CN114653907B - Method to improve the homogeneity of high carbon steel billet based on new reduction mode - Google Patents

Abstract

The invention belongs to the technical field of metallurgy, and particularly relates to a method for improving the homogeneity of a high-carbon steel billet casting blank based on a brand new depressing mode, which comprises the following steps: starting the electromagnetic stirring of a crystallizer and the electromagnetic stirring of the tail end in the casting process, wherein the electromagnetic stirring of the tail end corresponds to the solid phase rate fs=0.1-0.2 of the center of the casting blank, and the pulling speed is controlled to be 1.6-3.0m/min; soft reduction is carried out at the solidification tail end of the casting blank, the soft reduction interval corresponds to the central solid phase rate fs=0.4-0.85 of the casting blank, the reduction is 8-16mm, and the casting blank is distributed to a plurality of rollers for small-quantity multi-roller continuous soft reduction operation; and (3) carrying out single-roller heavy reduction on the first compression roller corresponding to the central solid phase ratio fs of the casting blank of 1. The method not only realizes homogenization under the condition of ensuring high efficiency of the production of the high-carbon steel billets, opens up a brand new production process way for producing high-quality high-carbon steel billets with energy conservation, low consumption and low cost, but also lays an important foundation for producing high-quality high-carbon special steel by using the billets.

Description

Method to improve the homogeneity of high carbon steel billet based on new reduction mode

Technical field

The invention belongs to the field of metallurgical technology, and specifically relates to a method for improving the homogeneity of high carbon steel billet based on a new reduction mode.

Background technique

High carbon steel is prone to serious internal defects such as core macrosegregation, center porosity, shrinkage cavities, and internal cracks during the continuous casting process. The formation of these defects will greatly reduce the homogeneity of the cast slab. Without excluding further adverse effects in subsequent processes, if these defects cannot be eliminated or significantly improved through the heating and rolling processes, it is likely to lead to significant differences or abnormalities in the structure and properties of subsequent rolled products, which will further affect the steel industry. During the processing process, such as cup and cone breakage during drawing, or different failure problems may occur during other uses.

In order to improve the homogeneity of the cast slab, the technical measures usually adopted mainly include low superheat pouring, high-intensity secondary cooling and drawing speed control, electromagnetic stirring and reduction technology, etc. ^[1-6] . Among them, low superheat pouring has extremely high requirements for temperature control during the pouring process, which can easily cause fluctuations in production flow and pouring stability. High-intensity secondary cooling technology and casting speed control can have a positive effect on center segregation, etc., but will produce slabs. The probability of crack defects will increase significantly, and production efficiency will also be damaged. After continuous development and improvement, electric stirring technology, especially electromagnetic stirring technology, has achieved a high industrial application coverage in the continuous casting process. However, a single electromagnetic stirring is not suitable for Improvements to interior quality are relatively limited.

Continuous casting solidification end reduction technology has been widely used in recent years. This technology is generally considered to be an effective method to improve the center segregation and density of continuous casting billets. However, this method is currently mainly used in larger cross-section circles ^[7] , square ^[8,9] and plate ^[10,11] cast billets, there are few reports and applications on small billets (below 200mm). The reason is that the improvement effect of light pressing before small sections is not significant, mainly due to the liquid core Small, the reduction effect is difficult to control and is not as obvious as that under the condition of large cross-section and large liquid core. Therefore, the previous reduction process was mainly used in large-section billets. In terms of the form of reduction, the current reduction technology usually focuses on light reduction before the slab is completely solidified, or only heavy reduction at the end of solidification or after complete solidification; at the same time, the setting of the reduction process parameters is The decisive factor that affects the reduction effect is that improper reduction will not only fail to improve the internal quality of the slab, but may also cause the internal segregation distribution of the slab to intensify and cracks and other slab defects.

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[2] Wang Tao, Chen Weiqing, Wang Hongbin, et al. Effects of continuous casting parameters and terminal electromagnetic stirring on carbon segregation in the center of 82B steel billet [J]. Special Steel, 2013, 34(1): 49-51

[3] He Jinping, Wu Jianpeng, Wang Guoping. Improvement of center segregation of SWRH82B continuous casting billet [J]. Steelmaking. 2005.21(3):5-8

[4] Jia Yanlu, Miao Feng, Zhao Wencheng, et al. Terminal electromagnetic stirring Influence of carbon segregation in cast slabs[J]. Thermal Working Technology, 2012, 41(7):61-65

