Method for improving flaw detection qualified rate of wear-resistant steel head furnace continuous casting billet

Abstract

The application provides a method for improving the flaw detection qualified rate of head furnace continuous casting billets of wear-resistant steel, and belongs to the technical field of metallurgy; the method adjusts the molten steel composition of the continuous casting billet, controls non-metallic inclusions, hydrogen diffusion in the steel, reduces the segregation of the billet, and improves the two-cooling strength of the continuous casting, so that the flaw detection qualified rate of the head furnace continuous casting billets of the high wear-resistant steel is stably controlled above 99.5%; the method is simple, has strong operability, and is convenient for popularization and application; the method can effectively improve the flaw detection qualified rate of the head furnace continuous casting billets of the wear-resistant steel, and further significantly improves the production qualified rate of the same batch of products.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of metallurgy, and particularly relates to a method for improving the flaw detection qualified rate of head furnace continuous casting billets of wear-resistant steel. BACKGROUND

[0002] In the case of unsteady casting, the internal quality of the slab is difficult to be effectively controlled. In the beginning stage of a casting cycle in continuous casting production, that is, the opening casting stage of the first furnace, the liquid level of the tundish and the crystallizer is unstable, the pulling speed is large, and phenomena such as slag entrapment and secondary oxidation are prone to occur, the content of inclusions in the molten steel is greatly increased, the internal quality of the head furnace continuous casting billet of the wear-resistant steel is deteriorated, and the flaw detection is unqualified.

[0003] In addition, in the production process of the wear-resistant steel, micro-cracks are prone to occur in the continuous casting billet, which aggravates the center segregation and banded structure of the continuous casting billet. After the continuous casting is completed, direct air cooling is performed, stress release is not complete, the continuous casting billet of the wear-resistant steel is buckled, and the flaw detection qualified rate is not high.

[0004] At present, only optimization and improvement are made in the continuous casting process in the prior art, further optimization and improvement are not made in other main production processes, and the production organization of the head furnace continuous casting billet is not improved, and therefore, a method for improving the flaw detection qualified rate of the head furnace continuous casting billet of the wear-resistant steel is needed. SUMMARY

[0005] In view of some deficiencies in the prior art, the application provides a method for improving the flaw detection qualified rate of the head furnace continuous casting billet of the wear-resistant steel. The method can stabilize the flaw detection qualified rate of the head furnace continuous casting billet of the high wear-resistant steel at more than 99.5% by adjusting the composition of the molten steel of the continuous casting billet, controlling non-metallic inclusions, hydrogen diffusion in the steel, reducing segregation of the billet, and improving the secondary cooling strength of the continuous casting. The method is simple, has strong operability, and is convenient to popularize and apply. The method can effectively improve the flaw detection qualified rate of the head furnace continuous casting billet of the wear-resistant steel, and further significantly improve the production qualified rate of the same batch of products.

[0006] In order to achieve the above technical purposes, the following technical means are adopted in the application.

[0007] The method for improving the flaw detection qualified rate of the head furnace continuous casting billet of the wear-resistant steel specifically comprises the following steps of LF refining, VD vacuum treatment, and continuous casting.

[0008] (1) The LF refining process is as follows: the temperature of the molten steel is controlled to be 1480-1520 DEG C by adopting the refining ladle package power-on, and then the power is turned off to feed aluminum for deoxidation for 40-60 min at one time.

[0009] (2) The VD vacuum treatment is as follows: the molten steel is vacuum preserved under the condition that the vacuum degree is 50-70 Pa, argon is introduced during the preservation process to make the hydrogen content in the molten steel be less than 0.6 ppm, and after the vacuum is broken, argon is soft blown for 25-30 min.

[0010] (3) continuous casting: the molten steel with superheat of 15-35℃ is injected into a crystallizer to crystallize, and after crystallization, the continuous casting billet is obtained by being drawn out from the crystallizer at a drawing speed of 0.7-0.8 m / min, being sent into a secondary cooling zone to be cooled, and being stacked to be slowly cooled after the cooling is completed.

[0011] Preferably, in step (1), the content of Al in the molten steel after refining is 0.020-0.040%, and the content of S is ≤0.005%.

