A method for reducing occurrence of pinhole defects in automotive panels

Abstract

The present application relates to a kind of methods for reducing the incidence of automobile plate pinhole defects, belong to steel metallurgy continuous casting method technical field.The technical scheme of the present application is: by accurately identifying the length of slab continuous casting furnace inter-furnace handover billet, and using the method of casting billet cutting optimization, the handover billet of casting billet is degraded treatment.The beneficial effects of the present application are: successfully solve the technical problem of increasing production cost caused by large amount of handover billet degradation products, while effectively reducing the incidence of automobile plate "pinhole" defects.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for reducing the occurrence rate of pinhole defects of automobile sheet, belonging to the technical field of steel metallurgy continuous casting method. BACKGROUND

[0002] Automobile sheet steel has very strict requirements on non-metallic inclusions in the steel. In recent years, with the demand of vehicle enterprises for weight reduction, cost reduction and energy saving, the thickness of automobile sheet has been gradually reduced. This makes the size of inclusions that can cause pinhole defects in automobile sheet also decrease accordingly, which significantly increases the difficulty of controlling inclusions when steel enterprises produce automobile sheet steel. Research shows that the inter-batch transfer billet (also known as transition billet) formed by multi-batch continuous casting often causes stamping cracking during stamping processing in vehicle enterprises. The main reason is that after the end of casting of the last batch of ladle, the long nozzle of the next batch of ladle is lowered to immerse into the molten steel in the tundish. At this time, the long nozzle will cover part of the tundish covering agent on the surface of the molten steel into its pipe. After the start of casting of the next batch of ladle, the covering agent is broken into small slag droplets by the molten steel flow. Due to the small size, it is difficult to float to the surface from the inside of the molten steel and be removed, so it remains in the molten steel as non-metallic inclusions. Although such inclusions are small in size, they are sufficient to cause pinhole-like micro-cracking when automobile steel sheet with greatly reduced thickness is subjected to large deformation stamping.

[0003] In order to reduce the occurrence rate of pinhole defects of automobile sheet, steel and iron plants can only adopt the processing strategy of artificially downgrading or reclassifying the inter-batch transfer billet. For the judgment of the transfer billet, simply downgrading the last billet of the last batch and the first billet of the next batch, the downgraded product rate caused by the transfer billet is as high as nearly 40%. Since the thinning of automobile sheet is the future development trend, it is expected that more automobile sheet parts will be thinned to 0.65mm or even thinner. Therefore, under the existing production technology, the transfer billet must be downgraded. If the amount of downgraded transfer billet cannot be reduced, the production cost of automobile sheet steel in steel and iron plants will be greatly increased. SUMMARY

[0004] The purpose of the present application is to provide a method for reducing the occurrence rate of pinhole defects of automobile sheet, which accurately identifies the length of the inter-batch transfer billet of the continuous casting furnace, and adopts a billet cutting optimization method to downgrade the transfer billet of the billet, successfully solving the technical problem of increased production cost caused by large amount of downgraded transfer billet, effectively reducing the occurrence rate of pinhole defects of automobile sheet, and effectively solving the above problems existing in the background art.

[0005] The technical scheme of the present application is: a method for reducing the occurrence rate of pinhole defects of automobile sheet, comprising the following steps:

[0006] Step S1, after the ladle reaches the casting position, the transfer billet judgment model is automatically started with the start of casting of the ladle, and the weight of molten steel in the tundish at the time of casting is recorded as W0;

[0007] Step S2, as the casting proceeds, the handover billet determination model records the weight of the molten steel in the ladle as W1, and the weight of the molten steel flowing into the crystallizer from the tundish as W2;

[0008] Step S3, the handover billet determination model records the proportion of the weight of the molten steel entering the tundish after the start of casting to the weight of the molten steel in the tundish, i.e., wt% = W1 / (W0+W1-W2) x 100%;

[0009] Step S4, after long-term tracking of the rolling of the cast billet, when wt% = 10%, the starting position L1 of the furnace-to-furnace handover billet is recorded, which is displayed on the main control interface and the cast billet cutting interface; when wt% = 40%, the median point of the furnace-to-furnace handover billet is recorded, which is displayed on the main control interface and the cast billet cutting interface; when wt% = 80%, the end position L2 of the furnace-to-furnace handover billet is recorded, which is displayed on the main control interface and the cast billet cutting interface;

[0010] Step S5, after the starting position L1 and the end position L2 of the handover billet are determined, the cast billet between L1 and L2 is the furnace-to-furnace handover billet L s ;

[0011] Step S6, after the determination of the furnace-to-furnace handover billet, the main interface of the continuous casting cutting workshop is displayed, if the handover billet is only in one cast billet, no size optimization is needed; if the handover billet is in two cast billets, the handover billet is controlled in one cast billet by increasing and decreasing the length of the non-handover billet.

