JPS6040689A - Arc welding method of cr-mo steel for high temperature service - Google Patents

Abstract

PURPOSE:To obtain a high C-low Ti-V weld metal having excellent low-temp. toughness by using a high-basicity low hydrogen type welding rod which consists principally of CaCO3 metallic fluoride such as CaF2 or the like and contains TiO2 at the lower rate than in the prior art. CONSTITUTION:The component for the coating material of a coated arc welding rod is composed of the essential components consisting, by weight %, of 45-60 CaCO3, 10-25 metallic fluoride, 2-7 SiO2, 1.5-5 Si and 1-4 Mg and the components limited to <=1 TiO2, <=0.5 C, <=2.5 Mn, <=9 Cr, <=4 Mo and <=0.3 V in relation with the content of a core wire. The components of the core wire are composed of <=0.18 C, <=0.7 Si, <=1 Mn, <=4 Cr, <=1.5 Mo, <=0.15 Ti, <=0.08 V and the balance Fe with inevitable impurities. The coating component is coated on said core wire by using a binder prepd. by mixing 1 or >=2 kinds among sodium silicate, potassium silicate and lithium silicate to manufacture a coated arc welding rod. Arc welding is executed by using such rod.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of arc welding □r-Mo based high temperature steel, particularly so-called 2 1/4 ar-I MO and aa
Targeting 0r-No type high temperature steel such as r-L MO steel,
The present invention relates to an arc welding method for obtaining an attractive welded joint that has particularly high low-temperature toughness and low susceptibility to temper embrittlement while maintaining high-temperature strength.

In recent years, in order to improve the operational efficiency of petroleum plants, the pressure vessels used in them have become larger or the operating temperature has been raised. In order to prevent fractures due to deterioration of toughness, good toughness at low temperatures is also required.

In response to this, progress has been made in making high-temperature steel base metals higher in strength and toughness. In situations where welding is employed, the resulting weld metal is also required to be such that its strength and toughness do not deteriorate due to post-weld heat treatment and long-term use.

In this regard, conventionally, high-temperature steels and welding materials used for them have been used with sufficient consideration given to their drawing strength and creep strength at high temperatures during plant operation, as well as embrittlement caused by long-term use. There is. However, on the other hand, it cannot be said that impact performance, especially impact performance at low temperatures assuming a shutdown start, has not been taken into consideration, and for this reason, the performance of conventional products has recently become more demanding.80 It was far from satisfying the impact performance at temperatures as low as -40°C. Therefore, with conventional temporary arc welding materials for high-temperature steel, even if the strength of the weld metal at high temperatures is satisfactory, the toughness in the low-temperature range is unsatisfactory. There was a problem.

Therefore, from the above-mentioned viewpoint, the inventors of the present invention aimed to improve the toughness, especially the toughness in the low temperature range, while ensuring the strength of the weld metal, especially the high-temperature strength, in arc welding using temporary arc welding rods for high-temperature steel. In order to find an arc welding method that produces weld metal that does not deteriorate in toughness after long-term use,
After conducting research mainly on the composition of temporary arc welding rods, we found that the components in the weld metal, especially C, were depleted by increasing the amount of C compared to conventional methods, contrary to the common sense that improved toughness leads to lower carbon content. Precipitation of metal carbides is observed, and as a result, the structure becomes finer and the toughness improves.As for Ti, a relatively large amount of Ti, which is conventionally used for deoxidation and slag cleaning, is present in the weld metal. We came to know that due to the migration, titanium carbide precipitates, which increases the hardness of the weld metal and increases the variation, resulting in a decrease in toughness.Based on this, we determined the composition and composition of the weld metal that should exhibit the desired properties. As a result of examining the composition of temporary arc welding rods for this purpose, we found that we used metal fluorides such as Ga008, OaF, etc. as the main ingredients to obtain a high C-low Ti-V weld metal, and compared to conventional welding metals with low TlO2, high basicity, and low By welding with a hydrogen-based welding rod, it is possible to obtain a weld metal that fully satisfies high-temperature strength, improves toughness in the low-temperature range, and is less susceptible to temper embrittlement after long-term use. As a result, the present invention was completed.

