US3836407A - High strength and high toughness alloy - Google Patents

High strength and high toughness alloy Download PDF

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Publication number
US3836407A
US3836407A US00249585A US24958572A US3836407A US 3836407 A US3836407 A US 3836407A US 00249585 A US00249585 A US 00249585A US 24958572 A US24958572 A US 24958572A US 3836407 A US3836407 A US 3836407A
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United States
Prior art keywords
steel
toughness
strength
phase
cryogenic
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US00249585A
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English (en)
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E Parker
V Zackey
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US Atomic Energy Commission (AEC)
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US Atomic Energy Commission (AEC)
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Priority to US00249585A priority Critical patent/US3836407A/en
Priority to GB1818173A priority patent/GB1383623A/en
Priority to SE7305497A priority patent/SE387663B/xx
Priority to FR7315760A priority patent/FR2183184A1/fr
Priority to JP48049642A priority patent/JPS4948515A/ja
Priority to DE2322102A priority patent/DE2322102A1/de
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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
    • C22C38/08—Ferrous alloys, e.g. steel alloys containing nickel

Definitions

  • This invention relates to structural steels, and more particularly to a structural steel and method for producing a steel possessing both high strength and high toughness suitable for use in cryogenic service.
  • the design requirements of structures intended for cryogenic service are demanding and complex. Among the most important of these is safety. Consequently, high fracture toughness is mandatory. Another requirement is that the yield strength should be as high as possible to minimize section thickness. The user of thinner material enhances fracture toughness and minimize cost.
  • the present invention fills the above-mentioned need in the art for structural steels which possess both high strength and high toughness at low temperatures, this being accomplished by a thermally induced phase transformation in iron-rich alloys of the Fe-Ni-Ti system.
  • a further object of the invention is to provide a cryogenic steel which includes no carbon in the composition thereof.
  • Another object of the invention is to provide a high toughness cryogenic steel which utilizes a thermally induced phase transformation in the processing thereof.
  • Another object of the invention is to provide a method for producing a high strength, high toughness steel.
  • Another object of the invention is to provide a method for producing an Fe-Ni-Ti steel.
  • FIG. 1 is a phase diagram of the inventive Fe-Ni-Ti system showing the transformation temperatures for the l2Ni-0.5Ti steel;
  • FIG. 2 graphically illustrates the heat treating temperature vs. the room temperature hardness for the l2Ni-0.5Ti steel
  • FIG. 3 graphically illustrates the heat treating temperature vs. the Charpy-V notch value at l96C for the l2Ni-0.5Ti steel, with the heavy bar on the abscissa indicating the three phase region (a-l-y-l- Ni Ti);
  • FIG. 4 is a comparative plot of the yield strength and the toughness, both measured at 196C, for two prior art commercial cryogenic steels and the inventive Fe- Ni-Ti system for the l2Ni-0.5Ti steel.
  • the present invention provides a superior cryogenic alloy which utilizes an intermetallic compound believed to be Ni -Ti, to provide high strength, with no carbon or nitrogen content, and thus does not embrittle at low temperatures, thereby producing a steel which possess both high strength and high toughness.
  • the inventive cryogenic alloy was discovered by using the basic principles of materials science. In terms of defect theory, strength is enhanced by immobilizing dislocations. Toughness is increased, at a given strength level, by providing a high density of mobile dislocations. The latter are necessary for the degree of plasticity that is required for high fracture toughness. This desirable combination is generally absent in the prior art cryogenic alloys, but is found in the present inventive structural steel, whereby high strength and high toughness are obtained.
  • phase diagram shown in FIG. 1 is based on dilatometric and metallographic tests of the steel or alloy composition chosen (12 percent Ni, 0.5 percent Ti) to conduct the tests, and it is clear that iron-rich Fe-Ni-Ti system consists ofa two phase (BCC) region (i.e.,a+l ⁇ li Ti,,) at low temperatures (up to about 650C); three phases (i.e., a-l-y-i- Ni Ti) at an intermediate temperature (about 650C to about 720C); and a single phase (7) in the FCC region at the highest temperature (above about 720C).
  • the nickel-titanium phase is believed to be hexagonal Ni Ti.
  • the existence of the three phase region at intermediate temperature, as illustrated in FIG. 1 between the dash lines, provides for selectively decorating some dislocations, with the opportunity to allow others to be free to move when a stress exceeding the yield strength is applied.
  • the a: transformation during fast cooling presumably produces dislocations that are free to move.
  • the upper (right) dash line in FIG. 1 represents the start of the y a transformation, while the lower (left) dash line represents the end of the 7- a transformation on cooling.
  • the precipitation of Ni Ti occurs only on dislocations in the BCC phase, and only at elevated temperatures.
  • the ratio of the densities of immobilized and mobile dislocations can be controlled by regulating the ratio of the volume fractions of BCC (a) and FCC ('y) phases during heat treatment in the three phase field.
  • the latter ratio is uniquely determined by the heat treating temperature.
  • the FCC phase trnsforms to BCC by a martensitic reaction, producing a large number of mobile dislocations.
  • FIG. 2 The influence of the heat treating temperature on the hardness at room temperature is shown in FIG. 2, while the influence of the heat treating temperature on the toughness (as measured by the Charpy-V-notch value at l96C), is shown in FIG. 3.
  • the heavy bar shown on the abscissa of FIG. 3 indicates the approximate temperature range (about 650C to 720C) of the three phase region described above with respect to FIG. 1.
  • temperatures corresponding roughly to equal proportions of gamma and alpha between the dash lines in FIG.
  • the toughness and yield strength at -196C for the two above-mentioned commercial steels are contrasted with those of the inventive l2Ni-0.5Ti steel in FIG. 4.
  • the AISI Type 304 steel (An FCC steel) has high toughness but low yield strength
  • the 9Ni steel (a BCC steel) has high yield strength but low toughness.
  • the inventive Fe-Ni-Ti steel (a BCC steel) has the high toughness of the type 304 steel and the high yield strength of the 9Ni, thereby filling a need for a structural steel which possess both desired characteristics.
  • the following is directed to the operational sequence for producing the l2Ni-0.5Ti alloy: 1. Heat to 800 l,000C for a time period long enough to desolve the Ni-Ti compound. This time will vary from 15 minutes to several hours, depending on the thickness of the material. 2. Cool rapidly to room temperature. Thin pieces may be air cooled, with thicker pieces being water or oil quenched. 3. Reheat to 650 720C. The furnace utilized may be a commercial furnace utilized for heat treating stainless steels. This step dissolves the fraction of the volume of the compound that is in the high temperature phase (FCC). The part of the volume that remains in the low temperature phase (BCC) does not dissolve. This temperature is maintained from 15 minutes to 8 10 hours, depending on the material thickness. 4. Cool to room temperature. If thick, over A inch for example, it may be desirable to oil or water cool, otherwise air cooling is sufficient.
  • FCC high temperature phase
  • BCC low temperature phase
  • the invention has provided a structural steel which contains no carbon and possesses both high strength and high toughness, thus having particular application for cryogenic service.
  • a method for producing an iron rich alloy containing a nickel-titanium compound phase having both high strength and high toughness utilizing thermally induced phase transformation following heating in a threephase field in an iron-rich alloy of a Fe-Ni-Ti system comprising the steps of: heating to a single high temperature gamma phase region at a temperature in the range of about 800 to 1000C an alloy composition composed of about 12 percent nickel, about 0.5 percent titanium, with the remainder iron for sufficient time to dissolve the nickel-titanium compound; rapidly cooling the thus heated alloy to room temperature and the thus reheated alloy to room temperature.

