Carbon to weld metal

Information

  • Patent Application
  • 20080011731
  • Publication Number
    20080011731
  • Date Filed
    July 11, 2006
    18 years ago
  • Date Published
    January 17, 2008
    17 years ago
Abstract
Various flux compositions for increasing carbon contents in welds are disclosed. The flux compositions can be provided in a variety of different forms such as in an agglomerated form, fused form, sintered form, or provided as a coating. The fluxes are particularly adapted for use in submerged arc welding processes.
Description
PREFERRED EMBODIMENTS

The present invention provides various strategies for increasing carbon contents in welds. Preferably, the strategies enable selective carbon contents to be obtained in welds and in a controllable fashion. The strategies are particularly directed to submerged arc welding.


In accordance with the present invention, selectively controllable carbon contents in weld deposits can be achieved by incorporating (i) one or more carbon additives and/or (ii) one or more carbon-bearing agents in a flux. The flux can be in a variety of different forms such as a flux coating composition, an agglomerated flux, a fused flux, and/or a sintered flux. The flux can be utilized in a cored electrode or as a separate free flowing flux composition used in a submerged arc welding process. The present invention provides techniques for increasing carbon content in a weld by utilizing the fluxes described herein in an electrode or as a free flowing flux in a submerged arc welding process.


Non-limiting examples of carbon additives include graphite, carbon black, high carbon, vitreous carbon, pyrolytic graphite, hexagonal graphite, diamond, and combinations thereof. If carbon black or graphite is used, a wide variety of different types of commercially available carbon black or graphite can be used.


Examples of suitable commercially available carbon blacks and graphite include those available from Southwestern Graphite of Burnet, Tex.; KETJEN BLACK® from Armak Corp.; VULCAN® XC72, VULCAN® XC72, BLACK PEARLS 2000, and REGAL 250R available fro Cabot Corporation Special Blacks Division; THERMAL BLACK® from RT Van Derbilt, Inc.; Shawinigan Acetylene Blacks available from chevron chemical Company; furnace blacks; ENSACO® Carbon Blacks and THERMAX carbon Blacks available from R.T. Vanderbilt Company, Inc.; and GRAPHITE 56-55.


As noted, the preferred embodiment fluxes can contain one or more carbon-bearing agents. The term “carbon-bearing agent” as used herein refers to an agent that contains carbon, however in chemically bound form. Carbon-bearing agents release carbon upon decomposition of the agent when exposed to high temperatures of the welding environment. Preferably, all or a portion of the flux or flux agent includes, or is coated or otherwise associated with a carbon-bearing agent. Non-limiting examples of such carbon-bearing agents include polytetrafluoroethylene (PTFE) and its various grades. Additional examples of preferred carbon-bearing agents include, but are not limited to, polyethylene, bakelite, or other hydrocarbons. Polytetrafluoroethylene, typically referred to as Teflon™ is in small, particulate powder form, so it can be evenly distributed throughout the flux composition or coating. Teflon™ has a tendency to be consumed by a burning action during welding. The high temperatures cause the polytetrafluoroethylene to disassociate and produce elemental carbon at the weld site.


In a particularly preferred embodiment, from about 0.1 to about 10% (by weight of the flux composition), more preferably from about 0.5 to about 8%, and most preferably from about 1 to about 2% PTFE is added to a flux cored electrode or to a free flowing flux composition. Preferred PTFE carbon-bearing agents for incorporation in the welding consumables described herein include, but are not limited to, unfilled PTFE, carbon filled PTFE, graphite filled PTFE, and combinations thereof. It is also preferred to utilize PTFE in a flux coating composition.


The various fluxes described herein can utilize (i) carbon additives alone, (ii) carbon-bearing agents alone, (iii) a combination of carbon-bearing agents and carbon additives, and (iv) a combination of carbon-bearing agents, carbon additives, and other carbon sources. For compositions of types (iii) and (iv), the ratio of carbon additives to carbon-bearing agents can range from about 0.01:100 to about 100:0.01 parts by weight respectively, more preferably about 0.1:10 to about 10:0.1, and in certain applications about 1:5 to about 5:1.


