Wear-resistant steel is the general name of steel materials with strong wear resistance, and wear-resistant steel is one of the most used wear-resistant materials today.
Wear is one of the main forms of workpiece failure, which causes a lot of consumption of energy and raw materials. According to incomplete statistics, the energy from 1/3 to 1/2 is consumed by friction and wear. According to the estimation of the technical department of the former Federal Republic of Germany, the annual loss caused by wear and tear in the former Federal Republic of Germany reaches 654.38+000 billion marks. A development plan to reduce friction and wear proposed by American Society of Mechanical Engineers (ASME) and American Energy Development Agency (ERDA) can save $654.38+0.6 billion annually, which is equivalent to 654.38+065.438+0% of energy consumption. According to the statistics of American publications, the annual losses caused by wear and tear of several major products in the United States are: $654.38+03.4 billion for airplanes, $6.4 billion for ships, $40 billion for automobiles and $2.8 billion for tools. China lacks comprehensive statistics on losses caused by friction and wear. According to the investigation reports of China Ministry of Machinery 1974 to 1975, 230,000 tons of steel are used for automobile parts every year, of which two thirds are used for maintenance, and most of them are caused by wear and tear. According to the incomplete statistics of China's electric power, building materials, metallurgy, coal mine and agricultural machinery, the annual consumption of steel for spare parts is above 6.5438+0.5 million tons. Taking the scraper conveyor used in coal mine as an example, the annual loss caused by the abrasion of the middle trough is 65.438+0 ~ 200 million yuan. If we consider the economic losses and steel consumption caused by the wear and tear of other mechanical equipment, it will be amazing. Therefore, it is of great significance to improve the quality of wear-resistant steel, develop new high-performance wear-resistant steel, and conduct extensive and in-depth research on the wear mechanism of steel to reduce the loss caused by wear.
Edit material wear in this section.
There is no uniform definition of "material wear" at present. Generally speaking, wear is a phenomenon that the working surface material of an object is constantly destroyed or lost in relative motion. There are many classification methods of wear, which can be divided into abrasive wear, adhesive wear, corrosion wear, erosion wear, contact fatigue wear, impact wear and fretting wear according to wear mechanism. In the industrial field, abrasive wear and adhesive wear account for the largest proportion of workpiece wear failure, while erosion, corrosion, fatigue, fretting and other wear failure modes are paid more and more attention because they often occur in the operation of some important components. Under working conditions, several wear forms often appear at the same time or successively, and the interaction of wear failure presents more complicated forms. Determining the type of workpiece wear failure is the basis of reasonable selection or development of wear-resistant steel. In addition, the wear of parts is a systematic engineering problem, which is influenced by many factors, including working conditions (load, speed, motion mode), lubrication conditions and environmental factors (humidity, temperature, surrounding media, etc.). ), material factors (composition, microstructure, mechanical properties), surface quality and physical and chemical properties of parts. The change of each factor may change the amount of wear and even the wear mechanism. It can be seen that the material factor is only one of the factors that affect the wear of the workpiece. To improve the wear resistance of steel parts, it is necessary to start with the overall friction and wear system under specific conditions in order to achieve the expected results.
Edit this part of wear-resistant steel
The brief history of wear-resistant steel as a special steel began in the second half of the 19th century. 1883, hadfield, an Englishman, first obtained a patent for high manganese steel, which has a history of more than 100 years. High manganese steel is a kind of wear-resistant steel with high carbon and manganese. This ancient steel with a history of 100 years has strong work hardening ability, good toughness and plasticity. In recent decades, the development and application of medium and low alloy wear-resistant steel have developed rapidly. Because these steels have good wear resistance and toughness, simple production process, comprehensive economy and rationality, they are suitable for various working conditions and are welcomed by users. In order to meet the needs of the development of mine transportation machinery and construction machinery, the developed high-hardness wear-resistant steel plates were serialized and standardized internationally in the 1970s and 1980s. This kind of steel is developed on the basis of low alloy and high strength weldable steel. Generally, it is strengthened by direct quenching and tempering after rolling, or by controlled rolling and controlled cooling, which can save energy. The alloy element content is low and the price is low, but the hardness and wear resistance are high and the process performance is acceptable. Because of these advantages, this kind of wear-resistant steel plate is very popular with users. Some steel companies in Japan, Britain, the United States and other countries produce this kind of wear-resistant steel.
classify
There are many kinds of wear-resistant steel, which can be generally divided into high manganese steel, medium-low alloy wear-resistant steel, Cr-Mo-Si manganese steel, cavitation-resistant steel, corrosion-resistant steel and special wear-resistant steel. Some common alloy steels, such as stainless steel, bearing steel, alloy tool steel and alloy structural steel, are also used as wear-resistant steels under certain conditions. Because of its convenient source and excellent performance, it also occupies a certain proportion in the use of wear-resistant steel.
