Patent Application
20050257853
The present invention relates to welding wires for welding modified 9Cr-1Mo steels, which are used for various types of heat-resistant and pressure-resistant piping, including a boiler for power generation, a turbine, and the like. More particularly, the invention relates to welding wires for modified 9Cr-1Mo steels, which are used for performing a submerged arc welding (SAW) process of the modified 9Cr-1Mo steel, and/or a tungsten inert gas (TIG) welding process thereof, and to welding materials comprising the combination of the welding wire and a flux.
A modified 9Cr-1Mo steel (hereinafter referred to as “Mod.9Cr-1Mo steel”) is made of a 9Cr-1Mo steel with Nb and V added thereto. For example, the modified 9Cr-1Mo steel is SA387Gr.91, or SA213Gr.T91, which is specified in the American Society for Testing and Materials (ASTM) Specification/American Society of Mechanical Engineers (ASME) Specification, X10CrMoVNb9-1, which is specified in the European standards (EN) Specification, or KA-STBA28, KA-STPA28, KA-SCMV28, or KA-SFVAF28, which is specified in the Technical Standard for Thermal Power Generating Facilities. Hitherto, welding materials, such as welding wires, for welding these Mod.9Cr-1Mo steels, have been developed variedly in view of design of the components thereof for improving crack resistance, creep rupture strength, and toughness.
For example, a welding wire has been proposed in Japanese Patent No. 2631228 which contains 0.030 to 0.065% by mass of carbon, which is relatively small, the atomic ratio of Nb and V to C, namely, ((Nb+V)/C), being adjusted within a range of 0.26 to 0.35, so as to have good crack resistance, creep rupture strength, and toughness. Further, in the welding wire material, Mn is added to the wire for deoxidation and for maintaining strength, and Ni is also added thereto for improvement of toughness and for decrease of embrittlement in use under high temperature and pressure conditions for a long time. This document discloses an example in which a post weld heat treatment (PWHT) temperature is 740° C.
JP-A No. 258894/1989 discloses a submerged arc welding method using a flux with a Li compound added thereto so as to have good resistance to intercrystalline crack. This welding method comprises addition of Mn to a welding wire for deoxidation and for maintaining strength, and addition of Ni to the wire for decrease of embrittlement in use under high temperature and pressure conditions for a long time. Further, this publication discloses an example in which the PWHT temperature is 740° C.
A welding wire disclosed in Japanese Patent No. 2668530 is a welding wire for a gas-shielded arc welding process. The welding wire contains a small content of carbon, and optimized contents of Nb and V so as to have good crack resistance, creep rupture strength, and toughness. Further, in the welding wire, Mn is added to the wire for deoxidation and for maintaining strength, and Ni is also added thereto for decrease of embrittlement in use under high temperature and pressure conditions for a long time. This document discloses an example in which the PWHT temperature is 740° C.
Japanese Patent No. 2529843 discloses a submerged arc welding method which comprises restricting a Si content of a welding wire to 0.05% by mass or less, while restricting a SiO2 content of a flux to 5% by mass or less so as to have good resistance to intercrystalline crack. This welding method further comprises addition of Mn to the welding wire for deoxidation and for maintaining strength, and addition of Ni thereto for decrease of embrittlement in use under high temperature and pressure conditions for a long time. Also, this document discloses an example in which the PWHT temperature is 740° C.
In welding wires disclosed in Japanese Patent No. 2594265 and JP-B No. 36996/1994, an element W is added to the wire, and a relationship between the W content and the Mo content is optimized, so as to obtain good creep rupture strength. Further, Mn is added to the welding wire for deoxidation and for maintaining strength, and Ni is added thereto for decrease of embrittlement in use under high temperature and pressure conditions for a long time. These documents also disclose examples in which the PWHT temperature is 750° C.
In welding materials disclosed in Japanese Patent No. 2908228 and Japanese Patent No. 2928904, Ni and Cu are combined and added to the materials so as to obtain excellent high-temperature strength, high-temperature corrosion resistance, and toughness. Further, Mn is added to the material so as to fix the S content, thereby preventing harmful effects caused by the element S, including welding cracks, creep embrittlement, and the like, while Ni is added thereto so as to ensure toughness by improving toughness of a matrix, and restricting the residual δ-ferrite. Further, these documents also disclose examples in which the PWHT temperature is 740° C.
