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
  • C22C38/24—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
  • C22C38/22—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
  • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium

Definitions

• vanadium carbide is an eflicient strengthener for high temperature creep and the finely dispersed vanadium carbides result in high hardness and creep-rupture strength, but at the same time a higher incidence of creep-rupture embrittlement.
• a primary object of the invention is to achieve in high temperature Cr-Mo-V steels high rupture ductility and high creep-rupture strength at one and the same time.
• the invention relates to increasing the high temperature creep-rupture ductility at high creep-rupture strengths of cast and wrought ferritic steels of the Cr- Mo-V class by the addition to the molten alloy of aluminum and titanium. It has been found that in an alloy of the above class comprising by weight about 0.05 to 0.6% carbon, .5 to 3% chromium, 0.3 to 1.75% molybdenum, 0.15 to 1% vanadium, 0.2 to 1.5% manganese,
• the rupture ductility of the alloy at high creep-rupture strengths is maintained by the addition to the molten alloy of such quantities of aluminum and titanium that at least about 0.02% aluminum and at least about 0.04% of titanium based on the weight of the molten alloy are present in the final alloy, the remainder of the aluminum and titanium added being in the combined state.
• up to .2% residual aluminum and titanium have been found useful.
• the alloys of the invention are austenitized at such temperatures generally over 1800 Fl that essentially all of the vanadium carbides are dissolved. The alloy is then cooled to allow transformation to a predominantly bainitic structure and tempered as above.
• the Cr-Mo-V steel alloys of the present invention are the result of a balance of ingredients or constituents which combine to provide the improved characteristics obtained.
• the carbon content of the alloy should be held to .05 to .6% if the optimum combination of high temperature characteristics is to be obtained. With carbon contents less or greater than those prescribed, it has been found that the high temperature creep-rupture strength of the steel is significantly lowered. Lower amounts of carbon within the above range are used where welda-bility is an important factor.
• the chromium content of the all-0y is likewise quite critical and should be held to between .5 and about 3%. Additionally, a minimum of about .5% is required to provide resistance to g'raphitization.
• oxidation resistance from about .75 to 1.5% provides for oxidation resistance and this amount may be increased to about 3% when maximum oxidation resistance is desired. More than about 3% of chromium on the whole results in an undesirable reduction in creep-rupture strengths.
• the molybdenum content of the alloy should be maintained between about 0.3 to 1.75%. Less than about 0.3% molybdenum results in poor creep-rupture strength while more than about 1.75 molybdenum promotes the undesirdable development of molybdenum carbides at the expense of vanadium carbide, again giving a lower creeprupture strength. Vanadium in amounts of from about 0.15 to 1% results in improved creep-rupture strength.
• the prescribed manganese content of about 0.2 to 0.5% insures at its lower level that sulfur is in the form of manganese sulfide and larger amounts of manganese enhance the hardenability of the alloy. While amounts of manganese over about 1% lead to some slight decrease in creep-rupture strength, this is not significant in amounts up to about 1.5%.
• Table I Listed in Table I below are the percent by weight compositions of a number of alloys made in connection with the present invention. Shown in Table II are the room temperature, the tensile strength, yield strength, percent elongation and reduction in area under physical testing.
• Alloys 1 through 21, 30 through 35 and 41 were prepared in an induction furnace. Alloys 22 through 24 and 36 through 38 were made in an electric furnace while alloys 26 through 29 were made in a plasma arc furnace. These varying modes of preparation account in part for the varying amounts of residual aluminum and titanium compared to the amounts added.
• Alloys 30 through 35 were heat-treated for 15 hours at 1925 27 1103 gag F., furnace-cooled, further heat-treated for 15 hours at 28 J56 L24 (1 13-64; F. and air-coiolfed.
• 12Alloys 36 tl11ggufih138 wgrehall initia ly heat-treate or ours at an en .15 40 29 12 1 25 96 46 8 furnace-cooled.
• Alloy 36 was further treated for 20 hours 30 &3 mm at 1350 F. and air-cooled, alloy 37 was further heat- 31 .16 .60 1.32 .93 .56 .110 .024 10 treated at 1350 F. for 7 hours, while alloy 38 was further 3 16 64 1 30 99 57 3% 2?
• Alloys 1, 22 through 38 and 41 were cast wh1le alloys 22 1,100 38,000 407-6 13-7 9 1, 100 35, 000 1, 410. 1 14. 2 76 9 through 21 and 41 were forged. Alloy l was heat- 1,100 33,000 3,3324 14,7 73 treated for 16 hours at a temperature of 1.875 to 1925 i ggg 888 g g-g 3% F., air-cooled, heat-treated for 15 hours at 1325 F. and 23 I 33: 50 30416 1 air-cooled. The forged materials of alloys 9 through 15 $33 333 23-? g-g 21 were heat-treated at 1900 F.
• Alloys 11100 321000 44511 g1; g3 18 and 19 after the above heat treatment were again re 5 1,138 2% 888 113.9 3.2 3: heated at 1200" F. for 52 hours.
• Alloy 21 was further 28 1:100 351000 5 41 heat-treated at 1200 F. for 40 hours.
