JP6310605B1 - Laser-welded section and manufacturing method thereof - Google Patents

Abstract

The present invention provides a laser welded shape steel having excellent weld strength, particularly fatigue strength. A laser welded shape steel (1) formed of a web material (4) and a flange material (3) made of a steel plate, the composition of the steel plate, and the web material (4) and the flange material (3). The hardness of the welded portion (2) that is the joint portion of the laser beam satisfies the predetermined condition, and the surface (2a) on the laser light source side in the welded portion (2) all includes the surface (4a) of the web material (4). It is located closer to the laser light source than the plane. Ceql = C + (Si / 50) + (Mn / 25) + (P / 2) + (Cr / 25) + Ti (1) [Selection] FIG.

Description

  The present invention relates to a laser welded shape steel and a method for producing the same.

  Conventionally, shape steels such as T-shaped steel and H-shaped steel have been used for various applications such as structural materials for buildings. One of the methods for producing such a shape steel is a laser welding method. In the laser welding method, the flange material and the web material are welded to each other by irradiating laser light to a T-shaped joint portion formed by vertically butting the end of the web material against the flange material.

  Various techniques for efficiently forming a shaped steel satisfying desired properties by laser welding have been proposed (see, for example, Patent Documents 1 to 3).

  Further, Patent Document 4 describes a web edge pre-upsetting method in which a thickened portion is formed at the end in the width direction of the web material without buckling deformation. By this method, when performing high-frequency welding in which a contact portion between the flange material and the web material is welded by flowing a high-frequency current, the area of the contact portion can be increased.

JP 2009-119485 A (released on June 4, 2009) JP2011-83781A (released on April 28, 2011) JP 2012-152820 A (released on August 16, 2012) JP 2003-285136 A (released on October 7, 2003)

  In recent years, there has been a demand for further improving the strength of laser welded sections manufactured by laser welding. In order to improve the strength of the laser welded shape steel, (i) to improve the strength of the flange material and the web material itself, and (ii) the strength of the welded portion formed by laser welding. And satisfying workability are required.

  Here, generally, in the laser welding method, a recess may be formed in a welded portion (weld bead). This is caused by spattering of the molten metal due to sputtering, drooping of the weld bead on the side opposite to the laser irradiation side, and the like. Such a depression can be a stress concentration part.

  Therefore, in order to improve the fatigue strength of the welded portion, it is preferable to weld the flange material and the web material so that the above-described depression is not formed.

  In view of such a current situation, an object of the present invention is to provide a laser welded shape steel having excellent weld strength, particularly fatigue strength.

  In order to solve the above-mentioned problems, the present inventors diligently studied. As a result, the following findings (A) and (B) were obtained, and the present invention was completed. That is, (A) The composition condition of the said steel plate and the conditions of the laser welding part which can implement | achieve both improving the intensity | strength of the steel plate itself as a raw material and improving the intensity | strength of a laser welding part are discovered. It was. In general, in the laser welding method, the protruding portion formed in the welded portion is smaller than in the arc welding method or the like. Even in the case of a laser-welded steel having a weld with such a small protrusion (small cross-sectional area), the strength of the laser weld can be improved by satisfying the conditions found by the present inventors. . Then, the present inventors have further studied, and (B) the formation of the depression is made by using a filler wire (filler material) or installing a plurality of laser oscillators for one welding pass. The present inventors have found a method that can be prevented without any problem.

  That is, the present invention includes the following inventions.

[1] A laser welded shape steel formed of a web material and a flange material made of a steel plate, wherein the steel plate has a carbon equivalent C _eql given by the formula (1) of 0.07 or more and 0.12 or less, and Ti The content is 0.01% by mass or more and 0.1% by mass or less, and the hardness of the welded portion which is a joint portion between the web material and the flange material is 1.2 times or more the hardness of the steel plate 2 .8 times or less, the surface of the web material irradiated with laser is the first surface, the side on which the first surface is located with respect to the web material as the first side, and the first side All the surfaces of the welded part are located on the first side with respect to a plane including the first surface of the web material.

  [2] The length of the welded portion protruding from the flange material on the first side is α, the length of the welded portion protruding from the first surface to the first side is γ, and the web material is As a reference, the length of the welded portion protruding from the flange material on the second side opposite to the first side is β, and the length of the web material from the second surface opposite to the first surface is the first. When the length of the welded portion protruding to the side 2 is δ, the length of the protruding welded portion represented by α, β, γ, and δ is 1 mm or less. 1] The laser welded shape steel according to item 1.

  [3] The laser welded section steel according to [1] or [2], wherein the web material has a plate thickness of 6 mm or less.

[4] A method of manufacturing a laser welded shape steel formed of a web material made of a steel plate and a flange material, wherein the end portion of the web material has a thickness at the center in the plate width direction of the web material. Including a thickness increasing step for increasing the thickness to exceed 100% with respect to the plate thickness of the part, and a joining step for joining the web material and the flange material by laser welding after the thickness increasing step, The steel sheet has a carbon equivalent C _eql given by formula (1) of 0.07 to 0.12 and a Ti content of 0.01% to 0.1% by mass, and the web material and the flange The hardness of the welded portion, which is a joining portion with the material, is 1.2 times or more and 2.8 times or less of the hardness of the steel plate, and in the joining step, the surface on which the web material is irradiated with laser is the first. The first surface is based on the web material. Laser welding is performed such that the position on the first side is the first side and the surface of the welded portion on the first side is located on the first side with respect to the plane including the first surface of the web material. A method for producing a laser-welded section.

