JB/T 8118.2-1999 This standard is a revision of NJ 326-84 "Metallographic Inspection Standard for Internal Combustion Engine Piston Pins". During the revision, only editorial changes were made according to relevant regulations, and the main technical content remained unchanged. This standard is part of the JB/T 8118 "Internal Combustion Engine Piston Pins" series of standards, which includes the following three parts: JB/T 8118-1997 Technical conditions for internal combustion engine piston pins JB/T 8118.2-1999 Metallographic inspection of internal combustion engine piston pins JB/T 8118.3-1999 Technical conditions for magnetic particle inspection of internal combustion engine piston pins This standard specifies the metallographic structure level, carburized layer depth, inspection and evaluation methods of 20, 15Cr, 20Cr or 20Mn2 steel piston pins after heat treatment. This standard is applicable to the inspection of metallographic structure and carburized layer depth of piston pins of reciprocating internal combustion engines with cylinder diameter less than or equal to 200mm. This standard was first issued in 1984. JB/T 8118.2-1999 Metallographic inspection of piston pins of internal combustion engines JB/T8118.2-1999 Standard download decompression password: www.bzxz.net

ICS 27: 020
Machinery Industry Standard of the People's Republic of China
JB/T 8118.2-1999
Internal combustion engines Piston pin-Metallographic inspection
1999-09-17 Issued
National Bureau of Machinery Industry
2000-01-01 Implementation
JB/T8118.2—1999
This standard is a revision of NJ326-84 "Metallographic Inspection Standard for Internal Combustion Engine Piston Pin". Editorial changes were made to the original standard during the revision, and the main technical content remained unchanged.
This standard replaces NJ 326-84 from the date of implementation. This standard is proposed and managed by the National Technical Committee for Standardization of Internal Combustion Engines. This standard was drafted by Shanghai Internal Combustion Engine Research Institute. The main drafter of this standard is Li Guoen.
The standard was first issued in 1984.
1 Scope
Mechanical Industry Standard of the People's Republic of China
Internal combustion engines-Piston pinMetallographic inspection
Internal combustion engines-Piston pinMetallographic inspection
JB/T 8118.2—1999
Replaces N 326—84
This standard specifies the metallographic structure level, carburized layer detection, inspection and evaluation methods of 20, 15Cr, 20Cr or 20Mn2 steel piston pins after heat treatment.
This standard applies to the inspection of the metallographic structure and carburized layer depth of piston pins of reciprocating internal combustion engines with a cylinder diameter less than or equal to 200mm.
2 Referenced standards
The provisions contained in the following standards constitute the provisions of this standard by reference in this standard. When this standard is published, the versions shown are valid. All standards will be revised. Parties using this standard should explore the possibility of using the latest version of the following standards. JB/T8118-1997 Technical conditions for piston pins of internal combustion engines 3 Technical requirements
3.1 Carburized layer depth
3.1. The carburized layer depth is the hypereutectoid layer plus the eutectoid layer plus 1/2 transition layer. 3.1.2 The carburized layer depth shall be in accordance with the provisions of JB/T 8118. 3.1.3 For the outer cylindrical surface with a carburized layer depth less than or equal to 0.6mm, the sum of the super-eutectoid layer and the eutectoid layer shall account for 25%-70% of the carburized layer depth, and no eutectoid layer is allowed.
