Welding Tungsten Carbide to Stainless Steel in Vacuum Furnaces
Joining tungsten carbide to stainless steel is a critical requirement in many industrial applications where extreme wear resistance must be combined with structural strength and corrosion resistance. Tungsten carbide is widely used in cutting tools, wear parts, ultrasonic tooling, and high-load components, while stainless steel provides mechanical toughness and ease of fabrication.
From a manufacturing standpoint, however, WC to stainless joints are among the most demanding metallurgical interfaces in industry. Direct fusion welding almost always leads to cracking and premature failure. Controlled brazing or diffusion bonding in a high-performance vacuum furnace offers a robust solution, provided that the joint design, filler metal selection, and thermal cycles are properly engineered.
The primary obstacle in joining WC to SS is the significant difference in their Coefficient of Thermal Expansion (CTE).
Stainless Steel (300/400 series): ≈ 10 – 17 × 10^-6/K
Tungsten Carbide: ≈ 5 × 10^-6/K
During the cooling phase of a traditional welding process, the stainless-steel contracts at nearly triple the rate of the carbide. This creates massive residual tensile stresses at the interface, leading to "ice-cracking" or delamination of the carbide insert.
Vacuum brazing is the preferred method for joining tungsten carbide to stainless steel because it allows precise control over temperature, atmosphere, and time. In this process, a filler alloy melts and flows into the joint by capillary action without melting the base materials. The vacuum environment eliminates oxidation, removes the need for flux, and ensures excellent wetting of both carbide and stainless-steel surfaces. The result is a clean, high-strength joint with minimal residual stress.
Filler Metal Selection
Silver-based brazing alloys are commonly used for applications operating at moderate service temperatures, typically up to 300 - 400 °C, due to their excellent wetting behavior and ductility. For high-temperature or high-load applications, nickel-based brazing alloys are preferred, as they provide superior strength and thermal stability. To further accommodate thermal expansion mismatch and reduce stress concentration, interlayers such as nickel, copper, or molybdenum are often applied between the tungsten carbide and stainless steel. These interlayers act as diffusion barriers and stress absorbers, significantly improving joint reliability.
Vacuum Brazing Process Parameters
A controlled vacuum brazing cycle typically employs heating rates of approximately 3-7 °C/min to minimize thermal shock, with brazing temperatures ranging from 780 °C to 950 °C depending on the selected silver- or nickel-based filler alloy, and soak times of 5-15 minutes to ensure complete wetting and filler flow.
High vacuum levels, typically in the range of 0.001 to 0.01 Pa, are required to prevent oxidation and eliminate the need for flux, while optional nickel, copper, or molybdenum interlayers are commonly used to reduce residual stresses and limit carbon diffusion at the carbide-steel interface. Cooling is carried out in a controlled manner under vacuum or inert gas backfill to minimize residual stress and prevent cracking.
For this application, Normantherm’s VF Series vacuum brazing furnaces are suitable choices because they are engineered specifically for high-vacuum brazing of hard alloys, stainless steel, and carbide components. Models such as the VF1300-422 vacuum brazing furnace provide a horizontal chamber with maximum temperatures up to 1300 °C, excellent temperature uniformity (±5 °C), precise control (±1 °C), and high vacuum capability down to ≈6.67 × 10^-4 Pa cold state / ≈6.67 × 10^-3 Pa at temperature, making them ideal for controlled brazing cycles of dissimilar materials such as tungsten carbide to stainless steel.
The shown tungsten carbide to stainless steel assembly was successfully brazed in Normantherm’s vacuum brazing furnace.
Conclusion
Direct fusion welding of tungsten carbide to stainless steel is not feasible due to extreme differences in thermal expansion, brittleness of the carbide, and adverse metallurgical reactions. Vacuum brazing provides a technically sound and industrially proven solution by enabling controlled joining without melting the base materials. With appropriate filler alloy selection, carefully defined heating specifications, and the use of advanced vacuum furnace technology such as that offered by Normantherm, high-performance and durable carbide-to-stainless-steel joints can be reliably achieved.
Edited by: Shristi Paudyal
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