JPS60159159A - Galvannealing furnace - Google Patents

Abstract

PURPOSE:To provide a titled furnace which enables adequate selective formation of plating compsn. by the constitution consisting in providing an evacuating means permitting free adjustment of the flow rate on the outlet side of a heating zone and a holding zone and providing a means for supplying cooling fluid to the holding zone. CONSTITUTION:A galvanealing furnace 1 is constituted of a heating zone 4 and a holding zone 5 for heating and holding respectively a galvanized steel strip 3 conveyed continuously toward an arrow direction from a galvanizing bath 2 to and at prescribed temp. An evacuating means which consists of evacuating ducts 7, 10 provided respectively with dampers 6, 9 and permits free adjustment of the flow rate is provided on the outlet side of said zone 4 and zone 5. A blower 8 is provided to the zone 5 to supply cooling air. The heat pattern in the furnace 1 is adequately ajusted by the above-mentioned constitution, by which the Fe-Zn alloy of the plating layer is adequately selectively formed to the alloy consisting essentially of an delta1 phase or xsi phase. The strip 3 having desired weldability and excellent workability is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of the Invention) The present invention relates to an alloying heat treatment furnace for hot-dip galvanized steel strip, that is, a galvanil furnace, in particular, comprising a heating zone and a holding zone sequentially from the furnace entry side to the furnace exit side. For galvanyl furnaces
related.

(Prior art) Today, alloying treatment of hot-dip galvanized steel sheets, that is, galvanization treatment, has become widely used.Because of the excellent properties of the alloyed steel sheets, they are used in automobiles, home appliances, etc.
Since such alloyed steel sheets (hereinafter also referred to as GA steel sheets) are used in large quantities for applications such as fixtures, it is necessary to supply them in large quantities and at low cost.

By the way, when hot-dip galvanized steel slip is subjected to alloying heat treatment, the alloying reaction when the base steel is thermally diffused into the galvanized layer first produces Fe + Zn - ζ phase by this reaction, and then This ζ phase and Fe are Fe+ζ−
Due to the reaction of δ1, δ□ phase is generated and alloying progresses.

Therefore, the composition of the plating layer alloyed in this manner may be mainly composed of the ζ phase or mainly composed of the 61 phase depending on the relationship between temperature and treatment time. Conventionally manufactured GA steel sheets have a composition mainly composed of δ1 phase.

This is because conventionally, GA steel sheets are required to have good weldability due to spot welding, etc., and it was desired to produce a plating layer composition mainly composed of δ1 phase that has particularly good weldability. Therefore, even in the currently used galvanil furnace, the above-mentioned Fe + Zn → ζ, then re + ζ -
The furnace is operated with an internal heat pattern that maintains the furnace at high temperature for a relatively long time until each reaction in 6□ is completed.
The reality is that there are. In other words, it was necessary to make the retention band sufficiently long.

Note that the properties of an alloyed steel sheet are not only determined by the type of alloy ratio phase in the plating layer, but also may be influenced by the Fe content even if the alloy ratio phase is the same.

In recent years, even in the above-mentioned applications, not only weldability but also high formability such as press formability and drawability are required, and some products have even higher G
There are now cases where workability is primarily required even for A steel sheets. However, since it is required to manufacture in large quantities and at low cost, it is not cost effective to install a dedicated furnace, so any type of GA steel sheet can be manufactured as needed using the same furnace. It is hoped that this will be possible.

Moreover, it is known that depending on the Fe content in the alloying phase of a GΔ steel sheet, there is a substantial difference in the final properties even if the same alloying ratio phase is formed. It is also desired to establish means that can appropriately adjust the temperature.

(Summary of the Invention) The object of the present invention is to reduce the Fe content in the plating layer,
Another object of the present invention is to provide a galvanil furnace that allows the composition of the plating layer to be appropriately divided into those mainly composed of the ζ phase and the δ1 phase.

