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

　　Part of the chromium in high-speed steel exists in M6C type carbides, and can also form M23C6 type carbides. M23C6 can be completely dissolved at lower quenching temperatures, so that the solid solution can reach carbon-chromium 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℃, part of the 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 non-uniformity of the carbide will also increase.

　　Because chromium increases High-speed steel rolls the amount of M7C3 carbides, reduces the amount of MC carbides, and the hardness of M7C3 carbides is lower than that of MC carbides, which is detrimental to wear resistance. However, for rolls with low chromium content, due to the preferential wear of the substrate and the adhesion of the rolling material to the roll surface, the roll surface is easily roughened, which increases the rolling friction coefficient and rolling force. By increasing the chromium content to make the rolls contain a certain amount of M7C3 type carbides, it is beneficial to improve the surface roughness resistance of the rolls and reduce the rolling force. The increase in chromium content is also beneficial to improve the thermal shock resistance of high-speed steel rolls. Therefore, the suitable chromium content in high-speed steel bars is 4.0%-7.0%.

　　Continuous cold rolling requires high performance of the rolls, especially when the mill is fully integrated with pickling lines and/or continuous annealing lines, high productivity requires higher performance of the work rolls, especially the ability to maintain proper roughness during rolling. Therefore, the deterioration of the work roll surface is one of the main issues to be considered in cold rolling. The rolls need to have wear resistance and the ability to maintain roughness, because a low level of roughness is crucial for ensuring the friction required for rolling.

　　In recent years, the output of cold rolling work rolls has been greatly improved, and rolling technology and roll materials have greatly contributed to this. This is an ongoing process. First, half High-speed steel rolls used for hot rolling, and then for cold rolling. Now, high-speed steel rolls (HSS) are introduced into cold rolling. These high-alloy cast materials will become an effective substitute for forged steel rolls.

　　Generally, in order to expand the application range of forged steel rolls, in many cases, their surface needs to be chrome-plated. High-speed cast steel rolls have good wear resistance, so they can achieve similar rolling effects without chrome plating, and will not produce additional costs and environmental impact. In addition to these characteristics, high-speed steel rolls also have many characteristics during grinding.