WO2015068443A1

WO2015068443A1 - Method for producing weld joint

Info

Publication number: WO2015068443A1
Application number: PCT/JP2014/070878
Authority: WO
Inventors: 熊谷　達也; 修一中村
Original assignee: 新日鐵住金株式会社
Priority date: 2013-11-08
Filing date: 2014-08-07
Publication date: 2015-05-14
Also published as: BR112015029349B1; MY158148A; BR112015029349A2; KR101655057B1; PH12015502625B1; MX2015017087A; CA2915026C; CN105339132A; MX352525B; CA2926569C; CN105339132B; AU2014345139B2; WO2015068261A1; AU2014345139A1; PH12015502625A1; CA2926569A1; KR20150136551A; CA2915026A1

Abstract

This weld joint production method is a method for producing a weld joint by subjecting a steel plate having a predetermined Vickers hardness HV, plate thickness, C content, and CEN to gas-shielded arc welding by using a flux-cored wire in which a steel-made outer sheath is filled with a flux, wherein: at the time of said gas-shielded arc welding, no preheating operation is performed in cases where the temperature of the steel plate is 10°C or higher, and, in cases where the temperature of the steel plate is below 10°C, preheating operation is performed such that the temperature of the steel plate is raised to 10°C or higher; the weld metal of the weld joint has a predetermined chemical composition; the weld metal has a CEN of from 0.20 to 0.58 mass%; and the average Vickers hardness HV at a depth 1 mm below the surface of the weld metal is from 337 to 440.

Description

Manufacturing method of welded joint

The present invention has a weld metal that has high hardness, excellent wear resistance, and is resistant to low-temperature cracking when welding high-hardness steel plates with excellent wear resistance used in the construction machinery and industrial machinery fields. The present invention relates to a method for manufacturing a welded joint.
This application claims priority based on PCT / JP2013 / 080242 internationally filed on November 8, 2013, the contents of which are incorporated herein by reference.

Steel plates used for construction machines for excavation and civil engineering work in mines often need to be replaced due to wear, but in order to extend their service life, wear-resistant steel with increased steel hardness Is used. The hardness of the steel sheet varies depending on the environment and purpose of use, but in general, it is HB400 grade (Brinell hardness standard value HB360 to HB440, Vickers hardness standard value HV380 to HV469), HB450 grade (Brinell hardness) Standard values of HB410 to HB490, Vickers hardness standard value of HV435 to HV533), HB500 class (Brinell hardness standard value of HB450 to HB550, Vickers hardness standard value of HV478 to HV585) or HB600 class ( Abrasion-resistant steel sheets having a standard value of Brinell hardness of HB550 to HB650 and a standard value of Vickers hardness of HV585 to HV693) are often used.

Most wear-resistant steels are welded, but the weld metal may require wear resistance close to that of the base material (wear-resistant steel). In order to increase the wear resistance of the weld metal, it is also necessary to increase its hardness. However, when the hardness of the weld metal is increased, low temperature cracks caused by hydrogen that enters during welding are very likely to occur. Furthermore, since the wear-resistant steel having high hardness is used as the base material, the strengthening of the restraining force is also a cause of low temperature cracking.

In order to avoid such cold cracking, preheating is generally performed prior to welding. However, since wear-resistant steel is more likely to be reduced in hardness by heating than ordinary steel, it cannot take a very high preheating temperature.
The hardness of the weld metal is preferably about the same as that of the base material. For example, when HB400 or HB500 class wear resistant steel is used as a base material, it is desirable that the hardness of the weld metal is at least HV337 (HB320) or higher, preferably HV380 (HB360) or higher.

Further, in the weld metal part, what is important from the viewpoint of wear resistance is the hardness near the surface. In multi-layer welding, the weld metal in the lower layer is reheated by subsequent passes, so that the hardness is slightly reduced. In multi-layer welding, the weld metal in the uppermost layer is used. It is sufficient that the vicinity of each surface of the metal has sufficient hardness.
From the above, in a welded joint using a high-hardness wear-resistant steel of HV380 or more and HV693 or less as a base material, the surface hardness is HV337 or more and HV533 or less and having sufficient wear resistance, A welding method for forming a weld metal that does not generate cold cracks even without preheating, or a surface hardness of HV380 or higher and HV533 or lower and sufficient wear resistance, and low temperature cracks without preheating. A welding method that forms a weld metal that does not occur is considered extremely useful.

For example, methods disclosed in Patent Documents 1 to 5 have been proposed as techniques for suppressing the low-temperature cracking caused by hydrogen generated in a high-strength weld metal.
Among these, patent document 1 prevents generation | occurrence | production of a cold crack by making a retained austenite function as a hydrogen trap site about the steel plate used for uses, such as a high intensity | strength line pipe. Patent Document 2 prevents the occurrence of cold cracking by causing an oxide to function as a hydrogen trap site for a steel sheet that is also used for applications such as a high-strength line pipe.

Patent Document 3 discloses a technique for preventing the occurrence of cold cracking by causing Mo carbide to function as a trap site for a steel material having a tensile strength of 800 to 1150 MPa. Patent Document 4 discloses that the amount of diffusible hydrogen in the weld metal immediately after welding is reduced to about 3.0 to 4.0 ml / 100 g by adding an appropriate amount of Mg to the coating material of the coated arc welding material, thereby increasing the tensile strength. A technique for improving cold cracking resistance of a steel material of 880 to 1180 MPa is disclosed. Patent document 5 is disclosing the technique which suppresses a low temperature crack by restrict | limiting the amount of hydrogen contained in the flux cored wire for gas shield arc welding.
These are technologies that can improve the low-temperature cracking property of weld metal having a base metal and weld metal strength of less than 1200 MPa, and having a hardness of HV380 (approximately 1200 MPa in terms of tensile strength) or more and wear resistance. is not.

Furthermore, generally, when an austenitic stainless steel welding material is used, the penetration of hydrogen into the weld metal is greatly reduced, so that the low temperature cracking susceptibility can be lowered. Moreover, since it is an austenite structure, a ductile fall cracking is hard to produce. However, a weld metal using an austenitic stainless steel welding material is not easy to increase strength, that is, hardness, and cannot be expected to have wear resistance.

For this reason, in a welded joint made of a high hardness wear resistant steel of HV 380 or higher and HV 693 or lower, the surface hardness is HV 337 or higher and HV 533 or lower. It is demanded to form a weld metal that is difficult to be welded or a weld metal that has a surface hardness of HV380 or more and HV533 or less and that is excellent in wear resistance and that does not easily cause cold cracking by gas shield arc welding.

Japanese Unexamined Patent Publication No. 2012-176434 Japanese Unexamined Patent Publication No. 2012-218034 Japanese Unexamined Patent Publication No. 2005-40816 Japanese Unexamined Patent Publication No. 11-147196 Japanese Unexamined Patent Publication No. 2009-255168

An object of the present invention is a welded joint using a high-hardness steel plate having a high C content and a surface hardness of HV380 or more and HV693 or less as a base material, and having a surface hardness of HV337 or more and HV533 or less. A method for producing a welded metal having excellent wear resistance and low-temperature cracking, or a welded joint having a surface hardness of HV380 to HV533 and having excellent wear resistance and low-temperature cracking. Is to provide.

In conventional wear-resistant steels, the preheating temperature at the time of welding was important to prevent low temperature cracking, so it was common to weld with the preheating temperature as the top priority with a welding material for mild steel. Therefore, the problem was that the hardness of the weld metal part was low and wear was very likely to occur. In contrast to this, the present invention has newly found that when the hardness of the weld metal part is increased, the weld metal itself is very susceptible to cracking, not the heat-affected part of the base material. Therefore, after investigating the relationship between weld metal CEN and cracks, we found the appropriate range of weld metal CEN.

低温 Cold cracks that occur in the weld metal during welding are affected by the strength of the weld metal, the joint restraint force, and the amount of diffusible hydrogen in the weld metal. The inventors reliably suppress low-temperature cracking with a high-hardness weld metal having a surface hardness of HV337 or more and HV533 or less, or with a higher hardness of a weld metal with a surface hardness of HV380 or more and HV533 or less. As a result of various investigations on the method for achieving this, the most reliable method is to sufficiently reduce the amount of diffusible hydrogen in the weld metal and to reduce the CEN defined by the alloy component in the weld metal from 0.20 to 0.00. The conclusion that it is 58 mass% was obtained.

FIG. 1 shows that the y-type weld cracking test specified in JIS Z3158 was carried out under various conditions with various steel sheets and welding materials with different flux compositions, etc. It is the result of having produced the weld metal which has the amount of diffusible hydrogen, and calculated | required the limit preheating temperature which suppresses the crack generation. FIG. 1 shows the relationship between the amount of diffusible hydrogen in the weld metal and the limit preheating temperature at which cracking is suppressed, organized according to the hardness level of the weld metal.
Here, the low-temperature cracking test was conducted at room temperature (25 ° C.) in accordance with JIS Z3158 (y-type weld cracking test method: 1993), and was accepted as having passed on the surface and the cross section. The measurement test of the amount of diffusible hydrogen was carried out by a gas chromatograph method based on JIS Z3118 (method for measuring the amount of hydrogen in steel welds; 2007).

As shown in FIG. 1, if the amount of diffusible hydrogen in the weld metal immediately after welding is less than 1.0 ml / 100 g, the limit preheating temperature for the occurrence of cold cracking does not depend much on the hardness of the weld metal. Therefore, by setting the amount of diffusible hydrogen to less than 1.0 ml / 100 g, the low-temperature cracking susceptibility between a weld metal having a hardness of HV337 to HV533 and a weld metal having a hardness of HV380 to HV533 is greatly reduced. Can do.

However, reducing the amount of diffusible hydrogen in the weld metal immediately after welding up to this level has not been easy with the prior art. The inventors have made various studies and have newly found that the amount of diffusible hydrogen in the weld metal can be stably reduced to a level that has been difficult in the past by improving the flux composition of the flux-cored wire. . Specifically, the weld metal contains a certain amount of fluoride such as CaF ₂ in the flux component, the amount of oxide is adjusted, and the compounding ratio of fluoride and oxide is within a certain range. It was found that the amount of diffusible hydrogen therein can be stably suppressed to less than 1.0 ml / 100 g.

低温 Low-temperature cracking susceptibility of weld metal depends greatly on the hardness of the weld metal, but is also affected by alloying elements. The inventors investigated the relationship between various alloy compositions and low-temperature cracking susceptibility (cracking suppression preheating temperature) of a weld metal of HV337 to HV533 and a weld metal of HV380 to HV533. The low temperature cracking test is conducted in accordance with JIS Z3158 (y-type weld cracking test method: 1993), and the minimum preheating temperature that does not cause low temperature cracking by changing the preheating temperature is determined as the crack initiation limit preheating temperature. did. In welding, the flux-cored welding wire of the present invention described below is used, and the amount of diffusible hydrogen in the weld metal is less than 1.0 ml / 100 g.

