KR101466358B1 - Evaluation method for validation of cracks in piece by using friction - Google Patents

Abstract

Disclosed in the present invention is a method to evaluate the occurrence of cracks on a cast-piece using friction. According to an embodiment of the present invention, the method to evaluate the occurrence of cracks on a cast-piece using friction measures the friction generated between a mold and a solidified shell by a cast-piece unit at preset time intervals; calculates an average value (C) of the measured friction; and evaluates the occurrence of the cracks on the cast-piece using a crack occurrence potential index (P) defined as the following math formula: [Math Formula] Here, ABS indicates an absolute value, a indicates a constant value according to the width of a cast-piece, A indicates a middle value of friction of the cast-piece where cracks collected in a constant molding condition do not occur, and B indicates a standard deviation value of the cast-piece where cracks collected in a constant molding condition do not occur.

Description

TECHNICAL FIELD [0001] The present invention relates to a method for evaluating the presence or absence of cracks in a cast steel using friction force,

The present invention relates to a method for evaluating the occurrence or nonexistence of cracks in castings using friction force.

In general, a continuous casting machine is a machine that is produced in a steelmaking furnace, receives molten steel transferred to a ladle, and supplies the molten steel to a mold for a continuous casting machine to produce a cast steel having a predetermined size.

The continuous casting machine includes a ladle for storing molten steel, a continuous casting machine mold for initially cooling the molten steel introduced from the tundish and the tundish into a casting having a predetermined shape, and a plurality of casting machines connected to the mold for moving the casting Of pinch rolls.

In other words, the molten steel injected into the mold gradually cools down, and the casting starts to form at the lower part of the mold. At this time, the casting existing in the lower part of the mold coagulates the epidermis, . When the molten steel injected into the mold reaches a preset level, the mold starts to oscillate in the vertical direction, and the casting of the casting starts by the pinch roll at the bottom of the mold. At the same time, the casting is cooled by the cooling water by the cooling water injection device, And a completely cooled casting to the inside thereof.

BACKGROUND OF THE INVENTION [0002] The background art of the present invention is disclosed in Korean Unexamined Patent Publication No. 2002-0022083 (published on March 12, 2012, a friction force monitoring apparatus in a mold and its method).

In the embodiment of the present invention, the frictional force generated between the mold and the solidification shell is measured at intervals of a predetermined interval in units of pieces, and the frictional force average value (C), which is an average value of the measured frictional forces, The present invention provides a method for evaluating the presence or absence of cracks in a cast steel using a friction force capable of easily evaluating the occurrence of cracks in the cast steel produced in the continuous casting process.

According to an aspect of the present invention, a frictional force generated between a mold and a solidification shell is measured in units of a piece of material at predetermined time intervals, and a frictional force average value (C), which is an average value of the frictional forces thus measured, A method for evaluating the presence or absence of cracks in the cast steel using friction force can be provided by using the probability of occurrence of cracks (P).

[Mathematical Expression]

Where A is the absolute value, a is the constant value according to the casting width (width), A is the intermediate value of the frictional force that does not cause cracks collected under a certain casting condition, Represents the standard deviation value of the casting where no crack occurs.

When the value of the probability of cracking (P) is 100% or more, it can be judged that a crack has occurred in the produced cast steel.

The method for evaluating the crack occurrence probability of cast steel further includes a step of removing cracks occurring in the cast steel when the crack is generated in the cast steel produced in the continuous casting process using the crack probability index P can do.

The step of removing the cracks may include a scarfing process.

The intermediate friction force value A and the standard deviation value B may be a reference value obtained by measuring a plurality of pieces of steel at intervals of predetermined time intervals for each piece of steel for each carbon ratio under a constant casting condition.

The casting speed may be 1.3 to 1.4 m / min.

The intermediate value (A) and the standard deviation value (B) obtained by measurement under a constant casting condition are values obtained by using the frictional force of the normal cast steel where cracks have not occurred and the frictional force of the abnormal cast steel where cracks have occurred And the reference value of the crack presence / absence evaluation using the frictional force can use the frictional force intermediate value (A) and the standard deviation value (B) based on the frictional force of the non-cracked caliper.

