US3755004A - Method for producing ultra fine-grained microstructure in ferrous alloys - Google Patents

Method for producing ultra fine-grained microstructure in ferrous alloys Download PDF

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Publication number
US3755004A
US3755004A US00182331A US3755004DA US3755004A US 3755004 A US3755004 A US 3755004A US 00182331 A US00182331 A US 00182331A US 3755004D A US3755004D A US 3755004DA US 3755004 A US3755004 A US 3755004A
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austenite
percent
martensite
temperature
tempering
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R Miller
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United States Steel Corp
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Steel Corp
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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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment

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  • ABSTRACT Ferrous alloys containing up to about 25 percent Ni, 15 percent Mn, 1.2 percent C, 0.5 percent N are cooled to form a martensitic or bainitic structure.
  • the material is then worked to an extent sufficient to remove the principal nucleating effect of the prior austenite boundaries and other microstructural interfaces, so that when subsequently heated into the multiphase region, recrystallization occurs by random nucleation of extremely fine austenite crystals thoughout the material.
  • Excep tionally fine equiaxed grains in the micron and submicron range are achieved, thereby providing unique combinations of both increased strength along with increased ductility and increased notch toughness.
  • This invention pertains to a method of imparting an ultrafine-grained microstructure to steel alloys containing martensitic or bainitic constituents and to those which are capable of conversion to martensite or bainite.
  • the alloys processed by the method of this invention manifest a unique combination of high ductility and notch toughness together with high strength.
  • ferrous compositions capable of conversion to structures such as martensitic platelets, or bainitic
  • ferrite-carbide aggregates are (l) austenitized and (2) cooled to produce such martensitic or bainitic structures, and (3) then worked to a sufficient degree (as hereinafter described) followed by (4) heating in the multiphase region, wherein one of the phases is austenite; microstructures are achievable with grain sizes in the micron and submicron range, i.e., smaller than ASTM No. 16.
  • thermomechanical method for achieving an ultra fine-grained microstructure in a wide variety of ferrous alloys.
  • FIG. 1 is a plot of the room temperature hardness and the austenite content of an Fe5.7 percent Mn-0.l percent C alloy after 1 hour at temperature;
  • FIG. 2, a through f are electron transmission micrographs showing the effect of severe working prior to or during annealing in the critical multiphase range
  • FIG. 3 depicts the effects of severe cold working on mechanical properties after annealing at 600 C
  • FIG. 4 depicts the effects of severe cold working on mechanical properties after annealing at 640 C
  • FIGS. 5a and 5b show the effects of severe cold work on toughness (one-half width CVN specimens);
  • FIG. 6 depicts the effects of severe working at temperatures within the critical multiphase region, on mechanical properties
  • FIGS. 7a, 7b, 7c and 7d are micrographs showing the long time stability of Fepercent Ni alloys, cold worked and tempered at 500 C;
  • FIG. 8 is a plot of the proportion of equiaxed, finegrained structure in the cross section of initially 1% inch thick plate, cold rolled to varying degrees and annealed. Micrographs at 21 ,OOOX show the structure at the center of the cross section.
  • the method of this invention is applicable to any steel capable of conversion to martensite or bainite, when cooled from an austenitizing temperature. If such an alloy were then tempered in the multiphase region (i.e., at a temperature above that at which austenite formation begins), austenite would nucleate principally in boundary regions, such as prior austenite grain boundaries, martensitic plate interfaces (or bainitic, aggregate interfaces) and perhaps low angle subgrain boundaries. Thus, even after long periods of annealing within this region, the microstructure would retain an appearance similar to that of the original structure. However, if these materials are deformed, to a critical extent, the relative nucleating effect of such boundary regions may be greatly diminished and nucleation would occur randomly.
  • the inventive method is applicable to those compositions which contain a sufficient amount of the austenitizing elements, e.g. Ni, Mn, N and C, so that the austenite which forms during the aforesaid tempering treatment is retained on cooling to room temperature.
  • these austenitizing elements are insufficient to impart such stability, and part or all of this austenite isconverted, on cooling, to well-known transformation products such as pearlite, bainite or martensite.
  • the material is further tempered at a lower temperature to provide increased ductility.
  • the tempering range must be defined in terms of nonequilibrium designations.
  • A is that temperature at which the start of austenite nucleation may be detected by holding at temperature for one hour.
  • A is that temperature at which the finish of the transformation to austenite is detected, for a one-hour hold at temperature.
  • Analogous, A -A regions have been previously determined by various investigators employing metallographic and hardness measurements.
  • the tempering treatment of this invention may preferably be performed in the lower portion of A,-A, range, e.g. within the range A, 150 C.
  • Such lower temperature tempering will provide the advantage of even smaller grains, (and therefore even greater improvement in mechanical properties) when compared with that of tempering near the upper portion of A,,-A, range.
  • FIGS. 2 through 6 The enhanced effect of severe working (well above the critical minimum) prior to or during tempering in the critical range may be seen by reference to FIGS. 2 through 6.
