WO2016031958A1 - Metal material and processing/treatment method - Google Patents

Metal material and processing/treatment method Download PDF

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Publication number
WO2016031958A1
WO2016031958A1 PCT/JP2015/074400 JP2015074400W WO2016031958A1 WO 2016031958 A1 WO2016031958 A1 WO 2016031958A1 JP 2015074400 W JP2015074400 W JP 2015074400W WO 2016031958 A1 WO2016031958 A1 WO 2016031958A1
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Prior art keywords
metal material
processing
deformation
stainless steel
austenitic
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PCT/JP2015/074400
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French (fr)
Japanese (ja)
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博己 三浦
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国立大学法人豊橋技術科学大学
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Priority to JP2016545634A priority Critical patent/JP6747639B2/en
Publication of WO2016031958A1 publication Critical patent/WO2016031958A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
    • B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21B—ROLLING OF METAL
    • B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
    • B21B3/02—Rolling special iron alloys, e.g. stainless steel
    • 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
    • C21D1/30—Stress-relieving
    • 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
    • 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
    • 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
    • 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
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese

Definitions

  • the present invention relates to a metal material and a processing method, and particularly to a metal material having high strength and high ductility and a processing method for obtaining the metal material.
  • the strength of general steel materials is limited to about 1 GPa at most in terms of tensile strength.
  • the technique of cold rolling for increasing the strength is well known, but generally the upper limit is 70 to 80%.
  • ARB method As a giant strain processing method, there is a repeated lap joint rolling method (Accumulative Roll-Bonding: ARB method).
  • This ARB method uses rolling as a giant strain processing process for obtaining an ultrafine crystal grain material having an average grain size of 1 ⁇ m or less, and the once rolled material is divided into two equal parts in the longitudinal direction and overlapped. Rolling-bonding is also applied.
  • this ARB method is applied to IF steel, it has been reported that the average crystal grain size is 200 nm and the tensile strength is 820 MPa (see Non-Patent Document 1).
  • the ARB method is provided for SUS304 stainless steel, it has been reported that the average crystal grain size is about 200 nm and a hardness three times that of the annealed material can be obtained (see Non-Patent Document 2). .
  • MDF method multi-direction forging
  • SUS316 stainless steel has achieved a finer crystal grain structure and higher strength (tensile strength of about 2.2 GPa).
  • This MDF method is a giant strain processing method in which forging from multiple directions is repeated.
  • Non-Patent Documents 2 and 3 Although the results reported in the above-mentioned Non-Patent Documents 2 and 3 are preferable, the manufacturing process is complicated in any of the huge strain processing methods, and cannot be said to be suitable for practical use. .
  • the demand for higher strength of machine structural materials is increasing, but even in the case of steel, which is in high demand as a mechanical material, its strength is limited. It was.
  • the true strain of giant strain processing is 2 or more, but the true strain obtained by strong rolling is from around 2 to at most about 4. Therefore, here, the term “strong strain processing” is referred to as “giant strain processing”. We decided to use them separately.
  • the present invention has been made in view of the above-described points, and an object of the present invention is to provide a high-strength and ductile metal material by a simple strong rolling method and heat treatment regardless of a complicated process. At the same time, the processing method is provided.
  • the present invention relating to a metal material is a metal material formed by processing a stable austenitic steel or a ferrite / austenite duplex stainless steel, and a fine grain structure generated by a high strain processing by simple strong rolling has a lamellar structure. It is characterized in that a group-like structure based on deformation twins is formed in a dispersed manner, and a plurality of shear bands are formed in the lamellar structure.
  • deformation-induced microstructures such as lamellar structure, deformation twins, and shear bands develop with high density and complexity by simple strong rolling of stable austenitic steel or ferritic / austenitic duplex stainless steel.
  • An ultrafine grained structure can be obtained.
  • a high-strength metal material can be obtained.
  • the formation of the shear band has been considered as a useless structure in the rolling process because the surface of the metal material does not become smooth.
  • the formation of the shear band provides suitable ductility.
  • a metal material can be provided.
  • the lamellar structure preferably further has a deformation twin formed therein.
  • individual lamellar structures are formed by fine deformation twins, and an ultrafine structure in which deformation-induced microscopic structures are developed more densely and complicatedly is obtained. be able to.
  • the strength of the entire metal material can be improved.
  • the lamellar structure is preferably formed in a layered shape, and the average interval is preferably 100 nm or less. According to such a configuration in which the average interval of the lamellar tissue is narrow, the deformation-induced microscopic tissue is further densified, and the overall strength is improved.
  • the present invention relating to a metal material is a metal material obtained by processing a stable austenitic steel, and a fine grain structure generated by a strong strain process by simple strong rolling is based on a lamellar structure, and is a deformation twin. It is characterized in that a group-like structure is formed in a dispersed manner, and a plurality of shear bands are surrounded around these dispersed deformation twin-like group-like structures. .
  • the above configuration is obtained by processing a stable austenitic steel, but by subjecting the stable austenitic steel to simple strong rolling, it is possible to form a group structure of deformation twins moderately dispersed in the austenitic phase. it can.
  • the austenite phase becomes a fine structure as a lamellar structure, and by forming the shear band so as to surround the group structure by the deformation twin, the strength by the group structure of the deformation twin and the ductility by the shear band are obtained. Will be able to.
  • the present invention relating to a metal material is a metal material obtained by processing a ferrite / austenite duplex stainless steel, and the fine grain structure produced by the high strain processing by simple strong rolling is a folite phase and an austenite phase.
  • the austenite phase is formed by dispersing a group structure of deformed twins and surrounds the periphery of the dispersed deformed twin group structures As described above, a plurality of shear bands are formed in both the ferrite phase and the austenite phase.
  • the above configuration is obtained by processing a ferritic / austenitic duplex stainless steel, but by subjecting this duplex stainless steel to simple strong rolling, deformation twins can be formed exclusively in the austenitic phase. Then, the ferrite phase and the austenite phase form a layered composite material, and both form a lamellar structure. Further, by forming a shear band across the composite material, a layered and complex structure is formed by these fine grain structures, and a metal material having high strength and ductility can be provided.
  • the area ratio observed in the TEM image is 0% to 40% when the group-like structure is within the area of an arbitrary area of 35 ⁇ m 2 in the surface structure. That is, it is desirable that the group-like structure formation ratio due to deformation twins is small. Since the formation of the group-like structure forms a shear band so as to surround the periphery thereof, the higher the ratio of formation of the group-like structure, the higher the formation ratio of the shear band, which has high ductility. However, it is desirable to suppress the formation of a group-like structure in order to obtain higher strength than improved ductility. In addition, since an arbitrary 35 ⁇ m 2 area portion is determined by TEM image observation, it is not assumed that there is no group-like structure. However, even if there is no group-like structure, the strength is slightly low but sufficient. The strength can increase.
  • the internal strain generated by the high strain processing is reduced by an aging treatment that also serves as annealing.
  • the aging treatment can be performed by annealing, and the internal strain can be reduced by annealing. As the internal strain is reduced, both the tensile strength and the ductility can be improved.
  • the fine grain structure may include a martensite phase.
  • the martensite phase is generally considered to increase the strength of the steel, in the present invention, it is preferable to keep the volume ratio of the martensite phase low.
  • Stable austenitic steel or ferritic / austenitic duplex stainless steel is less susceptible to martensite phase and can have a relatively low volume ratio.
  • the present invention relating to a processing method is a method for processing a stable austenitic steel or a ferrite / austenitic duplex stainless steel, and is cold-rolled at 80% or more of the stable austenitic steel or ferrite / austenitic duplex stainless steel. Including a simple strong rolling process.
  • the present invention related to the thermomechanical processing method is a method of treating a stable austenitic steel or a ferrite / austenite duplex stainless steel by a thermomechanical process in which an aging treatment is performed after simple strong rolling, wherein the stable austenitic steel or ferrite / Simple strong rolling process in which 80% or more cold rolling is applied to austenitic duplex stainless steel, and aging treatment that also serves as an annealing condition under the condition that recrystallization does not occur in the structure generated by the simple strong rolling process And a heat treatment step of applying.
  • a process means the process which does not give an aging process (annealing) and a process heat treatment means the process containing an aging process (annealing), when both are named generically, it describes as a process.
  • the heat treatment step is performed after the simple strong rolling step, the internal strain generated by the high strain processing can be reduced.
  • the aging treatment is performed by annealing in a condition where recrystallization does not occur with respect to the fine grain structure, the strength of the fine grain structure is maintained without substantially expanding the refined structure. Can do.
  • the fine grain structure exists in a fine grain state, the tensile strength and ductility can be improved as the internal strain is reduced.
  • the heat treatment step is preferably annealed at an absolute temperature of 873 K or lower, and more preferably annealed at an absolute temperature of 773 K or lower.
  • the heat treatment step in the case of duplex stainless steel, it is preferable to perform an annealing treatment of 864 ⁇ 10 2 seconds or more, and in the case of stable austenitic steel, it is preferable to perform an annealing treatment of 72 ⁇ 10 2 seconds or more.
  • the processing by the processing method is composed mainly of a lamellar structure, a deformation twin group structure, a shear band, and a martensite phase (that is, a deformation-induced microscopic structure as a main component).
  • a hetero-nano-structured metal material can be obtained.
  • a fine grain structure is formed by the effect of strong strain processing by simple strong rolling, but the fine grain structure in this case has not been performed so far. It is produced by cold rolling of 80% or more. And by such simple strong rolling, a group-like structure in which deformation twins are aggregated is formed on the basis of a lamellar structure, and a shear band can be formed. Is.
  • Such a structure state is an ultrafine grain structure in which the deformation-induced microscopic structure is developed in a high density and in a complicated manner, and high strength can be achieved.
  • a deformation twin can be formed exclusively in the austenite phase, and a shear band can be formed across the ferrite phase and the austenite phase.
  • Stable austenitic steel or ferritic / austenitic duplex stainless steel treated by the above processing method has a tensile strength of about 3 GPa, and is capable of plastic working of more than a dozen percent in total elongation and 5% or more in plastic elongation. Ductility can be obtained.
  • the metal material processed in this way can be used as a mechanical material that requires high strength, and can be used in various fields as a material that can be easily processed while having high strength due to suitable ductility.
  • FIG. 1 is a schematic diagram which shows the state of the structure
  • (B) is a schematic diagram which shows the state of the structure
  • FIG. It is a TEM image in tissue analysis 2. It is a TEM image in tissue analysis 3.
