Method for thickness control of cryogenic pressure vessel steel plate

Abstract

The application discloses a thickness control method for a low-temperature pressure container steel plate, which comprises the following steps: configuring different work roll convexities according to different support roll periods, limiting a furnace charging window period and a rolling window period of the steel plate, and limiting the rolling force of the last pass of the steel plate with different widths, and formulating a thickness gauge thickness and a hot gauge thickness reference table during the rolling of the steel plate, so that the thickness precision of the steel plate after cooling, shot blasting and heat treatment meets the delivery requirements through the accurate control of the previous process. The application has the advantages of reducing the rolling cost of the steel plate, improving the thickness hitting precision of the steel plate after rolling and tempering, and improving the qualified rate of the steel plate after rolling and heat treatment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of steel rolling process, and particularly relates to a thickness control method for low-temperature pressure vessel steel plate. BACKGROUND

[0002] The nickel-based low-temperature pressure vessel quenched and tempered steel plate has super-high low-temperature impact performance, and is used for high-grade storage tanks such as low-temperature washing towers, natural gas storage tanks and ethylene storage tanks of the national strategic ultra-low-temperature container market, but the manufacturing process thereof is relatively complex. In recent years, domestic steel plants have made great progress in the localization road by overcoming difficulties. However, since the steel plates are mostly used for ship-type storage tanks, very strict requirements are put forward for the finished thickness of the steel plate in order to maximize the stability of the ship body. The low-temperature pressure vessel quenched and tempered steel plate requires that the delivery tolerance band of the steel plate is +0.0 to +0.4 mm, and the order tolerance band width is only 0.4 mm.

[0003] Meanwhile, unlike ordinary rolled delivery orders, the nickel-based low-temperature container quenched and tempered steel plate will have a certain degree of thickness expansion from the hot state stage to the cold state stage, and further thickness change of the steel plate will occur after quenching and tempering. These characteristics add many interference factors to the accurate thickness control of the steel plate on site. SUMMARY

[0004] The purpose of the application is to solve the problems of great difficulty and low precision in thickness control of the existing low-temperature pressure vessel steel plate, and provide a thickness control method for low-temperature pressure vessel steel plate, which quantifies the process parameters of the low-temperature pressure vessel quenched and tempered steel plate in each process during rolling, reduces the rolling cost of the steel plate, improves the thickness hitting precision of the steel plate after rolling and quenching and tempering, and improves the qualified rate of the steel plate after rolling and quenching and tempering.

[0005] In order to achieve the above purpose, the application adopts the following technical scheme:

[0006] A thickness control method for low-temperature pressure vessel steel plate, the specific steps are as follows, comprising:

[0007] (1) Configuration of roll shape system: configuring different work roll crown for different support roll periods to ensure the roll crown during steel plate rolling;

[0008] (2) Limitation of rolling window period: limiting the furnace charging window period and the rolling window period of the steel plate to ensure the roll crown during steel plate rolling;

[0009] (3) Solidification of finishing mill last pass rolling force: optimizing the steel rolling process parameters, limiting the size of the last pass rolling force of the steel plate with different widths to ensure the crown during steel plate rolling;

[0010] (4) Thickness control standard reference establishment: Establish the thickness gauge thickness and hot gauge thickness reference table during the rolling of the steel plate, and through the accurate control of the previous process, further ensure that the thickness precision of the steel plate after the cooling, shot blasting and heat treatment meets the delivery requirements in the final state of the quenched and tempered finished product.

[0011] Further, in the step (1), the finishing mill backup roll is ground six times with a compound curve roll type, and the curve equation is y=a0+a1x+a2x 2 +a3x 3 +a4x 4 +a5x 5 +a6x 6 .

[0012] Further, in the step (1), for the convexity of 1.0 mm of the finishing mill backup roll, a0=0, a1=0.0046332, a2=-8.94441e -006 , a3=9.20917e -009 , a4=-5.33350e -012 , a5=1.64741e -015 , a6=-2.12022e -019 .

