JPS5970494A - Coated electrode for welding cr-mo steel - Google Patents

Abstract

PURPOSE:To provide a coated electrode for welding Cr-Mo steel which improves the strength, toughness, etc. of a weld metal by incorporating specific amts. of elements such as C, Si, Mn, Cr, Mo, N or the like into a welding electrode produced by applying a coating material on a steel core wire. CONSTITUTION:A coating material contg. 30-70wt% metallic carbonate, 10- 30% metallic fluoride, and 4-25% metallic oxide is applied on a steel core wire at 20-40% based on the total weight of the welding electrode. The coating material and core wire are incorporated therein with >=1 kinds elements of the group consisting of 0.04-0.15% C, 0.2-1.6% Si, 0.4-1.6% Mn, 6.5-13% Cr, 0.2-1.5% Ni, 0.02-0.25% V, 0.02-0.25% Nb, 0.0005-0.005% B. The contents of V, Nb and B are so adjusted as to be incorporated at 0.4% in total. The PFA value calculated by a specific equation is kept within a range of 4-20. If such an arc welding electrode is used, the weld metal having the toughness equivalent to the toughness of the Cr-Mo steel which is the base metal is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION 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 rod that exhibits excellent performance for welding 9% Cr steel.

Recently, in the design of boilers and other heating and pressurizing equipment, there has been a shift toward increasing the temperature and pressure during heating and pressure in order to improve thermal efficiency and pressure efficiency. 1 regarding properties, corrosion resistance, high temperature strength, etc.
9Cr-2MO steel and 9Cr-IM steel are required to meet these requirements.
Cr-Mof7I4, such as o-Nb-V steel, has been developed.

On the other hand, 9Cr-IMO welding rods are mainly used as welding materials for Cr-MO steel, but the f# joints obtained with these welding rods have poor high-temperature strength and long-term creep rupture strength. One of the reasons for this is that it is not possible to obtain joint performance comparable to that of the base metal, and it is not possible to meet the above-mentioned demands for higher temperatures and pressures.
It is thought that this is because the coarse ferrite phase that precipitates 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 Nl and Mn are contained in the welding material to reduce the coarse ferrite phase in the weld metal, but excessive NI causes long-term creep rupture. reduce the strength,
Furthermore, excessive amounts of Ni and Mn reduce the cracking resistance of the weld metal, making it impossible to obtain the desired high-performance welded joint.

The present inventors focused on the above 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. Intensive research has been carried out 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: 80 to 70% (weight %: the same below), metal fluoride: io to 80%, metal oxide: 4 A coating material containing ~25% 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 the welding rod. Carbon: 0.04-0.15%, silicon 51:0 based on total weight
．． 2-1.6%, Mn: 0.4-1.6%, Cr
:6.5-18%, MO:0.7-2.8%, N:0.
In addition to containing 0.01 to 0.04%, Ni: 0.2 to 1.
5%, V: 0.02-0.26%, Nb: 0.02-0
．． 25% and B: contains one or more elements selected from the group consisting of 0.0005 to 0.005%, and V
, adjusted so that the sum of Nb and B is 0.4% or less,
Or the PF□ value calculated by the following formula is 4 to 20 for ¥
The gist lies in the fact that it has been adjusted so that it becomes .

That is, in the Anzu invention, 51, ■, ¥o, Cr and Nb, which have the effect of suppressing the precipitation of the coarse ferrite phase and stabilizing the ferrite F phase, and Mn, which has the effect of stabilizing the austenite phase,
Nl and! 'i- Welding material Welding material contains an appropriate amount in the fire to reduce the coarse ferrite phase and reduce the amount of ferrite in the weld metal, thereby increasing high-temperature strength and high-temperature coupe strength to the same level as the base metal. , increased toughness, increased softening resistance against SR treatment, and ensuring excellent welding workability can be achieved all at once.

The reasons for setting the component composition in the present invention will be explained in detail below.

First, in the present invention, the content of metal carbonate, metal fluoride, and metal oxide in the coating material and the Fjk coverage were determined for the following reasons.

Metal carbonate: 80 to 70% If it is less than 80%, the viscosity of the molten slag is too low, and the slag during welding tends to advance, resulting in poor welding workability.
Welding workability cannot be satisfied due to worsening of removability of solidified slag, etc. 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: 10-80Φ If it is less than 10%, the viscosity of the molten slag will be too high and the appearance of the bead will deteriorate, while if it exceeds 80%, the viscosity of the molten slag will be too low and welding workability will deteriorate. In either case, satisfactory welding workability cannot be obtained.

Metal oxide: 4 to 25 g6 If it is less than 4%, welding workability will deteriorate and the appearance of the bead will also be noticeably bad, while if it exceeds 25%, the viscosity of the molten slag will decrease and the peelability of the coagulated Nufugu will deteriorate. The number of other Nubatta outbreaks also increases significantly.

Covered 1! Lit rate: 20-40% Coverage rate means the weight i% of the coating material based on 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. If the amount is too low, the appearance of the bead will become abrupt, while if it exceeds 40%, the amount of slag will be too large, making it easy to cause slag entrainment defects. becomes difficult.