  • the treatments represented therein were performed on a Fe-5.7 percent Mn-0.l percent C steel.
  • FIGS. 2a and 2b show typical micrographs of the annealed martensitic structure, without any prior working.
  • FIG. 2a shows relatively large austenite crystals in a prior austenite grain boundary, and thin, elongated austenite crystals in the boundaries between martensitic plates (the dark streaks in 2b). Even after relatively long annealing, the structure retains an appearance resembling the original martensite.
  • FIGS. 2e and 2f Specimens were warm worked by rolling out ofa molten lead bath to 75 percent reduction in thickness. Multiple passes were employed in which the specimens were returned to the lead bath between each pass. It may be seen that the microstructure resembles that of FIGS. 2c and 2d, except that it is not fully annealed. The grain size is even smaller than that of the cold worked and annealed structure (2d).
  • FIGS. 3 through 6 show the influence of the foregoing microstructures on mechanical properties.
  • FIGS. 3 and 4 show the amount of austenite formed and the effect of percent prior cold reduction on 1 tensile properties after tempering at 600 and 640 C, respectively. It may be noted that although the austenite contents are quite similar, the material which has been severely worked prior to annealing shows an improvement in nearly all properties. Note especially, that yield strength increases of about 30 percent were achieved, with no sacrifice (improvement in most cases) in ductility, as measured by reduction in area and elongation.
  • the ultra fine-grained microstructure is particularly noteworthy in its effect on toughness, as shown in FIGS. 5a and 5b. A significant improvement in notch toughness (as measured by ft.-lbs. of energy absorbed) is achieved, particularly at low test temperatures.
  • results from specimens cold worked 60 percent and tempered at four temperatures are compared with results from specimens warm worked percent in the critical tempering range. Since, in both cases, the extent of deformation was above the critical amount (i.e., that amount which substantially negates the nucleating effect of boundaries) it may be seen that where the tempering temperatures are the same, quite similar properties are obtained. This similarity results from the fact that, as previously noted in FIG. 2, the microstructures are also quite similar.
  • PROPERTIES OF FE-NI ALLOYS Austen- Grain Upper Lower ltv Ferrite size yield yield yield yield Treatment, volume, volume, (1, stress, stress,
  • the critical minimum amount of working required to produce the desired random nucleation will depend on a variety of factors.
  • the degree of deformation required will depend upon the initial structure, eg martensite or bainite.
  • Thicker specimens will, in general require a greater amount of deformation to provide an equiaxed microstructure, which is essentially uniform across the entire cross-section (as compared with a structure in which only the surface region has received the required amount of deformation).
  • the type of deformation employed (rolling, swaging, drawing, etc.) will itself play a role, due to the differing effects of these modes of deformation on the internal energy of the metal. Even for a specific type of deformation, e.g. by rolling, the amount of deformation will depend, to some extent, on the roll diameter, the surface conditions of the rolls, the type of lubrication and the amount of reduction per pass.
  • the extent of working (whether at room temperature or above) must be such that the multi-phase region tempering will result in a substantially equiaxed structure.
  • This critical amount may be determined, for a particular set of conditions, by a rather simple test, such as that outlined below.
  • the instant method may be effectually applied to all compositions, which on cooling can be transformed to martensite or bainite.
  • a composition containing a level of nickel far in excess of about 25 percent the austenite will be too stable for such a necessary conversion.
  • a level of manganese far in excess of about percent (or a lesser combination of manganese, nickel and/or nitrogen) will provide a composition which is too stable to provide the desired starting structure of martensite or bainite.
  • austenite stability other compositional constraints may be noted.
  • an alloy containing greater than about 1.2 percent carbon or about 0.5 percent nitrogen will be too hard to be worked sufficiently, such that the recrystallization during tempering in the multiphase region will result in the desired equiaxed morphology.
  • the quantity of austenitizing elements (Mn, Ni and C) was sufficient, so that the ultrafine austenite which formed on tempering in the critical range, was stable even after cooling to well below room temperatures.
  • lf leaner compositions are employed (e.g., Fe-2 percent Mn-l.0 percent Ni-O.2 percent C) in which the austenite will be comparatively less stable, the austenite can then transform (depending on cooling rates employed) to the well-known transformation products.
  • lf leaner compositions e.g., Fe-2 percent Mn-l.0 percent Ni-O.2 percent C
  • the austenite can then transform (depending on cooling rates employed) to the well-known transformation products.
  • a method for treating ferrous structures selected from the group consisting of martensite or bainite so as to achieve an essentially uniform, ultrafine grain size which comprises;
  • a method for producing an essentially uniform, ultrafine grain size in ferrous alloys capable of conversion to martensite or bainite which comprises;
  • said alloy is selected from the range, consisting essentially of the austenitizing elements of up to about 25 percent nickel, up to about 15 percent manganese, up to about 1.2 percent carbon, up to about 0.5 percent nitrogen and mixtures thereof with the balance iron and incidental steelmaking impurities.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Mechanical Engineering (AREA)
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  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Heat Treatment Of Steel (AREA)
US00182331A 1971-09-21 1971-09-21 Method for producing ultra fine-grained microstructure in ferrous alloys Expired - Lifetime US3755004A (en)

