Provisional Application Serial No. 60/053,787, filed July 25,1997.

INTRODUCTION This invention relates to spray-coating of heavy-gauge steel strip with temperature-controlled metal particulate, prior to cold-rolling gauge reduction to a thickness desired for commercial fabrication of cold-reduced flat- rolled steel. And, in one of its more specific aspects, is concerned with correlating quantitative metallic coating with selected cold-rolling gauge-reduction to produce precoated flat-rolled mild steel of suitable thickness gauge and substrate characteristics for commercial fabrication of flat-rolled steel product.

BACKGROUND Tonnage production of flat-rolled steel with a protective metal surface coating has been significantly limited to Tin Mill Product or Sheet Mill Product carried out in complex continuous-strip processing lines by electrolytic technology or hot-dip technology, respectively. And, such protective coating has been carried out substantially at a finish thickness gauge for the strip.

SUMMARY OF THE INVENTION The metal spray-coating of the invention is carried out on heavy-gauge steel substrate. Molten metal is atomized in preparing for particulate-metal spray-coating, which is carried out under controlled atmosphere and controlled temperature conditions enabling coating of flat- rolled steel with selected metals and alloys not previously available for commercial flat-rolled steel production,.

Spray-coating and subsequent processing are carried out so as to sustain desired mechanical properties of the steel substrate for fabrication of flat-rolled steel product when spray-coating lower melt temperature metals or alloys; or, to permit subsequently establishing desired mechanical properties in the steel substrate when spray-coating higher melt temperature metals or alloys.

The above and other advantages and contributions are set forth in more detail in describing the invention with references to the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a box diagram for describing processing of the invention including surface preparation and particulate-metal spray-coating of heavy-gauge mild steel substrate, and subsequent processing to produce corrosion- protected flat-rolled steel at a selected gauge desired for commercial fabrication; FIG. 2 is a schematic general arrangement view for describing sequential stages for continuous-line production of metal spray-coated flat-rolled steel strip in accordance

with the invention; FIG. 3 is a schematic view, partially in cross section, for describing processing steps and apparatus of the invention for atomizing molten metal and separately spray-coating each surface of heavy-gauge steel strip, while moving horizontally, including subsequent processing with cold-rolling to decrease thickness gauge of the coated substrate; FIG. 4 is a schematic view, partially in cross section, for describing processing steps and apparatus of the invention which enable dual coating of each surface of heavy-gauge continuous-strip steel, while moving vertically, followed by selective subsequent processing including cold-rolling reduction of precoated flat-rolled steel-to desired fabricating gauge; FIG. 5 is an enlarged schematic cross-sectional view for describing atomizing of molten metal for particulate- metal spray-coating of heavy-gauge steel substrate in accordance with the invention; FIG. 6 is a cross-sectional view for describing particulate-metal spray-coated heavy-gauge mild steel of the invention; FIG. 7 is a cross-sectional view for describing cold- rolled particulate-metal spray-coated mild steel of the invention; FIG. 8 is a cross-sectional view for describing multi- layer particulate-metal spray-coated heavy-gauge mild steel of the invention;

FIG. 9 is a cross-sectional view, with a portion in enlarged cross section, for describing another embodiment of the invention, and FIG. 10 is a cross-sectional view, with a portion in enlarged cross section, for describing a further embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION Coating practices available in the steel industry for large scale production of cold-rolled steel for commercial fabrication of home appliance shells, architectural and building construction components and accessories, automotive sheet metal, can stock, and like flat-rolled mild steel, have been significantly limited to processing finish-gauge flat-rolled steel in continuous-strip electrolytic metal-plating lines or continuous-strip hot- dip metal coating lines.

The present invention is concerned with: (a) coating mild steel (having a carbon content of about 0.2% C to about. 25% C, which includes so-called low- carbon steel, (b) providing new combinations of flat-rolled steel coating steps and apparatus (i) for protecting flat-rolled steel product, (ii) for coating metals or alloys not previously contemplated for large scale commercial production of coated flat-rolled steel, and (iii) for cold- rolling of corrosion-protected heavy gauge mild steel strip to a thickness gauge desired for commercial fabrication.

