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
  • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
• • 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
• • E—FIXED CONSTRUCTIONS
  • E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
  • E01B—PERMANENT WAY; PERMANENT-WAY TOOLS; MACHINES FOR MAKING RAILWAYS OF ALL KINDS
  • E01B5/00—Rails; Guard rails; Distance-keeping means for them
  • E01B5/02—Rails
• • 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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/26—Methods of annealing
  • C21D1/28—Normalising
• • 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
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/005—Ferrite

Definitions

• a steel rail section which contains a grain refining element and which has been subjected to normalising or controlled rolling to produce a ferrite grain size finer than A.S.T.M. 8 has a greater resistance to brittle fracture than current rail sections especially at low temperatures while retaining good tensile properties.
• the addition of a hardening element benefits wear resistance.
• Suitable grain refining elements are aluminium, vanadium, titanium, niobium, zirconium, while suitable hardening elements are manganese, silicon, chromium, nickel and molybdenum.
• Carbon levels can be between 0.2 and 0.85% by weight but are preferably not more than 0.39%, below the level for conventional rail steel. Between 0.5 and 2.5% by weight manganese or up to 1.5% by weight silicon are preferred as the hardening elements. For grain refining it is preferred to use aluminium or vanadium with a normalising treatment, or aluminium and niobium together with a controlled rolling process.
• This invention relates to steel, and more particularly to rail steel and rail sections fabricated therefrom.
• rail steel has chiefly been made with a carbon content of about 0.5% and a manganese content of about 1.0%.
• the as-rolled rails are normally straightened and machined to length before being put into service. Typical of such rails are those described in the following standard specifications:
• the rails have adequate tensile strength (normally not less than 44 t.s.i., 69 kg./mm. and wear resistance.
• the steel steel structure is generally a coarse grained essentially pearlite structure possessing a very poor impact strength, typically under ft.-lbs. (1.39 kgm.) at room temperature, as measured by the Charpy test using a 2 mm. V-notch specimen.
• the steel usually has a prior austenite grain size of about A.S.T.M. 3, and a ferrite grain size of about A.S.T.M. 4.
• brittle fracture can occur from relatively small defects which may have developed in service e.g. from fatigue cracks which may form from bolt holes through the web of the rail, and also from cracks and defects in the rail.
• a steel rail section which embodies a grain refining element and, preferably, a hardening element and which has been subjected to either normalising or a controlled rolling process, as herein defined, in producing a fine grain structure, the type and amount of the grain refining element in the steel and the fine graining process to which it is subjected being such as to produce a ferrite grain size finer than A.S.T.M. 8, and preferably finer than A.S.T.M. 9.
• normalizing is defined as a heat treatment process in which the steel is reheated to a temperature which is in excess of its upper critical point and is then air cooled.
• the upper critical point may typically be about 850 C.
• controlled rolling as used herein is defined as a rolling process performed on the steel down to temperatures in the range 700 C. to 900 C., instead of the normal finish rolling temperature of about 1000 C.
• the grain refining element may be one or more of aluminium, niobium, vanadium, titanium and zirconium, preferably in the proportion by weight, based on the total weight of the steel, of 0.015% to 0.1% aluminium, 0.01% to 0.1% niobium, or 0.05% to 0.2% vanadium.
• Suitable hardening elements are silicon, manganese, chromium, nickel and/or molybdenum. Silicon is desirably present in the proportion, based on the total weight of the steel, of 0.05% to 1.5% by weight; chromium, from 0.25% to 1.5% by weight, and manganese from 0.5% to 2.5% by weight.
• Nitrogen is usually present between 0.003 and 0.030%, more preferably with a maximum of 0.025%, by weight, based on the total weight of the steel.
