JPS6032693B2 - Continuous annealing furnace - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a continuous annealing furnace that can perform sintering treatment on a thin steel plate and also control the hardness of the same. When manufacturing thin steel sheets such as tin plates, the final step is cold rolling to improve the mechanical properties of the product and give it a glossy surface finish. The original sheet of thin steel sheet that is formed is heat treated in a Rentsugi hammer furnace and then cold rolled. Conventional sintering furnaces consist of heating, soaking, slow cooling, and quenching zones, and the effect of dull conditions such as heating temperature and soaking time on the thin steel sheet product is extremely small. For example, Figure 1 is a graph showing the relationship between the competitive anchoring conditions in the above-mentioned subordinate anchor furnace and the hardness of the steel plate after moth dulling, when the heating temperatures were set to 690 qo and 640 qo, and these were soaked for the same time. As shown in this graph, the influence of competing anchor conditions on the product is extremely small, so conventionally the hardness of the product has been controlled by adjusting the steel components during steel manufacturing. For this reason, variations in the composition at the time of steel manufacturing, segregation in the longitudinal direction of the strip (belt-shaped thin steel plate), or variations in processing conditions during intermediate steps such as rolling directly result in variations in the hardness of the product. Figure 2A shows the variation in hardness between the coils of tin plate blanks treated in a conventional continuous phosphor furnace, and Figure 2B' is based on the final end of the strip wound into a coil.

This is a graph showing the variation in hardness in the longitudinal direction with the value set to [0], and in the conventional technology, the hardness of the product varied to this extent. The hardness of steel changes depending on the amount of C dissolved in Fe crystals and the amount of C precipitated outside Fe crystals. Steel heated to a high temperature changes the amount of C dissolved in Fe crystals depending on the temperature. If it is rapidly cooled, it will reach room temperature without sufficient precipitation of C.
More solid solute C remains in the Fe crystal at room temperature than in the case of slow cooling, and the hardness of the steel becomes higher than in the case of slow cooling. This relationship is shown in FIG. 3, and as shown in the figure, the strip that has been soaked contains a solid solution carbon amount a corresponding to the temperature t2 in the Fe. This solid solution C
In the cooling process after the slow cooling zone, C is precipitated outside the Fe crystal as the solid solubility of C decreases as the strip temperature decreases, but in a continuous competitive hammer furnace, the cooling rate is fast as shown in AI, so C is If the precipitation of C is insufficient, the amount of solid solute C remaining at room temperature becomes al. This solid lacquer C that exists in Fe at room temperature has the effect of distorting the crystal lattice of Fe and hardening the material, and the greater the amount of solid solution C at room temperature, the greater the effect. A2 in the figure is a graph showing the change in the amount of residual solid solution C when a steel plate at a temperature of 82 is slowly cooled, and the amount of solid solution C existing in Fe when cooled at room temperature is a2. On the other hand, if cooling is temporarily interrupted between 300 qC and 500 qo during the cooling process of the continuous Akatsuki hammer and low-temperature soaking is performed, the solid solute C precipitates over time even though the temperature remains unchanged, and the solid solute C at room temperature decreases. An over-aging phenomenon occurs in which the material softens. This state is shown as A3 in Figure 3, and a4
Due to the overaging phenomenon shown by , the amount of surface melting C at room temperature becomes a3. By changing the amount a3 of solid solution C, a steel plate having a desired amount, that is, a desired hardness, can be obtained by changing the overaging time. The purpose of the present invention is to utilize the above-mentioned overaging phenomenon to perform overaging treatment in a competitive hammering furnace, thereby obtaining high quality steel sheets with no variation in hardness. The continuous annealing furnace is separated into the quenching zone, the first quenching zone, and the first quenching zone, and a suitable aging zone for performing overaging treatment is provided between these quenching zones, and the continuous annealing A comparator that compares the signal from a hardness meter that continuously measures the hardness of the plate to be annealed sent out from the furnace with the signal from the target hardness setting device, and a motor that drives the roll for moving the plate to be annealed. a speed controller for controlling the speed of the annealing according to a hardness deviation signal from the comparator, and controlling the time during which the plate to be annealed passes through the overaging zone. be. FIG. 4 is a schematic diagram showing a specific example of the present invention. tropical 4
It has a primary quenching zone 5 and a secondary quenching zone 6 for rapidly cooling the phosphor dull plate 2, and an overaging zone 7 incorporated between these quenching zones 5 and 6. A non-contact type hardness meter 8 is provided to continuously measure the hardness of the anchor slope 2 to be burned, which is sent out from the secondary quenching zone after the hammering is completed. As a non-contact type hardness tester, a magnetic type hardness tester or a radiation type hardness tester is used. The signal from the hardness meter 8 is sent to a comparator 9, and this comparator 9 is connected to the target hardness setting device 1.
