AU2004221793B2 - A method of controlling surface defects in metal-coated strip - Google Patents
A method of controlling surface defects in metal-coated strip Download PDFInfo
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- AU2004221793B2 AU2004221793B2 AU2004221793A AU2004221793A AU2004221793B2 AU 2004221793 B2 AU2004221793 B2 AU 2004221793B2 AU 2004221793 A AU2004221793 A AU 2004221793A AU 2004221793 A AU2004221793 A AU 2004221793A AU 2004221793 B2 AU2004221793 B2 AU 2004221793B2
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- strontium
- calcium
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- molten bath
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- 238000000034 method Methods 0.000 title claims description 65
- 230000007547 defect Effects 0.000 title claims description 29
- 229910052751 metal Inorganic materials 0.000 title claims description 21
- 239000002184 metal Substances 0.000 title claims description 21
- 229910052712 strontium Inorganic materials 0.000 claims description 82
- CIOAGBVUUVVLOB-UHFFFAOYSA-N strontium atom Chemical compound [Sr] CIOAGBVUUVVLOB-UHFFFAOYSA-N 0.000 claims description 82
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 claims description 72
- 239000011575 calcium Substances 0.000 claims description 72
- 229910052791 calcium Inorganic materials 0.000 claims description 72
- 229910000676 Si alloy Inorganic materials 0.000 claims description 45
- -1 aluminium- zinc-silicon Chemical compound 0.000 claims description 41
- 229910000831 Steel Inorganic materials 0.000 claims description 39
- 239000010959 steel Substances 0.000 claims description 39
- 238000000576 coating method Methods 0.000 claims description 38
- 239000011248 coating agent Substances 0.000 claims description 36
- 229910045601 alloy Inorganic materials 0.000 claims description 14
- 239000000956 alloy Substances 0.000 claims description 14
- 239000004411 aluminium Substances 0.000 claims description 13
- 229910052782 aluminium Inorganic materials 0.000 claims description 13
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 12
- 238000010438 heat treatment Methods 0.000 claims description 12
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 claims description 11
- 229910052749 magnesium Inorganic materials 0.000 claims description 11
- 239000011777 magnesium Substances 0.000 claims description 11
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims description 6
- 229910052804 chromium Inorganic materials 0.000 claims description 6
- 239000011651 chromium Substances 0.000 claims description 6
- 238000003618 dip coating Methods 0.000 claims description 6
- 229910052720 vanadium Inorganic materials 0.000 claims description 6
- LEONUFNNVUYDNQ-UHFFFAOYSA-N vanadium atom Chemical compound [V] LEONUFNNVUYDNQ-UHFFFAOYSA-N 0.000 claims description 6
- JGFZNNIVVJXRND-UHFFFAOYSA-N N,N-Diisopropylethylamine (DIPEA) Chemical compound CCN(C(C)C)C(C)C JGFZNNIVVJXRND-UHFFFAOYSA-N 0.000 claims description 5
- 229910000861 Mg alloy Inorganic materials 0.000 claims 1
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 4
- 230000001143 conditioned effect Effects 0.000 description 4
- 238000001816 cooling Methods 0.000 description 4
- 238000005096 rolling process Methods 0.000 description 4
- 239000010703 silicon Substances 0.000 description 4
- 229910052710 silicon Inorganic materials 0.000 description 4
- 210000004894 snout Anatomy 0.000 description 4
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 3
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 3
- 239000011701 zinc Substances 0.000 description 3
- 229910052725 zinc Inorganic materials 0.000 description 3
- 230000009286 beneficial effect Effects 0.000 description 2
- 238000011835 investigation Methods 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 150000002739 metals Chemical class 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 238000005275 alloying Methods 0.000 description 1
- 150000001398 aluminium Chemical class 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 239000010960 cold rolled steel Substances 0.000 description 1
- 239000000356 contaminant Substances 0.000 description 1
- 238000011109 contamination Methods 0.000 description 1
- 238000010924 continuous production Methods 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- VBMVTYDPPZVILR-UHFFFAOYSA-N iron(2+);oxygen(2-) Chemical group [O-2].[Fe+2] VBMVTYDPPZVILR-UHFFFAOYSA-N 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
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- Coating With Molten Metal (AREA)
Description
PCT/AU2004/000345 Received 6 June 2005 1 A METHOD OF CONTROLLING SURFACE DEFECTS IN METAL-COATED STRIP The present invention relates to controlling surface defects, as described hereinafter, in steel strip that has a corrosion-resistant metal coating that is formed on the strip by hot-dip coating the strip in a molten bath of coating metal.
