GB1565874A

GB1565874A - Manufacture of galvanized steel sheets

Info

Publication number: GB1565874A
Application number: GB1121577A
Authority: GB
Original assignee: Arbed SA
Current assignee: Arcelor Luxembourg SA
Priority date: 1976-03-16
Filing date: 1977-03-16
Publication date: 1980-04-23
Also published as: FR2344646A1; FR2344646B1; IT1082174B; BE852490A; LU74569A1; DE2711041A1

Description

(54) MANUFACTURE OF GALVANIZED STEEL SHEETS (71) We, ARBED S.A. (formerly known as Acieries Reunies De Burbach Eich-Dudelange Societe Anonyme en abbreviation ARBED), a Luxembourg Company, of Avenue de la Liberte, Luxembourg Ville, Luxembourg, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to a method of manufacturing galvanized steel sheets. The method is particularly useful in that it usually gives the sheets an excellent combination of elastic limit and elongation, together with very uniform properties over their entire width, so that the sheets are very suitable for drawing. Such qualities are specially required e.g. for sheets having a high elastic limit used in the car industry.

According to the present invention, there is provided a method of manufacturing galvanized steel sheet, which comprises bringing the sheet to a temperature between 650 and 950"C, and subsequently cooling it by immersing it first in a molten salt bath and then in a zinc bath.

In a preferred embodiment of the invention, the molten salt bath is at a temperature between 420 and 500"C.

In one embodiment of the method according to the invention, the molten salt bath and the zinc bath are contained in the same vessel, the baths being superposed at the vessel inlet. In this case, the vessel preferably has two compartments of the "siphon" kind, and, in the inlet compartment, the molten salt bath forms a layer floating on the surface of the zinc bath whereas only zinc is present in the outlet compartment. The latter embodiment prevents air being entrained by the sheet into the zinc bath and also ensures the removal of the salt before the sheet comes out into the atmosphere.

In order to obtain complete recrystallization of the cold-hardened structure of a cold-rolled sheet, the sheet may be kept at a temperature equal to the temperature of the end of heating or at a temperature between the temperature at the end of heating and the temperature at the beginning of cooling for a time greater than 30 seconds.

Advantageously, the sheet, after being withdrawn from the zinc bath, is subjected to a super-ageing operation wherein the sheet is heated to a temperature between 300 and 420"C, thus increasing the ductility of the metal. In this case, the sheet, after being brought to a temperature between 300 and 420"C, if preferably kept at the same temperature for a time between 30 seconds and 120 seconds.

When a sheet having a high elastic limit is to be manufactured, the method according to the invention preferably comprising heating the sheet to a temperature between 800 and 9500 C, then immersing the sheet in a molten salt bath to cool the sheet to a temperature between 420 and 500"C, and then immersing the sheet in a zinc bath.

When a sheet for drawing is to be manufactured, the method according to the invention preferably comprises heating the sheet to a temperature between 650 and 850"C, subsequently cooling the sheet by immersing it first in a molten salt bath and then in a zinc bath, and, at the outlet of the zinc bath, reheating the sheet to a temperature between 300 and 420"C for a time between 30 seconds and 120 seconds.

The method of the invention can be carried out in an installation comprising a furnace for heating the sheet and, if desired, maintaining it at the chosen temperature for a given time, and a vessel containing a molten salt bath and a zinc bath for cooling the sheet. The installation may also comprise a super-ageing furnace for bringing the cooled sheet to a temperature of about 400"C and, if desired, maintaining it at the same temperature for a given time, means for cooling the sheet to ambient temperature after it has been treated at 400"C, and means for unwinding the sheet at the beginning of treatment and rewinding it at the end of treatment.

