JPH0733542B2 - Steel material heating method in continuous heating furnace - Google Patents

Description

The present invention relates to a method for heating a steel material in a continuous heating furnace, and more specifically, in a continuous heating furnace of a hot rolling mill, a decarburized layer during operation. The present invention relates to a heating method capable of efficiently heating a high-grade steel material such as a round bar of a product that needs to limit the depth of the product, and performing stable production of high-grade steel.

2. Description of the Related Art Generally, billets and other steel materials are uniformly heated in a continuous heating furnace, and then sent to a hot rolling facility to be rolled into a predetermined product. In this continuous heating furnace, the steel material is uniformly heated to the inside by heating, and the internal structure is made uniform, but during this time the steel material is heated and the carbon inside diffuses to the surface and It is removed by reaction with oxidizing gas. Therefore, in continuous heating furnace operation, it is extremely important to control the in-furnace time that mainly affects this decarburization reaction, that is, to control the charging interval of the steel material that affects this in-furnace time, but the charging interval is mainly It is controlled based on the standards established mainly for standard operations and the experience and intuition of the person in charge of operations. In addition, recently, due to the demand for higher quality, quality assurance of the surface and inside of the product is required, and in particular, it is necessary to limit the decarburization depth for round bar products, etc. Many steel grades are regulated due to shortening of time and high load operation of heating zone of continuous heating furnace.

However, in such a case, in the control of the charging interval as described above, in actual operation, it is impossible to immediately determine and set how to limit the charging interval of the steel material, In addition, at that time, the optimum charging interval varies depending on the rolling capacity of the preceding steel material and heating conditions, so in the conventional example, the upper limit value of the total in-furnace time in the continuous heating furnace is used as a guideline for actual operation. For the charging interval of, the charging interval corresponding to this standard in-furnace time is determined as a standard, and the downtime etc. caused by restrictions on factory operation at the time of charging are considered in each case at the judgment of the site operator. The charging interval is determined. By charging and heating the steel material in the continuous heating furnace by the standardized charging interval in this way, the energy loss is large due to the decrease of the steel material filling rate into the heating furnace, unnecessary high load operation, etc. This has also led to a reduction in rolling efficiency in hot rolling equipment.

Problems to be Solved by the Invention That is, as in the conventional example, when the steel material is charged at the standardized charging interval in the steady state, it is difficult to finely reflect the above-mentioned operational restrictions. ,Also,
This charging interval is created under standard heating conditions and rolling conditions. For this reason, in the setting of the charging interval in the conventional example, it is not possible to respond to changes in the rolling capacity due to changes in detailed manufacturing specifications in the rolling line, etc., and at times, target values for heating, for example, furnace time, extraction of steel materials There are also situations where the temperature deviates.

Further, in order to solve such a problem, in the conventional example, the charging interval determined by standardizing the heating condition in the standard operation is set relatively large and is often set to the safe side. However, if the charging interval is increased, the filling rate of the steel material in the heating furnace decreases, the heating fuel consumption rate increases, and the rolling efficiency decreases due to the restriction of the steel material transportation time such as walking beam or walking hearth in the furnace. Often.

The present invention aims to solve the above drawbacks, specifically, by controlling the charging interval of the steel material to an optimal charging interval corresponding to the operating conditions regulated by the steel material, the steel material is continuously heated in a furnace. We propose a method of charging and heating.

<Structure of the Invention> Means for Solving the Problems and Its Actions That is, the method of the present invention comprises charging the steel material in a continuous heating furnace that continuously heats the steel material before hot rolling. The heating and heating curve of the steel material in the continuous heating furnace is assumed based on the previously determined charging interval of the preceding steel material, the rolling capacity of the hot rolling equipment, the target extraction temperature of the steel material from the continuous heating furnace, etc. Judging whether or not the steel material is kept at 900 ° C or higher for a fixed time of 15 minutes or more on the heating / heating curve, and the steel material charging interval or the steel material charging interval and the preceding are checked so that this condition is satisfied. It is characterized in that the steel material is charged and heated in a continuous heating furnace by controlling the charging interval of the steel material.

