JPS5816793A - Build up welding method for low alloy steel - Google Patents

Abstract

PURPOSE:To obtain sound padding metal which does not peel by specifying the contents of the specific components in weld metal and the composition of a flux in such a way as to satisfy the equationsIand II simultaneously. CONSTITUTION:In a method of performing build-up welding by spraying a flux in the surface of a low alloy steel contg. <=0.2% (wt%) C, <=1.0% Si, <=1.0% Mn, <=1.0% Ni, <=3.5% Cr, <=2.0% Mo, <=0.1% Al, and consisting of the balance Fe and unavoidable impurities, the weld metal of the 1st layer is so welded as to contain <=0.1% C, <=1.0% Si, <=7.0% Mn, 7-30% Ni, 16-30% Cr, <=3.0% Mo, and to consist of the balance Fe and unavoidable impurities, and the contents of the Si, P, S, O in the weld metal and the compsn. of the flux are so specified as to satisfy the equationIand the equation II.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for overlay welding of low alloy steel, and in particular to an interface between stainless thread overlay weld metal and base material low alloy steel, which is formed on the inner surface of a container etc. that handles high temperature and high pressure hydrogen. Regarding the method for preventing cracks (hereinafter referred to as peeling) that occur in The present invention relates to an overlay welding method that prevents peeling caused by hydrogen intrusion during use by properly adjusting the present invention.

High-temperature, high-pressure hydrogen is used in desulfurization, hydrogenolysis, lime liquefaction reactions, etc. in the oil refining industry.
- It is customary to use low-alloy steel such as MO-based steel, and to form an overlay welded layer of molten stainless steel on the inner surface to prevent corrosion. There is a transition region of approximately 20 to 100 μm at the boundary between this type of base metal low alloy steel and overlay stainless steel, and in this region the component composition changes continuously from the base metal composition to the overlay metal composition. ing. However, the returned element becomes ash and precipitates in this region, and a concentration peak occurs in the transition region.

By the way, when this container is operated with high-temperature, high-pressure hydrogen stored in it, the hydrogen diffuses into the material of the container, and this hydrogen remains in the material of the container even after the operation is stopped, causing the steel to become brittle, especially in the above-mentioned transition region. may cause cracks. This crack (
In other words, the factors that cause delamination are: (1) the composition in the transition region is highly susceptible to hydrogen embrittlement; (2) the occurrence of internal stress and strain due to the difference in thermal expansion coefficients between austenite and ferrite; 02 points are possible, but
In any case, peeling will not occur unless hydrogen is present.

The present inventors have focused on the above-mentioned circumstances, and have conducted research to clarify the cause of this occurrence and to establish means for preventing it, in order to eliminate peeling between the low-alloy steel base material and overlay metal.

As a result, we found that flaking is a grain boundary fracture that occurs along the grain boundaries existing in the transition region, and that P and S segregate at these grain boundaries, promoting grain boundary embrittlement, and that Sl also I learned that it promotes embrittlement. Peeling susceptibility is also affected by the crystal grain size in the transition region; if the crystal grain size is large, the grain boundary area decreases, so P%, an element that promotes embrittlement, decreases.
Segregation of s and si to grain boundaries increases, increasing susceptibility to peeling. Therefore, we conducted research on the factors that control the grain size in the transition region and found that the composition of the flux used during overlay welding has a large influence. That is, CaO.

Basic components such as BIO, MgO, CaF2, BaF2,
If a flux containing a large amount of agglomerates such as MgF is used, the arc temperature will rise, or the conductivity of the slag will become good, increasing the amount of heat generated by resistance and raising the temperature of the molten pool, which will reduce the cooling rate of the weld metal. decreases and the crystal grain size increases. In addition, with basic flux, the cleanliness of the molten metal increases and the amount of crystal nuclei generated at the time of solidification decreases, so the crystal grain size increases.

Based on the knowledge described above, the inventors of the present invention have investigated the composition of the base metal, the composition of the flux for overlay welding, the composition of the transition region, etc. in order to prevent the peeling of overlay weld metal. Comprehensive research has been carried out mainly on the composition of the first layer overlay weld metal that provides the The present invention was completed as a result of such research, and its composition is as follows: C: 0.2 - (weight: the same below) or less, Si: 1.01 L or less, Mn: t, o or less, Ni : 1.0 or less, Cr: 8.5% or less, MO:
2. (Contains 0.1% or less, A#: 0.1% or less, and the remainder is F
- In a method in which blanks are sprinkled on the inner surface of low alloy steel containing unavoidable impurities and sensual welding is performed, the first layer weld metal has C: 0,111. Hereinafter, S l: 1.
Below 0, Mn near, below 0, Ni near ~80%.