That is, the present invention is characterized by arc welding Or-Mo-based high-temperature steel using a temporary arc welding rod of a specific composition, and using a high-low Ti-
The purpose is to obtain a V-based weld metal, and specifically, as a following arc welding salary, (a) cutting material component t OaO08345~60%, metal fluoride: lO~25%
, SiO2: 2-7%, Si: 1.5-5% and HiM
g: Ti0. 1%, 0 < 0.5%, In < f
Coating material consisting of arbitrary components added within the limits of ll, 5%, Or < 9.0%, MO < 4.0% and V < 0.8% (However, each component of Si and In5Or is ferro When added in the form of an alloy, each component shall be converted.) (b) Core component: 0 < o, t s%, Si≦0.7%, In≦1.0
%.

Or<4. , Q%, yo<t, s%, Ti≦0.1
5%, v < o, o s%, the remainder being Fe and unavoidable impurities. Arc welding the Or-MO high-temperature steel base material using a coated arc welding rod in which the core wire is coated with a mixture of two or more types, (c) Weld metal component element O+ 0.10 to o , ts%, Si: 0.25~
0.60%, Mn: 0.88-0.90%, Or
: 1.5~f11.5%, MO+ 0.7~1.5%
, Ti<0.015% and V: 0.02-0.06
Weld metal, including %.

The present invention will be explained in detail below.

First, the reasons for limiting the weld metal components in the present invention and the reasons for limiting the core wire and temporary composition component ranges will be explained.

Weld metal component 0: If it is less than 0.10%, the precipitation of carbides will be reduced and the fjlkiR formation of the prior austenite structure will not be achieved, thus the toughness will decrease and the susceptibility to tempering embrittlement will increase.
The lower limit was set to 0.10%. On the other hand, when C exceeds 0.18%, the effect of carbide precipitation becomes small, and not only can no further improvement in toughness be expected, but also the hardness of the weld metal becomes too high due to welding hot cracking. , since there is a risk of hydrogen cracking, the upper limit was set at O, tS%.

Si: If it is less than 0.25%, the deoxidizing power decreases, the amount of oxygen in the weld metal increases, and the toughness not only decreases, but also the welding workability deteriorates due to increased fluidity and properties of the welded molten metal. So,
The lower limit was set at 0.25%. On the other hand, if it exceeds 0.60%, the toughness deteriorates and cracking susceptibility increases, so O, aO
The upper limit was %.

'Mn: If it exceeds 0.90%, the susceptibility to tempering embrittlement increases, so 0.90% is set as the upper limit. 0.88% for the lower limit
Since we could only experimentally confirm the range up to 0.88%, we set the lower limit as 0.88%.

If L is less than 1.5%, high temperature strength is insufficient and oxidation resistance and corrosion resistance are reduced, so L is set at 5% as a lower limit.

On the other hand, if it exceeds 8.5%, tempering embrittlement will occur even when used at high temperatures for a long period of time, and this will not be a problem. Since no technical effect could be obtained, the upper limit was set at 8.5%.

If MO = less than 0.7%, high temperature @ temperature may be insufficient.
The lower limit was set at 0.7%. On the other hand, if it exceeds 1.5%, the susceptibility to tempering embrittlement increases and the expected high toughness in the low temperature range cannot be obtained, so 1.5% is set as the upper limit.

Ti: If it exceeds 0.015%, the precipitation of titanium carbides will increase, which will hinder the precipitation of chromium carbides, which is the main objective of the present invention, and not only will there be no improvement in toughness, but the hardness will increase too much, and the hardness distribution will change. The upper limit was set at 0.15% because the dispersion in the content becomes large and the susceptibility to long-term tempering increases.゛■=■ improves toughness in relation to the precipitation of chromium carbides, especially fine chromium carbides, but if it is less than 0.02%, the desired toughness cannot be obtained, so 0.02% was set as the lower limit.

