JPS60115369A - Build-up welding method - Google Patents

Abstract

PURPOSE:To improve remarkably resistace to detaching and cracking by adjusting the compsn. of the build-up weld metal of root pass in association with a base metal. CONSTITUTION:The following conditions are satisfied with respect to the contents, by weight per cent, of the respective components elements occupying in the compsn. of a base metal and the weld metal of root pass: The weld metal contg. C, Si, Mn, Ni, Cr, Mo, Nb and N satisfying the relation (NieqD-NieqB)/ (CreqD-CreqB)<=(9.84-NieqB)/(16.66-CreqB) when the Cr equiv. of the base metal and weld metal expressed by (%Cr)+(Mo)+1.5X(%Si)+0.5X(%Nb) are respectively designated as CreqB, CreqD and the Ni equiv. of the base metal and weld metal expressed by (%Ni)+30X[(%C)+(%N)]+0.5X(%Mn) are designated respectively as NieqB, NieqD.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a build-up welding method, and particularly to a build-up welding part of a stainless steel inner surface such as a reaction vessel that handles high-temperature, high-pressure hydrogen, it is possible to obtain a weld metal with excellent peeling resistance during use. Regarding how it can be done.

Used in oil refining equipment or coal liquefaction equipment, etc. 1. .

In many cases, austenitic stainless steel is overlay welded onto the inner surface of the reaction vessel.

These vessels operate under high temperature and high pressure hydrogen environments, so
The overlay weld metal and the base material of the container absorb hydrogen during operation, and they also absorb hydrogen when the operation is stopped.

In this process, a large amount of hydrogen accumulates at one boundary between the base metal and the weld metal, and exfoliation cracks may occur at the austenite grain boundaries on the weld metal side near the boundary, which is a major problem.

As a countermeasure against such peeling cracks, Japanese Patent Application Laid-Open No. 54-5107
No. 458, JP-A-54-71746, JP-A-55-1
No. 4171 each proposes a method in which a weld metal with a composition close to that of the same metal or a ferritic stainless steel weld metal is underlaid on the base metal, and then austenitic stainless steel with the required components is overlaid by overlay welding. However, these methods require welding an extra layer of underlay, which has the disadvantage of reducing welding efficiency. Also, JP-A-55-1175
Publication No. 11 proposes a method of overlay welding austenitic stainless steel containing a martensitic phase,
However, even though the resistance to exfoliation cracking is improved, there are drawbacks such as hydrogen embrittlement of the martensitic phase. Further, as a countermeasure against peeling cracks, a method of selecting a welding method or welding conditions has been proposed, but peeling cracks cannot be completely prevented even with these methods.

The reality is that there is not.

The inventors of the present invention have conducted extensive research to solve these problems, and as a result have obtained the knowledge based on the experiments shown below. Composition in relation to the base material.

We have discovered a build-up welding method that can significantly improve peel cracking resistance by adjusting it downward.

Peeling cracks that occur after exposure to high-temperature, high-pressure hydrogen occur on the weld metal side near the boundary between the weld metal and the base metal, and along the boundary, austenite coarse grain boundaries are formed in y-parallel. .

Occurs in Furthermore, the susceptibility to peel cracking depends on the degree of development of the coarse austenite grains, and if the coarse austenite grains are eliminated, the peel cracking resistance is significantly improved. Therefore, a method for eliminating the austenite coarse particles was investigated. □ Austenite coarse grains are grains that have grown epitaxially from old austenite grains in the base metal toward the weld metal, and in the weld where austenite coarse grains develop, martensite (M) → austenite (A) → A
+ The structure has a (111 transition) like delta ferrite (F), and coarse austenite grains are developed from M to A, and the grain boundaries are held in place by the presence of the delta ferrite phase. There is.

However, the precipitation region of delta ferrite was moved further to the base metal side than before, and the structure change of the transition phase was changed from 5 base metal to M+
When F-+A10F is used, it is possible to eliminate coarse austenite grains. That is, if sufficient delta ferrite exists at the boundary between the martensite and austenite phases to prevent grain boundary growth, the peeling resistance will be improved. However, I.

It is virtually impossible to measure the amount of delta ferrite (FA-M) at the interface between martensite and austenite phases.

However, in the present invention, the amount of delta ferrite in the weld metal is calculated by combining the de150ng diagram estimated from the composition of the weld metal and the martensite precipitation line experimentally determined by the inventors. and the amount was estimated.

Figure 1 shows a prong diagram and an experimentally determined martensite precipitation line.

(4) The composition change from material to weld metal is shown on the prong diagram) as y
The transition occurs linearly as shown by the broken line in the figure. However, the FA-M amount is the delta ferrite amount estimated from the composition indicated by the intersection of the broken line and the Martensitic precipitation line.