Therefore, the structure and operation of this means will be described in more detail with reference to the drawings.

1 is a vertical cross-sectional view of an example of a controller for a continuous heating furnace for carrying out the present invention, and FIG. 2 is a plan view thereof.

First, in FIG. 1 and FIG. 2, reference numeral 1 is a walking beam, 2 is a fixed beam, 3 is a steel material to be heated, and the steel material 3 is sent in the arrow direction in FIG. , Reaches the charging table on the charging side, and the charging roller 7b of the charging table causes the steel material 3 to enter the continuous heating furnace. In the continuous heating furnace, the walking beam 1 repeats a reciprocating motion at a predetermined pitch, and by this movement, the steel material 3 passes through the continuous heating furnace and is heated to a target heating temperature from the extraction side and extracted. To be done. In this continuous heating furnace, the steel material 3 is placed on the fixed beam 2 and heated by the heating burner 6 provided downward on the ceiling portion of the furnace body 5. Further, the walking beam 1 is driven by the driving device 4 so as to repeat the reciprocating motion of a predetermined pitch, the conveying roller 7a is driven by the driving device 8a, and the charging roller 7b of the charging table is driven by the driving device 8b. It

Next, in the continuous heating furnace configured as described above, each drive of each driving device 4, 8a, 8b such as the walking beam 1, the conveying roller 7a, and the charging roller 7b is controlled to adjust to an appropriate charging interval. In order to do so, a control device 9 is provided, and a charging interval calculation device 10 is connected to this control device 9. This calculator 10
As will be described later, for example, manufacturing information at the time of hot rolling before charging of n steel materials 3 and the like are provided to the host computer 12, the data processing device.
11 and the information from these devices 11 and 12 is calculated by the computing device 10
Then, as will be described later, the extraction interval and the heating / heating curve in the furnace are predicted for the steel material 3 before charging. That is, the calculation device 10 predicts the heating / heating curve for each steel material 3 in the furnace, and the charging interval between the steel materials 3 is obtained by this, and the controller 9 causes the drive devices 4, 8a, 8b, etc. to be obtained. Control the drive of.

Therefore, in the case where the steel material 3 is continuously heated by controlling the proper charging interval of the steel material 3 before charging the steel material into the continuous heating furnace by the controller of the continuous heating furnace having the above-described configuration, Do it on the street.

First, when charging a steel material that requires an operation restriction different from that of the preceding steel material, the target steel material is n before the preceding steel material of the continuous heating furnace charging, and the charging of the target steel material is controlled. The number of these n pieces is not necessarily limited, and the optimum value is determined by the capacity of the continuous heating furnace to be controlled, the capacity of each combustion zone, etc. Normally, the maximum value of the steel material in the continuous heating furnace is determined. The capacity is set.

Next, including the preceding steel material for the calculation target steel material that requires this operation regulation, the upper-level calculation device 12 and the data processing device 11
Based on the rolling capability and the charging interval of the preceding steel material that has already been determined, the calculation device 10 obtains the in-reactor time predicted value for the calculation target steel material. It should be noted that as the rolling capacity, it is optimal to use a model in which the extraction intervals on the rolling line for each steel material are modeled for each hot rolling factory.

Next, find the average in-furnace atmosphere temperature for each combustion zone in the continuous heating furnace required to satisfy the heating target value (steel material temperature, etc.) according to the in-react time predicted for the steel material to be calculated. . Here, in order to determine the atmosphere temperature in the furnace in the calculation device 10, the following equation (1) is used.

θ = f (θg, θo, α, t, D) (1) where θ: average temperature of steel materials θg: atmospheric temperature θo: charging temperature of steel materials α: heat between steel materials and furnace atmosphere Transfer coefficient t: Elapsed time from charging the furnace D: Shape factor of cross section of steel (thickness when slab-like,
(If the rectangle is one side, the length of one side) Next, based on the in-furnace time and each atmosphere temperature obtained as described above, predict the heating / heating curve in the continuous heating furnace for the steel material to be calculated, and calculate this. Set. At this time, the relationship between the atmospheric temperature θg and the heat quantity Qs received by the steel material is obtained in the form of radiant heat transfer using the following equation (2), and the steel material temperature change due to heat transfer in the steel material is three-dimensional. The difference method is used.

