Spheroidizing annealing process for medium carbon steel plate in bell furnace

Abstract

The invention relates to a medium carbon steel plate bell-type furnace spheroidizing annealing method, which orderly comprises the following steps that: (1) a hot-rolled blank steel coil is subject to the cutting and acid cleaning; (2) the longitudinal rolling is adopted, and the rolling deformation is between 28 and 41 percent; (3) the single sheet stack annealing is adopted, and a steel plate is loaded into an electric heating bell-type furnace; wherein, a. a plate temperature thermocouple is adopted to control the temperature, and at least two armored thermocouples are inserted; b. the heating in the furnace adopts two-section type furnace platform and furnace mantle resistance bands; c. protective gas in the furnace platform and the furnace mantle is nitrogen; d. after the steel sheet is loaded into the furnace, a safety cover and a heating mantle are fastened to electrify and increase the temperature for 60 to 70 hours, the heat preservation is performed for 4 to 6h when the temperature is increased to between 690 and 720 DEG C, and the surface temperature of the steel plate is less than or equal to 720 DEG C during the heat preservation; e. then the heating mantle is hoisted away to cool naturally, and the steel plate is taken out of the furnace when the temperature of the core of the steel plate is cooled to be below 250 DEG C. The medium carbon steel plate bell-type furnace spheroidizing annealing method adopts one-time annealing, and the spheroidizing qualification rate of metallurgical structures is apparently improved.

Description

technical field [0001] The invention relates to a spheroidizing annealing method for a medium-carbon steel plate, that is, No. 45 steel bell-type furnace. Background technique [0002] With the rapid development of the steel industry, the market demand for medium carbon steel plates is increasing, and the quality requirements for medium carbon steel plates are getting higher and higher. Medium carbon steel plates are widely used in the automotive and aviation industries. After cold rolling and annealing, medium carbon steel plates It is required that the steel plate has a narrow high-mechanical performance band, and at the same time, it is required that the steel has a good metallographic structure, that is, a spheroidized pearlite structure. [0003] The national standard requires that the medium carbon steel plate can be shipped according to the spheroidized pearlite structure or the non-spheroidized pearlite structure. However, the plasticity and toughness of the medium c...

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Problems solved by technology

[0003] The national standard requires that the medium carbon steel plate can be shipped according to the spheroidized pearlite structure or the non-spheroidized pearlite structure. However, the plasticity and toughness of the medium carbon steel plate can be significantly improved after spheroidizing, which is convenient for machining and avoids stamping deformation and cracking. Therefore, the user requires that the medium-carbon steel plate must be delivered according to spheroidizing annealing, and the medium-carbon steel plate is a hypoeutectoid steel. Due to its low carbon content, there are few remaining undissolved carbon points in the austenite, and spheroidizing is very difficult.

Due to the particularity of the heat treatment method for medium-carbon steel plates, the current heat treatment method for medium-carbon steel plates is to perform spheroidizing annealing in a gas hood annealing furnace in advance, and then perform recovery recrystallization annealing on the cold deformed metal after cold rolling, and spheroidize after annealing The pass rate is low and can only reach about 60%. Due to the particularity of the process, the pre-annealing process is difficult to achieve under the huge thermal inertia of the electric heating bell furnace, and the user sometimes cracks during the stamping process.

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