2023 Volume 64 Issue 7 Pages 1410-1418
It has been reported that severely cold worked Fe–24.6Ni–5.8Al–0.4C (mass%) had a yield strength of 2 GPa and a fracture elongation of 20%, in which huge amount of Lüders-type deformation was observed. In the present article, we summarize the reports for high-strength Fe–Ni–Al–C, Fe–Mn, Fe–Cr–Ni and Fe–Ni–Mn base steels with the Lüders-type deformation so far, and provide our latest data on the effects of alloying elements and the cold-rolling reduction on the microstructure and mechanical properties of cold-rolled Fe–Ni–Al–C alloys. Previous reports imply that the phase stability of γ phase affects the size of Lüders elongation, while the strategies to control the microstructure to achieve high strength and high ductility are currently unknown. Our latest study also shows that the γ-phase stability affects the Lüders strain. In addition, it is confirmed that severe cold rolling by 80% enables the prolonged Lüders strain as much as 25% in nominal strain. This prolonged Lüders strain is achieved by multiple propagation of Lüders-type bands.
Fig. 8 Stress-strain curves obtained by tensile tests for 5.0Al specimens.
In recent years, there has been a growing demand for light-weight materials in terms of efficient use of resources and energy. Weight reduction decreases the energy required for movement in applications for automobiles, so it is effective to use ultrahigh-strength steels as a structural material for automobiles to reduce weight while maintaining stiffness and strength required for driving performance and crash safety. However, it is generally believed that there is a trade-off between strength and ductility in high-strength metallic materials; the steels with higher strength have lower ductility. Under such circumstances, Furuta et al. reported in 2015 that severely cold worked Fe–24.6Ni–5.8Al–0.4C (mass%) had a yield strength of 2 GPa and a fracture elongation of 20%,1) which attracted attention since such combination of strength and ductility exceeds the conventional trade-off. In relation to these mechanical properties, they also reported that the Lüders-type band propagates multiple times during tensile tests, resulting in high ductility.
After the first report by Furuta et al., several high-strength steels, Fe–Ni–Al–C, Fe–Mn, Fe–Cr–Ni, Fe–Ni–Mn base ones, have been reported to show the similar Lüders-type deformation when they were processed with cold working.2–12) In these reports, it has been shown that the chemical composition and the processing conditions affected austenite (γ) stability, microstructure formation behavior, and other metallographic factors. However, the relationship between Lüders-type deformation and mechanical properties has not been well understood.13) We think that clarifying the mechanism for high strength and high ductility with Lüders-type deformation in these steels is essential for the development of novel practical steels with high strength and high ductility.
In the present article, we summarize the reports for the Lüders-type deformation in high-strength Fe–Ni–Al–C, Fe–Mn, Fe–Cr–Ni, Fe–Ni–Mn base steels1–12) so far. However, the conditions that allow the Lüders deformation to continue until the later stage of plastic deformation have not been clarified yet. This is because there have been only a limited number of reports in which the chemical compositions and the processing conditions were systematically varied. So, we also provide our latest data on the effects of alloying elements and the cold-rolling reduction on the microstructure and mechanical properties of Fe–Ni–Al–C alloys and discuss mechanisms for deformation behavior with Lüders-type deformation to obtain a clue to develop novel high-strength steels.
Furuta et al. designed the alloy composition of Fe–24.6Ni–5.8Al–0.4C1) by considering the phase stability, where they controlled the averaged valence electron number to generate lattice softening.13) Lattice softened alloys, Ti–Nb–Ta–Zr–O,14–17) and the Fe–Ni–Co–Ti18,19) base alloys, have been reported to have high strength and high ductility by applying severe plastic deformation. The crystal structure of these two lattice-softened alloys is bcc or fcc, although a part of the specimens transforms during severe cold working. The mechanical properties can be related to averaged valence electron number which determine the elastic properties.13) On the other hand, Fe–Ni–Al–C alloys often have two phases, fcc (γ) and bcc (α′), in which the mechanical behavior cannot be understood only by averaged valence electron number. Therefore, we must evaluate the volume fraction of the γ phase and the γ phase stability and discuss the relation between such information and mechanical behavior. From this viewpoint, the results of previous reports are summarized in this section.