Contains Cr: 1@~80%, Mo: Jl, Q% or less,
.

Or, together with these, Nb:C contains 8 times or more and 101 or less, and is overlay welded so that the remainder consists of Fe and unavoidable impurities, and is adjusted to satisfy the following formulas (I) and (IF). A gist exists.

0.6≦(S 1+5 (0) + As mentioned above, the factors that affect the peeling of overlay weld metal are:
P on the grain boundaries in the transition region between the base metal and the overlay weld metal
, segregation of S and Si, and crystal grain size in the region. Therefore, among the factors considered to influence these, a comprehensive study was conducted on the composition of the base material low alloy steel, the composition of the scattered blank, and the composition of the first PfI weld metal.

After conducting many experiments and organizing the data, as shown in the experimental example below, we found that in order to prevent the overlay metal from peeling off, *81% of the overlay metal contained in the first layer must be
It is necessary to appropriately adjust the interrelationship between the amount of P%S and the composition of the blank used (especially oxides and hybrids), and the relationship between the two should be adjusted so that it satisfies the above CI) formula. That's what I found out.

However, even if the content of 2%51,5 in the overlay metal is reduced, for example, if the base material Cr-Mo low alloy copper has a high P content, cracking may occur due to solid diffusion from the base material to the transition region. Since the sensitivity increases, the higher content of P, Sl, and 8 in both metals determines whether or not cracking occurs. Therefore, sufficient consideration must be given to the selection of the base material. On the other hand, 8 in overlay metal
Although it is not necessarily desirable to keep the 81 content low considering welding workability, as a result of experiments, we found that if the lower limit of the 81 content is set in relation to the blank composition, the amount of acid residue in the overlay weld metal It became clear that both cracking susceptibility and welding workability could be satisfied.

In other words, if a blank containing a large amount of woodcutter-based components and fluoride is used, and the amount of 81 and 0 in the weld metal is small, the weld bead will not fit well and defects such as poor fusion will occur frequently, and this poor fusion will occur. promotes peeling of overlay weld metal.

Therefore, in order to satisfy both cracking sensitivity and welding workability, we conducted detailed research on the 81 and 0 content in the weld metal and the flux composition, and found that the content of each component satisfies the conditions of the CH2 formula. We have reached the conclusion that the above objective can be achieved by specifying the following.

In addition, in formula (I[), the upper limit [? The reason for setting it to 8.6 is as follows. That is, as mentioned above, Sl is an element that causes grain boundary embrittlement, so it must be kept as low as possible, and if the 0 content is too high or a blank with a large amount of acidic components is used, it will be difficult to form good beads, and This is because nonmetallic inclusions in the weld metal increase, resulting in poor mechanical properties and corrosion resistance.

In this way, by specifying the amount of Si and p%S10 in the weld metal and the blank composition so as to simultaneously satisfy formula CI) and formula (II), a sound overlay metal t- Obtainable. Furthermore, these (I), (
The reason for determining the requirements of the formula It) will be further clarified in the experimental examples described later.

In addition to the above-mentioned requirements, the present invention strictly defines the component compositions of the base material low alloy steel and weld metal, and the reason for this is as follows.

First, the first layer of weld metal will be explained.

A smaller amount of C is preferable in order to improve the corrosion resistance of the stainless steel weld metal, and the upper limit was set at 01- in consideration of the amount of penetration from the base metal during overlay welding. 53 and Mu are used as oxidizing agents for welding materials, but if there are too many, the mechanical properties and corrosion resistance will deteriorate as well as weldability, so 5t is t, OS, and Mn are 7.0 liters. is set as the upper limit of Chi4.

Ni and (r) are basic components for increasing the corrosion resistance of weld metal, and in austenitic steel, N1 is usually about 7 or more,
The Cr content is about 16%, which is high, but if it is too high, problems such as high N3 cracking during welding and embrittlement due to heat treatment will occur, so the appropriate range is NI of 7 to 801j11 Cr of 1.
6 to 80% was determined respectively.

MO has the effect of increasing high-temperature strength, but if it is too large, sigma phase will precipitate and impair corrosion resistance and impact resistance.
Must be kept below.

Although it is not essential when the amount of Nb#iC is small, when the amount of C is relatively large, it exerts an important function as a strong reversion product-forming element, fixing Cvi- in the weld metal and preventing intergranular corrosion. . In order to completely fix C, it is necessary to contain at least 8 times the amount of C, but if it is too large, a sigma phase will precipitate and corrosion resistance and impact resistance will decrease, so it must be kept below ion.

