JP2017074602A - Weld zone of spheroidal graphite cast iron with each other or spheroidal graphite cast iron and steel, welding material used for the welding and heat treatment of the weld zone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a weld zone having excellent mechanical characteristics where carbon is spheroidized and deposited in a crystal grain while preventing the occurrence of welding defects when welding spheroidal graphite cast iron.SOLUTION: In a weld zone where spheroidal graphite cast iron with each other or the spheroidal graphite cast iron and steel are welded with an Ni-Fe-based welding material: the respective content of C and Si contained in the metallic structure of the welded metal are, by wt.%, 0.5-1.0% of C and 0.5-1.0% of Si; C contained in the welded metal is deposited in a crystal grain as spheroidal graphite; the component of a welding wire 4 as the weld material is, by wt.% in the welding wire 4, 0.3-1.3% of C, 0.3-1.3% of Si, 0.5-2.0% of Mn, 30-70% of Ni and the balance Fe with inevitable ingredients.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a welded portion having a metal structure having good mechanical properties in welding of spheroidal graphite cast irons to each other or spheroidal graphite cast iron and steel, a welding material used for the welding, and a heat treatment method for the welded portion Is.

For example, when welding different materials of cast iron and steel, a Ni—Fe based welding material is used to prevent the formation of cementite in the weld metal.
However, when welding is performed using a Ni-Fe-based welding material, particularly when multi-layer welding or welding is performed at a high preheating temperature, the cooling rate of the weld metal becomes slow, and the carbon in the weld metal becomes a grain boundary during the cooling process. It begins to precipitate as graphite. Therefore, the grain boundary strength is remarkably lowered, and cracks and the like are likely to occur.
In order to solve this problem, cracks in the weld metal are prevented by adding Al, rare earth metals, V, Ti, Nb, etc. to the welding materials such as welding wires and welding rods and stabilizing the carbon as carbides. The method to do is taken.

  For example, in Patent Document 1 shown below, Mn: 1.5 to 3%, rare earth metal: 0.001 to 0.2%, Al: 0.005 as an alloy component in a Ni—Fe welding wire. 0.5%, Ni: 40-60%, further Ti: 0.01-0.5%, Nb: 0.01-3%, Ta: 0.01-3% One or more of them are contained, the remainder is composed of Fe and unavoidable impurities, and the contents of C and Si components as unavoidable impurities are C: 0.5% or less, Si: 1.5% or less, A welding wire is shown. There is a description that the use of this welding wire eliminates the occurrence of hot cracking in the weld bead and has excellent impact resistance (third column 38th line to fourth column 30th line).

  Incidentally, hot cracking is a weld defect that occurs in a weld metal or weld heat affected zone that is heated in the vicinity of the melting point or higher during welding. Hot cracks include, for example, solidification cracks that break when the weld metal solidifies, and liquefaction cracks that occur in the weld metal and the weld heat affected zone. Solidification cracking occurs when the molten weld metal solidifies and the thermal phase acts while the liquid phase still remains between the solid phases, causing the liquid phase to separate. Liquefaction cracks are caused by partial melting of the grain boundaries where elements that lower the solidus temperature are segregated in the weld metal and the weld heat affected zone, and welding thermal stress acts on this.

  Patent Document 1 describes that it is necessary to specify the contents of Mn and C in the welding wire in order to suppress hot cracking.

  Mn has a deoxidation / desulfurization action and stabilizes low melting point compounds such as sulfides. This sulfide is spheroidized and distributed in the crystal grains, thereby preventing hot cracks from occurring in the weld bead. According to Patent Document 1, there is a description that the Mn is effective in preventing hot cracking when it coexists with a rare earth metal.

  Moreover, about C, there exists a deoxidation effect | action, and there exists description that it melts and solidifies in a base material and strengthens and the hot water flow of a welding metal is improved. However, there is a description that the C content in the welding wire should not exceed 0.5% in order to prevent the occurrence of hot cracks in the weld bead.

