JP6864266B2 - Heat-affected zone width estimation method for welded parts and welding method using this estimation method - Google Patents

Description

The present invention relates to a method for estimating the width of a heat-affected zone of a welded portion and a welding method using this estimation method.

In the field of welding metal members, creep property is one of the mechanical properties for evaluating a welded joint of a metal member, particularly a heat-resistant steel used in a high temperature environment such as a boiler.

Creep refers to a phenomenon in which a member is deformed over time when a constant load is applied, and creep characteristics refer to creep properties peculiar to a member. Usually, it is preferable that the amount of deformation due to creep is small even after a lapse of time, and it can be said that the smaller the amount of deformation due to creep, the higher the resistance to creep, that is, the creep resistance property, and the better the mechanical property.

By the way, it is known that the creep characteristic of a welded joint of a metal member has a high correlation with the width of the heat-affected zone around the welded portion of the metal member, that is, the width of the heat-affected zone (HAZ width: Thickness of Heat Affected Zone). It is expected that the creep resistance will be improved by narrowing the width of the heat-affected zone.

Therefore, various techniques have been developed for improving the mechanical properties of welded joints of metal members by controlling the width of the heat-affected zone to a predetermined width or less. Further, a technique for reducing the width of the heat-affected zone by using laser welding has also been proposed (Patent Document 1).

Japanese Unexamined Patent Publication No. 2002-3984

In order to narrow the width of the heat-affected zone, it is effective to reduce the welding heat input during welding.
However, for example, in laser welding, unlike arc welding, welding work is often performed with one layer and one pass, so if the welding heat input is made smaller than necessary, welding defects due to undissolved residue may occur on the back surface side. is there. Further, in laser arc hybrid welding in which laser welding and arc welding are combined, it is necessary to appropriately set two parameters, heat input by laser welding and heat input by arc welding, so that welding heat input becomes small.

In order to obtain the optimum welding heat input in these laser welding and laser arc hybrid welding, the welding conditions of laser welding and arc welding are variously changed according to the plate thickness and composition of the metal member, and the joint cutting-cross section is changed each time. The width of the heat-affected zone must be measured and confirmed through the steps of polishing, corrosion, and observation, and there is a problem that it takes a lot of time and effort to obtain a good heat-affected zone width.

The present invention has been made in view of such a problem, and an object of the present invention is a method for estimating the heat-affected zone width of a welded portion, which can easily estimate the width of the heat-affected zone in the welded portion, and an estimation method thereof. The purpose is to provide the welding method used.

In order to achieve the above object, the heat-affected portion width estimation method of the welded portion of the first aspect of the present invention includes a bead width measuring step of measuring the bead widths of the front surface and the back surface of the welded portion of the metal member, and the bead width measuring step. The shape coefficient calculation step of calculating the shape coefficient based on the bead widths of the front and back surfaces measured in the width measurement step and the plate thickness of the metal member, and the shape coefficient calculated in the shape coefficient calculation step are within a predetermined range. The feature is that the process comprises a heat-affected portion width estimation step of estimating the width of the heat-affected portion at the center of the plate thickness of the metal member based on the shape coefficient.

In the heat-affected zone width estimation method of the welded zone of the second aspect, in the heat-affected zone width estimation step, the shape coefficient in the predetermined range and the welded portion of the metal member obtained by measuring in the predetermined range are obtained. The width of the heat-affected zone is estimated from a linear approximation formula obtained in advance based on the width of the heat-affected zone at the center of the plate thickness.

The heat-affected zone width estimation method for the welded portion of the third aspect is characterized in that the predetermined range of the shape coefficient is in the range of 0.05 to 0.15, which is a value at which the welding conditions are appropriate.
In the heat-affected zone width estimation method of the welded portion of the fourth aspect, the metal member is characterized by being heat-resistant steel.

The welding method of the first aspect of the present invention is a welding method in which metal members are welded and joined by laser welding, the heat-affected zone required width setting step for setting the required width of the heat-affected zone, and the above-mentioned first. In the method for estimating the width of the welded portion according to any one of the first to fourth aspects, the heat-affected zone width estimation step is used in reverse, and the shape coefficient is such that the width of the heat-affected zone becomes the required width. A shape coefficient target value setting step for setting a target value, and a welding condition setting step for setting welding conditions for laser welding so that each bead width for calculating the shape coefficient satisfies the target value. It is characterized by being composed of.

