Method for controlling longitudinal cracks of medium-carbon chromium steel continuous casting small square billet

Abstract

The invention belongs to the technical field of metallurgy, and relates to a control method for longitudinal cracks of medium-carbon chromium steel continuous casting small square billets. Comprising the following process steps that (1) continuous casting is conducted, specifically, a small square billet of 150 * 150 mm is adopted, the water volume of a crystallizer is 1850 L / min, the secondary cooling specific water volume is 0.5 L / kg, the pulling speed is 1.8 m / min, and the straightening temperature is larger than or equal to 950 DEG C; and (2) casting blank stack cooling: the stack entering temperature is greater than or equal to 700 DEG C, and the stack cooling time is greater than 24 hours. A casting blank is weakly cooled in the crystallizer and in a secondary cooling area, the temperature of the blank discharged from the crystallizer is larger than or equal to 1150 DEG C, the temperature of a blank shell is increased on the premise that the thickness of the blank shell is guaranteed, and plasticity is effectively improved; aerial fog cooling is adopted for secondary cooling, and the secondary cooling strength is properly reduced; and high-temperature stack entering and stack cooling are carried out, stress is slowly released, uniformity and obdurability unification of a solidified blank shell in a high-temperature area are achieved, and the problem of longitudinal cracking of a medium-carbon chromium steel small square billet casting blank is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy and relates to a method for controlling longitudinal cracks in a medium-carbon chromium steel continuous casting billet. Background Art

[0002] Economic development is placing increasing demands on metallurgical technology, including increasingly stringent requirements for the surface quality of continuously cast ingots. The primary surface quality issue for continuously cast ingots is cracking, with longitudinal cracking in medium-carbon chromium steel ingots being particularly prominent. Therefore, effectively controlling the occurrence of longitudinal cracking defects in medium-carbon chromium steel ingots is a crucial research topic in steelmaking and continuous casting.

[0003] Due to the characteristics of the steel grade, longitudinal cracks in medium carbon chromium steel occur frequently and are difficult to eliminate, seriously affecting the surface quality of the steel. Therefore, research on production technology to control longitudinal cracks in medium carbon chromium steel continuous casting billets is of great significance. Summary of the Invention

[0004] To achieve the above-mentioned object, the present invention provides a method for controlling longitudinal cracks in medium carbon chromium steel continuous casting billets, which solves the problems existing in the prior art.

[0005] The technical solution adopted by the present invention is a method for controlling longitudinal cracks in medium carbon chromium steel continuous casting billets, comprising the following process steps:

[0006] (1) Continuous casting: 150*150mm billet, mold water volume 1850L / min, secondary cooling water volume 0.5L / kg, casting speed 1.8m / min, straightening temperature ≥950℃;

[0007] (2) Billet stack cooling: the stacking temperature is ≥700℃ and the stack cooling time is greater than 24 hours;

[0008] The chemical composition of the steel is as follows by weight: C: 0.38%-0.43%, Si: 0.10%-0.30%, Mn: 0.60%-0.90%, P≤0.020%, S≤0.015%, Cr: 0.90-1.20%, Al≥0.020%, and the rest is Fe and unavoidable impurities.

[0009] Furthermore, the ingot is weakly cooled in the crystallizer and in the first secondary cooling zone, and the temperature of the ingot out of the crystallizer is ≥1150°C, and the secondary cooling adopts mist cooling.

[0010] Preferably, in the continuous casting stage, the straightening temperature is 971°C or 966°C.

[0011] Preferably, in the stack cooling stage of the ingot, the stacking temperature is 727° C. or 721° C., and the stack cooling time is 25 or 24 hours.

[0012] The beneficial effects of the present invention are as follows: the billet is weakly cooled in the crystallizer and in the first secondary cooling zone, the billet temperature out of the crystallizer is ≥1150°C, the billet shell temperature is increased while ensuring the thickness of the billet shell, and the plasticity is effectively improved; the secondary cooling adopts mist cooling, and the secondary cooling intensity is appropriately reduced to avoid γ-α phase transformation stress, so that the surface temperature of the billet and the shrinkage of the billet shell are uniform, and the phenomenon of excessive cooling and a sharp drop in the surface temperature of the billet shell is reduced, while the thermal stress and mechanical stress are reduced; the high-temperature stack cooling is carried out to slowly release the stress, so that the uniformity and strength and toughness of the solidified billet shell in the high-temperature zone are achieved, and the difficult problem of longitudinal cracking of medium-carbon chromium steel billet billets is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0014] Figure 1 This is the organizational diagram of the casting blank of Example 1;

[0015] Figure 2 This is the organizational diagram of the ingot of comparative example 1. DETAILED DESCRIPTION

[0016] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0017] The present invention will be further described below with reference to the embodiments.

