Several main factors that affect the service life of automobile leaf springs are the physical and chemical inspection organization and performance. Ma, Gan Chunjin. Gong Ning, Dong Wenling Henan Anyang Iron and Steel Group Corporation. Several important factors of the service life of Anyang 455004, that is, the choice of materials, raw material defects, heat treatment defects, horizontal shot peening quality.
i Introduction Automobile leaf springs are elastic elements in automobile suspensions, which require a higher elastic limit and a higher tensile strength. The ratio of yield limit to tensile strength is close to 1 and the maximum elastic specific work plate spring. The gabion works under alternating stress conditions. Most of its sharp effects are fatigue fracture. Therefore, in addition to maintaining high fatigue strength, elastic yellow steel must also have good plasticity and the maximum stress on the surface of the primary leaf spring, and fatigue fracture starts from the work piece. Therefore, it is also required that good steel is tempered at medium temperature after quenching, and the surface is then shot peened. The normal organization is tempered Torquat 1. In practical use, the service life of the leaf suspension of the car suspension system with similar structure is only relatively poor. The one used by our company and the leaf spring of the car make the life as long as 1 Father 43 is around 104, part of the leaf spring is only 200030001 and the leaf spring of the truck imported from Japan runs 6010480104. The highest is 106 or more. To this end, we conducted a comparative analysis of a variety of domestically-made trucks imported from Japan 8151, to find out the main flashlights that affect the service life of automobile steel sheets.
2 The main factors affecting the service life of automobile leaf springs 2.1 The choice of materials is in China's spring steel standards. Carbon bullet steel has low flash hardenability and is rarely used in automobile suspensions; hardened steel has good hardenability, but is prone to fire cracking and has tempering brittleness. Therefore, anvil manganese steel is as 6 The new-grade silicon-manganese steel, such as 5.18, is widely used in China. Silicon manganese steel has low processing cost, good hardenability, high tensile strength yield point and elastic limit, and good tempering stability. However, silicon-manganese steel is an intrinsically coarse-grained steel, which is sensitive to overheating, has a large tendency to decarburize, and is prone to graphitization. Adding He, He, and other alloy elements on the basis of Guimeng Steel, its hardenability is greatly improved than that of original silicon steel, and its performance and fatigue properties are better than silicon steel. The chromium-manganese steel has high hardenability, and its comprehensive mechanical properties are better than that of silicon-manganese steel. The service life of Japanese leaf springs is much higher than that of domestic leaf springs.
China's spring steel standard is equivalent to the corresponding Japanese standard, so the steel type corresponds to 550 in China! . Because steel is a strong carbonization element, its carbide exists near the grain boundary, which can effectively prevent the growth of grains. Therefore, the heat treatment 1 structure of this type of steel plate is extremely fine tempered toustenite, which has high strength and hardness, particularly good plasticity and initial properties. Winter 2,4 nitric acid alcohol solution erodes 2.2 raw material defects 2.2. Silicon anvils have better hardenability and higher tempering stability than steel, but they also tend to form silicate inclusions. Among the leaf springs, there are often 3, 12, 3, and 2 aluminum baby salt. 050 calcium silicate and so on. Such inclusions have poor plasticity and are often regarded as the origin of micro-cracks. 3. It has a certain degree of influence on the plasticity and toughness of leaf springs, especially on fatigue strength. Such inclusions are also the main internal cause of banding. 4. In addition, the spherical oxide is also 4 nitric acid alcohol solution erosion of the brittle inclusions often in leaf springs, and its fatigue strength to leaf springs is more harmful than that of anvilate inclusions, ask 5.
4 Nitric alcohol solution erodes 2.2.2 Banded structure In the raw materials, banded segregation often occurs due to processing or internal inclusions. When heat treatment is performed, the original banded structure is retained due to insufficient heating temperature or holding time + eye Make the mechanical properties of steel anisotropic. In addition, the workpiece with band structure is easy to deform during heat treatment, and makes the hardness uneven. 6 is serious 4 nitric acid alcohol solution erosion 2.3 heat treatment defects 2.3.1 steel plate should be subjected to multiple heating and annealing in the process of forming, if certain protective measures are not taken, such as salt bath furnace vacuum furnace heating, protective materials are applied to control furnace gas reduction Wait, the steel surface will be seriously decarburized. Decarburization will significantly reduce the steel's Pinghuo hardness, wear resistance and fatigue performance. Experiments have shown that even a slight decarburization can lead to a rapid decrease in fatigue strength, the depth of the decarburized layer is doubled, and its life is reduced by about twice. If decarburization occurs in the layer, the surface is decarburized during heat treatment to ensure that austenite weave is not obtained. During rapid cooling, austenite to martensite transformation will inevitably occur, forming surface cracks. 7. The Japanese leaf spring surface has almost no decarburization layer.