Referring to FIG. 1, heavy-gauge steel substrate 14 is

provided as hot-rolled steel strip having a thickness gauge in the range of about point zero twenty-five inch (. 025", . 648mm) to about point twenty-five inch (. 25", 5.84mm), or as continuously-cast thin steel strip, in a thickness range from about point two inch (0.2", 5.08mm) to about point five inch (0.5", 10.16mm). Edge trimming of substrate 14 is carried out at station 16. Temper rolling (skin pass) at station 18 improves substrate flatness and presentation of substantially-planar extended-area surfaces, which can facilitate uniform spray-coating.

Surface preparation preferably includes surface cleansing carried out at station 20 and removal of surface oxidation at station 22 in order to augment adhesion of particulate-metal spray-coating. Dislodging of continuous- casting scale or hot-rolling mill scale can be carried out by shot blasting, which can also be used for removal of surface oxidation. Separation of contaminating particulate from surface cleansing liquids, as disclosed in co-owned and copending application Serial No. 08/794,783, entitled CONTINUOUS PARTICLE SEPARATION OPERATION, filed 2/3/97, can facilitate adequate continuous-strip surface cleansing.

Removal of surface oxidation is preferably augmented by "pickling"with an acidic liquid or a chemically-reducing atmosphere.

Heavy-gauge steel strip is directed along controlled atmosphere passage 24 (FIG. 1) into temperature conditioning station 26 prior to introduction into particulate-metal spray-coating station 28. A

substantially uniform temperature is established across the steel substrate thickness and width for spray-coating; the objective is to enhance adherence of the particulate-metal as spray-coating takes place.

Controlled atmosphere for coating, referred to in relation to FIGS. 1-5, can be a non-oxidizing or deoxidizing atmosphere. Substrate surface preparation is carried out for purposes of increasing receptivity for particulate metal spray-coating and, also, to facilitate adherence of such sprayed metal. A controlled atmosphere is preferably used for processing after removal of surface oxidation at 22, e. g. in passage 24 of FIG. 1, during substrate temperature conditioning (26), particulate-metal spray-coating (28), during subsequent heat treatment. (30) and, also, within passage means designated 31,33 in FIG.

1; and can be used in passage 35. That is, exposure of a substrate surface, or coated surface, is limited to a controlled atmosphere in circumstances where surface oxidation could be detrimental to subsequent processing.

Preferably, both extended-area planar surfaces of the heavy-gauge steel strip are prepared for protection.

Substrate thickness and the thickness of particulate-metal spray-coating are correlated at a ratio of about ten to one, per surface, in order to sustain surface protection during cold-rolling gauge-reduction of the invention.

Heat treatment of the coated substrate at station 30 in FIG. 1 is preselected to augment surface-bonding by inter-migration of metal atoms. Also, cold-rolling gauge-

reduction of the coated heavy-gauge steel strip, carried out at 32, can augment such migration.

Surface passivation for selected metal spray-coatings, such as tin or zinc, is carried out after cold-rolling gauge-reduction at station 38 in FIG. 1; the objective of the surface passivation is to provide for extended storage and/or for packaging preparation at station 40.

Cold-rolling gauge-reduction at station 32 is correlated based on selected coating metal (s) and coating thickness so as to produce desired coating characteristics.

Coating metal selection can also facilitate later heat treatment to control desired mechanical characteristics of the substrate (such as ductility) for fabrication of the cold-rolled precoated steel. The coated flat-rolled steel can be coiled at full width, or slit into narrow widths for coiling in continuous-length, or cut into sheets for packaging at station 40.

In FIG. 2, heavy-gauge strip from supply coils 42 and 43 is fed into station 44 for shearing, lateral edge trimming, and welding into a continuous-length. Roll stand 50 helps to provide substantially-planar surfaces for the heavy-gauge continuous-length steel strip.

Removal of continuous-casting scale (or hot-rolling mill scale) is carried out at surface preparation station 52. The continuous-strip substrate is directed through atmosphere passage 53 which can be atmosphere controlled for surface oxide removal at station 56. Atmosphere control is preferably maintained in passage 57 leading into

station 58; the latter station provides for substantially uniform temperature control throughout strip thickness and across full strip width.

