Tungsten Carbide Knowledge Explanation - Performance And Heat Treatment

The tungsten carbide is an alloy which has the main component of powders including tungsten carbide, titanium carbide and metal powder such as cobalt, nickel, etc, as an adhesive, obtained through the powder metallurgical method. It is mainly used to make high-speed cutting tools and hard, tough material cutting edges, and high wear parts for fabrication of cold dies, measuring tools.

Mechanical And Physical Properties Of Tungsten Carbide

1.Wear resistance

The wear resistance of the tungsten carbide is its most important feature. In practical applications, carbides are 20-100 times longer than some wear-resistant steel alloys.

2.Bending resistance

The sintered carbide has a high elastic modulus and the smallest bend is obtained when subjected to bending force.

3.Corrosion resistance

It is usually used in many chemical and corrosive environments because carbides are typically chemically inert.

4.Torsional strength

The amount of torsion is two times than the high-speed steel and the carbide is the preferred material for high-speed operation applications.

5.Compressive strength

Some grades of cobalt carbide and cobalt have perfect performance under ultra-high pressure and is very successful in pressure applications of up to 7 million kPa.

6.Toughness

Cemented carbide grades with high binder content have excellent impact resistance.

7.Low temperature wear resistance

Even at an extremely low temperature, the carbide remains good to wear resistance and provides relatively low friction coefficients without using a lubricant.

Applications Of Tungsten Carbide

Cutter tool

Tungsten carbide cutter tool is the widest application, used for making lathe tool, milling cutter, planner tool, drilling bit, etc. Among them, the tungsten cobalt carbide is suitable for black metal, non-ferrous metals, processing of non-metallic materials, such as cast iron, cast brass, colloidal wood, etc. Tungsten titanium cobalt is suitable for long chip processing of steel and other black metals. In the same alloy, what has more cobalt content suitable for rough machining, what has less cobalt content suitable for fine machining.

Mold material

The cemented carbide is mainly used for cold wire drawing dies, cold stamping dies, cold extrusion dies, and other cold work molds.

Under the wear-resistant working conditions of the impact or strong impact, the tungsten carbide dies are required to have good anti-polishing toughness, fracture toughness, fatigue strength, bending strength, and good wear resistance.

In general, the relationship between the wear resistance and toughness of the carbide is contradictory, the increase in wear resistance will result in a decrease in toughness, and the increase in toughness will inevitably lead to a decrease in wear resistance. Therefore, when choosing a tungsten carbide grade, it is necessary to meet specific usage requirements based on the processing objects and machining conditions.

If the selected grade is easy to produce early cracks and damage, it is advisable to use the grade with high toughness. If the selected grades are easily damaged as the wear, it is appropriate to choose a grade with a higher hardness and better wear resistance.

Measuring tool and wear parts

The tungsten carbide is used in the easy to wear surface inlay and parts of the measuring tool, grinding machine precision bearing, the wear parts such as guide plate and guide rod of centerless grinder, lathe center.

Heat Treatment Of Tungsten Carbide

The hear treatment process of tungsten carbide can be divided into four basic stages

1.Removal of the molding agent and the pre-sintering

In the initial stage of sintering, the molding agent gradually decomposes or vaporizes, excluding the sintered body, while at the same time, molding agents carburize sintering and the amount of carbon will vary depending on the type, quantity and the sintering process. The powder surface oxide is reduced, and hydrogen can reduce oxides of cobalt and tungsten at a sintering temperature. When the reaction between carbon and oxygen is not strong, the contact stress between the powder particles is gradually eliminated. The bonding metal powder begins to generate reply and recrystallization and the surface diffusion begins to occur. The strength of the block is improved.

2.The solid phase sintering stage (800°C - eutectic temperature)

In the presence of the liquid phase, in addition to the process of continuing the previous stage, solid-phase reactions and diffusion exacerbating with plastic flow enhancement, and the sintered body appears obvious contraction.

3. Liquid phase sintering stage (eutectic temperature - sintering temperature)

When the liquid phase of the sintered body occurs, the contraction is quickly completed and then a crystallization transition is generated. The basic organization and structure of the carbide are formed.

4.Cooling stage (sintering temperature - room temperature)

At this stage, the organizational and phase components of the tungsten carbide have certain changes with the different cooling conditions, which can utilize this feature, heat treatment of the cemented carbide will improve its physical-mechanical performance.

Summary

Tungsten carbide has high performance with excellent mechanical and physical properties including high wear resistance, corrosion resistance, bending strength, torsional strength, etc, widely used for the making of cutter tools, cold mold, wear parts, etc. The article also briefly introduces the four basic stages of tungsten carbide heat treatment which can improve physical mechanical performance of the cemented carbide.