Does Bohler K390 manganese Parkerize using only a phosphoric acid dip?

[rdmi]

I soaked Bohler K390 in Boeshield Rust Free, which is weak phosphoric acid, at room temperature. Unlike other steels, which develop a light gray haze, it turned deep black. What happened? Did the 0.4% manganese in K390 react with the phosphoric acid to produce manganese phosphate, essentially Parkerizing the steel without normal Parkerizing solution?

 

[Obsessed with Edges]

K390's carbon content is extremely high at 2.50%. Compare to mainstream cutlery steels, which will have carbon not too far above 1-1.5% or so, and many (or most) somewhat lower than 1%. Not a lot of chromium in it either at 4%, which at 10-12% levels or higher might otherwise lend some resistance to corrosion/oxidation. Just looking at those two aspects, it doesn't really surprise me that the steel's reaction to an acid would be more extreme. Non-stainless steels with high carbon content will tend to react like that anyway, and more so as the carbon content increases.

http://www.zknives.com/knives/steels/steelgraph.php?nm=k390

 

[Ben Dover]

Whatever you did, it's beautiful!