This standard specifies the method for determining the depth of decarburization layer on the surface of steel rolling bearing parts. This standard is applicable to the determination of the depth of decarburization layer on the surface of finished and semi-finished steel rolling bearing parts. JB/T 7362-1994 Method for inspecting decarburization layer on rolling bearing parts JB/T7362-1994 Standard download decompression password: www.bzxz.net

Mechanical Industry Standard of the People's Republic of China
JB/T 7362—94
Decarburization layer inspection method for rolling bearing parts
Published on 1994-07-26
Ministry of Machinery Industry of the People's Republic of China
Implementation on 1995-07-01
Mechanical Industry Standard of the People's Republic of China
Decarburization layer inspection method for rolling bearing parts
1 Subject content and scope of application
This standard specifies the method for determining the depth of decarburization layer on the surface of steel rolling bearing parts. This standard is applicable to the determination of the depth of decarburization layer on the surface of finished and semi-finished steel rolling bearing parts. 2 Reference standards
GB/T 4342
JB1255
3 Definitions
3.1 Decarburization
Metallic microscopic Vickers hardness test method
Technical conditions for heat treatment of rolling bearing parts of high carbon chromium bearing steel JB/T 736294
The loss of carbon content in the surface layer of rolling bearing parts is called decarburization. Decarburization can be partial decarburization or full (or nearly full) decarburization.
3.2 Total decarburization
The sum of the partial decarburization depth and the full decarburization depth is the total decarburization. 3.3 Total decarburization layer depth
The distance from the surface of the part to the point where the carbon content is equal to the carbon content of the matrix (except for parts made of carburized bearing steel). 4 Determination methods
The determination methods of the decarburization layer on the surface of bearing parts mainly include metallographic method, hardness method and carbon content determination method. The choice of method and its accuracy depend on the decarburization degree, microstructure, carbon content and shape of parts of the product. Various determination methods have their application scope. Which method to use for determination should be specified by relevant technical conditions or agreements. When there is no clear stipulation, metallographic method is generally used, and microhardness method is used for dispute determination. 4.1 Metallographic method
Metallographic method is the most commonly used method for routine inspection. The key point is to observe the organizational changes from the surface to the center of the sample under an optical microscope as the carbon content changes.
This method is suitable for forging, forging annealing parts and various bearing parts. 4.1.1 Selection and preparation of samples
The inspection surface of the sample should be perpendicular to the working surface of the product. When the inspection surface cannot be perpendicular to the working surface, the measured decarburization layer depth () needs to be converted into the decarburization layer depth (hx) perpendicular to the working surface. When inspecting a steel ball, if its diameter is D, the diameter of the inspection grinding surface is d, and the decarburization layer depth measured on the inspection surface is h, then the actual decarburization layer depth is xd/Dh. For samples with a perimeter of ≤25mm, the entire perimeter is inspected and the deepest value is taken; for samples with a perimeter of >25mm. To ensure the representativeness of the sampling, several parts of the same cross section of the sample can be cut to ensure that the total detection perimeter is ≥35mm. The number of samples and the corresponding parts shall be in accordance with the provisions of JB1255.
The sample preparation shall be in accordance with the requirements for the preparation of surface metallographic analysis samples. Grinding and polishing shall ensure that the edges of the sample shall not be chamfered or curled. For this reason, the sample can be protected by inlay or special fixtures. If necessary, the outer surface of the sample to be inspected can be protected by electroplating metal (iron, nickel, chromium, etc.). Approved by the Ministry of Machinery Industry on July 26, 1994
Implemented on July 1, 1995
4.1.2 Determination
JB/T7362-94
The determination of decarburized layer usually refers to the determination of the total decarburized layer depth. In addition to carburized bearing steel, the steel used for bearing parts is mainly hypereutectoid steel. In hypereutectoid steel, the decarburized layer is distinguished by the change of carbide content relative to the carbon content of the matrix. With the help of a micrometer eyepiece, or directly on the ground glass screen of the microscope, measure the distance from the surface to the point where the structure is no longer different from the matrix.
