A high-molybdenum austenitic stainless steel thin strip hot continuous rolling control method

Abstract

The application discloses a kind of high molybdenum austenitic stainless steel thin strip hot continuous rolling control method, it is related to high molybdenum austenitic stainless steel hot rolling technical field.For the problem that 317J1 stainless steel hot working window is narrow, easy to produce edge crack and traditional secondary heating process is low in efficiency, the application sequentially carries out five-stage slow speed step heating to the square billet of specific component, square billet rough rolling, intermediate billet finish rolling and curling processing.In the rolling stage, rough rolling opening rolling temperature is strictly controlled to be 1130~1190 DEG C, enters finish rolling temperature >=1080 DEG C, and final rolling temperature >=1000 DEG C, and the rolling speed of rough rolling and finish rolling all show increasing trend gradually.The application reduces internal thermal stress from source by five-stage temperature control heating, cooperates with whole-process temperature control and deformation heat compensation, ensures that material is always in plastic zone when deforming, completely eliminates edge crack hidden danger, realizes efficient straight rolling forming under single heating, and significantly improves production efficiency and yield.

Description

Technical Field

[0001] This invention relates to the field of hot rolling technology for high-molybdenum austenitic stainless steel, and in particular to a method for controlling the hot continuous rolling of high-molybdenum austenitic stainless steel strip. Background Technology

[0002] 317J1 is a high-molybdenum austenitic stainless steel. This material was developed from conventional stainless steel by increasing the molybdenum content and optimizing the nickel and chromium ratio, and is designed to cope with extreme corrosive environments.

[0003] Because 317J1 stainless steel contains high levels of alloying elements (such as Cr, Mo, and Ni), its thermoplastic window at high temperatures is extremely narrow, resulting in poor hot working properties. In traditional rolling processes, when temperature control is inadequate, the edge areas of the stainless steel strip cool down rapidly due to faster heat dissipation, making them highly susceptible to edge cracking under immense rolling forces. To eliminate severe edge cracks and ensure product dimensions and quality, the cracked portions often must be cut off in subsequent processes, significantly reducing the yield. Furthermore, severe edge cracks can lead to production accidents such as steel pushing and strip breakage, seriously affecting the stability and continuity of large-scale rolling production and causing substantial economic losses.

[0004] To address this edge cracking problem, existing technologies (such as the method for manufacturing martensitic stainless steel disclosed in patent application CN121087261A) employ a process of reheating the stainless steel strip in a furnace after rough rolling, followed by finish rolling. While this process can alleviate the edge cracking problem, the secondary reheating significantly increases production time and energy consumption, and also substantially reduces production efficiency.

[0005] Therefore, how to propose a hot continuous rolling control method that can solve the problem of edge cracking in hot rolling of high alloy stainless steel, avoid secondary remelting, and improve production efficiency is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a hot continuous rolling control method for high molybdenum austenitic stainless steel strip.

[0007] To solve the above technical problems, the technical solution of the present invention is as follows: A hot continuous rolling control method for high-molybdenum austenitic stainless steel strip, wherein the chemical composition of the high-molybdenum austenitic stainless steel by mass percentage includes: C≤0.08%, Si≤1.00%, Mn≤2.00%, P≤0.045%, S≤0.030%, Cr: 18.00%~20.00%, Ni: 11.00%~15.00%, Mo: 3.00%~4.00%, with the balance being Fe and unavoidable impurities; The hot strip rolling control method includes the following steps: Step 1: Obtaining the heated billet: The high-molybdenum austenitic stainless steel billet is loaded into the heating furnace and heated in a segmented heating method to obtain the heated billet. The segmented heating includes five stages in sequence: preheating section, heating section one, heating section two, heating section three, and soaking section. Step 2: Obtaining intermediate billets: The square billets that have undergone segmented heating are fed into the roughing mill for roughing treatment that combines vertical rolling and horizontal rolling to produce intermediate billets; wherein, the starting rolling temperature of the roughing mill is controlled at 1130~1190℃. Step 3: Obtaining finished finished product: The intermediate billet is sent to the finishing mill for a combination of vertical and horizontal rolling to produce finished finished product; wherein, the entry temperature of the intermediate billet into the finishing mill is ≥1080℃, and the final rolling temperature of the finishing mill is controlled to be ≥1000℃. Step 4, winding: The finished strip is fed into the winding machine via a flat chain to obtain the thin strip finished product.