According to another aspect of the present invention, there is provided a method of measuring a friction force, the method comprising: measuring a frictional force generated between a mold and a solidification shell in units of a preform at a predetermined time interval and calculating an average value C of the frictional force magnitude; Calculating a P value by substituting the average frictional force value (C) into a crack occurrence probability index (P) defined by the following equation; Comparing the P value (%) with a preset reference value; And judging that cracks have occurred in the cast steel when the P value (%) is equal to or greater than the reference value, a method for evaluating the presence or absence of cracks in cast steel using friction force may be provided.

[Mathematical Expression]

Where A is the absolute value, a is the constant value according to the casting width (width), A is the intermediate value of the frictional force that does not cause cracks collected under a certain casting condition, Represents the standard deviation value of the casting where no crack occurs.

According to the embodiment of the present invention, the frictional force generated between the mold and the solidification shell is measured at intervals of predetermined time intervals in units of pieces, and the average frictional force (C) It is possible to evaluate the presence or absence of cracks in the casting produced in the continuous casting process more simply and quickly and to carry out the subsequent process.

1 is a conceptual diagram schematically showing a continuous casting machine according to an embodiment of the present invention.
Fig. 2 is a conceptual view enlarging and explaining a part of the continuous casting machine of Fig. 1 around the flow of molten steel M. Fig.
3 is a flowchart schematically illustrating a method for evaluating the occurrence or non-occurrence of cracks on a cast steel using a frictional force according to an embodiment of the present invention.
FIG. 4 is a graph illustrating the presence or absence of a crack generated in a casting condition under a specific casting condition by using a crack occurrence probability index (P) value according to a frictional force, using a method for evaluating crack occurrence occurrence using cast iron according to an embodiment of the present invention FIG.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is capable of various modifications and various embodiments, and specific embodiments are illustrated in the drawings and described in detail in the detailed description. It is to be understood, however, that the invention is not to be limited to the specific embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Referring to the accompanying drawings, the same or corresponding components are denoted by the same reference numerals, do.

Fig. 1 is a conceptual diagram schematically showing a continuous casting machine according to an embodiment of the present invention. Fig. 2 is a conceptual view enlarging and explaining a part of the continuous casting machine of Fig. 1 around the flow of molten steel M. Fig.

Continuous casting is a casting process in which a molten metal is continuously cast into a bottomless mold while continuously drawing a steel ingot or steel ingot. The shape of a continuous casting machine is classified into a vertical type and a vertical bending type. In Fig. 1, a vertical bending type is illustrated.

1, a continuous casting machine may include a ladle 10 and a tundish 20, a mold 30, secondary cooling bands 60 and 65, a pinch roll 70, a cutter (not shown) have.

A tundish 20 is a container for receiving molten metal from a ladle 10 and supplying molten metal to a mold 30. In the tundish 20, the supply rate of the molten metal flowing into the mold 30 is controlled, the molten metal is distributed to each mold 30, the molten metal is stored, and the slag and the nonmetallic inclusions are separated.

The mold 30 is formed such that a solidified shell or a solidified shell 81 is formed so as to maintain the shape of the casting pluck pulled out from the mold 30 and to prevent the molten metal from being hardly outflowed from flowing out. .

The mold 30 has a pair of structurally opposed faces open to form a hollow portion for receiving molten steel. For example, when manufacturing a slab, the mold 30 may include a pair of barriers and a pair of end walls connecting these barriers. Here, the end wall has a smaller area than the barrier.

The degree of solidification of the molten steel (M) varies depending on the carbon content according to the type of steel, the type of powder (strong cooling type, complete cooling type, etc.), casting speed and the like.

The mold 30 is oscillated by the mold vibrator 40 to prevent the molten steel M from adhering to the wall surface of the mold. A lubricant is used to reduce the friction between the mold 30 and the solidification shell 81 during oscillation and to prevent burning. Lubricants include flour oil to be sprayed and powders added to the molten metal surface in the mold. A powder feeder 50 is installed to feed the powder into the mold 30. The portion of the powder feeder 50 for discharging the powder is directed to the inlet of the mold 30.

The secondary cooling stand (60) further cools the molten steel that is primarily cooled in the mold (30). The primary cooled molten steel is directly cooled by the spraying means 65 for spraying water while being maintained by the support roll 60 so that the coagulation angle is not deformed. Most of the solidification of the cast steel is accomplished by the secondary cooling.

The pulling device employs a multi-drive type or the like in which a plurality of pinch rolls (70) are used so as to pull out the casting slides without slipping. The pinch roll 70 pulls the solidified leading end portion of the molten steel in the casting direction so that molten steel passing through the mold 30 can be continuously moved in the casting direction.