It compares with the signal from 0 and sends a hardness deviation signal △day.
The hardness deviation signal △day is sent to the calculator 11, where the overaging processing time correction amount is determined based on the relationship between the hardness deviation △day and the overaging processing time set in advance as shown at 12 in FIG. Δt is calculated. This correction amount Δt is determined by the controller 13 that controls the speed of the motor that drives the roll for moving the wave phosphor plate.
is converted into a speed control signal △v and has a processing speed value of 1.
4 controls the voltage of the motor to control the time during which the chick plate 2 passes through the overaging zone 7. An example of a case where an anchor plate to be sintered is heat-treated using the continuous dawn anchor furnace 1 of the present invention is shown in FIG. , the hardness of the product at the furnace outlet changed as shown. FIG. 6C is a diagram showing the heating cycle of the continuous cold hammering furnace 1 of the present invention in comparison with the conventional technology, and as shown in FIG. The heating cycle of the conventional continuous competitive hammering furnace la consisting of 6a is shown by the broken line in FIG. The cycle is shown by a solid line. In the illustrated embodiment, appropriate aging treatment is performed by controlling only the processing speed of the plate 2 to be annealed, but the furnace temperature may also be controlled in conjunction with this. According to the present invention, the hardness of the plate to be fired is continuously measured at the exit side of the furnace, the hardness difference between this measured value and the target hardness is fed back to the speed control system, and the plate passing speed is controlled. Since the hardness is controlled to the target value, the hardness variation of the product thin steel sheet is reduced, and a product with more stable quality can be obtained. Even if there is material that deviates from the controlled rolling temperature during the inter-rolling process, it is now possible to rescue it using the Akatsuki Anchor Furnace.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between hammering conditions and hardness after dulling in a conventional hammering furnace, and Figure 2 is a graph showing the inter-coil variation A and longitudinal variation B of thin steel sheets produced in a conventional hammering furnace. Fig. 3 is a graph showing the relationship between cooling conditions and residual melting strength - amount of carbon, Fig. 4 is a schematic diagram showing an example of the continuous morning hammering furnace of the present invention, and Fig. 5 is an over-aging zone. FIG. 6A is a graph showing the relationship between processing speed, i.e., overage time, and product hardness at the furnace outlet side in the Rentsugi sintering furnace of the present invention, which has a conventional continuous sintering furnace. FIG. 6B is a schematic diagram showing the Rentsugu hammer furnace of the present invention, and FIG. 6C is a graph showing the heating cycle of the conventional technology and the Rentsugi hammer furnace of the present invention. In the drawing, 1 is a continuous dulling furnace, 2 is a plate to be hammered, 3 is a heating zone,
4 is a soaking zone, 5 is a primary quenching zone, 6 is a secondary quenching zone, 7 is an overaging zone, 8 is a hardness meter, 9 is a comparator, 10 is a target hardness setting device, 11 is a calculator, 12 is a speed controller. Figure l Figure 2 Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1 Overaging in which the quenching zone of a continuous annealing furnace having a heating zone, soaking zone, and quenching zone is separated into a first quenching zone and a second quenching zone, and overaging treatment is performed between these quenching zones. a comparator for comparing a signal from a hardness meter that continuously measures the hardness of the plate to be annealed sent out from the continuous annealing furnace with a signal from the target hardness setter; and a comparator for moving the plate to be annealed. and a speed controller that controls the speed of a motor that drives the roll according to the hardness deviation signal from the comparator, and controls the time during which the plate to be annealed passes through the overaging zone. continuous annealing furnace.