KR20070068220A - Joining method of low carbon steel for endless hot rolling and the apparatus therefor - Google Patents

Abstract

A shear connection method capable of applying continuous hot rolling to low carbon steel, and shear connecting conditions that secure tension characteristics enabling a connecting portion of metal bars to sufficiently bear a load of finish rolling and to resist a tensile force between finish rolling stands in a finish rolling process when welding low carbon steel bars to each other are provided. A shear connection method of continuous hot rolled low carbon steel plates comprises: performing shear connection of the following metal bar and the preceding metal bar using a welder(100) for overlapping a top end of a following metal bar(60) with a tail end of a preceding metal bar(90), thereby welding the top end of the following metal bar to the tail end of the preceding metal bar in an apparatus for hot rolling a low carbon steel comprising, by weight percent, 0.30% or less of C, 1.8% or less of Mn, 0.55% or less of Si, 0.50% or less of P, 0.50% or less of S, and the balance of Fe and other inevitable impurities or a low carbon steel bar comprising, by weight percent, 0.30% or less of C, 1.8% or less of Mn, 0.55% or less of Si, 0.50% or less of P, 0.50% or less of S, 1.0% or less of at least one element of Cr, Cu, Ni, Mo or Al, and the balance of Fe and other inevitable impurities, and welding the metal bars to each other such that the connected metal bars are formed in such a shape that a connection face of the connected metal bars is inclined along a thickness direction of the metal bars.

Description

JOINING METHOD OF LOW CARBON STEEL FOR ENDLESS HOT ROLLING AND THE APPARATUS THEREFOR}

1 is a configuration diagram showing the basic configuration of a low carbon steel continuous hot rolling facility according to an embodiment of the present invention.

2 is a block diagram showing a metal bar in which bonding is completed as a bonding machine according to an embodiment of the present invention.

Figure 3 is a conceptual diagram showing the state of the bonded metal bar according to an embodiment of the present invention.

4 is a conceptual diagram showing a change in free energy of a solid state junction according to an embodiment of the present invention.

5 is a graph showing the relationship between the bonding ratio and the bonding strength ratio during solid state bonding according to an embodiment of the present invention.

6 is a conceptual diagram showing the bonding force acting on the bonding surface according to an embodiment of the present invention.

Figure 7 is a conceptual diagram showing the cause of the joint strength degradation and crack generation of the edge portion according to an embodiment of the present invention.

8 is a block diagram illustrating a correlation between a joint variable and each joint variable on the joint performance according to an embodiment of the present invention.

9 is a conceptual diagram illustrating the definition of a stroke rate and a lap according to an embodiment of the present invention.

10 is a graph showing a relationship between descaling temperature, joint strength ratio, and crack ratio according to an embodiment of the present invention.

11 is a graph showing a relationship between descaling pressure, joint strength ratio, and crack ratio according to an embodiment of the present invention.

12 is a graph showing a relationship between a joining temperature, a joint strength ratio, and a crack ratio according to an embodiment of the present invention.

Figure 13 is a graph showing the relationship between the wrap and the joint strength ratio according to an embodiment of the present invention.

14 is a graph showing a relationship between a stroke rate and a joint strength ratio according to an embodiment of the present invention.

Fig. 15 is a tissue photograph showing the relationship between the stroke rate and the top and bottom non-joint portions of the joint according to the embodiment of the present invention.

Figure 16 is a graph showing the plate test results of the joint finishing rolling according to an embodiment of the present invention.

The present invention relates to a method of joining a continuous hot rolled material that is continuously hot rolled by mutually bonding the hot rolled materials in a hot rolling process, and more particularly, the conditions for joining hot rolled materials in continuous hot rolling of low carbon steel. The present invention relates to a shear bonding method of a continuous hot rolled material that can be plated without breaking in the rolling stage by controlling and a continuous hot rolling facility therefor.

In the technical field of producing hot rolled metal sheets, there is a strong demand for improving productivity and quality and expanding the size of product manufacture by continually finishing finishing rolling.

An important point in this continuous hot rolling field is the joining technology of metal bars for joining the back end of the preceding hot rolled sheet material (hereinafter referred to as "metal bar") and the following metal bar to each other.

In the hot rolling process, the joining of the metal bars is performed between the rough mill and the finishing mill. Thus, when the metal bars are joined together in the post-rolling process, the metal bars rolled in the finishing mill process can be continuously rolled. do.

Therefore, in order to continuously perform the finishing rolling, it is necessary to join the metal bar and the metal bar at high speed, and various techniques have been proposed for such bonding.

Conventionally known bonding techniques are largely classified into a melt bonding method and a solid state bonding method.

