What Is The Difference Between Stellite 6 And 6B?

As two representative grades in the Stellite series of cobalt - based alloys, Stellite 6 and Stellite 6B share the basic characteristics of cobalt - based alloys, such as good wear resistance and high - temperature oxidation resistance. However, due to differences in chemical composition, there are certain distinctions in their performance and application fields.​
Chemical Composition​
Stellite 6 is a typical cobalt - based alloy. Its main chemical composition is cobalt, accounting for about 50 - 65%. It contains 27 - 32% chromium, 4 - 6% tungsten, and a small amount of carbon (about 1.0 - 1.4%), as well as trace elements such as nickel and iron. The carbon in Stellite 6 combines with elements like chromium and tungsten to form hard carbides, which are important for its wear resistance.​
Stellite 6B is an improved variant of Stellite 6. Its cobalt content is slightly higher, generally ranging from 60 - 70%. The chromium content is slightly lower than that of Stellite 6, about 24 - 28%. The tungsten content is basically the same as that of Stellite 6, at 4 - 6%. The most obvious difference is in the carbon content. The carbon content of Stellite 6B is lower, usually around 0.7 - 1.0%. In addition, it may contain a small amount of other elements such as silicon, but the content is very low and has little impact on the overall performance.​
Mechanical Properties​
Hardness and Wear Resistance​
Stellite 6 has a relatively high hardness, with a Rockwell hardness (HRC) of about 38 - 42. The higher carbon content in it leads to the formation of more hard carbides in the alloy structure. These carbides are evenly distributed in the matrix, which can effectively resist the intrusion of abrasive particles, so it has excellent wear resistance, especially in the face of abrasive wear and adhesive wear.​
Stellite 6B has a slightly lower hardness than Stellite 6, with a Rockwell hardness (HRC) of about 34 - 38. Due to the lower carbon content, the number of carbides in its structure is relatively reduced. Therefore, in terms of wear resistance, under the same wear conditions, its wear resistance is slightly inferior to that of Stellite 6. However, it still maintains good wear resistance compared with many other common alloys.​
Toughness and Ductility​
Stellite 6, due to the higher content of hard carbides, has relatively low toughness and ductility. In applications that are prone to impact or vibration, there is a certain risk of brittle fracture.​
Stellite 6B, with fewer carbides in its structure, has better toughness and ductility than Stellite 6. It can better absorb impact energy and is not easy to crack when subjected to external impact or alternating stress. This makes Stellite 6B more suitable for occasions that require a certain degree of toughness while having wear resistance.​
High - Temperature Performance​
Both Stellite 6 and Stellite 6B have good high - temperature resistance. They can maintain their structural stability at high temperatures up to 1000°C and have good oxidation resistance.​
In terms of high - temperature hardness, Stellite 6 retains higher hardness at high temperatures because of its higher carbide content. For example, at 600°C, its hardness is still above HRC 30, which enables it to maintain good wear resistance in high - temperature wear environments.​
Stellite 6B also has a certain high - temperature hardness, but it is slightly lower than that of Stellite 6 at the same high temperature. However, its high - temperature toughness is better. It is not easy to break when subjected to thermal shock, which is an advantage in environments with frequent temperature changes.​
Application Fields​
Stellite 6​
1.Wear - Intensive Static Components: It is widely used in the manufacture of valve seats, valve discs, and pump housings in the oil and gas industry. These components are in a relatively static state or have low - speed relative movement during use, but they need to withstand the long - term erosion of high - pressure fluids and abrasive particles. The high wear resistance of Stellite 6 can ensure their long - term service.​
2.High - Load Wear Parts: In the power industry, it is used to make coal mill rolls and grinding discs. These parts are under high load during the coal grinding process, and the coal particles have a strong abrasive effect. Stellite 6 can meet the requirements of wear resistance under high load.​
3.Molds and Tools: It is used to make molds for stamping hard materials and cutting tools for processing abrasive materials. The high hardness of Stellite 6 can ensure the service life of these tools and molds.​
Stellite 6B​
1.Dynamic Wear Components: It is often used in the manufacture of turbine blades, impellers, and other components in the aerospace and power industries. These components rotate at high speed during operation and are subject to both wear from fluid scouring and certain impact forces. The good combination of wear resistance and toughness of Stellite 6B can meet their working needs.​
2.Components Subject to Thermal Shock: In the field of metallurgy, it is used to make parts of continuous casting machines that are in contact with high - temperature molten metal and are cooled by water. These parts are in a state of alternating high and low temperatures, and Stellite 6B's good toughness and high - temperature resistance can prevent them from cracking due to thermal shock.​
3.Wear - Resistant Parts with Impact Loads: In the mining industry, it is used to make wear - resistant liners of crushers. These liners are not only subject to the wear of ore particles but also to the impact of large ore blocks. Stellite 6B can resist wear while withstanding impact.​
Processing Performance​
Stellite 6 has high hardness and more carbides, which makes its machining performance relatively poor. During machining, it is easy to cause tool wear, and higher cutting force and special cutting tools are required. In welding, due to its high carbon content, it is prone to the formation of carbide networks in the weld zone, which may reduce the toughness of the weld. Therefore, strict control of welding parameters is needed during welding.​
Stellite 6B has lower hardness and fewer carbides, so its machining performance is better than that of Stellite 6. It is easier to carry out turning, milling, and other machining operations, and the tool loss is relatively small. In terms of welding, the lower carbon content reduces the risk of carbide precipitation in the weld, making the welding process more stable, and the weld joint has better toughness.​
In conclusion, although Stellite 6 and Stellite 6B are both cobalt - based alloys, they have obvious differences in hardness, wear resistance, toughness, and processing performance due to the difference in carbon content and the corresponding changes in other element contents. Stellite 6 is more suitable for static or low - impact wear occasions that require high wear resistance, while Stellite 6B is more suitable for dynamic or impact - bearing wear occasions that require a balance between wear resistance and toughness. When selecting, it is necessary to consider the specific working conditions such as the degree of wear, the presence of impact, and processing requirements to make a reasonable choice.