CN114737123A - Method for preventing Q235B casting blank longitudinal section stress crack from generating - Google Patents
Method for preventing Q235B casting blank longitudinal section stress crack from generating Download PDFInfo
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- CN114737123A CN114737123A CN202210411958.4A CN202210411958A CN114737123A CN 114737123 A CN114737123 A CN 114737123A CN 202210411958 A CN202210411958 A CN 202210411958A CN 114737123 A CN114737123 A CN 114737123A
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- 238000005266 casting Methods 0.000 title claims abstract description 146
- 238000000034 method Methods 0.000 title claims abstract description 45
- 238000005520 cutting process Methods 0.000 claims abstract description 101
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 27
- 239000010959 steel Substances 0.000 claims abstract description 27
- 238000009749 continuous casting Methods 0.000 claims abstract description 17
- 238000010438 heat treatment Methods 0.000 claims abstract description 10
- 229910052748 manganese Inorganic materials 0.000 claims abstract description 8
- 238000009628 steelmaking Methods 0.000 claims abstract description 8
- 238000001816 cooling Methods 0.000 claims abstract description 6
- 239000012535 impurity Substances 0.000 claims abstract description 6
- 239000000126 substance Substances 0.000 claims abstract description 6
- 230000007246 mechanism Effects 0.000 claims description 21
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 20
- 238000011010 flushing procedure Methods 0.000 claims description 15
- 239000002893 slag Substances 0.000 claims description 15
- 239000011572 manganese Substances 0.000 claims description 14
- 239000000498 cooling water Substances 0.000 claims description 13
- 238000005096 rolling process Methods 0.000 claims description 7
- 229910052698 phosphorus Inorganic materials 0.000 claims description 6
- 229910052799 carbon Inorganic materials 0.000 claims description 5
- 238000007493 shaping process Methods 0.000 claims description 3
- 229910000914 Mn alloy Inorganic materials 0.000 claims description 2
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 2
- 229910052782 aluminium Inorganic materials 0.000 claims description 2
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 2
- 238000007664 blowing Methods 0.000 claims description 2
- PYLLWONICXJARP-UHFFFAOYSA-N manganese silicon Chemical compound [Si].[Mn] PYLLWONICXJARP-UHFFFAOYSA-N 0.000 claims description 2
- 229910052760 oxygen Inorganic materials 0.000 claims description 2
- 239000001301 oxygen Substances 0.000 claims description 2
- 238000010079 rubber tapping Methods 0.000 claims description 2
- 235000012771 pancakes Nutrition 0.000 claims 1
- 230000035882 stress Effects 0.000 abstract description 15
- 230000007547 defect Effects 0.000 abstract description 9
- 239000000203 mixture Substances 0.000 abstract description 6
- 229910000734 martensite Inorganic materials 0.000 abstract description 5
- 230000008646 thermal stress Effects 0.000 abstract description 4
- 238000005265 energy consumption Methods 0.000 abstract description 3
- 238000004519 manufacturing process Methods 0.000 description 7
- 238000005204 segregation Methods 0.000 description 5
- 229910052717 sulfur Inorganic materials 0.000 description 5
- 238000005336 cracking Methods 0.000 description 3
- 229910001563 bainite Inorganic materials 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 238000003466 welding Methods 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- NINIDFKCEFEMDL-UHFFFAOYSA-N Sulfur Chemical compound [S] NINIDFKCEFEMDL-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000008602 contraction Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000005611 electricity Effects 0.000 description 1
- 230000006355 external stress Effects 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 229910001562 pearlite Inorganic materials 0.000 description 1
- 238000010583 slow cooling Methods 0.000 description 1
- 238000005728 strengthening Methods 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 230000003313 weakening effect Effects 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/12—Accessories for subsequent treating or working cast stock in situ
- B22D11/126—Accessories for subsequent treating or working cast stock in situ for cutting
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/16—Controlling or regulating processes or operations
- B22D11/22—Controlling or regulating processes or operations for cooling cast stock or mould
- B22D11/225—Controlling or regulating processes or operations for cooling cast stock or mould for secondary cooling
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Materials Engineering (AREA)
- Metallurgy (AREA)
- Organic Chemistry (AREA)
- Continuous Casting (AREA)
Abstract
