DIPPED GALVANNEAL STEEL SHEET

Background of the Invention

1. Field of the Invention

The invention relates to the fabrication of steel sheet. More particularly, the invention relates to optimizing the fabrication of coated steel sheet.

2. Description of the Related Art

When steel sheet is fabricated, oftentimes it is coated. The coating and the steel sheet create phases throughout the coating and out to the surface thereof. Some of the phases are acceptable, while others are less so due to the friction created by the phases or the less efficient post fabrication treatment that may be required.

Systems currently used include fluorescence spectroscopy, Glow Discharge - Optical Emission Spectroscopy (GD-OEM), Laser Induced Plasma Spectroscopy (LIPS) and Constant Potential Electrolysis. These systems are deficient in that they can only be used off-line away from actual production. X-ray diffraction methods have been tested on zinc-coating lines but are not widely used because of cost as well as a lack of worldwide availability.

Summary of the Invention

A method measures the surface conditions of a steel sheet during production of the steel sheet. The method includes transmitting a beam of light at a surface of the steel sheet to create a reflected beam of light. The reflected beam of light is received and an image is created of the surface of the steel sheet from the reflected beam of light. The image of the surface of the steel sheet is compared against a characterization database. The production of the steel sheet is modified to change the surface of the steel sheet when the image of the surface of the steel sheet contains structures that are not considered desirable. Brief Description of the Drawings

Advantages of the invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

Figure 1 is a schematic of a steel sheet fabrication assembly incorporating one embodiment of the invention;

Figure 2 is a logic chart of one embodiment of the inventive method;

Figure 3 is an SEM photograph of a surface of steel sheet; Figure 4 is an SEM photograph of a second surface of steel sheet;

Figures 5 a and 5b are exemplary images created by the inventive method;

Figures 6a through 6d are graphic representations of data collected using the inventive method.

Detailed Description of the Invention A method is disclosed for measuring the surface conditions of steel sheet.

More specifically, the method quantifies the crystallographic phase(s) and amorphous phase(s) in a coated surface on steel sheet. Surface conditions are very important in the production of steel sheet as the interface with a coating will determine how the steel sheet performs when it is being processed into its end product. The method is capable of measuring the surface conditions during the fabrication of the steel sheet to provide sufficient feedback to minimize waste.

Referring to Figure 1 , a sheet steel temper mill facility is generally indicated at 10. From the orientation of Figure 1, steel sheet 12 enters the temper mill facility 10 from the left and exits the right. When the steel sheet 12 enters the temper mill facility 10, it has already been hot rolled and coated to form galvanneal. The steel sheet 12 is immediately received by a deflector roll 14 to redirect the steel sheet 12 interim direction that facilitates its travel through the temper mill facility 10. A coating gauge 16 measures the thickness of the zinc coating on a surface of the steel sheet 12. The steel sheet 12 is then received by a first entry bridle roll 18. The first entry bridle roll 18 is matched up with a second entry bridle roll 20. The first 18 and second 20 entry bridle rolls control the tension of the steel sheet 12 as it passes through this portion of the temper mill facility 10. A tensiometer roll 22 is disposed between the first 18 and second 20 entry bridle rolls and provides a means by which the tension in the steel sheet 12 between the first 18 and second 20 entry bridle rolls may be measured.

As the steel sheet 12 leaves the second entry bridle roll 20, it enters the temper mill 24. The temper mill 24, with a wet rolling 26 disposed therebelow, is employed to improve the surface finish of the steel sheet 12. The temper mill 24 improves the surface finish, shape, flatness and yield strength of the steel sheet 12. It is in the temper mill 24 that many of the final characteristics of the coating of the steel sheet 12 will be formed per the design parameters required of the steel sheet 12.

Once the steel sheet 12 exits the temper mill 24, it is cleaned at a cleaning station 28 and dried at a drying station 30. A roughness gauge 32 generally measures the roughness of the steel sheet 12 after it has been processed by the temper mill 24. The roughness gauge 32 is disposed adjacent an interim bridle roll 34. A tension leveler 36 adjusts the tension of the steel sheet 12 as it is passing through this portion of the temper mill facility 10. A blowing station 38 removes any debris from the steel sheet 12 that may have collected on the surface during the processing of the steel sheet 12. The steel sheet 12 then exits through a pair of exit bridal roles 40, 42, whereafter the steel sheet 12 is redirected using an exit deflector roll 44.

Disposed directly above the second entry bridle roll 20 is an optical detection assembly 46. The optical detection assembly 46 emits or transmits electromagnetic radiation, graphically represented by rays 48, directly at the steel sheet 12 as it passes over the second entry bridle roll 20. The optical detection assembly 46 receives the emitted electromagnetic radiation as it is reflected off the steel sheet 12 back toward the optical detection assembly 46. In one embodiment, the optical detection assembly 46 emits and receives electromagnetic radiation in the visible light spectrum.

Referring to Figure 2, the inventive method is generally indicated at 110. The method begins at 112. Once the steel sheet 12 enters the temper mill facility 10, the tempering of the steel sheet 12 is begins at 114. It is determined at 116 that a particular stage of production will be used as the stage for capturing surface characteristics of the steel sheet 12. It should be appreciated by those skilled in the art that a particular stage of production for the steel sheet may vary depending on the characteristics of the surface that are desired. Regardless of what stage in the process the capture of surface characteristics occurs, the capture will occur at a place where the steel sheet 12 is physically supported to avoid any dimensional variations in focal positions due to sway or slack in the steel sheet 12 as it passes through the temper mill facility 10. In the embodiment shown in Figure 1, the capture of surface characteristics takes place when the steel sheet 12 is supported by the second entry bridle roll 20.

