Scottish Late 18th Century Blade - Tempered?

[Battara]

I am straightening a Scottish dirk from the late 18th century and was wondering if the blades from this period were tempered.

Does any one know?

[kronckew]

Have a look at https://hal.archives-ouvertes.fr/jpa-00222126/document

It also has a list of references at the end which may be useful.

Are you talking about heat treatment of steel, or just the tempering phase.

A synopsis of heat treating, the simple version:

High carbon steel, which can be hardened and tempered was not a science, but an art until the19c, but was done since the early Greeks.

HC Steel is heated to critical temp - around 800C. where it becomes non-magnetic. smiths often have a high strength magnet handy to check. It can then be quenched in the fluid most proper for the steel, ranging from air, water, various oils, etc. Historicaly even plunging into slaves, the blood would add a bit of case hardening carbon. when quenched, the steel is hard and a file (itself a hardened steel) will skate over it rather than cutting in. It is also brittle and can break if dropped or stressed.

It must be tempered, reheated well below the critical temp which reduces the hardness and 'toughens' the steel. The temperature is judged by eye by the smith, based on the colour the steel assumes, a nice blue is typical. More scientificly they can be heated in a modern temp. controlled oven to the temp. recommended by the steel supplier. It is then quenched in fluid again to lock the crystalline structure. The degree of tempering ischosen to give the required hardness, if too little, the edge will still chip brittley or too much and it will be too soft to hold an edge. This in the 18th century was still an art and results varied based on the competence of the smith.

Get it wrong, "lose your temper",and you may need to normalize or anneal the steel by re-heating it to critical and letting it slowly cool, either in air or packed in insulation, to reset the steel back to where it was before you heat treated it.

You can also 'differentially' heat treat by using an insulator like clay on parts of the blade, and/or by forge welding different carbon content steels on edgeg and the spine. when quenched you can get a hard edge for sharpness retention, and a softer spine for strength.

I've seen a Nepali Kami (smith) Harden AND temper a khukuri by heating it to critical, then pouring boiling water from a kettle onto the edge, but not the spine, the edge hardens, the spine cools slower & tempers itself. The kami allowed to do this is usually a master with a lot of skill. It's one form of differential heat treating.

Pattern welding to combine known high carbon steel to milder steel, then heat treating is also done, and called 'damascus'. It still has to be heat treated.


The answer to your question is 'probably', depends on how good the maker was. Some were likely very well tempered, some not so well. Depends on the maker and the acceptance standards and test of the purchaser. A good blade will pass the british proof tests, bending rather than snapping in two, but springing back in line. You probably should not try that at home.

19c they got better steels and better contolled heat treatments.

[Battara]

Many thanks kronckew. Very helpful.

[Jim McDougall]

I agree, fascinating insight into the metallurgical aspects of these blades, thank you Wayne!!! While I have always studied the history of these, this surely adds great dimension.

[kronckew]

Y'all are most welcome. It's the engineer in me. the Riddle of Steel.

[Helleri]

Originally Posted by kronckew

Have a look at https://hal.archives-ouvertes.fr/jpa-00222126/document

It also has a list of references at the end which may be useful.

Are you talking about heat treatment of steel, or just the tempering phase.

A synopsis of heat treating, the simple version:

High carbon steel, which can be hardened and tempered was not a science, but an art until the19c, but was done since the early Greeks.

HC Steel is heated to critical temp - around 800C. where it becomes non-magnetic. smiths often have a high strength magnet handy to check. It can then be quenched in the fluid most proper for the steel, ranging from air, water, various oils, etc. Historicaly even plunging into slaves, the blood would add a bit of case hardening carbon. when quenched, the steel is hard and a file (itself a hardened steel) will skate over it rather than cutting in. It is also brittle and can break if dropped or stressed.

It must be tempered, reheated well below the critical temp which reduces the hardness and 'toughens' the steel. The temperature is judged by eye by the smith, based on the colour the steel assumes, a nice blue is typical. More scientificly they can be heated in a modern temp. controlled oven to the temp. recommended by the steel supplier. It is then quenched in fluid again to lock the crystalline structure. The degree of tempering ischosen to give the required hardness, if too little, the edge will still chip brittley or too much and it will be too soft to hold an edge. This in the 18th century was still an art and results varied based on the competence of the smith.