However, Qs: amount of heat received by the steel material Qg: ambient temperature in the furnace Qs: surface temperature of the steel material φCG: overall heat transfer coefficient Next, after setting the heating curve for heating in this way, Each section of the area retention regulation, that is,
In the soaking zone of a continuous heating furnace, the high temperature holding temperature range of 900 ℃ or higher
If this condition is satisfied and heating is possible, the preceding steel material is conveyed and heated as it is in the continuous heating furnace at the charging interval that has already been set, and the steel material to be calculated is the fuel. The charging interval (usually, this charging interval is the minimum interval that can be carried and heated in the continuous heating furnace) is set so that the basic unit is minimized, and the controller 9 calculates the charging interval at this charging interval. The steel material is conveyed and heated in a continuous heating furnace. Contrary to this, if the heating / heating curve of the steel material to be calculated set in advance does not satisfy the above conditions and if it is determined that heating is not possible as it is, it is preceded by not charging the continuous heating furnace. Extend the charging interval of the steel material by about one rank, repeat the above calculation, and obtain the heating / heating curve by this, and determine whether the expected temperature and holding time by this satisfy the above conditions. It is judged whether or not the optimum charging interval of the steel material to be calculated is set.

In order to extend the charging interval in this way, it depends on the transfer equipment of the continuous heating furnace, but in the case of a normal walking beam type transfer device, one or both of the feeding stroke of the walking beam and its feeding number Perform one rank at a time. Further, when the charging interval of the preceding steel material is extended in this way, it is not necessary to extend the charging interval to the preceding steel material having the effective furnace length of the continuous heating furnace or more.
That is, the range that affects the steel material to be calculated as the preceding steel material is when the total charging interval is within the effective furnace length. Therefore, the number n of the preceding steel materials for which the charging interval should be expanded is sequentially decreased each time the above calculation is repeated, and the heating basic unit can be greatly reduced by minimizing the expansion range.

In addition, the reason for determining whether or not the center temperature of the steel material to be calculated is maintained within a certain period of time, such as 330 minutes at 900 ° C or higher, is that it is strict that decarburization from the steel surface is affected. Is based on the steel surface temperature. Generally, it is said that the decarburization depth in a continuous heating furnace is proportional to the in-furnace time and the heating temperature, but when the present inventors examined the relationship between the in-furnace time and the decarburization depth, it was found that the proportion was proportional. It turns out that there are considerable variations. Therefore, further studying this relationship revealed that the region where the decarburization depth is exactly proportional to the in-furnace time is the high temperature region where the steel surface temperature is 900 ° C or higher, and the holding time in this region is within 30 minutes, for example. This is because a certain quality can be maintained within a certain time. However, the holding time must be at least 15 minutes, although it depends on the product dimensions and specifications. The reason for this is that if it is not kept at 900 ° C. or higher for at least 15 minutes, the cementite cannot be diffused to make the structure uniform.

Example Next, an example will be described.

First, the following steel products to be manufactured were conveyed and heated in the continuous heating furnace by the method of the present invention and the conventional method, and then rolled by a common hot rolling facility, and the quality of these products was compared.
It was the street.

(A) Steel to be manufactured Product diameter = 32φ (straight bar), standard = S45C, allowable decarburization depth = 0.
15 mm, the extraction steel target temperature 1100 ° C. (b) equipment conditions steel material 150φ × 13m, weight 2. ² TON (average) mill 18STD VH mill, rolling speed 10 m / s, the average Azuroru time 40 seconds cooling bed Rehhen Required interval between type bars (= extraction interval) = 20 seconds Heating furnace Upper and lower belt type walking bee heating furnace (capacity
150T / H) Table 1 shows the walking beam strokes of 200 mm and 300 mm, one cycle time for each stroke, and the maximum number of materials stored in the furnace.

The standard charging interval in this heating furnace is 200 mm.

