EP1050591A2 - Thermal treatment process for manufacturing surface hardened unalloyed or low alloyed, elongated or flat steel products - Google Patents
Thermal treatment process for manufacturing surface hardened unalloyed or low alloyed, elongated or flat steel products Download PDFInfo
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- EP1050591A2 EP1050591A2 EP00108714A EP00108714A EP1050591A2 EP 1050591 A2 EP1050591 A2 EP 1050591A2 EP 00108714 A EP00108714 A EP 00108714A EP 00108714 A EP00108714 A EP 00108714A EP 1050591 A2 EP1050591 A2 EP 1050591A2
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- 238000004519 manufacturing process Methods 0.000 title claims abstract description 8
- 229910000831 Steel Inorganic materials 0.000 title claims description 22
- 239000010959 steel Substances 0.000 title claims description 22
- 238000007669 thermal treatment Methods 0.000 title 1
- 238000000034 method Methods 0.000 claims abstract description 56
- 229910000734 martensite Inorganic materials 0.000 claims abstract description 55
- 238000001816 cooling Methods 0.000 claims abstract description 44
- 230000008569 process Effects 0.000 claims abstract description 25
- 229910001566 austenite Inorganic materials 0.000 claims abstract description 15
- 238000010438 heat treatment Methods 0.000 claims abstract description 10
- 239000000956 alloy Substances 0.000 claims abstract description 4
- 238000006243 chemical reaction Methods 0.000 claims description 9
- 239000002344 surface layer Substances 0.000 claims description 6
- 229910045601 alloy Inorganic materials 0.000 claims description 3
- 238000005096 rolling process Methods 0.000 claims description 3
- 229910001294 Reinforcing steel Inorganic materials 0.000 claims description 2
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- 239000000203 mixture Substances 0.000 abstract description 2
- 229910000851 Alloy steel Inorganic materials 0.000 abstract 2
- 239000000463 material Substances 0.000 description 9
- 238000010791 quenching Methods 0.000 description 6
- 229910052748 manganese Inorganic materials 0.000 description 5
- 239000011572 manganese Substances 0.000 description 5
- 230000000171 quenching effect Effects 0.000 description 5
- 230000009466 transformation Effects 0.000 description 5
- 230000006978 adaptation Effects 0.000 description 4
- 238000005496 tempering Methods 0.000 description 4
- 229910000746 Structural steel Inorganic materials 0.000 description 3
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- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000010276 construction Methods 0.000 description 2
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- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 229910000640 Fe alloy Inorganic materials 0.000 description 1
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
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Classifications
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- 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
- C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
- C21D8/08—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires for concrete reinforcement
-
- 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
- C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
-
- 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
- C21D2221/00—Treating localised areas of an article
- C21D2221/10—Differential treatment of inner with respect to outer regions, e.g. core and periphery, respectively
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S148/00—Metal treatment
- Y10S148/902—Metal treatment having portions of differing metallurgical properties or characteristics
Definitions
- the invention relates to a heat treatment process for the production of surface hardened layers Long and flat products made of unalloyed or low-alloyed Steels, comprising the following steps: a first cooling process of the workpiece for setting a martensitic structure in the workpiece edge area and a second cooling process of the workpiece at a cooling rate below the lower critical cooling rate for cooling the workpiece core.
- the lower critical cooling rate understand the cooling rate, which is just enough, to form 1% martensite, i.e. the workpiece core is cooled down slowly, that there is not a martensitic, but a ferritic-pearlitic structure sets.
- a hardening structure is usually obtained from the austenitizing temperature with the aid of a suitable cooling device (usually by means of water cooling) in the surface layer of the workpiece one-time quenching process is set by falling below the martensite start temperature M s , which is then started after the cooling has been terminated by the residual heat still present inside the long product.
- a suitable cooling device usually by means of water cooling
- M s martensite start temperature
- the steels used for this procedure are generally low-alloy structural steels with a carbon content between 0.03 to 0.25%, a manganese content of 0.3 to 1.6% and different admixtures of other alloy components.
- the quenching of reinforcing steels for steel construction in a water cooling section is known. After setting a defined depth of martensitically transformed structures in the edge area of the long product, self-tempering follows due to the residual heat inside the workpiece. Depending on the material analysis and the extent of the tempered surface layer, this results in a certain combination of strength and toughness properties (ductility).
- the invention is based on the object a heat treatment for the production of surface hardened long and To create flat products that compared to the known after Process treated workpieces while maintaining the better strength Have toughness properties.
- the first cooling process becomes the conversion of austenite in martensite in several, repeating steps carried out, each process step being composed of cooling to a temperature below the martensite start temperature to the martensitic Conversion of only part of the workpiece edge area and one part each subsequent relaxation phase of the already formed martensitic Structural parts and / or marginal areas martensite / austenite.
- the basis for understanding the invention lies in the nature of the martensitic transformation. If an iron alloy is heated to temperatures above A c3 (the temperature at which the conversion of the ferrite to austenite ends in warming) and then quenched with a sufficiently high cooling rate, the austenitic structure transforms martensitic.
