JPS62234668A - Shielded arc welding method - Google Patents

Abstract

PURPOSE:To restrain the immersion of a hydrogen component into a welding metal from the atmosphere by performing a shielded arc welding with shielding the arc periphery by a low temp. gas, in welding the material easy to generate a low temp. crack with its preheating. CONSTITUTION:The welding is performed by using a coated arc electrode 2 by executing a preheating on the welding base material 7 easy to generate a low temp. crack. In this case, the gas shielding zone 6 of a low temp. gas is formed so as to surround an arc 5 on this periphery by feeding a low temp. gas from a nozzle 3. In this way no hydrogen component in the atmosphere is made to immerse into a molten pool 8 or welding metal 1. The hydrogen immersion into the welding metal can thus be restrained and the prevention effect of a low temp. crack is obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a covered arc welding method for materials that are prone to cold cracking, such as high-strength steel, low-alloy steel, and even martensitic stainless steel. The present invention relates to a covered arc welding method that can improve workability by lowering the heating temperature for preheating or postheating to suppress low-temperature cracking.

[Conventional technology] As various structures become larger and the range of use expands, high-grade steel (
Opportunities to use high-strength steel, low-alloy steel, martensitic stainless steel, etc.) are increasing. Although these materials exhibit excellent effects such as high tensile strength and high corrosion resistance, they have a common defect of being susceptible to cold cracking. It is known that the occurrence of cold cracking is caused by diffusible hydrogen contained in the weld metal, and the hydrogen is supplied from organic matter and moisture in the coating material that drips into the coated arc welding rod or from atmospheric moisture. It is also known that For this reason, care is taken to strictly select flux components and drying control in the manufacturing process of coated arc welding rods, and to pay attention to re-drying the coated arc welding rods immediately before welding work. However, even after these steps are taken, there is still some residual hydrogen in the weld metal, so the residual hydrogen in the weld metal must be actively released by preheating the base metal before welding or by post-heating. This is also being done. However, if the welded structure is large or has a complicated shape, raising the temperature to the required preheating temperature (generally 100 to 250°C) and maintaining the crystallization requires quite difficult work and a huge amount of cost. However, there was also the drawback that the working environment deteriorated. A similar problem occurred in the case of post-heat treatment. That is, with conventional means, the amount of residual hydrogen in the weld metal increases, so the preheating temperature and postheating temperature have to be increased. Therefore, the following measures have been proposed as a means to reduce the amount of hydrogen penetrating into the weld metal as much as possible, with the ultimate goal of lowering the preheating temperature and postheating temperature.

(a) A method of lowering the hydrogen partial pressure around the arc using a low-hydrogen coated rod.

(b) Carbon dioxide welding method using solid wire.

(c) Carbon sludge welding method using flux-cored wire.

[Problems to be Solved by the Invention] The above-mentioned method (a) of using a low-hydrogen coated arc welding rod is a method of lowering the hydrogen partial pressure by including a large amount of carbonate in the coating material. However, if the carbonate content is too large, the arc becomes unstable and the welding performance decreases, so there is a limit to the carbonate content, and therefore there is a limit to the effect of reducing the amount of hydrogen.

Furthermore, there is a tendency to use high current at welding sites to increase welding efficiency, but as shown in FIG. 2 (graph), the amount of hydrogen tends to increase as the welding current increases.

This is thought to be because the shielding properties around the arc deteriorate as the welding current increases.

Next, in the carbon dioxide welding method using a solid wire (b), it is convenient to achieve low hydrogenation without hydrogen supply from the coating material, or the alloy in the wire matches the alloy composition of welding 1. As the amount of elements increases (alloying elements cannot be added from flux, the necessary alloying elements must be added to the wire and then supplied from the wire), the hardness of the wire increases or The wire becomes susceptible to work hardening, making it difficult to draw the wire. If the wire is severely hardened, it becomes impossible to draw the wire, and the manufacturing cost of the wire becomes extremely high.

In addition, in the carbon dioxide welding method using a flux-cored wire (c) above, the alloying elements necessary for the weld metal can be supplied from the flux, and the drawability of the wire can be ensured. However, there is a hoop joint in the outer metal covering the flux, and there is a high risk that the flux will absorb moisture due to the outside air entering through this joint, and the amount of hydrogen in the weld metal will not be as low as expected. Furthermore, because of the need to maintain high welding efficiency, the amount of flux cannot be increased unnecessarily, and therefore there is a limit to the amount of carbonate added to lower the hydrogen partial pressure.

Therefore, the present inventors conducted various studies aimed at suppressing the amount of hydrogen penetrating into weld metal, and as a result, they completed the present invention.

[Means for Solving the Problems] The present invention, which has achieved the above object, has a gist in that covered arc welding is performed while shielding the periphery of the arc with a low-humidity gas.

[Effects] The coating material of coated arc welding rods contains carbonates as mentioned above, and the carbon dioxide gas generated by decomposition due to welding heat shields the area around the arc from the atmosphere to some extent.
Since there is a limit to the amount of carbon dioxide gas generated as mentioned above, it is not possible to completely shut it off from the atmosphere. Therefore, if the humidity in the atmosphere increases, this moisture will enter the arc atmosphere.
Eventually, hydrogen components will be mixed into the weld metal,
Cold cracking is more likely to occur.

Therefore, in the present invention, the area around the arc is shielded with a low-humidity gas to suppress intrusion of hydrogen components (moisture) from the atmosphere τ. As a result, by reducing the amount of hydrogen penetrating into the weld metal, it has become possible to reduce the heating temperature and heating time for N, preheating or postheating, and it has become possible to perform efficient welding work.

