JP2007175767A - Method for shear-joining continuously hot-rolled low-carbon steel material, and continuous hot-rolling apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for shear-joining continuously-hot-rolled material, which method can pass a low-carbon steel strip when continuously hot-rolling it without causing fracture of the strip in a finish rolling step by controlling joining conditions of the hot-rolled material, etc. <P>SOLUTION: This method is directed to a low-carbon steel bar, which contains 0.30 or less mass% C, 1.8 or less mass% Mn, 0.55 or less mass% Si, 0.50 or less mass% P, 0.50 or less mass% S, other unavoidable impurities and the balance Fe. The low-carbon steel bar is shear-joined using a joining machine for joining the metallic bars by overlapping the leading edge of the following metallic bar and the tail edge of the preceding metallic bar in a line of the hot rolling apparatuses. In this case, the metallic bars are joined such that the joined surface of the joined metallic bars is formed so as to tilt with respect to the thickness direction of the metallic bars. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a continuous hot rolled material shear joining method and continuous hot rolling for continuous hot rolling by joining hot rolled materials to each other in a hot rolling process. In continuous hot rolling, a method for shear joining continuous hot rolled material that can be passed without controlling the joining conditions of the hot rolled material, etc. and causing plate breakage in the finish rolling stage, and continuous heat for the same It relates to hot rolling equipment.

In the technical field of producing metal sheet materials by hot rolling, there is a strong demand for improving productivity and quality and increasing the manufacturable size of products by continuing finish rolling.
An important point in the field of such continuous hot rolling is a metal bar joining technique in which a rear end of a preceding hot-rolled sheet (hereinafter referred to as “metal bar”) and a subsequent metal bar are joined to each other.

  In the hot rolling process, the joining of the metal bars is performed between the roughing mill and the finishing mill, and if the metal bars are joined in the process after the roughing mill, the finishing rolling process is performed. It becomes possible to continuously roll the metal bar that is rolled in step (b).

Therefore, in order to perform finish rolling continuously, it is necessary to join the running metal bar and the metal bar at high speed, and various techniques have been proposed for such joining.
Conventionally known joining techniques are roughly classified into a melt joining method and a solid phase joining method.

  When the metal bars are joined together by the melt joining method, the melted joint is softened due to the fact that the temperature of the melted joint is higher than the temperature of the adjacent part, and the joint strength of the joint is higher than that of the base metal part There is a disadvantage of being inferior.

As a technique known in the solid phase bonding method, there is a metal plate bonding method disclosed in Patent Document 1.
The invention of this Patent Document 1 is generated in a shearing process by overlapping the rear end portion of the preceding metal bar and the front end portion of the subsequent metal bar vertically and shearing the two superimposed metal bars simultaneously. This is a technique in which the shear surfaces of two metal bars are directly contacted and joined.

  Since the invention of Patent Document 1 is joined by shearing, it is simple and can be joined in a short time, and the required space is small and the temperature drop during finish rolling is small. As having many advantages.

  However, the invention of Patent Document 1 has a disadvantage in that the shape of the joined part is non-uniform and the surface scale is mixed into the joined surface, thereby significantly reducing the joint strength of the joined part. .

  In addition, when the metal bar is joined by applying the invention of Patent Document 1, unjoined portions are generated at the upper and lower portions of the joint section and both ends in the width direction, and there are portions where the joining force is weak. In addition to the problems, there is a problem that the surface strength is mixed into the bonding surface and the bonding strength is lowered.

  On the other hand, low carbon steel has C of 0.30 mass% or less, Mn of 1.8 mass% or less, Si of 0.55 mass% or less, P of 0.50 mass% or less, and S of 0.50 mass% or less. This steel is composed of other inevitable impurities and the remaining Fe, and is used for general purposes. In addition, low-carbon steel has a basic composition of low-carbon steel, such as elements such as Cr, Cu, Ni, Mo, and Al, or V, Nb, B, Ti, etc. in order to ensure various properties such as strength and corrosion resistance. Such special elements may be produced by adding 1.0% by mass or less.

Low carbon steel is the most versatile steel type widely used in various fields such as various structures such as ships, buildings, bridges, and pressure vessels.
When continuous hot rolling is performed by applying a joining technique to such a low carbon steel, there are many advantages such as an increase in productivity and a reduction in thickness.

  However, when joining such general-purpose low carbon steel in a continuous hot rolling process, the joining conditions are not known in detail.

Japanese Patent Laid-Open No. 9-174117 JP 2005-46661 A

  Therefore, the present invention is for solving the above-mentioned problems, and an object of the present invention is to provide a shear bonding method and continuous hot rolling capable of applying continuous hot rolling to low carbon steel. It is to provide rolling equipment.

  Another object of the present invention is that when joining a low carbon steel metal bar, the joint of the metal bar can sufficiently bear the load of the finish rolling in the finish rolling process, and the tensile tension between the finish rolling stands. It is intended to provide a shear bonding method and continuous hot rolling equipment that ensure tensile properties that can withstand.