Molten metal is atomized to provide for particulate- metal spray-coating in atmosphere-controlled station 60.

Such uniform temperature control and spray-coating can be combined in a single temperature and atmosphere controlled enclosure. The temperature of the substrate is correlated with selection of particulate-metal, and its temperature, for spray-coating.

Controlled atmosphere protection can continue in passage 61 (FIG. 2) to protect a substrate surface, or coated metal surface, from ambient atmosphere prior to entry into coiling preparation station 62. The latter station (62) can include initiating heat treatment for diffusion bonding at the interface between the steel and the selected metal coating. Passivation for extended storage protection of a surface which has not been metal spray-coated, or for protection of one or more surfaces spray-coated with a selected metal (such as tin or zinc) is preferably carried out at 63 before forming coil 64.

Referring to the particulate-metal spray-coating embodiment of FIG. 3, surface-prepared heavy-gauge steel strip 65 is directed into a controlled atmosphere enclosure 66, shown in interrupted lines; such enclosure can be subdivided horizontally for spray-coating each surface at a selected temperature, during horizontal travel of such continuous strip. Substrate temperature is controlled

within enclosure 66 at station 67. Molten metal from tundish 68, under control of valving and molten metal atomizing structure at 69, provides for particulate-metal spray-coating of a single planar surface (70).

As taught herein, when spray-coating metals having a melt temperature above 2000°F, such as nickel alloys at about 2350°F to about 2650°F, austenitic and ferritic stainless steels having a melt temperature of about 2500°F to about 2800°F, or titanium alloys having a temperature of about 3000°F, the temperature of heavy gauge steel strip is controlled such that the substrate acts as a heat sink for controlled solidification/cooling of such particulate-metal as spray-coated.

In a preferred practice with medium melt temperature metals, such as copper and magnesium/aluminum alloys having a melt temperature range of about 1500°F to about 1980°F, the steel strip can be selected at a temperature which is approximately the melt temperature of the selected metal.

With lower melt temperature metals, such as tin or zinc in a range of about 400°F to about 800°F, a steel strip temperature can be selected in a range of about the melt temperature for the coating metal to about fifty degrees Fahrenheit (50°F) above such melt temperature; the latter can facilitate surface bonding.

Also, cooling of spray-coated metal can be augmented by directing incoming controlled atmosphere onto the substrate, for example at 72, prior to passage around roll 74. A preliminary"skin-pass"for compaction and improved

uniformity of the coating metal is carried out at station 75.

Selective use of the apparatus of FIG. 3 provides for horizontal travel and. metal spray-coating of a single surface. Also, the remaining surface 76 can be particulate-metal spray-coated with metal from tundish 68 under control of molten metal valving and atomizing structure located at 77. Temperature control of the metal in tundish 68 is carried out by heating means, such as induction coils 79. Sprayed metal on surface 76 can be further cooled, if required, at blower station 82 before passage around roll 83.

Another arrangement for the structures of FIG. 3 comprises separating tundish 68 into two separate metal supplies, each with a separate heating coil, and separating the controlled atmosphere enclosure 66 to have a separate substrate temperature and atmosphere control for surface 76, so as to enable coating with a differing metal having properties which can be correlated with those of the metal coated on surface 70.

Particulate-metal, as oversprayed along edges of the heavy-gauge steel substrate, is collected at station 84 (FIG. 3); station 84 can also be subdivided if differing metals are spray-coated on each surface, as described earlier. And"skin rolling"for augmenting surface uniformity of spray-coating metal, and compaction of the coating metal can be carried out at roll stand 85.

In FIGS. 3 and 4, particulate-metal spray-coating is

described in terms of a moving steel substrate; in practice, cut sheets of substrate can be spray-coated with particulate-metal by moving spray-coating nozzle (s). In either case, selecting relative rates of movement between the substrate and spray nozzle (s) comprises one control measure for obtaining desired metal spray-coating weight; and, selection of flow rate of the molten metal being atomized comprises another measure for coating weight control.

