Welding of 45# steel and 20CrMnTi
Welding of 45# steel sprocket and 20CrMnTi sleeve
Table of Contents
- Welding of 45# steel sprocket and 20CrMnTi sleeve
The working conditions of agricultural machinery are bad. The power transmission parts are welded with 45# steel and 20CrMnTi, which can improve the service life of the parts. In addition to preheating before welding, thermal insulation after welding and appropriate welding parameters, measures can also be taken from the aspects of part heat treatment process, matching connection, welding position and weld length, so as to ensure welding quality and improve the ability of load transfer.
The general working environment of agricultural machinery is relatively poor, with frequent start and reverse, and large impact load. Some agricultural machines use sprockets to transmit power. If the torque of plate sprockets is transmitted by ordinary flat keys, it is easy to cause roll key failure. Therefore, the structure shown in the attached figure is adopted.
Agricultural machinery sprocket
Two smooth holes are machined at the end face of the chip sprocket close to the teeth, and two sleeves made of 20CrMnTi are welded in the smooth holes. In order to improve the strength, the sprocket teeth are induction heated, Quenched and tempered, with a hardness of 45 ~ 55HRC; The sleeve is carburized and quenched, and the hardness is 58 ~ 62Hrc. The two materials are different, and both have been heat treated, and the weldability is relatively poor. Waste products often appear in the early stage of trial production. After analysis, it can be improved from structural design, heat treatment, welding and other links, and finally improve the product qualification rate.
Welding performance analysis
The WC of 45# steel is 0.42% ~ 0.5%, belonging to medium carbon steel, with high mechanical strength, poor plasticity and poor welding performance; At the same time, due to the quenching and tempering of the tooth, the metallographic structure near the welding sleeve has changed into a mixed structure of pearlite and martensite. The closer the tooth is, the more the martensite composition is, the worse the welding performance is.
20CrMnTi is a low-carbon alloy steel with WC = 0.17% ~ 0.24%. After carburizing and quenching, the surface becomes martensitic metallographic structure, and the welding performance becomes worse.
If the two are directly welded, the transition layer will form brittle martensite structure, which is easy to form cold and hot cracks, pores and hydrogen embrittlement, and the welding quality can not meet the quality requirements. In order to improve the welding performance and welding strength, in addition to adopting appropriate groove form, materials, welding parameters, preheating before welding and thermal insulation after welding, the following methods can also be adopted to improve the welding performance.
Change the welding position on the sprocket to avoid the heat treatment affected zone caused by induction quenching and stay away from the martensite structure on the sprocket as far as possible. The center distance of the welding hole has been determined in the design, and the size cannot be changed, but the hole can be machined directly below the tooth top of the sprocket. It is relatively far away from the heat treatment affected area. According to the observation of metallographic microscope, there is very little martensite and relatively more pearlite and ferrite. Compared with the lower part of the tooth groove of the sprocket, the lower part of the tooth top is easy to weld, and the tendency of welding defects is less.
During carburizing of 20CrMnTi sleeve, in order to avoid too much free carbon penetrating into the welding surface of the sleeve, a layer of anti-seepage paste can be coated on the surface of the sleeve to avoid the occurrence of martensite at the welding position as far as possible. In this way, after carburizing and quenching, other surface hardness of the sleeve meets the requirements, and the structure of the outer surface is also convenient for welding.
In order to improve the connection strength and avoid welding defects, the interference fit can also be used for the fit between the sleeve and the sprocket. In fact, the press in interference fit of H7 / S6 can be used. At the same time, in order to avoid tooth annealing caused by welding, it can not be welded near the tooth.
Before welding, the sprocket and sleeve shall be cleaned to remove oil stain, rust and oxide scale. After drying, the sleeve shall be pressed into the sprocket, and an annular groove shall be generated after press fitting, which can be regarded as a welded groove. At the same time, ensure that there is no oil stain after welding and keep it dry.
The welding equipment is a CO2 protection welding machine with the model of yd200kr2hge, and the power is 6.5kw; The brand of welding wire is ER50-6, F1 0mm, the shielding gas is bottled liquid CO2.
Preheat the product into the heating furnace and heat it to 200 ℃ for 2h. By preheating the product, the tendency of hot crack and reheat crack can be reduced, and the tendency of cold crack can be reduced. With the increase of cooling rate, the strain rate in the weld area also increases, which is easy to produce thermal cracks. Preheating can change the heat cycle during welding and reduce the cooling speed. Therefore, preheating can reduce the tendency of thermal cracks. The product has accumulated internal stress in the sprocket through induction quenching, sleeve carburizing quenching, press fitting and other processes. Internal stress concentration has a great influence on reheat crack. The more concentrated the stress is, the greater the tendency of reheat crack is. Preheating can reduce the internal stress, which reduces the tendency of reheat crack. The dissolution of hydrogen in the weld and its diffusion in the welding zone are important factors causing cold cracks. When welding under preheating conditions, most of the hydrogen can escape from the welding area at higher temperature; At lower temperatures, the residual diffusive hydrogen is not enough to cause cold cracks. Therefore, preheating can reduce the generation of cold cracks.
