Method for controlling edge crack of NM400 wear-resistant steel

Abstract

The invention relates to an NM400 wear-resistant steel edge crack control method, and belongs to the technical field of steelmaking continuous casting methods. According to the technical scheme, when first-stage displacement is carried out, in the outward width adjusting process, the relative displacement of a copper plate is equal to the difference between target displacement and a gap; in the inward width adjusting process, the target displacement of the width adjusting screw rod and the target displacement of the copper plate are both negative displacement; in the additional stroke stage, the displacement of the copper plate after the additional stroke needs to be added with a part which cannot be reached due to a gap; at the final position, the final displacement of the width adjusting screw rod considers the influence of the extra stroke displacement, and the final displacement of the copper plate is matched with the target displacement and the gap filling condition. According to the invention, the consistency of the actual displacement and the target displacement is ensured, so that the accurate control of the taper is ensured; and the quality and the production stability of the casting blank are remarkably improved, the rejection rate in the production process is reduced, the overall performance of the continuous casting process is optimized, and higher production efficiency and economic benefits are brought to the steel smelting industry.

Description

Technical Field

[0001] The invention relates to a method for controlling edge cracks of NM400 wear-resistant steel, belonging to the technical field of steelmaking and continuous casting methods. Background Art

[0002] Mold taper is a key parameter in slab continuous casting, significantly impacting production stability and slab quality. During casting, large deviations from the set mold taper can impair heat transfer from the slab to the mold, increase casting resistance, wear the mold copper plate, and even cause cracks in the slab shell, leading to breakouts. The mold taper is adjusted using a width adjustment mechanism, which is then clamped and secured by a clamping device that acts on the worm gear drive. Due to continuous mold vibration and inherent precision limitations, play can easily form between the width adjustment screw nut and the mechanism, leading to excessive or insufficient taper on the narrow side of the mold. These issues can exacerbate longitudinal cracking. Taper must not be altered during normal continuous casting, as this can alter the cooling effect of the slab and cause defects such as corner cracks, narrow side bulging, and localized concavity on the narrow side. However, even with mechanical width adjustment, mold taper deviation persists, impacting slab quality. In severe cases, corner cracks and bulging breakouts can occur, damaging the continuous casting equipment and reducing both machine availability and mold life.

[0003] From January to June 2024, a total of eight incidents of longitudinal cracking of wear-resistant steel ingots occurred in the continuous casting workshop of the steel plant, seriously impacting product quality. Currently, edge cracking of NM400 wear-resistant steel in the continuous casting workshop is the primary cause of low first-pass yields for ingots, accounting for 86.4% of all quality anomalies. Longitudinal cracking of wear-resistant steel edges is a secondary factor affecting first-pass yields, accounting for 9.7%. Therefore, it is crucial to research the mechanism of longitudinal cracking in wear-resistant steel and develop preventative measures to improve production efficiency and ingot yields. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for controlling edge cracks of NM400 wear-resistant steel. By compensating for the tiny gap between the width-adjusting screw and the copper plate, the consistency between the actual displacement and the target displacement is ensured, thereby ensuring precise control of the taper. It not only significantly improves the quality and production stability of the ingot and reduces the scrap rate in the production process, but also optimizes the overall performance of the continuous casting process, brings higher production efficiency and economic benefits to the steel smelting industry, and effectively solves the above-mentioned problems existing in the background technology.