4 Nitric acid alcohol solution erosion 2.3.2 Quenching underheated structure appears in the matrix to maintain the tempering of the martensite, and there are white ferrite in the form of mesh and needle distribution. Microstructure, 8. The heating temperature of quenching is too low, so that the network iron is not dissolved into austenite. At this time, the composition of the austenite is not in a loose state due to insufficient diffusion, and the supercooled austenite occurs during quenching The martensite transforms, and after tempering, it gets tempered tousite.
Due to the existence of more ferrite in the structure and the distribution of the Wei structure, the mechanical properties of the steel are seriously reduced, and the permanent plastic deformation of the spring during use is easily caused, which greatly reduces the service life of the spring.
The ferrite 500 and nitric acid solution distributed in the form of a net and needles eroded 2.3.3 feather-like structure If the quenching and cooling rate is slow, or the large-section steel near the center area may form feather-like bainite structure. This is mainly due to insufficient cooling due to high isothermal temperature or high molten salt temperature during graded quenching during isothermal quenching 3 leaf spring medium temperature tempering plant 7, needle-shaped martensite becomes tempered tortoise due to precipitation of carbides However, bainite still maintains its morphology during quenching. 9. The appearance of bainite in spring steel not only reduces the strength and hardness of the steel, but also affects its fatigue strength. According to the requirements of the 38721984 metallographic inspection standard for automobile leaf springs, only a small amount of bainite is allowed to exist on the tempered bainite matrix.
4 Nitric acid alcohol solution erosion 2.3.4 Insufficient heating and quenching cooling, slowly showing a white network ferrite, and a mixed structure of tempered toustenite.
Xie Tie is called quenching. The cooling speed is particularly slow. The shape of the fire should be ocean fire martensite. After tempering, it becomes tempered martensite. Cementite and ferrite are not effective during tempering, so they are retained, and the carbides in the quenched tonicite are distributed in layers, which is very different from the tempered tonicite performance lamp. The use level of this truck 5 has the above two situations. The results show that the service life of flat springs with flat plates is 46 times higher than those with low levels.
2.5 Shot peening quality 4 Nitrogen alcohol solution corrosion In order to improve the fatigue life of the spring, the shot peening treatment is widely used in the manufacture of automobile leaf springs. Not only does the shot peening produce a strengthening layer, but also removes minor defects and decarburization on the spring surface Phenomenon, reduce stress set, etc., while the quality of shot peening is poorly printed. There are also 3 reasons for the difference in the life of the steel plate spring and the service life. For automotive leaf springs, it is recommended to use chromium manganese spring steel and silicon chromium spring yellow steel as alloy materials. If silicon manganese spring steel is used, it can be used in hot places. , Special attention should be paid to the increase in the tendency of decarburization of the total steel surface and the graphitization of the steel. 2.3.5 The tempering temperature is too high, and the quenching time is short. When the tempering temperature is higher than 500, the structure is tempered sorbite At this time, the strength and toughness are matched, but the fatigue strength is greatly reduced. The quenching heat preservation time is short, so that a very small amount of ferrite fails to dissolve into austenite, and it remains in the matrix after quenching, resulting in the hardness and strength of the spring. Sentence 1 is that there is a very small amount of ferrite in the fifth generation body. The hardness of this leaf spring is only 38, which is lower than the standard hardness of 4147.
Strengthen the inspection of the raw material organization, and the materials with a large amount of non-metallic inclusions and severe band-like organization should not be used.
Adopt appropriate heat treatment process to ensure normal and perfect shot peening process, choose appropriate compressive stress, improve the yellow surface of the bomb, and improve the driving level of the island gas drive 4. Rough driving is prohibited. 4 Nitric acid alcohol solution is eroded. 2.4 The use of horizontal automobile leaf springs is mainly affected by the vertical force, but at the same time it is also subjected to various other vertical and horizontal horizontal forces and torques. These loads vary with factors such as driving conditions and road conditions. Road conditions and the level of driver manipulation are also very important factors that affect the service life of leaf springs. Driving on a straight road, the load is recorded in the rated load, the driving is only operated, the first car is careful, its leaf spring life is far higher, the road conditions are bad, the overload is severe, and the leaf spring of the driver is violently overloaded. In the same year, I purchased a Japanese brand l Shanghai 1 Machinery Manufacturing Technology Research Institute. Metallographic analysis technology. 1. Shanghai Shanghai Science and Technology Literature Publishing House, 1987.2963.
12 Zhang Yinghui. Liu Huihang. Wang Decheng. The spring manual is called. Beijing Machinery Industry Press. 1997.6 3 Wang Guangsheng. Wait. Metal hot spot, defect analysis and case 1. Beijing Machinery Industry Chukusha. 1997.12.
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