JPH04333394A - Production of flux cored wire for welding - Google Patents

Abstract

PURPOSE:To improve productivity by omitting a heat treating stage in the drawing process of the flux cored wire for welding. CONSTITUTION:A thin steel strip contg. <=0.01wt.% C is used as a thin steel strip enclosing a welding flux and after molding of this thin steel strip, both ends of the steel strip are so welded that the difference HV between the max. hardness in a weld zone and the min. hardness in a non-weld zone attains <=40.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the manufacture of arc welding flux cored wire containing welding flux, which is used in gas shielded arc welding.

0002

[Prior Art] Regarding welding flux cored wires, for example, as disclosed in Japanese Patent Laid-Open No. 63-115697, a metal strip is curved and filled with welding flux, and both ears of the metal strip are filled with welding flux. A method in which the metal strips are brought into contact with each other and then wire drawn, a method in which the abutting portions of the metal strips are filled with welding flux and then welded and wire drawn as disclosed in JP-A-56-148494; Generally, a method is adopted in which a metal strip is formed in advance to form a steel pipe body, and the steel pipe body is filled with flux.

Among the above-mentioned conventional techniques, Japanese Patent Application Laid-Open No. 1983-11
The technique disclosed in 5697 has the advantage that the wire manufacturing procedure is relatively simple and the manufacturing cost is low. However, since the two ends of the steel strip are simply butted together, flux easily spills and the wire is easily twisted. The aim accuracy was poor, and it also had the disadvantage of easily absorbing moisture. These drawbacks are fatal in automatic welding using modern robots, and when Cu plating is applied to improve electrical conductivity, it is difficult for pickling solution or plating solution to penetrate through the butt joints. Since this is unavoidable, it has been impossible to manufacture wires with Cu plating. From this point of view, in the flux cored wire for welding,
Ideally, a method of welding the butt portions of metal strips as disclosed in Publication No. 148494 would be ideal.
At present, simply following the conventional techniques inevitably leads to an increase in manufacturing costs, as described below, and is not suitable for industrial production.

[0004] In other words, in a type of wire in which the butt portions of steel strips that envelop flux are welded, the welded portion is rapidly heated and cooled, so that the base metal material portion (hereinafter simply referred to as the non-welded portion) is a non-welded portion. ) has higher hardness. Furthermore, the weld zone consists of the molten and solidified weld metal and the unmelted heat-affected zone, which is affected by heat, but in welding without filler metal, the weld metal and the heat-affected zone have the same hardness; Even if we tried to soften the weld metal using a new material, the heat-affected zone would inevitably become harder, so in any case, there would be a part that was harder than the base metal.

[0005] Microscopically, the presence of a high hardness portion in the steel strip surrounding the flux brings about a significant disadvantage in the wire drawing process. That is, during the wire drawing process, shear stress was generated at the boundary between the high-hardness part and the low-hardness part due to the difference in plastic deformability between the high-hardness part and the low-hardness part, which inevitably caused microscopic longitudinal cracks. These vertical cracks are observed not only near the boundary between welded and non-welded parts, but also inside welded parts. The original purpose of seam welding could not be achieved using flux-cored wire. Therefore, wire manufactured by such a method requires heat treatment such as intermediate annealing or intermediate normalization to be performed multiple times during the wire drawing process, which causes high costs. Furthermore, the heat treatment described above also had the disadvantage of poor arc stability due to the deterioration of the included flux.

[0006]

[Problem to be Solved by the Invention] When manufacturing a flux cored wire for welding by applying a method of welding the end of a steel strip surrounding flux, it is possible to improve wire drawability without performing intermediate heat treatment. It is an object of this invention to propose a method by which wires of good quality can be obtained.