The choice of magnification depends on the depth of the decarburized layer. Usually 100 times magnification is used, and 500 times magnification can also be used for observation. See Appendix A (reference).
Preliminary observation at low magnification to find out the deepest decarburization. The deepest point is the total depth of the decarburized layer. 4.2 Hardness method
4.2.1 Selection and preparation of specimens
The selection and preparation of specimens are the same as those of the metallographic method (see 4.1.1). However, whether the specimen is etched or not is based on the ability to correctly measure the indentation size (generally light etching is preferred).
4.2.2 Determination
Hardness method mainly uses microscopic (Vickers) hardness measurement method. This method is to measure the distribution gradient of microhardness value in the direction perpendicular to the surface on the cross section of the sample.
Microscopic (Vickers) hardness measurement method is determined according to GB/T4342. In order to reduce the error of the measurement data, the load should be as large as possible. In principle, the load is 0.981N～9.81N (100gf1000gf). The distance between the indentations is at least 2.5 times the length of the diagonal line of the indentation. The total decarburized layer depth is defined as the distance from the surface to the point where the hardness value is stable (i.e. the inflection point of the hardness curve). 4.3 Determination of carbon content method
This method is to determine the distribution gradient of carbon content in the direction perpendicular to the surface of the part, and it can be used for any organizational state of steel. 4.3.1 Chemical analysis method
This method can be applied to all bearing parts or semi-finished products suitable for mechanical delamination. 4.3.1.1 Selection and testing of samples
Use mechanical processing to remove test chips layer by layer parallel to the surface of the parts, with each layer being 0.05 to 0.10 mm thick. Be careful to prevent any contamination. Collect the metal test chips from each layer separately and determine the carbon content by chemical analysis. 4.3.2 Energy spectrum analysis method
Use the method of 4.3.1.1 to peel the bearing parts layer by layer, and perform electron energy spectrum measurement of carbon on each layer. 4.3.3 Arrangement of results (chemical and energy spectrum analysis method) Based on the results of layer-by-layer analysis, draw a curve of the relationship between depth and carbon content, and measure the distance from the surface to the point where the carbon content reaches the specified value.
5 Test report
The test report should include the following parts: a.
Part model, category and manufacturer; Material steel grade and heat treatment status;
Number of specimens and sampling locations;
Determination method;
Depth of decarburized layer (expressed in mm).
JB/T7362-94
Appendix A
Schematic diagram of decarburized layer on bearing steel surface
(reference part)
A1 Schematic diagram of decarburized layer on bearing steel surface is shown in Figure A1~Figure A6. Figure A1100×
Figure A2500×
JB/T7362--94bZxz.net
Figure A4500X
Figure A5100×
Magnification
Additional instructions:
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JB/T7362--94
Figure A6500×
Heat treatment state
Humidification + tempering
Metallurgical structure picture description
Complete decarburization
Ferrite
Coarse needle-shaped martensite + fine
Small needle-shaped martensite + less
Amount of residual carbides + more
Retained austenite
Normal structure
Fine crystalline martensite + hidden||tt| |crystalline martensite + a small amount of
retained carbides + a large amount of
residual
austenite
magnification of the above structure
martensite + secondary carbides
and primary carbides + a small amount of
retained austenite
martensite + a small amount of
secondary carbides and primary carbides + a small amount of retained austenite
magnification of the above structure
acicular martensite + crystalline martensite + a small amount of
retained carbides + a small amount of retained austenite
amplification of the above structure
this standard is proposed by the Standardization Technical Committee of the Rolling Bearing Industry. This standard is drafted by the Luoyang Bearing Research Institute of the Ministry of Machinery Industry. The main drafters of this standard are Zhao Chuanguo, Liang Hua, and Lu Shujun. Sample etchant
4% nitric acid alcohol
fine solution
hydrochloric acid 5mL,
picric acid 1g,
alcohol 100mL
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