Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/10—Supplying or treating molten metal
  • B22D11/108—Feeding additives, powders, or the like
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
  • B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
  • B22D11/10—Supplying or treating molten metal
  • B22D11/11—Treating the molten metal

Definitions

• This invention relates generally to casting of boron treated steel, and more specifically to an improved filled tubular article and method of controlled insertion of preselected materials within the filled tubular article into the molten metal as it is being cast.
• Such slag formation at the nozzles not only detrimentally affects the controlled flow rate of molten metal into the mold, but detrimentally affects the ratio of external surface area of the poured stream to the total stream cross section so that there is undesirably an increased oxidation and nitriding tendency.
• the formation of slag also detracts from the amount of residual aluminum available for obtaining the desired grain refinement.
• the material additions such as titanium, zirconium and boron, in singular or combined form, which have been made to the tundish or ladle to improve the response of the material to heat treatment have heretofore been relatively ineffective because there has been a reaction with the atmosphere and a fading phenomena as a result of prolonged exposure of the additional materials to the atmosphere at» he elevated temperature.
• the article ⁇ or billet that is formed has a less homogeneous and coarser structure than it should have for the expense of the material additions and a lower hardenability than is desired.
• several feet of the continuously cast billets are not usable because of imperfections, and so such sections are cut off resulting in a waste of time and material.
• the present invention is directed to overcom one or more of the problems as set forth above.
• a filled tubular article for con trolled insertion into a molten metal for making boron treated steel, the filled tubular article having an elongate conduit, an elongate, non-particulate member of primarily aluminum material in the conduit, and a master composition including ferroboron particulate material in the conduit.
• a filled tubular article having an elongate ferrous metal conduit, an elongate substan tially aluminum member in the conduit, and a master composition including ferroboron and ferrotitanium particulate materials in the conduit.
• the master composition also includes ferrovanadium particu late material.
• a method of casting boron treated steel includes intro ⁇ ducing aluminum in the form of a non-particulate elongate member and ferroboron particulate material in preselected percentages by weight below the surface of the molten steel in the mold by means of a containing conduit.
• the instant invention has successfully made boron treated steel in a continuous as-cast round bar manufacturing facility by introducing preselected amounts of ferroboron, ferrotitanium, and ferrovanadium particulate materials and an aluminum rod in a protective conduit and effecting melting thereof at a preselected depth below the level of the molten steel in the mold. Its success has been determined by a study of boron factors, performance criteria, and chemical analyses of the elements of a plurality of heat-treated parts including experimental tests and comparison base tests.
• Fig. 1 is a diagrammatic, elevational view of a continuous casting facility including an apparatus for progressively feeding a filled tubular article constructed in accordance with the present invention into the molten metal in the mold.
• Fig. 2 is an enlarged, fragmentary and diagram ⁇ matic elevational view of the upper portion of the casting facility of Fig. 1 with a portion illustrated in section to better illustrate details of the present invention.
• Fig. 3 is an enlarged, diagrammatic, cross sectional view of the filled tubular article illustrated in Figs. 1 and 2.
• Fig. 4 is a graph showing the relationship between actual boron factor and carbon content.
• Fig. 5 is a tabular listing of seven experi ⁇ mental rod members and the additive material ratio additions in each.
• a rotary continuous casting facility 10 is illustrated of the type utilized by the MacSteel Division of Quanex Corporation and located in Jackson, Michigan. Such facility produces continuous as-cast round bars by utilizing a large bottom pour ladle 12 to pour argon-gas-stirred molten steel 13 into a tundish 14. Liquid steel is teemed from the tundish via a bent nozzle 16 having a relativel small outlet opening at 18, for example about 16 mm (5/8") dia., and into a water cooled mold 20 at a precise angle with respect to a central vertical axis 22.
• the generally cylindrical mold 20 is of copper and has a precisely contoured or tapered internal bore 24 to allow for solidification shrinkage and to maintain mold contact with the solidifying hot bar for optimum cooling.
• the copper mold 20 has an enlarged annular head portion or top end 26 and a lower cylindrical body portion or bottom end 28, and vertically spaced apart seal means 30 are provided between the mold and a suitable support member 32 to define a chamber 34 through which liquid coolant such as water is circulated.
• the mold 20 is oscillated at a rate of about 60 cycles per minute through a range of about 16 mm (0.625") in the direction of the vertical axis 22 on which it is centered, while at the same time it is rotated at a speed of about 60 revolutions per minute as is schematically shown in Fig. 1 by the movement indicating arrows "A" and "B" respectively.
• the emergin bar or strand depends -from the mold and passes through a water spray system 35. Thereafter the bar is cut to length by a carriage mounted saw, not shown, that clamps to the bar and travels with it during the cut.
• a carriage mounted saw not shown, that clamps to the bar and travels with it during the cut.