This martensite precipitation line is (%Cr) + (%M
O) +, 1.5X (%Si) +〇, 5X (%N
The chromium equivalent represented by b) is Creq, and (%N1
)+aoxB%C)+(%N))+○,5X(%Mn
) is the nickel equivalent expressed by Ni eq, then the following formula.

It is expressed mathematically as follows.

N1eq --b (Creq-28,8) However, b
-19,8/28.8 Also, the transition line 1 of the composition from the base metal to the weld metal is N1eqD-NieqB -a (CreqD-Cre
qB)NieqD: Nickel equivalent of weld metal.

N1eqB: Nickel equivalent of base material CreqD: Chromium equivalent of weld metal CreqB: Base material The composition of these intersection points is expressed by the following equation.

However, in FA-7, the above intersection point composition is expressed by the following formula, which is the delta ferrite amount shown by the prong diagram: delta ferrite amount = 8.2Creq -2,5Ni
It is rounded by substituting eq -24,7.

Next, the limit amount of FA and -M for improving peel cracking resistance was investigated.

For overlay welding, use 5A887Gr shown in Table-1.

22 steel plate is used, and nickel equivalent and chromium are added to it.

(7) Horizontal electroslag overlay welding was performed in combination with fusion flux. Welding conditions were 2500A.

28V, 14cm7m1n, 690℃ after welding,
After 28 hours of heat treatment, the structure near the boundary 5 between the base metal and weld metal was observed using an optical microscope. The length ratio of austenite grain boundaries) was measured.

In addition, in order to investigate the resistance to exfoliation cracking caused by high temperature and high pressure hydrogen,
A test piece with a width of 55 mm and a length of 100 inches was prepared and exposed in an autoclave at 455° C. under a high temperature and high pressure hydrogen environment of 150% for 80 hours at 23° (8) and then air cooled. One week after cooling, an ultrasonic flaw detection test was carried out from the base metal side of the test piece 1 to examine the presence or absence of peeling cracks and the extent of them.

As a result of the above experiments, the relationship between the amount of FA-M, coarse grain ratio, and peeling cracks is shown in Figure 2. From the same figure, the coarse grain ratio 5 is 0 to 5.
% had no peeling cracks at all, and FA
It has been found that if the -7 amount is 4% or more, the coarse grain ratio can be suppressed to almost zero.

The initial layer weld metal with a weight of 4% or more is defined as, in Fig. 1, the slope of the straight line connecting the point 1° indicating the composition of the base metal and the weld metal is the point indicating the composition of the base metal and the delta. - In other words, it can be said to be a weld metal having a composition that makes the slope of the straight line connecting points on the martensite precipitation line where the ferrite content is 4% smaller than the slope.

The point on the martensitite precipitation line where the amount of delta ferrite is 4% is N1eq = -19・8/2B, B (Creq 28
．． 8) 4-8J Creq -2,5N1eq -24
, 7 (N1eq% creq),
(N1eqs Creq) = (9,84,16,66
).

Therefore, the weld metal with an FA-M amount of 4% or more is (NieqD-NieqB)/(CreqD-Creq
B)≦(9,84N1eqB)/(16,66-Cre
C, Si, Mn, Ni, in amounts that satisfy the relational expression qB),
The weld metal contains Cr, NMo, Nb, and N.

In addition, the present inventors previously published Japanese Patent Application Laid-Open No. 57-66861 [
We have shown that the initial layer Ill overlay weld metal made of low-Si and B-added stainless steel has excellent peel cracking resistance.
Next, in the previous vertical, weld metal with an amount of 4% or more and low Si, B
The amount of added weld metal and FA-W is 4% or more and low Si
, B-added weld metal were exposed to even more severe conditions, ie, a high temperature, high pressure hydrogen environment of 456° C. and 1° hydrogen pressure ao o kJ− for 80 hours to investigate peeling cracks.

The results are shown in Table-2.

Table 2 From this, FA- and amount should be 4% or more, and low 81,
It was found that the B-added weld metal did not cause any peeling cracks even under the severe conditions mentioned above, and was a more effective measure to prevent peeling cracks.

Next, the appropriate range of each amount of 81 and B in a weld metal with an FA-M amount of 4% or more was investigated.

As a result, the temperature was 455°C and the hydrogen pressure was 117. −
81 in the weld metal against the harsh high temperature and high pressure hydrogen
exceeds 0.4%, or B in the weld metal becomes 0.
It was found that when the content is less than 10%, slight peeling cracks occur, and the anti-peeling cracking effect of Sl and B weakens. Furthermore, if the content of 81 in the weld metal is less than 0.1%, deoxidation during welding will not be achieved sufficiently, and the cleanliness of the weld metal will deteriorate, as well as welding workability. Moreover, if B in the weld metal exceeds 0.0200%, hot cracking will occur during welding, making it impossible to obtain a sound overlay weld metal.

