The characteristics of high-speed steel rolls are mainly reflected in the following seven aspects:
1) Carbide hardness is high.
The rolls used in the past mostly distributed Fe3C or M7C3 eutectic carbides on the matrix, with coarse structures and low hardness. High-speed steel rolls generally use high-C, high-V high-speed steel, and also contain more alloying elements such as Cr, Mo, W, Nb, and Co. During solidification and heat treatment, these alloying elements form primary and secondary carbonization. things. High chromium cast iron roll carbides are M7C3 (2500 Hv) and M23C6 (1600 Hv). In infinite chilled cast iron rolls, the carbide is Fe3C (l300 Hv). The high-speed steel rolls mainly contain MC (3000 Hv), M7C3 (2500 Hv), and M6C (2000 Hv), which can replace ordinary rolls to improve wear resistance. In addition, with the increase of V content, the skeletal M6C carbide in the high-speed steel structure transforms into the granular VC type.
2) Good thermal stability.
High-speed steel rolls contain more 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 significantly with the increase in temperature, while high-speed steel rolls at 600 ℃ still maintain 500 Hv, which will greatly improve the wear resistance of the roll. Especially when the Co element distributed in the matrix is added, this tendency is more obvious.
3) It is easy to form an oxide film during use.
During the rolling process, if a continuous, dense, uniform and well-bonded oxide film is formed on the surface of the roll, it can not only reduce the friction coefficient between the roll and the rolled material but also improve the dimensional accuracy and surface quality of the rolled material. In the initial stage of use, ordinary rolls are more worn due to a lack of oxide film protection. Oxide film can be formed quickly during the use of high-speed steel rolls. The appearance of the oxide film can reduce the friction between the strip steel and the roll surface, prevent the roll from sticking to the steel, and improve the lives of the roll. Compared with ordinary rolls, the initial wear of high-speed steel rolls is lower, which is very beneficial for improving the wear resistance of high-speed steel rolls.
4) Good hardenability.
The high-speed steel roll has good hardenability. At room temperature, within 50mm of the working layer, the hardness drop from the roll surface to the core is less than 3HS, which can ensure that the roll has good wear resistance from the outside to the inside.
5) Excellent toughness.
Compared with general infinite chilled cast iron, high chromium cast iron, and semi-steel rolls, high-speed steel rolls have better basic mechanical properties, tensile strength, and fracture toughness than high-chromium cast iron rolls and infinite chilled cast iron rolls, and semi-steel rolls near.
6) Good thermal crack resistance.
Due to its unique structure characteristics, high-speed steel can effectively inhibit the formation and propagation of cracks. In actual use, it is found that high-speed steel rolls do have better thermal cracking resistance than high-chromium cast iron rolls. Therefore, if a general production accident occurs, the impact of the accident can be eliminated through the normal grinding amount or a small additional grinding amount, which simplifies the processing process and saves costs.
7) Good wear resistance.
Compared with semi-steel, high-chromium cast iron and high-nickel-chromium infinitely chilled cast iron rolls, the rolling tonnage of high-speed steel rolls has been greatly increased. F1-F4 stands are about 10,000t, and F5 stands are about 6,000t, showing that high-speed steel rolls have Good abrasion resistance. The increase in the rolling tonnage of high-speed steel rolls has led to a significant decrease in roll consumption. Under the same rolling conditions, the roll consumption of high-speed steel rolls is 1/5 of that of high-chromium cast iron rolls in the F1 frame, and the high-chromium cast iron rolls in the F2 frame. The F4 frame is 1/13 of the high nickel-chromium infinite chilled cast iron roll, and the F5 frame is 1/8 of the high nickel-chromium infinite chilled cast iron roll.