• the straight bar length or overall height "OH" is about 10 m (33'), and the bar diameter "D" can be varied from, for example, about 100 to 180 mm (4 to 7") .
• An apparatus for introducing additives into the casting mold 20 is generally indicated by the reference numeral 36.
• the additives utilized in the present invention are in the form of a relatively ductile filled tubular article or treating rod 38 having a lower or distal end 40.
• the filled tubular article is progressively urged downwardly when viewing the drawings by a wire feed mechanism 42 which unreels the article from a rotatable reel 44.
• a feed rate of about 64 mm/sec. (2 y/sec.) was found to be satisfac ⁇ tory in one instance.
• a hollow tubular guide member 46 is located below the feed mechanism, and is generally aligned with a plane through the central axis 22; however, the guide member has a preselected angle of inclination with respect to the axis so that the distal end 40 of the filled tubular article is below a surface 48 of the molten steel 13 in the mold 20 by a preselected distance "L" as indicated in Fig. 2 and so that the distal end is adjacent the central axis thereat.
• U. S. Patent No. 3,991,808 issued November 16, 1967 to J. R. Nieman, et al.
• the filled tubular article 38 melts at its distal end 40 to add preselected materials below the surface 48 simultaneous with reciprocation and rotation of the mold.
• heat is removed from the copper mold by the water in the chamber 34, and progressive solidification occurs at the periphery of the tapered bore 24 so that a cylindrical bar 50 is continuously formed along the axis 22.
• the retraction rate or formation rate of the bar is about 2m/min. (79"/min.). It is to be understood that the central part of the bar does not immediately solidify, but rather the solidifi ⁇ cation progresses radially inwardly with time and with the downward movement of the bar.
• the filled tubular article 38 can be seen to include an elongate metal conduit 56, an elongat non-particulate member 58 located within the conduit, and a preselected particulate master composition 60 compactly contained within the conduit.
• the master composition 60 includes ferroboron
• the non- particulate member 58 is primarily of aluminum material
• the conduit 56 is of preferably a ferrous material
• the conduit 56 can have the following composition in percentage by weight:
• the master composition 60 should preferably include preselected weight percent- ages cf ferrotitanium and ferrovanadium particulate materials intermixed with a preselected weight percent ⁇ age of ferroboron particulate material. I have found it desirable to compact the master composition 60 within the conduit 56 to a relatively dense state in order to assure rapid internal dissolution of the conduit. For example, the preferred density of the core is equivalent to a degree of compaction in excess of 10% above the tapped density thereof.
• tapped density refers to the known procedure described in "HANDBOOK OF METAL POWDERS" - Poster, Reinhold Publishing Co., New York, New York, 1966, page 57.
• boron treated steel can be made best by progressively inserting a filled tubular article 38 consisting essentially of the following elements in the proportions indicated into and below the surface of molten metal in the mold:
• ferrous metal portions of the protecting conduit 56 and the selected three particulate materials designated immediately above is not significant since such ferrous portions have a negligible diluent influence on the molten metal. Rather this compatibility factor can be utilized with advantage because ferroalloys of boron, titanium and vanadium are available in the marketplace at economical prices and because the reaction thereof is more tame than the reaction of the purer basic element forms.
• Another way to state the preferred material relationship is to designate the ratio of the four ele ⁇ ments as about 9:1:28:24 which reflects the weight analysis ratio of aluminum, boron, titanium and vanadium in the filled tubular article 38.
• low cost aluminu serves as an effective deoxidizer and denitrider and imparts the desired degree of grain refinement in the cast article by removing dissolved gases from the melt.
• a level of about 0.070 Wt.% the ductility of the cast article can be expected to be adversely affected and an undesired amount of inclusions noted therein.
• a level of about 0.015 Wt.% the amount would be ineffective as a grain refiner. It must be present in a non-particulate or non-powder form for the reason
• Ferroboron particulate material provides the desired degree of hardenability to the steel article while replacing an appreciable percentage of more expensive alloying ingredients. Above a boron level of about 0.00462 Wt.% an undesirable secondary reaction occurs involving the precipitation of iron borides that tend to embrittle the article. Below a level of about 0.0008 Wt.% there is insufficient boron available to provide the hardenability effect on the heat treat of the article. The ferroboron particulate material that I used had 17 1/2 Wt.% boron. The preferred addition of ferrotitanium serves as a powerful deoxidizer and denitrider. Above a titanium level of about 0.150 Wt.% there is so much titanium that some would be available to link up with the carbon and detrimentally affect the heat treatment capability of the cast article and its hardenability. This is so because titanium is an exceptionally strong
• the preferred ferrovanadium addition serves as a somewhat weaker deoxidizer, a stabilizer, a hardenability agent, a grain refiner and a means of increasing the strength of the boron steel article. Above a level of about 0.147 Wt.% vanadium there would be massive carbide precipitation that would result in a loss of hardenability. Below a level of about 0.022
• the master composition 60 is ferrovanadium, about 43 1/2% is ferrotitanium, and about 6 1/2% is ferroboron.