As a result, as shown in FIG. 2, if CEN calculated by Equation 1 (see Welding Form 10. “Welding of Steel Materials”, Industrial Publication (1999), p. 163) is 0.58% by mass or less. It has been found that the cracking limit preheating temperature can be set to room temperature (25 ° C.) or less, and the occurrence of low temperature cracking can be suppressed without preheating.
CEN = [C] + (0.75 + 0.25 × tanh (20 × ([C] −0.12))) × ([Si] / 24 + [Mn] / 6 + [Cu] / 15 + [Ni] / 20 + ([Cr] + [Mo] + [Nb] + [V]) / 5 + 5 × [B]) (Formula 1)
However, the element with [] represents the content (% by mass) of each element. If there is no additive element, zero is substituted in [].

The present invention has been made on the basis of the above findings, and the gist thereof is as follows.

(1) The method for manufacturing a welded joint according to the first aspect of the present invention has a Vickers hardness HV of 380 to 514, a plate thickness of 20 to 100 mm, and a C content of 0.120 to 0. .300 mass%, CEN calculated by the following formula 1 is 0.20 to 0.75 mass%, Vickers hardness HV is more than 514 and less than 565, and the thickness is 12 to 100 mm. A steel sheet having a C content of 0.120 to 0.300 mass%, a CEN calculated by the following formula 1 of 0.20 to 0.75 mass%, and a Vickers hardness HV of 565 It is ultra 693 or less, the plate thickness is 6 to 12 mm, the C content is 0.350 to 0.450 mass%, and CEN calculated by the following formula 1 is 0.20 to 0.85. For any one of the steel plates, A method of manufacturing a welded joint by performing gas shielded arc welding using a flux-cored wire filled with metal, wherein (a) the temperature of the steel sheet is 10 ° C. or higher during the gas shielded arc welding. If the temperature of the steel plate is less than 10 ° C, the preheating operation is performed so that the temperature of the steel plate is 10 ° C or higher, and (b) the flux-cored wire is CaF ₂ , When one or more of BaF ₂ , SrF ₂ , and MgF ₂ are contained and the total content thereof is α, the α is 3.3 to 8.0 in terms of mass% with respect to the total mass of the flux-cored wire. %, And containing at least one of Ti oxide, Si oxide, Mg oxide, and Al oxide, where β is the total content, β is the total mass of the flux-cored wire Vs. That is from 0.10 to 1.50 percent by _{_{_{mass%, CaCO 3, BaCO 3,}}} SrCO 3, the total content of MgCO ₃ is less than 0.60% by mass% relative to the total weight of the flux-cored wire Yes, the content of iron powder in the flux is less than 10.0% by mass% with respect to the total mass of the flux-cored wire, and the ratio of the CaF ₂ content to α is 0.90 or more. The ratio of α to β is 3.0 or more and 80.0 or less, and the content of CaO is less than 0.20% by mass% with respect to the total mass of the flux-cored wire. The chemical components in the flux-cored wire, excluding oxides and metal carbonates, in mass% with respect to the total mass of the flux-cored wire: C: 0.010 to less than 0.060%; Si: 0.0. 5 to 1.80%; Mn: 0.50 to 4.00%; P: 0.050% or less; S: 0.020% or less; Al: 0.005 to 0.150%; Cu: 0 to 0 Ni: 0 to less than 1.00%; Cr: 0 to 3.50%; Mo: 0 to 1.50%; Ti: 0 to 0.150%; Nb: 0 to 0.15%; V: 0 to 0.45%; B: 0 to 0.0500%; Mg: 0 to 2.0%; Ca: 0 to 2.0%; REM: 0 to 0.0150%; balance: Fe and impurities (C) the chemical composition of the weld metal of the weld joint is in mass%: C: 0.100 to 0.170%; Si: 0.05 to 0.80%; Mn: 0.20 to 2.50%; Al: 0.0050 to 0.1000%; P: 0.050% or less; S: 0.020% or less; N: 0.015% or less; Cu: 0 to 0.50% Ni: 0 to less than 0.70%; Cr: 0 to 2.50%; Mo: 0 to 1.00%; Ti: 0 to 0.100%; Nb: 0 to 0.100%; V: 0 to 0.30%; B: 0 to 0.0100%; O: 0 to 0.100%; Mg: 0 to 0.100%; Ca: 0 to 0.100%; REM: 0 to 0.0100%; The balance: Fe and impurities; CEN of the weld metal calculated by the following formula 1 is 0.20 to 0.58% by mass, and the average Vickers hardness HV is 1 mm below the surface of the weld metal. 337 to 440, which satisfies all of the above (a) to (c).
CEN = [C] + (0.75 + 0.25 × tanh (20 × ([C] −0.12))) × ([Si] / 24 + [Mn] / 6 + [Cu] / 15 + [Ni] / 20 + ([Cr] + [Mo] + [Nb] + [V]) / 5 + 5 × [B]) (Formula 1)
However, the element with [] represents the content (% by mass) of each element.

(2) In the method for manufacturing a welded joint according to the second aspect of the present invention, the Vickers hardness HV is 380 to 514, the plate thickness is 20 to 100 mm, and the C content is 0.120 to 0. .300 mass%, CEN calculated by the following formula 1 is 0.20 to 0.75 mass%, Vickers hardness HV is more than 514 and less than 565, and the thickness is 12 to 100 mm. A steel sheet having a C content of 0.120 to 0.300 mass%, a CEN calculated by the following formula 1 of 0.20 to 0.75 mass%, and a Vickers hardness HV of 565 It is ultra 693 or less, the plate thickness is 6 to 12 mm, the C content is 0.350 to 0.450% by mass, and CEN calculated by the following formula 1 is 0.20 to 0.85. For any one of the steel plates, A method of manufacturing a welded joint by performing gas shielded arc welding using a flux-cored wire filled with metal, wherein (a) the temperature of the steel sheet is 10 ° C. or higher during the gas shielded arc welding. If the temperature of the steel plate is less than 10 ° C, the preheating operation is performed so that the temperature of the steel plate is 10 ° C or higher, and (b) the flux-cored wire is CaF ₂ , When one or more of BaF ₂ , SrF ₂ , and MgF ₂ are contained and the total content thereof is α, the α is 3.3 to 8.0 in terms of mass% with respect to the total mass of the flux-cored wire. %, And containing at least one of Ti oxide, Si oxide, Mg oxide, and Al oxide, where β is the total content, β is the total mass of the flux-cored wire Vs. That is from 0.10 to 1.50 percent by _{_{_{mass%, CaCO 3, BaCO 3,}}} SrCO 3, the total content of MgCO ₃ is less than 0.60% by mass% relative to the total weight of the flux-cored wire Yes, the content of iron powder in the flux is less than 10.0% by mass% with respect to the total mass of the flux-cored wire, and the ratio of the CaF ₂ content to α is 0.90 or more. The ratio of α to β is 3.0 or more and 80.0 or less, and the content of CaO is less than 0.20% by mass% with respect to the total mass of the flux-cored wire. The chemical components in the flux-cored wire, excluding oxides and metal carbonates, in mass% with respect to the total mass of the flux-cored wire: C: 0.060 to 0.350%; Si: 0.05 1.80%; Mn: 0.50 to 4.00%; P: 0.050% or less; S: 0.020% or less; Al: 0.005 to 0.150%; Cu: 0 to 0.75 Ni: 0 to less than 1.00%; Cr: 0 to 3.50%; Mo: 0 to 1.50%; Ti: 0 to 0.150%; Nb: 0 to 0.15%; V: B: 0 to 0.0500%; Mg: 0 to 2.0%; Ca: 0 to 2.0%; REM: 0 to 0.0150%; balance: Fe and impurities; (C) the chemical composition of the weld metal of the weld joint is in mass%: C: 0.120-0.250%; Si: 0.05-0.80%; Mn: 0.20-2. 50%; Al: 0.0050 to 0.1000%; P: 0.050% or less; S: 0.020% or less; N: 0.015% or less; Cu: 0 to 0.50%; N : 0 to less than 0.70%; Cr: 0 to 2.50%; Mo: 0 to 1.00%; Ti: 0 to 0.100%; Nb: 0 to 0.100%; V: 0 to 0 30%; B: 0 to 0.0100%; O: 0 to 0.100%; Mg: 0 to 0.100%; Ca: 0 to 0.100%; REM: 0 to 0.0100%; CEN of the weld metal calculated by the following formula 1 is 0.20 to 0.58% by mass, and the average Vickers hardness HV 1 mm below the surface of the weld metal is 380 to 533, which satisfies all of the above (a) to (c).
CEN = [C] + (0.75 + 0.25 × tanh (20 × ([C] −0.12))) × ([Si] / 24 + [Mn] / 6 + [Cu] / 15 + [Ni] / 20 + ([Cr] + [Mo] + [Nb] + [V]) / 5 + 5 × [B]) (Formula 1)
However, the element with [] represents the content (% by mass) of each element.
(3) The method for manufacturing a welded joint according to the third aspect of the present invention has a Vickers hardness HV of more than 565 and not more than 693, a plate thickness of 12 to 20 mm, and a C content of 0.350 to 0. .450% by mass, CEN calculated by the following formula 2 is 0.20 to 0.85% by mass, and the Vickers hardness HV is more than 565 to 693 and the plate thickness is more than 20 mm and 50 mm. Any one of the following: a steel sheet having a C content of 0.350 to 0.450 mass% and a CEN calculated by the following formula 2 of 0.20 to 0.85 mass% On the other hand, a method of manufacturing a welded joint by performing gas shielded arc welding using a flux-cored wire in which a steel outer sheath is filled with flux, (a) during the gas shielded arc welding, The plate thickness is 20m In the following cases, the preheating operation is performed so that the temperature of the steel plate is 100 ° C. or more. When the plate thickness of the steel plate is more than 20 mm, the preheating operation is performed so that the temperature of the steel plate is 150 ° C. or more. (B) The flux-cored wire contains one or more of CaF ₂ , BaF ₂ , SrF ₂ , and MgF ₂ , and when the total content is α, the α is the flux-cored wire. It is 3.3 to 8.0% by mass with respect to the total mass, and contains at least one of Ti oxide, Si oxide, Mg oxide, and Al oxide, and the total content is β and The β is 0.10 to 1.50% by mass% with respect to the total mass of the flux-cored wire, and the total content of CaCO ₃ , BaCO ₃ , SrCO ₃ , and MgCO ₃ is the flux-cored wire. The whole quality of Less than 0.60% by mass% with respect to the content of iron powder in said flux is less than 10.0% in percentage by weight relative to the total weight of the flux-cored wire, inclusion of the CaF ₂ with respect to the α The ratio of the amount is 0.90 or more, the ratio of α to β is 3.0 or more and 80.0 or less, and the content of CaO is 0.20 by mass% with respect to the total mass of the flux-cored wire. % Of the chemical component in the flux-cored wire, excluding metal fluoride, metal oxide, and metal carbonate, in terms of mass% with respect to the total mass of the flux-cored wire: C: 0.060-0. 350%; Si: 0.05 to 1.80%; Mn: 0.50 to 4.00%; P: 0.050% or less; S: 0.020% or less; Al: 0.005 to 0.150 %: Cu: 0 to 0.75% Ni: 0 to less than 1.00%; Cr: 0 to 3.50%; Mo: 0 to 1.50%; Ti: 0 to 0.150%; Nb: 0 to 0.15%; V: 0 to 0.45%; B: 0-0.0500%; Mg: 0-2.0%; Ca: 0-2.0%; REM: 0-0.0150%; balance: Fe and impurities; (C) The chemical composition of the weld metal of the weld joint is in mass%: C: 0.120 to 0.250%; Si: 0.05 to 0.80%; Mn: 0.20 to 2.50% Al: 0.0050 to 0.1000%; P: 0.050% or less; S: 0.020% or less; N: 0.015% or less; Cu: 0 to 0.50%; Ni: 0 to 0 Less than 70%; Cr: 0 to 2.50%; Mo: 0 to 1.00%; Ti: 0 to 0.100%; Nb: 0 to 0.100%; V: 0 to 0.30%; B O: 0 to 0.100%; Mg: 0 to 0.100%; Ca: 0 to 0.100%; REM: 0 to 0.0100%; balance: Fe and impurities; The CEN calculated by the following formula 2 of the weld metal is 0.20 to 0.58% by mass, and the average Vickers hardness HV 1 mm below the surface of the weld metal is 380 to 533. All of the above (a) to (c) are satisfied.
CEN = [C] + (0.75 + 0.25 × tanh (20 × ([C] −0.12))) × ([Si] / 24 + [Mn] / 6 + [Cu] / 15 + [Ni] / 20 + ([Cr] + [Mo] + [Nb] + [V]) / 5 + 5 × [B]) (Formula 2)
However, the element with [] represents the content (% by mass) of each element.

