Ferritic-austenitic duplex stainless steel hot-rolled strip thick material coiling process

Abstract

The application discloses a ferrite-austenite duplex stainless steel hot-rolled strip steel thick material coiling process, characterized by setting the initial setting of the roll gap of the pinch roll set and the coiling aid roll set; the 1# coiling aid roll, the 2# coiling aid roll and the 3# coiling aid roll are pressed against the surface of the hot-rolled strip steel thick material, and the coiling is started; the head of the hot-rolled strip steel thick material enters the pinch roll set, the pressure setting value of the upper pinch roll and the lower pinch roll is 200-250 KN, until the head of the hot-rolled strip steel thick material contacts the coiler mandrel and the coiling aid succeeds, after the stable tension is established, the coiling tension is 150-250 KN, the upper pinch roll no longer contacts the strip steel, the 2# coiling aid roll and the 3# coiling aid roll are opened, the 1# coiling aid roll continues to be pressed against the surface of the strip steel, until the strip steel is completely coiled and the coiling is finished; when the tail of the strip steel leaves the finishing mill, the coiling tension is 30-50 KN. The application has the beneficial effect that under the premise of not improving the coiling temperature, the coiling shape of the steel coil is improved by adjusting the coiling process parameters.

Description

Technical Field

[0001] This invention belongs to the field of stainless steel strip coiling technology, and particularly relates to a coiling process for thick hot-rolled ferritic-austenitic duplex stainless steel strip. Background Technology

[0002] SA2507 stainless steel is a ferritic-austenitic duplex stainless steel that combines the most beneficial properties of many ferritic and austenitic steels. With a pitting equivalent PREN > 41, it exhibits excellent corrosion resistance and high mechanical properties in harsh environments containing chlorides and acids. It is a substitute for 6Mo type super austenitic stainless steel, titanium, and glass fiber reinforced plastics, and is widely used in power, papermaking, petrochemical, and marine engineering fields. In the prior art, Chinese patent application CN202110433767.3 (application date: April 21, 2021) and CN113210420A (publication date: August 6, 2021) discloses a duplex stainless steel coil and its manufacturing method. The coil is made of 2507 stainless steel, and the production process is as follows: electric furnace → converter → refining furnace → continuous casting → billet grinding → first hot rolling → intermediate billet → billet grinding → second hot rolling. In actual production, the strip needs to be coiled after the second hot rolling. Currently, conventional coiling devices in the industry include side guides, pinch rolls, auxiliary coiling rolls, and a coiling core shaft. Before the strip enters the coiling device, the device selects the corresponding process parameters according to different steel grades and size specifications to complete the initial settings. Then, the strip sequentially enters the gap between the side guides, pinch rolls, auxiliary coiling rolls, and the coiling drum rolls, thus forming a coil. According to actual production experience, the maximum coiling temperature of SA2507 stainless steel must be controlled below 780℃. When the temperature is too high, a sigma phase (σ-phase) is easily generated, leading to strip breakage and affecting yield and production efficiency. However, at the same time, as the coiling temperature decreases, the hardness of SA2507 stainless steel increases very rapidly, which can easily lead to increased fluctuations in the pinch roll gap and abnormal situations such as the strip tail tension not reaching the set value, resulting in problems such as misalignment and loose coiling. Summary of the Invention

[0003] 1. Technical problems to be solved

[0004] In existing technologies, the maximum coiling temperature of thick SA2507 stainless steel strip must be controlled below 780℃. As the coiling temperature decreases, its hardness increases rapidly, which can easily lead to increased fluctuations in the gap between the coiling pinch rolls and abnormal situations such as the strip tail tension not reaching the set value, resulting in problems such as misalignment and loose coiling. The purpose of this invention is to provide a coiling process for thick hot-rolled ferritic-austenitic duplex stainless steel strip. Without increasing the maximum coiling temperature, this process adjusts the coiling process parameters to adapt to the changes in stainless steel hardness caused by the temperature decrease, quickly completing the coiling operation of stainless steel strip and obtaining SA2507 stainless steel coils with good coil shape.

[0005] 2. Technical Solution

[0006] To achieve the above objectives and technical effects, the present invention adopts the following technical solution:

[0007] A coiling process for thick hot-rolled ferritic-austenitic duplex stainless steel strip is disclosed, characterized in that the ferritic-austenitic duplex stainless steel is SA2507 stainless steel, and the target thickness of the SA2507 stainless steel is ≥7.0mm. The coiling process is carried out by a coiling device, which includes: a pinch roll group, an auxiliary coiling roll group, and a coiling machine mandrel. The pinch roll group is disposed between the finishing mill and the coiling machine mandrel, and includes an upper pinch roll and a lower pinch roll. The auxiliary coiling roll group includes a #1 auxiliary coiling roll, a #2 auxiliary coiling roll, and a #3 auxiliary coiling roll, which surround the outside of the coiling machine mandrel.