A welding wire disclosed in JP-A No. 96390/1995 contains optimized contents of Mn, Ni, and N to obtain good creep rupture strength and toughness. The Mn is added to the wire for ensuring the strength and for prevention of formation of bulky ferrite, and the Ni is also added thereto for prevention of formation of the bulky ferrite to stabilize the toughness. Further, this document also discloses an example in which the PWHT temperature is 740° C.
The above-mentioned prior art, however, has the following problems. In some existing welding methods, approaches are taken in terms of working conditions to improve the creep rupture strength and toughness. More specifically, such an approach involves increasing the PWHT temperature, which is carried out on the overseas working conditions. In statutes pertaining to electrical work pieces in Japan (the Technical Standard for Thermal Power Generating Facilities), the PWHT temperature of high Cr ferrite steels, such as the Mod.9Cr-1Mo steel, is set to 760° C. or less. For this reason, on the working conditions in Japan, the PWHT temperature is intended to be set within a range of 740 to 750° C., taking into consideration variations in the temperature of a heat treatment furnace, resulting in the actual temperature that does not exceed 760° C. inmost cases. On the other hand, in statutes in other countries, the PWHT temperature is set to be raised up to an Acl transformation temperature of a base material according to the ASME specification, for example. Strictly speaking, there are no rules in other countries that limit the PWHT temperature to 760° C. or less.
Thus, in some welding processes in other countries, the PWHT temperature is intended to be set to 760° C. for the purpose of improving the creep rupture strength and toughness, and the PWHT temperature is often increased until the actual temperature reaches 780° C. In this case, a problem of the Acl transformation temperature for a deposited metal arises. Concretely, when the PWHT is carried out at a temperature above the Acl transformation temperature of the deposited metal, phase transformation occurs in the deposited metal, resulting in a danger that the creep rupture strength may be significantly degraded. Some recent reports have suggested that, even if the PWHT temperature does not exceed the Acl transformation temperature of the deposited metal, the creep rupture strength is degraded at the PWHT temperature extremely close to the transformation temperature.
From such a background, the American Welding Society (AWS) Specification and the EN Specification tend to restrict the total content of Mn and Ni in the welding material to 1.5% by mass or less for the purpose of enhancement of the Acl transformation temperature of the deposited metal. Since there is a negative correlation between the total content of Mn and Ni and the Acl transformation temperature, decrease in the total content of Mn and Ni can raise the Acl transformation temperature of the deposited metal. Furthermore, as disclosed in the above-mentioned cited documents, since Mn and Ni each have effects of ensuring and improving toughness, just restriction of the total content of Mn and Ni in the welding material under the high PWHT temperature condition disadvantageously leads to failure in improvement of the toughness. The above-mentioned documents do not take into consideration the welding material whose PWHT temperature is not less than 760° C. In the welding materials disclosed in these documents, when the PWHT temperature exceeds the Acl transformation temperature of the deposited metal, phase transformation might occur in the deposited metal, resulting in significantly degraded creep rupture strength. Accordingly, a welding wire for the Mod.9Cr-1Mo steel is required which is usable at the PWHT temperature of 760° C. or above, and has good toughness.
The present invention has been accomplished in view of those problems encountered with the prior art, and it is an object of the invention to provide a welding wire for a modified 9Cr-1Mo steel that provides good toughness without degradation of creep rupture strength even at the PWHT temperature of 760° C. or above.
A welding wire according to one aspect of the invention consists essentially of, by mass, C: 0.070 to 0.150%, Si: more than 0.15%, but not more than 0.30%, Mn: not less than 0.30%, but less than 0.85%, Ni: 0.30 to 1.20%, Cr: 8.00 to 13.00%, Mo: 0.30 to 1.40%, V: 0.03 to 0.40%, Nb: 0.01 to 0.15%, N: 0.016 to 0.055%, P: not more than 0.010%, S: not more than 0.010%, Cu: less than 0.50%, Ti: not more than 0.010%, Al: less than 0.10%, B: less than 0.0010%, W: less than 0.10%, Co: less than 1.00%, O: not more than 0.03%, and balance: Fe and unavoidable impurities, the total amount of Mn and Ni being not more than 1.50%.