[0008] The beneficial effects of this invention are: (1) In view of the problem that 317J1 high molybdenum alloy is prone to thermal stress, the present invention adopts a fine five-stage slow step heating process, which effectively reduces the heating rate and avoids the huge thermal stress caused by the rapid increase of the surface temperature of the billet and the lag of the core temperature due to direct high temperature heating. This makes the core temperature of the billet and the surface temperature synchronized and consistent, thereby minimizing the risk of core or corner edge breakage in subsequent rolling.

[0009] (2) This invention addresses the extremely narrow thermoplastic window of high-molybdenum steel by strictly limiting the roughing rolling temperature to 1130–1190°C, and further controlling the finishing rolling temperature to ≥1080°C and the final rolling temperature to ≥1000°C. This tight "temperature chain" ensures that the entire deformation process of the billet from roughing to finishing rolling is always within the high-temperature plastic zone of the material, completely solving the problem of edge cracking caused by excessively rapid temperature drop. This successfully eliminates the time-consuming and energy-intensive "secondary reheating" process, reducing the rolling time of a single billet to less than 2.5 minutes and significantly improving production efficiency.

[0010] (3) The specific roughing (3 vertical, 6 horizontal) and finishing (2 vertical, 9 horizontal) processing sequences designed in this invention scientifically alternate between thickness reduction (horizontal rolling) and width control (vertical rolling) processes. Combined with the stepwise reduction deformation rate control of 75%~85% in roughing and 90%~95% in finishing, localized concentrated stress is effectively released, ensuring uniform internal metal flow in thin strips with large width-to-thickness ratios during rolling, and avoiding tearing of the edges due to severe deformation in one direction.

[0011] (4) As the thickness of the rolled piece decreases and the elongation increases, the rolling speed of the roughing and finishing rolling is increased simultaneously in each pass. This not only conforms to the principle of continuous rolling with equal metal flow rate per second, but also significantly shortens the exposure time of the rolled piece between the stands and in the air, playing a key role in "heating up" and providing a solid dynamic guarantee for the final rolling temperature ≥1000℃. Attached Figure Description

[0012] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1 A schematic diagram of the finished hot-rolled thin strip of 317J1 high-molybdenum austenitic stainless steel produced in an embodiment of the present invention. Detailed Implementation

[0014] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0015] This invention provides a method for controlling the hot continuous rolling of high-molybdenum austenitic stainless steel strip, the specific steps of which are detailed below: Step 1, Billet Heating: High-molybdenum austenitic stainless steel billets with the following chemical composition by mass percentage: C≤0.08%, Si≤1.00%, Mn≤2.00%, P≤0.045%, S≤0.030%, Cr 18.00%~20.00%, Ni 11.00%~15.00%, Mo 3.00%~4.00%, with the balance being Fe and unavoidable impurities, are loaded into the heating furnace. The preheating section is controlled at 600~650℃ and held for 30~50 min; the first heating section is controlled at 800~950℃ and held for 30~50 min; the second heating section is controlled at 1000~1100℃ and held for 30~55 min; the third heating section is controlled at 1150~1200℃ and held for 50~70 min; and the soaking section is controlled at 1240~1280℃ and held for 55~75 min. The total heating time is 200-280 minutes to obtain the heated billet.

[0016] Step 2, rough rolling of the billet: The heated billet is fed into the rough rolling mill without high-pressure water descaling, and the initial rolling temperature is controlled at 1130–1190℃. Three vertical rolling passes and six horizontal rolling passes are used, in the following sequence: vertical rolling → horizontal rolling → horizontal rolling → vertical rolling → horizontal rolling → horizontal rolling → vertical rolling → horizontal rolling → horizontal rolling. The horizontal rolling deformation rates are 20%–25%, 25%–30%, 25%–30%, 25%–30%, 25%–30%, and 25%–30% respectively, with a total deformation of 75%–85%. The rolling speed of the six horizontal rolling passes increases progressively from 0.5 m / s to 2.5 m / s, forming an intermediate billet.