On the other hand, even if it exceeds 0.06%, the toughness and ductility also decrease, so o, o a% was set as the upper limit.

Next, regarding the core wire of the temporary arc welding cord and each temporary wire composition, the purpose of use as a combination for obtaining the above-mentioned weld metal composition of the present invention, and the combination for obtaining normal welding workability. It was established to accomplish two purposes: the purpose of being used as a Therefore, when determining the weld metal component composition, it means that it is possible to add from either or both of the core wire and/or temporary cutting. However, since there are limits to the amounts added, the reasons for these limitations will be described below.

Cord component C: If 0.48% is added, ○ in the weld metal exceeds 0.18%, so the upper limit was set to 18%. On the other hand, 0.1θ%
If welding is less than 0.10%, welding will be less than 0.10%, but in such cases, by adding alloying elements such as graphite and high carbon ferromanganese to the temporary fixing agent, we can increase the C% content in the weld metal to the specified value. Therefore, 0.18%
The following is fine. The same applies to the following alloy components.

Si: If σ exceeds 7%, Si in the weld metal may reach 0.6%, so 0.7% is set as the upper limit.

Mn: If it exceeds 1.0%, Mn in the weld metal exceeds 0.9%, so 1.0% is set as the upper limit.

Cr: If it exceeds 4%, Or in the weld metal will exceed 8.5%, so 4.0% is set as the upper limit.

MO: If it exceeds 1.5%, MO in the weld metal exceeds 1.5%, so 1.5% was set as the upper limit.

T1: If it exceeds 0.15%, Ti in the weld metal is 0.015%
, the upper limit was set at 0.15%.

■ If it exceeds 0.98%, V in the weld metal exceeds 0.06%, so the upper limit was set at 0.08%.

The core wire of the welding rod used in the present invention contains iron and unavoidable impurities in addition to the above-mentioned alloying elements, and unavoidable impurities such as PlSb and 5nSAs are included. Therefore, PSSb.

It is desirable that the total amount of Sn and As be <0.01%.

The temporary agent component oaao8+ 0aOO8 decomposes in the arc and generates CO2 gas, which insulates the weld metal from the atmosphere and generates basic slag. If the amount added is less than 45%, the amount of gas generated is insufficient and pores are generated, making it impossible to obtain good beads, so 45% was set as the lower limit. On the other hand, if it exceeds 60%, the melting point of the slag will rise and the fluidity of the slag will deteriorate.
Since the bead shape would be poor, the upper limit was set at 60%.

Metal fluoride 2 The metal fluoride referred to in the present invention is 0FLF2, M9F2,
Refers to NaF z A/F8, Na3AlF6, etc., and the total of one or more of these is 10 to 25% in the preparation.
have Such metal fluorides are added to lower the melting point of the slag and increase the fluidity of the slag. If the metal fluoride content is less than 10%, the slag will be too viscous, while if it is added in excess of 25%, the fluidity will be too high and good beads cannot be obtained, so the content is limited to 10 to 25%.

Sin! If it is less than 2%, the melting point of the slag will rise too much and slag entrainment will occur, while if it exceeds 7%, the salt thickness of the slag will decrease and non-metallic inclusions in the weld metal will increase, reducing toughness. Therefore, it is limited to 2 to 7%.

If Tie, j exceeds 1%, T1 in the weld metal will reach 0.015%, so 1% was set as the upper limit.

0: If it exceeds 0.6%, even if the O in the core wire is sufficiently low, the O in the weld metal will exceed 0.18, so 0.5
The upper limit was %. For this addition of C, carbon present in graphite, activated carbon, ferromanganese, ferrosilicon, and carbon may be used, and the effect remains the same regardless of the addition 8151.