In the present invention, the total content of Mn and Ni is restricted to not more than 1.50% by mass, and the Co content is also restricted to less than 1.00% by mass, so that the creep rupture strength is not degraded even at the PWHT temperature of 760° C. or above. The contents of Mn, Ni, Si, Cr, Mo, V and Nb, each of which might affect the toughness, are optimized, while the contents of Al, W, Ti, B, C, and O, each of which might degrade the toughness, are restricted, resulting in the good toughness.
Preferably, in the welding wire, the Ni content may be 0.40 to 1.00% by mass, the Mo content 0.80 to 1.10% by mass, the Cu content not more than 0.10% by mass, and the Al content less than 0.05% by mass. This improves the toughness and the creep rupture strength.
A submerged-arc welding material according to another aspect of the invention consists essentially of, the welding wire with the aforesaid components, and a flux. The flux comprises, by mass, CaF2: 10 to 60%, CaO: 2 to 25%, MgO: 10 to 50%, Al2O3: 2 to 30%, and Si and SiO2: 6 to 30% in terms Of SiO2.
A welding wire for a modified 9Cr-1Mo steel according to the present invention will be hereinafter described in details. The applicant et al have obtained the following findings from the study of the relationship between wire components and toughness so as to solve the aforesaid problems. That is, the applicant et al have found that each of Mn and Ni contents should be optimized to have good toughness, and that the best toughness is achieved by setting the total content of Mn and Ni within a range of 0.60% to 1.50% by mass. Further, the applicant et al have found that loadings of the ferrite stabilizing elements should be restricted so as to prevent the residual δ-ferrite, which might adversely affect the toughness. For example, when the Mn content, and the Ni content, and the total content of Mn and Ni are restricted, in particular, the contents of Si, Cr, Mo, V, Nb, Al, and W among the ferrite stabilizing elements necessarily should be restricted.
Although the element Cu has an effect of preventing the δ-ferrite from remaining in a weld metal, the excessive amount of added Cu causes embrittlement in the weld metal, resulting in decreased toughness. Also, although the Co has a high effect on improving the toughness by preventing the δ-ferrite from remaining in the weld metal, the excessive amount of added Co decreases an Acl transformation temperature and creep rupture strength. The element N has effects of improving the creep rupture strength and of preventing the δ-ferrite from remaining in the weld metal. The excessive amount of N is required to exhibit an effect of improving the toughness by addition of the N to the wire, which might lead to blowholes. Ti and B are precipitated as fine carbide particles and fine boride particles, respectively, resulting in significant degradation of the toughness. Thus, the contents of these elements need to be restricted.
Now, the reason for numeric restriction of a chemical composition of the welding wire for the modified 9Cr—Mo steel according to the invention will be explained below.
C: 0.070 to 0.150% by Mass
The element C has an effect of precipitating various kinds of carbides in combination with the elements Cr, Mo, W, V, and Nb to improve the creep rupture strength. Note that in the case of the C content of less than 0.070% by mass, this effect is not sufficient. In contrast, excessive addition of the element C, for example, when the C content exceeds 0.150% by mass, leads to degradation in crack resistance. Accordingly, the C content is preferably 0.070 to 0.150% by mass.
Si: More than 0.15% by Mass, but not More than 0.30% by Mass
The element Si has an effect of acting as a deoxidizing agent to decrease the oxygen amount of a deposited metal, thereby improving the toughness of the weld metal. Note that the welding wire with the Si content of 0.15% by mass or less does not exhibit the effect. In contrast, since the Si is one of the ferrite stabilizing elements, excessive addition of the Si, for example, when the Si content exceeds 0.30% by mass, causes the residual δ-ferrite in the weld metal, thus resulting in degradation of the toughness of the weld metal. Accordingly, the Si content is preferably more than 0.15% by mass, but not more than 0.30% by mass.