  According to one aspect of the present invention, there is an effect that it is possible to provide a laser welded shape steel having excellent weld strength, particularly fatigue strength.

It is an example of the photograph which shows the cross section which cut | disconnected the welding part of the laser welded shape steel manufactured with the general laser welding method in the plane perpendicular | vertical to a longitudinal direction. (A) is a figure which shows the cross section perpendicular | vertical to the longitudinal direction of the laser welded shape steel in embodiment of this invention. (B) is an example of the cross-sectional photograph which shows the welding part in the laser welded shape steel shown to (a). It is a figure which shows the relationship between carbon equivalent _Ceql and the hardness of a welding part. It is the elements on larger scale of the welding part in the cross section perpendicular | vertical to the longitudinal direction of the laser welded shape steel shown in FIG. It is a figure which shows an example in case a shape steel is used as structural members, such as a building, (a) is the lightweight welded shape steel as a comparative example, (b) is the laser in embodiment of this invention The welded shape steel is shown. It is a schematic diagram explaining the method of smoothing and thickening the end surface of a web material by pressing a masher roll. It is a schematic diagram which shows the laser welding method. It is a figure which shows an example of the method of measuring the amount of depressions in the surface of a welding part. It is a schematic diagram of the fatigue test in an Example. (A) And (b) is a schematic diagram of the diagonal crack test in an Example.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description is for better understanding of the gist of the invention and does not limit the present invention unless otherwise specified. Further, unless otherwise specified in the present specification, “A to B” representing a numerical range indicates that it is A or more and B or less.

(Comparative example of laser welded section)
In order to facilitate understanding of the laser welded shape steel in the embodiment of the present invention, first, a general laser welded shape steel as a comparative example will be described with reference to FIG.

  FIG. 1 is an example of a cross-sectional photograph of a welded portion of a laser welded shape steel 100 manufactured by a general laser welding method, cut along a plane perpendicular to the longitudinal direction. Usually, the laser welded shape steel 100 is manufactured as follows. First, the flange member 110 is arranged such that the short side direction is along the direction of gravity, and the end surface of the web member 120 is pressed against the plate surface of the flange member 110. Laser light is irradiated obliquely from the upper side in FIG. 1 to the contact portion between the flange member 110 and the web member 120. Thereby, the laser welding part 130 is formed.

  As shown in FIG. 1, the laser welded shape steel 100 has a recess 140 having a depth of about 0.2 mm in the laser welded portion 130. The reason why the dent 140 is generated is that (i) the slit edge (cut end surface) of the web material 120 is not smooth, so that a gap is generated in the pressing portion (contact portion), and (ii) the laser beam melts. The molten metal drooped by gravity. In addition, (iii) Insufficient force (upset) to press the web material 120 against the flange material 110, (iv) Spattering of molten metal by sputtering, and (v) Spraying of shield gas to the molten portion The influence of gas pressure, etc. can be cited as a cause.

  The formation of the depression 140 in the laser weld 130 is not preferred and is therefore rarely declared. However, in practice, for reasons such as (i) to (v) above, indentations 140 may inevitably occur in the laser welded shape steel 100 manufactured by a general laser welding method.

<Laser welded section 1>
Below, the laser welded shape steel 1 in embodiment of this invention is demonstrated. (A) of FIG. 2 is a figure which shows the cross section perpendicular | vertical to the longitudinal direction of the laser welded shape steel 1 in this Embodiment. FIG. 2B is an example of a cross-sectional photograph showing the welded portion 2 in the laser welded shape steel 1 shown in FIG.

  As shown in FIG. 2 (a), the laser welded shape steel 1 includes two flange members 3 made of steel plates and a web member 4 made of steel plates that connect the flange members 3 to each other by laser welding. Shape steel. In addition, although this embodiment describes the case where the laser-welded shape steel 1 is an H-section steel whose cross section perpendicular to the longitudinal direction is an H-shape, the present invention is not limited to this. That is, the laser welded shape steel 1 may be a shape steel having a T-shaped joint portion manufactured by laser welding, and may be various shape steels such as an I-shaped steel and a T-shaped steel. . Hereinafter, the flange material 3 and the web material 4 may be referred to as a base material. Further, the welded portion 2 of the laser welded shape steel 1 may be referred to as a laser welded portion.

  The laser welded shape steel 1 has a welded portion 2 formed by melting the flange material 3 and the web material 4 at a joint portion between the flange material 3 and the web material 4.

  As shown in (b) of FIG. 2, even if the laser welded shape steel 1 in the present embodiment is the most depressed portion of the welded portion 2, the position of the apex of the depression of the portion is that of the web material 4. The welded portion 2 is formed so as not to be positioned on the inner side of the web material 4 from the extended line of the surface which is a non-welded portion. In addition, about the method of forming such a weld part 2, it mentions later by description of the manufacturing method of the laser welded shape steel 1 of this embodiment.

