Heat treatment process 14Cr17Ni2 pallet self-locking screw Shanghai Ruiman Machinery Manufacturing Co., Ltd. (200245) Bai Liqing Yin Xiuyin m flat punching cold heading plate self-locking nut is a complicated manufacturing process, technical difficulty, and has added value The self-locking military fastener products are mainly used for the connection of sheet metal parts and stamping parts on aircraft, and are widely used in the field of aerospace. Products include single ear, binaural, angular, swimming and airtight plate nuts and many other models, as shown.
In recent years, with the aerospace industry's requirements for 篼 strength, 篼 self-locking and 篼 corrosion resistant pallet nuts, the traditional structural steel materials and process manufacturing of the pallet nuts have not been able to meet the requirements. Research shows that the self-locking nut made of martensitic stainless steel 14Cr17Ni2 material can solve the shortcomings of poor performance of the original pallet nut and meet the demanding conditions. Of course, how to effectively control the inter-process annealing and final heat treatment of 14Cr17Ni2 materials has become the key to product development. This paper will start with the characteristics of 14Cr17Ni2 material, focusing on the annealing and final heat treatment process between the pallet nuts.
14Cr17Ni2 is a low-carbon martensitic stainless steel. It is based on the Cr13 type and has a Cr content of wm=2%. The chemical composition is shown in Table 1. Such an alloying design maintains the austenite transformation so that the steel can still be strengthened by quenching the martensite structure. Among martensitic stainless steels, 14Cr17Ni2 steel has the best corrosion resistance and the strongest strength, especially with relatively high electrochemical corrosion properties. Therefore, 14Cr17Ni2 material has good corrosion resistance in seawater and nitric acid. .
Table 1 14Cr17Ni2 material chemical composition (mass fraction) 14Cr17Ni2 material has the disadvantage of strong cold work hardening characteristics, process control is difficult, must be annealed after many processes to restore the plasticity and toughness of the material to be machined. In addition, due to the relatively low degree of alloying of the 14Cr17Ni2 material, the austenite forming region is very narrow and the temperature sensitivity is large, so the final heat treatment process control is also complicated.
The process flow of the material pallet self-locking nut (see) is as follows.
Trimming and trimming, chamfering and tapping in the reaming. Closing 14Crl7Ni2 double ear plate Xiao lock nut forming process flow preparation - cold heading - flattening - cleaning and drying - inter-process annealing - secondary flattening - cleaning and drying - inter-process annealing - trimming - punching - I The hot rainbow seat is made, 20é’¤. Interesting mechanical deburring - drilling - reaming - internal chamfering - tapping - closing - cleaning and drying - final heat treatment - surface polishing - passivation treatment - inspection - finished packaging into the warehouse.
Between ~M10, the process flow has also been adjusted, especially the inter-process annealing and final heat treatment adjustments are the largest, in order to achieve the optimal control of the process.
After the flattening process, the 14Crl7Ni2 pallet nut has a strong cold work hardening due to the large deformation, so that the hardness after flattening reaches 520 ~ 560 HV, which is about 220 HV higher than the hardness of the ball after the cold rolling is 300 ~ 336 HV. . Therefore, the flattened billet must be annealed between processes to restore and recrystallize the billet, reduce the hardness and brittleness of the material, and restore the plasticity and toughness of the material for subsequent processing.
The annealing process varies depending on the shape and size of the nut. In general, small-sized single-ear, double-ear plate nuts require only two annealings. For angled, floating pallet nuts, and large-size single-ear, binaural pallet nuts, three annealings are required to meet the process requirements.
The annealing equipment adopts SA-208 type nitrogen protection vacuum well type annealing furnace manufactured by Shanghai Suai Electromechanical Complete Equipment Co., Ltd., and the final use temperature can reach 9 °C. The 14Crl7Ni2 nut blank is cleaned, degreased, dried and packed into The heat-resistant steel cylinder is placed in the furnace and the following annealing process is employed.
Small-sized pallet nut (M3 preheated for 30min, using annealing process close to recrystallization temperature, 740C heat preservation for 2h, with furnace cooling to 495C. The hardness after annealing is relatively uniform, reaching 26-27HRC. A little hardness can avoid The small-sized nut with a thin plate thickness is bent and deformed when the trimming is blanked.
The large-size pallet nut (M6~M10) 650C is preheated for 30min, and it is annealed in subcritical process. It is kept at 680~700C for 2h. It is cooled to 495C with the furnace. The hardness reaches 23~25HRC. The hardness is slightly lower, which is beneficial to the big one. Follow-up drilling and tapping of the specification nut.
The final heat treatment of the 14Cr17Ni2 pallet self-locking nut includes two processes of quenching and tempering. The hardness requirement of the self-locking nut of 14Cr17Ni2 pallet is 33-39HRC. At the same time, the index of locking torque is evaluated. The stainless steel special mesh belt furnace is used for quenching, and the SA-X308 nitrogen protection vacuum box annealing furnace is used for tempering.