2.1 Summary of the recent results for Fe–Mn, Fe–Cr–Ni and Fe–Ni–Mn base steelsTable 1 shows a list of the selected reports1–12) of high-strength steel with Lüders-type deformation, in which relatively high amount of Lüders strain is observed. Also, typical mechanical properties and Lüders deformation behavior in these reports are summarized in Fig. 1. Figure 1(a) shows the relationship between tensile strength and total elongation, while Fig. 1(b) shows the relationship between stress of Lüders deformation, σL, and Lüders strain. There is no clear correlation between σL and Lüders strain. If we focus on the shape of the stress-strain curves during tensile testing, we found that the Fe–Ni–Al–C,1,2,4,7) Fe–Cr–Ni8,9) and Fe–Ni–Mn12) steels, with relatively large Lüders strain, do not show significant strain hardening after the Lüders deformation, while the Fe–Mn steels,3,6,10,11) with smaller Lüders strain, shows a large hardening after the Lüders deformation. Here, we will summarize the information in previous reports on Fe–Mn, Fe–Cr–Ni and Fe–Ni–Mn base steels with a focus on Lüders deformation and mechanical properties.
Mechanical properties and Lüders deformation behavior in the literature, where the number indicated at each plot corresponds to the alloy number shown in Table 1. (a) Total elongation vs. UTS, (b) Lüders strain vs. stress of Lüders deformation, σL. ●: Fe–Ni–Al–C,1,2,4,7) ○: Fe–Mn,3,5,6,10,11) △: Fe–Cr–Ni,8,9) ×: Fe–Ni–Mn.12)
There have been several reports on Fe–Mn base steels, in which Lüders strain is always below 10%. Wang et al.3) visualized the Lüders band in Fe–7Mn–0.14C–0.23Si by temperature measurement and found strain induced martensitic transformation by the band propagation. He et al.5) changed the time for heat treatment at 400°C after cold rolling in Fe–10Mn–0.4%C–2Al–0.7V and reported that the strength decreased and the Lüders strain increased with longer heat treatment time. Zhang et al.6) studied the mechanical properties and Lüders deformation behavior in Fe–7Mn–0.14C–0.2Si cold-rolled and annealed, and found that the grain size of ferrite (α), which was 0.93 µm in the sample heat treated for 3 min at 620°C, became as large as 2.54 µm after 96 hours of heat treatment, while the strength decreased from 1046 MPa to 630 MPa. They also reported that the Lüders strain reached its maximum with a heat treatment for 3 min at 620°C. In addition, they also examined the effect of the test temperature on mechanical properties and found a large Lüders strain at the temperature ranging from 25 to 60°C. Koyama et al.10) showed that a large amount of γ is transformed into martensite (α′) during the Lüders deformation in Fe–5Mn–0.1C, and that the α phase does not contribute to Lüders deformation. They also examined the effect of strain rate in the range of 10−2 to 10−5 s−1 and found that the strain rate had no effect on Lüders strain. Koyama et al. further studied the details in Lüders band in Fe–5Mn–0.1C in another paper11) and found the precursor phenomenon of the band propagation and propose a model for discontinuous band propagation. In addition to the ones mentioned above, several reports have been made on the Lüders deformation in Fe–Mn base steels.20–25)
Regarding Fe–Cr–Ni base steels, Gao et al.8) visualized the bands at the onset of Lüders deformation by digital image correlation (DIC) analysis in Fe–18.16Cr–8.06Ni–0.85Mn–0.41Si–0.06C and found that the transformation from γ to α′ occurred by band propagation. It is noted that Lüders strain in their specimen is as much as 30%. Hosoya et al.9) performed heat treatment at 300, 400, and 500°C after cold rolling by 97% in Fe–16.8Cr–4.7Ni–0.67Mn–2.7Mo–0.38Si–0.08C–0.1N and found that both strength and elongation showed maximum values in the specimen heat treated at 400°C. Other reports have been also made on the Lüders deformation in Fe–Cr–Ni base steels.26,27)
Recently, an Fe–Ni–Mn base steel12) has been reported to show similar mechanical behavior to Fe–Ni–Al–C. Du et al.12) performed heat treatment at 300°C after cold rolling by 50% in Fe–10Ni–2Mn–0.4C–1.6Si and found that the specimen showed high strength and good elongation with Lüders strain of 8%. Some other reports have been made on the mechanical behavior of this Fe–10Ni–2Mn–0.4C–1.6Si steel.28–31)
The above results on Fe–Mn, Fe–Cr–Ni and Fe–Ni–Mn base steels are informative since they show the influence of the heat treatment conditions after cold working on the mechanical properties or the behavior of the Lüders bands and the possibility of the importance of stability of the γ phase in the Lüders deformation behavior and mechanical properties. However, the influence of various factors on the magnitude of Lüders elongation and the strategies for controlling the microstructure to achieve high strength and high ductility have not yet been elucidated.