  It will be as follows if the shape of the welding part 2 in the laser welded shape steel 1 is demonstrated in detail.

  Before laser welding the flange material 3 and the web material 4, the end surface of the web material 4 is brought into contact with the plate surface of the flange material 3 to form a contact portion (not shown). The contact portion is irradiated with laser obliquely from the upper side in FIGS. 2A and 2B to form the welded portion 2.

  Here, when a laser is irradiated onto the contact portion, a side on which a laser oscillator (not shown) that emits the laser is arranged is a laser light source side (first side). In other words, the laser light source side is the side on which the laser beam of the web material 4 is irradiated as the first surface, and the first surface is located with respect to the web material 4 as a reference. Moreover, the said 1st surface in the web material 4 is made into the surface 4a, and the surface located in the said laser light source side in the welding part 2 is made into the surface 2a.

  In the laser welded shape steel 1 of the present embodiment, the surface 2a of the welded portion 2 is all located closer to the laser light source than the plane including the surface 4a of the web material 4.

  Further, the shape of the welded portion 2 can be expressed as follows based on the cross section shown in FIG.

  Here, before laser welding, a corner is formed by the plate surface of the flange material 3 and the surface 4 a of the web material 4 by bringing the end surface of the web material 4 into contact with the flange material 3. The cross section of the welded portion 2 when the laser welded steel 1 after laser welding is cut along a plane perpendicular to the direction in which the corner line extends is a cross section shown in FIG. Even when the laser welded shape steel 1 is cut at an arbitrary position along the line of the corner, in the cross section, the surface 2a of the welded portion 2 is entirely from a plane including the surface 4a of the web material 4. Is also located on the laser light source side.

  More specifically, in the welded portion 2 of the laser welded structural steel 1 according to the present embodiment, even if a depression is formed on the surface 2 a, the bottom of the deepest depression forms the surface 4 a of the web material 4. It does not become deeper than the plane including it, in other words, the vertex of the deepest depression is not located on the inner side of the web member 4 than the plane including the surface 4a.

  As described above, the welded portion 2 of the laser welded shape steel 1 does not have the recess 140 in the general laser welded shape steel 100 described above. Therefore, stress concentration is suppressed and the fatigue strength of the welded portion 2 can be improved.

  Further, in the laser welded shape steel 1 in the present embodiment, a recess that can be a stress concentration portion on the opposite side (second side) of the laser light source side with respect to the web material 4 as described above. Is not formed. Specifically, with the web material 4 as a reference, the side opposite to the laser light source side is defined as the non-laser irradiation side (second side), and the surface of the web material 4 positioned on the non-laser irradiation side is the surface 4b (second surface). The surface located on the non-laser irradiation side in the welded portion 2 is defined as a surface 2b.

  On the non-laser irradiation side, the surface 2b of the welded portion 2 is all located on the non-laser irradiation side with respect to the plane including the surface 4b of the web material 4. Even when the laser welded shape steel 1 is cut at any position in the longitudinal direction, the surface 2b of the welded portion 2 is not irradiated with the non-laser than the plane including the surface 4b of the web member 4 in the cross section. Formed on the side.

  Further, in the laser welded steel 1 in the present embodiment, the length of the welded portion 2 protruding from the surface 4a to the laser light source side (the length γ described later with reference to FIG. 4) is different from the surface 4b. It is larger than the length of the welded portion 2 protruding to the laser irradiation side (length δ described later with reference to FIG. 4). In other words, in the welded part 2, the amount of protrusion on the laser light source side is larger than the amount of protrusion on the non-laser irradiation side.

  Next, the composition of a steel plate that is a base material for forming the laser welded structural steel 1 in the present embodiment will be described below.

  As a steel plate generally used for laser welding, for example, a C-Mn steel plate showing a 400 MPa class tensile strength is known. In order to further improve the strength of the base material, increasing the C (carbon) content in the composition of the base material is considered as one measure.

  However, since the laser welded portion has a rapid heating and quenching structure, the hardness of the portion is greatly affected by the amount of C contained in the base material. Therefore, when the C content in the base material increases, the laser weld becomes harder accordingly. As a result, the laser weld can become brittle. That is, when the C content in the composition of the base material is increased, the strength of the base material is improved, but on the other hand, cracking of the welded portion is likely to occur. Therefore, there is a limit to increasing the C content in the base material and improving the strength of the laser welded shape steel.

  Therefore, the present inventors have intensively studied and, as a result, found that the base material strength and the laser weld strength can be improved by satisfying the following conditions.

That is, in the welded portion 2 of the laser welded steel 1 in the present embodiment, the carbon equivalent C _eql represented by the following formula (1) is 0.07 or more and 0.12 or less, and the Ti content is 0.01 mass% or more. It is 0.1 mass% or less. In the following formula (1), each element symbol represents the mass% concentration of each element in the weld zone 2.

Here, the carbon equivalent C _eql in the welded part 2 may be obtained by directly measuring the concentration of each element in the welded part 2, but using the mass% concentration of each element in the web material 4 and the flange material 3. Also good. This is because, unlike arc welding, laser welding does not use filler wires, so that a weld 2 having the same composition as the web material 4 and the flange material 3 is formed. In addition, what is necessary is just to let the average value be a composition of the welding part 2 when using the steel plate from which a composition differs by the web material 4 and the flange material 3. FIG.