(4) In the method for manufacturing a welded joint according to (1) to (3) above, the content of the CaO in the flux-cored wire is 0.15% or less by mass% with respect to the total mass of the flux-cored wire. It may be.

(5) The method for manufacturing a welded joint according to any one of (1) to (4) above, wherein the metal-containing fluoride, the metal oxide, and the metal carbonate are excluded from the flux-cored wire. The chemical composition may be Ni: 0 to 0.1% by mass% with respect to the total mass of the flux-cored wire.

(6) The method for producing a welded joint according to any one of (1) to (5) above, wherein the metal-containing fluoride, the metal oxide, and the metal carbonate are excluded from the flux-cored wire. The chemical composition is in mass% with respect to the total mass of the flux-cored wire: Cu: 0 to 0.50%; Cr: 0 to 1.00%; Mo: 0 to 0.50%; 050%; Nb: 0 to 0.05%.

(7) In the method for manufacturing a welded joint according to any one of (1) to (6) above, there may be a slit-like gap in the steel outer sheath of the flux-cored wire.
(8) In the method for manufacturing a welded joint according to any one of the above (1) to (6), there may be no gap on the slit in the steel outer shell of the flux-cored wire.

(9) In the method for manufacturing a welded joint according to any one of (1) to (8) above, perfluoropolyether oil may be applied to the surface of the flux-cored wire.

According to each aspect of the present invention, a welded joint using a high-hardness steel plate having a high C content and a surface hardness of HV380 or more and HV693 or less as a base material, the surface hardness of HV320 or more and HV533 or less. It is possible to obtain a weld metal having a weld metal that is excellent in wear resistance and hardly generates low temperature cracks, or has a surface hardness of HV380 or more and HV533 or less and that has excellent wear resistance and low temperature cracks. be able to.

It is a figure which shows the relationship between the hardness of a base material, the amount of diffusible hydrogen in a weld metal, and a crack generation limit preheating temperature. It is a figure which shows the relationship between CEN and a crack generation limit preheating temperature in the weld metal which is HV337 or more and HV533 or less and the amount of diffusible hydrogen in a weld metal is less than 1.0 ml / 100g. It is a figure which shows the cut cross section of a wire. It is a figure which shows the cut cross section of a wire. It is a figure which shows the cut cross section of a wire.

In a welded joint using a high-hardness steel plate as a base material, the inventors, as described above, have a cold crack initiation limit preheating temperature if the amount of diffusible hydrogen in the weld metal immediately after welding is less than 1.0 ml / 100 g. Has found that it does not depend much on the hardness of the weld metal and can greatly reduce the low-temperature cracking susceptibility between a weld metal of HV 337 and HV 533 and a weld metal of HV 380 and HV 533.

Furthermore, the inventors have repeatedly studied various combinations and combinations of flux components of the flux-cored wire in order to reduce the amount of diffusible hydrogen in the weld metal immediately after welding to less than 1.0 ml / 100 g. It was.
As a result, fluorides such as CaF ₂ are particularly effective in reducing hydrogen. By containing a certain amount of the flux component, the amount of diffusible hydrogen in the weld metal can be greatly reduced. The inventors have found that the amount of diffusible hydrogen can be stably suppressed to less than 1.0 ml / 100 g by adjusting the amount and keeping the blending ratio of fluoride and oxide within a certain range.

The present invention has been made based on such studies. Hereinafter, an aspect of the method for manufacturing the welded joint according to the present embodiment will be described.
The present invention uses, as a base material, a high-hardness thick steel plate having a C content of 0.12 to 0.45% by mass, HV380 or more and HV693 or less, which is widely used as a wear-resistant steel plate. The target is a welded joint formed by gas shielded arc welding.
In the present invention, the weld metal has the chemical composition described in (1) or (2) above.
Hereinafter, the reason for limiting the chemical composition of the weld metal will be described. In the following description, “%” means “% by mass” unless otherwise specified.

(C: 0.100 to 0.250%)
C is an element that most affects the hardness of the weld metal. When the base metal hardness is HV380 or higher, it is desirable that the surface hardness of the weld metal is at least HV337 in order to ensure a certain degree of wear resistance in the weld metal. For that purpose, the C content of the weld metal needs to be 0.100% or more. Further, when the base metal hardness is HV380 or more, it is desirable that the surface hardness of the weld metal is HV380 or more in order to ensure wear resistance close to that of the base material. When the surface hardness of the weld metal needs to be HV380 or more, the C content of the weld metal needs to be 0.120% or more. However, if the C content exceeds 0.250%, the hardness of the weld metal exceeds HV533 and the toughness of the weld metal may decrease, so the upper limit of the C content is set to 0.250%. Note that the C content of the weld metal of a welded joint made using a flux-cored wire having a C content of 0.010 to less than 0.060%, which will be described later, may be 0.100 to 0.170%. It is normal. In order to stably obtain a base material hardness of HV380 or higher, the lower limit of the C content may be 0.130% or 0.140%. Moreover, in order to acquire the toughness of a weld metal stably, it is good also considering the upper limit of C content as 0.230% or 0.210%.

(Si: 0.05-0.80%)
Si is a deoxidizing element, and a certain amount is added to the flux in order to reduce the O content of the weld metal and increase the cleanliness. Therefore, the Si content in the weld metal is also 0.05% or more. If necessary, the lower limit of the Si content may be 0.10%, 0.15%, or 0.20%. If Si is contained in an amount exceeding 0.80%, the toughness of the weld metal may be deteriorated, so this is the upper limit. In order to improve the toughness of the weld metal, the upper limit of the Si content may be 0.70%, 0.65%, 0.60%, or 0.50%.

(Mn: 0.20-2.50%)
Since Mn has the effect of forming MnS and suppressing grain boundary embrittlement due to S, it is contained in the weld metal at least 0.20% or more. Further, since Mn is an element that has the effect of ensuring the hardenability of the weld metal and increasing the strength, it is desirable to contain 0.50% or more in order to stably obtain the hardness. In order to improve the hardness of the weld metal, the lower limit of the Mn content may be 0.60%, 0.70%, 0.80%, or 0.90%. On the other hand, if Mn exceeds 2.50%, the grain boundary embrittlement susceptibility increases and the toughness of the weld metal deteriorates, so this is the upper limit. In order to improve the toughness of the weld metal, the upper limit of the Mn content may be limited to 2.30%, 2.10%, 1.90%, 1.70%, or 1.50%.

(Al: 0.0050 to 0.1000%)
Al is a deoxidizing element and, like Si, has the effect of improving the cleanliness of the weld metal by reducing the O content in the weld metal, so a certain amount needs to be added to the flux. . The weld metal of the welded joint obtained using the flux cored wire according to the present embodiment usually contains 0.0050% or more of Al. When the amount of Al is less than 0.0050%, the low temperature toughness of the weld metal may be reduced. On the other hand, if the content exceeds 0.1000%, nitrides and oxides are formed and the toughness of the weld metal is deteriorated, so this is the upper limit. In order to improve the toughness of the weld metal, the upper limit of the Al content may be limited to 0.0900%, 0.0800%, 0.0700%, or 0.0600%.

(P: 0.050% or less)
P is an impurity element and degrades toughness. Therefore, although it is necessary to reduce as much as possible, the P content of the weld metal is limited to 0.050% or less as a range in which an adverse effect on toughness can be tolerated. If necessary, the upper limit of the P content may be limited to 0.030%, 0.0250%, 0.0200%, or 0.0150%. There is no need to limit the lower limit of the P content. The lower limit of the P content is 0%.

(S: 0.020% or less)
S is also an impurity element, and if it is excessively present in the weld metal, it deteriorates both toughness and ductility, so it is preferable to reduce it as much as possible. As a range in which an adverse effect on toughness and ductility can be tolerated, the S content of weld metal is limited to 0.020% or less. If necessary, the upper limit of the S content may be limited to 0.015%, 0.010%, 0.008%, or 0.006%. There is no need to limit the lower limit of the S content. The lower limit of the S content is 0%.

(N: 0.015% or less)
N is inevitably contained in the weld metal, but if it exceeds 0.015%, coarse AlN or BN is formed and the toughness is lowered. The N content is limited to 0.015% or less as an upper limit that can allow an influence on the weld metal. If necessary, the upper limit of the N content may be limited to 0.010%, 0.008%, or 0.006%. There is no need to limit the lower limit of the N content. The lower limit of the N content is 0%.