Flat welding is adopted for welding. The welding parameters are adjusted to voltage (22 ± 2) V, current 100A, wire walking speed 18m / min, shielding gas CO2 nozzle distance 20mm, gas flow 10L / min, welding wire extension length 20mm and welding speed 0cm / min.
Heat preservation after welding. After welding, put the product in the heat preservation furnace, heat preservation at 280 ℃ for 2h and air cooling. In this way, hydrogen diffusion can escape from the weld. It can be known from the function of preheating above that hydrogen removal can prevent cold cracks.
Clean up the welding slag, grind the weld with manual grinding wheel to ensure beautiful appearance and remove the splashed welding slag.
The weld and heat affected zone shall be free of cracks, slag inclusion, undercut, pores and other welding defects, and there shall be no spattering welding slag.
Ultrasonic flaw detection is used for internal inspection, which meets the provisions of GB11345 standard.
The welding of two kinds of heat treated materials can not only adopt preheating before welding, thermal insulation after welding and appropriate welding parameters, but also analyze and improve from the aspects of heat treatment process, matching connection, welding position and weld length, so as to improve the welding quality.
Through the above improvements, the scrap rate can be reduced; The product has stable performance in use and is suitable for transmission of agricultural machinery with poor working conditions.
What electrode is used for 20CrMnTi welding? What is the process before and after welding and post weld heat treatment?
20CrMnTi is carburized steel, which is usually low carbon steel with carbon content of 0.17% – 0.24% It is often used to make transmission gears in cars It is a medium hardenability Carburized Steel Medium Cr Mn Ti steel. It has high hardenability and has high strength and toughness under the condition of ensuring hardenability, especially high low-temperature impact toughness. 20CrMnTi steel for surface carburizing and hardening treatment Good processability, small machining deformation and good fatigue resistance
Usage: used for gear, shaft, piston parts, etc Used for various special parts of automobile and aircraft
Characteristics and scope of application: it is carburized steel with good performance, high hardenability, hard and wear-resistant surface and tough core after carburization and quenching, high low-temperature impact toughness, medium weldability and good machinability after normalizing. It is used to manufacture important parts with section < 30mm that bear high-speed, medium or heavy load, impact and friction, such as gear, ring gear, gear shaft crosshead, etc.
It is a substitute steel of 18crmnti, which is widely used as carburized parts in automobiles Tractors are used in industry with cross section below 30mm and bear high speed Medium or heavy load and impact Important carburized parts of friction, such as gears Shaft Ring gear Gear shaft Main shaft of sliding bearing Crosshead Dog clutch Worm, etc.
- J857cr low alloy high strength steel electrode.
- J857cr low alloy high strength steel electrode conforms to: GB e8515-g equivalent: AWS E12015-G. Description: j857cr is a low alloy high strength steel electrode with low sodium hydrogen coating.
- Preheat 200 before welding and temper 500-700 after welding (or dark red).
What kind of welding rod is used for 45 steel?
When welding with J507 alkaline electrode, it is necessary to preheat 420 ℃, reduce stress by hammering during welding and cool slowly after welding, otherwise hydrogen cracks are easy to occur.
Generally, J422 welding rod is used, and j506 or J507 welding rod is used under heavy stress.
Chapter III of welding manual welding methods and equipment volume 1 compiled by welding society of China Mechanical Engineering Society:
J422 electrode shall be used for 45 steel, and j506 or J507 electrode shall be used under large stress. During welding, attention shall be paid to the poor welding performance of low bottom current and high carbon content of base metal.
45 steel is a common medium carbon quenched and tempered structural steel. The cold plasticity of the steel is general, and the annealing and normalizing are slightly better than those during quenching and tempering. It has higher strength and better machinability. After appropriate heat treatment, it can obtain certain toughness, plasticity and wear resistance, and the material source is convenient. Suitable for hydrogen welding and argon arc welding, not suitable for gas welding. Preheating is required before welding, and stress relief annealing shall be carried out after welding.
45 steel is widely used in machinery. Without heat treatment: HB ≤ 229; Heat treatment: normalizing; Impact energy: Aku ≥ 39j;; High strength, good plasticity and toughness. 45# steel plate is qualified if its hardness is greater than HRC55 (up to HRC62) after quenching and before tempering.
After heat treatment, re quenching can reach hrc42-46, which can not only ensure its good mechanical properties, but also obtain the surface hardness requirements. It is used to make small section quenched and tempered parts with large load, large normalized parts with small stress, and surface quenched parts with low requirements for core strength.
Source: China Large Diameter Flange Manufacturer – Yaang Pipe Industry (www.epowermetals.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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