Welded joint and method for manufacturing a welded joint

Abstract

This invention provides a welded joint with excellent resistance to weld cracking. A welded joint is formed by welding wear-resistant steel plates with a surface hardness of 400 HBW or higher on a Brinell hardness tester to each other. During welding, the steel plates used for welding, the welding materials, and the welding conditions are adjusted so that the weld metal has the following composition by mass percent: C: 0.20–0.80%, Si: 0.10–0.90%, Mn: 15.0–28.0%, P: 0.030% or less, S: 0.030% or less, Ni: 0.01–10.00%, Cr: 0.4–1.9%, Mo: 0.01–5.00%. Therefore, a welded joint can be manufactured without preheating or post-heating to prevent the formation of weld cracks.

Description

Technical Field

[0001] This invention relates to welded joints made by welding wear-resistant steel plates together, suitable for use as components in industrial machinery, transportation equipment, etc., and particularly to improved resistance to weld cracking. Background Technology

[0002] In industrial machinery and transportation equipment used in construction, civil engineering, mining, and other fields, the lifespan is generally determined by the amount of wear on the components. Therefore, steel plates with excellent wear resistance (wear-resistant steel plates) are used as components. Wear resistance is strongly dependent on the hardness of the steel plate; therefore, most wear-resistant steel plates are high-hardness steel plates with a surface hardness of 400 HBW or higher on a Brinell hardness scale.

[0003] It is known that high-hardness wear-resistant steel plates are prone to low-temperature cracking caused by hydrogen in the heat-affected zone during welding. To prevent low-temperature cracking, preheating before welding or post-weld heating is generally effective in removing diffusive hydrogen. Especially for thick-walled wear-resistant steel plates with a surface Brinell hardness of 400 HBW or higher and a plate thickness of 50 mm or more, preheating to above 75°C is generally recommended during welding.

[0004] However, high-temperature preheating during welding is labor-intensive and time-consuming, reducing welding efficiency. Therefore, research was conducted on preventing low-temperature cracking during welding by adjusting the alloy element content of wear-resistant steel plates.

[0005] For example, Patent Document 1 describes "a wear-resistant steel plate with excellent weldability". Patent Document 1 describes a wear-resistant steel plate having the following composition: by mass % containing one or more of the following: C: 0.38-0.50%, Si: 0.05-1.0%, Mn: 0.1-0.5%, Nb: 0.005-0.05%, Ti: 0.005-0.05%, B: 0.0003-0.0030%, Al: less than 0.1%, P: less than 0.010%, S: less than 0.005%, and further Cu: 0.1-1.0%, Ni: 0.1-2.0%, Cr: 0.1-1.0%, Mo: 0.05-1.0%, V: 0.005-0.10%, W: 0.05-1.0%, Ceq* less than 0.60%, DI* more than 45, and the remainder consisting of Fe and unavoidable impurities. Patent document 1 describes a wear-resistant steel plate with a surface hardness of 560HBW or higher, excellent weldability, and no low-temperature cracks even when the preheating temperature is as low as 150°C.

[0006] Furthermore, Patent Document 2 describes "a wear-resistant steel plate". The wear-resistant steel plate described in Patent Document 2 has the following composition, comprising a total of 400 pieces / mm². 2The wear-resistant steel plate with an average particle size of 0.5 μm or more, consisting of Ti carbides and Ti-Mo composite carbides, contains the following composition: C: 0.20–0.50%, Si: 0.1–1.0%, Mn: 0.1–2.0%, P: less than 0.04%, S: less than 0.04%, Ti: 0.2–1.0%, Mo: 0.2–2.0%, B: 0.0003–0.01%, N: less than 0.01%, and contains Mo and Ti to satisfy Mo / Ti ≥ 1.0… (1). The remainder consists of Fe and unavoidable impurities. It should be noted that Cu, Ni, Cr, and Al may be further included. The wear-resistant steel plate described in Patent Document 2 can prevent low-temperature cracking during welding by preheating at 50°C to 200°C.