  • TEM image in tissue analysis 4 It is a TEM image as a reference material in the tissue analysis 4.
  • 10 is a TEM image in tissue analysis 5.
  • 10 is a TEM image in tissue analysis 6. It is a graph which shows the result of having measured Vickers hardness in example 3 of an experiment.
  • 12 is a TEM image after aging treatment at 1023K according to Experimental Example 3.
  • 10 is a graph of a stress-strain curve showing the result of a tensile test in Experimental Example 4.
  • Fig.1 (a) is a schematic diagram which shows the state of the structure
  • a stable austenitic steel is roll-rolled in several times and subjected to high strain processing by 80% or more simple strong rolling, a group in which deformation twins partially gather A group-like structure is dispersed based on a low-angle lamellar structure formed in an austenite phase. Further, a plurality of shear bands are generated so as to surround the periphery of the dispersed group-like tissue.
  • the true strain of the giant strain processing is generally 2 or more, but the true strain obtained by the strong rolling is from about 2 to about 4 at the most. Is distinguished from giant strain machining.
  • the lamellar structure develops in a substantially uniform state, and the average interval between the layers forming the lamellar structure is about 30 nm to about 100 nm.
  • the group structure by deformation twins is smaller than 1 ⁇ m, and the initial orientation is shifted by about 60 ° with respect to the parent phase. This gradually changes from the initial orientation every several rolls.
  • the initial orientation of the shear band is gradually changed from the initial orientation for each roll rolling from a state where the initial orientation is shifted by about 15 ° at the maximum. Due to this misorientation, a strong texture is difficult to develop in these tissues.
  • Each of these constituent structures is a deformation-induced microscopic structure, and an ultrafine grain structure is formed by developing these in a high density and complicated manner. By generating an ultrafine grain structure having such a structure, the development of an extremely strong rolling texture is effectively suppressed, and ductility is obtained while having high strength.
  • FIG. 1 (b) is a schematic diagram showing the state of the structure when the high strain processing by simple strong rolling of 80% or more is applied to the ferrite / austenitic duplex stainless steel.
  • a lamellar structure is formed in each of a ferrite phase and an austenite phase, and the average interval between layers forming the lamellar shape is about 30 nm to about 300 nm as a whole.
  • the proportion of the austenite phase is large, the interval between the layers tends to be small, and when the proportion of the ferrite phase is large, the interval between the layers tends to be large.
  • the state of the structure common to stable austenitic steel and ferritic / austenitic duplex stainless steel is based on a low-angle lamellar structure, and a group structure of dispersed deformed twins is formed.
  • the shear band is formed so as to surround the periphery of the tissue.
  • the fine grain structure grows in a complicated manner by subjecting it to high strain processing by cold rolling to the extent that a shear band is formed (that is, until the cross-sectional area reduction rate reaches 80% or more).
  • a metal material having high strength and ductility is obtained.
  • the internal strain is reduced while maintaining the state of each constituent structure.
  • the heat treatment condition at this time is such that the above structure hardly develops recrystallization. That is, a fine grain structure that has grown in a complicated manner by high strain processing is prevented from being enlarged by recrystallization.
  • the metal material with reduced internal strain is further improved in strength and ductility, and becomes a metal material having higher strength and suitable ductility.
  • the simple strong rolling process and the heat treatment process performed in the thermomechanical processing method will be described.
  • the base material is rolled by 80% or more by general cold rolling.
  • the strong rolling of 80% or more is a type of so-called high strain processing, in which plastic working is performed until the cross-sectional area reduction rate becomes 80% or more.
  • a heat treatment process is based on the aging treatment which served as annealing.
  • This process is an aging treatment (annealing) under conditions that do not cause recrystallization of the structure generated by the simple strong rolling process. Therefore, in addition to heating to a temperature at which recrystallization does not occur, there may be a case of heating for a short time at which a recrystallization does not occur at a temperature higher than the temperature. For example, it may be heated to a temperature lower than the temperature at which recrystallization does not occur and annealed by air cooling. Specifically, an annealing process of 864 ⁇ 10 2 seconds or more is performed at an absolute temperature of 773 K or less.
  • annealing when processing at a higher temperature for a short period of time, it may be a process in which annealing is performed for a short time while maintaining the temperature or higher.
  • annealing By such an aging treatment (annealing), the tensile strength reaches a maximum of 2.7 GPa, and the strength can be increased as compared with the end of the simple strong rolling process.
  • ductility will fall, about 5% ductility can still be maintained.
  • the Vickers hardness was measured for these. The result is shown in FIG. As is apparent from this figure, the hardness increased as a whole, although it varied depending on the annealing time. In particular, in SUS316 and DIN1.4462, a result exceeding the hardness of general hardened steel could be obtained.
  • the observed microstructure was a general strong rolling structure extending in the rolling direction, but it was found that the degree of development of the texture was extremely low. That is, immediately after rolling, a peak value of 7.3 due to the development of texture appeared on the (001) plane, and a peak value of 5.0 appeared on the (111) plane after the heat treatment. Unlike the (101) plane or (112) plane texture, both of which tend to develop after strong rolling, the orientation is less likely to cause a decrease in ductility, and the degree of integration is relatively low. Therefore, when considered together with the results of the tensile test, it is understood that the material has good plastic workability while having high strength.
  • FIG. 6 shows a TEM image of the test material after simple strong rolling of SUS316 stainless steel.
  • the structure is an ultrafine grain structure in which lamellar structures, deformation twins, and shear bands are intricately complicated.
  • the lamellar structure developed almost uniformly, and as determined from FIG. 6, the average interval between the layers was about 30 nm.
  • the deformation twin has an initial orientation shifted by about 60 ° with respect to the parent phase, and this changes gradually with each rolling. Further, the initial orientation of the shear band was shifted by about 15 ° at the maximum. This also changes gradually with each rolling operation. Furthermore, although it was not found in the TEM image, there is a possibility that martensite is included.
  • FIG. 3 a TEM image of DIN 1.4462 after simple strong rolling is shown in FIG. Also in this TEM image, it can be seen that the structure is an ultrafine grain structure in which a lamellar structure, a deformation twin, and a shear band are complicatedly arranged.
  • the lamellar structure is formed in both the ferrite phase and the austenite phase, and it can be seen that a composite material is formed by both phases.
  • a relatively large photograph at the center is a group-like structure formed by deformation twins, and a shear band is formed around the structure.
  • martensite was not confirmed in this TEM image, there is a possibility that martensite is included. Although it is not clear from FIG.
  • the lamellar interval is further widened by the longer aging treatment.
  • some of the aging treatments for a longer time began to recrystallize and the lamellar structure disappeared.
  • the strength also decreased.
  • the deformation twins generated in the initial stage of rolling form a group-like structure, and the remaining part develops into a lamellar structure, but it is thought that the deformation twins are introduced inside the process.
  • interval changes with the growth and recovery
  • interval after an aging treatment will be about 42 nm as above-mentioned, and 100 nm or less It is in a state that fits in.
  • Example 4 In addition, the same tensile test as in Experimental Example 2 was performed on DIN1.4462 that was aged in Experimental Example 3. The tensile test was performed only on DIN 1.4462 after the aging treatment at an absolute temperature of 1023K, and was treated with a plurality of aging times. The result is shown in FIG. In the case of aging at an absolute temperature of 1023 K, the value of Vickers hardness was large at an appropriate annealing time. However, as shown in FIG. This is considered to be caused by precipitation of the sigma phase. In addition, since precipitation of sigma phase is promoted by Cr or Mo, it is considered that it was remarkable in the duplex stainless steel containing a large amount of these.

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Abstract

[Problem] To provide a metal material exhibiting high strength and ductility, using a simple strong rolling method and heat treatment, without using a complex process, and to provide a treatment method therefor. [Solution] This metal material is formed such that, in the fine grain structure formed as a result of strong strain processing performed by simple strong rolling, a low-angle lamellar structure serves as a base, group structures formed by aggregated deformation twins are dispersed, and the peripheries of these dispersed deformation-twin group structures are surrounded by a plurality of shear bands. In other words, this metal material comprises a hetero-nanostructure having, as a main constituent component, a deformation-induced microstructure. This processing/heat treatment method includes: a simple strong rolling step in which stable austenitic steel or ferritic/austenitic two-phase stainless steel is subjected to cold rolling at 80% or more; and a heat treatment step in which the structure formed as a result of the simple strong rolling step is subjected to combined annealing/ageing treatment under conditions which do not induce recrystallization.

Description

金属材料および加工処理方法Metal material and processing method
　本発明は、金属材料および加工処理方法に関し、特に高強度かつ高延性を有する金属材料と、当該金属材料を得るための加工処理方法に関するものである。 The present invention relates to a metal material and a processing method, and particularly to a metal material having high strength and high ductility and a processing method for obtaining the metal material.
　鉄鋼材料の高強度化のために様々な技術が研究・開発されているところ、一般的な鉄鋼材料の強度は、引張強度でせいぜい１ＧＰａ程度が限度であった。高強度化のために冷間圧延を施す技術は周知であるが、一般的には、７０～８０％を上限としていた。 As various techniques have been researched and developed to increase the strength of steel materials, the strength of general steel materials is limited to about 1 GPa at most in terms of tensile strength. The technique of cold rolling for increasing the strength is well known, but generally the upper limit is 70 to 80%.
　さらに、マルエージング鋼等の特殊な鋼も開発されおり、その強度は２ＧＰａに達するものがある。しかしながら、析出硬化型ステンレス鋼と同様の極めて特殊な合金組成と、時効析出硬化処理という特殊な加工熱処理プロセスとを必要とするため、一般的な機械材料として利用されていないのが現状である。 Furthermore, special steels such as maraging steels have also been developed, and some have strengths reaching 2 GPa. However, since it requires a very special alloy composition similar to that of precipitation hardening stainless steel and a special work heat treatment process called aging precipitation hardening, it is not currently used as a general mechanical material.