A method for preventing Q235B casting blank longitudinal section stress crack from generating comprises converter steelmaking and continuous casting processes, wherein the chemical composition percentage of steel in the converter steelmaking process is controlled as follows: c: 0.06-0.10%, Mn: 0.65-0.80%, Si: less than or equal to 0.15 percent, P: less than or equal to 0.025 percent, S: less than or equal to 0.025 percent, Als: 0.010-0.030%, the balance of inevitable impurities, and the Mn/S is more than or equal to 30; in the continuous casting process, a transverse cutting device and a longitudinal cutting device are sequentially arranged along the advancing direction of a casting blank, the transverse cutting device transversely cuts the casting blank according to the fixed length of the casting blank, and the longitudinal cutting device longitudinally cuts the casting blank into a plurality of casting blanks with narrow sizes in a thermal state according to the width requirement of the casting blank. The invention has the following advantages: 1. the composition of steel grades is adjusted, and the generation of martensite in the cooling process is reduced. 2. The casting blank thermal state longitudinal cutting is adopted, and the defect that cracks are generated due to local thermal stress concentration caused by uneven temperature of cold-cut casting blanks is overcome. 3. The energy consumption required by heating the casting blank is saved.
Description
Technical Field
The invention relates to a method for preventing Q235B casting blank longitudinal section stress crack from generating, and belongs to the technical field of steel making.
Background
At present, small continuous casting machines (rectangular billets and square billets) are gradually eliminated due to poor capacity and low production efficiency, but the requirements of downstream customers on narrow strip steel are still large, and the required width is between 350 and 850 mm. The requirements of different strip steel widths on the width of a casting blank are different, so the casting blanks with different widths need to be produced to meet the requirements of different customers on the width of the strip steel, the process equipment for determining the specification of the casting blanks in slab production is a crystallizer, the width of the crystallizer needs to be frequently adjusted to meet the requirements of different strip steel widths, the production efficiency is low, and the production of small-section casting blanks restricts the exertion of steelmaking productivity. Based on long pouring cycle, large temperature drop and high consumption of related wind, water, electricity and devices in the production of the molten steel by the small-section casting blank, some steel enterprises longitudinally cut the wider casting blank, and longitudinally cut the casting blank by flame cutting according to the width requirements of different strip steels, thereby ensuring the delivery requirements of the narrower strip steels and simultaneously reducing the related production consumption.
The cross section size of the Q235B casting blank is 200 multiplied by 920 and 1120mm, and the casting blank is longitudinally cut according to the requirement of products. In the prior art, when a casting blank is placed in a cold state (at ambient temperature), a flame cutting gun is used for longitudinally cutting a plurality of channels along the length direction of the casting blank according to the width requirement of rolled strip steel, and then the casting blank is sent for rolling. The problems with this conventional approach are: after cold cutting and casting blank rolling, edge cracking defects at the edge of the strip steel corresponding to a cutting surface are frequently found, cracks vertical to the longitudinal cutting surface and center looseness exist at the center of the cutting surface of the longitudinal cutting surface of the casting blank, the vertical cracks extend towards the inside of the casting blank, the length is about 1.5cm, the depth is about 1cm, when the casting blank enters a heating furnace and is rolled, the defects extend about 5mm along the transverse deepest part of the strip steel, and the requirements of downstream customers are seriously influenced.
Disclosure of Invention
The invention aims to solve the problems in the prior art and provides a method for preventing the generation of stress cracks on the longitudinal section of a Q235B casting blank, aiming at the generation reasons of the cracks on the longitudinal section of the casting blank, the method solves the problem of the cracks on the longitudinal section by means of designing the components of the casting blank, controlling secondary cooling parameters of continuous casting, longitudinally cutting the hot casting blank and the like, and achieves the aim of smoothly producing the Q235B longitudinally cut casting blank.
