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
  • C21D11/00—Process control or regulation for heat treatments
• • 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
  • C21D11/00—Process control or regulation for heat treatments
  • C21D11/005—Process control or regulation for heat treatments for cooling

Definitions

• the invention relates to a method for cooling workpieces, in particular for cooling rolled products and here profile rolled products made of rail steels with a fine pearlitic or ferritic / pearlitic structure, the warm workpiece, i.e. Workpiece with an austenitic structure, passed through a cooling section with an entry and an exit area and subjected to a cooling process and undergoes a transformation into a pearlitic or ferritic / pearlitic structure.
• Rail steels are mainly used for the production of rails and their connecting and fastening elements.
• the vertical and lateral forces acting on the rail via the wheel such as normal, guiding, accelerating and braking forces, lead to very high dynamic loads in the immediate area of impact and generally to plastic deformation of the steel. These loads cause signs of wear in the form of material wear, abrasion, material breakouts, local material fatigue or cracks.
• An improvement in the resistance of a rail to signs of wear can be achieved by increasing its yield strength and tensile strength as well as its fatigue strength in conjunction with a pearlite structure that is as fine-streaked as possible.
• Rail steels with a ferritic-pearlitic structure have tensile strengths in a range from 700 to 900 N / mm 2 , while steels with a purely pearlitic structure achieve tensile strength values of over 900 N / mm 2 .
• the essential properties of the rail steels are determined by the proportion of the structure of ferrite / pearlite and by their morphological formation. Both at The lamellar spacing plays a role in ferritic / pearlitic as well as in pearlitic steels.
• the invention is based on the object of proposing a cooling method for producing workpieces, in particular rolled profile products, from rail steel, with improved mechanical properties and a finely streaked pearlite or ferrite / pearlite structure.
• the workpiece for example a rolled or possibly extruded profile product, coming from the (rolling) heat
• a cooling section which is composed of individual, independent cooling modules with independently adjustable cooling parameters, intermediate areas between the cooling modules for Thermal compensation or for thermal relaxation are provided with means for determining the actual temperature of the respective workpiece in these intermediate areas, and the specific cooling parameters, in particular the cooling intensity, of at least the respective subsequent cooling module depending on the respective actual temperature values of one or each intermediate area
• a defined (surface) temperature of the workpiece can be regulated during the entire passage through the cooling section, the defined temperature of the workpiece in each case above a critical temperature at which bainitic Ge Form parts to be joined.
• the basic idea is to regulate the cooling of a workpiece made of rail steel in a cooling section, provided that the surface temperature of the workpiece made of rail steel is cooled in such a way that the desired pearlitic or ferritic / pearlitic structure is obtained, by passing through relaxation phases and a constantly checking the Temperature conditions in preferably every intermediate area and, if necessary, regulation of the cooling parameters of the individual cooling modules ensures that the temperature does not fall below a critical temperature and thus the supercooling is not so high that bainite conversion takes place and thus undesirable bainitic structural components form.
• the cooling process is composed of individual cooling process steps and depending on the running intermediate areas for structural relaxation from time phases of reheating and / or from time phases of thermal holding and / or from time phases of slow cooling.
• the workpiece can go through the same time phases of relaxation in all intermediate areas or different time zones in different intermediate areas.
• the reheating takes place either through the residual heat still present inside the workpiece and / or through external heat supply. In this way, an approximately sawtooth-like cooling curve is set, which has a favorable effect on the final structure which is established and thus on the mechanical properties. Bainite formation is counteracted by setting the parameters of the cooling section in such a way that bainite formation cannot begin at any point in the cooling process.
• the intermediate areas are used for thermal compensation via the workpiece, in particular rolled product, or for cooling at slow cooling speeds.
• the specific cooling parameters of the subsequent cooling zone and, at the same time, the cooling parameters of the previous cooling module are preferably regulated as a function of the respective measured actual temperature value of each intermediate area. This means that a workpiece or rolled product, insofar as it is of a predetermined target temperature, which results in a should have the correct point in time or in an intermediate range, deviates, is adjusted back to the target temperature by a specific change in the cooling parameters in the subsequent cooling module and, at the same time, the previous cooling module is adjusted for subsequent workpieces.
