CN-117867362-B - Production method for avoiding longitudinal cracks of medium-carbon manganese steel

CN117867362BCN 117867362 BCN117867362 BCN 117867362BCN-117867362-B

Abstract

The invention belongs to the technical field of carbon steel preparation, and discloses a production method for avoiding longitudinal cracks of medium carbon manganese steel. The method comprises the steps of smelting in a converter to obtain molten steel, carrying out double slag-stopping tapping, adding functional materials into the steel ladle to obtain outbound molten steel, carrying out LF refining on the outbound molten steel, carrying out protective casting to obtain a straightened casting blank, feeding the straightened casting blank into a first slow cooling pit to be slowly cooled to obtain a slow cooling casting blank, heating the slow cooling casting blank to obtain a heated casting blank, and sequentially carrying out initial rolling, continuous rolling, sawing, cold bed stepping and slow cooling of the second slow cooling pit on the heated casting blank to obtain the medium carbon manganese steel without longitudinal cracks. The invention solves the problem of longitudinal crack of the medium carbon manganese steel by strictly controlling the nitrogen content in the steel, adopting proper high secondary cooling strength (namely higher than water amount) for continuous casting, straightening casting blank slow cooling and adopting a low-temperature preheating technology for steel rolling heating on the premise of not increasing the cost and not bringing other influences to the quality of the steel.

Inventors

LIU HAITAO
LU FENG
ZHANG JIANYUAN
ZHAO YANG
ZHANG LONG
LIU YAN
Du Dongfu
ZHANG YINGYING

Assignees

凌源钢铁股份有限公司

Dates

Publication Date: 20260508
Application Date: 20231226

Claims (9)

