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YILIAN SHENG

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As a representative of the 'advanced' forces, Mingzhi Technology fully demonstrates its important position in technological innovation, industrial advancement, and driving the forward development of the Chinese economy.

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2024

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YILIAN SHENG

Common detection methods for high-speed steel rolls

High-speed steel rolls have good wear resistance and resistance to thermal cracking, but they are sensitive to cracks caused by improper cooling, use, or mechanical damage. Surface cracks are the main cause of high-speed steel roll failure. Typically, mechanical cracks, reticulated "heat" cracks, stress cracks, and fatigue cracks are easily generated on the surface of high-speed steel rolls. Manufacturers generally adopt good non-destructive testing methods and procedures to regularly inspect the rolls and repair or replace high-speed steel rolls with problems in advance to avoid rolling accidents. So, let's learn about the common detection methods of high-speed steel rolls. Common detection methods for high-speed steel rolls mainly include: 1. Eddy current automatic flaw detection Advantages: It is automatic flaw detection, with an automatic recording system, which can accurately determine the axial position of defects on the roll. The detection sensitivity is high, and some small surface or near-surface defects can be found, which is incomparable to other flaw detection methods such as ultrasonic waves. Disadvantages: It cannot determine the type, shape, and depth of the crack, and cannot determine the true equivalent of the defect. Sometimes it will be affected by various factors, such as: the distance between the probe coil and the tested roll, the material, size, shape, conductivity, permeability, and defect type of the roll, etc. Regularly calibrate the eddy current sensitivity and other flaw detection

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2023

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YILIAN SHENG

Characteristics and Usage Process of High-Speed Steel Rolls

High-speed steel rolls are a rapidly developing and widely used hot-rolled material in recent years. They are alloy steels with relatively complex compositions. They can be hardened. The working layer material uses high-carbon steel, and the roll core material uses ductile iron, graphite steel, or forged steel. Two different materials are combined through centrifugal casting or CPC processes. The matrix microstructure is generally tempered martensite + bainite + carbide, with carbides distributed in a highly dispersed form in the matrix, thus having very high wear resistance and toughness, making machining difficult. Below, we will understand the characteristics and usage process of high-speed steel rolls. Characteristics of high-speed steel rolls: Good thermal stability, good hardenability, high carbide hardness, easy to form an oxide film, good resistance to thermal cracking and wear resistance, and much lower requirements for cooling water than cemented carbide. Its single-pass rolling capacity can reach 45 times that of cast iron rolls. It is conducive to negative tolerance control of rolled materials and improves the surface quality of rolled materials. It is mainly aimed at the application of online bar products and pre-frame products, as well as the development of new materials for slitting pre-cutting and slitting passes. The hardness can reach HSD78-90, with high wear resistance, good impact resistance, and good resistance to thermal fatigue. With the popularization of high-speed steel rolls in online bar rolling mills, R&D and manufacturing manufacturers have rapidly expanded. However, various manufacturers have different...

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2023

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YILIAN SHENG

Advantages of high-speed steel rolls

High-speed steel rolls are high-carbon high-speed steel composite rolls and have become an important part of the development of modern steel rolling production. After 20 years of development, they have been widely used in rolling mills around the world. Currently, cast high-speed steel rolls are not only widely used in the finishing stands of cold and hot strip rolling mills, but also in the finishing stands of wire and bar rolling mills. This is a very good application, so let's learn about the advantages of high-speed steel rolls. Advantages of high-speed steel rolls: 1. High hardness of carbides: In the past, the rolls used were mostly distributed with Fe3C or M7C3 eutectic carbides on the matrix, with a coarse structure and low hardness. High-speed steel rolls generally use high-C, high-V high-speed steel, and also contain a larger amount of alloying elements such as Cr, Mo, W, Nb, and Co. During solidification and heat treatment, these alloying elements form primary and secondary carbides. High-chromium cast iron roll carbides include M7C3 (2500Hv) and M23C6 (1600Hv). In infinite cold-hard cast iron rolls, the carbide is Fe3C (1300Hv). 2. Good thermal stability: High-speed steel rolls contain a larger amount of elements such as W, Cr, Mo, V, and Nb, and have good thermal stability. Studies have found that the hardness of ordinary roll materials decreases with increasing temperature

