KR100765038B1 - Joining method of austenite stainless steel for endless hot rolling - Google Patents

Abstract

The present invention is to control the bonding conditions of the hot rolled materials in the continuous hot rolling of austenitic stainless steel, the shear bonding method of the continuous hot rolled material that can be mailed without breaking the plate in the finishing rolling step and the continuous hot for the same It relates to a rolling equipment.

The present invention comprises austenitic stainless steel or Cr containing 12% to 26% of Cr, 6% to 22% of Ni, and other unavoidable impurities and remaining Fe by weight; 12% to 26%, Ni; 6 to 22% contains at least one or more elements of Si, Mn, P, S, Cu, Mo, Al, V, etc. up to 3.00% and other unavoidable impurities and remaining Fe The austenitic stainless steel metal bar is shear-bonded using a jointer that overlaps the leading end of the metal bar and the preceding end of the preceding metal bar in a hot rolling facility, and the joining surface of the joined metal bar is the thickness of the metal bar. Provided is a shear bonding method of an austenitic stainless steel continuous hot rolled material for joining metal bars to be inclined along a direction.

Austenitic stainless steels, continuous rolling, hot rolling, shear bonding, bonding conditions, wraps, descaling pressures

Description

[JOINING METHOD OF AUSTENITE STAINLESS STEEL FOR ENDLESS HOT ROLLING} Austenitic Stainless Steel Continuous Hot Rolled Material

1 is a block diagram showing a basic configuration of an austenitic stainless 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 scale mixing 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.

15A and 15B are graphs showing the results of a sheet test of joint mapping rolling according to an embodiment of the present invention.

The present invention relates to a method of joining a continuous hot rolled material in which hot rolled materials are joined to each other in a hot rolling process and continuously hot rolled. More particularly, the present invention relates to a method of joining hot rolled materials in continuous hot rolling of an austenitic stainless steel. The present invention relates to a shear joining method of a continuous hot rolled material that can be plated without breaking a sheet during finishing rolling by controlling the bonding conditions, and a continuous hot rolling facility for the same.

In the technical field of producing hot rolled metal sheets, there is a strong demand to improve productivity, quality and automate operations 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, austenitic stainless steel is composed of mostly austenitic microstructures at room temperature, and is nonmagnetic, has low thermal conductivity, excellent toughness, excellent ductility, good corrosion resistance, and is suitable for construction materials, kitchen appliances, industrial equipment, electronic parts, Widely used for self-contained parts.

When austenitic stainless steel is subjected to continuous hot rolling by applying a bonding technology, there are many advantages such as increased productivity and thinning.

However, these austenitic stainless steels are scaled at high temperatures, and since these scales are relatively thin in thickness but very dense in scale, it is very difficult to remove them in the rolling process. do.

Conventionally known joining techniques for continuous rolling include induction heating methods (see Japanese Patent Laid-Open Publication Nos. 1993-000202 and 1997-314216) and laser welding methods (Japanese Laid-Open Patent Publications 1995-024504 and No. 1) which are melt joints. See 1997-010803).

In the case of induction heating, continuous rolling is performed by heating the plate and pressing it, and then removing the beads. Scales existing on the butt joint surface of the trailing plate are transferred to the beads outside the joint during the pressing process. Pushed back.

However, the stainless steel scales are difficult to remove because they are in close contact with the base metal and the scale itself is soft. Therefore, there is a problem that the scale remaining in the induction heating junction significantly reduces the bonding strength.

In order to prevent this, induction heating may be considered in a reducing atmosphere, but in this case, only a specific part of the hot rolling line exposed to the atmosphere should be controlled as a reducing atmosphere, so it is very difficult to control the atmosphere only in a large facility. Production costs are also a major source of cost hikes.

In the case of laser welding, since the laser beam is very small, the joining is possible only when the joining surfaces are in close contact.

For this purpose, a method of using a welding material may be considered. However, in the method of using the welding material, it is important to control the gap between the joining surfaces.