　そこで、近年では、一般的な鋼の強度上昇のための研究が行われており、巨大ひずみ加工法を利用した結晶粒超微細化と高強度化との関係が報告されている。巨大ひずみ加工法としては、繰り返し重ね接合圧延法（Accumulative Roll-Bonding：ＡＲＢ法）がある。このＡＲＢ法は、平均粒径を１μｍ以下の超微細結晶粒材料を得るための巨大ひずみ加工プロセスとして圧延を利用するものであり、一度圧延した材料を長手方向に二等分し、重ね合わせて接合を兼ねた圧延（Roll-Bonding）を施すものである。このＡＲＢ法をＩＦ鋼に適用した場合、平均結晶粒径が２００ｎｍで、引張強度が８２０ＭＰａの結果を得たことが報告されている（非特許文献１参照）。また、ＡＲＢ法をＳＵＳ３０４ステンレス鋼に提供した場合には、平均結晶粒径が約２００ｎｍであり、焼鈍材の３倍の硬さを得ることができることが報告されている（非特許文献２参照）。 Therefore, in recent years, research for increasing the strength of general steel has been carried out, and the relationship between ultrafine grain refinement using a large strain processing method and increased strength has been reported. As a giant strain processing method, there is a repeated lap joint rolling method (Accumulative Roll-Bonding: ARB method). This ARB method uses rolling as a giant strain processing process for obtaining an ultrafine crystal grain material having an average grain size of 1 μm or less, and the once rolled material is divided into two equal parts in the longitudinal direction and overlapped. Rolling-bonding is also applied. When this ARB method is applied to IF steel, it has been reported that the average crystal grain size is 200 nm and the tensile strength is 820 MPa (see Non-Patent Document 1). In addition, when the ARB method is provided for SUS304 stainless steel, it has been reported that the average crystal grain size is about 200 nm and a hardness three times that of the annealed material can be obtained (see Non-Patent Document 2). .
　本願の発明者は、多軸鍛造法（Multi-Directional Forging：ＭＤＦ法）をＳＵＳ３１６ステンレス鋼に適用し、さらに微細な結晶粒組織と高強度（引張強度約２．２ＧＰａ）を実現させるに至った（非特許文献３参照）。このＭＤＦ法は、多方向からの鍛造を繰り返す巨大ひずみ加工法である。 The inventor of the present application has applied a multi-direction forging (MDF method) to SUS316 stainless steel, and has achieved a finer crystal grain structure and higher strength (tensile strength of about 2.2 GPa). (Refer nonpatent literature 3). This MDF method is a giant strain processing method in which forging from multiple directions is repeated.
　前掲の非特許文献２および３において報告される結果は好適なものではあるが、いずれの巨大ひずみ加工法においても製造プロセスが煩雑なものであり、実用化に適したものとは言い得なかった。また、機械・産業技術の高度化に伴い機械構造材料の高強度化に対する要求はさらに高まっているものの、機械材料として需要の高い鋼の場合であっても、その強度には限界を有していた。なお、一般的に巨大ひずみ加工の真ひずみは２以上であるが、強圧延で得られる真ひずみは２前後からたかだか４程度までであるため、ここでは強ひずみ加工という用語を巨大ひずみ加工とは区別して使用することとした。 Although the results reported in the above-mentioned Non-Patent Documents 2 and 3 are preferable, the manufacturing process is complicated in any of the huge strain processing methods, and cannot be said to be suitable for practical use. . In addition, with the advancement of machinery and industrial technology, the demand for higher strength of machine structural materials is increasing, but even in the case of steel, which is in high demand as a mechanical material, its strength is limited. It was. In general, the true strain of giant strain processing is 2 or more, but the true strain obtained by strong rolling is from around 2 to at most about 4. Therefore, here, the term “strong strain processing” is referred to as “giant strain processing”. We decided to use them separately.
　本発明は、上記諸点にかんがみてなされたものであって、その目的とするところは、複雑なプロセスによらず、単純な強圧延法と熱処理によって、高強度で延性を有する金属材料を提供するとともに、その処理方法を提供することである。 The present invention has been made in view of the above-described points, and an object of the present invention is to provide a high-strength and ductile metal material by a simple strong rolling method and heat treatment regardless of a complicated process. At the same time, the processing method is provided.
　そこで、金属材料に係る本発明は、安定オーステナイト鋼またはフェライト／オーステナイト二相ステンレス鋼を加工処理してなる金属材料であって、単純強圧延による強ひずみ加工によって生成される微細粒組織が、ラメラー状組織を基礎とし、変形双晶によるグループ状組織が分散して形成され、かつ、前記ラメラー状組織に複数のせん断帯が形成されたものであることを特徴とするものである。 Therefore, the present invention relating to a metal material is a metal material formed by processing a stable austenitic steel or a ferrite / austenite duplex stainless steel, and a fine grain structure generated by a high strain processing by simple strong rolling has a lamellar structure. It is characterized in that a group-like structure based on deformation twins is formed in a dispersed manner, and a plurality of shear bands are formed in the lamellar structure.
　上記構成の金属材料によれば、安定オーステナイト鋼またはフェライト／オーステナイト二相ステンレス鋼の単純強圧延によって、ラメラー状組織、変形双晶、せん断帯等の変形誘起微視組織が高密度かつ複雑に発達した超微細粒組織を得ることができる。この超微細粒組織の形成により、高強度な金属材料を得ることができるのである。また、一般的には、せん断帯の形成は、金属材料の表面が平滑とならないため、圧延加工では無用な組織とされていたが、このせん断帯が形成されることにより、好適な延性を備える金属材料を提供することができるのである。 According to the metal material of the above configuration, deformation-induced microstructures such as lamellar structure, deformation twins, and shear bands develop with high density and complexity by simple strong rolling of stable austenitic steel or ferritic / austenitic duplex stainless steel. An ultrafine grained structure can be obtained. By forming this ultrafine grain structure, a high-strength metal material can be obtained. In general, the formation of the shear band has been considered as a useless structure in the rolling process because the surface of the metal material does not become smooth. However, the formation of the shear band provides suitable ductility. A metal material can be provided.
　上記構成において、前記ラメラー状組織は、さらに、その内部に変形双晶が形成されていることが好ましい。このような組織である場合、結果的には微細な変形双晶によって個々のラメラー状組織が形成されていることとなり、変形誘起微視組織が一層高密度かつ複雑に発達した超微細組織を得ることができる。このような構成のラメラー状組織によって、金属材料全体の強度を向上させることができる。 In the above configuration, the lamellar structure preferably further has a deformation twin formed therein. In the case of such a structure, as a result, individual lamellar structures are formed by fine deformation twins, and an ultrafine structure in which deformation-induced microscopic structures are developed more densely and complicatedly is obtained. be able to. With the lamellar structure having such a configuration, the strength of the entire metal material can be improved.
　さらに、上記構成において、前記ラメラー状組織が、層状に形成されたものであり、その平均的な間隔が１００ｎｍ以下であることが好ましい。このようなラメラー状組織の平均間隔が狭い構成によれば、変形誘起微視組織をさらに高密度化することとなり、全体としての強度を向上させることとなる。 Furthermore, in the above configuration, the lamellar structure is preferably formed in a layered shape, and the average interval is preferably 100 nm or less. According to such a configuration in which the average interval of the lamellar tissue is narrow, the deformation-induced microscopic tissue is further densified, and the overall strength is improved.
　また、金属材料に係る本発明は、安定オーステナイト鋼を加工処理してなる金属材料であって、単純強圧延による強ひずみ加工によって生成される微細粒組織が、ラメラー状組織を基礎とし、変形双晶によるグループ状組織が分散して形成され、かつ、これら分散した変形双晶のグループ状組織の周辺を複数のせん断帯が包囲するように形成されたものであることを特徴とするものである。 Further, the present invention relating to a metal material is a metal material obtained by processing a stable austenitic steel, and a fine grain structure generated by a strong strain process by simple strong rolling is based on a lamellar structure, and is a deformation twin. It is characterized in that a group-like structure is formed in a dispersed manner, and a plurality of shear bands are surrounded around these dispersed deformation twin-like group-like structures. .
　上記構成は、安定オーステナイト鋼を加工処理したものであるが、安定オーステナイト鋼に対して単純強圧延を施すことにより、オーステナイト相内に適度に分散した変形双晶のグループ状組織を形成させることができる。オーステナイト相はラメラー状組織として微細な組織となり、せん断帯が変形双晶によるグループ状組織を包囲するように形成させることによって、変形双晶のグループ状組織による強度と、せん断帯による延性とを得ることができることとなる。 The above configuration is obtained by processing a stable austenitic steel, but by subjecting the stable austenitic steel to simple strong rolling, it is possible to form a group structure of deformation twins moderately dispersed in the austenitic phase. it can. The austenite phase becomes a fine structure as a lamellar structure, and by forming the shear band so as to surround the group structure by the deformation twin, the strength by the group structure of the deformation twin and the ductility by the shear band are obtained. Will be able to.
　さらに、金属材料に係る本発明は、フェライト／オーステナイト二相ステンレス鋼を加工処理してなる金属材料であって、単純強圧延による強ひずみ加工によって生成される微細粒組織が、フォライト相とオーステナイト相とのそれぞれに形成されるラメラー状組織を基礎とし、前記オーステナイト相の内部に変形双晶によるグループ状組織が分散して形成され、かつ、これら分散した変形双晶のグループ状組織の周辺を包囲するように、フェライト相およびオーステナイト相の双方に複数のせん断帯が形成されたものであることを特徴とするものである。 Furthermore, the present invention relating to a metal material is a metal material obtained by processing a ferrite / austenite duplex stainless steel, and the fine grain structure produced by the high strain processing by simple strong rolling is a folite phase and an austenite phase. Based on the lamellar structure formed in each of the above, the austenite phase is formed by dispersing a group structure of deformed twins and surrounds the periphery of the dispersed deformed twin group structures As described above, a plurality of shear bands are formed in both the ferrite phase and the austenite phase.
　上記構成は、フェライト／オーステナイト二相ステンレス鋼を加工処理したものであるが、この二相ステンレス鋼に対して単純強圧延を施すことにより、専らオーステナイト相に変形双晶を形成させることができる。そして、フェライト相およびオーステナイト相は、層状の複合材を形成し、いずれもラメラー状組織が形成される。さらに、この複合材に跨がってせん断帯が形成されることにより、これらの微細粒組織によって層状かつ複雑な組織が形成され、高強度かつ延性を有する金属材料を提供し得るものである。 The above configuration is obtained by processing a ferritic / austenitic duplex stainless steel, but by subjecting this duplex stainless steel to simple strong rolling, deformation twins can be formed exclusively in the austenitic phase. Then, the ferrite phase and the austenite phase form a layered composite material, and both form a lamellar structure. Further, by forming a shear band across the composite material, a layered and complex structure is formed by these fine grain structures, and a metal material having high strength and ductility can be provided.