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2023

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YILIAN SHENG

The role of tungsten and molybdenum in high-speed steel rolls

The Role of Tungsten and Molybdenum in High-Speed Steel Rolls Tungsten and molybdenum are the main alloying elements in ordinary high-speed steel rolls. Tungsten and molybdenum have similar chemical properties, and their effects on the microstructure transformation and properties of high-speed steel rolls are almost the same. The difference is that molybdenum causes structural transformation at a lower temperature. The main reason for using high-speed steel to manufacture rolls is to utilize the excellent red hardness of high-speed steel to improve the high-temperature wear resistance of the rolls. The excellent red hardness of high-speed steel rolls is primarily attributed to the strong anti-agglomeration of M2C and MC. A large amount of retained austenite can also be obtained in the quenched microstructure of ordinary carbon steel and low-alloy steel. The decomposition of these retained austenites at high temperatures rarely increases hardness. The austenite in these steels usually decomposes at lower temperatures, while the precipitated Fe3C-type carbides rapidly agglomerate at slightly higher temperatures. The agglomeration of carbides is the direct cause of softening. In high-speed steel, carbide precipitation into very fine particles and the decomposition of retained austenite together lead to secondary hardening, and the carbides always maintain their fine size, so high-speed steel has good red hardness. In high-speed steel, the elements that affect the formation of this phenomenon are tungsten and molybdenum. The atomic size of tungsten and molybdenum in high-speed steel is much larger than that of any other element, and the diffusion rate is slower. In order for the carbides to continue to accumulate, not only chromium is needed

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2022

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YILIAN SHENG

What is the role of chromium in high-speed steel rolls?

What is the role of chromium in high-speed steel rolls? Chromium in high-speed steel is partially present in M6C-type carbides and can also form M23C6-type carbides. M23C6 can be completely dissolved at lower quenching temperatures, allowing the solid solution to reach chromium-carbon saturation without affecting the grain size. Chromium can also promote the complete dissolution of M6C in austenite, thereby improving the hardenability and red hardness of high-speed steel. In addition, when high-speed steel is tempered at 450-525℃, some chromium precipitates from the martensite, which promotes dispersion hardening; another part of the chromium remains in the solid solution α to prevent softening when heated to higher temperatures. Adding 3%-4% chromium can achieve slightly higher hardness. Chromium can also significantly reduce oxidation in high-speed steel. However, if the chromium content is too high, the excess chromium will participate in the formation of carbides precipitated during tempering. This chromium-containing carbide is easily precipitated at lower temperatures, reducing the thermal stability of high-speed steel. If the chromium content is too high, the inhomogeneity of the carbides will also increase. Because chromium increases the amount of M7C3 carbide in high-speed steel rolls and reduces the amount of MC carbide, and the hardness of M7C3 carbide is lower than that of MC carbide, this is detrimental to wear resistance. However, for rolls with low chromium content...

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2022

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YILIAN SHENG

Introduction to the Development of Rolling Mills

Introduction to Roll Development: The main working parts and tools used for the continuous plastic deformation of metals on rolling mills. Rolls are mainly composed of three parts: roll body, roll neck, and shaft head. The roll body is the middle part of the roll, which is actually involved in rolling metals. It has a smooth cylindrical or grooved surface. The roll neck is mounted in the bearing, and the roll force is transmitted to the frame through the bearing seat and clamping device. The drive end shaft head is connected to the gear seat through a connecting shaft, transmitting the rotating torque of the motor to the roll. Rolls can be arranged in the form of two rolls, three rolls, four rolls, or multiple rolls in the mill frame. With the development of metallurgical technology and rolling equipment, the varieties and manufacturing processes of rolls are also constantly developing. In the Middle Ages, low-strength gray cast iron rolls were used to roll soft non-ferrous metals. In the mid-18th century, Britain mastered the technology of producing cold cast iron rolls, which were used to roll steel plates. In the second half of the 19th century, the advancement of European steelmaking technology required the rolling of larger ingots. Neither gray cast iron rolls nor cold-hard cast iron rolls could meet the requirements in terms of strength. This led to the birth of ordinary cast steel rolls with a carbon content of 0.4% ~ 0.6%. The emergence of large forging equipment further improved the strength and toughness of forged rolls of this composition. At the beginning of the 20th century, the use of alloying elements

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Address: Chaoyang Liucheng Economic Development Zone, Chaoyang County, Chaoyang City, Liaoning Province
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