Next, the base material will be explained.

C is an essential component to ensure hardenability and strength, but if it is too large, toughness and weldability will deteriorate, and furthermore, hydrogen corrosion resistance will become poor, so it must be kept below 0.2 ml. .

Sl increases tensile strength, but if it is too large, toughness and hydrogen corrosion resistance decrease, so the upper limit was set at 1.0% t-.

Although Mll has the effect of increasing strength, too much Mll promotes tempering embrittlement, so the upper limit was set at vil-t and o-l.

Ni improves hardenability, but if it is too large, weldability becomes linear, so it should be kept at 1.0 seconds or less. (R and Mo have the effect of increasing hydrogen corrosion resistance, oxidation resistance, and high-temperature strength, but if they are too large, weldability deteriorates, so the upper limit of each is set at 8.
*AJ defined as 6 liters and 2 liters is used as a deoxidizing agent, but too much will deteriorate toughness, so the content should be 0.1% or less.

There are many reasons for setting the component composition and numerical range in the present invention as outlined above, but in order to further clarify the reasons for these limitations, experimental examples will be given and explained in detail.

An austenitic stainless steel hoop (thickness Q,
Perform overlay welding using 4 am 1 width 75 m1),
The composition of the fufutuks used (7V fraction) is shown in Table 1.
The chemical components of the base materials are shown in Table 2.

Tables 8 (a) to (e) show the chemical compositions of the hoops used and the weld metals obtained.

For each obtained overlay welded steel, actual machine 11? In order to determine the peeling resistance due to hydrogen under simulated conditions, a hydrogen peeling test was conducted using the following method developed by the applicant himself through calculations and experiments. That is, FIG. 1 is a partially cutaway diagram 9 schematically showing this test method, in which two screw holes 2 are orthogonally inserted into a cubic steel ingot 1.1. On the other hand, each of the overlay welded steels obtained above is punched into a cylindrical shape as shown in Fig. 2, and a male thread 8 is formed on the outer periphery of the upper part to obtain a specimen 4 (A in the figure is the base metal, B is the overlay welded steel). metal). Each of the obtained specimens 4 was screwed into the screw hole 2 so that the overlay weld metals faced each other as shown in FIG. Then, the pipe 5 is separated and connected to a hydrogen cylinder (not shown). After hydrogen gas is pressurized into the space 6 in the center of the test object, it is charged into a furnace and heated, and maintained at a temperature of 450° C. and a hydrogen pressure of 150 atmospheres for about 50 hours. As a result of the experiment under these severe conditions, hydrogen penetrated into the meat-weld metal, and the zero-order test specimen, which can almost accurately simulate the hydrogen penetration and distribution conditions during steady operation of the actual machine, was removed from the furnace. Cool to room temperature in about 1 hour. The cooling rate was determined through calculations and analytical experiments so that a sufficient amount of hydrogen would remain in the overlay weld metal. When cooled to room temperature and left to stand in this manner, in the case of overlay weld metal with poor peeling resistance, peeling occurs after an incubation period of ten to several tens of hours.

Therefore, peeling resistance was detected by an ultrasonic flaw detection test after cooling and leaving for 48 hours.

The results are shown in Table 8 (a) to (e).

If the results obtained in the above experiment are organized as the relationship between 51 and (P+(S)) for each flux composition, the 8th to
The relationship shown in Figure 6 is obtained. As is clear from these figures,
When (81+50P-1158) exceeds a certain *t- determined by the composition of each flux, peeling occurs, and below this it does not occur, and these trends are very clear. 'Also, Figure 7 is a graph organized as the relationship between (Sl+60F+258) and flux composition.
Sl+50? +! ! 68) is a value determined as a function of the flux composition (particularly the content of oxides and fluorides: molar S): If it exceeds this value, peeling has occurred, and this condition is an important factor in determining the presence or absence of peeling. It is clear that.

That is, Examples 1 to 22 in Table 8 are examples that satisfy the above requirements, and have good weldability and peeling resistance in all cases, but Comparative Examples 28 to 48, which deviate from the above requirements, are examples that satisfy the above requirements. Also, Comparative Examples 49 to 58 have poor peeling resistance and cannot achieve the objective of the present invention, and Comparative Examples 49 to 58 deviate from the requirements of the above formula (I [), that is, the values deviate from the range of 0.6 to 8.6. This is a comparative example, and in this case, welding workability was poor, a good bead shape could not be obtained, and poor fusion occurred frequently, making it impossible to obtain a healthy meat II joint, and the problem was more than peeling resistance. It is.