The total carbon content of the preferred embodiment fluxes ranges from about 0.01 to about 0.6% by weight of the flux. The specific carbon content is generally dictated by the end use application and by estimating transfer losses. For example, if a weld metal carbon content of 0.25% is desired, and if transfer loss is estimated to be 50%, then the carbon content of the flux is 0.5%. Alternately, if a 30% transfer is estimated and a weld metal carbon content of 0.18% is desired, the flux carbon content is 0.6%. The foregoing is based upon a system in which the flux is the only source of carbon. In the event that carbon is present in other welding feed sources, the calculations are adjusted accordingly.


The carbon additives and/or carbon-bearing agents can be incorporated in an agglomerated flux in which flux particles are dispersed within a binder. Alternatively, the carbon additives and/or carbon-bearing agents can be incorporated in a fused flux. Generally, for fused fluxes, the carbon additives and/or carbon-bearing agent can be added after fusing. Moreover, the carbon additives and/or carbon-bearing agents can be incorporated in a sintered flux.


As noted, the preferred embodiment fluxes can be utilized in a welding electrode such as a cored electrode. And, the preferred embodiment fluxes can be utilized in a separate free flowing flux such as used in a submerged arc welding process.


The preferred embodiment flux cored electrode includes a filling composition that enhances the deposition of the metal onto a workpiece and facilitates in obtaining the desired deposited metal composition. The filling composition typically includes, by weight percent of the electrode, about 5-15 weight percent slag system and the balance alloying agents. In one specific embodiment, the filling composition constitutes about 20-50 weight percent by electrode and includes, by weight percent of the electrode, about 8-12 weight percent slag system and the balance alloying agents.


In yet another preferred embodiment, the present invention provides a technique for increasing carbon content in a weld by incorporating iron powder, reground slag, or both, which can contain relatively high amounts of carbon into a welding consumable, and specifically, into the flux portion thereof. In certain applications, the various preferred embodiment fluxes described herein can include iron powder, reground slag, or both.


The preferred embodiment flux composition is particularly adapted for use in submerged arc welding processes, where high strength properties are desired. Generally, in such an application, a bare wire or stick electrode is fed to a workpiece. A separate flux feed, as described herein, is provided at or ahead of the electrode to generate protective gases and slag, and to optionally add alloying elements to the weld pool. Shielding gas is generally not required.


The preferred embodiment fluxes for submerged arc welding can be in a variety of forms for example, the fluxes can be in a fused form, a sintered form, or an agglomerated form. In addition, these flux compositions, or conventional flux compositions can be coated with the fluxes described herein.


In forming a fused flux, the flux ingredients are mechanically mixed with each other and the mixture is placed in a graphite crucible and heated until it melts. After heating the molten mixture for about 20 more minutes to insure complete fusion, it is quenched to room temperature and then ground and crushed to the desired granular size.


In forming a sintered flux, the sintering technique comprises making a mechanical mixture of the flux ingredients and heating in an oven at about 1650° F. for about 1½ hours. The mixture is then cooled, crushed, screened to obtain the desired particle distribution and used in the same manner as the fused material.


In forming an agglomerated flux, the flux can be prepared by a bonding technique in which the flux agents are combined with a binder (such as for example sodium silicate solution) in a ratio of about one part of binder to forty parts of the flux mixture. The mass is then heated to about 900° F. for 3 hours or more, crushed and screened to obtain the desired granular size.


Alternately, a preferred embodiment agglomerated flux is made by dry blending powders. The powders which are dry blended are generally sufficiently fine so as to pass through a 149 micrometer screen. After being thoroughly dry blended, an aqueous binder such as containing alkali metal silicate and a carbohydrate (e.g. invert sugar) is added to the dry blended ingredients. The dry and wet ingredients are then thoroughly blended and baked in air at about 480° to 540° C. for about 1-3 hours. After baking, the flux is removed from the baking equipment and crushed to convenient size.