Here, the present invention provides a galvaneal furnace equipped with a heating zone and a holding zone that heat and maintain continuously fed hot-dip galvanized steel strip at a predetermined temperature, respectively, and an exhaust means that can freely adjust the flow rate on the outlet side of the heating zone. A galvaneal furnace characterized in that a cooling fluid supply means for cooling the steel strip is provided in the retaining band.

(Aspects of the invention) The invention will be further explained with reference to the accompanying drawings.

(Figure 1 of the drawings is a schematic cross-sectional view of the galvaneal furnace 1 according to the present invention.
consists of a heating zone 4 and a holding zone 5, which respectively heat and maintain the steel strip 3, which is continuously fed in the direction of the arrow after leaving the hot-dip galvanizing bath 2, at a predetermined temperature.

A series of burners are installed in the heating zone 4 to rapidly heat the incoming strip, but these burners have been omitted from the figure for the sake of brevity.

According to the present invention, an exhaust duct 7 is provided on the outlet side of the heating zone 4, that is, at the boundary with the holding zone 5, and is equipped with an exhaust means that can freely adjust the flow rate, that is, a damper 6 in the figure.

Further, the retaining strip 5 is provided with a means for supplying a cooling fluid for cooling the steel strip, for example cooling air, at an appropriate position, generally on the inlet side, that is, at an inlet portion of the retaining strip 5, such as an annular blower 8 for blowing air in the figure. It is provided. An exhaust duct 10 equipped with a damper 9 is provided on the outlet side of the holding band 5, as in the conventional galvaneal furnace.

Therefore, according to the galvanil furnace 1 according to the present invention,
By combining the operation of the damper 6 of the heating zone 4 and the operation of blowing cooling air from the blower 8, it is possible to appropriately achieve both long- and short-time furnace heat patterns, and accordingly, the plating layer is The composition can also be differentiated into one mainly composed of δ1 phase and one mainly composed of ζ phase.

FIG. 2 is an explanatory diagram showing an example of the furnace heat pattern obtained by the above-mentioned operation, and the solid line in the figure is the furnace heat pattern when the damper 6 is closed and the blower 8 is stopped. On the other hand, when the damper 6 is opened and the blower 8 starts operating, the heat pattern in the furnace changes as shown by the dotted line in the figure.

In addition, in the above example, when the in-furnace heat pattern (heat pattern-1) of A-B-→C is taken, and Δ
-B--D Furnace Heat Pattern (Heat Pattern-■
) are summarized in the table below. The percentage of Fe in the plating layer can be changed as appropriate by thoroughly adjusting the operating conditions described above.

Table 2 As described above, according to the galvanil furnace according to the present invention, it is possible to manufacture the plating layer by appropriately changing the composition of the plating layer from one mainly composed of 61 phase to one mainly composed of ζ phase. Even the Fe content contained therein can be adjusted. Moreover, such changes can be made continuously, that is, immediately during the threading operation.

Accordingly, the present invention makes a significant contribution to the art, as will be apparent to those skilled in the art from the foregoing description.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a galvanic furnace according to the present invention:
and FIG. 2 is a diagram showing an example of an in-furnace bee 1 pattern obtained by the galvanyl furnace according to the present invention. 1: Galvanil furnace 2: /8 melting! 11i lead oak bath 3
: Steel strisozo 4: Heating zone 5; Holding '+'k 6: Dunbar 7: Exhaust duct I/8; Professional "No applicant Patent attorney Akira Hirose, agent for Sumitomo Kinku Kogyo Co., Ltd. - Figure 1

Claims (1)

[Claims] In a galvaneal furnace equipped with a heating zone and a holding zone that heat and maintain continuously fed hot-dip galvanized steel strips and strips at a predetermined temperature, a flow of N is applied to the exit side of the heating zone.
A galvaneal furnace characterized in that it is provided with adjustable exhaust means and that the retaining band is provided with a cooling fluid supply means for cooling the steel strip.