[0012] Preferably, in step (2), the time of vacuum holding is ≥25 min.

[0013] Preferably, in step (2), the flow rate of argon gas during the holding is 250-400 NL / min, and the pressure of argon gas is 0.3-0.5 MPa.

[0014] Preferably, in step (2), the flow rate of soft-blowing argon gas after the breaking of vacuum is 100-150 NL / min, and the pressure of argon gas is 0.1-0.2 MPa.

[0015] Preferably, in step (3), the specific water consumption of the secondary cooling water in the secondary cooling zone during the continuous casting is 0.5-1.0 L / kg.

[0016] Preferably, in step (3), the cooling is performed to 400-450℃ in the secondary cooling zone, and then the stacking and slow cooling are performed for 48-72 h.

[0017] Preferably, in step (3), the chemical composition of the continuous casting billet comprises C: 0.09-0.13%, Si: 0.38-0.80%, Mn: 0.46-0.62%, P: ≤0.012%, S: ≤0.005%, Al: 0.020-0.040%, Cr: 0.08-0.31%, Ti: 0.01-0.04%, and the balance is Fe and inevitable impurities.

[0018] Compared with the prior art, the present application has the following beneficial effects:

[0019] (1) Since the non-metallic inclusions MnS are generated during the crystallization of the casting billet to affect the internal structure of the continuous casting billet, the MnS and the hydrogen enriched in the center of the steel plate can generate structure stress during the cooling of the steel plate, so that the delayed micro-cracks can appear in the center of the steel plate, resulting in the unqualified flaw detection of the continuous casting billet. The present application can avoid the generation of the plastic inclusions MnS by reducing the content of Mn and S in the continuous casting billet, so as to improve the qualified rate of the flaw detection of the continuous casting billet.

[0020] (2) The present application further deoxidizes and desulfurizes by optimizing the process in the LF refining, and controls the generation of non-metallic inclusions by adjusting the composition of the molten steel of the continuous casting blank. The present application makes the gas in the molten steel fully release by the argon gas input during the VD vacuum treatment process and the soft argon gas blowing after the vacuum breaking, and enables the inclusions in the molten steel to float up, thereby reducing the hydrogen content and the non-metallic inclusion content in the molten steel during the continuous casting, so as to effectively improve the flaw detection rate of the continuous casting blank.

[0021] (3) The present application avoids the internal shrinkage and porosity defects of the continuous casting blank and the warping phenomenon due to incomplete stress release during cooling by controlling the temperature through optimizing the superheat degree of the molten steel during the continuous casting process, the drawing speed after crystallization, the secondary cooling water ratio of the secondary cooling zone and the time of the stacking and slow cooling, further improves the flaw detection qualified rate of the high wear-resistant steel head furnace continuous casting blank, and enables the flaw detection qualified rate of the high wear-resistant steel head furnace continuous casting blank to be stably controlled above 99.5%; the method is simple and has strong operability, and is convenient for popularization and application; the method can effectively improve the flaw detection qualified rate of the wear-resistant steel head furnace continuous casting blank, and further significantly improves the production qualified rate of the same batch of products. DETAILED DESCRIPTION

[0022] The present application will be further described below in combination with specific examples, but the protection scope of the present application is not limited thereto.

[0023] Example 1

[0024] The chemical composition and mass percentage of the wear-resistant steel head furnace continuous casting blank prepared in this example are as follows: C: 0.09%, Si: 0.38%, Mn: 0.46%, P: 0.006%, S: 0.005%, Al: 0.020%, Cr: 0.08%, Ti: 0.01%, and the balance is Fe and unavoidable impurities.

[0025] The preparation method is as follows:

[0026] (1) LF refining process: the temperature of the molten steel is controlled to be 1480℃ by adopting the refining seat package power-on, and then the power is turned off to feed aluminum for deoxidization for 40min once, so that the Al content of the molten steel after refining is 0.020%, and the S content is 0.005%;

[0027] (2) VD vacuum treatment: the molten steel is vacuum preserved for 25min under the condition of a vacuum degree of 50Pa, argon gas is input during the preservation process to make the hydrogen content in the molten steel lower than 0.6ppm, wherein the flow of the argon gas input during the preservation process is 250NL / min, and the argon gas pressure is 0.3MPa; soft argon gas is blown for 25min after the vacuum breaking, at this time the flow of the argon gas is 100NL / min, and the argon gas pressure is 0.1MPa.