The various flux compositions described herein can be specifically tailored to be basic, acidic, and/or neutral. Of the constituents set forth in the base flux, magnesium oxide, aluminum oxide and calcium fluoride are the typical components. The other materials used in the preferred embodiment, include the carbon additives, carbon-bearing agents, and other components dictated by the specific, end use application. Various modifications of the primary constituents and the remaining constituents can be made.


The raw materials used to prepare the flux of the present invention are preferably of the usual commercial purity, however incidental impurities that do not affect the function of the welding flux appreciatively may be present. The raw materials are preferably of a particle size that will pass through a 400-mesh screen.


The preferred embodiment fluxes, if in an agglomerated, fused, or sintered form, are preferably in a particulate or granular form. Although any particle size or size range can be used, it is generally preferred that the flux particles are of a size such that they can pass through a 10 US mesh size screen, more preferably a 12 US mesh size screen, and most preferably a 20 US mesh size screen.


Additional details of arc welding materials and specifically, cored electrodes for welding are provided in U.S. Pat. Nos. 5,369,244; 5,365,036; 5,233,160; 5,225,661; 5,132,514; 5,120,931; 5,091,628; 5,055,655; 5,015,823; 5,003,155; 4,833,296; 4,723,061; 4,717,536; 4,551,610; and 4,186,293; all of which are hereby incorporated by reference. Additional details of submerged arc welding processes, materials, and flux compositions are provided in U.S. Pat. Nos. 5,300,754; 5,004,884; 4,764,224; 4,675,056; 4,561,914; 4,500,765; 4,436,562; 4,338,142; and 4,221,611.


The foregoing description is, at present, considered to be the preferred embodiments of the present invention. However, it is contemplated that various changes and modifications apparent to those skilled in the art, may be made without departing from the present invention. Therefore, the foregoing description is intended to cover all such changes and modifications encompassed within the spirit and scope of the present invention, including all equivalent aspects.

