:

IMO, Scott made two mistakes when he made his Burke bar:  He hardened the bar, then tempered it.  Despite spending quite a bit of time discussing tempering, i don't think he tempered it to a high enough temperature.  The other mistake was that he left a forging defect right at the bend of the bar; he called it a "Beauty Mark".

Scott made this bar for fellow YTer Andrew Camarata - and Andrew promptly broke it.  He very briefly shows the repaired bar in one of his videos and it appears it broke right at the forging defect near as I can tell.  The repair?  Andrew welded it right up; says it has worked fine since then (see his comments in the video in the OP.

So, relevance to this thread:  Everything I've read for pry bar tempering is to leave it as-is after normalizing; the failure mode should be bending, not breaking.  Granted my normalizing procedure may not have hot  enough or long enough to cool or whatever.  This steel has never been hardened or quenched since it left the factory; it's been brought to forging temps, not once but twice and it sat in a "tempering" oven for 6-8 hours total.  I plan to heat it up one more time to at least a dark blue temp before I put it into any heavy use.

If it breaks, so be it; I've got tons of leaf springs hanging around here.

Im curious what the broken Burke bar looked like in the middle of the broken section itself. Steels grain structure never lies and can easily be seen with the naked eye. A coarse, sandy grain structure is a sign of overheating in the quenching process and even though it may be hard, makes for very weak steel. The steel, when quenched at the appropriate critical temperature and then broken (prior to tempering) will look smooth as silk. If it is given an appropriate temper after being quenched at the correct critical temperature, it essentially cannot be broken. Scott did temper the steel long enough and hot enough for the intended purpose although its typically a good idea to give it a 1 hour tempering cycle to insure there is no untempered martensite. Based on the blue color he described, the steel was at approximately 550°F. What he did is called flash tempering.  I believe he might have gone wrong resulting in a break for one of two reasons: 1. Didnt quench at critical temp or 2. He finished the cooling process in water. It is very risky to finish cooling medium to high carbon steels in water. Once its temperature has been driven down to about 400°F in the first few seconds of quenching, it will continue to air harden as it cools. Also, not to pick at him too much but Scott was a bit off on his terms-kinda funny hearing his discription of the heat treating process. The terms are actually:

Martensite is hardened, untempered steel;

Austenite is steel at critical temperature

Ferrite is steel in its annealed state

 

[ThomasPowers]

And Pearlite, Bainite, Cementite? 

[swedefiddle]

And Pearlite, Bainite, Cementite? 

You can buy them from the Hardware Grocery Store!!  LOL

Neil

[Alaskan Bladesmith]

Thomas Powers, yes sir!