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 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 at least 0.04%. However, if it is too large, the cracking resistance of the weld metal deteriorates, so it must be kept at 0.15% or less.

Si: 0.2 to 1.6% The main purpose is to deoxidize the weld metal, and if the content in the welding rod is less than 0.2%, deoxidation is insufficient and pores such as blowholes will occur in the weld metal. Defects are more likely to occur, while 1.6%
If it exceeds this, 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 1.6%
If it exceeds this, fine ferrite in the weld metal disappears, quench hardenability becomes excessive, and cracking resistance deteriorates.

Cr: 6.5-18% 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. This effect of Cr is effectively exhibited by containing 6.6 to 1896 in the welding rod.

MO: 0.7 to 2.8% MO has the effect of increasing the high temperature strength and the cracking resistance of the weld metal, and must be contained at 0.4% or more, preferably 0.7% or more. However, if it is too large, it increases the carbon equivalent and impairs weldability, so it is necessary to suppress it to 2.8% or less.

N: 0.01 to 0.0496 It is one of the stable austenitizing elements, and has the effect of refining the prior austenite F crystal grains, improving the impact resistance. However, a normally contained amount of 0.01% or less does not have this effect, and on the other hand, a content of 0.04% or more increases the strength more than necessary and lowers the impact value. Furthermore, if it exceeds the upper limit, pore defects such as blowholes are likely to occur in the weld metal, so it should be kept at 0.04% or less.

Nt: 0.2-1.54JS, V: 0.02
~0.254JS, Nb:0.02~0.25% and B
: 0.0005 to 0.005% of one or more of these elements. V, Nb, and B can be contained individually or in combination of two or more to mutually enhance the effect of adding MO. However, below the lower limit of each, the effect is not effectively exhibited, especially in the case of B, 0.0005%
Welding with less than (9) /IQQ
It is extremely difficult to control the amount added to the metal. On the other hand, if the respective upper limits are exceeded, the toughness of the weld metal decreases and welding workability also decreases. These 8
If the sum of the elements exceeds 0.4Ji, the impact strength becomes poor. In addition, when the amount of Mo is 1.5 to 2.8%, these 8
Sufficient high-temperature strength can be obtained without using any other elements, so
Although these eight elements were not specifically defined as essential elements,
If MO exceeds 1.4%, coarse ferrite tends to occur, so it is necessary to compensate for the above-mentioned drawbacks of MO by containing 10.2% or more of Nl. 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. Note that Ns may be used alone, or V
, Nb and B can also be used together.

Although the essential elements in the present invention are as described above, the core wire is composed of Fe and unavoidable impurities in addition to the above elements, and the impurities include s, p, and 0 fathoms.

- 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, but the functions of each element are all taken into consideration. death,
In order to more effectively improve the high-temperature strength, high-temperature creep strength, toughness, cracking resistance, etc. of weld metal, it is said that it is extremely effective to keep the PFAl [k4 to 20] calculated from the following formula. I got the conclusion.

That is, if the P,□ 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, if it exceeds 20, the amount of coarse ferrite in the weld metal will become too hard. The high temperature strength and high temperature creep strength decrease.

Although each of the above alloying elements may be contained in either the steel core wire or the coating material, as an example, a preferred method of containing Cr and MO, which are the main alloying elements, is as follows: Cr is contained in the steel core wire. About 5-12% (generally 7-9%),
Approximately 4 to 0% (more generally 2 to θ%) in the coating material,
0.4 to 2% (more generally 0.5 to 1.5%) in the fcMOa copper core wire and 2 to θ% (more generally 1.5 to θ%) 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 amount of elements in the weld metal is the same. (Cr and MO'lk in the core wire:
If added in full amount, 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 types of core wires can be integrated, ■ Alloy components in the core wire Reducing the amount is advantageous in terms of manufacturing, and can be expected to have effects such as being able to provide the product at a lower 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 496 or less.

Outline of the wire of the present invention The wire is constructed as described above, and by specifying the type and content of alloying elements contained in the coating and core wire, a weld metal with physical properties comparable to those of the Cr-Mo steel base material can be produced. As a result, the quality of high-temperature product-pressure reaction equipment, etc. that uses the special steel of this mallet as a base material can be greatly improved.

Next, the configuration and effects of the present invention will be specifically explained with reference to experimental examples.

Example Cr-, MO steel core wire (5N) with a coverage ratio of 2.8 on the outer periphery
A coating agent was applied to the coating material in an amount of .about.80% to produce a coated arc welding rod having the composition shown in Table 1.

Using each of the obtained welding rods, a welding trial was conducted using a 9Cr-IMO steel plate as a base material, and the results shown in Table 2 were obtained.

The welding conditions are lower axle through, and after welding is completed, the temperature is 720°C.
．． After performing strain relief annealing for 9 hours, physical property tests were conducted.