Claims
  • 1. A free-flowing flux adapted for use in submerged arc welding, the flux being an agglomerated flux, the agglomerated flux including at least one of (i) carbon additives, (ii) carbon-bearing agents, and (iii) combinations thereof, the total carbon content in the flux ranging from about 0.01 to about 0.6% by weight.
  • 2. The flux of claim 1 wherein the carbon additive is selected from the group consisting of graphite, carbon black, high carbon, vitreous carbon, pyrolytic carbon, hexagonal graphite, diamond, and combinations thereof.
  • 3. The flux of claim 1 wherein the carbon-bearing agent is polytetrafluoroethylene (PTFE).
  • 4. The flux of claim 3 wherein the flux includes from about 0.1 to about 10% PTFE by weight of the flux.
  • 5. The flux of claim 4 wherein the flux includes from about 0.5 to about 8% PTFE by weight of the flux.
  • 6. The flux of claim 5 wherein the flux includes from about 1 to about 2% PTFE by weight of the flux.
  • 7. The flux of claim 3 wherein the PTFE is selected from the group consisting of unfilled PTFE, carbon filled PTFE, graphite filled PTFE, and combinations thereof.
  • 8. The flux of claim 1 wherein the flux further includes (i) iron powder containing carbon, (ii) reground slag containing carbon, and (iii) combinations thereof.
  • 9. The flux of claim 1 wherein the flux is in the form of particles having a size such that the particles pass through a 400-mesh screen.
  • 10. A free-flowing flux adapted for use in submerged arc welding, the flux being fused flux, the fused flux including at least one of (i) carbon additives, (ii) carbon-bearing agents, and (iii) combinations thereof, the total carbon content in the flux ranging from about 0.01 to about 0.6% by weight.
  • 11. The flux of claim 10 wherein the carbon additive is selected from the group consisting of graphite, carbon black, high carbon, vitreous carbon, pyrolytic carbon, hexagonal graphite, diamond, and combinations thereof.
  • 12. The flux of claim 10 wherein the carbon-bearing agent is polytetrafluoroethylene (PTFE)
  • 13. The flux of claim 12 wherein the flux includes from about 0.1 to about 10% PTFE by weight of the flux.
  • 14. The flux of claim 13 wherein the flux includes from about 0.5 to about 8% PTFE by weight of the flux.
  • 15. The flux of claim 14 wherein the flux includes from about 1 to about 2% PTFE by weight of the flux.
  • 16. The flux of claim 12 wherein the PTFE is an agent selected from the group consisting of unfilled PTFE, carbon filled PTFE, graphite filled PTFE, and combinations thereof.
  • 17. The flux of claim 10 wherein the flux further includes (i) iron powder containing carbon, (ii) reground slag containing carbon, and (iii) combinations thereof.
  • 18. The flux of claim 10 wherein the flux is in the form of particles having a size such that the particles pass through a 400-mesh screen.
  • 19. A free-flowing flux adapted for use in submerged arc welding, the flux being a sintered flux including at least one of (i) carbon additives, (ii) carbon-bearing agents, and (iii) combinations thereof, the total carbon content in the flux ranging from about 0.01 to about 0.6% by weight.
  • 20. The flux of claim 19 wherein the carbon additive is selected from the group consisting of graphite, carbon black, high carbon, vitreous carbon, pyrolytic carbon, hexagonal graphite, diamond, and combinations thereof.
  • 21. The flux of claim 19 wherein the carbon-bearing agent is polytetrafluoroethylene (PTFE)
  • 22. The flux of claim 21 wherein the flux includes from about 0.1 to about 10% PTFE by weight of the flux.
  • 23. The flux of claim 22 wherein the flux includes from about 0.5 to about 8% PTFE by weight of the flux.
  • 24. The flux of claim 23 wherein the flux includes from about 1 to about 2% PTFE by weight of the flux composition.
  • 25. The flux of claim 21 wherein the PTFE is an agent selected from the group consisting of unfilled PTFE, carbon filled PTFE, graphite filled PTFE, and combinations thereof.
  • 26. The flux of claim 19 wherein the flux further includes (i) iron powder containing carbon, (ii) reground slag containing carbon, and (iii) combinations thereof.
  • 27. The flux of claim 19 wherein the flux is in the form of particles having a size such that the particles pass through a 400-mesh screen.
  • 28. A free-flowing flux adapted for use in submerged arc welding, the flux including a coating composition, wherein the coating composition includes at least one of (i) carbon additives, (ii) carbon-bearing agents, and (iii) combinations thereof, the total carbon content in the coating composition ranging from about 0.01 to about 0.6% by weight.
  • 29. The flux of claim 28 wherein the carbon additive is selected from the group consisting of graphite, carbon black, high carbon, vitreous carbon, pyrolytic carbon, hexagonal graphite, diamond, and combinations thereof.
  • 30. The flux of claim 28 wherein the carbon-bearing agent is polytetrafluoroethylene (PTFE)
  • 31. The flux of claim 30 wherein the flux includes from about 0.1 to about 10% PTFE by weight of the flux.
  • 32. The flux of claim 31 wherein the flux includes from about 0.5 to about 8% PTFE by weight of the flux.
  • 33. The flux of claim 32 wherein the flux includes from about 1 to about 2% PTFE by weight of the flux.
  • 34. The flux of claim 30 wherein the PTFE is an agent selected from the group consisting of unfilled PTFE, carbon filled PTFE, graphite filled PTFE, and combinations thereof.
  • 35. The flux of claim 28 wherein the flux further includes (i) iron powder containing carbon, (ii) reground slag containing carbon, and (iii) combinations thereof.
  • 36. The flux of claim 28 wherein the flux is in the form of particles having a size such that the particles pass through a 400-mesh screen.