wear-resisting low-alloy steel

Low alloy steel is widely used when wear is the main failure mode. This type of low-alloy steel mainly includes low-alloy welding wear-resistant steel, low-alloy wear-resistant steel for construction machinery parts and low-alloy wear-resistant steel for agricultural machinery.

Low alloy welded wear-resistant steel is a new type of steel developed on the basis of low alloy and high strength welded steel. In the past few decades, Japan, the United States, Germany and the former Soviet Union and other countries have been the tensile strength of 590 ~ 785MPa high strength steel plate is widely used in mining machinery and construction machinery wear-resistant parts manufacturing. In order to further improve the service life of these components, since the 1970s, low-alloy high-hardness steel plates have been developed. This type of steel has a very high hardness (Brinell hardness can reach HB500) and has good weldability. Usually, this type of steel is made into plates or sections by rolling methods, and then welded into components. It is mainly used in the middle trough bottom plate of coal mine plate conveyor, wear-resistant lining plate of mining machinery, protection plate, liner plate for large dump truck box bucket and so on. Some steel companies in Japan and other countries have serialized these steels to form standards. For example, Japan's Nippon Steel Corporation has 16 grades of high hardness steel, Japan Steel Pipe Corporation has 10 grades, and Japan's Sumitomo Metal Corporation has 5 grades. The carbon content of these steels generally does not exceed 0.21% ~ 0.24% (when the Brinell hardness HB≥400 ~ 500 is required, the carbon content is less than 0.35%), usually using manganese and boron as the main strengthening elements, the manganese content does not exceed 1.6% ~ 1.7%, and the boron content is less than 0.005%. When the steel plate is thick or has other performance requirements, chromium, molybdenum, vanadium, copper, nickel and other elements need to be added at the same time. For example, the main elements in Wel-TenAR235E ~ AR360E steel of Nippon Steel Company of Japan are carbon ≤0.22%, manganese ≤1.60%, boron ≤0.005%, chromium ≤0.50%. The other group of Wel-TenAR235 ~ AR400, in addition to containing manganese, boron, chromium, also contains copper 0.15% ~ 0.50%, nickel 0.40% ~ 1.50%, molybdenum 0.15% ~ 0.60%, vanadium ≤0.10%. Their hardness can reach HB≥235 ~ 361 or HB≥235 ~ 401, respectively. Plate thickness up to 50 or 100mm. 

The production process of this kind of low-alloy wear-resistant steel mainly includes: first smelting, then rolling or forging, and finally heat treatment to improve the overall strength and toughness of the workpiece. In this process, some alloying elements such as silicon, chromium, nickel, molybdenum and so on will also be added as needed.

Low alloy wear-resistant steel for construction machinery parts is mainly used for the main part of construction machinery such as bulldozers and loaders. Since most of these machines work with mud, sand and rock, especially the walking mechanism and working device of crawler bulldozers and loaders (including excavators), their parts are subject to strong abrasive wear. The fault analysis of the bulldozer shows that the repair and replacement cost of the walking mechanism parts accounts for about 60% of the total repair cost from the new car to the scrap of the bulldozer, and the repair cost caused by wear and tear is dominant. The main wear parts of this kind of construction machinery are track plate, chain rail joint, pin sleeve, drive wheel, guide wheel, weight support wheel, blade, bucket teeth (bucket blade), soil reducer teeth and so on. The materials used are mostly medium carbon manganese steel or manganese boron steel, and sometimes silicon, chromium, nickel, molybdenum and other alloying elements are added according to needs. When rolling, forging or casting, heat treatment, while ensuring the overall strength and toughness of the workpiece, pay more attention to improving the hardness of the surface layer of the workpiece. Table 2 lists the main chemical composition, heat treatment method and hardness of steel commonly used in Japanese bulldozers, loaders and working devices.

Low alloy wear-resistant steel for agricultural machinery is mainly used in ploughshare, rake, hoe and other parts of agricultural machinery. When working, these parts are worn by the constant friction of soil, stone particles and roots, and often collide with sand and stone blocks, roots, etc., which may cause fracture or collapse, therefore, they are required to have high wear resistance and sufficient strength and toughness. Table 3 lists the chemical composition of low-alloy wear-resistant steels for agricultural machinery in some countries. Table 4 shows the heat treatment and hardness values of typical low-alloy wear-resistant steel parts of agricultural machinery. The service life of the share is determined by the hardness, strength, heat treatment quality and the structure and properties of the soil. Increasing the hardness of materials is the main way to improve the wear resistance of agricultural machinery.

It is the main development trend of low alloy wear-resistant steel to improve its performance from the production process. For example, taking refining measures from smelting, reducing the content of inclusions and gases in steel, changing the shape and distribution of inclusions, is beneficial to improving wear resistance. Since the 1980s, Japan and other countries in the production of low-alloy wear-resistant steel plates pay more attention to the use of direct hardening after rolling steel plates instead of the traditional reheating hardening method, which not only saves energy, but also improves the hardenability of steel, so as to reduce the type and content of alloying elements added. At the same time, MN-B or Ti-B series steels have been developed accordingly, and good results have been achieved in reducing the cost of steel plates and improving their process properties. In the production of low-alloy wear-resistant steel parts for construction machinery and agricultural machinery, under the condition of ensuring the overall strength and toughness of the workpiece, more attention is paid to the use of strengthening (hardening) measures on the surface of the workpiece or specific parts, such as the implementation of medium and high frequency quenching and chemical heat treatment processes. The method of quenching or deformation heat treatment is often used in forging parts, which can significantly improve the strength, toughness and wear resistance of the workpiece.