Heat-treating method for improving wear-resistance and corrosion-resistance of chromium-plated steel substrate

• US 6,846,367 B2
• Filed: 02/11/2003
• Issued: 01/25/2005
• Est. Priority Date: 11/25/2002
• Status: Expired due to Fees

• Current Assignee: Korea Institute of Machinery & Materials (Dawonsys Co., Ltd.)
• Original Assignee: Korea Institute of Machinery & Materials (Dawonsys Co., Ltd.)
• Inventors: Kim, Dong-Soo, Kim, Man, Lee, Gun-Hwan, Nam, Kee-Seok, Kwon, Sik-Cheol, Chang, Do-Yon, Lee, Kyu-Hwan
• Primary Examiner(s): WYSZOMIERSKI, GEORGE P
• Application Number:
  US10/364,832
• Publication Number:
  US 20040099344A1
• Time in Patent Office: 714 Days
• Field of Search: 148/217, 148/218, 148/277, 148/287
• US Class Current: 148/217
• CPC Class Codes: C23C 8/02 Pretreatment of the material to be coated C23C8/04 takes precedence
• CPC Class Codes: C23C 8/34 more than one element being applied in more than one step
• CPC Class Codes: C25D 3/06 from solutions of trivalent chromium
• CPC Class Codes: C25D 5/50 by heat-treatment

Abstract

Disclosed is a method for improving the wear- and corrosion-resistance of a chromium-plated steel substrate by heat-treating the chromium-plated steel substrate under optimum conditions to inhibit a drop in corrosion-resistance of a steel substrate due to fine cracks formed at a chromium layer, and to improve a hardness of the chromium layer. The heat-treating method comprises the steps of: plating the chromium layer onto the steel substrate; and heating the chromium-plated steel substrate in an oxidizing gas environment at above atmospheric pressure to form oxidized layers containing magnetite (Fe₃O₄) on the surface of the steel substrate, the surface of the steel substrate being partly exposed to the air through penetrating cracks formed in the chromium layer.

In accordance with the heat-treating method, the chromium-plated steel substrate having excellent corrosion- and wear-resistance can be easily obtained by plating chromium onto the steel substrate, followed by oxidizing the chromium-plated steel substrate. In addition, the heat-treating method contributes to fewer defects, low manufacturing costs and long life span of chromium plating-related products.

Claims

1. A heat-treating method for improving the wear- and corrosion resistance of a chromium plated steel substrate, comprising the steps of:

plating a chromium layer onto a steel substrate;

forming iron nitrides in the form of ε

-phase (Fe_2-3N) by nitrocarburising at above atmospheric pressure on the portion of the steel substrate surface exposed to the air through fine cracks formed at the chromium layer; and

forming iron oxides containing magnetite (Fe₃O₄) on the portion of the above iron nitrides in the form of ε

-phase (Fe_2-3N).

2. The heat-treating method for improving the wear- and corrosion resistance of a chromium-plated steel substrate as set forth in claim 1, wherein the step of nitrocarburising is carried out by heating in a carbon and nitrogen gas atmosphere at 500˜

650°

C. for 30˜

240 minutes.

3. The heat-treating method for improving the wear- and corrosion resistance of a chromium-plated steel substrate as set forth in claim 1, wherein the step of forming iron oxides is carried out by heating in a steam or air atmosphere at 350˜

560°

C. for 10˜

180 minutes.