[0007] Furthermore, Patent Document 3 describes "a welding material with excellent impact resistance and wear resistance." The welding material described in Patent Document 3 is a welding material for submerged arc welding or gas-shielded metal electrode welding, exhibiting excellent weldability, low-temperature impact characteristics, and wear resistance. The welding material described in Patent Document 3 has the following composition: by weight %: C: 0.12–0.75%, Si: 0.2–1.2%, Mn: 15–27%, Cr: 2–7%, S: 0.025% or less, P: 0.020% or less, with the remainder consisting of Fe and unavoidable impurities. It should be noted that, in addition to the above composition, it may also contain N: 0.4% or less, Ni: 10% or less, V: 5% or less, Nb: 5% or less, Mo: 7% or less, W: 6% or less, Cu: 2% or less, and B: 0.01% or less. Using this welding material, it is possible to produce welded joints with excellent low-temperature impact characteristics and wear resistance.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2008-214651

[0011] Patent Document 2: Japanese Patent No. 4894288

[0012] Patent Document 3: WO 2015 / 083928 A1 Summary of the Invention

[0013] However, in the technologies described in Patent Documents 1 and 2, preheating or post-heating of the steel plate is required to prevent low-temperature cracking during welding, and the preheating of the steel plate during welding is not completely omitted. During welding construction, a large amount of manpower and time are required to perform the preheating of the steel plate, which reduces construction efficiency. Therefore, from the viewpoint of improving welding construction efficiency and reducing welding construction costs, it is required to further reduce the preheating temperature or omit the preheating process.

[0014] Furthermore, according to the research of the inventors, when using the welding material described in Patent Document 3 to form a multilayer weld metal, there is a problem that the reheated portion of the weld metal is prone to cracking (high-temperature cracking).

[0015] In view of the problems of the prior art, the object of the present invention is to provide a welded joint with excellent weld crack resistance, which can suppress (prevent) the generation of weld cracks without preheating and post-heating in welded joints formed by welding wear-resistant steel plates together. It should be noted that "excellent weld crack resistance" as used herein refers to the situation where no low-temperature cracks or high-temperature cracks are found when a welded joint is formed by multi-layer welding with a V-groove or X-groove shape without preheating.

[0016] To achieve the above objectives, the inventors conducted in-depth research on various important factors affecting weld crack resistance. Their results showed that making the weld metal austenitic is effective in suppressing low-temperature cracking caused by hydrogen. The hydrogen solid solution limit of austenitic structures is much higher than that of ferrite structures, thus preventing embrittlement even with the amount of hydrogen introduced during welding. Furthermore, if the weld metal is austenitic, it absorbs the hydrogen introduced during welding, inhibiting (preventing) hydrogen diffusion to the heat-affected zone that solidifies during welding. Therefore, the initiation of low-temperature cracking is suppressed (prevented).

[0017] It should be noted that the weld metal formed using the welding material described in Patent Document 3 has an austenitic structure, but according to the research of the inventors, it is prone to high-temperature cracking. Therefore, the cause of high-temperature cracking was investigated, and it was found that in cases with a high Cr content, Cr carbides precipitate at the austenitic grain boundaries (Cr... 23 C6), the grain boundaries become embrittled, thus opening due to thermal strain introduced during welding, resulting in high-temperature cracks. Through further research, the inventors discovered that by adjusting the Cr content of the weld metal to 1.9% or less, the formation of such high-temperature cracks can be prevented.

[0018] This invention was completed based on further research conducted according to the above-mentioned insights. The main points of this invention are as follows.

[0019] [1] A welded joint, characterized in that it is a welded joint formed by welding steel plates together.

[0020] The aforementioned steel plate is a wear-resistant steel plate with a surface hardness of over 400 HBW measured by a Brinell hardness tester.

[0021] The weld metal part has the following composition: by mass % C: 0.20-0.80%, Si: 0.10-0.90%, Mn: 15.0-28.0%, P: less than 0.030%, S: less than 0.030%, Ni: 0.01-10.00%, Cr: 0.4-1.9%, Mo: 0.01-5.00%, with the remainder consisting of Fe and unavoidable impurities.

[0022] [2] The welded joint according to [1] is characterized in that, in addition to the above-mentioned welded metal component, it further contains, by mass %, one or more of the following: V: 1.0% or less, Ti: 1.0% or less, Nb: 1.0% or less, and W: 1.0% or less.

[0023] [3] The welded joint according to [1] or [2] is characterized in that, in addition to the above-mentioned welded metal composition, it further contains, by mass %, one or more of the following: Cu: 1.0% or less, Al: 0.10% or less, Ca: 0.010% or less, REM: 0.020% or less.

[0024] [4] The welded joint according to any one of [1] to [3] is characterized in that the wear-resistant steel plate has the following steel plate composition: containing, by mass %, C: 0.10 to 0.50%, Si: 0.10 to 0.90%, Mn: 0.40 to 2.00%, P: less than 0.030%, S: less than 0.030%, Cr: 0.10 to 2.00%, Mo: 0.10 to 1.00%, with the remainder consisting of Fe and unavoidable impurities.

