JPH093552A - Continuous hot dip galvanizing equipment for effectively producing hot dip galvanized steel sheet - Google Patents

Abstract

PURPOSE: To shorten an annealing time and a line enabling a high temp. annealing and free-schedule for passing a strip by arranging a heating device setting an optimum parameter value during heating and soaking in in-line annealing type galvanizing equipment. CONSTITUTION: In the equipment successively arranging the galvanizing device succeeded with the continuous annealing equipment composed of a heating zone, soaking zone and cooling zone, the heating device for auxilially executing rapid temp.-raising in a short time at an arbitrary position in the soaking zone for heating and soaking a steel strip to a prescribed temp. so that the annealing parameter(AP) value becomes >=-33, is successively arranged. Successively, a forced cooling device and the galvanizing device are successively arranged in the advancing direction of the steel strip. By this constitution, high temp. annealing to give the workability and BH property can easily be executed, and the shortenings of the annealing time and the line enabling the free-schedule for passing the strip, can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous galvanizing equipment for steel sheets, and more particularly to continuous hot-dip galvanizing of steel sheets capable of improving the workability of cold-rolled steel sheets and imparting BH property with high functionality and productivity. The present invention relates to a continuous hot dip galvanizing facility for plating.

[0002]

2. Description of the Related Art In-line annealing continuous hot dip galvanizing equipment is a basic technique for improving the workability of hot-dip galvanized steel sheets, such as deep drawability and overhangability, and for imparting BH properties to hot-dip galvanized steel sheets. The high temperature annealing technique in is well known. In that case, the cold-rolled steel strip is uncoiled and inserted into a continuous hot-dip galvanizing facility for recrystallization annealing, but the pattern basically consists of heating, soaking, and cooling to improve workability. The annealing temperature is high. In addition, the heating method is direct-fired heating with a gas burner or radiant heating with a radiant tube.

On the other hand, application of electric heating to continuous annealing is also known. For example, as disclosed in JP-A-56-116830 and JP-A-56-16831, the steel sheet passing through the furnace is directly energized to heat the steel sheet itself as a heating element to heat it, and then a high frequency By utilizing vibration to promote crystal grain growth, the steel sheet properties such as the deep drawability are improved and the equipment cost is reduced. Further, Japanese Patent Laid-Open No. 2-166234 discloses that the steel plate temperature is 600 to 700 ° C. in the low temperature range and 800 to 900.
It is divided into a high temperature region reaching ℃ and direct flame reduction heating in the low temperature region and induction heating in the high temperature region.
No. 47 is an annealing furnace for galvanizing, in which an induction heating furnace is connected through an atmosphere gas sealing device to the inlet side of a heating zone for heating a steel strip in a reducing atmosphere continuously provided at the inlet side of a cooling zone. A device for doing so is disclosed.

Further, in JP-A-61-204319, in continuous annealing of a Ti-added cold-rolled steel sheet, in the soaking zone of a continuous annealing line, the temperature is 200 to 30 from the soaking temperature.
Disclosed is a continuous annealing method for cold-rolled steel sheets, which is characterized by rapidly raising the temperature by 0 ° C. and then rapidly cooling it. However, there is no description about application to an in-line annealing continuous hot dip galvanizing process.

[0005]

As described above, when high-temperature annealing is performed in order to improve the workability of cold-rolled steel sheets and impart BH properties, deterioration of the threading material such as heat buckle and plate breakage and Deterioration of surface quality occurs due to surface defects. Further, there is a problem that productivity is lowered due to the increase of energy cost and the necessity of changing the annealing temperature accompanying the production of steel sheets of different grades and grades. On the other hand, in the electric heating method in each of the above-mentioned patent publications, it is heated at once from room temperature to a recrystallization temperature or higher, or is combined with a conventional continuous annealing furnace in a completely separate and independent manner from a normal annealing furnace. Therefore, there is a problem that the heating temperature range is wide and the electric energy cost is high, and the equipment cost is high because the two heating methods are used separately.

