15N20 vs 1084
This is the most important pairing in pattern-welded damascus, and one of the least understood. 1084 and 15N20 are welded together precisely because they are metallurgically compatible but visually opposite — they forge-weld at the same heat, heat treat on the same schedule, and then etch to completely different colours. They are also, separately, two very good knife steels.
Quick Verdict
For damascus, this is not an either-or: use both, roughly 2:1 in favour of 1084 by thickness. As standalone steels, 15N20 is the better blade — tougher, capable of higher hardness, and finer grained — while 1084 is cheaper, thicker-stocked and easier to find.
Toughness
15N20 wins clearly. Roughly 2% nickel refines grain and improves impact resistance, so 15N20 stays tough even at 61 to 62 HRC where 1084 would be getting brittle. In a welded billet the pairing lands between the two, following the weaker partner more closely than the stronger one.
Edge Retention
15N20, by way of hardness rather than chemistry. Neither steel has meaningful alloy carbides, so edge life tracks hardness — and 15N20's toughness lets it live at 61 to 62 HRC while 1084 typically runs 58 to 60. Same carbide story, better operating point.
Corrosion Resistance
15N20 is slightly better, and this is the entire reason the pair works visually. Nickel resists ferric chloride, so in an etch the 1084 goes dark and the 15N20 stays bright silver. In a kitchen sink, neither is stainless and both need drying.
Heat Treat
Almost identical, which is exactly why they are welded together. Both austenitize around 1475 to 1500°F and quench in fast oil. The only real divergence is tempering: 1084 usually gets 400 to 425°F, while 15N20 can be tempered lower at 300 to 350°F to hold its higher hardness. A damascus billet of the two is heat treated as if it were 1084.
Grinding
Both are easy. 15N20 is usually sold in thin stock, so it heats quickly on the belt and needs frequent dipping. Welded damascus of the two grinds as one steel, though the nickel layers show up differently under a hand-sanding progression.
Best-Use Scenarios
Together: every classic pattern-welded billet — ladder, twist, raindrop, feather. 15N20 alone: thin kitchen knives, slicers, EDC. 1084 alone: first knives, forged camp and utility blades, and any build heat treated without a kiln.