Mn: not Less than 0.30% by Mass, but Less than 0.85% by Mass, Ni: 0.30 to 1.20% by Mass, and Mn+Ni: not More than 1.50% by Mass in Total
The element Mn has an effect of acting as a deoxidizing agent to decrease the oxygen amount of the deposited metal, thereby improving the toughness of the weld metal. Mn and Ni are austenite forming elements, and each of them has an effect of preventing the degradation of the toughness due to the residual δ-ferrite in the weld metal. Note that in the case of the Mn content of less than 0.30% by mass, or in the case of the Ni content of less than 0.30% by mass, such an effect is not obtained, resulting in the degraded toughness. In contrast, in the case of the Mn content of at least 0.85%, or in the case of the Ni content of above 1.20% by mass, the toughness of the weld metal is degraded. In a case where the total content of Mn and Ni exceeds 1.50% by mass, the toughness of the weld metal is degraded, while the Acl transformation temperature of the deposited metal is decreased, thus resulting in the degraded creep rupture strength. Accordingly, the Mn content is preferably not less than 0.30% by mass, but less than 0.85% by mass, the Ni content 0.30 to 1.20% by mass, and the total content of Mn and Ni not more than 1.50% by mass. Note that the Ni content is more preferably 0.40 to 1.00% by mass. This further improves the toughness of the weld metal.
Cr: 8.00 to 13.00% by Mass
The element Cr is an important element of the Mod.9Cr-1Mo steel, for which the welding wire of the invention is used, and essential for ensuring the oxidation resistance and the high-temperature strength. It should be noted that when the Cr content is less than 8.00% by mass, the oxidation resistance and the high-temperature strength are insufficient. In contract, since the Cr is one of the ferrite stabilizing elements, excessive addition of the Cr, for example, when the Cr content is greater than 13.00% by mass, causes the residual δ-ferrite, thus resulting in degradation of the toughness. Accordingly, the Cr content is preferably 8.00 to 13.00% by mass. This provides the excellent oxidation resistance and high-temperature strength.
Mo: 0.30 to 1.40% by Mass
The element Mo is a solid solution strengthening element, and has an effect of improving the creep rupture strength. Note that when the Mo content is less than 0.30% by mass, the sufficient creep rupture strength is not obtained. In contract, since the Mo is one of the ferrite stabilizing elements, excessive addition of the Mo, for example, when the Mo content is greater than 1.40% by mass, causes the residual δ-ferrite in the weld metal, thus resulting in degradation of the toughness thereof. Accordingly, the Mo content is preferably 0.30 to 1.40% by mass, and more preferably 0.80 to 1.10% by mass. This improves the creep rupture strength and the toughness.
V: 0.03 to 0.40% by Mass
The element V is a precipitation strengthening element, and has an effect of precipitating as carbonitride to improve the creep rupture strength. Note that when the V content is less than 0.03% by mass, the sufficient creep rupture strength is not obtained. In contract, since the V is one of the ferrite stabilizing elements, excessive addition of the V, for example, when the V content is greater than 0.40% by mass, causes the residual δ-ferrite in the weld metal, thus resulting in degradation of the toughness thereof. Accordingly, the V content is preferably 0.03 to 0.40% by mass.
Nb: 0.01 to 0.15% by Mass
The element Nb is an element which precipitates as a solid solution strengthening nitride to contribute to stabilization of the creep rupture strength. Note that when the Nb content is less than 0.01% by mass, the sufficient creep rupture strength is not obtained. In contract, since the Nb is one of the ferrite stabilizing elements, excessive addition of the Nb, for example, when the Nb content is greater than 0.15% by mass, causes the residual δ-ferrite in the weld metal, thus resulting in degradation of the toughness thereof. Accordingly, the Nb content is preferably 0.01 to 0.15% by mass.
N: 0.016 to 0.055% by Mass
The element N is an element which precipitates as a solid solution strengthening nitride to contribute to stabilization of the creep rupture strength. Note that when the N content is less than 0.016% by mass, the sufficient creep rupture strength is not obtained. In contract, excessive addition of the N, for example, when the N content is greater than 0.055% by mass, causes blowholes. Accordingly, the N content is preferably 0.016 to 0.055% by mass.
P: not More than 0.010% by Mass
The element P is an element enhancing the sensitivity to hot cracking. When the P content exceeds 0.010% by mass, the hot cracking occurs. Accordingly, the P content is restricted to not more than 0.010% by mass.
S: not More than 0.010% by Mass
The element S is an element enhancing the sensitivity to hot cracking. When the S content exceeds 0.010% by mass, the hot cracking occur. Accordingly, the S content is restricted to not more than 0.010% by mass.
