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Machinery Industry Standard of the People's Republic of China
JB/T7711-95
Heat treatment of gray cast iron parts
Published on June 20, 1995
Ministry of Machinery Industry of the People's Republic of China
Implementation on January 1, 1996
Machinery Industry Standard of the People's Republic of China
Heat treatment of gray cast iron parts
1 Subject content and scope of application
This standard specifies the heat treatment equipment, process and quality inspection methods for gray cast iron parts. This standard is applicable to the annealing, normalizing, tempering and isothermal heat treatment processes of gray cast iron parts. 2 Reference standards
GB5614
GB7216
GB7232
GB9439
GB9452
GB/T6051
JB/Z234.9
Metal Rockwell hardness test method
Metal Brinell hardness test method
Gray cast iron mechanical properties test method
Name, definition and code of heat treatment state of cast iron Metallographic structure of gray cast iron
Terminology of metal heat treatment process
Gray iron parts
Method for determining effective heating zone of heat treatment furnace
Heat treatment process and quality inspection of ductile iron
Heat treatment process specification of special iron parts
3 Application of heat treatment process
JB/T7711-95
3.1 High temperature graphitization annealing is used for castings with more eutectic cementite in the matrix structure to reduce hardness and improve machinability. 3.2
Low temperature graphitization annealing is used for castings with too high hardness, no eutectic cementite in the matrix structure, and high formability and toughness are required.
Stress relief annealing is used to reduce residual stress in casting, casting welding, machining, etc., to ensure the stability of casting size. Complete austenitization normalizing is used for gray cast iron with too much iron wire and low hardness to improve the strength, hardness and wear resistance of castings. 3.4
Partial austenitizing normalizing is used for castings with relatively uniform matrix structure and certain strength and toughness. 3.6 Full austenitizing tempering and tempering are used to use matrix structures with different tempering temperatures to improve the strength, hardness and wear resistance of castings. 3.7
Fully austenitizing isothermal tempering is used to obtain bainite matrix structure and improve the comprehensive performance of castings. 3.8 Surface tempering is used to improve the strength, surface hardness and wear resistance of castings. 3.9 Chemical heat treatment is used to obtain special physical, chemical and mechanical properties of the surface of the part to be treated. 4 Heat treatment equipment
4.1 Heating equipment
4.1.1 Use gas, oil, coal and resistance heating furnaces. According to the production requirements of parts, non-oxidizing heating equipment, controlled atmosphere heating furnaces and continuous operation furnaces can also be used.
4.1.2 The flame of the fuel heating furnace cannot directly contact the shoe casting, and the controlled gas heating furnace should be able to adjust and control the atmosphere in the furnace. Continuous operation furnaces should be able to adjust the conveying speed so that the parts can maintain the necessary heating time in the furnace. Approved by the Ministry of Machinery Industry on June 20, 1995
Implementation on January 1, 1996
JB/T 771195
4.1.3 The temperature uniformity and temperature accuracy of the heat treatment furnace should meet the process requirements. The effective heating zone determination method shall be implemented in accordance with the provisions of GB9452. 4.2 Temperature measurement and recording instruments
4.2.1 Heat treatment heating and cooling equipment should be equipped with temperature measurement, temperature control and automatic recording devices. 4.2.2 The total error of the temperature measuring device shall not exceed the provisions of Table 1. Table 1
Predetermined temperature
Total error of temperature indication
Note: T is the heating temperature.
≤400
4.2.3 Thermocouples and furnace temperature instruments should be calibrated regularly and relevant records should be kept. 4.3 Cooling equipment and cooling medium
±(T/100)
4.3.1 The cooling equipment should ensure that all parts of the treated parts are evenly cooled. The heat treatment furnace used for annealing and normalizing should be equipped with cooling holes and blast cooling and other fast cooling devices.
4.3.2 The air volume of the blast device and the spray volume of the spray device should be able to meet the cooling requirements. 5 Heat treatment process
5.1 Preparation before heat treatment
5.1.1 Macroscopically inspect the appearance, geometric shape and size of the heat-treated parts. There should be no defects such as pores, shrinkage cavities, looseness, cracks, etc. 5.1.2 According to the chemical composition, grade, original organization and technical requirements of the parts to be treated, formulate the heat treatment process regulations and operating precautions for cast iron parts in accordance with JB/Z234.9.
5.1.3 Check the integrity of heating, ventilation, lifting and other equipment and temperature measuring instruments. If any fault is found, timely measures should be taken. 5.2 Furnace loading
5.2.1 Load the furnace in the effective heating area, and the test rod should be placed in the specified position with the same furnace and other parts. 5.2.2 The brand and wall thickness of the castings heat treated in the same furnace should be similar. Thin parts, small parts and workpieces with complex shapes should be placed farther away from the heat source.
