Electric heating – Metal heating – Weld rod composition
Reexamination Certificate
1999-11-12
2002-01-15
Elve, M. Alexandra (Department: 1725)
Electric heating
Metal heating
Weld rod composition
C219S146220, C219S146100, C219S145220, C148S024000
Reexamination Certificate
active
06339209
ABSTRACT:
INCORPORATION BY REFERENCE
Incorporated by reference herein is Godai 4,345,140 relating to a composite electrode containing a flux including a silica and a specific metal oxide with a low melting point of no more 10 than 888° C.; Kotecki 5,120,931 relating to a composite electrode containing a silica containing flux system and a slag releasing agent; Kotecki 4,449,031 relating to a composite electrode containing a zirconium oxide based flux system; and Nishikawa 5,219,425 and Nishikawa 5,378,871 relating to a composite electrode containing a titania flux system and a specific amount of titanium metal and a fluoride.
BACKGROUND OF INVENTION
The invention is applicable to welding of ferrous metals, and particularly to arc welding of stainless steel by a flux cored electrode having at least about 1-30% chromium and it will be described with particular reference thereto; however, the invention has broader applications and may be used for coated electrodes and submerged arc welding of various ferrous metals, high chromium 20 steels, chromium bearing alloys and other types of metal.
When welding a high chromium-bearing alloy such as stainless steel, it is somewhat common practice to weld such metals with a flux cored electrode and to use a shielding gas such as CO
2
during the electric arc welding process. The electrode includes an outer steel sheath surrounding an inner core. The inner core includes a flux system in granular form and, in some instances, includes alloying agents and iron powder. The cored electrode may also include chromium in an appropriate amount, generally as powder within the core of the electrode. The alloying agents are selected so that the formed metal alloy has a similar composition to the workpieces being welded. The core material in the electrode core is generally divided into the fluxing system or flux and the alloying constituents. In a high chromium electrode of the type used for flux cored arc welding of stainless steel, the fluxing system or flux often includes titanium dioxide, silica which may be in the form of a silicate, calcium fluoride and various other non-metallic compounds which react in the arc of the arc welding process to create a slag that forms over the outer surface of the weld bead. The slag is formulated to protect the weld bead until it has solidified and is appropriately joined to the workpiece. This slag also helps in forming the shape of the weld metal in the weld bead as well as protecting the molten alloy material in the weld bead until it has appropriately solidified. Stainless steel and other chromium bearing alloys produce substantial problems in slag formation. The chromium of the steel normally produces a chromium oxide which tends to adhere the nonmetallic slag onto the outer surfaces of the weld bead. As a result, the slag adheres rigidly and tenaciously to the molten alloy of the weld bead as it is solidified. Due to the differential in thermal expansion coefficients, often the slag will be placed in compression and actually explode from the weld bead during cooling of the chromium bearing alloy forming the weld bead. When the slag explodes from the weld bead during the solidification process, the surface of the weld bead is exposed to the atmosphere thus resulting in premature oxidation of the weld metal. In addition, special precautions must be taken to protect against the detrimental effect of exploding hot slag created during the welding process. Another difficulty experienced when welding chromium bearing alloy, and is believed to be also associated with the formation of chromium oxide, is that the weld metal tends to adhere to the slag during the solidification weld bead. If the slag remains on the weld bead during cooling, the slag is extremely difficult to remove, thus resulting in substantial cost and time to grind the slag from the weld bead or otherwise removing the slag from the solidified molten chromium bearing alloy of the weld bead. All of these difficulties in welding chromium bearing alloy are well known in the arc welding art Thus, there is and always has been a need for a particular flux system that does not result in premature and/or violent removal of the slag during the cooling process, while also allowing convenient and inexpensive slag removal after the weld bead containing the chromium bearing alloy has solidified and cooled. Thus, there is a substantial desire for a welding system to be used in a high chromium welding electrode or with a high chromium welding wire which will produce a slag that adheres to the molten metal alloy of the weld bead as it is being solidified for surface protection, but which can be easily removed from the weld bead after the weld bead has cooled.
U.S. Pat. Nos. 4,449,031 and 5,120,931 disclose a flux system which addressed many of the problems associated with slag when welding a chromium containing workpiece. Kotecki 4,449,031 discloses a flux mixture that includes large amounts of zirconium oxide and small amounts of silica which is used in association with a stainless steel electrode to produce a high melting slag during welding. Zirconium oxide is disclosed as the key slag ingredient since it forms a high melting slag which supports the molten weld metal during out-of-position welding. Zirconium oxide is included in the slag mixture in an amount of about 15-60 weight percent of the slag mixture. Titanium oxide is included in the slag mixture to add bulk to the slag. The titanium oxide assists in supporting the molten weld metal during out-of-position welding. Silicon dioxide can be, but is not required to be, added to the slag mixture in an amount of up to 10 weight percent to reduce spatter during welding. Fluorides can also be added to the slag mixture to combat weld porosity, raise the electrode's voltage tolerance during welding and to shield the welding weld metal during welding.
Kotecki 5,120,931 discloses a silica containing slag mixture which primary components are silica and titania and a bismuth slag releasing agent. The slag mixture includes large amounts of silica and small amounts of zirconium oxide. Kotecki 5,120,931 discloses a different approach from Kotecki 4,449,031 to overcome the slag popping and slag removal problems associated with welding chromium containing metals. Kotecki 5,120,931 discloses a high silica-titanium oxide containing slag mixture having significantly less zirconium oxide than the slag mixture of Kotecki 4,449,031. Kotecki 5,120,931 discloses a slag mixture that overcomes the spattering problems of the slag by adding large quantities of silica to the slag mixture. When welding stainless steel having a significant chromium content, the addition of silica in the slag reduces spatter during welding. However, the increased amount of silica adversely affects slag behavior during welding and causes the slag to become difficult to be removed from the weld bead. To overcome this slag adhesion problem, Kotecki 5,120,931 discloses a slag mixture that includes a bismuth slag releasing agent. Kotecki 5,120,931 discloses that a silica content of less than 10 weight percent results in spattering to the weld metal which results in a lower quality weld bead. The silica content of the slag mixture is disclosed as being about 10-80 weight percent. The bismuth slag releasing agent is present in an amount of at least 0.5 weight percent of the slag mixture. Titanium oxide is included in the slag mixture to add bulk to the slag. Zirconium oxide is added to the slag mixture in the amount of 5-20 weight percent. The present invention is an improvement over the slag mixture disclosed in Kotecki 5,120,931 and Kotecki 4,449,031.
SUMMARY OF THE INVENTION
The present invention relates to a flux to be used with a high chromium weld bead, such as a weld bead having over 1.0% chromium and preferably for a stainless steel having greater than 15% chromium, wherein the slag will protect the chromium bearing alloy as it is being solidified subsequent to the welding process, but which can be removed easily after cooling of the chromium bearing alloy in th
Elve M. Alexandra
Lincoln Global Inc.
Vickers Daniels & Young
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