The working conditions of the power station valve is usually high temperature of 540 ℃ water vapor, so the material selection of the valve body 25 or 12CrMoV, the sealing surface of the valve body surfacing material selection cobalt-based alloy D802 (STI 6) electrode. D802 the corresponding GB 984 standard models EDCoCr-A, equivalent the AWS in ERCoCr-A. D802 materials in high temperature and high pressure continuous opening and closing work, has excellent abrasion resistance, impact resistance, oxidation resistance, corrosion resistance and anti-cavitation.
AWS standard ERCoCr-A and Filler wire welded weld metal is characterized by distribution the eutectic network by about 13% of chromium carbide in a solid solution matrix of cobalt-chromium-tungsten composition hypoeutectic crystal organization. The result is a perfect combination of material has resistance to low stress and wear properties and resistance to some kind of program impact toughness. Cobalt alloy having a good anti-wear performance in the metal of a metal, particularly in the anti-abrasion performance under the high-load state. The high content of alloying elements in the matrix can provide excellent resistance to corrosion and oxidation resistance. Cobalt-based alloy does not occur allotropic transformation, the deposited metal of the cobalt-based alloy is in a hot state (650 ℃), its hardness is reduced is not obvious, only when the temperature is increased to above 650 ℃, hardness was decreased, When the temperature returns to below the thermal state, its hardness and revert to a hardness close to the original. That is, when the base material after welding heat treatment, the performance of the seal surface without loss.
Power plant valve seat sealing surface of the cobalt-based alloys in the middle hole of the valve body portion with welded method of surfacing processed into, because the sealing surface is in a deeper position of the middle hole of the valve body, and easy to produce when the surfacing of the slag and cracks, etc. defects. Processed specimen method to which deep surfacing D802 process test required. Easy to produce defects in the process during the test to find reasons. ① welding consumables surface contamination. ② to welding consumables moisture. ③ base metal and filler metal contains more impurities and oil. ④ body welding rigid parts (especially of DN32 ~~ 50 mm). ⑤ preheat and post-weld heat treatment process specification improper selection. The improper selection ⑥ welding parameters. The ⑦ welding material inappropriate choice of.
The power station valve body cracks in the cobalt-based alloy surfacing mainly due to body rigidity. Form a puddle, the arc in the welding process to the welding site continuously melting heated after welding temperature has decreased rapidly, the molten metal solidifies to form the weld. If the preheating temperature is low, the temperature of the solder layer must soon decline. In the case of the rapid cooling of the solder layer, the shrinkage of the weld layer faster than the shrinkage rate of the valve body, in this under stress quickly make the solder layer and the base material forming an internal tensile stress, the solder layer tensile. Should be strictly prohibited in the processing of welded parts appear sharp corners.
The preheating temperature is too low, the rapid dissemination of heat during the welding process. Layer temperature is too low, the rapid cooling rate of the solder layer is very unfavorable for surfacing materials. Consumables cobalt-based alloy itself has high red hardness, the hardness can be maintained at 500 ~ 700 ℃ work 300 ~ 500HB, but the low toughness, crack resistance, easy to form the crystalline cracks or cold crack, so before welding must be preheated. Preheat temperature depending on the size of the workpiece, general Preheat range to take 350-500 ° C
Prior to welding electrode covering must be kept intact to avoid moisture absorption. At 150 ℃ before welding electrode insulation barrel into baking 1h. The deep hole surfacing groove arc R angle larger value, as far as possible in the process allow the premise is generally R ≥ 3 mm. DN10 ~ 25mm diameter valve body in a deep hole at the bottom of welding electrodes all full, must ensure that the inter-layer temperature ≥ 250 * (2, in the middle of the closing arc, closing arc welding rod should be slow to lift. Workpiece welding furnace (250 ° C forward ) heated to 350 ten 20 ° C insulation 1.5h after welding clear each floor welding after welding slag control layer temperature ≥ 250 "C, surfacing completed to remove welding slag after welding Body must immediately into the furnace (450 ℃) heat until the batch or the furnace welding Albert warming to 710 ± 20 ℃ tempering, heat 2h followed by furnace cooling, air cooling to room temperature when the oven temperature <250 ℃ to subsequent processing.
DN ≥ 32mm valve the surfacing groove should be processed into a U-shape, to solve the surfacing cobalt-base alloy to produce excessive rigidity caused by the problem of uneven shrinkage. Before surfacing operation, the workpiece is clean, the workpiece into the furnace (furnace temperature of 250 ° C), heated to 450 to 500 ℃, heat 2h, baked welding. Using cobalt-based alloy electrode surfacing sealing surface, each layer welding after to clear welding slag, is also required to control interpass temperature ≥ 250 ℃, after the removal of welding slag surfacing completed. U-shaped groove welding with austenitic stainless steel electrode (high Cr, Ni content in stainless steel welding rod) full. Into the furnace immediately after all of the body welding insulation (450 ℃), subject to the batch or the furnace heated to 720 ± 20 ℃ tempering after welding. Heating speed 150 ° C / h, incubated 2h after cooled in the furnace, air cooled to room temperature can be carried out subsequent processing (Figure 3) when the furnace temperature <250 ℃. No effect on this process to improve the performance of the product, can completely eliminate the internal stress of the valve body in the surfacing of the cobalt-based alloy with a U-shaped groove, and the tensile strength of austenitic stainless steel welding consumables, high elongation , thereby reducing the welding cracks, improve the pass rate. Non-destructive testing results show that the products pass rate of 95% or more
Article explains:
Paper series site or of self-publish, the site post aims to deliver more information to the visitor.
2, involving work content, copyright and other issues, please contact site within 30 days, we will be the first time to make appropriate treatment! About copyright issues, please contact: 13515194999
3, Zhuanzhai this article please indicate from: Jiangyin City Oulei Si valve valve repair factory www.olschina.com
4 other links:
Valve repair valve repair valve repair equipment valve grinding machine imported valve repair power station valve maintenance
|