  In order to achieve the above object, the method for shear joining of a low carbon steel continuous hot-rolled material according to the present invention is that C is 0.30 mass (wt) or less, Mn is 1.8 mass or less, and Si is 0. .55 mass% or less, P is 0.50 mass% or less, S is 0.50 mass% or less, a low carbon steel metal bar made of other inevitable impurities and the remaining Fe, or C is 0.30 mass% Hereinafter, Mn is 1.8% by mass or less, Si is 0.55% by mass or less, P is 0.50% by mass or less, S is 0.50% by mass or less, and any one of Cr, Cu, Ni, Mo, or Al. The tip of a metal bar containing at least 1.0% by mass of one or more elements, followed by a low-carbon steel metal bar consisting of other inevitable impurities and the remaining Fe in the hot rolling equipment row Are joined by shear bonding using a bonding machine that overlaps and joins the rear ends of the preceding metal bars. Wherein the bonding surface of the metal bar is so joined together metal bar to be formed to be inclined from the thickness direction of the metal bars.

  In addition, the low-carbon steel continuous hot-rolled material shear joining method according to the present invention for achieving the above object is characterized in that the joining portion of the metal bar is descaled at a pressure of 60 MPa or less. .

  Further, in the shear joining method of the low carbon steel continuous hot-rolled material according to the present invention for achieving the above object, the distance between the upper blade and the lower blade of the joining machine overlapping when the metal bar is shear joined. The lap range is 2 mm to 19 mm, and shear bonding is performed.

  Further, in the shear joining method of the low carbon steel continuous hot rolled material according to the present invention for achieving the above object, when the metal bar is shear joined, the upper blade and the lower blade of the joining machine are moved. A shear rate is obtained by dividing the total distance by the thickness of the metal bar to a stroke rate of 1.33 to 1.60.

  And in the shear joining method of the low carbon steel continuous hot rolled material according to the present invention for achieving the above object, when the metal bar is shear joined, both the upper blade and the lower blade of the joining machine are moved up and down simultaneously. It is characterized in that it is sheared while moving or only one of the upper blade and the lower blade is sheared while moving.

  In addition, the continuous hot rolling facility according to the present invention for achieving the above object, C is 0.30 mass% or less, Mn is 1.8 mass% or less, Si is 0.55 mass% or less, and P is added. Low carbon steel slab containing 0.50 mass% or less, S 0.50 mass% or less, other inevitable impurities and the remaining Fe, or C 0.30 mass% or less, Mn 1.8 mass %, Si is 0.55 mass% or less, P is 0.50 mass% or less, S is 0.50 mass% or less, and one or more elements of Cr, Cu, Ni, Mo, or Al are 1. A coarse rolling mill for roughly rolling a low carbon steel slab comprising 0% by mass or less and comprising other inevitable impurities and the remaining Fe; a coil box for winding the coarsely rolled metal bar into a coil; Joining metal bars unwound from the coil box coiler A descaling device for descaling the fixed part, and press-fitting the descaled metal bar from both sides in a state where the rear end of the preceding metal bar and the front end of the subsequent metal bar are overlapped to sandwich the overlapped part A low-carbon steel metal bar is continuously hot-rolled, comprising a shear joining device provided with a pair of shear blades for shear joining while shearing, and a finish rolling mill for finish-rolling the shear-joined metal bar It is characterized by doing so.

  The low-carbon steel continuous hot-rolled material shear joining method according to the present invention is a technical technique in which a low-carbon steel hot-rolled material that has not been applied so far can be joined by shear-joining to enable continuous hot rolling. effective.

  In addition, when joining low carbon steel metal bars according to the present invention, the joint of the metal bars can sufficiently bear the load of finish rolling in the finish rolling process and withstand the tensile tension between the finish rolling stands. There is a technical effect of providing shear bonding conditions that ensure tensile properties that can be achieved.

  Furthermore, the present invention provides a process variable that can continuously perform rolling without sheet breakage in the subsequent finish rolling process even when the metal bars are joined together when continuously rolling low carbon steel. Has a technical effect.

  As described above, if the process condition range of the present invention is applied, even a low carbon steel, the joint of the metal bar is sufficiently resistant to a strong compressive load due to finish rolling and a tensile load applied between the stands. Thus, continuous hot rolling is possible without causing plate breakage, that is, joint breakage, in finish rolling.

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

  The low carbon steel in the present invention is 0.30 mass (wt)% (% means mass% unless otherwise specified), Mn is 1.8% or less, Si is 0.55% or less, Carbon steel containing P of 0.50% or less, S of 0.50% or less, other inevitable impurities and the remaining Fe, or C of 0.30% or less, Mn of 1.8% or less, Si 0.55% or less, P is 0.50% or less, S is 0.50% or less, and one or more elements of Cr, Cu, Ni, Mo or Al are contained in 1.0% or less, It means carbon steel composed of other inevitable impurities and the remaining Fe.

