A method for improving corner cracks in 55SiCr ingot

Abstract

The present invention relates to a method for reducing micro cracks at the corners of 55SiCr spring steel billet continuous casting crystallizer by changing the chamfering structure and size. The changes in the crystallizer structure and size include the chamfering of the billet using a 1 / 4 arc, the chamfering radius is 15-23 mm; the thickness of the copper mold of the chamfered crystallizer is 10-18 mm, and the back taper is 0.1-0.5%. In the continuous casting process, the pulling speed is controlled to be 2.0-2.5 m / min, the superheat is 15-25° C., the crystallizer cooling water flow is 1500-1850 L / min, the vibration frequency is 150-200 Hz, the amplitude is 4.0-5.0 mm, and the secondary cooling water volume is about 0.8-1.0 L / kg. The present invention optimizes the chamfering structure and size of the continuous casting crystallizer by design, and cooperates with the continuous casting process to quickly and effectively reduce the probability of cracks at the corners of the billet. At the same time, the utilization rate of steel is also greatly increased.

Description

Technical Field

[0001] The invention relates to a method for improving corner cracks of 55SiCr casting blanks, belonging to the technical field of steel continuous casting. Background Art

[0002] Corner transverse cracks are a common quality problem of continuous casting billets, and grinding or peeling is required to ensure the quality of rolled products. However, the problem of corner transverse cracks in continuous casting billets of some special steel grades has not been solved, and most companies are unable to improve or eliminate it. Under the premise of avoiding the third brittle zone during the continuous casting straightening or bending stage, low-melting point compounds such as sulfides (FeS-MnS-FeO) or eutectic phases precipitate at the austenite grain boundaries, which will cause stress concentration on the billet and cause corner cracks.

[0003] Hou Zibing et al. found in the ship plate steel continuous casting billet that the plasticity decreased at 900-950℃ due to the low melting point eutectic phase liquid film; the plasticity decreased between 850-900℃ due to the combined effect of the low melting point eutectic phase liquid film and the grain boundary ferrite film, and the formation of the liquid film was inferred to be the formation of (FeS+FeO) or (MnS+FeS+FeO) low melting point eutectic phase at the grain boundary (see "High Temperature Mechanical Properties and Fracture Liquid Film Phenomenon of Ship Plate Steel Continuous Casting Billet"). This study focused on the mechanism of crack generation and did not implement improvement measures in production. Chinese Patent Publication No. CN 111136228 A proposes a control method for improving transverse cracks at the corners of continuous casting billets. The core of the method is that the cross-sectional size of the large chamfered continuous casting billet is 280×325mm, the angle between the corner of the continuous casting billet and the wide surface of the billet is controlled to be 50-60°, and the length of the bevel of the continuous casting billet is 50-70mm, which increases the temperature of the corner of the continuous casting billet in the straightening section and reduces the risk of transverse cracks at the corner of the continuous casting billet. Chinese Patent Publication No. CN111286576A proposes a crystallizer with a chamfer arc radius of R80 to 82 degrees and a chamfer arc diameter width of 39 to 40mm, which reduces the cooling intensity of the corners of the billet produced, eliminates corner cracks and sharp corners. However, for small square billets, how to reduce the probability of corner cracks has not been reported in the above literature. Summary of the invention

[0004] The purpose of the present invention is to provide a method for improving the corner cracks of 55SiCr small square billet castings, effectively solve the quality problem of corner cracks of 55SiCr small square billet continuous castings, reduce the grinding work before rolling, reduce the material waste caused by grinding, and save material loss.

[0005] The present invention provides a method for improving corner cracks of 55SiCr ingot, which specifically comprises the following steps:

[0006] (1) The cross-sectional dimensions of the 55SiCr billet are designed to be 150×150 mm; a continuous casting mold that meets the design dimensions of the 55SiCr billet is used, and the chamfer of the continuous casting mold adopts a 1 / 4 arc, i.e., a round chamfer, with a radius of 15 to 23 mm; wherein the copper mold thickness of the round chamfered crystallizer is 10 to 18 mm, and the back taper is 0.1 to 0.5%;

[0007] (2) 55SiCr billet was prepared by continuous casting process;

[0008] The parameters of continuous casting include: pulling speed 2.0~2.5m / min, superheat 10~25℃, crystallizer cooling water flow 1850~1950L / min, vibration frequency 150~200Hz, amplitude 4.0~5.0mm, and secondary cooling water volume 0.8~1.0L / kg.

