High-speed steel is a high-carbon high-alloy steel containing a large number of W, Mo, Cr, V and Co. The composition of high-speed steel is as follows: C_0.7%-1.65%, W_0%-12%, Mo_0%-10%, about Cr_4%, V_1%-5% and Co_0%-12%. High-speed steel has high heat hardness after heat treatment, and often contains other alloying elements such as Al, Nb, Ti, Si and rare earth elements, the total amount is less than 2%. When the cutting temperature is above 600 C, the hardness still does not decrease significantly. The cutting speed of the tool manufactured with it can reach more than 60 meters per minute, which is named after it.
1. Tool performance and tool material selection:
1. Property of Tool Material
In metal cutting, the cutting part of the tool directly contacts with the workpiece and cutting, bears a great deal of cutting pressure and impact, and is subjected to severe friction between the workpiece and cutting, resulting in a high cutting temperature. That is to say, the cutting part of the tool works under the harsh conditions of high temperature, high pressure and severe friction. Therefore, the cutting materials of cutting tools should have the following basic properties:
1) High hardness
The hardness of the tool material must be higher than that of the processed material. It is generally required that the hardness of tool materials at room temperature must be above HRC62.
2) Good wear resistance and heat resistance
Cutting tools are subjected to severe friction during cutting, so tool materials should have high wear resistance. Wear resistance and heat resistance of tool materials are closely related, and their heat resistance is usually measured by their ability to maintain high hardness at high temperatures. The better the heat resistance, the higher the allowable cutting speed.
3) Good thermal conductivity
The thermal conductivity of tool materials is expressed by thermal conductivity. High thermal conductivity means good thermal conductivity. The heat generated during cutting is easy to spread out, thus reducing the temperature of cutting parts and tool wear.
4) Adequate strength and toughness
The material in the cutting part of the tool bears a great deal of cutting force and impact force in cutting, so the tool material must have enough strength and toughness.
5) Good technicality and economy
The cutting tool material itself is required to have good machinability, wear resistance, heat treatment performance, welding performance, and rich resources and low price.
2. Selection of common tool materials:
Common high speed steel W6Mo5Cr4V2 (M2) belongs to molybdenum high speed steel. Its carbide distribution uniformity, toughness and high temperature plasticity are all higher than those of W18Cr4V, but its grinding performance is poor.
Carbon tool steel T8A steel is eutectoid steel. It is easy to overheat when quenched and heated, and has large deformation, low plasticity and strength. It is not suitable to manufacture tools with high impact resistance, but it has high hardness and wear resistance after heat treatment.
The cold-working die steel Cr12MoV of high carbon and high chromium type Ledeburite has good hardenability. The cross-section of Cr12MoV cold-working die steel can be hardened completely below 300-400 mm, and has high wear resistance. The volume change is small during quenching. The carbon content of Cr12 steel is much lower than that of Cr12 steel, and a small amount of molybdenum and vanadium is added, so the hot workability, impact toughness and carbide distribution of the steel have been significantly improved.
Cold working die steel Cr12Mo1V1
Main features: Ledeburite cold working die steel of high carbon and chromium type, cobalt is not required as an additive when there is no special requirement. Because molybdenum and vanadium are higher than Cr12Mo1V steel, the structure and grain of the steel are further refined, and the hardenability, strength and toughness of the steel are improved, so that the comprehensive properties of the steel are better than those of Cr12Mo1V steel.