[0006]

In order to solve the above-mentioned problems, the present invention has been earnestly developed by the present inventors. As a result, in-line annealing type continuous hot dip galvanizing equipment is used for heating and soaking. By setting the optimum annealing parameter value by supplementary heating for rapid and short time at any stage, it becomes possible to easily perform high temperature annealing for imparting workability and BH property, and to make the strip running schedule free. It is an object of the present invention to provide a continuous hot-dip galvanizing equipment in which a continuous annealing equipment and a hot-dip galvanizing equipment, which can shorten the annealing time and line as much as possible, are connected in series. The gist of the invention is as follows. (1) In a facility in which a hot-dip galvanizing facility is continuously provided after a continuous annealing facility including a heating zone, a soaking zone and a cooling zone,
Heating that heats the steel strip to a predetermined temperature and assists rapid and short-time temperature rise in any part of the soaking zone where the temperature is soaked, and performs heating control so that the value of the annealing parameter (AP) becomes -33 or more. A continuous hot-dip galvanizing equipment for efficiently producing hot-dip galvanized steel sheets, which is characterized in that an apparatus is installed, and then a forced cooling device and a hot-dip galvanizing equipment are connected in series in the traveling direction of the steel strip.

(2) In the continuous hot-dip galvanizing equipment as described in (1), the steel strip is heated to a predetermined temperature, and a rapid and short-time temperature increase is assisted at any part of the soaking zone for uniform heating to anneal. A heating device that controls heating so that the value of the parameter (AP) becomes −33 or more is provided, and then a cooling device, a hot dip galvanizing facility, and a reheating device that alloys the plated layer are installed in the traveling direction of the steel strip. An alloying continuous hot-dip galvanizing facility for efficiently producing hot-dip galvanized steel sheets, which is characterized by being continuously installed. (3) In the continuous hot-dip galvanizing equipment according to (1) or (2), a heating device for assisting a rapid and short-time temperature rise at any part of the soaking zone where the temperature is soaked is an electric heating device or an induction heating device. The present invention relates to a continuous hot-dip galvanizing facility for efficiently producing hot-dip galvanized steel sheets.

[0008]

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a process diagram showing the overall structure in which a continuous annealing facility and a hot dip galvanizing facility are connected in series. As shown in FIG. 1, a payoff reel 2 for rewinding and supplying the steel strip 1 is provided, and a steel strip cleaning device 3 is provided in the next stage of the payoff reel 2 to remove oil and oil attached to the surface. Contamination such as iron powder is removed and supplied to the entrance looper 4. The steel strip 1 is heated through the entry looper 4 to heat or maintain the temperature so that the steel strip 1 heated to the soaking temperature in the soaking zone 6 is the cooling zone 7 and, if necessary, the second cooling zone. Annealed through a third cooling zone (not shown) (not shown). The annealed steel strip 1 is guided to the hot dip galvanizing tank 10 through the sealing device 8 from the snout 9 in the same non-oxidizing atmosphere while being kept at a temperature higher than the plating temperature. Hot dip galvanizing tank 1
The hot-dip galvanized steel strip in 0 is wiped away from the bath surface by the gas wiper 11 above the bath surface and the excess amount of the hot-dip galvanized metal is wiped off and adjusted to a predetermined amount, and then an alloying device is used if necessary. The alloying treatment is performed by 12, the temper rolling is performed by the temper rolling mill 13, the oil is further applied, and the product is wound on the tension reel 14 to be a galvanized steel strip product. In continuous annealing in such equipment, in order to continuously anneal the steel strips of each size to a desired uniform quality, an electric heating device or an induction heating device 15 that assists rapid and short-time temperature rise is uniformly leveled. It is placed at any position in the tropics 6.

FIG. 2 is a diagram showing an example of a heat pattern implemented in the present invention. As shown in this figure, a is a stage in which a steel strip as cold rolled is unwound and heated in a continuous annealing furnace, and the heating pattern is a heating rate of 1 to 200 ° C./se.
c, the ultimate temperature is 500 to 900 ° C. b is a stage of soaking the steel strip, the soaking temperature is 500 to 900 ° C., and the holding time is 0 to 300 sec. In c, the temperature rises rapidly and in a short time due to electric heating, which is a feature of the present invention. The heating rate is 50 to 1000 ° C./sec,
Heat to 750-910 ° C. d is a step of cooling after rapid heating for a short period of time until it is immersed in molten zinc with an inert gas. Further, e is cooled to room temperature at the stage of f after hot dip galvanizing. This is a method for producing a hot-dip galvanized steel sheet in which a Zn-Fe alloying reaction does not occur in the plating layer. On the other hand, in the method for producing a galvannealed steel sheet, the alloy is subjected to an alloying reaction in the plating layer by reheating after being immersed in the hot dip galvanized bath, and then cooled to room temperature at the stage of h. Further, in the case of equipment having an overaging zone at the stage of e, it is cooled immediately after the rapid heating, and the overaging temperature is 25
After being held at 0 to 450 ° C., it is cooled to room temperature.