Get it wrong, "lose your temper",and you may need to normalize or anneal the steel by re-heating it to critical and letting it slowly cool, either in air or packed in insulation, to reset the steel back to where it was before you heat treated it.

You can also 'differentially' heat treat by using an insulator like clay on parts of the blade, and/or by forge welding different carbon content steels on edgeg and the spine. when quenched you can get a hard edge for sharpness retention, and a softer spine for strength.

I've seen a Nepali Kami (smith) Harden AND temper a khukuri by heating it to critical, then pouring boiling water from a kettle onto the edge, but not the spine, the edge hardens, the spine cools slower & tempers itself. The kami allowed to do this is usually a master with a lot of skill. It's one form of differential heat treating.

Pattern welding to combine known high carbon steel to milder steel, then heat treating is also done, and called 'damascus'. It still has to be heat treated.


The answer to your question is 'probably', depends on how good the maker was. Some were likely very well tempered, some not so well. Depends on the maker and the acceptance standards and test of the purchaser. A good blade will pass the british proof tests, bending rather than snapping in two, but springing back in line. You probably should not try that at home.

19c they got better steels and better contolled heat treatments.

A few things here...

~ Heat treating temperatures can vary a fair bit. It depends on the carbon content of the steel, What amount by weight and what type of impurities are present, The thickness of the piece, and what degree and type of heat treating is desired.

But 800°C is far too high (more than double) the maximum temperatures needed in virtually any steel tempering process. 170°C-390°C is the range at the extremes for steel tempering.

~ Plunging a heated blade into a slave to temper or case harden is in my estimation complete fantasy. I've never seen any compelling evidence for this trope of fiction having actually been a practice in any time or any place.

Moreover it makes no sense. Given the investment one would have in a slave (housing, feed etc.) This would be economically not viable. I've also heard that this would be done with criminals who were condemned to die. But even then it makes no sense. A blade is effectively not sharpened at the point of heat treatment. And while very hot, it's not hot enough to make it's passage through flesh any easier for being not sharpened. Plunging a blade into a person at this point would be damn near impossible.

That's not to say that metal workers have not used a variety of pasty concoctions to case harden blades (Though this is mostly done by blacksmiths for things like files and rasps). Some recipes of which may include crushed bone, shell, minerals, livestock blood, and even animal urine. Though the efficacy of these are questionable at best.

Largely because we can't test them. As most metal workers who engaged in any type of heat treatment if long enough in the game had such a paste, powder, or fluid. But kept the majority of it's ingredients (at least) a secret. But also because such things are more akin to alchemy than chemistry.

[kronckew]

You are again confusing heat treatment's HARDENING phase with tempering.

Hardening is done from the critical temperature where the steel is no longer magnetic, it varies on the steel composition a bit, 800 is just an approximation.

Tempering is indeed done at a much lower temperature in the range you mentioned to relieve brittleness and give a softer but tougher structure as a final phase.

Using the term 'Tempering' to cover both phases is inaccurate. Differential heat treating where a blade is hardened at the edge and self tempered at the spine is a technique used by some experienced bladesmiths mostly with varying results.

The live slave thing is of course a myth, but corpses would be readily available.

[Helleri]

Sorry I actually just misread what you wrote regarding hardening vs. tempering.

[Battara]

The blade seemed to be moderately hard but not brittle. After I did some more research and read your comments here, I slowly and carefully bent the steel blade back into straight form without snapping it.

So I did not need to reheat but will keep this as a second option should I get into a similar situation.

Again many thanks to all of you for your input.

The first picture is how I got the blade which was roughly 20 degrees off center.

The second picture is after I worked on it, which is now roughly straight.

[Battara]

I was debating on brazing the crack with silver, but have decided to leave it as is for now. The blade is from a cut down Scottish or English sword.

For more pictures, here is the thread: http://www.vikingsword.com/vb/showthread.php?t=24495