QuickLinks -- Click here to rapidly navigate through this document



SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM 11-K


ý

Annual report pursuant to Section 15(d) of the Securities Exchange Act of 1934

For the fiscal year ended December 31, 2003

Commission File Number 1-5725

A.
Full title of the plan and the address of the plan, if different from that of the issuer named below:
B.
Name of the issuer of the securities held pursuant to the plan and the address of its principal executive office:


REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

The Benefits Committee
Quanex Corporation
Houston, Texas

Re: Quanex Corporation Employee Savings Plan

We have audited the accompanying statements of net assets available for benefits of the Quanex Corporation Employee Savings Plan ("the Plan") as of December 31, 2003 and 2002, and the related statements of changes in net assets available for benefits for the years then ended. These financial statements are the responsibility of the Plan's management. Our responsibility is to express an opinion on these financial statements based on our audits.

We conducted our audits in accordance with the standards of the Public Company Accounting Oversight Board (United States). Those standards require that we plan and perform the audit to obtain reasonable assurance about whether the financial statements are free of material misstatement. An audit includes examining, on a test basis, evidence supporting the amounts and disclosures in the financial statements. An audit also includes assessing the accounting principles used and significant estimates made by management, as well as evaluating the overall financial statement presentation. We believe that our audits provide a reasonable basis for our opinion.

In our opinion, such financial statements present fairly, in all material respects, the net assets available for benefits of the Plan as of December 31, 2003 and 2002, and the changes in net assets available for benefits for the years then ended in conformity with accounting principles generally accepted in the United States of America.

Our audits were conducted for the purpose of forming an opinion on the basic financial statements taken as a whole. The accompanying supplemental schedule of assets (held at end of year) as of December 31, 2003 is presented for the purpose of additional analysis and is not a required part of the basic financial statements but is supplementary information required by the Department of Labor's Rules and Regulations for Reporting and Disclosure under the Employee Retirement Income Security Act of 1974. The supplemental schedule is the responsibility of the Plan's management. This supplemental schedule has been subjected to the auditing procedures applied in our audits of the basic financial statements and, in our opinion, are fairly stated in all material respects when considered in relation to the basic financial statements taken as a whole.

/s/  DELOITTE & TOUCHE, LLP      
DELOITTE & TOUCHE, LLP
   

Houston, Texas
June 23, 2004



QUANEX CORPORATION
EMPLOYEE SAVINGS PLAN

STATEMENTS OF NET ASSETS AVAILABLE FOR BENEFITS

 
  DECEMBER 31,
 
  2003
  2002
Assets:            
  Investments at fair value (see Note C)   $ 39,733,499   $ 32,058,143
  Employee contributions receivable     342,945     356,244
  Employer contributions receivable     101,004     113,299
   
 
      443,949     469,543
   
 
Net assets available for benefits   $ 40,177,448   $ 32,527,686
   
 

See notes to financial statements.



QUANEX CORPORATION
EMPLOYEE SAVINGS PLAN

STATEMENTS OF CHANGES IN NET ASSETS AVAILABLE
FOR BENEFITS

 
  DECEMBER 31,
 
 
  2003
  2002
 
Investment income:              
  Interest and dividends   $ 535,886   $ 514,757  
  Net appreciation (depreciation) in fair value of investments (see Note C)     6,528,652     (4,621,304 )
   
 
 
      7,064,538     (4,106,547 )
   
 
 
Contributions:              
  Employer (net of forfeitures)     563,242     602,697  
  Employee     2,769,718     2,393,260  
   
 
 
      3,332,960     2,995,957  
   
 
 
    Total additions     10,397,498     (1,110,590 )
   
 
 
Benefit payments     2,968,828     4,082,674  
Administrative fees (see Note D)     80     34  
   
 
 
    Total deductions     2,968,908     4,082,708  
   
 
 
Transfers between plans (see Note G)     221,172     343,202  
   
 
 
Decrease in net assets available for benefits     7,649,762     (4,850,096 )
Net assets available for benefits:              
  Beginning of year     32,527,686     37,377,782  
   
 
 
  End of year   $ 40,177,448   $ 32,527,686  
   
 
 

See notes to financial statements.


QUANEX CORPORATION
EMPLOYEE SAVINGS PLAN
EIN: 38-1872178; PN 012


Schedule H, Line 4i — Schedule of Assets (Held at End of Year)
December 31, 2003

(a)




  (b)
Identity of issue,
borrower, lessor
or similar party

  (c)
Description of investment including
maturity date, rate of interest,
collateral, par, or maturity value

  (d)


Cost

  (e)

Current
Value

*   Fidelity   Puritan Fund   $ 3,913,070   $ 4,175,069
*   Fidelity   Magellan Fund     7,735,117     7,911,776
*   Fidelity   Contrafund     4,025,948     4,170,182
*   Fidelity   Growth & Income Fund     3,592,640     3,575,480
*   Fidelity   Independence Fund     2,989,722     2,409,062
*   Fidelity   Overseas Fund     1,343,639     1,397,221
*   Fidelity   Balanced Fund     916,173     1,020,368
*   Fidelity   Blue Chip Fund     2,309,222     2,174,709
*   Fidelity   Asset Manager Fund     398,514     391,839
*   Fidelity   Low-Priced Stock Fund     3,092,545     3,779,001
*   Fidelity   Government Money Market Fund     5,038,268     5,038,268
    Templeton   Foreign Fund   $ 393,092   $ 435,839
    Neuberger & Berman   Partners Trust Fund     114,881     120,556
           