FIG. 3 is a diagram illustrating a relationship between the carbon equivalent C _eql represented by the formula (1) and the hardness of the welded portion 2. The carbon equivalent C _eql represented by the formula (1) was found by the inventors of the present invention as a result of intensive studies. As shown in FIG. 3, between the carbon equivalent C _eql and the hardness of the weld 2, It can be seen that there is a correlation.

  When the base material contains 0.01 mass% or more and 0.1 mass% or less of Ti, the strength of both the base material and the welded portion 2 can be improved while keeping the C content low. Specifically, the base material can have a tensile strength of 590 MPa class. In addition to that, the tensile strength of the welded portion 2 can be made larger than that of the base material, and the welded portion 2 can be prevented from becoming excessively hard and fragile.

  Here, the laser welding method is suitably used for manufacturing a shaped steel made of a plated steel plate. This is because the influence on the plating layer at the time of welding can be reduced as compared with high-frequency welding or arc welding. When the composition of the base material contains Ti, an effect of preventing liquid metal embrittlement cracking (LMEC) (LMEC prevention effect) can also be achieved. Therefore, when using a plated steel plate as a base material, the laser welded shape steel 1 can be manufactured more suitably. Furthermore, the composition of the base material may contain another element (for example, B) that can promote the effect of preventing LMEC by co-addition with Ti.

As shown in FIG. 3, when the carbon equivalent C _eq1 represented by the formula (1) is 0.07 or less, the strength of the welded portion 2 is not sufficient. This was confirmed from the fact that the weld 2 can break in the tensile test. Moreover, when the carbon equivalent _Ceql shown by Formula (1) is 0.12 or more, the weld 2 becomes excessively hard and brittle. This was confirmed from the fact that cracks could occur in the welded part 2 in the oblique crack test.

  When the composition of the base material contains 0.1% by mass or more of Ti, the tensile strength of the base material is excessively increased, the elongation value is decreased, and the workability and toughness of the base material are decreased. Therefore, the Ti content in the base material is preferably 0.1% by mass or less.

  Further, in the laser welded shape steel 1 according to this embodiment, the hardness of the welded portion 2 is 1.2 times or more and 2.8 times or less of the hardness of the base material composed of the web material 4 and the flange material 3. Moreover, it is preferable that the hardness of the welding part 2 is 1.6 times or more and 2.5 times or less of the hardness of a base material. In addition, the hardness as used in this embodiment is Vickers hardness (Hv0.2). The hardness of the welded part 2 is the abutting part (contact part) between the web material 4 and the flange material 3 in the welded part 2 and is the hardness at the center of the web material 4 in the thickness direction. For example, the hardness in the welded part 2 is the hardness at the position 2c shown in FIG. Moreover, when the hardness of the web material 4 and the hardness of the flange material 3 differ, let the average value be the hardness of a base material.

  In the laser welded shape steel 1, the hardness ratio represented by (hardness of welded portion 2) / (hardness of base material) can be controlled by the composition of the base material, laser welding conditions, and the like.

  When the said hardness ratio is larger than 2.8, the welding part 2 will become hard too much and a crack may generate | occur | produce in the welding part 2 in an oblique crack test. When the hardness ratio is less than 1.2, the tensile strength and fatigue strength are lowered, and the weld 2 can be broken in the tensile test and fatigue test.

  In addition, the steel plate (flange material 3 and web material 4) used for the laser welded shape steel 1 in the present embodiment may be a steel plate that has been subjected to a tempering treatment such as quenching or tempering. It may be a non-tempered steel sheet that has not been treated.

(Advantages of laser welded section 1)
As described above, the composition of the base material in the laser welded shape steel 1 of the present embodiment is such that the carbon equivalent C _eql given by the formula (1) is 0.07 or more and 0.12 or less, and the Ti content is 0. It is 0.01 mass% or more and 0.1 mass% or less. Moreover, the hardness of the welding part 2 is 1.2 times or more and 2.8 times or less of the hardness of a base material. And the welding part 2 does not have a hollow which becomes a stress concentration part.

  Thereby, the intensity | strength of the laser welded shape steel 1 can be improved. Therefore, the laser welded shape steel 1 is difficult to break even when a high load stress is applied. And it is suppressed that the welding part 2 fractures | ruptures ahead of a base material, and a crack arises in the welding part 2. FIG. Therefore, the laser welded shape steel 1 has a strength equivalent to the design strength, and the reliability of the strength can be increased.

  In particular, since the fatigue characteristics of the welded portion 2 are good, even if it is subjected to repeated loads, it will not break if it is within the design load. This design load (basic load for design) can be, for example, within 70% of the tensile strength standard of the base material.

  Moreover, since the laser welded shape steel 1 has an LMEC prevention effect, it is excellent in weldability with other members. That is, even when the base material of the laser welded shape steel 1 or another member welded to the laser welded shape steel 1 has a plating layer, LMEC due to the plated metal is unlikely to occur.

(Other configurations)
Furthermore, it is preferable that the laser welded structural steel 1 in the present embodiment has the following configuration.

