JPH11287745A - Method for evaluating junction state of welded part and method for determining weld condition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To evaluate a junction state correctly and quantitatively in a short time by deep drawing a sample at a plurality of points in a breadthwise direction of a steel band and evaluating the junction state from a press depth of a punch when a welded connection part cracks. SOLUTION: A clamping load is applied by a dice 4 and a plate retainer 6 at all times to a sample plate 5 processed and collected by a deep drawing process apparatus. In this state, a punch 3 is raised from below and pressed into a weld junction part 2 which is being confirmed from above. This process is carried out via an equal distance from 50 mm away from an edge part at each end of a steel band for a constant stroke. If the weld junction part 2 cracks, a junction intensity evaluation point is obtained from a state of the crack point and a measured press amount. At this time, the smaller (larger) the press amount of the punch 3 is, the smaller (larger) a weld intensity is and the larger (smaller) the evaluation point is. A junction state of the weld junction part 2 can be correctly quantitatively evaluated in a short time by using the evaluation point.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating a welding condition of a preceding material and a succeeding material in a continuous strip line of a steel strip and a method for determining welding conditions.

[0002]

2. Description of the Related Art In a continuous stripping line of a steel strip, for example, in continuous pickling, a tail of a preceding material and a tip of a following material are first welded and joined together. Thereafter, when the line passing is performed, the welded joint is subjected to tensile force and repeated bending. It is necessary for this welded joint to have a welded joint strength that can withstand tensile force and repeated bending.
If the welding joint strength is insufficient, the joint may be broken in the middle of the line passing, and there is a risk that productivity will be greatly impaired.

[0003] Therefore, in order to prevent breakage at the time of line passing due to insufficient strength of the welded joint, optimal welding conditions, especially at the time of continuous steel sheet passing line, especially at the time of new steel type sheet passing, are to be prevented.
Specifically, it is indispensable to grasp the welding current and the welding electrode moving speed with respect to the thickness of the steel type. In addition, even when the welded plate breaks in the continuous steel strip, it is necessary to quantitatively evaluate the welded joint state in the shortest possible time in order to review the welding conditions.

[0004] In the conventional method of evaluating the state of welding and joining, a sample was cut out from a continuous threading line, polished, subjected to hardness examination and metallurgical examination of the structure near the welded joint by a microscope. Further, a test piece for a repeated bending test was cut out from the sample, and a welded joint state evaluation test was performed. FIG. 1 is a diagram showing a schematic configuration of equipment used for a conventional welded joint state evaluation test. 1 is a test piece, 2 is a welded joint, 3 is a punch, and 4 is a die. As shown in the figure, a test piece 1 was diced with a punch 3 (R: 50 mm).
, And a 180 ° bending test was performed repeatedly to confirm the number of bendings before cracking occurred.

[0005]

However, the conventional method has the following problems. After polishing the specimen,
The metallurgical examination of the structure near the welded joint by hardness examination and microscopy, and the repeated bending test are repeated until cracks occur. , The number of tests is also limited. In addition, since the R of the punch 3 in the conventional repeated bending test is large, the entire material of the sample is evaluated, and the evaluation of the welded joint cannot be accurately performed. For example, when performing a repeated bending test of a welded portion of ordinary steel and special steel, if the test piece is pushed in from above with a punch, the soft ordinary steel portion will bend, and the welded portion will not be bent, and the welded joint will not be bent. In some cases, strength evaluation cannot be performed accurately.

Accordingly, the present invention has been made in view of the above-mentioned problems, and it is not necessary to conduct a metallurgical investigation, and even if the steel type to be joined is a different steel type, the strength of the welded portion can be continuously passed without breaking the plate. Provides a way to reliably evaluate
It is an object of the present invention to provide a method for quickly determining welding conditions on a machine side of a welding machine when a new steel type is passed.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and a first aspect of the present invention is to provide a continuous strip passing line for a steel strip, in which a weld between a preceding material and a following material is welded. When evaluating the joining condition, the sample of the welded joint was deep-drawn to a certain depth in the width direction of the steel strip. An object of the present invention is to provide a method for evaluating a welding state of a welded portion for evaluating a bonding state.

According to a second aspect of the present invention, a target range of a welding joint state point for each steel type and sheet thickness to be passed is determined in advance from the data obtained by the evaluation method according to the first embodiment, and the welding joint state is determined. An object of the present invention is to provide a welding condition determining method for determining a welding current and an electrode moving speed so as to be within a target range.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A sample in the width direction of a weld is taken from a continuous strip line of a steel strip. FIG. 2 is a diagram showing a schematic configuration of the deep drawing apparatus according to the present invention, wherein 5 is a sample plate, 6 is a plate holder, and 4 is a die 3 is a punch. As shown in the drawing, a deep drawing test is performed on a sample collected using a deep drawing apparatus. As a test method, the punch 3 (R: 35 mm) was lifted from the lower side while a tightening load was constantly applied to the sample plate by the die 4 and the plate retainer 6, and a constant stroke (stroke amount was set at the time of passing the plate). (Depending on steel type and plate thickness with different tensile strength). The punch 3 is pushed in while checking the welded portion from the upper side, and if a crack occurs in the welded joint, the amount of push-in at that time is measured. At this time, it is necessary to fix the sample plate and to accurately push the sample plate around the welded joint. This operation is performed at several places in the width direction of the sample (normally, the test is performed at about five places with an M width material). FIG. 3 is a schematic view of a deep drawing position of a sample. The deep drawing test of the sample is performed at equal intervals from 50 mm from both ends of the steel strip. Deep drawing of the sample plate is performed up to a certain stroke. When a crack occurs in the welded portion, the stroke height at that time is read. The state of the cracked portion of the sample plate where the crack occurred and the amount of punching in at the time of the occurrence of the crack are measured, and the evaluation point of the bonding strength is obtained by the following equation. Evaluation point = (1 / X _WS + 1 / X _WQ + 1 / X _c + 1 / X _DQ +
1 / X _DS ) * 100 (X: punching amount at each location) FIG. 4 shows the state of cracks in the welded part after deep drawing, and the state of cracks is constant as shown in the figure. In the case of no cracking or cracking of the base material even if the stroke is pushed, the reciprocal (1 / X) of the pushing amount at the position is set to 0. In addition, the mixture of the base material crack and the weld crack is allowed, the weld line crack is determined to be defective, and the indentation amount at that time is used.