When the metal bars are bonded to each other by the melt bonding method, since the temperature of the molten joint is higher than the temperature of the adjacent portion, softening of the molten joint occurs, and thus the joint is inferior in bonding strength to the base material.

As a technique known as the solid phase bonding method, there is a method of joining a metal plate disclosed in Japanese Patent Laid-Open No. 9-17411 (hereinafter referred to as "411 invention").

This invention 411 overlaps the leading end of the preceding metal bar and the trailing end of the following metal bar up and down, and by shearing the two overlapping metal bars at the same time by directly contacting and joining the shear surfaces of the two metal bars generated in the shearing process to be.

The 411 invention has many advantages as a hot continuous rolling equipment such as simple and short time bonding because the bonding is performed by shearing, and the required space is small, so that the temperature decreases during finishing rolling.

However, the 411 invention has disadvantages in that the bonded joints are inhomogeneous in shape and surface scale is mixed on the bonded surfaces, thereby significantly reducing the joint strength of the bonded joints.

In addition, when applying a metal bar by applying the 411 invention, there is a disadvantage in that an unbonded portion is generated or a weakly bonded portion exists at both ends of the lower portion and in the width direction on the cross section of the joint, and the surface scale is also mixed as the joint surface. There is a problem that the strength drops.

On the other hand, low carbon steel is C in weight%; 0.30% or less, Mn; 1.8% or less, Si; 0.55% or less, P; 0.50% or less, S; It is used universally as a steel containing 0.50% or less and composed of other unavoidable impurities and the remaining Fe. In addition, low carbon steels contain 1.0% or less of elements such as Cr, Cu, Ni, Mo, Al, or special elements such as V, Nb, B, Ti, etc. to secure various properties such as strength and corrosion resistance in the basic composition of low carbon steel. It may be prepared by addition.

Low carbon steel is the most common type of steel widely used in various fields such as vessels, construction, bridges, and pressure vessels.

When the continuous hot rolling is performed by applying the bonding technology to such a low carbon steel, there are many advantages such as increased productivity and thinning.

However, when joining such general purpose low carbon steel in the continuous hot rolling process, there is no detailed knowledge of the joining conditions.

Therefore, the present invention is to solve such a conventional problem, an object of the present invention to provide a shear bonding method that can be applied to continuous hot rolling for low carbon steel.

It is still another object of the present invention to bond a low carbon steel metal bar in the finishing rolling process in which the joint of the metal bar can sufficiently bear the load of the finishing rolling and secure the tensile properties that can withstand the tensile tension between the finishing rolling stands. To provide a condition.

In order to achieve the above object, the present invention, by weight% C; 0.30% or less, Mn; 1.8% or less, Si; 0.55% or less, P; 0.50% or less, S; Low carbon steel or C containing not more than 0.50% and consisting of other unavoidable impurities and the remaining Fe; 0.30% or less, Mn; 1.8% or less, Si; 0.55% or less, P; 0.50% or less, S; 0.50% or less of Cr, Cu, Ni, Mo, or Al containing 1.0% or less of the element, and other inevitable impurities and the low carbon steel metal bar consisting of the remaining Fe, followed by the leading end of the metal bar in the hot rolling facility. Shear bonding method of low carbon steel continuous hot rolled material which is bonded by shearing using a jointer which overlaps and joins the rear end of the metal bar, and the metal bars are bonded to each other so that the joined surface of the bonded metal bar is inclined along the thickness direction of the metal bar. To provide.

In another aspect, the present invention provides a method of shear bonding of a low carbon steel continuous hot rolled material to descale the joining portion of the metal bar to a pressure of 60 MPa or less.

In another aspect, the present invention provides a shear bonding method of the low carbon steel continuous hot rolled material to shear bonding the range of the wrap that is the distance that the upper blade and the lower blade of the adapter overlap each other when shear bonding the metal bar to 2mm to 19mm. .

In another aspect, the present invention is a low-carbon steel continuous hot rolled material for shear bonding the shear rate by dividing the sum of the distance traveled by the upper blade and the lower blade of the adapter divided by the thickness of the metal bar to 1.33 to 1.60 It provides a shear bonding method of.

And when shear bonding the metal bar in the present invention, both the upper blade and the lower blade of the bonder while simultaneously shearing the shear joint while shearing or moving any one of the upper blade and the lower blade shear of the continuous hot rolling material Provide a bonding method.

