JPS61266199A - Coated electrode for welding cr-mo steel - Google Patents

Abstract

PURPOSE:To solve the problem of a high temp. crack and to obtain a welding rod having excellent high-temp. strength, high-temp. creep strength and resistance to high-temp. cracking by specifying the ratios of C, Si, Mn, Cr, V, etc. and Ti+0.02TiO2 in the total welding rod and adjusting the PFA calculated by the formula to a specific value. CONSTITUTION:A coating material contg. 30-70% (wt%, hereafter the same) metallic carbonate, 10-30% metallic fluoride and 4-25% metallic oxide is coated on 20-40% core of the total welding rod and 0.01-0.15% C, 0.2-1.6% Si, 0.4-2.2% Mn, 6.5-13% Cr, 0.7-2.3% Mo, <=0.04% N and 0.05-0.60% (Ti+0.02TiO2) are incorporated into the total welding rod; in addition elements of at least >=1 kinds selected from the group consisting of 0.2-1.5% Ni, 0.02-0.40% V, 0.02-0.25% Nb and 0.0005-0.005% B are incorporated therein. The sum total of V, Nb and B is so adjusted as to attain <=0.55% and further the PFA value calculated by the formula is so adjusted as to attain 2.5-20.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a coated arc welding rod for welding Cr-Mo steel;
In particular, the present invention relates to a coated arc welding material that not only exhibits excellent high temperature strength and high temperature creep strength when used for welding 9% Cr steel, but also exhibits excellent performance in hot cracking resistance.

[Prior art 1] Recently, when designing heating and pressurizing equipment such as boilers, there has been a tendency to increase the temperature and pressure during operation in order to improve thermal efficiency and pressure efficiency. Since higher oxidation resistance, corrosion resistance, high-temperature strength, etc. are required for the constituent materials, Cr-2Mo steel such as 9Cr-2Mo steel and 9Cr-IMo-Nb-VW4 meet these requirements. Mo steel has been developed.

On the other hand, the welding material for such Cr-Moo steel is generally 9
Cr-2Mo type welding cup and 9Cr-IM.

However, the welds obtained with these welding materials lacked sufficient high-temperature strength and long-term high-temperature creep rupture strength. Therefore, it was not possible to meet the demands for higher temperatures and higher pressures as mentioned above.One of the reasons for this is that the coarse ferrite phase that precipitates in the weld metal reduces the strength, toughness, and cracking resistance of the weld metal. As an improvement measure, a method has been proposed in which large amounts of austenite phase stabilizing elements such as Ni and Mn are included in the welding material to reduce the coarse ferrite phase in the weld metal. Leaf Ni reduces long-term high temperature creep rupture strength,
In addition, excessive amounts of Ni and Mn reduce the cracking resistance of the weld metal, making it impossible to obtain a welded joint with the desired high performance.

Under these circumstances, the present inventors developed Cr-MO steel nJ.
As a result of conducting various research in the hope of developing a coated arc welding rod for welding Cr-Mo steel that can secure high-temperature strength and high-temperature creep strength comparable to that of Cr-Mo steel, we first published JP-A-59-704.
The welding rod disclosed in No. 94 was proposed. If the invention is described in
By strictly specifying the type and content of alloying elements contained in the coating material and core wire, it is possible to suppress the precipitation of coarse ferrite phase as much as possible, and to meet the required properties for high temperature strength and high temperature creep strength. You can get a fully satisfying welded joint.

[Problems to be Solved by the Invention] However, there are still unresolved problems in the welding material of the first invention. The problem is that the high temperature cracking properties are insufficient, especially for thick IT? When applied to welding materials, the difficulties listed in item 1-1 become apparent. That is, in the prior invention, only consideration was given to cold cracking resistance or bendability with the aim of improving high temperature strength and high temperature creep strength, and there was no consideration given to hot cracking resistance. In order to prevent hot cracking, welding conditions had to be strictly controlled in order to prevent hot cracking, but such control is not always fully achieved and is sometimes not observed.・Even if the requirements were met, the occurrence of hot cracking could not be avoided, and repair welding had to be performed after gouging, etc.

