EP2135962A1 - Einsatzgehärtetes stahlrohr mit hervorragender bearbeitbarkeit und herstellungsverfahren dafür - Google Patents

Einsatzgehärtetes stahlrohr mit hervorragender bearbeitbarkeit und herstellungsverfahren dafür Download PDF

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EP2135962A1
EP2135962A1 EP08739140A EP08739140A EP2135962A1 EP 2135962 A1 EP2135962 A1 EP 2135962A1 EP 08739140 A EP08739140 A EP 08739140A EP 08739140 A EP08739140 A EP 08739140A EP 2135962 A1 EP2135962 A1 EP 2135962A1
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Prior art keywords
steel
tube
steel tube
temperature
annealing
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French (fr)
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EP2135962B1 (de
EP2135962A4 (de
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Kenichi Beppu
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Nippon Steel Corp
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Sumitomo Metal Industries Ltd
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    • 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
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/32—Ferrous alloys, e.g. steel alloys containing chromium with boron
    • 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
    • C21D1/26—Methods of annealing
    • C21D1/28—Normalising
    • 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
    • C21D1/26—Methods of annealing
    • C21D1/32—Soft annealing, e.g. spheroidising
    • 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
    • C21D6/02—Hardening by precipitation
    • 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
    • C21D7/02—Modifying the physical properties of iron or steel by deformation by cold working
    • C21D7/04—Modifying the physical properties of iron or steel by deformation by cold working of the surface
    • 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
    • C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
    • 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
    • C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
    • C21D8/105—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies 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
    • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
    • C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
    • C21D9/085—Cooling or quenching
    • 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
    • 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
    • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium 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
    • C22C38/26—Ferrous alloys, e.g. steel alloys containing chromium with niobium or tantalum
    • 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
    • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium
    • 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
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • 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
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • 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
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/02—Pretreatment of the material to be coated
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/40—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using liquids, e.g. salt baths, liquid suspensions
    • C23C8/42—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using liquids, e.g. salt baths, liquid suspensions only one element being applied
    • C23C8/44—Carburising
    • C23C8/46—Carburising of ferrous surfaces
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/80—After-treatment
    • 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
    • C21D2211/003—Cementite
    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D2211/00—Microstructure comprising significant phases
    • C21D2211/005—Ferrite

