JPH0253159B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a coated arc welding rod for welding Cr-Mo steel, and particularly to a coated arc welding rod that exhibits excellent performance for welding 9% Cr steel. Recently, when designing boilers and other heating and pressurizing operating equipment, there has been a movement to increase the temperature and pressure during operation in order to improve thermal efficiency and pressure efficiency.
Along with this, a high degree of oxidation resistance, corrosion resistance, high temperature strength, etc. is required for the constituent materials.
Cr- such as 9Cr-2Mo steel and 9Cr-1Mo-Nb-V steel
Mo steel has been developed. On the other hand, 9Cr-1Mo welding rods are mainly used as welding materials for Cr-Mo steel.
The welds obtained with these welding rods do not have sufficient high-temperature strength or long-term creep rupture strength, making it impossible to obtain joint performance comparable to that of the base metal, and meeting the above-mentioned demands for higher temperatures and higher pressures. I was unable to respond. One of the reasons for this is thought to be that the coarse ferrite phase precipitated in the weld metal reduces the strength, toughness, crack resistance, etc. of the weld metal. Therefore, as an improvement measure, a method has been proposed in which a large amount of austenite phase stabilizing elements such as Ni and Mn is contained in the welding material to reduce the coarse ferrite phase in the weld metal, but excessive Ni causes long-term creep rupture. Since the strength is reduced, and more Ni and Mn than necessary reduce the cracking resistance of the weld metal, it is not possible to obtain the desired high-performance welded joint. The present inventors focused on the above-mentioned circumstances, and reduced the coarse ferrite phase without impairing high temperature strength, high temperature creep strength, or cracking resistance, and achieved strength, toughness, and cracking resistance comparable to that of the base material. We have been conducting intensive research in an attempt to provide a coated arc welding rod for welding Cr-Mo steel that can ensure the following. The present invention was completed as a result of such research, and its composition is: metal carbonate: 30-70% (weight %: the same hereinafter), metal fluoride: 10-30%, metal oxide: 4-70%. A coating material containing 25% of the total weight of the welding rod is applied to the outer periphery of the steel core wire in an amount of 20 to 40% based on the total weight of the welding rod, and the coating material and/or the steel core wire contains a Carbon by weight: 0.04-0.15%,
Silicon: 0.2-1.6%, Mn: 0.4-1.6%, Cr: 6.5-13
%, Mo: 0.7 to 2.3%, N: 0.01 to 0.04%, Ni: 0.2 to 1.5%, V: 0.02 to 0.25%,
Contain one or more elements selected from the group consisting of Nb: 0.02 to 0.25% and B: 0.0005 to 0.005%, and adjust so that the sum of V, Nb and B is 0.4 or less, or further Calculated by the formula
The gist lies in adjusting the _PFA value to be between 4 and 20. P _FA value = (Si + V + Mo + Cr + Nb) / (Mn + Ni + N) (weight ratio) In other words, in the present invention, Si, V, which has the effect of suppressing the precipitation of the coarse ferrite phase and the effect of stabilizing the ferrite phase,
Mo, Cr, and Nb, and Mn, Ni, and N, which have austenite phase stabilizing effects, are contained in appropriate amounts in the welding material to refine the coarse ferrite phase and control the amount of ferrite in the weld metal. In addition to increasing high-temperature strength and high-temperature creep strength to the same level as the base metal, it also increases toughness.
It is possible to increase the softening resistance against SR treatment and ensure excellent welding workability all at once. The reasons for setting the component composition in the present invention will be explained in detail below. First, the reason why the content and coverage of metal carbonate, metal fluoride, and metal oxide in the coating material are determined in the present invention is as follows. Metal carbonate: 30-70% If it is less than 30%, the viscosity of the molten slag becomes too low and the slag during welding tends to precede it, resulting in poor welding workability, as well as poor removability of solidified slag, etc.
Welding workability cannot be satisfied. On the other hand, if it exceeds 70%, the viscosity of the molten slag becomes too high, spatter increases and the bead appearance deteriorates. Metal fluoride: 10-30% If it is less than 10%, the viscosity of the molten slag becomes too high and the appearance of the bead deteriorates, while if it exceeds 30%, the viscosity of the molten slag becomes too low and welding workability deteriorates, etc. In either case, satisfactory welding workability cannot be obtained. Metal oxide: 4 to 25% If it is less than 4%, welding workability deteriorates and the appearance of the bead becomes significantly worse. On the other hand, if it exceeds 25%, the viscosity of the molten slag becomes low and the removability of the solidified slag deteriorates, as well as spatters. The amount generated also increases significantly. Coverage rate: 20 to 40% Coverage rate means the weight percent of the coating material to the total weight of the welding rod. If it is less than 20%, the function as a protective tube will be insufficient, resulting in increased spatter, and the amount of slag generated will be reduced. The bead appearance worsens due to the deficiency, while 40
%, the amount of slag becomes too large, which tends to cause defects such as slag entrainment, and makes rod handling difficult when applied to welded joints with narrow groove widths. Next, the essential elements to be contained in the above-mentioned welding rod, that is, either the coating material or the steel core wire, will be explained in detail. C: 0.04-0.15% C is present in the weld metal and has the effect of suppressing the precipitation of coarse ferrite phase, and must be contained in the welding rod at least 0.04%. However, if it is too much, the cracking resistance of the weld metal will deteriorate.
