Control method for transverse corner cracks of niobium-containing steel casting blank

Abstract

The invention discloses a control method for a transverse corner crack of a niobium-containing steel casting blank, which comprises the following steps: controlling the argon blowing flow of a long nozzle to be 200-300 l / min, controlling the argon flow between tundish plates to be 20-40 l / min, and adding a covering agent after the molten steel of the tundish is discharged to 10 tons and submerges the lower opening of the long nozzle; starting up the furnaces to add 200-350 kg of the casting blank, 100-200 kg of a stopper rod area and 100-150 kg of an impact area, adding 100-150 kg of the impact area in the second furnace, 80-100 kg of the casting blank in the third furnace and 50-80 kg of the casting blank in the fourth furnace, reducing the secondary cooling water in the third furnace to 100-150 l / min, increasing the surface temperature of the casting blank to 1000 DEG C or above during bending, increasing the surface temperature of the casting blank to 50-80 l / min during straightening, and increasing the surface temperature of the casting blank to 950 DEG C or above during straightening; the degree of superheat of a starting or inserting head furnace is less than or equal to 40 DEG C;

Description

Technical Field

[0001] The invention relates to a method for controlling transverse cracks at corners of a niobium-containing steel ingot, and belongs to the field of steel smelting and material processing. Background Art

[0002] Adding Nb to carbon manganese steel can refine the grains, strengthen the steel through phase transformation and precipitation, and improve the mechanical properties of the steel. However, when Nb is added to the steel, the columnar crystals of the ingot are well developed. During the solidification process, the microsegregation of Nb at the dendrite boundary leads to the precipitation of precipitates at high temperatures. Its second phase particles sink to the bottom of the coarse austenite grain boundary, reducing the grain boundary strength and easily causing transverse cracks in the ingot. Literature search: (1) The "Proceedings of the 8th (2011) China Iron and Steel Annual Conference" published the "Research on the Control Technology of Transverse Cracks on the Surface of 400mm Extra Thick Slabs" in 2011. This study adopts a weak cooling method for the vertical section and straightening section to increase the shell temperature and avoid the brittle temperature zone; adopts low-frequency, high-amplitude vibration parameters; and optimizes the protective slag to improve the transverse cracks on the surface of the slab. (2) "The Effect of Nb, V, and Ti Microalloying Elements on the Surface Quality of Continuous Casting Ingots" was published in the 4th issue of Wide and Heavy Plates in 2003. By reducing the secondary cooling water volume, reducing the Nb, V, and Ti microalloying elements, and increasing the drawing speed to avoid the brittle temperature range of steel from the high temperature side, the incidence of corner cracks in the ingots was significantly reduced. Summary of the invention

[0003] The purpose of the present invention is to provide a method for controlling transverse cracks at the corners of a niobium-containing steel ingot, which can reduce the N content during the continuous casting process and reduce the precipitation of NbN at the grain boundaries. At the same time, only the cooling water volume in zones 3 and 7 is reduced, and the bending straightening temperature is increased. The method has strong applicability and operability and reduces the probability of cracks on the surface of the ingot.

[0004] The implementation method of the present invention is a method for controlling transverse cracks at the corners of a niobium-containing steel ingot, which is implemented according to the following steps: (1) The argon blowing flow rate of the long nozzle is controlled at 200-300 l / min to ensure that the nozzle is immersed in the molten pool of the tundish, the liquid surface in the impact zone is turned over appropriately, and a small amount of steel flowers are splashed; the argon gas flow rate between the tundish plates is controlled at 20-40 l / min to ensure that no air is inhaled between the plates; (2) After the molten steel in the tundish reaches 10 tons, add covering agent when the molten steel covers the lower mouth of the long nozzle; the amount of covering agent added: 200-350kg is added to the start-up furnace, 100-200kg to the stopper area, and 100-150kg to the impact area. Add the impact area first, 100-150kg to the second furnace, 80-100kg to the third furnace, 50-80kg to the fourth furnace, and add an appropriate amount according to the liquid level after the fifth furnace to ensure that the liquid surface is covered and no molten steel is leaking; (3) The secondary cooling water in zone 3 is reduced to 100-150 l / min, and the surface temperature of the ingot is raised to above 1000°C during bending. The secondary cooling water in zone 7 is reduced to 50-80 l / min, and the surface temperature of the ingot is raised to above 950°C during straightening. (4) The overheat of the furnace when starting or inserting the climbing head is ≤40℃, and the overheat of the continuous casting furnace is ≤30℃ to reduce the growth of columnar crystals; (5) All ingots are sent hot and hot loaded into the heating furnace for rolling to prevent cracks from regenerating and expanding during the slow cooling process.