[0008] The hot-rolled strip steel thick material coiling process includes:

[0009] Before winding, the initial parameters of the winding device are set. The initial setting value of the first roll gap between the upper and lower pinch rolls is 0.2 to 0.3 mm smaller than the target thickness of the strip. The setting value of the second roll gap between the No. 1 auxiliary winding roll and the winding machine core shaft is the target thickness of the strip * 1.4. The setting value of the third roll gap between the No. 2 auxiliary winding roll and the winding machine core shaft is the target thickness of the strip * 1.2. The setting value of the fourth roll gap between the No. 3 auxiliary winding roll and the winding machine core shaft is the target thickness of the strip * 1.1.

[0010] The head of the hot-rolled strip steel enters the pinch roll group, the second roll gap, the third roll gap, and the fourth roll gap in sequence until the head of the hot-rolled strip steel contacts the coiler core shaft. The No. 1, No. 2, and No. 3 auxiliary coiling rolls press against the surface of the hot-rolled strip steel, and the coiler core shaft begins to coil. The set values ​​of the second, third, and fourth roll gaps cannot be too high or too low. If they are too high, they will not have the effect of assisting coiling; if they are too low, steel may pile up.

[0011] After the head of the hot-rolled strip enters the pinch roll group, the pressure of the upper pinch roll and the lower pinch roll is set at 200-250KN until the head of the hot-rolled strip contacts the mandrel of the coiler and is successfully coiled. Stable tension is generated between the mandrel and the finishing mill.

[0012] After the head of the hot-rolled strip steel is successfully coiled, the upper clamping roller is quickly lifted and opened until it no longer contacts the hot-rolled strip steel. The No. 2 and No. 3 coiling rollers are opened, and the No. 1 coiling roller continues to press against the surface of the hot-rolled strip steel. The pressing force is set to 100-200KN until the hot-rolled strip steel is completely coiled.

[0013] After the head of the hot-rolled strip is successfully coiled, the coiler mandrel and the finishing mill establish tension. The tension value is set to 150-250KN, and the relationship between tension and strip thickness and width satisfies: tension = thickness * width * unit tension.

[0014] The unit tension is selected based on the thickness of the hot-rolled strip steel. The relationship between unit tension and thickness is as follows:

[0015]

[0016] When the tail of the hot-rolled strip leaves the finishing mill, the coiling tension is set to 30-50 kN. If the tension value is set too high, it will lead to problems such as faster strip speed, increased difficulty in controlling coiling temperature, and abnormal tail stopping position.

[0017] Furthermore, when the strip generates stable tension between the mandrel and the finishing mill, the coiler mandrel coils the hot-rolled strip about 5 turns.

[0018] Furthermore, after the head of the hot-rolled strip steel is successfully coiled, the upper clamping roller is quickly lifted, and the first roll gap is opened to more than 30mm.

[0019] Furthermore, the chemical composition of the SA2507 stainless steel, by mass percentage, includes: C≤0.03%, Si≤0.80%, Mn≤1.2%, Cr:24-26%, Ni:6-8%, S≤0.02%, P≤0.035%, Mo:3-5%, N:0.24-0.32%.

[0020] 3. Beneficial effects

[0021] Compared with the prior art, the beneficial effects of the present invention are: without increasing the coiling temperature, by adjusting the coiling process parameters, it adapts to the change in stainless steel hardness caused by the temperature reduction, quickly completes the coiling operation of stainless steel strip, reduces the misalignment from about 40mm to less than 10mm, reduces the occurrence rate of interlayer friction marks caused by misalignment from 13% to 3%, and improves the coil shape of SA2507 stainless steel hot-rolled strip thick material. Attached Figure Description

[0022] To more clearly illustrate the specific embodiments of the invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the winding device of the present invention.

[0024] In the diagram: 1-coiler core shaft; 2-upper pinch roll; 3-lower pinch roll; 4-1# auxiliary coiling roll; 5-2# auxiliary coiling roll; 6-3# auxiliary coiling roll; 7-hot-rolled strip steel thick material. Detailed Implementation

[0025] The technical solution of the invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the invention. Based on the embodiments of the invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of the invention.

[0026] Example 1

[0027] In this embodiment, SA2507 stainless steel strip with a width of 1560mm and a target thickness of 10mm is selected.

[0028] Before winding, the initial gap between the upper clamping roller 2 and the lower clamping roller 3 is set to 9.8mm; the gap of the No. 1 auxiliary winding roller 4 is set to 14mm, the gap of the No. 2 auxiliary winding roller 5 is set to 12mm, and the gap of the No. 3 auxiliary winding roller 6 is set to 11mm.

