Company: ZEUS
Filing Date: 2025-10-30
Form Type: 425
Source: 0001193125-25-257069
Chunk: 14

Company: OLYMPIC STEEL INC
Filing Date: 2025-10-30
Form: 425
Chunk 14
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, Olympic Steel, Inc. and Richard Marabito.             |
| 104     |     | Cover Page Interactive Data File (formatted in Inline XBRL and contained in Exhibit 101)                                                        |

| * | Schedules and exhibits have been omitted pursuant to Item 601(a)(5) and (a)(6) of Regulation S-K. Ryerson hereby undertakes to furnish supplemental copies of any of the omitted schedules and exhibits upon request by the SEC. |

SIGNATURES Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

| Date: October 29, 2025 |     | RYERSON HOLDING CORPORATION 
 By:                         |     | /s/ James J. Claussen                                |
|:-----------------------|:----|:----------------------------|:----|:-----------------------------------------------------|
|                        |     | Name:                       |     | James. J. Claussen                                   |
|                        |     | Title:                      |     | Executive Vice President and Chief Financial Officer |

Exhibit 2.1

AGREEMENT AND PLAN OF MERGER

among

OLYMPIC STEEL, INC.,

RYERSON HOLDING CORPORATION,

and

CRIMSON MS CORP.

Dated as of October 28, 2025

TABLE OF CONTENTS

|                                                         |     |                                                                                |     | Page |    |
| ARTICLE 1 THE MERGER                                    |     |                                                                                |     |      |  2 |
| 1.1                                                     |     | The Merger                                                                     |     |      |  2 |
| 1.2                                                     |     | Closing                                                                        |     |      |  2 |
| 1.3                                                     |     | Effective Time                                                                 |     |      |  2 |
| 1.4                                                     |     | Articles of Incorporation and Code of Regulations of the Surviving Corporation |     |      |  2 |
| 1.5                                                     |     | Directors and Officers of the Surviving Corporation                            |     |      |  3 |
| 1.6                                                     |     | Presence in Cleveland                                                          |     |      |  4 |
| ARTICLE 2 CONVERSION OF SECURITIES IN THE MERGER        |     |                                                                                |     |      |  4 |
| 2.1                                                     |     | Conversion of Securities                                                       |     |