The present invention relates particularly but not exclusively to metal coated steel strip that can be cold formed by roll forming) into an end-use product, such as roofing products.
The present invention relates particularly but not exclusively to metal coated steel strip having an aluminium-zinc-silicon alloy coating that can be cold formed by roll forming) into an end-use product, such as roofing products. The applicant is interested particularly in aluminium-zinc-silicon alloy coated steel strip that is sold in Australia under the Registered trade mark ZINCALUME and in other countries under the Registered trade mark GALVALUME.
The present invention also relates particularly but not exclusively to metal coated steel strip having an aluminium-zinc-silicon alloy coating with small spangle size, i.e. a coating with an average spangle size of the order of less than 0.5mm. Coated steel strip products with larger spangle size do not tend to show the generally small defects because the defects are camouflaged by the appearance of the spangle pattern.
The term "aluminium-zinc-silicon alloy" is understood herein to mean alloys comprising the following ranges in weight percent of the elements aluminium, zinc and silicon: Amended Sheet
IPEA/AU
WO 2004/083480 PCT/AU2004/000345 2 Aluminium: 50-60 Zinc; 37-46 Silicon: 1.2-2.3 The term "aluminium-zinc-silicon" alloy is also understood herein to mean alloys that may or may not contain other elements, such as, by way of example, any one or more of iron, vanadium, chromium, and magnesium.
In the conventional hot-dip metal coating method, steel strip generally passes through one or more heat treatment furnaces and thereafter into and through a bath of molten coating metal, such as aluminium-zinc-silicon alloy, held in a coating pot. The furnaces may be arranged so that the strip travels horizontally through the furnaces. The furnaces may also be arranged so that the strip travels vertically through the furnaces and passes around a series of upper and lower guide rollers. The coating metal is usually maintained molten in the coating pot by the use of heating inductors. The strip usually exits the heat treatment furnaces via an outlet end section in the form of an elongated furnace exit chute or snout that dips into the bath. Within the bath the strip passes around one or more sink rolls and is taken upwardly out of the bath. After leaving the coating bath the strip passes through a coating thickness control station, such as a gas knife or gas wiping station, at which its coated surfaces are subjected to jets of wiping gas to control the thickness of the coating. The coated strip then passes through a cooling section and is subjected to forced cooling. The cooled strip may thereafter be optionally conditioned by passing the coated strip successively through a skin pass rolling section (also known as a temper rolling section) and a tension levelling section. The conditioned strip is coiled at a coiling station.
WO 2004/083480 PCT/AU2004/000345 3 The present invention is concerned particularly but not exclusively with minimising the presence of particular surface defects on steel strip that has been hot dip coated with an aluminium-zinc-silicon alloy.
The particular surface defects are described by the applicant as "rough coating" and "pinhole uncoated" defects. Typically, a "rough coating" defect is a region that has a substantial variation in coating over a 1mm length of strip, with the thickness varying between micron thick and 40 micron thick. Typically, a "pinhole uncoated" defect is a very small region (<0.5mm in diameter) that is uncoated.
In general terms, the present invention provides a method of controlling surface defects of. the type described above on a steel strip coated with an aluminiumzinc-silicon alloy which includes the steps of: successively passing the steel strip through a heat treatment furnace and a bath of molten aluminium-zincsilicon alloy, and: heat treating the steel strip in the heat treatment furnace; and hot-dip coating the strip in the molten bath and thereby forming a coating of the alloy on the steel strip; and which method is characterised by controlling the concentration of strontium or (ii) calcium or (iii) strontium and calcium in the molten bath to be at least 2ppm.
The invention is based on the results of work carried out by the applicant that established that strontium and calcium, separately and in combination, WO 2004/083480 PCT/AU2004/000345 4 substantially reduce the number of the above-described surface defects that form on steel strip that is hot dip coated in a molten bath of aluminium-zinc-silicon alloy.