Japanese Examined Patent Publication No. 62-50233

In order to weld cast iron and use it for various applications, it is necessary that the welded part has the desired mechanical characteristics in addition to being able to perform welding without defects.
In general, when welding cast iron using Ni-Fe welding material, if welding is performed after multi-layer welding or preheating at a high temperature, the cooling rate of the weld metal is slowed down, and during the cooling process Carbon is deposited as graphite at the grain boundaries. As a result, the grain boundary strength is remarkably reduced, and the mechanical properties of the weld metal are inferior.

  In addition, in the interface between the weld metal and the base material, that is, in the vicinity of the bond portion, the carbon concentration increases due to the penetration of the base material, and accordingly, the Ni concentration decreases to easily generate a brittle cementite phase. In addition, the mechanical properties of the welded portion are deteriorated. When heat treatment is performed to eliminate the cementite phase and graphitize, carbon precipitates as graphite during the high temperature holding process and cooling process.

  In the technique of the above-mentioned known document 1, although there is a description about avoiding hot cracking during welding, the heat treatment characteristics of the weld metal are not taken into consideration. Therefore, even when cast iron is used for various structures, desired mechanical characteristics cannot be obtained, and the application range of cast iron has certain limitations.

  Further, the technique of the above-mentioned known document 1 requires the addition of expensive special elements such as Ti and Ta, and there is still room for improvement in order to obtain a general-purpose welding wire.

  Therefore, when welding spheroidal graphite cast iron, carbon is graphitized while preventing the occurrence of weld defects, and precipitated in crystal grains, and a weld with good mechanical properties is obtained, and There is a demand for the development of a welding material from which such a weld is obtained.

The characteristic configuration according to the welded portion of the present invention is as follows:
In a welded portion in which spheroidal graphite cast irons or spheroidal graphite cast iron and steel are welded with a Ni—Fe based welding material, C and Si contained in the metal structure of the weld metal are both C: 0.5 to 1.0 by weight%. %, Si: 0.5 to 1.0%, and C contained in the weld metal is precipitated as spherical graphite in the crystal grains.

  For example, cementite having poor ductility may be generated in the vicinity of the bond portion of the welded portion due to high heat input during welding, and the welding strength may be reduced. Therefore, it is necessary to post-heat the weld and graphitize the cementite. Therefore, as in this configuration, by defining the content of C and Si with respect to the composition in the Ni—Fe-based alloy, the carbon present in the weld metal is spheroidal graphitized during the post-heat treatment and precipitated in the crystal grains. . Thereby, the intensity | strength of a weld metal improves, generation | occurrence | production of a crack can be prevented and a highly ductile weld part can be obtained.

  Here, the expression that the appearance of carbon as graphite is precipitated. This is due to the fact that a lot of carbon appears in the metal structure in the solid state. However, since some carbon appears (crystallizes) in the solidification process, in this embodiment, the precipitation includes crystallization.

  As a characteristic configuration according to the welded portion of the present invention, it is preferable that the base material of the spheroidal graphite cast iron is ferritic base spheroidal graphite cast iron solid-solution strengthened with either one or both of Si and Ni.

  As in this configuration, by softening the ferrite matrix using Si or Ni, softening in the vicinity of the bond portion after the heat treatment can be suppressed.

The characteristic configuration according to the welding material of the present invention is:
C: 0.3 to 1.3% by weight% of welding material,
Si: 0.3 to 1.3%
Mn: 0.5 to 2.0%,
Ni: 30 to 70%,
The remainder is composed of Fe and inevitable components.

When welding parts are formed between spheroidal graphite cast irons or between spheroidal graphite cast iron and ordinary steel materials using the welding material of this component, in welding between spheroidal graphite cast irons, the C content and Si content in the weld metal The amount increases slightly from the spheroidal graphite cast iron side. On the other hand, in welding of spheroidal graphite cast iron and steel material, the C content and Si content in the weld metal are slightly reduced by being diluted as the steel material is melted.
However, by defining the content of each component of the welding material as in the present configuration, the C content and the Si content become appropriate values at any location of the weld metal. As a result, carbon is spheroidal graphitized and precipitated not in the crystal grain boundaries but in the crystal grains, thereby improving the strength of the weld metal and improving the crack resistance and ductility.

