DRILLSTAR CARBIDE TOOLS ARE WORKING IN MANY PLACES AROUND THE WORLD
Views: 108 Author: Site Editor Publish Time: 2024-03-12 Origin: Site
Hard alloy is an alloy made by powder metallurgy with one or several refractory carbides (tungsten carbide, titanium carbide, etc.) as the main component, and metal powders (cobalt, nickel, etc.) added as adhesives. It is mainly used for manufacturing high-speed cutting tools and cutting tools for hard and tough materials, as well as for making cold work molds, measuring tools, and high wear-resistant parts that are not affected by impact and vibration.
1.The characteristics of hard alloys
(1) High hardness, wear resistance, and red hardness
The hardness of hard alloy at room temperature can reach 86~93HRA, equivalent to 69~81HRC. It can maintain high hardness and excellent wear resistance at 900~1000 ℃. Compared with high-speed tool steel, the cutting speed can be 4-7 times higher, the lifespan can be 5-80 times longer, and it can cut hard materials with a hardness of up to 50HRC.
(2) High strength and elastic modulus
The compressive strength of hard alloy is as high as 6000MPa, and the elastic modulus is (4-7) × 105MPa, which is higher than that of high-speed steel. But its bending strength is relatively low, generally between 1000~3000MPa.
(3) Good corrosion resistance and oxidation resistance
It generally has good resistance to corrosion such as atmospheric, acid, and alkali, and is not easily oxidized.
(4) Low coefficient of linear expansion
When working, the shape and size are stable.
(5) Formed products no longer require processing or regrinding
Due to the high hardness and brittleness of hard alloys, they are no longer subjected to cutting or regrinding after powder metallurgy forming and sintering. When further processing is required, only electrical discharge machining, wire cutting, electrolytic grinding, or specialized grinding wheels can be used. Products of certain specifications, usually made of hard alloy, are used by brazing, bonding, or mechanical clamping on the blade or mold.
2.Common hard alloys
Commonly used hard alloys are divided into three categories based on their composition and performance characteristics: tungsten cobalt, tungsten titanium cobalt, and tungsten titanium tantalum (niobium). The most widely used in production are tungsten cobalt and tungsten titanium cobalt hard alloys.
(1) Tungsten cobalt hard alloys
The main components are tungsten carbide (WC) and cobalt, with the brand code YG (the first two characters of "hard" and "cobalt" in Chinese Pinyin), followed by the percentage value of cobalt content. YG6 represents a tungsten cobalt hard alloy with a cobalt content of 6%, and a tungsten carbide content of 94%.
(2) Tungsten titanium cobalt hard alloys
The main components are tungsten carbide (WC), titanium carbide (TiC), and cobalt. The brand name is represented by the code YT (the initials of "hard" and "titanium" in Chinese Pinyin), followed by the percentage value of titanium carbide content. YT15 represents tungsten titanium cobalt hard alloys with 15% titanium carbide content.
(3) Tungsten titanium tantalum (niobium) based hard alloys
This type of hard alloy, also known as universal hard alloy or universal hard alloy, is mainly composed of tungsten carbide (WC), titanium carbide (TiC), tantalum carbide (TaC) or niobium carbide (NbC) and cobalt. The brand name is represented by adding an ordinal number after the code YW (the initials of "hard" and "ten thousand" in Chinese Pinyin).
3.The characteristics of hard alloys
(1) High hardness, wear resistance, and red hardness
The hardness of hard alloy at room temperature can reach 86~93HRA, equivalent to 69~81HRC. It can maintain high hardness and excellent wear resistance at 900~1000 ℃. Compared with high-speed tool steel, the cutting speed can be 4-7 times higher, the lifespan can be 5-80 times longer, and it can cut hard materials with a hardness of up to 50HRC.
(2) High strength and elastic modulus
The compressive strength of hard alloy is as high as 6000MPa, and the elastic modulus is (4-7) × 105MPa, which is higher than that of high-speed steel. But its bending strength is relatively low, generally between 1000~3000MPa.
(3) Good corrosion resistance and oxidation resistance
It generally has good resistance to corrosion such as atmospheric, acid, and alkali, and is not easily oxidized.
(4) Low coefficient of linear expansion
When working, the shape and size are stable.
(5) Formed products no longer require processing or regrinding
Due to the high hardness and brittleness of hard alloys, they are no longer subjected to cutting or regrinding after powder metallurgy forming and sintering. When further processing is required, only electrical discharge machining, wire cutting, electrolytic grinding, or specialized grinding wheels can be used. Products of certain specifications, usually made of hard alloy, are used by brazing, bonding, or mechanical clamping on the blade or mold.
4.Application of hard alloys
(1) Tool material
Hard alloys are widely used as cutting tool materials and can be used to make turning tools, milling cutters, planers, drill bits, etc. Tungsten cobalt based hard alloys are suitable for short chip processing of black and non-ferrous metals, as well as processing of non-metallic materials such as cast iron, cast brass, bakelite, etc; Tungsten titanium cobalt hard alloys are suitable for long chip machining of black metals such as steel. Among similar alloys, those with higher cobalt content are suitable for rough machining, while those with lower cobalt content are suitable for precision machining. The processing life of general-purpose hard alloys for difficult to machine materials such as stainless steel is much longer than that of other hard alloys.
(2) Mold material
Hard alloy is mainly used as cold working molds such as cold drawing molds, cold punching molds, cold extrusion molds, and cold pier molds.
The commonality of hard alloy cold heading dies under wear-resistant working conditions that withstand impact or strong impact is that hard alloys are required to have good impact toughness, fracture toughness, fatigue strength, bending strength, and good wear resistance. Usually, medium to high cobalt and medium to coarse-grained alloy grades are selected, with common ones such as YG15C.
Generally speaking, the relationship between the wear resistance and toughness of hard alloys is contradictory: an increase in wear resistance will lead to a decrease in toughness, and an increase in toughness will inevitably lead to a decrease in wear resistance. Therefore, when selecting alloy grades, it is necessary to meet specific usage requirements based on the processing object and working conditions.
If the selected brand is prone to early cracking and damage during use, it is advisable to choose a brand with higher toughness; If the selected brand is prone to early wear and damage during use, it is advisable to choose a brand with higher hardness and better wear resistance. The following grades: YG15C, YG18C, YG20C, YL60, YG22C, YG25C from left to right, with reduced hardness, reduced wear resistance, and improved toughness; On the contrary, the opposite is true.
(3) Measuring tools and wear-resistant parts
Hard alloy is used for easy to wear surface inlay and parts of measuring tools, precision bearings of grinding machines, guide plates and rods of centerless grinding machines, and wear-resistant parts such as lathe tips.