2.2 Reports on Fe–Ni–Al–C alloysAs shown in Fig. 1, the severely cold worked Fe–Ni–Al–C base steels are characterized by both high strength and high ductility, as well as a high ratio of Lüders strain to total elongation, compared to the other steels. Results of previous reports on the Fe–Ni–Al–C base steels are summarized here. Ma et al.4) reported that the strength increased with increasing cold rolling reduction, 50, 70 and 90%, but elongation did not decrease; this result is almost identical to the one by Furuta et al. Ma et al. also visualized the Lüders band by DIC analysis. The samples used by Furuta et al.1) and Ma et al.4) contained a second phase (B2 phase) particles of Fe–Ni–Al, and they are considered to exert some effects on the mechanical properties or Lüders deformation. Miyazaki et al.7) investigated the effect of cold rolling reduction and test temperature on the deformation behavior of Fe–24.1Ni–4.06Al–0.43C, which has no B2 phase because of low amount of aluminum. Their tensile tests revealed that γ phase after cold working is thermally stable and plastically unstable and the deformation-induced transformation was assisted by the simultaneous occurrence of mechanical twinning due to its contribution to the relaxation of the constraints to the martensite phase. In addition, they also found a significant effect of test temperature on Lüders deformation behavior. Furuta et al.32) observed the deformation microstructure of cold-rolled Fe–24.1Ni–4.06Al–0.43C and reported that the heterogeneous microstructure in the alloy exhibited a mixture of four kinds of morphology, formed through different deformation processes activated by the specific phase stability with the lattice softening. Kaveh et al.2) studied the effect of test temperature on the deformation behavior of a specimen with the same composition as that of Furuta et al.1) which were subjected to high-pressure torsion and reported tensile strengths of 1.9–2.2 GPa and elongations of 16–19%.
Figure 1 shows that the Fe–Ni–Al–C base steels, to which only severe cold working is applied, are stronger and more ductile than the other steels cold-worked and subsequently heat-treated. Therefore, heat treatment after severe cold working is not required for high strength and high ductility, at least in Fe–Ni–Al–C steels. However, the results of Miyazaki et al.7) show that γ stability affects deformation behavior, and it is expected that heat treatment after severe cold working will also affect deformation behavior in the Fe–Ni–Al–C steels. At present, there are no reports where such an investigation has been conducted, and future studies are required.
Besides the above reports on high-strength steels, the factors affecting Lüders deformation behavior, such as grain size, dislocation density and solute atoms, have been reported so far in various kind of steels.33–36) However, there have been no reports on the effects of such factors on Lüders deformation behavior in Fe–Ni–Al–C steels. In this section, some latest results of an investigation on the effects of aluminum addition and cold rolling on the mechanical properties and deformation behavior with Lüders deformation of Fe–Ni–Al–C base steels.
Alloys with the chemical compositions shown in Table 2 were melted and cast and hot rolled at 1100°C. After solution treatment at 1100°C for 1 h and water quenching, the plate specimens were cold rolled by 60%. In addition, the 5.0Al alloy was cold rolled by 20%, 40% and 80% to study the effect of cold rolling reduction on mechanical behavior. Tensile test specimens with a gage length of 12 mm and a width of 5.0 mm were prepared with the tensile axis parallel to the rolling direction. The tensile test was conducted in air at an initial strain rate of 1.38 × 10−4 s−1. For DIC analysis, a black-and-white random pattern was applied to the gage section of the test pieces, and static images were recorded every second during the tensile test. Microstructure was analyzed by X-ray diffraction and volume fraction of the α′ phase was measured by FERITSCOPE FMP30, Fischer. The texture developed by cold rolling and change in grain orientation during tensile deformation was analyzed on the 5.0 Al sample using electron backscatter diffraction (EBSD).