[0017] Step 3, Intermediate Billet Finishing: After passing through a flying shear head, the intermediate billet is fed into the finishing mill at an entry temperature ≥1080℃. Two vertical rolling passes and nine horizontal rolling passes are used, in the following sequence: vertical rolling → horizontal rolling → vertical rolling → horizontal rolling → horizontal rolling → horizontal rolling → horizontal rolling → horizontal rolling → horizontal rolling → horizontal rolling → horizontal rolling. The horizontal rolling deformation rates are successively 30%–35%, 30%–35%, 30%–35%, 25%–30%, 25%–30%, 20%–25%, 10%–20%, 10%–15%, and 10%–15%, with a total deformation of 90%–95%. The rolling speed of the nine horizontal rolling passes increases progressively from 1.5 m / s to 13.5 m / s. During the process, two fine descaling stages are initiated. The descaling pressure of the first stage is ≥18MPa, and the descaling pressure of the second stage is ≥12MPa. The final rolling temperature is controlled to be ≥1000℃ to obtain a finely rolled thin strip. Cooling water is turned on before the strip enters the flat conveyor belt after fine rolling.

[0018] Step 4, winding: The cooled precision-rolled thin strip is fed into the winding machine via a flat chain. The inlet temperature of the flat chain is controlled at 800-900℃, and the winding temperature is ≥350℃ to obtain high-molybdenum austenitic stainless steel thin strip.

[0019] The above technical solution will be further explained below through specific embodiments.

[0020] Example 1: This example provides a hot continuous rolling control method for high-nickel heat-resistant 317J1 stainless steel strip. The original billet size used in production is 220mm (thickness) × 220mm (width) × 6300mm (length), and the target rolled product size is 3mm (thickness) × 245mm (width). The actual chemical composition (mass percentage) of this batch of 317J1 high-molybdenum austenitic stainless steel is: C: 0.07%, Si: 0.78%, Mn: 1.46%, P: 0.023%, S: 0.006%, Cr: 19.2%, Ni: 12.9%, Mo: 3.45%.

[0021] The above-mentioned hot strip rolling control method specifically includes the following steps: Step 1: Slow-speed stepped heating of the billet.

[0022] Specifically, to eliminate the internal and external temperature difference of the large cross-section square billet, the 317J1 square billet of the above dimensions is loaded into the heating furnace, and the following five temperature control and heat preservation operations are performed sequentially: First, the material is slowly preheated at 616℃ in the preheating section and held for 41 minutes to ensure that the material safely passes through the low-temperature brittleness zone. Then it enters the heating stage, raising the temperature to 869℃ and holding it for 40 minutes; Entering the second heating stage, the temperature steadily rises to 1082℃ and is held for 35 minutes; Enter the third heating stage, set the temperature to 1187℃, and hold for 64 minutes to allow the alloying elements to fully dissolve. Finally, it enters the soaking zone, where it is heated to a maximum temperature of 1260℃ for 63 minutes to ensure that the temperature difference between the surface and core of the billet is minimized. The entire heating process lasts steadily for 243 minutes.

[0023] Step 2: Hot continuous roughing of continuously cast billets (temperature control and heat preservation stage).

[0024] Specifically, the billet is sent to the roughing mill immediately after exiting the furnace. To prevent the high-pressure water impact from carrying away surface heat and causing the edges to cool down too quickly, the high-pressure water descaling operation before roughing is deliberately eliminated in this process.

[0025] The actual rolling temperature was precisely controlled at 1146℃. In the roughing stage, three vertical rolling passes and six horizontal rolling passes were alternately interspersed (in the following order: vertical-horizontal-horizontal-vertical-horizontal-horizontal-vertical-horizontal-horizontal).

[0026] To balance the reduction amount and edge crack prevention, the reduction deformation rate of each pass of flat rolling is strictly controlled as follows: 23.6%, 28.5%, 26.7%, 26.1%, and 26.4%, with the total deformation amount reaching 84.5% in this stage.

