Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
• • 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
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/005—Modifying the physical properties by deformation combined with, or followed by, heat treatment of ferrous alloys
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
• • 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
  • 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
  • C21D2211/004—Dispersions; Precipitations

Definitions

• the invention relates to metallurgy, and more specifically the field of steels for the manufacture of parts to withstand significant stresses.
• such parts are made of hardened and tempered steel or, as far as possible, of forged steel with a ferrito-pearlitic structure which is supposed to offer a better technical-economic compromise, but whose mechanical performance is still limited. .
• Ferritic-pearlitic steels often used for this purpose are types XC70, 45Mn5, 30MnSiV6 and 38MnSiV5, and undergo, after rolling or forging, simple cooling in line with still air. Their method of implementation is therefore relatively economical, but their service life in the presence of high demands is limited.
• the object of the invention is to propose an association between a steel grade and a part manufacturing process, having economic advantages over existing associations without the metallurgical performance being altered, or even improving these performances.
• the part thus manufactured will have to withstand heavy fatigue stresses.
• this manufacturing process should, in particular, be adaptable to any forging line.
• the steel contains from 5 to 50 ppm B.
• the steel contains 0.005 to 0.04% Ti.
• the Ti content is preferably at least 3.5 times the N content of the steel.
• the steel contains from 0.005 to 0.06% Nb.
• the steel contains from 0.005 to 0.2% of S.
• the steel contains at least one of the elements Ca up to 0.007%, Te up to 0.03%, Se up to 0.05%, Bi up to 0.05% and Pb up to 0.1%.
• the C content of the steel is between 0.06 and 0.20%.
• the Mn content of the steel is then preferably between 0.5 and 1.5%, and the Cr content is preferably between 0.3 and 1.2%.
• the Ni content of the steel can then be preferably between traces and 1%.
• the Ni content of the steel can then also be between 2 and 4.5%, and the Al content is then between 1 and 2%.
• the precipitation yield is in the general case preferably between 425 and 600 ° C.
• the precipitation yield is preferably between 425 and 500 ° C for 1 to 10h.
• the precipitation is preferably between 500 and 600 ° C for more than 1 hour.
• the precipitation is preferably between 500 and 550 ° C for more than 1 hour.
• Said hot deformation may be a rolling.
• Said hot deformation may be forging.
• the controlled cooling of the blank is carried out at a rate of less than 3 ° C / s between 600 and 300 ° C.
• a steel part obtained by the process according to the invention has a bainitic microstructure, and typically a tensile strength Rm of 750 to 1300 MPa and a yield strength Re greater than or equal to 500 MPa.
• the invention consists of the combination of a steel grade and a post-casting treatment process comprising a hot forming step of the part, a controlled cooling being carried out in calm air or in pulsed air and a precipitation income preceding or following the machining of the room.
• the composition of the selected steel ensures that, regardless of the cooling mode, the fatigue strength results of the parts manufactured from this steel will be sufficient to meet the requirements of the users.
• the hot forming operation may consist of one or more rolling, or rolling followed by forging, or forging alone.
• the bottom line is that the last hot deformation brings the steel between 1100 and 1300 ° C, and the controlled cooling takes place from this temperature.
• the chemical characteristics of the steel and its heat treatments after casting aim at obtaining a bainitic microstructure, and also at obtaining optimized mechanical characteristics.
• This bainitic microstructure must be able to be obtained after cooling in still air, but must also be compatible with forced air cooling.
• the parts of the process of the invention can be produced on any existing installation, that it allows after forging or rolling a forced air cooling, or that it allows only a cooling in the calm air .
• a forging installation initially designed to treat ferritic-pearlitic microstructure steel parts can without difficulty, and without special adaptations, treat bainitic microstructure parts of the process of the invention.
• the bainitic microstructure steels previously used for these purposes required pulsed air cooling, and therefore could not always be processed on standard design facilities.
• the last hot deformation is carried out at 1100-1300 ° C and is followed by air-controlled cooling in hot rolling or forging, in still air or forced air. This gives a rough sketch of the piece.
• blade it should be understood that here is meant a bar, or a half-product in another form, from which the final piece will be obtained by machining, and this regardless of the mode of hot deformation practiced: rolling, forging or their combination.