(O: 0 to 0.100%)
O is inevitably contained in the weld metal, but the O content of the weld metal is limited to 0.100% or less as a range in which an adverse effect on toughness and ductility can be tolerated. If necessary, the upper limit of the O content may be 0.080%, 0.060%, 0.050%, or 0.040%. There is no need to limit the lower limit of the O content. The lower limit of the O content is 0%.

(Cu: 0 to 0.50%)
Since Cu can improve the strength and toughness of the weld metal, it can be contained as a selective element. However, if the Cu content exceeds 0.50%, the toughness may decrease, so the Cu content of the weld metal is set to 0.50% or less. If necessary, the upper limit of Cu content may be 0.40% or 0.30%. There is no need to limit the lower limit of the Cu content. For this reason, the minimum of Cu content is 0%. On the other hand, in order to obtain a sufficient strengthening effect, the weld metal may be contained by 0.10% or more. As a method for incorporating Cu into the weld metal, there are a method of plating the outer surface of the wire, or a method of adding it as a simple substance or an alloy element to the flux.

(Ni: 0 to less than 0.70%)
Ni can be contained as a selective element that is effective for improving toughness. However, when the C content is high, the effect is limited and it is also an expensive element, so the Ni content in the weld metal is less than 0.70%. If necessary, the upper limit of the Ni content may be 0.60%, 0.40%, or 0.20%. There is no need to limit the lower limit of the Ni content. For this reason, the lower limit of the Ni content is 0%. On the other hand, in order to obtain the effect of improving toughness, 0.05% or more may be contained in the weld metal.

(Cr: 0-2.50%)
Cr is an element effective for improving the hardness of the weld metal by increasing the hardenability, and can be contained as a selective element. However, if the content exceeds 2.50% excessively, the toughness may be reduced, so the upper limit of the Cr content is 2.50%. If necessary, the upper limit of the Cr content may be 1.50%, 1.00%, 0.70%, or 0.40%. There is no need to limit the lower limit of the Cr content. For this reason, the lower limit of the Cr content is 0%. On the other hand, when it is added for the purpose of improving the hardness of the weld metal, it may be contained by 0.10% or more in order to obtain the effect.

(Mo: 0-1.00%)
Mo is an element effective for improving the hardness of the weld metal by increasing the hardenability, and can be contained as a selective element. However, if the content exceeds 1.00% excessively, the toughness may be lowered, so the Mo content is limited to 1.00%. If necessary, the upper limit of the Mo content may be 0.70%, 0.60%, 0.40%, or 0.20%. There is no need to limit the lower limit of the Mo content. For this reason, the lower limit of the Mo content is 0%. On the other hand, when added for the purpose of improving the hardness, 0.05% or more may be contained in order to obtain the effect.

(Ti: 0 to 0.100%)
Ti, like Al, is effective as a deoxidizing element, has an effect of reducing the O content in the weld metal, and can be contained as a selective element. It is also effective for fixing the solid solution N and mitigating the adverse effect on toughness. However, when the Ti content in the weld metal exceeds 0.100%, it becomes a coarse oxide. Since the possibility of toughness deterioration due to excessive toughening due to excessive precipitation strengthening increases, the upper limit of the Ti content is set to 0.100%. If necessary, the upper limit of the Ti content may be 0.080%, 0.050%, 0.030%, or 0.020%. There is no need to limit the lower limit of the Ti content. For this reason, the lower limit of the Ti content is 0%. You may make it contain 0.010% or more for the purpose of toughness improvement.

(Nb: 0 to 0.100%)
Nb has the effect of improving the hardness of the weld metal by solid solution, and can be contained as a selective element. However, if the content exceeds 0.100%, it is not preferable because it is excessively contained in the weld metal and coarse precipitates are formed to deteriorate toughness. Therefore, the upper limit of the Nb content is 0.100%. To do. If necessary, the upper limit of the Nb content may be 0.080%, 0.050%, 0.030%, or 0.020%. There is no need to limit the lower limit of the Nb content. For this reason, the lower limit of the Nb content is 0%. You may make it contain 0.010% or more for the purpose of the hardness improvement of a weld metal.

(V: 0 to 0.30%)
V is an element effective for improving the hardness of the weld metal by increasing the hardenability, and can be contained as a selective element. However, if the content exceeds 0.30%, the toughness may be lowered, so the V content is 0.30% as the upper limit. As needed, it is good also considering the upper limit of V content as 0.25%, 0.20%, or 0.15. There is no need to limit the lower limit of the V content. For this reason, the lower limit of the V content is 0%. You may make it contain 0.01% or more for the hardness improvement of a weld metal.

(B: 0 to 0.0100%)
When an appropriate amount of B is contained in the weld metal, it has an effect of forming a BN in combination with the solid solution N and reducing the adverse effect on the toughness of the solid solution N. B also has the effect of enhancing the hardenability and contributing to the strength improvement, and can be contained as a selective element. In order to obtain these effects, 0.0003% or more may be contained. On the other hand, when the B content exceeds 0.0100%, B in the weld metal becomes excessive, and coarse toughness is deteriorated by forming coarse B compounds such as BN and Fe ₂₃ (C, B) _6. Is not preferable. Therefore, the upper limit of the B content when B is contained is 0.0100%. If necessary, the upper limit of the B content may be 0.0080%, 0.0060%, 0.0040%, or 0.0020%. There is no need to limit the lower limit of the B content, and the lower limit of the B content is 0%.

(Mg: 0 to 0.100%)
There is no need to limit the lower limit of the Mg content, and the lower limit of the Mg content is 0%. However, Mg is a strong deoxidizing element, and may be contained by 0.001% or more in order to reduce the O content in the weld metal and improve the ductility and toughness of the weld metal. However, if the Mg content in the weld metal exceeds 0.100%, a decrease in toughness due to the formation of coarse oxides in the weld metal cannot be ignored. For this reason, also when it contains Mg, Mg content shall be 0.100% or less. If necessary, the upper limit of the Mg content may be 0.0080%, 0.0060%, 0.0040%, or 0.0020%.

(Ca: 0 to 0.100%)
(REM: 0-0.0100%)
There is no need to limit the lower limit of Ca and REM content, and the lower limit of Ca and REM content is 0%. However, both Ca and REM are effective in improving the ductility and toughness by changing the structure of the sulfide in the weld metal and reducing the size of the sulfide and oxide. You may contain REM 0.0002% or more. On the other hand, if it is contained excessively, it causes coarsening of sulfides and oxides, leading to deterioration of ductility and toughness. Therefore, the upper limit of each inclusion is 0.100% for Ca and 0.0100% for REM. To do.

The weld metal containing the above chemical composition may contain impurities that are mixed in during the manufacturing process, etc., as long as the balance containing iron (Fe) as a main component does not hinder the characteristics of the welded joint according to the present embodiment. .

(CEN: 0.20 to 0.58 mass%)
As shown in FIG. 2, in a weld metal of HV380 or more and HV533 or less, when the amount of diffusible hydrogen in the weld metal is less than 1.0 ml / 100 g, CEN calculated by Formula 1 is 0.58% by mass or less. By doing so, in the y-type weld cracking test of JIS Z3158, the crack initiation limit preheating temperature is 25 ° C. or less, and welding without substantially preheating becomes possible.
Here, in order to reliably prevent weld cracking, the upper limit of CEN may be set to 0.55% by mass, 0.53% by mass, 0.50% by mass, 0.47% by mass, or 0.45% by mass. In order to make the hardness of the weld metal HV380 or more, the lower limit of CEN is 0.20% by mass. The higher the hardness of the weld metal, the better the wear resistance. Therefore, the lower limit of CEN may be 0.24 mass%, 0.28 mass%, 0.30 mass%, or 0.32 mass%.
(A) The base material has a Vickers hardness HV of 380 to 514 (corresponding to HB 360 to 475), the base material has a thickness of 20 to 100 mm, and the base material has a C content of 0.120 to A base material having 0.300% and CEN calculated by Formula 1 of 0.20 to 0.75% by mass.
(B) The Vickers hardness HV of the base material is 514 to 565 or less (corresponding to HB475 to 530 or less), the thickness of the base material is 12 to 100 mm, and the C content of the base material is 0.120 to A base material having 0.300% and CEN calculated by Formula 1 of 0.20 to 0.75% by mass.
(C) The base material has a Vickers hardness HV of over 565 to 693 (corresponding to HB 530 of over 650), the base material has a thickness of 6 to 12 mm, and the base material has a C content of 0.350 to A base material having 0.450% and CEN calculated by Formula 1 of 0.20 to 0.85 mass%.
If the base metal temperature satisfying any one of the above (a) to (c) is 10 ° C or higher during gas shielded arc welding, there is no need to perform preheating work during welding. When the temperature of the material is less than 10 ° C., it is necessary to perform preheating work so that the temperature of the base material becomes 10 ° C. or higher. That is, it is necessary to perform the preheating work so that the temperature of the base material (steel plate) is 10 ° C. or higher only when the temperature of the base material (steel plate) is less than 10 ° C. The upper limit of the base material temperature (preheating temperature) is not particularly required, but may be less than 75 ° C or less than 50 ° C.
(D) The base material has a Vickers hardness HV of more than 565 and less than 693 (corresponding to more than HB 530 and less than 650), the thickness of the base material is 12 to 20 mm, and the C content of the base material is 0.350 to A base material having 0.450% and CEN calculated by Formula 1 of 0.20 to 0.85 mass%.
(E) The Vickers hardness HV of the base material is more than 565 to 693 or less (corresponding to HB 530 or more and 650 or less), the thickness of the base material is more than 20 mm and 50 mm or less, and the C content of the base material is 0.350. A base material having a CEN of 0.20 to 0.85% by mass calculated from Equation 1.
For a base material satisfying the above (d) or (e), when the thickness of the base material is 20 mm or less during gas shielded arc welding, the base material is preheated to 100 ° C. or more, and the thickness of the base material is In the case of over 20 mm, the base material is preheated to 150 ° C. or higher. The upper limit of the base material temperature (preheating temperature) is not particularly required, but may be less than 175 ° C or less than 150 ° C. Moreover, in order to make it HV380 or more, CEN shall be 0.20 mass% or more.
CEN = [C] + (0.75 + 0.25 × tanh (20 × ([C] −0.12))) × ([Si] / 24 + [Mn] / 6 + [Cu] / 15 + [Ni] / 20 + ([Cr] + [Mo] + [Nb] + [V]) / 5 + 5 × [B]) (Formula 1)
However, the element with [] represents the content (% by mass) of each element.

