JP5032940B2 - High strength Cr-Mo steel weld metal - Google Patents

Description

  The present invention relates to a weld metal of high-strength Cr-Mo steel formed by submerged arc welding of high-strength Cr-Mo steel.

  Cr-Mo low-alloy heat-resistant steel containers used in high-temperature and high-pressure environments such as power plants and chemical plants are made of high-strength Cr-Mo steel added with V, Nb, etc. Along with this, the thickness is increased, and for the welding, mainly covering arc welding, gas shielded arc welding, submerged arc welding, etc. with good welding efficiency are adopted. In weld metal formed by welding such high strength Cr-Mo steel, heat resistance (high temperature strength), SR cracking resistance (do not cause intergranular cracking during annealing for stress removal), toughness, In addition, improvement of anti-tempering embrittlement characteristics (less embrittlement during use in a high temperature environment) is required.

For example, Patent Document 1 discloses a parameter defined by ((Si) + [Mn]) × ([P] + [Sn] + [Sb] + [As]) / [C] for an additive element (in the formula, The element represented by [] is a TIG wire for high-strength Cr-Mo steel in which the content of each additive element described in [] is limited to a certain amount, including all temper embrittlement resistance. The characteristics can be secured in a well-balanced manner. Patent Document 2 is a weld metal formed by submerged arc welding in which the composition of the residue collected from the weld metal by electrolytic extraction is V: 65% by mass or less and the Fe concentration is twice or less the Cr concentration. By suppressing cementite precipitation at the prior austenite grain boundaries, SR cracking resistance can be improved and all properties can be secured in a well-balanced manner.
Japanese Patent No. 2742201 (paragraphs 0019-0022) Japanese Patent No. 3283762 (paragraphs 0022-0024, 0038-0041)

  However, since the wire disclosed in Patent Document 1 is for TIG welding and TIG welding has low construction efficiency, it is not a desirable welding method in recent years when high-strength Cr-Mo steel is thickened. Moreover, in welding constructions other than TIG welding, the oxygen content in the weld metal is inevitably higher than TIG welding, so it was necessary to study component design. On the other hand, although the weld metal disclosed in Patent Document 2 is a weld metal formed by submerged arc welding, the tempering embrittlement resistance is not sufficient and there is room for improvement.

  This invention is made | formed in view of the said problem, and it aims at providing the weld metal of the high strength Cr-Mo steel excellent in the tempering embrittlement resistance.

The inventors of the present invention have hitherto considered that the tempering embrittlement resistance is attributed to impurities (Patent Document 1), but they often embrittle even if the impurity level is reduced. It was found that it is the carbide form that dominates the temper embrittlement characteristics. Specifically, the present inventors promote the growth of MC carbide containing Nb as a main component during the embrittlement promotion treatment (step cooling) and also carbide containing Cr as a main component (M ₂₃ C ₆ carbide, M ₇ C ₃ carbide) was successfully suppressed. Moreover, it became clear that control of these carbide | carbonized_material forms can also improve SR cracking resistance and toughness. Furthermore, it has been found that in order to realize these carbide forms in the weld metal, the components (C, Cr, Mo, Nb, V) of the submerged arc welding material and the welding conditions may be appropriately controlled. In addition, it is necessary to add an element capable of refining the structure, and as a result of various studies, the present inventors set the C content high. Furthermore, Al was added to effectively promote deoxidation.

That is, the high strength Cr—Mo steel weld metal according to claim 1 is a high strength Cr—Mo steel weld metal formed by submerged arc welding, C: 0.10 to 0.15 mass%, Si: 0.10 to 0.5 mass%, Mn: 0.5 to 1.0 mass%, Al: 0.02 to 0.05 mass%, Cr: 2.00 to 3.25 mass%, Mo: 0.0. 9-1.2% by mass, Nb: 0.01-0.03% by mass, V: 0.2-0.7% by mass, B: 0.0002-0.003 % by mass , O: 0.030- It contains 0.050% by mass, the balance is made of Fe and inevitable impurities, and the Cr precipitation amount obtained from the residue collected by electrolytic extraction from only the weld metal base part is 0 with respect to the weld metal base part. Less than 5% by mass, and the Nb deposition amount is 0.005% by mass or more.