[0009] The invention discloses a method for improving corner cracks of 55SiCr ingot, wherein the secondary cooling water volume is 0.9-1.0 L / kg.

[0010] The invention discloses a method for improving corner cracks of 55SiCr casting blank, with a vibration frequency of 150-180 Hz.

[0011] As one of the preferred solutions, the present invention provides a method for improving corner cracks of 55SiCr ingot, which specifically comprises the following steps:

[0012] (1) The cross-sectional dimensions of the 55SiCr billet are designed to be 150×150 mm; a continuous casting mold that meets the design dimensions of the 55SiCr billet is used, and the chamfer of the continuous casting mold adopts a 1 / 4 arc, i.e., a round chamfer, with a radius of 15 mm; the copper mold thickness of the round chamfered crystallizer is 18 mm, and the back taper is 0.5%;

[0013] (2) 55SiCr billet was prepared by continuous casting process;

[0014] The continuous casting parameters include: casting speed 2.5m / min, superheat 15-25℃, crystallizer cooling water flow 1850L / min, vibration frequency 178Hz, amplitude 4.4mm, and secondary cooling water volume 0.98L / kg.

[0015] As one of the preferred solutions, the present invention provides a method for improving corner cracks of 55SiCr ingot, which specifically comprises the following steps:

[0016] (1) The cross-sectional dimensions of the 55SiCr billet are designed to be 150×150 mm; a continuous casting mold that meets the design dimensions of the 55SiCr billet is used, and the chamfer of the continuous casting mold adopts a 1 / 4 arc, i.e., a round chamfer, with a radius of 23 mm; the copper mold thickness of the round chamfered crystallizer is 18 mm, and the taper is 0.5%;

[0017] (2) 55SiCr billet was prepared by continuous casting process;

[0018] The continuous casting parameters include: casting speed 2.5m / min, superheat 15-25℃, crystallizer cooling water flow 1850L / min, vibration frequency 178Hz, amplitude 4.4mm, and secondary cooling water volume 0.98L / kg.

[0019] During the technical exploration process, it was also found that the following technologies are also suitable for the present invention:

[0020] The present invention provides a method for improving corner cracks of 55SiCr ingot, which specifically comprises the following steps:

[0021] (1) The cross-sectional dimensions of the 55SiCr billet are designed to be 150×150 mm; a continuous casting mold that meets the design dimensions of the 55SiCr billet is used, and the chamfer of the continuous casting mold adopts a 1 / 4 arc, i.e., a round chamfer, with a radius of 23 mm; the copper mold thickness of the round chamfered crystallizer is 10 mm, and the taper is 0.1%;

[0022] (2) 55SiCr billet was prepared by continuous casting process;

[0023] The continuous casting parameters include: casting speed 2.0m / min, superheat 15-25°C, crystallizer cooling water flow 1500L / min, vibration frequency 150Hz, amplitude 4.4mm, and secondary cooling water volume 1.1L / kg.

[0024] The principle of the present invention: by designing and optimizing the chamfer structure and size of the continuous casting crystallizer, the solidification of the molten steel at the corner of the billet is closer to one-dimensional heat transfer, thereby reducing the slow cooling rate of the corner of the billet, and the corner solidification structure will not be bent or straightened too early due to the excessively fast cooling rate, that is, avoiding the corner solidification structure in the bending or straightening area in the high-temperature third brittleness of the steel type, thereby causing cracks at the corner of the billet, and the precipitation of low-melting point compounds or eutectic phases such as sulfides (FeS-CrS-FeO), causing stress concentration on the billet, resulting in corner crack problems. Thereby, the probability of cracks at the corner of the small square billet is quickly reduced. At the same time, due to the increase in the round chamfer, the utilization rate of steel is greatly increased. The present invention optimizes the chamfer structure and size of the continuous casting crystallizer by design, and cooperates with the continuous casting process to quickly and effectively reduce the probability of cracks at the corner of the small square billet. At the same time, the utilization rate of steel is also greatly increased.

[0025] Beneficial effects of the present invention:

[0026] (1) The present invention reduces the incidence of cracks at the corners of the ingot.

[0027] (2) The present invention reduces the grinding rate and grinding depth of the corners of the ingot, greatly increases the utilization rate of steel, and can save steel resources and costs.