[0028] (3) Continuous casting: the steel with superheat of 15°C is injected into a crystallizer to crystallize, and after crystallization, it is pulled out from the crystallizer at a pulling speed of 0.7 m / min, sent to a secondary cooling zone for cooling, and after the cooling is completed, it is stacked for slow cooling to obtain a continuous casting billet. During the continuous casting process, the secondary cooling water ratio of the secondary cooling zone is 0.5 L / kg, and after cooling to 400°C in the secondary cooling zone, it is stacked for slow cooling for 48 h.

[0029] The continuous casting billet prepared by the above process is subjected to ultrasonic flaw detection, and the qualified rate of the flaw detection is 99.5%.

[0030] Example 2:

[0031] The chemical composition and mass percentage of the continuous casting billet of the wear-resistant steel prepared in this example are as follows: C: 0.13%, Si: 0.80%, Mn: 0.62%, P: 0.012%, S: 0.003%, Al: 0.040%, Cr: 0.31%, Ti: 0.04%, and the balance is Fe and unavoidable impurities.

[0032] The preparation method is as follows:

[0033] (1) LF refining process: the temperature of the molten steel is controlled to be 1520°C by using a refining seat package power-on, and then the power is turned off to feed aluminum for deoxidation once for 60 min, so that the Al content of the molten steel after refining is 0.040%, and the S content is 0.003%;

[0034] (2) VD vacuum treatment: the molten steel is vacuum preserved for 30 min under a vacuum degree of 70 Pa, and argon is introduced during the preservation process to make the hydrogen content in the molten steel lower than 0.6 ppm, wherein the flow rate of the argon introduced during the preservation process is 400 NL / min, and the argon pressure is 0.5 MPa; after breaking the vacuum, argon is blown for 30 min, at this time the flow rate of the argon is 150 NL / min, and the argon pressure is 0.2 MPa.

[0035] (3) Continuous casting: the steel with superheat of 35°C is injected into a crystallizer to crystallize, and after crystallization, it is pulled out from the crystallizer at a pulling speed of 0.8 m / min, sent to a secondary cooling zone for cooling, and after the cooling is completed, it is stacked for slow cooling to obtain a continuous casting billet. During the continuous casting process, the secondary cooling water ratio of the secondary cooling zone is 1.0 L / kg, and after cooling to 450°C in the secondary cooling zone, it is stacked for slow cooling for 72 h.

[0036] The continuous casting billet prepared by the above process is subjected to ultrasonic flaw detection, and the qualified rate of the flaw detection is 99.8%.

[0037] Example 3:

[0038] The chemical composition and mass percentage of the head furnace continuous casting billet of wear-resistant steel prepared in the embodiment are as follows: C: 0.011%, Si: 0.60%, Mn: 0.55%, P: 0.080%, S≤0.003%, Al: 0.030%, Cr: 0.024%, Ti: 0.02%, and the balance of Fe and inevitable impurities.

[0039] The preparation method is as follows:

[0040] (1) LF refining process: the temperature of molten steel is controlled to be 1500°C by adopting a refining ladle through power-on, and then the power is turned off to feed aluminum for deoxidization once for 50 min, so that the Al content of the molten steel after refining is 0.030%, and the S content is 0.003%;

[0041] (2) VD vacuum treatment: the molten steel is vacuum-pressurized for 35 min under a vacuum degree of 60 Pa, and argon is introduced during the vacuum-pressurizing process to make the hydrogen content in the molten steel be less than 0.6 ppm, wherein the flow rate of the introduced argon is 350 NL / min, and the argon pressure is 0.4 MPa; after the vacuum is broken, argon is blown for 27 min, at this time, the flow rate of the argon is 130 NL / min, and the argon pressure is 0.15 MPa.

