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Study on Low Temperature Deformation Annealing of 20G and 12Cr1MoVG Seamless Steel Tubes
Date:2019-07-26      Views:225Time      Label:Study on Low Temperature Deformation Annealing of 20G and 12Cr1MoVG Seamless Steel Tubes
20G and 12Cr1MoVG are representative of high-quality carbon steel and alloy steel for boilers, and have been widely used and developed in practice. 12Cr1MoVG is a low-alloy pearlitic heat-strength steel that has been developed earlier and has a relatively mature application. It has low carbon content, good processability and thermal conductivity, and has high durability and long-lasting plasticity. It is generally used in the manufacture of headers, steam pipes with steam temperatures below 540 °C, superheaters, reheaters and some castings and forgings with a metal wall temperature not exceeding 580 °C. It is the most common main steam used in high-parameter thermal power plants. One of the steels for pipes and reheater pipes. With the sharp increase of the operating parameters and single-unit capacity of power station units in China and the need for the development of high-temperature boiler pipes to large diameters, further research on high-temperature and high-strength boiler tubes has been promoted, and the maximum outer diameter specifications of hot-rolled seamless steel tubes that can be produced in China at present 720mm, larger diameter seamless steel pipe can only be achieved by thermal expansion process. Compared with the hot-rolled seamless steel pipe with high production cost and expensive production equipment, the push-type thermal expansion process with simple production process, stable quality, economical and practical characteristics can increase the diameter of the steel pipe in a short time. The cost is low and the production efficiency is high. Because of this, the push-type thermal expansion steel pipe, which is the main line of smelting and rolling pipe, fills the blank of the non-standard and special-type large-diameter seamless steel pipes produced by major steel mills at home and abroad, and solves the special needs of users. .

The push-type thermal expansion pipe process is essentially a special deformation heat treatment. The 20G and 12Cr1MoVG seamless steel tubes, the original tubes and the steel tubes after the subsequent heat treatment were compared and analyzed in the microstructure and room temperature mechanical properties, and the evaluation was carried out with reference to the GB5310-2008 standard.

The chemical composition of the experimental materials meets the requirements of GB5310-2008. The main parameters of the push-type low-temperature deformation annealing specification are: 20G (expansion temperature 80-730°C, expansion ratio 1.30, expansion speed 300mm/min, coil size 750mm, coil frequency 2500Hz and 910°C normalizing heat treatment). 12Cr1MoVG (The tube temperature is 750-800 ° C, the expansion ratio is 1.27, the tube expansion speed is 170 mm/min, the coil size is 750 mm, the coil frequency is 2500 Hz, and the 990 ° C normalizing +740 ° C tempering).

The results show that the 20G and 12Cr1MoVG seamless thermal expansion tubes produced by push-type low-temperature deformation annealing retain the ferrite and pearlite structure of the original tube, and its grain size, non-metallic inclusions and room temperature mechanical properties all reach GB5310-2008. The requirements of the 12Cr1MoVG follow-up heat treatment can be omitted from the economic cost, energy saving and emission reduction and the current requirements of promoting a low carbon economy. The banded structure produced by the 20G seamless original tube after low temperature deformation annealing can be eliminated by subsequent normalizing heat treatment, and the subsequent heat treatment tube has better comprehensive performance, which meets the requirements of GB5310-2008.