[5] An Hanghang, Bao Yanping, Wang Min, et al. Solidification law of high carbon wear-resistant ductile steel bloom continuous casting process and its application in light reduction process [J]. Journal of Central South University (Natural Science Edition) .2018,49(05):1037-1046

[6] Zhao Junpu, Liu Liu, Fan Jianwen, et al. Light reduction technology and its research and application in continuous casting [J]. Materials Herald. 2016, 30(15): 57-61

[7] Cao Xuequan, Wang Ying, Chen Jie. Finite element analysis of light reduction in continuous casting of large round billets [J]. Continuous Casting, 2018, 43(4): 14-16 [8] Seiji Nabeshima, Hakaru Nakato, Tetsuya Fujii,et al.Control of CenterlineSegregation in Continuously Cast Blooms with Continuous Forging Process[J].CAMP-ISIJ,1994(7):179-182

[9] Li Yujun, Li Liang, Lan Peng, et al. Research on dynamic light reduction model of special steel bloom [J]. Continuous Casting, 2018, 43(4): 27-32

[10] Meng Huaijun, Xing Fei. Discussion and optimization of roll gap shrinkage control technology of slab continuous caster [J]. Wide and Thick Plate, 2013, 19(2): 31-35

[11]Sei H, Akihiro Y, Yoshihisa S, et al. Development of new continuous casting technology (PCCS) for very thick plate [J]. Materia Japan, 2009, 48 (1): 20-22.

Contents of the invention

The present invention provides a method for improving the homogeneity of high carbon steel billets based on a new reduction mode. It innovatively utilizes the effective combination of dynamic light reduction and heavy pressing of billets, and continuously reduces the billets during the solidification interval. Combining single-point reduction and further utilizing the synergistic effect of electromagnetic stirring on the structure control of the cast billet, the homogeneity of high carbon steel billets can be effectively improved.

The specific technical solution adopted to achieve the purpose of the present invention is: a method for improving the homogeneity of high carbon steel billet based on a new reduction mode, involving the composition of the high carbon steel billet: C: 0.67-1.0 %, Si: 0.12-0.50%, Mn: 0.02-0.80%, P ≤ 0.025%, S ≤ 0.025%, the rest is the specific addition of alloy and Fe for each steel type, billet size 145-200mm (section side length, preferred The section of the slab is 175mm*175mm).

Cast the 175mm*175mm section billet at a pulling speed of 1.6-3.0m/min and appropriate secondary cooling conditions.

During the pouring process, the mold electromagnetic stirring (M-EMS) and the terminal electromagnetic stirring (F-EMS) are turned on. The final stirring position corresponds to the solid phase rate fs=0.1-0.2 in the center of the casting slab. At this time, the liquid core in the center of the casting slab still has a good It has excellent fluidity and can perform horizontal rotational motion under the action of electric stirring, exerting the effect of electric stirring on uniformizing the composition and temperature of the molten steel at the end of solidification and reducing the accumulation of solute elements in the two-phase area of solidification. Electric stirring uses alternating stirring, that is, reversing intermittent stirring. On the one hand, the molten steel stirred at the solidification front will not continue to form a regular strong stirring motion, which can avoid the occurrence of "banded segregation". At the same time, the intermittent stirring is conducive to the recovery of columnar crystals. Continue to grow and control the excessive proportion of equiaxed crystals to avoid the adverse effects of large shrinkage, thick dendrites, and severe V-shaped segregation caused by dendrite collapse caused by excessive proportion of equiaxed crystals.

The setting of the stirring current and frequency is based on the generation of electromagnetic torque. As a preferred option, the setting range of the electromagnetic stirring electromagnetic torque of the crystallizer is 13-20N·mm, and the setting range of the electromagnetic stirring electromagnetic torque of the terminal electromagnetic stirring is 15-30N·mm.

Light reduction is carried out at the end of the solidification of the slab. The reduction interval corresponds to the center solid phase ratio of the slab fs = 0.4-0.85, the reduction amount is 8-16mm, and is allocated to multiple rollers for small-volume multi-roller continuous light reduction operations. On the one hand, the feeding is effectively carried out to avoid the negative pressure generated by shrinkage, which draws and enriches the molten steel to the center of the slab, reducing the subsequent feeding pressure under heavy pressure. On the other hand, it promotes the formation of solute elements between the dendrites in the center area of the slab. The molten steel should be properly refluxed to the liquid phase to re-distribute the solute (cannot reflux to an excessive extent, otherwise negative segregation will be aggravated), and at the same time prevent the adverse effects of compression cracks and billet bulging on the solidification front under low central solid phase ratio.