  The shear bonding in the present invention is a plastic flow deformation generated by the pressure at which the shearing surfaces of the metal bars are pressed against each other in the process of shearing with the shearing blades, where the shearing blades facing the joints of the stacked metal bars are positioned. This means that the metal bars are joined to each other, and the joint surface of the joint at this time is formed so as to be inclined from the thickness direction of the metal bar.

  First, refer to FIGS. 1 to 4 for hot rolling equipment for performing continuous hot rolling by shear joining low carbon steel according to the present invention, and a method for shear joining low carbon steel using this equipment. To explain.

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

  Referring to FIG. 1, the low-carbon steel continuous hot rolling facility according to the present invention is roughly divided into a rough rolling mill 10, a coil box 20, a joining device 30, and a finishing rolling mill 40 including a plurality of rolling mills from the upstream side. And a down coiler 50.

  A low carbon steel metal bar produced by rolling a low carbon steel slab with the roughing mill 10 is wound around a coiler of the coil box 20 in a coil shape. Such a coil box 20 adjusts the speed difference between the metal bars running on the roughing mill 10 and the finishing mill 40.

  The trailing metal bar 60 unwound from the coiler of the coil box 20 is cut by the partial descaling device 81 with the partial descaling device 81 after the tip of the trailing metal bar 60 is cut by the inlet-side crop shear 70. It is scaled and overlapped on the rear end of the preceding metal bar 90 by the overlapping device 80 of the joining device 30. At this time, the end of the preceding metal bar can be cut by the inlet side crop shear 70 as necessary.

  The leading end of the trailing metal bar 60 and the trailing end of the preceding metal bar 90 are joined by the joining machine 100 of the joining device 30, and the crop at the joined portion is cut by the crop processing device 120. The metal bar 110 joined by the joining device 30 and brought into a continuous state is transferred to the finishing mill 40.

  Here, the joining device 30 is equipment for joining the rear end of the preceding metal bar 90 and the front end of the following metal bar 60 in a traveling state, and is a short-time joining device capable of shear joining in a short time. .

  And in order to carry out the shearing joining of the metal bar in the running state, the joining machine 30 can move following the running of the metal bar, and the joining machine 30 swings following the running of the metal bar. Can be additionally installed.

  For example, as will be described later, the joining device 100 of the joining device 30 is press-fitted from both sides with an overlapped portion where the rear end of the preceding metal bar 90 and the front end of the succeeding metal bar 60 are sandwiched. A pair of shearing blades that are sheared while being sheared are provided.

  Then, the metal bar 110 transferred to the finishing mill 40 is sequentially hot-rolled through a plurality of rolling mills to be manufactured to a desired thickness, and is then wound around the down coiler 50.

  Here, in FIG. 1, reference numerals 130 and 140 indicate levelers installed on the respective outlet sides of the coil box 20 and the joining device 30, and reference numeral 150 indicates a crop shear installed on the inlet side of the finishing mill 40. Reference numeral 160 represents an edge heater disposed between the leveler 140 and the crop shear 150, and reference numeral 170 represents a bar heater disposed in front of the edge heater 160.

  The levelers 130 and 140, the crop shear 150, the edge heater 160, and the bar heater 170 can be selectively arranged depending on the material to be hot rolled and the hot rolling conditions. In FIG. The installation or non-installation is shown as an example, and can be variously changed.

  The crop shear 70 that cuts the rear end of the preceding metal bar 90 and the front end of the subsequent metal bar 60 is necessary when the metal bars are butted and joined. In the case of shear bonding, it may be omitted when not necessary.

Next, the joining machine 100 and the low carbon steel metal bar in the shear joining process according to the present invention will be described in detail with reference to FIGS.
Referring to FIG. 2, the joining machine 100 according to the present invention includes an upper blade assembly 180, a lower blade assembly 190, and a housing 101 that movably supports them.

  Here, the upper blade assembly 180 includes an upper blade 181, an upper clamp 182, and an upper support device 183, all of which are integrally formed. The lower blade assembly 190 includes a lower blade 191, a lower clamp 192, and a lower support device 193, all of which are integrally formed.

  The upper blade assembly 180 and the lower blade assembly 190 are guided by a post portion (not shown) of the housing 101, and the thickness direction of the leading metal bar 90 and the trailing metal bar 60 (direction perpendicular to the rolling surface). ) To be able to move in a direction inclined in the metal bar traveling direction. Further, the upper blade assembly 180 and the lower blade assembly 190 are configured to be able to approach and separate by a link mechanism (not shown). The inclination direction is a case where the embodiment shown in FIG. 2 is a cross section along the metal bar traveling direction, and may be inclined in another direction.

  In such a joining machine 100 according to the present invention, the leading end of the trailing metal bar 60 is guided on the trailing end of the leading metal bar 90 made of low carbon steel.

