JPH027759B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing flux-cored wire for stainless steel, and in particular, to recovery of ductility of flux-cored wire that has been hardened during wire drawing processes and removal of oil, fat, and moisture attached to the surface. The present invention relates to a method for efficiently manufacturing flux-cored wire for stainless steel by electrical annealing, which has good feedability during welding, and provides high-quality weld metal.

For shielding gas welding of stainless steel, solid wire as shown in Figure 1 or flux-cored wire as shown in Figure 2 is generally used, but the former has problems such as oxidation of the bead surface and a decrease in X-ray performance. Due to this problem, the places where it can be applied are limited. On the other hand, the latter method does not have the above-mentioned drawbacks, and it is possible to manufacture wires of various quality by changing the flux composition, so it has the advantage that it can be used depending on the type of base material, etc.

By the way, these wires are fed from a wire reel through a straightening roller and a feeding roller into a conduit tube, and then energized at the welding tip to generate an arc between the welding tip and the base metal before being fed to the welding part. However, in order to stabilize welding conditions and obtain high-quality weld metal, the wire must always be fed at a constant speed. In order to do this, the ductility of the wire, which has hardened during the wire drawing process, is restored so that it can be straightened easily, and the oil, fat (mainly lubricant) and moisture on the wire surface that causes slips are removed as a final product. It must be completely removed during the finishing stage. In particular, flux-cored wires have slightly lower rigidity than solid wires, and it is difficult to completely remove oil and fat from the seams, which often causes problems due to poor feeding. .

In order to deal with such problems, a method has been used in which the drawn flux-cored wire is heat treated to restore the ductility of the casing through the annealing effect and to burn off oil and fat. Such heat treatment methods include the batch method and the strand method, and the batch method is currently the mainstream. This method is
The wire is bundled into a coil and placed in a heating furnace.
Although this method involves heating in an inert gas atmosphere for several hours to several tens of hours, differences in the degree of contact with the atmospheric gas tend to occur because the convection of the inert gas is insufficient. This may cause local deterioration of the flux, or there is a problem that carbon in the oil and fat at the wire overlapping portions is carbonized and mixed into the weld metal, causing weld cracks. Moreover, in the batch type, the temperature inside the furnace is not necessarily uniform, so the annealing effect becomes uneven and the tensile strength tends to vary.
Furthermore, it has been pointed out that the wire buckles at the outlet of the feed roller during welding due to bending caused by bundling.

On the other hand, the strand type heats the pipe indirectly by passing a wire through the pipe, resulting in poor thermal efficiency and extremely low productivity.

The inventors of the present invention have focused on the above-mentioned circumstances and have conducted intensive research in order to develop a method that can efficiently heat-treat flux-cored wire without causing the above-mentioned problems. The present invention was completed as a result of such research, and its structure is such that when manufacturing a flux-cored wire for stainless steel by filling an austenitic stainless steel hoop with flux and then drawing the flux, After the cored wire is drawn to the product diameter, it is passed through multiple power supply rollers and energized, and the wire passing between the electrodes is held at 800 to 1000℃ for 0.05 to 2.0 seconds to conduct current annealing. exists.

The present invention employs an electric heating method to heat the flux-cored wire, which involves heating the wire by bringing it into contact with a power supply roller while running in its axial direction, and generating heat generated inside the wire. It raises the temperature to a certain temperature, and can be heated continuously in an extremely short period of several seconds, resulting in high productivity. Moreover, since the wire is heated uniformly while running in the axial direction, there is no local heating or bending, and a high-quality product wire can be obtained.

FIG. 3 is a conceptual diagram showing an embodiment of the present invention, showing a heat treatment process of a flux-cored wire W that has been drawn to a product diameter. That is, the processing apparatus is composed of a wire feeding section A, a heat treatment section B, and a wire take-up section C. In the feeding section A, the wire W drawn out from the feeding machine 1 is guided to the heat treatment section B through the straightener 2.