　上記構成の場合には、前記グループ状組織が、表面組織中の任意の３５μｍ２の面積部分の範囲内おいて、ＴＥＭ像で観察される面積率が０％～４０％であることが好ましい。すなわち、変形双晶によるグループ状組織の形成割合が少ないことが望ましいのである。前記グループ状組織の形成により、その周辺を包囲するようにせん断帯が形成されることから、グループ状組織が形成される割合が高ければせん断帯の形成割合も高くなり、高い延性を備えることができるが、延性の向上よりも高強度を得るためには、グループ状組織の形成を抑えることが望ましいのである。なお、任意の３５μm２の面積部分についてＴＥＭ像観察によって判断されることから、グループ状組織が皆無であることは想定していないが、仮に皆無であったとしても、強度はやや低くなるが十分に強度は上昇し得る。 In the case of the above configuration, it is preferable that the area ratio observed in the TEM image is 0% to 40% when the group-like structure is within the area of an arbitrary area of 35 μm 2 in the surface structure. That is, it is desirable that the group-like structure formation ratio due to deformation twins is small. Since the formation of the group-like structure forms a shear band so as to surround the periphery thereof, the higher the ratio of formation of the group-like structure, the higher the formation ratio of the shear band, which has high ductility. However, it is desirable to suppress the formation of a group-like structure in order to obtain higher strength than improved ductility. In addition, since an arbitrary 35 μm 2 area portion is determined by TEM image observation, it is not assumed that there is no group-like structure. However, even if there is no group-like structure, the strength is slightly low but sufficient. The strength can increase.
　上記の各発明においては、前記強ひずみ加工によって生じた内部ひずみを、焼鈍を兼ねた時効処理によって低減させたものであることが好ましい。時効処理としては焼鈍によることができ、焼鈍によって、内部ひずみを低減させることができる。内部ひずみの低減に伴って、引張強度および延性の向上を両立させることができる。 In each of the above inventions, it is preferable that the internal strain generated by the high strain processing is reduced by an aging treatment that also serves as annealing. The aging treatment can be performed by annealing, and the internal strain can be reduced by annealing. As the internal strain is reduced, both the tensile strength and the ductility can be improved.
　また、これらの構成において、微細粒組織にマルテンサイト相が含まれていてもよい。ただし、マルテンサイト相は、一般的に鋼の強度を上昇させると考えられているが、本発明においては、マルテンサイト相の体積率は低く抑えることが好ましい。安定オーステナイト鋼またはフェライト／オーステナイト二相ステンレス鋼は、マルテンサイト相が発生し難く、比較的低体積率とすることができる。 In these configurations, the fine grain structure may include a martensite phase. However, although the martensite phase is generally considered to increase the strength of the steel, in the present invention, it is preferable to keep the volume ratio of the martensite phase low. Stable austenitic steel or ferritic / austenitic duplex stainless steel is less susceptible to martensite phase and can have a relatively low volume ratio.
　加工処理方法に係る本発明は、安定オーステナイト鋼またはフェライト／オーステナイト二相ステンレス鋼を加工処理する方法であって、前記安定オーステナイト鋼またはフェライト／オーステナイト二相ステンレス鋼に対し８０％以上の冷間圧延を施す単純強圧延工程を含むことを特徴とするものである。 The present invention relating to a processing method is a method for processing a stable austenitic steel or a ferrite / austenitic duplex stainless steel, and is cold-rolled at 80% or more of the stable austenitic steel or ferrite / austenitic duplex stainless steel. Including a simple strong rolling process.
　上記構成によれば、工業的な生産加工に用いられる一般的な単純強圧延により、高強度かつ好適な延性を備えるような処理を実現し得る。このとき、安定オーステナイト鋼またはフェライト／オーステナイト二相ステンレス鋼を使用することによりマルテンサイト相の発生を抑えることができる。マルテンサイト相の発生を抑えることにより、マルテンサイトの体積率を低下させ、好適な強度を得ることができるのである。 According to the above configuration, it is possible to realize a process having high strength and suitable ductility by a general simple strong rolling used for industrial production processing. At this time, generation of martensite phase can be suppressed by using stable austenitic steel or ferrite / austenite duplex stainless steel. By suppressing the generation of the martensite phase, the volume fraction of martensite can be reduced and a suitable strength can be obtained.
　また、加工熱処理方法に係る本発明は、安定オーステナイト鋼またはフェライト／オーステナイト二相ステンレス鋼を、単純強圧延の後に時効処理を行う加工熱処理プロセスによって処理する方法であって、前記安定オーステナイト鋼またはフェライト／オーステナイト二相ステンレス鋼に対し８０％以上の冷間圧延を施す単純強圧延工程と、前記単純強圧延工程により生成された組織に対して再結晶が発現しない条件下において焼鈍を兼ねた時効処理を施す熱処理工程とを含むことを特徴とするものである。なお、加工処理とは、時効処理（焼鈍）を施さない加工を意味し、加工熱処理とは、時効処理（焼鈍）を含む加工を意味するが、両者を総称した場合は加工処理と記載する。 Further, the present invention related to the thermomechanical processing method is a method of treating a stable austenitic steel or a ferrite / austenite duplex stainless steel by a thermomechanical process in which an aging treatment is performed after simple strong rolling, wherein the stable austenitic steel or ferrite / Simple strong rolling process in which 80% or more cold rolling is applied to austenitic duplex stainless steel, and aging treatment that also serves as an annealing condition under the condition that recrystallization does not occur in the structure generated by the simple strong rolling process And a heat treatment step of applying. In addition, although a process means the process which does not give an aging process (annealing) and a process heat treatment means the process containing an aging process (annealing), when both are named generically, it describes as a process.
　上記構成によれば、単純強圧延工程の後に熱処理工程を施すことから、強ひずみ加工によって生じた内部ひずみを低減させることができる。なお、熱処理工程において、微細粒組織に対して再結晶が発現しない条件化における焼鈍による時効処理を行うことから、微細化した組織をほとんど拡大させることがなく、微細粒組織による強度を維持させることができる。しかも、微細粒組織が微細粒の状態で存在することにより、内部ひずみが低減したことに伴って引張強度および延性を向上させ得るものである。 According to the above configuration, since the heat treatment step is performed after the simple strong rolling step, the internal strain generated by the high strain processing can be reduced. In addition, in the heat treatment process, since the aging treatment is performed by annealing in a condition where recrystallization does not occur with respect to the fine grain structure, the strength of the fine grain structure is maintained without substantially expanding the refined structure. Can do. In addition, since the fine grain structure exists in a fine grain state, the tensile strength and ductility can be improved as the internal strain is reduced.
　上記の加工熱処理方法に係る発明においては、熱処理工程が、例えば、絶対温度８７３Ｋ以下で焼鈍することが好ましく、さらに絶対温度７７３Ｋ以下で焼鈍処理することが好適である。この場合、二相ステンレス鋼の場合は８６４×１０２秒以上の焼鈍処理を施すことが好ましく、また、安定オーステナイト鋼の場合は７２×１０２秒以上の焼鈍処理を施すことが好ましい。ただし、より高温度で、再結晶が起こらない短時間時効（焼鈍）を行う熱処理プロセスであってもよい。 In the invention related to the above-described thermomechanical processing method, for example, the heat treatment step is preferably annealed at an absolute temperature of 873 K or lower, and more preferably annealed at an absolute temperature of 773 K or lower. In this case, in the case of duplex stainless steel, it is preferable to perform an annealing treatment of 864 × 10 2 seconds or more, and in the case of stable austenitic steel, it is preferable to perform an annealing treatment of 72 × 10 2 seconds or more. However, it may be a heat treatment process in which aging (annealing) is performed at a higher temperature for a short time without causing recrystallization.
　このような構成の場合には、安定オーステナイト鋼およびフェライト／オーステナイト二相ステンレス鋼に限定した場合、ラメラー状組織、変形双晶、せん断帯、マルテンサイト等の主たる結晶組織が再結晶することを抑えつつ、内部ひずみを低減させることができることとなる。 In such a configuration, when limited to stable austenitic steels and ferrite / austenitic duplex stainless steels, the main crystal structures such as lamellar structures, deformation twins, shear bands, and martensite are prevented from recrystallizing. However, internal strain can be reduced.
　なお、前記加工処理方法による処理によって、ラメラー状組織、変形双晶のグループ状組織、せん断帯、マルテンサイト相を主たる組織構成要素として組成されている（すなわち、変形誘起微視組織を主たる構成要素としたヘテロナノ構造の）金属材料を得ることができる。 The processing by the processing method is composed mainly of a lamellar structure, a deformation twin group structure, a shear band, and a martensite phase (that is, a deformation-induced microscopic structure as a main component). A hetero-nano-structured metal material can be obtained.
　金属材料の加工熱処理方法に係る本発明によれば、単純強圧延による強ひずみ加工の効果によって微細粒組織が形成されるものであるが、この場合の微細粒組織は、これまで行ってこなかった８０％以上の冷間圧延により生成されるものである。そして、このような単純強圧延によって、ラメラー状組織を基礎として、変形双晶が集合してなるグループ状組織が分散した状態で形成されるものであり、かつ、せん断帯を形成することができるものである。このような組織状態は、変形誘起微視組織が高密度かつ複雑に発達した超微細粒組織であり、高強度を達成することができる。 According to the present invention relating to the thermomechanical processing method of a metal material, a fine grain structure is formed by the effect of strong strain processing by simple strong rolling, but the fine grain structure in this case has not been performed so far. It is produced by cold rolling of 80% or more. And by such simple strong rolling, a group-like structure in which deformation twins are aggregated is formed on the basis of a lamellar structure, and a shear band can be formed. Is. Such a structure state is an ultrafine grain structure in which the deformation-induced microscopic structure is developed in a high density and in a complicated manner, and high strength can be achieved.
　そして、安定オーステナイト鋼を使用する場合には、変形双晶のグループ状組織の周辺を複数のせん断帯によって包囲している状態を形成させることができ、フェライト／オーステナイト二相ステンレス鋼を使用する場合には、専らオーステナイト相に変形双晶を形成するとともに、せん断帯をフェライト相とオーステナイト相とに跨がって形成させた状態とすることができる。このような複雑な微細粒組織の形成により、高強度および好適な延性を備えた金属材料を得ることができるのである。 And when using stable austenitic steel, it is possible to form a state in which the periphery of the group structure of deformation twins is surrounded by a plurality of shear bands, and when using ferrite / austenitic duplex stainless steel For example, a deformation twin can be formed exclusively in the austenite phase, and a shear band can be formed across the ferrite phase and the austenite phase. By forming such a complex fine grain structure, a metal material having high strength and suitable ductility can be obtained.