  The characteristic structure according to the heat treatment method for the welded portion of the present invention is that the welded portion is welded at a temperature of 850 ° C. or higher after welding the spheroidal graphite cast iron and steel or welding the spheroidal graphite cast irons using the above-mentioned welding material. It is in the point of holding for 30 minutes or more and then cooling in the furnace or air.

  By welding, cementite and martensite with poor ductility are formed in the vicinity of the bond portion. Therefore, by subjecting the welded portion to post-heat treatment as in this configuration, the ferrite / pearlite and martensite structures are once changed to austenite, and cementite is graphitized. Furthermore, carbon present in the weld metal is spheroidized and precipitated in the crystal grains. By slowly cooling this, the austenite of the heat-affected zone changes to ferrite or pearlite. The strength of the weld metal is improved, cracking can be prevented, and a highly ductile weld can be obtained.

Explanatory drawing showing the outline of the weld Table showing base metal, welding wire and weld metal components Table showing mechanical properties of welds Structure photograph of welded part using welding wire of this embodiment (FCD500 as weld) Structure photograph of welded part using welding wire of this embodiment (FCD500 PWHT) Structure photograph of welded part using welding wire of this embodiment (SSFDI500 as weld) Structure photograph of welded part using welding wire of this embodiment (SSFDI500 PWHT) Structure picture of welded part using welding wire of comparative example (commercial product) (FCD500 as weld) Structure image of welded part using welding wire of comparative example (commercial product) (FCD500 PWHT) Structure photograph of welded part using welding wire of comparative example (commercial product) (SSFDI500 as weld) Structure photograph of welded part using welding wire of comparative example (commercial product) (SSFDI500 PWHT)

Embodiments according to the present invention will be described below with reference to the drawings.
In FIG. 1, the schematic diagram of the welding part which welded the spheroidal graphite cast iron which is the base material 1 using the Ni-Fe-type welding material is shown. A base material 1 of spheroidal graphite cast iron is welded on both sides of the center weld metal 2. Specifically, this is an example in which V-shaped grooves are formed between the base materials 1 and finish welding is performed on the second layer while forming a back welded portion on the first layer. Welding was performed by MIG welding (Metal Inert Gas welding). A welding wire 4 as a welding material was supplied from the welding tip 3 and an inert gas 6 was supplied from the tip of the welding torch 5 to perform welding while shielding the periphery of the welding arc 7.
Note that one of the base materials 1 across the welded portion may use a normal steel material.

  The component composition of each region in such a welded joint is substantially the same as that of the base material 1 in the structure on the base material 1 side from the bond portion 8, which is the boundary between the weld metal 2 and the base material 1. On the other hand, the component composition of the weld metal 2 is slightly changed by the fusion of the base material 1 and the welding wire 4.

  In general, the mechanical properties of the welded joint are dominated by the properties in the vicinity of the bond portion 8. That is, the components of the base material 1 and the welding wire 4 are mixed, and the metal structure may change greatly depending on the welding heat input. In particular, when welding spheroidal graphite cast iron, the structure of the welded part is eliminated such that the spheroidal graphite structure on the side of the base material 1 in the vicinity of the bond part 8 is eliminated, or the carbon present on the weld metal 2 side is not precipitated in a spherical shape. Is difficult to control. The technique according to the present embodiment is to obtain a welded portion having excellent mechanical characteristics while performing welding of spheroidal graphite cast iron or by appropriately performing post heat treatment after welding.

  The component composition of the base material 1 used in this embodiment is shown in FIG. Among these, FCD500 is a spheroidal graphite cast iron standardized in JIS G 5502, and SSFDI500 is a spheroidal graphite cast iron corresponding to the European spheroidal graphite cast iron standard EN1563 GJS500-14. S35C is a carbon steel for machine structural use specified in JIS G 4051. In any case, the remaining components are Fe and inevitable components. As is clear from FIG. 2, the spheroidal graphite cast irons of FCD500 and SSFDI500 both contain C and Si by one order more than S35C.

  The spheroidal graphite cast iron that is the base material 1 may be one that has been solid-solution strengthened using Si or Ni. Due to the solid solution strengthening of Si or Ni, the base metal structure becomes a stronger ferrite-base spheroidal graphite cast iron. In this case, softening in the vicinity of the bond portion 8 can be suppressed even when post-heat treatment or the like is performed.