The problems of the invention are solved by the following technical scheme:
a method for preventing the Q235B casting blank from generating stress cracks on the longitudinal section comprises the working procedures of converter steelmaking and continuous casting, wherein the chemical composition percentage of steel in the working procedure of converter steelmaking is controlled as follows: c: 0.06-0.10%, Mn: 0.65-0.80%, Si: less than or equal to 0.15 percent, P: less than or equal to 0.025 percent, S: less than or equal to 0.025%, Als: 0.010-0.030%, the balance of inevitable impurities, and the Mn/S is more than or equal to 30;
the continuous casting process is characterized in that a transverse cutting device and a longitudinal cutting device are sequentially arranged along the advancing direction of a casting blank, the transverse cutting device transversely cuts the casting blank according to the fixed length of the casting blank, and the longitudinal cutting device longitudinally cuts the casting blank into a plurality of casting blanks with narrow sizes in a thermal state according to the width requirement of the casting blank; and conveying the cut casting blank along a roller way, and feeding the casting blank into a heating furnace for rolling.
The method for preventing stress cracks of the longitudinal section of the Q235B casting blank from being generated comprises a longitudinal cutting device, a cutting gun, a transverse adjusting mechanism and a slag flushing component, wherein the lower portion of the longitudinal cutting frame is fixed with a supporting bottom beam, the supporting bottom beam is fixed on two sides of a casting blank roller way, the transverse adjusting mechanism comprises a stepping motor, a moving trolley and a scale, the stepping motor and the scale are respectively fixed on the longitudinal cutting frame, the stepping motor is connected with a lead screw, a nut is connected with the moving trolley, the lead screw is in threaded connection, a pointer is arranged on the lower portion of the moving trolley and corresponds to the scale, the cutting gun is installed on the moving trolley, and the scale is fixed on the longitudinal cutting frame.
According to the method for preventing the Q235B casting blank longitudinal section stress crack from generating, the longitudinal cutting frame is provided with the transverse rail, the lower part of the movable trolley is provided with the roller, and the roller is positioned on the transverse rail.
According to the method for preventing the Q235B casting blank longitudinal section stress crack generation, three sets of transverse adjusting mechanisms are arranged and are respectively positioned in a front row and a rear row, wherein two sets of transverse adjusting mechanisms are symmetrically arranged in one row, one set of transverse adjusting mechanism is arranged in the other row, and the front position and the rear position of a cutting gun position of the three sets of transverse adjusting mechanisms are consistent.
According to the method for controlling the flat rolling of the hot-rolled strip steel, the slag flushing component comprises the slag flushing water pipes which are symmetrically arranged, water nozzles are installed at the outlets of the slag flushing water pipes, and the water nozzles correspond to the rollers.
According to the method for preventing the Q235B casting blank longitudinal section stress crack from generating, the cooling water in the second continuous casting process adopts a cooling mode of firstly strong and then weak, the specific water amount is 0.70-0.80L/kg, the drawing speed is controlled within the range of 1.35-1.50m/min, and the inner and outer arc cooling water in the sector section 1-2 groups is started in the pouring process, so that the thickness of the casting blank shell of the casting blank and the casting blank shaping in the higher drawing speed mode are ensured; and (3) closing the inner arc cooling water of the sector section groups 3-6, reducing the surface temperature drop of the casting blank and ensuring that the surface temperature of the blank is more than or equal to 800 ℃ before the thermal-state longitudinal cutting of the casting blank.
According to the method for preventing the Q235B casting blank longitudinal section stress crack from generating, the converter end point temperature is controlled at 1640-1660 ℃, P is controlled to be less than or equal to 0.020 percent, S is controlled to be less than or equal to 0.020 percent, aluminum deoxidation and silicon-manganese alloy addition are carried out in the tapping process, oxygen is determined after the converter, O in steel is less than or equal to 20ppm, and the total soft blowing time is guaranteed to be more than or equal to 10 minutes.
According to the method for preventing the stress crack of the longitudinal section of the Q235B casting blank, the distance between the transverse cutting device and the longitudinal cutting device is not less than 2.5 meters.
The method for preventing the Q235B casting blank longitudinal section stress crack from generating has the tundish temperature controlled between 1540 and 1560 ℃.