　さらに、強ひずみ加工の後の焼鈍を兼ねた時効処理がされた金属材料にあっては、当該強ひずみ加工によって生じた内部ひずみを低減させることができ、さらに強度および延性を向上させることができるものである。 Furthermore, in a metal material that has been subjected to an aging treatment that also serves as annealing after high strain processing, internal strain generated by the strong strain processing can be reduced, and strength and ductility can be further improved. Is.
　上記の加工処理方法によって処理された安定オーステナイト鋼またはフェライト／オーステナイト二相ステンレス鋼は、約３ＧＰａの引張強度となり、全伸びで十数％、塑性伸びで５％以上の塑性加工が可能な程度の延性を得ることができる。 Stable austenitic steel or ferritic / austenitic duplex stainless steel treated by the above processing method has a tensile strength of about 3 GPa, and is capable of plastic working of more than a dozen percent in total elongation and 5% or more in plastic elongation. Ductility can be obtained.
　従って、単純強圧延および時効処理（焼鈍）という一般的な加工手段および処理方法によることから、従来型の大量生産が可能であり、新たな生産設備や特殊な装置が不要となり、低コストによる加工熱処理を実現し得るものである。また、この方法によれば、これまで実現できなかった高強度かつ延性を備えた金属材料を得ることができるものである。 Therefore, because of the general processing means and processing methods of simple strong rolling and aging treatment (annealing), conventional mass production is possible, new production equipment and special equipment are not required, and processing at low cost is possible. Heat treatment can be realized. In addition, according to this method, a metal material having high strength and ductility that has not been realized so far can be obtained.
　そして、このように加工処理された金属材料は、高強度が要求される機械材料として使用でき、好適な延性により、高強度でありながら加工が容易な材料として各分野に利用可能である。 The metal material processed in this way can be used as a mechanical material that requires high strength, and can be used in various fields as a material that can be easily processed while having high strength due to suitable ductility.
（ａ）は、安定オーステナイト鋼を加工処理した際の組織の状態を示す模式図である。（ｂ）は、フェライト／オーステナイト二相ステンレス鋼を加工処理した際の組織の状態を示す模式図である。(A) is a schematic diagram which shows the state of the structure | tissue at the time of processing a stable austenitic steel. (B) is a schematic diagram which shows the state of the structure | tissue at the time of processing a ferrite / austenitic duplex stainless steel. 実施例において使用した三種類のステンレス鋼の化学組成を示す表である。It is a table | surface which shows the chemical composition of three types of stainless steel used in the Example. 実験例１におけるビッカース硬さを計測した結果を示すグラフである。It is a graph which shows the result of having measured Vickers hardness in example 1 of an experiment. 実験例２における引張試験の結果を示す応力－ひずみ曲線のグラフである。6 is a graph of a stress-strain curve showing the result of a tensile test in Experimental Example 2. 組織解析１におけるＯＩＭ観察結果を示す図である。It is a figure which shows the OIM observation result in the structure | tissue analysis 1. FIG. 組織解析２におけるＴＥＭ像である。It is a TEM image in tissue analysis 2. 組織解析３におけるＴＥＭ像である。It is a TEM image in tissue analysis 3. 組織解析４におけるＴＥＭ像である。It is a TEM image in tissue analysis 4. 組織解析４における参考資料としてのＴＥＭ像である。It is a TEM image as a reference material in the tissue analysis 4. 組織解析５におけるＴＥＭ像である。10 is a TEM image in tissue analysis 5. 組織解析６におけるＴＥＭ像である。10 is a TEM image in tissue analysis 6. 実験例３におけるビッカース硬さを計測した結果を示すグラフである。It is a graph which shows the result of having measured Vickers hardness in example 3 of an experiment. 実験例３による１０２３Ｋでの時効処理後のＴＥＭ像である。12 is a TEM image after aging treatment at 1023K according to Experimental Example 3. 実験例４における引張試験の結果を示す応力－ひずみ曲線のグラフである。10 is a graph of a stress-strain curve showing the result of a tensile test in Experimental Example 4.
　以下、本発明の実施の形態を図面に基づいて説明する。まず、単純強圧延を施すことにより生成される組織状態について説明する。図１（ａ）は、安定オーステナイト鋼に対し８０％以上の単純強圧延による強ひずみ加工を施した際の組織の状態を示す模式図である。 Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, the structure state produced | generated by performing simple strong rolling is demonstrated. Fig.1 (a) is a schematic diagram which shows the state of the structure | tissue at the time of giving the high strain processing by 80% or more of simple strong rolling with respect to stable austenitic steel.
　この図に示されるように、安定オーステナイト鋼に対し、数回に分けてロール圧延を施し、８０％以上の単純強圧延により強ひずみ加工がなされると、変形双晶が部分的に集合するグループ状組織を形成し、オーステナイト相に形成された低角ラメラー状組織をベースとして、グループ状組織が分散した状態となる。さらに、この分散したグループ状組織の周囲を包囲するように複数のせん断帯が生成される。なお、前述したが、一般的に巨大ひずみ加工の真ひずみは２以上であるが、強圧延で得られる真ひずみは２前後からたかだか４程度までであるため、実施形態における説明においても強ひずみ加工という用語を巨大ひずみ加工とは区別している。 As shown in this figure, when a stable austenitic steel is roll-rolled in several times and subjected to high strain processing by 80% or more simple strong rolling, a group in which deformation twins partially gather A group-like structure is dispersed based on a low-angle lamellar structure formed in an austenite phase. Further, a plurality of shear bands are generated so as to surround the periphery of the dispersed group-like tissue. As described above, the true strain of the giant strain processing is generally 2 or more, but the true strain obtained by the strong rolling is from about 2 to about 4 at the most. Is distinguished from giant strain machining.
　ラメラー状組織は、ほぼ均一な状態で発達し、ラメラー状を形成する各層の平均間隔は約３０ｎｍ～約１００ｎｍである。変形双晶によるグループ状組織は、１μｍよりも小さく、母相に対して初期方位が約６０°ずれた状態となっており、これは、数回のロール圧延ごとに初期方位から徐々に変化し、せん断帯の初期方位も最大で１５°前後ずれた状態から、ロール圧延ごとに初期方位から徐々に変化することとなる。この方位のずれによって、これらの組織中で強い集合組織は発達し難い構造となっている。これらの各構成組織は変形誘起微視組織であり、これらが高密度かつ複雑に発達しすることによって超微細粒組織が形成される。このような構造の超微細粒組織の生成により、極めて強い圧延集合組織の発達が効果的に抑制され、高強度でありながら延性を得ることとなるのである。 The lamellar structure develops in a substantially uniform state, and the average interval between the layers forming the lamellar structure is about 30 nm to about 100 nm. The group structure by deformation twins is smaller than 1 μm, and the initial orientation is shifted by about 60 ° with respect to the parent phase. This gradually changes from the initial orientation every several rolls. The initial orientation of the shear band is gradually changed from the initial orientation for each roll rolling from a state where the initial orientation is shifted by about 15 ° at the maximum. Due to this misorientation, a strong texture is difficult to develop in these tissues. Each of these constituent structures is a deformation-induced microscopic structure, and an ultrafine grain structure is formed by developing these in a high density and complicated manner. By generating an ultrafine grain structure having such a structure, the development of an extremely strong rolling texture is effectively suppressed, and ductility is obtained while having high strength.
　なお、安定オーステナイト鋼を使用しているため、マルテンサイト相の発生を抑えることができ、図１（ａ）にはマルテンサイト相を表示していない。しかしながら、比較的低体積のマルテンサイト相が形成されている場合があるので、構成組織にマルテンサイトを含めてもよい。ただし、マルテンサイトの体積率は可能な限り低いほうが望ましい。 In addition, since stable austenitic steel is used, generation | occurrence | production of a martensite phase can be suppressed and the martensite phase is not displayed in Fig.1 (a). However, since a relatively low volume martensite phase may be formed, martensite may be included in the constituent structure. However, it is desirable that the volume ratio of martensite is as low as possible.
　次に、フェライト／オーステナイト二相ステンレス鋼における微細粒組織の状態を説明する。図１（ｂ）は、フェライト／オーステナイト二相ステンレス鋼に対し８０％以上の単純強圧延による強ひずみ加工を施した際の組織の状態を示す模式図である。 Next, the state of the fine grain structure in the ferrite / austenite duplex stainless steel will be described. FIG. 1 (b) is a schematic diagram showing the state of the structure when the high strain processing by simple strong rolling of 80% or more is applied to the ferrite / austenitic duplex stainless steel.
　この図に示されるように、フェライト／オーステナイト二相ステンレス鋼に対し、８０％以上の単純強圧延により強ひずみ加工がなされると、フェライト相とオーステナイト相が層状となる複合材が形成される。このとき、フェライト相およびオーステナイト相には、低角ラメラー状組織が形成され、変形双晶は専らオーステナイト相にグループ状組織を形成することとなる。さらに、せん断帯は、変形双晶のグループ状組織の周囲を包囲しつつ、フェライト相およびオーステナイト相の双方に跨がるように形成されるものである。なお、二相ステンレス鋼の場合には、ラメラー状組織が、フェライト相およびオーステナイト相のそれぞれに形成され、全体として、ラメラー状を形成する各層の平均間隔は約３０ｎｍ～約３００ｎｍである。ただし、オーステナイト相の割合が大きい場合は、各層の間隔は小さくなり、フェライト相の割合が大きい場合は、各層の間隔は大きくなる傾向にある。 As shown in this figure, when a high strain processing is performed on a ferrite / austenite duplex stainless steel by simple strong rolling of 80% or more, a composite material in which a ferrite phase and an austenite phase are layered is formed. At this time, a low-angle lamellar structure is formed in the ferrite phase and the austenite phase, and the deformation twins form a group structure exclusively in the austenite phase. Furthermore, the shear band is formed so as to straddle both the ferrite phase and the austenite phase while surrounding the deformation twin crystal group structure. In the case of duplex stainless steel, a lamellar structure is formed in each of a ferrite phase and an austenite phase, and the average interval between layers forming the lamellar shape is about 30 nm to about 300 nm as a whole. However, when the proportion of the austenite phase is large, the interval between the layers tends to be small, and when the proportion of the ferrite phase is large, the interval between the layers tends to be large.
