WO2019094400A1 - Pièces forgées en acier inoxydable fortement allié sans recuit de mise en solution - Google Patents

Pièces forgées en acier inoxydable fortement allié sans recuit de mise en solution Download PDF

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Publication number
WO2019094400A1
WO2019094400A1 PCT/US2018/059518 US2018059518W WO2019094400A1 WO 2019094400 A1 WO2019094400 A1 WO 2019094400A1 US 2018059518 W US2018059518 W US 2018059518W WO 2019094400 A1 WO2019094400 A1 WO 2019094400A1
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forging
billet
hot
carried out
forgings
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PCT/US2018/059518
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English (en)
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Gerhard H. Schiroky
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Swagelok Company
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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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
    • 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
    • C21D1/34—Methods of heating
    • C21D1/40—Direct resistance heating
    • 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
    • C21D1/34—Methods of heating
    • C21D1/42—Induction heating
    • 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
    • C21D1/56—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering characterised by the quenching agents
    • C21D1/60—Aqueous agents
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/005—Heat treatment of ferrous alloys containing Mn
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • C21D6/008—Heat treatment of ferrous alloys containing Si
    • 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
    • C21D7/00—Modifying the physical properties of iron or steel by deformation
    • C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C19/00—Alloys based on nickel or cobalt
    • C22C19/03—Alloys based on nickel or cobalt based on nickel
    • C22C19/05—Alloys based on nickel or cobalt based on nickel with chromium
    • C22C19/051—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W
    • C22C19/055—Alloys based on nickel or cobalt based on nickel with chromium and Mo or W with the maximum Cr content being at least 20% but less than 30%
    • 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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • 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
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
    • B21J1/00—Preparing metal stock or similar ancillary operations prior, during or post forging, e.g. heating or cooling
    • B21J1/003—Selecting material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21J—FORGING; HAMMERING; PRESSING METAL; RIVETING; FORGE FURNACES
    • B21J1/00—Preparing metal stock or similar ancillary operations prior, during or post forging, e.g. heating or cooling
    • B21J1/06—Heating or cooling methods or arrangements specially adapted for performing forging or pressing operations
    • 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
    • C21D2211/004—Dispersions; Precipitations
    • 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
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • 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
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • 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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P10/00—Technologies related to metal processing
    • Y02P10/25—Process efficiency

Definitions

  • Fig. 1 schematically illustrates a conventional process for producing multiple hot forgings in series.
  • billet 10 which is typically derived by sectioning forging stock obtained from the foundry, is heated to forging temperature in heater 12.
  • pyrometer 14 which is aimed at the side wall of the billet as it exits heater 12, can be used to monitor and record the billet's temperature as it exits the heater for record purposes.
  • Heated billet 10 is then moved to a forging station 16 where a series of forging dies forge the billet into the desired shape, thereby producing the hot forging.
  • two or more forgings can be made from a single billet. In other instances, a single forging is made from each billet.
  • the heated hot forging so made is then rapidly quenched from its elevated temperature, usually by immersion in quench tank 18 containing water or other cooling liquid, while any flash that might have been created is deposited in a scrap bin, not shown.
  • Completed metal parts are then typically made by subjecting the hot forging so made to some sort of shaping operation, such as machining or the like.
  • Fig. 1 shows only one hot forging being made, it will be understood that in actual commercial practice, the process of Fig. 1 is continuous in the sense that multiple hot forgings are made in series by repeating the process shown there over and over again.
  • the process may be automated in the sense that a suitable automatic control system (not shown) is employed to control one or more operations of the process including movement of billet 10 through each station of the process as well as the operation of one or more pieces of equipment in each station.
  • Fig. 2 is an isothermal time-temperature-transformation (TTT) diagram for such an alloy, in particular an AISI-2205 duplex stainless steel.
  • TTT time-temperature-transformation
  • Extrapolation of the upper portion of TTT-curves to very long times yields an upper critical temperature above which intermetallic phases are thermodynamically unstable.
  • Extrapolation of the lower portion of TTT-curves to very long times leads to a lower critical temperature below which intermetallic phases do not form for kinetic reasons.
  • the temperature range defined by the upper and lower critical temperatures is called the critical temperature range for intermetallic phase formation. If the alloy is held at a temperature above the critical range, all of the elements in the alloy including those already present in intermetallic phases, tend to redistribute themselves into a uniform solid solution. Meanwhile, once the alloy is at a temperature below the critical range, the elements in the alloy are completely immobile with respect to one another no matter how long the alloy is held at that temperature.