[0013] Further, in the step (1), the convexity of the upper work roll in a backup roll period is 0.05, 0.1, 0.15, 0.2 and 0.25 in sequence, and the corresponding convexity of the lower work roll is all 0, and the matching use number of the upper work roll and the lower work roll is 2, 6, 6, 8 and 2 in sequence.

[0014] Further, in the step (1), the roll type of the upper work roll is a stepped roll type curve, which includes a middle platform and a stepped ladder connected to the arc on both sides of the platform, the convexity of the middle platform is 0, the height of the stepped ladder is 0.05-0.25 mm, and the stepped ladder height corresponds to the roll convexity of the roll.

[0015] Further, in the step (2), the transverse same plate difference Δh of the steel plate is defined, the thickness of the edge of the steel plate is h e , the thickness of the middle of the steel plate is h c , and the transverse same plate difference is equal to the absolute value of the difference between the thickness of the edge of the steel plate and the thickness of the middle, that is: Δh =︱h e -h c ︱.

[0016] Further, in the step (2), when the steel plate is directly rolled after the roll change of the finishing mill, the transverse same plate difference is Δh0, when the same batch of steel plates is rolled 1 hour after the roll change of the finishing mill, the transverse same plate difference is Δh1, and in sequence, the transverse same plate difference rolled 2, 3, 4…n hours after the roll change is Δh2, Δh3, Δh4…Δhn Wherein, when n=3, 4, 5, i.e. the rolling roller period is 3-5h, the average value of the transverse same plate difference is controlled to be <0.05mm, and the best thickness receiving effect can be obtained.

[0017] Further, in the step (3), when the order width is successively 1500-1800mm, 1800-2000mm, 2000-2200mm and 2200-2500mm, the finishing mill last pass rolling force is successively given as 13000-16000kN, 16000-19000kN, 19000-22000kN, 22000-27000kN.

[0018] Further, in the step (4), according to different order thickness specifications and width specifications, the thickness control lower limit of the thickness gauge stage is +0.2-0.3mm, +0.35-0.45mm, +0.4-0.5mm, and the thickness control of the hot card is successively +0.15mm, +0.25mm, +0.3mm.

[0019] Compared with the prior art, the technical scheme of the present application has the following advantages:

[0020] (1) The present application adopts step roller matching, which can effectively avoid the rapid wear of the roll convexity during the rolling process, and at the same time, as the single set of supporting roller is used, the convexity value of the finishing mill working roller is continuously increased, thereby ensuring the superposition of the supporting roller and the working roller;

[0021] (2) The present application compares the transverse same plate difference, and obtains the rolling roller period that can obtain the best thickness effect, thereby providing convenience for the on-site production organization, and adopting the best rolling window period to arrange the slab furnace production;

[0022] (3) The present application provides a table of the finishing mill last pass rolling force under different widths, which can obtain the minimum transverse same plate difference of the steel plate under the condition that the finishing mill does not leak oil;

[0023] (4) The present application formulates different thickness control reference standards according to the thickness change of the steel plate at different stages, and the low-temperature pressure vessel steel plate with different thickness and width at different stages, from the thickness of the thickness gauge, the hot card thickness to the thickness after the final quenching and tempering heat treatment, so as to ensure that the steel plate thickness after the final quenching and tempering heat treatment can hit the extremely strict heat treatment order narrow tolerance band of +0.0 to +0.4mm, and the quantitative standard is prepared in advance from the thickness control standard of the previous process, and the thickness control of the previous process is optimized and adjusted according to the quantitative standard. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 It is the working roller profile curve diagram of the present application. Embodiment

[0025] Embodiment

[0026] In order to make the present application clearer, the following further describes a thickness control method of a low-temperature pressure vessel steel plate according to the present application with reference to the accompanying drawings, and the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0027] The thickness control method of the low-temperature pressure vessel steel plate realizes accurate thickness control of a low-temperature pressure vessel steel plate with a narrow tolerance, and specifically comprises:

[0028] (1) Roll shape system

[0029] The finishing mill support roll is ground 6 times with a composite curve roll shape, and the curve equation is:

[0030] y=a0+a1x+a2x 2 +a3x 3 +a4x 4 +a5x 5 +a6x 6 ;

[0031] For a convexity of 1.0 mm finishing mill support roll, a0=0, a1=0.0046332, a2=-8.94441e -006 , a3=9.20917e -009 , a4=-5.33350e -012 , a5=1.64741e -015 , and a6=-2.12022e -019 .

