Slurry blasted hot rolled base hot dip aluminized steel strip

Abstract

Preparation of coated steel comprising the steps of hot or cold rolling, slurry blasting and coating. A hot or cold rolling step in which a steel ingot is rolled to form a steel strip. A slurry blasting step comprising slurry blasting at least one side of the steel strip. A coating step following slurry blasting comprising coating the steel strip with an aluminum based coating.

Description

[Technical field]

[0001] This application claims priority to U.S. Provisional Application No. 63 / 329,084, entitled "Slurry-Blasted Hot-Roll-Based Hot Dip Aluminated Steel Strip," filed April 8, 2022, the disclosure of which is incorporated herein by reference. [Background technology]

[0002] The present invention relates to aluminized carbon steel. Aluminizing can be performed on steel to coat one or more surfaces of the steel with an aluminum-based coating. Such aluminum-based coatings can be alloyed with other elements in some circumstances. For example, in a Type 1 aluminized coating, aluminum can be alloyed with silicon. Such alloying can be desirable to enhance certain mechanical properties of the coating. In other circumstances, commercially pure aluminum can be used without alloying. Such commercially pure aluminized coatings are sometimes referred to as Type 2 aluminized coatings.

[0003] In some situations, either Type 1 or Type 2 aluminized coatings with high adhesion may be desirable. While many factors can contribute to improved adhesion, surface preparation of the steel substrate is one factor that may contribute to adhesion. In hot or cold rolled steels, scale may build up on the surface of the steel during hot or cold rolling. The presence of scale on the surface of the steel substrate may generally be undesirable during aluminization, as the scale may introduce contaminants to the steel-aluminum interface, thereby preventing complete adhesion. Therefore, it may be desirable to remove scale from the surface of the hot or cold rolled steel prior to aluminization. Summary of the Invention [Problem to be solved by the invention]

[0004] One method of descaling that may be used may include pickling, in which a chemical agent is used to consume scale on the surface of the steel substrate. In some circumstances, pickling may be combined with other mechanical descaling processes such as peening, grinding, and / or others. These processes, while relatively efficient at removing scale, have a high tendency to produce uneven or non-uniform surface preparation. Therefore, it may be desirable to eliminate descaling processes such as pickling and / or mechanical descaling in favor of other processes that provide a more uniform and / or homogeneous surface preparation with efficiency comparable to pickling and / or mechanical descaling processes. [Brief description of the drawings]

[0005] [Figure 1] FIG. 2 shows the surface appearance of the aluminized coating on a first sample, which is pickled prior to aluminizing. [Diagram 2] FIG. 13 shows the surface appearance of the aluminized coating on a second sample, which is pickled prior to aluminizing. [Diagram 3] FIG. 13 shows the surface appearance of the aluminized coating on a third sample, which is slurry blasted prior to aluminization. [Figure 4] FIG. 13 shows the surface appearance of the aluminized coating on a fourth sample, which is slurry blasted prior to aluminization. [Diagram 5] FIG. 5 shows the fifth and sixth samples after performing bend adhesion testing of the aluminized coating, the fifth and sixth samples being slurry blasted prior to aluminization. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] The present invention relates to aluminized steel. Aluminized steel may be desirable because it provides corrosion resistance comparable to stainless steel at a lower cost. Additionally, aluminized steel may exhibit heat reflective properties. Thus, aluminized steel may be desirable in service environments that may be corrosive and / or hot.

[0007] Aluminized coatings may be referred to as Type 1 and Type 2 aluminized coatings. In Type 1 aluminized coatings, aluminum may be alloyed with silicon to form an aluminum-silicon alloy on one or more surfaces of the steel. Such aluminum-silicon alloys in Type 1 aluminized coatings may contain about 5 to 11% silicon and the balance of aluminum and impurities. The presence of silicon (Si) may control the formation of an intermetallic layer between the steel substrate and the coating during the hot-dip coating process. For example, the presence of silicon may contribute to retarding the growth of the intermetallic layer during the hot-dip coating process. In the as-coated state, limiting the growth of the intermetallic layer may be desirable to improve the heat resistance of the aluminized coating. Thus, in situations where heat resistance is desirable, Type 1 aluminized coatings may be desirable.

[0008] In contrast, type 2 aluminized coatings include commercially pure aluminum without additional alloying elements. Without the presence of additional alloying elements, the formation of intermetallic compound layers is less controlled during the hot dip process compared to type 1 aluminized coatings. However, without the presence of additional alloying elements, aluminized coatings are more corrosion resistant compared to type 1 aluminized coatings. Thus, type 2 aluminized coatings are desirable in situations where corrosion resistance takes precedence over heat resistance. It should be understood that aspects of the present disclosure relate to either type 1 aluminized coatings or type 2 aluminized coatings. Thus, the principles described herein can be applied to both type 1 and type 2 aluminized coatings, even when the aluminizing process is generally referred to without specific reference to type 1 or type 2 aluminized coatings.

