The high-speed steel roll material contains high alloy elements such as vanadium, tungsten, chromium, molybdenum, niobium, etc. The types of carbides in the roll structure are mainly MC type and M2C type. Compared with ductile iron rolls and high-nickel-chromium rolls, the single-groove (time) steel passing is higher, which saves roll changing time, improves rolling mill operation rate, reduces roll consumption, reduces production costs, and improves the overall benefit of the factory.
The high-speed steel roll material has a large expansion coefficient and good thermal conductivity. While the roll wears a small amount of the groove during the rolling process, due to the expansion of the high-speed steel material itself, the hole shape continues to become smaller. Therefore, the high-speed steel roll is rolling. During the process, the change of the rolling groove is small, and the consistency of the pass size is maintained for a long time, especially when rolling bars or rebars, it is more conducive to control the negative tolerance of the rolling material.
Since the core of the centrifugally cast high-speed steel roll is made of alloy ductile iron, the roll neck strength is high.
An obvious trend in the development of rolls is the extensive use of alloying elements to form various carbides in the roll material. The hardness, morphology, quantity and distribution of carbides, as well as the structure and properties of the matrix, have an impact on the wear resistance, thermal fatigue resistance, thermal fatigue resistance of the roll. The properties of resistance to peeling and surface roughness play a decisive role. The following table shows the types and microhardness of alloy carbides formed by different material rolls.
Roll material | Main Carbide Type | carbide form | Carbide microhardness (HV) | |
high speed steel |
MC | VC | granular | 2800 |
WC | granular | 2400 | ||
NbC | granular | 3000 | ||
TiC | granular | 3200 | ||
M2C | Mo2C / W2C | stick / feather | 2000 | |
M6C | Fe3 / W3C | fishbone | 1500-1800 | |
high chromium cast iron | M7C3 | Cr7C3 | chrysanthemum | 1200-1600 |
M23C6 | Cr23C6 | granular | 1200 | |
High nickel chromium molybdenum cast iron | M3C | Fe3C | mesh | 840-1100 |
Metallographic structure of high-speed steel rolls and rolls of other materials
The performance of the roll depends on the microstructure of the final roll. For cast high-speed steel, the morphology of carbides cannot be changed by deformation. It can only be changed by adjusting the chemical composition, solidification conditions and heat treatment process to meet the requirements of the roll performance.
Obtaining high hardness granular carbide and fine matrix structure is the basic guarantee to improve the performance of the roll. It can be seen from the metallographic photos that the morphology, quantity, size and distribution of carbides in the metallographic structure of the high-speed steel roll, as well as the matrix structure and grain size are much better than other materials.