[0025] [5] The welded joint according to [4] is characterized in that, in addition to the above-mentioned steel plate composition, it further contains, by mass %, one or more of the following: Cu: less than 1.0%, Ni: less than 2.0%, V: less than 0.5%, Ti: less than 0.5%, Al: less than 0.20%.

[0026] [6] A method for manufacturing a welded joint, characterized in that it is a method for manufacturing a welded joint by welding steel plates together.

[0027] The aforementioned steel plate is a wear-resistant steel plate with a surface hardness of over 400 HBW measured by a Brinell hardness tester.

[0028] The weld metal part has the following composition by mass: C: 0.20-0.80%, Si: 0.10-0.90%, Mn: 15.0-28.0%, P: less than 0.030%, S: less than 0.030%, Ni: 0.01-10.00%, Cr: 0.4-1.9%, Mo: 0.01-5.00%, with the remainder consisting of Fe and unavoidable impurities.

[0029] [7] The method for manufacturing a welded joint according to [6] is characterized in that, in addition to the above-mentioned welded metal component, it further contains, by mass %, one or more of the following: V: 1.0% or less, Ti: 1.0% or less, Nb: 1.0% or less and W: 1.0% or less.

[0030] [8] The method for manufacturing a welded joint according to [6] or [7] is characterized in that, in addition to the above-mentioned welded metal component, it further contains, by mass %, one or more of the following: Cu: 1.0% or less, Al: 0.10% or less, Ca: 0.010% or less and REM: 0.020% or less.

[0031] [9] The method for manufacturing a welded joint according to any one of [6] to [8] is characterized in that the wear-resistant steel plate has the following steel plate composition: containing, by mass %, C: 0.10 to 0.50%, Si: 0.10 to 0.90%, Mn: 0.40 to 2.00%, P: less than 0.030%, S: less than 0.030%, Cr: 0.10 to 2.00%, Mo: 0.10 to 1.00%, with the remainder consisting of Fe and unavoidable impurities;

[0032] The above welding is a gas-shielded metal arc welding. The welding material used in this gas-shielded metal arc welding is a solid welding wire with the following composition: the welding wire composition, by mass%, contains C: 0.20-0.90%, Si: 0.10-1.00%, Mn: 16.0-30.0%, P: less than 0.030%, S: less than 0.030%, Ni: 0.01-12.00%, Cr: 0.1-2.5%, Mo: 0.10-6.00%, with the remainder consisting of Fe and unavoidable impurities.

[0033]

[10] The method for manufacturing the welded joint according to [9] is characterized in that, in addition to the above-mentioned steel plate composition, the wear-resistant steel plate further contains one or more of the following: Cu: 1.0% or less, Ni: 2.0% or less, V: 0.5% or less, Ti: 0.5% or less, Al: 0.20% or less.

[0034]

[11] The method for manufacturing a welded joint according to [9] or

[10] is characterized in that, in addition to the above-mentioned welding wire composition, the solid welding wire further contains, by mass %, one or more of the following: V: 1.0% or less, Ti: 1.0% or less, Nb: 1.0% or less and W: 1.0% or less, and / or, one or more of the following: Cu: 1.0% or less, Al: 0.10% or less, Ca: 0.010% or less and REM: 0.020% or less.

[0035] According to the present invention, welded joints can be manufactured without preheating or postheating of the steel plate during welding to suppress (prevent) the generation of welding cracks, thereby improving welding construction efficiency, reducing welding construction costs, and achieving significant industrial benefits.

[0036] Furthermore, according to the present invention, a weld joint with excellent resistance to weld cracking can be provided. Detailed Implementation

[0037] [Welded joint]

[0038] The welded joint of the present invention is a wear-resistant steel welded joint formed by making two or more steel plates into wear-resistant steel plates with a surface hardness of 400HBW or more by a Brinell hardness tester, forming a weld metal part between the steel plates and welding them together.

[0039] Wear-resistant steel plate

[0040] To ensure the desired wear resistance, the wear-resistant steel plate used as the welding material is a steel plate with a surface hardness of 400 HBW or higher on a Brinell hardness tester. While there is no particular upper limit to the Brinell hardness, it is preferably 600 HBW or lower from the viewpoint of avoiding cracking during gas cutting. The wear-resistant steel plate is preferably any wear-resistant steel plate capable of ensuring the aforementioned surface hardness range. Such a wear-resistant steel plate is, for example, any steel plate composition containing suitable other alloying elements in the range of C: 0.10 to 0.50% by mass, according to the desired properties (e.g., strength, toughness, etc.), without particular limitation. For example, a steel plate with a surface hardness of 400 HBW or higher, a plate thickness of 6 to 100 mm, and containing C: 0.10 to 0.50%, Si: 0.10 to 0.90%, Mn: 0.40 to 2.00%, P: less than 0.030%, S: less than 0.030%, Cr: 0.10 to 2.00%, and Mo: 0.10 to 1.00% as basic alloying elements, or may further contain one or more of Cu: less than 1.0%, Ni: less than 2.0%, V: less than 0.5%, Ti: less than 0.5%, and Al: less than 0.20% as arbitrary alloying elements, with the remainder consisting of Fe and unavoidable impurities.

