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What are the processes for the production process of austenitic stainless steel?Release Date: December 14, 2016
Austenitic stainless steel refers to stainless steel having an austenitic structure at normal temperature. When steel contains about 18% Cr, Ni 8% ~ 10%, and C about 0.1%, it has a stable austenite structure. Austenitic chromium-nickel stainless steels include the well-known 18Cr-8Ni steels and high Cr-Ni series steels developed by increasing the Cr and Ni content and adding elements such as Mo, Cu, Si, Nb, and Ti. Austenitic stainless steel is non-magnetic and has high toughness and plasticity, but its strength is low. It cannot be strengthened by phase transformation. It can only be strengthened by cold working. If S, Ca, Se, Te and other elements are added, it has good Machinability.
The austenitic stainless steel production process performance is good, especially chromium-nickel austenitic stainless steel, the conventional methods of producing special steel can smoothly produce a variety of commonly used specifications of plates, tubes, strips, wires, rods and forgings and castings. Due to the high content of alloying elements (especially chromium) and the low carbon content, arc furnaces with argon-oxygen decarburization (AOD) or vacuum deoxidation decarburization (VOD) methods are often used to mass produce such stainless steel materials. Batch products can be smelted in vacuum or non-vacuum non-induction furnaces, and remelted with electroslag if necessary.
The excellent thermoplasticity of chromium-nickel austenitic stainless steel makes it easy to apply hot working such as forging, rolling, hot perforation, and extrusion. The heating temperature of steel ingot is 1150-1260 ℃, and the deformation temperature range is generally 900-1150 ℃. Nitrogen and steels stabilized with titanium and niobium lean to low temperatures, while high chromium and molybdenum steels lean to high temperatures. Due to poor thermal conductivity, the holding time should be longer. After thermal processing, the workpiece can be air-cooled. Chromium-manganese austenitic stainless steel is more sensitive to thermal cracking. When the ingot is opened, it must undergo small deformation and multiple passes. Can be cold-rolled, cold-drawn and spinning and other cold processing processes and stamping, bending, hemming and folding and other forming operations. The chromium-nickel austenitic stainless steel has a weaker work hardening tendency than the chromium-manganese steel, and the cold deformation amount can reach 70% to 90% after one annealing. However, due to the large deformation resistance, the chromium-manganese austenitic stainless steel has a strong work hardening tendency and should be softened in the middle Number of annealing. Generally, the intermediate softening annealing process is water-cooled at 1050 to 1100 ° C.
Austenitic stainless steel can also produce castings. In order to improve the fluidity of the molten steel and improve the casting performance, the alloy composition of the cast steel should be adjusted: increase the silicon content, relax the range of chromium and nickel content, and increase the upper limit of the content of sulfur, the impurity element.
The austenitic stainless steel should be subjected to a solution treatment before use, in order to maximize the solid solution of various precipitates such as carbides in the steel into the austenite matrix, while also homogenizing the structure and eliminating stress, so as to ensure excellent Corrosion resistance and mechanical properties. The correct solution treatment system is water cooling after heating at 1050 ～ 1150 ℃ (thin and thin parts can also be air cooled). The solution treatment temperature depends on the degree of alloying of the steel: non-molybdenum or low-molybdenum steel grades should be lower (& 1100 ° C), and higher alloyed grades such as 00Cr20Ni18Mo-6CuN, 00Cr25Ni22Mo2N, etc. should be higher (1080 ~ 1150 ° C).
Advanced technologies are widely used in production. For example, the refining rate outside the furnace reaches more than 95%, and the continuous casting ratio exceeds 80%. High-speed rolling mills, precision and fast forging machines are generally popularized. In particular, electronic computer control is realized during smelting and processing, which ensures the reliability and stability of product quality and performance.