In order to control the gap between the surfaces to be joined, it is very important to cut the joining material by the crop shear located in front of the joining machine.However, the process aspect and the ductility and toughness of rolling at high temperature are very high. Because of the inherent characteristics of austenitic stainless steel, it is very difficult to secure the precision of the cut surface of the joining material.

Due to the above problems, austenitic stainless steel hardly applies continuous hot rolling.

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

It is still another object of the present invention to secure a tensile property that can join a metal bar of austenitic stainless steel to fully bear the load of finishing rolling in the finishing rolling process and overcome the tensile tension between the finishing rolling stands in the finishing rolling process. To provide shear bonding conditions.

In order to achieve the above object, the present invention is austenitic stainless steel or Cr containing Cr; 12% to 26%, Ni; 6 to 22% by weight and other unavoidable impurities and the remaining Fe; 12% to 26%, Ni; 6 to 22% contains at least one or more elements of Si, Mn, P, S, Cu, Mo, Al, V, etc. up to 3.00% and other unavoidable impurities and remaining Fe The austenitic stainless steel metal bar is shear-bonded using a jointer that overlaps the leading end of the metal bar and the preceding end of the preceding metal bar in a hot rolling facility, and the joining surface of the joined metal bar is the thickness of the metal bar. Provided is a shear bonding method of an austenitic stainless steel continuous hot rolled material for joining metal bars to be inclined along a direction.

In another aspect, the present invention provides a method for shear joining austenitic stainless steel continuous hot rolled material which descales the joining portion of the metal bar to a pressure of 50 MPa or less.

In addition, the present invention is a shear bonding method of the austenitic stainless steel continuous hot rolled material to be sheared in the range of the range that the upper edge and the lower blade of the bonding machine overlaps when the metal bar is shear bonded to the range of 3mm to 19mm. To provide.

In addition, the present invention is an austenitic stainless steel continuous to shear bonding the shear rate by dividing the sum of the distance traveled by the upper blade and the lower blade of the adapter by the thickness of the metal bar when shear bonding the metal bar to 1.30 to 1.65 It provides a shear bonding method of hot rolled material.

In the present invention, when the metal bar is shear bonded, an austenitic stainless steel continuous hot pressure for shear bonding while both the upper blade and the lower blade of the joint move up and down at the same time, or shear bonding while only one of the upper blade and the lower blade is moved. Provides shear bonding method of soft materials.

In addition, the present invention is austenitic stainless steel or Cr containing Cr; 12% to 26%, Ni; 6 to 22% by weight and consisting of other unavoidable impurities and the remaining Fe; 12% to 26%, Ni; 6 to 22% contains at least one or more elements of Si, Mn, P, S, Cu, Mo, Al, V, etc. up to 3.00% and other unavoidable impurities and remaining Fe Rough rolling mill for rough rolling the austenitic stainless steel slab made;

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 austenitic stainless 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, the austenitic stainless steel in the present invention contains Cr; 12% to 26%, Ni; 6 to 22% by weight (% in the present invention means% by weight unless otherwise specified), and other unavoidable. Mainly refers to Fe-Cr-Ni stainless steel consisting of impurities and the remaining Fe. In addition, the austenitic stainless steel is made of mostly austenite structure at room temperature, and Mn and N may be added to replace expensive Ni.

Therefore, the austenitic stainless steel in the present invention means that the Fe-Cr-Ni-based as a basic component system and all of the stainless steel having austenitic structure of the microstructure. Therefore, if the Fe-Cr-Ni-based base composition and contains at least one element, such as Si, Mn, P, S, Cu, Mo, Al, or at least one special element such as V, Nb, Ti, B (In this case, the content of each element is not limited, but 3.00% or less is preferable.) All are considered to be contained in the austenitic stainless steel.

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 joining austenitic stainless steel according to the present invention, and a method of shear joining austenitic stainless steel using this equipment with reference to FIGS. 1 to 4. Explain together.

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 metal bars of the austenitic stainless steel manufactured by rolling the austenitic stainless steel slab in the roughing mill 10 are 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 may be cut by the crop shear.

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, referring to Figures 2 and 3, the abutment 100 and the metal bar of the austenitic stainless steel of 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).