  On the other hand, the composition of the weld metal 2 is largely determined by the components of the welding wire 4. The component composition of the welding wire 4 used in this embodiment is shown in FIG. Note that FIG. 2 also shows commercially available welding wires 4 for cast iron used in Examples and Comparative Examples described later.

  The welding wire 4 according to this embodiment is used particularly for welding to spheroidal graphite cast iron. For example, it is formed as a wire for MIG, MAG (Metal Active Gas welding) and carbon dioxide gas welding. It can also be used for TIG welding. The base material 1 to be welded to each other may be spheroidal graphite cast iron or may be spheroidal graphite cast iron and a general-purpose structural steel material.

  Specific components are C: 0.3 to 1.3% by weight, Si: 0.3 to 1.3%, Mn: 0.5 to 2%, Ni: 30 to 70%, and the balance is Fe. And inevitable ingredients. The welding wire 4 can obtain better weldability by using a flux cored wire or a flux cored wire containing an alloy element. However, it may be a solid wire having no flux. As the flux, a substance that can ensure the stability of the welding arc 7 and has a deoxidizing effect is preferable. For example, the alloy element components include Na, Al, Mn, Si, F, and the like. In welding with a flux cored wire, welding spatter is less than that of a solid wire, and a weld portion having a smooth appearance can be obtained. In addition, when setting it as a flux cored wire, the combination of the alloy component included in an internal flux and the alloy component included in an outer_skin | epidermis is arbitrary.

〔Example〕
Below, the Example which produced the welding part using the welding wire 4 which concerns on this embodiment is shown.
The plate materials used as the base material 1 are: FCD500 (Spheroidal graphite cast iron): JIS G5502 FCD500-7 equivalent, SSFDI500 (Spheroidal graphite cast iron): EN1563 GJS500-14 equivalent, S35C (Carbon steel for machine structure): JIS G4051 There are three types. The plate thickness is 5 mm for all.

The welding in the examples was performed by the MIG welding method using shield gas (Ar-2% O ₂ ). Specifically, gas flow rate: 20 liters / minute, welding speed: 500 mm / minute, no preheating, torch angle: advance angle 20 degrees, welding current: 220 A, welding voltage: 22 V, wire protrusion length: 10 mm. A V groove was formed at the butt portion between the base materials 1, and the first layer was a two-layer, two-pass welding with back wave welding.

On the other hand, the welding conditions according to the comparative example were such that the welding current / voltage of the first layer was 175 A, 22 V, and the second layer was 185 A, 22.6 V. The wire protruding length was 15 mm.
The reason why the welding conditions are different between the embodiment and the comparative example is that the optimum conditions are different depending on the type of the welding wire 4 to be used. For example, while the examples are flux-cored wires, the comparative examples used commercially available solid wires. In the flux-cored wire, since flux and alloy elements are added inside, the amount of deposited metal per unit length of the wire is different, so that the heat input conditions during welding are different.

  The heat treatment conditions after welding are as follows. About each base material 1, the test piece with what was welded (as weld) and the thing which performed post-weld heat processing (PWHT: Post Weld Heat Treatment) was produced. The post-weld heat treatment was performed under the conditions of holding at 900 ° C. for 1 hour after welding and then air-cooling and maintaining the temperature at 900 ° C. for 1 hour after welding and then gradually cooling in the furnace.

  In FIG. 2, the component composition of the weld metal 2 is shown. As the welding wire 4, the welding wire 4 of the example (development product) and the 55Ni-Fe solid wire which is the welding wire 4 for the ductile cast iron of the comparative example (commercial product) were used. On the other hand, for the base material 1, a combination in which one of the welded joints is FCD500 and the other is S35C, and a combination in which one of the welded joints is SSFDI500 and the other is S35C.

