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Study on Low Temperature Deformation Annealing of Seamless Steel Tube

As a representative of high-quality carbon steel and alloy steel for boilers, 20G and 12Cr1MoVG have been widely applied and developed in practice. 12Cr1MoVG was developed earlier, the application of more mature low-alloy pearlite hot-rolled steel, low carbon content, process, good thermal conductivity, high durability and long-lasting plasticity. Generally used in the manufacture of steam temperature below 540 ¡æ header, steam pipes, metal wall temperature does not exceed 580 ¡æ superheater, reheater and some castings and forgings, is currently the most commonly used high-parameter thermal power plant main steam One of the pipes, reheater pipe steel. With the rapid increase of unit operating parameters and single unit capacity of power station in our country and the need of high-temperature boiler pipe to develop in large diameter, further research on high temperature and high strength boiler tubes is promoted. At present, the largest hot-rolled (drawn) seamless steel pipe that can be produced domestically Diameter specifications of 720mm, larger diameter seamless steel pipe can only be achieved by thermal expansion technology. Compared with the hot rolled seamless steel pipe with high production cost and expensive production equipment, the use of push-type thermal expansion process with simple production process, stable quality, economical and practical features can increase the diameter of steel pipe in a relatively short period of time, And low cost, high production efficiency. Precisely because of this, the push-type thermal expansion pipe which is the main line of smelting and rolling pipe well fills the blank of non-standard and special type large-caliber seamless steel pipe production at major domestic and foreign mills and solves the special needs of users .
Push-type thermal expansion pipe process is essentially a special deformation heat treatment. The comparative analysis of the 20G and 12Cr1MoVG seamless steel tubes, the original tube and the subsequent heat-treated steel tube in the microstructure and mechanical properties at room temperature were carried out by referring to the GB5310-2008 standard.
The chemical composition of experimental materials meet the requirements of GB5310-2008. The main parameters of the push-type low-temperature deformation annealing specification are: 20G (expansion temperature 80 ~ 730 ¡æ, expansion ratio of 1.30, tube expansion speed 300mm / min, coil specifications 750mm, coil frequency 2500Hz and 910 ¡æ normalizing heat treatment); 12Cr1MoVG Tube temperature 750-800 ¡æ, diameter expansion ratio 1.27, tube expansion speed 170mm / min, coil size 750mm, coil frequency 2500Hz and normalizing at +990 ¡æ +780 ¡æ tempering).
The results show that the 20G, 12Cr1MoVG seamless thermal expansion pipe produced by push-type low-temperature deformation annealing retains the ferrite + pearlite structure of the original pipe, and its grain size, non-metallic inclusions and room temperature mechanical properties reach GB5310-2008 Requirements, from the economic costs, energy saving and emission reduction and the current reality of promoting low-carbon economy requirements point of view, 12Cr1MoVG subsequent heat treatment can be omitted. The band-like structure produced by the low-temperature deformation annealing of the 20G seamless seamless tube can be eliminated by the subsequent normalizing heat treatment, and the subsequent heat-treatment tube has better overall performance and meets the requirements of GB5310-2008

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