  • intermetallic phases which are typically rich in chromium and molybdenum, adversely affect the corrosion resistance of the areas immediately surrounding these phases which become depleted in these elements.
  • these intermetallic phases can also substantially lower the impact resistance of the alloy. For this reason, the ASTM A182 standard specification, as well as the NORSOK M-650 supply chain qualification standard, require that forgings made from duplex and super duplex stainless steels be subjected to a post-forge solution anneal.
  • the NORSOK M-650 standard also requires post-forge solution annealing of forgings made from super austenitic 6-moly alloys, i.e., austenitic stainless steels with at least 6% molybdenum. Because of these requirements, it is standard practice in industry to subject hot forgings made from these and other highly alloyed metals to a conventional solution anneal after the forging has cooled to room temperature, or at least a "safe" temperature below the alloy's lower critical temperature.
  • post-forge solution annealing is done by heating the forging up to an elevated temperature above its upper critical temperature, maintaining the forging at this elevated temperature long enough to dissolve any intermetallic phases that might be present, and then cooling the forging to below its lower critical temperature rapidly enough so that formation of new intermetallic phases is avoided or at least minimized.
  • Fig. 3 shows continuous cooling transformation curves, or "CCT curves,” for this alloy (2205).
  • Fig. 3 shows that, if this alloy is cooled from 950° C to below 600° C within roughly 25 minutes according to the cooling regime represented by the solid line in this figure, it will develop about 1% deleterious sigma phase.
  • the alloy is cooled by the cooling regimes represented by the other lines in this figure, it will develop about 3%, 5% or even 10% of this deleterious sigma phase depending on which cooling rate is followed.
  • post-forge solution annealing is expensive. In addition, it may also lead to various technical and commercial problems such as surface oxidation, lower mechanical properties due to grain growth, added production time and cost and negative environmental impact including consumption of energy and cooling water. Accordingly, it would be desirable to eliminate this step, if possible.
  • this invention provides an improvement in continuous, automatic processes for making multiple hot forgings in series from multiple billets made from a highly-alloyed metal, the improvement wherein the hot forgings are made without subjecting these hot forgings to post-forging solution anneal.
  • this invention also provides an improvement in processes for making metal parts which are useful in one or more applications including chemical processing, scrubbers, pulp mills, bleach washers, food processing and oil field piping, in which process a hot forging made from a highly-alloyed metal is shaped into a metal part, the improvement comprising shaping the hot forging into the metal part without subjecting this hot forging to post-forging solution anneal.
  • this invention also provides an improvement in metal parts which are (a) made by shaping a hot forging of a highly-alloyed metal and (b) useful in one or more applications including chemical processing, scrubbers, pulp mills, bleach washers, food processing and oil field piping, the improvement wherein the metal part is made without subjecting the hot forging to post-forging solution anneal.
  • this invention also provides a process for making a metal part from a billet, the process comprising
  • step (d) forming the metal part by machining the hot forging of step (c) without subjecting this hot forging to post-forging solution anneal.
  • Fig. 1 is a schematic illustration of a conventional hot forging process
  • Fig. 2 is an isothermal time-temperature-transformation (TTT) diagram for an AISI-2205 duplex stainless steel alloy
  • Fig. 3 is a diagram of the continuous cooling transformation curves, or "CCT curves," for the alloy of Fig. 2; and Fig. 4 is a thermal history diagram illustrating the relationship between time and temperature in the manufacture of a hot forged product in accordance with the invention.
  • Fig. 5a is a photomicrograph of the microstructure of a hot forging produced without a post-forging solution anneal in accordance with this invention.
  • Fig. 5b is a photomicrograph of the microstructure of a comparative hot forging otherwise identical to that of Fig. 5a but which was produced with a post-forging solution anneal in accordance with conventional practice.
  • “Automatic” and “automatically” as they relate to processes for making multiple hot forgings from multiple billets means that one or more automatic control systems are used to control at least some portion of the operation of the process including the movement of billets and forgings through each station of the process as well as the operation of the equipment in each station.
  • Such processes can be fully automatic meaning that all portions of the operation of the process are controlled by the automatic control systems or semi-automatic meaning that some but not all portions of the operation of the process are controlled by the automatic control systems.
  • “Billet” means the piece of metal on which the forging steps of the inventive process are carried out. Normally, a billet is obtained by subdividing a piece of forging stock into sections of appropriate size.
  • Discharged to waste means that the billet or forging being referred to does not become, or form part of, a final product produced by the inventive process. It does not mean that the billet or forging is abandoned completely, as most such billets and forgings will be used for scrap or some other purpose.