In Formula 1, an element that is not contained substitutes zero in [] corresponding to the element. This calculation method is common to the base material (steel plate) and the weld metal.

In the present invention, the average Vickers hardness of 1 mm below the surface of the weld metal is further set to HV337 or higher and HV533 or lower, or HV380 or higher and HV533 or lower. In the present invention, the amount of diffusible hydrogen immediately after welding is set to be less than 1.0 ml / 100 g for the weld metal.
If the hardness at a position 1 mm below the surface is HV337 or higher and HV533 or lower, the wear resistance requirement necessary for the weld metal is satisfied. If it is less than HV337, the wear resistance is insufficient. If it exceeds HV533, cold cracking is likely to occur.
The hardness is measured by cutting a cross section perpendicular to the welding direction in a weld metal, collecting a polished sample, measuring 10 points of Vickers hardness at a position 1 mm below the surface of the weld metal, and calculating an average value. Shall be determined by

Further, as described above with reference to FIG. 1, the amount of diffusible hydrogen in the weld metal immediately after welding is less than 1.0 ml / 100 g. It does not depend much on the hardness, and the cold cracking susceptibility of the weld metal having a hardness of HV337 to HV533 and the weld metal of HV380 to HV533 can be greatly reduced.
The amount of diffusible hydrogen is measured by a gas chromatographic method based on JIS Z 3118 (Method for measuring the amount of hydrogen in steel welds; 2007).
Since the diffusion rate of hydrogen is relatively high at room temperature, the amount of diffusible hydrogen in the weld metal must be measured immediately after welding. For this reason, unless it measures immediately after welding, the amount of diffusible hydrogen cannot be measured correctly.

In order to manufacture a welded joint having a weld metal as described above, a high-hardness thick steel plate to be welded is used as a base material, and, for example, the two base materials are set at a welding position so as to form a groove therebetween. Then, by performing gas shielded arc welding using a flux-cored welding wire and generating a weld metal between the base materials, a weld joint composed of the weld metal and base metal plates on both sides thereof is formed.
Hereinafter, steel plates, flux-cored welding wires, welding conditions and the like used for forming the weld metal will be described.

As a steel plate used as a base material, a high-hardness thick steel plate having a C content of 0.120% or more and 0.450% or less and HV380 or more and HV693 or less in mass% is an object.
As the plate thickness of the steel plate to be used, the thickness of 6 mm or more and 100 mm or less, which is generally referred to as a thick plate, is targeted.
Steel sheets satisfying such conditions are widely used in places where wear resistance is required, such as machinery for civil engineering and construction work, and there is no particular limitation on the chemical composition other than the C content. For example,
C: 0.120 to 3.000%, Si: 0.10 to 0.55%, Mn: 0.20 to 2.00%, Al: 0.01 to 0.10%, P: 0.020% Hereinafter, S: 0.015% or less, Cu: 0.50% or less, Ni: 1.00% or less, Cr: 1.20% or less, Mo: 0.60% or less, Nb: 0.05% or less, There is steel containing V: 0.10% or less and B: 0.0050% or less. Further, the CEN calculated by the equation 1 is 0.20 to 0.85% by mass.
In order to prevent weld cracks from occurring in the weld heat affected zone (HAZ) of the base metal, the upper limit of CEN is set to 0.85% by mass. In order to prevent weld cracking in the HAZ part more reliably, the upper limit of CEN is 0.80 mass%, 0.75 mass%, 0.73 mass%, 0.70 mass%, 0.68 mass%, 0 It is good also as .65 mass%, 0.63 mass%, or 0.60 mass%. In order to make the hardness of the base material HV380 or more, the lower limit of CEN is 0.20% by mass. In order to increase the hardness of the base material, the lower limit of CEN may be 0.24 mass%, 0.28 mass%, 0.30 mass%, 0.32 mass%, 0.35 mass% or 0.38 mass%. Good. A steel sheet having a base metal hardness of HV565 or less generally has a CEN of less than 0.75% by mass. Therefore, the upper limit of the CEN of a steel sheet having a base metal hardness of HV565 or less is set to 0.75% by mass. .
The method for measuring the hardness of the base material is a method in which five or more Vickers hardnesses at a position 1 mm below the surface of the cross section in the thickness direction of the base material are measured to obtain an average value.

Subsequently, the flux-cored welding wire to be used will be described separately for the flux component and the alloy component. In addition, content of the component in description about a flux cored welding wire represents the mass% with respect to the total mass of a flux cored welding wire.
First, the flux component inserted into the inside of the steel outer sheath of the wire will be described.

One or more metal fluorides of CaF ₂ , BaF ₂ , SrF ₂ , MgF ₂ , Ti oxide (eg TiO ₂ ), Si oxide (eg SiO ₂ ), Mg oxide (eg MgO), By containing a certain amount of one or more metal oxides of Al oxide (for example, Al ₂ O ₃ ) in the welding wire and keeping the ratio of the fluoride and oxide within a certain range. The amount of diffusible hydrogen in the weld metal can be stably reduced to less than 1.0 ml / 100 g.
In order to obtain this effect, when the total amount of CaF ₂ , BaF ₂ , SrF ₂ and MgF ₂ to be contained is α, the total amount α is 3.3% or more by mass% with respect to the total mass of the flux-cored wire, 8 0.0% or less, and when the total amount of Ti oxide, Si oxide, Mg oxide and Al oxide contained is β, the total amount β is 0% by mass with respect to the total mass of the flux-cored wire. The ratio of the CaF ₂ content to the α is 0.90 or more, and the ratio of the total amount α to the total amount β ([total amount α ] / [Total amount β]) is 3.0 or more and 80.0 or less.

If the total amount α of the metal fluoride contained is less than 3.3%, the amount of diffusible hydrogen in the weld metal cannot be stably reduced to less than 1.0 ml / 100 g. In order to further reduce the amount of diffusible hydrogen in the weld metal, the lower limit of the total amount α may be 3.5%, 3.7%, or 3.9%. On the other hand, if it exceeds 8.0%, welding fume and slag are excessively generated, so that welding workability is remarkably lowered, which is not preferable. In order to avoid excessive formation of welding fume and slag, the upper limit of the total amount α may be 7.5%, 7.0%, 6.5%, 6.0%, or 5.7%. If the total amount β of the metal oxides contained is less than 0.10%, the shape of the weld bead may be deteriorated, and if it exceeds 1.50%, the toughness may be lowered. In order to improve the shape of the weld bead, the lower limit of the total amount β may be 0.20%, 0.30%, 0.40%, or 0.50%. In order to improve toughness, the upper limit of the total amount β may be 1.30%, 1.20%, 1.10%, 1.00%, 0.90%, or 0.80%.
Further, if the ratio of the total amount α to the total amount β is less than 3.0, the amount of diffusible hydrogen in the weld metal cannot be stably reduced to less than 1.0 ml / 100 g, and if it exceeds 80.0 Since welding fume and slag are excessively generated, welding workability is remarkably lowered, which is not preferable. In order to further reduce the amount of diffusible hydrogen in the weld metal, the lower limit of the ratio ([total amount α] / [total amount β]) is set to 3.2, 3.5, 3.7, or 4.0. Also good. In order to avoid excessive generation of welding fume and slag, the upper limit of the ratio ([total amount α] / [total amount β]) is set to 40.0, 30.0, 20.0, 15.0 or 13. It may be 0. When the ratio of the content of CaF _{2 to} α is less than 0.90, the amount of diffusible hydrogen in the weld metal cannot be made less than 1.0 ml / 100 g. This is because CaF ₂ has the greatest effect of reducing the amount of diffusible hydrogen among metal fluorides. The ratio of the content of CaF ₂ with respect to α is maximized when no metal fluoride other than CaF ₂ is contained in the flux. Therefore, the upper limit of the ratio of the content of CaF _{2 to} α is 1.0.

From the above, the ratio of the total amount α of metal fluoride to the total amount α of metal fluoride, the total amount β of metal oxide, and the total amount β of metal oxide is limited as described above.
The total amount β is the content in the flux-cored wire, and the total content is also included in binders (water glass containing SiO ₂ as a main component) used for flux granulation. .

In the flux-cored welding wire according to this embodiment, one or more metal carbonates of CaCO ₃ , BaCO ₃ , SrCO ₃ , and MgCO ₃ are further added for the purpose of improving the arc stability action and the arc concentration. it can. However, if one or more of these metal carbonates are added in an amount of 0.60% or more, the arc concentration is too strong, resulting in an increased amount of spatter and an increased amount of oxygen in the weld metal. Therefore, when these metal carbonates are contained, the total content is less than 0.60%. The lower limit of the total content of these metal carbonates is 0%. The upper limit may be set to 0.50%, 0.40%, 0.20%, or 0.10% in order to suppress the amount of spatter generated.

The reason why metal fluoride reduces the amount of diffusible hydrogen is not necessarily clear, but was metal fluoride decomposed by a welding arc, and the generated fluorine combined with hydrogen and dissipated into the atmosphere as HF gas? Alternatively, it is considered that hydrogen is fixed as HF in the weld metal as it is.

In the present invention, it is preferable not to add CaO to the flux. Therefore, the lower limit value of the CaO content is 0%. However, CaO may be contained in the flux raw material. In that case, the CaO content is limited to less than 0.20%. Preferably it is 0.15% or less or 0.10% or less. If the content is limited to less than 0.20%, the effect of the welded joint manufacturing method according to the present embodiment can be obtained. Since CaO changes to CaOH when exposed to the atmosphere, it may increase diffusible hydrogen in the weld metal.

The amount of alloying elements in the flux-cored wire excluding metal fluorides, metal oxides, and metal carbonates is also limited as follows.

(C: When the average Vickers hardness HV 1 mm below the surface of the weld metal is 337 to 440, it is 0.010 to 0.350%, and the average Vickers hardness HV 1 mm below the surface of the weld metal is 380 to 533. In the case of 0.060 to 0.350%)
If the C content in the flux-cored wire is less than 0.010%, the C content in the weld metal is less than 0.100% and the hardness of the weld metal is less than HV337. The C content is 0.010% or more. Furthermore, if the C content in the flux-cored wire is less than 0.060%, the C content of the weld metal is less than 0.120% and the hardness of the weld metal is less than HV380. In order to set the thickness to HV380, the C content in the flux-cored wire is set to 0.060% or more. In order to improve the hardness of the weld metal, the lower limit value of the C content may be 0.020% or 0.030%. In order to further improve the hardness of the weld metal, the lower limit of the C content may be 0.070%, 0.080%, 0.090%, 0.100%, or 0.110%. If the C content in the flux-cored wire exceeds 0.350%, the C content in the weld metal exceeds 0.250%, so the C content in the flux-cored wire is 0.350% or less. . In order to improve the cold cracking resistance of the weld metal, the upper limit of the C content may be 0.300%, 0.250%, 0.180%, 0.170%, or 0.160%.