• Cast alloy 22 was 138 88% 39 7 13.12 g9 heat-treated for 12 hours at 1922 to 1940 F., air-cooled 29 1:100 301000 6 1 1 and heated for 28 hours at 1319 to 1328 F.
• Cast alloy 1.100 27,000 50443 0.3 88 a 1, 25, 000 1, 030. 7 16. 0 33 23 was heat-treated 01.
• Alloy 18 illustrates the same effect for a forged material.
• Alloy 24 illustrates a cast material in which, while both aluminum and titanium are present, the relatively low amount of aluminum below the presently prescribed limits produces a material which is lacking in desirable rupture ductility.
• Alloy 14 illustrates this same effect of a deficient amount of aluminum for a forged product.
• Alloy 27 is illustrative of a cast alloy in which, while a substantial amount of aluminum is present, there is a deficiency of titanium, once again, resulting in an undesirable rupture ductility. Alloy 28 shows that an increase in the amount of aluminum, still keeping the titanium at a low level, produces no pronounced improvement.
• Alloy 15 (which contains 0.0016 boron for hardenability) illustrates a material having desirable rupture ductility by reason of its content of aluminum and titanium. Alloys 19, 22 and 34 are further illustrative of suitable materials according to the present invention.
• Alloys 2 6, 27, 2'8 and 29 represent compositions which were obtained by making progressive additions of aluminum and finally 0.15% titanium to the same base heat of steel, castings being poured off after each addition. It will be noted that the rupture ductility progressively decreases through alloy 28 as the amount of aluminum is increased, showing that aluminum alone does not produce high rupture ductility. However, the addition of 0.15% titanium in alloy 29 results in a steel that shows no loss in creep-rupture ductility at all.
• Alloys 9, 10, 11, 14 and 15 illustrate the eifect of varying amounts of titanium and aluminum.
• Alloy 9 contains no deliberate additions of aluminum or titanium and shows low rupture ductility.
• Alloy contains additional titanium but still shows no significant change in ductility.
• alloys 17, 18, 19 and 21 show the beneficial efiect of titanium and aluminum additions 6 as in alloy 21 as compared to alloy 17 with aluminum alone or alloy 18 with titanium alone as pointed out above.
• alloys listed in Table I cover materials which are useful for many purposes.
• Alloys 17 through 21, for example, represent compositions which with the prescribed heat treatments are suitable for heavy forgings such as steam or turbine rotor forgings for high temperature service.
• Alloys 9 through 15 represent compositions and heat treatments suitable for smaller forgings and mill products such as plate and bar such as are used in pressure vessel construction for high temperature service.
• the remainder of the alloys represents compositions and heat treatments suitable for the production of castings, forgings or mill products for high temperature service where lower carbon contents are desirable for welding purposes.
• the order in which the aluminum and titanium are added is not critical and suitable steels have been made by adding either the aluminum or titanium first and also by adding both simultaneously. However, the recovery of the elements added is diflicult to predict in some cases. However, it is believed that the most consistent melting practice results if the aluminum is added first or simultaneously with the titanium. 'It is also useful to combine the aluminum and titanium as a single pre-alloyed master alloy with suitable proportions of the critical ingredients indicated.
• the additions of aluminum and titanium should preferably be made after the oxidizing and refining proportion of the steelmaking practice and just prior to tapping if the additions are to be made in the furnace. The additions can also be made in the ladle during or after tapping and all of the above practices have been used with equal success.
• vacuum degassing produces in some partial degree the beneficial results obtained by adding the present materials so that with vacuum degassing lesser amounts of the additives are required.
• the present invention is intended to cover such practice.
• the present invention means for realizing to the fullest extent the high creep-rupture strengths which are obtainable in Cr-Mo-V steels, at the same time providing such steels which have a desirably high rupture ductility.
• a high temperature alloy characterized by high rupture ductility and high creep-rupture strength and having a bainitic structure with finely dispersed precipitated vanadium carbide, said alloy consisting essentially of by weight about .05 to .6% carbon, .5 to 3.0% chromium, 0.3 to 1.75% molybdenum, 0.15 to 1.0% vanadium, 0.2 to 1.5% manganese, from about .02 up to about 0.2% aluminum and from about 0.04 up to about 0.2% of titanium, with the remainder essentially iron.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Heat Treatment Of Steel (AREA)
• Turbine Rotor Nozzle Sealing (AREA)

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Cited By (15)

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Citations (5)

• 1964
  • 1964-06-17 US US375921A patent/US3291655A/en not_active Expired - Lifetime
• 1965
  • 1965-05-07 GB GB19410/65A patent/GB1107154A/en not_active Expired
  • 1965-06-03 DE DE1483218A patent/DE1483218C3/de not_active Expired
  • 1965-06-14 FR FR20701A patent/FR1444988A/fr not_active Expired
  • 1965-06-16 CH CH843165A patent/CH458757A/de unknown

Patent Citations (5)

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