Methods and Systems for Preventing Iron Oxide Formulation and Decarburization During Steel Tempering

Abstract

The technology described herein provides a method and system to prevent iron oxide formation and decarburization during strand heat treating of a steel product without the subsequent required use of acid pickling, which has associated health and environmental risks. Additionally, this technology provides placing a coating, such as copper plating, to the surface of a steel wire prior to strand heat treating to avoid both iron oxide formation and decarburization through the surface of the steel wire by preventing interactions between the steel wire and the furnace atmosphere. To remove oxides formed by the plating metal, the oxides are chemically reduced by passing the steel wire through a reducing gas, electrolytically reduced by plating with the wire anodic, mechanically reduced through the use of brushes, or the like, or chemically reduced by acid pickling.

Description

FIELD OF THE INVENTION[0001]The technology described herein relates generally to metal heat treating processes such as annealing, patenting, or tempering. More specifically, the technology described herein relates to a method and system to prevent iron oxide formation and decarburization during strand heat treating of a steel product without the required use of acid pickling. Additionally, this technology relates to placing a coating, such as copper plating, to the surface of a steel wire prior to strand heat treating to avoid both iron oxide formation and decarburization through the surface of the steel wire by preventing interactions between the steel wire and the furnace atmosphere.BACKGROUND OF THE INVENTION[0002]Patenting is a heat treatment process for a metal or alloy. Patenting is used to soften a steel metal or alloy and remove any existing brittleness. Control of both time and temperature during the patenting process is critical in order to achieve a final product with app...

AI Technical Summary

Benefits of technology

[0021]In one exemplary embodiment, the technology provides a method to prevent iron oxide formation and decarburization during the patenting of steel wire. The method includes coating a steel wire with a metal plating prior to heat treating the steel wire, thereby masking the steel to prevent carbon from leaving a surface of the steel wire. The method includes austenitizing the plated steel wire in a gas furnace, wherein the steel wire is protected against iron oxide formation and decarburization, which would otherwise occur as a result of exposure to the atmosphere of the furnace, because of the plating. The method includes immediately cooling the austenitized and metal plated steel wire in a controlled cooling process environment. The method includes reducing oxides formed by the oxidation of the metal plating in the atmosphere of the furnace. The method also includes cooling the steel wire to room temperature. The coating of the steel wire with the metal plating prior to heat treating prevents iron oxide formation and decarburization during the heat treating, without a required use of acid pickling. The coating used for metal plating a steel wire is an electrolytic copper pyrophosphate plating, and electrolytic copper sulfate coating or hot dip copper plating. The method also includes austenitizing the plated steel wire in a gas furnace to a temperature of 950° C. to 1050° C. and cooling the steel wire to within the range of 500° C. to 650° C.

[0023]The method also includes lightly etching, with a mild acid solution, the steel wire to help improve subsequent electroplating. This etching is subsequent to the reducing of oxides formed. The method also includes, prior to coating a steel wire rod with a metal plating, drawing the steel wire from a steel wire rod taken from a steel coil, descaling the steel wire of any mill scale, or preexisting iron oxides used to prevent further oxidation during shipment, and rinsing the steel wire to remove any extraneous debris from the surface of the wire.

[0025]Advantageously, this technology provides a method and system to prevent iron oxide formation and decarburization during strand heat treating of a steel product without the required use of acid pickling. Additionally, this technology provides placing a coating, such as copper pyrophosphate electrolytic plating, to the surface of a steel wire prior to strand heat treating to avoid both the iron oxide formation and decarburization through the surface of the steel wire by preventing interactions between the steel wire and the furnace atmosphere.

Problems solved by technology

Pickling acids, such as concentrated hydrochloric acid, HCl, or sulfuric acid, H2SO4, are expensive and environmentally unfriendly.

Furthermore, such pickling acids create maintenance and health issues related to disposal, potential spills, and fumes.

When decarburization occurs, generally at the hot surface of the steel wire, and in the presence of water vapor resulting from combustion of gases like natural gas, the wire is unfit for subsequent conversion.

Additionally the wire may exhibit property degradation such as low strength, low fatigue life, and / or unsuitable draw ability.

It is also known that the rate of diffusion of copper into steel is slow, making it unlikely for copper-steel alloys to form at the surface of the wire.

However, copper is not known or used in the art as a “mask” to prevent carbon from leaving the surface of a steel part.

It is very difficult to control both the wire temperature and the furnace atmosphere; any shift in the furnace atmosphere will result in a change in the wire temperature.

Therefore, the gas-rich portion of the furnace shifts toward the furnace entrance, reducing the oxygen-rich zone and resulting in a decrease in convective heat transfer and a corresponding decrease in wire temperature.

Both of these furnaces, by definition, heat wire indirectly and are relatively energy inefficient.

In addition, cost to produce and maintain such a furnace atmosphere in a strand furnace, which is open at both ends, is prohibitively expensive.

These and other problems exist.

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