  Thus, by limiting the C concentration to a range higher than that of the prior art, the carbide form is controlled, and the tempering embrittlement resistance, SR cracking resistance, and toughness are improved.

  Furthermore, the weld metal of high-strength Cr—Mo steel according to claim 2 is Cu: less than 0.20 mass%, Ni as the inevitable impurity of the weld metal of high-strength Cr—Mo steel according to claim 1. : Restricted to less than 0.05% by mass.

  Further, the weld metal of high strength Cr—Mo steel according to claim 3 is characterized in that P and S are each 0 as the inevitable impurities of the weld metal of high strength Cr—Mo steel according to claim 1 or claim 2. It is limited to less than 0.012% by mass.

  Thus, by limiting the Cu, Ni, P, and S concentrations that promote temper embrittlement, the temper embrittlement resistance can be improved.

Furthermore, the weld metal of the high strength Cr—Mo steel according to claim 4 is a parameter CP calculated by the following formula (1) in the weld metal of the high strength Cr—Mo steel according to claims 1 to 3. Is 60 or less.
CP = 1000 × [C] × [Nb] / ([Cr] / 52 + [Mo] / 96 + [Nb] / 93 + [V] / 51) Formula (1)
(In formula (1), the element represented by [] is the content (% by mass) of each component in the weld metal of the high-strength Cr—Mo steel described in []).

  Thus, it is possible to moderately control the growth of MC carbide by limiting the correlation of the content of each element in the weld metal.

  The weld metal of high strength Cr-Mo steel according to the present invention controls toughness and temper resistance embrittlement by controlling the carbide morphology that governs the temper resistance resistance of weld metal by submerged arc welding with excellent welding efficiency. To meet the demands for improved toughness and tempering embrittlement resistance of welded metal in Cr-Mo low alloy heat-resistant steel containers used in high-temperature and high-pressure environments such as power plants and chemical plants in recent years. Can do.

  Hereinafter, the best mode for realizing a weld metal of high-strength Cr—Mo steel according to the present invention (hereinafter referred to as “weld metal” as appropriate) will be described.

  The weld metal of high-strength Cr—Mo steel according to the present invention is a metal constituting a welded portion formed by submerged arc welding on a welded portion of a welded material made of high-strength Cr—Mo steel. And the weld metal of the high strength Cr-Mo steel which concerns on this invention is C: 0.10-0.15 mass%, Si: 0.10-0.5 mass%, Mn: 0.5 as an essential component. -1.0 mass%, Al: 0.02-0.05 mass%, Cr: 2.00-3.25 mass%, Mo: 0.9-1.2 mass%, Nb: 0.01-0 0.03% by mass, V: 0.2 to 0.7% by mass, B: 0.003% by mass or less, O: 0.030 to 0.050% by mass, with the balance being Fe and inevitable impurities It is what is done. First, the numerical range of the content of each component constituting the weld metal of the high-strength Cr—Mo steel according to the present invention and the reason for limiting the numerical range will be described.

(C content in weld metal: 0.10 to 0.15 mass%)
C is an element that greatly affects the hardenability of the weld metal and plays an important role in ensuring strength and toughness at room temperature and high temperature. C also has the effect of refining the structure. When the C content is less than 0.10% by mass, these effects are small. On the other hand, excessive addition of C increases carbides mainly composed of Cr, and if the C content exceeds 0.15% by mass, the toughness decreases due to the coarsening of the structure and the tempering embrittlement resistance deteriorates. . Therefore, the C content in the weld metal is set to 0.10 to 0.15 mass%. Preferably it is 0.11-0.13 mass%.