The tip 220 of the trailing metal bar 60 is guided in the state in which the trailing metal bar 60 is superposed on the rear end 210 of the aforesaid metal bar 90 of the austenitic stainless steel.

Then, the front end 61 of the trailing metal bar 60 overlaps the rear end 91 of the front metal bar 90 of the austenitic stainless steel, and the portion of the front end 61 and the rear end 91 overlaps the upper blade. And between the projections 124 and 134 of the lower blade. 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 austenitic stainless 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 placed. ), The lower crop is cut. 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, it is necessary to maintain the bonding strength enough to pass the finishing mill 40 without breaking the abutment portion of the austenitic stainless steel metal bar.

Hereinafter, the process parameters of the bonding process for controlling the bonding strength of the joint when shear bonding the austenitic stainless steel metal bar 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, it is necessary to reduce the scale in order to secure the joint strength sufficient in the continuous hot rolling of austenitic stainless 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 at a plane where two metal bars overlap, and scale is instantaneously generated even if descaling to remove it. .

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 joining the austenitic stainless 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 compressive load pressed by the upper blade 121 and the lower blade 131, and two forces generated by shearing 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 joining force of the joint by controlling 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 do not have a scale that can be generated at the same time as shearing. Therefore, since only the new surfaces are joined by shearing, there is no scale, and it is possible to prevent subsequent process problems such as plate breakage, which may occur. It is possible to apply to stainless steel.

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 the pore mixing problem as well as the scale mixing problem in the bonding process of the austenitic stainless steel.

Therefore, the shear joining method according to the present invention is a very useful method for joining austenitic stainless steel in a 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 shear bonding of the austenitic stainless steel in consideration of this point will be described through the examples.

EXAMPLE

Process variables of shear bonding of metal bars in the continuous hot rolling facility shown in FIGS. 1 to 3 were tested using the metal bars of austenitic stainless steel having the composition shown in Table 1 below.

Steel grade Chemical composition (wt%) C Si Mn P S Cr Ni Cu Mo Al V STS304 0.058 0.521 1.11 0.029 0.003 18.44 8.10 0.283 0.153 0.002 0.078 STS316 0.041 0.57 1.06 0.027 0.003 17.00 10.30 0.193 2.03 0.003 0.045 STS304L 0.018 0.36 1.17 0.029 0.003 18.65 10.20 0.223 1.162 0.002 0.056

10 to 15 show the average experimental values of the steel grades shown in Table 1 below. This is similar to the characteristics of the bonding strength ratio (described later) as a result of various experiments as shown in FIGS. 10 to 15 for typical austenitic strainless steels such as STS304, STS316, and STS304L shown in Table 1. Therefore, the physical properties of the drawings and the austenitic stainless steels described below are shown as average values for the steel grades in Table 1.

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 metal part of the joint / strength of the base material 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 austenitic stainless 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 filamentary 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 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 above experiment, it can be seen that when de-scaling pressure of the descaling device 81 before the splicer 100 is controlled to 50 MPa or less when the austenitic stainless steel is shear bonded to the splicer.

As described above, the austenitic stainless steel has a high high temperature strength, so that even at a high pressure of about 50 MPa, the extent of decrease in bonding strength and the increase in edge crack rate are small.

In the case of the austenitic stainless steel, descaling can be omitted, even when the descaling pressure is 0 MPa, because a bonding strength and a low edge crack ratio that can be used in the finishing rolling process are obtained.

12 shows the bonding strength ratio according to the bonding temperature during shear bonding of the austenitic stainless steel.

However, as shown in FIG. 12, the bonding temperature of the austenitic stainless steel during shear bonding had little effect on the joint strength ratio and did not affect the edge cracking rate.

Figure 13 shows the strength ratio of the joint portion according to the change of the lap when shear bonding of the austenitic stainless 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 bonding strength ratio as the lap increased, and began to meet the mailing standards (described later) above 3mm, and began to decrease again above 16mm.

The reason why the range of the lap satisfies the mail order standard in the range of 3 mm to 19 mm 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 3mm to 19mm.