[Example] FIG. 1 is an explanatory diagram showing the method of the present invention. A coated arc welding rod 2 is brought close to the welding base material 7 to generate an arc 5 and form a molten pool 8. In the part where the molten metal 1 and 8 have solidified, weld metal 1 and slag 4 are sequentially formed. From the nozzle 3, a low-level gas (for example, dry carbon dioxide scum) is supplied to surround the arc 5 and create a gas seal)
A ζ region 6 is formed to protect hydrogen components (moisture) in the atmosphere from entering the molten pool 8 and, furthermore, the weld metal 1.

The welding method is to hold the CO7 blowing nozzle in one hand, operate the welding porter with the other hand, and operate the covered rod so that shielding scum is supplied diagonally from the arc generation point. Go.

Experimental Example 1 +3Cr-4N of 5mmφ was prepared by the method shown in Figure 1.
The amount of diffusible hydrogen in the weld metal was measured when an ultra-low hydrogen coated arc welding rod for steel was used. The amount of hydrogen was measured using a gas chroma l-graph method with an extraction time of 48 hours, a welding current of 210A, and a rod operating ratio of 08. The atmospheric atmosphere during welding is (a) (FA degree 20℃ - relative humidity 70
% and (b) The test was carried out under the conditions of a temperature of 30° C. and a relative humidity of 80%. Carbon dioxide sludge shielding was carried out by using a 6 mmφ nozzle and supplying dry carbon dioxide gas at a flow rate of 20 fl/min. A conventional method (comparative example) was carried out under exactly the same conditions as above, except that carbon dioxide shielding was not performed. These results are shown in FIG. 3 (graph).

The filled circles in the graph indicate the measurement results when welding by the conventional method, and the open circles indicate the measurement results when the method of the present invention is used.

As is clear from the graph, in the conventional method without carbon dioxide shielding at low humidity, the amount of diffusible hydrogen in the weld metal increases due to the influence of the atmospheric atmosphere. On the other hand, the method of the present invention shows the same results as X even if the atmospheric atmosphere is changed, and it can be seen that the method is hardly influenced by the atmosphere.

FIG. 4 shows the change in the amount of diffusible hydrogen when the welding current is changed using the same welding rod as above. Note that each mark in the graph is the same as in the above example, and the atmospheric atmosphere has a temperature of 20° C. and a relative humidity of 80%. These results indicate that in the conventional method, the amount of diffusible hydrogen in the weld metal increases as the welding current increases, whereas when using the method of the present invention, the amount of diffusible hydrogen (J) increases even if the welding current increases. A weld metal that is almost unchanged and has a low hydrogen content is obtained.

Experimental Example 2 An experiment similar to Experimental Example 1 was conducted using a commonly used low hydrogen welding rod (LB47 manufactured by Kobe Steel, Ltd.) corresponding to JIS 04316. The measurement results of the amount of diffusible hydrogen are shown in FIG. 5 (graph). A welding rod with a diameter of 4 mm was used, and the atmosphere was set at a temperature of 30° C. and a relative humidity of 80%. As seen in FIG. 5, as in Experimental Example 1, it was revealed that the amount of diffusible hydrogen in the weld metal could be lowered when the method of the present invention was used (white circles).

Similar effects were also obtained when an Illumina l-based welding rod was used.

Experimental Example 3 A U-shaped weld cracking test was conducted in accordance with JIS Z 3157 using 0.05C-12,5Cr-3,8N i cast steel, and the relationship between preheating temperature and cross-sectional crack thickness was investigated. The atmospheric atmosphere is at a temperature of 30°C and a relative humidity of 80%, and in the method of the present invention, a 6 mm nozzle is used to produce 20 fl/min.
low-humidity carbon dioxide gas was supplied around the arc.

Figure 6 (graph) shows the results of the above experiment,
As in the previous example, black circles indicate the measurement results by the conventional method, and white circles indicate the measurement results by the method of the present invention. As is clear from the graph, in the conventional method, cross-sectional cracking was likely to occur when preheating was less than 120°C, whereas in the method of the present invention, no cracking occurred even when welding was performed without preheating.

Further, when the present invention is utilized, there is no need to perform post-heating as well as pre-heating.

The shielding scum used in the present invention is not limited to the carbon dioxide scum in the above example, but low-humidity air may also be used, and the welding workability is higher when using air than when using carbon dioxide gas.

[Effects of the Invention] By using the method of the present invention, hydrogen intrusion from the atmosphere is suppressed and the amount of diffusible hydrogen in the weld metal is reduced, so low-temperature cracking can be prevented even without high-temperature preheating or postheating. A suppressive effect is exerted.

Therefore, the working environment has been improved and welding work can be carried out more efficiently.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing an example of the method of the present invention, Fig. 2 is a graph showing the relationship between welding current and the amount of diffusible hydrogen in the conventional method, and Fig. 3 is a graph showing changes in the atmospheric atmosphere during welding and diffusivity. A graph showing the relationship between changes in the amount of hydrogen, Figure 4 is a graph showing the relationship between changes in welding current and changes in the amount of diffusible hydrogen, and Figure 5 is the amount of diffusible hydrogen when using a welding rod equivalent to JIS D4318. FIG. 6 is a graph showing the relationship between cross-sectional cracking rate and preheating temperature. 1... Welding metal 2... M welding rod 3...
Nozzle 4...Slug 5...Arc
6... Seal 1 Migas 7... Welding base material
8... Molten pool 1, OLn-J's - 缄＄, -Takara-Hipe ■ Ln ++j's N. (a) −+j r to 6 hearts

Claims (1)

[Claims] A coated arc welding method characterized by shielding the periphery of the arc with a low-humidity gas when preheating materials that are prone to low-temperature cracking and welding them using a coated arc welding rod.