(Si: 0.05-1.80%)
If the Si content in the flux-cored wire is less than 0.05%, the Si content in the weld metal is less than 0.05%, so the Si content in the flux-cored wire is 0.05% or more. . In order to reduce the O content in the weld metal, the lower limit of the Si content may be 0.10%, 0.20%, 0.30%, or 0.40%. If the Si content in the flux-cored wire exceeds 1.80%, the Si content in the weld metal exceeds 0.80% even if oxidation consumption is taken into consideration, so the Si content in the flux-cored wire is 1 80% or less. In order to improve the toughness of the weld metal, the upper limit of the Si content may be 1.50%, 1.20%, 1.00%, 0.80%, or 0.60%.

(Mn: 0.50 to 4.00%)
If the Mn content in the flux-cored wire is less than 0.50%, the Mn content in the weld metal is less than 0.20%, so the Mn content in the flux-cored wire is 0.50% or more. . In order to improve the hardness of the weld metal, the lower limit of the Mn content may be 0.70%, 0.80%, 0.90%, 1.00%, or 1.10%. If the Mn content in the flux-cored wire exceeds 4.00%, the Mn content of the weld metal exceeds 2.50% even if oxidation consumption is taken into consideration, so the Mn content in the flux-cored wire is 4. 00% or less. In order to improve the toughness of the weld metal, the upper limit of the Mn content may be 3.00%, 2.50%, 2.20%, 2.00%, or 1.80%.

(P: 0.050% or less)
If the P content in the flux-cored wire exceeds 0.050%, the P content in the weld metal may exceed 0.050%, so the P content in the flux-cored wire is 0.050%. The following. If necessary, the upper limit of the P content may be limited to 0.030%, 0.025%, 0.020%, or 0.015%. There is no need to limit the lower limit of the P content. The lower limit of the P content is 0%.

(S: 0.020% or less)
If the S content in the flux-cored wire exceeds 0.020%, the S content in the weld metal may exceed 0.020%, so the S content in the flux-cored wire is 0.020%. The following. If necessary, the upper limit of the S content may be limited to 0.015%, 0.010%, 0.008%, or 0.006%. There is no need to limit the lower limit of the S content. The lower limit of the S content is 0%.

(Al: 0.005 to 0.150%)
If the Al content in the flux-cored wire is less than 0.005%, the Al content in the weld metal is less than 0.005%, so the Al content in the flux-cored wire is 0.005% or more. . In order to further reduce the O content in the weld metal, the lower limit of the Al content may be 0.007%, 0.010%, or 0.012%. If the Al content in the flux cored wire exceeds 0.150%, the Al content in the weld metal may exceed 0.100%, so the Al content in the flux cored wire is 0.150%. The following. In order to improve the toughness of the weld metal, the upper limit of the Al content may be limited to 0.090%, 0.070%, 0.050%, or 0.040%.

(Cu: 0 to 0.75% or less)
If the Cu content in the flux-cored wire exceeds 0.75%, the Cu content in the weld metal exceeds 0.50%, so the Cu content in the flux-cored wire is 0.75% or less. . In order to reduce the Cu content of the weld metal, the Cu content may be 0.50% or less. If necessary, the upper limit of Cu content may be 0.40% or 0.30%. There is no need to limit the lower limit of the Cu content. For this reason, the minimum of Cu content is 0%. On the other hand, in order to improve the hardness of the weld metal, the weld metal may contain 0.10% or more of Cu.

(Ni: 0 to less than 1.00%)
When the Ni content in the flux-cored wire is 1.00% or more, the Ni content of the weld metal is 0.70% or more, and the alloy cost of the wire becomes high. Therefore, the Ni content in the flux-cored wire is Less than 1.00%. In order to prevent solidification cracking of the weld metal, the upper limit of the Ni content may be 0.50%, 0.40%, 0.30%, 0.20%, or 0.10%. There is no need to limit the lower limit of the Ni content. For this reason, the lower limit of the Ni content is 0%.

(Cr: 0 to 3.50%)
If the Cr content in the flux-cored wire exceeds 3.50%, the Cr content in the weld metal exceeds 2.50%, so the Cr content in the flux-cored wire is 3.50% or less. . If necessary, the upper limit of the Cr content may be 1.50%, 1.00%, 0.50%, or 0.10%. There is no need to limit the lower limit of the Cr content. For this reason, the lower limit of the Cr content is 0%. On the other hand, when added for the purpose of improving the hardness of the weld metal, 0.05% or more may be contained in order to obtain the effect.

(Mo: 0 to 1.50%)
If the Mo content in the flux-cored wire exceeds 1.50%, the Mo content in the weld metal exceeds 1.00%, so the Mo content in the flux-cored wire is 1.50% or less. . In order to improve toughness, the upper limit of the Mo content may be 0.70%, 0.50%, 0.30%, or 0.20%. There is no need to limit the lower limit of the Mo content. For this reason, the lower limit of the Mo content is 0%. On the other hand, when added for the purpose of improving the hardness of the weld metal, 0.05% or more may be contained in order to obtain the effect.

(Ti: 0 to 0.150%)
If the Ti content in the flux-cored wire exceeds 0.150%, the Ti content of the weld metal exceeds 0.100%, so the Ti content in the flux-cored wire is 0.150% or less. . In order to improve toughness, the upper limit of the Ti content may be 0.100%, 0.080%, or 0.050%. There is no need to limit the lower limit of the Ti content. For this reason, the lower limit of the Ti content is 0%. You may make it contain 0.010% or more for the purpose of toughness improvement.

(Nb: 0 to 0.15%)
If the Nb content in the flux-cored wire exceeds 0.15%, the Nb content in the weld metal exceeds 0.10%, so the Nb content in the flux-cored wire is 0.15% or less. . In order to improve toughness, the upper limit of the Nb content may be 0.10%, 0.08%, or 0.05%. There is no need to limit the lower limit of the Nb content. For this reason, the lower limit of the Nb content is 0%. You may make it contain 0.01% or more for the purpose of the hardness improvement of a weld metal.

(V: 0 to 0.45%)
If the V content in the flux-cored wire exceeds 0.45%, the V content in the weld metal exceeds 0.30%, so the V content in the flux-cored wire is 0.45% or less. . In order to improve toughness, the upper limit of the V content may be 0.25%, 0.20%, or 0.15%. There is no need to limit the lower limit of the V content. For this reason, the lower limit of the V content is 0%. You may make it contain 0.01% or more for the hardness improvement of a weld metal.

(B: 0-0.0500%)
If the B content in the flux-cored wire exceeds 0.0500%, the B content in the weld metal exceeds 0.0100%, so the B content in the flux-cored wire is 0.0500% or less. . In order to improve toughness, the upper limit of the B content may be 0.0400%, 0.0200%, 0.0100%, or 0.0050%. There is no need to limit the lower limit of the B content, and the lower limit of the B content is 0%.

(Mg: 0-2.0%)
If the Mg content in the flux-cored wire exceeds 2.0%, the Mg content in the weld metal exceeds 0.10%, so the Mg content in the flux-cored wire is 2.0% or less. . In order to improve the toughness and ductility of the weld metal, the upper limit of the Mg content may be 1.5%, 1.0%, 0.4%, or 0.2%. There is no need to limit the lower limit of the Mg content, and the lower limit of the Mg content is 0%.

(Ca: 0 to 2.0%)
If the Ca content in the flux-cored wire exceeds 2.0%, the Ca content in the weld metal exceeds 0.10%, so the Ca content in the flux-cored wire is 2.0% or less. . In order to improve the toughness and ductility of the weld metal, the upper limit of the Ca content may be 1.5%, 1.0%, 0.5%, or 0.3%. There is no need to limit the lower limit of the Ca content, and the lower limit of the Ca content is 0%.

(REM: 0-0.0150%)
If the REM content in the flux-cored wire exceeds 0.0150%, the REM content in the weld metal exceeds 0.0100%, so the REM content in the flux-cored wire is 0.0150% or less. . In order to improve the toughness and ductility of the weld metal, the upper limit of the REM content may be 0.0100%, 0.0050%, or 0.0030%. There is no need to limit the lower limit of the REM content, and the lower limit of the REM content is 0%.

The above is the reason for limitation regarding the chemical composition of the flux-cored wire according to the present embodiment. Other chemical components of the remaining alloy may contain impurities mixed in the manufacturing process or the like as long as the balance containing Fe as a main component does not hinder the characteristics of the welded joint according to the present embodiment. The Fe component includes Fe in the steel outer shell, iron powder added in the flux, and Fe in the alloy component. The content of iron powder in the flux is less than 10.0% in mass% with respect to the total mass of the flux-cored wire. When there is much iron powder content, the amount of oxygen may increase. If necessary, the iron powder content may be less than 5.0% or less than 1.0%. Since it is not necessary to contain iron powder, the lower limit of the iron powder content is 0%.

Subsequently, the form of the flux-cored wire will be described.
A flux-cored wire includes a seamless wire without a slit-like seam in the steel outer shell (that is, a wire in which the steel outer seam is welded), and a wire having a seam with a slit-like gap at the steel outer seam. And can be broadly divided. In the present invention, any cross-sectional structure can be adopted, but it is preferable that there is no slit-like seam (seamless wire) in order to suppress cold cracking of the weld metal.

水素 Hydrogen that penetrates into the weld during welding diffuses into the weld metal and on the steel side, accumulates in the stress concentration part, and causes cold cracking. This hydrogen source can increase moisture contained in the welding material, moisture mixed in from the atmosphere, rust and scale attached to the steel surface, etc., but under the welding where the cleanliness of the weld and the gas shield conditions are sufficiently controlled. Then, hydrogen mainly contained in water in the wire is a main factor of diffusible hydrogen existing in the weld joint.

For this reason, it is desirable to make the steel outer shell into a slit-like seamless (seamless) pipe, and to suppress the invasion of hydrogen in the atmosphere from the steel outer shell to the flux after the wire is manufactured and used. . In the case of a pipe with a slit-like seam (having a seam) in the steel outer skin, moisture in the atmosphere easily enters the flux from the slit-like seam (seam part) of the outer skin, and as it is, hydrogen such as moisture Source intrusion cannot be prevented. Therefore, when the period until use after production is long, the entire wire is preferably vacuum-packed or stored in a container that can be kept dry.
Further, in order to improve the wire feedability, lubricating oil may be applied to the wire surface. From the viewpoint of reducing diffusible hydrogen, the lubricating oil applied to the wire surface is preferably an oil that does not contain hydrogen, such as perfluoropolyether (PFPE) oil.