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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)
  • Heat Treatment Of Articles (AREA)
US00249585A 1972-05-02 1972-05-02 High strength and high toughness alloy Expired - Lifetime US3836407A (en)

Priority Applications (6)

Application Number Priority Date Filing Date Title
US00249585A US3836407A (en) 1972-05-02 1972-05-02 High strength and high toughness alloy
GB1818173A GB1383623A (en) 1972-05-02 1973-04-16 High strength and high toughness iron-rich ternary alloy
SE7305497A SE387663B (sv) 1972-05-02 1973-04-18 Forfarande for framstellning av en jernrik fe-ni-ti-legering
FR7315760A FR2183184A1 (enExample) 1972-05-02 1973-05-02
JP48049642A JPS4948515A (enExample) 1972-05-02 1973-05-02
DE2322102A DE2322102A1 (de) 1972-05-02 1973-05-02 Stahl

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US00249585A US3836407A (en) 1972-05-02 1972-05-02 High strength and high toughness alloy

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US46634674A Division 1974-05-02 1974-05-02

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US (1) US3836407A (enExample)
JP (1) JPS4948515A (enExample)
DE (1) DE2322102A1 (enExample)
FR (1) FR2183184A1 (enExample)
GB (1) GB1383623A (enExample)
SE (1) SE387663B (enExample)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4202751A (en) * 1977-11-28 1980-05-13 Kobe Steel, Ltd. Sacrificial anode and apparatus employing same for treating hot sea water
US4214902A (en) * 1979-01-25 1980-07-29 The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration High toughness-high strength iron alloy

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB352964A (en) * 1929-02-16 1931-07-07 Wilhelm Kroll Process for improving iron-titanium alloys
US2048163A (en) * 1929-04-15 1936-07-21 Int Nickel Co Iron-nickel-titanium alloy
CH194508A (de) * 1936-03-23 1937-12-15 Krupp Ag Verfahren zur Herstellung von Maschinenteilen, die mit geringer Ampèrewindungszahl hohe Induktionswerte ergeben.
US2105652A (en) * 1933-05-01 1938-01-18 Honda Kotaro Steel for permanent magnets
US2266481A (en) * 1939-10-27 1941-12-16 Int Nickel Co Age hardenable, low expansion, nickel-iron-titanium alloy

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB352964A (en) * 1929-02-16 1931-07-07 Wilhelm Kroll Process for improving iron-titanium alloys
US2048163A (en) * 1929-04-15 1936-07-21 Int Nickel Co Iron-nickel-titanium alloy
US2105652A (en) * 1933-05-01 1938-01-18 Honda Kotaro Steel for permanent magnets
CH194508A (de) * 1936-03-23 1937-12-15 Krupp Ag Verfahren zur Herstellung von Maschinenteilen, die mit geringer Ampèrewindungszahl hohe Induktionswerte ergeben.
US2266481A (en) * 1939-10-27 1941-12-16 Int Nickel Co Age hardenable, low expansion, nickel-iron-titanium alloy

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
Fiz. Metal Metalloved, 24, No. 6, pgs. 126 128. *
Henon et al., Memoires Scentifigues Rev. Metallurg. LXIII No. 2, 1966, pgs. 99 108. *
Journal of the Iron and Steel Institute, July 1968, pg. 748. *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4202751A (en) * 1977-11-28 1980-05-13 Kobe Steel, Ltd. Sacrificial anode and apparatus employing same for treating hot sea water
US4214902A (en) * 1979-01-25 1980-07-29 The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration High toughness-high strength iron alloy

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JPS4948515A (enExample) 1974-05-10
SE387663B (sv) 1976-09-13
GB1383623A (en) 1974-02-12
DE2322102A1 (de) 1973-11-22
FR2183184A1 (enExample) 1973-12-14

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