• a precipitation income is then made. This is either before or after machining the workpiece from said blank.
• the carbon content is between 0.06 and 0.25%. This content makes it possible to govern the type of microstructure obtained. Less than 0.06%, the microstructure obtained would not be interesting for the objectives. Above 0.25%, in combination with the other elements, a sufficiently bainitic microstructure would not be obtained after cooling with still air.
• the manganese content is between 0.5 and 2%. This element added to more than 0.5% gives its quenchability to the material, and allows to obtain a broad bainitic range regardless of the cooling mode. A content greater than 2% would, however, be likely to cause excessive segregation.
• the silicon content is between traces and 3%. This element, which is not obligatory, is advantageous in that it hardens the bainite by passing it in solid solution.
• silicon avoids the problems associated with the presence of copper during hot forming. A content greater than 3% can however pose problems of machinability of the material.
• the nickel content is between traces and 4.5%. This non-obligatory element promotes quenchability and stabilization of austenite. If the aluminum content allows it, it can form very hardening NiAl precipitates, giving the metal high mechanical characteristics. In the case where copper is present in a relatively large quantity, nickel can play the same role as silicon. Above 4.5%, the addition of nickel is unnecessarily expensive in view of metallurgical objectives.
• the aluminum content is between traces and 3%.
• This non-obligatory element is a strong deoxidizer, and even added at a low level, it makes it possible to limit the amount of dissolved oxygen in the liquid steel, thus improving the inclusiveness of the room if it has been possible to avoid reoxidation too much. important during casting. At high levels, as has been said, it is likely to form NiAl precipitates if nickel is present in large quantities. It is not useful for the aluminum content to exceed 3%.
• chromium content a non-mandatory element, is between traces and 1.2%. Like manganese, chromium contributes to the improvement of quenchability. Its addition becomes unnecessarily expensive beyond 1.2%.
• the molybdenum content is between traces and 0.30%. This element, which is not mandatory, prevents the formation of coarse-grained ferrite and makes it possible to obtain the bainitic structure more definitely. Its addition is unnecessarily expensive beyond 0.30%.
• the vanadium content is between traces and 2%. This element, not mandatory, serves to harden the bainite by passing it in solid solution. At high content, it also makes it possible to obtain precipitation hardening of carbides and / or carbonitrides. Its addition is unnecessarily expensive beyond 2%.
• the copper content is between traces and 3.5%.
• This element which is not mandatory, can improve machinability and, by precipitating, cause secondary hardening of the material. But beyond 3.5% it makes hot formatting of the problematic part. As has been said, it is advisable to associate a significant nickel or silicon content to minimize hot forming problems. Beyond 3.5% its addition is in any case unnecessarily expensive.
• the boron content can be between 5 and 50 ppm. It can improve the hardenability, but must be in solid solution to be effective. In other words, it must be avoided that almost all the boron is found in the form of nitrides or carbonitrides of boron.
• the minimum titanium content, for this purpose is 0.005%, for the lowest nitrogen contents usually encountered. However, it is advisable not to exceed a titanium content of 0.04%, otherwise we obtain titanium nitrides too large.
• Titanium also has the function of limiting the magnification of the austenitic grain at high temperature, and can, for this, be added independently of boron, at a content of between 0.005 and 0.04%.
• Niobium may also be added at levels of between 0.005 and 0.06%. He too can precipitate in the form of carbonitrides in the austenite, and can thus bring about a hardening of the material.
• the machinability of the material can be improved by adding sulfur (from 0.005% to 0.2%), to which a calcium addition can also be added (up to 0.007%), and / or or tellurium (up to 0.03%) and / or selenium (up to 0.05%), and / or bismuth (up to 0.05%) and / or lead (up to 0.1%).
• the part blank is forged or not according to the usual methods. It is heated to 1100-1300 ° C, then the deformations giving rise to the piece blank are carried out.
• controlled cooling of the room is carried out, either in still air or in forced air.
• the part is forced to cool at a speed less than or equal to 3 ° C / s between 600 and 300 ° C.
• the precipitation yield is preferably between 425 and 600 ° C.
• the temperature of the income and its duration are optimally adapted to the targeted characteristics.
• the precipitation of copper is preferably obtained by treatment at 425-500 ° C for 1 to 10 hours.