  FIG. 4 is a partially enlarged view of the welded portion 2 in the laser welded structural steel 1.

  In the laser welded shape steel 1, the protruding amount of the welded portion 2 is 1 mm or less, and preferably 0.75 mm or less. The protruding amount of the welded portion 2 is the length of the welded portion 2 protruding from the flange material 3 and the welded portion 2 protruding from the web material 4 in an arbitrary cross section perpendicular to the longitudinal direction of the laser welded structural steel 1. Is the length of the largest one of the lengths.

  That is, as shown in FIG. 4, the protruding amount of the welded portion 2 is the length α of the welded portion 2 protruding from the flange material 3 on the laser light source side, and the protruding amount from the flange material 3 on the non-laser irradiation side. The length β of the welded portion 2, the length γ of the welded portion 2 projecting from the surface 4 a of the web material 4 to the laser light source side, and the surface 4 b on the opposite side of the web material 4 projecting to the non-laser irradiation side. Of the length δ of the welded portion 2, the maximum length. In the laser welded steel 1 in the present embodiment, it is preferable that the length of the protruding welded portion indicated by α, β, γ, and δ is 1 mm or less in any cross section.

  Here, the thickness of the web material 4 is preferably 6 mm or less. This is due to the following reason. That is, when the thickness of the web material 4 exceeds 6 mm, it is necessary to increase the amount of heat input when the flange material 3 and the web material 4 are welded using laser welding. As a result, the protruding amount of the welded portion 2, particularly the length of the back bead indicated by β and δ in FIG. 4, may exceed 1 mm. In addition, the plate | board thickness of the flange material 3 is not specifically limited.

  Advantages of the laser welded shape steel 1 will be described below with reference to FIG. FIG. 5 is a diagram showing an example of the case where the shape steel is used as a structural member such as a building, where (a) shows a lightweight welded shape steel as a comparative example, and (b) shows an example of the present invention. The laser welded shape steel 1 is shown.

  Conventionally used shape steels such as lightweight welded shape steels are manufactured by a high frequency welding method or an arc welding method. As shown to (a) of FIG. 5, in such a lightweight welded shape steel, a protrusion part is formed in the junction part of a web material and a flange material. By the way, when such a shape steel is used as a structural member such as a building, a reinforcing member may be disposed in a portion surrounded by the web material and the flange material. In such a case, in a conventionally used shape steel such as a light-weight welded shape steel, a protruding portion is formed at the joint portion between the web material and the flange material, which restricts the arrangement and shape of the reinforcing member. . Further, a stress concentration portion such as a notch can be formed. And if a protrusion part is removed by cutting etc., there exists a problem that intensity | strength will fall.

  On the other hand, as shown in FIG. 5B, in the laser welded steel 1 according to the present embodiment, since the protruding amount of the welded portion 2 is 1 mm or less, the degree of freedom of the arrangement and shape of the reinforcing member is high. Moreover, such a shaped steel may be used by joining with other members. Even in such a case, since the protruding amount of the welded portion 2 is 1 mm or less, the welded portion 2 does not hinder the joining with other members. Thus, the laser welded structural steel 1 in this embodiment is more advantageous in terms of design and construction when used as a structural member than the conventional structural steel.

  The laser welded shape steel 1 in this embodiment can provide a laser welded shape steel having excellent weld strength, particularly fatigue strength, as described above, even when the amount of protrusion of the weld 2 is 1 mm or less.

<Laser welded section manufacturing method>
A method for manufacturing the laser welded shape steel 1 of the present embodiment will be described below with reference to FIGS. 6 and 7. FIG. 6 is a schematic diagram for explaining a method of smoothing and increasing the thickness of the end face of the web material 4 by pressing a masher roll. FIG. 7 is a schematic diagram showing a laser welding method.

  Here, for example, in the laser welded shape manufacturing method described in Patent Document 1, in order to suppress the formation of a dent in the welded portion 2, the end of the web material is pressed against the flange material, and the web material itself is A large amount is melted to compensate for the shortage of joining metal in the joint. However, this case has the following problems.

  That is, the slit edge of the web material is not necessarily flat, and by pressing the end of the web material against the flange material, the drooping of the welded portion downward in the direction of gravity can be promoted. Therefore, even when trying to melt a large amount of web material by pressing the end of the web material against the flange material in order to compensate for the shortage of joining metal in the joint, the web material is not always flat, so the web material is melted. It is difficult to control the amount and the downward protrusion amount.

  Therefore, the present inventors can prevent the depression of the welded portion 2 from becoming a stress concentrated portion while suppressing the decrease in the strength of the welded portion 2 and the increase in the amount of protrusion. Various studies were conducted. As a result, it has been found that the above object can be achieved by appropriately smoothing and increasing the thickness of the end face of the web material 4 with a masher roll.

(Thickening process)
In the manufacturing method of the laser welded shape steel 1 of this embodiment, the thickness increasing process which performs the process which increases the thickness of the edge part of the web material 4 is included before performing laser welding.