• the surface temperature of the workpiece at the end of the intermediate area i.e. after the end of the area for structural relaxation.
• the temperature measurement in the intermediate areas can also be used for quality monitoring.
• the surface temperature measurement is carried out by means of an optical and non-contact measurement, i.e. using a pyrometer.
• the control of the cooling parameters and here in particular the cooling intensity is preferably carried out by regulating the pressure with which the cooling medium hits the surface of the workpiece and / or by means of regulated adjustment of the temperature of the cooling medium and / or by means of regulated adjustment of the volume flow of the cooling medium by selecting the cooling nozzle geometry.
• Cooling water is preferably used as the cooling medium.
• the pressure control is preferably carried out by a pressure control valve in the supply line to the nozzles, which are arranged on chilled beams.
• the cooling intensity is also possible by controlling a different number of nozzles per chilled beam or chilled beam arrangement.
• the cooling medium ie in particular the cooling water
• the cooling medium be preheated to such an extent before it occurs on the workpiece surface that the temperature does not fall below the suffering frost temperature or occurs very late.
• the Leidenfrost phenomenon is the non-wetting behavior of a liquid when the temperature of the body touched is above the boiling point of the liquid. Water, for example, is protected from further evaporation by a gas skin from evaporated water and thus loses the cooling effect for a certain time.
• the suffering frost temperature can be influenced by the cooling water flow temperature.
• the suffering frost temperature increases with a higher cooling water supply temperature, and the cooling becomes weaker.
• the cooling water be preheated so that the temperature does not fall below the suffering frost temperature or takes place very late. This has the advantage that the cooling becomes weaker and therefore more reproducible.
• the temperature of the workpiece is measured before entering or upon entering the cooling section and this temperature value is used for presetting the cooling parameters in order to preset the cooling parameters of the individual cooling modules, in particular the setting of the pressure with which the cooling medium strikes the workpiece surface , to reach.
• Figure 1 is a schematic overview of a cooling section in which the inventive method is carried out.
• Fig. 2 is a temperature-time diagram with the cooling curves of five measuring points in or on the rail head of a conventional rail steel with about 0.8% C. and 1.0% Mn, which is subjected to a cooling process in such a way in a cooling section that the bainite temperature is not fallen below;
• the cooling section 1 shown in FIG. 1 adjoins a profile rolling section (not shown), for example a rolling section for rail profiles made of rail steels.
• the cooling section 1 is composed of five cooling modules 2a-e, but is not limited to this number of cooling modules.
• the individual cooling modules 2a-e are constructed, for example, in such a way that they comprise one or more cooling beams or cooling nozzle arrangements.
• the pressure at which the cooling water emerges from the individual nozzles can be set via a pressure control valve 3a-e.
• the current pressure is measured using the pressure gauges 4a-e.
• Intermediate areas 5a-e are arranged between the individual cooling modules 2a-e.
• a pyrometer 6a-e for contactless optical measurement of the surface temperature of the rolled product located in this intermediate region is arranged at the end of each intermediate region 5a-e, the surface temperature at the rail head being measured in the case of a rail profile.
• An additional pyrometer 6f is arranged in front of the first cooling module 2a at the beginning or entry area (12) of the cooling section 1.
• the individual pyrometers 6a-f are connected to a computer unit 8 via signal lines 7a-g.
• the computer unit 8 is connected via corresponding control lines 9a-e for changing the individual control valves 3a-e of the coolant nozzles.
• the cooling medium in particular cooling water (KW)
• KW cooling water
• a control loop of the pressure measuring devices 4a-e with the computer unit 8 is also provided (signal lines 11ae).
• a current surface temperature value is recorded by means of the first pyrometer 6f, for example a two-color pyrometer.
• This first surface temperature value is forwarded to the computer unit 8, which already effects a presetting of the individual control valves for setting the cooling water pressure and the cooling water temperature as a function of this individual value.
