Brief History

Wear-resistant steel as a special steel began in the second half of the nineteenth century. 1883 British Hadfield (R0.A0.Hadfield) first obtained a patent for high manganese steel, so far there are more than 100 years of history, high manganese steel is a high carbon and manganese content of wear-resistant steels, this has more than a hundred years of history of the old steel, as it is in the large impact of abrasive wear conditions when using Has a strong work hardening ability, both good toughness and plasticity, as well as the production process is easy to grasp and other advantages, therefore, it is still wear-resistant steel in the largest amount of a (especially in mining and other sectors). In recent decades, the development and application of low and medium alloy wear-resistant steel development and application of rapid development, due to these steels have better wear resistance and toughness, the production process is relatively simple, the overall economy is reasonable, applicable in many working conditions, by the user's welcome. In order to meet the needs of the development of mining and transportation machinery and construction machinery, the development of high hardness wear-resistant steel plate, the 20th century 70 ~ 80 years in the international has formed a series and standardization. This kind of steel is in the low-alloy high-strength weldable steel on the basis of the development, they are generally used directly after rolling quenching and tempering, or the implementation of controlled rolling, controlled cold process for strengthening, can save energy, and alloying element content is low, the price is cheaper, but the high hardness, wear-resistant, process performance is still available, as a result of these advantages of this kind of wear-resistant steel plate is very popular with users. Japan, Britain, the United States and other countries, some steel companies are producing such wear-resistant steel. [2]

Classification

Wear-resistant steel variety, generally can be divided into high manganese steel, medium and low alloy wear-resistant steel, chromium, molybdenum and silicon-manganese steel, cavitation-resistant steel, wear-resistant steel, as well as special wear-resistant steel and so on. Some general alloy steels such as stainless steel, bearing steel, alloy tool steel and alloy structural steel are also used as wear-resistant steels under specific conditions, due to their convenient sources, excellent performance, so in the use of wear-resistant steel also occupies a certain proportion.

Chemical composition

Medium and low alloy wear-resistant steel this kind of steel usually contains chemical elements such as silicon, manganese, chromium, molybdenum, vanadium, tungsten, nickel, titanium, boron, copper, rare earths and so on. Many large and medium-sized ball mill liners in the United States are made of chromium-molybdenum silicon manganese or chromium-molybdenum steel. And most grinding balls in the U.S. are made of medium- and high-carbon chromium-molybdenum steel. At higher temperatures (such as 200 to 500 ℃) in the abrasive wear conditions of the workpiece or due to frictional heat so that the surface undergoes higher temperatures of the workpiece, can be used chromium-molybdenum-vanadium, chromium-molybdenum-vanadium-nickel or chromium-molybdenum-vanadium-tungsten and other alloys of wear-resistant steels, such as steel quenched, tempered by the medium-temperature or high-temperature tempering, the effect of a secondary hardening.

APPLICATIONS

Wear-resistant steel is widely used in mining machinery, coal mining, engineering machinery, agricultural machinery, building materials, power machinery, railroad transportation and other sectors. For example, ball mill balls, liners, excavator teeth, buckets, various crusher mortar wall, tooth plate, hammer head, tractor and tank track plate, fan mill strike plate, railroad rutting forks, coal mine scraper conveyor with the middle groove in the plate, groove gangs, chain, bulldozers shovel blade, shovel teeth, large electric wheelbarrow bucket liner, oil and open-pit iron ore perforation with tine bits and so on, the above list of Also mainly limited to the application of wear-resistant steel belonging to the abrasive wear, and a variety of machinery where there is relative motion of the workpiece asked, will produce various types of wear, will have to improve the wear resistance of the workpiece material requirements or requirements for the use of wear-resistant steel, examples in this regard are innumerable. The grinding media (balls, rods and liners) used in ore and cement mills are highly consumed steel wear parts. In the United States, grinding balls are mostly forged or cast from carbon and alloy steels, which account for 97% of the total consumption of grinding balls. In Canada, the consumption of grinding balls in the steel ball accounted for 81%. According to the statistics in the late 80's, China's annual consumption of grinding balls about 80 to 1 million tons, the annual consumption of the national mill liner nearly 200,000 tons, the vast majority of which are steel products. The central groove of scraper conveyor for coal mine in China consumes 60,000 to 80,000t of steel plate every year.

Production process

Wear-resistant steel are smelted by electric furnace or converter, and the products are mostly castings, in recent years, forging, rolling and other hot processing materials are increasing. In general machinery used in the production of wear-resistant steel parts and other workpieces are not very different, only in the heat treatment process or surface treatment process should be required to ensure that the demand for wear resistance. For those material metallurgical purity significantly affects the wear resistance of steel parts should take refining measures, and harmful impurities and gases to put forward limited requirements. In addition to the matrix outside the second phase of the number, shape and distribution of the wear resistance of steel parts often have a significant impact on the performance of the steel, this time the need to design the chemical composition from the steel, smelting, hot processing, heat treatment (including thermo-mechanical treatment) and so on, so as to strive to achieve from the metallurgical factors to improve the wear resistance of the requirements. Strengthening technology

Wear is the process that occurs on the surface of the workpiece, therefore, strengthening the surface of the workpiece is very important. Steel surface strengthening technology has a long history, for example, carburizing technology can be traced back to at least two dry years ago in the Han Dynasty in China, and more than a thousand years ago in the Chinese history books on the carbon and nitrogen co-infiltration process has been recorded. In recent decades, a variety of surface strengthening technology and equipment to develop rapidly, take the necessary surface strengthening and surface modification measures, not only can save a lot of raw materials, but also can give the surface layer of the workpiece to a variety of special, as a whole material is difficult to get the organizational structure and properties, so as to achieve the most excellent wear resistance and great economic benefits. Nowadays, surface strengthening technology has become an important development direction for the research and application of wear-resistant steel (including wear-resistant materials).

