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
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/02—Hardening articles or materials formed by forging or rolling, with no further heating beyond that required for the formation
• • 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
  • C21D1/18—Hardening; Quenching with or without subsequent tempering
• • 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
  • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
  • C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
  • C21D8/0226—Hot rolling
• • 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
  • C21D2211/001—Austenite
• • 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
  • C21D2211/002—Bainite
• • 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
• • 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

• the invention relates to a method and a plant for the production of dual-phase steels from the hot-rolled state with a two-phase structure made of 70 to 90% ferrite and 30 to 10% martensite through a controlled temperature control and defined cooling strategy during the cooling of the steels, inter alia by means of Water cooling after its finish rolling, the cooling curve running into the ferrite area in a first cooling stage and further cooling to temperatures below the martensite starting temperature in a second cooling stage after reaching the necessary proportion
• the targeted microstructure conversion by appropriate cooling of the steel is known.
• DE 44 16 752 AI describes a process for producing hot wide strip, in which the surface temperature of the slab is sufficiently deep (at least before the first forming between the continuous casting machine and a compensating furnace) 2 mm) to the extent that a structural change from austenite to Fernt / Perlite occurs.
• the cooling time is selected so that at least 70% austenite is converted to Fernt / Perlite.
• the compensating furnace there is then a renewed conversion to Austenite with reorientation of Austenite Grain boundaries
• second-choice scrap in particular scrap containing copper, can be used as a raw material without undesired accumulation of copper at the grain boundaries of the P ⁇ maraustenite
• sufficient ferrite formation is achieved, for example, by cooling with water to a temperature of around 620 - 650 ° C with subsequent air cooling.
• the duration of the air cooling (approx. 8 seconds) is selected so that at least 70% of the austenite is converted to ferrite before the second cooling stage begins During the first cooling stage and during air cooling, a conversion in the Perht stage should be avoided
• the task is solved with the characterizing measures of claim 1 in that during the first cooling stage the cooling curve of the steels is set with a cooling rate of 20 K / s to 30 K / s so low that the cooling curve is at such a high temperature enters the ferrite area so that the ferrite formation can take place quickly and at least 70% of the austenite has already been converted into ferrite before the start of the second cooling stage
• the cooling curve runs into the ferrite area later at a higher temperature than in the known processes, i.e. the conversion of the austenite into ferrite begins somewhat delayed but at a higher temperature than at the known methods, and it also runs faster due to the higher temperature. It has an advantageous effect if the ferrite area is reached as quickly as possible with a high transformation temperature
• the principle of loosened cooling is used according to the invention. This is water cooling, in which water is applied to the cooling material from water cooling stages arranged one behind the other by influencing the number of water cooling stages, their distance from one another and The effective length of the water cooling stages allows the cooling rate or the amount of water applied to the cooling material (its cooling material mass and / or the surface of the cooling material) to be optimally adjusted.
• the cooling can also be achieved with an infinitely variable quantity of coolant
• the loosened cooling can be extended until the desired degree of conversion is reached, without the risk - as in the known methods with fast cooling - that the cooling curve leaves the ferrite area beforehand due to excessive cooling
• the production of dual-phase steels can take place on part of the cooling section.
• the part of the cooling section used is much shorter than in the known processes with Air cooling If the required structural components for dual-phase steels can be set without air cooling, this results in significant advantages for the operator. Fewer system components are required for the production of dual-phase steels.
• the production spectrum can be modified with changed process and strip parameters (e.g. higher strip speed). compared to be expanded so far.
• a system for carrying out the method of the invention is characterized by a cooling section arranged behind the last finishing mill stand, comprising a plurality of water cooling stages or cooling systems arranged one behind the other with a continuously variable amount of coolant.
• the number of water cooling stages, their effective length and their distance from one another can be changed according to the invention, so that this cooling section can be adapted in a simple manner to changed geometries of the goods to be cooled and to different belt speeds
• Fig. 1 is a schematic representation of the rapid cooling and the loosened cooling and their assignment in a rolling mill
• Fig. 3 shows the degree of Ausemtumumwandung with the fast
• Fig. 4 shows the degree of Ausemtumumwandung with the loosened
• FIG. 1 the end of a rolling mill is shown schematically, consisting of the last finish rolling stand (1), the rolling stock or cooling stock (2) and a reel (3) with deflection rollers or driver (4) Above this part of a rolling train are two different cooling sections drawn in With the cooling section (5) according to the prior art, an early, rapid cooling of the cooling material (2) is brought about by a coherent water supply. In the cooling section (6), according to the invention, water cooling stages (7) are arranged one behind the other, thereby cooling "loosened up"
• the cooling curve (9) shows the cooling process with the strategy commonly used today (early, rapid cooling to a certain holding temperature with subsequent air cooling, then further cooling to low temperatures below the martensite start temperature)
• the cooling curve (10) with its first cooling stage (14) reaches the ferrite area (F) at point (15) later in the loosened cooling compared to the cooling curve (9). Since the loosened cooling is initially maintained after reaching the ferrite area (F) no time-consuming holding time with air cooling is required and the cooling curve (10) leaves the ferrite area (F) earlier
• the loosened cooling is maintained within the ferrite area (F) until the desired degree of conversion is reached. Then the further cooling with the second cooling stage (16) takes place immediately.
• the invention is not limited to the exemplary cooling curves described in the illustrations, but also other cooling curves, such as, for example, in cooling systems with an infinitely variable amount of cooling agent, which in the sense of the invention lead to higher conversion temperatures, are also possible.
• the invention is not restricted to water cooling , but other cooling systems can be used, which lead to an early reaching of the ferrite area at high temperatures

Landscapes

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

Priority Applications (6)

Applications Claiming Priority (2)

Publications (1)

Family

ID=7875154

Family Applications (1)

Country Status (11)

Cited By (2)

Families Citing this family (7)

Citations (6)

Family Cites Families (5)

• 1998
  • 1998-07-24 DE DE19833321A patent/DE19833321A1/de not_active Withdrawn
• 1999
  • 1999-07-07 MY MYPI99002855A patent/MY124339A/en unknown
  • 1999-07-17 BR BR9912310-0A patent/BR9912310A/pt not_active IP Right Cessation
  • 1999-07-17 CA CA2338743A patent/CA2338743C/en not_active Expired - Lifetime
  • 1999-07-17 JP JP2000561368A patent/JP2002521562A/ja active Pending
  • 1999-07-17 AT AT99938282T patent/ATE224959T1/de not_active IP Right Cessation
  • 1999-07-17 DE DE59902877T patent/DE59902877D1/de not_active Expired - Lifetime
  • 1999-07-17 WO PCT/EP1999/005113 patent/WO2000005422A1/de active IP Right Grant
  • 1999-07-17 CN CNB998091405A patent/CN1173048C/zh not_active Expired - Lifetime
  • 1999-07-17 RU RU2001105194/02A patent/RU2225453C2/ru active
  • 1999-07-17 EP EP99938282A patent/EP1108072B1/de not_active Expired - Lifetime
  • 1999-07-17 KR KR1020017000810A patent/KR100578823B1/ko active IP Right Grant

Patent Citations (6)

Non-Patent Citations (1)

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