[0029] The pressure after the head of the hot-rolled strip 7 enters the first roll gap is set to 250KN. The head of the hot-rolled strip 7 then enters the second roll gap, third roll gap, and fourth roll gap between the No. 1 coiling roller 4, No. 2 coiling roller 5, No. 3 coiling roller 6 and the coiler core shaft 1 in sequence. After the head of the hot-rolled strip 7 is successfully coiled, the upper pinch roller 2 is quickly lifted, and the first roll gap is opened to 34mm. After the No. 1 coiling roller 4, No. 2 coiling roller 5, and No. 3 coiling roller 6 coil 20 times, the No. 2 coiling roller 5 and No. 3 coiling roller 6 are opened, and the No. 1 coiling roller 4 continues to press against the surface of the hot-rolled strip 7 with a pressing force set to 196KN. After the head of the hot-rolled strip 7 is successfully coiled, tension is established between the coiler core shaft 1 and the finishing mill, and the tension value is set to 250KN.

[0030] When finishing rolling is completed and the tail of the hot-rolled strip 7 leaves the finishing mill, the coiling tension is set to 40KN.

[0031] The hot-rolled thick strip material 7 automatically stops at the appropriate position at the tail end, and the winding ends.

[0032] Without increasing the coiling temperature, by adjusting the coiling process parameters, the coiling operation of stainless steel strip can be quickly completed to adapt to the change in stainless steel hardness caused by the temperature reduction. The misalignment is reduced from about 40mm to less than 10mm, and the occurrence rate of interlayer friction marks caused by misalignment is reduced from 13% to 3%. The shape of SA2507 stainless steel hot-rolled thick coil is good.

[0033] Comparative Example 1

[0034] This comparative example uses SA2507 stainless steel strip with a width of 1560mm and a target thickness of 10mm.

[0035] Before winding, the initial gap between the upper clamping roller 2 and the lower clamping roller 3 is set to 9.8mm; the gap of the No. 1 auxiliary winding roller 4 is set to 14mm; the gap of the No. 2 auxiliary winding roller 5 is set to 912mm; and the gap of the No. 3 auxiliary winding roller 6 is set to 811mm.

[0036] The pressure after the head of the hot-rolled strip 7 enters the first roll gap is set to 250KN. After the head of the hot-rolled strip 7 is successfully coiled, the pressure of the first roll gap is set to 223KN. The head of the hot-rolled strip 7 enters the second roll gap, third roll gap, and fourth roll gap of the coiler core shaft 1 in sequence through the No. 1 coiling roller 4, No. 2 coiling roller 5, No. 3 coiling roller 6 and No. 1 coiling roller 4, No. 2 coiling roller 5, and No. 3 coiling roller 6 coil 5 times. Then, No. 2 coiling roller 5 and No. 3 coiling roller 6 open. No. 1 coiling roller 4 continues to press against the surface of the hot-rolled strip 7. The pressing force is set to 98KN. After the head of the hot-rolled strip 7 is successfully coiled, the coiler core shaft 1 establishes tension with the finishing mill. The tension value is set to 249KN.

[0037] When finishing rolling is completed and the tail of the hot-rolled strip 7 leaves the finishing mill, the coiling tension is set to 211KN.

[0038] The hot-rolled thick strip material 7 automatically stops at the appropriate position at the tail end, and the winding ends.

[0039] Under this coiling process, due to the change in the hardness of stainless steel caused by cooling, the first roll gap between the upper pinch roll 2 and the lower pinch roll 3 fluctuates violently, the strip misalignment reaches more than 40mm, interlayer friction marks occur, and the shape of SA2507 stainless steel hot-rolled thick coil is poor.

[0040] Comparative Example 2

[0041] This comparative example uses SA2507 stainless steel strip with a width of 1560mm and a target thickness of 10mm.

[0042] Before winding, the initial gap between the upper clamping roller 2 and the lower clamping roller 3 is set to 9.8mm; the gap of the No. 1 auxiliary winding roller 4 is set to 14mm, the gap of the No. 2 auxiliary winding roller 5 is set to 12mm, and the gap of the No. 3 auxiliary winding roller 6 is set to 11mm.

[0043] The pressure after the head of the hot-rolled strip 7 enters the first roll gap is set to 250KN. The head of the hot-rolled strip 7 then enters the second roll gap, third roll gap, and fourth roll gap between the No. 1 coiling roller 4, No. 2 coiling roller 5, No. 3 coiling roller 6 and the coiler core shaft 1 in sequence. After the head of the hot-rolled strip 7 is successfully coiled, the upper pinch roller 2 is quickly lifted, and the first roll gap is opened to 34mm. After the No. 1 coiling roller 4, No. 2 coiling roller 5, and No. 3 coiling roller 6 coil 20 times, the No. 2 coiling roller 5 and No. 3 coiling roller 6 are opened, and the No. 1 coiling roller 4 continues to press against the surface of the hot-rolled strip 7 with a pressing force set to 196KN. After the head of the hot-rolled strip 7 is successfully coiled, tension is established between the coiler core shaft 1 and the finishing mill, and the tension value is set to 250KN.