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JP (1) JPS5644130B2 (enrdf_load_stackoverflow)
BE (1) BE788922A (enrdf_load_stackoverflow)
DE (1) DE2245520A1 (enrdf_load_stackoverflow)
FR (1) FR2161900B1 (enrdf_load_stackoverflow)
GB (1) GB1412637A (enrdf_load_stackoverflow)
IT (1) IT975020B (enrdf_load_stackoverflow)
NL (1) NL7212730A (enrdf_load_stackoverflow)

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4046598A (en) * 1975-01-22 1977-09-06 Uddehoms Aktiebolag Procedure for manufacture of steel band or strip
US4186037A (en) * 1975-09-12 1980-01-29 Italsider S.P.A. Thermal treatment of intermediate quenching and quick tempering through eddy currents and a device for applying said treatment to high productivity rolling plants for flat products
US4437900A (en) 1981-12-28 1984-03-20 Exxon Research And Engineering Co. Thermal mechanical treatment for enhancing high temperature properties of cast austenitic steel structures
US5200005A (en) * 1991-02-08 1993-04-06 Mcgill University Interstitial free steels and method thereof
WO1995001459A1 (en) * 1993-06-29 1995-01-12 The Broken Hill Proprietary Company Limited Strain-induced transformation to ultrafine microstructure in steel
EP0903412A3 (en) * 1997-09-22 2001-01-24 National Research Institute For Metals Ultra-fine texture steel and method for producing it
US20030070737A1 (en) * 2001-10-12 2003-04-17 Jackson Tom R. High-hardness, highly ductile ferrous articles
US6572716B2 (en) * 1997-09-22 2003-06-03 National Research Institute For Metals Fine ferrite-based structure steel production method
US20040060620A1 (en) * 2000-10-05 2004-04-01 Johns Hopkins University High performance nanostructured materials and methods of making the same
US20070130714A1 (en) * 2000-01-24 2007-06-14 Makolle Williams Paint roller
US20100065164A1 (en) * 2008-09-18 2010-03-18 Searete Llc, A Limited Liability Corporation Of The State Of Delaware System and method for annealing nuclear fission reactor materials
US20100065992A1 (en) * 2008-09-18 2010-03-18 Searete Llc, A Limited Liability Corporation Of The State Of Delaware System and method for annealing nuclear fission reactor materials
US20100065165A1 (en) * 2008-09-18 2010-03-18 Searete Llc, A Limited Liability Corporation Of The State Of Delaware System and method for annealing nuclear fission reactor materials

