Nitriding process for maraging steel

a nitriding process and maraging steel technology, applied in the field of nitriding process of maraging steel, can solve the problems of insufficient performance, insufficient production, increased toughness of notch, etc., and achieve the effect of facilitating nitriding of maraging steel, increasing surface titanium concentration, and increasing titanium oxide concentration

US20120241050A1Inactive Publication Date: 2012-09-27HONDA MOTOR CO LTD
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Patent Information

Authority / Receiving Office
US · United States
Patent Type
Applications(United States)
Current Assignee / Owner
Publication Date
2012-09-27
Estimated Expiration
Not applicable · inactive patent

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Abstract

A nitriding process for a maraging steel is provided in order to increase the compressive residual stress of the maraging steel. A workpiece is made of maraging steel in which titanium is solid solved, and a partial amount of the titanium is oxidized at the surface of the workpiece so that titanium oxide is positively generated and concentrated at the surface. Then a reducing treatment is sufficiently performed as a pretreatment of a nitriding step, thereby removing oxygen. As a result, surface concentration of the titanium in an activated state is increased. Next, by performing the nitriding treatment, the reduced titanium and the solid solved titanium combine with nitrogen as titanium nitride. The titanium is in the activated state and is thereby easily nitrided. Moreover, the surface concentration of the titanium in the activated state is high, whereby a large amount of nitrogen infiltrates into the workpiece.
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Description

TECHNICAL FIELD

[0001] The present invention relates to a nitriding process for a maraging steel containing titanium, and specifically, the present invention relates to an improvement in a technique for controlling the degree of compressive residual stress.BACKGROUND ART

[0002] In order to improve strengths of steels, compressive residual stress may be generated at the surface of the steels by a nitriding treatment. In this case, if excessive degrees of the compressive residual stress are generated, there may be cases in which notch sensitivity is increased or toughness is decreased. Therefore, it is necessary to generate an appropriate degree of the compressive residual stress.

[0003] When a nitriding treatment is performed on a steel with low nitridability, an oxide layer existing at the surface of the steel prevents nitriding of the steel. For example, in a case of maraging steel, if surface concentrations of atoms that easily combine with oxygen, such as titanium, are high, oxide lay...

Examples

Embodiment Construction

[0018]The present invention will be described in detail with reference to specific practical examples hereinafter. In the Examples, the nitriding process for the maraging steel of the present invention is applied to the production method of an endless metal belt.

[0019]In the production of the endless metal belt, as shown in FIG. 2, first, a sheet 1 made of maraging steel is welded at both ends so as to have a cylindrical shape, thereby forming a drum 2 (a welding step). In this case, the drum 2 has a portion 2a that is hardened by the heat of the welding. Therefore, the drum 2 is subjected to a first solution heat treatment in a heating furnace 3, whereby the hardness of the drum 2 is homogenized (a first solution heat treating step). Next, the drum 2 is cut into predetermined widths, thereby forming plural rings 4 with an endless belt shape (a drum cutting step). Then, the rings 4 are rolled so as to have a predetermined thickness (a ring rolling step). In this case, the metallic s...