JPH0191993A - Crack repairing method for steel structure under stress fluctuation - Google Patents

Abstract

PURPOSE:To effectively repair without generating a welding crack even under stress fluctuation by forming a wide groove part in advance prior to the joining of the steel stock contg. an inhibiting element a lot. CONSTITUTION:In executing under stress fluctuation the crack repairing welding of the installed steel structure 1 contg. a lot the element inhibiting a high temp. ductility of C, P, S, etc., for instance, shaping is executed on a crack part 2 to form the groove part having a comparatively wide root gap (a). Then, a joint part is formed by joining the steel stock having less inhibiting element contg. amt. to one part or the whole face of at least one face of the opposing faces of the groove part and thereafter welding is executed on this joint part. Namely, crack generation can be prevented even if welding R is executed under stress fluctuation by building up the steel stock L having less containing amt. of the inhibiting element in advance on the end face of the groove part.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention can be applied to welding cracks that have occurred in existing steel structures, such as bridges and offshore structures, where fluctuating stress repeatedly acts. The present invention relates to a crack repair method that can form a welded part with excellent properties.

(Prior art) Bridges are subject to repeated fluctuating stress due to the passage of vehicles, etc., and offshore structures are repeatedly subjected to fluctuating stress due to the influence of waves. In some cases,
The weld groove opening is naturally subject to displacement. Figure 1 shows the amount of displacement of the root gap of the weld groove opening when a vehicle passes through a bridge having the weld groove opening (root gap a = 2 mm) as shown in Figure 1a. In FIG. 1a, l is the base material and 2 is the root.

When welding under such fluctuating stress, the weld metal is repeatedly stretched and compressed at high temperatures where it does not have sufficient ductility, so cracks often occur immediately after welding (during solidification and cooling), and even worse. During service, cracks may develop further starting from these cracks, and the lifespan of structures such as bridges may be forced to be shortened.

In order to solve this problem, the inventors have conducted various studies on welding wire and flux components, but apart from recently constructed structures, some existing bridges etc. As shown in Table 1, the content of C1P, S, Cu, and Ni, which significantly inhibits the high-temperature ductility of weld metal, is significantly higher than that of current steel materials. Most cases are high (especially in classes B and C).

In other words, existing bridges, etc. that require repair work are often constructed many years ago, and therefore, the composition of the steel materials used at the time is based on the steel manufacturing technology of the time, etc., and the hardness of the weld metal before welding is lower than that of current steel materials. It often contains large amounts of impurity elements such as c, p, and s, which expand the liquidus temperature and reduce high-temperature ductility.
Cu.

It often contained large amounts of elements such as Nt and Cr.

(Problem to be Solved by the Invention) For this reason, even if these members are welded using a welding rod that exhibits excellent resistance properties even when welding under fluctuating stress, the - Dilution of chemical components into the weld metal to the extent of t% (hereinafter simply expressed as %) (including melt penetration)
Therefore, when welding under strong fluctuating stress, the problem remains that cracks cannot be avoided due to a decrease in high-temperature ductility.

This invention was developed in view of the current situation as described above, and is intended to prevent the occurrence of cracks even when welding existing steel structures under fluctuating stress that contain many chemical elements that inhibit the high-temperature ductility of weld metal. The purpose is to propose a welding method that can be advantageously avoided.

(Means for solving the problem) As a result of extensive research into the cause of weld cracking under fluctuating stress, the inventors concluded that this weld cracking is caused by high-temperature ductility during the weld solidification and cooling process. It was also discovered that there is a close relationship, and that such cracking is concentrated only in the initial layer where the displacement is large, and that the weld metal composition and the amount of displacement at this time have the strongest influence.

This invention is based on the above knowledge.

In other words, in this invention, when performing crack repair welding of an existing steel structure containing a large amount of elements that inhibit high-temperature ductility under fluctuating stress, the crack is shaped to create a relatively wide root gap. A groove is formed, and then a joint is formed by joining a steel material with a low content of the inhibiting element to at least one of the opposing surfaces of the groove, and then this joint A method of repairing cracks in steel structures under fluctuating stresses, which involves welding the parts.

In this invention, build-up welding and fixing of plate materials are advantageously suitable for joining the steel material with a low content of inhibiting elements to the groove portion.

Further, in this invention, since a wide groove is formed in advance before joining the steel materials, fluctuating stress does not act upon joining the steel materials, and therefore there is no risk of cracking.

(Function) As mentioned above, even if a welding rod with excellent welding crack resistance is used, the steel material being constructed contains a large amount of components that are likely to cause welding cracking (solidification cracking, hot cracking). If this is the case, these components will dissolve into the weld metal, making it impossible to effectively prevent weld cracking.

Here, penetration of the base metal components into the weld metal is determined by the weld area B of the base metal shown in FIG. 2, which is the surface of the weld metal.

For example, element [X] that worsens high-temperature ductility and solidification cracking.
When overlaying a @ plate containing ml of X with a welding rod that produces a deposited metal containing n amount of 30, the content of rXu in the weld metal produced by welding at this time is P + =0.70 n +
0.30m (-th layer) P z =0.70
n + 0.30 P + (second layer) P, 4=0
．． 7On+0.30PH-1 (Nth layer), man
If so, the content of component X can be brought close to n.

That is, the content of various inhibiting elements that are likely to induce hot cracking and solidification cracking in each weld build-up layer P, ~ P8, especially P, is within a range that does not have an adverse effect on subsequent welding under fluctuating stress. If the chemical composition and number of overlay welding electrodes are adjusted in such a way, welding can be carried out on all steel structures without cracking even under fluctuating stress.