The welding method of the second aspect of the present invention is a welding method in which metal members are welded and joined by laser arc hybrid welding, which is a combination of arc welding and laser welding, and a required width of the heat-affected portion is set. In the heat-affected portion required width setting step and the method for estimating the thermal-affected portion width of the welded portion according to any one of the first to fourth aspects, the thermal-affected portion width estimation step is used in reverse, and the width of the thermal-affected portion is increased. The shape coefficient target value setting step for setting the target value of the shape coefficient so as to have the required width, and the arc welding so that each bead width for calculating the shape coefficient satisfies the target value. It is characterized by comprising a welding condition setting step of setting the welding condition of the laser welding.

According to the heat-affected zone width estimation method of the welded portion of the present invention, when the shape coefficient calculated based on the bead widths of the front surface and the back surface of the welded portion of the metal member and the plate thickness of the metal member is within a predetermined range. Based on a certain correlation between the shape coefficient and the width of the heat-affected zone, the width of the heat-affected zone, which has a high correlation with the creep characteristics of the welded joint of the metal member, can be easily estimated.

Then, according to the welding method of the present invention, the method for estimating the width of the heat-affected portion of the welded portion is used for welding and joining metal members by laser welding or laser arc hybrid welding, and the shape coefficient in which the width of the heat-affected portion is the required width. Since the welding conditions of laser welding and laser arc hybrid welding are set so that each bead width for which the shape coefficient is calculated satisfies the target value, the creep resistance is improved and stable. Welding quality welded joints can be realized.

It is a figure which shows the bead width of the front surface side and the bead width of the back surface side, the plate thickness, and the HAZ width at the center of the plate thickness of the weld metal. It is a figure which shows the relationship between the shape coefficient and HAZ width. FIG. 2 is a diagram in which an approximate straight line is also shown.

Hereinafter, the method for estimating the heat-affected zone width of the welded portion according to the present invention will be described with reference to the drawings.
The method for estimating the width of a heat-affected portion of a welded portion according to the present invention is to perform welding capable of forming weld metal from the front surface to the back surface of the metal member in butt welding joint between metal members, particularly welding using a laser beam. By performing laser welding that can sufficiently form weld metal from the front surface to the back surface of the metal member, and arc welding that welds and joins by arc discharge with the laser welding, it is even more sufficient from the front surface to the back surface of the metal member. It is applied to laser arc hybrid welding that can form weld metal.

Here, the technical contents and construction methods of laser welding and laser arc hybrid welding are known, and the description thereof will be omitted here.
When welding metal members together, heat-affected zone (HAZ) is generated around the welded part of the metal member due to the heat during welding, and the width of this heat-affected zone, that is, the width of the heat-affected zone (hereinafter referred to as the width of the heat-affected zone). As described above, the HAZ width (Thickness of Heat Affected Zone) is known to have a high correlation with the creep characteristics of welded joints of metal members, and the narrower the HAZ width, the better the creep resistance characteristics. it is conceivable that.

However, as in the conventional case, welding is performed by changing various welding conditions, and the welding conditions for obtaining an appropriate HAZ width can be determined by repeating the steps of joint cutting-cross-section polishing-corrosion-observation. As you can see, it takes a lot of time and effort, which is not preferable.

Therefore, the inventors have developed a method for estimating the HAZ width without cutting the welded joint.
Hereinafter, the method for estimating the heat-affected zone width of the welded portion according to the present invention will be described in detail.
According to the research by the inventors, the width of each weld metal appearing on the front surface and the back surface of the welded joint (hereinafter referred to as the front surface side bead width, the back surface side bead width, or simply each bead width) and the plate of the metal member. It was found that when the shape coefficient calculated from the thickness is within a predetermined range, there is a certain correlation between the shape coefficient and the HAZ width at the central portion of the plate thickness.

As shown in FIG. 1, the front surface side bead width of the weld metal appearing on the front surface of the welded joint is W1, the back surface side bead width of the weld metal appearing on the back surface is W2, and the plate thickness of the metal member is set. Expressed by t, the shape coefficient F is defined by the following equation (1).
F = (W1-W2) / 2 / t ... (1)

Further, in FIG. 1, W _HAZ indicates the HAZ width at the central portion of the plate thickness.
With reference to FIG. 2, the plate thickness t made of a metal member is 7 mm (◆ mark and ◇ mark: 7 t), 9 mm (black square mark: 9 t), 12 mm (black triangle mark: 12 t), 16 mm (● mark: 16 t). Laser arc hybrid welding is performed on each of the test pieces in the above form with various welding conditions, and the bead widths W1 and W2 on the front and back surfaces of the joined welded joint are measured and the shape coefficient F is obtained from the above equation (1). , The joined welded joint is cut and the HAZ width W _HAZ is measured and obtained, and the relationship between these shape coefficients F (horizontal axis) and the HAZ width W _{HAZ (vertical axis) obtained in this way is shown.} .. As the metal member, for example, heat-resistant steel (for example, 9Cr1Mo steel) that requires high creep resistance is selected, but the metal member is not limited to heat-resistant steel.

