JP7587341B2 - Welding structure and welding method - Google Patents

Description

The present invention relates to a welded structure and a welding method.

A welding method that can reduce manufacturing costs has been proposed (see Patent Document 1). In this welding method, a laser beam is focused and irradiated onto the butted portion between the first and second members to melt the welding metal material while laser welding the first and second members. This welding method is characterized in that no groove preparation is performed on the butted portion between the first and second members, and the focused diameter of the laser beam is set to φ0.2 mm or less.

JP 2011-161506 A

In the welding method described in Patent Document 1, the focused diameter of the laser light is reduced, making it possible to suppress the occurrence of distortion of the welded product due to welding. However, in this welding method, the molten components of the welding metal material are not stirred sufficiently in the depth direction of the weld. This causes problems such as cracks in the weld and a decrease in the strength of the weld.

The present invention has been made in consideration of the problems associated with the conventional technology. The present invention aims to provide a welded structure and welding method that can suppress or prevent the occurrence of distortion caused by welding in a welded structure, and can suppress or prevent the occurrence of cracks in the welded portion and the weakening of the welded portion.

The inventors conducted extensive research to achieve the above objective. As a result, they discovered that the above objective could be achieved by specifying the width of the weld and the composition of the weld, and thus completed the present invention.

The present invention provides a welded structure and welding method that can suppress or prevent the occurrence of distortion caused by welding in a welded structure, as well as suppress or prevent the occurrence of cracks in the welded portion and the weakening of the welded portion.

FIG. 1 is a schematic diagram of a welding structure for explaining a welding structure and a welding method. FIG. 2 is a cross-sectional view taken along line aa shown in FIG. 1 before welding. FIG. 3 is a view seen from the direction of the arrow b shown in FIG. FIG. 4 is a cross-sectional view taken along line dd shown in FIG. FIG. 5 is a cross-sectional view taken along line aa shown in FIG. 1 after welding. FIG. 6 is an enlarged cross-sectional view showing a main part of the welded structure according to the embodiment, which corresponds to FIGS. 2 and 5. In FIG.

The welding structure and welding method according to one embodiment of the present invention will be described in detail below. First, the welding structure according to one embodiment of the present invention will be described in detail. Next, the welding method according to one embodiment of the present invention will be described in detail. After that, an example of the welding structure and welding method will be described in detail with reference to the drawings.

<1> Welded structure The welded structure of this embodiment includes a cast iron member made of cast iron, a steel member made of carbon steel or alloy steel, and a welded portion joining the cast iron member and the steel member. The welded portion has a width direction size of 3.0 mm or less. The welded portion also contains nickel and silicon. Furthermore, the welded portion has a silicon concentration of 0.9 mass% or more at any position on the center line of the welded portion.

The cast iron in the cast iron member is not particularly limited, but examples include FCD450, FCD600, FCD700, and FCD800 as specified in the Japanese Industrial Standards. Although not particularly limited, it is preferable to use FCD450.

The carbon steel or alloy steel in the steel member is not particularly limited as long as it has a lower silicon content than cast iron, but examples include SCr417H, SCr420H, SCM420H, SCM418H, and SNCM420H, as specified in the Japanese Industrial Standards. Although not particularly limited, it is preferable to use SCM420H.

The "width direction of the weld" means the direction perpendicular to the "length direction of the weld" and the "depth direction of the weld".

The "widthwise size of the weld" refers to the widthwise length of the weld at the end surface formed by the end surface of the cast iron member on the laser beam irradiation side and the end surface of the steel member on the laser beam irradiation side. For example, X in FIG. 5 indicates the widthwise size of the weld. When considering such a surface, fine irregularities on the surface of the weld may be ignored. The end surface formed by the end surface of the cast iron member on the laser beam irradiation side and the end surface of the steel member on the laser beam irradiation side is sometimes referred to as the "surface of the welded structure."

Furthermore, "center line of the weld" means a line parallel to the depth direction of the weld that halves the length of a bisector of the weld that halves the distance from the surface of the welded structure to the deepest position of the weld.

The silicon concentration can be measured, for example, by an X-ray fluorescence analyzer or an electron probe microanalyzer (EPMA). The nickel concentration and carbon concentration, which will be described later, can also be measured in the same manner as above.

Although not particularly limited, it is preferable to measure the silicon concentration and nickel concentration with an X-ray fluorescence analyzer (measurement conditions are, for example, voltage: 50 kV, current: 200 μA, and live time: 100 sec). Also, although not particularly limited, it is preferable to measure the carbon concentration with an electron probe microanalyzer (EPMA) (measurement conditions are, for example, voltage: 10 kV, current: 70 nA, and spot analysis area: φ0.05 to 0.5 μm).

As an example of an X-ray fluorescence analyzer, a micro-area X-ray fluorescence analyzer (M4 TRADO, manufactured by Bruker) can be used. As an example of an electron probe microanalyzer (EPMA), an electron probe microanalyzer (EPMA) (EPMA-1600, manufactured by Shimadzu Corporation) can be used.

As described above, the welded structure of this embodiment has a cast iron member made of cast iron, a steel member made of carbon steel or alloy steel, and a specified weld that joins the cast iron member and the steel member. The specified weld has a width dimension of 3.0 mm or less, contains nickel and silicon, and has a silicon concentration of 0.9 mass% or more at any location on the center line of the weld. Therefore, it is possible to suppress or prevent the occurrence of distortion caused by welding in the welded structure, and to suppress or prevent the occurrence of cracks in the weld and the weakening of the weld.