At this time, the respective limit values for each component (P8) cannot be strictly numerically limited because they change depending on the fluctuating stress situation, welding material, welding conditions, etc. in which welding is performed under the following fluctuating stress. However, when a welding rod with the weld metal composition shown in Table 2 (test method JIS Z 3213-1977) is used (4 mm diameter, downward welding, 22 KJ 7 cm)
In the case, the component composition after overlay welding is C≦0.20%,
Si≦0.40%, Mn =0.30-2.00%
, P≦0.025%, S≦0.020%, Cu≦0.4
0%.

Ni ≦0.20%, B ≦0.0020%,
As long as A j2 ≦0.80% and Ti ≦0.050%, no cracking was observed even during welding under varying stress equivalent to actual bridge repair.

Table 2 (%) (Example) The materials to be welded were various combinations of the three steel materials A to C shown in Table 1 above, and the welding rods shown in Table 2 above (41 diameter) were used. Welding was performed in the following manner.

A test piece as shown in Fig. 3 (w = 300 mm,
I! .

=1000mm, t =12mm, d = 2
mm, g = 2 mm, tx = 60°), set it in a fatigue testing machine, and then subjected it to a fluctuation cycle as shown in Figure 1 (the amount of displacement during the test was ±0.2
horizontal position, 170 A,
Welding was performed under conditions of 24 to 25 V and 10 cm/min. Since weld cracking is likely to occur in the first layer, only the first layer welding was performed, and after welding, the test piece was immediately removed, and 30 cross sections of the weld were cut out.
After polishing, crack resistance was evaluated by observing the presence or absence of cracks using a microscope.

FIG. 4 shows a case where the two pieces were butt-welded to a steel material as they were, but no cracking was observed in steel material A because it contained a small amount of components that inhibited cracking resistance.

In this regard, as shown in FIG. 5, when steel materials B containing a large amount of inhibiting elements were welded together as they were, cracks occurred.

Figure 6 shows that prior to welding steel materials B containing a large amount of interfering elements as described above, a steel material with a low content of inhibiting elements is welded overlay on both sides of the groove opening in advance, and then the obtained steel materials are welded together. This is a case where the joints are butt welded.

For build-up welding, a 4 mm diameter low hydrogen all-position welding rod with the weld metal composition shown in Table 2 was used.
~160A, 24V, 10~20cm 7m1
Under the conditions of n (preheating, inter-bath temperature: 150°C or less), overlay welding (2 layers, 7 to 9 baths) in a horizontal position was applied to the end face of the groove as shown in Figure 7. This was carried out over the entire length in the width direction, and then the irregularities on the surface were ground with a portapul grinder to form a joint part.

As is clear from Fig. 6, even if steel material B has a high content of inhibiting elements, if steel material with a low content of inhibiting elements is built up in advance on the end face of the tip, welding will be possible under fluctuating stress. No cracking occurred even after applying the coating.

Figure 8 shows a steel material C with a medium content of inhibiting elements, which was prepared by butt welding after overlaying a steel material with a low content of inhibiting elements on both end faces of the groove in advance, as in the case of Figure 6. However, no cracking occurred at all.

Next, Fig. 9 shows the example in Fig. 6, after welding (2 layers, 4 baths) weld metal with a low content of inhibiting elements only on the part corresponding to the welding of the first layer under fluctuating stress. , when welding was performed under varying stress, but no cracking occurred in this case either.

Figure 10 shows a case in which a steel material with a low content of inhibiting elements is previously welded to the grooved end surface instead of the build-up welding in Figure 6, but in this case as well, no cracks occur at all as in the case of build-up welding. There wasn't.

FIG. 11 and FIG. 12 show examples in which a copper material containing a low content of inhibiting elements was joined to one end face of the groove, and no cracking was observed in either case.

(Effects of the Invention) Thus, according to the present invention, even if cracks occur in an existing steel structure constructed of steel containing a large amount of elements that inhibit high-temperature ductility, the cracks can be removed during service, i.e. Even under fluctuating stress, it can be effectively repaired without causing weld cracking, and therefore repair work or remodeling work can be carried out under fluctuating stress without being affected by the components of the structure. Great for on-site construction of steel structures.

[Brief explanation of the drawing]

Figure 1a is a cross-sectional view of the welding groove, and Figure 2 is a graph showing the relationship between displacement and time in the welding groove shown in Figure 1a. 3 is a perspective view of a test piece used in a weld cracking test under varying stress, and FIGS. 4 to 12 are explanatory views of welding procedures. Figure 1 a Figure 1 Figure 2 - (D- Figure 4 Figure 5 Figure 6 Figure 7 Figure 8

Claims (1)

[Claims] 1. When performing crack repair welding under fluctuating stress in an existing steel structure containing a large amount of elements that inhibit high-temperature ductility, the crack portion is shaped to reduce the root gap. forming a relatively wide groove, and then joining a steel material with a low content of the inhibiting element to at least one of the opposing surfaces of the groove to a part or the entire surface to form a joint, A method for repairing cracks in a steel structure under fluctuating stress, the method comprising then welding the joint. 2. The method according to claim 1, wherein the joining of the steel material with a low content of high-temperature ductility-inhibiting elements to the groove portion is by build-up welding. 3. The method according to claim 1, wherein the joining of the steel material with a low content of high-temperature ductility-inhibiting elements to the groove portion is by fixing the plate material.