[0009] The hot or cold rolling process can cause scale to accumulate on the surface of the hot or cold rolled steel strip. The presence of scale on the surface of hot or cold rolled steel strip prior to aluminization is generally undesirable because the presence of scale can introduce contamination into the coating itself and / or into the intermetallic layer between the steel substrate and the aluminized coating. As a result of such contaminants, the bond strength between the steel substrate and the aluminized coating can be reduced, which can result in the aluminized coating having an uneven, spotty, or poor surface quality.

[0010] Some processes for removing scale may include pickling or mechanical stripping processes. Pickling in particular may be desirable because the process can be efficiently and continuously performed in-line after hot or cold rolling and before coiling of the strip. However, due to variations in the operating conditions of the pickling process, the surface of the pickled strip may be uneven or inconsistent, even if it effectively removes scale. Such uneven or inconsistent surface treatment may be observed anywhere on the strip after coiling, although a concentration at the ends of the coil has been observed.

[0011] When the steel strip undergoes molten aluminum processing, such uneven or inconsistent conditions on the surface of the steel strip may result in an uneven or patchy aluminization coating. This uneven or patchy aluminization coating may be the result of poor wetting characteristics of the surface of the steel strip during molten aluminum processing. Therefore, some process may be desirable to improve the surface treatment of hot or cold rolled steel strip prior to molten aluminum processing.

[0012] Aspects of the present disclosure relate to the use of slurry blasting to prepare one or more surfaces of hot or cold rolled steel strip for molten aluminization. Slurry blasting is a process that involves mixing an abrasive with a pressurized fluid (e.g., water) and then directing the mixture at high velocity at the surface. Slurry blasting has not previously been used for molten aluminization due to challenges associated with the cost and time requirements of moving an entire coil of steel to perform testing. In this form, slurry blasting can be performed on hot or cold rolled steel strip at one or more points during the steel production process. For example, as described in more detail below, slurry blasting may be performed immediately after hot or cold rolling and prior to coiling. Alternatively, slurry blasting may be performed independently after coiling and prior to molten aluminization. In either case, slurry blasting may be performed in association with either Type 1 or Type 2 aluminization. Alternatively, in some versions, slurry blasting may be performed in association with other forms of coating, such as galvanization or zinc-based coatings.

[0013] In a first aspect of the present disclosure, the slurry blasting is performed in a multi-step process. In the multi-step process, a coil of hot rolled steel strip (or alternatively cold rolled steel strip) can be unwound from a wound shape to a longitudinally unwound shape. The steel strip in the unwound shape can then be subjected to slurry blasting. During the slurry blasting step, scale can be removed from one or more surfaces of the steel strip. Control of the slurry blasting process can be performed in real time by an operator. In particular, the operator can adjust operational parameters such as feed rate and pressure in real time to sufficiently remove scale from one or more surfaces of the steel strip.

[0014] After the slurry blasting process is complete, the strip can be dried and recoiled and then transferred to a hot-dip aluminizing line where the recoiled strip can be uncoiled again and subjected to hot-dip aluminizing with molten aluminum having Type 1 or Type 2 characteristics.

[0015] In some versions of the first aspect of the present disclosure, the slurry blasting process can be performed continuously. For example, unrolling of the steel strip can occur at one end of the line and rolling can occur at the opposite end of the line. The slurry blasting process can then occur between the unrolling and rolling ends of the line. In this configuration, the steel strip can be slurry blasted continuously as the coil is unrolled and rerolled simultaneously.

[0016] In a second aspect of the disclosure, the slurry blasting is performed in an integrated process (or single process). In an integrated process, the slurry blasting process can be combined with the hot-dip aluminizing process. Specifically, the steel strip can be transferred to a hot-dip aluminizing line after hot rolling (or alternatively cold rolling). Optionally, in some versions, pickling or other descaling can be performed in conjunction with hot rolling. In other versions, other forms of descaling, including pickling, can be omitted entirely.

[0017] Once the coiled steel strip is transferred to the hot dip aluminizing line, the coil may be unwound and placed into the hot dip aluminizing line. Slurry blasting may then be performed as part of a pre-cleaning process used in the hot dip aluminizing line. The slurry blasting step may be performed to remove scale from one or more surfaces of the steel strip. Control of the slurry blasting process may be performed in real time by an operator. Specifically, the operator may adjust operational parameters such as feed rate and pressure in real time to adequately remove scale from one or more surfaces of the steel strip.