  • Essentially free of intermetallic phases means a concentration of intermetallic phases in a metal product which is so small that it does not adversely affect the properties of the metal product in any significant way.
  • Many commercial metal products, including intermediate products, are made to have a desired set of properties as determined by product specifications for that particular metal product.
  • a metal product which is essentially free of intermetallic phases will be understood to mean a metal product which, although possibly containing intermetallic phases which may adversely affect its properties, contains these intermetallic phases in concentrations which are so small that the metal product still meets its product specifications.
  • Forming stock means a metal product which has been obtained by subj ecting an ingot to one or more metal working operations such as hot or cold rolling, forging or the like to reduce its thickness dimension. In some instances, metal working will be done at the foundry, while in other instances, metal working will be done at a separate forging shop. Typically, forging stock will be in the form of a rod, bar or strip whose length exceeds its thickness.
  • Highly alloyed metal means a metal alloy which is formed from a base metal such as Fe or Ni and which includes a substantial amount of one or more other metal elements such that the metal alloy tends to form intermetallic phases when heated to elevated temperature.
  • Hot forging means a metal product whose shape has been obtained, at least in part, by subjecting a metal billet which has been heated to a forging temperature above its upper critical temperature for intermetallic phase formation to substantial localized compressive forces. These substantial localized compressive forces are normally delivered by a hammer or other suitable implement, but may also be delivered by deforming the billet between two mating dies. Specific forging operations include roll forging, swaging, cogging, open-die forging, closed-die forging, impression-die forging, press forging, automatic hot forging, radial forging, and upset forging. For the sake of clarity, "hot forging” does not imply that the forging is hot— only that temperature at which forging was carried out, the forging temperature, was above the critical temperature mentioned above.
  • “Ingot” means the metal product obtained when a molten metal is solidified. When such a product is continuously cast, “ingot” will also be understood to include longitudinal sections of such a product. “Ingot” is intended to distinguish products which are obtained by reducing the thickness of an ingot by some form of hot or cold working procedure such as hot or cold rolling, forging, and the like.
  • the inventive forging process is carried out on highly alloyed metals.
  • the inventive forging process is carried out on ferrous based alloys which contain significant amounts of additional metal elements other than Fe.
  • ferrous based alloys which contain significant amounts of additional metal elements other than Fe.
  • examples include martensitic stainless steels, ferritic stainless steels, austenitic stainless steels, highly alloyed austenitic stainless steels, super austenitic stainless steels, and austenitic-ferritic stainless steels such as lean duplex, duplex, super duplex, and hyper duplex stainless steels.
  • the CP value is a relative indication of the kinetics of precipitation of intermetallic phases in an alloy. It is described in U.S. 5,494,636, the disclosure of which is incorporated herein by reference.
  • the CP value of an alloy can be calculated using the following formula, wherein the percentages are weight percentages based on total alloy weight:
  • CP 20x%Cr + 0.3 x%Ni+ 30x%Si + 40x%Mo + 5 x%W + 10x%Mn + 50x%C - 200x%N.
  • Alloys having CP values of less than 500 are not especially prone to developing deleterious intermetallic phases rapidly when heated to elevated temperatures.
  • those which exhibit CP values of 500 - 700 show some tendency to do so, while those exhibiting CP values of 700-750 are even more prone to do so.
  • alloys having CP values of 750- 800 and above are especially prone to develop these deleterious intermetallic phases when heated to elevated temperatures.
  • billets made from all such alloys and especially those exhibiting CP values of 500 - 700, 701-750 and 751-800 and above can be used as raw materials for the inventive process to make hot forgings exhibiting little or no deleterious intermetallic phases, even though such forgings have been made without a post- forging solution anneal.
  • superstainless steels there are two types of superstainless steels, those that exhibit an austenitic phase structure and those that exhibit a duplex phase structure.
  • Superstainless steels exhibiting an austenitic phase structure normally contain about 19 to 25 wt.% Cr and 5 to 8 wt.% Mo and are sometimes referred to as "super-austenitic 6-moly alloys.”
  • Examples of such steels include AISI-N08367 (alloy 6XN or AL6XN), AISI-S31254 (alloy 254), AISI-N08925 (alloy 1925hMo) and AISI-S31266 (alloy B66).
  • Superstainless steels exhibiting a duplex phase structure normally contain about 24 to 26 wt.% Cr and 3 to 5 wt.% Mo and are sometimes referred to as "superduplex" stainless steels.
  • Examples of such steels include AISI-S32750 (alloy 2507) and AISI-S32760 (alloy Zeron 100).