Preferably, the pressure rollers used for light reduction are 5-10 pairs of continuously distributed pressure rollers, and the reduction rate range is controlled at 2mm/m-6mm/m.

Subsequently, after the solid phase ratio fs in the center of the cast slab is 1, that is, after complete solidification, the corresponding first pressure roller is pressed by a single roller, and the reduction amount is preferably 10-15 mm. At this time, heavy reduction with a larger reduction amount can greatly avoid the risk of cracks in the reduction center. At the same time, it is more conducive to utilizing the temperature difference between the core and the surface to effectively transfer the reduction to the core of the cast slab without causing significant widening of the cast slab. Department, fully press the center shrinkage hole to eliminate looseness.

Compared with the existing technology, the present invention has the following technical advantages:

The method of the present invention innovatively performs dynamic mechanical reduction on billets, using a combination of light reduction and heavy reduction, continuous reduction and single-point reduction in a reasonable reduction interval, making full use of light reduction. The positive and superimposed effects of reduction on billet segregation and heavy pressing on the density of the billet have achieved a significant and effective improvement in the internal quality of high carbon steel billet under high production efficiency conditions; while dynamic reduction The reasonable online adjustment of the implementation and reduction parameters creates positive conditions for the stable output of high-quality cast slabs under the conditions of changing steel type, changing temperature, changing cooling and variable pulling speed, which greatly enhances the steel type and pouring of the inventive method. Conditional applicability; in addition, the synergistic effect of electromagnetic stirring in the control of the internal structure of the slab is used to further enhance the control and improvement of the homogenization of the core of the slab; ultimately, the central segregation index of the high carbon steel billet is stably controlled at Within 1.08, in terms of central density, there are no obvious shrinkage cavities and large-scale looseness, and there are no obvious naked eye cracks on the surface and inside of the cast slab. It not only achieves homogenization while ensuring the high efficiency of high carbon steel billet production, but also opens up a new production process for the energy-saving, low-cost and low-cost production of high-quality high-carbon steel billets, and also makes billet production popular. High-quality high-carbon special steel has laid an important foundation.

Detailed ways

The present invention is not limited to the following specific embodiments. Based on the disclosure of the present invention, those of ordinary skill in the art can adopt a variety of other specific embodiments to implement the present invention, or simply change or adopt the design structure and ideas of the present invention. Any modifications fall within the protection scope of the present invention. It should be noted that, as long as there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

The present invention will be further described in detail below in conjunction with the examples:

For each of the above representative steel types, the casting speed is 2.0-2.8m/min, the specific water volume is 0.25-1.2L/kg, and the superheat is 20-35°C. The specific corresponding basic pouring parameters for each steel type are shown in Table 1.

During the pouring process, the electromagnetic stirring of the crystallizer and the terminal electromagnetic stirring are turned on. The implementation parameters of the electromagnetic stirring of the crystallizer and the electromagnetic torque of the terminal electromagnetic stirring for each steel type are listed in Table 2. The final stirring adopts reversing intermittent stirring, and the specific interval is set to 10s-3s-10s, that is, the forward rotation lasts for 10s, stops for 3s, and reversely rotates for 10s. This is a cycle of action. The end electromagnetic stirring action position corresponds to the solid phase ratio fs of the slab center, which are 0.12, 0.15, 0.13 and 0.18 respectively.

Continuous multi-roller dynamic light reduction is implemented at the end of the solidification of the cast slab (continuous multi-roller light reduction within the range of fs: 04-0.85). The relevant parameters of dynamic light reduction for each representative steel type are shown in Table 3. Among them, the reduction interval corresponds to the range of solid phase ratio fs in the center of the slab, which is mainly concentrated in 0.4-0.85. The corresponding value of the specific steel type is slightly different due to the difference in distribution of the two phases caused by the characteristics of the steel type and the pouring conditions. The total dynamic light reduction increases from 10mm to 16mm as the carbon content of the representative steel increases, and the number of roller pairs increases from 5 pairs to 10 pairs. The reduction rate in the light reduction interval varies due to the difference in the reduction amount of each roller and the distance between rollers. Varies between 2-6mm/m.

During the pouring process of each steel type, the cast slab is completely solidified, that is, after fs=1, the first roller is pressed again at a single point, and the reduction amount of each representative steel type is 10-15mm.

