Classifications

• • 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
  • E01B5/08—Composite rails; Compound rails with dismountable or non-dismountable parts
• • 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
  • C21D9/04—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for 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
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/008—Martensite

Definitions

• This invention relates to rails and in particular to rails exhibiting improved strength, hardness and toughness.
• Modern high performance rails are currently made by rolling steel of an appropriate composition and then cooling it.
• the rail may be cooled either directly after leaving the rolling mill, perhaps having been reheated, or after subsequent heat treatment. Cooling is controlled and the object is to create pearlite as the main component of the rail head.
• This pearlite has particular qualities of hardness and the cooling rate is in fact controlled to be below a particular rate for the steel composition in question so that it passes into what is known as the perlitic area on the continuous cooling transition (CCT) diagram for the steel.
• the cooling may be particularly controlled so that the path on the CCT diagram to passes through what is known as the "perlitic nose" when a pearlite of a fine inter lamellar spacing and consequently higher strength and hardness is produced.
• modern rail technology is now approaching the limits of hardness that can be achieved by a perlitic head because of the reductions in toughness brought about by the processing for increased hardness.
• a rail for use in a railway having a head and a foot the head being a traffic carrying surface composed of low carbon martensite.
• the rail may be rolled from a low carbon steel, and the head, and optionally the foot, may be rapidly cooled by the application of water or water/air sprays.
• the carbon content of the rail may be between 0.1 and 0.4% and the rail may have alloying elements to improve the hardenability and may also contain titanium and niobium.
• the hardenability may fall into the ranges shown in Table 3 and the rail may be allowed to self temper by terminating the spray cooling and allowing the residual heat in the rail head to equalise under natural cooling.
• Figure 1 is a diagram of a martensitic headed rail
• Figure 2 is a representation of the Brinell hardness results for such a rail
• Figure 3 is a diagram of the relationship between wear rate and hardness for pearlitic and martensitic rails
• Figure 4 is a diagram of the Jominy Hardenability data for a low carbon alloy steel
• Figure 5 is a diagram of the variation of the Charpy V-notch impact energy for martensitic and pearlitic rails at varying temperatures
• Figure 6 is a schematic diagram of one cooling arrangement for the production of rails
• Figure 7 is a diagram of the hardenability bands for the production of martensitic rails.
• Figure 8 is a schematic representation of the continuous cooling transformation diagram for a 0.8% carbon steel.
• Figure 1 shows a conventionally shaped flat bottomed railway rail 1. It has a foot 2 and head 3.
• the micro structure of the head in the shaded area 4 is martensite, while in region 5, where clearly the rate of cooling from external sprays is less it is a mixture of martensite and bainite.
• the foot has been cooled it is also largely martensite and the composition of the web 6 joining the foot and the head is not usually of great significance since in practice the performance required for the web is exceeded by most rails steels and heat treatments.
• the rail is made from a low carbon steel of composition as shown in Table 1. Brinell hardness tests were conducted on a section of such a rail and the results are shown in Figure 2.
• FIG. 3 A comparison of the Brinell hardness for various rails is shown in Figure 3 where these are plotted along the abscissa. The ordinate is the wear rate in milligrammes per metre of slip.
• the rails fall into four groups: (a) in as-rolled condition and (b) is a 1% chromium steel, again in as rolled condition.
• the results (c) are those of various head hardened and heat treated pearlitic rails of conventional manufacture while (d) is the low carbon martensitic steel rail of the invention. It will be seen from Figures 2 and 3 that the hardness of the martensitic rail is high, and the wear rate is clearly comparable with modern day pearlitic rails.
• the corresponding figures for the pearlitic steel were a tensile strength of 1,210 N/mm , and an elongation at break of 10%, and Brinell hardness of 360. This clearly shows that the resistance to fracture initiation is higher in the martensitic rail than the pearlitic, even at low temperatures.
• the fracture toughness of the martensitic rail has found to be between 100 and 110 MpA/ ⁇ r' , compared to typical values for pearlitic rails of 35-40 MPam 1 / 2 .
• FIG. 8 Such a diagram is shown in Figure 8 which is for 0.8% carbon steel.
• the area 54 is austenite (the form of steel at high temperatures), and temperature is shown on the ordinate and time, on a log scale is shown on the abscissa. Austenite is present at 50 and martensite at 51. Pearlite is shown by 52 and Bainite by 53. In between these areas a mixture of steel microstructures is produced.
• Dotted path X presents the path for normal air cooling and it will be seen that the path leads to the pearlitic state.
• the point marked Z is that point known as the pearlite nose. and controlled cooling along the path Y aims to pass the rail through the pearlitic nose producing the fine pearlite previously mentioned.
• the path M marks a typical path for the production of a martensitic rail, and it would be seen that it passes directly from the austenitic region to the martensitic region. Clearly this requires a high rate of cooling and this is achieved by the use of water, either as simple water sprays or mixed air water sprays.
• hardenability An important consideration in the production of rails is the quality known as hardenability. This is the ability of a steel to achieve a given hardness at a point remote from the point of application of cooling, particularly forced cooling.
• the hardenability data for a low carbon steel of the composition given in Table 1 is shown in Figure 4. This shows as the ordinate the Brinell hardness (BHN) and the abscissa are, from top to bottom, cooling rate in degree Celsius per second at 700°C, the equivalent plate thickness in mm, and the distance from the quenched face in mm. Data reference (a) is for a thickness of 40mm and that at (b) is for 65mm. This diagram shows the variation in Brinell hardness as one progresses further from the quenched outside surface of the rail.
• BHN Brinell hardness
• abscissa are, from top to bottom, cooling rate in degree Celsius per second at 700°C, the equivalent plate thickness in mm, and the distance from the quenched face in mm.
• Hardenability of this steel is acceptable because the martensite is produced at these deeper levels.
• the main elements that re known to effect hardenability are manganese, to a lesser, molybdenum, vanadium, chromium, nickel and copper.
• the calculation of hardenability from alloying elements is quite difficult, and although it can be predicted to a reasonable extent it must in the end always be measured.
• the data for point (c) are from laboratory based steel melts.
• the elements titanium and niobium are added for the usual reasons, titanium to improve weldability and niobium as a general precipitation strengthening element.
• the process produces a rail with the hardenability characteristics of a high carbon steel while also allowing the formation of a low carbon martensite with its correspondingly high intrinsic hardness.
• Figure 7 shows the acceptable hardenability bands and these are also set out in Table 3.
• the preferred hardenability band is shown for the J positions (sixteenths of an inch from the quenched end of a 1.0 inch diameter bar) 1, 5, 12 and 20.
• the area 70 is the preferred band although the area 71 would be acceptable for such rails.
• Figure 6 shows a typical arrangement of the sprays that might be used to produce the cooling required for such a martensitic rail.
• compositions for grades of martensitic rail steels that have been found to lie within the preferred hardenability bands are set out in Table 2 where each grade shows the range of compositions that might fall within it.
• martensitic rail is that the higher intrinsic hardness of martensite, required levels of hardness are easier to achieve. Therefore the manufacturing process can be modified so that less attention need be paid to the optimising of the hardness of the head, with the results that the parameters for the process can be varied to improve other characteristics.
• self tempering of the rail head to produce a higher feature toughness and impact resistance can be carried out by stopping the spray when the core of the inside of the rail head has fallen to temperatures of up to approximately 500°C. The rail is then allowed to cool naturally, and the heat from the interior of the rail head will spread to the whole of the head slowly raising the temperature before the whole rail finally cools to ambient.
• rail heads can comprise low carbon martensite.
• hardness namely rolling contact wear and rolling contact fatigue

