Hanging chart of metallographic rating standards for heavy-duty gears

Hanging chart of metallographic rating standards for heavy-duty gears

one Grading of carburized metallographic structure （JB/T6141.3-1992)

1 Martensitic and residual austenite grades（1-6Grade)

2 Carbide grade （1-6Grade)

3 Heart tissue level （1-6Grade)

two Metallographic discrimination of carbon content on carburized surface（JB/T6141.4-1992）

13Zhang

Grade of carburizing metallographic structure（JB/T6141.3-1992)

Topic content and scope of application

This standard specifies the technical requirements and metallographic grades for the metallographic structure inspection of heavy-duty gear carburizing, quenching and tempering.

This standard is applicable to the metallographic examination of heavy-duty carburized gears made of steel such as 20CrMnTi, 20CrMnM0, 20CrNi2M0, 12CrNi3M0, 15CrNi3M0, and 20Cr2Ni4.

Technical Requirement 2

2.1 Metallographic structure of carburized layer

2.1.1 Martensite and residual austenite should be measured at the center of the normal section of the tooth width in the tooth shaped sample after quenching and tempering of the carburizing sample in the furnace, at a distance of 0.05-0.15mm from the surface. The metallographic structure consists of hidden crystals or fine needle martensite with less than 30% residual austenite. Levels 1-4 are considered qualified, level 5 can be negotiated between the supply and demand parties, and level 6 is considered unqualified.

2.1.2 Carbides

After quenching and tempering, the size, shape, and distribution of surface carbides are measured at the most severe location on the carburizing sample. The metallographic structure should consist of uniformly distributed fine granular carbides, and continuous network, needle like, and angular carbides are not allowed. Levels 1-3 are considered qualified, level 4 can be negotiated between the supply and demand parties, and levels 5-6 are considered unqualified (the level of carbide at the tooth tip angle can be relaxed by one level). 2.1.3 Heart tissue

At the center of the furnace carburizing sample, the tooth profile sample should be measured at the intersection of the centerline of the normal section of the tooth and the tooth root circle in the middle of the tooth width. The metallographic structure should consist of low-carbon martensite or lower bainite with a small amount of free ferrite, and a large amount of blocky, network like, or needle like ferrite is not allowed. Levels 1-4 are considered qualified, level 5 can be negotiated between the supply and demand parties, and level 6 is considered unqualified.

2.2 Corrosive agents and amplification factors

2.2.1 The corrosive agent is a 4% nitric acid alcohol solution.

2.2.2 The metallographic structure level is evaluated at 400x.

Metallographic organization classification

3.1 Grades of Martensite and Residual Austenite

According to the size of the martensitic needle and the amount of residual austenite, the grade is evaluated, as shown in Table 1 and Appendix A (Supplementary) Figure A1 Grade Diagram. 3.2 Classification of carbides

According to the size, shape, quantity, and distribution of carbides, the grade is evaluated as shown in Table 2 and Appendix B (Supplementary Parts) Grade Chart. 3.3 Levels of Heart Organization

Grade based on the size, shape, and quantity of ferrite in the heart tissue. Refer to Table 3 and Appendix C (Supplementary) for the level chart.

two Metallographic discrimination of carbon content on carburized surface（JB/T6141.4-1992）

Topic content and scope of application

This standard specifies the metallographic examination method for the carbon content on the carburized surface of heavy-duty gears.

This standard is applicable to steel parts such as 20CrMnTi, 20CrMnM0, 20CrNi2M0, 12CrNi3M0, 15CrNi3M0, 20Cr2Ni4, etc. Other steel grades can refer to the implementation.

This standard is a metallographic method for controlling the surface carbon content of parts during carburizing process. Identify non-conforming parts during the heating process in order to adjust process parameters in a timely manner and ensure product quality.

2 samples

2.1 Materials and Dimensions

Use steel with the same composition range as the parts to make samples with a diameter of 15-20 mm and a length of 80-100 mm. 2.2 Handling

During the carburizing process, samples should be taken out at different times according to the process requirements. The samples taken out of the furnace should be quickly placed in a small heating furnace at 800~820 ℃, protected by carbon black and cooled to below 500 ℃. After being taken out of the furnace and cooled, a section should be cut off to make metallographic samples. 2.3 Use a 4% nitric acid alcohol solution as a metallographic etchant.

3 Inspection methods

3.1 Inspection location: Inspect the metallographic structure of the sample surface up to 0.15mm.

3.2. Refer to the rating standard chart [see Appendix A (Supplementary) 1], and use an optical microscope at 400X based on the shape, quantity, and distribution of carbides

Assess the carbon content.

3.3 When the cooling is too fast, non-equilibrium structures such as martensite may appear, and the upper limit should be taken to determine the carbon content,