RU2307183C2 - Oxide-hardened iron-base composition material producing method - Google Patents

Abstract

FIELD: powder metallurgy, namely production of dispersion oxide hardened steels, possibly manufacture of refractory envelopes of fuel elements of fast-neutron nuclear reactors.

SUBSTANCE: method comprises steps of mixing powder of iron oxide not very stable at deformation and powder of steel alloyed with elements forming thermally stable nano-oxides; subjecting prepared mixture to mechanical alloying at intensive cold shear deformation and annealing it. Method provides possibilities for mechanically alloying steel matrix with oxygen at less degree of cold deformation.

EFFECT: shortened time period of manufacturing cycle.

2 dwg, 2 tbl

Description

The invention relates to the field of powder metallurgy, and in particular to the development of a technology for the manufacture of hardened by dispersed oxides of steel, and can be used, in particular, for the production of heat-resistant shells of fuel elements (fuel elements) of fast neutron reactors.

Currently, mechanical alloying of alloys is gaining popularity, the purpose of which, in particular, is to create oxide dispersion strengthened (ODS) reactor steels with increased strength and heat resistance characteristics (Cayron C., Rath E., Chu I ., Launois SJ Nucl. Mater. 2004. V.335. P.83-102). It is known that the creation of high-strength DUO steels requires the production of yttrium nano oxides with a diameter of several nm during annealing. This requires the preliminary dissolution of sufficiently large sparingly soluble starting Y ₂ O ₃ oxides in a steel powder matrix during cold deformation by shear under high pressure or when grinding the powder in a ball mill (Ukai S., Harada M., Okada N. et al., J Nucl. Mater. 1993. V.204. P.65; Sagaradze VV, Shalaev VI, Arbuzov VL, Goshchitskii BN, Yun Tian, Wan Qun, Sun Jiguang. J. Nucl. Mater. 2001. V.295. P. 265-272). During deformation, a large number of point defects are formed, and in iron alloys, low-temperature (~ 300 K) deformation-induced transport of atoms over distances significantly exceeding interatomic becomes possible. Subsequent heating (for example, during sintering) of steel mechanically alloyed with oxygen and yttrium leads to the release of yttrium nano oxides with a diameter of 2-4 nm, which sharply increase the strength and heat resistance of steel, since these oxides are thermally stable and do not dissolve in the matrix when heated to 1200 ° C and higher.

Closest to the claimed method is a method of producing hardened by oxides of steel, including mechanical alloying during cold deformation of a mixture of particles of oxides Y ₂ About ₃ (~ 0.4 wt.%) With an average size of 30 nm and a powder of components of ferritic reactor steel (steel matrix) 13Cr -2W-1 Ti (Shalaev V.I., Sagaradze V.V., Kochetkova T.N., Vildanova N.F., Tian Yun, Dzhiguan Sun, Chun Van. FMM. 2001. T. 91. No. 3. S.103-109). Mechanical alloying was carried out in a ball mill for a long time (48 hours) at a rotational speed of the mill drum of 150 revolutions per minute. Such deformation led to almost complete dissolution of the oxides in the ferrite matrix. This made it possible to obtain secondary Y ₂ TiO ₅ nanooxides (with a diameter of 2-4 nm and a density of 1.6 × 10 ¹⁷ cm ^-3 ) during the subsequent sintering of the powder when heated to 1000-1100 ° C under hot deformation. The release of such nano oxides led to a significant increase in the heat resistance of dispersion-hardened ferritic steel as compared to ordinary ferritic steel, as well as to an increase in the yield strength by more than 2 times - up to 515 MPa at 650 ° C.

The disadvantage of this method is the extremely long process of mechanical alloying, which requires the implementation of large degrees of cold deformation for the strain dissolution of the initial sufficiently large special oxides Y ₂ O ₃ in a steel matrix, which leads to premature damage to mills and the cost of the process of obtaining DUO-steels. Reducing the time of mechanical alloying in a mill from 48 to 36 hours causes incomplete dissolution of the starting Y ₂ O ₃ oxides (Shalaev V.I., Sagaradze V.V., Kochetkova T.N., Vildanova N.F., Tian Yun, Dzhiguan Sun , Chun Wang. FMM. 2001. T. 91. No. 3. S.103-109), which is the reason for the decrease in the number of hardening secondary yttrium nano oxides during subsequent annealing (from 0.30 to 0.06%, respectively). The latter circumstance causes a significant drop in the strength and heat resistance of the iron-based composite material reinforced with oxides.