- a c3 the temperature at which the conversion of the ferrite to austenite ends in warming
- the special thing about martensite transformation - compared to the diffusion-controlled transformation mechanisms - is that it takes place athermally. This means that the conversion does not continue by holding at a certain temperature, but only continues in the form of a cascade with further cooling. An isothermal hold time does not cause an increase in the proportion of the amount of martensite in the overall structure, as in the case of diffusion-controlled conversion.
- the size of the growing martensite crystals is limited by the former austenite limits.
- the martensite itself is converted in two steps according to the models that are now considered to be secure: a lattice-changing deformation step from cubic surface-centered (automotive) to cubic space-centered (krz) lattice and a lattice-preserving adjustment of the newly formed martensite.
- a lattice-changing deformation step from cubic surface-centered (automotive) to cubic space-centered (krz) lattice
- krz cubic space-centered
- this adaptation deformation does not take place without material separations, so that engineering steels have been shown to be quenched in the martensite level have a more or less high number of microcracks.
- These micro cracks themselves reduce the toughness and the ductility of the material, since under mechanical stress (e.g. in tensile tests) the cracks as germs act for the further material separation and thus the general failure of the Introduce the material.
- a heat treatment method is used according to the invention proposed in which the martensite conversion is not in a one-time quenching process, but takes place gradually and with short relaxation breaks between the individual conversion phases.
- the workpiece is only briefly cooled to the martensite stage, the temperature is then equalized and the quenching treatment is carried out again to temperatures below the martensite start temperature.
- the temperature is compensated either by self-tempering of the martensitic structural parts formed in the corresponding cooling process due to the residual heat in the workpiece to temperatures below A 1 and the associated reduction in lattice stresses. It is also proposed that the workpiece be brought back to the austenitizing temperature during the relaxation phase of the individual process steps for the partial reconversion of the martensite already formed into austenite. In addition to the resulting structural refinement, there are significantly fewer microcracks during the martensitic transformation.
- the proposed procedure has two effects: firstly the size of the areas to be converted at the same time is smaller. This creates at the phase boundary austenite-martensite, overall lower adaptation stresses, which reduces the risk of microcracks. On the other hand has the austenite surrounding the martensite due to the relaxation phases ongoing recovery processes (mainly due to dislocation gliding) Possibility to reduce adjustment tensions. This will result in an overshoot the breaking voltage of the motor vehicle-krz phase boundary, which is also due to the temporal superposition of the voltage fields of several neighboring phase boundaries can occur, counteracted overall.
- the proposed heat treatment can be directly related to a rolling process connect the workpiece, but it is also conceivable that it immediately to a previous heat treatment, for example normalizing, connects.
- Figure 1 shows the temperature-time curves of a rebar with a total diameter of 40 mm with hardened according to the proposed method Marginal areas. It is the temperature profiles for the surface (1) and the core (2) of the long product and on average (3).
- the workpiece passes through a cooling section, which consists of several cooling zones with different Length composed.
- the coolant is water. Expressed by the workpiece becomes a high or low ⁇ value in the cooling zones 2, 4, 6 and 8 quenched to a temperature below the martensite start temperature, but which is above the martensite finish temperature.
- cooling zones 1, 3, 5, 7 and 9 it comes to the temporal relaxation phases, here by means of Start yourself.
- the material is of a temperature Coming from about 1000 ° C, briefly to a temperature in the cooling zone 2 quenched below the martensite start temperature.
- the martensite start temperature is dependent on the steel composition and lies with the exemplary Steel at around 410 ° C.
- the material passes through in the subsequent cooling section a relaxation phase during which the already martensitic transformed Areas left on due to the residual heat present in the workpiece become.
- the austenite surrounding the martensite can Reduce adaptation tensions.
- Figure 3 shows the temperature-cooling time curves for the same Steel, but for a smaller diameter of the long product (20 mm).
- the Workpiece is moved at higher speed through the individual cooling sections transported, here for example at 15.00 m / s.
- the individual cooling process steps therefore run faster in comparison, but here too the processes are Quenching to a temperature below the martensite start temperature as well
- the relaxation phase of the structure is clearly recognizable through self-tempering.
- To Passage through the nine cooling zones is approximately 30% of the cross-section of the long product martensitic converted ( Figure 4).
- Figures 5 and 6 illustrate the difference between what is proposed according to the invention Process with the known process for hardening the surface layer of Long products. Although 35% also according to the conventional method Martensite structure is reached in the peripheral areas, it does happen because of one-time quench treatment with subsequent one-time self-starts microcracks in the structure and associated poor toughness properties, which are improved by the method according to the invention. It is clear that the toughness properties increase with the same strength values Figures 7 and 8, in which the elongation at break is above the yield point or tensile strength of an unalloyed structural steel are shown in the comparison surface hardened according to the conventional (I) and the process (II) according to the invention is.
- reinforcing steels in particular are hardened on the outer layer. They are mainly used as reinforcement steel for manufacturing of beams in steel construction.