  As a result, the leading edge 61 of the trailing metal bar 60 is overlapped on the trailing edge 91 of the low-carbon steel leading metal bar 90, and the portion where the leading edge 61 and the trailing edge 91 overlap is the protrusion 184 of the upper blade. And the protrusion 194 of the lower blade. In other words, the upper blade protrusion 184 and the lower blade protrusion 194 come into contact with the surfaces of the front end 61 and the rear end 91.

  The upper clamp 182 and the lower clamp 192 are in contact with the portion where the rear end 91 of the preceding metal bar 90 and the front end 61 of the subsequent metal bar 60 are overlapped. The upper clamp 182 is supported by the upper support device 183 with hydraulic pressure, and the lower clamp 192 is supported by the lower support device 193 with hydraulic pressure.

  If the upper blade 181 and the lower blade 191 shear the leading metal bar 90 and the trailing metal bar 60 in such a state, the shear surfaces of the leading metal bar 90 and the trailing metal bar 60 are shear-bonded to each other by plastic flow deformation. Thus, the metal bar 110 is integrally connected.

  If the shear bonding of the ends of the low carbon steel is completed in this way, the upper crop separated from the tip 61 of the trailing metal bar 60 is located at the joining portion of the connected metal bars, and similarly, A lower crop separated from the rear end 91 of the metal bar 90 is located. When the metal bars are joined to each other, the upper blade 181 and the lower blade 191 retreat so as to be separated by a certain distance.

  The upper and lower crops cut by the metal bar shearing are removed by the crop processing device 120 shown in FIG. 1, and the connected metal bars 110 are continuously transferred to the finishing mill 40.

When the joint portion of the metal bar passes through the finishing mill 40, strong compressive stress, bending during finish rolling, and external force such as bending or tension acts between each stand of the finishing mill, so the joint portion Will be subjected to harsh process conditions.
At this time, the joint portion of the low carbon steel metal bar needs to maintain a joining strength that can pass through the finishing mill 40 without breaking.

  Hereinafter, when the low carbon steel metal bar is shear-joined by continuous hot rolling, process variables of the joining process for controlling the joining strength of the joint will be described in detail.

First, with reference to FIG. 4, the process of solid-phase joining two metal bars will be described in terms of metal thermodynamics.
Solid state bonding can be said to be a process in which two free surfaces become one interface. In this case, when the change of the free energy γ in the solid phase bonding process is calculated thermodynamically, it is as shown in Equation 1.

In Equation 1, since the interfacial energy has a value of 30% or less of the _{free surface} energy, the change in free energy can be represented by -1.7γ _{free surface} . And since γ _{free surface} has a positive value, the change in overall energy has a negative value. This means a spontaneous reaction, that is, the two surfaces are naturally joined without any external force.

  However, in reality, the two surfaces are not naturally joined without any external force in the atmosphere. This is because the unevenness and scale on the surface of the plate obstruct the joining of the two surfaces.

  In order for two metal bars to be joined together, an attractive force must act between the atoms on the surface of the metal bars to be joined. In order for the attractive force between atoms to work, the interatomic distance must be Å class.

  However, since the surface of the metal bar is uneven even after machining, the interatomic distance between the surfaces of the two metal bars is far greater than the soot class. Considering this point, a strong pressure (compressive force) is applied in normal solid-phase bonding, and a very large force is required at room temperature, so the metal bar is heated to a high temperature.

  However, even if such a strong pressure is applied, the scale existing on the surface of the metal bar or generated on the surface of the metal bar when the metal bar is heated reduces the bonding force. Therefore, in order to ensure a sufficient joint strength at the time of continuous hot rolling of low carbon steel, the scale must be reduced.

  In some cases, the conventional solid-phase bonding method in which two metal bars are bonded can extremely exceptionally prevent bonding of scale. However, in this case as well, since hot rolling is performed at a high temperature of about 1,000 ° C., scale due to high-temperature oxidation naturally occurs on the surface where two metal bars are to be stacked, and descaling is performed to remove this. Even if you do, a scale is generated on the surface instantly.

  Moreover, since the softness of the material is very high at a high temperature, scales existing on the surfaces to be stacked are mixed into the joint. Such scale contamination acts as a cause of reducing the bonding strength.

  Hereinafter, with reference to FIG. 5, in the case where two metal bars are bonded in a hot state as described above, a bonding rate and a bonding strength ratio of the bonding portion will be described.

  In FIG. 5, the solid line (straight line) shows the relationship between the bonding rate and the bonding strength when it is assumed that no scale is mixed in the bonded portion and there is theoretically no bonding force between the scales. As described above, theoretically, the bonding rate and the bonding strength are shown as a linear relationship. Therefore, if the bonding rate increases, the bonding strength ratio must also increase. Here, the joining rate is expressed as a percentage obtained by dividing the length of the joined portion that is completely scaled without the scale by the entire length of the joined portion. This indicates that the greater the amount of scale mixed in the joint, the lower the joining rate, and thus the lower the joint strength ratio.