The flux cored wire used in the present invention can be manufactured by the same manufacturing process as that of a normal flux cored wire manufacturing method.
That is, first, a steel strip to be an outer skin and a flux containing metal fluoride, an alloy component, a metal oxide, a metal carbonate, and an arc stabilizer are prepared so as to have predetermined contents. While feeding the steel strip in the longitudinal direction, it is formed into an open tube (U-shaped) with a forming roll to form a steel outer shell. During this forming, flux is supplied from the opening of the open tube, and the opposing edge surface of the opening is Butt seam welding. A seamless pipe obtained by welding is drawn and annealed during or after the drawing process to obtain a slit-like seamless (seamless) wire having a desired wire diameter. Further, a wire having a slit-like seam (having a seam) is obtained by supplying a flux from an opening of an open pipe, then forming a pipe with a seam without seam welding, and drawing the wire. A cross section of a wire without slit-like gaps made by butt seam welding looks like FIG. 3A. If this cross section is polished and etched, welding marks are observed, but if not etched, no welding marks are observed. Therefore, it may be called seamless. It is described as “seamless type” in the “New Edition Introduction to Welding and Joining Technology” (2008) Sangyo Shuppan, p.111, edited by the Japan Welding Society. As shown in FIG. 3B, a wire without slit-like gaps can be obtained even after brazing and brazing or brazing as shown in FIG. 3C. In FIG. 3B and FIG. 3C, the wire as it is without brazing becomes a wire having a slit-like gap.

In the present invention, for the steel sheet, using a flux-cored wire that meets the above-mentioned conditions, by performing multi-layer welding by gas shield arc welding, and forming a weld metal that meets the above-described conditions, The object can be achieved, and the method of gas shield arc welding is not particularly limited, and a commonly used method can be adopted. For example, as the shielding gas, in addition to 100% CO ₂ gas, a mixed gas of Ar gas and 3 to 20 vol% CO ₂ gas can be used. The flow rate of the shielding gas can be a normal condition, that is, about 15 to 30 L / min.
The welding conditions such as current and voltage are, for example, a current of 200 to 350 A and a voltage of 25 to 35 V. The welding speed may be controlled so that the welding heat input is 10 to 50 kJ / cm.

The shape of the welded joint to be manufactured is determined according to the application and is not particularly limited. It can be applied to welded joints that form grooves, such as ordinary butt joints, square joints, and T joints. Therefore, the shape of the steel plate to be welded is not limited as long as at least the portion forming the welded joint is plate-like, and the whole may not be a plate, and includes, for example, a shape steel. Moreover, it is not limited to what is comprised from a separate steel plate, The butt-welding joint of what shape | molded one steel plate in predetermined shapes, such as a tubular shape, may be sufficient.

Next, the feasibility and effect of the welded joint according to the present embodiment will be described by way of examples.
A steel plate having the components shown in Table 1 was used as a base material. In addition, the same steel plate as the base material was used for the backing metal for welding.
While forming the steel strip in the longitudinal direction, it is formed into an open tube by a forming roll. During this forming, a flux is supplied from the opening of the open tube, and the opposite edge surfaces of the opening are butt-seamed and welded to form a slit. A seamless pipe was used, and annealing was performed in the course of drawing the drawn wire, and a flux-cored wire with a final wire diameter of φ1.2 mm was made as a trial product. A part of the tube was a slit-like pipe that was not seam-welded, and a wire with a wire diameter of φ1.2 mm was prototyped by drawing it. In the case of a wire having a slit-like gap, the entire wire was vacuum-packed and stored in a container that can be kept dry until welding.
The analysis of the chemical composition of the prototype flux cored wire was performed as follows. First, the filled flux was taken out from the flux-cored wire, and the flux-cored wire was divided into a steel outer shell and a flux. The chemical component of the steel outer skin was determined by measuring the content of each metal component by chemical analysis. The chemical composition of the flux was performed according to the following procedure. First, quantitative evaluation of the constituents and components of the flux was performed by X-ray diffraction and fluorescent X-ray analysis. Thereafter, the flux was separated into a slag component and an alloy component using a beneficiation method such as flotation and magnetic beneficiation, and each chemical component was analyzed by performing chemical analysis and gas analysis. Tables 2-1-1 to 2-2 and Tables 3-1-1 to 3-2 show the chemical compositions of the prototype flux cored wires.

Using this flux-cored wire, the above base material was abutted at a root gap of 16 mm and a groove angle of 20 °, and using a backing metal, under the welding conditions shown in Tables 4-1-1 to 4-2-3 Welding was performed. The groove surface of the base material and the surface of the backing metal were subjected to buttering with two or more layers and a height of 3 mm or more using a flux-cored wire to be tested.
Here, Ti oxide, Si oxide, Mg oxide, Al oxide, respectively by using the _{_{TiO 2, SiO 2, MgO,}} Al 2 O 3. In Tables 2-2 and 2-4, the metal carbonates are CaCO ₃ , BaCO ₃ , SrCO ₃ , and MgCO ₃ .

The chemical composition analysis results of the obtained weld metal are shown in Table 5-1-1, Table 5-1-2, Table 5-2-1, Table 5-2-2, Table 5-2-4, and Table 5-2. Shown in -5. A sample obtained by polishing a cross section perpendicular to the welding direction was taken from this weld metal, measured at 10 points of Vickers hardness at a position 1 mm below the surface of the weld metal, and Brinell hardness from SAE J417 (1983) hardness conversion table. Converted to Further, a No. 4 Charpy test piece (2 mmV notch) based on JIS Z3111 (2005) was sampled, and the Charpy absorbed energy at −40 ° C. of the weld metal was measured. A sample having an absorption energy of −40 ° C. or more of 27 J or more was regarded as acceptable.
The obtained hardness and Charpy test results are shown in Tables 5-1-3, 5-2-3 and 5-2-6.

Moreover, the low temperature crack test and the diffusible hydrogen content measurement test were done to the welded joint obtained by the same welding conditions, respectively. The low-temperature cracking test was conducted at room temperature (25 ° C.) in accordance with JIS Z3158 (y-type weld cracking test method: 1993). The diffusible hydrogen content measurement test was carried out by a gas chromatograph method based on JIS Z3118 (Method for measuring the hydrogen content of steel welds; 2007). This diffusible hydrogen content was less than 1.0 ml / 100 g.
The results are shown in Table 5-1-3, Table 5-2-3, and Table 5-2-6.

著しい During welding, the remarkable level of fume or slag generation was judged as poor welding workability. The level at which both fume and slag are less likely to be generated was judged to have good welding workability. The results are shown in Table 5-1-3, Table 5-2-3, and Table 5-2-6.

As shown in the test results of Table 5-1-3, the weld metals of Examples 1 to 54, which are examples of the present invention, are all excellent in hardness, toughness, cold crack resistance, and welding workability. there were.
On the other hand, as shown in the test results of Tables 5-2-3 and 5-2-6, the weld metals of Comparative Examples 101 to 165 do not satisfy the requirements specified in the present invention. At least one of cold cracking resistance and welding workability was rejected. The underlined numbers in the comparative examples in Tables 5-2-1 to 5-2-6 indicate that they are outside the scope of the present invention.

According to the present invention, in a welded joint whose base material is a high hardness steel plate having a high C content and a surface hardness of HV380 or more and HV693 or less, the surface hardness is HV337 or more and HV533 or less, and wear resistance Weld metal with excellent surface resistance or weld metal with surface hardness of HV380 or higher and HV533 or lower and excellent wear resistance can be obtained without generating low-temperature cracks without preheating. And the value in the industry is extremely high.