If the width of the weld exceeds 3.0 mm, distortion due to welding of the welded structure is likely to occur. From the viewpoint of suppressing or preventing the occurrence of distortion due to welding of the welded structure, the smaller the width of the weld, the better. Although not particularly limited, the width of the weld is preferably 2.0 mm or less, more preferably 1.0 mm or less, and even more preferably 0.5 mm or less.

On the other hand, as long as it is possible to suppress or prevent the occurrence of cracks in the welded portion or the weakening of the welded portion, there are no particular limitations, but the width of the welded portion is preferably 0.1 mm or more, more preferably 0.2 mm or more, and even more preferably 0.3 mm or more.

The lower limit of the width of the weld can be set appropriately according to the width of the weld, which is set according to the required performance, but is not limited to this. The lower limit of the width of the weld can be set appropriately according to the distance from the butt to the position where the fiber laser beam is irradiated (welding point offset amount) when the fiber laser beam is irradiated to a position shifted from the butt to the cast iron member side in a welding method described in detail later. Although not particularly limited, when the width of the weld is set to 0.1 mm, it is preferable that the distance from the butt to the position where the fiber laser beam is irradiated (welding point offset amount) is 50 μm or less.

In addition, if nickel and silicon are not included, cracks are more likely to occur in the welds and the strength of the welds will decrease.

Furthermore, if the silicon concentration at any point on the center line of the weld is less than 0.9 mass%, cracks are likely to occur in the weld and the strength of the weld is likely to decrease. From the viewpoint of suppressing or preventing cracks from occurring in the weld and the strength of the weld, the higher the silicon concentration at any point on the center line of the weld, the more preferable it is. Although not particularly limited, it is preferable that the silicon concentration at any point on the center line of the weld is 1.1 mass% or more.

On the other hand, as long as it is possible to suppress or prevent the occurrence of cracks in the welded portion or the weakening of the welded portion, there are no particular limitations, but the silicon concentration at any point on the center line of the welded portion is preferably 4.0 mass% or less, more preferably 3.0 mass% or less, and even more preferably 2.0 mass% or less.

The upper limit of the silicon concentration at any point on the center line of the weld can be set appropriately depending on, for example, the cast iron member used, but is not limited to this. The upper limit of the silicon concentration at any point on the center line of the weld can be set appropriately depending on, for example, the distance from the butt joint to the position where the fiber laser beam is irradiated (welding point offset amount) when the fiber laser beam is irradiated to a position shifted from the butt joint toward the cast iron member in the welding method described in detail later.

At present, we believe that the above-mentioned effects have been achieved for the following reasons:

When welding a cast iron member made of cast iron and a steel member made of carbon steel or alloy steel, a nickel-containing welding metal material is supplied to the butt joint where the cast iron member and the steel member are butted together. Then, by irradiating a fiber laser beam to a position shifted from the butt joint toward the cast iron member while supplying the nickel-containing welding metal material, the width of the welded portion formed can be reduced to 3.0 mm or less. As a result, the occurrence of distortion due to welding in the welded structure can be suppressed or prevented.

When welding a cast iron member made of cast iron and a steel member made of carbon steel or alloy steel, a nickel-containing welding metal material is supplied to the butt joint where the cast iron member and the steel member are butted together. Then, as the nickel-containing welding metal material is supplied, a fiber laser beam is irradiated to a position shifted from the butt joint toward the cast iron member, and silicon components from the cast iron member dissolve into the components of the nickel-containing welding metal material supplied to the butt joint.

In general, the silicon content (mass%) of cast iron components is greater than the silicon content (mass%) of steel components. Therefore, compared to irradiating a fiber beam at a position shifted toward the steel component, irradiating a fiber laser beam at a position shifted toward the cast iron component allows a greater amount of silicon to be effectively dissolved into the components of the nickel-containing welding metal material.

This reduces the viscosity and surface tension of the molten components of the nickel-containing welding metal material, promoting the stirring of the molten components of the nickel-containing welding metal material in the depth direction of the weld to be formed, and the components of the nickel-containing welding metal material are supplied deep into the weld. As a result, the occurrence of cracks in the weld and the weakening of the weld can be suppressed or prevented.

In addition, the viscosity and surface tension of the molten components of the nickel-containing welding metal material are reduced, promoting the stirring of the molten components of the nickel-containing welding metal material in the depth direction of the weld that is formed. This suppresses the formation of martensite, a brittle structure, in the weld and promotes the formation of austenite, a ductile structure. As a result, it can be considered that the occurrence of cracks in the weld and the weakening of the weld are suppressed or prevented. The correlation between the carbon content of the weld and austenite can be predicted from the Schaeffler phase diagram.

However, it goes without saying that even if the above-mentioned effects were achieved for reasons other than those mentioned above, they would still be within the scope of the present invention.

Although not particularly limited, it is preferable that the silicon concentration at any location on the center line of the weld is 1.1 mass% or more, and the average silicon concentration (average silicon concentration) on the center line of the weld is 1.5 mass% or more.