For a better understanding of the invention, reference will now be made, by way of example, to the accompanying drawing, which shows an installation suitable for carrying out the method of the invention. The installation shown in the drawing consists of: (a) a inlet region 1 comprising an unwinding means and a welding device; (b) an electrolytic degreasing chamber 2 for removing rolling oils, if any; (c) an inlet storage tank 3; (d) a heating furnace 4; (e) a chamber 5 for maintaining the sheet at a temperature near that chosen as the starting point of rapid cooling: (f) a tank 6 in which the sheet is immersed, the tank having two compartments connected by a siphon 11, the inlet compartment containing a molten salt layer 12 floating on a zinc bath 13, the temperature of the molten salt layer being kept between the desired limits, inter alia for the sheet-cooling process, by means of for example immersed pipes in which a cooling liquid flows; (g) a super-ageing furnace 7; (h) a final cooling region 8; (i) an outlet storage tank 9; and (j) an outlet region 10 comprising a winding means, shears, edge shears if required, a planing machine or "skin-pass" and a processing line.

WHAT WE CLAIM IS: 1. A method of manufacturing galvanized steel sheet, which comprises bringing the sheet to a temperature between 650 and 950"C, and subsequently cooling it by immersing it first in a molten salt bath and then in a zinc bath.

2. A method according to claim 1, wherein the molten salt bath is at a temperature between 420 and 500"C.

3. A method according to claim 1 or 2, wherein the molten salt bath and the zinc bath are contained in the same vessel, the baths being superposed at the vessel inlet.

4. A method according to claim 3, wherein the vessel has two compartments of the "siphon" kind; and wherein, in the inlet compartment, the molten salt bath forms a layer floating on the surface of the zinc bath whereas only zinc is present in the outlet compartment.

5. A method according to any of claims 1 to 4, wherein the sheet is kept at a temperature equal to the temperature at the end of heating or at a temperature between the temperature at the end of heating and the temperature at the beginning of cooling for a time greater than 30 seconds.

6.-A method according to any of claims I to 5, wherein the sheet, after being withdrawn from the zinc bath, is subjected to a super-ageing operation wherein the sheet is heated to a temperature between 300 and 420or, thus increasing the ductility of the metal.

7. A method according to claim 6, wherein the sheet, after being heated to a temperature between 300 and 420or, is kept at the same temperature for a time between 30 seconds and 120 seconds.

8. A method of manufacturing galvanized steel sheet having a high elastic limit, which comprises heating the sheet to a temperature between 800 and 950"C, then immersing the sheet in a molten salt bath to cool the sheet to a temperature between 420 and 500"C, and then immersing the sheet in a zinc bath.

9. A method of manufacturing galvanized steel sheet for drawing, which comprises heating the sheet to a temperature between 650 and 850"C, subsequently cooling the sheet by immersing it first in a molten salt bath and then in a zinc bath, and, at the outlet of the zinc bath, reheating the sheet to a temperature between 300 and 420"C for a time between 30 seconds and 120 seconds.

10. A method according to claim 1 of manufacturing galvanized steel sheet, substantially as described herein with reference to the accompanying drawing.

11. Galvanized steel sheet which has been manufactured by the method claimed in any of claims I to 10.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. at the beginning of treatment and rewinding it at the end of treatment. For a better understanding of the invention, reference will now be made, by way of example, to the accompanying drawing, which shows an installation suitable for carrying out the method of the invention. The installation shown in the drawing consists of: (a) a inlet region 1 comprising an unwinding means and a welding device; (b) an electrolytic degreasing chamber 2 for removing rolling oils, if any; (c) an inlet storage tank 3; (d) a heating furnace 4; (e) a chamber 5 for maintaining the sheet at a temperature near that chosen as the starting point of rapid cooling: (f) a tank 6 in which the sheet is immersed, the tank having two compartments connected by a siphon 11, the inlet compartment containing a molten salt layer 12 floating on a zinc bath 13, the temperature of the molten salt layer being kept between the desired limits, inter alia for the sheet-cooling process, by means of for example immersed pipes in which a cooling liquid flows; (g) a super-ageing furnace 7; (h) a final cooling region 8; (i) an outlet storage tank 9; and (j) an outlet region 10 comprising a winding means, shears, edge shears if required, a planing machine or "skin-pass" and a processing line. WHAT WE CLAIM IS:

1. A method of manufacturing galvanized steel sheet, which comprises bringing the sheet to a temperature between 650 and 950"C, and subsequently cooling it by immersing it first in a molten salt bath and then in a zinc bath.