[0010] That is, the smaller the punching amount when a crack occurs in the welded sample, the smaller the welding strength of the welded portion and the higher the evaluation point. Conversely, the greater the punch indentation amount, the greater the welding strength and the smaller the evaluation point.
Using this evaluation point, the joining state of the welded portion can be quantitatively evaluated. In addition, in this method, even in the case of welding between different types of steel as described above, a punch can be pushed in while applying a load to both ends of the sample plate, so that a test aimed at the weld joint can be reliably performed, and the evaluation point calculation method Therefore, the evaluation of the welded joint can be performed more reliably than the conventional repeated bending test. The deep drawing test according to the present invention takes about 5 minutes per one place.

Further, in the method for determining welding conditions according to the next invention, the above-described deep drawing test is performed in advance for each steel type and plate thickness having different plate tensions to calculate an evaluation point, and the past plate passing results are calculated. In this method, a target range of an evaluation point that does not cause plate breakage is determined, and the welding voltage and the electrode moving speed of the welding machine are adjusted within the target range. In order to determine the target range of the evaluation point from the past threading performance, it is possible to use the result of the conventional repeated bending test. FIG. 5 shows the relationship between the welding state evaluation point and the number of times of repeated bending. From this relationship curve, the conventional number of times of repeated bending without breaking is equal to or higher than the reference value, and by determining the target range below the corresponding welding state evaluation point, it is possible to determine the range in which the plate does not break during passing. As another method, a deep drawing test is performed on a plurality of passed welded samples, and the welding state evaluation points are classified and arranged by steel type and sheet thickness, and the target range of welding state evaluation points that do not cause sheet fracture is determined. You can decide. To adjust the welding conditions to the target range, set the welding current and electrode moving speed of the welding machine to constant conditions, weld the corresponding preceding and succeeding materials, and each time the deep drawing prepared on the welding machine side It is possible to calculate the welding state evaluation point with a processing test machine, change the welding current or the electrode moving speed so that the evaluation point falls within the target range, and repeatedly perform welding.

[0012]

EXAMPLE A tail portion of a preceding material and a tip portion of a succeeding material were welded and joined by a flash butt welding machine at the entry side of the rolling equipment line, and the welded joint state was evaluated by the method of the present invention. FIG. 6 shows the relationship between the welding state evaluation points of the steel types carried out on the thick material (sheet thickness 6.0 mm). Steel grade is S35
C, S55C, and SUP6 represent respective welding state evaluation points. As can be seen from the figure, SUP6 has a higher welding state evaluation point than S35C and S55C, has a lower joint strength at the welded portion, and has poor weldability.

FIG. 7 shows the relationship between the welding conditions in SUP6 and the welding state evaluation points. The welding current and the electrode moving speed of flash butt welding are selected as welding conditions.
The welding current is data at low current, medium current, and high current, and is data at high, medium, and low electrode moving speeds, respectively. From the figure, when the welding current is low, the welding state evaluation point increases when the electrode moving speed increases, and is equal to or lower than the target value (X). However, when the welding current is high, the welding state evaluation is performed regardless of the electrode moving speed. Points are target values (X)
As described below, the joining strength of the welded portion is ensured, and the weldability is improved.

[0014]

According to the present invention, when the method of the present invention is used to evaluate the joining strength of a welded portion, the evaluation can be performed in a shorter time, more accurately, and quantitatively than when the conventional method is used. Therefore, optimum welding conditions can be found and set. As a result, it is possible to prevent a breakage accident of the welded joint during operation in the continuous line, and to prevent a decrease in productivity due to line stoppage and an increase in cost required for re-welding.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of equipment used for a conventional weld strength evaluation test.

FIG. 2 is a diagram showing a schematic configuration of a deep drawing apparatus of the present invention.

FIG. 3 is a schematic view of a deep drawing processing position of a sample plate.

FIG. 4 is a diagram showing the state of cracks in a sample plate after deep drawing is performed.

FIG. 5 is a diagram showing a relationship between a welding state evaluation point and the number of times of repeated bending.

FIG. 6 is a diagram showing the relationship between steel types and welding state evaluation points.

FIG. 7 is a diagram showing a relationship between welding conditions and welding state evaluation points.

[Explanation of symbols]

 Reference Signs List 1 test piece 2 welded joint 3 punch 4 die 5 sample plate 6 plate holder

Claims (2)

[Claims] In a continuous strip passing line of a steel strip, a sample of a welded joint is deep-drawn to a certain depth in a width direction of a steel strip when evaluating a welded state of a preceding material and a following material. A method for evaluating the joint state of a welded part, which performs processing and evaluates the jointed state of the welded part based on the depth of the punch when a crack occurs in the welded joint. 2. A method according to claim 1, wherein a target range of a welded joint state point for each steel type and sheet thickness to be passed is determined in advance, and the welded joint state is set within the target range. A welding condition determining method for determining a welding current and an electrode moving speed.