Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
  • B23K35/24—Selection of soldering or welding materials proper
  • B23K35/30—Selection of soldering or welding materials proper with the principal constituent melting at less than 1550°C
  • B23K35/3053—Fe as the principal constituent
  • B23K35/308—Fe as the principal constituent with Cr as next major constituent
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
  • B21B—ROLLING OF METAL
  • B21B27/00—Rolls, roll alloys or roll fabrication; Lubricating, cooling or heating rolls while in use
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/38—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for roll bodies
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/38—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of manganese

Definitions

• the roll may 3 3 12/1966 comprisea" ferrous metal body to which the metal contacting surface of chromium Ohtake ..;.75/l26 C mill is preferably iron or steel above its critical temperature.
• This invention relates to a method of hot rolling metal and particularly to operations performed on metal in its hot forgeable temperature ranges, particularly in a hot rolling mill.
• the invention is concerned with the drastic temperatureextremes, necessarily cyclic in nature, to which certain working parts of the mill, especially rolls, are subjected and the damage. which thermal shocks caused by the cyclic temperature changes do to the working parts of the mill and to improvement of the performance and efficiency of the mill which can be effected by importantly, in accordance with the invention, improving the resistance of such working parts of the mill to damage by thermal shock.
• Rolls Contact with hot metal being rolled in a hot rolling mill, is made principally by rolls. These may be the rolls which transport the hot metal and on which it may rest for a period while awaiting the next processing step or the work rolls which produce plastic deformation by applying squeezing pressure to the metal.
• heat is rapidly transferred to the surface of the roll by conduction and radiation. In some locations even convection may contribute to the transfer but in any case the roll surface receives an intense local heating.
• a roll surface is cooled to prevent too much build up of heat in the roll which would reduce its strength and cause the sticking of hot metal on subsequent contacts.
• Roll cooling is normally done by water sprays although there are a few locations in a mill where a blast of air at ambient temperature may ,be adequate.
• the rate of formation and propagation of fire cracks in a mill roll varies with the hot working temperature of the metal being processed; steel is commonly handled above its critical temperature in the range of l,450 to 2,200'F., nickel at about 1,200 to 2,300 F., copper at about l,200 to l,6.00 F. and aluminum at about 900 to 950 F. Because of the large tonnage rolled and the high-hot working temperature the rolling of steel is responsible for most fire crack damag to mill rolls. While the fire cracking of rolls cannot be stopped it can be slowed down as this invention teaches.
• the conduct of the rolling operation can thereby be greatly improved by reducing the rate at which fire cracking spreads into extensive and insupportable damage whereby the mill product becomes increasingly marked and the hazard of roll breakage increases with the deepening cracks which act as fatigue notches.
• mill operation becomes a gamble of additional tonnage before a roll change against breakage in the mill.
• Roll failure by wear is bad enough but wear can be observed and followed and a replacement part scheduled for a time when a mill is down.
• Roll failure by breakage during mill operation is the most expensive type of failure and minimization of the risk of roll breakage isof the utmost importance to mill operations.
• a welded roll must be used substantially as deposited since the finished bearings at either end will not tolerate exposure to a heat treatment such as the annealing treatment commonly used on a new roll body while still in the unfinished condition.
• a roll produced by applying a weld deposit to a supporting structure such as a used roll body represents the more restricted situation and a material which performs satisfactorily in the weld deposited form without benefit of heat treatment can therefore also be employed as a new roll material where heat treatments can be added.
• tungsten in an amount of about 1.3 to 2 percent as an aid to grain refinement, hot hardness and tempering resistance and it has been stated that when dissolved in the matrix tungsten is extremely reluctant to precipitate on tempering, and when it does, at temperatures of 950 to l,l00 F., probably in the fonn of W C, it accounts for the phenomenon of secondary hardness and, in the high-speed steel tools, for red hardness. It has also been said that because molybdenum has a smaller atomic weight than tungsten it will produce twice as many atoms for alloying in the steel; thus l percent molybdenum can be substituted for 1.6 to 2 percent tungsten.
• molybdenum also imparts high-temperature strength to steels when present in amounts as low as about 0.5 percent, that molybdenum when present alone, however, promotes decarburization and that small amounts of chromium minimize this effect. It has still further been said that vanadium present in virtually all the chromium-molybdenum steels is highly effective in promoting hot hardness at l,l00 F. and that 0.5 percent vanadium is as effective as l.5 percent vanadium.
• chromium itself is well known. It imparts oxidation resistance to steel and greatly increases its hardenability. in conjunction with molybdenum an optimum increase in high-temperature strength is accomplished at about 2 percent chromium.