As described above, there is a problem in the reliability of welded joints, and there is also a problem in that post-welding treatment requires considerable effort.

In view of these circumstances, the present invention aims to provide a coated arc welding rod for welding Cr--Mo steel that satisfies the requirements not only for high-temperature strength and high-temperature creep strength but also for hot cracking resistance.

Means for Solving Problem E 1 The coated arc welding rod for Cr-Mo steel welding according to the present invention contains metal carbonate tii: 30-70%, metal fluoride = 10-3
0%, metal oxide: 4 to 25%, or in addition to these, 40% or more F iron powder (in this case, the preferred content of metal carbonate is 20 to 70%). The welding rod is coated on the outer periphery of the steel core wire at a concentration of 20 to 40% with respect to the welding rod. .01-0.15%, Si:0
．． 2-1.6%, Mn: 0.4-2.2%, C
r: 8.5-13%, Mo2 0.7-2.3%, N
: 0.04% or more and (T i +0.02T i
02): 0.05 to 0.60% (however, TiO
2 is added only from the coating material), and N i :
0.2-1.5%, V: 0.02-0.40%,
Nb: 0.02-0.25% and B: 0.0
containing at least one element selected from the group consisting of 0.005 to 0.005%, adjusted so that the total of 11 V, Nb and B is 0.55% or less, and further The gist lies in the fact that the PFA value calculated from the formula is 2.5 to 20.

(The element symbols in the formula each indicate the content based on the I-Regulations.) [Function] In the present invention, an appropriate amount of Ti is particularly used in the coating material and/or the steel core wire.
By containing TiO2 and/or TiO2 (however, TiO2 is contained in the coating material), the hot cracking resistance, which was still unsolved in the prior invention, can be improved, thereby improving high temperature strength and high temperature creep strength. and Cr-M which satisfies all of the requirements of hot cracking resistance.

A coated arc welding rod for steel welding can be obtained.

The reasons for determining the composition of the coating material, the list of elements contained in all welding rods, etc. in the present invention will be clarified below.

First, the reason why the component composition and coverage rate of the coating material were determined is as follows.

Metal carbonate = 30 to 70% If it is less than 30%, the viscosity of the molten slag becomes too low and the slag tends to advance during welding, resulting in poor welding workability.
The solidified slag removability deteriorates, and welding workability becomes unsatisfactory. On the other hand, if it exceeds 70%, the viscosity of the molten slag becomes too high, resulting in increased spatter and poor bead appearance. In the present invention, workability especially during DC welding can be further improved by incorporating iron powder as a coating component as described below. Even if the salt star is reduced to about 20%, a high level of welding workability can be maintained.

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. 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 noticeably worse, while if it exceeds 25%, the viscosity of the molten slag becomes low and the releasability of the solidified slag deteriorates, as well as spatter. Accruals also increase significantly.

The essential components of the coating material in the welding rod of the present invention are the three compounds listed in 1-1 above, and when iron powder is added in an amount of about 40% or less, the workability during DC welding can be greatly improved. However, if the iron powder is added too quickly, the insulation properties of the cured material will deteriorate.
Otherwise, the problem of stick burn may easily occur, so it must be kept below 40%.

Coverage rate = 20 to 40% Coverage rate refers to the weight percentage of the coating agent to the entire electric resistance welding rod. If it is less than 20%, the function as a protection tube will be insufficient, resulting in increased spatter and generated slag. If the amount is insufficient, the appearance of the bead will deteriorate, while if it exceeds 40%, there will be too much slag, which will easily cause defects such as slag entrainment, and when applied to welded joints with narrow groove widths. Unbō becomes difficult.

Next, the essential elements to be contained in the welding rod (1), that is, the coating material and the steel core wire, will be explained in detail.