Abstract
Description
Die Erfindung betrifft ein Wärmebehandlungsverfahren zur Herstellung randschichtgehärteter Lang- und Flachprodukte aus unlegierten oder niedriglegierten Stählen, umfassend folgende Schritte: einen ersten Abkühlprozeß des Werkstücks zum Einstellen eines martensitischen Gefüges im Werkstückrandbereich sowie einen zweiten Abkühlprozeß des Werkstücks mit einer Abkühlgeschwindigkeit unterhalb der unteren kritischen Abkühlgeschwindigkeit zur Abkühlung des Werkstückkerns. In diesem Zusammenhang wird unter der unteren kritischen Abkühlgeschwindigkeit die Abkühlgeschwindigkeit verstanden, die gerade noch ausreicht, um 1% Martensit zu bilden, d.h. der Werkstückkern wird so langsam abgekühlt, daß sich nicht ein martensitisches, sondern ein ferritisch-perlitisches Gefüge einstellt.The invention relates to a heat treatment process for the production of surface hardened layers Long and flat products made of unalloyed or low-alloyed Steels, comprising the following steps: a first cooling process of the workpiece for setting a martensitic structure in the workpiece edge area and a second cooling process of the workpiece at a cooling rate below the lower critical cooling rate for cooling the workpiece core. In this context, the lower critical cooling rate understand the cooling rate, which is just enough, to form 1% martensite, i.e. the workpiece core is cooled down slowly, that there is not a martensitic, but a ferritic-pearlitic structure sets.
Bei einem bekannten Verfahren zur Herstellung randschichtgehärteter und selbstangelassener Langprodukte (Draht, Stabstahl, Profilhalb- und Fertigzeug, und andere) wird für gewöhnlich von Austenitisiertemperatur kommend mit Hilfe einer geeigneten Kühleinrichtung (in der Regel mittels Wasserkühlung) in der Randschicht des Werkstückes ein Härtungsgefüge durch einen einmaligen Abschreckvorgang durch Unterschreiten der Martensitstarttemperatur Ms eingestellt, das nach Abbruch der Kühlung durch die noch im Innern des Langprodukts vorhandene Restwärme nachfolgend angelassen wird. Diese Verfahrensweise wird üblicherweise direkt aus der Walzhitze kommend angewendet, kann grundsätzlich jedoch auch bei einer nachgeschalteten Wärmebehandlung (beispielsweise Normalisierung) zum Einsatz kommen. Bei den für diese Verfahrensweise verwendeten Stählen handelt es sich in der Regel um niedrig legierte Baustähle mit einem Kohlenstoffgehalt zwischen 0,03 bis 0,25 %, einem Mangangehalt von 0,3 bis 1,6 % und unterschiedlichen Beimengungen weiterer Legierungsbestandteile. So ist zum Beispiel das Abschrecken von Bewehrungsstählen für den Stahlbau in einer Wasserkühlstrecke bekannt. Nach dem Einstellen einer definierten Tiefe von martensitisch umgewandelten Gefüge im Randbereich des Langproduktes schließt sich ein Selbstanlassen durch die Restwärme im Inneren des Werkstücks an. Hieraus ergibt sich je nach Werkstoffanalyse und Ausmaß der vergüteten Randschicht eine bestimmte Kombination aus Festigkeit- und Zähigkeitseigenschaften (Duktilität).In a known method for producing surface-hardened and self-tempered long products (wire, bar steel, semi-finished and finished products, and others), a hardening structure is usually obtained from the austenitizing temperature with the aid of a suitable cooling device (usually by means of water cooling) in the surface layer of the workpiece one-time quenching process is set by falling below the martensite start temperature M s , which is then started after the cooling has been terminated by the residual heat still present inside the long product. This procedure is usually applied directly from the rolling heat, but can in principle also be used in a subsequent heat treatment (for example normalization). The steels used for this procedure are generally low-alloy structural steels with a carbon content between 0.03 to 0.25%, a manganese content of 0.3 to 1.6% and different admixtures of other alloy components. For example, the quenching of reinforcing steels for steel construction in a water cooling section is known. After setting a defined depth of martensitically transformed structures in the edge area of the long product, self-tempering follows due to the residual heat inside the workpiece. Depending on the material analysis and the extent of the tempered surface layer, this results in a certain combination of strength and toughness properties (ductility).
Ausgehend von diesem Stand der Technik liegt der Erfindung die Aufgabe zugrunde, eine Wärmebehandlung zur Herstellung von randschichtgehärteten Lang- und Flachprodukten zu schaffen, die im Vergleich zu den nach dem bekannten Verfahren behandelten Werkstücken bei Beibehaltung der Festigkeits- bessere Zähigkeitseigenschaften aufweisen.Starting from this prior art, the invention is based on the object a heat treatment for the production of surface hardened long and To create flat products that compared to the known after Process treated workpieces while maintaining the better strength Have toughness properties.
Diese Aufgabe wird mittels eines Verfahrens mit den Merkmalen des Anspruchs 1
gelöst. Vorteilhafte Ausgestaltungen des Verfahrens sind in den Unteransprüchen
offenbart.This object is achieved by means of a method with the features of
Gemäß dem vorgeschlagenen Verfahren wird der erste Abkühlprozeß zur Umwandlung von Austenit in Martensit in mehreren, sich wiederholenden Schritten durchgeführt, wobei sich jeder Prozeßschritt zusammensetzt aus einem Abkühlen auf eine Temperatur unterhalb der Martensitstarttemperatur zur martensitischen Umwandlung nur jeweils eines Teils des Werkstückrandbereichs und einer sich anschließenden zeitlichen Entspannungsphase der bereits gebildeten martensitischen Gefügeteile und/oder Randbereiche Martensit/Austenit.According to the proposed method, the first cooling process becomes the conversion of austenite in martensite in several, repeating steps carried out, each process step being composed of cooling to a temperature below the martensite start temperature to the martensitic Conversion of only part of the workpiece edge area and one part each subsequent relaxation phase of the already formed martensitic Structural parts and / or marginal areas martensite / austenite.