[0005] The transverse crack rate of the niobium-containing steel ingot produced by this method is reduced by half, mass production is achieved, the surface crack rate of medium and thick plates is greatly reduced, and the one-time fulfillment rate of the contract is improved. The method of the present invention reduces the N content added during the continuous casting process, reduces the precipitation of NbN at the grain boundary, and only reduces the cooling water volume in zones 3 and 7, increases the bending straightening temperature, has strong applicability and operability, and reduces the probability of surface cracks on the ingot. Implementation

[0006] A method for controlling transverse cracks at the corners of a niobium-containing steel ingot is implemented according to the following steps: (1) The argon blowing flow rate of the long nozzle is controlled at 200-300 l / min to ensure that the nozzle is immersed in the molten pool of the tundish, the liquid surface in the impact zone is turned over appropriately, and a small amount of steel flowers are splashed; the argon gas flow rate between the tundish plates is controlled at 20-40 l / min to ensure that no air is inhaled between the plates; (2) After the molten steel in the tundish reaches 10 tons, add covering agent when the molten steel covers the lower mouth of the long nozzle; the amount of covering agent added: 200-350kg is added to the start-up furnace, 100-200kg to the stopper area, and 100-150kg to the impact area. Add the impact area first, 100-150kg to the second furnace, 80-100kg to the third furnace, 50-80kg to the fourth furnace, and add an appropriate amount according to the liquid level after the fifth furnace to ensure that the liquid surface is covered and no molten steel is leaking; (3) The secondary cooling water in zone 3 is reduced to 100-150 l / min, and the surface temperature of the ingot is raised to above 1000°C during bending. The secondary cooling water in zone 7 is reduced to 50-80 l / min, and the surface temperature of the ingot is raised to above 950°C during straightening. (4) The overheat of the furnace when starting or inserting the climbing head is ≤40℃, and the overheat of the continuous casting furnace is ≤30℃ to reduce the growth of columnar crystals; (5) All ingots are sent hot and hot loaded into the heating furnace for rolling to prevent cracks from regenerating and expanding during the slow cooling process.

Claims

1. A method for controlling transverse cracks at the corners of a niobium-containing steel ingot, characterized in that Follow these steps to implement: (1) The argon blowing flow rate of the long nozzle is controlled at 200-300 l / min to ensure that the nozzle is immersed in the molten pool of the tundish, the liquid surface in the impact zone is turned over appropriately, and a small amount of steel flowers are splashed; the argon gas flow rate between the tundish plates is controlled at 20-40 l / min to ensure that no air is inhaled between the plates; (2) After the molten steel in the tundish reaches 10 tons, add covering agent when the molten steel covers the lower mouth of the long nozzle; the amount of covering agent added: 200-350kg is added to the start-up furnace, 100-200kg to the stopper area, and 100-150kg to the impact area. Add the impact area first, 100-150kg to the second furnace, 80-100kg to the third furnace, 50-80kg to the fourth furnace, and add an appropriate amount according to the liquid level after the fifth furnace to ensure that the liquid surface is covered and no molten steel is leaking; (3) The secondary cooling water in zone 3 is reduced to 100-150 l / min, and the surface temperature of the ingot is raised to above 1000°C during bending. The secondary cooling water in zone 7 is reduced to 50-80 l / min, and the surface temperature of the ingot is raised to above 950°C during straightening. (4) The overheat of the furnace when starting or inserting the climbing head is ≤40℃, and the overheat of the continuous casting furnace is ≤30℃ to reduce the growth of columnar crystals; (5) All ingots are sent hot and hot loaded into the heating furnace for rolling to prevent cracks from regenerating and expanding during the slow cooling process.