Table 1 Basic continuous casting implementation parameters

Table 2 Electromagnetic stirring implementation parameters

Table 3 Implementation parameters of new combined pressing mode

Under the above implementation conditions, the test results of the homogenization index of each representative steel type cast slab are shown in Table 4. It can be seen from the table that after implementation, the center segregation index corresponding to the five-point drilling method for 175mm*175mm billet is controlled within 1.08. The uniformity rating is carried out according to the YB/T153-2015 standard. The center porosity does not exceed 0.5 level, and no center is found. Shrinkage cavities and various internal cracks rarely occur, and the maximum level does not exceed 0.5.

Table 4 Examples of slab homogeneity quality indicators

*Five-point cross-section drilling sample of cast slab, carbon and sulfur analysis of Ф5mm drill cuttings, segregation index = center point C content/average body C content

#Execution standard YB/T153-2015

Comparative Example 1: Low pulling speed and no pressure, only electromagnetic stirring, the other parameters are optimized and adjusted

Steel composition: C: 0.72%, Si: 0.23%, Mn: 0.56%, P: 0.011%, S: 0.009%, the rest is Fe.

The casting speed is 1.6m/min, the specific water volume is 0.56L/kg, and the superheat is 15-20°C.

Turn on the electromagnetic stirring and terminal electromagnetic stirring of the crystallizer. The electromagnetic torque of the electromagnetic stirring of the crystallizer is 15N·mm, and the electromagnetic torque of the terminal electromagnetic stirring is set to 30N·mm. The final stirring adopts one-way continuous stirring. The end electromagnetic stirring action position corresponds to the solid phase rate fs=0.35 in the center of the slab.

Comparative Example 2: The pressing range covers fs: 0.4≤fs＜1, under the heavy pressing of 0.9≤fs＜1.0, the remaining parameters are optimized and adjusted

Steel composition: C: 0.82%, Si: 0.25%, Mn: 0.68%, P: 0.022%, S: 0.010%, the rest is Fe.

The casting speed is 2.5m/min, the specific water volume is 0.25L/kg, and the superheat is 20-35°C.

Turn on the electromagnetic stirring of the crystallizer and the electromagnetic stirring at the end. The electromagnetic torque of the electromagnetic stirring of the crystallizer is 15N·mm, and the electromagnetic torque of the electromagnetic stirring at the end is set to 23N·mm. The final stirring adopts reversing intermittent stirring, and the specific interval is set to 10s-3s-10s, that is, the forward rotation lasts for 10s, stops for 3s, and reversely rotates for 10s. This is a cycle of action. The end electromagnetic stirring action position corresponds to the solid phase rate of the slab center fs = 0.15.

At the end of the solidification of the cast slab, dynamic light pressing and heavy pressing are continuously implemented (light pressing within fs: 0.2-0.9, and continuous heavy pressing within 0.9-1.0). The reduction interval corresponds to the solid phase rate fs in the center of the cast slab. The range is 0.4-1, the light reduction action range is fs: 0.4-0.9, the light reduction amount is 14mm, and is implemented through six groups of continuous pressure rollers. The reduction rate of this process is 1-5mm/m. Subsequently, single-point heavy pressing was implemented again in the interval of 0.9≤fs<1.0, and the reduction amount was 7mm.

Comparative Example 3: The reduction is concentrated at low fs, and the remaining parameters are optimized and adjusted.

Steel composition: C: 0.86%, Si: 0.22%, Mn: 0.54%, P: 0.014%, S: 0.009%, the rest is Fe.

The casting speed is 2.6m/min, the specific water volume is 0.60L/kg, and the superheat is 20-35°C.

Turn on the electromagnetic stirring of the crystallizer and the electromagnetic stirring at the end. The electromagnetic torque of the electromagnetic stirring of the crystallizer is 15N·mm, and the electromagnetic torque of the electromagnetic stirring at the end is set to 23N·mm. The final stirring adopts reversing intermittent stirring, and the specific interval is set to 10s-3s-10s, that is, the forward rotation lasts for 10s, stops for 3s, and reversely rotates for 10s. This is a cycle of action. The end electromagnetic stirring action position corresponds to the solid phase rate of the slab center fs = 0.15.

Dynamic light reduction and heavy reduction are carried out in sections at the end of the solidification of the slab. The light reduction interval corresponds to the solid phase ratio fs in the center of the slab, which ranges from 0.2 to 0.6. The light reduction amount is 14mm. The reduction is carried out by four pairs of rollers. , the process reduction rate is 2.5-5mm/m, and the reduction distribution and reduction rate are optimized and adjusted based on the low center solid phase rate. Then, after complete solidification fs = 1, single-point heavy pressing is carried out again, and the reduction amount is 14 mm.

