Classifications

• • 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
  • C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
• • 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
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment

Definitions

• the present invention provides a novel and improved process for the production of colurnbium containing steels having improved properties. More particularly, it relates to the production of rolled sheets, plates, bars and tubes, and includes correlated improvements and discoveries whereby the properties of steels are decidedly improved.
• An object of the present invention is to provide a process in accordance with which a steel maybe produced having a line grain, With improved physical properties, such as yield strength and low temperature impact strength, in the ans-rolled condition.
• a particular object of the invention is the provision of a process whereby steels may be produced through the utilization of columbium, for example as elemental columbium or in the form of an alloy such as ferrocolumbium, preferably having a low melting point which suitably is substantially equal to or lower than the temperature of the steel melt in the ladle. Also, there may be utilized a composition containing columbium oxide with a reducing agent.
• the improved process of the present invention may be used with rimmed, killed and semi-killed steels of alloy and of carbon grades, and the steel may be manufactured by procedures which involve no unusual steps.
• the process of the present invention especially avoids adversely affecting the low temperature transverse impact properties of colurnbium steels prepared according to convcntional produces, retaining the fine grain, While also resisting grain growth at elevated temperatures.
• the process of the present invention is also highly advantageous in that it produces semidcilled, killed or rimmed steels which have exceptionally good properties in the as-rolled" condition, and yet may be subjected to further heat treatment to develop other desirable physical properties.
• the process of the present invention also avoids the relatively poor ductilit high transition temperatures and low impact values which characterize conventional columbium containing rolled steels which have been made by the usual processes, and which generally contain small en velopes of columbium carbide especially around the grain boundaries.
• the properties of rimmed, killed or semi-killed steels are decidedly improved by the addition of an appropriate and definite amount of columbium suitably in the form of a self-reducing mixture of columbium oxide and a reducing agent or an alloy with iron, namely, a lerrocolumbiurn, and preferably with an alloy which has a melting point which is substantially equal to or lower than the temperature of the steel melt in the ladle.
• the amount of the columbium may vary from about 0.005% to about 0.050% based on the weight of the melt. More desirably, it may be in an amount of from 0.015% to 0.037% for either semi-killed, killed or rimmed steels.
• the composition of the fcrro-columbium may be from about 81% to 25% iron and from about 19% to about of columbiurn.
• the percentage of iron may be about 50% and the amount of columbium about 43% with about 7% impurities.
• the analyses of the columbium-containing steels for use with the present invention show a carbon content of 0.02% to 0.50%, silicon from 0.005% to 0.5%, manganese from 015% to l.6% and colurnbium from 0.005% to 0.050%.
• the following tables show more particular analysis ranges for semi-killed, killed and rimmed steels:
• Columbium 0.005 to 0.050%, preferably 0.015 to 0.030%. Phosphorus and sulfur impurities in normal amounts.
• the procedure comprises preparing a steel melt, adding thereto when the steel is ready either during furnacing or to the ladle or to the ingot mold, a columbium containing material having a melting point substantially not higher than the temperature of the melt.
• the colurnbium containing material may be in the form of an alloy, e.g., a ferro-eolurnbium, having the melting point as above indicated, or as a selfreducing mixture containing columbiurn oxide.
• the coiumbium may be added to the ingot mold and in an effective amount not more than about 1.0 pound of colurnbium per ton of steel. Additionally, the addition of the columbium may be partially in the furnace and partially in the ladle, or in the ingot mold. If desired, the melt may be deoxidized at a suitable stage in the manufacture through the utilization, e.g., of ferrosilicon, calcium, silicon, form-manganese, and the like. The addition of the columbium containing material may be effected at different phases of the melting and furna-cing and in any convenient and effective manner.
• the columbium material may be added to the ingot mold or partly to the furnace and partly to the mold.
• the ingots, slabs or bars prepared as above, and including from 0.015% to 0.030% columbium are heated in heating furnaces, prior to rolling, and are soaked for a period of from 7 to hours at a temperature of from about 2300" F. to 2450 F. after which it is rolled to the desired finished size.
