SU1266886A1 - Method for recrystallization annealing of cold-rolled low-carbon steel stabilized with aluminium - Google Patents

Abstract

The method relates to ferrous metallurgy and can be used in the rolling industry for annealing; tightly wound coils or feet of cold rolled carbon-carbon sheets, predominantly aluminum-stabilized steel. The purpose of the invention is to increase the level and uniformity of the physicomechanical properties of steel throughout the entire set-up volume while simultaneously reducing the total duration of annealing. The essence of the method lies in the fact that the heating in front of the grains is carried out by thermal pulses and is carried out in a temperature-lagging part of the charge in a two-stage annealing mode with a pre-crystallization intermediate caliper. The method, on average over the volume of the set, provides an increase in the size and degree of elongation (L of the grain by 1 point, a decrease in hardness by 4 HRB and a yield strength per IO MPa with an almost unchanged strength limit, an increase in the uniformity of properties by a factor of 2-3, as well as an increase in the yield of metal of the highest cathodes of the stretching categories by 17–20% with a reduction by 20–25% of the total duration of annealing. 1 or 2 tablespoons about 00 00 about:

Description

The invention relates to ferrous metallurgy and can be used in the rolling industry during annealing of tightly wound rolls or stop sheets of cold rolled low carbon, mainly aluminum stabilized steel, intended for cold forming of parts.

The aim of the invention is to increase the level and uniformity of the physicomechanical properties throughout the set volume while simultaneously reducing the total duration of annealing.

The drawing shows a graph of the heating mode, where t, t temperatures at the top and bottom. Technological thermocouples; t.j is the temperature in the zonal thermocouple. Broken lines indicate automatic temperature control.

Example. Cold rolled sheets of 0810 steel, size 0.80x800x15 0 mm, positions 10СВА are packaged on a stand in four feet with a height of 1650 mm and weights up to 65 tons. Annealing is carried out in industrial hood gas furnaces without bottom heating of the stand and forced circulation of the protective atmosphere. Composition 30

shielding gas: 3-7% hydrogen and 9793% nitrogen. The temperature of the metal was controlled by two process thermopairs, installed one under the top sheets (thermocouple tj) and a friend on the bottom stand sheet (thermocouple t), which corresponds to the leading (top) and lagging (bottom) parts of the charge cage. Automatic on-off temperature control is performed on the upper process thermocouple using electronic potentiometers KSP-4 and actuators that control the gas supply and ejector air.

After packing the metal on the stand, the vessel is covered with a muffle, a heating cap and annealed in the following sequence. The top of the charge is heated at a rate of 5070 ° C / h to 710-730 ° C using a thermocouple t, and maintained at a constant (0-3 h) until the bottom of the cage reaches an intermediate prerecryhalization exposure of 480-520 ° C using a thermocouple c, after which the temperature of the top of the tank is reduced to 590620 ° C (first heat pulse) -. Then, at this temperature, the top of the charge is kept until the end of the intermediate holding time (no more than 10 hours) in the bottom of the load.

Again raise the temperature of the top of the tank to 710–730 ° C, keep it constant (1–7 h) until the bottom of the tank reaches the minimum temperature. of the final charge, then lower the temperature of the top of the charge to 680-700 ° C (second heat pulse) and carry out a final exposure of at least 4 hours to the bottom of the load. Upon completion of heating for 38–40 hours, remove the cap and cool the metal under the muffle until the bottom of the charge reaches 150 ° C.

Annealed sheets are subjected to drainage with compression of 0.8-1.2%. The test results of the mechanical properties of steel sheets 08U are presented in Tables 1 and 2.

The proposed method of annealing on average in terms of the charge provides

an increase in grain size and degree of elongation by 1 point, a decrease in hardness of 4 HRB and a yield strength of 10 MPa with almost unchanged

metal of higher categories of extraction by 17–20%, as well as an increase in the uniformity of properties along the height of the charge by 23 times.

The proposed method allows to reduce the total duration of annealing by 20–25% compared to limestone.

Claims (1)

Invention Formula The method of recrystallization annealing of cold-rolled low-carbon aluminum-stabilized steel, including heating, intermediate exposure, final exposure and cooling of the metal charge, characterized in that, in order to increase the level and uniformity of the physicomechanical properties throughout the entire charge, while reducing the total annealing time, heating is carried out by thermal pulses, while first the top of the tank is heated at a speed of 50-70 ° C / h to 710-730 ° C, and the bottom is heated to 480-520 ° C, then the temperature of the top of the charge decreases barely durability, increased yield  j1266886 They are boiled up to 590-620 s and held between 640 ° C and lower than 640 ° C, then the temperature of the top of the cage is reduced to 680 from the bottom of the cage within 10 hours, after what. and spend the final winnings, the cages are again heated to 710 for at least 4 hours, and  followed by exposure to dostazh-5 cooling, lead to reaching the bottom The minimum temperature of the ni-cage. Table 1 ; 1300 140 1700 340 Famous 45.8 43.1 10.62 1.30 69 80 Offer- General U5.9 39.2 10.74 1.56 89 97  The coefficient of normal plastic anisotropy, 3.0 2.0 0.050 2.0 5.5 0.25 0.52 1.1 1.2 0.150 1.9 3.0 0.15 0.23 195, 331 0.590 185 333 0.557 Continued table. one .Table 2