In addition, the present invention by weight% C; 0.30% or less, Mn; 1.8% or less, Si; 0.55% or less, P; 0.50% or less, S; Low carbon steel or C containing not more than 0.50% and consisting of other unavoidable impurities and the remaining Fe; 0.30% or less, Mn; 1.8% or less, Si; 0.55% or less, P; 0.50% or less, S; A rough rolling mill containing about 1.0% or less of Cr, Cu, Ni, Mo or Al in an amount of 0.50% or less and roughly rolling a low carbon steel slab composed of other unavoidable impurities and the remaining Fe;

A coil box for winding the roughly rolled metal bar in a coil state;

A descaling device for descaling a joining portion of the metal bar released from the coiler of the coil box;

A shear bonding device provided with a pair of shear blades for shearing the descaled metal bar by overlapping the rear end of the preceding metal bar and the leading end of the trailing metal bar by pressing the overlapping portion from both sides thereof in the state of the door; And

A finishing mill for finishing rolling the shear bonded metal bar

It provides a hot rolling facility for continuously hot rolling a low carbon steel metal bar comprising a.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

In the present invention, low carbon steel is represented by weight% (hereinafter, in the present invention,% means weight% unless otherwise specified). 0.30% or less, Mn; 1.8% or less, Si; 0.55% or less, P; 0.50% or less, S; Low carbon steel or C containing not more than 0.50% and consisting of other unavoidable impurities and the remaining Fe; 0.30% or less, Mn; 1.8% or less, Si; 0.55% or less, P; 0.50% or less, S; It means a low carbon steel containing less than 1.0% of any one element of Cr, Cu, Ni, Mo or Al in 0.50% or less and other inevitable impurities and the remaining Fe.

In addition, in the present invention, the shear bonding means that the metal bar is formed by the plastic flow deformation caused by the shear pressure that is pressed by the shear surfaces of the joints in the process of shearing the shear blades facing each other by the transfer blades. In this case, the bonding surface of the bonding portion is formed to be inclined along the thickness direction of the metal bar.

First, a hot rolling facility for performing continuous hot rolling by shear bonding low carbon steel according to the present invention and a method of shear bonding low carbon steel using the same will be described with reference to FIGS. 1 to 4.

1, the whole structure of the hot rolling facility which concerns on the example of one Embodiment of this invention is shown.

Referring to Figure 1, the hot rolling equipment according to the present invention, the rough rolling mill 10, the coil box 20, the joining device 30, a rolling mill 40 consisting of a plurality of rolling mills from the upstream side and down It consists of a coiler 50.

The low carbon steel bar manufactured by rolling the low carbon steel slab in the roughing mill 10 is wound in a coil state in the coiler of the coil box 20. Such a coil box 20 is to adjust the speed difference of the metal bar running in the roughing mill 10 and the finishing mill 40.

The trailing metal bar 60 released from the coiler of the coil box 20 is descaled by the partial descaling device 81 after the front end thereof is cut by CropShier and then the surface of the joining part of the metal bar to be joined is descaled. The overlapping device 80 of the bonding device 30 overlaps with the rear end of the preceding metal bar 90. At this time, if necessary, the end of the preceding metal bar can be cut by the crop.

The leading end of the trailing metal bar 60 and the trailing end of the preceding metal bar 90 are joined at the bonding machine 100 of the bonding apparatus 30, and the crop of the bonding portion is cut by the cropping apparatus 120. The metal bars 110 joined in the bonding apparatus 30 to be in a continuous state are transferred to the finishing mill 40.

Here, the bonding apparatus 30 is a facility which joins the rear end of the leading metal bar 90 and the tip of the trailing metal bar 60 in the running state, and is a short time joining apparatus which can shear-bond in a short time.

And, in order to shear-bond the metal bars in the running state, the adapter 30 is to be able to move in accordance with the running of the metal bar, the adapter 30 is to be installed additionally to the equipment to swing as the metal bar running. Can be.

For example, the joining device 100 of the joining apparatus 30 has an overlapping portion where the rear end of the leading metal bar 90 and the leading end of the trailing metal bar 60 overlap with each other in the state of door, as will be described later. A pair of shear blades is provided for shear bonding while being pressed and sheared.

Then, the metal bar 110 transferred to the finishing mill 40 is hot rolled sequentially through a plurality of rolling mills to be manufactured to a required thickness, and then wound in the downcoiler 50.

In FIG. 1, reference numerals 130 and 140 are level lines installed at each outlet side of the coil box 20 and the bonding apparatus 30, and reference numeral 150 is a crop shear installed at the inlet side of the finishing mill, and reference numeral 160 Denotes an edge heater disposed between the leveler 140 and the crop shear 150, and reference numeral 170 denotes a bar heater disposed in front of the edge heater 160.

