CN112410653B - Method for effectively preventing 40Cr cold thin slab slitting cracks from being generated - Google Patents

Abstract

The invention discloses a method for effectively preventing 40Cr cold thin slab slitting cracks from generating, which specifically comprises the steps of smelting by adopting a top-bottom combined blown converter, and carrying out deoxidation alloying on aluminum iron, silicon-manganese alloy, silicon iron, high-carbon ferrochrome and the like; LF refining, whole-process protective pouring, and reasonable storage of qualified continuous casting billets after being off-line, so that casting billet cracks caused by too fast cooling are avoided; when the 40Cr wide thin slab of the alloy structural steel is cut, the surface of a cutting line is preheated, the low-speed cutting speed of 50-80 mm/min is adopted, the cutting support is straight, and the uniform stress of each cut small slab supporting point is ensured. The small plate blank after cutting is placed into a heating furnace for heating within 4 hours after cutting, the preheating section and the heating section adopt a heating mode with the speed of 5-15 ℃/min, and then a mode of 'firstly transverse rolling and then longitudinal rolling' is adopted on a medium plate rolling mill, so that the defect of cutting cracks of the high-carbon high-chromium alloy steel due to local uneven heating can be effectively avoided, and the alloy structural steel with various thicknesses and various width sizes can be conveniently produced.

Description

Method for effectively preventing 40Cr cold thin slab slitting cracks from being generated

Technical Field

The invention relates to the technical field of production of high-carbon high-chromium (Cr) alloy steel plates, and mainly relates to a method for effectively preventing 40Cr cold thin slab slitting cracks from generating.

Background

The 40Cr high-carbon alloy steel is one of GB/T3077-1999 alloy structural steel standards, and has wide application, 40Cr of wires and bars is mainly used for manufacturing parts such as worms, spindles, crankshafts, connecting rods, screws, nuts and the like, and 40Cr of plates is mainly used for manufacturing parts such as gears, brake pads and the like.

When purchasing 40Cr steel plates, users have the characteristics of small quantity and large specification, so that a medium plate manufacturer is difficult to complete an order by using a continuous casting plate blank with a fixed width dimension. The continuous casting slab with one width is required to be used, and after the slab is transversely and longitudinally cut according to the size of an order, rolling is carried out to complete all orders, so that the production times of the continuous casting slab with various sections in the continuous casting process can be reduced, and the production cost is reduced.

When the alloy structural steel 40Cr is cut into a high-temperature continuous casting slab, the slab is not easy to have cutting cracks, but the slab after cooling is not reasonable in cutting process and storage condition after cutting, small cutting cracks are easy to appear, the small cracks on the cut edge are further expanded in the subsequent slab heating process, and after the transverse-longitudinal rolling process, the edge part (the cut edge of the slab) of a finished steel plate has an intermittent and large V-shaped notch, so that the requirement of a user on the size of the steel plate cannot be met finally. Therefore, an effective 40Cr cold plate blank cutting and storing production process is formulated, so that cold plate blank cutting cracks are avoided, stable product quality is ensured, and order requirements are timely and effectively completed.

Disclosure of Invention

The invention aims to provide a method for effectively preventing the generation of 40Cr cold thin slab slitting cracks, which can realize that a continuous casting slab with one width is slit after being cooled, can produce 40Cr alloy structural steel plates with various specification ranges, meets the order requirements of users on small batches and multiple specifications, has low cost and simple process, and is suitable for the production of medium and heavy plates with small orders and multiple specifications.

In order to achieve the purpose, the invention adopts the technical scheme that:

a method for effectively preventing 40Cr cold thin slab slitting cracks from generating comprises the following steps:

step one, steel making, namely smelting the steel into molten steel by adopting an oxygen top-bottom combined blowing converter, and deoxidizing and alloying by adopting aluminum iron, silicon-manganese alloy, ferrosilicon and high-carbon ferrochrome; controlling the bottom blowing flow (300-500 NL/min) of the steel ladle in the LF refining process, and keeping soft stirring; adding modifier, lime and other white slag to eliminate S from steel and adding calcium and iron wire for modifying sulfide inclusion; keeping the soft stirring time to be more than or equal to 8min after refining is finished, improving the cleanliness of molten steel, wherein the chemical composition of 40Cr meets the specification of GB/T3077-2015 Table 1;