　このように、安定オーステナイト鋼およびフェライト／オーステナイト二相ステンレス鋼に共通する組織の状態は、低角ラメラー状組織を基礎とし、分散した変形双晶のグループ状組織が形成され、さらに、このグループ状組織の周辺を包囲するようにせん断帯が形成されることである。そして、せん断帯が形成される程度（すなわち断面積減少率が８０％以上となるまで）冷間圧延により強ひずみ加工を施すことにより、微細粒組織が複雑に成長することとなり、このような組織の形成によって高強度と延性を備えた金属材料となるのである。 Thus, the state of the structure common to stable austenitic steel and ferritic / austenitic duplex stainless steel is based on a low-angle lamellar structure, and a group structure of dispersed deformed twins is formed. The shear band is formed so as to surround the periphery of the tissue. Then, the fine grain structure grows in a complicated manner by subjecting it to high strain processing by cold rolling to the extent that a shear band is formed (that is, until the cross-sectional area reduction rate reaches 80% or more). Thus, a metal material having high strength and ductility is obtained.
　さらに、上記のような組織状態を形成する材料に対して焼鈍（時効処理）を施すことにより、各構成組織の状態を維持しつつ内部ひずみを低減させるのである。このときの熱処理条件は、上記組織が再結晶をほとんど発現しない程度とすることである。すなわち、強ひずみ加工によって複雑に成長した微細粒組織を再結晶によって拡大しないようにするのである。内部ひずみが低減した金属材料は、さらに強度および延性が向上し、一層の高強度かつ好適な延性を有する金属材料となるのである。 Furthermore, by subjecting the material forming the above-described structure state to annealing (aging treatment), the internal strain is reduced while maintaining the state of each constituent structure. The heat treatment condition at this time is such that the above structure hardly develops recrystallization. That is, a fine grain structure that has grown in a complicated manner by high strain processing is prevented from being enlarged by recrystallization. The metal material with reduced internal strain is further improved in strength and ductility, and becomes a metal material having higher strength and suitable ductility.
　ここで、加工熱処理方法において実施される単純強圧延工程および熱処理工程について説明する。単純強圧延工程では、一般的な冷間圧延により基礎材料を８０％以上の圧延を行うものである。８０％以上の強圧延とは、断面積減少率が８０％以上となるまで塑性加工するものであり、いわゆる強ひずみ加工の一種である。 Here, the simple strong rolling process and the heat treatment process performed in the thermomechanical processing method will be described. In the simple strong rolling process, the base material is rolled by 80% or more by general cold rolling. The strong rolling of 80% or more is a type of so-called high strain processing, in which plastic working is performed until the cross-sectional area reduction rate becomes 80% or more.
　この強ひずみ加工によって、前述の構成組織が高密度かつ複雑に発達した超微細粒組織を得るのである。この状態において、基礎材料の安定オーステナイト鋼またはフェライト／オーステナイト二相ステンレス鋼は、約２ＧＰａ程度の引張強度と、全伸び十数％以上の塑性変形可能な材料に変化させることができる。 </ RTI> By this high strain processing, an ultrafine grain structure in which the above-mentioned structural structure is developed in a high density and in a complicated manner is obtained. In this state, the stable austenitic steel or ferrite / austenitic duplex stainless steel as the base material can be changed to a plastically deformable material having a tensile strength of about 2 GPa and a total elongation of 10% or more.
　熱処理工程は、焼鈍を兼ねた時効処理によるものである。この工程では、単純強圧延工程により生成された組織に対して再結晶を発現させない条件下による時効処理（焼鈍）である。そのため再結晶を生じない温度に加熱する場合のほか、当該温度を超える高い温度で再結晶が起こらない短時間加熱の場合があり得る。例えば、再結晶が生じない温度よりも低い温度まで加熱し、空冷により焼き鈍す場合がある。具体的には、絶対温度７７３Ｋ以下で、８６４×１０２秒以上の焼鈍処理を施すものである。他方、より高温度で短期間処理する場合には、前記温度以上としつつ短時間の焼鈍を行うプロセスとしてもよい。このような時効処理（焼鈍）により、引張強度は最大で２．７ＧＰａに達し、単純強圧延工程終了時よりも強度を増大させることができる。また、延性は低下することとなるが、それでも約５％の延性を維持させることができる。 A heat treatment process is based on the aging treatment which served as annealing. This process is an aging treatment (annealing) under conditions that do not cause recrystallization of the structure generated by the simple strong rolling process. Therefore, in addition to heating to a temperature at which recrystallization does not occur, there may be a case of heating for a short time at which a recrystallization does not occur at a temperature higher than the temperature. For example, it may be heated to a temperature lower than the temperature at which recrystallization does not occur and annealed by air cooling. Specifically, an annealing process of 864 × 10 2 seconds or more is performed at an absolute temperature of 773 K or less. On the other hand, when processing at a higher temperature for a short period of time, it may be a process in which annealing is performed for a short time while maintaining the temperature or higher. By such an aging treatment (annealing), the tensile strength reaches a maximum of 2.7 GPa, and the strength can be increased as compared with the end of the simple strong rolling process. Moreover, although ductility will fall, about 5% ductility can still be maintained.
　次に、実験例について説明する。現実に、安定オーステナイト鋼と、フェライト／オーステナイト二相ステンレス鋼とを使用し、加工熱処理を施す実験を行った。使用した基礎材料は、安定オーステナイト鋼として、ＳＵＳ３１０Ｓオーステナイトステンレス鋼およびＳＵＳ３１６オーステナイトステンレス鋼の二種類を使用し、二相ステンレス鋼として、ＤＩＮ１．４４６２を使用した。これらの化学組成を図２に示す。 Next, experimental examples will be described. Actually, an experiment was performed in which a heat treatment was performed using stable austenitic steel and ferrite / austenitic duplex stainless steel. As the basic material used, two kinds of SUS310S austenitic stainless steel and SUS316 austenitic stainless steel were used as stable austenitic steel, and DIN1.4462 was used as a duplex stainless steel. These chemical compositions are shown in FIG.
［実験例１］
　これら三種のステンレス鋼を使用し、まず、ロール圧延を繰り返すことによる単純強圧延（冷間圧延）により、断面積減少率が９２％となるまで塑性加工し、その後、絶対温度７３３Ｋにおいて、焼鈍時間を変更しながら複数の加工熱処理した金属材料を得た。 [Experimental Example 1]
Using these three types of stainless steel, first, plastic processing is performed by simple strong rolling (cold rolling) by repeating roll rolling until the cross-sectional area reduction rate becomes 92%, and then annealing time at an absolute temperature of 733K. A plurality of heat-treated metal materials were obtained while changing the above.
　これらについてビッカース硬さを測定した。その結果を図３に示す。この図から明らかなとおり、焼鈍時間によって異なるが、総じて硬さが増大した。特に、ＳＵＳ３１６およびＤＩＮ１．４４６２においては、一般的な焼入れ鋼の硬さを超える結果を得ることができた。 The Vickers hardness was measured for these. The result is shown in FIG. As is apparent from this figure, the hardness increased as a whole, although it varied depending on the annealing time. In particular, in SUS316 and DIN1.4462, a result exceeding the hardness of general hardened steel could be obtained.
［実験例２］
　次に、ＳＵＳ３１６およびＤＩＮ１．４４６２の二種類の基礎材料について、実験例１と同様に単純強圧延により断面積減少率が９２％となるまで、室温において塑性加工し、その後、焼鈍時間を変化した複数の金属材料について引張試験を行った。その結果を応力－ひずみ曲線として図４に示す。なお、図中の「ＡＲ材」とは、単純強圧延のみの材料を意味する。また、「ＲＤ」は単純強圧延の際に延伸された方向への引張試験を意味し、「ＴＤ」は延伸方向に対して垂直な方向への引張試験を意味する。また、「Ｔ＝２９３Ｋ」とあるのは室温を意味する。応力－ひずみ曲線に付された数字は、グラフの枠外に示した時効処理の時間に対応するものである。 [Experiment 2]
Next, two basic materials of SUS316 and DIN1.4462 were subjected to plastic working at room temperature until the cross-sectional area reduction rate reached 92% by simple strong rolling in the same manner as in Experimental Example 1, and then the annealing time was changed. Tensile tests were performed on a plurality of metal materials. The result is shown in FIG. 4 as a stress-strain curve. In addition, "AR material" in a figure means the material only for simple strong rolling. “RD” means a tensile test in the direction stretched during simple strong rolling, and “TD” means a tensile test in a direction perpendicular to the stretching direction. “T = 293K” means room temperature. The numbers attached to the stress-strain curve correspond to the aging time shown outside the frame of the graph.
　この図から明らかなとおり、ＲＤ方向（延伸方向）への引張試験では、単純強圧延のみ（ＡＲ材）により、既に引張強度が１．５ＧＰａまたは１．７ＧＰａに達しており、熱処理を施すことにより、さらに強度が増大している。また、ＴＤ方向に至っては、単純強圧延のみ（ＡＲ材）でも１．９ＧＰａまたは２．０ＧＰａに達しており、さらに熱処理により、最大で２．７ＧＰａまたは２．６ＧＰａに達するものが得られた。 As is clear from this figure, in the tensile test in the RD direction (stretching direction), the tensile strength has already reached 1.5 GPa or 1.7 GPa only by simple strong rolling (AR material). Further, the strength is increased. Further, in the TD direction, only simple strong rolling (AR material) reached 1.9 GPa or 2.0 GPa, and further, heat treatment reached a maximum of 2.7 GPa or 2.6 GPa.
［組織解析１］
　そこで、ＤＩＮ１．４４６２について、９２％の単純強圧延後の状態（以下、供試材という場合がある）と、さらに絶対温度７７３Ｋにおける８６４×１０２秒の焼鈍後の状態との微視組織を、方位マッピング（ＯＩＭ：Orientation Imaging Microscopy）で観察した。その結果を図５に示す。 [Tissue analysis 1]
Therefore, for DIN 1.4462, a microstructure of a state after 92% simple strong rolling (hereinafter sometimes referred to as a specimen) and a state after annealing at 864 × 10 2 seconds at an absolute temperature of 773 K This was observed by orientation mapping (OIM). The result is shown in FIG.