Table 1 shows the measured values of the plate thickness t at each point in FIG. 2, the bead widths W1 and W2, the shape coefficient F, and the HAZ width W _HAZ.

In FIG. 2, it was confirmed that there is a certain correlation between the shape coefficient F and the HAZ width W _HAZ , particularly in the range where the shape coefficient F has a value of 0.05 to 0.15 (predetermined range). .. That is, in FIG. 2, in the range where the shape coefficient F is a value of 0.05 to 0.15, there are four points having a plate thickness t of 7 mm (marked with ◆), points of 9 mm (black square mark), and 12 mm (marked with a black square). There are 3 points (black triangle mark) and 1 point each of 16 mm (● mark), but these points are lined up in a line almost linearly, and the shape coefficient F and HAZ width W _HAZ are abbreviated. It can be seen that it shows a proportional relationship.

On the other hand, in the figure, in the region where the shape coefficient F is less than 0.05 or more than 0.15, the shape coefficient F is a value between each point as shown by the point where the plate thickness t is 7 mm (marked with ◇). It can be seen that there is no substantially proportional relationship as seen in the range of 0.05 to 0.15.

Further, in FIG. 2, one point out of four points having a plate thickness t in the range of a shape coefficient F of 0.05 to 0.15 and a plate thickness t of 7 mm (marked with ◆), a point of 9 mm (black square mark), and 12 mm. Of the 6 points (black triangle mark) and 16 mm (● mark), and the plate thickness t in the region where the shape coefficient F is less than 0.05 or exceeds 0.15 is 7 mm (◇ mark). The cut surface of the welded joint is also shown for the three points. According to these figures, when the shape coefficient F is in the range of 0.05 to 0.15, the welding conditions are appropriate and the degree of penetration of the weld metal in the welded joint is good, while the shape coefficient F is a value of 0. In the region of less than .05 or more than 0.15, the welding conditions tend to be inappropriate, and it can be seen that the degree of penetration of the weld metal in the welded joint is uneven.

In FIG. 3, an approximate straight line obtained by using the least squares method or the like based on the above seven points in which the shape coefficient F is in the range of 0.05 to 0.15 and shows a substantially proportional relationship in FIG. 2 is also shown. ing.
The general formula of the linear approximation formula of the approximate straight line obtained in this way is shown by the following equation (2).

W _HAZ = a ・ F + b ・ ・ ・ (2)
Here, a is the slope of the approximate straight line, and b is the value of the HAZ width W _HAZ when the shape coefficient F is assumed to be 0. Based on the above 7 points in which the shape coefficient F is in the range of 0.05 to 0.15, for example, a is a value of 24.874 and b is a value of −0.0914. However, by increasing the number of test pieces and increasing the number of _{samples for obtaining the shape coefficient F and the HAZ width W HAZ} , it is possible to obtain more appropriate a and b, and it is possible to improve the accuracy of the approximate straight line. ..

In this way, in welding in which weld metal can be formed from the front surface to the back surface of the metal member in the butt welding joint between the metal members, particularly in laser welding and laser arc hybrid welding, the shape coefficient F has a value of 0.05 to 0.15. In the range, it is possible to obtain a linear approximation formula based on the fact that there is a substantially proportional relationship between the shape coefficient F and the HAZ width W _{HAZ, and the shape coefficient F has a value of 0.05 to 0 from this linear approximation formula. The HAZ width W HAZ} at the central portion of the plate thickness corresponding to the range of .15 can be easily estimated.

Specifically, as an estimation method, the plate thickness t of the metal member is measured, and the front side bead width W1 and the back surface side bead width W2 of the weld metal are measured (bead width measurement step), and these plate thickness t are used. The bead widths W1 and W2 are substituted into the above equation (1) to obtain the shape coefficient F (shape coefficient calculation step), and when the obtained shape coefficient is in the range of the value 0.05 to 0.15, the above equation. _{The HAZ width W HAZ} corresponding to the shape coefficient F is estimated from the linear approximation formula of (2) (heat-affected zone width estimation step).

_{In this way, the HAZ width W HAZ} corresponding to the shape coefficient in the range of values 0.05 to 0.15 is estimated in the range of values 1.1 to 3.6, for example.
_{Then, it can be said that the range of the HAZ width W HAZ} consisting of the estimated values 1.1 to 3.6, for example, is a sufficiently narrow dimensional range for improving the creep resistance characteristics.