• Precipitation of vanadium is preferably obtained by treatment at 500-600 ° C for more than 1 hour.
• Precipitation of NiAl is preferably obtained by treatment at 500-550 ° C for more than 1h.
• the tensile strength Rm is from 1000 to 1300 MPa and the yield strength Re is of the order of 900 MPa or more.
• the carbon content is limited to 0.06-0.2%, so as to obtain a bainite of hardness limited to 300-330 Hv30.
• the manganese content should be between 0.5 and 1.5%, the chromium content between 0.3 and 1.2%, and the nickel content can be up to 1% if it is not that a good quenchability, or go from 2 to 4% if one seeks a NiAl precipitation as we have seen. In the latter case, the aluminum content is between 1 and 2%.
• the tensile characteristics (yield strength, strength) of the product obtained after rolling or forging and cooling with controlled air are not particularly high: typically the tensile strength Rm is of the order of 750 -1050 MPa and the elasticity limit Re of the order of 500 to 750 MPa. But these steels have good machinability.
• This example is representative of the variant of the invention for which a relatively low carbon content can be used, and precipitation hardening is achieved by the addition of copper.
• composition of the steel is as follows, expressed in 10 -3 % by weight: VS mn Yes S P Or Cu Cr MB al Ti B NOT 80 1500 300 85 10 1500 2500 280 50 25 - - 6
• a bainitic microstructure After hot forging at a temperature of 1250-1200 ° C and cooling with still air (average cooling rate of 1 ° C / s between 700 and 300 ° C) a bainitic microstructure is obtained with a moderate hardness of 265Hv30, providing a resistance of less than 900 MPa. With this level of mechanical characteristics, machinability is not a problem. Then, an income at 450 ° C, with a hold time of one hour, allows to increase the resistance characteristics to reach more than 340Hv30 hardness, providing a resistance of 1100MPa.
• This example is representative of the variant of the invention for which a relatively low carbon content can be used, and precipitation hardening is carried out by the addition of vanadium.
• composition of the steel is as follows, expressed in 10 -3 % by weight: VS mn Yes S P Or Cu Cr MB al Ti V 150 1230 250 80 20 150 200 205 50 30 - 820
• This example is representative of the variant of the invention for which a relatively low carbon content can be used, and precipitation hardening is carried out by means of conjugate additions of nickel and aluminum.
• composition of the steel is as follows, given in 10 -3 % by weight: VS mn Yes S P Or Cu Cr MB al Ti B NOT 95 1150 200 80 10 3000 206 220 60 1500 - 3 3
• a bainitic microstructure After hot forging at a temperature of 1250-1200 ° C and cooling with still air (average cooling rate of 1 ° C / s between 700 and 300 ° C) a bainitic microstructure is obtained with a moderate hardness of 240Hv30, providing a resistance of less than 800 MPa. With this level of mechanical characteristics, machinability is not a problem. Then, an income at 520 ° C, with a holding time of 10 hours, increases the strength characteristics to reach more than 370Hv30 hardness, providing a resistance of the order of 1200MPa.
• composition of the steel is as follows, given in 10 -3 % by weight: VS mn Yes S P Or Cu Cr MB al Ti V B 230 1500 700 80 11 150 150 800 70 20 25 190 3

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• Chemical & Material Sciences (AREA)
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• Mechanical Engineering (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Heat Treatment Of Steel (AREA)
• Forging (AREA)
• Heat Treatment Of Sheet Steel (AREA)

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• 2002
  • 2002-12-03 FR FR0215226A patent/FR2847908B1/fr not_active Expired - Fee Related
• 2003
  • 2003-11-27 ES ES03292950T patent/ES2331949T3/es not_active Expired - Lifetime
  • 2003-11-27 AT AT03292950T patent/ATE441730T1/de not_active IP Right Cessation
  • 2003-11-27 EP EP03292950A patent/EP1426452B1/fr not_active Expired - Lifetime
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  • 2003-11-28 MX MXPA03010998A patent/MXPA03010998A/es active IP Right Grant
  • 2003-12-01 CA CA002452647A patent/CA2452647C/fr not_active Expired - Fee Related
  • 2003-12-02 US US10/724,641 patent/US7354487B2/en not_active Expired - Fee Related
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