Solingen steel could be any of several steels, but the more common ones that I know about are 420HC in stainless and the DIN equivalent to AISI 1070 for the carbon steels. Boker has used quite a bit of 440C over the years. I've seen some tool type steels listed with certain knives. Common German slipjoints available nowadays are most likely either the 420HC or 1070. I have no idea how long they'll hold their edges, as I've never had the opportunity to subject any of my knives to severe enough useage to really get them that dull, but they sharpen up razor sharp and seem to cut well enough for me. From what I've experienced, the slipjoints with the carbon steel blades usually are ground thinner, so they cut better than the thicker blades on many other knives. May not be the case with all of the German knives, just the ones I've seen so far. I've always wanted to get ahold of a good Boker in 440C and see how the edges held up. The stag copperheads and big folding hunters they make in 440C are some beautiful knives.