Dark steel plate is a crafting component in The Witcher 3: Wild Hunt that can be dismantled into a dark steel ingot.
Crafting Requirements 
One is also always found in a small red-glowing chest inside the nekker monster den east of Ursten. It can also be found as random loot or purchased from the following merchants:
- All armorers and blacksmiths, except the one at Ardaiso Quarry
- Armors and weapons merchants in Nilfgaardian Army Group 'Center' Camp
- Merchant in the boatyard south of Refugees' Camp
- Merchant at Calveit Watchtower
- Merchant at Coast of Wrecks
- Merchant in Ursten
- Merchant by the road west of White Eagle Fort
- Merchant at the sawmill northeast of Rannvaig
- Merchant at the Isolated Hut on Hindarsfjall
- Merchant in Mohrin Village
- Merchant in Stacheier
- Ofieri merchant at Upper Mill
Dark steel plates can also be obtained by dismantling any of the non-grandmaster Wolven armor pieces and the following items:
- Angrenian cuirass (crafted)
- Ban Ard breastplate
- Hindarsfjall heavy armor
- Mag Deira cuirass
- Nilfgaardian guardsman armor
- Oathbreaker armor
- Thyssen armor (crafted)
- New Moon armor
- Toussaint knight's trousers (quest)
- Manticore trousers
- Legendary Manticore trousers
- Grandmaster Wolven trousers
- Grandmaster legendary Wolven trousers
Needed to craft:
Witcher gear:
Other items:
- Angrenian cuirass
- Ban Ard breastplate
- Executioner's boots
- Hindarsfjall heavy armor
- Mag Deira cuirass
- Mahakaman trousers
- Nilfgaardian guardsman armor
- Thyssen armor
- Ofieri scale armor (New Game + only)
- Order of the Flaming Rose armor
- Toussaint Color Guardsman's armor
- Toussaint Ducal Guard Captain's armor
- Toussaint knight's boots
- Toussaint knight's gauntlets
- Toussaint knight's trousers
- Toussaint knight's tourney armor