The applicant has observed that "rough coating" and "pinhole uncoated" surface defects are always associated with small areas where the metal coating has not alloyed with the steel strip.
Whilst not wishing to be bound by the following comments, the applicant believes that oxides on the surface of the strip may be one factor that causes the absence of alloying of the aluminium-zinc-silicon alloy coating and the steel strip in the small areas. The applicant also believes that one major source of the oxides is the surface of the molten bath. The surface oxides are solid oxides that are formed from metals in the molten bath as a result of reactions between molten bath metal and water vapour in the snout above the molten bath. In a molten bath of an aluminium-zinc-silicon alloy, in addition to aluminium, zinc, and silicon, the molten bath contains minor amounts of other metals including magnesium. The applicant believes that surface oxides are taken up by strip as the strip passes through the oxide layer in order to enter the molten bath. The applicant has established that strontium and calcium minimise the amount of oxides that form on the bath surface and suspects that these elements may reduce the amount of oxides that are available to be taken up by the strip. The applicant also suspects that, alternatively or in combination, strontium and calcium may modify the properties of the surface oxides and, for example, increase the strength of the oxides whereby there is less likelihood that oxides will break away from the bath surface and be taken up by strip.
The above-described method is characterised by the deliberate inclusion of the elements strontium and/or WO 2004/083480 PCT/AU2004/000345 calcium in the coating aluminium-zinc-silicon alloy. In the context of the present invention, the elements are regarded as beneficial.
The aluminium-zinc-silicon alloy may include other elements.
However, preferably the aluminiumn- zinc-silicon alloy does not contain the elements vanadium and/or chromium as deliberate alloy elements as opposed to being present in trace amounts for example due to contamination in the molten bath.
In a situation in which the molten bath contains strontium and no calcium, preferably the method includes controlling the concentration of strontium in the molten bath to be in the range of 2-4ppm.
More preferably the strontium concentration is 3ppm.
In a situation in which the molten bath contains calcium and no strontium, preferably the method includes controlling the concentration of calcium in the molten bath to be in the range of 4-8ppm.
More preferably the calcium concentration is 6ppm.
In a situation in which the molten bath contains strontium and calcium, preferably the method includes controlling the concentration of strontium and calcium in the molten bath to be at least 4ppm.
Preferably the method includes controlling the concentration of strontium and calcium in the molten bath to be in the range of 2-12ppm.
WO 2004/083480 PCT/AU2004/000345 Preferably the method includes controlling the concentration of strontium or (ii) calcium or (iii) strontium and calcium in the molten bath to be at no more than 150ppm.
More preferably method includes controlling the concentration of strontium or (ii) calcium or (iii) strontium and calcium in the molten bath to be no more than The applicant has found that the control of strontium and calcium concentrations in the molten bath has a particularly beneficial effect on aluminium-zinc-silicon alloys that contain magnesium.
Preferably aluminium-zinc-silicon alloys have a magnesium concentration of less than 1%.
More preferably aluminium-zinc-silicon alloys have a magnesium concentration of less than The concentration of strontium or (ii) calcium or (iii) strontium and calcium in the molten bath may be controlled by any suitable means.
One option, which is preferred by the applicant, is to specify a minimaum concentration(s) of strontium and/or calcium in the aluminium that is supplied to form the aluminium-zinc-silicon alloy for the molten bath.
Another, although not the only other, option is to periodically dose the molten bath with amounts of strontium and/or calcium that are required to maintain the concentration(s) at a required concentration.
00 0 The present invention is particularly Sadvantageous for "minimum spangle" metal coated strip.
The term "minimum spangle" metal coated strip is S 5 understood herein to mean metal coated strip that has spangles that are less than 0.5mm, preferably less than 0.2mm, in the major dimension of the spangles substantially across the surface of the strip.
By way of example, the above-mentioned dimensions Sare measured using the average intercept distance method as described in Australian Standard AS1733.
Standard spangled strip obscures the surface defects. Minimum spangle strip does not obscure the surface defects.
Minimum spangle metal coated strip may be formed by any suitable method steps, such as described in International application PCT/US00/23164 (WO 01/27343) in the name of Bethlehem Steel Corporation. The disclosure in the specification of the International application is incorporated herein by cross-reference.