[0012] In step S5, the starting time t1 and the ending time t2 of the handover billet are calculated by the handover billet determination system as follows:

[0013]

[0014]

[0015] wherein a and b represent the width a and the thickness b of the crystallizer, respectively, in units of m; v is the casting speed of the cast billet, in units of m / min; and p is the density of the molten steel, in units of kg / m 3 ; W0 is the weight of the molten steel in the tundish at the start of casting of the ladle, in units of kg; and Q is the amount of molten steel flowing into the tundish from the long nozzle of the ladle, in units of kg / min.

[0016] The length of the handover billet is:

[0017] L s = v(t2-t1) (3)

[0018] wherein L sis the length of the transfer billet, in m; v is the billet drawing speed, in m / min; t1 and t2 are the start and end times of the transfer billet determination respectively.

[0019] In step S6, the distance between the transfer billet and the flame cutting point is 45 m, which is the length of five billets.

[0020] In step S6, when the transfer billet is between two casting billets, that is, the first billet in the previous furnace and the last billet in the next furnace.

[0021] The beneficial effects of the present invention are: by accurately identifying the length of the handover billets between furnaces of the slab continuous casting furnace and adopting a method for optimizing the cutting of the cast billets, the handover billets of the cast billets are downgraded, successfully solving the technical problem of increased production costs caused by a large amount of downgraded handover billets, and effectively reducing the incidence of "pinhole" defects in automotive plates. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of the present invention;

[0023] Figure 2 is a flow chart of the present invention;

[0024] Figure 3 This is a graphic of the actual furnace-to-furnace handover of the unoptimized continuous casting slab displayed on the main control interface of the cutting workshop in Example 1 of the present invention;

[0025] Figure 4 This is a graphic showing the actual furnace-to-furnace transfer of billets after optimization in the first embodiment of the present invention on the main control interface of the cutting workshop;

[0026] Figure 5 This is a graphic of the actual furnace-to-furnace handover of the unoptimized continuous casting slab displayed on the main control interface of the cutting workshop in Example 2 of the present invention;

[0027] Figure 6 This is a graphic showing the actual furnace-to-furnace transfer of billets after optimization in the second embodiment of the present invention on the main control interface of the cutting workshop;

[0028] Figure 7 This is a diagram showing the improvement effect of the pinhole defect incidence rate of the automobile sheet steel of the present invention;

[0029] Figure 8 This is a diagram showing the improvement effect of the degradation rate caused by handing over the blanks in the present invention;

[0030] In the figure: molten steel 1, tundish 2, crystallizer 3, transfer billet 4, L1 starting position 5, L2 ending position 6, midpoint 7, casting direction 8. DETAILED DESCRIPTION

[0031] 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.

[0032] A method for reducing the incidence of pinhole defects in automotive panels comprises the following steps:

[0033] Step S1: After the ladle reaches the pouring position, the billet handover judgment model is automatically started when the ladle starts pouring, and the weight of the molten steel in the tundish at the time of pouring is recorded as W0;

[0034] Step S2: As the casting progresses, the handover determination model records in real time the weight of the molten steel poured from the ladle into the tundish as W1 and the weight of the molten steel flowing from the tundish into the crystallizer as W2;

[0035] Step S3, the handover determination model records in real time the ratio of the weight of the molten steel entering the tundish after pouring to the weight of the molten steel in the tundish, i.e., wt% = W1 / (W0+W1-W2)×100%;

[0036] Step S4, after long-term tracking of the billet rolling situation, it is determined that when wt% = 10%, it is recorded as the starting position L1 of the billet transferred between furnaces, and displayed on the main control interface and the billet cutting interface; when wt% = 40%, it is recorded as the median point of the billet transferred between furnaces, and displayed on the main control interface and the billet cutting interface; when wt% = 80%, it is recorded as the ending position L2 of the billet transferred between furnaces, and displayed on the main control interface and the billet cutting interface;

[0037] Step S5: After determining the starting position L1 and the ending position L2 of the transfer billet, the billet between L1 and L2 is the transfer billet L between furnaces. s ;

[0038] Step S6, after the inter-furnace handover billet is determined, it is displayed on the main interface of the continuous casting and cutting workshop. If the handover billet is only in one billet, no size optimization is required; if the handover billet is between two billets, the handover billet is controlled to be in one billet by increasing and decreasing the billet length of the non-handover billet.

