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Hi there, as per my previous post I’m using the F1 Ultra to engrave ID marks onto tools. The material is polished High Carbon Steel. I’m using the settings for Stainless steel but is this correct? The metal engraves but I also get a black deposit. Any help would be greatly appreciated. 
Settings are

Unknown material 

81% power

80mm/sec

Fiber IR

PASS 1

30kHz

Bi-directional

Lines per cm 100