Method for obtaining steel ingots of austenitic class with nanocrystalline structure

FIELD: metallurgy.

SUBSTANCE: ingot manufacturing method involves tempering of an ingot, multiple forging with series change of orientation axis through 90° at the temperature interval of 773-923 K with total true deformation degree of not less than 3 and further annealing at the temperature above isothermic forging temperature by 50 K during 1-5 hours.

EFFECT: obtaining an austenitic steel ingot with nanocrystalline structure and improved strength properties.

2 dwg, 1 ex

 

The invention relates to the field of metallurgy, mainly to processing of metals by pressure, in particular to a technology for billet steel austenitic with a nanocrystalline structure, and can be used in the manufacture of pressure vessels for heat and power engineering and chemical industry.

Known methods of grinding grains can be divided into three groups. The first group includes those purely metallurgical processes based on the variation of the temperature and speed of solidification conditions, the doping of the melt modifying elements such as Nb, Ti, Zr, Al, V, ultrasound or electromagnetic effect on the melt [1], ultrafast quenching of the tape [2], the evaporation and condensation of the material in an inert environment [3, 4], plasma spraying [5, 6], the electrical explosion of conductors [7], non-equilibrium condensation in high-speed gas flows [8, 9], etc. the Second group of methods of grinding grains in alloys is associated with the methods chemical synthesis, for example, obtaining multicomponent ultrafine powders heterophase interaction in alkaline solutions, electrolytic layer-by-layer deposition and crystallization of amorphous [10, 11]. The third group of methods includes various methods of processing materials, such as traditional thermomechanical treatment (TMT), different types of integration of the intensive plastic deformation (SPD) with dynamic [12, 13] or subsequent static [14] recrystallization, as well as the processing of powder materials in ball mills (the so-called mechanical alloying) [15].

Methods of the first and second groups typically receive a nanocrystalline structure with a grain size of about 10 nm. Most of them are based on the compaction of powders. Some of these methods have been successfully used to generate and study the structure and properties of nanocrystalline materials. However, the development of these methods is problematic due to the presence of porosity (up to 10%) in compacted, sintered samples, their high fragility and complexity of controlling the chemical purity of the alloy in the process of getting it. In addition, these methods do not provide a solid billet with a nanocrystalline structure sufficient to conduct a full study of physical-mechanical properties and fabrication of semi-finished products for industrial applications.

Using the methods of the third group allows to obtain a nanocrystalline structure in materials with an average grain size of about 100 nm with a special high-boundaries [16] and have two important advantages: it does not lead to the formation of porosity, can be used as pure metals and alloys and intermetallic compounds is the third. Methods SDI is based on the creation of material of high density of crystalline defects (dislocations, grain boundaries) in the original perfect (or almost perfect) poly - and single crystals. Under SDI refers to the true extent of deformation e≥5 [17].

Applied to austenitic steels a method of processing cold deformation with intermediate anneals. Thus, in patent US 4421572 (publ. 20.12.1983) proposed a method of cold deformation processing with intermediate anneals at temperatures 1010-1038°C for 60-90 seconds to reduce radiation-induced swelling in AISI 316.

The processing method that combines SDI and TMO, presented in the patent UA 79726 C2 (2007). Getting in steel 18CR10NITI patterns with fragment size less than 1 micron is achieved by a combination of the following operations: plastic deformation method overall compression at low temperatures -40...-100°C (resulting in the formation of martensite with the size of the fragments 0,06-0,09 ám), heating to a temperature above the temperature of aging and aging at this temperature until the end of the conversion of martensite into austenite and quenching the austenite. Steel with the obtained structure has high strength.

Closest to the proposed invention is a method for ultrafine-grained structure in austenitic steels, a revelation the first article [18]. In [18] the samples were deformed austenitic steel in vacuum at 873 K using the multiple forging a consistent axis orientation by 90°. The true degree of deformation in one draught were 0.4 at strain rate of 8×10-4with-1the total deformation rate reached 6.4. After each deposition the samples were cooled in water and then heated to 873 K in a period of 0.6-0.8 CSEC. As a result of this processing was obtained ultrafine-grained structure with an average grain size of 300 nm. The disadvantage of this method is that it is not possible to obtain a nanocrystalline structure in steels, the high complexity of the forging process due to the presence of cooling and heating of the workpiece after each precipitation.