[0005] The technical solution of the present invention is: a method for controlling edge cracks of NM400 wear-resistant steel, comprising the following steps: (1) In the initial position, the width adjustment screw and the copper plate are both at the starting point, and the relative position is 0; (2) When the first stage of displacement is performed, during the outward width adjustment process, if there is a gap, the width adjustment screw drives the outer side of the copper plate to open outward, and the relative displacement of the width adjustment screw is equal to the target displacement. The relative displacement of the copper plate takes into account the size of the gap, and its relative displacement is less than the target displacement; during the inward width adjustment process, if the gap is zero, the width adjustment screw drives the inner side of the copper plate to close inward, and the target displacements of the width adjustment screw and the copper plate are both negative displacements; (3) In the extra stroke stage, the width adjustment screw moves the extra stroke based on the target displacement, and the displacement of the copper plate after the extra stroke needs to be added with the part that cannot be achieved due to the gap; (4) At the final position, both the width adjustment screw and the copper plate reach the expected displacement position. The final displacement of the width adjustment screw takes into account the influence of the additional stroke displacement, and the final displacement of the copper plate matches the target displacement and the gap filling situation.

[0006] In the step (2), during the outward widening process of the first stage displacement, the relative displacement of the copper plate is equal to the target displacement minus the size of the gap.

[0007] In the step (3), the relative displacement of the width-adjusting screw in the additional stroke stage is equal to the target displacement plus the additional stroke, and the relative displacement of the copper plate is equal to the target displacement plus the additional stroke minus the gap.

[0008] In the step (4), the final displacement of the width-adjusting screw is the relative displacement of the width-adjusting screw in the step (3) minus the extra stroke; the final displacement of the copper plate is the relative displacement of the copper plate in the step (3) minus the difference between the extra stroke and the gap.

[0009] The beneficial effects of the present invention are as follows: by compensating for the tiny gap between the width-adjusting screw and the copper plate, the consistency between the actual displacement and the target displacement is ensured, thereby ensuring precise control of the taper; it not only significantly improves the quality and production stability of the ingot and reduces the scrap rate in the production process, but also optimizes the overall performance of the continuous casting process, bringing higher production efficiency and economic benefits to the steel smelting industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 Schematic diagram of Example 1 comparing the running cone width before and after the implementation of the present invention without online adjustment; Figure 2 2 is a schematic diagram comparing the online width adjustment of the running cone before and after the implementation of the present invention in Example 2. DETAILED DESCRIPTION

[0011] In order to make the purpose, technical solutions and advantages of the invention implementation cases clearer, the technical solutions in the invention implementation cases will be clearly and completely described below in conjunction with the drawings in the implementation cases. Obviously, the implementation cases described are only a small part of the implementation cases of the present invention, rather than all the implementation cases. Based on the implementation cases in the present invention, all other implementation cases obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0012] A method for controlling edge cracks of NM400 wear-resistant steel comprises the following steps: (1) In the initial position, the width adjustment screw and the copper plate are both at the starting point, and the relative position is 0; (2) When the first stage of displacement is performed, during the outward width adjustment process, if there is a gap, the width adjustment screw drives the outer side of the copper plate to open outward, and the relative displacement of the width adjustment screw is equal to the target displacement. The relative displacement of the copper plate takes into account the size of the gap, and its relative displacement is less than the target displacement; during the inward width adjustment process, if the gap is zero, the width adjustment screw drives the inner side of the copper plate to close inward, and the target displacements of the width adjustment screw and the copper plate are both negative displacements; (3) In the extra stroke stage, the width adjustment screw moves the extra stroke based on the target displacement, and the displacement of the copper plate after the extra stroke needs to be added with the part that cannot be achieved due to the gap; (4) At the final position, both the width adjustment screw and the copper plate reach the expected displacement position. The final displacement of the width adjustment screw takes into account the influence of the additional stroke displacement, and the final displacement of the copper plate matches the target displacement and the gap filling situation.

[0013] In the step (2), during the outward widening process of the first stage displacement, the relative displacement of the copper plate is equal to the target displacement minus the size of the gap.

[0014] In the step (3), the relative displacement of the width-adjusting screw in the additional stroke stage is equal to the target displacement plus the additional stroke, and the relative displacement of the copper plate is equal to the target displacement plus the additional stroke minus the gap.

[0015] In the step (4), the final displacement of the width-adjusting screw is the relative displacement of the width-adjusting screw in the step (3) minus the extra stroke; the final displacement of the copper plate is the relative displacement of the copper plate in the step (3) minus the difference between the extra stroke and the gap.