Figure 2 shows the volume fraction of B2 phase before cold rolling; higher aluminum content increases the B2 volume fraction. Figure 3 shows the effect of cold rolling reduction on the volume fraction of α′, which indicates the α′ volume fraction increased due to rolling in all the three alloys. The larger the Al content, the larger the increase in the volume fraction of the α′ phase due to cold rolling. This may be because the larger volume fraction of B2 phase, which contains larger amount of nickel atoms than the matrix, decreased the stability of the γ phase.
Second phase volume fraction before cold rolling.
Effect of cold rolling reduction on α′ volume fraction.
Figure 4 shows tensile stress-strain curves of the specimens after cold rolling by 60%, and a-n represent points where Lüders type deformation was confirmed by DIC analysis. The 5.0Al specimen has a yield point of about 1000 MPa and a total elongation of about 39%, and the 5.5Al specimen with higher amount of aluminum, has higher strength and lower ductility. In 6.0Al, higher deformation stress was found after the yield point drop, but it fractured in lower strain.
Stress-strain curves obtained by tensile tests for specimens rolled by 60%.
The maps for local strain distribution obtained by DIC analysis at a-n in Fig. 4 are shown in Fig. 5, and the profiles for local strain along the center line parallel to tensile axis in gage section at each point, a-n, in the stress-strain curves are shown in Fig. 6. In 5.0Al–60%CR (Fig. 6(i)), the local strain increases near 10 mm of the gage section at point a, after the yield point drop, and the local strain profile changes as the nominal strain increases to point c; the local strain increases and the deformation area expands over the entire test specimen, indicating that typical Lüders-type deformation proceeds. In 5.5Al–60%CR (Fig. 6(ii)), a Lüders-type band was formed at point g after the yield point drop and the profile change to the points at j and k is similar to the Lüders band propagation observed in 5.0Al–60%CR specimen. In 6.0Al–60%CR (Fig. 6(iii)), a Lüders-type band was formed at point l after the yield point drop, but after the band expanded to point n, it started to deform uniformly and fractured in lower strain. Figure 7 shows the volume fraction of the α′ phase before and after the tensile test for 5.0Al and 6.0Al, respectively, and it looks that the α′ volume increase rate during tensile test is larger in 6.0Al specimen.
DIC local strain maps captured at nominal strains shown in Fig. 4 in 5.0Al–60%CR (a)–(f), 5.5Al–60%CR (g)–(k), 6.0Al–60%CR (l)–(n).
Local strain profiles along tensile axial in the gage section of the specimens in 5.0Al–60%CR (i), 5.5Al–60%CR (ii), 6.0Al–60%CR (iii).
Effect of 60% cold rolling on α′ volume fraction.
Figure 8 shows tensile stress-strain curves for the 5.0 Al specimens cold rolled by 20, 40, 60, 80%. The result of specimen before cold rolling is also shown in the figure. The yield point is about 800 MPa and the total elongation is about 34% in the 20% rolled specimen. The strength of the rolled specimens increased with rolling reduction, but there was no significant loss of ductility. The specimen before rolling uniformly deformed to failure, whereas the rolled specimens exhibited Lüders-type bands after the yield point, which spread over the entire test specimen.
Stress-strain curves obtained by tensile tests for 5.0Al specimens.
The strain range of Lüders-type band propagation determined by DIC analysis, similar one such as shown in Figs. 5 and 6, is indicated by arrows with dashed line in Fig. 8. The specimens cold-rolled by 20% and 40% show Lüders-type band propagation and after the band spread out entire gage section, uniformly deformed with work hardening and fracture. On the other hand, the specimen cold rolled by 60% showed multiple occurrences of bands after uniform deformation, and it is noted that the specimen cold rolled by 80% does not show uniform deformation; the Lüders-type band propagation is continuously observed until fracture.
The relation between α′ volume fraction and local strain for the cold rolled 5.0 Al specimens is shown in Fig. 9, where the results of specimens before cold rolling is also shown. In all samples, the α′ volume fraction increased with increasing local strain. It can also be confirmed that the α′ volume fraction in the region before Lüders band propagation does not increase even the local strain increases.
Effect of local strain on α′ volume fraction for 5.0Al specimens.