[0018] Example 1:

[0019] A method for controlling longitudinal cracks in medium-carbon chromium steel continuous casting billets is disclosed. The billets have a size of 150 x 150 mm. The chemical composition of the steel is as follows by weight: C: 0.40%, Si: 0.18%, Mn: 0.70%, P: 0.016%, S: 0.005%, Cr: 0.95%, Al: 0.023%, with the remainder being Fe and unavoidable impurities.

[0020] The key process steps include

[0021] (1) Continuous casting: rectangular billet 150*150mm, mold water volume 1850L / min, secondary cooling water volume 0.5L / kg, casting speed 1.8m / min, straightening temperature 971℃; mold billet temperature ≥1150℃, secondary cooling adopts mist cooling.

[0022] (2) Billet stack cooling: stacking temperature 727℃, stack cooling time 25 hours.

[0023] Ingot structure Figure 1 shown.

[0024] Example 2:

[0025] A method for controlling longitudinal cracking in medium-carbon chromium steel continuous casting billets is described. The billets have a size of 150 x 150 mm. The chemical composition of the steel is as follows: C: 0.41%, Si: 0.20%, Mn: 0.68%, P: 0.013%, S: 0.004%, Cr: 1.10%, Al: 0.028%, with the remainder being Fe and unavoidable impurities. The key process steps are as follows:

[0026] (1) Continuous casting: rectangular billet 150*150mm, mold water volume 1850L / min, secondary cooling water volume 0.5L / kg, casting speed 1.8m / min, straightening temperature 966℃; mold billet temperature ≥1150℃, secondary cooling adopts mist cooling.

[0027] (2) Billet stack cooling: stacking temperature 721℃, stack cooling time 24 hours.

[0028] Comparative Example 1:

[0029] A method for controlling longitudinal cracks in medium-carbon chromium steel continuous casting billets is disclosed. The billets have a size of 150 x 150 mm. The chemical composition of the steel is as follows by weight: C: 0.40%, Si: 0.18%, Mn: 0.70%, P: 0.016%, S: 0.005%, Cr: 0.95%, Al: 0.023%, with the remainder being Fe and unavoidable impurities.

[0030] The key process steps include:

[0031] (1) Continuous casting: rectangular billet 150*150mm, mold water volume 2000L / min, secondary cooling water volume 0.8L / kg, casting speed 2.0m / min.

[0032] (2) The ingot is not pile-cooled.

[0033] The structure of the ingot is as follows Figure 2 shown.

[0034] In summary, by adopting the technical solution of the present invention, the billet is weakly cooled in the crystallizer and in the second cooling zone, and the billet temperature out of the crystallizer is ≥1150°C. The shell temperature is increased while ensuring the shell thickness, which effectively improves the plasticity. The second cooling adopts mist cooling, and the second cooling intensity is appropriately reduced to avoid γ-α phase transformation stress, so that the surface temperature of the billet and the shrinkage of the billet shell are uniform, and the phenomenon of excessive cooling and a sharp drop in the surface temperature of the billet shell is reduced. At the same time, the thermal stress and mechanical stress are reduced, and the high-temperature stack cooling is carried out to slowly release the stress, thereby achieving the uniformity and strength and toughness of the solidified billet shell in the high temperature zone, and solving the problem of longitudinal cracking of medium carbon chromium steel billet.

[0035] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention are included in the scope of protection of the present invention.

Claims

1. A method for controlling longitudinal cracks in medium carbon chromium steel continuous casting billets, characterized in that: The process steps include: (1) Continuous casting: 150*150mm billet, mold water volume 1850L / min, secondary cooling water volume 0.5L / kg, casting speed 1.8m / min, straightening temperature ≥950℃; (2) Billet stack cooling: the stacking temperature is ≥700℃ and the stack cooling time is greater than 24 hours; The chemical composition of the steel is as follows by weight: C: 0.38%-0.43%, Si: 0.10%-0.30%, Mn: 0.60%-0.90%, P≤0.020%, S≤0.015%, Cr: 0.90-1.20%, Al≥0.020%, and the rest is Fe and unavoidable impurities.

2. The method for controlling longitudinal cracks in medium carbon chromium steel continuous casting billets according to claim 1, characterized in that: The casting is weakly cooled in the crystallizer and the first secondary cooling zone. The temperature of the casting out of the crystallizer is ≥1150℃. The secondary cooling adopts gas mist cooling.

3. A method for controlling longitudinal cracks in medium carbon chromium steel continuous casting billets according to claim 1 or 2, characterized in that: The continuous casting stage: the straightening temperature is 971°C or 966°C.

4. A method for controlling longitudinal cracks in medium carbon chromium steel continuous casting billets according to claim 1 or 2, characterized in that: The ingot stack cooling stage: the stacking temperature is 727° C. or 721° C., and the stack cooling time is 25 or 24 hours.

Images