Application of the hottest high strength material

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Application of high-strength materials in trackless rubber tyred vehicles

with the development of coal mine production to high yield and efficiency, underground auxiliary transportation machinery is also developing in the direction of portability and reliable operation. Trackless rubber tyred vehicle is a new type of efficient underground auxiliary transportation machinery, which has the characteristics of high transportation efficiency, fast and flexible, time-saving and labor-saving, high safety and low operating cost, and has a broad application prospect. Trackless rubber tyred vehicles have been used in Britain, the United States, Australia and other countries for more than 20 years, and have achieved remarkable results. At present, there is no finalized product in China. Therefore, on the basis of digesting truk4 and pet6 passenger and freight dual-purpose vehicles in Australia, combined with the domestic use situation, the development of fkh6 Underground Explosion-proof low pollution medium-sized passenger and freight dual-purpose rubber tyred vehicles is carried out, so as to accelerate the modernization of coal mine auxiliary transportation in China and narrow the gap with the world advanced level

fkh6 Underground Explosion-proof low pollution medium-sized passenger and cargo rubber tyred vehicle is mainly composed of explosion-proof engine device, air intake and exhaust and electrical explosion-proof system, hydraulic transmission device, driving control device, articulated frame, passenger and cargo compartment, hydraulic and pneumatic system and other components. Among them, the frame is an important bearing structural member of the vehicle, which is divided into two parts: the front and rear frames, both of which adopt the welded structure of high-strength steel plates. The front and rear frames are hinged through the hinged turntable. The rack is mainly used to install power, transmission, travel control and other components and carry materials, and the stress condition is relatively complex. Therefore, its structural performance has a direct relationship with the service performance and service life of the whole vehicle. In order to ensure the overall service performance and transportation efficiency of rubber tyred vehicles, the frame is required to reduce its own weight as much as possible under the condition of high strength, stiffness and reliable bearing capacity, so as to improve its load capacity, reduce costs and obtain higher economic benefits. For this reason, we selected the high-strength steel plates 1008, 10083 and 10072 of the British Terex EEMs series as the frame materials of trackless rubber tyred vehicles, and explored the technical ways of their use

In recent years, with the large-scale development of equipment, countries all over the world are strengthening the research and development of high-strength steel plates, developing low-alloy steels with good processing performance, excellent service performance and low cost, such as boron steel, manganese steel, high silicon steel, etc., and adopting advanced metallurgical technology and steel rolling process. Do not covet the low price and heat treatment process to improve the metallurgical quality, strength and toughness of steel. For high-strength steel plates, whether used for structural parts or wear-resistant parts, most of them need to be welded. Therefore, improving the strength, toughness and weldability of materials has become a worldwide trend of the development of low-alloy high-strength steel, and its application range is also increasingly extensive. For example, such materials have been widely used in construction machinery and mining equipment. The following focuses on the mechanical and welding properties of 072 steel plate, the representative eems10, which uses servo electromechanical as the power source

1.1 chemical composition and mechanical properties of eems10072 steel plate

eems10072 steel is a low-carbon manganese boron steel with quenching and tempering treatment from British Terex company. The best comprehensive properties can be obtained by controlling the rolling temperature. After hot rolling, quenching (calibration and quenching are required for each gear of water) and tempering treatment higher than 430 ℃, it has high strength and plasticity, especially high low-temperature toughness, and good ductility and formability. Therefore, it has been widely used in large dump trucks of construction machinery, which has the characteristics of high reliability and long fatigue life. The chemical composition and mechanical properties of the steel are shown in Table 1 and table 2 respectively

Table 1 chemical composition of eems10072 steel%

carbon equivalent of eems10072 steel plates with different plate thickness can be calculated according to the carbon equivalent calculation formula recommended by the International Welding Society (see Table 3):

Table 3 carbon equivalent of eems10072 steel plates CEQ

the higher the CEQ value, the greater the hardening inclination of the steel and the greater the cold cracking sensitivity. When (CEQ)> 0.45% - 0.55%, cold cracks are easy to occur in welding. It can be seen from table 3 that when the plate is thin (<12mm), the weldability is good; For 12mm plates, preheating before welding and technical treatment after welding should be carried out to avoid cracks