The present invention is also particularly advantageous for steel strip that does not have a surface appearance, such as spangled strip, that obscures the surface defects and has not been conditioned by heavily skin pass rolling the strip to obscure the surface defects.
An example of such a non-heavy skin passed rolled strip is steel strip that is conditioned to have a residual stress of no more than 100 MPa in the strip as described by way of example in Australian complete application 43836/01 in the name of the applicant. The disclosure in the Australian complete application is incorporated herein by crossreference.
N: \Meboume\Case\Ptent\4BOOO-48999\P4877.AU. 1Specis\Sr Ca Addition Cican- amended doc 29110/08 PCT/AU2004/000345 Received 6 June 2005 7a The furnace may be any suitable furnace, such as a horizontal furnace or a vertical furnace.
Preferably the furnace has an elongated furnace Amended Sheet
IPEA/AU
WO 2004/083480 PCT/AU2004/000345 8 exit chute or snout that extends into the bath.
According to the present invention there is also provided a steel strip coated with an aluminium-zincsilicon alloy produced by the above-described method.
The present invention is described further by way of example with reference to the accompanying drawings of which: Figure 1 is a schematic drawing of one embodiment of a continuous production line for producing steel strip coated with aluminium-zinc-silicon alloy in accordance with the method of the present invention Figure 2 a graph of the estimated concentration of strontium over a 5 month time period in a molten bath containing an aluminium-zinc-silicon alloy that forms part of a steel strip coating line of the applicant at a plant of the applicant at Westernport, Victoria; and Figure 3 is a graph of the frequency of the above-described surface defects in the aluminium-zincsilicon alloy coatings formed by hot dip coating steel strip through the molten bath during part of the time period covered by the Figure 2 graph.
With reference to Figure 1, in use, coils of cold rolled steel strip are uncoiled at an uncoiling station 1 and successive uncoiled lengths of strip are welded end to end by a welder 2 and form a continuous length of strip.
The strip is then passed successively through an accumulator 3, a strip cleaning section 4 and a furnace assembly 5. The furnace assembly 5 includes a preheater, a preheat reducing furnace, and a reducing furnace.
WO 2004/083480 PCT/AU2004/000345 9 The strip is heat treated in the furnace assembly by careful control of process -variables including:(i) the temperature profile in the furnaces, (ii) the reducing gas concentration in the furnaces, (iii) the gas flow rate through the furnaces, and (iv) strip residence time in the furnaces (ie line speed).
The process variables in the furnace assembly are controlled so that there is :removal of iron oxide residues from the surface of the strip and removal of residual oils and iron fines from the surface of the strip.
The heat treated strip is then passed via an outlet snout downwardly into and through a molten bath containing an aluminium-zinc-silicon alloy held in a coating pot 6 and is coated with aluminium-zinc-silicon alloy. Preferably the aluminium-zinc-silicon alloy contains the elements strontium and/or calcium. Preferably the aluminium-zinc-silicon alloy does not contain the elements vanadium and/or chromium. The aluminium-zincsilicon alloy is maintained molten in the coating pot by use of heating inductors (not shown). Within the bath the strip passes around a sink roll and is taken upwardly out of the bath. Both surfaces of the strip are coated with the aluminium-zinc-silicon alloy as it passes through the bath.
After leaving the coating bath 6 the strip passes vertically through a gas wiping Etation (not shown) at which its coated surfaces are subjected to jets of wiping gas to control the thickness of the coating.
The coated strip is then passed through a cooling section 7 and subjected to forced cooling.
The cooled, coated strip, which typically is minimum spangle strip, is then passed through a rolling WO 2004/083480 PCT/AU2004/000345 section 8 that conditions the surface of the coated strip.
The coated strip is thereafter coiled at a coiling station The above-described method is characterised by controlling the concentration of strontium or (ii) calcium or (iii) strontium and calcium in the aluminiumzinc-silicon alloy in the bath to be at least 2ppm, more preferably at least 3ppm, and preferably less than 150ppm and more preferably less than As is indicated above, the applicant established the importance of strontium and calcium in the course of work carried out by the applicant.