  As shown in FIG. 6, in the thickening step in the method for manufacturing the laser welded shape steel 1 of the present embodiment, the web material 4 cut to a predetermined plate width by the slit is masked on the slit edge (cut end face) 10. The roll 9 is pressed. Thereby, the slit edge 10 is smoothed and thickened. The diameter of the masher roll is, for example, 100 mm.

  The web material 4 that has been cut into a predetermined plate width by the slit may not have a smooth shape of the slit edge 10. The end face of the web material 4 is smoothed and thickened by the above-described thickening process. Specifically, in the thickness increasing step, the end portion of the web material 4 is increased in thickness so that the thickness of the end portion exceeds 100% with respect to the thickness of the central portion in the plate width direction of the web material 4. .

  In the manufacturing method of the laser welded shape steel 1, the thickness increase rate of the end portion of the web material 4 is expressed as “(plate thickness of the end portion of the web material 4 after the thickness increasing process) / (center in the plate width direction of the web material 4). Part thickness) ”. The thickness increase rate can be adjusted by the pressing force of the masher roll and the reduction rate of the width of the web material 4 before and after the thickness increase process. When the thickness increase rate exceeds 100%, it is possible to suppress the formation of a dent in the welded portion 2 during laser welding after the thickness increasing step.

  Moreover, it is preferable to set the thickness increase rate as follows.

  In general, when the material is selected so that the strength of the base material is improved, the fatigue strength of the welded portion 2 is also expected to improve with the material strength, but in practice, the influence of the shape of the welded portion 2 is large. Fatigue strength is difficult to improve as expected. Therefore, the thickness increase rate is increased as the material strength of the base material is higher. Thereby, the joining width of the welding part 2 can be ensured and the fatigue strength of the welding part 2 can be improved appropriately.

  In addition, the joining width of the welding part 2 is the length of the part by which the end surface of the web material 4 is joined with the surface of the flange material 3 by welding, and if it demonstrates using FIG. Is the sum of the length γ of the weld protruding from the laser light source side, the plate thickness of the web material 4, and the length δ of the weld protruding from the surface 4b of the web material 4 to the non-laser irradiation side.

In particular,
(I) When the tensile strength of the base material is 400 N / mm ² , the joining width may be equal to or greater than the thickness of the web material 4. For example, if the thickness of the web material 4 is 2.3 mm, the joining width is set to 2.3 mm or more. For this purpose, the thickness increase rate of the web material 4 should be greater than 100%.

(Ii) When the tensile strength of the base material is 490 N / mm ² , for example, if the thickness of the web material 4 is 2.3 mm, the joining width is set to 2.4 mm or more. For this purpose, the thickness increase rate of the web material 4 is preferably 104.5% or more.

(Iii) When the tensile strength of the base material is 590 N / mm ² , for example, if the thickness of the web material 4 is 2.3 mm, the joining width is set to 2.52 mm or more. For this purpose, the thickness increase rate of the web material 4 is preferably 109.5% or more.

  In addition, you may perform a thickening process using apparatuses other than a masher roll. Moreover, in the welding line which performs laser welding, the location and time at which the thickening step is performed may be any location and time before the joining step, and may be arbitrarily set by the designer of the welding line. Or after storing the steel plate as the web material 4 after the thickness increase process of the slit edge once, this steel plate may be thrown into the laser welding line.

(Joining process)
And the manufacturing method of the laser welded shape steel 1 of this embodiment includes the joining process of joining the web material 4 and the flange material 3 by laser welding after the said thickness increasing process.

  As shown in FIG. 7, in the joining step, the plate surface of the flange material 3 and the end surface of the web material 4 are brought into contact with each other and laser welding is performed. For example, laser welding is performed by irradiating the laser beam 5 from the laser torch 6 using a fiber laser welding machine (not shown). In general, the laser is irradiated from the upper side to the lower side in the direction of gravity from the viewpoint of safety. This point is the same also in the manufacturing method of the laser welded shape steel 1 of this embodiment. That is, the vertical direction in FIG. 7 is the direction of gravity. Therefore, the welded portion 2 is likely to hang down to the non-laser irradiation side, and a dent is likely to occur.

  In the manufacturing method of the laser welded shape steel 1 according to the present embodiment, in the joining step, all the surfaces 2a of the welded portion 2 on the laser light source side protrude from the plane including the surface 4a of the web material 4 to the laser light source side. The weld 2 is formed. Thereby, the laser welded shape steel 1 which does not have the hollow used as a stress concentration part in the welding part 2 can be manufactured. It should be noted that a recess is not formed in the welded portion 2 on the non-laser irradiation side as well.

  In the joining step, it is preferable that some upset force is applied to the butted state of the flange member 3 and the web member 4 by a squeeze roll. Further, it is preferable to defocus the laser target position. Thereby, it can prevent more reliably that a hollow arises in the welding part 2. FIG.

  That is, in the manufacturing method of the laser welded shape steel 1 of the present embodiment, not only the web material 4 is pressed against the flange material 3, but also the technology of smoothing and increasing the thickness of the slit edge of the web material 4 is combined. As a result, it is possible to stably form the welded portion 2 having a clean shape and no depression.