C: 0.01-0.15% C remains in the weld metal and has the effect of suppressing the precipitation of coarse ferrite phase, and must be contained in the welding rod in an amount of at least 0.04%. However, if it is too large, the crack resistance of the weld metal deteriorates, so it must be kept below 0.15%.

S i: 0.2 to 1.6% The main purpose is to deoxidize the weld metal, and the I content in the weld cup is 0.2
If it is less than 1.6%, pore defects such as blowholes are likely to occur in the weld metal due to insufficient deoxidation, while if it exceeds 1.6%, coarse ferrite phase tends to precipitate and the toughness of the weld metal decreases.

Mn: 0.4-2.2% It is an essential component to increase the strength of weld metal and must be contained at least 0.4%, but 1.6%
If it exceeds this, fine ferrite in the weld metal disappears, quenching hardenability becomes excessive, and cracking resistance deteriorates.

Cr: 6.5-13% It is a non-Fi element that increases the oxidation resistance, corrosion resistance, and high-temperature strength of the weld metal, and is the main component in this type of component system. It is effectively exhibited by containing 6.5 to 13%.

Mo: 0.7 to 2.3% It has the effect of increasing the high temperature strength and the cracking resistance of the weld metal, and must be contained in an amount of 0.4% or more, preferably 0.7% or more. However, if it is too large, it increases the carbon content and impairs welding performance, so it is necessary to keep it below 2.3%.

N: 0.04% or less It is one of the austenite stabilizing elements and improves the impact value by refining the 11 prior austenite crystal grains (there is movement, and these effects are less than 0.01% -1-
By containing it, 41 effects are exhibited. However, in the present invention, as will be described later, by prematurely containing Ti in the welded body, the crystal grains of the weld metal are refined to 1-min, and the #Ids value is accordingly shifted toward I-, so N is not necessary. is also not required. However, if an appropriate amount of N is added, the impact of the weld metal will be further reduced. However, if the N content is too large, the strength will not only increase to the required level and the impact value will decrease, but also pore defects such as blowholes will be more likely to occur, so it should be set at 0.04% or less. .

Nj: 0.2-1.5%, ■, 0.02-0.40%
, Nb: 0.02-0.25% and B: 0.00
05 to 0.005% of 1 insert-1- Among these elements, V, Nb, and B can be contained individually or in combination of 2 inserts 1- to improve the M
It has the effect of synergistically increasing the effect of O addition, but the effect is not effectively exhibited below the lower limit of each, and in particular, in the case of B, it is difficult to control the addition rate to the weld metal at less than 0.0005%. Actually-L is extremely difficult. -Taifu”
If it exceeds the two limits, on the contrary, the toughness of the weld metal decreases and welding workability also decreases.

Among these elements, especially V, Nb, and H, if the sum of these exceeds 0.55%, the impact value decreases. In addition, when the Mo amount 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 Mo
If Ni exceeds 1.4%, coarse ferrite is likely to be formed, so Ni is added to the MO by 0.2% or more.
It is necessary to compensate for the shortcomings listed in item 1. However, if the Ni content is too large, the high-temperature strength and high-temperature creep strength will be significantly lowered, 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 or V
, Nb and B.

(TI + 0.02T i 02 ) 0.05~
0.60% This element is the most characteristic component in the present invention, and is an indispensable component for improving the hot cracking resistance, which remained an unresolved problem in the welded body of the prior invention. be. In addition, compared to the case where it is blended as metallic Ti, when it is blended in the coating material as TiO2, very little amount of Ti is retained in the weld metal as Ti, so considering the yield at this time, TiO2 is When blending as , a coefficient of rO,02J is applied. If the value is less than 0.05%, the effect of Ti is not effectively exhibited, and the hot cracking resistance of the weld metal cannot be improved. On the other hand, when this value exceeds 0.60%, the f#I impact value tends to decrease. The reason why the hot cracking resistance is significantly improved by containing an appropriate amount of Ti can be considered as follows. That is, Ti refines the crystal grains of the weld metal and also reduces the #element tIt in the weld metal.
It appears that these additive or synergistic effects greatly improve the hot cracking resistance of the weld metal. However, it is thought that if too much T i 1,1 remains in the weld metal, the weld metal will be excessively hardened, and the impact value will decrease on the contrary.