The heat treatment section B is divided into a power supply section _B1 and a cooling section _B2 , in which power supply rollers a, b, and c and guide rollers d, e, and f for suppressing wire runout are arranged, respectively.
Power is supplied by the method shown in FIG. The number and arrangement of the power supply rollers and guide rollers, voltage and current adjustment during energization heating, etc. may be appropriately set depending on the composition, diameter, etc. of the wire W (hoop and flux). Further, in the example shown in FIG. 4, the heat treatment temperature of the wire W can be controlled by adjusting the power supplies P ₁ and P ₂ between the power supply rollers a and b and between the power supply rollers b and c. A double tube 3 is arranged in the cooling section _B2 , and the wire W passing through the inner tube is cooled by flowing cold water to the outer tube side, and the wire W at the outlet section is cooled. The temperature is approx.
The length and inner diameter of the double pipe 3 are set so that the temperature is below 300°C. However, the cooling method itself is of course not limited to this, and any indirect cooling method may be used, such as an air cooling method.

The cooled wire W is sent to a take-up section C, passes through a take-up machine 4, and is wound up by a winding machine 5.

The heat pattern in the above heat treatment process is as shown in FIG. 5, for example, but this pattern can be changed arbitrarily by controlling the current supply as described above. The heating conditions may be adjusted depending on the type and amount of deposits, etc. to obtain the optimum heating conditions for burning or evaporating them.

By the way, the present inventors investigated the feed resistance during gas-shielded arc welding using a flux-cored wire using an austenitic stainless steel hoop, and found that it was approximately 3.0 kg under poor conditions. It is recommended to design the wire strength based on the standard. The relationship between the tensile strength and buckling strength of flux-cored wire is as shown in Figure 6. When the wire tensile strength becomes 45 kg/mm ² or less, the buckling strength of the welding wire changes to the maximum resistance (approximately 3.0 It can be seen that if the weight falls below the weight (kg), buckling etc. will occur and feeding problems will occur more easily. Furthermore, FIG. 7 is an experimental graph showing the influence of heating holding time on wire tensile strength at various current heating temperatures.
When the heat treatment temperature becomes high, the tensile strength rapidly decreases even if the temperature is maintained for a short time, making it difficult to adjust the tensile strength.
Therefore, in order to stably obtain a tensile strength of 45 Kg/mm ² or more, the wire heating temperature must be set to 1000°C or less and the heat retention time must be set to 2.0 seconds or less.

On the other hand, the present inventors have confirmed that when the tensile strength of the flux-cored wire exceeds 115 Kg/mm ² , the wire tends to come loose at the wire reel, resulting in poor feeding. Looking at Figure 7 from this perspective, in order to reduce the tensile strength to less than 120Kg/ ^mm2 ,
It is understood that the heating temperature should be at least 800°C and the holding time should be at least 0.05 seconds.

That is, the heat pattern during electrical heating in the present invention is not particularly limited as described above, but from the viewpoint of tensile strength related to the buckling strength of the wire, the upper limits of the heat retention temperature and heat retention time are limited to 1000°C and 2.0 seconds, respectively. On the other hand, from the viewpoint of wire disintegration, which is directly linked to feeding defects, the lower limits of heat retention temperature and time are 800℃ and 800℃, respectively.
Limited to 0.05 seconds. In other words, by setting the electrical heating conditions within the above-mentioned preferred temperature and time, a high quality flux-cored wire for austenitic stainless steel can be obtained stably and with good productivity.

Furthermore, FIG. 8 is a graph of experimental results showing how the amount of hydrogen derived from the lubricating oil, moisture, etc. in the wire changes depending on the heat retention time and heat retention temperature of the wire. Hydrogen in the wire is closely related to welding defects such as blowholes and pinholes, and it has been confirmed that when the amount of hydrogen exceeds 100 ppm, welding defects such as those described above are likely to occur. Within the range of temperature and holding time of electrical annealing described above, the amount of hydrogen is 100 ppm or less, indicating that there is no problem with the amount of hydrogen.

