JPH0677868B2 - Crack repair method for steel structures under fluctuating stress - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention is resistant to welding even in the case of welding a crack portion that has occurred in an existing steel structure such as a bridge or an offshore structure where fluctuating stress repeatedly acts. The present invention relates to a crack repairing method capable of forming a welded portion having excellent properties.

(Prior art) Bridges are used for traffic such as vehicles, and offshore structures are repeatedly subjected to fluctuating stress under the influence of waves, etc. When
The welding groove opening is naturally displaced. Fig. 1b shows the displacement of the root gap of the welding groove opening when the vehicle passes through the bridge having the welding groove opening (root gap a = 2 mm) as shown in Fig. 1a. In FIG. 1a, 1 is a base material and 2 is a root.

During welding under such variable stress, since the weld metal is repeatedly stretched and compressed in a high temperature range where ductility is insufficient, cracks often occur immediately after welding (solidification and cooling). In some cases, the cracks may further grow from the cracks during service, and the life of the structure such as a bridge may be shortened in some cases.

In order to solve such a problem, the inventors have conducted various studies on welding wires and flux components, but some existing bridges, etc., are more than 10 years old, not to mention recently constructed structures. As shown in Table 1, the contents of C, P, S, Cu and Ni, etc., which significantly impede the high temperature ductility of the weld metal, are higher than those of the current steel materials. In most cases (especially B and C steels).

In other words, existing bridges that require repair work are often over a long period of time since they were erected.Therefore, due to the steelmaking technology at the time, the composition of the steel materials was higher than that of the current steel materials, and Expands the liquidus temperature and causes deterioration of hot ductility
It often contains a large amount of impurity elements such as C, P and S. Also, as an existing bridge steel material, Cu, N is used for the purpose of improving weather resistance.
In many cases, a large amount of elements such as i and Cr were contained.

(Problems to be solved by the invention) Therefore, even if these members are welded using a welding rod that exhibits excellent resistance to cracking even during welding under fluctuating stress, 20 to 40 wt. % (Hereinafter simply indicated as%)
Since there is a certain degree of dilution (melting) of the chemical components into the weld metal, there remains a problem in that the occurrence of cracks due to the decrease in high temperature ductility cannot be avoided during welding under strong fluctuating stress.

The present invention has been developed in view of the above-mentioned current situation, and cracks are generated even during welding under varying stress of an existing steel structure containing many chemical constituent elements that hinder the high temperature ductility of the weld metal. The purpose is to propose a welding construction method that can be advantageously avoided.

(Means for Solving Problems) As a result of intensive studies on the cause of weld cracking under fluctuating stress, the inventors have found that the weld crack is extremely close to the high temperature ductility in the welding solidification / cooling process. It was also clarified that there is a relationship and that such cracks concentrate only in the first layer with large displacement, and that the composition of the weld metal composition and the amount of displacement at this time have the strongest influence.

The present invention is based on the above findings.

That is, in the present invention, when crack repair welding of an existing steel structure containing a large amount of an element that inhibits high temperature ductility is performed under variable stress, the cracked portion is shaped to have a relatively wide root gap. A groove portion is formed, and then at least one of the facing surfaces of the groove portion is joined to a part or the entire surface thereof by joining a steel material having a small content of inhibitory elements to form a joint portion. It is a method for repairing cracks in a steel structure under fluctuating stress, which consists of welding parts.

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

Further, according to the present invention, since the wide groove portion is formed in advance prior to the joining of the steel materials, the fluctuating stress does not act upon the joining of the steel materials, and therefore, there is no possibility of cracking.

(Operation) As mentioned above, even if a welding rod with excellent weld crack resistance is used, the steel material to be welded contains a large amount of components that are prone to weld cracking (solidification cracking, hot cracking). If it is present, these components will dissolve into the weld metal, so that weld cracking cannot be effectively prevented.

The penetration of the base metal component into the weld metal is based on the weld metal area B of the base metal and the weld metal area A + B shown in FIG. It is represented by.

For example, the element "X" that worsens hot ductility and solidification cracking
When overlay welding is performed on a steel plate containing m in the amount of x with a welding rod that also produces a weld metal containing n in the amount of x, when A = 0.70, B = 0.30 at the penetration rate shown above. , the content of the "X" in the weld metal produced by welding at this time is P ₁ = 0.70n + 0.30m (first _{layer) P 2 = 0.70n + 0.30P 1} ( second layer) P _N = 0.70n + 0. 30P _N-1 (Nth layer), and if m> n, the content of the component X can approach n.

That is, the content of various inhibitory elements that easily induce hot cracking and solidification cracking in each weld overlay P _{1 to} P _N, especially P
_{If the} composition of the welding rod for overlay welding and the number of overlay layers are adjusted so that ₁ is within the range that does not adversely affect the subsequent welding under varying stress, the variable stress will be applied to all steel structures. Even in this case, welding can be carried out without cracking.

The respective limit values (P _N ) for each component at this time will vary depending on the fluctuating stress conditions for welding under the following fluctuating stress, welding material, welding conditions, etc. No, but the composition of the deposited metal components shown in Table 2 (Test method JI
SZ 3213-1977) with a welding rod (4 mm diameter,
In downward welding, 22KJ / cm), the composition of components after overlay welding is C0.20%, Si0.40%, Mn = 0.30 to 2.00%, P0.02
5%, S0.020%, Cu0.40%, Ni0.20%, B0.0020%, A
In the range of 0.80% and Ti0.050%, no cracking was observed even in welding under variable stress equivalent to repair of actual bridge.