[0028] (3) The present invention can be directly used in industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the designed copper mold for the crystallizer;

[0030] Figure 2 The corner cracks of the ingot and its SEM-EDS of the product obtained in Comparative Example 1;

[0031] Figure 3 The inverted taper of the crystallizer copper mold. DETAILED DESCRIPTION

[0032] The present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0033] Comparative Example 1

[0034] The chamfer of the 55SiCr billet continuous casting mold adopts a 1 / 4 arc, the radius of the chamfer is 6mm, the thickness of the copper mold of the chamfered mold is 18mm, and the taper is 0.5%. When the size of the mold chamfer is 6mm, the continuous casting speed is 2.5m / min, the superheat is controlled at 15-25℃, the cooling water flow of the mold is 1850L / min, the vibration frequency is 178Hz, the amplitude is 4.4mm, and the secondary cooling water volume is 9.8L / kg.

[0035] A total of 94 transverse cracks were found on the 300mm long billet in the extended drawing direction of the investigated billet. A total of 20 billets were counted, of which corner cracks accounted for about 70% of the total cracks. At the same time, a small amount of longitudinal microcracks were also found, and the corner grinding depth was 7-8mm.

[0036] Example 1

[0037] The chamfer of the 55SiCr billet continuous casting mold adopts a 1 / 4 arc, the radius of the chamfer is 15mm, the thickness of the copper mold of the chamfered mold is 18mm, and the taper is 0.5%. When the size of the chamfer of the mold is 15mm, the continuous casting speed is 2.5m / min, the superheat is controlled at 15-25℃, the cooling water flow of the mold is 1850L / min, the vibration frequency is 178Hz, the amplitude is 4.4mm, and the secondary cooling water volume is about 0.98L / kg.

[0038] A total of 20 transverse cracks were found on the 300mm long billet in the extended drawing direction of the investigated billet. A total of 20 billets were counted, and the corner cracks accounted for 15% of the total number of cracks; no longitudinal microcracks were found, and the corner grinding depth was 2-3mm.

[0039] Example 2

[0040] The chamfer of the 55SiCr billet continuous casting mold adopts a 1 / 4 arc, the radius of the chamfer is 23mm, the thickness of the copper mold of the chamfered mold is 18mm, and the taper is 0.5%. When the size of the chamfer of the mold is 23mm, the continuous casting speed is 2.5m / min, the superheat is controlled at 15-25℃, the cooling water flow of the mold is 1850L / min, the vibration frequency is 178Hz, the amplitude is 4.4mm, and the secondary cooling water volume is about 0.98L / kg.

[0041] A total of 10 transverse cracks were found on the 300mm long billet in the extended drawing direction of the investigated billet. A total of 20 billets were counted, and the corner cracks accounted for less than 5% of the total number of cracks; no longitudinal microcracks were found, and the corner grinding depth was 1-2mm.

[0042] Comparative Example 2

[0043] The chamfer of the 55SiCr small square billet continuous casting crystallizer adopts a 1 / 4 arc, the radius of the chamfer is 15mm, the thickness of the copper mold of the chamfered crystallizer is 18mm, and the taper is 0.5%. When the size of the crystallizer chamfer is 15mm, the continuous casting speed is 2.5m / min, the superheat is controlled at 15-25℃, the vibration frequency is 178Hz, the amplitude is 4.4mm, and the secondary cooling water volume is about 9.8L / kg. Compared with Example 1, only the cooling water flow rate of the crystallizer is changed to 1500L / min. A total of 50 transverse cracks were found on the 300mm casting direction of the investigated casting. A total of 20 castings were counted, and the corner cracks accounted for 16% of the total number of cracks, and the corner grinding depth was 4-5mm. It shows that the change of the cooling water volume of the crystallizer will have an important impact on the surface quality of the continuous casting billet.

[0044] Comparative Example 3

[0045] The chamfer of the 55SiCr small square billet continuous casting crystallizer adopts a 1 / 4 arc, the radius of the chamfer is 15mm, the thickness of the copper mold of the chamfered crystallizer is 18mm, and the taper is 0.5%. When the size of the crystallizer chamfer is 15mm, the continuous casting speed is 2.5m / min, the superheat is controlled at 15-25℃, the vibration frequency is 178Hz, the amplitude is 4.4mm, and the cooling water flow of the crystallizer is 1850L / min. Compared with Example 1, only the secondary cooling water ratio is changed by about 1.5L / kg. A total of 125 transverse cracks were found on the 300mm casting direction of the investigated casting. A total of 20 castings were counted, and the corner cracks accounted for 32% of the total number of cracks, and the corner grinding depth was 10-11mm. It shows that the change of the secondary cooling water ratio of the crystallizer will have an important impact on the surface quality of the continuous casting billet.