continuous casting, namely performing whole-process protective casting to prevent secondary pollution of molten steel and improve the quality of a casting blank, wherein the continuous casting process is performed on a wide and thin slab continuous casting machine, the thickness of the continuous casting blank is 150mm, the maximum width of the continuous casting blank is 3250mm, and the maximum length of the continuous casting blank is 18000 mm;

step three, storing the plate blank, namely stacking and storing the 40Cr plate blank produced in the continuous casting process at positions of vents such as doors and windows of a plate blank warehouse, avoiding the positions of the vents such as the doors and the windows, ensuring slow cooling of the plate blank and preventing the edge of the casting blank from cracking due to large internal stress generated during rapid cooling of the 40Cr continuous casting plate blank; the plate blank which does not need to be cut is slowly cooled and then directly sent into a heating furnace to be heated and then rolled;

and fourthly, preparing for cutting the continuous casting cold plate blank, hoisting the cooled 40Cr plate blank to a plate blank cutting area, requiring the cutting support to be straight, ensuring that the stress of each small blank supporting point after cutting is even, and avoiding stress concentration caused by overlarge local stress of the plate blank in the cutting process. According to the requirement of the order on the blank size, determining a tangent line on the plate blank, automatically or manually cutting along the width direction of the 40Cr plate blank, or firstly longitudinally cutting from the middle along the length direction of the 40Cr plate blank and then transversely cutting along the width direction of the 40Cr plate blank;

and step five, cutting the continuous casting cold plate blank, wherein the surface of the cutting line is preheated before cutting because the carbon content of the alloy structural steel 40Cr is high, the Cr content is high, the heat conductivity coefficient is low, and the cutting crack is easy to appear, and the cutting line is manually moved back and forth by using high-temperature flame of a cutting gun, so that the cutting line range of the plate blank is preheated to 50-150 ℃. The cutting gas is acetylene and oxygen (acetylene burns to provide heat to melt the plate blank, and oxygen reacts with metal to produce oxide, so that the plate blank is convenient to separate), and the cutting speed is 50-80 mm/min;

sixthly, storing the cut plate blanks and feeding the cut plate blanks into a furnace, wherein the cut 40Cr small plate blanks are transported to a plate blank storage area of a heating furnace as soon as possible, stacked and stored, and the positions of ventilation openings such as doors and windows of a plate blank warehouse are avoided, so that the plate blanks are required to be loaded into the heating furnace for heating within 4 hours or less after being cut;

seventhly, heating and rolling the slit plate blank, putting the slit 40Cr plate blank into a heating furnace, adopting a slow heating mode in a preheating section and a heating section, wherein the heating speed is 5-15 ℃/min, the total in-furnace time is 180-240 min, the plate blank discharging temperature is 1230 +/-20 ℃, ensuring that alloy elements are fully dissolved, and simultaneously preventing the plate blank from cracking due to high alloy content and weak heat transfer capacity of 40Cr and easily generating larger thermal stress when the plate blank is heated; and rolling the heated small plate blank in a medium plate rolling mill in a transverse and longitudinal rolling mode, and finishing the steel plate.

Preferably, in the third step, the slabs are stacked and stored by avoiding the positions of ventilation openings such as doors and windows of the slab warehouse, so that the slabs are ensured to be cooled slowly, and the edges of the cast slabs are prevented from cracking due to the generation of large internal stress when the 40Cr continuous cast slabs are cooled rapidly.

Preferably, in the fourth step, the cutting bracket is straight when the structural alloy steel 40Cr wide thin slab is slit, so that the supporting point of each slit small slab is uniformly stressed.

Preferably, in the fifth step, before the 40Cr wide thin slab of the alloy structural steel is cut, the surface of the cutting line is preheated to 50-150 ℃, so that the cutting cracks caused by local uneven heating are avoided, and the cutting speed is 50-80 mm/min.

Preferably, in the sixth step, the slit small alloy structural steel 40Cr slabs are loaded into a heating furnace for heating within less than or equal to 4 hours.