  • Additional metal alloys on which the inventive forging process can be carried out are the nickel based alloys which contain at least about 2 wt.% Mo and at least 18 wt.% Cr. Specific examples include alloys AISI-N0820 (alloy C20 or "Carpenter 20"), AISI- N08031 (alloy 31) and AISI-N08825 (alloy 825).
  • Still other alloys on which the inventive forging process can be carried out are the "super- austenitic 7 moly” alloys, examples of which include AISI-S32654 (alloy 654) and AISI-S31277 (alloy 27-7Mo), the "highly alloyed austenitic” stainless steels such as AISI-N08904 (alloy 904L), the "lean duplex” alloys such as AISI-S32101 (alloy LDX 2101), regular duplex alloys such as AISI-S32205 (alloy 2205), the "hyper duplex” alloys such as AISI-S33207 (alloy SAF 3207) and the well-known "conventional" austenitic stainless steels such as AISI-S31600 (alloy 316) and AISI-S31700 (alloy 317).
  • AISI-S32654 alloy 654
  • AISI-S31277 alloy 27-7
  • the first of these features which may be regarded as optional and conventional but is still important, relates to the manner in which the billet on which the inventive process is carried out is selected.
  • the billet on which the inventive process is carried out is selected.
  • only those billets that are essentially free of intermetallic phases are selected for this purpose.
  • billets which are not essentially free of intermetallic phases are rejected for carrying out this invention, and as further discussed below.
  • the forging stock is not necessarily in a fully solution annealed state when obtained from the foundry or forging shop.
  • the elevated temperatures commonly used to hot work an ingot, or to hot-roll barstock, of the alloy into forging stock are roughly the same as the elevated temperatures needed to solution anneal the alloy.
  • the hot working temperatures actually used in particular foundry operations may be less than the minimum temperature required to achieve effective solution anneal.
  • rapid quenching may not have been rapid enough. So, there is a real risk that such forging stock will contain substantial amounts of intermetallic phases, since its thermal history may have been insufficient to remove all of these phases.
  • the forging stock is solution annealed at the foundry or forging shop before being shipped to the customer.
  • the foundry or forging shop assures the customer that this forging stock is free of intermetallic phases because it was solution annealed before being shipped.
  • the solution annealing process actually carried out was insufficient to remove essentially all of the intermetallic phases that might have been present.
  • the foundry or forging shop provides the customer with a certified analysis of the composition, properties and phase structure of the forging stock being delivered based on actual analytical tests carried out on this particular piece of forging stock or on representative samples of this forging stock. In these situations, the risk that the forging stock received still contains intermetallic phases is less.
  • a certified analysis of the phase structure of the billet, the forging stock from which the billet is derived, or at least representative samples of this forging stock are necessary before it can be assumed that the billet selected for use in the inventive hot forging process is, in fact, essentially free of intermetallic phases.
  • the party carrying out the inventive hot forging process can, itself, obtain such a certified analysis. Additionally or alternatively, the party carrying out the inventive hot forging process may also rely on such a certified analysis obtained from its foundry/supplier in those circumstances in which the party finds it reasonable to do.
  • the starting material of the inventive process i.e., the billet on which the inventive hot forging process is practiced, be selected to be essentially free of the intermetallic phases that give rise to poor alloy properties in the ultimate hot forging product produced.
  • still another step that can be taken to help insure that the hot forgings produced by the inventive process are essentially free of intermetallic phases is to restrict the maximum thickness of the hot forging which is produced. Because of inherent heat transfer restrictions, the larger a forging becomes, the more difficult it is to rapidly cool its core. What this means in practical terms is that, as the thickness of a forging becomes larger, cooling the core of the forging after solution anneal rapidly enough to prevent intermetallic phases from forming becomes more difficult or even impossible. So, in some embodiments of this invention, the maximum thickness or diameter of the forging being made is restricted to a value which is small enough to avoid this heat transfer problem from occurring.
  • the maximum thickness or diameter of the hot forging being made is restricted to 25 centimeters, 20 centimeters, 15 centimeters, 12 centimeters, 9 centimeters, 6 centimeters, 5 centimeters, 4 centimeters or even 3 centimeters.
  • Fig. 4 is a thermal history diagram illustrating the relationship between time and temperature in the manufacture of hot forgings in accordance with this invention.
  • the forging stock is subjected to a solution anneal procedure at the foundry or forging shop in which it is first heated to point 22 which is above the critical temperature range CTR of the alloy. It is then maintained at this temperature for a suitable period of time to ensure that essentially all of the deleterious intermetallic phases that might be present in the alloy redissolve.
  • point 24 the forging stock is then rapidly cooled, typically by quenching with water or other cooling liquid, back down to room temperature at point 26.