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4047979A (en) * 1976-10-08 1977-09-13 United States Steel Corporation Heat treatment for improving the toughness of high manganese steels
JPS61181014U (enrdf_load_stackoverflow) * 1985-04-30 1986-11-12
JP2611922B2 (ja) * 1993-06-21 1997-05-21 株式会社万陽 パーツフイーダー

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3196053A (en) * 1962-08-13 1965-07-20 United States Steel Corp Production of heat-treated sheets
US3235413A (en) * 1961-11-20 1966-02-15 United States Steel Corp Method of producing steel products with improved properties
US3502514A (en) * 1968-01-30 1970-03-24 United States Steel Corp Method of processing steel

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3235413A (en) * 1961-11-20 1966-02-15 United States Steel Corp Method of producing steel products with improved properties
US3196053A (en) * 1962-08-13 1965-07-20 United States Steel Corp Production of heat-treated sheets
US3502514A (en) * 1968-01-30 1970-03-24 United States Steel Corp Method of processing steel

Cited By (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4046598A (en) * 1975-01-22 1977-09-06 Uddehoms Aktiebolag Procedure for manufacture of steel band or strip
US4186037A (en) * 1975-09-12 1980-01-29 Italsider S.P.A. Thermal treatment of intermediate quenching and quick tempering through eddy currents and a device for applying said treatment to high productivity rolling plants for flat products
US4437900A (en) 1981-12-28 1984-03-20 Exxon Research And Engineering Co. Thermal mechanical treatment for enhancing high temperature properties of cast austenitic steel structures
US5200005A (en) * 1991-02-08 1993-04-06 Mcgill University Interstitial free steels and method thereof
WO1995001459A1 (en) * 1993-06-29 1995-01-12 The Broken Hill Proprietary Company Limited Strain-induced transformation to ultrafine microstructure in steel
EP0903412A3 (en) * 1997-09-22 2001-01-24 National Research Institute For Metals Ultra-fine texture steel and method for producing it
US6572716B2 (en) * 1997-09-22 2003-06-03 National Research Institute For Metals Fine ferrite-based structure steel production method
US20070130714A1 (en) * 2000-01-24 2007-06-14 Makolle Williams Paint roller
US8060975B2 (en) * 2000-01-24 2011-11-22 Makolle Williams Paint roller
US20040060620A1 (en) * 2000-10-05 2004-04-01 Johns Hopkins University High performance nanostructured materials and methods of making the same
US20030070737A1 (en) * 2001-10-12 2003-04-17 Jackson Tom R. High-hardness, highly ductile ferrous articles
US20100065164A1 (en) * 2008-09-18 2010-03-18 Searete Llc, A Limited Liability Corporation Of The State Of Delaware System and method for annealing nuclear fission reactor materials
US20100065992A1 (en) * 2008-09-18 2010-03-18 Searete Llc, A Limited Liability Corporation Of The State Of Delaware System and method for annealing nuclear fission reactor materials
US20100065165A1 (en) * 2008-09-18 2010-03-18 Searete Llc, A Limited Liability Corporation Of The State Of Delaware System and method for annealing nuclear fission reactor materials
US8529713B2 (en) 2008-09-18 2013-09-10 The Invention Science Fund I, Llc System and method for annealing nuclear fission reactor materials
US8721810B2 (en) 2008-09-18 2014-05-13 The Invention Science Fund I, Llc System and method for annealing nuclear fission reactor materials
US8784726B2 (en) 2008-09-18 2014-07-22 Terrapower, Llc System and method for annealing nuclear fission reactor materials
US9011613B2 (en) 2008-09-18 2015-04-21 Terrapower, Llc System and method for annealing nuclear fission reactor materials
US9677147B2 (en) 2008-09-18 2017-06-13 Terrapower, Llc System and method for annealing nuclear fission reactor materials

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FR2161900B1 (enrdf_load_stackoverflow) 1977-08-26
JPS5644130B2 (enrdf_load_stackoverflow) 1981-10-17
NL7212730A (enrdf_load_stackoverflow) 1973-03-23
BE788922A (fr) 1973-03-15
JPS4838826A (enrdf_load_stackoverflow) 1973-06-07
DE2245520A1 (de) 1973-03-29
FR2161900A1 (enrdf_load_stackoverflow) 1973-07-13
GB1412637A (en) 1975-11-05
IT975020B (it) 1974-07-20

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