SIXTH AMENDMENT TO REVOLVING CREDIT AGREEMENT

EXHIBIT 10.20

SIXTH AMENDMENT

TO

REVOLVING CREDIT AGREEMENT

This SIXTH AMENDMENT TO REVOLVING CREDIT AGREEMENT is made and entered into as of July 14, 2003 (this “ Amendment ”), among (a) CALIFORNIA STEEL INDUSTRIES, INC. , a Delaware corporation (the “ Borrower ”), (b) THE BANKS , (c) BANK OF AMERICA, N.A. , as loan and collateral agent for the Banks (in such capacity, hereinafter the “ Loan and Collateral Agent ”), (d) BANK OF AMERICA, N.A. , as letter of credit agent for the Banks (in such capacity, hereinafter the “ Letter of Credit Agent ”) and (e) BANK OF TOKYO-MITSUBISHI, LTD , as documentation agent. Capitalized terms used but not defined in this Amendment shall have the same meanings to such terms in the Credit Agreement defined below.

WHEREAS , the Borrower, the Banks, the Loan and Collateral Agent, the Letter of Credit Agent and the Arrangers have entered into that certain Revolving Credit Agreement, dated as of March 10, 1999 (as amended, restated, supplemented or otherwise modified and in effect from time to time, the “ Credit Agreement ”) pursuant to which the Banks have extended credit to the Borrower on the terms set forth therein;

WHEREAS , the Borrower has requested that the Banks amend the Credit Agreement upon the terms and subject to the conditions contained herein; and

WHEREAS , the Banks have agreed to amend the Credit Agreement upon the terms and subject to the conditions contained herein;

NOW, THEREFORE , in consideration of the foregoing and for other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, the parties agree as follows:

1. Amendment to the Credit Agreement . Subject to satisfaction of the condition set forth in §4 below, the Borrower, the Agents and the Banks hereby agree to amend the Credit Agreement as set forth below.

1.1 Amendment to Definitions . Section 1.1 of the Credit Agreement is hereby amended as follows:

(a) The definition of “Applicable Margin” is hereby amended by deleting the chart contained therein and replacing it with the following:

(b) The definition of “Borrowing Base” is hereby amended by deleting clauses (a) through (e) in their entirety and substituting in lieu thereof the following new clauses:

“(a) 80% of Eligible Accounts Receivable for which invoices have been issued and are payable; plus

(b) the lesser of (i) 50% of the Net Book Value of Eligible Inventory and (ii) $80,000,000; minus

(c) Reserves; plus

(d) the Discretionary Amount.”

(c) The definition of “Consolidated Operating Cash Flow” is hereby amended by deleting the phrase “(ii) the amount of Distributions made during such period, plus (iii) income taxes” and substituting in lieu thereof the phrase “(ii) net income taxes”.

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(d) The definition of “Consolidated Tangible Net Worth” is hereby amended by (i) deleting the period (“.”) at the end of clause (d) and substituting in lieu thereof the text “; plus” and (ii) adding the following new clause (e):

“(e) the value of the Investment of the Borrowers and its Subsidiaries in any of its Affiliates (other than Companhia Siderurgica de Tubarao).”

(e) The definition of “Revolving Credit Loan Maturity Date” is hereby amended by deleting the date “March 10, 2004” and substituting in lieu thereof the date “June 30, 2006”.

(f) The following definition is added to §1.1 and inserted in correct alphabetical order:

“ Documentation Agent . Bank of Tokyo-Mitsubishi. The Documentation Agent shall have no rights, duties, obligations or responsibilities beyond those of a Bank.”

1.2 Amendment to Commitment Fee . Section 2.2 of the Credit Agreement is hereby amended by deleting the following proviso in the first sentence of such section:

“ provided , however , that notwithstanding the foregoing, the commitment fee shall be calculated with an Applicable Margin of 0.50% if during any quarter the average daily Revolving Credit Loans outstanding plus the average Maximum Drawing Amount and all Unpaid Reimbursement Obligations during such quarter is less than (i) $50,000,000, if the average Total Commitment during such quarter is more than $100,000,000, and (ii) $40,000,000, if the average Total Commitment during such quarter is $100,000,000 or less.”

1.3 Amendment to Distribution Restriction . Section 9.4 of the Credit Agreement is hereby deleted in its entirety and replaced by the following:

“9.4 Distributions . The Borrower will not make any Distributions; provided , however , so long as no Default or Event of Default exists or would result therefrom, the Borrower may (a) make semi-annual Distributions not to exceed 50% of the Consolidated Net Income of the Borrower for the prior fiscal quarters for which full Distribution has not already been made so long as (i) such Distributions are made after delivery to the Banks of the financial statements required by Sections 8.4(a) and 8.4(b), (ii) the Borrower has delivered calculations to the Agents, demonstrating in a format satisfactory to the

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Agents that (A) the making of such Distributions will not cause a Default or Event of Default on a projected basis for the next two fiscal quarters of the Borrower, (B) the ratio of (y) Consolidated Operating Cash Flow, minus the aggregate amount of such Distributions, for the four fiscal quarters most recently ended to (z) Consolidated Total Debt Service for such period is not less than 1.00:1.00 and (C) during the 30 days prior to the making of such Distributions and immediately thereafter, the lesser of the Borrowing Base and the Total Commitment shall exceed the sum of Revolving Credit Loans, the Maximum Drawing Amount and all Unpaid Reimbursement Obligations by not less than $10,000,000, and (iii) prior to making such Distributions the Borrower has paid its trade payables in the ordinary course and not altered such procedures in order to comply with the provisions of the previous part (ii)(C) above, and (b) make Distributions to the preferred stockholders of the Borrower not to exceed $3,000,000 per year.

Any amounts paid in connection with acquisitions permitted under §9.5.1(d) during any fiscal quarter shall be excluded from the calculation of Consolidated Operating Cash Flow in (y) above for such fiscal quarter.”

1.4 Amendment to Mergers and Acquisitions Restrictions . Section 9.5.1 of the Credit Agreement is hereby amended by (a) deleting the text “(d)” and substituting in lieu thereof the text “(e)” and (b) inserting immediately following the phrase “(c) the merger or consolidation of two or more Subsidiaries of the Borrower;” the following text:

“(d) the acquisition of all or any portion of any property subject to the #2 Continuous Galvanizing Line Lease Agreement, dated September 30, 1998, between the Borrower and State Street Bank and Trust Company of California, so long as (i) the aggregate purchase price paid by the Borrower or its Subsidiaries shall not exceed $19,500,000, (ii) prior to and after giving effect to such acquisition there shall be no Default or Event of Default, (iii) the Borrower has delivered to the Agents not less than 5 Business Days prior notice of such proposed acquisition accompanied by calculations demonstrating in a format satisfactory to the Agents that (A) the consummation of such acquisition will not cause a Default or Event of Default on a projected basis for the next two fiscal quarters of the Borrower and (B) during the 30 days prior to the making of such acquis