  However, due to the high temperature conditions in the actual hot rolling process, scales are always generated, and there is a weak bonding force between the scales, so the bonding strength ratio is slightly higher than the solid line (straight line), that is, the dotted line. To show a good relationship.

  Next, the joining conditions for controlling the joining strength of the joint when shearing the low carbon steel metal bar by continuous hot rolling will be described.

  A shear joining process of the joining machine 100 according to the present invention will be described with reference to FIG.

As shown in FIG. 6A, the force for joining the two metal bars by shear joining is a force in a direction perpendicular to the joining portion of the compression loads pressed by the upper blade 121 and the lower blade 131. Also, the friction between the two new surfaces generated by shearing improves the bondability.
Such a force causes opposing pressures to act as shown in FIG.

  At this time, this force is a function of the bonding machine 100 and the process conditions, and if this is insufficient, the bonded portion cannot have sufficient bonding strength. On the other hand, the protrusions 184 and 194 existing on the upper blade and the lower blade play a role of preventing the metal flow when the metal bar is sheared, thereby strengthening the joining force.

  Further, as shown in FIG. 7, in the width direction of the metal bar, the central portion has no problem with the surrounding restraint, but the both end portions are in a free surface state without any restraint.

In this way, the ends in the free surface state at the time of joining the metal bars have a gap in the outer direction as shown in FIG.
As a result, the joining strength of both ends of the metal bar is reduced, and as shown on the right side of FIG. This causes cracks during the subsequent finish rolling, and if the cracks become large, continuous part breakage of the continuous steel sheet occurs.

  The shape of the joint also affects the joint strength. When shear bonding is applied, unbonded portions exist at the upper and lower portions of the cross section of the bonded portion due to the characteristics of the bonding method, and the bonding strength varies depending on the position and size of the unbonded portion.

  Considering the above description, various control factors that affect the performance of the joint are arranged as shown in FIG.

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

  However, it is difficult to control the material properties and the joining device here, so when actually joining metal bars, it is easy to adjust the process variables to control the joining conditions, and the effect is certain. It is.

Such process variables include descaling conditions and joining conditions.
As the descaling condition, the temperature and pressure at the time of descaling can be controlled to suppress the scale mixture. As the joining conditions, the joining force and shape of the joint can be adjusted by controlling the temperature, lap, and stroke rate during joining of the metal bars.

  By appropriately adjusting the five process variables as described above, it is possible to control the mixing of scale, insufficient bonding force, and the shape of the bonded portion, which are factors that decrease the bonding strength. Moreover, the strength reduction of the metal bar joint can be suppressed by controlling such process variables.

Here, the definition of the stroke rate and the lap, which are the joining conditions of the process variables, will be described with reference to FIG.
The stroke rate is obtained by dividing the total distance (Δl _U + Δl _L ) moved up and down after contacting the metal bar where the upper blade 181 and the lower blade 191 of the joining machine 100 overlap with each other by the thickness (t) of the metal bar. Value.

Therefore, as the stroke rate = ((Δl _U + Δl _L ) / t) increases, the relative thickness of the joint decreases.

  The lap is a distance at which the upper blade 181 and the lower blade 191 overlap. However, the shearing blade (the upper blade and the lower blade) has a predetermined angle, and after the shearing blade is sheared, a slight difference from the set value may occur depending on the stroke rate. Therefore, when the metal bar is actually shear-joined, actual measurement is impossible. Therefore, it is preferable to control the set value of the joining machine.

  Since the hot rolling equipment and the joining method using the same according to the present invention described above perform shear joining, they can be applied to low carbon steel.

  Furthermore, since the joining method according to the present invention is solid phase joining, shear joining is performed within the temperature range of the metal bar itself heated to a hot state without supplying a separate heat source on the hot rolling equipment line. It can be carried out. Therefore, preheating and post-heating are unnecessary, and cracking of the metal bar joint can be prevented without introducing a separate heat source.

  Further, unlike the conventional welding joining method, only the shearing force is used, so that there is a technical effect that the problem of mixing scale and pores can be fundamentally prevented during the joining process of low carbon steel.

  Therefore, the shear joining method according to the present invention is a very useful method for joining low carbon steels in a continuous hot rolling process, and it is possible to ensure finish rolling plateability of the joint part by appropriately controlling only the process variables. Can do.

  In the following, considering such points, process variables and process conditions during shear bonding of low carbon steel will be examined through evaluation.

[Evaluation]
Experiments were carried out using a low carbon steel metal bar having the composition shown in Table 1 below with the continuous hot rolling facility shown in FIGS.

  Hereinafter, the experimental graphs shown in FIGS. 10 to 16 show the all-type average experimental values of the steel types shown in Table 1. In the case of low carbon steel, if it has the composition by each steel type shown in Table 1, it showed as an experimental result that the characteristics, such as joining strength ratio (after-mentioned), show similar patterns.