• Standard rail steel as currently produced usually has a prior austenite grain size of about A.S.T.M. 3, or a ferrite grain size of about A.S.T.M. 4.
• a prior austenite grain size finer than A.S.T.M. 6 and a ferrite grain size finer than A.S.T.M. 8 can be produced.
• the use of grain refining elements combined with the normalising heat treatment process can result in ferrite grain size finer than A.S.T.M. 10, or even A.S.T.M. 12.
• this improved resistance to brittle fracture which can be measured by improvement in im pact strength, can be provided by the use of the grain refining elements in the steel coupled with either a normalising hea treatment or a controlled rolling process.
• a suitable steel rail section in accordance with this invention contains by weight, based on the total weight of the steel:
• the steel rail section having been subjected either normalising or a controlled rolling process, as herein defined, in producing a ferrite grain structure finer than A.S.T.M. 8.
• the above rail section has a carbon content of from 0.2 to 0.6% and the grain refining element is aluminium, vanadium and/or niobium, the ferrite grain structure being finer than A.S.T.M. 9.
• a steel rail section falling within the above definition and being a modification, within the scope of the invention, of steel suitable for forming rail sections in accordance with current rail specifications such as B.S.11: 1959, has the following analysis:
• Aluminium 0.015 to 0.1%; or Vanadium: 0.05 to 0.2%; or Niobium: 0.01 to 0.1%
• the aluminium and niobium contents may be combined to give from 0.015 to 0.10% aluminium together with 0.01 to 0.10% niobium, in which case the rail section is preferably controlled rolled.
• Such rail sections may contain by weight, based on the total Weight of the steel:
• this steel is found in rail sections containing by weight from 0.02 to 0.06% aluminium, or from 0.10 to 0.15% vanadium and from 0.010 to 0.015% nitrogen, the rail section having been subjected to a normalising process; or, alternatively, rail sections containing by weight from 0.015 to 0.10% aluminium and additionally from 0.01 to 0.1% niobium, the rail section having been subjected to a controlled rolling process.
• the reduction in pearlite content, and an increase in ferrite content, is achieved by use of the lower carbon contents. This is, however, sometimes accompanied by a decrease in tensile strength and wear resistance.
• the tensile strength and wear resistance can then be improved by strengthening the increased fraction of the ferrite phase by solid solution hardening by the addition of a hardening element such as silicon, manganese, chromium, nickel or molybdenum, or combinations thereof.
• the invention further provides in its most preferred form a steel rail section containing from 0.28 to 0.39% carbon as defined above and containing as a hardening element from 1.2 to 2.5% by weight manganese, and/or from 0.8 to 1.2% by weight silicon.
• the hardening elements manganese, silicon, chromium, nickel and molybdenum may more generally be included in the ranges previously quoted.
• the preferred grain refining elements are aluminium or vanadium, the rail section being normalised, or aluminium and niobium together, the rail section being controlled rolled.
• Steel from a furnace having, for example, the following composition rangecarbon, 0.2 to 0.85%; manganese, 0.5% minimum; phosphorus, 0.06% maximum; sulphur, 0.06% maximum; nitrogen 0.003% to 0.025%, with a balance of iron, apart from the incidental impuritiesis tapped into a ladle into which the grain refining element is added.
• the temperature of the melt will generally be about 1600 C.
• the hardening element may also at this stage he added to the melt.
• the molten metal may then be teemed from the ladle into an ingot mould, and after solidifying, it may be subjected to one of two rolling processes to form the steel into rail sections:
• the ingot is heated to about 1300 C. before being fed into a cogging mill.
• the bloom issuing from this mill is then rolled to a temperature of about 950 C. to 1050" C.
• the rolled rail may have been produced directly from the ingot without any intermediate reheating; or alternatively the bloom from the cogging mill may have been reheated at temperatures of up to 1300 C.
• t e rolled rail will be cooled to a temperature below about 700 C. and then normalised, i.e., it is reheated to a temperature of the order of 850 C. to refine the grain and to form precipitates which restrict grain growth, and then cooled in air.