Comparative Example 4: No electromagnetic stirring, excessive light pressing, no heavy pressing

Steel composition: C: 0.92%, Si: 0.24%, Mn: 0.33%, Cr: 0.27%, P: 0.021%, S: 0.016%, the rest is Fe.

The casting speed is 2.7m/min, the specific water volume is 1.12L/kg, and the superheat is 20-35°C.

Turn on the electromagnetic stirring of the crystallizer, the electromagnetic torque of the electromagnetic stirring of the crystallizer is 15N·mm, and turn off the electromagnetic stirring at the end.

At the end of the solidification of the cast slab, a dynamic light reduction with a larger reduction amount is implemented. The light reduction interval corresponds to the solid phase ratio fs of the center of the cast slab, which ranges from 0.4 to 0.7. The light reduction amount is 32mm, and is carried out through eight sets of continuous pressure rollers. Implementation, the reduction rate of this process is 4.5-8.5mm/m (in this comparative example, the solid phase rate and reduction rate corresponding to the center of the slab corresponding to the light reduction interval are optimized and adjusted based on the large reduction amount).

Under heavy pressure after complete solidification is not implemented.

Table 5 Comparative example slab homogeneity quality index

*Five-point cross-section drilling sample of cast slab, carbon and sulfur analysis of Ф5mm drill cuttings, segregation index = center point C content/average body C content

#Execution standard YB/T153-2015

It can be seen from Table 5 that under the conditions of the comparative example, the center segregation of the slab increased significantly, the positive segregation was all at 1.13 and above, reaching the highest 1.21, and there was a center negative segregation caused by excessive reduction under low center solid phase ratio fs. Segregation; in terms of core density, there are still varying degrees of central porosity, and even obvious central shrinkage holes; as far as internal cracks are concerned, improper pressing in different comparative examples has led to varying degrees of cracks in different parts. internal cracks.

The above are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person familiar with the technical field can, within the technical scope disclosed in the present invention, implement the technical solutions of the present invention. Any equivalent substitutions or changes in the concepts thereof shall be included in the protection scope of the present invention.

Claims (3)

1. The method for improving the homogeneity of the high-carbon steel billet casting blank based on the brand new depressing mode is characterized by comprising the following steps of: the small square billet comprises the following components in mass: c:0.67-1.0%, si:0.12-0.50%, mn:0.02-0.80%, P is less than or equal to 0.025%, S is less than or equal to 0.025%, and the balance is specifically added alloy and Fe; the method comprises the following steps:

starting the electromagnetic stirring of the crystallizer and the electromagnetic stirring of the tail end in the casting process, wherein the electromagnetic stirring of the tail end corresponds to the solid phase rate fs=0.12-0.15 of the center of the casting blank, the pulling speed is controlled to be 2.0-2.7m/min, and the electromagnetic stirring of the tail end adopts alternate stirring; the specific water quantity in the casting process is 0.25-1.12L/kg, and the superheat degree is 20-35 ℃; the electric stirring electromagnetic torque setting range of the end electromagnetic stirring is 15-30 N.mm, and the alternating stirring method comprises the following steps: the forward rotation lasts for 10s, stops for 3s, and rotates reversely for 10s, so that the cycle action period is one;

soft reduction is carried out at the solidification tail end of the casting blank, the soft reduction interval corresponds to the central solid phase rate fs=0.4-0.82 of the casting blank, the reduction is 10-14mm, and the casting blank is distributed to a plurality of rollers for small-quantity multi-roller continuous soft reduction operation; the pressure roller for implementing the light pressure is 5-8 pairs of pressure rollers which are continuously distributed, and the pressure rate range is controlled to be 2-6 mm/m;

and (3) carrying out single-roller heavy pressing on a first pressing roller corresponding to the central solid phase fs of the casting blank of 1, wherein the single-roller heavy pressing amount is 10-14mm.

2. The method for improving the homogeneity of a high-carbon steel billet casting blank based on a brand new rolling mode according to claim 1, wherein the method comprises the following steps: the setting range of the electromagnetic stirring torque of the crystallizer is 13-20 N.mm.

3. The method for improving the homogeneity of a high-carbon steel billet casting blank based on a completely new rolling mode according to any one of claims 1 or 2, characterized in that: the section of the billet casting blank is 175mm.175mm.