FIG. 10 shows the relationship between the descaling temperature, the bond strength ratio, and the crack rate by the bonding machine provided in the low-carbon steel continuous hot rolling facility according to one embodiment of the present invention (the bond strength ratio and the crack ratio of the metal bar edge). It is a graph which shows the influence of scaling temperature.
Here, the bonding strength ratio is as shown in Equation 2 below.

  And the edge crack rate is like the following numerical formula 3.

  As shown in FIG. 10, in the case of low carbon steel, it can be seen that if the metal bar is shear bonded, the influence of the descaling temperature variable on the bonding strength ratio and the edge crack rate is not large.

  During finish rolling, if the bond strength ratio is low, the plate breaks in the first or second pass, and if the edge crack rate increases, the plate breaks in the subsequent stage.

FIG. 11 shows the relationship between the descaling pressure, the joint strength ratio, and the crack rate by the joining machine of the low carbon steel continuous hot rolling facility according to one embodiment of the present invention (the joint strength ratio and the crack ratio of the metal bar edge). It is a graph which shows the influence of scaling pressure.
As shown in FIG. 11, when the joined metal bars are finish-rolled with a finish rolling mill and tested for sheet-passability, if the joining strength ratio is 52% or more, finish rolling without breaking the joints of the metal bars is performed. It is understood that is possible. In the case of the edge crack rate, up to 30% could be passed.

  In the case of low carbon steel, even when the descaling pressure is 0 MPa, the joining strength that can be passed through in the finish rolling process and the low edge crack rate can be obtained, so descaling may be omitted.

  Further, as shown in FIG. 11, as the descaling pressure increases, the amount of scale mixed into the joint portion decreases, so the joint strength of the joint portion increases and the area of the unjoined portion at both ends in the width direction increases. The edge crack rate is also reduced.

  However, if the descaling pressure is too high, the amount of water injection increases and the temperature of the joint portion decreases significantly, making it difficult to secure the temperature required for finish rolling, which is a subsequent process.

  Moreover, the base material of the metal bar having a weak high-temperature strength is significantly damaged due to excessive descaling pressure, and many irregularities are generated on the surface of the joint portion, thereby deteriorating the bondability.

  As a result of the above experiments, it can be seen that when low-carbon steel is shear-joined with a joining machine, the descaling pressure in the descaling device 81 immediately before the joining machine 100 is preferably controlled to 60 MPa or less.

FIG. 12 shows the relationship between the bonding temperature and the bonding strength ratio by the bonding machine provided in the low-carbon steel continuous hot rolling facility according to one embodiment of the present invention (the bonding corresponding to the bonding temperature when the low-carbon steel is shear-bonded). It is a graph which shows intensity ratio.
As shown in FIG. 12, it can be seen that the bonding temperature when shear bonding low carbon steel has little effect on the bonding strength ratio. Although not shown, it can be seen that the edge crack rate is not affected.

FIG. 13 shows a relationship between a lap and a joining strength ratio by a joining machine provided in a low-carbon steel continuous hot rolling facility according to an embodiment of the present invention (a joining strength ratio due to a change in lap when low-carbon steel is shear-joined. ).
As shown in FIG. 13, it can be seen that the lap and the bonding strength ratio show a Gaussian distribution, that is, a parabola relationship.

  This is because the lap increases, that is, if the overlap length when the upper blade 181 and the lower blade 191 are in contact with the upper surface or the lower surface of the metal bar 60, 90 is increased, the bonding strength ratio is increased. (After-mentioned) began to be satisfied, and when it exceeded 19 mm, it began to decrease again, and if it exceeded 21 mm, the sheet passing standard could not be satisfied. Note that the overlap length is determined by the inclination angle of the bonding machine 100.

The reason why the lap range is 2 mm or more and 19 mm or less and satisfies the sheet passing standard is as follows.
In other words, the reason why the bonding strength increases as the lap increases is that the rising angle of the bonding surface from the rolling surface becomes smaller as the wrap increases, thereby the bonding surface of the pressing force of the shearing blade. This is because the component force in the direction perpendicular to the direction increases, and if the amount of wrap is greater than a predetermined value, the required load increases, and the bonding strength decreases.

  Therefore, the wrapping range is preferably 2 mm or more and 19 mm or less.

  On the other hand, the edge crack rate was greatly influenced by the descaling pressure, but almost no influence by wrapping was observed. This is because the bonding force increases due to the increase of the lap, but the phenomenon that a gap is formed in the width direction occurs at the edge portion and the bonding force is lowered.As a result, the edge portion is oxidized and the effect is remarkably small. Because it becomes.

  FIG. 14 shows the relationship between the stroke rate and the breaking load by the joining machine provided in the low-carbon steel continuous hot rolling facility according to one embodiment of the present invention (the breaking load of the metal bar due to the stroke rate when shearing low-carbon steel). It is a graph which shows.