[0016] In practical applications, the taper gap compensation during the outward widening process of the narrow side of the crystallizer is carried out in the following four steps after the start of the action.

[0017] A: In the initial position, the width adjustment screw and the copper plate are both at the starting point, and the relative position is 0.

[0018] B: When performing the first stage of displacement, if there is a gap (BL>0), the width adjustment screw drives the outer side of the copper plate to open outward, and its displacement remains at the theoretical displacement (RD = + TD). However, due to the existence of the gap, the relative displacement of the copper plate will be less than the target displacement because it needs to subtract the size of the gap (RD = + (TD - BL)).

[0019] C: During the additional stroke, both the width adjustment screw and the copper plate undergo additional displacement to fill the gap. The width adjustment screw's displacement after the additional stroke is (RD = + TD + ES). The copper plate's displacement after the additional stroke, due to the gap, must be increased by the amount not achieved due to the gap (RD = + (TD - BL) + ES).

[0020] D: At the final position, both the width adjustment screw and the copper plate have reached their intended displacement. However, due to the gap, the width adjustment screw's final position needs to account for the additional travel (FD = TD + ES - ES). The copper plate's final position also takes into account the effect of the additional travel to fill the gap (FD = TD = (TD - BL) + ES - (ES - BL)). In other words, the copper plate's final position is related to both the theoretical displacement and the gap filling, and the effect of the additional travel is already reflected in the process.

[0021] In summary, by listing the displacement parameters of the width-adjusting screw and the copper plate at different stages, the process and results of gap compensation after the opening movement are demonstrated.

[0022] The taper gap compensation during the inward widening process of the narrow side of the crystallizer is divided into the following four steps after the closing action.

[0023] A: In the initial position, the width adjustment screw and the copper plate are both at the starting point, and the relative position is 0.

[0024] B: When entering the first stage of displacement, if the gap is zero (BL=0), the width adjustment screw drives the inner side of the copper plate to close inward, and the displacement of the width adjustment screw and the copper plate are both negative displacements (RD = - TD).

[0025] C: During the additional stroke, both the width adjustment screw and the copper plate undergo additional displacement to fill the gap. The width adjustment screw's displacement after the additional stroke is (RD = -TD + ES). The copper plate's displacement after the additional stroke, due to the gap, must also be compensated for by the gap (RD = -TD + (ES - BL)).

[0026] D: At the final position, both the width adjustment screw and the copper plate have reached their intended displacement. However, due to the gap, the width adjustment screw's final position needs to account for the additional travel (FD = - TD + ES - ES). The copper plate's final position also takes into account the effect of the additional travel to fill the gap (FD = - TD = -TD + (ES - BL) -(ES - BL)). In other words, the copper plate's final position is related to both the theoretical displacement and the gap filling, and the effect of the additional travel is already reflected in the process.

[0027] In summary, by listing the displacement parameters of the width-adjusting screw and copper plate at different stages, the process and results of gap compensation after closing movement are demonstrated.

[0028] Note: "RD" stands for relative displacement.

[0029] "TD" stands for Target Displacement.

[0030] "BL" stands for Backlash.

[0031] "ES" stands for Extra Stroke.

[0032] “FD” stands for “FINAL DISPLACEMENT”. Example 1

[0033] During the 440534th pour, NM400 wear-resistant steel was produced using a Danieli continuous caster with two strands, both without online width adjustment. The cross-sections were 1700mm on the single strand side and 1650mm on the dual strand side. The target tapers were 10.3 and 10.0, respectively. During preparation, the tapers measured were 10.27° east and 10.3° west on the single strand side; and 9.85° east and 9.97° west on the dual strand side.

[0034] The control method of inward widening gap compensation is not used.