[0007]

[Means for Solving the Problems] The present invention involves sequentially forming a thin steel strip enclosing welding flux into a U-shape and an O-shape using forming rolls, supplying welding flux before the completion of the forming, and then supplying the welding flux. When wire drawing is performed on the filled steel pipe body, the above thin steel strip is C: 0.
．． By using a low carbon thin steel strip of 0.01 wt% or less,
After completing the O-forming of this thin steel strip, welding is applied to the joint portion of the steel strip, and the difference between the maximum hardness of the joint portion after welding and the minimum hardness of the non-welded portion of the steel strip is 40 in terms of Vickers hardness. This is a method for manufacturing a flux-cored wire for welding, which is adjusted as follows to omit intermediate treatment in wire drawing.

[0008]

[Action] C: 0.001 to 0.050 wt%, Mn
:0.1wt%, and other optional components such as Nb:
0.1 wt%, Ti: 0.008 wt%, the balance is Fe and unavoidable impurities, thickness 1.5 mm
Using several types of thin steel strips, this is sequentially formed into U-shape and O-shape, and finished into a steel pipe with a diameter of 15 mm, and before the forming is completed, a so-called luteal-based molten flux containing TiO2 as the main component is supplied. At the same time, high-frequency electric resistance welding is applied to the ends of the steel strips to join them (impederless, welding current 10.2A, welding voltage 15.8kV, frequency 330).
kHz), and the steel pipe body filled with the flux was then drawn with a die without intermediate annealing. The difference in minimum hardness of non-welded parts and the limit wire drawing speed were also investigated. The results are shown in Figure 1. The hardness of the welded portion and non-welded portion was measured using a micro Vickers meter with a load of 300 g or less at a measurement pitch of 0.3 mm.

As shown in FIG. 1, the drawability of wires that are welded depends strongly on the difference ΔHv between the hardness of the welded part and the hardness of the non-welded part, and if the difference ΔHv is 40 or less, intermediate heat treatment is not required. Even without this, the generation of microscopic shear stress due to the difference in plastic deformability becomes extremely small, and wire drawability can be significantly improved. ΔHv above
There is a strong correlation between the C content of the steel strip and the C content of the steel strip.
The content was adjusted to 0.01 wt% or less. In addition, in this invention, a welding method etc. are not specifically limited.

0010

[Example] Various low C content steel strips (thickness 1
．． 1mm), welded the ends of the steel strips while wrapping the welding flux in each steel strip to a diameter of 15mm.
Finished into a steel pipe of 1.2 m in diameter, and then drawn into a wire.
Finished with mφ wire. Welding method of each wire, ΔHV
Table 1 shows a comparison of wire drawing limits. In addition, high frequency electric resistance welding and TIG welding are applied for welding, and the conditions for electric resistance welding are a frequency of 335 kHz, a welding current of 10.1 A, and a welding voltage of 15.6 kV, and with an impeder, a frequency of 340 kHz and a welding current of 10 A. , welding voltage 15
．． The condition is 8kV, and the current for TIG welding is 200A.
The conditions were a voltage of 11 V and a speed of 4 m/min.

[0011]

[Table 1]

[0012] In Table 1, No. 1-3, No. 6
~8 and no. 11 to 13 are suitable examples, and good wire drawability is obtained by using a steel strip with a C content of 0.01 wt% or less and performing welding such that ΔHV is 40 or less when welding the step part of the steel strip. It was confirmed that it was possible to secure the

[0013]

Thus, according to the present invention, high-speed wire drawability can be significantly improved without performing intermediate heat treatment, and wires of good quality can be efficiently produced.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between ΔHV and wire drawing speed of a welding flux cored wire.

Claims (1)

[Claims] Claim 1: A thin steel strip enclosing welding flux is sequentially formed into a U-shape and an O-shape using forming rolls, and before the forming is completed, welding flux is supplied, and then the flux is stretched into a steel pipe body filled with the flux. When performing wire processing, by using a low carbon thin steel strip with C: 0.01 wt% or less as the thin steel strip, after the O-forming of this thin steel strip is completed, welding is performed on the joint portion of the steel strip, For welding, the difference between the maximum hardness of the mating part after welding and the minimum hardness of the non-welded part of the steel strip is adjusted to 40 or less in terms of Vickers hardness, and intermediate heat treatment in wire drawing is omitted. A method for producing flux fucored wire.