• the rail profile After passing through the first cooling module 2a and following the first cooling step, the rail profile enters the first intermediate area 5a, in which a relaxation phase for the structure takes place.
• a further surface temperature measurement (TIST) is carried out using a second pyrometer 6a, for example a two-color pyrometer.
• This recorded actual value is transferred to the computer unit 8 via the signal lines 7a and 7g and a difference calculation is carried out there between a target (T S OLL) and the actual value (TIST).
• the target value is always above a material-specific temperature at which bainite formation can occur.
• the setpoints are alloy-specific and can be determined from tests.
• a guideline for this critical temperature. which should not be undercut for rail steels in a cooling process is around 450-500 ° C.
• the subsequent one or more subsequent cooling modules are or are adjusted with regard to their cooling parameters, here the pressure of the incident cooling water, by changing the pressure control valves 3a-e.
• the pressure values are continuously controlled as a function of the measured actual pressure values.
• the control described is repeated depending on the temperature values recorded in each further intermediate area 5b-5e. It is preferably provided that not only the subsequent cooling module, but also the previous cooling module or modules for the subsequent rolling stock to be cooled are regulated.
• FIGS. 2 and 3 show the cooling curves of a rail head made of a material with 0.8% carbon with regulation and without regulation with the aid of temperature-time diagrams.
• the designation C80W60 or C80W65 makes it clear that the cooling rate in the core of the rail head (example of rail shape according to AREA 136 [delivery specification of the American Railway Engineering Association]) is less high than in the peripheral areas and that the conversion of austenite to pearlite or Ferrite-pearlite takes place at higher temperatures.
• the temperature curve over time is determined at five different measuring points on the rail head.
• 1 is a measuring point in the core of the rail head
• 2 is a measuring point which is arranged 5 mm below the surface
• 3 is a measuring point which is 5 mm below the side surface
• 4 is a measuring point on the side surface
• 5 is a measuring point on the head surface.
• the simulated cooling section can be individually controlled with five modules.
• the individual cooling curves in FIG. 2 show that a critical temperature at which bainite formation would start is never undercut.
• the sawtooth-like cooling curve with reheating in the intermediate or compensation zones becomes clear.
• Fig. 3 shows a comparison of a cooling section with five cooling modules, which are not individually controllable, so that there is a drop below the bainite temperature in the near-surface areas (curves 4 and 5) of the rail head.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Mechanical Engineering (AREA)
• Physics & Mathematics (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatment Of Articles (AREA)
• Control Of Heat Treatment Processes (AREA)
• Metal Rolling (AREA)
• Heat Treatments In General, Especially Conveying And Cooling (AREA)

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• 2001
  • 2001-08-01 DE DE10137596A patent/DE10137596A1/de not_active Withdrawn
• 2002
  • 2002-07-25 DE DE50202183T patent/DE50202183D1/de not_active Revoked
  • 2002-07-25 RU RU2004105954/02A patent/RU2266966C2/ru not_active IP Right Cessation
  • 2002-07-25 CN CNB028151186A patent/CN1232661C/zh not_active Expired - Fee Related
  • 2002-07-25 ES ES02776916T patent/ES2236592T3/es not_active Expired - Lifetime
  • 2002-07-25 JP JP2003517324A patent/JP4174423B2/ja not_active Expired - Fee Related
  • 2002-07-25 US US10/485,286 patent/US20040187974A1/en not_active Abandoned
  • 2002-07-25 KR KR1020047000443A patent/KR100583301B1/ko active IP Right Grant
  • 2002-07-25 AT AT02776916T patent/ATE288503T1/de active
  • 2002-07-25 EP EP02776916A patent/EP1412543B1/fr not_active Revoked
  • 2002-07-25 WO PCT/EP2002/008271 patent/WO2003012151A1/fr active IP Right Grant
• 2007
  • 2007-07-23 US US11/880,635 patent/US7854883B2/en not_active Expired - Fee Related

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