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Mechanical Engineering (AREA)
• Architecture (AREA)
• Civil Engineering (AREA)
• Structural Engineering (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatment Of Articles (AREA)
• Linear Motors (AREA)
• Current-Collector Devices For Electrically Propelled Vehicles (AREA)
• Train Traffic Observation, Control, And Security (AREA)
• Passenger Equipment (AREA)
• Braking Arrangements (AREA)
• Walking Sticks, Umbrellas, And Fans (AREA)
• Platform Screen Doors And Railroad Systems (AREA)
• Road Paving Structures (AREA)
• Fuel-Injection Apparatus (AREA)
• Valve Device For Special Equipments (AREA)
• Bearings For Parts Moving Linearly (AREA)

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• 1993
  • 1993-06-24 GB GB939313060A patent/GB9313060D0/en active Pending
• 1994
  • 1994-06-20 HU HU9503749A patent/HU9503749D0/hu unknown
  • 1994-06-20 US US08/557,169 patent/US5645653A/en not_active Expired - Fee Related
  • 1994-06-20 JP JP7502564A patent/JPH08512093A/ja not_active Withdrawn
  • 1994-06-20 AU AU69764/94A patent/AU679537B2/en not_active Ceased
  • 1994-06-20 EP EP94918448A patent/EP0705369B1/en not_active Expired - Lifetime
  • 1994-06-20 AT AT94918448T patent/ATE164899T1/de not_active IP Right Cessation
  • 1994-06-20 RU RU96101177A patent/RU2122056C1/ru not_active IP Right Cessation
  • 1994-06-20 GB GB9526104A patent/GB2295179B/en not_active Expired - Fee Related
  • 1994-06-20 WO PCT/GB1994/001326 patent/WO1995000707A1/en not_active Ceased
  • 1994-06-20 BR BR9406964A patent/BR9406964A/pt not_active IP Right Cessation
  • 1994-06-20 CN CN94192863A patent/CN1057810C/zh not_active Expired - Fee Related
  • 1994-06-20 CA CA002165775A patent/CA2165775A1/en not_active Abandoned
  • 1994-06-20 ES ES94918448T patent/ES2118416T3/es not_active Expired - Lifetime
  • 1994-06-20 DE DE69409524T patent/DE69409524T2/de not_active Expired - Fee Related
  • 1994-06-23 MY MYPI94001623A patent/MY111482A/en unknown
  • 1994-06-23 IN IN541MA1994 patent/IN184701B/en unknown
  • 1994-06-24 ZA ZA944557A patent/ZA944557B/xx unknown

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