Cu: Less than 0.50% by Mass
The element Cu is an element that degrades the toughness. In some cases, a surface of a wire is coated with Cu plating so as to improve energizing and feeding properties. As mentioned above, excessive addition of the Cu, for example, when the Cu content is not less than 0.50% by mass, causes the enbrittlement in the weld metal, resulting in degradation of the toughness. Accordingly, the Cu content in the whole wire including the plating is restricted to less than 0.50% by mass. Note that the Cu content is more preferably restricted to not more than 0.10% by mass. This improves the toughness.
Ti: not More than 0.010% by Mass
The element Ti is precipitated as fine carbide to harden the deposited metal, thus significantly degrading the toughness of the weld metal. For example, when the Ti content exceeds 0.010% by mass, the toughness is degraded. Accordingly, the Ti content is restricted to not more than 0.010% by mass.
Al: Less than 0.10% by Mass
The element Al is one of the ferrite stabilizing elements. Excessive addition of the Al, for example, when the Al content is not less than 0.10% by mass, causes the residual δ-ferrite, which might adversely affect the toughness of the weld metal. Accordingly, the Al content is restricted to less than 0.10% by mass. Note that the Al content is preferably restricted to less than 0.05% by mass. This improves the toughness.
B: Less than 0.0010% by Mass
The element B is precipitated as carbon boride and boride to harden the deposited metal, thus significantly degrading the toughness of the weld metal. For example, when the B content is not less than 0.0010% by mass, the toughness is degraded. Accordingly, the B content is restricted to less than 0.0010% by mass.
W: Less than 0.10% by Mass
The element W is one of the ferrite stabilizing elements. Excessive addition of the W, for example, when the W content is not less than 0.10% by mass, causes the residual δ-ferrite in the weld metal, resulting in degradation of the toughness thereof. Accordingly, the W content is restricted to less than 0.10% by mass.
Co: Less than 1.00% by Mass
The element Co is one of the austenite forming elements, and has an effect of preventing the residual δ-ferrite in the weld metal to improve the toughness thereof. However, excessive addition of the Co, for example, when the Co content is not less than 1.00% by mass, decreases the Acl transformation temperature of the deposited metal, thus resulting in degradation of the creep rupture strength. Accordingly, the Co content is restricted to less than 1.00% by mass.
O: not More than 0.03% by Mass
The element O remains as the oxide in the deposited metal to degrade the toughness of the weld metal. For example, when the O content exceeds 0.03% by mass, the amount of residual oxide is increased, leading to degradation of the toughness. Accordingly, the O content is restricted to not more than 0.03% by mass.
In cases where the welding wire of the invention is used for the welding methods, such as the submerged arc welding, current polarity significantly affects chemical components of the deposited metals, mechanical property, and welding workability. More specifically, direct current electrode positive (hereinafter referred to as DCEP) tends to increase the amount of oxygen in the deposited metal and to degrade the toughness of the weld metal, as compared to alternating current (AC). Further, the DCEP tends to have magnetic blow-outs, and to cause slug winding and incomplete fusion. In order to solve such problems, and to have good mechanical property, the welding wire of the invention is preferably combined in use with a flux, which comprises CaF2: 10 to 60% by mass, CaO: 2 to 25% by mass, MgO: 10 to 50% by mass, Al2O3: 2 to 30% by mass, and Si and SiO2: 6 to 30% in terms of SiO2 by mass in total.
Now, reasons for numeric restriction of a chemical composition of the flux to be used in combination with the welding wire for the modified 9Cr—Mo steel of the invention will be explained below.
CaF2: 10 to 60% by Mass
The compound CaF2 has an effect of enhancing the basicity of the slug to decrease the amount of oxygen in the deposited metal, thus improving the toughness of the weld metal. Also, the CaF2 has an effect of fixing the shape of a weld bead, since CaF2 decreases a melting point of the slug and improves its mobility. Note that when the CaF2 content in the flux is less than 10% by mass, such effects are not obtained. When the CaF2 content in the flux exceeds 60% by mass, the mobility of the slug is excessive, thus significantly impairing the shape of the bead. Accordingly, the CaF2 content in the flux is preferably 10 to 60% by mass.
