Steel plates is a crafting component in The Witcher 3: Wild Hunt that can be dismantled into steel ingot. It is needed to craft the following items:
Crafting Requirements 
It can 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
- Moving merchant in Blackbough, near Carsten or south of Gate of the Hierarch
- Scoia'tael merchant in the forest south of Novigrad
- Scoia'tael merchant in the forest east of Oxenfurt
- Merchant at the sawmill northeast of Rannvaig
- Merchant at the Isolated Hut on Hindarsfjall
- Merchant in Mohrin Village
- Merchant in Stacheier
- Clerk in Villa Vedette
- Merchant outside the The Cockatrice Inn
- Merchant in Dupont & Sons
- Merchant in Flovive
- Merchant in Francollarts
- Merchant in The Clever Clogs Tavern
- Merchant in the Wine Market in San Sebastian
- Wandering merchants in Toussaint
- Wine Merchant at Rivecalme Storehouse
Steel plates can also be obtained by dismantling:
- Angrenian cuirass (basic)
- Angrenian cuirass (relic)
- Axeman's trousers (crafted)
- Ban Ard breastplate (crafted)
- Cidarian cavalry armor
- Journeyman's armor repair kit
- Kaedweni cuirass
- Master's armor repair kit
- Redanian halberdier's armor
- Salmian brigandine (crafted)