I work with steel, mainly high carbon for making tools because high
carbon steel can be heat treated to make it either soft or
glass-hard, and anywhere between. Actually it’s the cooling from red
heat that determines the hardness; cool high carbon steel very
slowly to anneal, and quench in water for glass-hard. Tempering is
the gentle heating of glass-hard steel that reduces the hardness
(and brittleness) and increases the toughness.
Mild steel is softer than the softest high carbon steel. It’s great
for bending and forging into various shapes. It can be treated like
copper in that it will work harden and will anneal by heating to red
hot and letting it cool in the air. It can be given a glass-hard
surface by what’s known as case hardening.
Stainless comes in two main varieties, soft bendy and hard tough.
The former is more ‘stainless’ but cannot be hardened; it is non
magnetic. The latter is less ‘stainless’, is often very hard and/or
tough, and is magnetic (a magnet will stick to it).
All steels can be sawed and filed except for those in the hardened
state. A file is close to glass-hard, it is high carbon steel and
the teeth were formed while it was annealed, then it was hardened to
glass-hard, and then tempered just a little so that it won’t snap so
easily. A file will cut all steels that are softer than the file.
Saw blades are similar, but tempered a little more than a file for
High-speed steel and tungsten carbide are always hard and cannot be
softened. These steels are best cut with diamond tools, and they
will cut the harder steels.
The best place for small quantities of steel is the scrap pile
provided you can identify the various irons and steels. You need a
magnet, a file, and a grinder. Magnet says ‘soft stainless’ if it
doesn’t stick provided you can feel the weight and rule out
aluminium and it’s alloys. If the magnet sticks then try a file…
If the file teeth can grab and bite when filing then it’s softer
than the file. If the file skids over and cannot bite then your
steel is harder than the file.
The sparks from the grinder will tell the difference between mild
steel, high carbon steel, and cast iron. Red dots flying off the
grinder says cast iron, a few sparkles says mild steel. If the red
dots expolde into a sparkle they are saying ‘carbon’…the more
sparkles the higher the carbon in the iron; thus the the more
sparkles the better the steel. Cast iron gives all red dots and no
sparkles. High carbon steel gives all sparkles and no red dots on
Try known steels on your grinder and you will see. Knowing your
irons and steels is really good to know.