• the ingot, or the bloom from the cogging mill is cooled down to at least 700 C., preferably 500 C., and then reheated to a temperature between 1050 C. and 1250 C., i.e. of the order of 1150 C., and the rolling process is continued to give finishing temperatures in the range of 700C. to 900 C. (controlled rolling).
• the low reheating temperature used in this process results in the presence of grain refining agents during the actual rolling process, and these produce finegrained microstructures of a similar type to those produced during normalising.
• the alloy additions need not be made to the ladle. These additions could be made to the steel making furnace, and, in some instances, additions will be made to the furnace, the ladle and also the ingot mould. Additionally the melt in the ladle may not necessarily be teemed into ingot moulds, and, alternatively, it can be processed through a continuous casting machine or other bloom-forming techniques prior to rolling.
• Table I illustrates chemical composition and grain size, and Table II final mechanical properties.
• Example 1 is typical of rail steels (say to 8.5.11: 1959 specification) as currently produced. This example is included for purposes of comparison only, and does not illustrate the present invention. The low charpy impact test results should be noted for comparison with the results achieved in later examples which do embody the present invention.
• Examples 2 to 10 relate to steel rail sections in accordance with the invention. In all cases the steels had sulphur and phosphorus contents of below 0.06% and a ferrite grain size finer than A.S.T.-M. 8.
• Examples 2, 3 and 4 are typical of the results achieved by making additions of grain refiners to the normal quality (say B.S.11: 19'59) rail steel, and subsequently normalising the rolled rail section.
• Examples 2A and 2B show the use of aluminium, Example 3 vanadium, and Example 4 niobium.
• Examples 5, 6, 7 and 8 demonstrate the good impact properties which are achieved by the use of a lower carbon, higher manganese content, together with the addition of grain refining elements and subsequent normalising of the rolled rail section.
• Examples 5 and 6 illustrate the use of aluminium as grain refining element
• Examples 7 and 8 illustrate the use of vanadium.
• Examples 6 and 8 also show the inclusion of higher silicon contents in the steel as a means of achieving improved wear resistance.
• Examples 9 and 10 illustrate the use of aluminium together with niobium as the grain refining elements, the rail sections being controlled rolled.
• the composition corresponds to conventional rail steel with the addition of the grain refining elements, while in Example 10 the composition corresponds to the preferred lower carbon, higher manganese steel.
• the steel rail section having an essentially ferritic/pearlitic structure with a ferrite grain size finer than A.S.T.M. 8.
• a steel rail section according to claim 1 consisting essentially of the following elements in the stated proportions by weight, based on the total weight of the steel:
• a steel rail section according to claim 1 consisting i-g; 3 40 essentially of the following elements in the stated propor- 1 9 tions by weight, based on the total weight of the steel: 1.15 7 1.47 7 Carbon: 0.4 to 0.6%
• the balance being iron and incidental impurities; the steel having been subjected to a controlled rolling process.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Architecture (AREA)
• Civil Engineering (AREA)
• Structural Engineering (AREA)
• Heat Treatment Of Steel (AREA)

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Cited By (21)

Families Citing this family (13)

• 1970
  • 1970-03-20 GB GB1348770A patent/GB1342582A/en not_active Expired
• 1971
  • 1971-03-15 ZA ZA711670A patent/ZA711670B/xx unknown
  • 1971-03-19 CA CA108,187A patent/CA942541A/en not_active Expired
  • 1971-03-19 DE DE19712113418 patent/DE2113418A1/de active Pending
  • 1971-03-19 BE BE764566A patent/BE764566A/xx unknown
  • 1971-03-19 US US00126374A patent/US3726724A/en not_active Expired - Lifetime
  • 1971-03-19 LU LU62813D patent/LU62813A1/xx unknown
  • 1971-03-19 AT AT240871A patent/ATA240871A/de not_active IP Right Cessation
  • 1971-03-20 PL PL1971147057A patent/PL83139B1/pl unknown
  • 1971-03-22 FR FR7110021A patent/FR2087818A5/fr not_active Expired

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