(Si content in weld metal: 0.10 to 0.50 mass%)
Si has a deoxidizing effect and has an effect of cleaning the weld metal. Further, Si is an element that has the role of strengthening the solid solution of ferrite when the yield is increased and further improving the conformability of the weld bead. When the Si content is less than 0.10% by mass, these effects are small. On the other hand, when the Si content exceeds 0.50% by mass, the strength becomes too high and the toughness is lowered, and the tempering embrittlement resistance is also lowered. Therefore, the Si content in the weld metal is 0.10 to 0.50 mass%. Preferably it is 0.20-0.40 mass%.

(Mn content in weld metal: 0.5 to 1.0 mass%)
Mn has the effect of improving high temperature strength and toughness, particularly toughness before step cooling. Further, Mn has an action of controlling the amount of oxygen. When the Mn content is less than 0.5% by mass, these effects are insufficient. On the other hand, when the Mn content exceeds 1.0% by mass, the tempering embrittlement resistance and the SR cracking resistance deteriorate. Therefore, the Mn content in the weld metal is 0.5 to 1.0 mass%. Preferably it is 0.6-0.9 mass%.

(Al content in weld metal: 0.02-0.05 mass%)
Al has a deoxidizing effect and has an effect of cleaning the weld metal. When the Al content is less than 0.020% by mass, the effect is small. On the other hand, when the Al content exceeds 0.05% by mass, the toughness decreases due to the formation of coarse Al oxide. Therefore, the Al content in the weld metal is 0.02 to 0.05 mass%. Preferably it is 0.03-0.04 mass%.

(Cr content in weld metal: 2.0-3.25% by mass)
Cr is a basic component of high-strength Cr-Mo steel and is an important element for ensuring strength. If the Cr content is less than 2.0% by mass, the strength is insufficient. On the other hand, if the Cr content exceeds 3.25% by mass, the hardenability increases and the toughness decreases, and coarse carbides increase at the grain boundaries to deteriorate the tempering embrittlement resistance. Therefore, the Cr content in the weld metal is set to 2.0 to 3.25 mass%. Preferably it is 2.1-3.0 mass%.

(Mo content in weld metal: 0.9 to 1.2% by mass)
Mo is also a basic component of high-strength Cr—Mo steel together with Cr, and is an important element for ensuring strength. If the Mo content is less than 0.9% by mass, the strength is insufficient. On the other hand, if the Mo content exceeds 1.2% by mass, the hardenability increases and the toughness decreases. Therefore, the Mo content in the weld metal is set to 0.9 to 1.2% by mass. Preferably it is 1.0-1.1 mass%.

(Nb content in weld metal: 0.01 to 0.03 mass%)
Since Nb forms fine MC carbides by adding a small amount, Nb has the effect of controlling the carbide form and improving tempering embrittlement resistance and toughness. If the Nb content is less than 0.01% by mass, MC carbides do not grow sufficiently. On the other hand, when the Nb content exceeds 0.03% by mass, the toughness decreases. Therefore, the Nb content in the weld metal is set to 0.01 to 0.03% by mass. Preferably it is 0.015-0.025 mass%.

(V content in weld metal: 0.2-0.7 mass%)
V, as well as Nb, forms fine MC carbides, and therefore has the effect of controlling the carbide form and improving tempering embrittlement resistance and toughness. If the V content is less than 0.2% by mass, MC carbide does not grow sufficiently. On the other hand, when V content exceeds 0.7 mass%, toughness will fall. Therefore, the content of V in the weld metal is 0.2 to 0.7 mass%. Preferably it is 0.3-0.6 mass%.

(B content in weld metal: 0.003 mass% or less)
B has the effect of stabilizing the toughness of the weld metal. Furthermore, the carbide | carbonized_material which has Cr as a main component can be reduced by adding a suitable quantity of B, and it is preferable to contain 0.0003 mass% or more. On the other hand, when the B content in the weld metal exceeds 0.003% by mass, N and BN in the weld metal are formed and fixed, so that the amount of N dissolved in the weld metal decreases, so Cr, Mo It becomes difficult to form M ₂ C carbides mainly composed of. As a result, the fine MC carbide is excessive, and the tempering embrittlement resistance is deteriorated. In addition, the strength of the weld metal is excessively increased and not only the toughness is lowered, but also the sensitivity to hot cracking during welding is increased. Therefore, the B content in the weld metal is 0.003% by mass or less. Preferably, the B content is 0.002% by mass or less.