Here, the average silicon concentration on the center line of the weld is calculated by dividing the length of the center line of the weld into 10 or more equal lengths, measuring the silicon concentration of each divided region, and using the measured silicon concentration of each divided region to calculate the average value. When dividing the center line of the weld into equal lengths, there is no particular limit as long as a reasonable average value can be calculated, but it is preferable to divide it into 10 or more, and more preferable to divide it into 15 or more. When dividing the center line of the weld into equal lengths, there is no particular limit as to the upper limit of the number of divisions as long as a reasonable average value can be calculated, but it is preferable to divide it into 30 or less, and more preferable to divide it into 25 or less. In particular, it is preferable to divide it into 20.

As described above, by forming a welded structure having a weld in which the silicon concentration at any location on the center line of the weld is 1.1 mass% or more, and the average silicon concentration (average silicon concentration) on the center line of the weld is 1.5 mass% or more, it is possible to further suppress or prevent the occurrence of cracks in the weld and the weakening of the weld.

Although not particularly limited, the nickel concentration at any location on the center line of the weld is preferably 0.5 mass% or more and 40 mass% or less. From the viewpoint of cost reduction, although not particularly limited, the nickel concentration at any location on the center line of the weld is more preferably 30 mass% or less, even more preferably 20 mass% or less, and particularly preferably 10 mass% or less. When an inexpensive nickel-containing welding metal material with a nickel content of about 10 mass% is used, it is possible to make the maximum nickel concentration 5 mass% or less by controlling the position where the fiber laser beam is irradiated. In addition, it is also possible to make the minimum nickel concentration 0.50 mass%.

In a welding method in which silicon components from a cast iron member are dissolved into the components of a nickel-containing welding metal material, thereby reducing the viscosity and surface tension of the nickel-containing welding metal material, there is an advantage in that the desired effect can be obtained even when using an inexpensive nickel-containing welding metal material with a nickel content of about 10 mass%.

The nickel in the weld is usually derived from the nickel-containing metal material for welding, but is not limited to this and may be derived from cast iron or steel members. The upper limit of the nickel concentration is usually measured at the position where the fiber laser beam is irradiated (the welding point), and the lower limit of the nickel concentration is usually measured at the deepest position of the weld.

As described above, by forming a welded structure having a welded portion in which the nickel concentration at any point on the center line of the welded portion is 0.5 mass% or more and 40 mass% or less, it is possible to suppress or prevent the occurrence of distortion caused by welding in the welded structure, as well as to suppress or prevent the occurrence of cracks in the welded portion and the weakening of the welded portion.

Furthermore, although not particularly limited, when the weld is divided into divided regions that divide the length of the center line of the weld into 10 or more equal lengths, it is preferable that the nickel concentration ratio of the divided region with the minimum nickel concentration to the divided region with the maximum nickel concentration on the center line is 0.1 or more.

As described above, when the length of the center line of the weld is divided into 10 or more equal lengths, by forming a joint structure having a weld in which the nickel concentration ratio of the divided area with the minimum nickel concentration to the divided area with the maximum nickel concentration on the center line is 0.1 or more, it is possible to further suppress or prevent the occurrence of cracks in the weld and the weakening of the weld.

In addition, the nickel concentration ratio of the area with the minimum nickel concentration to the area with the maximum nickel concentration is an indicator that the nickel components derived from the nickel-containing welding metal material are supplied deep into the weld, and local concentration is suppressed. This shows that the nickel-containing welding metal material is being used effectively.

The upper limit of the nickel concentration ratio of the divided area of the minimum nickel concentration to the divided area of the maximum nickel concentration is theoretically 1 when the maximum nickel concentration and the minimum nickel concentration are the same. Furthermore, the maximum nickel concentration is usually measured at the position where the fiber laser beam is irradiated (the welding point), and the minimum nickel concentration is usually measured at the deepest position of the weld.

Although not particularly limited, when the weld is divided into divided regions such that the length of the center line of the weld is divided into 10 or more equal lengths, the carbon concentration of each divided region is measured, and the average value (average carbon concentration) calculated using the measured carbon concentrations of each divided region is preferably 1.0 mass% or more, more preferably 1.5 mass% or more, even more preferably 2.0 mass% or more, and particularly preferably 2.4 mass% or more.

On the other hand, as long as it is possible to suppress or prevent the occurrence of cracks in the welded portion and the weakening of the welded portion, there are no particular limitations, but the average carbon concentration (average carbon concentration) is preferably 4.0 mass% or less, more preferably 3.6 mass% or less, and even more preferably 3.2 mass% or less.

As described above, when dividing the length of the center line of the weld into 10 or more equal lengths, the carbon concentration of each divided area is measured, and a weld structure is created having a weld with an average value (average carbon concentration) of 1.0 mass% or more calculated using the measured carbon concentrations of each divided area, thereby suppressing or preventing the occurrence of cracks in the weld and weakening of the weld.

Although not particularly limited, the welded portion preferably has a ratio of the depth of the welded portion to the width of the welded portion (aspect ratio (Y/X)) of 4 or more. In FIG. 5, X indicates the width of the welded portion, and Y indicates the depth of the welded portion. From the viewpoint of suppressing or preventing the occurrence of distortion due to welding of the welded structure, and suppressing or preventing the occurrence of cracks in the welded portion and the weakening of the welded portion, the larger the ratio of the depth of the welded portion to the width of the welded portion (aspect ratio (Y/X)), the more preferable. Although not particularly limited, the ratio of the depth of the welded portion to the width of the welded portion (aspect ratio (Y/X)) is more preferably 8 or more, and even more preferably 12 or more. In addition, the upper limit of the ratio of the depth of the welded portion to the width of the welded portion (aspect ratio (Y/X)) at present is about 16.