Preferably, in the seventh step, in the heating process of the small plate blank, the preheating section and the heating section adopt a slow heating mode, and the heating speed is less than or equal to 5-15 ℃/min.

Compared with the prior art, the invention has the beneficial effects that:

1. in the technical scheme, a top-bottom combined blown converter is used for smelting steel, iron, silicon-manganese alloy, ferrosilicon, high-carbon ferrochromium and the like are adopted for deoxidation alloying, LF refining treatment is carried out, and modifier, lime and the like are added to make white slag for desulfurization, so that the accurate control of components and the extremely low content of P, S impurity elements are ensured.

2. According to the technical scheme, the whole-process protection pouring is adopted in the continuous casting process, so that good molten steel cleanliness, casting blank quality and final steel performance are guaranteed.

3. Among the above-mentioned technical scheme, production processes are simple, easily operation and control adopt the sheet metal continuous casting billet of a specification promptly, can satisfy the steel sheet of multiple specification of multiple rolling mill production, and manufacturing cost is lower.

4. The method is practiced on a 2800mm heavy and medium plate mill, has obvious effect, meets the requirement of users on producing small-batch 40Cr steel plates of alloy structural steel with various thickness and width size requirements by using a continuous casting plate blank with fixed width size, and has obvious economic benefit.

Detailed Description

The invention will be further explained by taking the practice of producing 40Cr hot rolled steel plate by rolling a casting blank produced by a second mill of the company in a 3500mm steckel mill or a 2800mm medium plate mill in a first mill as an example.

Example 1

The production process comprises the following steps: 150t top-bottom combined blown converter smelting, 150tLF furnace refining, 150mm 1800-3250 mm thin and wide slab continuous casting, casting blank slow cooling and 3500mm steckel mill slab heating and rolling in a second mill rolling mill of the company; or the cold casting blank is cut to a 2800mm medium plate mill plate blank of a first mill and mill to be heated and rolled.

The alloy structural steel 40Cr comprises the following components (wt%, smelting analysis): c: 0.41, Si: 0.29, Mn: 0.75, P: 0.015, S: less than or equal to 0.004, Cr: 0.98, and the balance of Fe and inevitable impurities.

1) Smelting steel by an oxygen top-bottom combined blowing converter, and deoxidizing and alloying by adopting aluminum iron, silicon manganese alloy, ferrosilicon, high-carbon ferrochrome and the like. Controlling the bottom blowing flow (300-500 NL/min) of the steel ladle in the LF refining process, and keeping soft stirring; adding modifier, lime and other white slag to eliminate S from steel and adding calcium and iron wire for modifying sulfide inclusion; keeping the soft stirring time to be more than or equal to 8min after refining is finished, and improving the cleanliness of molten steel;

2) continuous casting, namely producing a 40Cr continuous casting slab on an ultra-wide slab continuous casting machine, and adopting full-process protection casting to prevent secondary pollution of molten steel, wherein the slab is 150mm in thickness, 2650mm in width and 8400mm in length;

3) cooling the plate blank, namely stacking the 40Cr thin plate blank produced in the continuous casting process with the thickness of 150mm multiplied by 2650mm multiplied by 8400mm in a plate blank warehouse of a steckel mill in a second mill, avoiding the positions of ventilation openings such as a door, a window or a channel and the like, ensuring that the plate blank is slowly cooled at the cooling speed of less than or equal to 0.5 ℃/s until the plate blank is cooled to the room temperature;

4) the flow direction of the plate blank is that for a steel plate order with the thickness of 40mm, the width of 2650mm and the length of 10000mm, a 40Cr thin plate blank with the thickness of 150mm multiplied by 2650mm multiplied by 8400mm is directly loaded into a heating furnace of a production line of a 3500mm steckel mill for slow heating, the heating time is ensured to be 180-240 min, then a full longitudinal rolling mode is adopted in the 3500mm steckel mill, and the rolling can be finished for 9 times; however, for a steel plate order with the thickness of 20mm, the width of 2200mm and the length of 9000mm, a 40Cr thin plate blank with the thickness of 150mm multiplied by 2650mm multiplied by 8400mm needs to be cut into small plate blanks, and then the small plate blanks are rolled to produce a medium plate with the thickness of 2800 mm;