　ＯＩＭ観察によれば、観察される微視組織は、圧延方向に伸びた一般的な強圧延組織であったが、集合組織の発達の度合いが極めて低いことがわかった。すなわち、圧延直後は、（００１）面に集合組織の発達によるピーク値７．３が現れ、熱処理後は（１１１）面にピーク値５．０が現れる結果となった。これは、共に強圧延後に発達しやすい（１０１）面または（１１２）面の集合組織とは異なり、延性低下の要因となりにくい方位であり、その集積度も比較的低いものであった。従って、引張試験の結果とともに考察すれば、高強度でありながら良好な塑性加工性を有するものであることが理解される。 According to OIM observation, the observed microstructure was a general strong rolling structure extending in the rolling direction, but it was found that the degree of development of the texture was extremely low. That is, immediately after rolling, a peak value of 7.3 due to the development of texture appeared on the (001) plane, and a peak value of 5.0 appeared on the (111) plane after the heat treatment. Unlike the (101) plane or (112) plane texture, both of which tend to develop after strong rolling, the orientation is less likely to cause a decrease in ductility, and the degree of integration is relatively low. Therefore, when considered together with the results of the tensile test, it is understood that the material has good plastic workability while having high strength.
　なお、図示を省略するが、ＳＵＳ３１６ステンレス鋼についてもＯＩＭによる観察を行ったところ、（１０１）方位に９．６の集積が観察された。ただし、ＯＩＭのビーム径が組織サイズよりも大きいため、内部微視組織を正確に反映したものとは言い難く、そのため、透過型電子顕微鏡（ＴＥＭ）による観察を行った。 Although not shown, when SUS316 stainless steel was also observed by OIM, accumulation of 9.6 was observed in the (101) direction. However, since the beam diameter of OIM is larger than the tissue size, it cannot be said that the internal microscopic tissue is accurately reflected. Therefore, observation was performed with a transmission electron microscope (TEM).
［組織解析２］
　ＳＵＳ３１６ステンレス鋼の単純強圧延後の供試材のＴＥＭ像を図６に示す。このＴＥＭ像により観察され得る比較的大きい組織領域を観察すると、ラメラー状組織、変形双晶、せん断帯が複雑に入り組んだ超微細粒組織であることがわかる。なお、ラメラー組織はほぼ均一に発達しており、図６から判断されるところで、各層の平均間隔は約３０ｎｍであった。変形双晶は母相に対して初期方位が約６０°ずれており、これは、圧延の回数ごとに徐々に変化する。また、せん断帯の初期方位は最大で約１５°ずれていた。これも圧延の回数ごとに徐々に変化する。さらに、ＴＥＭ像では判明しなかったが、マルテンサイトが含まれている可能性もあり得る。 [Tissue analysis 2]
FIG. 6 shows a TEM image of the test material after simple strong rolling of SUS316 stainless steel. When a relatively large structure region that can be observed by this TEM image is observed, it can be seen that the structure is an ultrafine grain structure in which lamellar structures, deformation twins, and shear bands are intricately complicated. The lamellar structure developed almost uniformly, and as determined from FIG. 6, the average interval between the layers was about 30 nm. The deformation twin has an initial orientation shifted by about 60 ° with respect to the parent phase, and this changes gradually with each rolling. Further, the initial orientation of the shear band was shifted by about 15 ° at the maximum. This also changes gradually with each rolling operation. Furthermore, although it was not found in the TEM image, there is a possibility that martensite is included.
［組織解析３］
　念のため、ＤＩＮ１．４４６２の単純強圧延後のＴＥＭ像を図７に示す。このＴＥＭ像においても、ラメラー状組織、変形双晶、せん断帯が複雑に入り組んだ超微細粒組織であることがわかる。なお、ラメラー組織は、フェライト相とオーステナイト相との双方に形成されており、両相によって複合材が形成されていることがわかる。また、中央に比較的大きく撮影されているのは、変形双晶によるグループ状組織であり、その周辺にせん断帯が形成されているのがわかる。このＴＥＭ像においてもマルテンサイトが確認されなかったが、マルテンサイトが含まれている可能性もあり得る。なお、図７からは明確ではないが、ＴＥＭ像を精査すると、ＤＩＮ１．４４６２の場合は、前記ＳＵＳ３１６ステンレス鋼に比較して、変形双晶によるグループ状組織の形成が少なく、全体に占める体積率において５％を大幅に下回るものと判断された。 [Tissue analysis 3]
As a precaution, a TEM image of DIN 1.4462 after simple strong rolling is shown in FIG. Also in this TEM image, it can be seen that the structure is an ultrafine grain structure in which a lamellar structure, a deformation twin, and a shear band are complicatedly arranged. The lamellar structure is formed in both the ferrite phase and the austenite phase, and it can be seen that a composite material is formed by both phases. In addition, it can be seen that a relatively large photograph at the center is a group-like structure formed by deformation twins, and a shear band is formed around the structure. Although martensite was not confirmed in this TEM image, there is a possibility that martensite is included. Although it is not clear from FIG. 7, when a TEM image is closely examined, in the case of DIN1.4462, the formation of a group-like structure due to deformation twins is less than that of the SUS316 stainless steel, and the volume ratio occupies the whole. It was judged to be significantly below 5%.
［組織解析４］
　そこで、ＤＩＮ１．４４６２の供試材について、３５μｍ２の面積部分における変形双晶によるグループ状組織の面積割合をＴＥＭ像によって観察した。そのときのＴＥＭ像を図８に示す。この図には、僅かながらグループ状組織を見出すことができ、この面積部分全体に占める割合は約５％と判断し得る。グループ状組織の発見は、ラメラー状組織の境界線が歪んだ部分に存在するため、その歪みを目安にグループ状組織と断定した。比較のため、ＳＵＳ３１６ステンレス鋼の供試材についても、３５μｍ２の面積部分における変形双晶によるグループ状組織の面積割合をＴＥＭ像によって観察した。そのときのＴＥＭ像を図９に示す。この図には、広い範囲に点在するグループ状組織を明確に見出すことができる。この面積部分全体に占める割合は約５０％と判断し得る。なお、グループ状組織が点在することから、全体的にラメラー状組織の境界線が歪んでいるが、その周辺においてもラメラー状組織は存在していることがわかる。 [Tissue analysis 4]
Therefore, the area ratio of the group-like structure due to deformation twins in the 35 μm 2 area portion of the DIN 1.4462 specimen was observed by a TEM image. A TEM image at that time is shown in FIG. In this figure, a group-like structure can be found slightly, and it can be determined that the ratio of the entire area is about 5%. The group-like structure was found in the part where the boundary line of the lamellar structure was distorted. For comparison, the area ratio of the group-like structure due to deformation twins in the 35 μm 2 area portion was also observed with a TEM image for the SUS316 stainless steel specimen. A TEM image at that time is shown in FIG. In this figure, group-like structures scattered over a wide range can be clearly found. It can be determined that the proportion of the total area is about 50%. In addition, since the group-like structure is scattered, the boundary line of the lamellar structure is distorted as a whole, but it can be seen that the lamellar structure exists also in the vicinity thereof.
［組織解析５］
　さらに、ＳＵＳ３１６ステンレス鋼について、単純強圧延後に時効処理（焼鈍）後のＴＥＭ像を図１０に示す。時効処理（焼鈍）としては、絶対温度７７３Ｋで７２００秒の焼鈍を行ったものである。このＴＥＭ像によれば、単純強圧延後に得られたラメラー状組織の各層の間隔が約３０ｎｍであったのに対し、時効処理（焼鈍）後の間隔は約４２ｎｍまで広がっていることが判明した。これは、再結晶は起こっていないものの、回復により転位密度の減少と粒界移動により、ラメラー状組織の各層の間隔が増大したものと判断される。従って、より長時間の時効処理によって、ラメラー間隔はさらに広がるものと判断される。実際に、さらに長時間時効処理したものの中には再結晶が始まり、ラメラー状組織が消失したものもあった。ラメラー状組織が消失したものは強度も低下していた。 [Organization analysis 5]
Furthermore, about SUS316 stainless steel, the TEM image after an aging treatment (annealing) after simple strong rolling is shown in FIG. As the aging treatment (annealing), annealing is performed for 7200 seconds at an absolute temperature of 773K. According to this TEM image, it was found that the interval between layers of the lamellar structure obtained after simple strong rolling was about 30 nm, whereas the interval after aging treatment (annealing) was extended to about 42 nm. . Although recrystallization does not occur, it is considered that the spacing between the layers of the lamellar structure is increased due to the decrease in the dislocation density and the grain boundary movement due to the recovery. Accordingly, it is determined that the lamellar interval is further widened by the longer aging treatment. In fact, some of the aging treatments for a longer time began to recrystallize and the lamellar structure disappeared. In the case where the lamellar structure disappeared, the strength also decreased.
［組織解析６］
　また、前記組織解析５で使用したＳＵＳ３１６ステンレス鋼について、その組織中に形成されたラメラー状組織の内部を観察するために拡大したＴＥＭ像を撮影した。このＴＥＭ像を図１１に示す。この図から明らかなとおり、約１００ｎｍ間隔で形成されるラメラー状組織の内部に、変形双晶が微細に斜状に形成されているのがわかる。図のほぼ中央に撮影されているラメラー状組織の内部では、変形双晶が明確に表れているが、他のラメラー状組織の内部にも同様の変形双晶が形成されている。このことから、ラメラー状組織の一部は、変形双晶の発現によってさらに微細な組織に分断されている。圧延の初期過程で発生した変形双晶はグループ状組織を形成し、残りの部分はラメラー状組織へと発達するがその過程で内部に変形双晶が導入されると考えられる。なお、時効処理（焼鈍）により、ラメラー状組織の界面移動に伴う結晶粒の成長と回復によって、その間隔は変化するが、時効処理後の平均的な間隔は前記のとおり約４２ｎｍとなり、１００ｎｍ以下に収まる状態となっている。 [Organization analysis 6]
Further, for the SUS316 stainless steel used in the structure analysis 5, an enlarged TEM image was taken in order to observe the inside of the lamellar structure formed in the structure. This TEM image is shown in FIG. As is clear from this figure, it can be seen that the deformed twins are finely and obliquely formed inside the lamellar structure formed at intervals of about 100 nm. In the inside of the lamellar structure photographed almost in the center of the figure, a deformation twin appears clearly, but similar deformation twins are also formed in the other lamellar structures. From this, a part of the lamellar structure is divided into a finer structure due to the development of deformation twins. The deformation twins generated in the initial stage of rolling form a group-like structure, and the remaining part develops into a lamellar structure, but it is thought that the deformation twins are introduced inside the process. In addition, although the space | interval changes with the growth and recovery | restoration of the crystal grain accompanying the interface movement of a lamellar structure by aging treatment (annealing), the average space | interval after an aging treatment will be about 42 nm as above-mentioned, and 100 nm or less It is in a state that fits in.