The levelers 130 and 140 or the crop shear 150 and the edge heaters 160 and the bar heaters 170 may be selectively arranged according to the hot rolled material and the hot rolling conditions. The installation location or the presence of the installation is shown as an example and various modifications are possible.

The crop shear 70 for cutting the rear end of the leading metal bar 90 and the leading end of the trailing metal bar 60 is required for butt-bonding the metal bars, but is shear bonded in a process of overlapping and shearing the metal bars. It may be omitted since it is not necessary.

Next, with reference to Figures 2 and 3, the metal bar of the low carbon steel of the bonding apparatus 100 and the shear bonding process according to the present invention will be described in detail.

Referring to Figure 2, the adapter 100 according to the present invention is largely composed of the upper blade assembly 120 and the lower blade assembly 130 and the housing 110 for supporting them to be movable.

Here, the upper blade assembly 120 is composed of the upper blade 121, the upper clamp 122 and the upper support device 123, all of which are formed integrally. The lower blade assembly 130 includes a lower blade 131, a lower clamp 132, and a lower support device 133, all of which are integrally formed.

And the upper blade assembly 120 and the lower blade assembly 130 is guided by a post portion (not shown) of the housing 110, the movement in the thickness direction of the leading metal bar 90 and the trailing metal bar (60). Supported as possible. In addition, the upper blade assembly 120 and the lower blade assembly 130 is configured to be accessible and carried by a link mechanism (not shown).

As described above, the tip 220 of the trailing metal bar 60 is guided in the state of overlapping the rear end 210 of the preceding metal bar 90 of the low carbon steel into the adapter 100 according to the present invention.

Then, the front end 61 of the trailing metal bar 60 overlaps the rear end 91 of the leading metal bar 90 of the low carbon steel, and the end 61 and the rear end 91 overlap the upper and lower blades. The protrusions 124 and 134 of the will be bite. That is, the protrusions 124 and 134 of the upper blade and the lower blade come into contact with the surfaces of the front end 61 and the rear end 91.

In addition, the upper clamp 122 and the lower clamp 132 are in contact with a portion where the rear end 91 of the leading metal bar 90 and the leading end 61 of the trailing metal bar 60 overlap with each other. Here, the upper clamp 122 is supported by the hydraulic force by the upper support device 123, the lower clamp 132 is supported by the hydraulic force by the lower support device 133.

When the upper blade 121 and the lower blade 131 shears the leading metal bar 90 and the trailing metal bar 60 in such a state, each front of the leading metal bar 90 and the trailing metal bar 60 is moved. The cross sections are shear bonded to each other by plastic flow deformation to form a metal bar 110 that is integrally continuously joined.

As such, when the end of the low carbon steel completes the shear bonding, the upper crop in which the leading end 61 of the trailing metal bar 60 is cut is located at the joint portion of the continuous metal bar, and the rear end 91 of the preceding metal bar 90 is cut. Bottom crop will be placed. When the metal bars are bonded to each other, the upper blade 121 and the lower blade 131 retreat until they have a predetermined distance.

The upper crop and the lower crop cut by shear bonding of the metal bars are removed by the crop processing apparatus 120 shown in FIG. 1, and the continuous metal bars 110 are transferred to the finishing mill 40.

Here, when the joint of the metal bar passes through the finishing mill 40, a strong compressive stress and bending during finishing rolling and an external force such as bending or tension acts between each stand of the finishing mill, so that the joint is placed under severe process conditions. do.

At this time, the joint of the low carbon steel metal bar needs to maintain the bonding strength enough to pass through the finishing mill 40 without breaking.

Hereinafter, the process parameters of the bonding process for controlling the bonding strength of the joint when the low-carbon steel metal bar shear bonding in continuous hot rolling will be described in detail.

First, referring to FIG. 4, a process of solid-state bonding two metal bars is explained by metal thermodynamics.

Solid state bonding is a process in which two free surfaces become one interface. In this case, when the free energy change is calculated in the solid state bonding process, Equation 1 is used.

γ _interface -2γ _{free surface} = -1.7γ _{free surface} ----------- (1)

In Equation 1, since the interfacial energy has a value of 30% or less of the free surface energy, the free energy change may be represented as -1.7γ _{free surface} . And since the γ _{free surface} has a positive value, the change in total energy has a negative value, which means that the two surfaces will spontaneously join without spontaneous reaction, ie no external force.

In practice, however, the two surfaces do not bond naturally in the atmosphere without external forces, because the unevenness and scale of the plate surface prevent the joining of the two surfaces.

