JPS5841948B2 - Austenite silicon stainless steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a welding method with excellent joint ductility, which makes it possible to widen austenitic stainless steel sheets by fusion welding and use them as large plates for deep drawing.

In recent years, products produced by deep drawing austenitic thin stainless steel sheets, typically 18-8 stainless steel (SUS304), have come into widespread use.

However, because there is a limit to the width of thin stainless steel sheets currently produced in Japan, relatively large deep-drawn products,
For example, there are limitations to the production of bathtubs and sinks by deep drawing.

In order to deal with this drawback, a method of manufacturing a large plate by connecting thin stainless steel plates by welding and deep drawing this large plate can be considered, but conventionally, deep drawing was performed using such a welded blank. There is no method to obtain a good deep-drawn product other than the method disclosed in the deep-drawn product using a welded blank and its manufacturing method previously filed by the applicant of this patent.

Generally speaking, when austenitic stainless thin steel sheets are fusion welded without using a filler rod and a tensile test is performed on this welded part, the fusion welded part is
As disclosed in No. 466, arc welding is performed on steel or cast iron in a mixed gas of 1 to 70% nitrogen and 99 to 30% carbon dioxide or argon to create a weld or welded part containing nitrogen. This is because even though the obtained material has a high tensile strength, its ductility decreases and it cannot be used for deep drawing, and it will break at the butt weld.

In other words, the hardness and yield strength of the welded part are slightly higher than that of the base metal, so the initial deformation is smaller than that of the base metal, but once the deformation increases beyond a certain point, the rate of deformation of the welded part suddenly becomes faster ( Eventually, it will break.

Conventionally, welding methods such as TIG welding that does not use a filler rod (welding performed with tungsten as an electrode and covering the welded area with inert gas) and plasma welding have been used for austenitic stainless steel sheets with a thickness of 2.0 mm or less. However, even with such a welding method, if forming is performed, the welded part will break for the reasons mentioned above.

The present inventors have solved this drawback by melt welding thin austenitic stainless steel sheets to obtain a wide thick root, and in order to prevent the thick root from breaking at the welded point when deep drawing the thick root, the ductile The present invention was completed as a result of intensive research into a welding method that yields a welded part with excellent properties, that is, a large elongation at break.

In other words, the inventors first deep-drawed an austenitic stainless steel sheet that had been subjected to TIG welding and plasma welding, and found that the austenitic stainless steel sheet that had been plasma welded had a better deep drawing process than TIG welding. First, we focused on the fact that the welded part is unlikely to break when
As a result of research on plasma welding, we found that increasing the welding speed of plasma welding, that is, increasing the welding current or increasing the hydrogen content in the shielding gas, deteriorates the mechanical properties of the weld and causes problems such as butting during deep drawing. It was found that fractures occur frequently in welded parts.

Therefore, we sought welding conditions that would not deteriorate the mechanical properties of the welded part, especially deep drawability, even if high-speed plasma welding is performed on austenitic thin stainless steel sheets. As a result, we found that the hydrogen gas in the shielding gas of plasma welding does not deteriorate. If nitrogen gas is mixed instead of ※※, the nitrogen gas in the shielding gas will be activated by the high heat of the welding arc and mixed into the molten metal, improving the ductility of the butt weld and making it even easier to perform deep drawing. It has been found that the butt weld does not break even though sufficient elongation can be obtained at the butt weld and a good deep drawn product can be obtained.

If the mixing ratio of nitrogen gas mixed with argon gas in this shielding gas is less than 3%, the amount of nitrogen mixed into the molten metal will be too small and the ductility of the butt weld will not improve much.
If it exceeds 30%, defects such as hot cracks and blowholes will occur in the welded part, so it is necessary to mix nitrogen gas into the shielding gas in a range of 3 to 30%.

In this way, the present invention uses a gas mixture of 3 to 30% nitrogen gas in argon gas as a shielding gas when butt welding thin austenitic stainless steel sheets to widen the joint for deep drawing. The present invention relates to a welding method for austenitic stainless thin steel sheets, which is characterized by joining by plasma welding to improve the ductility of the joint.Experimental examples are shown in the following table to demonstrate this effect.

Shielding gas: Protective gas flowing around the center gas Base material: Steel type 5US304, plate thickness 1. mm Breaking elongation of base metal 160% Tensile test piece: JI No. 85 test piece, gauge distance 50 mrI
L tensile test speed: 30mm/1ni! Judgment: The elongation of the butt weld at break is 40% or more.

As is clear from this table, in conventional plasma welding using a mixture of hydrogen gas in argon gas as a shielding gas, the butt weld breaks at an elongation of approximately % of the elongation of the base metal. Welding blanks could not be used as blanks for deep drawing due to the poor joint ductility of butt welds, but the present invention's plasma method uses a mixture of argon gas and nitrogen gas as a shielding gas. When welding, it has almost the same strength as the base metal, and as shown in the drawing, when high current is not used, the elongation approaches the fracture elongation of the base metal, so welding blanks are used as blanks for deep drawing. However, there is no fear of breakage at the butt weld, so it can be used satisfactorily.

As detailed above, the welding method for austenitic thin stainless steel sheets according to the present invention is a method for welding thin austenitic stainless steel sheets by butt welding to form a joint in which the elongation of the welded portion is close to the elongation of the base material and has sufficient joint ductility. Since this is a welding method that can form a large plate formed by implementing the method of the present invention, for example, a large bathtub or a large sink can be drawn in one piece, producing products that could not be manufactured by conventional drawing processes. As with stainless steel bathtubs, which have become rapidly popular in recent years, the bottom plate, body plate, and upper edge had to be made separately and these parts were joined by welding. The industrial value of the present invention is extremely large, since it enables products that could not be obtained to be manufactured easily and inexpensively and quickly.

[Brief explanation of drawings]

The drawings show the fracture elongation of the welded part of 5US304 material plasma welded using a conventional shielding gas consisting of 6% H2 + 94% Ar, and the fracture elongation of the welded part of 5US3 material plasma welded using the shielding gas according to the present invention, which is better than 10% N2 + 90% Ar.
FIG. 2 is a diagram showing the relationship between the elongation at break of a welded portion of 04 material and welding current. A: Welded part of 5US304 material joined by the method of the present invention,
B: Welded part of 5US304 material joined by conventional method.

Claims (1)

[Claims] 1 When butt welding thin austenitic stainless steel sheets together to widen the joint for deep drawing, plasma welding is performed using a mixture of 3 to 30% nitrogen gas in argon gas as a shielding gas. A method for welding thin austenitic stainless steel sheets, which is characterized by joining to improve the ductility of the joint.