The thin-walled stainless steel fittings are made of 304 (06Cr19Ni10) austenitic stainless steel material, which is welded into a billet tube after forming, and then subjected to multiple passes of diameter reduction, wall stretching, and then the fittings are cleaned and dried, and annealed (solution treatment). Annealing is divided into general annealing and bright annealing two methods. General annealing refers to the role of annealing without protective gas, such as open fire heating continuous annealing furnace, this type of annealing stainless steel fittings, but also need to go through pickling to remove the surface in the annealing process generated by the iron oxide skin, due to acid corrosion, so the luster is poor, the surface looks white, not bright, toughness is poor.
Bright annealing is divided into two kinds, one is annealing with full hydrogen protection state, this hydrogen comes from electrolysis or third party supply, high purity and low dew point; the other is decomposition with ammonia, the decomposition of the gas after drying into the furnace as a protective gas, relatively speaking, the purity and dew point are worse. However, the similarity between the two methods is that they both use hydrogen as the protective gas, the furnace body structure is special, there is a thing called “muffle” inside, the flame first heats the “muffle”, and then the heat is transferred to the stainless steel pipe fittings through the method of heat conduction, so as to Avoid the oxidation of stainless steel pipe fittings, so after bright annealing stainless steel pipe fittings do not need to pickle again, so bright annealed stainless steel pipe fittings than the general annealed stainless steel pipe fittings to bright, better corrosion resistance.
The thin-walled stainless steel pipe fittings are bright annealed, and our products can increase the toughness of the fittings after bright annealing to prevent the fittings from springing back during the jamming process. In the production of thin-walled stainless steel fittings, due to production management, operation, process technology, raw and auxiliary materials and other factors, pipe bright annealing is prone to some quality problems, affecting the pipe bright effect.
So, what are the factors that affect the annealing of thin-walled stainless steel pipe fittings are bright?
1 the impact of the protective atmosphere using liquid ammonia decomposition gas as a protective atmosphere, liquid ammonia will decompose above 800 ℃. 2NH3 → 3H2 + N2 hydrogen as reducing gas, to liquid ammonia decomposition atmosphere as a protective gas, can make the surface of the welded pipe white bright and smooth.
2 furnace body sealing to ensure that thin-walled stainless steel pipe annealing bright, bright annealing furnace should be closed, isolated from the outside air.
3 solid solution treatment temperature solid solution treatment temperature is one of the most important parameters of the solid-liquid treatment process, too high or too low will directly affect the quality of the pipe, the temperature is too high welded pipe organization coarsening, performance decline, the temperature is too low solid solution is not complete, stress relief is not complete, choose 1080 ℃ ± 10 ℃, and proper insulation, carbide can be fully dissolved.
4 protective gas pressure in order to prevent micro-leakage, the furnace protective gas should be maintained at a certain positive pressure, if the hydrogen protective gas, generally requires more than 20kBar. 5 furnace water vapor furnace water vapor content is too high, will cause the atmosphere damage, so that thin-walled stainless steel pipe annealing brightness is affected. Water vapor on the one hand from the furnace material; on the other hand, from the residual water stains into the furnace stainless steel pipe fittings.