In a specific embodiment comprising a particulate- metal spray-coated galvanized product, mild steel strip is selected with a thickness, for example, in a range of about . 025" (. 625mm) to about 0.5" (12.5mm); and, molten galvanizing spelter (zinc, aluminum, silicon and minor percentages of other metals) is spray-coated in a range above 0.60 oz/ft2 to approximately 2.50 oz/ft2 (both surfaces). The 0.60 oz/ft2 metal spray-coating provides a thickness of about 0.0005"on a single surface; 2.50 oz/ft2 (both surfaces) provides a thickness of about 0.0022"on each surface.

The percentage aluminum in such galvanizing spelter is selected to prevent undesirable alloying of zinc with the steel substrate. Also, zinc and aluminum, along with minor <BR> <BR> percentages of other metal constituents, comprise a GALFAN° coating, while higher percentages of aluminum, up to about seventy percent (700) with the remainder zinc, comprise a GALVALUME coating. Such selections help to achieve selected coating characteristics, such as adhesion and

coating ductility for cold-rolling, which also contribute to intended product fabrication.

In a specific embodiment, a nominal starting gauge of 0.25" is selected for, the heavy-gauge hot-rolled steel strip, and molten galvanizing spelter is atomized for particulate-metal spray-coating to a selected thickness of about twelve hundredths of an inch (. 0012",. 03mm) on each surface of the steel substrate. Following a diffusion heat treatment, as shown in FIG. 3, a thickness gauge-reduction of thirty-three percent, carried out in subsequent cold- rolling, produces a cold-rolled steel substrate thickness of about point seventeen inch (. 17") with a galvanized coating. thickness of about eight thousandths of an inch (. 0008",. 02mm) on each surface.

In practice of the invention, tandem mill cold- reduction of spray-coated hot-rolled steel strip is selected within ranges partly determined by end product uses; thin-gauge flat-rolled steel products, such as can stock, utilize eighty to ninety percent gauge-reduction; about forty-five to seventy-five percent gauge-reduction is utilized for coated flat-rolled steel product for vehicular and home appliance uses. The correlation taught herein relates to achieving, or maintaining, desired substrate mechanical properties for particular uses and to sustaining a desired protective surface coverage of the spray-coated metal during selected cold-rolling gauge-reduction (s) so as to provide desired coating weight for fabricated product uses, or to provide for welding to form tubing. Examples

and ranges for hot-rolled steel strip and continuously-cast thin steel strip, and for spray-coating with particular metals and/or alloys, are considered in later descriptions relating to FIGS. 6-10., In addition to heat conditioning to provide a substantially uniform temperature throughout the thickness and across the width of the heavy-gauge substrate for the particulate-metal spray-coating, supplemental heat treatment (s) for the particulate-metal spray-coated substrate can be selected and carried out, as shown and described in relation to FIGS. 3,4. In FIG. 3, particulate-metal spray-coated steel strip 76 is skin- rolled at station 85 and directed around roll 87, into diffusion heat treatment station 88, for augmenting metallurgical bonding by migration of metal atoms of the spray-coated metal (s) and the steel substrate. The particulate-metal spray-coated heavy-gauge steel substrate is then cold-rolled in tandem mill 90 to produce a gauge desired for fabricating cold-reduced flat-rolled mild steel. The metal coated cold-rolled steel can be delivered as coil 92. Properly correlating spray-coating temperatures, cold-rolling gauge-reduction (s) and other diffusion heat treatments, as disclosed, provides desired coating adhesion, coating thickness for desired corrosion protection and, also, for mechanical properties of the steel substrate desired for fabrication. Mechanical properties, as referred to herein, describe the behavior of materials under mechanical usage, including, e. g. tensile

strength, hardness and ductility.

Surface preparation, coating and subsequent processing of FIG. 4, enable separately-applied particulate-metal spray-coatings on each surface of heavy-gauge substrate 94.

The arrangement of FIG. 4 facilitates particulate-metal spray-coating while the substrate is moving substantially vertically, by providing for dual spray-coatings on each substrate surface, or for spray-coating of metals under differing temperature conditions for each coating, and by providing a separate enclosure for spray-coating from each of a pair of molten metal tundishes. Separating a first coating operation from a second coating operation can be correlated for particulate-metal spray-coating of differing metals in each separate station; differing melt temperatures for each molten metal tundish, relative to the substrate, can be taken into account by a separate temperature-controlled enclosure for each separate coating operation.