5) and (3) slab slitting, namely lifting the 150mm multiplied by 2650mm multiplied by 8400mm slab to a cutting area of a steckel mill slab warehouse, slitting the slab along the rolling direction with equal width, namely slitting the slab into 2 slabs 150mm multiplied by 1325mm multiplied by 8400mm, then slitting the slab along the width direction of the casting slab with equal length of 8400mm into 4 sections, and finally cutting the slabs into small blanks 150mm multiplied by 1325mm multiplied by 2100 mm. In the cutting process, the cutting support is required to be straight, and the supporting points of each cut small blank are uniformly stressed. Before cutting, preheating a cutting line to 50-150 ℃, wherein the cutting gas is acetylene and oxygen, and the cutting speed is 50-80 mm/min;

6) the cut 40Cr small plate blanks are transported to a heating furnace of a 2800mm medium and heavy plate mill for plate blank stacking and storage within 4 hours or less, the positions of ventilation openings such as doors, windows and the like of a plate blank warehouse are avoided, and the plate blanks are loaded into the heating furnace for heating as soon as possible;

7) heating the plate blank, loading the cut 40Cr small plate blank into a heating furnace of a 2800mm medium and heavy plate mill production line of a first mill and mill, and then slowly heating in a preheating section and a heating section, wherein the heating speed is less than or equal to 5-15 ℃/min, the total in-furnace time is 180-240 min, and the tapping temperature of the plate blank is 1230 +/-20 ℃;

8) rolling the plate blank, namely rolling the heated 40Cr small plate blank on a 2800mm medium plate rolling mill in a rolling mill of a first mill plant by adopting a rolling mode of firstly transverse rolling and then longitudinal rolling, wherein 12 passes of rolling are performed, so that a steel plate with the thickness of 20mm multiplied by 2200 multiplied by 9000mm can be produced, edge cracks are prevented from appearing on the steel plate produced by the 40Cr small plate blank cut by the cold plate blank, and the order size requirement is ensured;

9) the production process can ensure that the alloy structural steel 40Cr is produced on two medium plate mill mills by using a fixed-length thin slab, and ensures that the small slab after slitting does not have cracks, thereby meeting the requirements of orders of various specifications and small batches.

Example 2

The production process comprises the following steps: 150t top-bottom combined blown converter smelting, 150tLF furnace refining, 150mm 1800-3250 mm thin and wide slab continuous casting, casting blank slow cooling and 3500mm steckel mill slab heating and rolling in a second mill rolling mill of the company; or the cold casting blank is cut to a 2800mm medium plate mill plate blank of a first mill and mill to be heated and rolled.

The alloy structural steel 40Cr comprises the following components (wt%, smelting analysis): c: 0.40, Si: 0.25, Mn: 0.76, P: 0.02, S: less than or equal to 0.004, Cr: 0.96, and the balance of Fe and inevitable impurities.

1) Smelting steel by an oxygen top-bottom combined blowing converter, and deoxidizing and alloying by adopting aluminum iron, silicon manganese alloy, ferrosilicon, high-carbon ferrochrome and the like. Controlling the bottom blowing flow (300-500 NL/min) of the steel ladle in the LF refining process, and keeping soft stirring; adding modifier, lime and other white slag to eliminate S from steel and adding calcium and iron wire for modifying sulfide inclusion; keeping the soft stirring time to be more than or equal to 8min after refining is finished, and improving the cleanliness of molten steel;

2) continuous casting, namely producing a 40Cr continuous casting slab on an ultra-wide slab continuous casting machine, and adopting whole-process protection casting to prevent secondary pollution of molten steel, wherein the slab is 150mm in thickness, 2800mm in width and 7800mm in length;

3) cooling the plate blank, stacking the 40Cr thin plate blanks with the thickness of 150mm multiplied by 2800mm multiplied by 7800mm produced in the continuous casting process in a plate blank warehouse of a steckel mill in a second mill and rolling mill, avoiding the positions of ventilation openings such as doors, windows or channels and the like, ensuring that the plate blank is slowly cooled at the cooling speed of less than or equal to 0.5 ℃/s until the plate blank is cooled to the room temperature;