In order to bond two metal bars to each other, the attraction of atoms on the surface of the metal bar to be bonded must be applied, and the distance between atoms must be Å (10 ^-8 m) for the attraction between atoms.

However, even if the surface of the metal bar is machined and uneven, the distance between atoms of the two metal bar surfaces is far greater than the unit of Å. In consideration of this point, in general solid state bonding, a strong pressure (compression force) is applied, and a very large force is required at room temperature, thereby heating the metal bar to a high temperature.

However, even when such a strong pressure is applied, the scale generated on the surface of the metal bar when the metal bar is present on the surface of the metal bar or when the metal bar is heated deteriorates the bonding force. Therefore, the scale must be reduced in order to secure the joint strength of sufficient joints during continuous hot rolling of low carbon steel.

In the conventional method of joining two metal bars by a solid state joining method, an extremely exceptional bonding may be possible to suppress scale mixing. However, even in this case, since hot rolling is performed at a high temperature of about 1,000 ° C., a scale due to high temperature oxidation naturally occurs in a predetermined surface where two metal bars overlap, and even if descaling to remove the scale, a scale is instantly formed on the surface. .

In addition, since the ductility of the material is very high at high temperature, the scale existing on the overlapping predetermined surface is mixed into the joint, and the mixing of the scale acts as a cause of lowering the bonding strength.

Referring to FIG. 5, the joining ratio and the joining strength ratio of the joining part when the two metal bars are joined in the hot manner will be described.

In FIG. 5, the straight line shows the relationship between the bonding ratio and the bonding strength when the scale is not mixed in the joint and theoretically there is no bonding force between the scales. In theory, the bond rate and the bond strength appear in a linear relationship, so the bond strength ratio should increase as the bond rate increases. Here, the joining rate is expressed as a percentage obtained by dividing the total length of the joint without a scale by the total length of the joint. This indicates that the more scale incorporation in the joint, the lower the bonding ratio and thus the lower the bond strength ratio.

However, in the actual hot rolling process, scale is inevitable due to high temperature conditions, and weak bonding force exists between scales, and thus, a relationship similar to that of a straight line is slightly higher than a straight line.

Next, the joining conditions for controlling the joint strength of the joint in the case of shear bonding the low carbon steel metal bar in continuous hot rolling will be described.

Referring to Figure 6 describes the shear bonding process of the adapter 100 according to the present invention.

As shown in FIG. 6, the force for joining the two metal bars by shear bonding is the component force in the direction perpendicular to the joint portion of the compression load pressed by the upper blade 121 and the lower blade 131, and the two forces generated by shearing here. Friction between the new faces of the dog increases the bonding force.

Due to such forces, the pressures facing each other act as shown in the right side of FIG.

At this time, this force is a function of the jointer 100 and the process conditions, the lack of this force does not have a sufficient joint strength. On the other hand, the protrusions (124, 134) on the upper blade and the lower blade serves to block the flow of the metal during shearing to strengthen the bonding force.

In addition, as shown in FIG. 7, the center portion in the width direction of the metal bar has no problem due to the restraint of the surroundings, but both ends of the metal bar width direction are in a free surface state without any restraint.

As such, both ends of the free surface state when the metal bar is joined are opened outward as shown in FIG. 7, and thus the force in the opposite direction is inclined.

Therefore, both ends of the metal bar are inferior in bonding strength and partial oxidation occurs in this part as shown in the right side of Fig. 7, which causes cracking during subsequent finishing rolling, and when the crack increases, plate breakage occurs. do.

In addition, the shape of the joint also affects the joint strength, and in the case of applying the shear joint, unbonded portions exist at the top and bottom of the joint section due to the nature of the joining method, and the joint strength changes according to the position and size of the unbonded joint. .

In consideration of the above description, the influence of various control factors on the performance of the joint is summarized as in FIG. 8.

As shown in FIG. 8, it can be seen that the material properties, process variables, and the joining device affect both the joint strength of the joint in the performance of the metal bar joint.

However, the material properties and the bonding apparatus are difficult to control, so in the case of joining a metal bar, it is easy to control the joining conditions and the effect is sure when controlling the metal bar.

These process variables include descaling conditions and bonding conditions.

Descaling condition can control the temperature and pressure during descaling to suppress the mixing of scale, and the bonding condition controls the temperature, lap and stroke rate when joining the metal bar, The shape of the joint can be adjusted.

By appropriately adjusting the above five process variables, it is possible to control the scale mixing problem, the lack of bonding force, and the shape of the joint, which are factors that reduce the joint strength. have.

Here, the definition of the stroke rate and the lap, which are the bonding conditions of the process variables, will be described with reference to FIG.

