JPS6347550B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an automatic welding method, specifically, a carbon content
This invention relates to an automatic welding method for overlay welding on steel or cast iron with a content of 1.3% by weight or more and 2.4% by weight or less. (Prior Art) Generally, rolling rolls used in steel mills and the like are required to have strength and wear resistance at high temperatures. For this reason, many high carbon cast steel, forged steel, and cast and forged adamite roll rollers with a carbon content of 1.0% by weight or more and 2.4% by weight or less are used as such rolling rolls. When such a roller is damaged or worn, it is desirable to repair or restore it by overlay welding, but cracks occur when overlay welding is performed using automatic welding. There are two types of such cracks, one of which is a crack that occurs at the weld boundary and heat-affected zone, where the weak ledebrite structure generated by welding heat cannot resist shrinkage stress. Measures to prevent such cracking are already known, such as preheating during welding to lower the interlaminar temperature.
This method involves raising the temperature to 300℃ or higher and slowly cooling it after welding is complete. Another type of cracking occurs in the weld metal, and when automatic welding is performed using conventional methods, it becomes noticeable when the carbon content of the base metal exceeds 1.3% by weight. (Problems to be Solved by the Invention) However, there is still no known measure to prevent such cracks from occurring in weld metal. As a result, there was a problem in that rollers with such a high carbon content could not be overlay-welded by automatic welding. Therefore, the present invention solves these problems and provides automatic overlay welding that does not cause cracks in the weld metal even when automatically overlaying a rolled roll roller or an adamite roll roller with a high carbon content. The purpose is to provide a welding method. (Means for Solving the Problem) In order to achieve the above object, the present invention provides an automatic welding method for overlay welding on steel or cast iron having a carbon content of 1.3% by weight or more and 2.4% by weight or less, and By using mild steel or low-alloy steel welding materials on steel or cast iron, we control the penetration of the base metal into the weld metal according to the carbon content of the base metal, and automatically perform overlay welding on the lower layer of overlay welding. , a first step of reducing the carbon content in the weld metal to 0.7% by weight or less, and a second step of automatically overlaying an overlay welding layer having a predetermined composition on the lower overlay welding layer. This is an automatic welding method characterized by the following features: (Example) Hereinafter, an example of the present invention will be described based on the drawings. FIG. 1 is a diagram showing an embodiment of an automatic welding method according to the present invention. First, the configuration will be explained. In Fig. 1, 1 is a base material, and this base material 1
is made of steel or cast iron with a carbon content of 1.3% by weight or more and 2.4% by weight or less. This base material 1 is, for example,
In the case of mill rolls, the steel or cast iron is high carbon cast steel, forged steel and cast and forged adamite. In the present invention, the carbon content of the base material 1 is set to 1.3% by weight or more and 2.4% by weight or less because if the carbon content of the base material is less than 1.3% by weight, under general automatic welding conditions, the carbon content in the weld metal is This is because cracks do not occur in the steel, and if it exceeds 2.4% by weight, it cannot be used as a roller. Generally, when overlay welding is performed, the surface layer of the base material 1 and the welding material melt and melt into each other.
In the present invention, the amount of penetration of the base metal 1 into the weld metal is expressed as a dilution ratio (α). Here, the dilution ratio refers to the ratio of the cross-sectional area of the melted metal of the base metal 1 to the cross-sectional area of the entire weld metal constituting the lower layer 3 of overlay welding, and the groove 2 is schematically shown in Fig. 1. The layer portion A located below the broken line is shown as the penetration amount of the base metal, and the layer portion B located above the broken line indicating the groove 2 is shown as the penetration amount of the welding material, and the dilution rate (α)
is calculated using the following formula. α=(A/A+B)×100(%) In this formula, to determine A and B, the test piece after the first process of automatic welding is placed in the transverse direction, that is, in the direction perpendicular to the welding direction. After cutting the cross section into sections and polishing it to make it smooth, a corrosion test is performed using a corrosive solution such as nitric alcohol. This allows the boundary line between the overlay welding lower layer 3 and the base metal 1 to be clearly identified. Next, the groove 2 (the shape of the base material before welding) is drawn on the above-mentioned cross section to define the boundary line between A and B, and the area of each of A and B is actually measured as the sum of the subdivided rectangular cross sections. In reality, the welding material and the base metal 1 melt and melt into each other as described above, but the dilution rate determined in the above manner substantially reduces the amount of penetration of the base metal 1 into the lower weld layer 3. It will be as shown below. The dilution rate is, for example, about 40% in the case of automatic welding without preheating, and about 50% in the case of automatic welding in which the base material 1 is preheated to 300° C. or higher. To carry out the first step of overlay welding, a groove 2 is first formed in the damaged portion of the base material 1 as shown by the broken line in FIG. Next, using a mild steel or low alloy steel welding material, the lower layer 3 is automatically overlaid by controlling the dilution rate according to the carbon content of the base metal 1 using an automatic welding machine. , the carbon content in the weld metal is 0.7% by weight or less. At this time, in order to reduce the carbon content in the weld metal to 0.7% by weight or less, the higher the carbon content of the base metal 1, the smaller the dilution rate. control so that it is reduced. The overlay welding lower layer 3 may be overlay welded by any welding method such as submerged arc welding, MIC welding (metal inert gas arc welding), or carbon dioxide gas welding, but in order to reduce the dilution rate, Effective methods include reducing the welding current and performing weaving during welding. The amount of penetration of the base metal 1 into the lower layer 3 of overlay welding increases when the digging action of the arc is large, so in order to reduce the dilution ratio, the welding current is reduced to reduce the digging action of the arc. . Weaving refers to moving the electrode in a zigzag pattern during welding. In the normal method of advancing the electrode straight, the arc always moves toward the new base metal and continues the digging action, but with weaving, the arc moves into the molten metal rather than the base metal 1. Since the occurrence rate increases and the digging action on the base metal 1 decreases, the amount of penetration of the base metal 1 into the lower layer 3 of overlay welding decreases. That is, the dilution rate becomes smaller. Next, as a second step, on the overlay welding lower layer 3,
The overlay welding upper layer 4 having a predetermined composition is overlay welded by automatic welding. Next, the effect will be explained. In this embodiment, in the first step of automatic welding, a base material such as a rolling roll, etc.
Base metal 1 using mild steel or low alloy steel welding material
The overlay welding lower layer 3 is automatically overlay welded by controlling the dilution rate (α) as described above according to the carbon content (1.3 to 2.4% by weight). Therefore, even if the base material 1 has a high carbon content such as a rolling roll, the carbon content of the overlay welding lower layer 3 is suppressed to 0.7% by weight or less. As a result, cracks do not occur in the weld metal, that is, in the overlay welding lower layer 3. When the carbon content of the overlay weld lower layer 3 exceeds 0.7% by weight, cracks occur in the weld metal as shown by the data (Comparative Examples 1 to 6) described below. The reason for this is
As the carbon content in the weld metal approaches the eutectoid point, brittle cementite precipitates within the weld metal, and when this cementite cools from high temperature to room temperature, it cannot resist shrinkage stress and cracks occur. considered to be a thing. Next, experimental examples of the present invention and comparative examples will be explained. First, carbon content ranges from 1.35% to 2.38% by weight
A plurality of base materials 1 were prepared. Next, an overlay lower layer 3 was automatically overlay welded onto the groove 2 of this base metal 1 while variously changing the welding means and welding conditions. The results are shown in Table 1.