2 welding method, materials and equipment of high-strength steel plate

2.1 welding method and materials

the welding method is flux cored wire CO2 arc welding

the welding materials are outershield71m (? 1.2) and outershield70 (2.4) flux cored wires of Lincoln company in the United States. The former is used for tack welding and welding of small weld beads (10mm). These two kinds of flux cored wires are low hydrogen series flux cored wires that can obtain both high strength and good impact toughness. They have the characteristics of good welding quality, less splash, easy slag removal, beautiful forming and high welding efficiency. They have been widely used in the welding engineering of all kinds of low carbon steel and low alloy steel

outershield71m and outershield70 welding wires' chemical composition and mechanical properties are shown in Table 4 and table 5

Table 4 chemical composition of deposited metal%

dc-400, dc-600 power supply, ln-9 wire feeder, welding gun and shielding gas device of American Lincoln company are adopted

3 formulation of welding process

in order to ensure the final quality and structural performance of structural parts, the following main measures should be taken when formulating welding process:

(1) preheating. Preheating before welding can slow down the cooling rate of the welded joint, prevent the generation of hardened structure and reduce the tendency of cold cracking. But the main problem is how to choose a reasonable preheating temperature and the lowest interlayer temperature according to the chemical composition of steel, the thickness of material and the degree of constraint of connection. The test shows that the steel plate with a thickness of less than 12mm can not be preheated. The preheating temperature of the steel plate with a thickness of 12 ~ 16mm is (10010) ℃, and the preheating temperature of the steel plate with a thickness of more than 16mm is (20010) ℃

(2) afterheat. For parts with a plate thickness of 12mm and greater than 12mm, in order to avoid transverse cracks in multi-layer welds and to prevent cracks caused by insufficient preheating before welding, heating and tempering stress relief treatment should be carried out immediately after welding to eliminate the welding stress between the weld and the base metal. The tempering temperature should be maintained at about 350 ℃

(3) DC reverse connection method. In order to increase the penetration and avoid defects in the fusion zone, the power supply adopts the DC reverse polarity connection method

(4) welding parameters. See Table 6 for the selection of welding parameters

table 6 welding parameters

(1) preheat the 12mm thick plate connecting weld bead and its vicinity with oxyacetylene flame, and measure it with a temperature measuring pen. It is suitable for users to analyze various complex data to ensure the preheating temperature requirements

(2) welding shall be carried out continuously without stopping halfway to ensure that the interpass temperature is higher than the preheating temperature

(3) welding tooling should be used, such as using process shaft to ensure the technical requirements such as coaxiality and parallelism between holes of structural parts, and using multi-channel process lacing to control deformation

(4) during the welding process, check the dimensions in all directions at any time to control and correct the deformation in time

(5) after each layer (pass) is welded, the slag shall be thoroughly removed, and any defects found shall be removed in time with a grinder for repair welding, and the preheating measures mentioned above shall still be taken during repair welding

(6) immediately after welding, heat the 12mm thick plate connection weld bead and its vicinity to 350 ℃ for tempering and stress relief treatment, and slowly cool it to room temperature

(7) after 24h of welding, remove the process shaft and process lacing, and then machine after natural aging to facilitate stress release

5 flaw detection

after the front and rear frames are welded and placed for 48h, the CTS-26 ultrasonic detector is used to conduct ultrasonic flaw detection according to cb/t standard, and it is proved that the welds are qualified; Through magnetic particle flaw detection, no defects are found in the welds

6 conclusion

it is proved by nondestructive testing and factory acceptance inspection that:

(1) high strength steel plate eems10072 has high strength, good weldability, ductility and good impact toughness, especially good low temperature toughness. Therefore, it is feasible to use this kind of steel plate in the frame of underground trackless rubber tyred car, and the expected design requirements have been achieved

(2) CO2 arc welding with flux cored wire, first, low cost; Second, it can improve the welding quality, form beautiful, and avoid defects such as pores and slag inclusions; Third, improve work efficiency, so that preheating, welding and post heat treatment can be completed at one time

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