The essential elements in the present invention are as described above, and the core wire is 1. In addition to the above elements, it is composed of Fe and unavoidable impurities, and examples of the impurities include S, P, and 0.

The types and preferred content of the elements contained in the welding cup of the present invention are as shown in I- below, and the functions of each element are comprehensively considered to improve the high-temperature strength, high-temperature creep strength, toughness, and low-temperature resistance of the weld metal. In order to more reliably improve crackability and hot cracking resistance, the P[^ value calculated from the following formula should be set to 2.5 to 2.
It is necessary to keep it within the range of o.

That is, in the prior invention, PEA (if the straightness is less than 4, the precipitated h1 of fine ferrite decreases and the weld metal tends to become too hard, resulting in a lack of crack resistance; on the other hand, if the straightness is less than 4,
When the
However, in the present invention, the crystal grains of the weld metal are refined by prematurely containing Ti in the welding rod, so the PEA value has a lower limit of 2. It can be expanded to.

Note that the reporter alloying element may be contained in either the steel core wire or the coating material, but as an example, the alloying element Cr
To give an example of a preferred method of containing Mo and Cr, Cr is about 5 to 12% (more generally 7 to 9%) in the steel core, and 4% or less (more generally 2% or less) in the coating material. ) degree, also M
O content is 0.4 to 2% (more generally 0.5 to 2%) in the steel core wire.
1.5%), and 2% or less (more generally 1.5% or less) in the coating material. If such a method is adopted, ■Compared to adding 100% from the steel core wire, stick burn during welding can be reduced even if the elemental content of the deposited metal is the same. (If the total weight of Cr or Mo is added to the core wire, the electrical resistance will increase, making it easier to cause stick burn.)
, ■ There is no need to prepare a large number of steel core wires with different content rates, and the number of types of core wires can be reduced. On the other hand, in the case of Cr etc., adding more than 1 h from the coating may cause segregation in the weld metal, so the addition rate of Cr from the coating is 4 It is best to keep it to less than %.

[Example 1 The coverage rate is 29~29 on the outer periphery of Cr-Mo steel core wire (5 mm”)
A coated arc welding rod having the composition shown in Table 1 was manufactured by applying a coating material to the coating material so that the coating material was 34%.

Using each of the obtained welding rods, a welding experiment was conducted on a 9Cr-IMo steel plate as a J material, and the results shown in Table 2 were obtained. The welding conditions were as described above, and after the completion of welding, stress relief annealing was performed for 1 hour at 720'0, and then physical property tests were conducted. Further, the conditions of the FISCO cracking test conducted to evaluate the hot cracking resistance were as follows.

Welding conditions〉 Current used: 21 OA Temperature between preheating passes: 200 to 250°C Groove shape used: Fig. 1
Welding position: downward FISCO cracking test> Test method: Compliant with JIS Z 3155 Groove shape:
Fig. 2 (A), (B) Welding current: 140A (AC) Number of repetitions: 21i1 Conventional method on the crack wheel side: After welding is completed, the weld is cooled, the crack is colored with nitric acid, and the crack length on the fracture surface is determined after welding. Measure y and find the cracking rate using the following formula.

However: Total length of cracks in each test bead L: Total length of each test bead From Table 1.2, it can be considered as follows.

Nos. t to 8 are all examples that satisfy all the specified requirements of the present invention, and have good room temperature strength, high temperature strength, and impact value, excellent hot cracking resistance, and good welding workability. be. In addition, in cases 4 to 6, the optimal iron powder was mixed in the coating material, so the workability of 1N style welding was good. On the other hand, the conventional forest and comparison bars of 9 to 18 have problems in their trade performance as shown below.