(O content in weld metal: 0.030 to 0.050 mass%)
O forms an oxide and ensures toughness by refining the structure. Moreover, O has the effect of improving the SR cracking resistance due to the refinement of the prior austenite grain size. These effects are small as O content is less than 0.030 mass%. On the other hand, when the O content in the weld metal exceeds 0.050% by mass, the oxide inclusions increase, so that the toughness decreases. Therefore, the O content in the weld metal is 0.030 to 0.050 mass%. Preferably, the O content is 0.035 to 0.040% by mass.

  Furthermore, as unavoidable impurities in the weld metal, Cu: less than 0.20 mass%, Ni: less than 0.05 mass%, P: less than 0.012 mass%, and S: less than 0.012 mass%, respectively. It is preferable.

(Cu in weld metal: less than 0.20 mass%)
Cu is an element effective for ensuring the toughness of the weld metal, but promotes temper embrittlement. Therefore, Cu as an inevitable impurity in the weld metal is preferably regulated to less than 0.20 mass%, more preferably regulated to less than 0.15 mass%. In submerged arc welding, Cu is inevitably mixed in the weld metal from solid wire plating by about 0.1% by mass.

(Ni in weld metal: less than 0.05% by mass)
Ni is an effective element for ensuring the toughness of the weld metal, but promotes temper embrittlement. Therefore, Ni as an inevitable impurity in the weld metal is preferably regulated to less than 0.05% by mass, and more preferably regulated to less than 0.03% by mass.

(P and S in weld metal: each less than 0.012% by mass)
P and S are components that segregate at the former γ grain boundaries as impurities and promote temper embrittlement. Therefore, P and S as inevitable impurities in the weld metal are preferably restricted to less than 0.012% by mass, more preferably less than 0.010% by mass.

  In addition to the above, Ti, Sn, Ab, As, etc. are inevitable impurities. When these contents are high, it causes SR cracking and temper embrittlement. Therefore, these contents are preferably regulated to be 0.010% by mass or less, and more preferably 0.005% by mass or less.

Furthermore, in the weld metal according to the present invention, in order to appropriately control the growth of MC carbide, it is preferable to manage the ratio of the number of C, Cr, Mo, Nb, and V atoms forming the carbide. That is, when the contents (mass%) of C, Cr, Mo, Nb, V in the weld metal are represented by [C], [Cr], [Mo], [Nb], [V], respectively. It is preferable to limit the parameter CP calculated by the following formula (1) to 60 or less.
CP = 1000 × [C] × [Nb] / ([Cr] / 52 + [Mo] / 96 + [Nb] / 93 + [V] / 51) Formula (1)
Constants 52, 96, 93 and 51 in the formula (1) are atomic weights of Cr, Mo, Nb and V, respectively. If the parameter CP exceeds 60, MC carbides are excessive, and the tempering embrittlement resistance may be deteriorated. Therefore, it is preferable to design the contents of C, Cr, Mo, Nb, and V so that the parameter CP is 60 or less, and more preferably, the parameter CP is 55 or less.

  In addition, the weld metal of the high strength Cr-Mo steel according to the present invention has a Cr precipitation amount obtained from a residue collected by electrolytic extraction only from the raw material portion in association with the components constituting the high strength Cr-Mo steel. The mass is less than 0.5% by mass and the Nb precipitation is 0.005% by mass or more.

(Cr precipitation amount in the raw material part: less than 0.5% by mass)
As described above, the weld metal according to the present invention controls the carbide form by suppressing carbides mainly composed of Cr. Carbides in the weld metal can be obtained by electrolytic extraction of the weld metal and collecting the residue. Furthermore, in the present invention, only the raw material portion that is particularly susceptible to embrittlement in the weld metal is electrolytically extracted. When the Cr precipitation amount obtained from the collected residue is 0.5 mass% or more with respect to the original part, coarse carbides mainly composed of Cr are growing, and the resistance to temper embrittlement deteriorates. To do. Therefore, the Cr precipitation amount is less than 0.5% by mass with respect to the original part.