[0035] The taper was remeasured when pouring was stopped, and no online width adjustment was performed. The single-stream side was 1700mm, and the double-stream side was 1650mm. The target tapers were 10.3 and 10.0 respectively. The taper measurements when pouring was stopped were 9.67 east and 9.38 west on the single-stream side; 9.06 east and 9.17 west on the double-stream side.

[0036] The NM400 wear-resistant steel produced in this casting suffered longitudinal cracks due to mold taper. The defect morphology of the longitudinal cracks in the 2# continuous annealing process was manifested as a long and thin "black line" with a width of 1-3mm and an irregular length (about 5~500mm). It appeared intermittently throughout the coil, mainly concentrated at 1 / 4 and 1 / 2 of the strip, and occasionally occurred in other parts. The degradation rate of machine-cleaned longitudinal cracks was 7.9%, and the rate of non-machine-cleaned longitudinal cracks was 13.7%.

[0037] During the 440599th continuous casting run, NM400 wear-resistant steel was produced using a Danieli continuous caster with two strands, both without online width adjustment. The cross-sections were 1700mm on the single strand side and 1650mm on the dual strand side. The target tapers were 10.3 and 10.0, respectively. During preparation, the tapers measured were 10.3° east and 10.3° west on the single strand side, and 9.97° east and 10.0° west on the dual strand side.

[0038] The control method of inward width adjustment gap compensation is used to ensure the accuracy of narrow side width adjustment.

[0039] The taper was remeasured when pouring was stopped, and no online width adjustment was performed. The single-stream side was 1700mm, and the double-stream side was 1350mm. The target tapers were 10.3 and 10.0 respectively. The taper measurements when pouring was stopped were 10.01 east and 10.13 west on the single-stream side; 9.67 east and 9.59 west on the double-stream side.

[0040] The NM400 wear-resistant steel produced in this casting has no obvious longitudinal cracks.

[0041] Table 1: Comparison of running cone width adjustment before and after the implementation of the measures

[0042] Example 2: During continuous casting run No. 450491, NM400 wear-resistant steel was produced using a Danieli continuous caster with two strands. The single strand side had online width adjustment, while the dual strand side remained unchanged. The cross-sections were 1650mm for the single strand and 1350mm for the dual strand. The target tapers were 9.7 and 8.2, respectively. During preparation, the tapers measured were 9.7° east and 9.6° west for the single strand, and 8.3° east and 8.4° west for the dual strand.

[0043] The control method of inward widening gap compensation is not used.

[0044] The taper was remeasured when pouring was stopped. The width of the single-stream side was adjusted online to 1600mm-1500mm, and that of the double-stream side was 1350mm. The target tapers were 9.4 and 8.2 respectively. The taper measurements when pouring was stopped were 8.64 in the east and 8.01 in the west on the single-stream side; and 7.38 in the east and 7.85 in the west on the double-stream side.

[0045] The NM400 wear-resistant steel produced in this casting suffered from longitudinal cracks caused by mold cone runaway. The defect morphology of the longitudinal cracks in the 2# continuous annealing process was manifested as long and thin "black lines" with a width of 1-4mm and irregular length (about 5-500mm). They appeared intermittently throughout the coil, mainly concentrated at 1 / 4 and 1 / 2 of the strip, and occasionally at other locations. The degradation rate of machine-cleaned longitudinal cracks was 8.6%, and the rate of non-machine-cleaned longitudinal cracks was 10.7%.

[0046] During continuous casting run No. 450503, NM400 wear-resistant steel was produced using a Danieli continuous caster with two strands. The single strand side had online width adjustment, while the dual strand side remained unchanged. The cross-sections were 1650mm for the single strand and 1350mm for the dual strand. The target tapers were 9.7 and 8.2, respectively. During preparation, the tapers measured were 9.67° east and 9.58° west for the single strand, and 8.25° east and 8.17° west for the dual strand.

[0047] The control method of inward width adjustment gap compensation is used to ensure the accuracy of narrow side width adjustment.