Compared with the prior art, the invention has the following advantages: 1. the components of the steel grade are adjusted, the carbon content is reduced, the Mn/S is improved, the central porosity of the casting blank is reduced, and the generation of martensite in the cooling process of the casting blank is reduced. 2. By adopting the thermal state longitudinal cutting of the casting blank, the defect that cracks are generated due to local thermal stress concentration caused by uneven temperature of the cold-cut casting blank is eliminated, meanwhile, the required field for slow cooling of the casting blank is reduced, and the production efficiency is improved. 3. The hot casting blank can be directly rolled after being longitudinally cut, and compared with cold cutting, the temperature of the casting blank when being loaded into a heating furnace can be increased, and the energy consumption required by heating the casting blank can be saved. 4. The slab (or square billet) continuous casting machine with small section does not need to be built, and the requirement of the specification of a rolled product can be met.
Drawings
The invention will be further explained with reference to the drawings.
FIG. 1 is a schematic configuration diagram of a transverse cutting device and a longitudinal cutting device in a continuous casting process of the present invention;
FIG. 2 is an enlarged view of a portion of FIG. 1 at A;
fig. 3 is a schematic view of a slitting apparatus.
The reference numbers in the figures are: 1. the device comprises a withdrawal and straightening machine, 2 parts of a casting blank, 3 parts of a transverse cutting device, 4 parts of a roller, 5 parts of a longitudinal cutting device, 5 parts of 1 part of a supporting bottom beam, 5 parts of 2 parts of a longitudinal cutting frame, 5 parts of 3 parts of a stepping motor, 5 parts of 4 parts of a lead screw, 5 parts of a moving trolley, 5 parts of 6 parts of a screw nut, 5 parts of 7 parts of a cutting gun, 5 parts of 8 parts of a scale, 5 parts of 9 parts of a slag flushing water pipe, 5 parts of 10 parts of a water nozzle, 5 parts of 11 parts of a transverse rail, 5 parts of 12 parts of a roller wheel.
Detailed Description
A sample is taken from a crack part and a crack-free part of a longitudinal cutting surface of a Q235B casting blank for metallographic analysis, the sample is corroded by 4% nitric acid alcohol solution after being polished and polished, the matrix structure of the sample is ferrite, pearlite and a small amount of bainite, and bainite and martensite are arranged near the crack. The main causes of cracking were analyzed as follows: 1. the components are as follows: because the C, S, P element is a strong center segregation element, the center segregation of the casting blank is serious, after the cold blank is hot cut, the upper end and the lower end of the casting blank of the cutting surface have low temperature and high center temperature, and the center segregation is aggravated; 2. the cutting process aspect: when a cold-state casting blank is cut, the temperature difference between the surface close to the welding gun and the surface far away from the welding gun is large, and the cutting surface deforms towards a non-cutting surface under the action of thermal expansion and cold contraction and stress, so that the casting blank deforms after being cut, and the crack tendency of the cutting surface is aggravated; meanwhile, the temperature of the cutting area is rapidly increased to more than 2000 ℃ under the action of high temperature of flame cutting, and the cut surface is rapidly cooled in the air, so that the structure of the cut surface of the casting blank is changed, and cracks vertical to the cut surface are formed under the action of thermal stress and external force; the external stress makes the crack expand along the segregation line to the width direction and the length direction to form micro-cracks which are exposed at the edge part of the casting blank, the exposed crack of the casting blank in the heating furnace is oxidized at high temperature, a large number of oxidation round points are formed around the crack and continue to expand, and the edge cracking defect is formed in the rolling process.