• alloys No. 2, No. 3, No. 6 and No. 8 l have achieved in a single weld deposit both unprecedented resistance to fire cracking and a good level of the properties which produce resistance to wear at elevated temperatures.
• Alloy No. l l illustrates the help which can be gained from use of low levels of vanadium in amounts up to 1 percent in-a composition which otherwise would be unsatisfactory in hot hardness or softening resistance.
• alloy No. ll the addition of about 0.7 percent molybdenum and 0.3 percent vanadium increased the hardenability, hot hardness and softening resistance to an acceptable level in the presence of only 2 percent chromium, it is believed more conservative to take 3 percent chromium as the minimum which should be used.
• Alloy No. 9 an alloy with about 7 percent chromium and about 1.5 percent molybdenum, has satisfactory hot hardness with marginal softening resistance. It may be noted that molybdenum above about 4 percent did cause premature failure by fire cracking due to a grain boundary phase. To insure against the possibility of a detrimental grain boundary condition, the upper limit for molybdenum is established at 2 percent.
• Alloy No. 8 which had a chromium and tungsten total of about 9 percent, exhibits good fire cracking properties and excellent elevated temperature behavior. There is danger of the formation of intergranular phases in deposits with too high an alloy content as exemplified by alloy no. 10. Therefore, a value of 9 percent of the total of chromium, molybdenum, tungsten and vanadium is established as a maximum.
• Certain residual elements normal to ferrous hard-facing deposits may also be present; the range of silicon is commonly from 0.2 percent to 2 percent and of manganese from 0.3 percent to 3 percent. Phosphorus and sulphur may be present in typically commercial amounts. The balance is substantially iron.
• a wear resistant hard-facing weld deposit resistant to fire cracking should contain vanadium (l-l 0- 0.5 about I manganese 0.3-3 0.3-2.5 about 2 silicon 0.2-2 0.22 about and with the sum of the percentages of chromium, molyb denum, tungsten and vanadium between about 4 and about 9, the balance being substantially iron.
• Chromium steels with alloy metal contents equal to those of my chromium steels but with carbon contents over 0.20 pcr cent and therefore unsuitable for rolling mill use have been used for many tool steels, for welding electrodes and also for steel mill rolls.
• Chromium steels with analyses which fall within the limits of my invention have been made previously. They have been shown to have properties and have been demonstrated as useful for purposes none of which remotely anticipates or foreshadows their useful employment as a working surface ofa roll in the hot rolling of metal.
• a steel within the analysis which I require for rolling mill use has been proposed as a valve surfacing material resistant to the corrosive attack of hot refinery oil.
• This is a very special type of corrosive attack by the sulfur and other compounds present in oil.
• the service is continuous and the temperature is maintained constant by the hot oil.
• This service is not characterized by the rapid and extreme temperature cycles which by alternate heating and quenching produce fire cracking by fatigue in rolling mill rolls.
• the property of resistance to corrosion by hot oil teaches nothing about resistance to fire cracking under violent thermal cycles.
• a method for improving the performance and efficiency of a hot rolling mill which accepts metal at hot forging tcmperature, moves it through the mill and plastically reduces the metal, the method consisting of the steps of providing the mill with a roll having a metal contacting surface of chromium alloy steel having the following composition:
• the sum of the percentages of chromium, molybdenum, tungsten and vanadium being between about 4 and about 9, the balance being substantially iron, whereby to simultaneously greatly improve the resistance to thermal fatigue cracking while maintaining a good level of resistance to wear of the roll at hot forging temperature engaging the metal at hot forging temperature by such roll and applying to the roll a coolant at a temperature below the boiling point ofwater so that the roll is subjected to repeated heating and cooling cycles.
• a method for improving the performance and efficiency of a hot rolling mill which accepts metal at hot forging temperature, moves it through the mill and plastically reduces the metal.
• the method consisting of the steps of providing the mill with a roll having a ferrous metal core and a metal contacting surface of chromium alloy steel having the following composition:
• a method for improving the performance and efficiency of a hot rolling mill which accepts metal at hot forging temperature, moves it through the mill and plastically reduces the metal, the method consisting of the steps of providing the mill with a roll having a ferrous metal core and a weld deposited metal contacting surface of chromium alloy steel having the following composition:

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Reduction Rolling/Reduction Stand/Operation Of Reduction Machine (AREA)

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• 1968
  • 1968-07-24 FR FR1574542D patent/FR1574542A/fr not_active Expired
  • 1968-07-25 GB GB35665/68A patent/GB1223164A/en not_active Expired
  • 1968-07-25 DE DE19681758703 patent/DE1758703B1/de active Pending
  • 1968-07-25 BE BE718540D patent/BE718540A/xx not_active IP Right Cessation
• 1969
  • 1969-06-23 US US835809A patent/US3640114A/en not_active Expired - Lifetime

Patent Citations (6)

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