[0018] After the slurry blasting step, the strip may further be fed into a molten aluminizing line to reheat the strip and subsequently immerse the strip in a molten aluminizing bath using molten aluminum having Type 1 or Type 2 properties. Once the aluminizing is complete, the coated strip may be uncoiled.

[0019] Example 1 A hot rolled steel strip coil sample was prepared. The hot rolled steel strip coil was pickled. After pickling, the steel strip was hot coated molten aluminized and then recoiled. In this example, hot coated molten aluminized refers to an aluminization process in which the steel strip is first heated to approximately the temperature of a molten aluminum bath and then the steel strip is immersed in the molten aluminum bath.

[0020] Figures 1 and 2 show the surfaces of the aluminized coating obtained after pickling treatment prior to aluminization. Specifically, Figure 1 shows a first sample in which the surface of the aluminized coating is relatively uneven, especially in the region on the left side of the page. Similarly, Figure 2 shows a second sample in which the surface of the aluminized coating is relatively uneven, especially in the region on the right side of the page.

[0021] Example 2 Additional samples of hot rolled steel strip coils were prepared. The hot rolled steel strip coils were subjected to a slurry blasting treatment. After the slurry blasting treatment, the steel strip was subjected to a hot coated hot molten aluminization treatment. The slurry blasting in this example was performed in the aluminizing line before the reheating furnace. After hot molten aluminization, the steel strip was recoiled.

[0022] 3 and 4 show the surface of the aluminized coating obtained after using slurry blasting prior to aluminizing. Specifically, FIG. 3 shows a third sample in which the surface of the aluminized coating is substantially uniform, particularly compared to the first and second samples shown in FIGS. 1 and 2, respectively. Similarly, FIG. 4 shows a fourth sample in which the surface of the aluminized coating is also substantially uniform, particularly compared to the first and second samples shown in FIGS. 1 and 2, respectively. Thus, it is shown that the use of slurry blasting rather than pickling to descale prior to hot dip aluminizing substantially improves the uniformity of the coating appearance. The degree of improvement in surface appearance by slurry blasting rather than pickling was unexpected. Furthermore, the performance in removing or otherwise reducing thick scale, such as that encountered at the ends of coils, was unexpectedly good.

[0023] Example 3 The steel strip coil of Example 2 above was further tested. Specifically, the coil was unwound and samples were taken from the head end of the coil (5th sample) and the tail end of the coil (6th sample). The resulting samples were then subjected to a bend adhesion test. The particular bend adhesion test used included a bend radius that varied with the thickness of the substrate.

[0024] Figure 5 shows the results of the bend adhesion test. The fifth sample is shown at the top and the sixth sample is shown at the bottom. As can be seen, the slurry blasted steel strip of Example 2 showed acceptable adhesion at both the head and tail ends of the coil. Thus, it is shown that the use of a slurry blasting process rather than a pickling process for descaling prior to hot dip aluminization results in acceptable adhesion performance of the aluminized coating.

[0025] Example 4 The coated steel was prepared according to the following steps. a. Hot or cold rolling of steel ingots to form steel strip; b) slurry blasting at least one surface of the steel strip; and c. After slurry blasting, the steel strip is coated with an aluminum based coating.

[0026] Example 5 A coated steel was prepared according to the method of Example 4, further comprising coiling the steel strip, uncoiling the steel strip prior to the step of slurry blasting, and recoiling the steel strip prior to the step of coating the steel strip with an aluminum-based coating.

[0027] Example 6 Coated steel was prepared according to the method of Example 5 and the slurry blasting process was carried out continuously as the steel strip was uncoiled and recoiled.

[0028] Example 7 Coated steel was prepared according to the method of Example 4, further comprising the steps of coiling the steel strip and transporting the coiled steel strip to an aluminizing line, and the step of slurry blasting was performed in the aluminizing line as part of a pre-cleaning step prior to coating the steel strip with an aluminum-based coating.

[0029] Example 8 The coated steels were prepared according to the method of any one or more of Examples 4-7, which is a process of hot or cold rolling a steel ingot including pickling the steel strip after hot or cold rolling.

[0030] Example 9 A coated steel prepared according to the method of any one or more of Examples 4 to 7, wherein the step of slurry blasting the steel strip comprises adjusting in real time a feed rate and pressure associated with the slurry blasting based on visual scale removal from the steel strip.