[0041] <Welded Metal Section>

[0042] Furthermore, in the welded joint of the present invention, the weld metal portion is characterized by containing, by mass percent, C: 0.20–0.80%, Si: 0.10–0.90%, Mn: 15.0–28.0%, P: less than 0.030%, S: less than 0.030%, Ni: 0.01–10.00%, Cr: 0.4–1.9%, Mo: 0.01–5.00%, with the remainder consisting of Fe and unavoidable impurities (weld metal portion composition). By forming a weld metal portion with such a basic composition, the generation of weld cracks can be suppressed (prevented) during welding without the need for preheating or post-heating.

[0043] First, the reasons for defining the composition of the welded metal part described above will be explained. It should be noted that, hereinafter, "mass %" in the composition will be abbreviated as "%".

[0044] C: 0.20~0.80%

[0045] Carbon (C) is an element that stabilizes the austenite phase. Furthermore, it enhances the wear resistance of weld metal by increasing its strength (hardness) through solid solution strengthening. To achieve this effect, a content of 0.20% or more is required. On the other hand, if the content exceeds 0.80%, high-temperature cracking during welding is likely to occur. Therefore, the C content is limited to the range of 0.20% to 0.80%. It should be noted that 0.40% or more is preferred. Furthermore, 0.60% or less is more preferable.

[0046] Si: 0.10–0.90%

[0047] Si is an element that acts as a deoxidizer and stabilizes the austenite phase by inhibiting carbide precipitation and allowing C to dissolve in the austenite phase. To achieve this effect, a content of 0.10% or more is required. On the other hand, if the content exceeds 0.90%, segregation occurs during solidification, forming a liquid phase at the solidification cell interface, reducing resistance to high-temperature cracking. Therefore, the Si content is limited to the range of 0.10% to 0.90%. It should be noted that 0.20% or more is preferred. Furthermore, 0.80% or less is more preferable.

[0048] Mn: 15.0~28.0%

[0049] Mn is an element that stabilizes the austenitic phase at low cost, and in this invention, it needs to contain 15.0% or more. If the Mn content is less than 15.0%, the stability of the austenitic phase is insufficient, thus forming a hard martensite phase in the weld metal, resulting in low-temperature cracking. On the other hand, if the content exceeds 28.0%, excessive Mn segregation occurs during solidification, inducing high-temperature cracking. Therefore, the Mn content is limited to the range of 15.0% to 28.0%. It should be noted that 16.0% or more is preferred. Furthermore, 26.0% or less is preferred.

[0050] P: below 0.030%

[0051] P is an element that can cause segregation at grain boundaries and induce high-temperature cracks. In this invention, it is preferable to minimize its content, but it is permissible if it is below 0.030%. Therefore, P is limited to 0.030% or less. It should be noted that excessive reduction leads to an increase in refining costs, so P is preferably adjusted to 0.003% or more.

[0052] S: below 0.030%

[0053] Sulfur (S) is an element that can cause segregation at grain boundaries and induce high-temperature cracking. In this invention, it is preferable to minimize its concentration, but it is permissible if it is below 0.030%. Therefore, S is limited to 0.030% or less. It should be noted that excessive reduction leads to an increase in refining costs, so S is preferably adjusted to 0.003% or more.

[0054] Ni: 0.01~10.00%

[0055] Ni is an element that strengthens austenite grain boundaries, suppressing the formation of high-temperature cracks by inhibiting grain boundary embrittlement. To achieve this effect, a content of 0.01% or more is required. Furthermore, Ni also has the effect of stabilizing the austenite phase. On the other hand, Ni is an expensive element, and a content exceeding 10.00% is economically unfavorable. Therefore, Ni is limited to 0.01% to 10.00%. It should be noted that 1.00% or more is preferred. Furthermore, 8.00% or less is more preferred.