  The components of the weld metal 2 are C: 0.5 to 1.0% by weight% and Si: 0.5 to 1.0%. Although the components contained in the welding wire 4 of the present embodiment are C: 0.3 to 1.3% and Si: 0.3 to 1.3%, the respective component ranges of the weld metal 2 are compared with these. Is narrowly prescribed. In the welded portion of spheroidal graphite cast iron, the strength tends to be insufficient in many cases in the vicinity of the weld metal 2 or the bond portion 8, because the structure of the weld metal 2 is later to improve the structure after welding in the vicinity of the bond portion 8. This is because the heat treatment tends to cause carbon to be precipitated at the crystal grain boundaries and to cause a decrease in strength.

  The component range of the welding wire 4 is wide, for example, both when using spheroidal graphite cast iron with a high C content as the base material 1 and when using structural steel with a low C content. It is to do. For example, when welding a material having a high C content, in order to suppress the C content in the weld metal 2, it is preferable that the C wire contained in the welding wire 4 is smaller. Conversely, when welding a material having a low C content, it is preferable that the C content contained in the welding wire 4 is large in order to increase the C content in the weld metal 2. In this way, by setting the contents of C and Si contained in the welding wire 4 widely, the contents of C and Si in the weld metal 2 can be set appropriately.

  In FIG. 3, the result of having done the tension test about an Example and a comparative example is shown.

  As for the mechanical properties of the welded part, the results of the example showed good results regardless of whether FCD500 or SSFDI500 was used as one base material 1. For example, when looking at each base material 1, there is not much difference between the case of as weld and the case of using the welding wire 4 of the example and the case of using the welding wire 4 of the comparative example (commercial product). I can't. However, with the post-weld heat treatment (PWHT), the tensile strength and elongation of the wire using the welding wire 4 of the example are significantly improved, whereas the welding of the comparative example (commercial product) In the case of using the wire 4, both the tensile strength and the elongation were greatly reduced.

In the case of using the welding wire 4 of the example, the fracture position was the cast iron side bond portion or the cast iron base material 1. In particular, in the case of PWHT, what was the cast iron side bond part moved to the base material 1 of cast iron. On the other hand, in the case of using the welding wire 4 of the comparative example (commercially available product), the one with as weld was the cast iron side bond portion, whereas the one with PWHT was all broken with the weld metal 2. In particular, what was broken at the weld metal 2 was broken at the weld metal 2 regardless of the presence or absence of extra welding at the weld. Usually, the cross-sectional area of the weld metal 2 with a surplus is larger than that of the weld metal 2 without a surplus. Even though the strength was lowered, the fact that the weld metal 2 that had a surplus welded immediately shifted to a situation where the weld was welded using the welding wire 4 of the comparative example (commercial product) significantly reduced the strength. I understand that.

  The composition of the weld metal 2 is shown in FIG. Welding was two-layer welding with respect to a V-shaped groove, and an analysis sample was taken from the second-layer weld metal 2.

  According to FIG. 2, any component included in the weld metal 2 showed a value between the component of the cast iron base material 1 and the component of the welding wire 4. However, since the amount of melting from the base material 1 is limited, the components of the welding wire 4 are dominant. Regarding C, the welded portion between FCD500 and S35C was 0.84% by weight, and the welded portion between SSFDI500 and S35C was 0.81% by weight. As for Si, the welded portion between FCD500 and S35C was 0.71% by weight, and the welded portion between SSFDI500 and S35C was 0.97% by weight.

  Regarding Mn, in both FCD500 and SSFDI500, the Mn content in the weld metal 2 is slightly higher than both the Mn content in the welding wire 4 and the Mn content in the base material 1. It was. As a possibility of this factor, for example, manganese oxide contained in the oxide film formed on the bead surface by the first layer welding is reduced by the arc heat during the second layer welding, and the weld metal It is thought that the amount of Mn in 2 increased.

  The component composition of the weld metal 2 in the present invention is preferably a Ni—Fe alloy, and in particular, the weight percentages of C and Si are C: 0.5 to 1.0% and Si: 0.5, respectively. ~ 1.0%. Of these, the C content disappears as various gases during welding. Since this disappearance varies depending on welding conditions and the like, the setting of the C content in the welding wire 4 is important. However, in this test, the C content was approximately the median value of 0.5 to 1.0% by weight, indicating good results.