4) the slab flow direction is that for a steel plate order with the thickness of 52mm, the width of 2800mm and the length of 11000mm, a 40Cr thin slab with the thickness of 150mm multiplied by 2800mm multiplied by 7800mm is directly loaded into a heating furnace of a 3500mm steckel mill production line for slow heating, the heating time is ensured to be 180-240 min, and then a full longitudinal rolling mode is adopted in the 3500mm steckel mill, and the rolling can be completed for 7 times; however, for a steel plate order with the thickness of 28mm, the width of 2300mm and the length of 8000mm, a 40Cr thin slab with the thickness of 150mm multiplied by 2800mm multiplied by 7800mm needs to be cut into small slabs, and then the small slabs are rolled to a medium plate with the thickness of 2800mm for production;

5) and (2) plate blank slitting, namely, lifting the 150mm multiplied by 2800mm multiplied by 7800mm plate blank to a plate blank cutting area of a production line of a steckel mill, longitudinally cutting the plate blank into 2 pieces of 150mm multiplied by 1400mm multiplied by 7800mm in an equal width direction along the rolling direction, then slitting 8400mm in an equal length into 3 sections along the width direction of the casting blank, and finally cutting the plate blank into small blanks of 150mm multiplied by 1400mm multiplied by 2600 mm. In the cutting process, the cutting support is required to be straight, the supporting points of each cut small blank are uniformly stressed, the cutting line is preheated to 50-150 ℃ before cutting, the cutting gas is acetylene and oxygen, and the cutting speed is 50-80 mm/min;

6) the cut 40Cr small plate blanks are transported to a heating furnace of a 2800mm medium and heavy plate mill for plate blank stacking and storage within 4 hours or less, the positions of ventilation openings such as doors, windows and the like of a plate blank warehouse are avoided, and the plate blanks are loaded into the heating furnace for heating as soon as possible;

7) heating the plate blank, loading the cut 40Cr small plate blank into a heating furnace of a 2800mm medium and heavy plate mill production line of a first mill and mill, and then slowly heating in a preheating section and a heating section, wherein the heating speed is less than or equal to 5-15 ℃/min, the total in-furnace time is 180-240 min, and the tapping temperature of the plate blank is 1230 +/-20 ℃;

8) rolling a plate blank, namely, loading a 40Cr thin plate blank with the thickness of 150mm multiplied by 2800mm multiplied by 7800mm into a heating furnace of a 3500mm steckel mill production line for slow heating, and directly rolling 7 times in a 3500mm steckel mill in a full longitudinal rolling mode to produce a steel plate with the thickness of 52mm multiplied by 2800 multiplied by 11000 mm; similarly, a 150mm multiplied by 2800mm multiplied by 7800mm plate blank is longitudinally and transversely cut, then is cut into 150mm multiplied by 1400mm multiplied by 2600mm small blank, after the small blank is slowly heated, rolling is carried out on a 2800mm medium plate rolling mill in a first mill by adopting a rolling mode of firstly transverse rolling and then longitudinal rolling, 12 passes of rolling are carried out in total, a steel plate with the thickness of 28mm multiplied by 2300 x 8000mm can be produced, edge cracks of the steel plate produced by the cut small plate blank for the alloy structural steel 40Cr are guaranteed not to appear, and the order size requirement is guaranteed;

9) the production process can ensure that the alloy structural steel 40Cr is produced on two medium plate mill mills by using a fixed-length thin slab, and ensures that the small slab after slitting does not have cracks, thereby meeting the requirements of orders of various specifications and small batches.

Example 3

The production process comprises the following steps: 150t top-bottom combined blown converter smelting, 150tLF furnace refining, 150mm 1800-3250 mm thin and wide slab continuous casting, casting blank slow cooling and 3500mm steckel mill slab heating and rolling in a second mill rolling mill of the company; or the cold casting blank is cut to a 2800mm medium plate mill plate blank of a first mill and mill to be heated and rolled.

The alloy structural steel 40Cr comprises the following components (wt%, smelting analysis): c: 0.39, Si: 0.24, Mn: 0.85, P: 0.021, S: less than or equal to 0.005, Cr: 1.02 and the balance of Fe and inevitable impurities.