The objective of the invention is to develop a method of casting of austenitic steels with a nanocrystalline structure, as well as reducing the complexity of forging.

The technical result is to

- obtaining a homogeneous nanocrystalline structure of the workpiece, due to which there is a significant increase in strength properties of steel at room and at elevated temperatures, due to the homogeneous nanocrystalline structure of the blanks in the implementation of the proposed method;

- reducing the complexity of forging.

Put ass the cha is solved by the proposed method casting austenitic steels with a nanocrystalline structure, including multiple isothermal forging the workpiece at a constant temperature with minimal real degree of deformation for one draught of not less than 0.4 and consistent change in axis orientation by 90°, which included the following new features:

preliminary hardening of the workpiece with 1373 K;

- multiple isothermal forging is carried out with strain rates from 10-2up to 10-1with-1and with a total true strain degree at least 3, at a temperature lying in the range of 773-C, followed by annealing the workpiece at a temperature higher than the temperature of isothermal forging at 50 To within 1-5 hours.

The main difference of the proposed method from the prototype are: higher strain rate in the sediment, absence of cooling and heating of the workpiece between the sediment, the presence of annealing to stabilize the microstructure after forging.

The present invention is characterized by the following graphics:

Figure 1. Scheme thermomechanical processing of steel 081810.

Figure 2. A photograph of the grain structure of the steel structure, obtained with a transmission electron microscope JEOL JEM-2100.

The example implementation.

In the example implementation used steel 081810, pre-tempered to 1373 K in water, with the original grain size of 25 µm. Billet 85×50×50 mm3the conference had been subjected to thermomechanical treatment (TMT), consisting of multiple isothermal forging a consistent axis orientation by 90° at 873 K with a true degree of deformation for one draught of 0.4 at a strain rate of 10-2up to 10-1with-1total number of residue 10, the total true strain degree 4 and subsequent annealing at 923 K for 3 hours (figure 1). Forging was carried out without cooling and heating of the workpiece between the sediment. The average grain size after TMO was 100 nm (figure 2).

Mechanical tensile tests were carried out according to GOST 1497-84 at room temperature and according to GOST 9651-84 at elevated temperatures (table 1).

Table 1
Mechanical properties of austenitic steel 081810 in the original coarse-grained and nanostructured States
293673773873923
Yield strength, MPaThe sample after TMO860710640385485
The sample to TMO300200190170170
Tensile strength, MPaThe sample after TMO960770680550570
The sample to TMO640520500450400
Elongation, %The sample after TMO13761722
The sample to TMO35-43-34

Sources of information

[1] Allabashi Superplasticity of industrial alloys. - M.: Metallurgiya, 1984. - 264 C.

[2] R. Wurschum, W. Greiner, Valtev THIS, M. Rapp, W. Sigle, O. Schneeweiss and Schaefev H.E. Interfacial Free Volumes in Ultra-Fine Grained Metals of Amorphous Alloys // Scr.Met.et Mater. - 1991. - P.456-564.

[3] BirrengerR. and Gleiter H. Nanocrystalline materials // Encyclopedia of Materials Science and Engineering ed. R.W.Cahn, Pergamon Press. - 1988. - Vol.1 (Suppl.). - P.339-349.

[4] F.H. Froes and Suryanarayna. Nanocrystalline Metals for Structural Applications // JOM. - 1989. No. 6. - P.12-17.

[5] ) I.D., L.I. Trusov, Lapovok V.I. Physical phenomena in ultra-dispersed environments. - M.: Nauka, 1984. - S; ) I.D., L.I. Trusov, Chizhik S. p. Ultrafine metal environment. - M.: Atomizdat, 1977. - 264 C.

[6] ) I.D., L.I. Trusov, Chizhik S. p. Ultrafine metal environment. - M.: Atomizdat, 1977. - 264 C.