(Nb precipitation amount in the raw material part: 0.005 mass% or more)
As described above, the weld metal according to the present invention controls the carbide form by promoting the growth of MC carbide containing Nb as a main component. Similarly to Cr, MC carbide is not sufficiently grown when the Nb precipitation amount obtained from the residue collected by electrolytic extraction only from the original part of the weld metal is less than 0.005% by mass with respect to the original part. It will be. Therefore, the Nb precipitation amount is set to 0.005% by mass or more with respect to the original part.

  In the electrolytic extraction, 10 volume% acetylacetone-1 volume% tetramethylammonium chloride-methanol solution was used as an electrolytic solution, and an electric charge of about 1000 C was applied to a saturated sweet potato electrode at room temperature under an electrolytic condition of 0 mV. About 2 g of a sample collected from the weld metal can be dissolved, and the electrolytic solution after electrolysis can be filtered using a filter having a filter pore diameter of about 0.2 μm. And the amount of Cr precipitation and the amount of Nb precipitation are obtained by quantitatively measuring Cr and Nb in the residue of filtration by ICP emission analysis.

〔Production method〕
A method of submerged arc welding for forming a weld metal of high strength Cr—Mo steel according to the present invention will be described. The material to be welded applied to the submerged arc welding is made of a known high-strength Cr—Mo steel. Solid wire is C: 0.12-0.18 mass%, Si: 0.15-0.70 mass%, Mn: 0.60-1.20 mass%, Al: 0.08-0.18 mass %, Cr: 2.2 to 3.6% by mass, Mo: 0.9 to 1.2% by mass, Nb: 0.03 to 0.10% by mass, V: 0.25 to 0.90% by mass, B: It is preferable to contain 0.0003 to 0.0075 mass%, with the balance being composed of Fe and inevitable impurities. By designing the component of the solid wire in such a configuration, the content of the essential component in the weld metal according to the present invention can be controlled. Moreover, the bond flux _{is, SiO 2, MgO, Al 2} O 3, and those containing a metal fluoride. In addition, about O content of a weld metal, it is influenced by the structure of bond flux besides the structure of a solid wire. Furthermore, in order to control the Si and Mn contents in the weld metal, Si and Mn may be added to the bond flux. Preferable welding conditions are welding current: 400 to 600 A, welding speed: 30 to 40 cm / min (welding heat input: 20 to 36 kJ / cm), preheating / interpass temperature: 200 to 250 ° C.

  Although the best mode for carrying out the present invention has been described above, an example in which the effect of the present invention has been confirmed will be specifically described below in comparison with a comparative example that does not satisfy the requirements of the present invention. . In addition, this invention is not limited to this Example.

[Sample preparation]
(welding)
FIG. 1 is a schematic cross-sectional view showing the shape of a welding base material (material to be welded) used in this embodiment. Two welded preforms made of high-strength Cr-Mo steel having the composition shown in Table 1 were formed into the shape shown in FIG. As shown in FIG. 1, the welding base material used in the present embodiment has a V-shaped groove, and a lower part of the V-shaped groove part has a chemical composition identical to that of the welding base material. The money is arranged. The plate thickness of the weld base material was 19 mm, the groove angle of the V-shaped groove portion was 10 °, and the gap width between the weld base materials in the portion where the backing metal was disposed was 22 mm.

  The welding base material was butt welded using a solid wire of each composition shown in Table 2 at a current of 500 A, a voltage of 30 V, a welding speed of 40 cm / min (welding heat input 22.5 kJ / cm), and 6 layers and 12 passes. A test material was used. The preheating / interpass temperature was 200 to 250 ° C.