[Welding conditions]

Current used: 210 amperes Temperature between preheating baths = 200 to 260°C Groove shape used: Fig. 1 (The inner surface of the welded part is
N battering is carried out at a field -10) Welding position: downward facing Q4 As is clear from Table 1.2, welds obtained using welding rods (positive numbers 1 to 7) that meet the requirements of the present invention are , room temperature strength,
It has superior performance in terms of high temperature strength, elongation and impact strength compared to conventional bars and comparative bars. Of these, welding rods 2 and 8 in particular are L* embodiments with a relatively large amount of MO, and in this case, the toughness can be sufficiently increased by containing an appropriate amount of Nl as a selective element.

Welding rods of 1.4 to 7 aMOJl are kept at relatively low levels, and in this case, by containing one or more of Nb, V, and B as selected elements, high temperature strength and impact resistance are sufficiently improved. can be increased to

On the other hand, the conventional bars (&8, 91) are insufficient in both high temperature strength and impact value, the FA values of comparison bars 10 and 11a' are out of the preferred range, and comparison bar 12 has too much V and B, so It also has an extremely low impact value.

Figure 2 shows the welding rod Nh 2 (with a relatively high Mo content) in Table 1 as the base composition, and the effect of varying the Ni content on the Charpy impact value of the weld was investigated. It is a graph. This figure shows that if the Ni content is less than 0.2Φ, no significant toughness improvement effect is observed, but if it exceeds this, the toughness rapidly improves and reaches a saturated level around 0.8%. If the content exceeds 1.5%, the toughness tends to decrease. Therefore, it is understood that in order to effectively exhibit the effect of Nl, its content* should be in the range of 0.2 to 1.596%, preferably 0.4 to 0.8%. .

Furthermore, Fig. 8 shows the results of the creep rupture test of weld metal obtained using the welding rod Nag. It shows high-temperature creep strength of at least 100%.

[Brief explanation of drawings]

Figure 1 is a diagram showing the groove shape used in the welding test, Figure 2 is a graph showing the relationship between the amount of Ni in the WI joint rod and the impact value of the weld metal, and Figure 8 is the result of the creep rupture test. It is a graph. Applicant: Kobe Steel, Ltd.'' = Intsu Senito Urine City Publication, October 14, 1982] 1. Indication of the case 1980 Patent Application No. 180762 2. Name of the invention Cr-Mo steel welding coating Arc welding rod 3, relationship with the amended case Patent applicant 3-18 (119) Wakihama-cho, Chuo-ku, Kobe City, Kobe Steel, Ltd. Representative Fuyuhiko Maki 4, Agent 530 Osaka City Shinko Building, 2-3-7 Dojima, Kita-ku, "Detailed Description of the Invention" section of the specification, drawing 6, and contents of amendments (1) "High-temperature coupe" on page 5, lines 17-18 of the specification was changed to " Corrected to ``High Temperature Creep.'' (2) "Physical property test" on page 13, line 14 of the specification will be corrected to "mechanical test." (3) rsioJ in the coating composition column in Table 1 on pages 15 and 16 of the specification cylinder was corrected to rsi Ox JK Ltf. (41, page 17.18, Table 2, rKg-fJ in the ``Room temperature strength, elongation'' column, ``High temperature strength at 600℃, elongation column, and ``Impact value'' column [(Corrected to gfJ) (5) Replace "Kg-f" in Figure 2 as shown in the attached drawing.
I will correct it to KgfJ. (6) “Kg
I will correct it to f. Q)

Claims (1)

[Claims] (1) Metal carbonate: 80-70% (weight%: same below)
, Metal fluoride = 10 to 80%, Metal oxide: 26%
The coating material used is 20% of the total weight of the welding rod.
It is applied to the outer periphery of the steel core wire in such a manner that the coating material and/or the steel core wire has a coating material of 0.04 to 0.15 *, Silicon: 0.1!
~t, a%, Mn: 0.4~1.6%, Cr: 6.6~
18 Grape and M (1: 0.7-2.8%, N': 0.01
Contains ~0.04 type, as well as N1: 0.2~1.6%
, v: o, j! 11-0.215, Nb: 0.0
2-0.254 and B; □0.0005-o, ooa%
(r-MoWI4P) contains at least one element selected from the group consisting of
lj welding coating arc welding coating arc welding rod salt: '80 to 70% (weight %: same below), metal fluoride = 10 to 80%, metal oxide: 4 to '2
Coating material containing 6% to 20 to 4% of the total weight of the welding rod
Carbon: 0.04 to 0.15% based on the amount of welding rod in the coating material and/or the steel core wire. Silicon: 0.2-1.6%
, MO: 0.4-1.6%, Cr: 6.5-18q6
and Mo: 0.7-2.8%, N: 0.01-0.04
%, Ni: 0.2 to 1.5%, V:
0.02 to 0.25%, Nb: 0.02 to 0.254, and B: 0.0005 to 0.005%;
, adjusted so that the sum of Nb and B is 0.4%, and
A Cr--Mo steel welding pad coated arc welding rod having a PFAIl value of 4 to 20 calculated from the following formula.