[0039] In step S5, the start time t1 and the end time t2 of the handover are calculated by the handover determination system and are:

[0040]

[0041]

[0042] Where a and b represent the mold width a and thickness b, respectively, in meters; v is the casting speed, in meters per minute; ρ is the density of the molten steel, in kg / m 3 ; W0 is the weight of the molten steel in the tundish when the ladle starts pouring, in kg; Q is the amount of steel flowing into the tundish from the ladle long nozzle, in kg / min.

[0043] The length of the transfer blank is:

[0044] L s =v(t2-t1) (3)

[0045] Among them, L s is the length of the transfer billet, in m; v is the billet drawing speed, in m / min; t1 and t2 are the start and end times of the transfer billet determination respectively.

[0046] In step S6, the distance between the transfer billet and the flame cutting point is 45 m, which is the length of five billets.

[0047] In step S6, when the transfer billet is between two casting billets, that is, the first billet in the previous furnace and the last billet in the next furnace.

[0048] In actual application, when the ladle reaches the casting position, the slide opens, and the transfer billet determination system automatically starts with the start of casting, while recording the weight of the tundish at this time, W0. As casting proceeds, the transfer billet determination model records in real time the weight of the molten steel poured into the tundish by the ladle as W1, and the mass of the molten steel flowing into the crystallizer from the tundish as W2. The transfer billet determination model records in real time the ratio of the weight of the molten steel entering the tundish after pouring to the weight of the molten steel in the tundish, i.e., wt% = W1 / (W0+W1-W2)×100%. When wt% = 10%, it is considered that the last furnace of molten steel has reached the tundish outlet, which is recorded as the starting position L1 of the furnace-to-furnace transfer billet. When wt% = 40%, it is considered that the mass fraction of the previous furnace of molten steel and the next furnace of molten steel at the tundish outlet is 50% each, which is recorded as the midpoint of the furnace-to-furnace transfer billet. When wt%=80%, it is considered that the tundish outlet is almost entirely filled with molten steel from the next furnace, which is recorded as the end position L2 of the furnace-to-furnace transfer billet.

[0049] The start time t1 and end time t2 of the handover billet determination system can be calculated as follows:

[0050]

[0051]

[0052] Where a and b represent the mold width a and thickness b, respectively, in meters; v is the casting speed, in meters per minute; ρ is the density of the molten steel, in kg / m3 W0 is the weight of the molten steel in the tundish at the beginning of the tapping, in kg; Q is the flow of the molten steel from the long nozzle of the ladle into the tundish, in kg / min.

[0053] After the start and end time of the interface billet is calculated, the length of the interface billet can be calculated as:

[0054] L s = v (t2-t1) (3)

[0055] wherein L s is the length of the interface billet, in m; v is the casting speed, in m / min; t1 and t2 are the start and end time of the interface billet determination, respectively.

[0056] After the length of the interface billet is calculated by the interface billet determination system, the position of the interface billet is displayed in the control system of the billet cutting.

[0057] Example 1

[0058] In this example, the width of the crystallizer is 1.5 m, the thickness is 0.237 m, the casting speed is 1.3 m / min, the density of the molten steel is 7200 kg / m 3 , the weight of the molten steel in the tundish at the beginning of the tapping is 55 t, and the flow of the molten steel from the long nozzle of the ladle into the tundish is 6.7 t / min. Through calculation, it is known that the start time of the interface billet is 0.8 min after the tapping, and the end time is 6.6 min after the tapping. Through equation (3), it is calculated that the length of the interface billet in this example is 7.52 m.

[0059] In this example, the interface billet determination system can record the start and end time of the interface billet, and record the entire position information and length of the interface billet on the operation platform of the billet cutting, such as Figure 3 The interface billet is located in the last billet of the previous furnace and the first billet of the next furnace, and the start position of the interface billet is 1.02 m away from the cutting position of the billet. In order to place the interface billet in one billet, the length of the previous several billets needs to be optimized.

[0060] In this example, according to the regulations, the size of the billet is 7.82-10.58 m, which meets the product requirements. In order to place the interface billet in one billet, only the length of No. 1 billet needs to be optimized to 8.5 m, and the lengths of the other several billets remain unchanged, so that the interface billet can be optimized to the first billet of the next furnace, such as Figure 4 Therefore, only one billet is downgraded, which improves the downgraded product rate of the automobile plate steel.

[0061] Example 2

[0062] This example is basically the same as Example 1, and the difference is that

[0063] The width of the crystallizer is 1.8m, the thickness is 0.237m, the pulling speed is 1.1m / min, and the density of the molten steel is 7200kg / m 3 When the ladle begins pouring, the weight of the molten steel in the tundish is 53 tons, and the flow rate of steel flowing from the ladle shroud into the tundish is 6.8 tons / min. Calculation shows that the transfer of the billet begins 0.78 minutes after pouring begins and ends 6.26 minutes after pouring begins. Using equation (3), we can calculate that in this example, the length of the transfer billet is 6.04 meters.