Molten steel (M) in the mold starts to solidify from the portion contacting the wall surface of the mold (30). This is because the periphery of the molten steel M is liable to lose heat by the water-cooled mold 30.

The non-solidified molten steel 82 moves together with the solidifying shell 81 in the casting direction as the pinch roll 70 (Fig. 1) pulls the tip end portion 83 of the fully-solidified cast slab 80. The non-solidified molten steel (82) is cooled by the spraying means (65) which injects the cooling water during the movement process. This causes the thickness of the non-solidified molten steel (82) to gradually decrease in the cast steel (80). The solidification casting 80 having been solidified is cut to a predetermined size at the cutting point 91 and is divided into a slab P such as a slab or the like.

The shape of the molten steel M in the mold 30 and its adjacent portion will be described with reference to Fig. Fig. 2 is a conceptual diagram showing the distribution pattern of the molten steel M in the mold 30 and its adjacent portion in Fig. 1. Fig.

The thickness of the solidifying shell 81 becomes thicker along the casting direction. The portion of the solidifying shell 81 located in the mold is thin. The solidifying shell 81 is supported by the support roll 60 and thickened by the spraying means 65 for spraying water.

In summary, the molten steel (M) flows into the mold through the tundish during the casting process, and solidification proceeds from the wall surface of the mold mold. Between the solidified shell 81 and the mold 30, the mold flux is injected to prevent direct contact between the solidified shell and the mold surface and smooth drawing of the casting, and the mold is vibrated up and down.

In general, the vibration of the mold is measured by using a hydraulic cylinder, and the pressure applied to the inside of the cylinder during vertical vibration is measured, and the friction force between the mold and the solidifying shell can be calculated using this information.

According to the present embodiment, the calculated frictional force value can be used to predict a break-out or to diagnose the quality of the cast steel.

3 is a flow chart schematically explaining a method for evaluating the presence or absence of crack occurrence in cast steel using the frictional force according to the present embodiment.

3, the method for evaluating the occurrence or non-occurrence of cracks in cast steel using the frictional force according to the present embodiment measures the frictional force generated between the mold 30 and the solidified shell 81 at intervals of predetermined time intervals The P value can be obtained by calculating the average value of the frictional force (C), which is the average value of the frictional force measured in this way, and substituting the index into the crack possibility index (P) defined by the following equation.

According to this embodiment, by utilizing the thus obtained P value, it is possible to more quickly evaluate the occurrence of cracks in the continuous casting produced in the continuous casting process as described above, for example, .

(A) and standard deviation (B) of the cast steel without surface cracks, and the average frictional force (C) of the currently measured cast steel units The probability of occurrence of crack (P) can be expressed as follows.

[Mathematical Expression]

Here, ABS is an absolute value, a is a constant value according to the width of the cast steel, and A is a casting condition in which the cracks are not measured at a predetermined time interval in terms of the carbon ratio, And B represents the standard deviation value of the casting which does not generate the cracks measured at the predetermined time intervals in the unit of the casting by the carbon ratio in a certain casting condition.

As described above, according to the present embodiment, the frictional force generated between the mold 30 and the solidifying shell 81 in the continuous casting process is measured at intervals of predetermined time in units of pieces, and the frictional force average value C, which is an average value of the frictional force magnitudes, Is calculated and substituted into the above-described crack probability index (P), it is possible to evaluate the presence or absence of cracks in the casting produced in the continuous casting process more easily and quickly to proceed with the subsequent process.

Specifically, the method for evaluating the occurrence or non-occurrence of cracks in cast steel using the frictional force according to the present embodiment is characterized by measuring the frictional force generated between the mold 30 and the solidifying shell 81 in units of casts at predetermined time intervals, (S20) of calculating the P value by substituting the average frictional force value (C) into the crack possibility index (P) defined by the above-mentioned equation (S20) (S30) comparing the P value (%) with a preset reference value, and if the P value (%) is greater than or equal to the reference value, determining that cracks have occurred in the cast product produced in the continuous casting process have.

In other words, it is possible to predict the cracks of the cast steel by using the degree of change in the frictional force between the mold 30 and the solidification shell 81 in the continuous casting process, Can be quickly removed.

First, the friction force generated between the mold 30 and the solidification shell 81 may be measured at intervals of predetermined time intervals in units of pieces, and the average value C of the measured frictional force magnitudes may be calculated (S10).