In a specific embodiment of FIG. 4, heavy-gauge steel substrate 94 is spray-coated with particulate-metal on surface 95 and/or 96, with molten metal supplied from tundish 97; molten metal flow and atomizing nozzle structures at 98 and/or 99 are utilized on each respective surface. A nozzle structure for atomizing molten metal and spraying particulate-metal is shown schematically in FIG.

5. Solidification of molten metal, as sprayed, within controlled-atmosphere and controlled-temperature enclosure 100, can be augmented by controlling the strip temperature

(which has a melt temperature of about 2760°F) to act as a heat sink for spray metals which have a melt temperature above about 2000°F to about 3000°F; for example, nickel alloys at about 2500°F, stainless steels at about 2800°F, and titanium at about 3100°F. Or, solidification of the sprayed metal can be augmented by temperature control of incoming controlled atmosphere discharge onto one or both surfaces of the coated substrate, for example at level 101, prior to passage through a coated metal"skin-pass"carried out at station 102.

In FIG. 4, coated substrate 103 is directed around bottom roll 104 toward a further coating pass; controlled atmosphere enclosure 100 can be subdivided to provide a differing temperature. Molten metal overspray at edges of metal substrate 103 is accumulated at collector station 105. Coated substrate 103 travels along a travel path, within enclosure 100, toward roll 106 and, then, around roll 107 into coating position by passage between atomizing spray nozzle structures at 108,109; such structures include molten metal flow control valving means. Molten metal from tundish 110, as atomized, provides for particulate-metal spray on either or both extended area surfaces 111,112.

Spraying differing metals and separate control of substrate temperature, as mentioned above, can be provided by dividing chamber 100 into two chambers and providing intermediate augmented heating or cooling, as determined from selection of the coating metals. The cooling of

coated substrate can be augmented at station 114, before being directed to coated metal compaction roll station 115.

The spray-coated substrate of FIG. 4 is directed around bottom roll 116 for exit from the controlled atmosphere enclosure 100. Any overspray of molten metal from such second coating station, around edges of metal substrate 118, is accumulated at collector station 119 for recycling or other use.

In FIG. 4, surface protected steel substrate 118 is further processed selectively by being directed along pass line 120 or along pass line 121 (as shown in interrupted lines).

Heavy-gauge substrate, as spray-coated, is directed in pass line 120 for diffusion heat treatment to augment migration of atoms, at the interface of the steel substrate and the spray-coated metal (s), carried out at station 122.

Such diffusion heating can be carried out at a temperature level to avoid alloying of a coating metal with the steel substrate; for example, when alloying of a particular spray-coated metal with the substrate would be detrimental to adhesion of that spray-coated metal. However, melting of dual coated metals on a surface can be implemented if alloying of those coating metals is desired to provide a particular alloy coating, such as brass. After diffusion heat treatment, the coated substrate is directed into tandem cold-rolling mill 124, from which the cold-reduced flat-rolled steel is formed into coil 126.

The alternate pass line indicated by interrupted line

121 of FIG. 4 provides for direct entry of the coated substrate into tandem cold-rolling mill 128 which, dependent on coating metals, can initiate desired metal atom migration. Cold-rolling gauge-reduction is carried out at tandem mill 128 prior to diffusion heat treatment at station 132 of thinner coating metal layers. Diffusion heat treatment can be augmented by providing for coiling the diffusion-heated cold-reduced strip to achieve heat soaking of the spray-coated metal in coil 134.

Such alternative path provides for augmenting diffusion of substrate steel and spray-coated metal (s) at each interface thereof. Metal atom migration, as augmented by heating, and exhibits a time/temperature relationship.

Selection of a diffusion temperature is correlated with the melt temperature of the coating metal (s) for diffusion-type metallurgical bonding while avoiding alloying where undesirable.