            Total Mutual Fund Assets     35,862,831     36,599,370
*   Quanex Corporation   Unitized common stock     981,736     1,599,317
*   Fidelity   Managed Income Portfolio     1,534,812     1,534,812
           
            Total Investments   $ 38,379,379   $ 39,733,499
           

* Party-in-Interest


QUANEX CORPORATION
EMPLOYEE SAVINGS PLAN


NOTES TO FINANCIAL STATEMENTS

YEARS ENDED DECEMBER 31, 2003 AND 2002

A.
DESCRIPTION OF THE PLAN
B.
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

(1)
Accounting Basis. The financial statements of the Plan are prepared on the accrual basis of accounting in accordance with accounting principles generally accepted in the United States of America.

(2)
Investment Valuation. The Plan recognizes net appreciation or depreciation in the fair value of its investments. Investments are reflected at fair value in the financial statements. Fair value of mutual fund assets is determined using a quoted net asset value. Fair value for Quanex Corporation common stock, which is listed on the New York Stock Exchange, is determined using the last recorded sales price. The recorded value of the common/commingled trust is at face value, which is fair value.

C.
INVESTMENTS
 
  December 31, 2003
  December 31, 2002
 
  Shares
  Amount
  Shares
  Amount
Fidelity Puritan Fund   226,046   $ 4,175,069   227,812   $ 3,597,150
Fidelity Magellan Fund   80,947     7,911,776   78,628     6,208,449
Fidelity Contrafund   84,502     4,170,182   80,443     3,105,092
Fidelity Growth & Income Fund   100,350     3,575,480   98,787     2,994,220
Fidelity Independence Fund   150,004     2,409,062   172,068     2,248,935
Fidelity Blue Chip Fund   54,875     2,174,709   *44,879     *1,433,434
Fidelity Low-Priced Stock Fund   108,011     3,779,001   92,405     2,325,835
Fidelity Government Money Market Fund   5,038,268     5,038,268   5,303,019     5,303,019
* presented for comparative purposes only                    
 
  2003
  2002
 
Mutual funds   $ 6,042,912   $ (5,024,195 )
Quanex unitized common stock     485,740     402,891  
   
 
 
    $ 6,528,652   $ (4,621,304 )
   
 
 
D.
RELATED PARTY TRANSACTIONS

E.
PLAN TERMINATION
F.
FEDERAL INCOME TAX STATUS
G.
TRANSFER OF ASSETS


SIGNATURES

        The Plan. Pursuant to the requirements of the Securities Exchange Act of 1934, the trustees (or other persons who administer the employee benefit plan) have duly caused this annual report to be signed on its behalf by the undersigned hereunto duly authorized.

  Quanex Corporation Employee Savings Plan

Date: June 28, 2004

/s/ Ricardo Arredondo

Ricardo Arredondo, Benefits Committee


INDEX TO EXHIBITS

23.1
Consent of Independent Registered Public Accounting Firm

99.1
Certification by chief executive officer and chief financial officer pursuant to Section 906 of the Sarbanes-Oxley Act of 2002



QuickLinks

REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM
QUANEX CORPORATION EMPLOYEE SAVINGS PLAN STATEMENTS OF NET ASSETS AVAILABLE FOR BENEFITS
QUANEX CORPORATION EMPLOYEE SAVINGS PLAN STATEMENTS OF CHANGES IN NET ASSETS AVAILABLE FOR BENEFITS
Schedule H, Line 4i — Schedule of Assets (Held at End of Year) December 31, 2003
NOTES TO FINANCIAL STATEMENTS YEARS ENDED DECEMBER 31, 2003 AND 2002
SIGNATURES
INDEX TO EXHIBITS

QuickLinks -- Click here to rapidly navigate through this document


Exhibit 23.1


CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

        We consent to the incorporation by reference in Registration Statement No. 33-38702 of Quanex Corporation on Form S-8 of our report dated June 23, 2004, appearing in this Annual Report on Form 11-K of the Quanex Corporation Employee Savings Plan for the year ended December 31, 2003.

/s/  DELOITTE & TOUCHE, LLP      
DELOITTE & TOUCHE, LLP
   

Houston, Texas
June 23, 2004




QuickLinks

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

QuickLinks -- Click here to rapidly navigate through this document


Exhibit 99.1


CERTIFICATION PURSUANT TO SECTION 906
OF THE SARBANES-OXLEY ACT OF 2002

        We hereby certify that the accompanying Report of Quanex Corporation Employee Savings Plan (the "Plan") on Form 11-K for the year ended December 31, 2003 fully complies with the requirements of Section 13(a) or 15(d) of the Securities Exchange Act of 1934 and that information contained in such Report fairly presents, in all material respects, the financial condition and results of operations of the Plan.

June 28, 2004

/s/  RAYMOND A. JEAN      
Raymond A. Jean
Chairman of the Board, President and
Chief Executive Officer
  /s/  TERRY M. MURPHY      
Terry M. Murphy
Vice President—Finance and
Chief Financial Officer



QuickLinks

CERTIFICATION PURSUANT TO SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002