This standard specifies the metallographic structure, inspection method and evaluation of the intake and exhaust valves of internal combustion engines. JB/T 6720-1993 Metallographic inspection of intake and exhaust valves of internal combustion engines JB/T6720-1993 Standard download decompression password: www.bzxz.net

Machinery Industry Standard of the People's Republic of China
JB/T 6720-1993
Metallographic Inspection of Intake and Exhaust Valves of Internal Combustion Engines
Issued on July 29, 1993
Ministry of Machinery Industry of the People's Republic of China
Implementation on January 1, 1994
Metallographic Inspection of Intake and Exhaust Valves of Internal Combustion Engines
1 Subject Content and Scope of Application
JB/T6720-1993
This standard specifies the metallographic structure, inspection method and evaluation of intake and exhaust valves (hereinafter referred to as valves) of internal combustion engines. This standard applies to the metallographic structure inspection and evaluation of valves of reciprocating piston internal combustion engines with a cylinder diameter less than or equal to 200mm. 2 Reference standards
GB5617
GB6394
GB9451
GB11354
Determination of effective hardened layer depth after induction quenching or flame quenching of steelMethod for determination of average grain size of metal
Determination of total hardened layer depth or effective hardened layer depth on thin surface of steel partsDetermination of nitriding layer depth and metallographic inspection of steel partsJB/T6012 Technical conditions for intake and exhaust valves of internal combustion engines3 Technical requirements
3.1 Matrix metallographic structure
3.1.1 The matrix structure of alloy structural steel shall be tempered bainite, and its free ferrite content shall not exceed 5% of the field of view area. It shall be evaluated according to the first-level diagram of this standard, and level 1 shall be qualified; the austenite grain size shall be evaluated according to GB6394, and shall be greater than or equal to level 6. 3.1.2 The matrix structure of martensitic heat-resistant steel shall be tempered troostite, and free ferrite and continuous network carbide are not allowed. The austenite grain size shall be evaluated according to GB6394 and shall be greater than or equal to level 6. 3.1.3 The matrix structure of austenitic heat-resistant steel shall be austenite, and the austenite grain size shall be evaluated according to GB6394 and shall be greater than or equal to level 3. The layered precipitates shall be inspected in accordance with the product drawings and technical documents and with reference to the second level diagram of this standard. 3.2 Nitriding layer
3.2.1 After nitriding of the valve, the depth of the nitriding layer shall comply with the provisions of the product drawings and technical documents. 3.2.2 The looseness of the nitriding layer shall be evaluated according to the looseness level diagram in GB11354, and levels 1 to 3 are qualified. 3.2.3 For martensitic steel valves treated with ion nitriding, the nitride level in the nitriding layer shall be evaluated with reference to the nitride level diagram in GB11354, and levels 1 to 3 are qualified.
3.3 Overlay
The overlay alloy layer and the base metal should be metallurgically bonded, and its metallographic structure and metallurgical quality should comply with the requirements of the product technical documents. 3.4 Quenching and hardening layer at the rod end
The depth of the hardened layer should comply with the requirements of JB/T6012 or product drawings. 4 Inspection method
4.1 Inspection of base metallographic structure
4.1.1 Sampling position
For integral valves, any cross section within 5mm from the tangent point of the valve neck and the rod to the end face of the disk shall be used as the metallographic inspection surface, and the entire grinding surface shall be inspected; for bimetallic welded valves, in addition to the above-mentioned specified positions, a cross section shall be taken from the martensitic heat-resistant steel part of the rod as the metallographic inspection surface, and this section shall avoid the welding affected area. Approved by the Ministry of Machinery Industry on July 29, 1993
Implemented on January 1, 1994
Etching method
JB/T 6720—1993
4.1.2.1 The display of austenite grain size of alloy structural steel adopts Etchant 1 or Etchant 2. a. Etchant 1: Saturated picric acid aqueous solution
1% Haiou brand detergent
b. Etchant 2: Picric acid
Sodium alkyl sulfonate 1~2g
Distilled water
Note: When using Etchant 2, it should be heated to boiling and etched for several seconds. 4.1.2.2 The display of free ferrite of alloy structural steel adopts Etchant 3. Etching agent 3: nitric acid 4mL
alcohol 100mL
martensitic heat-resistant steel austenite grain size and free ferrite display using etchant 4 or etchant 5.4.1.2.3
a. Etching agent 4: picric acid
b. Etching agent 5: ammonium persulfate 35g
Note: Etching agent 4 is used for electrolytic etching, voltage 0.4~0.8V, current 0.12A, time 10-20s. 4.1.2.4 If the alloy structural steel and martensitic heat-resistant steel samples cut by the above-mentioned etchants are difficult to show the grain boundary by direct observation, and the austenite grain size cannot be determined, the austenite grain size can be determined after processing according to the method specified in Article 3.2.1.4 of GB6394.