Spray-coating differing particulate-metals on steel substrate should take into account the desirability for unfettered recycling; for example, a tin coating should not be used with an aluminum coating.

Molten metals preferred for spray-coating of continuously-cast steel strip or hot-rolled steel substrate, in accordance with the invention, include: brass, stainless steel, bronze, tin, copper, titanium, Mg/Al alloys, zinc/Al spelter, and nickel.

Steel substrate heating is selected in a range of about 450°F (121°C); for example, for spray-coating tin, to about 2400°F (1300°C) for short intervals, for spray- coating stainless steels or titanium. Preferably, substrate temperature is selected for the higher melt temperature coating metals designated above to enable the substrate to act as a heat sink for graduated solidification of such spray-coated metals, in order to produce metal coating in a crystalline state rather than an amorphous state. Lower melt temperature coating metals can be alloyed with the substrate by maintaining the substrate at a temperature higher than the melt temperature for the coating metal.

Spray-coating of a metal having a melt temperature approaching, or higher than, the melt temperature (about 2760°F) of mild steel, such as titanium (about 3100°F), is carried out by selection of a heavier-gauge steel substrate and controlling its temperature so as to avoid any significant melting of the substrate surfaces during spray- coating.

Correlation, as taught herein, also coordinates coating thickness of the particulate-metal spray-coating with the thickness gauge for the hot mill steel strip, or for the continuously-cast thin steel strip, taking into consideration desired control of substrate mechanical characteristics, such as ductility, during post-coating cold-rolling gauge-reductions. Correlated selections are made to permit tandem mill cold-rolling gauge-reduction (s),

over a desired range, so as to produce steel substrate within selected ductility and tensile strength ranges for particular product fabrication. For example, can stock fabricating by processes disclosed in co-owned and copending U. S. patent applications, enables can part fabrication at tensile strengths in a range of seventy-five to one-hundred ten ksi. Specific embodiments are set forth during description relating to accompanying FIGS. 6-10.

In the molten metal flow regulated venturi-atomizing apparatus shown schematically in FIG. 5, a controlled atmosphere (136), which is pressurized, is directed, as indicated, into venturi nozzle structure 137. Molten metal is introduced into venturi 137, with a downwardly-oriented component of movement, and in transverse relationship to the flow of atomizing gas 136, by means of molten metal supply conduit (s) 138. The molten coating metal, as atomized, is distributed, as indicated, across the cross sectional area of nozzle 139 which directs particulate- metal toward a steel substrate (not shown in FIG. 5) for spray-coating. Molten metal atomizing apparatus, developed for forming solid metal billets by Osprey Metals Limited, West Glamorgan, United Kingdom, have been adapted by the present invention for spray-coating of steel substrate as taught herein, followed by cold-reduction-to produce precoated cold-reduced flat-rolled steel.

FIG. 6 shows heavy-gauge steel substrate 142 spray- coated with metal, as atomized using apparatus shown in FIG. 5, on each of its planar surfaces to produce

particulate-metal spray-coated surfaces 143,144. Each surface can be spray-coated to a substantially uniform thickness; or the surfaces can be selectively differentially coated. FIG. 7 shows flat-rolled steel 146, with cold-rolled precoated surfaces 147,148, after cold- rolling gauge-reduction of the spray-coated heavy-gauge substrate of FIG. 6. Spray-coating to differing coating weights on each surface can be used, for example, to produce a tin coated flat-rolled steel with an eleven mil (. 011") thickness having a tin coating weight on each surface selected in the range of about five tenths pound per base box (. 5 #/bb) to about two point five pounds per base box (2.5 #/bb).

Specific stainless steel and nickel alloy embodiments can be selected to correlate selected properties, such as coefficients of expansion of the coating metal (alloy) and properties of the steel substrate, over a selected temperature range where desired for use of certain products fabricated from precoated flat-rolled steel.