As described above, by forming a welded structure having a weld where the ratio of the depth of the weld to the width of the weld is 4 or more, it is possible to further suppress or prevent distortion caused by welding, further suppress or prevent the occurrence of cracks in the weld, and further suppress or prevent a decrease in the strength of the weld.

Furthermore, although not particularly limited, the ratio of the components derived from the cast iron member to the sum of the components derived from the cast iron member and the components derived from the steel member in the weld is preferably greater than 0.50, more preferably 0.60 or more, and even more preferably 0.75 or more. From the viewpoint of reliable formation of the weld, the upper limit of the ratio of the components derived from the cast iron member to the sum of the components derived from the cast iron member and the components derived from the steel member is preferably 0.99 or less.

Here, the "ratio of components originating from the cast iron member to the sum of components originating from the cast iron member and components originating from the steel member" can be calculated based on the deviation between the center line of the butt joint and the weld, if the butt joint between the cast iron member and the steel member can be observed even after welding. Also, if the butt joint between the cast iron member and the steel member cannot be observed after welding, the above ratio can be calculated from the composition ratio of the components of the cast iron member, the steel member, and the weld.

As described above, by forming a weld structure having a weld in which the ratio of the components derived from the cast iron material to the total of the components derived from the cast iron member and the components derived from the steel member is preferably greater than 0.5, more preferably 0.6 or more, and even more preferably 0.75 or more, the silicon concentration and carbon concentration in the weld can be increased. This reduces the viscosity and surface tension of the molten components of the nickel-containing welding metal material, promoting stirring of the molten components of the nickel-containing welding metal material in the depth direction of the weld to be formed, and the components of the nickel-containing welding metal material are supplied deep into the weld. In addition, the formation of martensite, which is a brittle structure, is suppressed in the weld, and the formation of austenite, which is a ductile structure, is promoted. As a result, the occurrence of cracks in the weld and the weakening of the weld can be suppressed or prevented.

Although not particularly limited, it is preferable that the cast iron member be the differential case and the steel member be the ring gear.

By forming a welded structure having a differential case made of cast iron material, a ring gear made of steel material, and the above-mentioned welded parts, it is possible to suppress or prevent the occurrence of distortion due to welding in the welded structure, as well as suppress or prevent the occurrence of cracks in the welded parts and the weakening of the welded parts. In addition, since the differential case and the ring gear are joined by welding, there is no need to join them using bolts, there is no need to form a flange on the differential case, and it is possible to thin the ring gear, which makes it possible to realize a lightweight welded structure in which the differential case and ring gear are welded.

<2> Welding method The welding method of this embodiment is one form of a welding method for forming a welded structure of the present invention. This welding method includes a step of supplying a nickel-containing welding metallic material to a butt joint between a cast iron member made of cast iron and a steel member made of carbon steel or alloy steel, and irradiating a fiber laser beam to a position shifted from the butt joint toward the cast iron member.

Here, the cast iron member made of cast iron and the steel member made of carbon steel or alloy steel are equivalent to those described in the above embodiment.

The nickel-containing welding metal material is not particularly limited, but may be, for example, nickel-containing welding wire. From the viewpoint of reducing costs, the lower the nickel content of the nickel-containing welding wire, the more preferable it is. For example, nickel-containing welding wire with a nickel content of 10% by mass or less is preferable from the viewpoint of reducing material costs and manufacturing costs. However, this is not limited, and for example, a nickel content of more than 10% by mass and 97% by mass or less may be applied. The nickel-containing welding wire is not particularly limited, but may be, for example, Y308, Y310, etc., as specified in the Japanese Industrial Standards. It is preferable to apply Y308, although this is not particularly limited.

Furthermore, the fiber laser welding machine that irradiates the fiber laser beam is not particularly limited as long as it can form the above-mentioned weld, and any conventionally known fiber laser welding machine can be used.

As described above, the welding method of this embodiment includes a step of supplying a nickel-containing welding metal material to a butt joint between a cast iron member made of cast iron and a steel member made of carbon steel or alloy steel, and irradiating a fiber laser beam to a position shifted from the butt joint toward the cast iron member. This suppresses or prevents the occurrence of distortion due to welding in the welded structure, and makes it possible to form a welded structure in which the occurrence of cracks in the welded portion and the weakening of the welded portion are suppressed or prevented.

Although not particularly limited, in the welding method of this embodiment, the irradiation position of the fiber laser beam is shifted toward the cast iron member with a high silicon content (mass %), and the silicon component is actively dissolved into the components of the nickel-containing welding metal material. This reduces the viscosity and surface tension of the nickel-containing welding metal material, and promotes the formation of austenite in the weld even if the nickel-containing welding metal material has a low nickel content. As a result, it is possible to effectively suppress or prevent cracks in the weld while suppressing manufacturing costs.

Although not particularly limited, it is preferable to set the position where the fiber laser beam is irradiated to a position shifted from the butted portion toward the cast iron member by 50 μm or more.