[0064] In this embodiment, the transfer billet determination system can record the start and end time of the transfer billet and record the entire position information and length of the transfer billet on the billet cutting operation platform, such as Figure 5 The transfer billet is located between the last billet of the previous furnace and the first billet of the next furnace, and the starting position of the transfer billet is 3.02m away from the cut position of the billet. In order to place the transfer billet in one billet, it is necessary to optimize the length of the previous billets.

[0065] In this embodiment, according to the regulations, the size of the billet is 7.82-10.58m, which meets the product requirements. In order to place the transfer billet in one billet, it is only necessary to optimize the length of billet No. 1 to 8.5m, and the lengths of the other billets remain unchanged. The transfer billet can be optimized to the first billet of the next furnace, such as Figure 6 .

[0066] By adopting the method provided by the present invention, the pinhole defect incidence rate and the degradation amount of the casting billet of automobile plate steel are significantly reduced. After data statistics of 175 castings, the comparison of the pinhole defect incidence rate and the degradation amount of the casting billet using the method provided by the present invention and not using the method provided by the present invention is as follows: Figure 7 and Figure 8 shown.

[0067] The above describes the embodiments of the present invention in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Various changes can be made according to the purpose of the invention. Any changes, modifications, substitutions, combinations or simplifications made according to the spirit and principles of the technical solution of the present invention should be equivalent replacement methods. As long as they comply with the purpose of the invention and do not deviate from the technical principles and inventive concepts of the present invention, they belong to the scope of protection of the present invention.

Claims

1. A method for reducing the incidence of pinhole defects in automobile panels, characterized in that The following steps are involved: Step S1: After the ladle reaches the pouring position, the billet handover judgment model is automatically started when the ladle starts pouring, and the weight of the molten steel in the tundish at the time of pouring is recorded as W0; Step S2: As the casting progresses, the handover determination model records in real time the weight of the molten steel poured from the ladle into the tundish as W1 and the weight of the molten steel flowing from the tundish into the crystallizer as W2; Step S3, the handover determination model records in real time the ratio of the weight of the molten steel poured from the ladle into the tundish to the weight of the molten steel in the tundish, i.e., wt% = W1 / (W0+W1-W2)×100%; Step S4, after long-term tracking of the slab rolling situation, it is determined that when wt% = 10%, it is recorded as the starting position L1 of the slab handover between furnaces and displayed on the main control interface and the slab cutting interface; When wt% = 40%, it is recorded as the median point of the furnace-to-furnace transfer billet, which is displayed on the main control interface and the billet cutting interface; When wt% = 80%, it is recorded as the end position L2 of the furnace-to-furnace transfer billet, which is displayed on the main control interface and the billet cutting interface; Step S5: After determining the starting position L1 and the ending position L2 of the transfer billet, the billet between L1 and L2 is the furnace-to-furnace transfer billet L. s ; Step S6, after the furnace-to-furnace handover billet is determined, it is displayed on the main interface of the continuous casting and cutting workshop. If the handover billet is only in one billet, no size optimization is required; if the handover billet is between two billets, the handover billet is controlled within one billet by increasing and decreasing the billet length of the non-handover billet.

2. The method for reducing the incidence of pinhole defects in automobile panels according to claim 1, characterized in that: In step S5, the start time t1 and the end time t2 of the handover are calculated by the handover determination model and are: Where a and b represent the mold width a and thickness b, respectively, in m; v is the casting speed, in m / min; ρ is the density of the molten steel, in kg / m 3 ; W0 is the weight of the molten steel in the tundish when the ladle starts pouring, in kg; Q is the amount of steel flowing into the tundish from the ladle long nozzle, in kg / min.

3. The method for reducing the incidence of pinhole defects in automobile panels according to claim 2, characterized in that: The length of the transfer blank is: L s =v(t2-t1) (3) Among them, L s is the length of the transfer billet, in m; v is the billet drawing speed, in m / min; t1 and t2 are the start and end times of the transfer billet determination respectively.

4. The method for reducing the incidence of pinhole defects in automobile panels according to claim 1, characterized in that: In step S6, the distance between the transfer billet and the flame cutting point is 45 m, which is the length of five billets.

5. The method for reducing the incidence of pinhole defects in automobile panels according to claim 1, characterized in that: In step S6, when the transfer billet is between two casting billets, that is, the last billet of the previous furnace and the first billet of the next furnace.

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