Company: ZEUS
Filing Date: 2025-10-30
Form Type: 425
Source: 0001193125-25-257069
Chunk: 0

Company: OLYMPIC STEEL INC
Filing Date: 2025-10-30
Form: 425
Chunk 0
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UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 FORM 8-K CURRENT REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 Date of report (Date of earliest event reported): October 28, 2025 Ryerson Holding Corporation (Exact name of registrant as specified in its charter)

| Delaware                        |     | 001-34735   |     | 26-1251524         |
| (State or other jurisdiction of 
 incorporation or organization)  |     | -Commission 
 File Number |     | -I.R.S. Employer   
 Identification No. |

| 227 W. Monroe St., 27th Floor, Chicago, Illinois, 60606 |
| (Address of principal executive offices) (Zip Code)     |

(312) 292-5000 (Registrant’s telephone number, including area code) (Former name, former address and former fiscal year, if changed since last report) Check the appropriate box below if the Form 8-Kfiling is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

| ☒ | Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425) |

| ☐ | Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 
 CFR 240.14a-12)                                                        |

| ☐ | Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b)) |

| ☐ | Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c)) |

Securities registered pursuant to Section 12(b) of the Act:

| Title of each class                                          |     | Trading   
 Symbol(s) |     | Name of each exchange       
 on which registered         |
| Common Stock, $0.01 par value, 100,000,000 shares authorized |     | RYI       |     | The New York Stock Exchange |

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2of the Securities Exchange Act of 1934 (§240.12b-2of this