Steel & Mithral armour is a hybrid metal armour consisting of steel elements covering most areas for protection with mithral bands and fine chain at the joints for greater movement and flexibility. It allows for some of the benefits that full mithral armour provides but at a fraction of the cost. If the armour normally imposes disadvantage on Dexterity (Stealth) checks the steel & mithral version of the armour doesn't, and any Strength requirement is reduced by 2.
Plate consists of shaped, interlocking metal plates to cover the entire body. A suit of plate includes gauntlets, heavy leather boots, a visored helmet, and thick layers of padding underneath the armor. Buckles and straps distribute the weight over the body.
Notes: Stealth Disadvantage: Remove, Combat, Warding, Str. 15 Required, Stealth Disadvantage
Frustratingly, despite setting the strength requirement for this armour to 13 when creating it, it's ignored this in the finished version - I've reported this to the bug forum.
Also, I house rule that full mithral armour is half the weight of normal armour as it has been in previous editions of the game. Traditionally this is what mithral has always been like and even the description in 5e states that "Mithral is a light, flexible metal." Thought this worth mentioning as the benefits of this homebrew creation are almost as good as full mithral RAW, but in my game full mithral would be half weight whereas steel & mithral armour would be normal weight.