Claims

Vickers hardness HV is 380 or more and 514 or less,
The plate thickness is 20-100mm,
The C content is 0.120 to 0.300 mass%,
A steel sheet having a CEN calculated by the following formula 1 of 0.20 to 0.75% by mass,
Vickers hardness HV is more than 514 and less than 565,
The plate thickness is 12-100mm,
The C content is 0.120 to 0.300 mass%,
A steel sheet having a CEN calculated by the following formula 1 of 0.20 to 0.75% by mass, and a Vickers hardness HV of more than 565 and not more than 693,
The plate thickness is 6-12mm,
The C content is 0.350 to 0.450 mass%,
A steel sheet having a CEN calculated by the following formula 1 of 0.20 to 0.85 mass%,
For any one of the above, a method for manufacturing a welded joint by performing gas shielded arc welding using a flux-cored wire filled with a flux in a steel outer shell,
(A) During the gas shielded arc welding, no preheating work is performed when the temperature of the steel plate is 10 ° C. or higher, and when the temperature of the steel plate is lower than 10 ° C., the temperature of the steel plate is 10 ° C. or higher. To perform the pre-heating work,
(B) The flux-cored wire is
When one or more of CaF 2 , BaF 2 , SrF 2 , and MgF 2 are contained and the total content is α, the α is 3.3% by mass% with respect to the total mass of the flux-cored wire. 8.0%,
When one or more of Ti oxide, Si oxide, Mg oxide, and Al oxide is contained, and the total content is β, the β is a mass% with respect to the total mass of the flux-cored wire. 0.10 to 1.50%,
The total content of CaCO 3 , BaCO 3 , SrCO 3 , MgCO 3 is less than 0.60% in mass% with respect to the total mass of the flux-cored wire,
The content of iron powder in the flux is less than 10.0% by mass% with respect to the total mass of the flux-cored wire,
The ratio of the content of CaF 2 to α is 0.90 or more,
The ratio of α to β is 3.0 or more and 80.0 or less,
The content of CaO is less than 0.20% by mass% with respect to the total mass of the flux-cored wire,
The chemical components in the flux-cored wire, excluding metal fluorides, metal oxides, and metal carbonates, in mass% with respect to the total mass of the flux-cored wire:
C: 0.010 to less than 0.060%;
Si: 0.05 to 1.80%;
Mn: 0.50 to 4.00%;
P: 0.050% or less;
S: 0.020% or less;
Al: 0.005 to 0.150%;
Cu: 0 to 0.75%;
Ni: 0 to less than 1.00%;
Cr: 0 to 3.50%;
Mo: 0 to 1.50%;
Ti: 0 to 0.150%;
Nb: 0 to 0.15%;
V: 0 to 0.45%;
B: 0 to 0.0500%;
Mg: 0 to 2.0%;
Ca: 0 to 2.0%;
REM: 0 to 0.0150%;
Balance: Fe and impurities;
Consists of
(C) The chemical composition of the weld metal of the weld joint is in mass%:
C: 0.100 to 0.170%;
Si: 0.05 to 0.80%;
Mn: 0.20 to 2.50%;
Al: 0.0050 to 0.1000%;
P: 0.050% or less;
S: 0.020% or less;
N: 0.015% or less;
Cu: 0 to 0.50%;
Ni: 0 to less than 0.70%;
Cr: 0-2.50%;
Mo: 0 to 1.00%;
Ti: 0 to 0.100%;
Nb: 0 to 0.100%;
V: 0 to 0.30%;
B: 0 to 0.0100%;
O: 0 to 0.100%;
Mg: 0 to 0.100%;
Ca: 0 to 0.100%;
REM: 0 to 0.0100%;
Balance: Fe and impurities;
Consists of
CEN calculated by the following formula 1 of the weld metal is 0.20 to 0.58% by mass,
The average Vickers hardness HV of 1 mm below the surface of the weld metal is 337 to 440,
A method for producing a welded joint satisfying all of the above (a) to (c).
CEN = [C] + (0.75 + 0.25 × tanh (20 × ([C] −0.12))) × ([Si] / 24 + [Mn] / 6 + [Cu] / 15 + [Ni] / 20 + ([Cr] + [Mo] + [Nb] + [V]) / 5 + 5 × [B]) (Formula 1)
However, the element with [] represents the content (% by mass) of each element.
Vickers hardness HV is 380 or more and 514 or less,
The plate thickness is 20-100mm,
The C content is 0.120 to 0.300 mass%,
A steel sheet having a CEN calculated by the following formula 1 of 0.20 to 0.75% by mass,
Vickers hardness HV is more than 514 and less than 565,
The plate thickness is 12-100mm,
The C content is 0.120 to 0.300 mass%,
A steel sheet having a CEN calculated by the following formula 1 of 0.20 to 0.75% by mass, and a Vickers hardness HV of more than 565 and not more than 693,
The plate thickness is 6-12mm,
The C content is 0.350 to 0.450 mass%,
A steel sheet having a CEN calculated by the following formula 1 of 0.20 to 0.85 mass%,
For any one of the above, a method for manufacturing a welded joint by performing gas shielded arc welding using a flux-cored wire filled with a flux in a steel outer shell,
(A) During the gas shielded arc welding, no preheating work is performed when the temperature of the steel plate is 10 ° C. or higher, and when the temperature of the steel plate is lower than 10 ° C., the temperature of the steel plate is 10 ° C. or higher. To perform the pre-heating work,
(B) The flux-cored wire is
When one or more of CaF 2 , BaF 2 , SrF 2 , and MgF 2 are contained and the total content is α, the α is 3.3% by mass% with respect to the total mass of the flux-cored wire. 8.0%,
When one or more of Ti oxide, Si oxide, Mg oxide, and Al oxide is contained, and the total content is β, the β is a mass% with respect to the total mass of the flux-cored wire. 0.10 to 1.50%,
The total content of CaCO 3 , BaCO 3 , SrCO 3 , MgCO 3 is less than 0.60% in mass% with respect to the total mass of the flux-cored wire,
The content of iron powder in the flux is less than 10.0% by mass% with respect to the total mass of the flux-cored wire,
The ratio of the content of CaF 2 to α is 0.90 or more,
The ratio of α to β is 3.0 or more and 80.0 or less,
The content of CaO is less than 0.20% by mass% with respect to the total mass of the flux-cored wire,
The chemical components in the flux-cored wire, excluding metal fluorides, metal oxides, and metal carbonates, in mass% with respect to the total mass of the flux-cored wire:
C: 0.060 to 0.350%;
Si: 0.05 to 1.80%;
Mn: 0.50 to 4.00%;
P: 0.050% or less;
S: 0.020% or less;
Al: 0.005 to 0.150%;
Cu: 0 to 0.75%;
Ni: 0 to less than 1.00%;
Cr: 0 to 3.50%;
Mo: 0 to 1.50%;
Ti: 0 to 0.150%;
Nb: 0 to 0.15%;
V: 0 to 0.45%;
B: 0 to 0.0500%;
Mg: 0 to 2.0%;
Ca: 0 to 2.0%;
REM: 0 to 0.0150%;
Balance: Fe and impurities;
Consists of
(C) The chemical composition of the weld metal of the weld joint is in mass%:
C: 0.120 to 0.250%;
Si: 0.05 to 0.80%;
Mn: 0.20 to 2.50%;
Al: 0.0050 to 0.1000%;
P: 0.050% or less;
S: 0.020% or less;
N: 0.015% or less;
Cu: 0 to 0.50%;
Ni: 0 to less than 0.70%;
Cr: 0-2.50%;
Mo: 0 to 1.00%;
Ti: 0 to 0.100%;
Nb: 0 to 0.100%;
V: 0 to 0.30%;
B: 0 to 0.0100%;
O: 0 to 0.100%;
Mg: 0 to 0.100%;
Ca: 0 to 0.100%;
REM: 0 to 0.0100%;
Balance: Fe and impurities;
Consists of
CEN calculated by the following formula 1 of the weld metal is 0.20 to 0.58% by mass,
The average Vickers hardness HV of 1 mm below the surface of the weld metal is 380 to 533,
A method for producing a welded joint satisfying all of the above (a) to (c).
CEN = [C] + (0.75 + 0.25 × tanh (20 × ([C] −0.12))) × ([Si] / 24 + [Mn] / 6 + [Cu] / 15 + [Ni] / 20 + ([Cr] + [Mo] + [Nb] + [V]) / 5 + 5 × [B]) (Formula 1)
However, the element with [] represents the content (% by mass) of each element.
Vickers hardness HV is more than 565 and less than 693,
The plate thickness is 12-20mm,
The C content is 0.350 to 0.450 mass%,
A steel sheet having a CEN calculated by the following formula 2 of 0.20 to 0.85 mass%, and a Vickers hardness HV of more than 565 and not more than 693,
The plate thickness is more than 20 mm and 50 mm or less,
The C content is 0.350 to 0.450 mass%,
A steel sheet having a CEN calculated by the following formula 2 of 0.20 to 0.85 mass%,
For any one of the above, a method for manufacturing a welded joint by performing gas shielded arc welding using a flux-cored wire filled with a flux in a steel outer shell,
(A) At the time of the gas shield arc welding, when the plate thickness of the steel plate is 20 mm or less, a preheating operation is performed so that the temperature of the steel plate is 100 ° C. or more, and the plate thickness of the steel plate is more than 20 mm The preheating operation is performed so that the temperature of the steel sheet is 150 ° C. or higher,
(B) The flux-cored wire is
When one or more of CaF 2 , BaF 2 , SrF 2 , and MgF 2 are contained and the total content is α, the α is 3.3% by mass% with respect to the total mass of the flux-cored wire. 8.0%,
When one or more of Ti oxide, Si oxide, Mg oxide, and Al oxide is contained, and the total content is β, the β is a mass% with respect to the total mass of the flux-cored wire. 0.10 to 1.50%,
The total content of CaCO 3 , BaCO 3 , SrCO 3 , MgCO 3 is less than 0.60% in mass% with respect to the total mass of the flux-cored wire,
The content of iron powder in the flux is less than 10.0% by mass% with respect to the total mass of the flux-cored wire,
The ratio of the content of CaF 2 to α is 0.90 or more,
The ratio of α to β is 3.0 or more and 80.0 or less,
The content of CaO is less than 0.20% by mass% with respect to the total mass of the flux-cored wire,
The chemical components in the flux-cored wire, excluding metal fluorides, metal oxides, and metal carbonates, in mass% with respect to the total mass of the flux-cored wire:
C: 0.060 to 0.350%;
Si: 0.05 to 1.80%;
Mn: 0.50 to 4.00%;
P: 0.050% or less;
S: 0.020% or less;
Al: 0.005 to 0.150%;
Cu: 0 to 0.75%;
Ni: 0 to less than 1.00%;
Cr: 0 to 3.50%;
Mo: 0 to 1.50%;
Ti: 0 to 0.150%;
Nb: 0 to 0.15%;
V: 0 to 0.45%;
B: 0 to 0.0500%;
Mg: 0 to 2.0%;
Ca: 0 to 2.0%;
REM: 0 to 0.0150%;
Balance: Fe and impurities;
Consists of
(C) The chemical composition of the weld metal of the weld joint is in mass%:
C: 0.120 to 0.250%;
Si: 0.05 to 0.80%;
Mn: 0.20 to 2.50%;
Al: 0.0050 to 0.1000%;
P: 0.050% or less;
S: 0.020% or less;
N: 0.015% or less;
Cu: 0 to 0.50%;
Ni: 0 to less than 0.70%;
Cr: 0-2.50%;
Mo: 0 to 1.00%;
Ti: 0 to 0.100%;
Nb: 0 to 0.100%;
V: 0 to 0.30%;
B: 0 to 0.0100%;
O: 0 to 0.100%;
Mg: 0 to 0.100%;
Ca: 0 to 0.100%;
REM: 0 to 0.0100%;
Balance: Fe and impurities;
Consists of
CEN calculated by the following formula 2 of the weld metal is 0.20 to 0.58% by mass,
The average Vickers hardness HV of 1 mm below the surface of the weld metal is 380 to 533,
A method for producing a welded joint satisfying all of the above (a) to (c).
CEN = [C] + (0.75 + 0.25 × tanh (20 × ([C] −0.12))) × ([Si] / 24 + [Mn] / 6 + [Cu] / 15 + [Ni] / 20 + ([Cr] + [Mo] + [Nb] + [V]) / 5 + 5 × [B]) (Formula 2)
However, the element with [] represents the content (% by mass) of each element.
The welding according to any one of claims 1 to 3, wherein a content of the CaO in the flux-cored wire is 0.15% or less by mass% with respect to a total mass of the flux-cored wire. A method for manufacturing a joint.
Except for the metal fluoride, the metal oxide, and the metal carbonate, the chemical composition in the flux-cored wire is in mass% with respect to the total mass of the flux-cored wire:
The method for producing a welded joint according to any one of claims 1 to 4, wherein Ni is 0 to 0.1%.
Except for the metal fluoride, the metal oxide, and the metal carbonate, the chemical composition in the flux-cored wire is in mass% with respect to the total mass of the flux-cored wire:
Cu: 0 to 0.50%;
Cr: 0 to 1.00%;
Mo: 0 to 0.50%;
Ti: 0 to 0.050%;
Nb: 0 to 0.05%
The method for producing a welded joint according to any one of claims 1 to 5, wherein:
The method for manufacturing a welded joint according to any one of claims 1 to 6, wherein there is no slit-like gap in the steel outer sheath of the flux-cored wire.
The method for manufacturing a welded joint according to any one of claims 1 to 6, wherein a slit-like gap is formed in the steel outer sheath of the flux-cored wire.
The method for manufacturing a welded joint according to any one of claims 1 to 8, wherein perfluoropolyether oil is applied to a surface of the flux-cored wire.