(C) Heating method in the conventional example From the data obtained by regressing the relationship between the in-furnace time and the product decarburization depth in the heating furnace of the present example under various conditions, the average value of the extracted steel material temperatures of the preceding steel materials is 1150 to 1180. Assuming that the temperature is ℃, the upper limit of the in-reactor time of 65 minutes was required. Therefore, the charging interval is 300mm x 2 times from the preceding 34 steels from the minimum in-reactor time at each charging pitch shown in Table 2. And

(D) Heating method according to the present invention The setting is changed each time depending on the rolling capacity of the charged steel material and the manufacturing specifications of the preceding steel material, but as an example, the target steel material has a large amount to be rolled and the preceding steel material has the same manufacturing conditions. The case of a large amount is shown together with a comparative example of the conventional case. The heating conditions of the present invention, the relationship between the temperature rising heating curve and decarburization of the actual steel material using a thermocouple in a continuous heating furnace was investigated under various manufacturing conditions, and the residence time at 900 ° C or higher was determined from the results. It was found that the decarburization depth could be suppressed within the specified range by keeping it within 30 minutes. Therefore, this was set as the high temperature range target value. From this result, the set value of the charging interval differs depending on the target value of the extracted steel temperature of the preceding steel, but the extraction temperature of the preceding steel is 1130 ° C.
When the temperature was less than 1, the charging interval was 300 mm x 1 time, and at 1130 ° C or higher, the charging interval was 200 mm x 2 times = 400 mm.

(E) Product quality: In the case of the present invention, the decarburization depth level of the product is 0.10 mm on average as in the conventional example, but the standard deviation is 0.02 mm in the conventional example and 0.015 mm in the present invention. It turned out to be stable.

(F) Rolling efficiency: 35 rolls / hour in the conventional example,
In this example, the efficiency was improved to 44 lines / hour on average.

(G) Efficiency improvement of operation: In the conventional example, the charging interval was set uniformly regardless of the difference due to the manufacturing specifications of the preceding steel material.
In the present invention, since the logic is examined and reflected in detail, the total operation level is improved.

<Effects of the Invention> As described in detail above, in the method of the present invention, prior to charging into the continuous heating furnace, a heating line for heating the continuous heating furnace for steel materials is assumed from the rolling temperature, the steel material extraction temperature, and the like. , In addition,
The optimum charging interval is set based on whether or not the steel material is held in the region of 900 ° C or higher for a certain time when heated by this curve, and while conveying the steel material with this charging interval. To heat. Therefore, even if the steel type whose operation is regulated, it can be heated while being conveyed with the shortest charging interval suitable for it, and the filling rate of the continuous heating furnace can be increased, greatly improving the thermal efficiency. You can Further, it was found that the high temperature region of 900 ° C or higher in the soaking zone of the continuous heating furnace and its holding time are deeply related to the decarburization depth, and the charging interval is controlled so as to satisfy this condition. A product of constant quality can be obtained, and in comparison with the conventional example, the heating / heating curve can be set to a low temperature level except for this high temperature region,
The unit quantity of heat can be greatly reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional view of an example of a controller for a continuous heating furnace for carrying out the present invention, and FIG. 2 is a plan view thereof. Reference numeral 1 ... Walking beam 2 ... Fixed beam, 3 ... Steel material 4 ... Driving device, 5 ... Furnace body 6 ... Heating burner, 9 ... Control device 10 ... Calculation device 11 ... Data processing device 12 ...... High-end computer

Claims (1)

[Claims] 1. A charging interval and a hot rolling facility for a preceding steel material before charging, which have already been determined before charging the steel material in a continuous heating furnace for continuously heating the steel material before hot rolling. Assuming a heating and heating curve of the steel material in the continuous heating furnace from the rolling capacity of the steel, the target extraction temperature of the steel material from the continuous heating furnace, etc., the steel material is kept at 900 ° C or higher for 15 minutes or more in this heating and heating curve. Judging whether the condition is maintained for a time or not, and controlling the charging interval of the steel material or the charging interval of the steel material and the charging interval of the preceding steel material so that this condition is satisfied, the continuous heating furnace A method for heating a steel material in a continuous heating furnace, which comprises charging and heating the steel material.