[0032] The work roll convexity and the number of sets used in one support roll period are shown in Table 1 as follows:

[0033]

[0034] In order to facilitate roll matching, the lower work roll convexity is always 0, and the upper work roll shape is a stepped roll shape curve, as shown in Figure 1 , the total length of the finishing mill work roll is 2690 mm, the total length of the middle platform is 1690 mm, and the platform has no convexity. There is a 500 mm long step on each side of the platform, and the step height is between 0.05-0.25 mm. The step height corresponds to the roll convexity. Using stepped roll matching can effectively avoid rapid wear of the roll convexity during rolling. At the same time, as the single set of support roll is worn, the convexity value of the finishing mill work roll is continuously increased, which ensures the superposition of the convexity effect of the support roll and the work roll.

[0035] (2) Rolling window period

[0036] Because the order width specification of low temperature pressure vessel steel plate changes greatly, the order width of the same batch order is between 1500-2500mm. In order to facilitate the production organization on site, the best rolling window period must be selected to arrange the production of slab charging. Define the transverse plate difference Δh of the steel plate, the edge thickness of the steel plate is h e , the middle thickness of the steel plate is h c , then the transverse plate difference is equal to the absolute value of the difference between the edge thickness and the middle thickness of the steel plate, that is:

[0037] Δh =︱h e -h c ︱

[0038] Select 3 slabs for each of the order widths 1500mm, 1800mm, 2000mm, 2200mm and 2500mm, a total of 15 slabs, one-time charging and rolling. When rolling under each width, the final pass rolling force of the finishing mill is kept constant. The average value of the transverse plate difference of the 15 slabs is calculated. When the finishing mill is directly rolled after the roll change, the transverse plate difference is defined as Δh0; when the finishing mill is rolled 1 hour after the roll change, the transverse plate difference is defined as Δh1. In turn, the roll change after 2, 3, 4 hours is named Δh2, Δh3, Δh4, etc.

[0039] The average value of the transverse plate difference under different rolling periods is shown in Table 2:

[0040]

[0041] It can be seen that when the roll period is 3-5 hours, the transverse plate difference is in a relatively ideal state, and the average value of the transverse plate difference is controlled to be less than 0.05mm. Therefore, selecting the rolling period of 3-5 hours for charging can obtain the best thickness reduction effect.

[0042] (3) Solidification of the final pass rolling force of the finishing mill

[0043] According to repeated tests on site, the given final pass rolling force of the finishing mill under different widths is given according to Table 3, which can obtain the smallest transverse plate difference of the steel plate under the condition of ensuring that the finishing mill does not leak oil.

[0044]

[0045] (4) Develop thickness control standard reference table

[0046] According to the thickness change of the steel plate at different stages, different thickness and width of low temperature pressure vessel steel plate at different stages of the steel plate, different thickness control reference standards are developed, as shown in Table 4:

[0047]

[0048] In the embodiment, taking the order thickness of 16 mm and the order width of 2300 mm as examples, the delivery thickness tolerance band of the order is 16.0-16.4 mm, the rolling is arranged to be performed 3-5 hours after the roll change in the on-site production arrangement, the final pass rolling force of the finishing mill is limited to 2350-2450 kN, the lower limit of the thickness control of the thickness gauge is +0.35, the hot gauge thickness is 16.25, after the final plate quenching and tempering heat treatment is completed, the average plate thickness is 16.2 mm, the delivery requirements of the plate are met, and the thickness after the plate quenching and tempering heat treatment hits the expectation.