Desired spray-coating metal thickness is controlled by correlating molten metal flow rates and relative movement rates between the particulate-metal spray nozzle and the heavy-gauge hot-rolled, or continuously-cast, thin steel strip. Spray-coating of a zinc spelter on heavy-gauge steel hot-rolled strip scheduled for a twenty-five percent (1.25: 1) cold reduction is correlated as follows : to achieve an ounce and a quarter per square foot (1.25 oz./ft2) total coating weight (both surfaces), approximately

0.832 oz./ft2 is initially spray-coated on each surface of a steel strip having a nominal thickness gauge of one-tenth inch (0.1"). A zinc spelter is chosen with percentage aluminum to substantially avoid alloying of the zinc with the steel substrate. Each substrate surface is particulate-metal spray-coated with such a zinc spelter of about fourteen mils (. 0014") thickness. A twenty-five percent (25k) cold-rolling gauge-reduction provides a steel substrate thickness of about seventy-five mils (. 025") with a zinc spelter spray-coating thickness on each surface of about one mil (. 001").

Assuming linear movement of the steel strip at a rate of ten ft/min, and substrate width of three feet, the flow rate of molten metal for particulate-metal spray-coating substrate should be about twenty-five ounces per minute (25 oz/min) of spray-coated zinc, per surface, to achieve a zinc spelter coating thickness of fourteen mils (0.0014") which corresponds to point eight hundred thirty-two ounce per square foot (0.832 oz./ft2) per surface. The flow rate of particulate-metal spray required for both surfaces, combined, is about fifty ounces per minute (50 oz/min or 0.833 oz/sec). Increasing aluminum content significantly above the minimum required, to avoid an undesirable level of alloying, and to provide increased coating ductility, decreases the weight of the coating metal without significantly decreasing the thickness of the coating metal.

Spray-coating molten stainless steel particulate to

achieve a coating thickness of about nine mils (0.009") of stainless steel on each surface corresponds to about six ounces per square foot per surface. Such spray coating is carried out at a line speed of about five feet per minute.

When metal spray coating a substrate having a width of about three feet, the flow rate of a molten stainless steel, per surface should be about ninety ounces per minute.

In FIG. 8, each surface of heavy-gauge steel substrate 150 is spray-coated, as shown, with a pair of spray-coating metal layers 151,152 and 153,154, respectively. In practice, one or both planar surfaces can be metal spray- coated with the same metal or a pair of differing metals and can be metal spray-coated to uniform thickness or differential thicknesses.

FIGS. 9 and 10 depict embodiments which provide for chemical treatment passivation after cold-reduction. A single steel substrate surface, which has not been particulate-metal spray-coated, is passivated in FIG. 9.

In FIG. 10, each cold-reduced surface has been spray- coated with a metal, such as tin or zinc; then, such spray- coated metal surfaces are passivated so as to provide advantages for coiling, shipment and extended storage.

Chemical passivation treatments are preselected dependent on the coating metal.

In FIG. 9, spray-coated substrate 160 is coated with metal spray-coat 162 on one surface with surface passivation coat 164 on its remaining surface. Passivation

treatment is selected dependent on the product and use. A chrome-based chemical passivation treatment, such as a cathodic di-chromate treatment, applied from about fifty to about seven hundred fifty yg/ft2 to such surface, is preferred for a mild steel surface. A polymer coating is subsequently applied to such passivated surface to enable cold-reduction of precoated heavy-gauge steel substrate of FIG. 9. Such polymer coating and cold-rolling of polymer- coated passivated steel is described in more detail in U. S. patent application Serial No. 08/887,832, filed 07/03/97, which is incorporated herein by reference.

In FIG. 10, cold-reduced steel substrate 166 includes precoated particulate-metal on each surface, coating metal 168,170, respectively, as applied before cold-reduction.

Each such particulate-metal spray-coated surface is then treated with passivation coating 172,174, respectively.

To facilitate long-term storage, a selected passivation coating for tin surfaces comprises a chrome-oxide chemical treatment; a phosphorous-based passivation treatment is preferred for storage of cold-reduced zinc-based particulate-metal spray-coated surfaces.

While specific materials, steps, apparatus, thickness gauges and other values have been set forth for purposes of describing the invention, it should be recognized that, in light of the above teachings, it is possible to modify certain of the above specifically disclosed data or steps without departing from the principle (s) of the invention; therefore, reference shall be made to the appended claims for purposes of determining the scope of the present invention.