As described above, by setting the position at which the fiber laser beam is irradiated to a position shifted by 50 μm or more from the butt joint toward the cast iron member, the occurrence of distortion due to welding in the welded structure is suppressed or prevented, and a welded structure can be formed in which the occurrence of cracks in the welded portion and the weakening of the welded portion are suppressed or prevented.

In addition, from the viewpoint of forming a welded structure in which the occurrence of cracks at the welded portion and the weakening of the welded portion are suppressed or prevented, the greater the distance from the butt joint to the position where the fiber laser beam is irradiated (welding point offset amount), the more preferable. For example, the distance from the butt joint to the position where the fiber laser beam is irradiated (welding point offset amount) is more preferably 100 μm or more, and even more preferably 150 μm or more. On the other hand, while there are no particular limitations as long as the occurrence of distortion due to welding of the welded structure is suppressed or prevented, the distance from the butt joint to the position where the fiber laser beam is irradiated (welding point offset amount) is preferably 1.5 mm or less, more preferably 1.0 mm or less, even more preferably 500 μm or less, and particularly preferably 200 μm or less.

<3> The welding structure and welding method will be described in detail below with reference to the drawings. Note that, although an example of welding a differential case and a ring gear is shown, the present invention is not limited to this. Also, the dimensional ratios in the drawings cited below have been exaggerated for the convenience of explanation and may differ from the actual ratios.

Figure 1 is a schematic diagram of a welded structure for explaining the welded structure and the welding method. As shown in Figure 1, the welded structure 10 has a differential case 12 and a ring gear 14. After welding, which will be described in detail later, a weld is formed at a butt joint A where the differential case 12 and the ring gear 14 are butted together, which is derived from the differential case 12, the ring gear 14, and the nickel-containing welding wire W. In other words, after welding, the welded structure 10 has the differential case 12, the ring gear 14, and a weld that joins the differential case 12 and the ring gear 14.

Here, the differential case 12 is formed of a cast iron member made of cast iron as described above, and the ring gear 14 is formed of a steel member made of carbon steel or alloy steel as described above.

Nickel-containing welding wire W is supplied to the butt joint A between the differential case 12 and the ring gear 14, and a fiber laser beam B is irradiated to form a welded joint between the differential case 12 and the ring gear 14, welding the differential case 12 and the ring gear 14 together. The butt joint A is formed by butting together the coaxially arranged circumferential portions 121, 141 provided on the differential case 12 and the ring gear 14.

The fiber laser beam B is emitted from a nozzle N disposed in the vicinity of the butted portion A. The nozzle N may include a gas flow passage (not shown) and may blow out a shielding gas such as argon (Ar) or nitrogen (N ₂ ).

Here, FIG. 2 is a cross-sectional view taken along line a-a in FIG. 1 before welding. And FIG. 3 is a view seen from the direction of arrow b in FIG. 1. Also, FIG. 4 is a cross-sectional view taken along line d-d in FIG. 3. Furthermore, FIG. 5 is a cross-sectional view taken along line a-a in FIG. 1 after welding. Note that X in FIG. 5 indicates the size of the weld in the width direction, and Y in FIG. 5 indicates the size of the weld in the depth direction. Also, the same components are given the same reference numerals to avoid redundant explanations.

As shown in FIG. 2, the differential case 12 has a protrusion 123 that protrudes in a direction along the rotation axis. The ring gear 14 has a hole 143 into which the protrusion 123 fits. The differential case 12 and the ring gear 14 are connected by fitting the protrusion 123 into the hole 143. The differential case 12 is connected to a rotary drive device that includes a motor and the like. The ring gear 14 rotates integrally with the differential case 12. The nozzle N is fixed.

During welding, the emission position and emission direction of the fiber laser beam B remain fixed, and as shown in FIG. 3 (and FIG. 1), the differential case 12 and the ring gear 14 rotate in the circumferential direction indicated by the arrow c. The irradiation position of the fiber laser beam B moves relatively in the circumferential direction of the circumferential portions 121, 141 while the differential case 12 and the ring gear 14 are welded. The differential case 12 and the ring gear 14 are welded around the entire circumference of the circumferential portions 121, 141.

The nickel-containing welding wire W is supplied by a wire feeding mechanism that feeds the nickel-containing welding wire W from a wire reel around which the nickel-containing welding wire W is wound. The nickel-containing welding wire W is supplied sequentially in accordance with the rotation of the differential case 12 and the ring gear 14.

The irradiation position of the fiber laser beam B and its vicinity are photographed by an imaging device C such as a CCD camera. During welding, the worker checks the image photographed by the imaging device C on a display device such as a liquid crystal display. The differential case 12 and the ring gear 14 are welded while the irradiation position of the fiber laser beam B is monitored.

As shown in FIG. 4, the irradiation position of the fiber laser beam B is shifted from the butt joint A toward the differential case 12, which is a cast iron member and has a relatively high silicon content (mass%) out of the differential case 12, which is a cast iron member, and the ring gear 14, which is a steel member. Therefore, as shown in FIG. 5, the weld 16 formed by melting the differential case 12, ring gear 14, and nickel-containing welding wire W by irradiation with the fiber laser beam B is positioned away from the butt joint A toward the differential case 12.

