What are the hard alloys for surface welding of mechanical seals?

Welding a layer of hard alloy on the surfaces of the sealing rings of the mechanical seals can improve their wear resistance and corrosion resistance , and this action’s prices are low, so it is a common practice. The hard alloys used for surfacing include chromium-based No. 1, cobalt-based No. 1 and cobalt-based No. 2. Their composition and properties are shown in the table below.

The chrome-based No. 1 surfacing layer has good cavitation resistance and corrosion resistance; the Co-based No. 1 surfacing layer has high hardness and good acid resistance; the Co-based No. 2 surfacing layer has high temperature resistance and and high hardness at high temperature. Although surfacing hard alloy has certain corrosion resistance, it is not resistant to strong acid and hot alkali corrosion. Besides，its hardness is not high, & its thermal crack resistance is poor, and the surfacing welding process poses quite high requirements, so it is not suitable for mechanical seals whose sealed medium are granular and mechanical seals at high-speed. For the above-mentioned two cases，the heat treatment requirements before and after surfacing welding are relatively strict, and defects such as pores and cracks are prone to occur in this process. 

A new type of hard alloy for surface welding has been developed in China. It is F e-Cr-C series, the models are EDZCr55-1 and EDZCr-60, and it is a welding electrode for surfacing welding with high wear resistance, good toughness and crack resistance. The hardness of EDZCr55-1 after surfacing is HRC55, and the impact toughness can reach more than 10N.m/c㎡; the hardness of EDZCr-60 is HRC60, but the toughness is slightly worse. This hard alloy has a simple surfacing process, and both AC and DC welding machines can be used.The preheating temperature of this cemented carbide before welding only needs to be about 200°C, no heat tracing is needed during the welding process, and it needs to be covered with insulating materials after welding only. The electrode is low in price and is a promising hard alloy for surfacing