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To overcome the problem of loose hot-mounted sealing rings, welded sealing rings were developed (Figure 24). The cemented carbide used is a sintered alloy material with Cr3C2 as the hard phase and Ni as the bonding phase. It has better corrosion resistance than hard alloys such as YG6, and exhibits excellent oxidation resistance at high temperatures; it shows no changes after being heated in air at 1000°C for 2 hours. However, its thermal conductivity is poor, at only 1/3 that of YG6 ； It has a high linear expansion coefficient, more than twice that of YG6, at 10.2x10-6/℃ (between 10~500℃). These two factors determine that its heat shock resistance is inferior to that of YG6. It is precisely because of its high linear expansion coefficient, which is similar to that of martensitic stainless steel (11x10-6/°C at 10–500°C), that it provides favorable conditions for welding to ring seats. During welding, a layer of nickel-based powder must be placed between the ring and the seat; it is then placed in a vacuum resistance furnace and welded at a high temperature of 1100°C, followed by tempering to eliminate welding stresses. Since it is a welded seal ring, the thickness of the cemented carbide ring can be thinner than that of YG6, and the thickness of the blank is only 3–3.5 mm. Also, due to its low density, which is half that of YG6 (7–7.5 g/cm3), it allows for the use of less precious metals, resulting in a lower price. The grade of this alloy is CN15, with 85% Cr3C2 and 15% Ni; it was developed by Beijing Cemented Carbide Factory.