Working conditions of power station valve is usually 540 ℃ high temperature steam, so the valve body material choose 25 or 12 crmov, Industrial Valves sealing surface surfacing material selection d802 cobalt base alloy, sti6) Electrode. The model edcocr d802 corresponding gb984 standard - A, in the equivalent of aws ercocr - a。 D802 material can work under high temperature and high pressure continuous opening and closing, with excellent abrasion resistance, impact resistance, oxidation resistance, corrosion resistance and cavitation resistance. The ercocr aws standard - A wire and wire filling deposited weld metal is characterized by distribution in tungsten cobalt chromium by about 13% of chromium in the solid solution matrix of eutectic carbide network eutectic organization. The result is to make the material has low stress abrasion resistance and impact resistance to certain procedures necessary to the perfect combination of toughness. Cobalt alloy has good resistance to metal abrasion performance between a metal, especially in the abrasion resistance of high load condition. The matrix of high content of alloy elements can provide excellent corrosion resistance and oxidation resistance. Cobalt base alloy without allotropic transformation, cobalt base alloy deposited metal is in hot state ( Below 650 ℃) Reduced, the hardness is not obvious, only when the temperature rise to more than 650 ℃, the hardness was obviously decreased, when the temperature back to hot, its hardness and reply to the hardness close to the original. When the parent metal heat treatment after welding, the performance of the sealing surface will not damage. Power station valve is in the middle of the valve body hole part use the method of welding welding cobalt base alloy processed into valve seat sealing surface, the position of the sealing surface in the body the middle hole deep, when welding defects such as slag and cracks easily. According to the need to adopt processing method for deep hole d802 surfacing process test specimens. In the process of process test to find out the causes of defects. 1) welding material surface contamination. (2) the welding material moisture absorption. (3) parent metal and the filler metal contains more impurities and oil pollution. (4) the body welding parts rigidity ( Especially the dn32 ~ 50 mm) 。 5. Preheat and heat treatment after welding process specification improper selection. 6. Improper selection of welding technology parameter. All landowners improper welding material selection, etc. Power station valve body in the cobalt base alloy welding crack reason mainly is the body rigidity. Form molten pool in the process of welding arc, welding parts to constant melting heat, and after welding and rapid decline in temperature, melting weld metal solidification formation. If the preheating temperature is low, welding layer temperature drops quickly. In welding layer of rapid cooling case, welding layer shrinkage rate faster than the body of the shrinkage rate, soon made under this stress in welding layer and the base to form a tensile stress, the weld cracking. In processing the wedge Angle appears in welded parts should be forbidden. Preheat temperature is too low, fast heat in the welding process. Interpass temperature is too low, welding layer cooling speed too fast for surfacing material is bad. Cobalt base alloy welding material itself has the very high red hardness, when he worked in 500 ~ 700 ℃, can maintain 300 ~ 500 hb hardness, but its low toughness, crack resistance is poorer, easy to crystallization crack and cold crack formation, so it must be preheated before welding. Depending on size of workpiece preheating temperature, general preheating take 350 - range 500℃。 Covering must be kept in good condition before welding, to avoid moisture absorption. Before welding under 150 ℃ for 1 h after the inside electrode insulation cylinder. Deep hole groove arc surfacing r Angle in technology allow the premise to use higher value as far as possible, for r 3 mm or more commonly. Dn10 ~ 25 mm small body with all full welding electrode at the bottom of the deep hole, must ensure that the interlayer temperature 250 * (or 2, in the middle of arc, arc should slow electrode. Workpiece welding furnace (forward 250℃） After 5 h welding, each layer of welding after removal of welding slag. Controlling interpass temperature 250 c or more at the same time, the welding after complete removal of welding slag. The body must be immediately into the furnace (after welding 450℃） Heat preservation, wait for the batch or this welding BiShengWen to 710-20 ℃ tempering furnace, heat preservation with furnace cooling after 2 h, when the furnace temperature dn 32 mm or higher body welding groove should be processed into u, to solve the welding cobalt base alloy produced when excessive shrinkage caused by uneven rigidity. In front of the welding operation, clean up the workpiece, the workpiece into the furnace ( Temperature of 250 ℃) , heating to 450 ~ 500 ℃, 2 h insulation, came up. With cobalt base alloy electrode welding sealing surface, each layer after welding welding slag, must control interlayer temperature 250 ℃ or higher at the same time, the welding after complete removal of welding slag. With austenitic stainless steel electrode ( The high content of cr, ni stainless steel electrode) Will u groove welding. After the valve body welding all immediately into the furnace ( 450℃） Heat preservation, wait for the batch or the furnace after the welding heat up to 720-20 ℃ tempering. Temperature of 150 ℃ / h, heat preservation with furnace cooling after 2 h.
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Among improvements to double flanged gate valve, nearly half of consumers considered quality and service as the most important change a business could make in its supply chain.