(Example) As the material to be welded, various combinations of the three types of steel materials A to C shown in Table 1 above were used, and as the welding rod, the one shown in Table 2 above (4 mm diameter) was used, and the procedure was as follows. Welded.

Test piece as shown in Fig. 3 (w = 300mm, l = 1000mm, t
= 12mm, d = 2mm, g = 2mm, α = 60 °), set it on the fatigue tester, and then change cycle as shown in Fig. 1b (displacement of ± 0.2mm in the test). The welding was carried out under the conditions of 170 A, 24 to 25 V, 10 cm / min in a horizontal position. Since welding cracks are likely to occur in the first layer, only the first layer welding is performed, and after the welding is completed, the test piece is immediately removed, and the cross-section of the welded portion at 30 locations is cut out and, after polishing, checked for cracks with a microscope. The crack resistance was evaluated by observing.

FIG. 4 shows the case where the steel materials A were butt-welded as they were, but since the steel material A had a small content of components that hinder the crack resistance, no cracking was observed.

In this respect, as shown in FIG. 5, when steel materials B containing a large amount of inhibitory elements were welded as they were, cracking occurred.

FIG. 6 shows that, before welding the steel materials B containing a large amount of the above-mentioned inhibitory elements, the steel materials having a low inhibitory element content are welded to both surfaces of the groove opening in advance and then obtained. This is the case when the joint parts are butt-welded.

In the case of build-up welding, a low hydrogen type all-position welding rod with a diameter of 4 mm, which has the composition of the deposited metal shown in Table 2, was used.
Under conditions of A, 24V, 10 to 20 cm / min (preheating, temperature between passes: 150 ° C or less), as shown in Fig. 7, the weld welding in the horizontal position (2 layer, 7 ~ 9 passes) was carried out over the entire length in the width direction of the test piece, and then the surface irregularities were ground with a portable grinder to obtain a joint part.

As is clear from FIG. 6, even with respect to the steel material B having a high inhibitory element content, if a steel material having a low inhibitory element content is built up in advance on the groove end face, welding under fluctuating stress will occur. No cracks were generated even after applying.

FIG. 8 shows a steel material C having a medium content of inhibitory elements, which is similar to the case of FIG. In some cases, no cracks were generated.

Next, FIG. 9 shows a case where the weld metal having a small inhibitory element content is welded to the portion corresponding to the welding of the first layer under variable stress in the example of FIG. 6 by overlay welding (two-layer welding, four passes). In the case of welding under fluctuating stress, no cracking occurred at all.

FIG. 10 shows a case where a steel material containing a low inhibitory element is previously joined to the open tip surface in place of the build-up welding in FIG. There wasn't.

FIG. 11 and FIG. 12 are examples of the case where a steel material containing a low inhibitory element was joined to one end face of the groove portion, but no crack was observed in any case.

(Effect of the invention) Thus, according to the present invention, even if a crack occurs in an existing steel structure constructed of a steel material containing a large amount of an element that inhibits high temperature ductility, such a crack is generated during the service, namely It can be effectively repaired even under fluctuating stress without generating weld cracks, and therefore repair work or remodeling work under fluctuating stress can be carried out without being affected by the components of the structure. It is a great achievement for the on-site construction of steel structures.

[Brief description of drawings]

1a is a sectional view of the weld groove portion, FIG. 1b is a graph showing the relationship between the displacement amount and time in the weld groove portion shown in FIG. 1a, and FIG. 2 is the dilution ratio. Explanatory drawing, FIG. 3 is a perspective view of a test piece used for a welding crack test under fluctuating stress, and FIGS. 4 to 12 are all explanatory views of a welding procedure.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Noboru Nishiyama No. 1 Kawasaki-cho, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Technical Research Headquarters (72) Inventor Yutaka Kawai 2-3 2-3 Uchisaiwai-cho, Chiyoda-ku, Tokyo Kawasaki Steel Works Co., Ltd. Tokyo Head Office (72) Inventor Yasumasa Nakanishi 1 Shin-Nakahara-cho, Isogo-ku, Yokohama-shi, Kanagawa (72) Inventor Takesuke Kono 1 Shin-Nakahara-cho, Isogo-ku, Yokohama, Kanagawa (72) Inventor Yoshitaka Nakamura 3-1-15-1 Toyosu, Koto-ku, Tokyo (72) Inventor Keiichi Sakai 3-1-15-1 Toyosu, Koto-ku, Tokyo

Claims (3)

[Claims] 1. When performing crack repair welding of an existing steel structure containing a large amount of an element that impairs high temperature ductility under variable stress, the crack portion is shaped so that the root gap is relatively small. Forming a wide groove portion, then at least one surface of the facing surface of the groove portion, to form a joint portion by joining a steel material having a small content of inhibitory elements to a part or the entire surface thereof,
After that, the joint part is characterized by welding.
A crack repair method for steel structures under variable stress. 2. The method according to claim 1, wherein the joining of the steel material having a low content of a high-temperature ductility-inhibiting element to the groove portion is performed by build-up welding. 3. The method according to claim 1, wherein the joining of the steel material having a low content of the high-temperature ductility-inhibiting element to the groove portion is performed by fixing the plate material.