To this end, the magnitude of the frictional force generated between the mold 30 and the solidifying shell 81 in accordance with the vibration of the mold 30 is collected at regular intervals (for example, at intervals of 1 second). In the present embodiment, the frictional force magnitude of each cast steel was measured at intervals of one second for a plurality of cast steel. By calculating the average value of the frictional force thus collected in the unit of the piece, the frictional force average value (C) of the continuous casting during the current continuous casting can be calculated.

The average frictional force value (C) calculated at the time of casting in the continuous casting is substituted into the above-described equation, thereby obtaining a cracking probability index (P) value, that is, a value of P (S20).

To this end, it is necessary to previously calculate and compute the intermediate value of friction force (A) and standard deviation value (B), which are variable values by carbon ratio (steel type), in advance according to the steel grade.

In this embodiment, the frictional force of each steel type cast piece unit in a constant casting condition (a condition having a normal casting condition or a constant casting speed) without any change in the casting speed is collected in advance and the frictional force intermediate value A and the standard deviation value B ) As a reference value.

Table 1 below is a table showing the results of the frictional force collection for each cast steel unit (steel type) in a constant casting condition (that is, a condition having a normal casting condition or a constant casting speed) without changing the casting speed.

Steel ([C] wt.%) Number of castings The intermediate value (A) Standard deviation (B) 0.07 2629 15.4 3.85 0.08 568 15.9 1.70 0.09 104 17.2 1.89 0.10 38 16.3 0.84 0.11 141 15.9 1.09

According to this embodiment, the value of the frictional force at which the casting speed changes by 0.1 m / min or more is judged to be an abnormal casting condition and excluded. Here, the results of the frictional force collection at the casting speed of 1.3 to 1.4 m / min are used as the normal casting conditions.

In other words, in order to obtain a reference value for obtaining the intermediate value of friction force (A) and its standard deviation value (B), a normal cast with no surface / internal crack (no crack) Friction force. In other words, for the evaluation of the cracks using the frictional force, the intermediate value (A) and the standard deviation value (B) of the frictional force of the crack having no crack were collected and selected as the reference value. This reason is because the frictional force has a certain range of variation depending on the vibration or casting condition of the mold during casting.

If the difference between the frictional force value and the reference value is out of a certain range, it can be considered that a crack has occurred. At this time, since the frictional force has a certain range of variation as described above, the influence of the degree of daily fluctuation can be minimized by dividing the frictional force value by the standard deviation.

In addition, since the frictional force depends on the casting width, it is necessary to multiply the constant (a) according to the casting width. The value of the constant (a) according to the casting width is shown in Table 2 below.

Casting width (mm) Width constant (a) 800 ~ 1200 1.30 1200 ~ 1600 1.10 1600-2000 1.00 2000 ~ 0.96

Therefore, the crack probability index P of casting can be expressed by the above-mentioned equation.

In this case, ABS means an absolute value, and a value indicates a constant value according to a casting width.

Next, the P value obtained by substituting the average frictional force value (C) in the present process into the above equation can be compared with a predetermined reference value (S30).

If the P value (%) is greater than or equal to the reference value, it can be determined that a crack has occurred in the cast steel produced in the continuous casting process (S40).

Since there is a difference in the degree of shrinkage of the solidified shell and the mechanical properties depending on the carbon content of the molten steel, it is possible to predict the possibility of cracking according to the degree of deviation of the frictional force depending on the carbon content in the normal casting condition.

In other words, if the difference between the P value and the reference value of the working or working cast is out of a certain range, it can be regarded as a crack occurred.

In this embodiment, 100% can be used as the reference value.

Table 3 below shows the calculation results of P value according to presence or absence of cracks in the casting process in actual casting process. FIG. 4 is a diagram for explaining the presence or absence of a crack generated in a casting condition under a specific casting condition by using a crack occurrence possibility index (P) value according to the frictional force, using the method of evaluating the crack occurrence occurrence rate using the frictional force according to this embodiment. FIG. 4 is a graph showing a calculation result of P value according to the carbon component in the normal casting condition of Table 3. FIG.

Steel ([C] wt.%) Number of castings P value Cracked cast steel Crack occurrence cast 0.07 5076 11% 141% 0.08 971 4% 112% 0.09 87 37% 105% 0.1 255 13% 127% 0.11 196 47% 187%

Referring to FIG. 4 and Table 3, it can be judged that the surface of the slab / internal crack occurs when the P value exceeds 100%.