The stroke rate represents a value obtained by dividing the sum of the distances that the upper blade 121 and the lower blade 131 of the adapter 100 moves up and down by the thickness of the metal bar. Therefore, as the stroke rate increases, the joint thickness decreases.

And the wrap is the distance that the upper blade 121 and the lower blade 131 overlap each other. However, since the shear blades (upper blades and lower blades) have a predetermined angle, a slight difference may occur with the set value depending on the stroke rate after the shear blades are sheared. Therefore, it is preferable to control the setting value of the bonding machine because the actual measurement is impossible in the case of actually shear bonding the metal bar.

The hot rolling facility and the joining method using the same according to the present invention described above can be applied to low carbon steel because the shear bonding is performed.

Furthermore, since the bonding method according to the present invention is a solid-state bonding, it is possible to perform shear bonding within the temperature range of the metal bar itself that is hotly heated without supplying a separate heat source on the hot rolling facility line, so that preheating and postheating are not necessary. Also, it is possible to prevent cracking of the metal bar joint due to the introduction of a separate heat source.

In addition, unlike the conventional welding method, since only the shear force is used, there is a technical effect of fundamentally preventing scale mixing problems and pore mixing problems in the bonding process of low carbon steel.

Therefore, the shear bonding method according to the present invention is a very useful method for joining low carbon steel in the continuous hot rolling process, and it is possible to secure the filamentary rolling plateability of the joint only by controlling the process variables appropriately.

Hereinafter, the process variables and the process conditions during the shear bonding of low carbon steels in consideration of this point will be described through the examples.

EXAMPLE

Using the low carbon steel metal bars having the composition shown in Table 1 below, the process variables during shear bonding of the metal bars in the continuous hot rolling facility shown in FIGS.

Steel grade Chemical composition (wt%) C Si Mn P S Cr Ni Cu Mo Al V SS400 0.148 0.012 0.688 0.012 0.005 0.021 0.016 0.023 0.002 0.044 <0.001 SPA-H 0.080 0.439 0.409 0.094 0.006 0.390 0.132 0.295 0.001 0.031 0.003 SS540 0.075 0.018 0.527 0.015 0.006 0.020 0.007 0.009 - 0.34 - SAE1026 0.245 0.102 0.714 0.016 0.003 0.024 0.010 0.017 - 0.022 -

10 to 16 show the average experimental values of the steel grades shown in Table 1 below. This is because, in the case of low carbon steel, characteristics such as bonding strength ratio (described later) in the case of having the composition according to each steel type shown in Table 1 show similar patterns.

FIG. 10 shows the effect of descaling temperature on the joint strength ratio and the edge crack ratio of the metal bar edge.

Wherein the strength ratio of the joint is as shown in Equation 2 below

Joint strength ratio = strength of the joint part of the metal bar / strength of the base material part of the metal bar-(2)

The edge crack ratio is shown in Equation 3 below.

Edge crack ratio = sum of left and right crack lengths / width of metal bars-(3)

In the case of low carbon steel as shown in FIG. 10, it can be seen that the descaling temperature parameter has little effect on the bonding strength ratio and the edge cracking rate when shearing metal bars.

In case of filament rolling, it was found that plate failure occurred in the first or second pass when the bond strength ratio was low, and plate failure occurred in the rear end when the edge crack ratio increased.

FIG. 11 shows the effect of descaling pressure on the joint strength ratio and the edge crack ratio of the metal bar edge.

As shown in FIG. 11, when the bonded metal bars were subjected to finishing rolling by using a finishing mill, test results were found that when the bonding strength ratio is 52% or more, finishing rolling can be performed without breaking the joints of the metal bars. And up to 30% of the edge crack rate was possible through mail.

In the case of low carbon steel, descaling can be omitted, even if the descaling pressure is 0 MPa, since the bonding strength and the low edge crack ratio that can be plated are obtained in the finishing rolling process.

In addition, as the descaling pressure increases as shown in Fig. 11, since the scale mixing into the joint decreases, the edge cracking rate also decreases because the joint strength of the joint increases and the area of the non-junction at both ends in the width direction decreases.

However, if the descaling pressure is too high, the amount of sprayed is increased and the temperature decreases at the junction, so that it is difficult to secure the temperature necessary for finishing the rolling process.

In addition, due to excessive descaling pressure, the base metal of the metal bar having high high temperature strength is severely damaged, and the unevenness is severely generated on the surface of the joint, resulting in poor bonding.

As a result of the experiment as described above it can be seen that the descaling pressure in the descaling device 81 before the splicer 100 is preferably controlled to 60MPa or less when shear bonding low carbon steel to the splicer.