Die einzelnen Schritte werden so oft wiederholt, bis das Gefüge in der gewünschten Randbereichstiefe vollständig martensitisch umgewandelt ist. Die sich bei dem vorgeschlagenen Wärmebehandlungsverfahren einstellenden besseren mechanischen Eigenschaften sind die Folge einer gegenüber dem bekannten Verfahren modifiziert ablaufenden Martensitbildung. Durch die Aufteilung des Abkühlprozesses in mehrere Unterschritte mit Pausen zwischen den einzelnen Prozessen wird ein Härtungsgefüge erzeugt, daß weniger Mikrorisse aufweist und somit bei mechanischer Beanspruchung (Kaltumformung) eine höhere Umformbarkeit aufweist, was sich unter anderem im Zugversuch in einer Steigerung der Bruchdehnungswerte bemerkbar macht.The individual steps are repeated until the structure is as desired Edge area depth is completely martensitic converted. The one with the proposed better mechanical treatment heat treatment process Properties are the result of a compared to the known method modified martensite formation. By dividing the cooling process into several sub-steps with breaks between the individual processes creates a hardening structure that has fewer micro cracks and thus mechanical Stress (cold forming) has a higher formability, which is reflected in an increase in the elongation at break values, among other things noticeable.
Die Grundlagen für das Verständnis der Erfindung liegen im Wesen der martensitischen Umwandlung. Wird eine Eisenlegierung auf Temperaturen oberhalb Ac3 (die Temperatur, bei der die Umwandlung des Ferrits in Austenit in einem Wärmen endet) erwärmt und diese dann mit ausreichend hoher Abkühlgeschwindigkeit abgeschreckt, so wandelt das austenitische Gefüge martensitisch um. Das besondere der Martensitumwandlung - im Vergleich zu den diffusionsgesteuerten Umwandlungsmechanismen - ist, daß sie athermisch erfolgt. Dies bedeutet, daß die Fortsetzung der Umwandlung nicht durch ein Halten auf einer bestimmten Temperatur erfolgt, sondern sie läuft nur bei einer weiteren Abkühlung kaskadenförmig weiter ab. Eine isotherme Haltezeit bewirkt nicht wie bei der diffusionsgesteuerten Umwandlung eine Zunahme des Anteils der Martensitmenge am Gesamtgefüge. Die Größe der wachsenden Martensitkristalle wird dabei durch die ehemaligen Austenitkomgrenzen beschränkt. Die Umwandlung des Martensit selber erfolgt nach dem heute als gesichert geltenden Modellen in zwei Schritten: einem gitterverändernden Deformationsschritt von kubisch-flächenzentrierten (kfz) zum kubisch-raumzentrierten (krz) Gitter und einer gittererhaltenden Anpassung des frisch gebildeten Martensits. Das Umklappen des Gitters vom kubischflächenzentrierten zum kubisch-raumzentrierten Typ und die Anpassung des frisch gebildeten Martensits führen nun zwangsläufig auch zu einer Deformation des Austenits, da die Martensitumwandlung zum einen mit einem Volumenzuwachs von ca. 3 % verbunden ist und an der Phasengrenze zudem zwei grundsätzlich unterschiedliche Gittertypen, nämlich kubisch-raumzentriert und kubischflächenzentriert, aufeinanderstoßen (vergleiche Figur 8). Soll es hierbei aufgrund der unvermeidbaren Anpassungsspannungen nicht zu Werkstofftrennungen an der Phasengrenze Martensit-Austenit kommen, muß der Austenit die auftretenden Deformationen durch Versetzungsgleiten oder Zwillingsbildung abfangen können. Hierbei ist nur das austenitische Restgefüge betroffen, da die Fließspannung des Martensit sehr viel höher ist als die des Austenits.The basis for understanding the invention lies in the nature of the martensitic transformation. If an iron alloy is heated to temperatures above A c3 (the temperature at which the conversion of the ferrite to austenite ends in warming) and then quenched with a sufficiently high cooling rate, the austenitic structure transforms martensitic. The special thing about martensite transformation - compared to the diffusion-controlled transformation mechanisms - is that it takes place athermally. This means that the conversion does not continue by holding at a certain temperature, but only continues in the form of a cascade with further cooling. An isothermal hold time does not cause an increase in the proportion of the amount of martensite in the overall structure, as in the case of diffusion-controlled conversion. The size of the growing martensite crystals is limited by the former austenite limits. The martensite itself is converted in two steps according to the models that are now considered to be secure: a lattice-changing deformation step from cubic surface-centered (automotive) to cubic space-centered (krz) lattice and a lattice-preserving adjustment of the newly formed martensite. The folding of the grid from the face-centered cubic to the body-centered cubic type and the adjustment of the newly formed martensite inevitably lead to a deformation of the austenite, since the martensite conversion is associated with a volume increase of approx. 3% on the one hand and two in principle at the phase boundary Different lattice types, namely cubic, body-centered and cubic surface-centered, collide (see Figure 8). If, due to the unavoidable adaptation stresses, material separations are not to occur at the martensite-austenite phase boundary, the austenite must be able to absorb the deformations that occur through dislocation sliding or twin formation. Only the austenitic residual structure is affected, since the yield stress of the martensite is much higher than that of the austenite.