Therefore, according to the present embodiment, as shown in FIG. 4 and Table 3, when the value of the probability of occurrence of crack (P) is 100% or more, it can be judged that a crack has occurred in the produced cast steel.

The method for evaluating the presence or absence of cracks in cast steel using the friction force according to the present embodiment may further include a step (S50) of removing cracks occurring in the cast steel.

That is, when it is determined that cracks are generated in the cast steel produced in the continuous casting process under specific casting conditions by comparing the value of the crack possibility index (P) with the above-mentioned reference value, (S50).

This subsequent processing may include a scarfing process.

The scarfing process is a kind of spark machining. It applies the principle of gas cutting to remove the defects by sparging the surface of the steel relatively low and wide. That is, it refers to cutting or digging a gas torch by dissolving a base metal (base metal) only in part.

As described above, according to the present embodiment, the frictional force generated between the mold 30 and the solidifying shell 81 in the continuous casting process is measured at intervals of predetermined time in units of pieces, and the frictional force average value C, which is an average value of the frictional force magnitudes, Is calculated and substituted into the above-described crack probability index (P), it is possible to evaluate the presence or absence of cracks in the casting produced in the continuous casting process more simply and quickly to proceed with the subsequent process.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, many modifications and changes may be made by those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims. The present invention can be variously modified and changed by those skilled in the art, and it is also within the scope of the present invention.

M: molten steel P: cast steel
10: Ladle 20: Tundish
30: Mold 40: Vibrator
50: Powder feeder 60: Secondary cooling zone
65: Spray means 70: Pitch roll
80: Continuous casting 81: Solidification shell
82: non-solidified molten steel 83:
91: Cutting point

Claims (8)

The frictional force generated between the mold and the solidification shell is measured at intervals of predetermined time intervals in units of billet, and the average frictional force (C), which is an average value of the frictional forces thus measured, is calculated to calculate the crackability index (P) defined by the following equation A method for evaluating the presence or absence of a crack in a cast steel using a friction force.
[Mathematical Expression]

Where A is the absolute value, a is the constant value according to the casting width (width), A is the intermediate value of the frictional force that does not cause cracks collected under a certain casting condition, Represents the standard deviation value of the casting where no crack occurs.
The method according to claim 1,
And the crack occurrence probability index (P) is 100% or more, it is judged that a crack has occurred in the produced cast steel.
The method according to claim 1,
If it is determined that cracks are generated in the cast steel produced in the continuous casting process using the crack probability index P,
Further comprising the step of removing a crack generated in the cast steel, wherein the cast steel has a crack.
The method of claim 3,
Wherein the step of removing the crack includes a scarfing process.
5. The method according to any one of claims 1 to 4,
Wherein the friction force intermediate value (A) and the standard deviation value (B) thereof are a reference value obtained by measuring a plurality of pieces of steel at intervals of predetermined time intervals for each piece of steel by carbon ratio under a constant casting condition. A Method for Evaluating the Occurrence of Cracks in Castings.
6. The method of claim 5,
Wherein the casting speed is in the range of 1.3 to 1.4 m / min.
5. The method according to any one of claims 1 to 4,
The intermediate value (A) and the standard deviation value (B) obtained by measurement under a constant casting condition are values obtained by using the frictional force of the normal cast steel where cracks have not occurred and the frictional force of the abnormal cast steel where cracks have occurred However,
A method for evaluating the presence or absence of crack occurrence in a casting sheet using a friction force, characterized by using a frictional force intermediate value (A) and a standard deviation value (B) based on a frictional force of a non-cracked calibrated cast steel using a frictional force .
Measuring a frictional force generated between the mold and the solidifying shell in units of a piece of material at a predetermined time interval and calculating an average value (C) of the frictional force magnitude;
Calculating a P value by substituting the average frictional force value (C) into a crack occurrence probability index (P) defined by the following equation;
Comparing the P value (%) with a preset reference value; And
And determining that a crack has occurred in the cast when the P value (%) is greater than or equal to the reference value.
[Mathematical Expression]

Where A is the absolute value, a is the constant value according to the casting width (width), A is the intermediate value of the frictional force that does not cause cracks collected under a certain casting condition, Represents the standard deviation value of the casting where no crack occurs.

Images