At the particular stage, data regarding the surface of the steel sheet 12 is collected. In one embodiment, the raw data is used for calculations. In another embodiment, the data creates a three dimensional image. Regardless of what is collected, the collection of information (data or an image) is done by emitting a light at the surface of the steel sheet 12 at 118. After the emitted light 48 impinges on the surface of the steel sheet 12, it is reflected back away from the surface. This reflected light is reflected back toward the optical detection assembly 46 at 120. It is this reflected light that is used to create the image to be reviewed. In the instance of data collection, the amplitude, direction and phase of the reflected light is collected and used for analysis or to create an "image" for review by an operator.

The emitted light 48 may be of any wavelength or from any energy source suitable for the creation of the images of the surface of the steel sheet 12. A non- exhaustive list of light includes white light and filtered light. The light may be collimated, e.g., a laser, or it may be non-collimated light that is focused using a lens system. In one embodiment, a 3D noncontact optical profiler or profilometer, produced by Wyko (Model NT 1100) is used to produce the light and capture the light reflected from the surface of the steel sheet 12.

Once the light is received, an image of the surface of the steel sheet 12 is formed at 122. In one embodiment, the image is quantified by an operator viewing the image and trained in identifying certain phases of the steel coating. In another embodiment, the quantifying of the image includes measuring the structures found in the image. This step occurs at 24. Various measurements and/or parameters within the image may be used to calculate specific characteristics of the surface of the steel sheet. The height of alloy phases (the difference between the highest peak and the lowest valley) and surface areas of various phases may be used to quantify the images in a manner that will allow them to be successfully compared against the data stored in the database. Every phase will have specific measurements associated with its topographic features and it is these measurements that can be mapped to the database and used to compare the values measured using the 3D profilometer. Regardless of whether the images are viewed or whether measurements are taken, the image characteristics are then compared to a database at 126 to determine the surface characteristics of the surface of the steel sheet 112. Depending on what is being searched, a determination as to whether the measurements are within predetermined limits at 128. If yes, production continues at 130. If it is not meeting the design parameters, the method modifies the production of the steel sheet at 132, based on the comparison between the measurements taken from the image created of the surface of the steel sheet 12 and the database. The method loops back and continues to take images and calculate differences so long as the production of the steel sheet 12 continues. Referring to Figures 3 and 4, two images of the galvanneal steel sheet 12 are shown. In Figure 3, elongated structures on the surface of the galvanneal steel sheet 12 show the extensive presence of the Zeta phase on the surface of the steel sheet 12. In most instances, this is an undesirable condition and the inventive method 110 allows for the modification of the steel production to minimize the amount of Zeta phase on the steel sheet 12. In Figure 4, the muted hexagonal shapes illustrate the extensive presence of Delta phase on the surface of the steel sheet 12. In many instances, the presence of Delta phase on the coatings of steel sheet is preferred.

Referring to Figures 5a and 5b, two images created using the inventive method of surfaces of galvanneal steel sheet are shown. In Figure 5b, characteristics of a Zeta phase show that there is minimum Zeta phase present, resulting in a desirable steel sheet surface for a particular production parameter. In Figure 5 a, a large amount of Zeta phase is present resulting in a less desirable surface of the steel sheet. By identifying the condition, the presence of Zeta phase in this example, it can be determined whether the production of the steel sheet needs to be modified to enhance the characteristics of the surface of the steel sheet to meet the specifications required for the production of that particular steel sheet. It should be appreciated by those skilled in the art that the inventive method may be used to measure other phases, e.g., Gamma, Gamma- 1, Delta and Zeta phase where applicable.

Test Results Ten hot dip galvanneal steel sheet samples were imaged using a scanning electron microscope (SEM) to validate the findings of the inventive method discussed above. From the surface topography of each sample, an area fraction of zeta phase present on the surface was assigned to each sample. The samples were then analyzed via the optical surface profilometer. Thirty scans taken across representative areas of the surface were averaged for several key surface texture metrics. Examples of the key surface texture metrics include, but are not limited to, peak density, root mean square surface slope, mean summit curvature, and developed interfacial area ratio. The peak density along the X axis (Stylus X Pc), measures the number of peaks per unit length in the X direction. A peak exists when the profile intersects consecutively a lower and upper boundary level set at a height above and depth below the mean line, equal to Ra, for the profile being analyzed. A root mean square (RMS) surface slope (Sdq) comprising the surface, evaluated over all directions. The mean summit curvature (Ssc) measures the mean for various peak structures, and developed interfacial area ratio (Sdr) is expressed as the percentage of additional surface area contributed by the texture as compared to an ideal plane the size of the measurement region. A meaningful correlation was confirmed between the area fraction of Zeta phase on the surface and these key surface texture metrics.

The phases of the galvanneal steel coatings are shown in the table below and include the various phases.

A coefficient of determination , R ² , was calculated for each of the tests performed. These coefficients of determination are shown in Figures 6a through

6d.

As may be appreciated by those skilled in the art, these graphs in Figures 6a through 6d demonstrate the existence of a correlation between the tests performed and the presence of the zeta phase seen in the images captured (Figures 3 and 4). The graphs are set up to show SEM Fraction along the x-axis with 100% being 100% zeta phase present and with 0%> being 100% Delta phase present and values between 0%> and 100% identifying when combinations of the two phases are present. The highest correlation existed using the Stylus X Pc test.

The invention has been described in an illustrative manner. It is to be understood that the terminology, which has been used, is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the invention may be practiced other than as specifically described.