[Table] In Table 1, the carbon content (weight %) of the overlay welding lower layer 3 was calculated using the formula shown below. Dc = Mc × α / 100 + Wc (1 - α / 100) where, Dc: Carbon content of the lower layer of overlay welding (%) Mc: Carbon content of base metal (%) α: Dilution rate (%) Wc: Welding Carbon content of material (%) Figure 2 plots the results in the table above, with the dilution rate on the vertical axis and the carbon content of base material 1 on the horizontal axis. , ○ indicates that no cracking occurred. From FIG. 2, it can be seen that in order to prevent cracking, the higher the carbon content of the base material 1, the lower the dilution rate must be. In addition, in Fig. 3, the vertical axis shows the overlay welding lower layer 3.
The results in the above table are plotted, with the carbon content of the base material 1 plotted on the horizontal axis, and the x marks indicate those with cracks, and the ○ marks indicate those with no cracks. From this figure 3, the carbon content of base material 1 is
In the range of 1.3% by weight or more and 2.4% by weight or less, the carbon content in the weld metal of the overlay welding lower layer 3 is
It can be seen that cracks do not occur when the content is 0.7% by weight or less. In the above embodiment, the case where the roller is repaired by removing the bevel has been explained, but in order to restore the wear of the roller, as shown in FIG. While rotating the material 1, the lower layer 3 of overlay welding is automatically welded over the entire surface in a spiral manner, and then the upper layer 4 of overlay welding is automatically welded on the lower layer 3 of overlay welding. Mold welding may also be used. (Effects of the Invention) As explained above, according to the method of the present invention, even when automatically overlay welding is performed on rolling roll rollers, adamite roll rollers, etc. with high carbon content,
No cracks will occur in the weld metal.

[Brief explanation of drawings]

Figures 1 to 5 are diagrams showing an embodiment of the automatic welding method according to the present invention. Figure 1 is a cross-sectional view of the welded part, and Figure 2 is the relationship between the dilution rate and the carbon content of the base material. Figure 3 is a graph showing the relationship between the carbon content of the lower layer of overlay welding and the carbon content of the base metal.
FIG. 4 is a photographic cross-sectional view of the weld metal of Experimental Example 2 in Table 1, FIG. 5 is a photographic cross-sectional view of the weld metal of Experimental Example 6 in Table 1, and FIG. FIG. 7 is a sectional view of a welded portion showing another example. 1... Base metal, 2... Groove, 3... Lower layer of overlay welding, 4... Upper layer of overlay welding.

Claims (1)

[Claims] 1 Automatic welding of overlay welding to steel or cast iron with a carbon content of 1.3% by weight or more and 2.4% by weight or less, using a mild steel or low alloy steel welding material to remove carbon from the base material. The first step is to reduce the carbon content in the weld metal to 0.7% by weight or less by automatically overlaying the lower layer of overlay welding by controlling the penetration of the base metal in the weld metal according to the carbon content. , a second step of automatically overlaying an overlay welding layer having a predetermined composition on the lower overlay welding layer.