As is clear from these results, in order to ensure a healthy overlay weld and to prevent overlay metal (D@M),
It is essential to simultaneously satisfy the requirements of formula (i) and formula (]I).

The present invention is roughly constructed as described above, and the tolerance limits of 81, P, and S, which inhibit the peeling resistance of overlay weld metal, are appropriately defined in relation to the flux composition used. A healthy overlay weld with excellent peelability was obtained. As mentioned above, it is possible to improve the peeling resistance by suppressing 31, P and sl in the overlay weld metal to extremely low levels on a laboratory scale. However, this requires careful selection of base metals and welding materials at the raw material stage, as well as devising a melting process, which increases manufacturing costs and is extremely unlikely to be realized on an industrial scale. On the other hand, in the present invention, as mentioned above, the permissible limit of elements that inhibit peeling resistance is defined in relation to the composition of fufux9, and this technology is extremely practical on an industrial scale. By applying this method to pressure vessels that handle hydrogen, it has become possible to prevent accidents caused by peeling of overlay weld metal layers.

[Brief explanation of the drawing]

Figure 1 is a partially cut-out schematic view of the peeling resistance testing device used in the experiment, Figure 2 is a sketch showing the test piece, and Figures 8 to 6 are 51 parts of the test piece during welding and welding. Figure 7 is a graph showing the relationship between (S i + 50P +
258) and a function of y-lux composition. 1...Steel ingot 8...Threaded hole 8...Male thread 4...Specimen A...Base metal
B... Overlay welding metal applicant Kobe Steel, Ltd. Figure 2 0.010 0.02 0.030 0. (+
40P+-25C'l) Fig. 7 0.5 1.0 (Si02+Ae203+0.7TiO,) (NaO
10BaO+-MgO+ 0.4 (caF + BaF
, 1MgF:) 12 ~ 6゜ Procedural Amendment (Shi) Sho+++ 56 (l19/2711 Commissioner of the Japan Patent Office Shima 1) Haruki, Japan Patent Office Chief Examiner, Japan Patent Office Examiner
Display of 111 items 1982 Patent Application No. 116880 Showa
2016 Trial and Judgment No. ``-;3 Supplement 11: ``Name (I+!'l) Representative of Kobe Steel, Ltd.
Takashi Takahashi +'i1 Deputy Director Postal Code Shiji 530 Address 2TII 3-7 Dojima, Kita-ku, Osaka
+;, Shinko Hill? 7, Supplement 11: Contents (1) "51o2AA'l-2" on page 8, issue 9 of the specification
o3'' Ir5lo A#203J is corrected to 1 (2) Same page 7 H? 12) rl, (I lower J t-
rl, 01 or less”k Correct. (3) Replace all of “Figure 7” with the attached sheet.

Claims (1)

[Claims] (13G: 0.2 liters (weight: the same applies hereinafter) or less, Sl:
i, os or less, Mn: 1.9% or less, Ni: 1. 0 or less, Cf: 8.811 or less, Mo: 2. Below O, A4! :O, tS or less, with the remainder being F and unavoidable impurities. In the method of performing tactile welding by dispersing 7x on the surface of low alloy steel, the first layer weld metal contains C: 0.11. Below, Si: 1゜〇- or less, Mal near, 0- or less, Ni near ~80s% Cr: 16-80
哄, MO:8. It is welded so that it contains less than 100% of Si and the remainder consists of FC and unavoidable impurities, and (Si+50?
+258)≦0.6≦[S amount +5 (0) + A method for overlaying low alloy steel, characterized by adjusting the amount to satisfy the following relationship. (2) C: 0.2° (weight II: same below) or less, Si
:1, O1 or less, Mn:t, os or less, ? Ji:1.0
Below 哄, Cr: 8.5 below 哄, MO21011+
The following contains Ajl: 0.1111 or less, and the remainder is ir
In the method of overlay welding by applying black t-e to the surface of low-alloy steel consisting of e and unavoidable impurities, the first layer weld metal has c: o, less than or equal to , si: 1.6
Less than 100%, Mn near, 9% or less, N': 7-8 (
1+, Cr: 16-80 liters, Mo: 8.0 liters or less,
Nb: Contains 8 times or more of C and 1.0 or less, and is welded so that the remainder consists of Fe and unavoidable impurities, and satisfies the relationship of (S i + 50P + 25s) ≦ 0.5 ≦ (S 1 + 5 (0) + A method for overlay welding of low alloy steel, which is characterized by adjusting it so as to