[0027] To compensate for the temperature drop by utilizing the heat generated during plastic deformation, the roughing mill was operated with a steadily increasing rolling speed across each pass. The speeds for each pass were recorded as follows: 0.54 m / s, 0.69 m / s, 0.89 m / s, 1.18 m / s, 1.58 m / s, and 2.17 m / s (i.e., falling entirely within the range of 0.5 to 2.5 m / s). After roughing, the 220 mm thick square billet was successfully rolled into a 34 mm thick roughing intermediate billet.

[0028] Step 3: High-speed precision rolling of intermediate billet (deformation and shaping stage).

[0029] Specifically, before the roughing mill intermediate billet is fed into the finishing mill, the head deformation area caused by uneven width expansion is removed by a flying shear.

[0030] Thanks to heat preservation and speed control during the roughing stage, the intermediate billet temperature at this stage is still as high as 1094℃ (far exceeding the safety threshold of 1080℃).

[0031] The finishing mill employs two vertical rolling passes for width control and nine horizontal rolling passes for thickness reduction (in the following sequence: vertical-horizontal-vertical-horizontal-horizontal-horizontal-horizontal-horizontal-horizontal-horizontal). The deformation rates for each horizontal rolling pass are controlled sequentially as follows: 32.3%, 30.4%, 31.2%, 27.3%, 26.7%, 20.6%, 16.9%, 11.9%, and 12.1%, with a total deformation of 91.1% throughout the entire finishing rolling process.

[0032] During this stage, two descaling systems are activated. The first descaling pressure is 18.8 MPa, and the second descaling pressure is 15.2 MPa, to remove secondary iron oxide scale and ensure a smooth surface finish. An aggressive, progressively accelerating finishing rolling speed strategy is employed, specifically: 1.52 m / s, 2.14 m / s, 3.11 m / s, 4.19 m / s, 5.46 m / s, 6.78 m / s, 8.51 m / s, 10.25 m / s, and 12.89 m / s. The deformation heat from high-speed rolling perfectly offsets the cooling effect of the descaling water, ensuring that the final rolling temperature remains stable at 1068℃ (within the plastic zone) at the end of finishing rolling, ultimately yielding a 3 mm thick finished product.

[0033] Step 4: Cooling and rolling into storage.

[0034] Specifically, after finishing rolling, the finished strip is immediately cooled by cooling water before entering the flat chain to prevent further grain growth.

[0035] The thin strip is fed into the winding machine via a flat chain. Monitoring shows that the temperature at the inlet of the flat chain has dropped to 879°C. Finally, the winding machine winds the thin strip into shape at a winding temperature of 423°C.

[0036] Implementation effect verification: Using the above method, a 6.3-meter-long 317J1 billet completed all hot rolling processes in just 2.5 minutes, resulting in a significant improvement in production efficiency. Figure 1 As shown, the produced 317J1 stainless steel hot-rolled thin strip has extremely excellent edge quality, with uniform width and thickness. Serious edge defects such as broken edges and burrs, which are common in traditional processes, are basically completely eliminated, eliminating the need for deep edge trimming. The yield and economic benefits have reached the advanced level in the industry.

[0037] In addition to the above embodiments, the present invention may have other implementation methods; all technical solutions formed by equivalent substitution or equivalent transformation fall within the protection scope claimed by the present invention.

Claims

1. A method for controlling the hot continuous rolling of high-molybdenum austenitic stainless steel strip, characterized in that: The chemical composition of the high-molybdenum austenitic stainless steel, by mass percentage, includes: C≤0.08%, Si≤1.00%, Mn≤2.00%, P≤0.045%, S≤0.030%, Cr: 18.00%~20.00%, Ni: 11.00%~15.00%, Mo: 3.00%~4.00%, with the balance being Fe and unavoidable impurities; The hot strip rolling control method includes the following steps: Step 1: Obtaining the heated billet: The high-molybdenum austenitic stainless steel billet is loaded into the heating furnace and heated in a segmented heating manner to obtain the heated billet. The segmented heating includes five stages in sequence: preheating section, heating section one, heating section two, heating section three, and soaking section. Step 2: Obtaining the intermediate billet: The heated square billet, after being heated in sections, is fed into the roughing mill for roughing treatment combining vertical and horizontal rolling to generate the intermediate billet; wherein, the starting rolling temperature of the roughing mill is controlled at 1130~1190℃. Step 3: Obtain the finished finished product: The intermediate billet is sent to the finishing mill for a combination of vertical and horizontal rolling to produce the finished finished product; wherein, the entry temperature of the intermediate billet into the finishing mill is ≥1080℃, and the final rolling temperature of the finishing mill is controlled to be ≥1000℃. Step 4: Winding: The finished rolled product is fed into a winding machine via a flat chain for winding to obtain a thin strip product.