Si: If it is less than 1.5%, there will be insufficient deoxidation, and the oxygen content in the weld metal will increase, reducing toughness. On the other hand, if it exceeds 5%, 81 in the weld metal will drop to 0.6%, so 1. .5% to 5%. Note that Si may be either metal Si and/or Fe-5i, and is added in an amount equivalent to S1.

If Mn + exceeds 2.5%, In in the weld metal exceeds 0.90%, so 2.5% was set as the upper limit. Mn is metal In and/or
Alternatively, Fe--Mn may be used, and the amount is added in terms of In.

Introducing Qr + 9.0%, even if the core wire does not contain Ar, Or in the weld metal exceeds 8.5%, so 9.
The upper limit was 0%. Or is metal Or and/or Fe-0
Any of r may be used, and it is added in an amount equivalent to Qr.

4. If MO exceeds 4.0%, MO in the weld metal exceeds 1.5% even if the core wire does not contain MO.
The upper limit was 0%.

■: If it exceeds 0.8%, the V in the weld metal will exceed 0.06% even if the core wire does not contain V, so 0.3
The upper limit was %.

Mg=M9, like Si and Al, is used as a devaporizer in arc welding. If it is less than 1%, the effect is not sufficient, so
The lower limit was set at 1%. On the other hand, if it exceeds 4%, M2O generated by the oxidation reaction increases, the melting point of the slag becomes too high, and the fluidity of the slag deteriorates, making it impossible to obtain good beads, so 4% was set as the upper limit.

Other alloy components: Al is the same as Si JpM9 (side, used as a deoxidizing agent, and in the present invention, it is used as an auxiliary deoxidizing agent for Si and Mg.
% range, but in fact, addition within this range has not been found to have any particular effect on mechanical properties. Also, T
Regarding the addition of i due to machining, in order to prevent a decrease in toughness, it can be added as long as it is 0.06% or less in view of the spirit of the present invention, but it is preferable not to add it.

Binder: As the binder, one or more selected from the group consisting of sodium silicate, potassium silicate, and lithium silicate is used, and the solid content is 4 to 4 in the outer frame based on the total amount of each of the threatened drug components. It is desirable to add and mix IO%.

If the LO% is exceeded, the alkali metal content will increase too much and the viscosity of the slag will decrease, making it difficult to obtain a good weld bead.
If it is less than that, the flux will not be sufficiently caking and there is a risk that the coating material will fall off during welding.

Next, the target base material in the present invention is the Or-MO type high-temperature steel used in oil plants, etc., as described above, and in particular, the so-called 2 1/4 Or-I Mo 11 and 30r-I MO1g. The target is mainly, but not limited to, cr-Mo high-temperature steel with a composition such that the specified weld metal can be obtained using the specified coated arc welding rod mentioned above. For example, it can be used as a base material.

Therefore, in the present invention, the coated arc welding rod is constructed as described above, and is used to weld Qr-Mo high-temperature steel, so that the high-temperature strength of the weld metal is sufficiently maintained.
In addition, the toughness, particularly the low temperature toughness, is improved, and the susceptibility to tempering embrittlement can be kept low even when used for a long time at high temperatures.

Examples of the present invention are shown below.

(Example) First, combinations of core wires and coating materials with various compositions shown in Table 1 were prepared, and sodium silicate, potassium silicate, and lithium silicate were added in four parts.
A coated arc welding rod having a diameter of 5 mm was manufactured by adding 6% of a solid component of a binder mixed with 1 part of egg (=8:8) to the above-mentioned coating material in the outer frame.

Using these coated arc welded bodies, 21/40r-I
Mo steel plate IO = 0.14%, Si = 0.35
%, Mn = 0.56%, Qr = 2.18%, Mo =
= 1.02%) was subjected to butt arc welding as shown in Fig. 1 to obtain weld metals having the compositions shown in Table 2. It was examined whether the components of each weld metal were within the composition range of the present invention, and the welding workability was also examined and determined. The results are also listed in Table 1.