The basis of the invention is to reduce the complexity and time of the technological process by reducing the degree of deformation during mechanical alloying, providing deformation dissolution of oxides and the formation of a solid solution of iron-oxygen.

The problem is solved in that in a method for producing an oxide-hardened composite material based on iron, comprising mechanical alloying of a mixture prepared from oxide powder and alloy steel powder, and subsequent annealing, according to the invention, an iron oxide powder which is unstable during deformation is used as an oxide powder, and as a powder of alloy steel, a powder of steel alloyed with elements forming heat-resistant nano oxides is used, and mechanical alloying is carried out at and Intense cold shear strain.

Wherein

as a powder of unstable during deformation of iron oxide, a powder of Fe ₂ O ₃ or Fe ₂ O _{4 is used} ;

using steel powder alloyed with yttrium and / or titanium, forming heat-resistant nano oxides.

The use of a powder of oxide of iron, which is unstable during deformation of iron oxide, Fe ₂ O ₃ or Fe ₂ O ₄ , instead of the previously difficultly soluble Y ₂ O ₃ oxides with a strong interatomic bond, significantly reduced the degree of deformation and, accordingly, the time of mechanical alloying required for dissolving oxides and obtaining a solid solution of iron-oxygen. The use of iron-based steel powder as alloy steel powder, previously alloyed with elements forming heat-resistant nano oxides, for example, yttrium and / or titanium, ensured the formation of secondary hardening nano oxides of the type Y ₂ TiO ₅ during post-deformation annealing, which made it possible to achieve the necessary high hardening, despite a noticeable reduction in process time.

Figure 1 shows the Mössbauer spectra of samples mechanically alloyed during cold deformation by shear under pressure (ε ~ 8) obtained from powder mixtures of 30% Y ₂ O ₃ + Fe (a) and 30% Fe ₂ O ₃ + ⁵⁶ Fe-1Y- 1Ti (b).

Figure 2 shows a dark-field image (in a composite reflex from Y ₂ TiO ₅ and Fe oxide) of the structure of the sample obtained from a powder mixture of Fe ₂ O ₃ + ⁵⁶ Fe-Y-Ti as a result of mechanical alloying by shear under pressure (ε ~ 8) and subsequent annealing at 700 ° C (an increase of 100,000).

A method of obtaining oxides hardened composite material based on iron is as follows.

As the initial powder mixture No. 1, 30 wt.% Hematite Fe ₂ O ₃ with an average particle size of 20 μm and 70% specially alloyed steel (alloy ⁵⁶ Fe-1Y-1Ti) prepared by filing from bulk samples was used. Steel was smelted based on non-resonant ⁵⁶ Fe to track the transition of ⁵⁷ Fe from oxide to alloy steel powder. A large number of oxides were used to obtain reliable Mössbauer and electron microscopy data when studying the process of mechanical alloying. For a comparative analysis of mechanical alloying according to a known technological scheme, a mixture of iron powders No. 2 with 30 wt.% Y ₂ O ₃ oxide (particle size ~ 20 μm) was used. The powder mixtures were subjected to mechanical alloying under intense cold deformation (~ 25 ° C) by shear under a pressure of ~ 8 GPa during torsion in Bridgman anvils at a speed of 1 rpm. This technique allows for very large deformation without fracture of the sample. After exposure, the sample was a monolithic disk (with a metallic sheen) with a diameter of 5-6 mm and a thickness of about 80 microns. For research, it was thinned on both sides to 30 microns or less. The number of revolutions of the anvils varied from 5 to 10, which corresponded to the true strain ε ~ 7 and ε ~ 8. The samples synthesized during deformation were investigated by Mössbauer and electron microscopy methods.

Figure 1 presents the Mössbauer spectra of shear deformed (ε ~ 8) samples No. 1 and No. 2, synthesized from mixtures No. 1 and No. 2, respectively. As can be seen from figa, the spectrum of the deformed (at 10 revolutions anvil) sample Fe + 30% Y ₂ About ₃ differs little from the spectrum of deformed iron, which indicates the practical absence of the process of dissolution of yttrium oxide in the Fe matrix under these deformation conditions. The spectrum of the deformed sample ⁵⁶ Fe-1Y-1Ti + 30% Fe ₂ О _{3 is} completely different (Fig. 1b), which indicates the decomposition and deformation dissolution of unstable iron oxide in the iron matrix with the formation of solid solutions “ ⁵⁶ Fe- ⁵⁷ Fe”, “ iron-oxygen "and some secondary iron oxides. A similar spectrum is also observed after deformation of the sample with a lesser degree (ε ~ 7 at 5 revolutions of the anvil).