  As shown in FIG. 14, the breaking load of the joint portion gradually increases as the stroke rate increases, and satisfies the passing plate standard at 1.33, and almost exhibits a saturation phenomenon at 1.50 or more. Had decreased again. However, it can be seen that the plate passing standard is satisfied up to 1.60.

  Therefore, in the case of low carbon steel, the stroke rate of the joining machine 100 is preferably 1.33 to 1.60 at the time of shear joining.

  At this time, the stroke can be sheared by simultaneously moving the upper blade and the lower blade of the bonding machine 100 up and down, and only one of the upper blade and the lower blade is moved to perform the shear bonding. You can also

  Unlike other joining conditions, the stroke rate affects the thickness of the joint. That is, if the stroke rate increases, the thickness of the joint becomes thinner. As a result, even if the joining strength increases, the breaking load may decrease, so the relationship between the stroke rate and the breaking load at the joint was investigated. As can be seen from FIG. 14, when the stroke rate is increased, the breaking load is increased even though the thickness of the joint portion is reduced, and this indicates that the joint strength ratio is significantly increased as the stroke rate is increased. Means.

  In addition, the stretch rate increased as the stroke rate increased, but the effect on the edge crack rate was not significant. The phenomenon in which the breaking stress and the breaking load increase as the stroke rate increases in this way is due to the increase in the stroke rate and the position and shape of the unjoined portion at the upper and lower portions in the thickness direction of the plate as shown in FIG. It is caused by appearing.

  FIG. 16 shows the results of a sheet passing experiment using a finishing mill after shear bonding of the low carbon steel according to the present embodiment with a hot rolling facility, and FIG. 16 confirms the sheet passing standard according to the present invention. it can.

  FIG. 16 is a graph showing the result of shear joining using a low-carbon steel material having the component composition shown in Table 1 and then rolling the joined metal bars with a finishing mill in a hot rolling factory.

  The experimental material shown in the graph of FIG. 16 is obtained by shear bonding a low carbon steel metal bar having a width of 450 mm, then welding the two sets of the experimental material joined to each other to obtain a width of 840 to 900 mm, and then again on the front and rear surfaces. A 9000 mm long metal bar made by welding bars of the same thickness. FIG. 16 shows the result of finishing rolling after heating such a metal bar in a heating furnace.

  As a result of such a test, in the metal bar having a bonding strength ratio of less than 52%, all the plates were broken by finish rolling, and in the metal bar having a bonding strength ratio of 52% or more, the plate was successfully passed (FIG. 16 ( b)).

  Thus, the joint edge crack of the metal bar that was successfully passed through the finish rolling was 15% or less.

  On the other hand, if the stroke rate is fixed, there is no problem even if the threading standard is set by the joint strength ratio, but if the stroke rate changes, the thickness of the joint will change. Is shown in FIG. Here, the bonding load ratio is as shown in Equation 4 below, and the threading plate standard for such a bonding load ratio is 31.5%.

  As described above, as shown in FIG. 16, the sheet passing standard in the finish rolling stage means that the joining strength ratio and the breaking load of the finish rolling are satisfied without breaking the metal bar.

  As mentioned above, although the preferable Example of this invention was described, this invention is not limited to the joining conditions in the junction part at the time of continuous hot rolling of the above low carbon steel, Such such a low carbon steel The present invention can be applied to various joining methods necessary for shear joining in continuous hot rolling.

  Accordingly, the present invention can be variously modified and implemented within the scope of the claims and the detailed description of the invention, and these also belong to the scope of the present invention.