[0056] Cr: 0.4–1.9%

[0057] Cr is an element that stabilizes the austenite phase at low temperatures. Additionally, Cr helps solidify weld metal, thus improving its wear resistance. Furthermore, Cr contributes to improving the corrosion resistance of weld metal. To achieve these effects, a content of 0.4% or higher is required. On the other hand, if the content exceeds 1.9%, Cr carbides (Cr2 carbides) will form at the austenite grain boundaries. 23C6), grain boundary embrittlement, induces high-temperature cracking. Therefore, Cr is limited to the range of 0.4% to 1.9%. It should be noted that 0.4% or more is preferred. Furthermore, 1.8% or less is preferred. More preferably, 0.6% or more is preferred. Furthermore, 1.6% or less is even more preferred.

[0058] Mo: 0.01–5.00%

[0059] Mo is an element that strengthens austenite grain boundaries, inhibits grain boundary embrittlement, and suppresses the formation of high-temperature cracks. Additionally, Mo also improves wear resistance by solidifying the weld metal. To achieve this effect, a content of 0.01% or more is required. On the other hand, if the content exceeds 5.00%, excessive solidification occurs within the grains, relatively weakening the grain boundaries and leading to high-temperature cracks. Therefore, the Mo content is limited to the range of 0.01% to 5.00%. It should be noted that 0.10% or more is preferred. Furthermore, 4.00% or less is more preferable.

[0060] The above-mentioned components are the basic components of the welded metal portion in the welded joint of the present invention. In the present invention, in addition to the above-mentioned basic components, one or more of the following elements may be selectively included as needed: V: 1.0% or less, Ti: 1.0% or less, Nb: 1.0% or less, and W: 1.0% or less, and / or one or more of the following elements may be selected as optional elements: Cu: 1.0% or less, Al: 0.10% or less, Ca: 0.010% or less, and REM: 0.020% or less.

[0061] Selected from one or more of the following: V: 1.0% or less, Ti: 1.0% or less, Nb: 1.0% or less, and W: 1.0% or less.

[0062] V, Ti, Nb, and W are all elements that form carbides and help improve the wear resistance of weld metals. One or more of these elements can be selectively included as needed.

[0063] V is a carbide-forming element that precipitates minute carbides within austenite grains, improving the wear resistance of the weld metal. To achieve this effect, a content of 0.001% or more is preferred. However, if the content exceeds 1.0%, excessive solidification occurs within the grains, and the grain boundaries become relatively weak, thus inducing high-temperature cracking during welding. Therefore, when present, V is limited to 1.0% or less. It should be noted that 0.01% or more is preferred. Furthermore, 0.8% or less is more desirable.

[0064] Furthermore, Ti is a carbide-forming element, precipitating minute carbides and improving the wear resistance of the weld metal. To achieve this effect, a content of 0.001% or more is preferred. However, if the content exceeds 1.0%, excessive solidification occurs within the austenite grains, and the grain boundaries become relatively weak, thus inducing high-temperature cracking during welding. Therefore, when present, the Ti content is limited to 1.0% or less. It should be noted that 0.01% or more is preferred. Furthermore, 0.8% or less is more desirable.

[0065] Furthermore, Nb, like V and Ti, is a carbide-forming element, precipitating minute carbides within the austenite grains and improving the wear resistance of the weld metal. To achieve this effect, a content of 0.001% or more is preferred. On the other hand, if the content exceeds 1.0%, excessive solidification occurs within the grains, and the grain boundaries become relatively weak, thus inducing high-temperature cracking during welding. Therefore, when present, Nb content is limited to 1.0% or less. It should be noted that 0.01% or more is preferred. Furthermore, 0.8% or less is more desirable.

[0066] W, like V, Ti, and Nb, is a carbide-forming element. It precipitates tiny carbides within the austenite grains, improving the wear resistance of the weld metal. To achieve this effect, a content of 0.001% or more is preferred. However, if the content exceeds 1.0%, excessive solidification within the grains occurs, and the grain boundaries become relatively weak, thus inducing high-temperature cracking during welding. Therefore, when present, W content is limited to 1.0% or less. It should be noted that 0.01% or more is preferred. Furthermore, 0.8% or less is more desirable.

[0067] Selected from one or more of the following: Cu: less than 1.0%, Al: less than 0.10%, Ca: less than 0.010%, and REM: less than 0.020%.

[0068] Cu is an element that stabilizes the austenitic phase, Al acts as a deoxidizer, and Ca and REM help suppress high-temperature cracking. They can be selectively included as needed.

[0069] Cu is an element that stabilizes the austenite phase, and to achieve this effect, it is preferable to contain 0.01% or more. However, if it contains a large amount exceeding 1.0%, a low-melting-point liquid phase is formed at the austenite grain boundaries, thus causing high-temperature cracks. Therefore, when present, Cu is preferably limited to 1.0% or less. It should be noted that 0.1% or more is more preferred. Furthermore, 0.8% or less is even more preferred.

