Exhibit 23.1

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Consent of Independent Registered Public Accounting Firm

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Reliance Steel & Aluminum Co. Master 401(k) Plan

Los Angeles, California

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We hereby consent to the incorporation by reference in the Registration Statement on Form S-8 (File No. 333-147226) of Reliance Steel & Aluminum Co. of our report dated June 25, 2020, relating to the financial statements and supplemental schedules of the Reliance Steel & Aluminum Co. Master 401(k) Plan which appear in this Form 11-K for the year ended December 31,2019.

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/s/ BDO USA, LLP

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Los Angeles, California

June 25, 2020