In der Regel erfolgt diese Anpassungsverformung nicht ohne Werkstofftrennungen, so daß technische Stähle nachgewiesenermaßen nach dem Abschrecken in der Martensitstufe eine mehr oder weniger hoher Zahl an Mikrorissen aufweisen. Diese Mikrorisse selber reduzieren die Zähigkeit sowie die Duktilität des Werkstoffes, da bei mechanischer Belastung (z. B. im Zugversuch) die Risse als Keime für die weitere Werkstofftrennung wirken und damit das generelle Versagen des Werkstoffes einleiten. Umgekehrt wirkt sich eine Reduzierung der Anzahl der Mikrorisse insgesamt positiv auf die Zähigkeit bzw. die Duktilität des Werkstoffes aus, was sich wiederum in höheren Werten für die Bruchdehnung im Zugversuch zeigt.As a rule, this adaptation deformation does not take place without material separations, so that engineering steels have been shown to be quenched in the martensite level have a more or less high number of microcracks. These micro cracks themselves reduce the toughness and the ductility of the material, since under mechanical stress (e.g. in tensile tests) the cracks as germs act for the further material separation and thus the general failure of the Introduce the material. Conversely, there is a reduction in the number of microcracks overall positive on the toughness or ductility of the material from, which in turn results in higher values for the elongation at break in the tensile test shows.
Im Hinblick auf die Reduzierung der Mikrorisse wird erfindungsgemäß ein Wärmebehandlungsverfahren vorgeschlagen, bei dem die Martensitumwandlung nicht in einem einmaligen Abschreckprozeß, sondern stufenweise abläuft und zwar mit kurzen Entspannungspausen zwischen den einzelnen Umwandtungsphasen. Hierzu wird das Werkstück immer nur kurzzeitig in die Martensitstufe abgekühlt, danach erfolgt ein Ausgleich der Temperatur und erneut eine Abschreckbehandlung auf Temperaturen unterhalb der Martensitstarttemperatur.With regard to the reduction of microcracks, a heat treatment method is used according to the invention proposed in which the martensite conversion is not in a one-time quenching process, but takes place gradually and with short relaxation breaks between the individual conversion phases. For this purpose, the workpiece is only briefly cooled to the martensite stage, the temperature is then equalized and the quenching treatment is carried out again to temperatures below the martensite start temperature.
Der Ausgleich der Temperatur geschieht entweder durch ein Selbstanlassen der bei dem entsprechenden Abkühlprozeß gebildeten martensitischen Gefügeteile aufgrund der Restwärme im Werkstück auf Temperaturen unterhalb A1 und einem damit verbundenen Abbau von Gitterspannungen. Ferner wird vorgeschlagen, daß während der Entspannungsphase der einzelnen Prozeßschritte das Werkstück wieder auf Austenitisiertemperatur gebracht wird zum teilweisen Rückumwandeln des bereits gebildeten Martensit in Austenit. Neben einer dadurch bedingten weiteren Gefügefeinung entstehen deutlich weniger Mikrorisse bei der martensitischen Umwandlung.The temperature is compensated either by self-tempering of the martensitic structural parts formed in the corresponding cooling process due to the residual heat in the workpiece to temperatures below A 1 and the associated reduction in lattice stresses. It is also proposed that the workpiece be brought back to the austenitizing temperature during the relaxation phase of the individual process steps for the partial reconversion of the martensite already formed into austenite. In addition to the resulting structural refinement, there are significantly fewer microcracks during the martensitic transformation.
Durch die vorgeschlagene Verfahrensweise werden zwei Effekte erzielt: zum einen ist die Größe der gleichzeitig umwandelnden Bereiche kleiner. Hierdurch entstehen an der Phasengrenze Austenit-Martensit insgesamt geringere Anpassungsspannungen, was die Gefahr der Mikrorißbildungen reduziert. Zum anderen hat der den Martensit umgebende Austenit durch die bei den Entspannungsphasen ablaufenden Erholungsvorgänge (hauptsächlich durch Versetzungsgleiten) die Möglichkeit, Anpassungsspannungen abzubauen. Dadurch wird einer Überschreitung der Trennbruchspannung der kfz-krz-Phasengrenze, die auch durch die zeitliche Überlagerung der Spannungsfelder mehrerer benachbarter Phasengrenzen eintreten kann, insgesamt entgegengewirkt.The proposed procedure has two effects: firstly the size of the areas to be converted at the same time is smaller. This creates at the phase boundary austenite-martensite, overall lower adaptation stresses, which reduces the risk of microcracks. On the other hand has the austenite surrounding the martensite due to the relaxation phases ongoing recovery processes (mainly due to dislocation gliding) Possibility to reduce adjustment tensions. This will result in an overshoot the breaking voltage of the motor vehicle-krz phase boundary, which is also due to the temporal superposition of the voltage fields of several neighboring phase boundaries can occur, counteracted overall.