Aiming at the reason of the crack generation of the longitudinal cutting surface of the Q235B casting blank, the invention improves the following steps: 1. the chemical composition of the Q235B steel is adjusted as follows: c: 0.06-0.10%, Mn: 0.65-0.80%, Si: less than or equal to 0.15 percent, P: less than or equal to 0.025 percent, S: less than or equal to 0.025 percent, Als: 0.010-0.030%, and the balance inevitable impurities. The weight percentages of C, Mn, S and P elements in the steel are controlled, the Mn/S is improved, and the Mn/S requirement in the component design of the invention is more than or equal to 30. The increase of Mn/S is beneficial to combining Mn of steel grade with sulfur to form MnS, and FeS in the steel is avoided. The FeS has a high melting point, and if not controlled, segregation inside the cast slab is likely to occur, which leads to the aggravation of the origin of the crack under the action of stress or the generation of the crack. And the low-C component design is adopted, so that the martensite structure in the casting blank cooling process is effectively reduced. The Mn and Si contents are properly increased to meet the requirement of mechanical property. 2. The casting blank is cut in a thermal state mode in an online thermal cutting mode, so that the casting blank is effectively prevented from being rapidly heated and quenched, martensite is reduced, the influence of thermal stress on a cutting surface is reduced, stress delay cracks after flame cutting are avoided, and cracks of the cutting surface are greatly reduced. Meanwhile, the hot casting blank can be directly rolled after being longitudinally cut, and compared with cold cutting, the temperature of the casting blank when being loaded into a heating furnace can be increased, and the energy consumption required by heating the casting blank can be saved. 3. The temperature of the tundish is controlled between 1540-plus 1560 ℃, the continuous casting secondary cooling water adopts a cold shortage mode of firstly strengthening and then weakening, the specific water amount is 0.70-0.80L/kg, the casting speed is controlled within the range of 1.35-1.50m/min, 1-2 groups of inner and outer arc cooling water of the sector section are started in the casting process (the equipment sector section is cooled into 9 groups, 1-2 groups are vertical sections, 3-6 sections are straightening sections, and the casting blank is changed from vertical to horizontal when passing through 3-6 groups), so that the shell thickness of the casting blank and the casting blank shaping in a higher casting speed mode are ensured. And meanwhile, the cooling water of the inner arcs of 3-6 groups of the fan-shaped sections is closed, so that the surface temperature drop of the casting blank is reduced, and the surface temperature of the casting blank is guaranteed to be more than or equal to 800 ℃ before the casting blank is subjected to thermal state longitudinal cutting.
In order to realize the on-line hot longitudinal cutting of the casting blank, the invention is additionally provided with a longitudinal cutting device on the basis of the original transverse cutting device in the continuous casting process. Referring to fig. 1 to 3, in the continuous casting process, a transverse cutting device 3 and a longitudinal cutting device 5 are sequentially arranged along the advancing direction of a casting blank 2, and the distance between the transverse cutting device and the longitudinal cutting device is not less than 2.5 meters. The cast blank 2 delivered by the withdrawal and straightening unit 1 is transported by rollers 4, first by a transverse cutting device and then by a longitudinal cutting device. The transverse cutting device transversely cuts the casting blank according to the fixed length of the casting blank, and the longitudinal cutting device longitudinally cuts the casting blank into a plurality of casting blanks with narrow sizes in a thermal state according to the width requirement of the casting blank; and conveying the cut casting blank along a roller way, and feeding the casting blank into a heating furnace for rolling.
Still referring to fig. 1-3, the slitting device includes a slitting frame 5-2, a cutting gun 5-7, a lateral adjustment mechanism, and a flushing slag assembly. The lower part of the longitudinal cutting frame is fixed with a supporting bottom beam 5-1, the supporting bottom beam is fixed on two sides of a casting blank roller way, and the longitudinal cutting frame spans the upper parts of the rollers 4 and the casting blanks 2. The transverse adjusting mechanism is used for adjusting the transverse position of the cutting gun according to the width size requirement of the longitudinally cut casting blank. The transverse adjusting mechanism is arranged at the longitudinal cutting frame and comprises a stepping motor 5-3, a moving trolley 5-5 