Therefore, regarding the annealing parameter (AP), which is the greatest feature of the present invention, in the annealing heat cycle shown in FIG. 2, the distance at which the iron atoms diffused due to the input thermal energy, in other words, the grain boundary was It is a dimensionless parameter related to the distance moved, and means that the larger the AP, the greater the effect of annealing. Therefore, the softening annealing has the meaning of releasing the strain introduced by cold rolling by annealing and imparting formability to the steel sheet. The inventors have found that such moldability can be uniquely expressed by AP. This AP can be expressed by the following equation. AP = ln {∫ (1 / T (t) exp (-Q / RT
(T) dt} where Q: activation energy for self-diffusion of Fe (60 kcal / mol) R: gas constant T: absolute temperature

FIG. 3 shows the annealing parameters (A
It is a figure which shows the relationship between P) and average r value, El value, and YP and TS. As the sample shown in FIG. 3, the ultra low carbon steel containing the ordinary addition of Ti and Nb shown in Table 1 was used as the hot rolling condition, and the slab heating temperature was 1180 ° C. and the hot rolling finishing temperature was 9
After hot rolling to a thickness of 4.0 mm at 09 ° C, it was wound at 622 ° C. Then, after pickling, cold rolling was performed to 0.8 mm, and then a (heating rate): 10 ° C./sec, b: 700 ° C. × 20 sec by the heat cycle shown in FIG.
c: 100 ° C./sec, d: 5 ° C./sec to 675 ° C. and then 20 ° C./sec, e: 470 ° C. molten zinc bath (containing 0.1% Al) for 2 sec,
g: 20 sec by heating to 520 ° C. at 20 ° C./sec
Soaking, h: Air cooling to room temperature at an average cooling rate of 20 ° C./sec. Then, a 0.8% temper-rolled steel strip was used as a test material. The equipment used in this case was an electric heating device that supplemented a rapid and short-term temperature rise to an arbitrary part of the soaking zone, for example, the final part of the soaking zone. The above-mentioned annealing parameter (AP) value and r value at that time,
It shows the relationship between the El value and YP and TS.

[0012]

[Table 1]

As shown in FIG. 3, by controlling heating so that the value of the annealing parameter (AP) becomes -33 or more, the average r value which is an index of deep drawability and the elongation which is an index of overhanging property. It shows that the El (%), the yield strength YP, and the tensile strength TS were able to obtain the target values or more, which are the performances of the hot-dip galvanized steel sheet with good deep drawability. That is, the average r value is 1.5 or more when AP is −33 or more, El (%) is 42% or more, YP is 180 N / mm ² or more, and TS is 320 N / m.
It is possible to obtain m ² or more. It should be noted that this is not limited to the ultra-low carbon steel in which Ti and Nb are added in combination as shown in Table 1, but in the case of Ti-added ultra-low carbon steel, Nb-added ultra-low carbon steel and low-carbon Al-killed steel sheet. Produces similar results. It was also confirmed that if the AP is the same, the tensile properties of the steel sheets obtained are the same regardless of the annealing heat cycle.