• boron factor In connection with the so-called boron factor, reference is made to the pioneering work of Marcus A. Grossman, such as his AIME Paper of February, 1942 on Hardenability Calculations from Chemical Compositions, and to ASTM Specification A255 relating to a standard method of End-Quench Test for hardenability of steel.
• the actual boron factor is generally defined as the actual D.I. in inches calculated from Jo iny divided by D. I. in inches calculated from the chemistry (without boron).
• the boron factor or its contribution to increased hardenability, is an inverse function of the carbon content. The higher the amount of carbon, the lower the boron factor and the less the contribution to increasing hardenability. This is observable by reference to the chart identified as Fig.
• FIG. 4 wherein the actual boron factor is plotted in the vertical direction of the ordinate and the carbon content of the steel is plotted in the horizontal direction of the abscissa.
• a target value or normal expectancy value is represented in Fig. 4 by the substan ⁇ tially straight shaded band or region identified by the reference letter A. The further that the actual boron factor is below the target value' in the band when viewing the chart, the more undesirable it is.
• some rods contained particulate ferrotitanium and/or silicon zirconium along with particulate ferroboron.
• the actual boron factors obtained varied from less than 1.0 to 2.07 and fluctuated too widely as may be noted by reference to the zone designated by the reference letter "B" in Fig. 4. From this and the chemical analyses of the various heats the conclusions were reached that furnace and ladle additions were erratic and wasteful, and that ferrotitanium additions within the rod were highly desirable. Furthermore, while zirconium additions within the sheath exhibited some degree of success on hardenability, the cost thereof was excessive for the effectiveness obtained. It was also learned that boron factors did not appear to relate to boron content.
• ⁇ - titanium needed within the rod could be reduced substan tially and still retain the desired level of harden ⁇ ability.
• the extra titanium in the heats of rod No. 3 when compared with the heats of No. 1 caused a higher boron factor, but not enough greater to justify the added expense.
• the amount of retained titani in some of the ingots was noted to be higher than desired, for example above about 0.10 Wt.%.
• Rod No. 5 differed from the first four rods by containi a preselected quantity of ferrovanadium. Boron factors in the neighborhood of 1.90 were noted indicating a definite success with that rod as a result of the vanadium influence. However, the chemical analyses of the ingots indicated that a relatively high residual proportion of the additive elements was retained and that the ratio of the elements within the rod was therefor too rich. Rod No. 6 was provided to reduce the amount of aluminum and titanium substantially, while keeping the amount of boron constant. Upon examining the ingots thus produced it was found that the same high boron factors of about 1.90 were observed. Thus, unexpectedly good results were obtained with less additive material, and this time the chemical analysis of the ingots indicated only minimal amounts of the additives present.
• the filled tubular article 38 having the preferred No. 6 rod construction 28 parts titanium; 1 part boron; 9 parts aluminum; and 24 parts vanadium
• a plain carbon steel having the following element analysis of primary interest in percentage by weight:
• the filled tubular article 38 was inserted into the mold 20 as indicated in Fig. 2 at the rate of about 64 mm/sec. (2 "/sec) , while the steel at about 1530°C (2790°F) * was poured into the mold at a rate of about 4.60 Kg/sec. (10.11 lbs./sec) .
• the filled tubular article at almost 8 mm dia. (5/16" dia.) exhibited a dissolution depth "L" of about 400 mm (16") . This corresponded to a rate of material addition of about 0.020 Wt.% Al, 0.0023 Wt.% B, 0.063 Wt.% Ti and 0.055 Wt. % V, reflected as a percentage of the molten metal addition to the mold. This enabled withdrawal of the - IB -
• the corresponding rate of materi addition was also about 0.020 Wt.% Al, 0.0023 Wt.% B, 0. Wt.% Ti, and 0.055 Wt.% V, and provided an article havin boron factor of 2.03 as indicated by the letter "D" on t graph of Fig. 4. This was achieved at a final chemistry retention level of about 0.03 Wt.% Al, .0020 Wt.% B, 0.0 Wt.% Ti and 0.06 Wt.% V.
• Wt.% B 0.045 Wt.% Ti, and 0.040 Wt.% V as reflected as a portion of the molten metal addition to the mold.
• the leaner mixture provided an excellent actual boron factor of 2.16 as indicated by the Letter "E” on the graph of Fig. 4 at a final chemistry retention level of about 0.02 Wt.% Al, 0.0012 Wt.% B, 0.03 Wt.% Ti, and 0.035 Wt.% V.
• the filled tubular article and method for casting boron treated steel in accordance with the present invention is extremely successful by providing high boron factors, by providing substantially the lowest practical levels of material additions at a late stage to reduce fade and contamination of the melt, and by providing a manufactured article with relatively low chemistry weight percentage levels of the additive elements.
• the articles thus produced have exhibited an extremely desirable clean microstructure morphology and/or a minimum of nonmetallic inclusions that are often charac- terized as "dirt". This is indicative that the recovery rate is high, and the process economically efficient.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Treatment Of Steel In Its Molten State (AREA)
• Continuous Casting (AREA)

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Citations (7)

• 1980
  • 1980-02-13 WO PCT/US1980/000155 patent/WO1981002310A1/en unknown
  • 1980-02-13 JP JP55501741A patent/JPS57500110A/ja active Pending
• 1981
  • 1981-01-12 CA CA000368268A patent/CA1148747A/en not_active Expired
  • 1981-02-12 EP EP81300574A patent/EP0034469A1/en not_active Ceased

Patent Citations (7)

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