Definitions

  • This invention relates to a case hardening steel tube (a steel tube made from case hardening steel) having a high strength and a high toughness and exhibiting a high fracture load after carburizing and quenching, and to a process for its manufacture.
  • this invention relates to a case hardening steel tube having improved workability and a process for its manufacture.
  • case hardening steel has been used for the manufacture of various types of structural parts for use in automobile or industrial machinery and particularly surface-hardened parts typified by shafts, CVJs (constant velocity joints), CVTs (continuously variable transmissions), and gears.
  • Case hardening steel which is a material to be worked is formed into a part having a desired shape by hot or cold forging and machining, for example.
  • the part which has been formed is then subjected to surface hardening treatment such as carburizing or carbo-nitriding in order to increase its wear resistance and fatigue strength.
  • Case hardening steel sometimes has problems such as a decrease in impact fracture strength, a decrease in fatigue properties, and a decrease in dimensional accuracy due to abnormal growth of crystal grains during carburizing and quenching treatment.
  • high temperature carburizing which is carried out in the temperature range of 990 - 1090 °C is employed in order to shorten the carburizing time from the viewpoint of rationalization of carburizing treatment, the problem occurs that coarse grains develop, thereby making it impossible to obtain the desired fatigue properties such as rolling fatigue properties.
  • Patent Document 1 proposes suppressing the formation of coarse grains during high temperature carburizing of case hardening steel by controlling the steel composition and the formation of Ti-containing precipitates.
  • JP H09-53150 A1 discloses a high-strength, high-toughness case hardening steel exhibiting a sufficiently high impact fracture load even when a notch is present in the carburized surface and a process of manufacturing a high-strength, high-toughness case hardening steel tube exhibiting improved workability and improved impact fracture strength after carburizing and quenching from this steel.
  • Patent Document 2 one of the causes of the problems of the prior art is the formation of an imperfect hardened structure.
  • the major cause of the formation of this imperfect hardened structure is the precipitation of carbides along austenite grain boundaries which occurs at the time of quenching of a carburized steel. Therefore, a steel composition design is employed in which B is added in order to prevent the above-described precipitation of carbides while N is reduced as much as possible so that B can adequately exhibit its effects.
  • the high-strength, high-toughness case hardening steel tube disclosed in Patent Document 2 has excellent properties particularly in the form of seamless steel tube of case hardening steel. However, since it has a relatively high hardness, problems sometimes develop with respect to workability, for example, at the time of forging by a user.
  • Patent Document 2 discloses (i) a process in which a steel tube obtained by hot tube forming is subjected to cold working followed by stress relief annealing (Example 3), and (ii) a process in which a steel tube obtained by hot tube forming is subjected to initial annealing followed by cold working and subsequent stress relief annealing (secondary annealing) (Examples 4 and 5).
  • the present invention provides a case hardening steel tube which has good workability or more specifically an HRB hardness (Rockwell B scale hardness) of 72 - 80 and which can form a carburized layer of high strength and good wear resistance as well as sufficiently improved resistance to impact fracture when it is formed into a final product by working for forming followed by carburizing and quenching under relatively mild conditions, along with a process for its manufacture.
  • HRB hardness Rockwell B scale hardness
  • the present invention is based on the following findings.
  • a steel tube manufactured by hot tube forming and having a steel composition which makes it possible to carburizing and quenching to perform thereon is subjected initially to normalizing, then to cold working and subsequently to stress relief annealing.
  • the annealing at least a portion of the pearlite in the ferrite + pearlite structure resulting from normalizing is spheroidized (namely, cementite in the pearlite is spheroidized), leading to softening of the steel, and a case hardening steel tube having excellent workability is manufactured in this manner.
  • a ferrite + pearlite structure is formed during normalizing, and this structure is subjected to subsequent steps of cold working and annealing.
  • the proportion of pearlite which is spheroidized during annealing can be varied. In this manner it is possible to perform fine adjustment of the steel hardness.
  • the present invention is a process for manufacturing a case hardening steel tube characterized by forming a tube from a steel having a steel composition comprising, in mass percent, C: 0.1 - 0.25%, Si: 0.2 - 0.4%, Mn: 0.3 - 0.9%, P: at most 0.02%, S: 0.001 - 0.15%, Cr: 0.5 - 0.9%, Mo: 0.15 - 1%, A1: 0.01 - 0.1%, B: 0.0005 - 0.009%, N: less than 0.006%, and a remainder essentially of Fe, subjecting the resulting steel tube to normalizing by holding at a temperature of 880 - 980 °C followed by cooling at a cooling rate of at most 70 °C per minute in a temperature range of 880 - 400 °C, performing cold working on the normalized steel tube, and then annealing the cold worked steel tube at a temperature of 700 - 820 °C.
  • the present invention is a cold finished, case hardening steel tube characterized by having a steel composition comprising, in mass percent, C: 0.1 - 0.25%, Si: 0.2 - 0.4%, Mn: 0.3 - 0.9%, P: at most 0.02%, S: 0.001 - 0.15%, Cr: 0.5 - 0.9%, Mo: 0.15 - 1%, A1: 0.01 - 0.1%, B: 0.0005 - 0.009%, N: less than 0.006%, and a remainder essentially of Fe, and having a steel structure which is a mixed ferrite + pearlite + spheroidized cementite structure or a mixed ferrite + spheroidized cementite structure.
  • the above-described steel composition may further contain one or more elements selected from the following (1) and (2):
  • the B content is preferably B: 0.0005 - 0.003%.
  • “Case hardening steel” and “case hardening steel tube” refer to steel and steel tube which undergo working to form a prescribed shape of a product (such as the above-described structural part of machinery) and finally carburizing and quenching to form a harder surface skin layer (carburized layer) before being used as a product.