Die vorgeschlagene Wärmebehandlung kann sich unmittelbar an ein Walzprozeß des Werkstücks anschließen, es ist aber auch denkbar, daß sie sich unmittelbar an eine vorher abgelaufene andere Wärmebehandlung, beispielsweise Normalglühen, anschließt. The proposed heat treatment can be directly related to a rolling process connect the workpiece, but it is also conceivable that it immediately to a previous heat treatment, for example normalizing, connects.
Weitere Einzelheiten und Vorteile der Erfindung ergeben sich aus den nachfolgenden Beschreibungen. Hierbei zeigen:
Figur 1- Temperatur-Zeitkurven eines Beton-Rippenstahls mit nach dem vorgeschlagenen Verfahren gehärteten Randbereichen mit einem Gesamtdurchmesser von 40 mm;
Figur 2- Temperaturverteilung über den Durchmesser des Beton-Rippenstahls
nach
Figur 1; Figur 3- Temperatur-Zeitkurven eines Beton-Rippenstahls mit nach dem vorgeschlagenen Verfahren gehärteten Randbereich mit einem Gesamtdurchmesser von 20 mm;
Figur 4- Temperaturverteilung über den Durchmesser des Beton-Rippenstahls
nach
Figur 3; Figur 5- Temperatur-Zeitkurven eines Beton-Rippenstahls mit nach dem herkömmlichen Verfahren gehärteten Randbereich mit einem Gesamtdurchmesser von 40 mm;
Figur 6- Temperaturverteilung über den Durchmesser des Beton-Rippenstahls
nach
Figur 5; Figur 7- Darstellung der Bruchdehnung über der Streckgrenze bei einem unlegierten Baustahl (C ≈ 0,25 %, Si ≈ 0,29 %, Mn ≈ 1,0 %) im Vergleich nach dem konventionellen und dem erfindungsgemäßen Verfahren randschichtgehärtet;
Figur 8- Darstellung der Bruchdehnung über der Zugfestigkeit bei einem unlegierten Baustahl (C ≈ 0,25 %, Si ≈ 0,29 %, Mn ≈ 1,0 %) im Vergleich nach dem konventionellen und dem erfindungsgemäßen Verfahren randschichtgehärtet;
Figur 9- Martensitumwandlung und Anpassungsverformung der umgebenden austenitischen Matrix.
- Figure 1
- Temperature-time curves of a ribbed steel with edge areas hardened according to the proposed method with a total diameter of 40 mm;
- Figure 2
- Temperature distribution over the diameter of the concrete rib steel according to Figure 1;
- Figure 3
- Temperature-time curves of a ribbed steel with an edge area hardened according to the proposed method with a total diameter of 20 mm;
- Figure 4
- Temperature distribution over the diameter of the concrete rib steel according to Figure 3;
- Figure 5
- Temperature-time curves of a ribbed steel with an edge area hardened according to the conventional method with a total diameter of 40 mm;
- Figure 6
- Temperature distribution over the diameter of the concrete rib steel according to Figure 5;
- Figure 7
- Representation of the elongation at break above the yield strength of an unalloyed structural steel (C ≈ 0.25%, Si ≈ 0.29%, Mn ≈ 1.0%) in comparison with the conventional and the method according to the invention hardened at the surface layer;
- Figure 8
- Representation of the elongation at break versus the tensile strength of an unalloyed structural steel (C ≈ 0.25%, Si ≈ 0.29%, Mn ≈ 1.0%) in comparison with the conventional and the method according to the invention hardened at the surface layer;
- Figure 9
- Martensite transformation and deformation of the surrounding austenitic matrix.
Figur 1 zeigt die Temperatur-Zeitkurven eines Beton-Rippenstahls mit einem Gesamtdurchmesser
von 40 mm mit nach dem vorgeschlagenen Verfahren gehärteten
Randbereichen. Es sind die Temperaturverläufe für die Oberfläche (1) und
dem Kern (2) des Langproduktes sowie im Durchschnitt (3) dargestellt. Das Werkstück
durchläuft eine Kühlstrecke, die sich aus mehreren Kühlzonen mit unterschiedlicher
Länge zusammensetzt. Das Kühlmittel ist Wasser. Ausgedrückt durch
einen hohen oder niedrigen α-Wert wird das Werkstück in den Kühlzonen 2, 4, 6
und 8 auf eine Temperatur unterhalb der Martensitstarttemperatur abgeschreckt,
die aber oberhalb der Martensitfinish-Temperatur liegt. In den Kühlzonen 1, 3, 5, 7
und 9 kommt es nachfolgend zu den zeitlichen Entspannungsphasen, hier mittels
Selbstanlassen. Bei den konkreten Beispiel wird der Werkstoff, von einer Temperatur
von etwa 1000°C kommend, in der Kühlzone 2 kurzzeitig auf eine Temperatur
unterhalb der Martensitstarttemperatur abgeschreckt. Die Martensitstarttemperatur
ist abhängig von der Stahlzusammensetzung und liegt bei dem beispielhaften
Stahl bei etwa 410° C. In der nachfolgenden Kühlstrecke durchläuft der Werkstoff
eine Entspannungsphase, während der die bereits martensitisch umgewandelten
Bereiche aufgrund der im Werkstück vorhandenen Restwärme selbst angelassen
werden. Zudem hat der den Martensit umgebende Austenit die Möglichkeit,
Anpassungsspannungen abzubauen. Figure 1 shows the temperature-time curves of a rebar with a total diameter
of 40 mm with hardened according to the proposed method
Marginal areas. It is the temperature profiles for the surface (1) and
the core (2) of the long product and on average (3). The workpiece
passes through a cooling section, which consists of several cooling zones with different
Length composed. The coolant is water. Expressed by
the workpiece becomes a high or low α value in the
Dieser Ablauf eines Abkühlteilschritts, d. h. Abschrecken und Selbstanlassen mit Abbau der Anpassungsspannungen zwischen Martensit und Austenit, wird mehrere Male wiederholt. Hierbei wandeln die noch vorliegenden austenitischen Gefügeabschnitte im Randbereich des Langprodukts ebenfalls in Martensit um. Figur 1 verdeutlicht, daß es nur im Randbereich zu einem Härten und Anlassen kommt, während der Kern des Werkstückes langsam abkühlt.This process of a cooling sub-step, i. H. Deter and self-start with Decreasing the adjustment stresses between martensite and austenite will be several Repeated times. Here, the austenitic structural sections still present change in the edge area of the long product also in martensite. Figure 1 illustrates that hardening and tempering only occur in the marginal area, while the core of the workpiece cools down slowly.