By welding while monitoring the irradiation position of the fiber laser beam B, the irradiation position does not deviate toward the ring gear side, and the fiber laser beam B is reliably irradiated at a position shifted toward the differential case 12 side. Therefore, the entire annular weld 16 formed around the rotating shaft is shifted toward the differential case 12 side, which is a cast iron member with a high silicon content (mass %). This effectively suppresses cracking throughout the entire weld 16, ensuring that the members are reliably joined together.

Unlike the above-mentioned welding method, when the differential case 12 and the ring gear 14 are fixed without rotation and welding is performed in the circumferential direction while changing the emission position and emission direction of the fiber laser beam B and the supply position of the nickel-containing welding wire W, a drive device for moving the nozzle N and the nickel-containing welding wire W, etc., and a control device for controlling them are required. This may result in a complex welding device. On the other hand, in the above-mentioned welding method, welding is performed by rotating the differential case 12 and the ring gear 14 in the circumferential direction while fixing the emission position and emission direction of the fiber laser beam B, so there is no need for a large-scale device as in the case of welding by moving the fiber laser beam B, and a simple welding device can be used.

The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to these examples.

(Examples 1 to 4, Comparative Examples 1 to 5)
6 is an enlarged cross-sectional view of a main portion of the welded structure of the embodiment, which corresponds to FIG. 2 and FIG. 5. As shown in FIG. 6, the differential case 22 and the ring gear 24, which form annular gaps 221, 241 around the rotation axis between the members when they are butted against each other, were actually welded to form the welded structure 20. In the embodiment, the components other than the gaps 221, 241 are substantially similar to those of the above-described embodiment.

Here, the differential case 22 was made of FCD450, a spheroidal graphite cast iron specified by the Japanese Industrial Standards. In the differential case 22, the carburized layer on the welded surface that forms the butt joint A was removed to form a groove as shown in FIG. 4.

The ring gear 24 is made of SCM420H, a case-hardened steel specified by the Japanese Industrial Standards. The ring gear is carburized.

The nickel-containing welding wire W used was made of Y308, which is specified in the Japanese Industrial Standards. The nickel-containing welding wire had a nickel content of 10% by mass and a diameter of φ0.6 mm. During welding, the nickel-containing welding wire was fed at a feed rate of 7 m/min.

At each of a plurality of irradiation positions (butt joint A is 0, the cast iron member side is (+), and the steel member side is (-), and set at -200 μm to +200 μm) set by shifting the position along the rotation axis of the differential case 22 and the ring gear 24, nitrogen (N ₂ ) as a shielding gas was blown out, and a fiber laser beam B (output: 3800 to 4200 W, spot diameter: φ0.2 mm, defocus: -2 mm (however, the internal direction of the material is (-))) was irradiated at a welding speed of 5 m/min to form a weld 26 and join the differential case 22 and the ring gear 24. In other words, a welded structure having the differential case 22, the ring gear 24, and the predetermined weld 26 formed by melting the differential case 22, the ring gear 24, and the nickel-containing welding wire W by a predetermined irradiation of the fiber laser beam B was formed.

Some specifications for each example are shown in Table 1.

The "beam irradiation position" in Table 1 is the distance from the butt joint A between the differential case 22 and the ring gear 24 in the direction along the rotation axis. When the beam irradiation position is positive (+), the beam irradiation position is located closer to the differential case 22 than the butt joint A. For example, when the beam irradiation position is +200 μm, this means that the fiber laser beam B is irradiated to a position shifted 200 μm toward the differential case 22 in the direction along the rotation axis from the butt joint A. On the other hand, when the beam irradiation position is negative (-), the beam irradiation position is located closer to the ring gear 24 than the butt joint A. For example, when the beam irradiation position is -200 μm, this means that the fiber laser beam B is irradiated to a position shifted 200 μm toward the ring gear 24 in the direction along the rotation axis from the butt joint A.

In addition, the "width of the weld (X)" in Table 1 is the length of the weld along the width of the weld on the surface of the welded structure in a cross section of the weld perpendicular to the length of the weld and parallel to the depth of the weld. Note that X in Figure 5 indicates the width of the weld.

Furthermore, the "depth of the weld (Y)" in Table 1 is the depth of the weld from the surface of the welded structure to the deepest position of the weld in a cross section of the weld perpendicular to the length of the weld and parallel to the depth of the weld. Note that Y in Figure 5 indicates the depth of the weld.

In addition, the "aspect ratio (Y/X)" in Table 1 is the ratio of the depth of the weld to the width of the weld.

Furthermore, the "average carbon concentration" in Table 1 is the arithmetic average value obtained by dividing the length of the center line of the weld into 20 equal-length divided regions and measuring the carbon concentration on the center line of each divided region using an electron probe microanalyzer (EPMA) (manufactured by Shimadzu Corporation, EPMA-1600) (measurement conditions: voltage: 10 kV, current: 70 nA, spot analysis region: φ0.05-0.5 μm).

The "minimum silicon concentration" in Table 1 is the minimum value of each silicon concentration obtained by dividing the length of the center line of the weld into 20 equal-length divided regions and measuring the silicon concentration on the center line of each divided region using a micro-area micro X-ray fluorescence analyzer (M4 TRADO, manufactured by Bruker) (measurement conditions: voltage: 50 kV, current: 200 μA, live time: 100 sec).