1) Smelting steel by an oxygen top-bottom combined blowing converter, and deoxidizing and alloying by adopting aluminum iron, silicon manganese alloy, ferrosilicon, high-carbon ferrochrome and the like. Controlling the bottom blowing flow (300-500 NL/min) of the steel ladle in the LF refining process, and keeping soft stirring; adding modifier, lime and other white slag to eliminate S from steel and adding calcium and iron wire for modifying sulfide inclusion; keeping the soft stirring time to be more than or equal to 8min after refining is finished, and improving the cleanliness of molten steel;

2) continuous casting, namely producing a 40Cr continuous casting slab on an ultra-wide slab continuous casting machine, and adopting full-process protection casting to prevent secondary pollution of molten steel, wherein the slab is 150mm in thickness, 2450mm in width and 9000mm in length;

3) storing the plate blank, namely stacking and storing the alloy structural steel sheet blank with the thickness of 150mm multiplied by 2450mm multiplied by 9000mm40Cr produced in the continuous casting process in a plate blank warehouse of a steckel mill in a second mill, avoiding the positions of ventilation openings such as doors, windows or channels and the like, ensuring that the plate blank is slowly cooled at the cooling speed of less than or equal to 0.5 ℃/s until the plate blank is cooled to the room temperature;

4) the slab flow direction is that for a steel plate order with the thickness of 42mm, the width of 2450mm and the length of 11000mm, a 40Cr thin slab with the thickness of 150mm, 2450mm and 9000mm is directly loaded into a heating furnace of a 3500mm steckel mill production line for slow heating, the heating time is ensured to be 180-240 min, and then the full longitudinal rolling mode is adopted in the 3500mm steckel mill, and the rolling can be completed for 9 times; however, for a steel plate order with the thickness of 18mm, the width of 1800mm and the length of 9500mm, a 40Cr thin plate blank with the thickness of 150mm multiplied by 2450mm multiplied by 9000mm needs to be cut into small plate blanks, and then the small plate blanks are rolled to a medium plate with the thickness of 2800mm for production;

5) and (3) slab slitting, namely lifting the slabs 150mm multiplied by 2450mm multiplied by 9000mm to a slab cutting area of a steckel mill production line, slitting along the width direction of casting blanks, dividing 9000mm into 5 sections with equal length, taking the casting blank width 2450mm as the length of small blanks, and finally cutting into small blanks 150mm multiplied by 1800mm multiplied by 2450 mm. In the cutting process, the cutting support is required to be straight, the supporting points of each cut small blank are uniformly stressed, the cutting line is preheated to 50-150 ℃ before cutting, the cutting gas is acetylene and oxygen, and the cutting speed is 50-80 mm/min;

6) the cut 40Cr small plate blanks are transported to a heating furnace of a 2800mm medium and heavy plate mill for plate blank stacking and storage within 4 hours or less, the positions of ventilation openings such as doors, windows and the like of a plate blank warehouse are avoided, and the plate blanks are loaded into the heating furnace for heating as soon as possible;

7) heating the plate blank, loading the cut 40Cr small plate blank into a heating furnace of a 2800mm medium and heavy plate mill production line of a first mill and mill, and then slowly heating in a preheating section and a heating section, wherein the heating speed is less than or equal to 5-15 ℃/min, the total in-furnace time is 180-240 min, and the tapping temperature of the plate blank is 1230 +/-20 ℃;

8) rolling a plate blank, namely putting a 150mm multiplied by 2450mm multiplied by 9000mm40Cr thin plate blank into a production line heating furnace of a 3500mm steckel mill for slow heating, and directly rolling the plate blank in the 3500mm steckel mill for 9 times by adopting a full longitudinal rolling mode to produce a 42mm multiplied by 2450 multiplied by 11000mm steel plate; equally cutting a 150mm × 2450mm × 9000mm plate blank into 5 equal parts along the length direction, cutting into small blanks of 150mm × 2450mm × 1800mm, slowly heating the small plate blanks, rolling the small plate blanks on a 2800mm medium plate rolling mill in a first mill by adopting a rolling mode of 'transverse rolling and then longitudinal rolling', rolling for 14 passes in total, producing a 28mm × 2300 × 8000mm steel plate, ensuring that edge cracks do not occur on the steel plate produced by the cut small plate blanks for the alloy structural steel 40Cr, and ensuring the order size requirement;

