Solid solution treatment of stainless steel valves
Steel heating to 1050 ~ 1100 ℃, then rapid cooling in water, to get a single-phase austenitic organization, this process is called solution treatment. Solution treatment temperature should choose according to the carbon content of stainless steel, usually take limit at high carbon content, carbon content lower limit, but the temperature is unfavorable and exorbitant, both also shoulds not be too low. Temperature is too high, will appear a large number of ferrite, and make the steel coarse grains, such bad, not only make the fabrication procedure and reduce steel uniform corrosion resistance. From the point of view of intergranular corrosion, the higher the heating temperature, the greater the degree of supersaturation of austenite, after precipitation of chromium carbide reheat temperature range, chromium carbide precipitation process is more intense, to increase the susceptibility to intergranular corrosion of steel. If the temperature is too low, the composition of the steel and the sufficient dissolving of carbide are not sufficient to achieve the effect of solidification.
Solution treatment should prevent surface carburizing, when heating for carburizing steel increases, the susceptibility to intergranular corrosion of the valve, the valve body, valve seat, a kind of direct contact with the working medium of the so-called internal parts, the performance requirements of general corrosion and intercrystalline corrosion resistance requirements is much taller than other stainless steel valve parts, therefore, internal parts of the surface of the solution treatment especially need to pay attention to carburizing. When heated, usually in neutral or slightly oxidizing atmosphere. Processing or machining allowance for after heat treatment is no longer a small parts, before heating furnace should be paid attention to cleanliness, and remove the oil on the surface of the parts, to prevent the dirt decompose when heated, make parts surface carburizing.
After the solidification process, the strength of the steel increases with the increase of carbon content. However, the strength of this kind of steel is not high in general, compared with the treatment of sensitization and stabilization. Therefore, the curing process is also the maximum softening treatment.
Solution treatment to dissolve carbide at high temperature in a steel is heated, and for the next fast cooling and fixed in austenite, so the corrosion resistance of steel with the highest of solution treatment, for not including 18-8 of titanium or niobium steel, solution treatment is one of the important means to prevent intergranular corrosion.
Solution treatment of heat preservation time shoulds not be too long, it have close relationship with the diameter and thickness of the parts, the material of 25 mm in diameter, according to can according to commonly 2 ~ 3 minutes/mm to calculate time of heat preservation.
Commonly used solution treatment, the cooling system of water-cooling, but for the cover sleeve, sleeve seat and jacketed valves outer jacket and thin wall parts and air cooling can be applied.
Source: China Valves Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)