The formation of an iron-oxygen solid solution during cold deformation and its subsequent decomposition during annealing (700 ° C) is confirmed by electron microscopy in the study of a sample mechanosynthesized from a mixture of ⁵⁶ Fe-1Y-1Ti + 30% Fe ₂ O ₃ . Figure 2 presents a dark-field image of the structure in the composite reflex from the oxide Y ₂ TiO ₅ and from the matrix (110) αFe. The presence of secondary extremely dispersed Y ₂ TiO ₅ nanooxides with a size of ~ 3-4 nm indicates the interaction of oxygen dissolved during deformation with yttrium and titanium atoms during annealing. As can be seen from Table 1, in the electron diffraction patterns one can find almost all fairly intense reflections close to reflections from the complex oxide Y ₂ TiO ₅ . Reflections from the iron matrix and from oxides Fe ₂ O ₄ , Fe ₂ O ₃ , FeO are also observed.

Thus, the use of iron oxides that are not very resistant to deformation (instead of yttrium oxides) allows mechanical alloying of the alloy steel powder with oxygen at a lower degree of cold deformation, which accelerates and reduces the cost of the process of producing dispersion-hardened steel oxides.

Table 1
Experimental (TEM) and tabular data on interplanar distances d (Å) of phases in the Fe ₂ О ₃ + ⁵⁶ Fe-1Y-1Ti alloy after shear deformation (ε ~ 8) and subsequent annealing at 700 ° С. d _exp. d _table , α Fe d _table , Fe ₂ About ₃ d _table Fe ₃ O ₄ d _table FeO d _table , Y ₂ TiO ₅ 5.42 5.17 4.83 4.85 4.11 3.77 3.81 3.48 3.53 3.01 3.01 2.82 2.96 2.94 2.66 2.69 2.63 2.51 2.52 2.53 2.52 2.46 2.47 2.32 2.30 2.28 2.29 2.22 2.21 2.15 2.10 2.15 2.02 2.03 1.88 1.84 1.74 1.71 1.67 1.65 1.61 1.61 1.60 1.51 1.48 1.51 1.50 1.41 1.43

Table 2 gives information on the amount of yttrium-titanium nanooxides in mechanically alloyed steels obtained by the well-known and proposed technological schemes for producing DUO steels. Here are approximate calculated values of the yield stress increase σ _0.2 as a result of dispersion hardening. It can be seen that cold deformation ε = 7–8 is sufficient for dissolving Fe ₂ О ₃ oxides that are unstable to deformation in the Fe matrix, subsequent formation of Y ₂ TiO ₅ nano oxides upon annealing, and steel-hardened steel by the proposed technological scheme. To dissolve the stable oxides of Y ₂ O ₃ and obtain a hardened DUO of steel, this degree of deformation ε = 8 is not enough.

table 2
Characteristics of nano oxides and calculated values of hardening in steels obtained by mechano-alloying from different powders. The original powder mixture The degree of deformation ε during mechanical alloying The average size of reinforcing nano oxides, nm Density of nano oxides after annealing, cm ^-3 Estimated increase Δσ _0.2 , MPa 30% Y ₂ O ₃ + Fe 8 four Less than 10 ¹⁵ Less than 35 30% Fe ₂ O ₃ + ⁵⁶ Fe-1Y-1Ti 7-8 four ~ 1.3 × 10 ¹⁷ ~ 350

Claims (3)

1. A method of producing an oxide-hardened composite material based on iron, comprising mechanically alloying a mixture prepared from an oxide powder and an alloy steel powder, and subsequent annealing, characterized in that an iron oxide powder which is unstable upon deformation is used as an oxide powder, as an alloy powder steel use steel powder alloyed with elements forming heat-resistant nano oxides, and mechanical alloying is carried out under intense cold shear deformation. 2. The method according to claim 2, characterized in that a powder of Fe ₂ O ₃ or Fe ₂ O ₄ is used as a powder of low stability during deformation of iron oxide. 3. The method according to claim 1, characterized in that they use a powder of steel alloyed with yttrium and / or titanium, forming heat-resistant nano oxides.

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