9) the production process can ensure that the alloy structural steel 40Cr is produced on two medium plate mill mills by using a fixed-length thin slab, and ensures that the small slab after slitting does not have cracks, thereby meeting the requirements of orders of various specifications and small batches.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims (1)

1. A method for effectively preventing the generation of 40Cr alloy structure cold thin slab slitting cracks is characterized by comprising the following steps:

step one, steel making, namely smelting the steel into molten steel by adopting an oxygen top-bottom combined blowing converter, and deoxidizing and alloying by adopting aluminum iron, silicon-manganese alloy, ferrosilicon and high-carbon ferrochrome; controlling the bottom blowing flow of the steel ladle in the LF refining process, and keeping soft stirring; adding modifier and lime to make white slag, removing S in steel, and simultaneously adding calcium-iron wires to perform sulfide inclusion denaturation; keeping the soft stirring time to be more than or equal to 8min after refining is finished, improving the cleanliness of molten steel, wherein the chemical composition of 40Cr meets the specification of GB/T3077-2015 Table 1;

continuous casting, namely performing whole-process protective casting to prevent secondary pollution of molten steel and improve the quality of a casting blank, wherein the continuous casting process is performed on a wide and thin slab continuous casting machine, the thickness of the continuous casting blank is 150mm, the maximum width of the continuous casting blank is 3250mm, and the maximum length of the continuous casting blank is 18000 mm;

step three, storing the plate blanks, namely stacking and storing the 40Cr plate blanks produced in the continuous casting process, wherein the thickness of the plate blanks is 150mm multiplied by 1800-3000 mm multiplied by 8000-18000 m, so that the positions of ventilation openings of doors and windows of a plate blank warehouse are avoided, the plate blanks are ensured to be slowly cooled, the cooling speed is less than or equal to 0.5 ℃/s, and the edge parts of the casting blanks are prevented from cracking due to larger internal stress generated when the 40Cr continuous casting plate blanks are rapidly cooled;

step four, preparing continuous casting cold plate blanks by cutting, hoisting the cooled 40Cr plate blanks to a plate blank cutting area, and requiring a cutting support to be straight, so as to ensure that the stress of each small blank supporting point after cutting is uniform; according to the requirement of the order on the blank size, determining a tangent line on the plate blank, automatically or manually cutting along the width direction of the 40Cr plate blank, or firstly longitudinally cutting from the middle along the length direction of the 40Cr plate blank and then transversely cutting along the width direction of the 40Cr plate blank;

step five, cutting the continuous casting cold plate blank, preheating the surface of the cutting line before cutting because the alloy structural steel 40Cr is high in carbon content, high in Cr content, low in heat conductivity coefficient and easy to generate cutting cracks, and manually moving the cutting line back and forth by using high-temperature flame of a cutting gun; preheating a plate blank cutting line to 50-150 ℃, wherein the cutting gas is acetylene and oxygen, and the cutting speed is 50-80 mm/min;

sixthly, storing the cut plate blanks and feeding the cut plate blanks into a furnace, wherein the cut 40Cr small plate blanks are transported to a plate blank storage area of a heating furnace as soon as possible, stacked and stored, and the positions of ventilation openings of doors and windows of a plate blank warehouse are avoided, so that the plate blanks are required to be fed into the heating furnace for heating within 4 hours or less after being cut;

seventhly, heating and rolling the slit plate blank, putting the slit 40Cr plate blank into a heating furnace, adopting a slow heating mode in a preheating section and a heating section, wherein the heating speed is 5-15 ℃/min, the total in-furnace time is 180-240 min, the plate blank discharging temperature is 1230 +/-20 ℃, ensuring that alloy elements are fully dissolved, and simultaneously preventing the plate blank from cracking due to high alloy content and weak heat transfer capacity of 40Cr and easily generating larger thermal stress when the plate blank is heated; and rolling the heated small plate blank in a medium plate rolling mill in a transverse and longitudinal rolling mode, and finishing the steel plate.