  On the other hand, the laser welded shape steel manufactured by the conventional method (for example, the method described in Patent Document 1) has the following problems. For example, when a plurality of laser welded shape steels are manufactured by using a method in which the web material is strongly pressed against the flange material, it is possible that a laser welded shape steel having no depression is obtained. However, such a laser-welded section is not stably obtained. In practice, a clean weld can be stably formed simply by supplementing the weld metal by pressing the web material against the flange material. It was difficult to do. The reason for this is as described above. In addition, if the welded part hangs down under the force of gravity by pressing the web material strongly against the flange material, the protruding length of the welded part increases, and the degree of freedom of the arrangement and shape of the reinforcing member decreases. Can occur.

  The present invention is not limited to the above-described embodiment, and various modifications are possible within the scope shown in the claims, and the present invention is also applied to an embodiment obtained by appropriately combining technical means disclosed in the embodiment. It is included in the technical scope of the invention.

  Hereinafter, although the laser welded shape steel of the present invention will be described in more detail with reference to Examples and Comparative Examples, the present invention is not limited to these Examples.

Using a web material and a flange material having a carbon equivalent C _eql as shown in Table 1, an H-shaped shape steel having a width of 100 mm and a height of 100 mm was prepared by laser welding (Examples 1 to 15 and Comparative Example 1). ~ 20).

  Here, a steel plate having a width of 100 mm and a length of 4 m was used as the flange material. As the web material, a steel plate having a length of 4 m was used. Moreover, about the width | variety of a web material, regardless of the presence or absence of the thickness increase process by a masher roll, the width | variety just before a joining process is [100- (total of plate | board thickness of two flange materials) / 2] mm. It was. Table 1 shows the thickness and base material strength of the flange material and web material used.

  Prior to the joining step, Examples 1-15, Comparative Examples 9-11, and Comparative Examples 13-20 were subjected to thickening using a masher roll as the thickening step.

  In the laser welding, as shown in FIG. 7, the web material 4 is abutted against the flange material 3, a fiber laser welding machine is used, and the beam spot diameter is set to 0.4 mm to 5.2 kW from the laser torch 6. This was performed by irradiating 6 mm of laser light 5. Further, the welding speed was 4 m / min, and the irradiation angle θ of the laser beam 5 on the flange material 3 was 10 °.

  And about Examples 1-15 and Comparative Examples 1-20, the amount of depressions of the surface (surface bead) on the front side of the welded part in an arbitrary cross section perpendicular to the longitudinal direction of the T-shaped shaped steel was measured.

  Here, an example of a method for measuring the amount of depression of the front bead will be described with reference to FIG. The cross section shown in FIG. 8 is a cross section obtained by cutting the welded portion 2 of the laser welded structural steel 1 along a plane perpendicular to the longitudinal direction. As shown in FIG. 8, the position of the surface 2 a of the welded portion 2 is measured from above the surface 4 a of the web member 4 using a laser distance meter 7. In the cross section shown in FIG. 8, the direction parallel to the surface 4a of the web material 4 is taken as the x-axis, and the direction perpendicular to the surface 4a is taken as the y-axis. Further, the position of the surface 4a of the web material 4 (where it is not a thickened portion) is defined as a reference position (y = 0).

  The laser distance meter 7 or the laser welded shape steel 1 is moved in the x-axis direction, and the height (position) of each point on the surface 2 a of the welded portion 2 is measured using the laser distance meter 7. Then, the height (position) of the most depressed portion on the surface 2a is recorded as the amount of depression. The most depressed portion is the position where the absolute value is the largest when the value of y is negative, and is convex downward in the curve formed by the surface 2a in the xy plane when the value of y is positive. This is the position of the inflection point (minimum point).

  In addition, you may measure the amount of depressions using the dial gauge which grind | polished and sharpened the single side | surface of the gauge instead of the laser distance meter 7. FIG. The method for measuring the amount of depressions is not particularly limited.

  Table 2 shows the measurement results of the presence or absence of the thickening step and the amount of depression of the front bead of the weld.

  Next, about Examples 1-15 and Comparative Examples 1-20, the hardness of a weld part and the hardness of a flange material and a web material (base material) are measured, and it shows by weld part hardness / base material hardness. The hardness ratio was calculated.

  Moreover, the fatigue test, the tensile test, and the diagonal crack fracture test were done with respect to the shape steel of Examples 1-15 and Comparative Examples 1-20. The contents of each test are as follows.

[Fatigue test]
FIG. 9 is a schematic diagram of a fatigue test. As shown in FIG. 9, the flange material 3 is fixed to the test machine base 13 with fixing bolts 12 so that the flange material 3 and the test machine base 13 are parallel to each other. And the web material 4 was hold | gripped with the chuck | zipper 11, the tensile load of 10 to 80% of base material strength was applied with respect to the web material 4 4 times / second, and the test was done by complete swing. Table 3 shows the positions at which the section steel fractured in the fatigue test.

[Tensile test]
The tensile test was performed according to JIS G 3353, and the breaking position was measured. Table 3 shows the measurement results.

[Slant crack test]
FIG. 10 is a schematic diagram of an oblique crack test. As shown in FIG. 10A, first, a T-shaped shape steel is slanted between the lower member 15 and the upper member 16 so that both the flange member 3 and the web member 4 are in contact with the lower member 15. Placed on. Then, a load in a direction toward the lower material 15 is applied to the upper material 16, and the flange material 3 is in close contact with the upper material 16 and compressed until the web material 4 is in close contact with the lower material 15 ((b in FIG. 10). )reference). And the presence or absence of the crack of the weld part after a test was measured. Table 3 shows the measurement results.