  • ⁇ the critical temperature range CTR of the alloy.
  • the heating step of the inventive process is represented by the line extending between points 28 and 30 in Fig. 4.
  • this heating step is done in a manner so that when it is completed, which will normally be when the heated billet is removed from heater 12 in Fig. 1, the heated billet obtained is essentially free of deleterious intermetallic phases.
  • the first of these practices is to heat the billet to its forging temperature as rapidly as possible, at least during the time period the billet is within its critical temperature range denoted by ⁇ 2 in this figure.
  • heating will normally be done by resistance or induction heating, since radiant heating inside a furnace is just too slow.
  • the billet is heated up as rapidly as possible to avoid formation of any new intermetallic phases to the greatest extent possible and hence ensure that the heated billet is essentially free of deleterious intermetallic phases.
  • this can be done in a continuous, automatic process such as illustrated in Fig. 1 is to determine a minimum acceptable heating rate for each particular alloy being processed and to discharge to waste any billet whose heating rate fails to achieve this minimum.
  • the rate of billet heating should be some predetermined minimum such as, for example, at least 400° F/min. (204° C/min.), at least 500° F/min (260° C/min.), at least 600° F/min. (333° C/min.), at least 700° F/min. (371° C/min.), or even at least 800° F/min.
  • Determining billet heating rate for this purpose can conveniently be done using the temperature of the front or rear face of the billet as it is being transported through heater 12.
  • a pyrometer focused on the center of the billet face can be used.
  • a thermocouple attached to the center of the face or received in a hole drilled in the face can be used.
  • the automatic control system of the process, or a separate automatic control system can be programmed to cause an automatically-operated gate or other suitable piece of equipment to discharge to waste each billet whose heating rate fails to conform to the predetermined heating rate minimum.
  • Another approach that can be used for ensuring that formation of new intermetallic phases is avoided during billet heat-up is to control billet temperature at the end of this heating step.
  • One way this can be done is to determine minimum and maximum acceptable billet temperatures at the end of this heating step and to discharge to waste any billet whose actual temperature is less than this minimum or greater than this maximum.
  • the target temperature of the billet at the end of this heating step should be some predetermined value such as, for example, 1,900° F (1,038° C), 2,000° F (1,093° C), 2, 100° F (1,149° C), 2,200° F (1,204° C), 2,300° F (1,260° C), 2,400° F (1,316° C) or even 2,500° F (1,371° C) and, in addition, that minimum actual temperature at the end of this cycle should not be less than this target temperature by a first predetermined temperature difference such as, for example, 150° F (83° C), 100° F (56° C), 75° F (42° C), 50° F (28° C) or even 25° F (14° C). Every billet whose actual temperature at the end of the heating step is below this minimum is then automatically discharged to waste, thereby further ensuring that formation of new intermetallic phases is
  • the measured temperature of the side wall of the billet as it exits its heater can be used.
  • the measured temperature of the front or rear face of the billet as described immediately above, can also be used.
  • Still another approach that can be used for ensuring that formation of new intermetallic phases is avoided during billet heat-up is to compare the measured temperature of the side wall of the billet as it exits its heater with the measured temperature of the front or rear face of the billet as it exits its heater and to discharge to waste all billets in which the difference between these two measured temperatures exceeds a predetermined maximum.
  • a predetermined temperature difference such as, for example, 200° F (111° C), 150° F (83° C), 100° F (56° C), 75° F (42° C), or even 50° F (28° C). Every billet in which the difference between these two measured temperatures exceeds this predetermined maximum is then automatically discharged to waste, thereby further ensuring that formation of new intermetallic phases is avoided reliably and consistently time after time for each billet being heated.
  • a still further approach that can be used for ensuring that formation of new intermetallic phases is avoided during billet heat-up is to continue heating the billet above its critical temperature range long enough to redissolve any intermetallic phases that may be present. For example, keeping the temperature of the billet above its upper critical temperature for a longer period of time than the billet was within its critical temperature range during billet heat-up (or at least within the most critical portion of this critical temperature range) will generally ensure that any deleterious intermetallic phases that might have formed during heat-up are eliminated before the forging step begins.
  • heating the billet at a temperature which is above the upper arm of its critical temperature range CTR e.g., from 1000° C to 1250° C
  • a period of times which is at least 3, at least 4, at least 5, at least 6, at least 7 or even at least 8 times as long as the period of time the temperature of the billet is within the most critical portion of its critical temperature range CTR e.g., 800° C to 900° C
  • billets which have been heated too hot may be difficult to forge and, in addition, may undergo excessive surface oxidation.