[0042] (3) Continuous casting: the molten steel with a superheat of 25°C is injected into a crystallizer to crystallize, and after crystallization, the molten steel is drawn out from the crystallizer at a drawing speed of 0.75 m / min, and is sent to a secondary cooling zone for cooling, and after the cooling is completed, the molten steel is stacked and slowly cooled to obtain a continuous casting billet. During the continuous casting process, the specific water consumption of the secondary cooling water in the secondary cooling zone is 0.7 L / kg, and after the molten steel is cooled to 425°C in the secondary cooling zone, the molten steel is stacked and slowly cooled for 62 h.

[0043] The continuous casting billet prepared by the above process is subjected to ultrasonic flaw detection, and the qualified rate of the flaw detection is 100%.

[0044] In summary, by adjusting the composition of the molten steel of the continuous casting billet, controlling non-metallic inclusions, hydrogen diffusion in the steel, reducing segregation of the billet, and increasing the secondary cooling intensity of the continuous casting, the flaw detection qualified rate of the head furnace continuous casting billet of wear-resistant steel is stably controlled to be more than 99.5% according to the method; the method is simple and has strong operability, and is convenient for popularization and application; the method can effectively improve the flaw detection qualified rate of the head furnace continuous casting billet of wear-resistant steel, and further significantly improve the production qualified rate of the same batch of products.

[0045] The embodiment is a preferred embodiment of the present application, but the present application is not limited to the above-mentioned embodiments, and any obvious improvement, replacement or modification made by a person skilled in the art without departing from the essential content of the present application shall fall within the protection scope of the present application.

Claims

1. A method for improving the flaw detection qualification rate of a head furnace continuous casting billet of a wear-resistant steel, characterized in that, The process comprises LF refining, VD vacuum treatment and continuous casting process; (1) LF refining process: the temperature of molten steel is controlled to be 1480-1520℃ by adopting the refining ladle through power on, and then the power is turned off to feed aluminum for deoxidation for 40-60 min at one time; the content of Al in the molten steel after refining is 0.020-0.040%, and the content of S is less than 0.005%; (2) VD vacuum treatment: the molten steel is vacuum preserved under the condition that the vacuum degree is 50-70 Pa, and argon is introduced during the vacuum preservation process to make the content of hydrogen in the molten steel be less than 0.6 ppm, and after the vacuum is broken, argon is soft blown for 25-30 min; (3) Continuous casting: the molten steel with superheat of 15-35℃ is injected into a crystallizer to crystallize, and after crystallization, the crystallizer is pulled out at a pulling speed of 0.7-0.8 m / min, and then the crystallizer is sent to a secondary cooling zone for cooling, and after cooling, the crystallizer is stacked and slowly cooled to obtain a continuous casting billet; During the continuous casting process, the secondary cooling water quantity of the secondary cooling zone is 0.5-1.0 L / kg; After cooling in the secondary cooling zone to 400-450℃, the crystallizer is stacked and slowly cooled for 48-72 h; The chemical composition and mass percentage of the continuous casting billet are as follows: C: 0.09-0.13%, Si: 0.38-0.80%, Mn: 0.46-0.62%, P: less than 0.012%, S: less than 0.005%, Al: 0.020-0.040%, Cr: 0.08-0.31%, Ti: 0.01-0.04%, and the balance is Fe and inevitable impurities.

2. The method of improving the flaw detection qualification rate of a head furnace continuous casting billet of a wear-resistant steel according to claim 1, characterized in that, In step (2), the vacuum preservation time is greater than or equal to 25 min.

3. The method of improving the flaw detection qualification rate of a head furnace continuous casting billet of a wear-resistant steel according to claim 1, characterized in that, In step (2), the flow rate of argon introduced during the vacuum preservation process is 250-400 NL / min, and the argon pressure is 0.3-0.5 MPa.

4. The method of improving the flaw detection qualification rate of a head furnace continuous casting billet of abrasion resistant steel according to claim 1, characterized by, In step (2), after the vacuum is broken, the flow rate of soft blowing argon is 100-150 NL / min, and the argon pressure is 0.1-0.2 MPa.