In addition, the obtained weld metals (excluding those with poor workability in Table 1, and some were added to determine the chemical composition range)
After post-heat treatment (SRI) under the conditions shown in Figure 2, a room temperature tensile test and an impact test at -40°C were conducted, and some of the samples were also subjected to a long-term use embrittlement test. The tempering embrittlement acceleration test treatment (SO
) and an impact test was conducted at -80°C. In addition, acid resistance and corrosion resistance tests were conducted on all weld metals.

These test results are also listed in Table 2. The test piece was taken from the position shown in Figure 1.

1 indicates the sampling position for the tensile test piece, 2 indicates the sampling position for the impact test piece, and a indicates the notch position.

As is clear from the results shown in each table, Comparative Examples AI, 8 to 17 and AI 8 have either too much or too little of either the core wire or the temporary agent in the accompanying arc welding sludge.
-20, except for those with poor welding workability, some of the components of the obtained weld metals have values outside the range of the present invention. As a result, 0% Si-, Or or Mo
In the comparative example (ml, 18.19) in which a weld metal with an unusually low content of any of the following components was obtained, the high temperature strength that it should have together with the base material high temperature steel was insufficient and ,vice versa,
Other comparative examples (169 to 1116) with good high-temperature strength
．． Even in the case of 17.20), the toughness after post-heat treatment and long-term use is poor.

On the other hand, the Examples (Flats 2 to 7) of the present invention not only have sufficient high-temperature strength, but also have a marked difference in toughness after post-heat treatment and toughness after long-term use compared to the comparative examples. It also has good welding workability, acid resistance, and corrosion resistance.

As detailed above, according to the present invention, a weld metal of a specific composition can be obtained in arc welding of Or-MO type high-temperature steel conventionally used in petroleum plants, etc. The high-temperature strength and high toughness of the steel are fully satisfactory, and the low-temperature toughness is also excellent.Therefore, it is regrettable that it is possible to completely prevent fracture accidents caused by toughness deterioration due to the decrease in ambient temperature that occurs especially at the time of shutdown start. It can cope with larger equipment and higher operating humidity, and greatly contributes to improving the operating efficiency of petroleum plants, etc.

[Brief explanation of drawings]

Figure 1 shows the joint after arc welding and the sampling positions of each test piece, Figure 2 shows the temperature and time conditions of post-heat treatment, and Figure 8 shows the heat treatment temperature conditions of the tempering embrittlement acceleration test. It is.

Claims (1)

[Claims] When arc welding L Cr-MO type high-temperature steel using an equipment arc welding rod, (a) 45 to 60% by weight of 0aOO8+ (hereinafter simply referred to as "%") as a placing agent component. ), metal fluoride: 10-25%, 5in2:
2-7%, si, + 1.5-5% and Mri: 1-4
TiO2
<1%, C≦0.5%, Mn<2.5%, Or<9.
0%, Mo < 4.0% and V ≦ 0.8%.
When each component of , In, and Or is added in the form of a ferroalloy, it shall be converted into each component. ), (b) As the core component, 0<0.18z, Si,<0. ? %, In
≦1.0%, Qr≦4.0%, MO<1.5%
, Ti < 0.15%, v < o, os%, the remainder being Fe and unavoidable impurities, and one or two of sodium silicate, potassium silicate, and lithium silicate as a binder. Or-Mo high-temperature steel is arc welded using a gastric arc welding rod coated with a mixture of the above, and (c) weld metal components: c: o, to ~0.18% , Si 70.25~
0.60%, Mn: 0.88-0.90%, Or
+1.5~8.5%, Mo: 0.7~1.5
%, Ti≦0.015% and V: 0.02-0.0
A method for arc welding Or-MO-based high-temperature steel, which is characterized by obtaining a high C-low Ti-V yarn weld metal containing 6% and especially excellent in low-temperature toughness.