Figure 10 shows the IPF maps and inverse pole figures of the γ and α′ phases of the 5.0 Al specimens before rolling, cold rolled by 20%, and cold rolled by 60%, respectively, before the tensile test. In the γ-phase after 20% rolling, the texture development of {101}⟨001⟩ γ (Goss orientation) and {101}⟨111⟩ γ was observed, which was not observed before rolling. In addition, the development of {101}⟨112⟩ γ (Brass orientation) was observed in the γ-phase after 60% rolling. This tendency of texture evolution is similar to the previous report in cold-rolled SUS304 steel.37) Regarding α′ phase, preferential orientation ⟨111⟩ along ND were observed after 20% rolling, while α′ grains were not observed after 60% rolling. This may be because the α′ phase generated by additional cold rolling is fragmentated by severe deformation, so the resolution of the present measurement is not enough.
Inverse poles figures maps obtained by EBSD analysis before cold rolling for 5.0Al specimens: (i) γ-ND, (ii) γ-RD, (iii) α′-ND, (iv) α′-RD, 20%CR: (v) γ-ND, (vi) γ-RD, (vii) α′-ND, (viii) α′-RD, 60%CR: (ix) γ-ND, (x) γ-RD, (xi) α′-ND, (xii) α′-RD.
Figure 11 shows the IPF maps and inverse pole figures of the γ and α′ phases at band initiation and after fracture in the tensile specimens of 5.0 Al alloy cold rolled by 20% and 60%, respectively. The deformation texture ⟨111⟩ γ // RD (= Tensile axis) were observed with tensile deformation in both specimens. Transformation from γ to α′ of ⟨001⟩ γ // ⟨101⟩ α′ // RD (= Tensile axis) was observed in the band at the initiation of Lüders-like deformation and that of ⟨112⟩ γ // ⟨112⟩ α′ // RD (= Tensile axis) after the fracture in both specimens.
Inverse poles figures maps obtained from RD by EBSD analysis for 5.0Al specimens after tensile deformation of 20%CR after Lüders-like deformation (i) γ-RD, (ii) α′-RD, after fracture, (iii) γ-RD, (iv) α′-RD, and 60%CR after Lüders-like deformation (v) γ-RD, (vi) α′-RD, after fracture (vii) γ-RD, (viii) α′-RD.
Based on the literature survey and the results in the previous section, factors affecting the microstructure and mechanical properties and Lüders-like deformation behavior in the cold rolled specimens are discussed.
The volume fraction of the second phase increases with aluminum content (Fig. 2), and that higher volume fraction of the second phase decreases the nickel content in the matrix, resulting the lower γ stability and the higher susceptibility to transformation from γ to α′ during cold rolling (Fig. 3). The γ to α′ transformation rate during tensile deformation also increases with increasing aluminum content (Fig. 7). As a result, higher aluminum content increases yield strength and decrease elongation due to high volume fraction of α′, while the presence of the second phase is also considered to increase strength and decrease ductility. The deformation stress would affect the transformation from γ to α′ during tensile deformation, so we will pay attention to γ stability and applied stress level in the following discussions.
Figures 4, 5, and 6 show that all the specimens rolled by 60% showed deformation with a Lüders-type band after the yield point. Comparing the tensile behavior of 5.0 Al and 5.5 Al specimens after the yield point, with large total elongation of 35% or more, the amount of deformation with a Lüders-type band is smaller in 5.5 Al specimen with higher aluminum content. This suggests that the lower γ-phase stability in this specimen reduces the Lüders strain. This tendency coincides with the previous report by Zhang et al.6) Regarding the γ phase in 6.0 Al specimen with the lowest stability among the present specimens, it is easy to transform to α′ martensite during tensile deformation, leading to premature rupture after small amount of uniform deformation before the second Lüders deformation starts.
The result in Fig. 4 also implies that higher strength level reduces Lüders strain, but there are examples in which higher strength specimens show larger Lüders strain, as shown in tensile stress-strain curves, Fig. 8. It can be seen from Fig. 8 that the Lüders deformation continues to nominal strain of 25% in the 80% rolled specimen. This prolonged Lüders strain is considered to have some relation to the superior combination of high strength and high ductility in the severely cold rolled Fe–Ni–Al–C steels. The analysis of strain distribution by DIC and microstructure evaluation by EBSD in 5.0 Al specimens with different rolling reduction showed that cold rolling affects the volume fraction and distribution of α′ phase and texture development, which in turn affect tensile deformation behavior and mechanical properties.