[0070] Al acts as a deoxidizer and increases the viscosity of the molten metal, stabilizes the weld bead shape, and reduces spatter. Furthermore, Al raises the liquidus temperature of the molten metal, helping to suppress high-temperature cracking in the weld metal. To achieve this effect, it is preferable to contain 0.001% or more. However, if the content exceeds 0.10%, the viscosity of the molten metal becomes too high, leading to increased spatter, poor weld bead diffusion, and other defects such as incomplete fusion. Therefore, when present, the Al content is preferably limited to 0.10% or less. It should be noted that 0.002% or more is more preferred. Furthermore, 0.06% or less is even more preferred.

[0071] In addition, Ca and REM are elements that help suppress high-temperature cracking and can be selectively included as needed.

[0072] In molten metal, Ca combines with S to form high-melting-point sulfides, CaS, which suppress the formation of high-temperature cracks. This effect becomes significant when the content is 0.001% or more. On the other hand, if the content exceeds 0.010%, the arc becomes disordered during welding, making stable welding difficult. Therefore, when present, the Ca content is preferably limited to 0.010% or less. It should be noted that 0.002% or more is more preferred. Furthermore, 0.008% or less is even more preferred.

[0073] REM: below 0.020%

[0074] REM is a powerful deoxidizer, existing in the weld metal as REM oxides. REM oxides act as nucleation sites during solidification, thereby altering the solidification morphology of the weld metal and helping to suppress high-temperature cracking. To achieve this effect, a content of 0.001% or more is required. However, if the content exceeds 0.020%, the stability of the arc decreases. Therefore, when present, the REM content is limited to 0.020% or less. It should be noted that 0.001% or more is more preferred. Furthermore, 0.015% or less is even more preferred. It should be noted that REM is a general term for rare earth elements such as La and Ce, and the content indicates the total amount of these elements.

[0075] The remaining components besides those mentioned above consist of Fe and unavoidable impurities. As unavoidable impurities, N: 0.120% or less and O (oxygen): 0.100% or less are permissible. N is an unavoidably present element, but if its content exceeds 0.120%, it forms nitrides, reducing the toughness of the weld metal. Therefore, N is preferably limited to 0.120% or less. O (oxygen) is an unavoidably present element, but if its content exceeds 0.100%, it forms oxides in the weld metal, reducing its toughness. Therefore, O (oxygen) is preferably limited to 0.100% or less.

[0076] [Manufacturing method of welded joint]

[0077] Next, a preferred manufacturing method for the welded joint of the present invention will be described.

[0078] First, prepare two or more wear-resistant steel plates with the aforementioned surface hardness. Then, perform beveling to form a bevel of a specified shape between the prepared steel plates. There are no particular limitations on the shape of the bevel, but for welded structures, commonly used V-grooves, X-grooves, etc., are preferred.

[0079] Next, the beveled steel plates are welded together using welding materials to form welded metal parts, thus creating a welded joint.

[0080] <Welding Method>

[0081] The welding method used is not particularly limited, but gas-shielded metal arc welding (also known as "electrode-type gas-shielded arc welding") that can form a weld metal part with the above composition and the desired properties using solid welding wire is preferred.

[0082] <Welding Materials>

[0083] It should be noted that the welding material used is a solid welding wire capable of forming the weld metal part with the above composition. The composition of a solid welding wire can be exemplified as follows: it contains, by mass %, C: 0.20–0.90%, Si: 0.10–1.00%, Mn: 16.0–30.0%, P: less than 0.030%, S: less than 0.030%, Ni: 0.01–12.00%, Cr: 0.1–2.5%, and Mo: 0.10–6.00% as basic alloying elements, or may further contain one or more selected from V: less than 1.0%, Ti: less than 1.0%, Nb: less than 1.0%, and W: less than 1.0%, and / or one or more selected from Cu: less than 1.0%, Al: less than 0.10%, Ca: less than 0.010%, and REM: less than 0.020% as arbitrary alloying elements, with the remainder consisting of Fe and unavoidable impurities.

