Brittle Strikers

[Sandhiler]

I took some old metal files I had and heated them till they lost magnetism. I let them cool to room temp slowly. I then worked them at about the same temp into strikers. I reheated them till they lost magnetism and then dipped them in salt water. They throw a huge amount of sparks. But the handles are brittle and one broke when dropped. What's the problem?

 

[ameling]

A flint striker made from a good file is hardened high carbon tool steel. Hardened high carbon tool steel is just ... brittle. Simple fact of life. They are MUCH more brittle than a knife blade, and much harder. So if you drop them on something hard, they can break.

But you can take several steps to make them ... less brittle, without lessing their ability to strike sparks. The one major step comes from a tip from a knife maker. It is called Thermal Cycling. When you are finished forging it up, you heat it to that critical temp where a magnet will no longer stick. You then pull it out of the heat and let it air cool till you do not see any color. Now heat it back up to that critical temp and pull it back out of the heat to air cool again. Do this a third time. Then do the final heat to non-magnetic, and quench. That thermal cycling relieves any internal stress in the steel from the forging, shaping, and bending. It also shrinks the internal grain structure.

After you have finished your heat treating, it will still be brittle - especially thin handle parts. When I have thin handle parts on a striker, I then selectively heat those areas back up - without heating the striking surface of the flint striker. I watch the colors of the metal, and try to get those areas well up into the Blue range. Then I quench it again. That softens up the steel in those areas, and makes them less brittle.

Some people do place their fully heat-treated strikers into an oven and bake them for an hour at 400, 450, or 500 degrees. That baking can also help relieve some of that internal stress in the striker. But it will still be heat-treated high carbon steel - and that will be brittle.

I have heard of various strikers that are almost indestructable. But you have to POUND them against your flint to get a few feeble sparks! They are just heat-treated too soft! To work well, they need to ge almost as hard as you can get them. And that is far harder than a knife blade - more like the edge of a wood chisel or razor blade. If you drop one of those on something hard, they will also chip/break.

So you did not do anything wrong. You just ran into one of the common problems when making a flint striker.

Hope this helps explain a few things.

Mikey - that grumpy ol' German blacksmith out in the Hinterlands

 

[ameling]

When you are forging up your flint strikers, you usually forge them at temps a bunch higher than that Critical Temp - where a magnet will no longer stick. You generally forge well above that temp - in the bright red, yellow, and almost white ranges. That Critical Temp only really applies in the final heat treat.

But if you heat the steel above that Critical Temp, the internal grain structure will increase in size - expand. The larger the internal grain structure is, the more susceptible the steel will be to cracking/breaking after it is quenched. So you end up taking a few steps to help shrink that internal grain structure back down.

Just a few additional thoughts to share.

Mikey

 

[Sandhiler]

Thanks. I appreciate your input and know how. I'll try it when the rain quits and I can get out into my big outdoor shop.

 

[paulvallandigham]

Try clamping some steel scrap stock to the striker portion of the tool when selectively heating the handle portion to the blue colors. The steel scrap will act as heat sinks, and keep the face of the striker from being softened, while allowing you to temper the handles so that they won't break when dropped. That will also go a long way to protecting even the face of the striker from breaking, too.

 

[ohio ramrod]

Steel will work . However I prever brass or copper heat sinks as they conduct heat faster. But if steel is what you have use it!