  • steps can be taken to ensure that the billets are not overheated during the billet heating step of this invention. This can be done, for example, by discharging to waste all billets whose actual temperature at the end of the heating step exceeds a predetermined maximum.
  • a third predetermined temperature difference such as, for example, 200° F (111° C), 150° F (83° C), 100° F (56° C), 75° F (42° C), or even 50° F (28° C).
  • Another approach that can be used for avoiding billet overheating is to discharge to waste any billet which remains in heater 12 for a holding time which exceeds a predetermined maximum.
  • some predetermined maximum such as, for example, 120 seconds, 90 seconds, 75 seconds, 50 seconds, 40 seconds, or even 30 seconds. Every billet in which the actual holding time exceeds this predetermined maximum is then automatically discharged to waste, thereby further ensuring that excessive surface oxidation of the forging produced is avoided.
  • the heated billet is converted into a forging by the application of substantial hot working.
  • This can be done by any known hot working technique including roll forging, swaging, cogging, open-die forging, closed-die forging, impression-die forging, press forging, automatic hot forging, radial forging, and upset forging.
  • this forging step is represented by the line extending from points 30 to 32. As shown there, this forging step begins at point 30, when the heated billet is removed from its heating source and ends at point 32 when rapid cooling of the forging produced begins.
  • this hot forging step is accomplished in such a way that essentially no intermetallic phases form during this step. This, in turn, is accomplished by insuring that the temperature of this billet/forging, or at least its core, does not drop below the upper boundary of its critical temperature range CTR at any time during this entire forging step.
  • this forging step normally involves a number of different operations including removing the billet from its heating source, transferring the heated billet to the forging apparatus, hot forging the billet, removing the forging so formed from the forging apparatus, transferring the forging to its rapid cooling station and initiating rapid cooling by contact with water or other cooling liquid.
  • completion of this forging step can take several tens of minutes to hours or even longer.
  • Fig. 4 as soon as the billet is removed from its heating source at point 30 it begins to cool rapidly.
  • the temperature of the billet/forging, or at least a substantial portion of the billet/forging drops below the upper boundary of its critical temperature range CRT for a not-insignificant period of time.
  • this conventional practice of relying on subsequent solution anneal and/or reheating the billet/forging during its forging step is avoided as being unnecessary, as keeping the temperature of the billet/forging above the upper boundary of its critical temperature range CRT at all times during this entire forging step insures that no deleterious intermetallic phases form during this time.
  • the most straightforward way of insuring that the temperature of billet/forging remains above the upper boundary of its critical temperature range CRT at all times during this entire forging step would appear to be to monitor the temperature of the billet at various times and/or stages of this forging step. In practice, however, this can prove to be impractical for a variety of reasons.
  • the easiest way of insuring that the temperature of billet/forging remains at this desired level is to monitor the time between the start and end of this forging step, i.e., the period of time which elapses between points 30 and 32 in Fig. 4.
  • the temperature of the billet at point 30, i.e., the temperature of the billet when it leaves heater 12 can also be monitored as well.
  • the entire forging step of the inventive process from beginning to end, will be carried out in less than 3 minutes, more commonly in less than 2 minutes, less than 90 seconds, less than 75 seconds, less than 60 seconds, less than 45 seconds or even less than 30 seconds.
  • carrying out this step so quickly normally requires that the billet/forging be fairly small, as a practical matter, which is the case for many hot forgings made from the heavily alloyed metals contemplated by this invention.
  • skilled metallurgists understand that, because of inherent heat transfer limitations, the rate at which the core of a metal workpiece heats or cools is normally slower than the rate at which surface of the workpiece heats or cools. In addition, skilled metallurgists further understand this difference becomes greater as the size of the workpiece becomes larger. Furthermore, skilled metallurgists also understand that a forge hammer or other hot working implement can act as a heat sink, in effect rapidly sucking the latent heat out of the particular surfaces of a billet which are struck by these implements, thereby causing these billet surfaces to cool very rapidly.
  • the temperature of the interior or core of the billet/forgings being processed may be different from the temperature at its surface.
  • the temperature of all portions of the billet/forging will remain above the upper boundary of the critical temperature range CRT at all times during this entire forging step.
  • the core of the billet/forging will remain above the upper boundary of the critical temperature range at all times, while some or all of the outer surfaces of billet forging may drop below this temperature for periods of time which are too short to enable deleterious intermetallic phases to form to any significant degree. It is also possible that in still other embodiments, even the core of the billet/forging may drop below this temperature for a very short period of time.