[0084] <Forming of Welded Metal Parts>

[0085] Typically, when steel plates are welded together using welding materials, molten metal from the steel plates (molten metal) and molten metal from the welding materials (deposited metal) mix to form weld metal. In multi-layer welding, the weld metal of the first layer (starting layer) generally has a higher penetration rate (dilution rate) compared to the weld metal of other layers. Therefore, it is preferable to adjust the penetration rate of the steel plates so that the composition of the weld metal of the first layer is within the aforementioned range. The penetration rate of the steel plate in the first layer of weld metal varies depending on the plate thickness, bevel shape, and welding conditions, but is particularly greatly affected by the welding heat input. Therefore, it is preferable to adjust the penetration rate of the steel plates by changing the welding heat input. It should be noted that, from the viewpoint of preventing high-temperature cracking, the welding heat input is preferably in the range of 5 to 70 kJ / cm.

[0086] <Manufacturing Method of Wear-Resistant Steel Plate>

[0087] It should be noted that any commonly used method for manufacturing wear-resistant steel plates, which are the materials to be welded, can be used. Preferably, molten steel having the above-mentioned steel plate composition is smelted using a common smelting method such as a converter or electric furnace, and then steel billets of specified dimensions are obtained through a common casting method such as continuous casting or ingot-dispersive rolling. It should be noted that secondary refining using a vacuum degassing furnace or similar method can be performed during smelting. Preferably, the obtained steel billet is further heated, hot-rolled, and then cooled to obtain a wear-resistant steel plate with a surface hardness of 400 HBW or higher.

[0088] <Methods for manufacturing welding materials>

[0089] In addition, the preferred manufacturing method for the welding material (solid welding wire) is as follows.

[0090] In the manufacture of the welding material (solid welding wire) used to manufacture the welded joint in this invention, all commonly used manufacturing methods for welding materials (solid welding wire) can be used.

[0091] For example, molten steel containing the aforementioned welding wire is melted using common smelting methods such as electric furnaces or vacuum melting furnaces, and then cast in molds of a specified shape. Next, the resulting steel ingot is heated to a specified temperature and hot-rolled to obtain a steel billet (bar shape) of a specified shape. Next, the obtained steel billet (bar shape) is preferably subjected to multiple cold rolling processes (cold drawing) and annealing as needed to obtain welding wire of a specified size. It should be noted that annealing is preferably performed at an annealing temperature of 800–1200°C.

[0092] The present invention will be further described below based on embodiments.

[0093] Example

[0094] Prepare a wear-resistant steel plate (thickness: 50 mm) with the steel plate composition shown in Table 1 and a surface hardness of 400 HBW to 560 HBW using a Brinell hardness tester. Take a test plate for joint fabrication from the prepared wear-resistant steel plate and perform beveling. The beveling is a V-groove (groove angle: 45°). Then, within this beveling, use solid welding wire (1.2 mm φ) with the composition shown in Table 2 as the welding material for gas-shielded metal arc welding (shielding gas atmosphere: 80% Ar + 20% CO2) to form a multi-layer weld metal part, obtaining a welded joint. It should be noted that welding is performed under the following conditions: no preheating, current: 180–350 A, voltage: 24–35 V, welding speed: 30 cm / min, interpass temperature: 100–250 °C, in a downward orientation using gas-shielded metal arc welding. The ambient temperature during welding is 20 °C, and the humidity is 60%.

[0095] The welding material (solid welding wire) used is manufactured as follows.

[0096] Molten steel with the composition shown in Table 2 (welding wire composition) was melted in a vacuum melting furnace to produce steel ingots (100 kgf). The obtained steel ingots were heated to 1200°C and then hot-rolled to obtain rod-shaped steel billets. The obtained rod-shaped steel billets were further subjected to multiple cold drawing processes with annealing in between to obtain solid welding wire (1.2 mm φ) for welding.

[0097]

[0098] After welding, analytical test pieces were taken from a φ10mm range at the center of the thickness and width of the welded metal section, and elemental analysis was performed using wet chemical analysis.

[0099] In addition, the weld metal and the heat-affected zone are observed using an optical microscope (magnification: 100x) to determine whether there are weld cracks. If a crack is confirmed in the heat-affected zone or the weld metal, it is evaluated as "present" weld crack; if no crack is confirmed, it is evaluated as "absent" weld crack.

[0100] The results are shown in Table 3.

[0101]

[0102]

[0103] In the examples of this invention, no welding cracks (high-temperature cracks and low-temperature cracks) were observed, and the welded joints can be considered to have excellent resistance to welding cracks. On the other hand, in the comparative examples that deviate from the scope of this invention, welding cracks (high-temperature cracks or low-temperature cracks) occurred, and the welded joints can be considered to have reduced resistance to welding cracks.