  In laser welded shape steel, there are two mounting methods: a case where the laser-irradiated side is placed on the upper side and a case where the laser-irradiated side is placed on the lower side. Conceivable. However, the mounting method is not particularly limited because the presence or absence of cracks in the welded portion does not change regardless of which method is used for testing.

  As shown in Table 3, in Comparative Examples 1 to 8 and Comparative Example 12 in which the processing by the masher roll is not performed, a recess that becomes a stress concentration portion is generated in the front bead, and the welded portion is easily broken in the fatigue test. I understand. Moreover, in Comparative Example 9 and Comparative Example 10 in which processing by a masher roll was performed, a recess that was a stress concentrated portion was generated in the front bead, and the weld was broken in the fatigue test. This is because the setting of the conditions for the thickening process by the masher roll was insufficient, and a depression was generated in the front bead. It can be seen that it is important to appropriately perform the thickness increasing process and the joining process so that the front bead is not depressed.

Moreover, it turns out that the comparative examples 11-13 whose carbon equivalent _Ceql is less than 0.07 are easy to fracture | rupture in a weld part in a tensile test irrespective of the presence or absence of the processing by a masher roll.
Furthermore, it turns out that the comparative examples 15-20 with a carbon equivalent _Ceql larger than 0.12 are easy to generate | occur | produce a crack in an oblique crack test, even if it processes with a masher roll. Thus, it was confirmed that the carbon equivalent C _eql needs to be 0.07 or more and 0.12 or less.

  In Comparative Examples 15 to 17 having a hardness ratio exceeding 2.8, cracks occurred in the oblique crack test. From this, it has been confirmed that the hardness ratio needs to be 2.8 or less.

  Further, it can be seen that in Comparative Example 14 in which the hardness ratio is less than 1.2, the welded portion is broken in the fatigue test and also in the tensile test. From this, it was confirmed that the hardness ratio should be 1.2 or more.

As shown in Table 3, the carbon equivalent C _{eql of the} base material is 0.07 or more and 0.12 or less, and the Ti content is 0.01% by mass or more and 0.1% by mass or less. The hardness of the material is not less than 1.2 times and not more than 2.8 times, and the front bead does not have a recess that becomes a stress concentration part, so that the welded part does not break in the tensile test and the welded part in the oblique crack test. It was confirmed that a laser welded shape steel having excellent fatigue life can be obtained without cracking.

  Further, in Example 4 in which the plate thickness of the web material exceeds 6 mm, the protruding amount of the welded portion is larger than in Examples 1 to 3 and 5 to 15 in which the plate thickness of the web material is 6 mm or less. It was confirmed that the thickness of the web material is preferably 6 mm or less.

DESCRIPTION OF SYMBOLS 1 Laser welding shape steel 2 Welding part 3 Flange material 4 Web material 9 Masher roll 10 Slit edge (cut end surface)

Claims (4)

A laser welded shaped steel formed by a web material and a flange material made of a steel plate,
The steel sheet has a carbon equivalent C _eql given by the formula (1) of 0.07 to 0.12, and a Ti content of 0.01% by mass to 0.1% by mass,
The hardness of the welded portion that is a joint portion between the web material and the flange material is 1.2 times or more and 2.8 times or less the hardness of the steel plate,
The surface of the web material irradiated with the laser is the first surface, and the side on which the first surface is located with respect to the web material is the first side,
The surface of the welded portion on the first side is located on the first side with respect to the plane including the first surface of the web material.
  The length of the welded portion protruding from the flange material on the first side is α, the length of the welded portion protruding from the first surface to the first side is γ, and the web material is used as a reference. The length of the welded portion protruding from the flange material on the second side opposite to the first side is β, the second side from the second surface opposite to the first surface of the web material The length of the protruding welded portion is represented by α, β, γ, and δ, and the length of the protruding welded portion is 1 mm or less. The laser welded shape steel described.   The laser welded section steel according to claim 1 or 2, wherein the web material has a plate thickness of 6 mm or less. A method of manufacturing a laser welded shape steel formed of a web material and a flange material made of a steel plate,
A thickening step of increasing the thickness of the end portion of the web material so that the thickness of the end portion exceeds 100% with respect to the thickness of the central portion in the width direction of the web material;
After the thickness increasing step, including a joining step of joining the web material and the flange material by laser welding,
The steel sheet has a carbon equivalent C _eql given by the formula (1) of 0.07 to 0.12, and a Ti content of 0.01% by mass to 0.1% by mass,
The hardness of the welded portion that is a joint portion between the web material and the flange material is 1.2 times or more and 2.8 times or less the hardness of the steel plate,
In the joining step, a surface on which the web material is irradiated with a laser is a first surface, a side on which the first surface is located with respect to the web material is a first side, and the welding on the first side is performed. The method of manufacturing a laser-welded section steel, characterized in that laser welding is performed so that all surfaces of the portions are located on the first side with respect to a plane including the first surface of the web material.