4.1.2.5 Etchants 6 are used to display the structure of austenitic heat-resistant steel after solid solution aging. Etchants 6: 55mL saturated picric acid aqueous solution, ferric chloride
4.1.3 Rating method
4.1.3.1 The evaluation of austenite grain size is in accordance with the provisions of GB6394. Generally, the comparison method is used, using series pictures I or II. If there is a dispute, the intercept method is used for arbitration.
4.1.3.2 The evaluation of free ferrite adopts the standard picture comparison method. The worst field of view is selected on the entire grinding surface. If three fields of view are unqualified, it is unqualified.
4.1.3.3 The evaluation of lamellar precipitates in austenitic heat-resistant steel adopts the standard picture comparison method. The worst field of view is selected on the entire grinding surface. If three fields of view are unqualified, it is unqualified.
4.2 Inspection of nitrided layer
4.2.1 Sampling location
For integral valves, take any cross section of the nitrided part of the valve stem as the metallographic inspection surface; for bimetallic welded valves on the stem, if the weld is located at the polished part of the stem, a cross section should be taken from the non-heat-affected zone on both sides of the weld as the metallographic inspection surface, otherwise, only a cross section should be taken from the non-heat-affected zone of the martensite section of the stem as the metallographic inspection surface. 4.2.2 The inspection method for the depth of nitrided layer shall comply with the provisions of GB11354. Generally, the metallographic method is used. In case of dispute, the hardness method is used for arbitration. 4.2.3 The inspection method for the looseness and nitride of nitrided layer shall comply with the provisions of GB11354. 4.3 Inspection of weld overlay
Sampling location
JB/T6720-1993
For the weld overlay on the end face of the rod, the longitudinal grinding surface through the axis of the rod end face is taken as the metallographic inspection surface; for the weld overlay on the cone face of the disc, the radial section of the disc is taken as the metallographic inspection surface.
4.3.2 Etching method
The structure of the weld overlay layer is displayed by using etchant 7 or etchant 8. a. Etching agent 7: hydrochloric acid
distilled water
ferric chloride
b. Etching agent 8:
distilled water
4.4 Inspection of the depth of the hardened layer at the end of the rod
4.4.1 Sampling location
Take a longitudinal grinding surface of appropriate length from the end face of the rod through the axis. 4.4.2 Etching method
4.4.2.1 Etching agent 3 is used for alloy structural steel. 4.4.2.2 Etching agent 4 is used for martensitic heat-resistant steel. 4.4.3 Evaluation method
4.4.3.1 Macro measurement method
In general, the macro method is used to measure the shortest distance from the rod end to the white line (see Figure 1). White line
Deepth of hardened layer
4.4.3.2 Hardness method
When there is a dispute over the use of the macro measurement method, the hardness method specified in GB5617 or GB9451 shall be used for measurement. 5
Grading standard of metallographic structure
5.1 Austenite grain size shall be evaluated in accordance with the provisions of GB6394. 5.2 Free ferrite
Inspect and evaluate according to the first level diagram under 500 times magnification, and the description of each level is shown in Table 1. Table 1
Free ferrite content%
5.3 The looseness of the nitriding layer and nitrides shall be evaluated according to GB11354. Figure
5.4 The lamellar precipitates of austenitic heat-resistant steel are inspected with reference to the second-level diagram under a magnification of 500 times. The description of each level is shown in Table 2. 3
Figure 21 level
Figure 41 level
JB/T6720—1993
Lamellar precipitate content%
First level diagram (500 times)
Second level diagram (500 times)
Figure 32 level
Figure 52 level
Additional description:
Figure 63 level
JB/T 67201993
This standard is proposed and managed by the Shanghai Internal Combustion Engine Research Institute of the Ministry of Machinery Industry. This standard is drafted by the Shanghai Internal Combustion Engine Research Institute of the Ministry of Machinery Industry. The main drafters of this standard are Zhao Minghao and Zhao Shiqun. Figure 74
From the date of implementation of this standard, NJ354-85 "Metallographic Inspection Standard for Intake and Exhaust Valves of Internal Combustion Engines" will be invalid. People's Republic of China
Mechanical Industry Standard
Metallographic Inspection of Intake and Exhaust Valves of Internal Combustion Engines
JB/T 67201993
Published and issued by the China Academy of Mechanical Science
Printed by the China Academy of Mechanical Science
(No. 2 Shouti South Road, Beijing
Postal Code 100044)
Word Count 10.000Www.bzxZ.net
1/16 Print Sheet 1/2
Format 880×1230
First Edition in December 1993
First Printing in December 1993
Print Quantity 1-500
Price 8.00 Yuan
Mechanical Industry Standard Service Network: http://www.JB.ac.cn661_09
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