CaO: 2 to 25% by Mass
The compound CaO is a basic component, and has an effect of decreasing the amount of oxygen in the deposited metal to improve the toughness of the weld metal, in the same manner as the above-mentioned compound CaF2. Also, the CaO has an effect of fixing the shape of the weld bead by adjusting the viscosity of the slug. Note that when the CaO content in the flux is less than 2% by mass, such effects are not obtained. When the CaO content in the flux exceeds 25% by mass, the amount of oxygen in the deposited metal is increased, leading to degradation of the toughness of the weld metal. Accordingly, the CaO content in the flux is preferably 2 to 25% by mass.
MgO: 10 to 50% by Mass
The compound MgO is a basic component, and has an effect of decreasing the amount of oxygen in the deposited metal to improve the toughness of the weld metal, in the same manner as the above-mentioned compound CaF2. Also, the MgO has an effect of fixing the shape of the weld bead by adjusting the viscosity of the slug. Note that when the MgO content in the flux is less than 10% by mass, such effects are not obtained. When the MgO content in the flux exceeds 50% by mass, the amount of oxygen in the deposited metal is increased, leading to degradation of the toughness of the weld metal. Accordingly, the MgO content in the flux is preferably 10 to 50% by mass.
Al2O3: 2 to 30% by Mass
The compound Al2O3 has an effect of enhancing a melting point of the slug to adjust its mobility, thereby fixing the shape of the weld bead. Note that when the Al2O3 content in the flux is less than 2% by mass, this effect is not obtained. When the Al2O3 content in the flux exceeds 30% by mass, slug seizing occurs, and impairs the external appearance of the bead. Accordingly, the Al2O3 content in the flux is preferably 2 to 30% by mass.
Si and SiO2: 6 to 30% by Mass in Total
The compound SiO2 has an effect of enhancing the viscosity of the slug to fix the shape of the weld bead. Note that when the SiO2 content in the flux is less than 6% by mass, this effect is not obtained. Since the SiO2 is reduced in an arc to be included in the deposited metal, excessive addition of the SiO2 increases the amount of reduced Si, which leads to degradation of the toughness due to the residual δ-ferrite in the deposited metal. The same goes for the element Si, which is arbitrarily added as a deoxidizing agent into the flux. For this reason, the total amount of Si and SiO2 in the flux needs to be restricted, including SiO2 in a soluble glass which is used as a binder when granulating the flux. Accordingly, the total content of Si and SiO2 in the flux is preferably 6 to 30% by mass in terms of SiO2.
Such essential components can be added in the form of a single material, a compound including these elements themselves, an ore, a fused flux, or the like. For example, a fluorite may be added as the CaF2; calcis and a melting flux as the CaO; a magnesia clinker and a melting flux as the MgO; alumina and a melting flux as Al2O3; and potassium feldspar, albite, a melting flux, and the like as the SiO2. In addition to the above-mentioned essential components, alloy powders, oxides, and/or fluorides may be arbitrarily added to the flux so as to adjust the alloy components and the welding workability. Note that unavoidable impurities in the welding wire of the invention include Sn, As, Sb, Ca, Mg, and the like.
Now, effects of the examples according to the invention will be explained by comparing with comparative examples, which depart from the scope of the invention. First, the welding wires with compositions shown in the following Tables 1 and 2 were used as first examples of the invention. A sample steel plate with a composition shown in Table 3, and having a thickness of 20 mm, a groove angle of 45 degrees, and a root gap of 13 mm, was welded using each of the above-mentioned welding wires in the submerged arc welding process under a condition shown in the following Table 4. The toughness and creep rupture strength of each of the thus-obtained weld metals were evaluated. The following Table 5 shows a composition of a combination flux. The combination flux was obtained by granulating flux raw materials and a water glass as a binder, sintering them at 500 to 550° C. for one hour, so that the content of 10×48 mesh grains in the whole flux was 70% by mass or more. Note that the balance shown in the Tables 1 and 2 are Fe and unavoidable impurities.