2. The hot continuous rolling control method for high-molybdenum austenitic stainless steel strip according to claim 1, characterized in that: In step one, the temperatures and holding times for each stage of the segmented heating are as follows: The temperature of the preheating section is 600~650℃, and the holding time is 30~50min; The heating section has a temperature of 800~950℃ and a holding time of 30~50min; The temperature of the second heating stage is 1000~1100℃, and the holding time is 30~55min; The three heating sections have a temperature of 1150~1200℃ and a holding time of 50~70min; The temperature of the heat spreader is 1240~1280℃, and the heat preservation time is 55~75min; The total heating time for the segmented heating is 200~280 minutes.

3. The hot continuous rolling control method for high-molybdenum austenitic stainless steel strip according to claim 1, characterized in that: In step two, a high-pressure water descaling process is not used before rough rolling; The roughing process consists of three vertical rolling passes and six horizontal rolling passes, and the order of the roughing process is as follows: vertical rolling, horizontal rolling, horizontal rolling, vertical rolling, horizontal rolling, horizontal rolling, vertical rolling, horizontal rolling, horizontal rolling.

4. The hot continuous rolling control method for high-molybdenum austenitic stainless steel strip according to claim 3, characterized in that: The deformation rate of each pass in the roughing process is controlled as follows: 20%~25%, 25%~30%, 25%~30%, 25%~30%, 25%~30%, and 25%~30%, and the total deformation of the roughing stage is controlled as 75%~85%.

5. The hot continuous rolling control method for high-molybdenum austenitic stainless steel strip according to claim 3 or 4, characterized in that: In the roughing process, the rolling speed of the six flat rolling passes is controlled within the range of 0.5 m / s to 2.5 m / s, and the rolling speed of each flat rolling pass increases sequentially.

6. The hot continuous rolling control method for high-molybdenum austenitic stainless steel strip according to claim 1, characterized in that: In step three, before entering the finishing mill, the intermediate billet is sheared off at the head and then fed in; the roughing process consists of two vertical rolling passes and nine horizontal rolling passes, and the order of the roughing process is as follows: vertical rolling, horizontal rolling, vertical rolling, horizontal rolling, horizontal rolling, horizontal rolling, horizontal rolling, horizontal rolling, horizontal rolling, horizontal rolling, horizontal rolling, horizontal rolling, horizontal rolling.

7. The hot continuous rolling control method for high-molybdenum austenitic stainless steel strip according to claim 6, characterized in that: The deformation rate of each pass in the finishing rolling process is controlled as follows: 30%~35%, 30%~35%, 30%~35%, 25%~30%, 25%~30%, 20%~25%, 10%~20%, 10%~15%, and 10%~15%, and the total deformation in the finishing rolling stage is controlled as 90%~95%.

8. The hot continuous rolling control method for high-molybdenum austenitic stainless steel strip according to claim 6 or 7, characterized in that: In the finishing rolling process, the rolling speed of the nine flat rolling passes is controlled within the range of 1.5m / s to 13.5m / s, and the rolling speed of each flat rolling pass increases sequentially.

9. The hot continuous rolling control method for high-molybdenum austenitic stainless steel strip according to claim 1, characterized in that: In the finishing rolling stage of step three, two finishing descaling processes are initiated, wherein the pressure of the first finishing descaling process is ≥18MPa and the pressure of the second finishing descaling process is ≥12MPa. After the finishing rolling stage is completed and before the finished finishing product enters the flat plate chain, cooling water is turned on for cooling.

10. The hot continuous rolling control method for high-molybdenum austenitic stainless steel strip according to claim 1, characterized in that: In step four, the inlet temperature of the flat chain is controlled within the range of 800~900℃; the curling temperature of the curling machine performing the curling operation is ≥350℃.

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