The authors consider that there exists a specific phase stability of γ phase and deformation texture which enables to maintain stable and prolonged Lüders deformation. The stable Lüders deformation suppresses subsequent uniform deformation with large work hardening, which rises the deformation stress and promote premature fracture. In addition to {101}⟨001⟩ γ (Goss orientation), {101}⟨112⟩ γ (Brass orientation) was observed in the 60% rolled specimen, while {101}⟨112⟩ γ (Brass orientation) was not observed in the 20% rolled one. The texture suggests that the development of the Brass orientation promotes the Lüders deformation behavior. However, the effect of texture cannot be confirmed from the results shown here. Further study is required to understand the deformation texture which develops during severe cold working.
The other factors, grain size, strain rate, temperature, etc., should be studied further to determine the mechanism for the Lüders deformation behavior and mechanical properties. Gao et al.8) found large Lüders strain in the ultrafine-grained Fe–18.16Cr–8.06Ni–0.85Mn–0.41Si–0.06C steel and Furuta et al.1,32) also reported the microstructure of their specimens has been refined during severe cold working and deformation microstructure is quite complicated. Regarding the effect of strain rate, Koyama et al.10) reported that strain rate of tensile tests does not affect tensile deformation behavior, including Lüders deformation, in the range of 10−2 to 10−5 s−1 in Fe–5Mn–0.1C. However, the results would be different in the other steels with different γ stability, or in the different range of strain rate. Koyama et al.11) also performed a detailed study on the propagation of the Lüders band. They have proposed a model for discontinuous band propagation based on their analysis of distribution of both strain and strain rate during Lüders deformation. Such detailed study will be also required for Fe–Ni–Al–C specimens to clarify the mechanisms for the Lüders deformation and mechanical properties. The Lüders deformation in low carbon steels is usually explained as discontinuous yielding with the dislocation locking mechanism by Cottrell atmosphere formed by interstitial atoms. Although the present Fe–Ni–Al–C steels have interstitial carbon, this simple mechanism cannot explain multiple propagation of Lüders-type bands in the Fe–Ni–Al–C steels. Besides the above mechanism of dislocation locking by interstitial atoms, the Lüders deformation has also been found in ultrafine grained materials including pure metals38–43) and alloys,44,45) which do not usually show the yield point phenomenon in coarse grain sizes. In these ultrafine grained materials, the discontinuous yielding is attributed to the lack of initial mobile dislocations in the annealed ultrafine grained materials.46) On the other hand, the dislocation density in the cold rolled Fe–Ni–Al–C would be significantly higher than the annealed ultrafine grained materials. It has been reported that severe plastic deformation introduces peculiar type of lattice defects,47,48) segregations,49) phase transformations50,51) and rearrangement of solute atoms52) which affect the mechanical or functional properties. The microstructure in the cold rolled Fe–Ni–Al–C specimens is very fine and complicated, so the further investigation on the effect of such microstructure on the discontinuous yielding is required in future.
Finally, the effect of temperature is quite important because γ stability against deformation changes by temperature. Zang et al.6) have reported the effect of test temperature on the deformation behavior in Fe–7Mn–0.14C–0.2Si in the range of −80 to 120°C, and Miyazaki et al. also have reported the effect of test temperature in the range of −30 to 90°C. In a practical sense, the mechanical properties should be optimized for the service at room temperature and the γ stability should be tuned not to be sensitive to deformation temperature. Recently, it has been reported that 92% cold-rolled Fe–17.8Cr–11.1Ni–2.52Mo–0.86Mn–0.18N had a yield strength of 2.2 GPa and a fracture elongation of 50%, with a prolonged Lüders strain at −196°C.53) Although, this specimen does not show high strength and large Lüders strain at room temperature,54) the optimized control of alloy compositions and process conditions would enable the improvement in the mechanical properties of Fe–Cr–Ni base steels at room temperature.
This paper summarizes the previous reports on Fe–Ni–Al–C, Fe–Mn, and Fe–Cr–Ni base high-strength steels with large Lüders strain processed with severe cold working, and also provide the latest experimental results by the present authors to discuss the effects of alloy compositions and cold rolling reduction on the Lüders-type deformation behavior and mechanical properties of Fe–Ni–Al–C alloys, which has the best strength-ductility balance among three steels. The influence of various factors on the deformation behavior is discussed and summarized as follows.
The results of this research were supported by the Iketani Science and Technology Foundation.