The work was carried out as part of an investigation by the applicant to identify the cause of an unexpected substantial increase in the number of the abovedescribed defects during a production phase on the aluminium-zinc-silicon alloy coating lines at the Westernport plant of the applicant. The coating lines were producing steel strip having a standard spangle coating.
The investigation was wide ranging and extensive and considered a significant number of possible causes of the surface defects before any consideration was given to the bath composition being the cause of the surface defects.
Unexpectedly, the applicant identified an absence of strontium in the molten baths in the coating lines as the cause of the sudden increase in the number of surface defects on the steel strip.
The applicant found that the onset of the substantial increase in the surface defects corresponded WO 2004/083480 PCT/AU2004/000345 11 well with a change in the composition of the molten baths in the coating lines. The company supplying the aluminium ingots used as feed material to make the molten aluminiumzinc-silicon alloy for the baths had mad.e a change to the manufacturing process for the aluminium ingots. Prior to the change, the aluminium supplied by th.e company included small amounts of strontium as a contaminant that resulted in bath concentrations of strontium estimated to be in the range of 10-18ppm. The change removed strontium altogether from the aluminium.
With reference to Figure 2, the change in the aluminium ingot feed for the molten metal for one of the lines occurred around 18 April 1995. This aluminium ingot feed was maintained until early July. T3he applicant found that there was a substantial increase in the number of surface defects in metal coated coils produced after 18 April. In order to establish the impact of bath strontium on the numbers of surface defects, the applicant decided to re-introduce strontium to the molten bath via the addition of aluminium-l0% strontium "piglets". The piglets were added to the molten bath in early July. The strontium had a dramatic impact on the number of surface defects. With reference to Figure 3, the arrow marked "Sr Added" indicates the dividing line between coated steel coils produced prior and after the addition of the piglets. It is evident from Figure 3 that there was a substantially lower number of surface defects in the coated coils produced after the addition of the piglets. Further work carried out by the applicant indicates that the bath concentration of strontium should be controlled to be at least 2ppm and more preferably at least 3ppm.
Many modifications may be made to the preferred embodiment described above without departing from the spirit and scope of the present invention.
Claims (31)
1. A method of controlling surface defects of the type described herein on a steel strip having an aluminium- zinc-silicon alloy coating with minimum spangle, as described herein, which includes the steps of: successively passing the steel strip through a heat treatment furnace and a bath of molten aluminium-zinc-silicon alloy, and: heat treating the steel strip in the heat treatment furnace; and hot-dip coating the strip in the molten bath and thereby forming a coating of the alloy on the steel strip; and which method is characterised by controlling the concentration of strontium or (ii) calcium or (iii) strontium and calcium in the molten bath to be at least 2ppm.
2. The method defined in claim 1 wherein, in a situation in which the bath contains strontium and no calcium, the method includes controlling the concentration of strontium in the molten bath to be in the range of 2- 4ppm.
3. The method defined in claim 2 wherein the concentration of strontium is 3ppm in the molten bath.
4. The method defined in claim i, wherein in a situation in which the molten bath contains calcium and no strontium, the method includes controlling the concentration of calcium in the molten bath to be in the range of 4-8ppm. The method defined in claim 4 wherein the Amended Sheet IPEMA/AU PCT/AU2004/000345 Received 6 June 2005 13 concentration of calcium is 6ppm.
6. The method defined in claim 1 includes controlling the concentration of strontium and calcium in the molten bath to be in the range of 2-12ppm.
7. The method defined in claim 1 includes controlling the concentration of strontium or (ii) calcium or (iii) strontium and calcium in the molten bath to be no more than
8. The method defined in any one of the preceding claims wherein the aluminium-zinc-silicon alloy does not contain the elements vanadium and/or chromium as deliberate alloy elements.
9. The method defined in any one of the preceding claims wherein the aluminium-zinc-silicon alloy contains magnesium. The method defined in claim 9 wherein the aluminium-zinc-silicon alloy has a magnesium concentration of less than 1%.
11. The method defined in any one of the preceding claims includes controlling the concentration of (i) strontium or (ii) calcium or (iii) strontium and calcium in the molten bath by specifying a minimum concentration(s) of strontium and/or calcium in the aluminium that is supplied to form the aluminium-zinc-silicon alloy for the molten bath.