and a scale 5-8. The stepping motor and the scale are respectively fixed on the longitudinal cutting frame, the stepping motor is connected with a lead screw 5-4, a nut 5-6 is connected with the movable trolley, and the lead screw and the nut are in spiral connection. The cutting torch is arranged on the movable trolley. In order to ensure the stable movement of the movable trolley and reduce the movement resistance, the longitudinal cutting frame is fixed with a transverse rail 5-11, the lower part of the movable trolley is provided with a roller 5-12, and the roller is positioned on the transverse rail. And a pointer is arranged at the lower part of the movable trolley and corresponds to the scale. The stepping motor rotates to drive the lead screw to rotate, the lead screw drives the screw nut, the screw nut drives the movable trolley to transversely move, and the movable trolley moves to a proper position according to the scale of the scale. In order to enable the longitudinal cutting device to meet the cutting requirements on different widths of casting blanks, three sets of transverse adjusting mechanisms are arranged and are respectively positioned in the front row and the rear row. Two sets of transverse adjusting mechanisms are symmetrically arranged in one row, and the two sets of transverse adjusting devices are respectively positioned on two sides; and the other row is provided with a set of transverse adjusting mechanism, the transverse adjusting mechanism corresponds to the middle part of the casting blank, and the cutting guns respectively arranged on the three sets of transverse adjusting mechanisms are kept consistent in front and back positions. When the casting blank is longitudinally cut, the positions of all the transverse adjusting mechanisms can be flexibly adjusted according to the width size of the casting blank and the cutting requirement, and a cutting gun needing to be ignited for cutting is determined. The slag flushing component comprises slag flushing water pipes 5-9 which are symmetrically arranged, water nozzles 5-10 are arranged at the outlets of the slag flushing water pipes, and the water nozzles correspond to the rollers by adjusting the angles of the water nozzles. The slag flushing component is used for flushing accumulated slag on the roller when the casting blank is cut when the device works.
Two specific examples are provided below.
Example 1: the chemical composition of the Q235B is controlled by the following percentage: c: 0.065%, Mn: 0.73%, Si: 0.12%, P: 0.015%, S: 0.012%, Als: 0.021%, and the balance inevitable impurities. The converter end point temperature was controlled at 1650 ℃. The drawing speed of the continuous casting process is 1.45m/min, the tundish temperature is 1550 ℃, and the specific water content is 0.75L/kg; in the casting process, the inner arc cooling water of the sector section 1-2 groups is started, and the inner arc cooling water of the sector section 3-6 groups is closed. The cutting surface temperature of the cast blank is 823 ℃. Two cutting guns positioned at two sides are ignited to cut the casting blank, the width of the casting blank is 1020mm when the casting blank is not cut, the casting blank is divided into two casting blanks with the width of 329mm and one casting blank with the width of 358mm after the cutting, and the width of a cutting gap is 2.0 mm.
The detection shows that no crack defect appears on the longitudinal cutting surface of the casting blank, and no crack edge defect exists on the edge of the rolled strip steel. The yield strength of the rolled strip steel is 336MPa, the tensile strength is 405MPa, and the elongation after fracture is 33.5 percent.
Example 2: the chemical composition of the Q235B is controlled by the following percentage: c: 0.061%, Mn: 0.70%, Si: 0.11%, P: 0.016%, S: 0.013%, Als: 0.019%, and the balance unavoidable impurities. The converter end point temperature was controlled at 1650 ℃. In the continuous casting process, the casting speed is 1.5m/min, the tundish temperature is 1551 ℃, and the specific water amount is 0.8L/kg; in the casting process, the inner arc cooling water of the sector section 1-2 groups is started, and the inner arc cooling water of the sector section 3-6 groups is closed. The surface temperature of the cut cast blank is 830 ℃. And (3) igniting a cutting gun positioned in the middle to cut the casting blank, wherein the width of the casting blank is 920mm when the casting blank is not cut, and the cut casting blank is divided into 2 casting blanks with the width of 459mm (the width of a cutting slit is 2.0 mm).
The detection shows that no crack defect appears on the cutting surface of the casting blank, and no crack edge defect appears on the edge of the rolled strip steel. The yield strength of the rolled strip steel is 323MPa, the tensile strength is 410MPa, and the elongation after fracture is 34.5%.