5.2.3 The furnace loading should not be overloaded, and there should be a good and even gas circulation. The layered loading of the parts should be stable, and the overhead distance of the pad position should not be too long to avoid point, line contact or staggered parts. 5.3 Process specifications
5.3.1 Heating method
Preheating can be used, low temperature heating with the furnace or heating at the specified heating temperature. 5.3.2 Heating speed
The heating speed should be selected according to the thickness and structural complexity of the casting. The heating speed of the casting with complex structure should be as slow as possible. For general solid or simple shaped castings, the heating speed can be faster. 5.3.3 Heating temperature
The specific heating temperature should be determined according to the casting grade, as-cast structure, workpiece shape, size and process method, etc. Refer to Appendix A (reference part). The process type and furnace temperature accuracy should comply with the provisions of Table 2. Table 2
Process type
High graphitization annealing
Low temperature graphitization annealing
Stress relief annealing
Complete austenitization normalizing
Furnace annealing accuracy
Process type
Partial austenitization normalizing
Complete austenitization annealing
Complete austenitization equal annealing
Furnace temperature accuracy
5.3.4 Holding time
JB/T7711-95
It is necessary to ensure that all parts of the workpiece are evenly heated to the required humidity to make the structure uniform. The holding time is related to the brand, wall thickness, furnace loading, etc. of the casting.
5.3.5 Cooling rate
Annealing cooling rate is determined by casting accuracy, furnace loading and matrix structure content. High-precision castings should be cooled as slowly as possible, and normalizing can be done in still air or by wind. Heavy castings and thick-walled castings have a faster average cooling rate, and castings are generally cooled with oil. The temperature of the isothermal quenching medium is generally 280-320°C, and it is generally not necessary to temper after cooling in the air after isothermal quenching. 5.3.6 Furnace
Annealing The furnace temperature is below 250-180°C, and the furnace temperature of large and complex parts should be lower. Before the temperature of the furnace casting drops to room temperature, it must not be exposed to rain, snow or water. Castings after being taken out of the furnace should be placed steadily, and small block castings can be stacked. After heat treatment, the oxide scale can be removed if necessary.
5.4 Surface heat treatment
HT250, HT300, HT350 gray cast iron can be subjected to surface treatment such as flame quenching, induction heating quenching, and electric contact quenching according to performance requirements.
5.5 Records
Necessary matters in the heat treatment process should be recorded and kept for future reference. 6 Quality inspection of heat-treated parts
6.1 Surface quality
Quality inspection should be carried out by visual inspection. The surface of the casting should be clean and no serious scale or rust is allowed. 6.2 Mechanical properties
6.2.1 Hardness test can be carried out on castings or representative test bars from the same furnace. Hardness test shall comply with GB230 and GB231. 6.2.2 Tensile test shall comply with GB977. If other performance tests (such as bending and impact) are required, the supply and demand parties must agree before heat treatment.
6.3 Metallographic structure
Metallographic inspection shall comply with GB7216.
6.4 Distortion
The distortion amount shall be within the technical requirements of the workpiece and shall not affect mechanical processing and use. 6.5 Flaw Detection
Surface cracks and surface scratches can be inspected visually, and magnetic particle inspection can be used when necessary. Ultrasonic and other methods can be used to inspect internal quality. 6.6 Stress
According to the quality requirements of castings, strain gauges can be attached to measure the residual strain value. 7 Status marking of treated parts
After the treated parts are inspected and qualified, they must be marked with the gray cast iron grade, heat treatment status, part number, name, etc. The marking method of heat treatment status code shall comply with GB5614.
High temperature graphitebZxz.net
Temperature annealing
A*ct+(50
Additional instructions:
Low temperature stone wall
Temperature annealing
Ac—(30
JB/T7711-95
Appendix A
Heat treatment process temperature of gray cast iron parts
(reference part)
Stress relief
Temperature for use in band
Complete austenitic
Normalizing
Ae +(40
This standard is proposed by the National Technical Committee for Heat Treatment Standardization. This standard is under the jurisdiction of Beijing Institute of Mechanical and Electrical Engineering. This standard is drafted by Tianjin Institute of Heat Treatment. The main drafter of this standard is Sheng Hongquan.
Partial austenitic
normalizing
A'c,A'c
between)
completely austenitic
normalizing
A'c +(30
～50)
High tempering, medium tempering, low temperature tempering
High temperature tempering
500～600
Medium temperature tempering
350'～500
Low tempering
140~250
Isotropic tempering
Complete austenitic
Isothermal
A'c+(30
～50)Commonly used
Isothermal tempering
Quality (280
～320)
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