Mild steel is the easiest and cheapest metal to mark with a fibre: it absorbs the beam well, reacts at low power and accepts both black marking and deep engraving. It is the reference material for tooling, industrial plates and mechanical parts.
Settings: what really matters
Three different results depending on settings: black marking (moderate power, high speed, several close passes), light grey annealing (low power, very fast) and recessed engraving (full power, low speed, many passes).
A reasonable starting point with a 20 W fibre: 80% at 500 mm/s, 30 kHz frequency, for contrast engraving. To dig in, drop the speed to 200 mm/s and stack passes.
Mild steel rusts: annealed marking lasts better than surface marking, because it changes the material instead of removing it.
Common thicknesses and pitfalls
Common thicknesses: 0.5 to 3 mm sheet, with no limit on solid parts since you only mark. A marking fibre does not cut steel: industrial fibre cutters are multi-kilowatt machines, unrelated to a workshop engraver.
Common pitfall: paint or a zinc coating. On galvanised steel the laser vaporises the zinc and releases hazardous zinc fumes. Strip the area to be marked or change material.
The protective oil on new sheet smokes and dirties the mark: always degrease.
Risks and finishing
Extraction is mandatory: marking produces fine metal particles. Use glasses rated for 1064 nm, never those from a diode engraver.
For finishing, a mark meant to last is protected with light oil or varnish. A deep engraving can be filled with epoxy paint then wiped flat: the design stays crisp and legible for life.
Every figure on LaserSettings comes with the machine, the laser source, the material and the thickness it was tested on. A setting published for a 10 W diode says nothing about a 40 W CO2, and a setting for 3 mm says nothing about 6 mm: check those four things before you copy any number.
Settings are confirmed or disputed by the members who reproduce them, so reliability comes from cross-checking rather than popularity. Photos of the result — cut edges, engraving shades, scorching — tell you more than a single number found on a forum.
Whatever the material, treat a published setting as a starting point: run a small power/speed test grid on an offcut, clean the lens, redo the focus, work with fume extraction and air assist, wear glasses rated for your wavelength and never leave the machine unattended.