Must be kept below 0.15%. Si: 0.2-1.6% The main purpose is to deoxidize the weld metal; if the content in the welding rod is less than 0.2%, pore defects such as blowholes will occur in the weld metal due to insufficient deoxidation. On the other hand, if it exceeds 1.6%, coarse ferrite phase tends to precipitate and the toughness of the weld metal decreases. Mn: 0.4-1.6% This is an essential component to increase the strength of weld metal, and it must be contained at least 0.4%, but if it exceeds 1.6%, the fine ferrite in the weld metal will disappear and the quench hardenability will be excessive. As a result, cracking resistance deteriorates. Cr: 6.5-13% This is an essential element for increasing the oxidation resistance, corrosion resistance, and high-temperature strength of weld metal, and is the main component in this type of component system. The effect of this Cr is 6.5 in the welding rod.
It is effectively exhibited by containing ~13%. Mo: 0.7-2.3% has the effect of increasing high temperature strength and cracking resistance of weld metal, 0.4% or more, preferably 0.7%
or more must be contained. However, if it is too large, the carbon equivalent will increase and weldability will deteriorate, so 2.3%
It is necessary to keep it below. N: 0.01 to 0.04% N is one of the stable elements for austenitization, has the effect of refining prior austenite crystal grains, and improves impact value. However, if the content is less than 0.01%, it will not have this effect, and if it is more than 0.04%, the strength will be increased more than necessary and the impact value will be lowered. Moreover, if the upper limit is exceeded, pore defects such as blowholes are likely to occur in the weld metal, so 0.04
It should be kept below %. Ni: 0.2-1.5%, V: 0.02-0.25%, Nb: 0.02
~0.25% and B: 0.0005~0.005% of one or more of these elements. By containing V, Nb, and B alone or in combination of two or more, the effect of adding Mo can be mutually enhanced. However, the effect is not effectively exhibited below the respective lower limits, and in the case of B in particular, it is actually extremely difficult to control the amount added to the weld metal at less than 0.0005%. On the other hand, if the respective upper limits are exceeded, the toughness of the weld metal and welding workability are reduced. When the sum of these three elements exceeds 0.4%, impact strength becomes poor. When the Mo content is 1.5 to 2.3%, sufficient high-temperature strength can be obtained without using these three elements together, so these three elements were not specified as essential elements, but when Mo exceeds 1.4%, Since coarse ferrite phase tends to occur, it is necessary to contain 0.2% or more of Ni to compensate for the above-mentioned drawbacks of Mo. However, if the Ni content is too large, the high temperature strength and high temperature creep strength will be significantly reduced, and the cracking resistance will also be impaired, so it must be kept at 1.5% or less. In addition, Ni may be used alone,
Alternatively, it can be used in combination with V, Nb and B. The essential elements in the present invention are as described above, and the core wire is composed of Fe and unavoidable impurities in addition to the above elements, and examples of the impurities include S, P, O, and the like. The types and preferred content of the elements contained in the welding rod of the present invention are as described above, and as long as the above requirements are satisfied, the purpose of the present invention is achieved. In order to more effectively increase the high-temperature strength, high-temperature creep strength, toughness, cracking resistance, etc. of weld metal, the P _FA value calculated from the following formula should be set to 4 to 4.
We concluded that it is extremely effective to keep it within the range of 20. P _FA value = (Si + V + Mo + Cr + Nb) / (Mn + Ni + N) (weight ratio) In other words, if the P _FA value is less than 4, the amount of fine ferrite precipitated will be small and the weld metal will tend to become too hard, resulting in insufficient cracking resistance. On the other hand, when it exceeds 20, the amount of coarse ferrite in the weld metal increases, and the high temperature strength and high temperature creep strength decrease. Each of the above-mentioned alloying elements may be contained in either the steel core wire or the coating material, but as an example, a preferred method of containing Cr and Mo, which are the main alloying elements, is as follows. ~12% (more generally 7 to 9%), approximately 4 to 0% (more generally 2 to 0%) in the coating material, and 0.4 to 2% (more generally 2 to 0%) in the steel core wire. 2 to 0% (more generally 1.5 to 1.5%) in the coating.
This is a method of containing about 0%). If such a method is adopted, compared to adding 100% from the steel core wire, even if the amount of elements in the weld metal is the same,
It is possible to reduce stick burn during welding (adding all Cr or Mo to the core wire increases the electrical resistance, making stick burn more likely to occur), and it is necessary to prepare a large number of steel core wires with different contents. The following effects can be expected: it is possible to integrate the types of core wires, it is advantageous in manufacturing to reduce the amount of alloy components in the core wires, and it can be provided at low cost. On the other hand, in the case of Cr, etc., if a large amount is added from the coating material, segregation may occur in the weld metal, so the addition rate of Cr from the coating material is preferably suppressed to 4% or less. The present invention is roughly constructed as described above, and by specifying the type and content of alloying elements contained in the coating and the core wire, welding that has physical properties comparable to those of the Cr-Mo steel base material can be achieved. It has become possible to obtain metals and greatly improve the quality of high-temperature, high-pressure reaction equipment that uses this type of special steel as a base material. Next, the configuration and effects of the present invention will be specifically explained with reference to Examples. Example: Coverage ratio is 28 on the outer periphery of Cr-Mo steel core wire (5 mm〓)
A coating agent was applied to the coating material to give a coating concentration of ~30%, and coated arc welding rods having the composition shown in Table 1 were manufactured. Using each of the obtained welding rods, a welding experiment was conducted using a 9Cr-1Mo steel plate as a base material, and the results shown in Table 2 were obtained. The welding conditions were as follows, and after welding, strain relief annealing was performed at 720°C for 1 hour, and then physical property tests were conducted. [Welding conditions] Current used: 210 amperes Temperature between preheating passes: 200 to 250°C Groove shape used: Fig. 1 (Two layers of buttering are performed with the same welding rod on the inner side of the welding part) Welding position: downward