  • the automatic control system of the process can be programmed to discharge to waste any forging with respect to which the forging step of the inventive process, as measured from the time when the billet is removed from its heating source to the time when rapid cooling begins, takes longer than a predetermined maximum period of time.
  • a predetermined maximum period of time For example, with respect to the particular alloy whose TTT and CCT curves are illustrated in Figs. 2 and 3, a determination can be made that the total time for this forging step should not is some predetermined maximum such as, for example, 120 seconds, 90 seconds, 75 seconds, 50 seconds, 40 seconds, or even 30 seconds. Every billet in which the actual time for this forging step exceeds this predetermined maximum is then automatically discharged to waste, thereby further ensuring that formation of new intermetallic phases is avoided, reliably and consistently, time after time, for each hot forging being made.
  • the forging obtained is rapidly cooled to a temperature which is below its critical temperature range CTR.
  • the rate at which the forging is quenched is fast enough to prevent intermetallic phases from forming in any significant amount.
  • this rapid cooling step is represented by the line extending from points 32 to 34, although in actual practice the forging will normally be rapidly cooled down to a temperature approaching room temperature, as represented by point 36.
  • this rapid cooling step begins at point 32, when the hot forging is first contacted with a cooling medium and ends at point 34 when the hot forging has cooled to a temperature which is below the lower limit of its critical temperature range CTR.
  • cooling of the hot forging in this cooling step is accomplished so that the time the hot forging is within its critical temperature range CTR, which is denoted by AU in this figure, is so short that deleterious intermetallic phases do not have an opportunity to form, at least to any significant degree. This can be done in any conventional way such as by contacting the hot forging with water or other cooling liquid, either by immersing the hot forging in the cooling liquid, by directing jets or sprays of the cooling liquid at the hot forging, or other suitable procedure.
  • this is accomplished by immersing each hot forging into the cooling liquid individually or as a small number of small forgings having been made from the same billet, rather than as a large number of forgings which are typically quenched together after solution annealing.
  • the normal way of rapidly quenching hot forgings which are relatively small in size is to arrange a group of the hot forgings in a tray or basket or other holding device and then immerse the tray and all of its contents in the cooling liquid.
  • This approach inherently slows the rapid cooling process down, because the close packing of the hot forgings with respect to one another plus the mass of the tray or other holder makes it more difficult for the cooling liquid to touch and hence remove heat from the surfaces of each hot forging.
  • the inventive process when the inventive process is carried out to make multiple hot forgings which are relatively small in the sense of having a maximum thickness or diameter of 25 centimeters, 20 centimeters, 15 centimeters, 12 centimeters, 9 centimeters, 6 centimeters, 5 centimeters, 4 centimeters or even 3 centimeters, these hot forgings are rapidly cooled by immersing each in a pool of cooling water or other liquid individually.
  • multiple hot forgings of this type will be made serially, i.e., one after the other, and so it is further contemplated that these individual hot forgings will be individually immersed in cooling liquid in the same serial fashion, as this not only speeds the rate at which cooling occurs, as mentioned above, but also minimizes the lag time between completion of forging and initiation of rapid cooling for each forging.
  • the temperature of the water or other cooling liquid used for this purpose be maintained at or below some predetermined maximum such as, for example, 175° F (79° C), 150° F (66° C), 125° F (52° C), 100° F (38° C), or even 75° F (24° C).
  • multiple forgings are made from the same billet, with multiple billets being processed serially to make these multiple hot forgings.
  • the group of forgings made from the same billet can be rapidly cooled together.
  • some predetermined maximum such as, for example, 175° F (79° C), 150° F (66° C), 125° F (52° C), 100° F (38° C), or even 75° F (24° C).
  • intermetallic phases can form during any stage in the manufacture of a hot forged product, starting with how the forging stock from which the product is derived is processed in the foundry or forging ship and ending with how the product is rapidly cooled after forging.
  • an important aspect of the inventive process is that in each of these manufacturing stages, care is taken to eliminate or at least minimize the amount of these deleterious intermetallic phases that form.
  • the ultimate hot forged product obtained is essentially free of these deleterious intermetallic phases in the sense that it meets its applicable product specifications.
  • hot forgings made by the inventive process when formed from the AISI-2205 duplex stainless steel of Figs. 2 and 3 as well as other highly alloyed steels like the super austentic alloys and the super duplex alloys having a CP value of at least 500, reliably and consistently exhibit a weight loss of no greater than 4 g/m 2 and no pitting when tested per ASTM-G48, as required by the NORSOK M650 standard.