3.2 Depth of hardened layer
3.2.1 The depth of hardened layer is the vertical distance from the outer cylindrical surface of the live cold pin to the specified hardness value inside. For high-quality carbon steel, the limit hardness value is 550HV: for alloy steel, the limit hardness value is 500HV. 3.2.2 The depth of hardened layer shall comply with the provisions of JB/T 8118. 3.3 Microstructure of carburized hardened layer on the outer cylindrical surface 3.3.1 Martensite
Martensite shall be evaluated according to the first level diagram of this standard, and grades 1 to 5 shall be qualified. 3.3.2 Carbide
Carbide shall be evaluated according to the second level diagram of this standard, and grades 1 to 3 shall be qualified. 3.4 Complete decarburization and carbon depletion on the inner surface
3.4.1 There shall be no complete decarburization layer on the inner surface. Approved by the Guohao Machinery Industry Bureau on September 17, 1999 and implemented on January 1, 2000
3.4.2 Carbon on the inner surface:
JB/T 8118.2 - 1999
a) For the inner surface that has not been carburized or has been carburized but the carburized layer is only composed of a transition layer, the depth of the carbon depletion layer shall not be greater than 0.05mm; b) For the inner surface that has been carburized and quenched and has a high-carbon martensite structure, there shall be no ferrite. 4 Inspection method
4.1 Sampling position
The cutting position of the sample should be 15~20mm away from the end face, and the cutting surface should be perpendicular to the outer surface. The sample is cut and polished for 1.5 hours, then etched with 4% nitric acid alcohol solution. The etching degree should be such that the whole structure is clearly displayed. 4.2 Measurement of carburized layer depth
The annealed sample should be annealed: Annealing specification is as shown in Table 1 Table 1
15Cr. 20Ct. 20Mn2
4.2.2 The sample should be measured at 100 times magnification. 4.2.3 Determination of the start and end position of the transition layer See Figure 14 4.3 Inspection of martensite
Time min
10--20
Cooling conditions
The inspection of martensite should be carried out at 500 times magnification, and the inspection position is within a field depth range from the surface, and is evaluated against the non-standard first-level diagram.
4.4 Inspection of carbides
The inspection of carbides shall be conducted at a magnification of 500 times. The worst visual field shall be used to evaluate the results against the second-level diagram of this standard. 4.5 Inspection of complete decarburization and carbon depletion on the inner hole surface 4.5.1 The inspection of complete decarburization and carbon depletion on the inner hole surface shall be conducted at a magnification of 100 times in the annealing and tempering state and evaluated at the worst visual field. The complete decarburization layer refers to a structure that is entirely ferrite, and is the part where other structures are first found from the inner hole surface to the bottom of the layer. 4.5.22
Carbon depletion layer refers to a part where only a part of the carbon is removed to increase the ferrite content, and is the part where the least ferrite content is first found from the inner hole surface to the bottom of the layer.
5 Metallographic structure classification
5. 1 Martensite classification:
a) Level 1 is hidden needle-shaped martensite;
b) Level 2 is fine needle-shaped martensite;
c) Level 3 is relatively fine needle-shaped martensite:
d) Level 4 is needle-shaped martensite:
e) Level 5 is medium needle-shaped martensite, with a needle blade length greater than 12~16μm:f) Level 6 is relatively coarse martensite, with a needle blade length greater than 16~24㎡;%) Level 7 is coarse needle-shaped martensite;
h) Level 8 is coarse needle-shaped martensite.
5. 2 Carbide classification:
a)! Grade 1 is evenly distributed granular carbides: JB/T B118.2—1999
b) Grade 2 is evenly distributed granular carbides, but a small amount of carbides are in the form of line segments; Grade 3 is discontinuous network distribution of granular carbides; Grade 4 is discontinuous carbides that are not completely closed: Grade 5 is discontinuous carbides that are in the form of closed networks, 6 Metallographic structure level diagram
6.1 The first level diagram (500×) is shown in Figures 1 to 8. Figure [Level
Figure 33 Level
Figure 22 Level
Figure 44 Level
Figure 55 Level
Figure 77 Level
6.2 The second level diagram (500×) is shown in Figures 9 to 13. JB/T 8118.2--1999
Figure 66 level
Figure 88 level
Figure 91 level
Figure 113 level
JB/T 8118.2--1999
Figure 102 level
Figure 124 level
JB/T 8118.2-1999
Figure 135 level
Over-lubrication is the starting line
Transition layer
Warning line of grade layer
JB/T 8118.2-—1999Www.bzxZ.net
Figure 14: Schematic diagram of the starting and ending positions of the carburized layer and transition layer (100×)
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