Knife steels with significant nickel additions are surprisingly rare, though there are a few key steels, especially “low alloy” steels typically used for forging and pattern-welded Damascus. The most common are 15N20, 8670, and L6.
The reason for the nickel additions is an increase in toughness. What nickel does to steel increase toughness takes a while to explain because I have to explain what “dislocations,” “ductile to brittle transition temperature,” and “cross slip” are, and people already complain about the articles being too long. But I did explain those terms and what nickel does in this article on cold temperature toughness. So you can go read that if you are curious.
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