Introduction to Heat Treatment of Sealing Surfaces for Coke Oven Flue Gate Valves

The heat treatment of the sealing surfaces on coke oven flue gate valves refers to the heat treatment of the cobalt-chromium-tungsten carbide hardfacing applied to the sealing surfaces of carbon steel valve bodies and gate discs. Following hardfacing of the Co-Cr-W carbide sealing surfaces on flue gate valves, stress relief annealing is required. Its primary purpose is to eliminate residual stresses generated during hardfacing and to improve machinability.

For gate valves with carbon steel substrates, overlaid with CoCrW hard alloy or SF-4 (137) alloy, or spray-welded with WF330 or Fe30 components, the stress-relief annealing heating temperature is selected based on the carbon steel substrate material, typically ranging from 600 to 650°C. The holding time depends on the effective thickness of the component, generally calculated as 1 hour per 25mm, with a minimum duration of 2 hours. Following holding, cool with the furnace to 300°C before removing for air cooling.

Given the varied media encountered in coke oven flue gate valves, different overlay seal materials may be selected. Valves handling water, steam, petroleum and its derivatives are typically overlaid with Cr13 stainless steel, though some manufacturers employ chromium-manganese alloys (85 alloy or 137 alloy), copper alloys, or iron-based alloys.

Based on heat treatment effects, overlay materials fall into two categories. One group, represented by Co-Cr-W carbide, exhibits hardness unalterable by heat treatment, with sealing surface hardness guaranteed solely by the overlay material. The other group, exemplified by Cr13 stainless steel, achieves modifiable hardness through heat treatment, typically attaining sealing surface hardness levels of 38–44 HRC.