［実験例３］
　つぎに、焼鈍温度および時間と強度の関係を把握するための実験を行った。実験には、ＤＩＮ１．４４６２を使用し、実験例１と同様に単純強圧延により断面積減少率が９２％となるまで塑性加工し、焼鈍の温度を絶対温度７７３Ｋのほかに、絶対温度８７３Ｋおよび１０２３Ｋとした場合のそれぞれについて、時効時間ごとのビッカース硬さを測定した。なお、絶対温度７７３による焼鈍の結果は、実験例１のものを使用した。 [Experiment 3]
Next, an experiment was conducted to grasp the relationship between the annealing temperature and time and the strength. In the experiment, DIN 1.4462 was used, and plastic processing was performed by simple strong rolling until the cross-sectional area reduction rate became 92% in the same manner as in Experimental Example 1, and the annealing temperature was set to an absolute temperature of 873 K in addition to the absolute temperature of 773 K. Vickers hardness for each aging time was measured for each of 1023K. In addition, the result of the annealing by the absolute temperature 773 used the thing of Experimental example 1.
　そのときの結果を図１２に示す。なお、図中の絶対温度７７３Ｋの結果は実験例１と同じであるが、時効時間１０５sを超える範囲での曲線の向きが異なっている。この図から明らかなとおり、絶対温度１０２３Ｋでは、焼鈍時間の変化に伴いビッカース硬さのピークを示すものであるが、その後、ビッカース硬さは顕著に減少する。また、絶対温度８７３Ｋの場合には、ビッカース硬さのピークは低く、ピーク後にやはり低下している。これらの硬度低下の原因としては、ラメラー状組織の再結晶化が挙げられる。念のため、ＴＥＭ像を図１３に示す。ＲＤ面（図１３（ａ））およびＴＤ面（図１３（ｂ））のいずれにおいても、再結晶に伴ってラメラー状組織が消失していることがわかる。 The result at that time is shown in FIG. In addition, although the result of the absolute temperature 773K in a figure is the same as Experimental example 1, the direction of the curve in the range exceeding aging time 10 < 5 > s differs. As is clear from this figure, the absolute temperature of 1023K shows a peak of Vickers hardness as the annealing time changes, but thereafter the Vickers hardness decreases significantly. In the case of an absolute temperature of 873 K, the peak of Vickers hardness is low and also decreases after the peak. The cause of these hardness reductions is recrystallization of lamellar structures. As a precaution, a TEM image is shown in FIG. It can be seen that the lamellar structure disappears with recrystallization in both the RD plane (FIG. 13A) and the TD plane (FIG. 13B).
［実験例４］
　また、前記実験例３において時効処理されたＤＩＮ１．４４６２について、実験例２と同様の引張試験を行った。引張試験は、絶対温度１０２３Ｋにおける時効処理後のＤＩＮ１．４４６２のみとし、複数の時効時間により処理したものについて行った。この結果を図１４に示す。絶対温度１０２３Ｋにおける時効の場合は、適当な焼鈍時間においてビッカース硬さの値が大きかったが、この図１４に示されるとおり、引張強度は、逆に低下している。これは、シグマ相の析出に起因するものと考えられる。なお、シグマ相はＣｒまたはＭｏによって析出が促進されることから、これらの総量が多く含まれる二相ステンレス鋼において顕著であったと考えられる。 [Experimental Example 4]
In addition, the same tensile test as in Experimental Example 2 was performed on DIN1.4462 that was aged in Experimental Example 3. The tensile test was performed only on DIN 1.4462 after the aging treatment at an absolute temperature of 1023K, and was treated with a plurality of aging times. The result is shown in FIG. In the case of aging at an absolute temperature of 1023 K, the value of Vickers hardness was large at an appropriate annealing time. However, as shown in FIG. This is considered to be caused by precipitation of the sigma phase. In addition, since precipitation of sigma phase is promoted by Cr or Mo, it is considered that it was remarkable in the duplex stainless steel containing a large amount of these.

Claims (11)

  1. 　安定オーステナイト鋼またはフェライト／オーステナイト二相ステンレス鋼を加工処理してなる金属材料であって、
    　単純強圧延による強ひずみ加工によって生成される微細粒組織が、ラメラー状組織を基礎とし、変形双晶によるグループ状組織が分散して形成され、かつ、前記ラメラー状組織に複数のせん断帯が形成された、変形誘起の微視組織を主として構成されている
    ことを特徴とする金属材料。     A metal material obtained by processing stable austenitic steel or ferrite / austenitic duplex stainless steel,
    The fine grain structure generated by the strong strain processing by simple strong rolling is based on the lamellar structure, the group structure is formed by deformation twins, and a plurality of shear bands are formed in the lamellar structure. A metal material comprising mainly a deformation-induced microscopic structure.
  2. 　前記ラメラー状組織は、内部に変形双晶が形成されている請求項１に記載の金属材料。 The metal material according to claim 1, wherein the lamellar structure has deformation twins formed therein.
  3. 　前記ラメラー状組織は、層状に形成されており、その平均的な間隔が１００ｎｍ以下である請求項１または２に記載の金属材料。 The metal material according to claim 1 or 2, wherein the lamellar structure is formed in a layer shape, and an average interval is 100 nm or less.
  4. 　安定オーステナイト鋼を加工処理してなる金属材料であって、
    　単純強圧延による強ひずみ加工によって生成される微細粒組織が、ラメラー状組織を基礎とし、変形双晶によるグループ状組織が分散して形成され、かつ、これら分散した変形双晶のグループ状組織の周辺を複数のせん断帯が包囲するように形成された、変形誘起の微視組織を主として構成されている
    ことを特徴とする金属材料。     A metal material obtained by processing stable austenitic steel,
    The fine grain structure generated by the strong strain processing by simple strong rolling is based on the lamellar structure, the group structure is formed by deformation twins, and the group structure of these dispersed deformation twins is formed. A metal material comprising mainly a deformation-induced microscopic structure formed so as to surround a plurality of shear bands.
  5. 　フェライト／オーステナイト二相ステンレス鋼を加工処理してなる金属材料であって、
    　単純強圧延による強ひずみ加工によって生成される微細粒組織が、フォライト相とオーステナイト相とのそれぞれに形成されるラメラー状組織を基礎とし、前記オーステナイト相の内部に変形双晶によるグループ状組織が分散して形成され、かつ、これら分散した変形双晶のグループ状組織の周辺を包囲するように、フェライト相およびオーステナイト相の双方に複数のせん断帯が形成された、変形誘起の微視組織を主として構成されている
    ことを特徴とする金属材料。     A metal material obtained by processing ferritic / austenitic duplex stainless steel,
    The fine grain structure produced by the strong strain processing by simple strong rolling is based on the lamellar structure formed in each of the folite phase and the austenite phase, and the group structure by deformation twins is dispersed inside the austenite phase. The deformation-induced microstructure is mainly composed of a plurality of shear bands formed in both the ferrite phase and the austenite phase so as to surround the group structure of these dispersed deformation twins. A metal material characterized by comprising.
  6. 　前記グループ状組織は、表面組織中の任意の３５μｍ２の面積部分の範囲内おいて、ＴＥＭ像で観察される面積率が０％～４０％である請求項５に記載の金属材料。 The metal material according to claim 5, wherein the group-like structure has an area ratio of 0% to 40% observed in a TEM image within an arbitrary area portion of 35 μm 2 in the surface structure.
  7. 　前記微細粒組織は、さらにマルテンサイト相を含んでいる請求項１ないし５のいずれかに記載の金属材料。 The metal material according to any one of claims 1 to 5, wherein the fine grain structure further includes a martensite phase.
  8. 　安定オーステナイト鋼またはフェライト／オーステナイト二相ステンレス鋼を加工処理する方法であって、
    　前記安定オーステナイト鋼またはフェライト／オーステナイト二相ステンレス鋼に対し８０％以上の冷間圧延を施す単純強圧延工程を含む
    ことを特徴とする加工処理方法。     A method of processing stable austenitic steel or ferritic / austenitic duplex stainless steel,
    The processing method characterized by including the simple strong rolling process which cold-rolls 80% or more with respect to the said stable austenitic steel or a ferrite / austenitic duplex stainless steel.
  9. 　安定オーステナイト鋼またはフェライト／オーステナイト二相ステンレス鋼を、単純強圧延の後に時効処理を行う加工熱処理プロセスによって処理する方法であって、
    　前記安定オーステナイト鋼またはフェライト／オーステナイト二相ステンレス鋼に対し８０％以上の冷間圧延を施す単純強圧延工程と、
    　前記単純強圧延工程により生成された組織に対して再結晶が発現しない条件下において焼鈍を兼ねた時効処理を施す熱処理工程とを含む
    ことを特徴とする加工熱処理方法。     A method of treating stable austenitic steel or ferritic / austenitic duplex stainless steel by a thermomechanical process in which aging treatment is performed after simple strong rolling,
    A simple strong rolling process in which 80% or more of cold rolling is applied to the stable austenitic steel or the ferrite / austenitic duplex stainless steel;
    And a heat treatment step of performing an aging treatment that also serves as annealing under a condition in which recrystallization does not occur on the structure generated by the simple strong rolling step.
  10. 　前記時効処理は、絶対温度８７３Ｋ以下の条件下における焼鈍である請求項９に記載の加工熱処理方法。 The thermomechanical processing method according to claim 9, wherein the aging treatment is annealing under a condition of an absolute temperature of 873K or less.
  11. 　前記時効処理は、強ひずみ加工によって生じた内部ひずみを低減させるための焼鈍を兼ねたものである請求項９または１０に記載の加工熱処理方法。 The thermomechanical processing method according to claim 9 or 10, wherein the aging treatment also serves as annealing for reducing internal strain generated by high strain processing.
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