Mit Hilfe von Figur 2 wird deutlich, daß es nur in den Kühlzonen 2, 4, 6 und 8 zu
martensitischen Gefügeumwandlungen kommt. Nach Ablauf von vier Abkühlprozeßschritten
ist bei diesem Beispiel 30 % des Ausgangsquerschnitts des Langproduktes
in Martensit umgewandelt. Nach Beendigung des ersten Abkühlprozesses
schließt sich ein Prozeß mit einer Abkühlgeschwindigkeit an, die unterhalb der
unteren kritischen Abkühlgeschwindigkeit liegt, wobei das noch austenitische
Kerngefüge ferritisch-perlitisch umwandelt.With the help of Figure 2 it is clear that it is only in the
Im Vergleich hierzu zeigt Figur 3 die Temperatur-Kühlzeitkurven für den gleichen Stahl, aber für einen kleineren Durchmesser des Langproduktes (20 mm). Das Werkstück wird mit höherer Geschwindigkeit durch die einzelnen Kühlstrecken transportiert, hier beispielhaft mit 15,00 m/s. Die einzelnen Abkühlprozeßschritte laufen deshalb im Vergleich schneller ab, dennoch sind auch hier die Vorgänge Abschrecken auf eine Temperatur unterhalb der Martensitstarttemperatur sowie Entspannungsphase des Gefüges durch Selbstanlassen deutlich erkennbar. Nach Durchlauf der neun Kühlzonen sind etwa 30 % des Querschnitts des Langproduktes martensitisch umgewandelt (Figur 4).In comparison, Figure 3 shows the temperature-cooling time curves for the same Steel, but for a smaller diameter of the long product (20 mm). The Workpiece is moved at higher speed through the individual cooling sections transported, here for example at 15.00 m / s. The individual cooling process steps therefore run faster in comparison, but here too the processes are Quenching to a temperature below the martensite start temperature as well The relaxation phase of the structure is clearly recognizable through self-tempering. To Passage through the nine cooling zones is approximately 30% of the cross-section of the long product martensitic converted (Figure 4).
Die Figuren 5 und 6 verdeutlichen den Unterschied des erfindungsgemäß vorgeschlagenen Verfahrens mit dem bekannten Verfahren zur Randschichthärtung von Langprodukten. Obwohl auch nach dem konventionellen Verfahren ebenfalls 35 % Martensitgefüge in den Randbereichen erreicht wird, kommt es doch aufgrund der einmaligen Abschreckbehandlung mit nachfolgenden einmaligen Selbstanlassen zu Mikrorissen im Gefüge und damit zusammenhängend schlechteren Zähigkeitseigenschaften, die nach dem erfindungsgemäßen Verfahren verbessert werden. Daß die Zähigkeitseigenschaften bei gleichen Festigkeitswerten steigen, verdeutlichen die Figuren 7 und 8, in der die Bruchdehnung über der Streckgrenze bzw. Zugfestigkeit eines unlegierten Baustahls dargestellt sind, der im Vergleich nach dem konventionellen (I) und dem erfindungsgemäßen Verfahren (II) randschichtgehärtet ist.Figures 5 and 6 illustrate the difference between what is proposed according to the invention Process with the known process for hardening the surface layer of Long products. Although 35% also according to the conventional method Martensite structure is reached in the peripheral areas, it does happen because of one-time quench treatment with subsequent one-time self-starts microcracks in the structure and associated poor toughness properties, which are improved by the method according to the invention. It is clear that the toughness properties increase with the same strength values Figures 7 and 8, in which the elongation at break is above the yield point or tensile strength of an unalloyed structural steel are shown in the comparison surface hardened according to the conventional (I) and the process (II) according to the invention is.
Nach dem vorgeschlagenen Verfahren werden insbesondere Betonstähle randschichtgehärtet. Die finden vor allem Anwendung als Bewehrungsstähle zur Herstellung von Trägern im Stahlbau.According to the proposed method, reinforcing steels in particular are hardened on the outer layer. They are mainly used as reinforcement steel for manufacturing of beams in steel construction.