Claims (9)
1. A method for preventing the generation of stress cracks on the longitudinal section of a Q235B casting blank comprises converter steelmaking and continuous casting processes, and is characterized in that: the chemical components of the steel in percentage in the converter steelmaking process are controlled as follows: c: 0.06-0.10%, Mn: 0.65-0.80%, Si: less than or equal to 0.15 percent, P: less than or equal to 0.025 percent, S: less than or equal to 0.025 percent, Als: 0.010-0.030%, the balance of inevitable impurities, and the Mn/S is more than or equal to 30;
the continuous casting process is characterized in that a transverse cutting device and a longitudinal cutting device are sequentially arranged along the advancing direction of a casting blank, the transverse cutting device transversely cuts the casting blank according to the fixed length of the casting blank, and the longitudinal cutting device longitudinally cuts the casting blank into a plurality of casting blanks with narrow sizes in a thermal state according to the width requirement of the casting blank; and conveying the cut casting blank along a roller way, and feeding the casting blank into a heating furnace for rolling.
2. The method for preventing the Q235B casting blank longitudinal section stress crack from generating as claimed in claim 1, wherein: the longitudinal cutting device comprises a longitudinal cutting frame, a cutting gun, a transverse adjusting mechanism and a slag flushing assembly, the lower portion of the longitudinal cutting frame is fixed with a supporting bottom beam, the supporting bottom beam is fixed on two sides of a casting blank roller way, the transverse adjusting mechanism comprises a stepping motor, a movable trolley and a scale, the stepping motor and the scale are respectively fixed on the longitudinal cutting frame, the stepping motor is connected with a lead screw, the movable trolley is connected with a nut, the lead screw is in screw connection with the nut, the lower portion of the movable trolley is provided with a pointer, the pointer corresponds to the scale, the cutting gun is installed on the movable trolley, and the scale is fixed on the longitudinal cutting frame.
3. The method for preventing the Q235B casting blank longitudinal section stress crack from generating as claimed in claim 2, wherein: the longitudinal cutting frame is provided with a transverse rail, the lower part of the movable trolley is provided with a roller wheel, and the roller wheel is positioned on the transverse rail.
4. The method for preventing the Q235B casting blank longitudinal section stress crack from generating as claimed in claim 3, wherein: the transverse adjusting mechanisms are provided with three sets and are respectively positioned in a front row and a rear row, wherein two sets of transverse adjusting mechanisms are symmetrically arranged in one row, one set of transverse adjusting mechanism is arranged in the other row, and the front position and the rear position of the cutting gun position of the three sets of transverse adjusting mechanisms are consistent.
5. The method of controlling hot rolled strip pancake coil as claimed in claim 4, wherein: the slag flushing component comprises slag flushing water pipes which are symmetrically arranged, and water nozzles are mounted at the outlets of the slag flushing water pipes and correspond to the rollers.
6. The method for preventing the Q235B casting blank longitudinal section stress crack from generating as claimed in claim 5, wherein: the cooling water in the second continuous casting procedure adopts a cooling mode of firstly strong and then weak, the specific water amount is 0.70-0.80L/kg, the casting speed is controlled within the range of 1.35-1.50m/min, and the inner and outer arc cooling water in 1-2 groups of the fan-shaped sections is started in the casting process to ensure the shell thickness of the casting blank and the shaping of the casting blank in a higher casting speed mode; and (3) closing the inner arc cooling water of the sector section groups 3-6, reducing the surface temperature drop of the casting blank and ensuring that the surface temperature of the blank is more than or equal to 800 ℃ before the thermal-state longitudinal cutting of the casting blank.
7. The method for preventing the stress crack generation of the longitudinal section of the Q235B casting blank according to claim 6, wherein the method comprises the following steps: the end point temperature of the converter is controlled at 1640-1660 ℃, P is controlled to be less than or equal to 0.020 percent, S is controlled to be less than or equal to 0.020 percent, aluminum is deoxidized during tapping, silicon-manganese alloy is added, oxygen is determined after the converter, the [ O ] in steel is less than or equal to 20ppm, and the total soft blowing time is ensured to be more than or equal to 10 minutes.
8. The method for preventing the Q235B casting blank longitudinal section stress crack from generating as claimed in claim 7, wherein: the distance between the transverse cutting device and the longitudinal cutting device is not less than 2.5 meters.
9. The method for preventing the Q235B casting blank longitudinal section stress crack from generating as claimed in claim 8, wherein: the temperature of the tundish is controlled between 1540 and 1560 ℃.
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