• the rapid cooling from the elevated temperature of 1550 to 1750 F. may be accomplished by using a cold steel mandrel or plug on the interior of the tube While it is rolled, thereby rapidly cooling the tube to a temperature of less than 1200 F. and preventing the precipitation of columbium carbide, especially at the grain boundaries.
• columbium to such steels, or to a steel built around columbium addition, produces a better low alloy high strength steel, which processes without difficulty and which can be utilized as Well as the others.
• the requirements for ship plate are certain tensile properties plus a low embrittlement temperature, and these are usually obtained by producing steel in a hot-top variety and then normalizing. Production of this steel by the semi-killed process leads to a greater yield and elimination of normalizing gives a lower cost steel.
• Columbium added to low carbon steels e.g., carburized grades and in amounts from about 0.015% to about 0.03 0% produces a very fine grain which persists at high temperature. It allows a higher carburizing temperature thus reducing the time required, and producing a steel lower in cost.
• an ingot of semi-skilled or rimmed steel having from 0.005% to 0.050% columbiurn is soaked for 7 to 10 hours at a temperature of from 2300 to 2450 F., the time of soaking depending on the size of the ingot.
• an ingot weighing about 25 tons and measuring about 32 by 66 by inches normally requires about 8 hours to attain a uniform temperature in the range of 2300 to 2450 F.
• the ingot is then rolled in accordance with conventional procedure, and when finished has a temperature of from l550 to 1750 F., and is often heated one or more times during the finishing operation, so as to maintain a good rolling temperature.
• the steel is immediately subjected to a heavy water spray so as to reduce its temperature from about 1550 to 1750 F. to a temperature in the range of 1050" to 1200" F., below the AC3 critical points, after which the steel is allowed to cool in air at a normal rate of cooling.
• the spraying may be begun at an earlier time and as soon as the temperature of the steel has been reduced to about 1800" F.
• the foregoing procedures may be employed for the production of semi-killed, killed and rimmed steels, and enables the producers to take advantage of the extra production yield obtained from semi-killed over that of killed steels.
• the increase in embrittlement temperature is of a very low order if the columbium is under 0.02%, but rises rapidly as this amount is exceeded unless the columbium containing steel is rapidly cooled, as by the water spray, from the range of 1550 to 1750 F. to the lower range of 1050 to 1200 F.
• the data in the following table shows the transverse impact values obtained from several different steels which had been finished at approximately 1650 F. for 8 hours prior to rolling, and which had also been sub jeoted to water spray cooling to cause them to cool rap- F idly from about 1600 to about 1200 R, after which they are air-cooled at a normal rate.
• a method for the production of steels which cornprises preparing a steel ingot containing from 0.005% to 0.050% of columbium, on a Weight basis, heating the ingot prior to rolling to a temperature of at least 2300" F. until the ingot is uniformly heated to a temperature from about 2300 to 2450 F, rolling the ingot so that when finished it has a temperature of from about 1550 to 1750 F., and subjecting the ingot to a water spray to rapidly cool the rolled steel from th finishing temperature 6 range of 1550 to 1750 F., to a temperature range of 1050 to 1200 F.
• a method for the production of steels which comprises preparing a steel ingot containing, on a weight basis, from 0.02% to 0.40% carbon, 0.005% to 0.5% silicon, 0.15% to 1.6% manganese and from 0.005% to 0.050% columbium, heating the ingot prior to rolling to a temperature of at least about 2300 F. until the ingot is uniformly heated to a temperature between about 2300 and 2450 F., rolling the ingot so that when it is finished it has a temperature of from about 1550" F. to i750 R, and subjecting the ingot to a water spray to cool it rapidly from a temperature exceeding 1550 F. to a temperature below 1200 F.
• a method as claimed in claim 2 in which the water spray is started While the steel is at a temperature of about 1800" F. and is continued until the steel is at a temperature of about 1050 F.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Heat Treatment Of Steel (AREA)

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Cited By (24)

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Citations (5)

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• 1960
  • 1960-08-10 US US48587A patent/US3102831A/en not_active Expired - Lifetime
• 1961
  • 1961-06-16 DE DEP1271A patent/DE1271738B/de active Pending
  • 1961-07-25 BE BE606507A patent/BE606507A/fr unknown
  • 1961-07-28 GB GB27474/61A patent/GB933843A/en not_active Expired
  • 1961-08-05 LU LU40478D patent/LU40478A1/xx unknown

Patent Citations (5)

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