Now, evaluation methods of respective items will be described hereinafter. First, for classification, radiographic testing (JIS specification Z3104) was performed on the samples after welding. Results corresponding to JIS Class 1 were judged as good, and then the samples with these results were subjected to the PWHT at 760° C. for two hours. Thereafter, creep rupture and Charpy impact tests were performed on these samples. The creep test used a specimen with a diameter of 6.0 mm as specified in JIS specification Z2273. And test conditions were as follows: 650° C., and 86 MPa. The Charpy impact test used a specimen as specified in JIS specification Z3114, and a test temperature was set to 20° C. The respective specimens for the creep rupture and impact tests were extracted from a center part of the weld metal located in the through-thickness center region of the obtained plate. Criterions for evaluation of those tests were as follows. In the radiographic testing, the results corresponding to JIS Class 1 were judged good (◯), and the results other than the JIS Class 1 judged bad (x). In the creep rupture test, results with a rupture time of not less than 1000 hours were judged as good (◯), and results with a rupture time of less than 1000 hours judged bad (x). In the Charpy impact test, results with vE20° C. average of not less than 40 J were judged good (◯), and results with vE20° C. average of less than 40 J judged bad (x). Those results are shown in the following Tables 7 and 9. The following Tables 6 and 8 show the chemical components of the deposited metals.
Now, in second examples of the invention, the welding wires of the examples No. W43 to W48 and No. W55 to W60 shown in the above Table 2 were subjected to wire drawing treatments until a diameter of each wire reached 1.6 mm. A sample steel plate with a composition shown in the above Table 3, and having a thickness of 12 mm, a groove angle of 45 degrees, and a root gap of 6 mm, was welded using each of the above-mentioned welding wires in the TIG welding process under a condition shown in the following Table 10. The toughness and creep rupture strength of each of the thus-obtained weld metals were evaluated in the same way and condition as those of the aforesaid first example. Results are shown in the following Table 11.
As shown in the above Tables 6 and 7, in the wire of the comparative example No. W1, the C content was less than that covered by the scope of the invention. Thus, the strength of the wire was insufficient, and the creep rupture time did not satisfy a predetermined requirement of performance. In the wire of the comparative example No. W2, the C content exceeded that covered by the scope of the invention, thus leading to occurrence of hot cracking in the radiographic testing. In the wire of the comparative example No. W3, since the Si content was less than that covered by the scope of the invention, the deposited metal lacked deoxidation, and the toughness of the weld metal did not satisfy the predetermined requirement of performance. In the wire of the comparative example No. W4, since the Si content exceeded that covered by the scope of the invention, the δ-ferrite remained in the weld metal, and the toughness did not satisfy the predetermined requirement of performance. In the wire of the comparative example No. W5, since the Mn content was less than that covered by the scope of the invention, the deposited metal lacked deoxidation, and the δ-ferrite remained in the weld metal. As a result, the toughness did not satisfy the predetermined requirement of performance. In the wire of the comparative example No. W6, the Mn content and the total content of Mn and Ni exceeded those covered by the scope of the invention, resulting in the decreased Acl transformation temperature of the deposited metal, and hence the creep rupture time did not satisfy the predetermined requirement of performance. Also, the toughness did not meet the predetermined requirement of performance.
In the wire of the comparative example No. W7, the P content exceeded that covered by the scope of the invention, thus leading to occurrence of hot cracking in the radiographic testing. Also, in the wire of the comparative example No. W8, the S content exceeded that covered by the scope of the invention, thus leading to occurrence of hot cracking in the radiographic testing. In the wire of the comparative example No. W9, since the Cu content exceeded that covered by the scope of the invention, the toughness did not meet the predetermined requirement of performance. In the wire of the comparative example No. W10, since the Ni content was less than that covered by the scope of the invention, the δ-ferrite remained in the weld metal, and the toughness did not satisfy the predetermined requirement of performance. In the wire of the comparative example No. W11, the Ni content and the total content of Mn and Ni exceeded those covered by the scope of the invention, resulting in the decreased Acl transformation temperature of the deposited metal, and hence the creep rupture time did not satisfy the predetermined requirement of performance. Also, the toughness did not meet the predetermined requirement of performance. In the wire of the comparative example No. W12, the Co content exceeded that covered by the scope of the invention, resulting in the decreased Acl transformation temperature of the deposited metal, and hence the creep rupture time did not satisfy the predetermined requirement of performance.
