SAO PAULO, Dec 13 (Reuters) - Brazilian miner Vale SA (VALE3.SA) said on Monday its subsidiary Vale Canada has signed a deal to sell its 50% stake in steelmaker California Steel Industries to Nucor Corporation (NUE.N) for $400 million. Vale said in a securities filing it expects the deal to be concluded in the first quarter of 2022, adding that it underscores its focus on core businesses and its commitment to a leaner portfolio. JFE Steel Corp holds the remaining 50% stake in California Steel Industries.