(SR processing)
Next, the welded specimen was subjected to heat treatment at 705 ° C. for 8 hours as SR treatment (stress removal annealing treatment). In the SR treatment, the test material is heated, and when the temperature of the test material exceeds 300 ° C., the heating condition is adjusted so that the heating rate is 55 ° C./h or less. Heat until reaching ° C. And after hold | maintaining for 8 hours at 705 degreeC, the specimen was cooled so that a cooling rate might be 55 degrees C / h or less until the temperature of the specimen became 300 degrees C or less. In this SR treatment, the temperature raising rate and the cooling rate are not defined in the temperature range where the temperature of the specimen is 300 ° C. or lower.

(Step cooling)
Next, step cooling was performed on the specimen after SR treatment as embrittlement promotion treatment. FIG. 3 shows a graph in which the vertical axis represents temperature and the horizontal axis represents time for explaining the processing conditions for step cooling. As shown in FIG. 3, the step cooling heats the test material, and when the temperature of the test material exceeds 300 ° C., the heating conditions are adjusted so that the temperature rising rate is 50 ° C./h or less, The sample was heated until the temperature reached 593 ° C. Then, after holding at 593 ° C. for 1 hour, the specimen was cooled to 538 ° C. at a cooling rate of 5.6 ° C./h and held for 15 hours, cooled to 524 ° C. at the same cooling rate and held for 24 hours, It cooled to 496 degreeC with the same cooling rate, and hold | maintained for 60 hours. Next, the specimen was cooled to 468 ° C. at a cooling rate of 2.8 ° C./h and held for 100 hours. Then, the sample material was cooled so that the cooling rate was 28 ° C./h or less until the temperature of the sample material became 300 ° C. or less. Note that, similarly to the SR treatment, in step cooling, the temperature increase rate and the cooling rate are not defined in the temperature range where the temperature of the test material is 300 ° C. or lower.

[Measurement and evaluation]
(Measurement of chemical composition of weld metal)
Samples for chemical component measurement were cut out from the specimen after SR treatment at the center of the weld metal (see FIG. 2) formed on the groove, and the spectrophotometric method (B), combustion-infrared absorption method (C , S), inert gas melting-thermal conductivity method (N, O), and inductively coupled plasma emission spectroscopy (other than the above elements) were used for chemical component analysis. The obtained chemical components are shown in Table 3.

(Evaluation of toughness and tempering embrittlement resistance)
A Charpy impact test was performed as an evaluation of toughness and temper embrittlement resistance. As the sample, a test piece having a shape defined in JISZ3114 was collected from the center of the weld metal of each of the test material after SR treatment and the test material after step cooling. And the Charpy impact test was implemented about the sample extract | collected from the test material after SR process, and vTr55 (Charpy transition temperature which shows 55J) was evaluated. Similarly, a Charpy impact test was performed on a sample collected from the specimen after step cooling, and the Charpy transition temperature vTr′55 was evaluated. Table 3 shows vTr55, vTr′55, and the transition amount ΔvTr55 (vTr′55−vTr55) of vTr55 after step cooling. Samples having vTr55 and vTr′55 of −50 ° C. or lower were evaluated as having good toughness. A sample having ΔvTr55 of 5 ° C. or lower was evaluated as having good tempering embrittlement resistance. When ΔvTr55 is negative (vTr55> vTr′55), ΔvTr55 is indicated as 0. This means that it is an excellent sample with little embrittlement due to high temperature.

(Measurement of chemical composition of residue collected by electrolytic extraction from weld metal base)
As for the sample for electrolytic extraction, assuming the form of carbide in the weld metal in which embrittlement has progressed, the weld metal original part (see FIG. 2) of the test material after step cooling was cut out and subjected to electrolytic extraction. Electrolytic extraction is conducted using 10 volume% acetylacetone-1 volume% tetramethylammonium chloride-methanol solution as the electrolytic solution, passing a current of about 1000 C at room temperature under an electrolysis condition of 0 mV to the saturated sweet potato electrode, and welding. About 2 g of the sample cut out from the metal raw material portion was dissolved. This solution was filtered through a filter having a filter pore size of 0.22 μm to obtain a residue. About this residue, Cr and Nb were quantitatively measured by ICP emission analysis. Table 3 shows the obtained Cr precipitation amount and Nb precipitation amount with respect to the weld metal primary part.

