Armorsmith specialization

When increasing your mastery level in smithing, every additional mastery point you invest in smithing will involve choosing one of the four affinity metals, or iron, as well as a gear type between weapons and armors. This will provide you with a specialization. Doing so will unlock the upgrades that you can bestow upon gear that meets the requirements. Furthering your specialization to higher tiers means investing the point in the same combination of metals and gear.

For example, when Detri reaches 5th level, he decides to specialize in Arcanite Weapons. Tier 2 Arcanite Weapon upgrades are thus made available to him. When he reaches 9th level, he decides to specialize in Orichalcum Armors, which would unlock Tier 2 Orichalcum Armor upgrades for him. When he reaches 13th level, he decides to further specialize in Arcanite Weapons, and doing so unlocks Tier 3 Arcanite Weapon Upgrades for him. If Detri chooses to invest the fourth mastery point into Arcanite Armors instead, however, he would not gain the Tier 3 Arcanite Weapon Upgrades, but instead yield him the ability to have Tier 2 Arcanite Armor Upgrades. ** There is no benefit to specializing in iron-weapon or arcanite-weapon twice as there are no Tier 3 weapon upgrades for those metals currently

Armor Upgrades
Tier 1 upgrades do not require specialization. For the benefit of having all possible armor upgrades together, they are included in the below table.

Save DC's:
When a weapon or armor calls for a saving throw, the DC is calculated as:

8 + Proficiency Bonus + Strength or Dexterity Modifier