Dwarven Steel is going to be the first metal that you are in short supply of. You may get just enough to bypass any major hunting that you are definitely going to need to do when you start needing Asgardian Ingots. Here is where to find Dwarven Steel.
Like many of the different crafting components in God of War Ragnarok, you will need to seek out the stone chests with the red glow to get Dwarven Steel. These chests are relatively common if you spend any amount of time exploring them.
These chests can often be found wrapped in the blue brambles or hidden away off the beaten path in various areas in the game. Dwarven steel will start to become more and more common as you progress further in the game. Early on, you may only get one or two pieces of it each time you open a chest. Later on, you can see 10+ but that is likely going to be at a point where you are no longer needing any of it.