The "average silicon concentration" in Table 1 is the arithmetic average value obtained by dividing the length of the center line of the weld into 20 equal-length regions and measuring the silicon concentration on the center line of each divided region using a micro-area micro X-ray fluorescence analyzer (M4 TRADO, manufactured by Bruker) (measurement conditions: voltage: 50 kV, current: 200 μA, live time: 100 sec).

The "maximum nickel concentration" and "minimum nickel concentration" in Table 1 are the maximum and minimum nickel concentrations obtained by dividing the length of the center line of the weld into 20 equal-length regions and measuring the nickel concentration on the center line of each divided region using a micro-area micro X-ray fluorescence analyzer (M4 TRADO, manufactured by Bruker) (measurement conditions: voltage: 50 kV, current: 200 μA, live time: 100 sec).

Furthermore, the "nickel concentration ratio" in Table 1 is the ratio of the minimum nickel concentration to the maximum nickel concentration.

The "cast iron component derived component ratio" in Table 1 was calculated based on the offset between the center line of the butt joint and the weld joint. For example, if there is no offset between the center line of the butt joint and the weld joint, the cast iron component derived component ratio is 0.5, and if the center line of the weld joint is offset toward the cast iron member relative to the butt joint, the cast iron component derived component ratio is over 0.5. The steel component derived component ratio can be calculated as 1 - (cast iron component derived component ratio).

[Performance evaluation]
The welded structures of the above examples were observed, measured, and evaluated for cracks in the welded joints, average hardness of the welded joints, and strength of the welded joints in the following manner. The results are shown in Table 2.

(Weld cracks)
The cross section of the welded portion of each example of the welded structure was observed using an optical microscope (Leica, DMI5000M, magnification: 100 to 500 times) to evaluate the presence or absence of cracks, etc. In Table 2, in the "Cracks in Welded Portion" section, "None" means that no cracks were observed, "Yes" means that cracks were observed, and "Yes (Micro)" means that cracks were observed, but the observed cracks were microscopic.

(Average hardness of welded part)
The average hardness of the welded portion of each example was measured and evaluated. The average hardness of the welded portion was determined by dividing the length of the center line of the welded portion into 20 equal lengths in the cross section of the welded portion of each example, and measuring the Vickers hardness on the center line of each divided region in accordance with the Vickers Hardness Test - Test Method (JIS Z 2244-2009) in the Japanese Industrial Standards at a test load of 300 gf, and the average hardness of the welded portion was determined as the arithmetic average value obtained from each Vickers hardness.

(Strength of welded joints)
The welded structure of each example was subjected to a four-point bending test (test conditions: lower support distance: 55 mm, upper support distance: 10 mm, and push-in speed: 2 mm/min) using a precision universal testing machine (Shimadzu Corporation, Autograph AG-X), and the fracture state was observed to evaluate the strength. In Table 2, "x" in the "Weld Strength" section means that the weld fractured without base material fracture, which is the fracture of the base material such as a cast iron member or a steel member, "○" means that the base material fracture occurred more frequently before the weld fractured, and "◎" means that the base material fracture (cast iron member side) occurred without the weld fracture.

From Tables 1 and 2, it can be seen that Examples 1 to 4, which are within the scope of the present invention, are able to suppress or prevent the occurrence of cracks in the welded parts and the weakening of the welded parts, compared to Comparative Examples 1 to 5, which are outside the present invention. Furthermore, as a result of visual observation, Examples 1 to 4 suppressed or prevented the occurrence of distortion due to welding in the welded structure.

The reason for this is believed to be that by shifting the irradiation position and irradiating the fiber laser beam to the differential case side, which is made of a cast iron member made of cast iron and a cast iron member made of carbon steel or alloy steel with a relatively high silicon content, a welded joint having the following characteristics (1) to (3) was formed.

(1) The weld has a width dimension of 3.0 mm or less.
(2) The weld contains nickel and silicon.
(3) The weld has a silicon concentration of 0.9 mass % or more at any location on the center line of the weld.

The reason why Examples 2 to 4 are able to suppress or prevent the occurrence of cracks in the welded parts and the weakening of the welded parts compared to Example 1 and Comparative Examples 1 to 5 is thought to be because, as described above, the fiber laser beam is irradiated onto the differential case side, forming a welded part that has the following characteristic (4) in addition to the characteristics (1) to (3) above.

(4) The weld has a silicon concentration of 1.1 mass% or more at any location on the center line of the weld, and the average silicon concentration (average silicon concentration) on the center line of the weld is 1.5 mass% or more.

The welded area has an average silicon concentration of 1.5 mass% or more, which indicates that the silicon component is effectively dissolved into the differential case, which is made of cast iron.

The reason why Examples 1 to 4 are able to suppress or prevent cracking and weakening of the welded parts compared to Comparative Examples 1 to 5 is thought to be because, as described above, the fiber laser beam is irradiated onto the differential case side, forming a welded part that has the following characteristic (5) in addition to the characteristics (1) to (3) or (1) to (4) above.

(5) The weld has a nickel concentration of 0.5% by mass or more and 40% by mass or less at any location on the center line of the weld.

Furthermore, the reason why Examples 2 to 4 are able to suppress or prevent the occurrence of cracks in the welded portion and the weakening of the welded portion compared to Example 1 and Comparative Examples 1 to 5 is thought to be because, as described above, the fiber laser beam is irradiated onto the differential case side, forming a welded portion having the following characteristic (6) in addition to any one of the characteristics (1) to (3), (1) to (4), or (1) to (5) above.