  The metal structure of the welded portion is shown in FIGS.

  4 and 5 show a welded portion of FCD500 (the base material on the right side in the drawing) and S35C (the base material on the left side in the drawing) using the welding wire 4 of the present embodiment. FIG. 4 shows a metal structure of as weld, and FIG. 5 shows a metal structure subjected to PWHT. Moreover, the enlarged photograph was shown about the specific part in each welding part.

  According to FIG. 4, it can be seen that graphite is precipitated in a spherical shape in the structure of weld metal 2 (A region and B region). On the other hand, in the vicinity of the bond portion 8 (C region and D region), spherical graphite is observed in both the base material 1 and the weld metal 2. However, in a very narrow range in the vicinity of the bond portion 8, a cementite phase is generated because the cooling rate is high.

  In FIG. 5 in which PWHT is performed, spherical graphite is precipitated in the weld metal 2 (A region and B region) as in the case of as weld. The spherical graphite is precipitated in the crystal grains, not in the crystal grain boundaries. In general, when PWHT is applied to eliminate the cementite phase in the vicinity of the bond portion 8, in the weld metal 2, carbon often precipitates as a graphite at the grain boundaries during the high temperature holding and cooling process. However, such a structure is not observed in the weld metal 2 of the example. This is considered to be based on the adjustment of the C content and the Si content to appropriate amounts with respect to the Ni—Fe welding wire 4.

  In the vicinity of the bond portion 8, slight precipitation of graphite is observed in a region where the component transitions between the base material 1 and the weld metal 2. This is presumably because the concentration gradient of the component in the vicinity of the bond portion 8 increased due to the stirring action of the weld metal 2 in the welding process, that is, the transition region of the component became very narrow.

  6 and 7 are welded portions of SSFDI 500 and S35C using the welding wire 4 of the present embodiment. FIG. 6 shows the metal structure of as weld (the left side of the weld metal 2 is the SSFDI 500 base material), and FIG. 7 shows the metal structure subjected to PWHT (the right side of the weld metal 2 is the base material of the SSFDI 500). An enlarged photograph of a specific part in each welded part is shown.

  Also in this case, spheroidal graphite was observed in the crystal grains in the weld metal 2 both in the as weld state and after the PWHT. In the case of PWHT, a slight martensite phase was observed in the vicinity of the bond portion 8 in the D region near the center of the plate thickness where the cooling rate was the slowest. However, spheroidal graphite was observed in the structures on both sides of the martensite phase. As apparent from the results of the tensile test shown in FIG. 3, the mechanical properties of the joint subjected to PWHT were the best. In the case of a tensile test piece with no surplus, it was broken at the bond part 8 on the SSFDI 500 side. It broke.

  FIGS. 8 and 9 are cross-sectional photographs of the welded part of FCD500 and S35C using the welding wire 4 (55Ni—Fe solid wire) of the comparative example (commercial product). FIG. 8 shows a metal structure of as weld (the right side of the weld metal 2 is FCD500), and FIG. 9 shows a metal structure subjected to PWHT (the left side of the weld metal 2 is FCD500).

  According to FIG. 8, almost no graphite was precipitated in any place in the weld metal 2 structure (A region and B region). Spherical graphite is observed in the region of the base material 1 in the vicinity of the bond portion 8 (C region and D region). On the other hand, a cementite phase is observed in a very narrow range near the bond portion 8.

  In FIG. 9 where the PWHT was performed, precipitation of graphite along the grain boundaries was observed in the weld metal 2 (A region and B region). For this reason, as is apparent from the results of the tensile test in FIG. 3, the test piece subjected to PWHT breaks with the weld metal 2 with and without extra filling, and the mechanical properties of the weld are reduced. It was confirmed that

  10 and 11 are cross-sectional photographs of a welded portion of SSFDI500 and S35C using welding wire 4 (55Ni—Fe solid wire) of a comparative example (commercial product). FIG. 10 shows the metal structure of as weld (the base metal on the left side of the weld metal 2 is SSFDI500), and FIG. 11 shows the metal structure subjected to PWHT (the base material on the left side of the weld metal 2 is SSFDI500).