The quenching structure of the 14Cr17Ni2 material pallet self-locking nut is low carbon martensite + a small amount of ferrite structure, the ACl temperature is about 860C, and the austenite forming area is very narrow. In the austenitizing process of 14Cr17Ni2 material, the slight fluctuation of the alloy composition will have a significant effect on the phase in the quenched structure, and the ferrite content will directly affect the mechanical properties of the quenched structure. The ferrite content is more Low, the hardness of the material after quenching is more ambiguous.
Table 2 shows the hardness of the 14Cr17Ni2 material plate nut at different quenching temperatures. When the quenching temperature reaches Aci+20~30C and the target is 880~890°C, the austenite formation area is small, and the material contains a large amount of phase in the austenitizing process, which makes the iron in the quenched structure. The elemental content is relatively low, resulting in low mechanical properties of the material after quenching. Therefore, the hardness of the material is only 29.8~30.6HRC. ~960C, the phase content in the phase is relatively small, and the ferrite content in the quenched structure is also low. Therefore, the impact on the performance of the quenched structure is also small, and the quenching hardness can reach 48.2-49.5HRC. At 1010C, the alloying elements are fully austenitized, the fluctuation of chemical composition is small, and the ferrite content in the quenched structure is reached. The lowest level, so the quenching hardness can reach 50.5~52.7HRC. Table 214Cr17Ni2 material plate nut hardness at different quenching temperatures No. quenching temperature / C measured hardness HRC (1) incomplete quenching is 14Cr17Ni2 plate nut incomplete quenching process The curve, according to the nut specifications, is 860 60min, furnace cooling 30min to 510C, rapid air cooling. The quenching structure is lath martensite + a large amount of ferrite structure, the hardness of the nut is 33. The ion nitriding process of the spheroidal graphite cast iron crankshaft of the 迕 迕 迕 滨 滨 滨 滨 海 海 海 海 256 256 256 256 256 256 256 256 256 256 256 256 256 256 256 256 256 College (Shandong 256624) Guo Tingting crankshaft is one of the most important parts in internal combustion engines. It combines with cylinders, pistons, connecting rods, etc. to form the power source of the engine, and outputs power from the crankshaft. The crankshaft is subjected to repeated bending and torsional loads while the main journal and the connecting rod neck are subjected to strong friction under idle rotation. Therefore, the damage form of the crankshaft is mainly the fatigue-induced fracture and the wear of the journal. The ion nitriding strengthening treatment is to improve the fatigue strength and wear resistance of the crankshaft. The 4105 cored ductile iron crankshaft (see) produced by our company has achieved certain effects through ion nitriding treatment.
The so-called ion nitriding is to use a glow discharge ionization gas generated between a workpiece (cathode) and an anode in a low vacuum nitrogen atmosphere of less than 2000 Pa. The positive ions bombard the surface of the workpiece to heat it and pass a series of physical and chemical processes. The process forms a chemical heat treatment process for the nitride layer. It is also a surface strengthening process that not only improves the wear resistance and corrosion resistance of the workpiece surface, but also improves the fatigue strength of the workpiece.
The base of the steel workpiece is generally free a ferrite, pearl oooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo By controlling the amount of ferrite in the quenched structure, the nut hardness of the nut can be directly achieved without tempering.
Table 314Cr17Ni2 stainless steel special mesh belt furnace incomplete quenching process control condition Nut specification hardness HRC (2) Complete quenching is the complete quenching + tempering process of the pallet nut, according to the different nut specifications, using 860~900"c preheating for 20min Heating to 970~1010"C for 60min, furnace cooling for 30min to 510C, rapid air cooling. The quenched structure is lath martensite + a small amount of ferrite structure, and the quenching hardness is 53~55HRC. Due to the tempering resistance of chrome in the 14Crl7Ni2 material and the rising point of 4 points, the tempering temperature of the quenching and tempering treatment is correspondingly Lifting and tempering will not completely recrystallize when tempered. Because the material has the 475C back cabinet 4WCrimi2 support according to the complete quenching of the screw loose + the same fire process brittleness, it is often cooled by rapid air cooling when tempering. The tempering process is: 570-580C heat preservation for 90min, tempering hardness of 33~39HRC, and tempering structure is a tempered sorbite structure that retains the martensitic orientation.
According to the characteristics of 14Cr17Ni2 material, the manufacturing process of the self-locking nut of the pallet is designed. Combined with different product specifications, the two key processes of inter-process annealing and final heat treatment of new products were analyzed in detail, and the related aerospace fastener products I, such as X-thermal rainbow seat processing, were produced. interest
During the production of highway painting, put glass bead into paint based on the ratio of 18-25% (weight percentage), so that the highway paint can still keep reflectivity during wear and friction. The ratio is refer to the specification of Communication Industry Standard of the People`s Republic of China No. JT/T280-2004, the standards which is different in different countries and areas.
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The appearance of glass bead should be colorless, loosen and spherical particle, should be clean without impurity, and without agglomeration |
According to the specification of Communication Industry Standard of the People`s Republic of China No.GB/T24722-2009, the granulometry is shown in the table below:
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