1. A production method for avoiding longitudinal cracks of medium carbon manganese steel, which is characterized by comprising the following steps: S1, feeding a steelmaking raw material into a converter, smelting the converter to obtain molten steel, carrying out double slag-stopping tapping to enable the molten steel to flow into a ladle for bottom argon blowing, adding a functional material into the ladle when the weight of the molten steel fed into the ladle is a first threshold value and enabling the molten steel to continuously flow into the ladle at the same time, and adding the functional material when the weight of the molten steel fed into the ladle is a second threshold value; The first threshold value is 0.20-0.30% of the weight of all molten steel in the converter before tapping; The second threshold value is 0.70-0.80% of the weight of all molten steel in the converter before tapping; The functional materials comprise a material for deoxidizing and alloying, a low-nitrogen carburant and a material for top slag modification; S2, carrying out LF refining on the outbound molten steel, namely feeding the outbound molten steel from a soft blowing station to a refining station, and carrying out electrifying, white slag refining, component tempering and wire feeding treatment to obtain LF refined molten steel; The white slag holding time is more than or equal to 20min; the time of the LF refined molten steel in the soft blowing station is more than or equal to 20min; The content of carbon in the LF refined molten steel is 0.38-0.41% and the content of manganese is 1.47-1.53% based on the total mass of the LF refined molten steel; S3, protective casting, namely, under the protection of argon, enabling the LF refined molten steel to flow into a tundish by adopting a ladle protective sleeve, enabling a sealed molten steel channel to be formed between the tundish and a crystallizer by adopting an inner water gap in the tundish, and sending the LF refined molten steel in the tundish into the crystallizer to obtain a casting blank; The specific water content is 0.175-0.185L/kg, and the blank pulling speed is 0.40-0.42m/min; The secondary cooling zone comprises a first secondary cooling zone, a second secondary cooling zone, a third secondary cooling zone and a fourth secondary cooling zone which are sequentially arranged from the crystallizer to the withdrawal and straightening device, wherein the ratio of the cooling water consumption of the first secondary cooling zone, the second secondary cooling zone, the third secondary cooling zone and the fourth secondary cooling zone is (20-30): 35-40): 20-30): 10-15; s4, feeding the straightened casting blank into a first slow cooling pit for slow cooling to obtain a slow cooling casting blank; before the straightened casting blank is sent into a first slow cooling pit for slow cooling, pit heating treatment is needed to be carried out on the first slow cooling pit, the number of pit heating casting blanks used for the pit heating treatment is more than or equal to 8, the pit heating treatment time is more than or equal to 4 hours, and the pit bottom temperature of the first slow cooling pit is more than or equal to 100 ℃; The pit entering temperature of the straightened casting blank fed into the first slow cooling pit is more than or equal to 600 ℃, and the pit exiting temperature of the straightened casting blank discharged from the first slow cooling pit is less than or equal to 350 ℃, wherein the time of slow cooling the straightened casting blank in the first slow cooling pit is more than or equal to 24 hours; S5, feeding the slow cooling casting blank into a heating furnace to heat to obtain a heating casting blank, and sequentially performing blooming, continuous rolling, sawing, cooling bed stepping and slow cooling of a second slow cooling pit on the heating casting blank to obtain the medium-carbon manganese steel without longitudinal cracks; the heating furnace is sequentially divided into a preheating section, a heating section II, a heating section III and a soaking section from an inlet of the heating furnace to an outlet of the heating furnace; the preheating section does not open a burner, and the temperature is less than or equal to 820 ℃; The residence time of the slow cooling casting blank in the heating furnace is not less than 380min, wherein the residence time of the slow cooling casting blank in the preheating section is not less than 100min, and the residence time of the slow cooling casting blank in the heating section III and the soaking section is not less than 150min.
2. The production method for avoiding longitudinal cracks in medium carbon manganese steel according to claim 1, wherein the medium carbon manganese steel without longitudinal cracks has a designation of 40Mn2.
3. The production method for avoiding longitudinal cracks in medium carbon manganese steel according to claim 1 or 2, wherein, in step S1: the carbon content in the molten steel is more than or equal to 0.08 percent based on the total mass of the molten steel; The double slag-stopping tapping is to use a slag stopper and a slag-stopping valve for tapping; adding functional materials into a ladle, namely sequentially adding the materials for deoxidizing alloying, the low-nitrogen carburant and the materials for top slag modification into the ladle, and simultaneously enabling the molten steel to continuously flow into the ladle; The content of carbon in the out-of-station molten steel is 0.30-0.36% and the content of manganese is 1.55-1.61% based on the total mass of the out-of-station molten steel.
4. The production method for avoiding longitudinal cracks of medium carbon manganese steel according to claim 3, wherein, The material for deoxidizing and alloying is at least one of aluminum ingot, silicon-manganese alloy and ferromanganese; the material for top slag modification is premelted calcium aluminate and/or refined lime.
5. The production method for avoiding longitudinal cracks in medium carbon manganese steel according to claim 1 or 2, wherein, in step S2: when the outbound molten steel is in the soft blowing station, the soft blowing station sequentially carries out argon strong blowing and argon weak blowing on the outbound molten steel until the outbound molten steel enters the refining station; the argon forced blowing is performed at the argon flow of 600-700NL/min, and the argon forced blowing time is 0.9-1.2min; The argon weak blowing is performed at an argon flow of 200-300NL/min; the refining station performs argon gas blowing, wherein the argon gas blowing flow is 400-500NL/min; The white slag refining further comprises power failure and sampling test when the temperature in the LF refining furnace reaches 1530-1540 ℃, wherein the sampling test comprises molten steel sampling test and slag sampling test, when the molten steel sampling test result is that the aluminum content in the molten steel in the LF refining furnace is less than or equal to 0.020%, the aluminum content in the molten steel in the LF refining furnace is adjusted to more than 0.025%, and slag condition judgment and slag property control are carried out on the obtained slag sample; The component tempering comprises adding at least one of medium carbon ferromanganese, ferrosilicon and low nitrogen carburant into molten steel in an LF refining furnace; the feeding speed of the feeding treatment is 1.2-2.0m/s.
6. The method for producing a medium carbon manganese steel according to claim 4, wherein the carbon content in the low nitrogen carburant is not less than 96.0% and the nitrogen content is not more than 0.025% based on the total mass of the low nitrogen carburant.
7. The production method for avoiding longitudinal cracks in medium carbon manganese steel according to claim 1 or 2, wherein, in step S3: because 3-15 furnaces of molten steel need to be prepared once, the temperature of the LF refined molten steel of the first furnace in the ladle protective sleeve is 1572-1582 ℃, and the temperature of the LF refined molten steel of the second furnace and the subsequent furnace times is 1539-1549 ℃; The temperature of molten steel in the tundish is 1510-1525 ℃; The water flow wide surface of the crystallizer is 80-86m 3 /h, and the narrow surface is 68-74m 3 /h; the electromagnetic stirring current of the crystallizer is 370-410A, the electromagnetic stirring frequency of the crystallizer is 1.4-1.6Hz, the electromagnetic stirring current of the solidification end is 390-410A, and the electromagnetic stirring frequency of the solidification end is 5.2-5.8Hz; the specification and the size of the casting blank are (380-400) mm multiplied by (500-520) mm.
8. The production method for avoiding longitudinal cracks in medium carbon manganese steel according to claim 1 or 2, wherein, in step S5: the heating furnace is a heat accumulating type walking beam heating furnace; The temperature of the heating section II is 850-1050 ℃; The temperature of the heating III section is 1180-1250 ℃; the temperature of the soaking section is 1160-1240 ℃; the initial rolling temperature is 1080-1120 ℃; the final temperature of the continuous rolling is 920-1000 ℃; the slow cooling time of the second slow cooling pit is more than or equal to 36 hours.
9. The production method for avoiding longitudinal cracks in medium carbon manganese steel according to claim 1, wherein the medium carbon manganese steel without longitudinal cracks has a grade of 45Mn2.