  Also in this case, as in the case of FCD500, graphite was precipitated at the crystal grain boundaries of weld metal 2 (A region and B region) subjected to PWHT. Even in the result of the tensile test in FIG. 3, it was recognized that the fracture occurred in the weld metal 2 regardless of the presence or absence of the welding surplus, and the strength of the welded portion was reduced.

  As described above, the mechanical characteristics of the welded portion produced using the Ni—Fe based welding wire 4 of the present embodiment show particularly good values depending on the C and Si components. The effects and preferred contents of addition of C and Si or other alloy elements are as follows.

  C: Carbon. C slightly dissolves in the Ni—Fe-based weld metal 2, but most of it is precipitated as carbide or graphite. When the amount of carbide forming elements is small, carbon is precipitated as graphite, and when the C content is 0 to 0.6%, the graphite is precipitated at the crystal grain boundaries, thereby significantly reducing the grain boundary strength. If the C content exceeds 0.6%, graphite precipitates in the crystal grains, and a decrease in grain boundary strength can be suppressed. However, if the C content exceeds 1.5%, the amount of graphite precipitation increases, resulting from CO gas formation. Pinholes are also generated, leading to a decrease in strength due to a decrease in effective area. Therefore, in consideration of the penetration ratio of the welding wire 4 in the weld metal 2, the C content in the welding wire 4 is set to 0.3 to 1.3%.

  Si: Silicon. Si has a deoxidation action and a graphitization promoting action. If it is 0 to 0.3%, pinholes due to lack of deoxidation or graphitization is caused. When it is 1.3% or more, weldability is deteriorated due to excessive addition. Therefore, the silicon content is set to 0.3 to 1.3%.

  Mn: Manganese. Mn has a deoxidizing action and a carbide stabilizing action. If it is 0 to 0.5%, pinholes are caused due to insufficient deoxidation. If it is 2% or more, the weldability is deteriorated due to excessive addition and the weld metal 2 becomes brittle due to carbide formation. Therefore, the manganese content is set to 0.5 to 2.0%.

  Ni: Nickel. Ni is a main element of the weld metal 2 and is an austenitizing element. If it is 0 to 30%, austenite becomes unstable, and the toughness of the weld metal 2 decreases. If it exceeds 70%, the strength is lowered and the economy is deteriorated. Therefore, the nickel amount is set to 30 to 70%.

As described above, by defining the C content and the Si content, carbon present in the weld metal during post-heat treatment can be graphitized and precipitated in the crystal grains.
Moreover, the composition component of the welding wire 4 used for that purpose is specified, and further, post-heat treatment after welding is performed, whereby the strength of the weld metal 2 is improved, cracking is prevented, and a highly ductile weld is obtained. I was able to.

  A welded part in which the spheroidal graphite cast irons of the present invention or spheroidal graphite cast iron and steel are welded with a Ni-Fe welding material, a welding material used for the welding, and a heat treatment method for the welded part include spheroidal graphite cast iron. It can be widely used for the welding point to be used.

1 Base material 4 Welding wire (welding material)
8 Bond Club

Claims (4)

In welded parts where spheroidal graphite cast irons or spheroidal graphite cast iron and steel are welded with Ni-Fe welding materials,
C and Si contained in the metal structure of the weld metal are both C: 0.5 to 1.0% and Si: 0.5 to 1.0% by weight,
A welded portion in which C contained in the weld metal is precipitated as spherical graphite in the crystal grains.   The weld according to claim 1, wherein the base material of the spheroidal graphite cast iron is ferrite-base spheroidal graphite cast iron that is solid-solution strengthened with either or both of Si and Ni. In order to obtain the weld according to claim 1 or claim 2,
C: 0.3 to 1.3% by weight% of welding material,
Si: 0.3 to 1.3%
Mn: 0.5 to 2.0%,
Ni: 30 to 70%,
A welding material comprising the balance of Fe and inevitable components. After welding the spheroidal graphite cast iron and steel or the spheroidal graphite cast iron using the welding material according to claim 3, the welded part is held at a temperature of 850 ° C. or higher for 30 minutes or more, and then furnace cooling or A heat treatment method for the air-cooled weld.