[0046] Example 3

[0047] The chamfer of the 55SiCr billet continuous casting mold adopts a 1 / 4 arc, the radius of the chamfer is 23mm, the thickness of the copper mold of the chamfered mold is 10mm, and the taper is 0.1%. When the size of the chamfer of the mold is 23mm, the continuous casting speed is 2.0m / min, the superheat is controlled at 15-25℃, the cooling water flow of the mold is 1500L / min, the vibration frequency is 150Hz, the amplitude is 4.4mm, and the secondary cooling water volume is about 1.1L / kg.

[0048] A total of 15 transverse cracks were found on the 300mm long billet in the extended drawing direction of the investigated billet. A total of 20 billets were counted, and the corner cracks accounted for 20% of the total number of cracks; no longitudinal microcracks were found, and the corner grinding depth was 2-3mm.

[0049] Table 1 Examples 1-3 and Comparative Examples 1-3

[0050]

[0051] In summary, under the synergistic effect of various parameters, the present invention significantly improves the quality of small-sized 55SiCr square billet castings, especially reduces the number of cracks and the corner grinding depth.

Claims

1. A method for improving corner cracks in 55SiCr ingot, characterized in that: The following steps are involved: (1) The cross-sectional dimensions of the 55SiCr billet are designed to be 150×150 mm; a continuous casting mold that meets the design dimensions of the 55SiCr billet is used, and the chamfer of the continuous casting mold adopts a 1 / 4 arc, i.e., a round chamfer, with a radius of 15 to 23 mm; wherein the copper mold thickness of the round chamfered crystallizer is 10 to 18 mm, and the back taper is 0.1 to 0.5%; (2) 55SiCr billet was prepared by continuous casting process; The parameters of continuous casting include: pulling speed 2.0~2.5m / min, superheat 10~25℃, crystallizer cooling water flow 1850~1950L / min, vibration frequency 150~200Hz, amplitude 4.0~5.0mm, and secondary cooling water volume 0.8~1.1L / kg.

2. The method for improving corner cracks of 55SiCr ingot according to claim 1, characterized in that: The secondary cooling water volume is 0.9~1.0L / kg.

3. The method for improving corner cracks of 55SiCr ingot according to claim 1, characterized in that: Vibration frequency: 150~180Hz.

4. The method for improving corner cracks of 55SiCr ingot according to claim 1, characterized in that: The following steps are involved: (1) The cross-sectional dimensions of the 55SiCr billet are designed to be 150×150 mm; a continuous casting mold that meets the design dimensions of the 55SiCr billet is used, and the chamfer of the continuous casting mold adopts a 1 / 4 arc, i.e., a round chamfer, with a radius of 15 mm; the copper mold thickness of the round chamfered crystallizer is 18 mm, and the back taper is 0.5%; (2) 55SiCr billet was prepared by continuous casting process; The continuous casting parameters include: casting speed 2.5m / min, superheat 15-25℃, crystallizer cooling water flow 1850L / min, vibration frequency 178Hz, amplitude 4.4mm, and secondary cooling water volume 0.98L / kg.

5. The method for improving corner cracks of 55SiCr ingot according to claim 1, characterized in that: The following steps are involved: (1) The cross-sectional dimensions of the 55SiCr billet are designed to be 150×150 mm; a continuous casting mold that meets the design dimensions of the 55SiCr billet is used, and the chamfer of the continuous casting mold adopts a 1 / 4 arc, i.e., a round chamfer, with a radius of 23 mm; the copper mold thickness of the round chamfered crystallizer is 18 mm, and the taper is 0.5%; (2) 55SiCr billet was prepared by continuous casting process; The continuous casting parameters include: casting speed 2.5m / min, superheat 10-18°C, crystallizer cooling water flow 1850L / min, vibration frequency 178Hz, amplitude 4.4mm, and secondary cooling water volume 0.98L / kg.

6. A method for improving corner cracks of 55SiCr ingot, characterized in that; The following steps are involved: (1) The cross-sectional dimensions of the 55SiCr billet are designed to be 150×150 mm; a continuous casting mold that meets the design dimensions of the 55SiCr billet is used, and the chamfer of the continuous casting mold adopts a 1 / 4 arc, i.e., a round chamfer, with a radius of 23 mm; the copper mold thickness of the round chamfered crystallizer is 10 mm, and the taper is 0.1%; (2) 55SiCr billet was prepared by continuous casting process; The continuous casting parameters include: casting speed 2.0m / min, superheat 15-25°C, crystallizer cooling water flow 1500L / min, vibration frequency 150Hz, amplitude 4.4mm, and secondary cooling water volume 1.1L / kg.

Images