Does tool steel conduct electricity?

Poor.

Against copper

Conductivity

7% IACS

What that means

A conductor of the same size carries about 7% of the current copper would for the same voltage drop, so replacing copper with it means increasing the cross-section by roughly 14.3×.

IACS is the International Annealed Copper Standard, and the reason the industry quotes percentages rather than absolute figures is that the comparison is what matters. Aluminium at 61 % needs a conductor about 1.6 times the cross-section of copper — and is still lighter, which is why every overhead transmission line is aluminium and no house is wired in it.

How it compares

The ones that surprise people

• Diamond is an electrical insulator and simultaneously the best thermal conductor known — about five times better than copper at moving heat. Structure decides both, not composition.
• Graphite is the same element as diamond and conducts electricity well, because its layered structure leaves one electron per atom free to move.
• Carbon fibre conducts. People treat composites as plastic, and lightning strike protection on composite aircraft is a serious design problem because of it.
• Pure water is an insulator. Tap water conducts because of dissolved ions — the hazard is what is in the water, not the water.
• Air is an excellent insulator until roughly 3 kV per millimetre, at which point it ionises and conducts. That is what a spark is.