Process development

In recent years, the surface strengthening of steel materials (wetting) technology is developing rapidly, the new technology, new techniques emerge one after another, for different needs can choose different surface strengthening technology to improve the wear resistance of steel parts in various types of wear conditions, to the lower price of the substrate material to make the workpiece instead of expensive alloy steel. Carburizing, carbonitriding, nitriding and other processes are still the main measures to strengthen the mechanical parts, the use of common seepage, composite seepage, boron penetration, metal seepage, spray welding, cladding, vapor deposition, brush plating, ion implantation, and other processes in the different pieces of a variety of working conditions have been achieved in order to improve the wear-resistant obvious results. In addition, casting seepage, composite casting and other casting processes in the manufacture of wear-resistant steel parts are also used.

Processing methods Podcast

1, steel plate cutting methods apply to cold cutting and hot cutting. Cold cutting, including water jet cutting, shearing, sawing or abrasive cutting; thermal cutting, including oxygen-fueled flame cutting (hereinafter referred to as "flame cutting"), such as particle cutting and laser cutting.

2, cutting methods: through the relevant process test, master the general characteristics of various cutting methods and cutting thickness range of steel plate.

3, high-level wear-resistant steel flame cutting method is as simple as ordinary low carbon and low alloy steel cutting, when cutting wear-resistant steel plate, need to pay attention to! With the increase of steel plate thickness and hardness, the tendency of cracks on the cutting edge increases. To prevent steel plate cutting cracks, the following recommendations should be followed when cutting:

Cutting Cracks: Steel plate cutting cracks are similar to hydrogen cracks produced during welding, if cracks are produced on the cut edge of the steel plate, they will not appear until the cut thickness has been cut for 48 hours to a few weeks. Therefore, cutting cracks are delayed cracks, the greater the thickness and hardness of the steel plate, the greater the occurrence of cutting cracks.

Preheat cutting: the most effective way to prevent steel plate cutting cracks, is to preheat before cutting. Before flame cutting, steel plate is usually preheated, the preheating temperature depends mainly on the quality level of steel plate and plate thickness. Preheating methods can be used flame burner, electronic heating pads, can also use the heating furnace heating. In order to determine the effect of preheating the steel plate, the required temperature should be tested at the heating point being surface.

Note: Preheating special attention to make the positive steel plate interface uniformly heated, so as to avoid contact with the heat source of the region of the phenomenon of localized overheating.

Low cutting speed: Another way to avoid cutting cracks is to reduce the cutting speed. If it is not possible to preheat the whole plate, the local preheating method can be used instead. Using the low-speed cutting method to prevent cutting cracks is not as reliable as preheating. It is recommended to preheat the cutting strip by air bubbling it with a flame gun a few times before cutting, with a preheating temperature of about 100°C being appropriate.

Special Note: Combining the two flame cutting methods of preheating and low speed can further reduce the chances of cutting cracks.

Requirements for post-cutting retardation: Regardless of whether or not the cut missing is preheated, retardation of the steel plate after cutting is effective in reducing the risk of cutting cracks. If the cut with the warmth of the missing for stacking, the use of thermal blankets to cover them, can also realize the slow cooling, the slow cooling requirements of the cooling to room temperature.

Heating requirements after cutting: for the cutting of wear-resistant steel plate, immediately after cutting to take heating (low temperature tempering), is also an effective method and measure to prevent cutting cracks. Steel plate cutting thickness by low temperature tempering treatment, can effectively eliminate the cutting involved in stress (low temperature tempering process; moisturizing time an 5min/mm), for the method of post-cutting heating, but also the use of combustion guns, electronic heating blankets and section of the heat of the heat of the heat furnace for the post-cutting heating.

4, reduce the softening of steel plate measures to resist softening characteristics of steel mainly depends on its chemical composition, microstructure and processing. For thermally cut parts, the smaller the part, the greater the risk of softening of the whole part. If the temperature of the steel plate exceeds 200-250°C, the hardness of the plate decreases.

Cutting method: When cutting small parts from steel plates, the heat supplied by the torch and preheating will build up in the workpiece. The smaller the missing size, the smaller the size of the cut part must not be less than 200mm, otherwise there will be a risk of softening of the part. The best way to eliminate the risk of softening is to cut cold, e.g. by water jet. If hot cutting must be used, there is a limited choice of plasma or laser cutting. This is because flame cutting provides more heat to the workpiece and therefore raises the temperature of the workpiece.

Underwater Cutting Methods: An effective method to limit and reduce the extent of the softening zone, water is used to flute the steel plate and cut surface during the cutting process. Therefore, the steel plate can be placed in the water cutting, can also be cut to the cutting surface of the water spray. The use of underwater cutting methods can choose between plasma or flame cutting. Underwater cutting has the following characteristics:

Small cutting heat-affected zone;

Preventing the hardness of the entire workpiece from decreasing;

Reducing the deformation of the cut workpiece;

The workpiece can be cooled directly after cutting.