[0049] After the method of the application is used, the production qualified rate of the low-temperature pressure vessel steel plate can be effectively improved by 2%, the benefit difference between qualified products and unqualified products is 3000 yuan per year for 8000 tons of steel plate production, and the benefit is 8000*2%*3000 = 480,000 yuan.

[0050] In addition to the above embodiments, the application can also have other implementation manners. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the application.

Claims

1.A thickness control method of cryogenic pressure vessel steel plate, the specific steps being as follows, characterized in that: (1) configuration of roll shape system: configuring different work roll crown for different support roll periods; (2) limitation of rolling window period: limiting the charging window period and the rolling window period of the steel plate rolling; (3) solidification of finishing mill last pass rolling force: optimizing the rolling process parameters, and limiting the size of the last pass rolling force of the steel plate of different widths; (4) establishment of thickness control standard reference: establishing a thickness gauge thickness and hot gauge thickness reference table during steel plate rolling, and further ensuring that the thickness precision of the steel plate after cooling, shot blasting and heat treatment meets the delivery requirements in the final quenched and tempered finished product state through accurate control of the previous process. 2.The thickness control method of cryogenic pressure vessel steel plate according to claim 1, characterized in that: In step (1), the finishing mill support roll is ground to a six-fold composite curve roll shape, with the curve equation y=a0+a1x+a2x. 2 +a3x 3 +a4x 4 +a5x 5 +a6x 6 . 3.The thickness control method of cryogenic pressure vessel steel plate according to claim 2, characterized in that: For the finishing mill backup roll with convexity 1.0 mm in step (1), a0=0, a1=0.0046332, a2=-8.94441e -006 , a3=9.20917e -009 , a4=-5.33350e -012 , a5=1.64741e -015 , a6=-2.12022e -019 . 4.The thickness control method of cryogenic pressure vessel steel plate according to any one of claims 1-3, characterized in that: in the step (1), the upper work roll crown in a support roll period is 0.05, 0.1, 0.15, 0.2 and 0.25 in turn, and the corresponding lower work roll crown is 0, and the matching use set number of the upper work roll and the lower work roll is 2, 6, 6, 8 and 2 in turn. 5.The thickness control method of cryogenic pressure vessel steel plate according to claim 4, characterized in that: in the step (1), the upper work roll shape is a stepped roll shape curve, which includes a middle platform and a stepped ladder connected to the arc on both sides of the platform, the crown of the middle platform is 0, and the height of the stepped ladder is 0.05-0.25 mm, and the stepped ladder height is the roll crown of the roll. 6.The thickness control method of cryogenic pressure vessel steel plate according to any one of claims 1-3, characterized in that: In the step (2), define the transverse plate thickness difference Δh of the steel plate, the thickness of the edge of the steel plate is h e , and the thickness of the middle of the steel plate is h c . The transverse plate thickness difference is equal to the absolute value of the difference between the thickness of the edge of the steel plate and the thickness of the middle of the steel plate, that is: Δh =︱h e -h c ︱. 7.The thickness control method of cryogenic pressure vessel steel plate according to claim 6, characterized in that: In the step (2), when the steel plate is directly rolled after the roll change of the finishing mill, the transverse same plate difference is Δh0, when the same batch of steel plates are rolled 1 hour after the roll change of the finishing mill, the transverse same plate difference is Δh1, and sequentially, the transverse same plate differences rolled 2, 3, 4, …, n hours after the roll change are Δh2, Δh3, Δh4, …, Δhn n Wherein, when n=3, 4, 5, that is, the rolling mill period is 3~5h, the average value of the transverse same plate difference is controlled to be <0.05mm, and the best thickness yield effect can be obtained. 8.The thickness control method of cryogenic pressure vessel steel plate according to any one of claims 1-3, characterized in that: in the step (3), when the order width is 1500-<1800 mm, 1800-<2000 mm, 2000-<2200 mm and 2200-2500 mm in turn, the finishing mill last pass rolling force is given as 13000-16000 kN, 16000-19000 kN, 19000-22000 kN and 22000-27000 kN in turn.

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