The basic configuration of the present invention is as described above,
In order to further improve the quality of flux-cored wire, it is desirable to take measures that also take into consideration the following problems. That is, the flux-cored wire
As shown in the figure, since it has seams, it is likely to be twisted during the wire drawing process, and its straightness is poorer than that of solid wire. Additionally, cleaning may be performed to roughly remove lubricants etc. prior to heat treatment, but since the lubricant that has entered the hoop joints cannot be sufficiently removed, Lubricants and the like with poor conductivity adhere to and accumulate on the power supply roller. Then, the contact between the power supply roller and the wire becomes poor, causing sparks, causing spark flaws on the surface of the wire, and sometimes even causing wire breakage. If these spark flaws are formed in a protruding manner on the wire surface, the stable feeding of the wire is inhibited and the arc length fluctuates, causing welding defects such as blowholes or sometimes even making feeding impossible.

However, the above problems can be easily solved by the method described below.

That is, as a first measure against sparks, as shown in FIG.
By arranging the straightener 2 and correcting the twist of the wire W and the large bending caused by the bobbin, the straightness of the wire W in the energized heating furnace is improved, and a lubricant removing member is installed inside the straightener 2. Therefore, the lubricant at the wire joints is removed as much as possible, and failures in current conduction are suppressed. Further, as a second means, guide rollers d, e, and f in the energizing heating furnace prevent wire runout during high-speed operation, thereby preventing energization failures caused by wire runout. Furthermore, as a third means,
As shown in Fig. 4, the power supplied between the power supply rollers P ₁ ,
Adjust P ₂ so that P ₁ > P ₂ to quickly burn off the lubricant on the wire surface that prevents conductivity between power supply rollers a and b, and improve the fit between power supply roller b and wire W. This increases contact stability. That is, in the energization heating process, the current i is divided by the power supply roller b into a current _i0 in the direction of the power supply roller a and a current _i1 in the direction of the power supply roller c, so the current flowing through the power supply roller b is the largest and the spark is the most. Since sparks are likely to occur in the roller b portion, if sparks can be suppressed in the power supply roller b portion by the above-described means, sparks in the entire electrical heating system can be substantially eliminated. As described above, in the present invention, by taking the above-mentioned three spark prevention measures, it is possible to carry out electrical heating more stably and efficiently.

The present invention is roughly configured as described above, and since the heat treatment after wire drawing is performed using Joule heat by energizing, the treatment itself is continuous and lubricating oil etc. are almost completely and efficiently removed. Furthermore, it has become possible to produce a flux-cored wire for austenitic stainless steel that has excellent buckling strength and low hydrogen content.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view of a solid wire, Fig. 2 is a cross-sectional view of a flux-cored wire, Fig. 3 is an explanatory view showing an embodiment of the present invention, Fig. 4 is an explanatory view showing a preferred electrical heating method, Figure 5 is a diagram illustrating the heat pattern of electrical annealing, Figure 6 is a graph showing the relationship between the buckling strength of the wire and the tensile strength of the wire, and Figure 7 is a graph showing the relationship between the buckling strength of the wire and the tensile strength of the wire.
The figure is a graph showing the relationship between the tensile strength of the wire and the heat retention time, and FIG. 8 is a graph showing the heat retention time and the effect of the heat retention time on the hydrogen content in the wire. 1... wire feeding machine, 2... straightener, 3...
...Double tube for cooling, 4...Tension machine, 5...Winding device, W...Wire, a, b, c... Current roller, d, e, f... Guide roller.

Claims (1)

[Claims] 1. When manufacturing a flux-cored wire for stainless steel by filling an austenitic stainless steel hoop with flux and then wire-drawing the flux-cored wire, the flux-cored wire is drawn to the product diameter and then passed through a plurality of power supply rollers. 1. A method for manufacturing a flux-cored wire for stainless steel, which comprises applying current to the wire and holding the wire at 800 to 1000°C for 0.05 to 2.0 seconds while passing between electrodes to carry out electrical annealing.