  • the above-described hardness is the hardness of the case hardening steel, i.e., the hardness before the steel undergoes working to be formed into the shape of a part (of course, the hardness prior to carburizing and quenching).
  • Forming into the prescribed shape of a product and carburizing and quenching are normally carried out by the customer (by the user).
  • a remainder essentially of Fe means that the remainder may contain unavoidable impurities.
  • the Cr content is limited in order to suppress embrittlement of grain boundaries resulting from carburizing, and hardenability is supplemented by the addition of B.
  • hardenability markedly decreases even if the carbon content reaches a high level, so supplementing hardenability of a carburized layer by addition of Mo is extremely important.
  • the Mo content is less than 0.15%, not only can hardenability not be adequately supplemented, but the amount of carbon which penetrates into the surface layer during carburizing treatment performed in a short length of time also decreases. From the standpoint of imparting the above-described effect, it is preferable for the Mo content to be large.
  • the Mo content is 0.15 - 1%, preferably 0.2 - 0.7%, and more preferably 0.2 - 0.6%.
  • heat treatment is carried out before cold working at a temperature of at least the Ac 3 point and specifically at a temperature of at least 880 °C.
  • This heat treatment is contemplated that B is once solutionized in order to achieve the object of decreasing hardness by annealing which is carried out after cold working. If the amount of B is too large, a long time is required for solutionize B and accordingly a long time is required in heat treatment for normalizing. Therefore, the B content is preferably on the lower side of the above-described range. Specifically, it is particularly desirable for the B content to be at most 0.003% (namely, in the range of 0.0005 - 0.003%).
  • the steel structure becomes a mixed structure of ferrite + spheroidized cementite.
  • the steel structure becomes a mixed structure of ferrite + pearlite + spheroidized cementite.
  • a case hardening steel tube according to the present invention can be characterized by this steel structure and the above-described steel composition.
  • Spheroidizing at least a portion of pearlite in this manner results in a decrease in the hardness of the steel tube.
  • a case hardening steel tube having good workability in the form of a hardness of 72 - 80 HRB can be manufactured according to the present invention.
  • the hardness can be adjusted to a desired value by varying the proportion of pearlite which is spheroidized during annealing by controlling the reduction ratio at the time of cold working and the annealing conditions.
  • carburizing and quenching are normally carried out by the user after fabrication of the part by working or forming.
  • carburizing and quenching conditions are carburizing by soaking at 920 °C for 2 hours and then quenching from 870 °C.
  • One-ton blooms having the steel compositions shown in Table 1 were produced by casting molten steel obtained by vacuum melting. The blooms underwent hot forging to obtain round billets, which were then underwent hot tube forming by piercing rolling, elongation rolling in a mandrel mill, and sizing rolling in a stretch reducer to produce mother tubes (steel tubes) with an outer diameter of 80 mm and a wall thickness of 6.1 mm.
  • the steel tubes were subjected to initial heat treatment (normalizing) under the conditions shown in Table 2 followed by cooling, and they then underwent cold drawing with a reduction in area of 28.4% to provide finished seamless steel tubes having dimensions of an outer diameter of 66.2 mm and a wall thickness of 5.3 mm. These steel tubes were then subjected to annealing under the conditions shown as secondary heat treatment in Table 2. Test pieces were cut from the steel tubes after the completion of the secondary heat treatment (annealing), and the Rockwell B scale hardness (HRB) of tube cross sections was measured for each tube. The results are shown in Table 2.
  • No. 1 and No. 2 in Table 2 had a heat treatment temperature in normalizing before cold working of 700 °C which was lower than the Ac 1 point, and they were finished to a hardness of at least 87 HRB.
  • Nos. 3 - 7 for which the heat treatment temperature before cold working exceeded the Ac 3 point, when the heat treatment temperature was lower than 880 °C, except for No. 3, the hardness was at least 82 HRB, and the object of softening to a value of at most 80 HRB could not be achieved.
  • the cooling rate after heat treatment (soaking) was made a slow value of 10 °C per minutes
  • the hardness was 77 HRB and the object of softening could be achieved.
  • the heat treatment time including the cooling step became long, and temperature holding equipment in the case of continuous treatment would become elongated, so this cooling rate is clearly not economical.
  • Nos. 8 - 18 are examples in which heat treatment prior to cold working was soaking at 880 °C or 930 °C.
  • the cooling rate after soaking exceeded 70 °C per minute and for Nos. 14 and 16 in which the annealing temperature after cold working was too low or high, the hardness exceeded 80 HRB and sufficient softening could not be achieved.
  • the cooling rate after soaking was at most 70 °C per minute and the annealing temperature after cold working was in the range of 700 - 820 °C
  • the object of softening to a hardness of at most 80 HRB could be achieved in each case.
  • Figure 1 shows a photomicrograph of a steel tube obtained by No. 11 of Table 2. It can be seen that carbides (cementite) were spheroidized in the ferrite + pearlite structure.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Organic Chemistry (AREA)
  • Mechanical Engineering (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Thermal Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Manufacturing & Machinery (AREA)
  • Heat Treatment Of Articles (AREA)
  • Heat Treatment Of Steel (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
EP08739140.5A 2007-03-29 2008-03-28 Einsatzgehärtetes stahlrohr mit hervorragender bearbeitbarkeit und herstellungsverfahren dafür Active EP2135962B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP2007088283 2007-03-29
PCT/JP2008/056016 WO2008123397A1 (ja) 2007-03-29 2008-03-28 加工性に優れた肌焼鋼管とその製造方法