Claims

1. A welded joint, characterized in that is a welded joint in which steel plates are welded to each other, the steel plate is a wear-resistant steel plate having a surface hardness of 400 HBW or more in terms of Brinell hardness, the weld metal portion is an austenite structure and has a weld metal portion composition containing, in mass%, C: 0.20 to 0.80%, Si: 0.10 to 0.90%, Mn: 15.0 to 28.0%, P: 0.030% or less, S: 0.030% or less, Ni: 0.01 to 10.00%, Cr: 0.4 to 1.9%, Mo: 0.01 to 5.00%, and the remainder consisting of Fe and inevitable impurities.

2. The welded joint of claim 1, wherein In addition to the weld metal portion composition, one or two or more kinds selected from the group consisting of, in mass%, V: 1.0% or less, Ti: 1.0% or less, Nb: 1.0% or less, and W: 1.0% or less are further contained. In addition to the weld metal portion composition, one or two or more kinds selected from the group consisting of, in mass%, Cu: 1.0% or less, Al: 0.10% or less, Ca: 0.010% or less, and REM: 0.020% or less are further contained.

3. Welded joint according to claim 1 or 2, characterized in that the steel plate has a steel plate composition containing, in mass%, C: 0.10 to 0.50%, Si: 0.10 to 0.90%, Mn: 0.40 to 2.00%, P: 0.030% or less, S: 0.030% or less, Cr: 0.10 to 2.00%, Mo: 0.10 to 1.00%, and the remainder consisting of Fe and inevitable impurities.

4. The welded joint according to any one of claims 1 to 3, characterized in that In addition to the steel plate composition, one or two or more kinds selected from the group consisting of, in mass%, Cu: 1.0% or less, Ni: 2.0% or less, V: 0.5% or less, Ti: 0.5% or less, and Al: 0.20% or less are further contained.

5. The welded joint of claim 4, wherein, is a method for manufacturing a welded joint in which steel plates are welded to each other, 6. A method of manufacturing a welded joint, characterized by the steel plate is a wear-resistant steel plate having a surface hardness of 400 HBW or more in terms of Brinell hardness, the weld metal portion is an austenite structure and has a weld metal portion composition containing, in mass%, C: 0.20 to 0.80%, Si: 0.10 to 0.90%, Mn: 15.0 to 28.0%, P: 0.030% or less, S: 0.030% or less, Ni: 0.01 to 10.00%, Cr: 0.4 to 1.9%, Mo: 0.01 to 5.00%, and the remainder consisting of Fe and inevitable impurities. In addition to the weld metal portion composition, one or two or more kinds selected from the group consisting of, in mass%, V: 1.0% or less, Ti: 1.0% or less, Nb: 1.0% or less, and W: 1.0% or less are further contained.

7. The method of producing a welded joint according to claim 6, characterized in that, In addition to the weld metal portion composition, one or two or more kinds selected from the group consisting of, in mass%, Cu: 1.0% or less, Al: 0.10% or less, Ca: 0.010% or less, and REM: 0.020% or less are further contained.

8. The method of producing a welded joint according to claim 6 or 7, characterized in that, ​ 9. The method of producing a welded joint according to any one of claims 6 to 8, characterized in that, The wear-resistant steel sheet has a steel sheet composition containing, in mass%, C: 0.10 to 0.50%, Si: 0.10 to 0.90%, Mn: 0.40 to 2.00%, P: 0.030% or less, S: 0.030% or less, Cr: 0.10 to 2.00%, Mo: 0.10 to 1.00%, with the remainder consisting of Fe and inevitable impurities; The welding is gas shielded metal arc welding, and a welding material used in the gas shielded metal arc welding is a solid wire having a wire composition containing, in mass%, C: 0.20 to 0.90%, Si: 0.10 to 1.00%, Mn: 16.0 to 30.0%, P: 0.030% or less, S: 0.030% or less, Ni: 0.01 to 12.00%, Cr: 0.1 to 2.5%, Mo: 0.10 to 6.00%, with the remainder consisting of Fe and inevitable impurities.

10. The method of producing a welded joint according to claim 9, characterized in that, The wear-resistant steel sheet further contains, in addition to the steel sheet composition, one or two or more selected from Cu: 1.0% or less, Ni: 2.0% or less, V: 0.5% or less, Ti: 0.5% or less, and Al: 0.20% or less.

11. The method of producing a welded joint according to claim 9 or 10, characterized in that, The solid wire further contains, in addition to the wire composition, one or two or more selected from V: 1.0% or less, Ti: 1.0% or less, Nb: 1.0% or less, and W: 1.0% or less, and / or one or two or more selected from Cu: 1.0% or less, Al: 0.10% or less, Ca: 0.010% or less, and REM: 0.020% or less, in mass%. ​

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