In the wire of the comparative example No. W13, since the Cr content was less than that covered by the scope of the invention, the strength of the wire was insufficient, and the creep rupture time did not satisfy the predetermined requirement of performance. In the wire of the comparative example No. W14, since the Cr content exceeded that covered by the scope of the invention, the δ-ferrite remained in the weld metal, and the toughness thereof did not satisfy the predetermined requirement of performance. In the wire of the comparative example No. W15, since the Mo content was less than that covered by the scope of the invention, the strength of the wire was insufficient, and the creep rupture time did not satisfy the predetermined requirement of performance. In the wire of the comparative example No. W16, since the Mo content exceeded that covered by the scope of the invention, the δ-ferrite remained in the weld metal, and the toughness did not satisfy the predetermined requirement of performance. Likewise, in the wire of the comparative example No. W17, since the Al content exceeded that covered by the scope of the invention, the δ-ferrite remained in the weld metal, and the toughness did not satisfy the predetermined requirement of performance. In the wire of the comparative example No. W18, the Ti content exceeded that covered by the scope of the invention, resulting in significantly enhancing the strength of the weld metal, and hence the toughness did not meet the predetermined requirement of performance. In the wire of the comparative example No. W19, the Nb content was less than that covered by the scope of the invention, leading to insufficient strength of the wire, resulting in the fact that the creep rupture time did not satisfy the predetermined requirement of performance. In the wire of the comparative example No. W20, since the Nb content exceeded that covered by the scope of the invention, the δ-ferrite remained in the weld metal, and the toughness did not satisfy the predetermined requirement of performance.
In the wire of the comparative example No. W21, the V content was less than that covered by the scope of the invention, leading to insufficient strength of the wire, and hence the creep rupture time did not satisfy the predetermined requirement of performance. In the wire of the comparative example No. W22, since the V content exceeded that covered by the scope of the invention, the δ-ferrite remained in the weld metal, and the toughness thereof did not satisfy the predetermined requirement of performance. In the wire of the comparative example No. W23, since the W content exceeded that covered by the scope of the invention, the δ-ferrite remained in the weld metal, and the toughness thereof did not satisfy the predetermined requirement of performance. Likewise, in the wire of the comparative example No. W24, the B content exceeded that covered by the scope of the invention, resulting in the residual δ-ferrite in the weld metal, and hence the toughness did not meet the predetermined requirement of performance. In the wire of the comparative example No. W25, the N content was less than that covered by the scope of the invention, leading to insufficient strength. Thus, the creep rupture time failed to satisfy the predetermined requirement of performance. In the wire of the comparative example No. W26, the N content exceeded that covered by the scope of the invention, leading to occurrence of blowholes in the radiographic testing.
In the wire of the comparative example No. W27, the O content exceeded that covered by the scope of the invention, resulting in an increased oxygen amount in the deposited metal, and thus the toughness did not meet the predetermined requirement of performance. In the wire of the comparative example No. W28, the total content of Mn and Ni exceeded those covered by the scope of the invention, resulting in decreased Acl crystal temperature of the deposited metal, and thus the creep rupture time did not satisfy the predetermined requirement of performance. Also, the toughness did not meet the predetermined requirement of performance. In the wire of the comparative example No. W29, since the Cu content exceeded that covered by the scope of the invention, the toughness did not satisfy the predetermined requirement of performance. Further, since the Nb content was less than that covered by the scope of the invention, the strength was insufficient, and hence the creep rupture time did not meet the predetermined requirement of performance. In the wire of the comparative example No. W30, the Ni content and the total content of Mn and Ni exceeded those covered by the scope of the invention, resulting in the fact that the toughness did not satisfy the predetermined requirement of performance. This decreased the Acl transformation temperature of the deposited metal. Even addition of the Nb in an amount more than that covered by the scope of the invention did not allow the creep rupture time to meet the predetermined requirement of performance.
In contrast, as shown in the above Tables 8 and 9, in the wires of the examples No. W31 to W60, since the component compositions were within the scope of the invention, even when performing the PWHT at 760° C. for two hours, the toughness and creep rupture time satisfied the predetermined requirements of performance. Especially, in the wires No. W49 to W60, the Cu, Ni, Mo, and Al contents each were adjusted within a preferable range, thereby achieving excellent toughness and creep rupture strength. As shown in the above Table 11, the wires No. W43 to W48, and wires No. W55 to W60 satisfied the predetermined requirement of performance even in the TIG welding process. In particular, the wires No. W55 to W60, in which the Cu, Ni, Mo, and Al contents each were within the preferable range, had significantly excellent toughness and creep rupture strength.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-148204 | May 2004 | JP | national |
