Flint and steel: what kind of steel?

[Keith_Beef]

It's been a long time since I poked my head around the door, and I'm here with a question.

What kind of steel do you use for a flint and steel?

I ask the question, because I had a vague memory that the mechanism of flint and steel relies on the flint knocking small chips off a piece of meium to high carbon steel, and that the striking converts kinetic energy into heat, then this heat ignites the carbon in the steel chip.

One day last summer, out walking about with a friend and his daughter, the daughter found a big couple of bug chunks of flint and started bashing them together to try to get a spark.

When we got home, I got a big old file from my scrap bin (it's waiting for me to turn it into a camp knife) and we tried to strike a spark from it. Well, it didn't work; we just broke the flint into two pieces.

So now, I wonder if an old file, annealed, would make a good striker.

 

[Ogri the trog]

An old file should make and ideal striker - but if you anneal it, you'll kill it!

I use old files to make strikers - cut to length and grind off some of the teeth, but keep it cool or be prepared to heat treat it afterwards. I have been caught out once or twice, when finding files that I thought were old, but turned out to be case-hardened mild steel - which will not throw a spark.

I am surprised that you didn't get anything from a file / flint combination as I use just that all the time.

ATB

Ogri the trog

 

[Wayland]

My best striker is made from an old file.

I usually grind the teeth out, forge them to shape and then heat them to red/yellow hot before cold quenching in water.

Sets my blacksmith friends teeth on edge but creates great sparks.

 

[Dave Budd]

Most likely the reason that your file didnt work was because of the rust! Grind it back to ckean steel (without over heating) and it'll work, assuming that your technique is ok ��

 

[Tommyd345]

I thought it was the flakes reacting to the oxygen in the air, causing the sparks? As the process of rusting gives you rust and heat, but a large object gives out an extremely low output. But a tiny shard gives out a lot or heat ergo the spark?

 

[Wayland]

I heard that it was the friction caused by separation that cased the fragments to burn but that of course also requires oxygen so it is probably a combination of the two.

Would be interesting to have that confirmed though.

 

[Ogri the trog]

I thought it was the flakes reacting to the oxygen in the air, causing the sparks? As the process of rusting gives you rust and heat, but a large object gives out an extremely low output. But a tiny shard gives out a lot or heat ergo the spark?

I heard that it was the friction caused by separation that cased the fragments to burn but that of course also requires oxygen so it is probably a combination of the two.

Would be interesting to have that confirmed though.

From what I think I have found out - it is indeed a combination of the two....

The tearing of the iron fragment from the surrounding material begins the heating process (just as any metal working process) - and with it being so tiny, the ratio of surface area to the mass of the fragment means that the oxidisation process starts to speed up - as it gets hotter, the reaction gets faster and faster until it becomes an incandescent spark. And the reason that other iron items don't simply burst into flame, is that the surface area to mass ratio is the polar opposite, conducting any heat away from the surface and not allowing the process to get any faster than basic rusting.

Oh, and the reason that it needs to be high carbon steel is that the heating effect of removing particles from a softer iron does not cause sufficient heating of the fragment.

ATB

Ogri the trog

 

[Janne]

It seems logic that it is the steel particles that are the spark, but what bout when you bash together Quartz? What can that spark be?

 

[Nice65]

It seems logic that it is the steel particles that are the spark, but what bout when you bash together Quartz? What can that spark be?

It's an electrical spark. The Pietzo Effect.

 

[Tommyd345]

Strike a sharp edge of the flint a glancing blow with the high carbon steel. Doing this just right takes practice. Very tiny particles of fresh iron fly out from the steel. Upon contact with oxygen in the air, the surfaces of the iron particles spontaneously ignite and give off heat as they oxidize (rust).

Direct quote from google

 

[Wayland]

And what does "Google" say about the residual Kinetic energy and friction in the process?

I have fine iron dust and filings all over my workshop that rust slowly without burning.

However, if those filings are caught by the heat of a gas flame they do burn and sparkle.

That suggests to me that some external source of heat is required to speed up the reaction.

The only external source I can see is the kinetic energy being converted to friction in the striking process.

 

[C_Claycomb]

There are three sources of heat in machining, which is what we are talking about when discussing a flint edge removing pieces from a steel striker. Deformation ahead of the cutting edge, shear at the cutting edge and friction of the chip over the edge. I believe that the deformation and shear are the largest two contributors. Like many reactions, energy is needed to get the exothermic iron/oxygen reaction started, up to to a point. Fine enough iron powder can combust all by itself, but grinders don't produce it that fine. Annealed steel will spark on a grinder because the grinder can put enough energy into removing the right size chips. Striking a flint has a lot less energy available and there is more time for dissipation.

Clearly, chrome content resists oxidation, hence stainless steels don't spark well. I am still thinking through why alloy tool steels, even O-1, spark less well than plain carbon steels at the same hardness. Is it the greater abrasion resistance making it more difficult to machine?

There is another factor that may make the file less willing to spark, in addition to needing the teeth ground off, and the rust removed, assuming it isn't just case hardened. My experience has been that I get better sparks from a narrower piece of steel. A 5mm thick file gives plenty of material to hold, but it has quite a wide striking face. The most impressive sparks I have ever seen struck were created by Mors Kochanski using a broken section of cheap all-hard carbon steel hacksaw blade. From a standing position he had sparks that hit the ground!

 

[mrostov]

In days past people would buy an iron striker from the local blacksmith. On the frontier they were a common trade item with the tribes.

This is the old style striker I have. It is is sold by Dixie Gun Works. http://www.dixiegunworks.com/product_info.php?products_id=3674

 

[Wayland]

I regularly hit the ground with sparks and have to be careful not to hit my audience sometimes.

I use a thick 6-7mm file as the base material of my most regular striker so I don't think thickness is an issue.

I do find that smoothness of the striking surface is important though.

My best strikers are so worn that they have no roughness on the surface at all.

When making them I usually polish the surface before hardening and slightly after.

[video=youtube_share;pmTssR5csdg]https://youtu.be/pmTssR5csdg?list=PL-AavLd_tC-d-4MLSjpp5ffWYCObmL4hs[/video]

 

[rancid badger]

heres a few I made a while back:

[video=youtube;984Jnu_l5LE]https://www.youtube.com/watch?v=984Jnu_l5LE[/video]

Some were made from vintage files and others from modern allen keys. They all worked fine eventually, some just needed re-heating and quenching.
Cheers

Steve

 

[John Fenna]

I have no idea about the whys and where-fors of the act of getting a good spark from flint and steel - all I know is the aesthetically rather unpleasing flint and steel firelighting kits that I make (and have sold hundreds of over the years) just use sections of old files (the older the better - some modern ones just do not work!) that I grind the edges of to a smooth finish....
They give showers of sparks!
All I do is snap the file to length, grind the edges smooth - and remove all sharp edges for safety - and strike them against sharp flint - not very pretty but very effective!
The strikers I have forged have relied on the same files, heated cherry red to forge them and quenched in water. Great sparkers!