12. The method defined in any one of claims 1 to includes controlling the concentration of strontium or (ii) calcium or (iii) strontium and calcium in the molten bath by periodically dosing the molten bath with amounts of strontium and/or calcium that are required to maintain the Amended Sheet IPEA/AU PCT/AU2004/000345 Received 6 June 2005 14 concentration(s) at a required concentration.
13. A method of controlling surface defects of the type described herein on a steel strip coated with an aluminium-zinc-silicon alloy, which aluminium-zinc-silicon alloy contains the elements strontium and/or calcium and does not contain the elements vanadium and/or chromium, which method includes the steps of: successively passing the steel strip through a heat treatment furnace and a bath of molten aluminium-zinc-silicon alloy, and: heat treating the steel strip in the heat treatment furnace; and hot-dip coating the strip in the molten bath and thereby forming a coating of the alloy on the steel strip; and which method is characterised by controlling the concentration of strontium or (ii) calcium or (iii) strontium and calcium in the molten bath to be at least 2ppm.
14. The method defined in claim 13 wherein, in a situation in which the bath contains strontium and no calcium, the method includes controlling the concentration of strontium in the molten bath to be in the range of 2- 4ppm.
15. The method defined in claim 14 wherein the concentration of strontium is 3ppm in the molten bath.
16. The method defined in claim 13, wherein in a situation in which the molten bath contains calcium and no strontium, the method includes controlling the concentration of calcium in the molten bath to be in the range of 4-8ppm. Amended Sheet IPEAIAU PCT/AU2004/000345 Received 6 June 2005
17. The method defined in claim 16 wherein the concentration of calcium is 6ppm.
18. The method defined in claim 13 includes controlling the concentration of strontium and calcium in the molten bath to be in the range of 2-12ppm.
19. The method defined in claim 13 includes controlling the concentration of strontium or (ii) calcium or (iii) strontium and calcium in the molten bath to be no more than The method defined in any one of claims 13 to 19 the preceding claims wherein the aluminium-zinc-silicon alloy contains magnesium.
21. The method defined in claim 20 wherein the aluminium-zinc-silicon alloy has a magnesium concentration of less than 1%.
22. The method defined in any one of claims 13 to 21 includes controlling the concentration of strontium or (ii) calcium or (iii) strontium and calcium in the molten bath by specifying a minimum concentration(s) of strontium and/or calcium in the aluminium that is supplied to form the aluminium-zinc-silicon alloy for the molten bath.
23. The method defined in any one of claims 13 to 21 includes controlling the concentration of strontium or (ii) calcium or (iii) strontium and calcium in the molten bath by periodically dosing the molten bath with amounts of strontium and/or calcium that are required to maintain the concentration(s) at a required concentration.
24. A method of controlling surface defects of the type described herein on a steel strip having a coating of Amended Sheet IPEA/AU PCT/AU2004/000345 Received 6 June 2005 16 an aluminium-zinc-silicon alloy that contains magnesium which includes the steps of: successively passing the steel strip through a heat treatment furnace and a bath of molten aluminium-zinc-silicon alloy, and: heat treating the steel strip in the heat treatment furnace; and hot-dip coating the strip in the molten bath and thereby forming a coating of the alloy on the steel strip; and which method is characterised by controlling the concentration of strontium or (ii) calcium or (iii) strontium and calcium in the molten bath to be at least 2ppm. The method defined in claim 24 wherein, in a situation in which the bath contains strontium and no calcium, the method includes controlling the concentration of strontium in the molten bath to be in the range of 2- 4ppm.
26. The method defined in claim 25 wherein the concentration of strontium is 3ppm in the molten bath.
27. The method defined in claim 24, wherein in a situation in which the molten bath contains calcium and no strontium, the method includes controlling the concentration of calcium in the molten bath to be in the range of 4-8ppm.
28. The method defined in claim 27 wherein the concentration of calcium is 6ppm.
29. The method defined in claim 24 includes controlling the concentration of strontium and calcium in Amended Sheet IFEAAU 00 the molten bath to be in the range of 2-12ppm. c-I O 30. The method defined in claim 24 includes controlling the concentration of strontium or (ii) Cl 5 calcium or (iii) strontium and calcium in the molten bath to be no more than
31. The method defined in any one of claims 24 to C- wherein the aluminium-zinc-silicon alloy does not contain the elements vanadium and/or chromium as deliberate alloy elements.