12 shows the bond strength ratio according to the junction temperature during shear bonding of low carbon steel.

However, as shown in FIG. 12, the joint temperature at the time of shear bonding of low carbon steel had little effect on the strength ratio of the joint and did not affect the edge crack ratio.

Figure 13 shows the strength ratio of the joint according to the change of the lap during shear bonding of low carbon steel.

As shown in FIG. 13, it can be seen that the lap and bond strength ratios show a Gaussian distribution, that is, a parabolic relationship.

This resulted in an increase in the bond strength ratio as the lap increased, and began to meet the mailing standards (described later) above 2mm, and began to decrease again above 19mm.

Thus, the reason for satisfying the mail order criteria in the range of 2mm to 19mm range is as follows.

That is, as the lap increases, the joint strength increases because the lap angle decreases as the lap increases, so the vertical component of the shear line increases in the vertical stress of the shear edge. As the load increases, the bond strength decreases.

Therefore, the range of the wrap is preferably in the range of 2mm to 19mm.

On the other hand, the edge crack ratio was greatly affected by the descaling pressure, but little by the lap. This is because the bonding force increases with the increase of the lap, but the gap occurs in the width direction at the edge portion, resulting in a decrease in the bonding force and thus oxidation of the edge portion, so that the effect is significantly insignificant.

14 is a graph showing the breaking load of the metal bar according to the stroke rate during shear bonding of low carbon steel.

As shown in FIG. 14, the breaking load of the joint gradually increased as the stroke rate was increased, and then passed through 1.33 to satisfy the mailing standard. However, it can be seen that the mail order standard is satisfied up to 1.60.

Therefore, in the case of low carbon steel, the stroke rate of the jointer 100 during shear bonding is preferably 1.33 to 1.60.

In this case, the stroke may be shear bonded by simultaneously moving the upper and lower blades of the adapter 100 upward and downward, or may be shear bonded while moving only one of the upper and lower blades.

Unlike other joint conditions, the stroke rate affects the thickness of the joint. In other words, as the stroke rate increases, the thickness of the joint becomes thinner, and thus the load may decrease even if the joint strength increases, so the relationship between the stroke rate and the breaking load of the joint is investigated. This increase results in an increase in the breaking load despite the thinning of the joint, which means that the joint strength ratio increases significantly as the stroke rate increases.

In addition, as the stroke rate increased, the elongation also improved, but the effect on edge cracking rate was not significant. As the stroke rate increases, the breaking stress and breaking load increase because the position and shape of the upper and lower unbonded portions in the plate thickness direction are different as shown in FIG. 15.

Figure 16 shows the results of the shear bonding of the low carbon steel according to the present embodiment to the hot rolling facility and the mailing test in the finishing mill, and by Figure 16 can be confirmed the mailing standards according to the present invention.

FIG. 16 shows the result of shear bonding using a low carbon steel having the composition shown in Table 1 and then rolling the bonded metal bar in a finishing mill in a hot rolling mill.

The specimen shown in the graph of Figure 16 is shear bonded to a low carbon steel metal bar having a width of 450mm, side welded two sets of bonded specimens to make a width of 840mm ~ 900mm, and then welded the same thickness bar on the front and back again It is made of a metal bar 900 mm long. The metal bars are heated in a furnace and then subjected to finishing rolling.

As a result of this test, all of the metal bars with a bonding strength ratio of 52% or less occurred in plate breaking during finishing rolling, and metal bars with a bonding strength ratio of 52% or more succeeded in mailing.

As such, the edge cracks of the joints of the metal bars, which were successful in finishing rolling, were 15% or less.

On the other hand, if the stroke rate is fixed, there is no problem even if the plate standard is set by the bonding strength ratio, but when the stroke rate is changed, the thickness of the joint is changed. The bond load ratio is as shown in Equation 4 below, and the mail order criterion for this bond load ratio is 31.5%.

Bond load ratio = bond break load / base material break load-(4)

As shown in FIG. 16, the plate standard in the finishing rolling stage means that the bonding strength ratio and the breaking load of the finishing rolling are satisfied without breaking the metal bar.

Although the preferred embodiments of the present invention have been described so far, the present invention is not specific to the bonding conditions at the joints during continuous hot rolling of low carbon steel, but is applied to various joining methods required for the shear joining of such continuous hot rolling of low carbon steel. It is possible to apply.

Therefore, the present invention can be modified and implemented in various ways within the scope of the claims and the detailed description of the invention, and this also belongs to the scope of the invention.