Therefore, in the present invention, the amount of Si in the weld metal is set to 0.1 to 0.
．． 4%, and the amount of B was 0.0010 to 0.0200%.

Furthermore, we also investigated the appropriate range of leaves containing delta ferrite. The delta ferrite phase contained in austenitic stainless steel overlay weld metal has the effect of preventing high-temperature cracking during welding and reducing grain boundary precipitation of chromium carbide15;
When heated for a long time, it changes to the σ phase, and the performance of the weld metal is significantly impaired by the precipitation of this phase, and the delta ferrite phase and the σ phase are embrittled by hydrogen. However, 455℃, hydrogen pressure 300kg/, L2 high temperature high pressure hydrogen 2. .

2 mm thick, 201 m from weld metal exposed for 80 hours to
As a result of taking and testing a surface bending test piece with a width of m and a length of 507F17W, it was found that the bending ductility of weld metal containing more than 20% delta ferrite deteriorates. Therefore, in the present invention, an austenitic stainless steel containing 20% or less of delta-ferrite is used.

(Example) Next, the prevention of peeling cracks in overlay welded parts of stainless steel according to the present invention will be explained using examples. 5A shown in Table-8In
887 Gr, 12, same Gr,! 22, same Gr, 21
s Same () r, 5 On a steel plate, a commercially available type 309L electrode shown in Table 4 was combined with a commercially available molten flux as a comparative example, and B was added to the electrode shown in Table 5 as an example. In combination with a molten type flux, the first layer was horizontally electro-slag overlay welded.

Furthermore, type 1347 was applied on these initial layer weld beads.
The second layer was overlay welded using the same horizontal electroslag overlay welding method using an electrode. The electrodes used had a thickness of 0.47r1m and a width of 150mm, and the welding conditions were 250mm.
0A, 28V, 14cIVTn1n. Melt.

After draining liquid and heat treating at 690℃ for 28 hours, the thickness is 40mm.
A test piece with a width of 55 m@s and a length of 100 mm was taken in an autoclave at 455°C and a hydrogen pressure of 800 kV.
After being exposed to an environment of n2 for 80 hours, it was air cooled, and one week after cooling, it was examined by ultrasonic flaw detection to determine the degree of peel cracking at 3°. After the ultrasonic flaw detection test, a chemical composition analysis sample and a surface bending test piece were taken from the first layer weld metal, and the chemical composition and bending ductility were investigated.

Table 6 shows the above test results.

0 (15) 399- As shown in the same table, the overlay welded part according to the present invention does not generate any peeling cracks even under severe high temperature and high pressure hydrogen conditions, and has extremely good peel cracking resistance. It was also demonstrated that the bending ductility was good.

As is clear from the detailed description above, the present invention aims to improve peel cracking resistance by adjusting the composition of the initial layer weld metal, which is involved in peel cracking, in relation to the base metal. It is effective regardless of the welding method or welding conditions, and is the first in terms of construction efficiency. .

There is no deterioration, and since the weld metal is austenitic stainless steel containing the delta ferrite phase like conventional weld metals, its hydrogen embrittlement resistance is exactly the same as conventional weld metals. It is something to play.

[Brief explanation of drawings]

Figure 1 shows the delta phase at the boundary between the martensite phase and the austenite phase in the transition layer between the base metal and the first weld metal.
Fig. 2 is an estimation of the amount of ferrite, and Fig. 2 is the delta ferrite estimation in Fig. 1. Quantitative determination (FA-weight), austenite coarse grain ratio and exfoliation
FIG. 3 is a diagram showing the relationship with the degree of abrasion. Patent applicant: Kawasaki Steel Corporation

Claims (1)

[Scope of Claims] 1. When performing surface overlay welding of stainless steel on a base material of carbon steel or low alloy steel, the composition of the weld metal of the base material or the first layer is preliminarily applied to the base material as an initial layer. (a) and (1) below regarding the weight percentage content of each component element in
satisfies the conditions l-1 and the delta ferrite phase is 20
Welding of austenitic stainless steel containing less than %
O gold metal overlay welding 4! Characteristic overlay welding and welding methods. Note (a): (%cr)+(%MO)+1.6X(%si
) + o, bx (%Nb) Cr equivalents of the base metal and the 15 welded parts are respectively Creq B s Creq
D, (%Ni) + 80X ((%C) + (%N))
When the N1 equivalents of the base metal and the weld metal expressed as +0.58 (%Mn) are each N1eq B 5Nieq D, 2po((N1eqD-NieqB)/(CreqD-C)
reqB )≦□(9,84-N1eqB ) /(
16,66-CreqB) is the quantity C that satisfies the relational expression
, 81, welding containing Mn5N1, Cr, Mo, Nb and N. metal. (b): 0, 81 and 0 between 1% and 0.4%
．． A weld metal containing 0.010% or more and 0.0200% or less of B.