Tesla has said that there will be some steel components used in the Model 3 where they are aluminium in the Model S. I wonder if this is what they will be using.http://www.gizmag.com/flash-bainite-automotive-testing/40774/
From another thread on a similar subject:
I rather hope the Tesla Model ≡ will continue the same construction methods as Model S and Model X. That is, primary construction of frame and body using aluminum, combined with critical structural supports made of hardened steel as needed. I understand there is a strong possibility that it may be instead:
1) primary construction of frame and body using lightweight steel throughout
2) frame in lightweight steel, with a body in aluminum
3) frame and body in lightweight steel, with some portions of aluminum and composite materials used in the cabin area as part of a 'life cell'
Tesla Motors already has a relationship with ALCOA as their primary supplier of aluminum. ALCOA also supplies Ford for their F-Series trucks. I believe ALCOA would not have an issue seeing to Tesla's needs for Model ≡ if given the opportunity.