[7] Couv Y.A., N.A. Jaworski Study of particles formed by the electric explosion of conductors // Physics and chemistry of materials processing. - 1978. No. 4. - P.24.

[8] ) I.D., L.I. Trusov, Lapovok V.I. Physical phenomena in ultra-dispersed environments. - M.: Nauka, 1984. - S; ) I.D., L.I. Trusov, Chizhik S. p. Ultradisperse metal environment. - M.: Atomizdat, 1977. - 264 C.

[9] ) I.D., L.I. Trusov, Chizhik S. p. Ultrafine metal environment. - M.: Atomizdat, 1977. - 264 C.

[10] ultra-fine grain metals. TRANS. from English. - M.: metallurgy, 1973. - 384 S.

[11] H. Gleiter, Nanostructured Materials: state of the art and perspectives // Nanostructured Materials. - 1995. - vol.6. - P.3-14.

[12] O. Kaibyshev, R. Kaibyshev, G. Salishchev Formation of submicrocrystalline structure in materials during dynamic recrystallization // Mater. Sci. Forum - 1993. - Vol.113-115. - P.423-428.

[13] S.V. Zherebtsov, Galeev, P.M., O.R. Valiakhmetov, Malyshev, S. p., Saliev GA, Myshlyaev M.M. Formation of submicrocrystalline is some structure in titanium alloys severe plastic deformation and mechanical properties // SN. - 1999. No. 7. - P.17-22.

[14] Valiev THIS, N.A. Krasilnikov and N.K. Tsenev Plastic deformation of alloys with submicron-grained structure // Mater. Sci. and Eng. - 1991. - A137. - P.35-40.

[15] Shhultz L., E. Hellstern Glass formation by mechanical alloying / in Science and Technology of Rapidly Quenched Alloys, ed. by M.Tenhover, L.E.Tanner, W.L.Jonson // Materials Science Society. - 1987. - Vol.24. - P.145-150.

[16] Valiev R.Z., Alexandrov I.V. Nanostructured materials from severe plastic deformation. - M.: Logos, 2000. - 272 S.

[17] Y. Saito, N. Tsuji, H. Utsunomiya et. al. Ultra-fine grained bulk aluminum produced by Accumulative Roll-Bonding (ARB) process // Scripta Mater. - 1998. No. 39. - P.1221-1227.

[18] A. Belyakov, Sakai T. and Miura H. Fine-Grained Structure Formation in Austenitic Stainless Steel under Multiple Deformation at 0.5Tm// Material Transactions, - 2000. - Vol.41. No. 4 - P.476-484.

A method of manufacturing billets steels austenitic with a nanocrystalline structure, including multiple isothermal forging the billet at a consistent axis orientation by 90° at a constant temperature and with minimal real degree of deformation for one draught of not less than 04, characterized in that the pre-hardened with temperature K the workpiece is subjected to multiple isothermal forging at a constant temperature in the range of 773-C with strain rates from 10-2up to 10-1with-1after reaching the total true strain is not less than 3 conduct annealing the workpiece at a temperature higher than the temperature of isothermal forging at 50 To within 1-5 hours



 

Same patents:

FIELD: metallurgy.

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1 tbl, 2 dwg, 1 ex

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2 tbl, 2 ex

FIELD: metallurgy.

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2 tbl, 2 ex

FIELD: personal use articles.

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28 cl, 2 tbl

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1 ex

FIELD: metallurgy.

SUBSTANCE: they are subjected to hardening by heating to 970-1020 °C and cooling in oil, then to a double tempering at 620-670 C, with the first tempering carried out for 4.5-5 hours, and the second one for 3.5-4.5 hours, and cooled after each tempering in water or oil.

EFFECT: increased impact strength across the deformation fibres of shafts made of steel 14H17H2.

1 ex, 4 tbl

FIELD: chemistry.

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EFFECT: composition is characterised by high modulus of elasticity of 3,8-4,2 GPa, which allows its use in making deformation-resistant articles from polymer composite materials with higher structural strength.

7 cl, 3 tbl, 12 ex

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