Faults 9, 10, 11: Conventional bars and comparison woods that do not contain Ti or TiO2 at all, and have good high temperature strength and impact clam resistance, but poor hot cracking resistance.

Fb, 12.13: Because there is too much (Ti+0.02TiO2), the weld metal becomes hard and the impact value becomes extremely low.

Since ri, 14+ (V+Nb+B) exceeds 1 -, the weld metal becomes hard, and the impact value is also low.

No. l5: Since the PF^ value exceeds the - limit, the amount of coarse ferrite increases, the high temperature strength is low, and the impact value is low.

Break, 16: Pr8 is less than the lower limit Ilr4 [1T
Since it does not contain i and TiO2, its hot cracking resistance is poor.

NO, 17: Since the V star exceeds the -1- limit, the weld metal is hardened and the impact i is low.

No. 18: Since the amount of metal carbonate 11i in the coating material is less than the lower limit of 4fi (20%) when iron powder is used in combination, the viscosity of the molten slag is too low and welding workability is reduced.

[Effects of the Invention] The present invention is configured as follows-1-, but the point is that in addition to the configuration of the prior invention, (T i +0.02T
By strictly specifying iO2), it is possible to solve the problem of hot cracking resistance, which was not solved even in the prior invention, and to meet the three major requirements of high temperature strength, high temperature creep strength, and hot cracking resistance. C that satisfies all the characteristics
A coated arc welding rod for welding r-Mo steel can now be provided. Furthermore, by incorporating early iron powder into the coating material, workability, especially during DC welding, can be further improved.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional explanatory diagram showing the groove shape in the welding method adopted in the example, and FIG. 2 is a diagram showing the sample jlI material used in the experiment and the groove shape.

Claims (2)

[Claims] (1) Metal carbonate: 30-70% (weight%: same below)
, metal fluoride: 10-30%, metal oxide: 4-25%
A coating material containing 20% to 40% of the total weight of the welding rod is applied to the outer periphery of the steel core wire, and the coating material and/or the steel core wire contains 20% to 40% of the total weight of the welding rod. Against C: 0.
01-0.15%, Si: 0.2-1.6%, Mn: 0
．． 4-2.2%, Cr: 6.5-13%, Mo: 0.7
~2.3%, N: 0.04% or less and (Ti+0.02
TiO_2): 0.05-0.60% (However, TiO_2
(added only from the coating material), Ni: 0.2
~1.5%, V: 0.02~0.40%, Nb: 0.0
Contains at least one element selected from the group consisting of 2 to 0.25% and B: 0.0005 to 0.005%, and the sum of V, Nb and B is 0.55% or less. P_F_A is further calculated from the following formula.
Cr-M characterized by having a value of 2.5 to 20
o Covered arc welding rod for steel welding. P_F_A value=(Si+V+Mo+Cr+Nb)/(M
n+Ni+N) (Each element symbol in the formula indicates the content based on the above regulations) (2) Metal carbonate: 20-70%, metal fluoride: 10-70%
30%, metal oxide: 4 to 25%, and iron powder: 40% or less, coated on the outer periphery of the steel core wire in an amount of 20 to 40% of the total weight of the welding rod, and The coating material and/or the steel core contains C: 0.0 with respect to the total weight of the welding rod.
1-0.15%, Si: 0.2-1.6%, Mn: 0.
4-2.2%, Cr: 6.5-13%, Mo: 0.7-
2.3%, N: 0.04% or less and (Ti+0.02T
iO_2): 0.05 to 0.60% (however, TiO_2 is added only to the coating material), and Ni: 0.2 to 0.60%.
1.5%, V: 0.40%, Nb: 0.02-0.25
% and B: contains 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 0.55% or less. , further, the P_F_A value calculated from the following formula is 2.5
A coated arc welding rod for welding Cr-Mo steel, characterized in that it has a thickness of 20 to 20. P_F_A value=(Si+V+Mo+Cr+Nb)/(M
n+Ni+N) (Each element symbol in the formula indicates the content based on the above regulations)