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Publication Number Publication Date
EP2135962A1 true EP2135962A1 (de) 2009-12-23
EP2135962A4 EP2135962A4 (de) 2015-03-04
EP2135962B1 EP2135962B1 (de) 2016-07-13

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WO2018022420A1 (en) * 2016-07-28 2018-02-01 The Gleason Works Heat treatment of steel parts, particularly friction-welded steel parts
EP4324941A1 (de) * 2022-08-19 2024-02-21 Benteler Steel/Tube GmbH Verfahren zur herstellung eines rohrförmigen halbzeugs
EP4186990A4 (de) * 2021-01-28 2024-06-05 Jiangyin Xingcheng Special Steel Works Co., Ltd Stahl für eine kugelkäfig-universalgelenkhalterung und herstellungsverfahren dafür

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CN103320597A (zh) * 2013-06-14 2013-09-25 攀钢集团成都钢钒有限公司 一种细化10Cr9Mo1VNbN钢管及锻件粗晶的方法
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WO2018022420A1 (en) * 2016-07-28 2018-02-01 The Gleason Works Heat treatment of steel parts, particularly friction-welded steel parts
EP4186990A4 (de) * 2021-01-28 2024-06-05 Jiangyin Xingcheng Special Steel Works Co., Ltd Stahl für eine kugelkäfig-universalgelenkhalterung und herstellungsverfahren dafür
EP4324941A1 (de) * 2022-08-19 2024-02-21 Benteler Steel/Tube GmbH Verfahren zur herstellung eines rohrförmigen halbzeugs

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KR20090125134A (ko) 2009-12-03
CN101646788B (zh) 2011-04-13
JPWO2008123397A1 (ja) 2010-07-15
JP5126857B2 (ja) 2013-01-23
WO2008123397A1 (ja) 2008-10-16
EP2135962B1 (de) 2016-07-13
EP2135962A4 (de) 2015-03-04
US20100051143A1 (en) 2010-03-04
CN101646788A (zh) 2010-02-10
MX2009010307A (es) 2009-10-16
KR101113575B1 (ko) 2012-03-13

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