This standard specifies the microstructure rating of the surface and core of thin-layer carbonitriding or thin-layer carburized steel parts and the determination method of the carburized layer depth. This standard is applicable to low-carbon and low-alloy steel parts such as 08F, Q215AF, Q235AF, 10, 15, 20, 20Cr, 20CrMnMo, etc. with a carbonitriding layer depth of less than or equal to 0.3mm. JB/T 7710-1995 Microstructure inspection of thin-layer carbonitriding or thin-layer carburized steel parts JB/T7710-1995 Standard download decompression password: www.bzxz.net

Mechanical Industry Standard of the People's Republic of China
JB/T7710-95
Thin layer carbonitriding or thin layer carburizing steel parts
Microstructure inspection
Issued on June 20, 1995
Ministry of Machinery Industry of the People's Republic of China
Implementation on January 1, 1996
Mechanical Industry Standard of the People's Republic of ChinabzxZ.net
Thin layer carbonitriding or thin layer carburizing steel parts
Microstructure inspection
1 Subject content and scope of application
JB/T7710-95
This standard specifies the method for rating the surface and core microstructures of thin layer carbonitriding or thin layer carburizing steel parts and determining the depth of the penetration layer. This standard applies to low-carbon and low-alloy steel parts such as 08F, Q215AFQ235AF, 1015, 20, 20Cr, 20CrMnMo, etc., with a carbonitriding or carburizing layer depth less than or equal to 0.3mm. 2 Reference standards
GB7232 Metal heat treatment process terms
GB9451 Determination of the total hardened layer depth or effective hardened layer depth of thin surface of steel parts 3 Test specimens
3.1 The test specimens shall be cut from thin-layer carbonitriding or thin-layer carburized steel parts, and can also be used as samples that are consistent with the material, heat treatment state, effective thickness, etc. of the steel parts and have been carbonitrided or carburized in the same furnace. 3.2 The form of the test specimen shall comply with the provisions of Article 3.3.1 of GB9451. 3.3 The surface carbon content of thin-layer carbonitriding steel parts shall not be less than 0.50%, and the nitrogen content shall not be less than 0.10%. The surface carbon content of thin-layer carburized steel parts shall not be less than 0.50%.
3.4 ​​During the preparation of the sample, the microstructure shall not be changed due to heat. The edges of the sample shall be rounded and the angle of the oblique section sample shall not be changed.
4 Measurement of the depth of the infiltration layer
The measurement is carried out under the equilibrium state.
4.2 When the microstructure of the infiltration layer has a hypereutectoid zone or an eutectoid zone, it shall be measured according to Figure 1a; when the microstructure has only a hypoeutectoid zone, it shall be measured according to Figure 1b. 4.3 The measurement method shall be carried out according to the following requirements:
The ground surface of the sample shall be etched with a 4% nitric acid alcohol solution; the magnification shall be 200 times:
The measurement position shall be carried out in accordance with the relevant technical conditions; the depth of the infiltration layer is the distance from the surface of the steel part along its vertical direction to the core structure, as shown in Figures 1a and b. 5 Rating of the microstructure of the infiltration layer
5.1 The rating is carried out under the fire state.
5.2 The ground surface of the sample shall be etched with a 4% nitric acid alcohol solution. 5.3 The magnification is 400 times.
5.4 When the microstructure of the carburized layer is mainly acicular martensite, the martensite grade and retained austenite grade shall be evaluated according to Figure 2, or determined according to the needle length and the retained austenite content, see Table 1. Approved by the Ministry of Machinery Industry on June 20, 1995
Implemented on January 1, 1996
Martensite grade
Microstructural characteristics
Hidden needle martensite + retained austenite
Needle martensite + retained austenite
JB/T7710-95
Maximum size of martensite needles
Coarse needle martensite + retained austenite
Coarse needle martensite + retained austenite
Coarse needle martensite + retained austenite
Retained austenite content
5.5 When the microstructure of the carburized layer is mainly lath martensite, the martensite grade is evaluated according to Figure 3, and the needle length is shown in Table 2. Table 2
Martensite grade
Microstructural characteristics
Lath martensite + fine needle martensite
Lath martensite + medium needle martensite Lath martensite + relatively coarse needle martensite Lath martensite + coarse needle martensite
Lath martensite + coarse needle martensite The ferrite grade in the center is evaluated according to Figure 4, and the ferrite characteristics and ferrite content are shown in Table 3. 5.6
Ferrite grade
Fe-based body characteristics
No free ferrite
A small amount of blocky free ferrite
A large amount of blocky free ferrite
A large amount of blocky free ferrite
A large amount of blocky free ferrite| |tt||Matrix boundary line
Maximum size of martensite needle
Ferrite content%
Matrix boundary line
Thin layer carbonitriding or thin layer carburizing Depth measurement diagram (200×) Level 1
JB/T7710-95
Martensite and retained austenite level diagram (400×) 3
JB/T7710-95
Figure 3 Martensite level diagram (400×)
Additional instructions:
JB/T7710-95
Figure 4 Core ferrite level diagram (400×) This standard was proposed by the National Technical Committee for Heat Treatment Standardization and is under the jurisdiction of Beijing Institute of Mechanical and Electrical Engineering. This standard was drafted by Shanghai Materials Research Institute of the Ministry of Machinery Industry, Shanghai Phoenix Bicycle Co., Ltd., Shanghai Zehuo Factory, etc. The main drafters of this standard are Zhou Fuxin, Lou Huifen, Yu Xianguo, Zhu Huiwen, etc.
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