Bearing component and method

Abstract

Bearing component providing unaffected material that has a surface, which has been subjected to a hard machining process during where the temperature of the surface did not exceed the austenitizing temperature of the unaffected material. The surface of the bearing component includes a white layer formed during the hard machining process. The white layer has a nano-crystalline microstructure that includes grains having a maximum grain size up to 500 nm. The white layer is located directly adjacent to the unaffected material of the bearing component, where no dark layer is formed during the hard machining process.

Description

CROSS REFERENCE[0001]This is a United States National Stage Application claiming the benefit of International Application Number PCT / SE2015 / 051278 filed on Nov. 27, 2015, which claims the benefit of Swedish Patent Application 1451555-5 filed on Dec. 16, 2014, both of which are incorporated herein by reference in their entireties.FIELD OF THE INVENTION[0002]The present invention concerns a bearing component comprising unaffected material, such as steel, iron or an iron-based metal having a hardness of at least 45 HRC for example, which has been subjected to a machining process, such as hard machining, e.g. turning, or hard turning. The present invention also concerns a method for manufacturing such a bearing component.BACKGROUND OF THE INVENTION[0003]Hard turning is a machining process applied to metallic materials with a hardness greater than 45 HRC (which corresponds to about 450 HV1), and is typically performed after a workpiece has been heat treated. In hard turning a cutting too...

AI Technical Summary

Benefits of technology

The invention aims to improve the performance of bearing components made of materials such as steel or iron that have been hard machined. The invention achieves this by creating a predominantly mechanically-induced white layer during the hard machining process. This layer has a unique microstructure and improved fatigue resistance, fracture toughness, and wear resistance compared to thermally-induced white layers. Ultimately, this results in a bearing component with enhanced rolling contact fatigue performance.

Problems solved by technology

A significant limitation of the widespread use of hard machining of metallic materials is the so-called “white layer” effect, which is a microscopic alteration of the as-machined surface of a workpiece which appears white under a Light Optical Microscope (LOM), which effect is produced in response to an extremely high thermo-mechanical load exerted at the as-machined surface of a workpiece by the cutting tool.

Such white layers have a high hardness and are brittle compared to the bulk material of the workpiece.

When high external loads are applied on such a triple-layered structure (i.e. a hard or very hard white layer, a soft dark layer and hard unaffected material) cracks may develop in the white layer between the white layer and the dark layer, or between the dark layer and unaffected material.

When these cracks extend and connect together, flaking can occur.

A thermo-mechanically-affected workpiece surface comprising an etching-resistant white layer has conventionally been undesired because of high tensile and surface stresses associated therewith, such as reduced fatigue-resistance, lower fracture toughness, and / or reduced wear resistance of parts produced.

The white layer (10) is generally a hard phase and leads to the surface becoming brittle causing crack permeation and product failure.

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