Classifications

• • 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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/62—Quenching devices
  • C21D1/667—Quenching devices for spray quenching

Definitions

• the present invention relates to an improved method for manufacturing rails, and in particular high resistance rails.
• high strength steels is meant specially steels containing 0.4% to 0.85% of C, 0.4% to 1% of Mn and O, 1% to 0.4% of Si, and preferably 0.6% to 0.85% C and 0.6% to 0.8% Mn.
• these steels can contain up to 1% of Cr, or up to 0.3% of Mo or up to 0.15% of V.
• the present invention specifically relates to a method for eliminating the drawbacks mentioned above.
• the process which is the subject of the present invention is essentially characterized in that, at the outlet from the hot rolling mill, the temperature of the rail is lowered to a value not less than that at which the pearlitic transformation begins in the bead, in that from this temperature, the rail in continuous travel is subjected to rapid cooling to a temperature below about 650 ° C., so that, at the end of this rapid cooling, the minus 80% of the aotenite-perlite allotropic transformation in the rail, and in that the rail is then cooled to room temperature.
• the rapid cooling rate is between 2 ° C / s and 10 ° C / s. -
• the method of the invention is advantageously implemented by adjusting the heat transfer coefficient between the rail and the cooling agent during rapid cooling.
• rapid cooling is carried out by spraying water onto the rail and by adapting the flow rate of projected water to the temperature of the rail.
• the projected water flow is adapted for rapid cooling to the massiveness of the various parts of the rail, so as to achieve substantially the same cooling rate in all parts of the rail ..
• an acceleration is applied to the rail, preferably substantially uniform in the rapid cooling zone and the value of this acceleration is adjusted as a function of the temperature difference measured between the ends of the rail at entering the cooling zone, so that the temperature of the rail leaving this zone is less than approximately 650 ° C. and at least 80% of the allotropic transformation is carried out at the exit from this zone austenite - perlite in the rail.
• this acceleration of the rail makes it possible to maintain a substantially constant rail temperature at the exit from the rapid cooling zone and to ensure that the recalescence, in any portion of the rail, always occurs at the appropriate place. from the rapid cooling zone.
• the method of the invention makes it possible to limit the effects of the difference in massiveness of the various parts of the rail (bead, core, shoe) and of the recalescence of the steel on the transient deformations during cooling.
• this process contributes to improving the straightness of the rails by greatly reducing the transient deformations during cooling and therefore reducing the importance of dressing after rolling.
• Three rails (A, B, C) of 12 m in length were subjected respectively to cooling by a known method of immersion in boiling water and by the method of the invention, on the one hand without acceleration and d on the other hand with acceleration of the rail during rapid cooling.
• the steel composition of the three rails was almost identical:
• the mechanical properties of the bead have been determined according to UIC standard 860.0, that is to say 2/5 of the height of the bead.
• Rail A was air-cooled to 695 ° C and then immersed in boiling water for 67 seconds. Its leaving water temperature was 560 ° C.
• the bead had a breaking load of 1115 MPa and an elongation of 10%.
• this rail A had a vertical deflection of 700 mm, which had disappeared after 300 sec. Although it straightened during the final cooling, this rail therefore presented a significant transient deformation.
• Rail B was cooled while running at a uniform speed of 0.16 m / s, by spraying water at a flow rate of 28 m 3 / h.
• the rapid cooling zone was 10.70 m long.
• the cooling time was therefore 67 sec. Its temperature at the entrance to the cooling zone was around 800 ° C and its temperature at the exit was 630 ° C.
• Rail C treated in the same way as rail B, but with an initial speed of 0.18 m / s and an acceleration of the order of 0.01 m / sec 2 , so that the duration of the treatment has was reduced to 46 sec.
• the cooling water flow rate was 34.2 m 3 / h.
• the rail temperature was 800 ° C. at the inlet and 620 ° C. at the outlet from the cooling zone.
• the bead had a breaking load of 1100 MPa and an elongation of 12.5%.
• the maximum vertical deflection during cooling was 20 mm, and the permanent vertical deflection after final cooling was also approximately 20 mm.

Landscapes

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

Applications Claiming Priority (2)

Publications (1)

Family

ID=19729964

Family Applications (1)

Country Status (7)

Cited By (2)

Families Citing this family (9)

Citations (4)

Family Cites Families (2)

• 1982
  • 1982-10-11 LU LU84417A patent/LU84417A1/fr unknown
• 1983
  • 1983-10-10 EP EP83201443A patent/EP0108436A1/de not_active Withdrawn
  • 1983-10-11 ZA ZA837540A patent/ZA837540B/xx unknown
  • 1983-10-11 JP JP58189796A patent/JPS5989721A/ja active Granted
  • 1983-10-11 CA CA000438708A patent/CA1213160A/en not_active Expired
  • 1983-10-11 US US06/540,523 patent/US4486243A/en not_active Expired - Lifetime
  • 1983-10-11 AU AU20039/83A patent/AU2003983A/en not_active Abandoned

Patent Citations (4)

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