32. The method defined in any one of claims 24 to 31 wherein the aluminium-zinc-silicon alloy has a magnesium concentration of less than 1%.
33. The method defined in any one of claims 24 to 32 the preceding claims includes controlling the concentration of strontium or (ii) calcium or (iii) strontium and calcium in the molten bath by specifying a minimum concentration(s) of strontium and/or calcium in the aluminium that is supplied to form the aluminium-zinc- silicon alloy for the molten bath.
34. The method defined in any one of claims 24 to 32 includes controlling the concentration of strontium or (ii) calcium or (iii) strontium and calcium in the molten bath by periodically dosing the molten bath with amounts of strontium and/or calcium that are required to maintain the concentration(s) at a required concentration. The method defined in any one of claims 24 to 34 wherein the aluminium-zinc-silicon-magnesium alloy coated steel strip is a minimum metal coated spangle strip, as described herein. N:\Melbourne\Cases\Patent\48000-48999\P48877 AU l\Spccis\Sr Ca Addition Clean- amended ,doc 29/10/08 PCT/AU2004/000345 Received 6 June 2005 18
36. A steel strip having an aluminium-zinc-silicon alloy coating with minimal spangle produced by the method defined in any one of claims 1 to 12.
37. A metal coated steel strip produced by the method defined in any one of the claims 13 to 34. Amended Sheet IPEA/AU
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AU2004221793A AU2004221793C1 (en) | 2003-03-20 | 2004-03-19 | A method of controlling surface defects in metal-coated strip |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AU2003901424 | 2003-03-20 | ||
| AU2003901424A AU2003901424A0 (en) | 2003-03-20 | 2003-03-20 | A method of controlling surface defects in metal-coated strip |
| AU2004221793A AU2004221793C1 (en) | 2003-03-20 | 2004-03-19 | A method of controlling surface defects in metal-coated strip |
| PCT/AU2004/000345 WO2004083480A1 (en) | 2003-03-20 | 2004-03-19 | A method of controlling surface defects in metal-coated strip |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| AU2004221793A1 AU2004221793A1 (en) | 2004-09-30 |
| AU2004221793B2 true AU2004221793B2 (en) | 2009-01-08 |
| AU2004221793C1 AU2004221793C1 (en) | 2023-09-28 |
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| AU2004221793A Expired AU2004221793C1 (en) | 2003-03-20 | 2004-03-19 | A method of controlling surface defects in metal-coated strip |
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| AU (1) | AU2004221793C1 (en) |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4456663A (en) * | 1981-12-02 | 1984-06-26 | United States Steel Corporation | Hot-dip aluminum-zinc coating method and product |
| US5217759A (en) * | 1990-04-13 | 1993-06-08 | Centre De Recherches Metallurgiques-Centrum Voor Research In De Metallurgie | Process for the continuous dip coating of a steel strip |
| JP2002241917A (en) * | 2001-02-14 | 2002-08-28 | Sumitomo Metal Ind Ltd | HOT DIP Al-Zn BASED ALLOY PLATED STEEL SHEET HAVING EXCELLENT APPEARANCE AND PRODUCTION METHOD TEHREFOR |
-
2004
- 2004-03-19 AU AU2004221793A patent/AU2004221793C1/en not_active Expired
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4456663A (en) * | 1981-12-02 | 1984-06-26 | United States Steel Corporation | Hot-dip aluminum-zinc coating method and product |
| US5217759A (en) * | 1990-04-13 | 1993-06-08 | Centre De Recherches Metallurgiques-Centrum Voor Research In De Metallurgie | Process for the continuous dip coating of a steel strip |
| JP2002241917A (en) * | 2001-02-14 | 2002-08-28 | Sumitomo Metal Ind Ltd | HOT DIP Al-Zn BASED ALLOY PLATED STEEL SHEET HAVING EXCELLENT APPEARANCE AND PRODUCTION METHOD TEHREFOR |
Also Published As
| Publication number | Publication date |
|---|---|
| AU2004221793A1 (en) | 2004-09-30 |
| AU2004221793C1 (en) | 2023-09-28 |
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