By arranging the electric heating or the induction heating in this case between the soaking zones, the partial heating can be carried out within the range of 0.5 to 15 seconds. In the present invention, the reason for using an electric heating device or an induction heating device is that, for example, as a heating system in a continuous annealing furnace of a cold rolled steel sheet, a direct fire type non-oxidizing heating system or a radiation tube heating system is used. However, since each of these methods is a heating method by heat transfer, the heating capacity per unit time is not so high, and in order to secure the necessary total amount of heat, it is necessary to take a long heating time, which is inevitable. The length of the heating zone becomes longer. On the other hand, in addition to the conventional direct-fired non-oxidizing heating method and radiant tube heating method, electric heating is adopted for heating in the high temperature heating section. That is, in the case of this electric heating, heating is performed while passing the steel strip along the conductor rolls on the inlet side and the outlet side respectively, and the rolls for guiding the steel strip made of such a conductive material are energized. The reason for this is that when a current is passed between the rolls through a steel strip which is a conductive material, the steel strip itself generates heat due to the electric resistance of the steel strip and is heated rapidly and in a short time.

The induction heating is to heat a steel strip by Joule loss by winding a heating coil around the steel strip and feeding power from a high frequency power source, and passing an induction current through the steel strip by the magnetic field created by the heating coil. This is because rapid heating is possible as well. Auxiliary heating is performed using these electric heating or induction heating devices, and the annealing parameter (A
P) can be easily controlled, and at the same time, the deteriorated portion at the end of the steel strip in the longitudinal direction can be compensated by partial heating, and uniform characteristics can be obtained in the longitudinal direction.

[0016]

As described above, with the equipment according to the present invention, it is possible to obtain a high surface quality that has good plateability without heat buckles or plate breakage, and that does not cause surface defects. Productivity is improved and costs are reduced by making the threading schedule free, and AP value is-
By controlling to 33 or more, it is possible to produce a hot-dip galvanized steel sheet excellent in workability and BH property, and it has an extremely excellent industrial effect. Further, in the case of low carbon Al killed steel, the hot-dip galvanized steel sheet produced by using this equipment is post-heat treated for non-aging, if necessary, to improve the industrial significance of this equipment. Can be demonstrated.

[Brief description of drawings]

FIG. 1 is a process diagram showing the entire structure in which a continuous annealing facility and a hot dip galvanizing facility are connected in series,

FIG. 2 is a diagram showing an example of a heat pattern carried out by the present invention,

FIG. 3 is an annealing parameter (AP) and an average r according to the present invention.
It is a figure which shows the relationship between a value, an El value, YP, and TS.

[Explanation of symbols]

 1 Steel strip 2 Payoff reel 3 Steel strip cleaning device 4 Inlet looper 5 Heating furnace 6 Soaking zone 7 Cooling zone 8 Sealing device 9 Snout 10 Hot dip galvanizing tank 11 Gas wiper 12 Alloying device 13 Temper rolling mill 14 Tension reel 15 Electric heating device or induction heating device

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Makoto Tezaba 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Corporation Stock of Kimitsu Steel Co., Ltd.

Claims (3)

[Claims] 1. A facility in which a hot-dip galvanizing facility is continuously provided after a continuous annealing facility comprising a heating zone, a soaking zone, and a cooling zone, and the steel strip is heated to a predetermined temperature at any portion of the soaking zone. A heating device is provided for assisting rapid and short-time temperature rise, and heating control so that the value of the annealing parameter (AP) becomes -33 or more. Then, a forced cooling device and hot dip galvanizing equipment are installed in the steel strip. A continuous hot-dip galvanizing facility for efficiently producing hot-dip galvanized steel sheets, which is characterized in that the hot-dip galvanized steel sheets are continuously provided in the advancing direction. 2. The continuous hot-dip galvanizing equipment according to claim 1, wherein the steel strip is heated to a predetermined temperature, and a rapid and short-time temperature rise is assisted at any part of the soaking zone where the temperature is soaked. A heating device that controls heating so that the value of (AP) becomes −33 or more is provided, and then a cooling device, a hot dip galvanizing facility, and a reheating device that alloys the plating layer are installed in the traveling direction of the steel strip. A continuous hot-dip galvanizing facility for efficiently producing alloyed hot-dip galvanized steel sheets, which is characterized by being connected in series. 3. The continuous hot-dip galvanizing equipment according to claim 1 or 2, wherein a heating device for assisting a rapid and short-time temperature rise at any part of the soaking zone where the temperature is soaked is an electric heating device or an induction heating device. The continuous hot-dip galvanizing equipment for efficiently producing hot-dip galvanized steel sheet characterized by the above.