As described above, the shear bonding method of the low carbon steel continuous hot rolled material in the present invention has a technical effect of enabling continuous hot rolling by joining the low carbon steel hot rolled material which has not been applied by shear bonding. have.

In addition, in the present invention, when joining a metal bar of low carbon steel, in the finishing rolling process, the joining part of the metal bar can bear the load of the finishing rolling and the shear bonding condition which secures the tensile property that can withstand the tensile tension between the finishing rolling stands. There is a technical effect to provide.

In addition, the present invention has a technical effect of providing a process variable capable of continuously performing rolling without breaking a plate in subsequent finishing rolling processes even when the metal bars are bonded to each other when continuous hot rolling of low carbon steel.

As described above, if the process conditions range of the present invention is applied, the joints of the metal bar have sufficient resistance against the strong compressive load due to the finishing rolling and the tensile load between the stand, even in the case of low carbon steel. Continuous hot rolling is possible without this happening.

Claims (10)

Weight percent C; 0.30% or less, Mn; 1.8% or less, Si; 0.55% or less, P; 0.50% or less, S; Low carbon steel or C containing not more than 0.50% and consisting of other unavoidable impurities and the remaining Fe; 0.30% or less, Mn; 1.8% or less, Si; 0.55% or less, P; 0.50% or less, S; 0.50% or less of Cr, Cu, Ni, Mo, or Al containing 1.0% or less of the element, and other inevitable impurities and the low carbon steel metal bar consisting of the remaining Fe, followed by the leading end of the metal bar in the hot rolling facility. Shear bonding method of low carbon steel continuous hot rolled material which is bonded by shearing using a jointer which overlaps and joins the rear end of the metal bar, and the metal bars are bonded to each other so that the joined surface of the bonded metal bar is inclined along the thickness direction of the metal bar. . In claim 1 A shear bonding method of a low carbon steel continuous hot rolled material which descales a joining scheduled portion of the metal bar to a pressure of 60 MPa or less. In claim 1 Shear bonding method of the low carbon steel continuous hot rolled material is shear bonding to the metal bar when the range of the wrap, the distance that overlaps the upper blade and the lower blade of the bonder is 2mm to 19mm. In claim 1 In the case of shear bonding the metal bar, the shear bonding method of the low carbon steel continuous hot rolled material, which is shear bonded at a stroke rate of 1.33 to 1.60 divided by the sum of the distance traveled by the upper and lower blades of the adapter by the thickness of the metal bar. . In paragraph 4 Shear bonding method of the low carbon steel continuous hot rolled material when the metal bar is shear bonded while the upper blade and the lower blade of the bonding machine simultaneously moves up and down simultaneously. In paragraph 4 Shear bonding method of a low carbon steel continuous hot rolled material when the metal bar is shear bonded while shearing any one of the upper blade and the lower blade of the bonding machine. In claim 2 Shear bonding method of the low carbon steel continuous hot rolled material is shear bonding to the metal bar when the range of the wrap, the distance that overlaps the upper blade and the lower blade of the bonder is 2mm to 19mm. In paragraph 7 In the case of shear bonding the metal bar, the shear bonding method of the low carbon steel continuous hot rolled material, which is shear bonded at a stroke rate of 1.33 to 1.60 divided by the thickness of the metal bar, which is the sum of the distances of the upper and lower blades of the adapter. . In claim 2 In the case of shear bonding the metal bar, the shear bonding method of the low carbon steel continuous hot rolled material, which is shear bonded at a stroke rate of 1.33 to 1.60 divided by the thickness of the metal bar, which is the sum of the distances of the upper and lower blades of the adapter. . Weight percent C; 0.30% or less, Mn; 1.8% or less, Si; 0.55% or less, P; 0.50% or less, S; Low carbon steel or C containing not more than 0.50% and consisting of other unavoidable impurities and the remaining Fe; 0.30% or less, Mn; 1.8% or less, Si; 0.55% or less, P; 0.50% or less, S; A rough rolling mill containing about 1.0% or less of Cr, Cu, Ni, Mo or Al in an amount of 0.50% or less and roughly rolling a low carbon steel slab composed of other unavoidable impurities and the remaining Fe; A coil box for winding the roughly rolled metal bar in a coil state; A descaling device for descaling a joining portion of the metal bar released from the coiler of the coil box; A shear bonding device provided with a pair of shear blades for shearing the descaled metal bar by overlapping the rear end of the preceding metal bar and the leading end of the trailing metal bar by pressing the overlapping portion from both sides thereof in the state of the door; And A finishing mill for finishing rolling the shear bonded metal bar Hot rolling equipment for continuously hot rolling a low carbon steel metal bar comprising a.

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