[0048] The taper is remeasured when pouring is stopped. The width is adjusted online to 1600mm-1500mm on the single-stream side and 1350mm on the double-stream side. The target tapers are 9.4 and 8.2 respectively. The taper measurement when pouring is stopped is 9.25 east and 9.13 west on the single-stream side; 8.05 east and 8.12 west on the double-stream side.

[0049] The NM400 wear-resistant steel produced in this casting has no obvious longitudinal cracks.

[0050] Table 2: Comparison of online cone width adjustment before and after implementation of measures

[0051] Implementation effect: Taper control significantly impacts the quality of NM400 wear-resistant steel produced during continuous casting. Accurate taper control can minimize gap unevenness between the mold copper plate and the ingot, thereby reducing the incidence of defects such as longitudinal cracks. Using a width adjustment gap compensation control method effectively improves the accuracy of narrow side width adjustment, further enhancing product quality. Continuous monitoring of the continuous casting process is essential to promptly identify and address factors that may affect product quality. Furthermore, this approach will continue to be employed in future continuous casting operations, with continuous optimization of process parameters and control methods based on actual production conditions to enhance product quality and production efficiency.

[0052] From January to June 2024, a total of eight incidents of longitudinal cracking of wear-resistant steel ingots occurred in the continuous casting workshop of our steel mill, seriously impacting product quality. After implementing a control method for longitudinal cracking during the continuous casting of NM400 wear-resistant steel in the continuous casting workshop, from July to December 2024, the number of incidents of longitudinal cracking of NM400 wear-resistant steel ingots decreased from eight in the first half of 2024 to two in the second half of 2024. The amount of NM400 wear-resistant steel ingots downgraded due to longitudinal cracking decreased by 1,450 tons compared to the first half of the year, a reduction of 62%. This has achieved significant results in reducing the amount of longitudinal cracking downgraded ingots, as shown in Table 3: Table 3: Comparison of longitudinal crack degradation of NM400 wear-resistant steel before and after implementation of measures

Claims

1. A method for controlling edge cracks of NM400 wear-resistant steel, characterized in that The following steps are involved: (1) In the initial position, the width adjustment screw and the copper plate are both at the starting point, and the relative position is 0; (2) When the first stage of displacement is performed, during the outward width adjustment process, if there is a gap, the width adjustment screw drives the outer side of the copper plate to open outward, and the relative displacement of the width adjustment screw is equal to the target displacement. The relative displacement of the copper plate takes into account the size of the gap, and its relative displacement is less than the target displacement; during the inward width adjustment process, if the gap is zero, the width adjustment screw drives the inner side of the copper plate to close inward, and the target displacements of the width adjustment screw and the copper plate are both negative displacements; (3) In the extra stroke stage, the width adjustment screw moves the extra stroke based on the target displacement, and the displacement of the copper plate after the extra stroke needs to be added with the part that cannot be achieved due to the gap; (4) At the final position, both the width adjustment screw and the copper plate reach the expected displacement position. The final displacement of the width adjustment screw takes into account the influence of the additional stroke displacement, and the final displacement of the copper plate matches the target displacement and the gap filling situation.

2. The method for controlling edge cracks of NM400 wear-resistant steel according to claim 1, characterized in that: In the step (2), during the outward widening process of the first stage displacement, the relative displacement of the copper plate is equal to the target displacement minus the size of the gap.

3. The method for controlling edge cracks of NM400 wear-resistant steel according to claim 1, characterized in that: In the step (3), the relative displacement of the width-adjusting screw in the additional stroke stage is equal to the target displacement plus the additional stroke, and the relative displacement of the copper plate is equal to the target displacement plus the additional stroke minus the gap.

4. The method for controlling edge cracks of NM400 wear-resistant steel according to claim 1, characterized in that: In the step (4), the final displacement of the width-adjusting screw is the relative displacement of the width-adjusting screw in the step (3) minus the extra stroke; the final displacement of the copper plate is the relative displacement of the copper plate in the step (3) minus the difference between the extra stroke and the gap.

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