(Evaluation)
In the weld metals of Examples 1 to 12, since the content of each component and the amount of Cr and Nb precipitated in the electrolytic extraction residue of the raw material part are within the scope of the present invention, vTr55, which is an indicator of toughness, and temper embrittlement resistance Both ΔvTr55 which is an index of In particular, the weld metals of Examples 1 to 11 had contents of C, Cr, Mo, Nb, and V such that the parameter CP was 60 or less, and were excellent in resistance to temper embrittlement.

  On the other hand, in Comparative Example 13, the toughness decreased because the C content of the weld metal was insufficient. On the other hand, since the comparative example 14 had excessive C content, toughness fell. Moreover, since the Si content was excessive in Comparative Example 15, toughness and tempering embrittlement resistance were deteriorated. In Comparative Example 16, since the Mn content of the weld metal was insufficient, the toughness and the resistance to temper embrittlement deteriorated. On the other hand, in Comparative Example 17, the Mn content was excessive, and thus the tempering embrittlement resistance was significantly lowered.

  In Comparative Example 18, since the Al content was insufficient, the O content was excessive and the toughness was lowered. On the other hand, in Comparative Example 19, the Al content and the B content were excessive, so that the toughness was lowered, and further, the B content was excessive, the tempering embrittlement resistance was lowered.

  In Comparative Example 20, since a solid wire containing no Nb was used, the Nb content of the weld metal was insufficient, and coarse carbides mainly composed of Cr grew. Beyond the scope of the present invention. As a result, in Comparative Example 20, the tempering embrittlement resistance was remarkably reduced. On the other hand, the comparative example 21 using the solid wire to which Nb was excessively added had reduced toughness. In Comparative Example 22, the toughness decreased because the V content was excessive.

  In Comparative Example 23, since a B-free solid wire was used, the B content of the weld metal was insufficient, and coarse carbides mainly composed of Cr could not be suppressed. Exceeded the scope of the present invention. As a result, Comparative Example 23 significantly deteriorated the tempering embrittlement resistance. On the other hand, in Comparative Example 24 using the solid wire to which B was added excessively, the toughness and the resistance to temper embrittlement deteriorated.

It is typical sectional drawing which shows the shape of the welding preform | base_material (to-be-welded material) used in the Example of this invention. It is typical sectional drawing which shows the weld metal and its original part in the Example of this invention. It is a graph explaining the step cooling process conditions in the Example of this invention.

Claims (4)

In weld metal of high strength Cr-Mo steel formed by submerged arc welding,
C: 0.10 to 0.15 mass%, Si: 0.10 to 0.5 mass%, Mn: 0.5 to 1.0 mass%, Al: 0.02 to 0.05 mass%, Cr: 2.00-3.25% by mass, Mo: 0.9-1.2% by mass, Nb: 0.01-0.03% by mass, V: 0.2-0.7% by mass, B: 0.0. 0002 to 0.003 % by mass , O: 0.030 to 0.050% by mass, with the balance consisting of Fe and inevitable impurities,
The Cr precipitation amount obtained from the residue collected by electrolytic extraction only from the weld metal raw material part is less than 0.5% by mass and the Nb precipitation amount is 0.005% by mass or more with respect to the weld metal raw material part. High strength Cr-Mo steel weld metal characterized by   The weld metal of high-strength Cr-Mo steel according to claim 1, wherein the inevitable impurities are limited to Cu: less than 0.20 mass% and Ni: less than 0.05 mass%.   The weld metal of high-strength Cr-Mo steel according to claim 1 or 2, wherein P and S are regulated to be less than 0.012% by mass as the inevitable impurities. The weld metal of high-strength Cr—Mo steel according to claim 1, wherein a parameter CP calculated by the following formula (1) is 60 or less.
CP = 1000 × [C] × [Nb] / ([Cr] / 52 + [Mo] / 96 + [Nb] / 93 + [V] / 51) Formula (1)
(In formula (1), the element represented by [] is the content (% by mass) of each component in the weld metal of the high-strength Cr—Mo steel described in []).

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