Claims (8)
dadurch gekennzeichnet,
characterized,
dadurch gekennzeichnet,
characterized,
dadurch gekennzeichnet,
characterized,
dadurch gekennzeichnet,
characterized,
dadurch gekennzeichnet,
characterized,
dadurch gekennzeichnet,
characterized,
dadurch gekennzeichnet,
characterized,
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19921286A DE19921286A1 (en) | 1999-05-07 | 1999-05-07 | Heat treatment process for the production of surface-hardened long and flat products from unalloyed or low-alloy steels |
| DE19921286 | 1999-05-07 |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| EP1050591A2 true EP1050591A2 (en) | 2000-11-08 |
| EP1050591A3 EP1050591A3 (en) | 2004-06-23 |
Family
ID=7907440
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP00108714A Withdrawn EP1050591A3 (en) | 1999-05-07 | 2000-04-22 | Thermal treatment process for manufacturing surface hardened unalloyed or low alloyed, elongated or flat steel products |
Country Status (4)
| Country | Link |
|---|---|
| US (1) | US6355119B1 (en) |
| EP (1) | EP1050591A3 (en) |
| JP (1) | JP2000328141A (en) |
| DE (1) | DE19921286A1 (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8968495B2 (en) * | 2007-03-23 | 2015-03-03 | Dayton Progress Corporation | Methods of thermo-mechanically processing tool steel and tools made from thermo-mechanically processed tool steels |
| US9132567B2 (en) * | 2007-03-23 | 2015-09-15 | Dayton Progress Corporation | Tools with a thermo-mechanically modified working region and methods of forming such tools |
| WO2009102848A1 (en) * | 2008-02-15 | 2009-08-20 | Dayton Progress Corporation | Methods of thermo-mechanically processing tool steel and tools made from thermo-mechanically processed tool steels |
| US8518195B2 (en) * | 2012-01-20 | 2013-08-27 | GM Global Technology Operations LLC | Heat treatment for producing steel sheet with high strength and ductility |
| CN106756504B (en) * | 2016-12-28 | 2018-05-15 | 鞍钢集团（鞍山）铁路运输设备制造有限公司 | A kind of ball grinding machine lining board and preparation method thereof |
| CN107480328B (en) * | 2017-07-04 | 2022-09-20 | 山东建筑大学 | Carbon distribution theory calculation method based on Q & P process |
Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1351423A (en) * | 1971-04-14 | 1974-05-01 | Koninklijke Hoogovens En Staal | Manufacture of profiled rod |
| US4016009A (en) * | 1975-01-29 | 1977-04-05 | Centre De Recherches Metallurgiques-Centrum Voor Research In De Metallurgie | Producing rolled steel products |
| DE2916218A1 (en) * | 1979-04-21 | 1980-10-23 | Florin Stahl Walzwerk | Rolled steel prods. with multilayer microstructure - where prod. leaving hot rolling mill is quenched intermittently to obtain several layers of tempered martensite |
| GB2087927A (en) * | 1980-10-16 | 1982-06-03 | Arbed | Manufacture of rolled steel products having good weldability, a high elastic limit, and toughness at very low temperatures |
| US4877463A (en) * | 1984-08-23 | 1989-10-31 | Dyckerhoff & Widmann Aktiengesellschaft | Method for producing rolled steel products, particularly threaded steel tension members |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4180418A (en) * | 1973-09-11 | 1979-12-25 | Stahlwerke Peine-Salzgitter A.G. | Method of making a steel wire adapted for cold drawing |
-
1999
- 1999-05-07 DE DE19921286A patent/DE19921286A1/en not_active Withdrawn
-
2000
- 2000-04-22 EP EP00108714A patent/EP1050591A3/en not_active Withdrawn
- 2000-05-02 JP JP2000133603A patent/JP2000328141A/en not_active Withdrawn
- 2000-05-05 US US09/566,206 patent/US6355119B1/en not_active Expired - Fee Related
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1351423A (en) * | 1971-04-14 | 1974-05-01 | Koninklijke Hoogovens En Staal | Manufacture of profiled rod |
| US4016009A (en) * | 1975-01-29 | 1977-04-05 | Centre De Recherches Metallurgiques-Centrum Voor Research In De Metallurgie | Producing rolled steel products |
| DE2916218A1 (en) * | 1979-04-21 | 1980-10-23 | Florin Stahl Walzwerk | Rolled steel prods. with multilayer microstructure - where prod. leaving hot rolling mill is quenched intermittently to obtain several layers of tempered martensite |
| GB2087927A (en) * | 1980-10-16 | 1982-06-03 | Arbed | Manufacture of rolled steel products having good weldability, a high elastic limit, and toughness at very low temperatures |
| US4877463A (en) * | 1984-08-23 | 1989-10-31 | Dyckerhoff & Widmann Aktiengesellschaft | Method for producing rolled steel products, particularly threaded steel tension members |
Also Published As
| Publication number | Publication date |
|---|---|
| EP1050591A3 (en) | 2004-06-23 |
| US6355119B1 (en) | 2002-03-12 |
| DE19921286A1 (en) | 2000-11-09 |
| JP2000328141A (en) | 2000-11-28 |
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