【table】

【table】

[Table] As is clear from Tables 1 and 2, welds obtained using welding rods (Nos. 1 to 7) that meet the requirements of the present invention have low room temperature strength, high temperature strength, elongation, and impact strength. In both cases, it has superior performance compared to conventional rods and comparison rods. Among these, welding rods No. 2 and 3 in particular are examples in which the amount of Mo is relatively increased,
In this case, the toughness can be sufficiently increased by containing an appropriate amount of Ni as a selective element.
In addition, welding rods No. 1, 4 to 7 have a relatively low amount of Mo, and in this case, as the selected element,
By containing one or more of Nb, V, and B, high temperature strength, impact value, etc. can be sufficiently increased. On the other hand, the conventional bars (No. 8 and 9) are insufficient in both high temperature strength and impact value, and the comparative bars 10 and 11 are
The P _FA value is out of the preferred range, and comparison bar 12 has too much V and B, so both have extremely low impact values. Figure 2 is an experimental graph that uses welding rod No. 2 in Table 1 (relatively high Mo content) as the base composition, and investigates the effect of varying the amount of Ni on the shear py impact value of the weld. It is. From this figure, Ni
It can be seen that when the amount is less than 0.2%, no significant toughness improvement effect is observed, but when this amount is exceeded, the toughness rapidly improves and reaches a saturation state at around 0.8%.
If the content exceeds 1.5%, the toughness tends to decrease. Therefore, in order to effectively exhibit the effect of Ni, the content should be 0.2 to 1.5%, more preferably 0.4%.
It is understood that it should be in the range ~0.8%. Fig. 3 shows the results of the creep rupture test of weld metal obtained using welding rod No. 2. It shows high-temperature creep strength comparable to or higher than that of

[Brief explanation of the drawing]

Figure 1 shows the groove shape used in the welding experiment.
FIG. 2 is a graph showing the relationship between the amount of Ni in the welding rod and the impact value of the weld metal, and FIG. 3 is a graph showing the results of the creep rupture test.

Claims (1)

[Claims] 1. Metal carbonate: 30 to 70% (weight %: the same below),
Coating material containing metal fluoride: 10-30%, metal oxide: 4-25%, based on the total weight of the welding rod, 20-40%
The coating agent and/or the steel core wire contain carbon: 0.04 to 0.15%, silicon: 0.2 to 1.6%, based on the total weight of the welding rod.
Mn: 0.4~1.6%, Cr: 6.5~13% and Mo: 0.7~
In addition to containing 2.3%, N: 0.01 to 0.04%, Ni:
0.2-1.5%, V: 0.02-0.25%, Nb: 0.02-0.25%
and B: Cr-Mo steel containing at least one element selected from the group consisting of 0.0005 to 0.005%, and adjusted so that the sum of V, Nb and B is 0.4 or less. Covered arc welding rod for welding. 2 Metal carbonate: 30 to 70% (weight%: same below),
Coating material containing metal fluoride: 10-30%, metal oxide: 4-25%, based on the total weight of the welding rod, 20-40%
The coating agent and/or the steel core wire contain carbon: 0.04 to 0.15%, silicon: 0.2 to 1.6%, based on the total weight of the welding rod.
Mn: 0.4~1.6%, Cr: 6.5~13% and Mo: 0.7~
In addition to containing 2.3%, N: 0.01 to 0.04%, Ni:
0.2-1.5%, V: 0.02-0.25%, Nb: 0.02-0.25%
and B: contains at least one element selected from the group consisting of 0.0005 to 0.005%, and is adjusted so that the sum of V, Nb, and B is 0.4% or less, and is calculated from the following formula. A coated arc welding rod for welding Cr-Mo steel, characterized by having a P _FA value of 4 to 20. P _FA value = (Si + V + Mo + Cr + Nb) / (Mn + Ni + N) (weight ratio)