From this, when performing laser welding or laser arc hybrid welding, for example, when it is desired _{to obtain a desired HAZ width W HAZ} having a value of 1.1 to 3.6, for example, the linear approximation formula of the above formula (2) can be used. By back-calculating, the target value of the corresponding shape coefficient F can be obtained, and the welding conditions in laser welding and the welding conditions for laser welding and arc welding in laser arc hybrid welding are set so that the shape coefficient F becomes this target value. It should be set properly.

Specifically, the desired HAZ width W _HAZ (required width) is first set (heat-affected zone required width setting step), and the linear approximation formula of the above formula (2) is back-calculated (reversely used) to obtain the desired HAZ width. HAZ width W _{Set the target value of the shape coefficient F corresponding to HAZ} (shape coefficient target value setting step), measure the plate thickness t of the metal member, and (W1-W2) / 2 of the above formula (1). Welding conditions for laser welding and laser arc hybrid welding are appropriately set so that each bead width W1 and W2 satisfy the target value of the shape coefficient F at / t (welding condition setting step).

In this way, for example, in laser welding and laser arc hybrid welding, the linear approximation equation of the above equation (2) is used in reverse, and the shape coefficient F is a value of 0.05 to 0.15 corresponding to the _{desired HAZ width W HAZ.} By setting appropriate welding conditions so as to be the target value in the range of, the HAZ width W _HAZ can always be kept in a _{sufficiently narrow dimensional range as the desired HAZ width W HAZ} , and the creep resistance is improved and stable. It is possible to realize a welded joint of excellent welding quality.

The description of the embodiment according to the present invention is completed above, but the embodiment is not limited to the above, and various modifications can be made without departing from the spirit of the invention.
For example, in the above embodiment, the case where the method for estimating the width of the heat-affected portion of the welded portion according to the present invention is applied to, for example, laser welding or laser arc hybrid welding has been described, but welded metal can be formed from the front surface to the back surface of the metal member. It is also possible to apply it to arc welding such as MIG welding and TIG welding if it is a good welding.

Further, in the above embodiment, the case where the heat-affected zone width estimation method of the welded portion according to the present invention is applied to the butt welding joint between metal members has been described, but the weld metal can be formed from the front surface to the back surface of the metal members. If it is welding, it is not limited to butt welding joints.

F Shape coefficient W1 Front side bead width W2 Back side bead width W _HAZ HAZ width (heat-affected zone width)
t Plate thickness

Claims (6)

A bead width measurement process for measuring the width of each bead on the front and back surfaces of a welded portion of a metal member,
A shape coefficient calculation step of calculating a shape coefficient based on the bead widths of the front and back surfaces measured in the bead width measurement step and the plate thickness of the metal member, and
When the shape coefficient calculated in the shape coefficient calculation step is within a predetermined range, the heat-affected zone width estimation step of estimating the width of the heat-affected zone at the center of the plate thickness of the metal member based on the shape coefficient
A method for estimating the width of a heat-affected zone of a welded zone. In the heat-affected zone width estimation step, it is obtained in advance based on the shape coefficient in the predetermined range and the width of the heat-affected zone at the center of the plate thickness in the welded portion of the metal member obtained by measuring in the predetermined range. The heat-affected zone width estimation method for a welded zone according to claim 1, wherein the width of the heat-affected zone is estimated from the linear approximation formula. The heat-affected zone width estimation method for a welded portion according to claim 1 or 2, wherein the predetermined range of the shape coefficient is a value in the range of 0.05 to 0.15 for which the welding conditions are appropriate. The method for estimating the heat-affected zone width of a welded portion according to any one of claims 1 to 3, wherein the metal member is heat-resistant steel. It is a welding method in which metal members are welded together by laser welding.
The heat-affected zone required width setting step for setting the heat-affected zone required width, and
The heat-affected zone width estimation step of the welded zone according to any one of claims 1 to 4 is used in reverse, and the width of the heat-affected zone becomes the required width. The shape coefficient target value setting process for setting the shape coefficient target value and the shape coefficient target value setting process
A welding condition setting step of setting welding conditions for laser welding so that each bead width for calculating the shape coefficient satisfies the target value.
Welding method consisting of. It is a welding method in which metal members are welded together by laser arc hybrid welding, which is a combination of arc welding and laser welding.
The heat-affected zone required width setting step for setting the heat-affected zone required width, and
The heat-affected zone width estimation step of the welded zone according to any one of claims 1 to 4 is used in reverse, and the width of the heat-affected zone becomes the required width. The shape coefficient target value setting process for setting the shape coefficient target value and the shape coefficient target value setting process
A welding condition setting step of setting welding conditions for arc welding and laser welding so that each bead width for calculating the shape coefficient satisfies the target value.
Welding method consisting of.

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