[0031] Example 10 A coated steel prepared according to the method of any one or more of Examples 4 to 9, wherein the aluminum-based coating comprises a Type 1 or Type 2 aluminized coating.

[0032] Example 11 A coated steel prepared according to the method of any one or more of Examples 4 to 10, wherein the aluminum-based coating contains 5 to 11% silicon.

[0033] Example 12 A coated steel prepared according to the method of any one or more of Examples 4 to 11, wherein the step of slurry blasting the steel strip includes the use of an abrasive medium, the abrasive medium including a mixture of water and abrasive particles.

[0034] Example 13 A coated steel prepared according to the method of any one or more of Examples 4 to 12, wherein the step of slurry blasting the steel strip comprises slurry blasting both sides of the steel strip.

[0035] Example 14 The coated steel was prepared using the following coating line system: The coating line system includes an aluminizing section including a molten bath including molten aluminum, a slurry blast section configured to direct a high velocity abrasive mixture at one or more surfaces of the steel strip, the slurry blast section operatively disposed prior to the aluminizing section, and the slurry blast section may be configured to act as a pre-cleaning process prior to aluminizing the steel strip through the aluminizing section.

[0036] Example 15 Coated steel was prepared using the coating line system of Example 14. The coating line system further includes a reheat furnace, with the slurry blast section operatively positioned prior to the reheat furnace.

[0037] Example 16 Coated steel was prepared using the coating line system of Examples 14 or 15. The slurry blast section included a feed rate control and a pressure control, both configured to allow real-time adjustment to control the removal of scale from one or more surfaces of the steel strip.

[0038] Example 17 Coated steel was prepared using any one or more of the coating line systems of Examples 14 to 16. The aluminizing section and the slurry blast section are configured to work together in continuous operation.

[0039] Example 18 Coated steel was prepared using any one or more of the coating line systems of Examples 14 to 17. The slurry blast section is configured to remove scale from a first surface and a second surface of the steel strip.

Claims

1. A method for producing coated steel, comprising the steps of: (a) hot or cold rolling a steel ingot to form a steel strip; (b) slurry blasting at least one surface of the steel strip; and (c) after said slurry blasting step, coating said steel strip with an aluminum based coating.

2. 10. The method of claim 1, further comprising uncoiling the steel strip prior to the steps of coiling and slurry blasting the steel strip, and uncoiling the steel strip prior to the steps of coating the steel strip with an aluminum based coating.

3. 3. The method of claim 2, wherein the step of slurry blasting is performed consecutively with the steps of unwinding and rewinding the steel strip.

4. 10. The method of claim 1, further comprising the steps of: reeling the steel strip; and transporting the reeled steel strip to an aluminum processing line, wherein the slurry blasting step occurs in the aluminum processing line as part of a pre-cleaning process prior to coating the steel strip with an aluminum based coating.

5. The method according to any one of claims 1 to 4, wherein the step of hot rolling or cold rolling the steel ingot comprises pickling the steel strip after hot rolling or cold rolling.

6. The method of any of claims 1 to 4, wherein the step of slurry blasting the steel strip includes adjusting a feed rate and pressure for the slurry blast in real time based on visual scale removal from the steel strip.

7. The method of any of claims 1 to 6, wherein the aluminum-based coating comprises a type 1 or type 2 aluminide coating.

8. The method according to any one of claims 1 to 7, wherein the aluminium based coating contains 5 to 11% silicon.

9. The method of any of claims 1 to 8, wherein the step of slurry blasting the steel strip comprises the use of an abrasive media comprising a mixture of water and abrasive particles.

10. The method of any of claims 1 to 9, wherein the step of slurry blasting the steel strip comprises the step of slurry blasting both sides of the steel strip.

11. 1. A system for preparing coated steel, comprising: (a) an aluminizing section including a molten bath containing molten aluminum; and (b) a slurry blast section configured to direct a high velocity abrasive mixture toward one or more surfaces of the steel strip, the slurry blast section operably positioned prior to the aluminizing section so as to act as a pre-cleaning process prior to aluminizing the steel strip via the aluminizing section.

12. The system of claim 11 , further comprising a reheat furnace, said slurry blast section operatively disposed prior to said reheat furnace.

13. 13. The system of claim 11 or 12, wherein the slurry blast section includes a feed rate control and a pressure control, both of the feed rate control and the pressure control configured to allow real-time adjustment to control the removal of scale from one or more surfaces of the steel strip.

14. 14. The system of any of claims 11 to 13, wherein the aluminizing section and the slurry blasting section are configured to operate together in continuous operation.

15. 15. The system of claim 11, wherein the slurry blast section is configured to remove scale from a first surface and a second surface of the steel strip.

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