During the process of solid solution treatment, stainless steel pipes need to pay attention to the influence of protective atmosphere, temperature and cooling speed.
The first is the light online solution treatment procedures, stainless steel pipe in the production process caused by rolling, drawing and welding heat effect, will lead to pipe structure and mechanical property will have no small change, will affect the quality of the stainless steel pipe to serious, changes may occur mainly cold hardening the phenomenon, it refers to the regular fault of a column or several columns appear atomic microstructure crystal lattice distortion, which, as a significant stress concentration zone, this phenomenon is also called dislocation. This is because of high temperature and uneven cooling will generate welding stress and the formation of ferrite in the original single austenite, carbide produced uneven organization, in order to increase the processing efficiency, ensure that the stainless steel pipe surface light level standards, to remove residual stress, single austenite microstructure and high quality stainless steel pipe, it must to take the online light solution treatment method.
The second is to protect the atmosphere, light online solution treatment is usually used as a protective atmosphere gas ammonia decomposition, ammonia at 400 ℃ will be decomposed into hydrogen and nitrogen, hydrogen is a reducing gas to restore some metal in the corresponding conditions, nitrogen is neutral gas. Using the liquid ammonia decomposition atmosphere as a protective gas, it can make the surface of the stainless steel pipe smooth and bright, so it is also the most cost-effective and effective protection gas.
In addition, the need to pay attention to the solution temperature, because it is one of the most important parameters in the process of solid-liquid processing, high or low temperature will directly affect the quality of the products of stainless steel pipe, high temperature will make the stainless steel pipe microstructure coarsening, reduced performance, low temperature will not dissolve completely, can not completely eliminate stress so, need the appropriate temperature and appropriate insulation, so as to fully dissolve carbide.
The effect of cooling rate should also be paid attention to in the later period of solution treatment. For austenitic stainless steel at 650 ℃ -850 ℃ interval, brittle phase may be occurred, in general is a form of needle flake in the austenite grain or grain boundary, will greatly plasticity, toughness and strength of the material decreases at 450 ℃ -850 ℃ interval is austenitic stainless steel intergranular corrosion in sensitive areas. The metal grain temperature range in the supersaturated solid solution of carbon atoms to grain edge diffusion, and edge layer of chromium carbide formation, and along the grain boundaries, which makes the grain edge because of poor chromium and loss of corrosion resistance, the austenitic stainless steel is heated to 1080 ℃ + 10 ℃, usually insulation, stainless steel the carbide can be fully dissolved, followed by rapid cooling, to prevent stainless steel at 450 ℃ -850 ℃ interval to stay, so not only can avoid phase sigma intergranular corrosion, also won’t let carbide Precipitation along austenite grain boundary can directly get the uniform saturated single austenite metallographic structure, so as to perfect the stainless steel pipe online bright solution treatment.
Source: China Stainless Steel Pipes Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)