Because of the high temperature strength of the material itself, stenite-based stainless steel has a relatively high lower limit of the wrap.

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 as the lap increases, but the bonding force decreases at the edge portion, or oxidation occurs at the edge portion, and the effect is remarkably insignificant.

And as the shear blade is used, the wear amount changes frequently, and the amount of wrap in the present invention is difficult to measure in the actual hot rolling line.

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

As shown in FIG. 14, as the stroke rate increased, the breaking load of the joint gradually increased, and then passed the 1.30 to satisfy the mailing criterion, which was almost saturated at 1.30 or more, and then decreased again at 1.60 or more. However, it can be seen that up to 1.65, it satisfies the mailing standard.

Therefore, in the case of austenitic stainless steel, the stroke rate of the jointer 100 during shear bonding is preferably 1.30 to 1.65.

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 bonding force increases as the stroke rate increases, and the position and shape of the lower unbonded part appear differently in the plate thickness direction.

FIG. 15 shows a result of shear bonding of austenitic stainless steel according to the present embodiment to a hot rolling facility and a mailing test in a finishing mill. FIG. 15 shows a mailing standard according to the present invention.

FIG. 15 shows the result of shear bonding using an austenitic stainless 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 test material shown in the graph of FIG. 15 was shear bonded to an austenitic stainless steel metal bar having a width of 450 mm, and then lateral welded to two sets of bonded test materials to form a width of 840 mm to 900 mm. The bars were welded to metal bars of 900 mm length. 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 that were successful in finishing rolling were found to be less than 20%.

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. 15, the plate standard in the finishing rolling step means that the bonding strength ratio and the breaking load of the finishing rolling are satisfied without breaking the metal bar.

Although 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 the austenitic stainless steel, but is a shear bonding of continuous hot rolling of the austenitic stainless steel. It is possible to apply to various joining methods required.

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 austenitic stainless steel continuous hot rolled material according to the present invention enables continuous hot rolling by joining the hot rolled material of the austenitic stainless steel by shear bonding, which has not been applied until now. There is a technical effect to make it possible.

In addition, in the present invention, when joining the metal bar of the austenitic stainless steel, the shear of the metal bar joint in the finishing rolling process to secure the tensile characteristics that can bear the load of the finishing rolling and can overcome the tensile tension between the finishing rolling stand There is a technical effect of providing the bonding conditions.

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 continuously hot rolling austenitic stainless steel.

As described above, if the process condition range of the present invention is applied, even in the case of austenitic stainless steel, the joining part of the metal bar has sufficient resistance against the strong compressive load caused by the finishing rolling and the tensile load applied between the stand, so that the plate breaks at the finishing rolling. That is, continuous hot rolling can be performed without breaking the joint.

Claims (10)

Austenitic stainless steel or Cr, containing 12% to 26% Cr by weight, 6% to 22% Ni, and other unavoidable impurities; 12% to 26%, Ni; 6 to 22% contains at least one or more elements of Si, Mn, P, S, Cu, Mo, Al, V, etc. up to 3.00% and other unavoidable impurities and remaining Fe The formed austenitic stainless steel metal bar overlaps the front end of the metal bar following the hot rolled equipment and the rear end of the preceding metal bar with a range of 3 mm to 19 mm that is a distance at which the upper and lower blades of the splicer overlap each other. The joint surface of the bonded metal bar is shear bonded by the sum of the distance traveled by the upper blade and the lower blade of the adapter by the thickness of the metal bar to be 1.50 to 1.65. Shear bonding method of the austenitic stainless steel continuous hot rolled material for bonding the metal bars to be inclined along the thickness direction of the metal bar. In claim 1 A method of shear bonding of an austenitic stainless steel continuous hot rolled material, which descales a joining scheduled portion of the metal bar to a pressure of 50 MPa or less. delete delete delete delete In claim 2 The shear bonding method of the austenitic stainless steel continuous hot rolled material to shear bonding the range of the overlapping distance of the upper blade and the lower blade of the adapter when the metal bar is sheared to each other 3mm to 19mm. delete delete delete

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