chemical composition
Medium-low alloy wear-resistant steel usually contains chemical elements such as silicon, manganese, chromium, molybdenum, vanadium, tungsten, nickel, titanium, boron, copper and rare earth. The linings of many large and medium-sized ball mills in the United States are made of Cr-Mo-Si-Mn or Cr-Mo steel, and their chemical compositions are shown in table 1. Most grinding balls in the United States are made of medium and high carbon Cr-Mo steel, and their chemical composition, heat treatment and hardness are shown in Table 2. Wear-resistant steel, such as Cr-Mo-V, Cr-Mo-V-Ni or Cr-Mo-V-W alloy, can be used for workpieces working under abrasive wear conditions at higher temperatures (such as 200-500℃), or workpieces whose surfaces are subjected to higher temperatures due to frictional heat. After quenching, these steels will have secondary hardening effect when tempered at medium and high temperature.
Wear-resistant steel is widely used in mining machinery, coal mining and transportation, construction machinery, agricultural machinery, building materials, motors, railway transportation and other departments. For example, steel balls and linings of ball mills, bucket teeth and buckets of excavators, mortar walls, toothed plates and hammers of various crushers, crawler plates of tractors and tanks, striking plates of fan mills, railway frog, middle grooved plates of coal mine scraper conveyors, grooved edges and circular chains, shovels and teeth of bulldozers, linings of large electric-powered automobiles, and roller bits perforated by petroleum and open-pit iron mines. The above list is mainly limited to the application of abrasive wear of wear-resistant steel. All kinds of machines will produce various types of wear as long as there is relative movement of workpieces, and there will be requirements for improving the wear resistance of workpiece materials or using wear-resistant steel. There are countless examples in this regard. The grinding media (balls, rods and linings) used in ore and cement mills are high-consumption steel wear parts. In the United States, most grinding balls are forged or cast with carbon steel and alloy steel, which account for 97% of the total consumption of grinding balls. In Canada, steel balls account for 8 1% of the consumed grinding balls. According to the statistics in the late 1980s, China consumes about 800 ~ 1 10,000 tons of grinding balls every year, and nearly 200,000 tons of mill linings are consumed nationwide, most of which are steel. The middle trough of scraper conveyor used in coal mines in China consumes 60 ~ 80 thousand tons of steel plates every year.
manufacturing technique
Wear-resistant steel is smelted by electric furnace or converter, and most of the products are castings. In recent years, there are more and more hot working materials such as forging and rolling. The production method of wear-resistant steel parts for general machinery is not much different from other workpieces, but there are requirements in heat treatment process or surface treatment process to meet the demand of ensuring wear resistance. For steel parts whose metallurgical purity significantly affects wear resistance, refining measures should be taken, and the requirements for harmful impurities and gases should be limited. The number, shape and distribution of the second phase outside the matrix often have a great influence on the wear resistance of steel parts. At this time, it is necessary to consider the chemical composition design, smelting, hot working, heat treatment (including thermomechanical treatment) and so on, in order to improve the wear resistance from metallurgical factors.
Surface strengthening technology
Wear is a process that occurs on the surface of the workpiece, so it is very important to strengthen the surface of the workpiece. The surface strengthening technology of steel has a long history. For example, carburizing technology can be traced back to Han Dynasty in China at least two years ago, and carbonitriding technology has been recorded in China history books more than one thousand years ago. In recent decades, various surface strengthening technologies and equipment have developed rapidly. Taking necessary surface strengthening and surface modification measures can not only save a lot of raw materials, but also endow the surface of the workpiece with various special structures and properties that are difficult to be obtained by the whole material, thus achieving the best wear resistance and huge economic benefits. Nowadays, surface strengthening technology has become an important development direction in the research and application of visible steel (including wear-resistant materials).
technological development
In recent years, the surface strengthening (wetting) technology of steel materials has developed rapidly, and new technologies and processes have emerged one after another. Different surface strengthening technologies can be selected according to different needs to improve the wear resistance of steel parts under various wear conditions, and cheaper matrix materials can be used to replace expensive alloy steel. At present, carburizing, carbonitriding and nitriding are still the main measures to strengthen mechanical parts. By adopting * * * carburizing, compound carburizing, boronizing, metallization, spray welding, surfacing, vapor deposition, brush plating, ion implantation and other processes, the wear resistance of different parts under various working conditions has been significantly improved. In addition, casting processes such as casting infiltration and composite casting are also used to manufacture wear-resistant steel parts.