It is a block diagram which shows the basic composition of the low carbon steel continuous hot rolling equipment which concerns on one Example of this invention. It is a joining machine which the low carbon steel continuous hot rolling equipment concerning one example of the present invention comprises, and is a lineblock diagram showing the metal bar completed joining. It is a conceptual diagram which shows the state of the metal bar joined by the joining machine which the low-carbon steel continuous hot rolling equipment which concerns on one Example of this invention comprises. It is a conceptual diagram which shows the change of the free energy of the solid phase junction by one Example of this invention. It is a graph which shows the relationship between the joining rate at the time of the solid-phase joining by one Example of this invention, and joining strength ratio. It is explanatory drawing which shows the joining force which acts on the joining surface by the joining machine with which the low carbon steel continuous hot rolling equipment which concerns on one Example of this invention comprises. It is explanatory drawing which shows the cause of the joining strength fall of the edge part of a metal bar by a joining machine, and crack generation. It is a block diagram explaining the correlation of the joining variable which acts on the junction part performance of the metal bar by a joining machine, and each joining variable. It is a conceptual diagram explaining the definition of a stroke rate and a lap. It is a graph which shows the relationship between the descaling temperature by the joining machine with which the low carbon steel continuous hot rolling equipment which concerns on one Example of this invention comprises, joining strength ratio, and a crack rate. It is a graph which shows the relationship between the descaling pressure by the joining machine with which the low carbon steel continuous hot rolling equipment which concerns on one Example of this invention comprises, joining strength ratio, and a crack rate. It is a graph which shows the relationship between the joining temperature and joining strength ratio by the joining machine with which the low carbon steel continuous hot rolling equipment which concerns on one Example of this invention comprises. It is a graph which shows the relationship between the lap | lap | lap by the joining machine with which the low carbon steel continuous hot rolling equipment which concerns on one Example of this invention comprises, and joining strength ratio. It is a graph which shows the relationship between the stroke rate by the joining machine with which the low carbon steel continuous hot rolling equipment which concerns on one Example of this invention comprises, and a breaking load. It is a structure | tissue photograph which shows the relationship between the stroke rate by the joining machine with which the low carbon steel continuous hot rolling equipment which concerns on one Example of this invention comprises, and the shape of the unjoined part of the upper and lower parts of a joined part. It is a graph which shows the plate test result of the joint finish rolling by the low carbon steel continuous hot rolling equipment which concerns on one Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Coarse rolling mill 20 Coil box 30 Joining apparatus 40 Finishing mill 50 Downcoiler 60 Trailing metal bar 61 Trailing metal bar tip 70 Entrance side crop shear 80 Stacking device 81 Descaling device 90 Leading metal bar 91 Leading metal bar Rear end 100 Joiner 101 Housing 110 Metal bar 120 Crop processing device 130, 140 Leveler 150 Exit side crop shear 160 Edge heater 170 Bar heater 180 Upper blade assembly 181 Upper blade 182 Upper clamp 183 Upper support device 184 Projection 190 Lower blade assembly Body 191 Lower blade 192 Lower clamp 193 Lower support device 194 Projection

Claims (7)

  0.30 mass (wt)% or less of C, 1.8 mass% or less of Mn, 0.55 mass% or less of Si, 0.50 mass% or less of P, 0.50 mass% or less of S, and others A low-carbon steel metal bar composed of the inevitable impurities and the remaining Fe, or C is 0.30 mass% or less, Mn is 1.8 mass% or less, Si is 0.55 mass% or less, and P is 0.50 mass%. %, S is 0.50 mass% or less, and one or more elements of Cr, Cu, Ni, Mo or Al are contained in an amount of 1.0 mass% or less. Other inevitable impurities and the remaining Fe A low carbon steel metal bar made of a material is shear-bonded and joined using a joining machine that joins the leading end of the following metal bar and the trailing end of the preceding metal bar in the hot rolling equipment row. The metal bar is formed so that the joining surface of the metal bar is inclined from the thickness direction of the metal bar. Shear-joining method of low carbon steel continuous hot rolled material, characterized in that the to be joined together.   The method for shear joining low carbon steel continuous hot-rolled material according to claim 1, wherein the joining portion of the metal bar is descaled at a pressure of 60 MPa or less.   3. When the metal bar is subjected to shear bonding, shear bonding is performed by setting a range of a lap, which is a distance at which the upper blade and lower blade of the bonding machine overlap, to be 2 mm or more and 19 mm or less. The shear joining method of the low-carbon steel continuous hot-rolled material as described.   When the metal bar is subjected to shear bonding, shear bonding is performed by setting the stroke rate obtained by dividing the total distance traveled by the upper blade and lower blade of the bonding machine by the thickness of the metal bar to 1.33 to 1.60. The shear joining method of the low carbon steel continuous hot-rolled material according to any one of claims 1 to 3.   5. The low carbon steel continuous material according to claim 1, wherein when the metal bar is shear-joined, both the upper and lower blades of the joining machine are shear-joined while simultaneously moving up and down. A method for shear joining hot rolled materials.   The low carbon according to any one of claims 1 to 4, wherein when the metal bar is subjected to shear bonding, only one of the upper blade and the lower blade of the bonding machine is moved while being sheared. A method for shear joining steel continuous hot rolled material. C is 0.30 mass% or less, Mn is 1.8 mass% or less, Si is 0.55 mass% or less, P is 0.50 mass% or less, S is 0.50 mass% or less, and other inevitable Low carbon steel slab composed of impurities and remaining Fe, or C is 0.30 mass% or less, Mn is 1.8 mass% or less, Si is 0.55 mass% or less, P is 0.50 mass% or less, 0.5% by mass or less of S is contained at least one element of Cr, Cu, Ni, Mo or Al in an amount of 1.0% by mass or less, and is composed of other inevitable impurities and the remaining Fe. A rough rolling machine for rough rolling a carbon steel slab;
A coil box that winds the roughly rolled metal bar into a coil;
A descaling device for descaling a joint portion of a metal bar unwound from a coiler of the coil box;
A pair of shearing blades that shear-join the descaled metal bar while being sheared by press-fitting from both sides in a state where the rear end of the preceding metal bar and the front end of the subsequent metal bar are overlapped to sandwich the overlapped portion. A shear bonding device provided; and
A finish rolling mill for finishing and rolling the shear bonded metal bar,
Continuous hot rolling equipment characterized by continuous hot rolling of low carbon steel metal bars.

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