Description

Production method for avoiding longitudinal cracks of medium-carbon manganese steel Technical Field The invention belongs to the technical field of carbon steel preparation, and particularly relates to a production method for avoiding longitudinal cracks of medium carbon manganese steel. Background In recent years, with the vigorous development of the automobile industry and the engineering machinery industry, the demand of steel for parts of automobiles and engineering machinery is driven to increase, and the quality requirement is also more stringent. 40Mn2 and 45Mn2 are taken as the typical brands of medium carbon quenched and tempered manganese steel, and are widely applied to manufacturing of automobile and engineering machinery parts working under heavy load conditions, such as 'four-wheel belt' wheel bodies, coal machine scraping plates, operating levers, worms, reinforcing rings and the like. 40Mn2 and 45Mn2 are used as automobile and engineering machinery parts working under heavy load, and have strict requirements on the surface quality, hardness uniformity, wear resistance and fatigue performance of steel. 40Mn2 has a carbon content of 0.37% -0.44%, a manganese content of 1.40% -1.80%, 45Mn2 has a carbon content of 0.42% -0.49%, and a manganese content of 1.40% -1.80%. Due to the characteristics of the medium carbon manganese steel, surface longitudinal cracks are very easy to generate in the cooling and heating processes of casting blanks, and the quality of steel is seriously affected. The invention discloses a production method for preventing the surface of a medium carbon manganese steel casting blank from longitudinal cracking, which is disclosed in China patent application No. 200910301243.8, wherein ferrotitanium is added on the basis of the original chemical components after final deoxidation, the titanium content is controlled to be 0.005% -0.0145%, and molten steel continuous casting is carried out after ferrotitanium is added. The aim of avoiding the surface longitudinal crack defect of the medium carbon manganese steel continuous casting blank is achieved through the improvement. However, although the method provided by the invention can prevent the medium carbon manganese steel casting blank from generating longitudinal cracks, the chemical element titanium is added into the steel, so that titanium nitride and titanium carbonitride inclusions are easy to generate, the cleanliness of the steel is influenced, and the production cost is increased. In addition, it is not mentioned how to avoid the crack generation in the rolling process of the medium carbon manganese steel casting blank. In the prior art, a simple and effective production method for avoiding the longitudinal cracks of the medium carbon manganese steel does not exist. Disclosure of Invention The invention aims at overcoming the defects of the prior art, and provides a production method for avoiding longitudinal cracks of medium-carbon manganese steel. The invention solves the problem of longitudinal crack of the medium carbon manganese steel by strictly controlling the nitrogen content in the steel, adopting proper high secondary cooling strength (namely higher than water amount) for continuous casting, straightening casting blank slow cooling and adopting a low-temperature preheating technology for steel rolling heating on the premise of not increasing the cost and not bringing other influences to the quality of the steel. In order to achieve the above object, the present invention provides a production method for avoiding longitudinal cracks of medium carbon manganese steel, the method comprising the steps of: S1, feeding a steelmaking raw material into a converter, smelting the converter to obtain molten steel, carrying out double slag-stopping tapping to enable the molten steel to flow into a ladle for bottom argon blowing, adding a functional material into the ladle when the weight of the molten steel fed into the ladle is a first threshold value and enabling the molten steel to continuously flow into the ladle at the same time, and adding the functional material when the weight of the molten steel fed into the ladle is a second threshold value; S2, carrying out LF refining on the outbound molten steel, namely feeding the outbound molten steel from a soft blowing station to a refining station, and carrying out electrifying, white slag refining, component tempering and wire feeding treatment to obtain LF refined molten steel; S3, protective casting, namely, under the protection of argon, enabling the LF refined molten steel to flow into a tundish by adopting a ladle protective sleeve, enabling a sealed molten steel channel to be formed between the tundish and a crystallizer by adopting an inner water gap in the tundish, and sending the LF refined molten steel in the tundish into the crystallizer to obtain a casting blank; s4, feeding the straightened casting blank into a first slow cooling pit for slow cooling to obta