  • each step of the inventive process be carried out to minimize formation of these intermetallic phases to the greatest extent possible or avoid formation of these intermetallic phases altogether. Rather, all that is necessary is that a combination of features be adopted, as discussed in this disclosure, so that the concentration of these deleterious intermetallic phases in the hot forged product ultimately produced is low enough so that it still meets its applicable product specifications.
  • machining will be understood to mean a process for shaping an object by removing material from a workpiece by some type of cutting or grinding operation. Examples include turning, milling, drilling, tapping, surface grinding, cylindrical grinding, belt grinding, electrical discharge machining, electrochemical machining, electrochemical grinding, chemical milling, ultra-sonic machining, electron beam machining and the like.
  • such metal parts are made from the hot forgings of this invention, which have been made without a post-forging solution anneal.
  • a first advantage of this approach is that the overall cost of producing such parts is decreased significantly, since the post-forging solution anneal steps normally carried out in their manufacture has been eliminated by this invention.
  • FIGs. 5a and 5b are photomicrographs showing the microstructures of two hot forgings made in the following working examples.
  • Fig. 5a shows the microstructure at the center of a hot forging made by the inventive process, i.e., without a post- forging solution anneal
  • Fig. 5b shows the microstructure at the center of an otherwise identical hot forging made with a post-forging solution anneal.
  • hot forgings were subjected to a conventional post-forging solution anneal in which the forging, after cooling to room temperature by water quenching, was heated and maintained at a temperature of 1177° C (2150° F) for at least 30 minutes, after which it was rapidly quenched by immersion in water.
  • the other hot forging, representing this invention, was recovered in its as-quenched condition— i.e., it was recovered without a post-forging solution anneal.
  • These hot forgings were then sectioned, and photomicrographs taken of the metal at the center of each forging.
  • Fig. 5a is the photomicrograph of the hot forging made in accordance with this invention, which had been produced without post-forging solution anneal. As can be seen, its grain structure was fine and uniform, suggesting excellent mechanical properties.
  • Fig. 5b is the photomicrograph of the comparative hot forging which had been produced with a conventional post-forging solution anneal. As can be seen, its grain structure was much larger and less uniform, suggesting lesser mechanical properties.

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Abstract

Selon l'invention, l'étape de recuit de mise en solution après le forgeage normalement effectuée sur des pièces forgées à chaud faites de métaux fortement alliés peut être éliminée tout en évitant la formation de phases intermétalliques nuisibles par adoption d'un certain nombre de conditions distinctes dans la manière dont le forgeage est effectué.
PCT/US2018/059518 2017-11-07 2018-11-07 Pièces forgées en acier inoxydable fortement allié sans recuit de mise en solution WO2019094400A1 (fr)

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US4554028A (en) * 1983-12-13 1985-11-19 Carpenter Technology Corporation Large warm worked, alloy article
US4721600A (en) * 1985-03-28 1988-01-26 Sumitomo Metal Industries, Ltd. Superplastic ferrous duplex-phase alloy and a hot working method therefor
US5494636A (en) 1993-01-21 1996-02-27 Creusot-Loire Industrie Austenitic stainless steel having high properties
US20040050463A1 (en) * 2001-04-27 2004-03-18 Jae-Young Jung High manganese duplex stainless steel having superior hot workabilities and method for manufacturing thereof
US20140238552A1 (en) * 2013-02-26 2014-08-28 Ati Properties, Inc. Methods for processing alloys
US20150129093A1 (en) * 2013-11-12 2015-05-14 Ati Properties, Inc. Methods for processing metal alloys
US20170166986A1 (en) * 2015-12-14 2017-06-15 Swagelok Company Highly alloyed stainless steel forgings made without solution anneal

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4554028A (en) * 1983-12-13 1985-11-19 Carpenter Technology Corporation Large warm worked, alloy article
US4721600A (en) * 1985-03-28 1988-01-26 Sumitomo Metal Industries, Ltd. Superplastic ferrous duplex-phase alloy and a hot working method therefor
US5494636A (en) 1993-01-21 1996-02-27 Creusot-Loire Industrie Austenitic stainless steel having high properties
US20040050463A1 (en) * 2001-04-27 2004-03-18 Jae-Young Jung High manganese duplex stainless steel having superior hot workabilities and method for manufacturing thereof
US20140238552A1 (en) * 2013-02-26 2014-08-28 Ati Properties, Inc. Methods for processing alloys
US20150129093A1 (en) * 2013-11-12 2015-05-14 Ati Properties, Inc. Methods for processing metal alloys
US20170166986A1 (en) * 2015-12-14 2017-06-15 Swagelok Company Highly alloyed stainless steel forgings made without solution anneal

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