Heat treatment technology has a crucial impact on high-strength fasteners, especially its intrinsic quality. Therefore, in order to produce high-quality high-strength fasteners, advanced heat treatment technology and equipment are required.
1 Dongfeng Motor high-strength fastener heat treatment status
Dongfeng Motor's high-strength fasteners have four performance grades, namely 8.8, 9.8, 10.9, and 12.9. These four grades of high-strength fasteners are subject to conditioning.
Heat treatment and quenching and tempering is to improve the comprehensive mechanical properties of the fastener to meet the tensile strength and yield ratio specified by the product. Therefore, the quenching and tempering process has strict requirements on raw materials, furnace temperature control, furnace atmosphere control, quenching medium, heat treatment quality inspection and control.
1.1 Materials
Dongfeng Motor's high-strength fastener materials mainly include ML35, 35K, ML40Cr, ML35CrMo steel, etc., of which 75% ML35CrMo steel is imported. The materials mainly have problems such as box segregation, decarburization and cracking. The material needs to be spheroidized and annealed before cold forming, and the annealing is carried out in an oil furnace. The furnace has no protective atmosphere and decarburization exists.
1.2 heat treatment quenching furnace
12.9 grade high strength fasteners are tempered on the cast furnace furnace production line. The temperature inside the furnace and the atmosphere are controlled by computer. Rx gas is used as the protective atmosphere. Heating and anti-oxidation decarburization can be effectively controlled, and the quality of the fasteners in the heating process is intact.
The 8.8-grade high-strength fasteners are quenched and tempered on the vibration hearth furnace. Due to the influence of the structure of the vibration hearth furnace, the furnace sealing performance is poor, the Rx atmosphere is difficult to control, the furnace temperature difference is large, and the parts are heated in the furnace. The collision and the length of time are not-caused, the quality of the fastener in the heating process is poor, there are decarburization, bumping, uneven heating and so on.
1.3 quenching medium
Dongfeng Motor has high-strength fasteners for quenching and tempering. There are two kinds of quenching media. ML35 is quenched with alkaline water, and medium carbon alloy steel is quenched with ordinary mechanical oil. Quenching in alkaline water has quench cracking. Quenching in ordinary mechanical oil has uneven hardness or even unqualified phenomenon, and it has to be repeatedly tempered in production.
1.4 detection
After the heat treatment of Dongfeng Automobile high-strength fasteners, the main tests are hardness, tensile strength, metallographic structure (qualitative test), Rx gas analysis, and 12.9 grade 100% magnetic powder non-destructive inspection cracks. The quenching medium cooling performance measurement, quantitative analysis of metallographic structure, intrinsic defects of parts and hardness sorting have not been detected.
2 foreign high-strength fastener heat treatment level
2.1 Materials
Spheroidizing annealing in material restructuring, Japan Kobe Steel Plant has leading technology, spheroidized steel provided by Kobe Steel Plant does not require re-spheroidizing annealing in the fastener manufacturer, so there is no annealing decarburization problem. The materials of some manufacturers in Taiwan Province of China and Russia are annealed by induction heating, and then enter the spheroidizing annealing of the furnace in the protective atmosphere. The process is advanced and the decarburization problem can be solved well. Most western countries use electric heating hood spheroidizing annealing furnace controlled by protective atmosphere to achieve spheroidizing annealing of materials, advanced equipment and technology, reliable spheroidizing quality and no decarburization.
2.2 heat treatment quenching furnace
Mesh belt or cast chain heat treatment and quenching and tempering lines are widely used abroad. In addition to the good sealing performance of the furnace, the quenching and tempering line also has advanced atmosphere, computer control of temperature and process parameters, equipment fault alarm and display. High-strength fasteners from the feeding-cleaning-heating-quenching-cleaning-tempering-coloring to the lower line, all automatic control operation, effectively guarantee the quality of heat treatment.
1 Dongfeng Motor high-strength fastener heat treatment status
Dongfeng Motor's high-strength fasteners have four performance grades, namely 8.8, 9.8, 10.9, and 12.9. These four grades of high-strength fasteners are subject to conditioning.
Heat treatment and quenching and tempering is to improve the comprehensive mechanical properties of the fastener to meet the tensile strength and yield ratio specified by the product. Therefore, the quenching and tempering process has strict requirements on raw materials, furnace temperature control, furnace atmosphere control, quenching medium, heat treatment quality inspection and control.
1.1 Materials
Dongfeng Motor's high-strength fastener materials mainly include ML35, 35K, ML40Cr, ML35CrMo steel, etc., of which 75% ML35CrMo steel is imported. The materials mainly have problems such as box segregation, decarburization and cracking. The material needs to be spheroidized and annealed before cold forming, and the annealing is carried out in an oil furnace. The furnace has no protective atmosphere and decarburization exists.
1.2 heat treatment quenching furnace
12.9 grade high strength fasteners are tempered on the cast furnace furnace production line. The temperature inside the furnace and the atmosphere are controlled by computer. Rx gas is used as the protective atmosphere. Heating and anti-oxidation decarburization can be effectively controlled, and the quality of the fasteners in the heating process is intact.
The 8.8-grade high-strength fasteners are quenched and tempered on the vibration hearth furnace. Due to the influence of the structure of the vibration hearth furnace, the furnace sealing performance is poor, the Rx atmosphere is difficult to control, the furnace temperature difference is large, and the parts are heated in the furnace. The collision and the length of time are not-caused, the quality of the fastener in the heating process is poor, there are decarburization, bumping, uneven heating and so on.
1.3 quenching medium
Dongfeng Motor has high-strength fasteners for quenching and tempering. There are two kinds of quenching media. ML35 is quenched with alkaline water, and medium carbon alloy steel is quenched with ordinary mechanical oil. Quenching in alkaline water has quench cracking. Quenching in ordinary mechanical oil has uneven hardness or even unqualified phenomenon, and it has to be repeatedly tempered in production.
1.4 detection
After the heat treatment of Dongfeng Automobile high-strength fasteners, the main tests are hardness, tensile strength, metallographic structure (qualitative test), Rx gas analysis, and 12.9 grade 100% magnetic powder non-destructive inspection cracks. The quenching medium cooling performance measurement, quantitative analysis of metallographic structure, intrinsic defects of parts and hardness sorting have not been detected.
2 foreign high-strength fastener heat treatment level
2.1 Materials
Spheroidizing annealing in material restructuring, Japan Kobe Steel Plant has leading technology, spheroidized steel provided by Kobe Steel Plant does not require re-spheroidizing annealing in the fastener manufacturer, so there is no annealing decarburization problem. The materials of some manufacturers in Taiwan Province of China and Russia are annealed by induction heating, and then enter the spheroidizing annealing of the furnace in the protective atmosphere. The process is advanced and the decarburization problem can be solved well. Most western countries use electric heating hood spheroidizing annealing furnace controlled by protective atmosphere to achieve spheroidizing annealing of materials, advanced equipment and technology, reliable spheroidizing quality and no decarburization.
2.2 heat treatment quenching furnace
Mesh belt or cast chain heat treatment and quenching and tempering lines are widely used abroad. In addition to the good sealing performance of the furnace, the quenching and tempering line also has advanced atmosphere, computer control of temperature and process parameters, equipment fault alarm and display. High-strength fasteners from the feeding-cleaning-heating-quenching-cleaning-tempering-coloring to the lower line, all automatic control operation, effectively guarantee the quality of heat treatment.
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