[0044] When finishing rolling is completed and the tail of the hot-rolled strip 7 leaves the finishing mill, the coiling tension is set to 211KN.

[0045] The hot-rolled thick strip material 7 automatically stops at the appropriate position at the tail end, and the winding ends.

[0046] Under this coiling process, when the tail of the hot-rolled strip steel leaves the finishing mill, the strip speed increases due to the absence of the clamping effect of the upper pinch roll 2 and the lower pinch roll 3. The tail coiling temperature exceeds the upper limit benchmark, causing the tail of the strip steel to break.

[0047] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention and should not be construed as limiting the specific implementation of the invention to these descriptions. For those skilled in the art, the architectural form of this invention can be flexibly varied without departing from its conceptual framework, leading to the derivation of a series of products. Any simple deductions or substitutions should be considered as falling within the patent protection scope defined by the submitted claims.

Claims

1. A coiling process for thick hot-rolled ferritic-austenitic duplex stainless steel strip, characterized in that: The ferritic austenitic duplex stainless steel is SA2507 stainless steel, and the target thickness of the SA2507 stainless steel is ≥7.0mm; The winding process is carried out by a winding device, which includes: a pinch roll group, an auxiliary winding roll group, and a winding machine mandrel; the pinch roll group is disposed between the finishing mill and the winding machine mandrel, and includes an upper pinch roll and a lower pinch roll; the auxiliary winding roll group includes a No. 1 auxiliary winding roll, a No. 2 auxiliary winding roll, and a No. 3 auxiliary winding roll, which surround the outside of the winding machine mandrel. The hot-rolled strip thick material coiling process includes: Before winding, the initial parameters of the winding device are set. The initial setting value of the first roll gap between the upper and lower pinch rolls is 0.2 to 0.3 mm smaller than the target thickness of the strip. The setting value of the second roll gap between the No. 1 auxiliary winding roll and the winding machine core shaft is the target thickness of the strip * 1.

4. The setting value of the third roll gap between the No. 2 auxiliary winding roll and the winding machine core shaft is the target thickness of the strip * 1.

2. The setting value of the fourth roll gap between the No. 3 auxiliary winding roll and the winding machine core shaft is the target thickness of the strip * 1.

1. The head of the hot-rolled strip steel thick material enters the pinch roll group, the second roll gap, the third roll gap, and the fourth roll gap in sequence until the head of the hot-rolled strip steel thick material contacts the core shaft of the coiler. The No. 1 auxiliary coiling roll, the No. 2 auxiliary coiling roll, and the No. 3 auxiliary coiling roll press against the surface of the hot-rolled strip steel thick material, and the core shaft of the coiler begins to coil. After the head of the hot-rolled strip enters the pinch roll group, the pressure of the upper pinch roll and the lower pinch roll is set at 200-250KN until the head of the hot-rolled strip contacts the coiler mandrel and is successfully coiled. Stable tension is generated between the hot-rolled strip mandrel and the finishing mill. After the head of the hot-rolled strip steel is successfully coiled, the upper clamping roller is quickly raised until it no longer contacts the hot-rolled strip steel. The No. 2 and No. 3 coiling rollers are opened, and the No. 1 coiling roller continues to press against the surface of the hot-rolled strip steel. The pressing force is set to 100-200KN until the hot-rolled strip steel is completely coiled. The coiling tension parameter is set as follows: after the head of the hot-rolled strip is successfully coiled, the coiler mandrel establishes tension with the finishing mill, and the tension value is set to 150-250KN; when the tail of the hot-rolled strip leaves the finishing mill, the coiling tension is set to 30-50KN.

2. The hot-rolled strip coiling process for ferritic-austenitic duplex stainless steel according to claim 1, characterized in that: When a stable tension is generated between the coiler mandrel and the finishing mill, the hot-rolled strip steel is wound up about 5 times by the coiler mandrel.

3. The hot-rolled strip coiling process for ferritic-austenitic duplex stainless steel according to claim 1, characterized in that: After the head of the hot-rolled strip steel is successfully coiled, the upper clamping roller is quickly lifted, and the first roll gap is opened to more than 30mm.

4. The hot-rolled strip coiling process for ferritic-austenitic duplex stainless steel according to any one of claims 1-3, characterized in that: The SA2507 stainless steel, by mass percentage, has the following chemical composition: C≤0.03%, Si≤0.80%, Mn≤1.2%, Cr:24-26%, Ni:6-8%, S≤0.02%, P≤0.035%, Mo:3-5%, N:0.24-0.32%.

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