(6) When the weld is divided into 20 equal-length divided regions along the center line, the nickel concentration ratio of the divided region with the minimum nickel concentration to the divided region with the maximum nickel concentration on the center line is 0.1 or more.

In addition, since the nickel concentration ratio is 0.1 or more, it can be seen that the silicon component dissolves into the components of the nickel-containing welding wire, the viscosity and surface tension of the molten components of the nickel-containing welding wire decrease, and the stirring of the molten components of the nickel-containing welding wire is promoted in the depth direction of the weld that is formed.

The reason why Examples 1 to 4 are able to suppress or prevent cracking and weakening of the welded parts compared to Comparative Examples 1 to 5 is thought to be because, by irradiating the differential case side with a fiber laser beam in the same manner as above, a welded part having the following characteristic (7) in addition to any of the characteristics (1) to (3), (1) to (4), (1) to (5), or (1) to (6) above is formed.

(7) The ratio of the depth of the weld to the width of the weld is 4 or greater.

The reason why Examples 1 to 4 are able to suppress or prevent cracking and weakening of the welded parts compared to Comparative Examples 1 to 5 is thought to be because, as described above, the fiber laser beam is irradiated onto the differential case side, forming a welded part having the following characteristic (8) or (9) in addition to any of the characteristics (1) to (3), (1) to (4), (1) to (5), (1) to (6), or (1) to (7) above.

(8) In the weld, the ratio of components derived from the cast iron member to the sum of components derived from the cast iron member and components derived from the steel member is greater than 0.50.
(9) In the welded portion, the ratio of components derived from the cast iron member to the sum of components derived from the cast iron member and components derived from the steel member is 0.60 or more.

The reason why Examples 1 to 4, and especially Examples 2 to 4, are able to suppress or prevent cracking and weakening of the welded parts compared to Comparative Examples 1 to 5 is thought to be because, by irradiating the differential case side with a fiber laser beam in the same manner as above, a welded part having the following characteristic (10) in addition to any of the characteristics (1) to (3), (1) to (4), (1) to (5), (1) to (6), (1) to (7), or (1) to (7), (8), or (9) above is formed.

(10) When the weld is divided into 20 equal-length divided regions, the carbon concentration of each divided region is measured, and the average value (average carbon concentration) calculated using the measured carbon concentrations of each divided region is preferably 1.0 mass% or more, more preferably 1.5 mass% or more, even more preferably 2.0 mass% or more, and particularly preferably 2.4 mass% or more.

In addition, the reason that Examples 2 to 4 are able to suppress or prevent the occurrence of cracks in the welded parts and the weakening of the welded parts compared to Example 1 and Comparative Examples 1 to 5 is thought to be due to the increased amount of austenite contained in the welded parts.

In other words, when the average hardness of the weld is 600 HV or more, the weld contains more brittle martensite than ductile austenite. On the other hand, when the average hardness of the weld is less than 600 HV, the weld contains more ductile austenite than brittle martensite. Therefore, it can be said that the increased amount of austenite in the sprayed part effectively prevents cracks in the weld.

Furthermore, the reason why Examples 1 to 4, especially Examples 2 to 4, are able to suppress or prevent the occurrence of cracks in the welded parts and the weakening of the welded parts compared to Comparative Examples 1 to 5 is thought to be because the fiber laser beam was irradiated with a shift of 50 μm or more, preferably 100 μm or more, toward the differential case side formed of a cast iron member made of cast iron and a cast iron member made of carbon steel or alloy steel with a relatively high silicon content, thereby forming a welded part having the above characteristics (1) to (3).

Thus, comparing Examples 2 to 4 with Example 1, it can be seen that when welding by irradiating a fiber laser beam, it is more preferable to shift the beam irradiation position by 100 μm or more from the ring gear side, which is made of a steel member made of carbon steel or alloy steel, to the differential case side, which is made of a cast iron member made of cast iron.

The present invention has been described above using a few embodiments and examples, but the present invention is not limited to these and various modifications are possible within the scope of the claims.

10, 20 Welded structure 12, 22 Differential case (cast iron member)
14, 24 Ring gear (steel member)
16, 26 Welded portion 121, 141 Circumferential portion 123 Protrusion 143 Hole 221, 241 Gap A Butt portion B Fiber laser beam C Photographing device N Nozzle W Nickel-containing welding wire (nickel-containing welding metal material)

Claims (2)

A welding method for forming a welded structure having a cast iron member made of cast iron, a steel member made of carbon steel or alloy steel, and a welded part joining the cast iron member and the steel member, comprising:
The weld has a width direction dimension of 3.0 mm or less, and the weld contains nickel and silicon;
The weld has a silicon concentration of 0.9% by mass or more and 2.0% by mass or less at an arbitrary site on a center line of the weld, and an average carbon concentration of the weld is 2.0% by mass or more and 3.2% by mass or less ,
A welding method comprising the steps of: supplying a nickel-containing welding metal material to a butt joint between the cast iron member and the steel member; and irradiating a fiber laser beam to a position shifted from the butt joint toward the cast iron member. 2. The welding method according to claim 1, wherein the position where the fiber laser beam is irradiated is a position shifted from the butted portion toward the cast iron member by 50 μm or more.

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