Kurdjumov-Sachs Orientation Relationship Research Articles

Unique Microstructure Evolution of HPT-Processed (α + γ) Two-Phase Stainless Steel

A high-pressure torsion (HPT) processed Fe-21Cr-5Ni-2Mo (mass%) two-phase stainless steel was used to study the morphology and crystallographic features of austenite (γ) precipitated from ferrite (α) during aging in the (α + γ) two-phase region. The starting material was a gas-atomized powder with a completely ferritic structure. The HPT process was carried out to produce a fully dense compact under 6 GPa for 5 revolutions. The compact was given an equivalent strain of about 130. After the HPT process, the matrix ferrite formed a pancake–like nanograined structure with a strong texture, i.e. ND (Normal Direction) // {110} α. By annealing at 1173 K for 3.6 k, an ultrafine (α + γ) microduplex structure with high-angle grain boundaries was formed. In addition, the strong texture formation of {110} α / {111} γ / ND plane was formed in the α and the γ grain duplex structure. The α and γ phases had average grain sizes of 2.1 μm and 1.6 μm, respectively. The area fraction of the γ phase was 37.2%, which exceeded that of a cold-pressed compact, 6.7%. Both ultrafine grain refinement and γ precipitation were accelerated by the HPT process. In other words, the application of the HPT process to the two-phase alloys enables the formation of the ultrafine microduplex structure. The Kurdjumov-Sachs (K-S) orientation relationship between α and γ phases is usually observed in the alloy, however, the K-S orientation relationship was not dominant except for the close packing plane parallel orientation relationship, {110} α / {111} γ, in the HPT-processed material.

Effects of additive manufacturing process parameters and heat treatment on texture evolution and variant selection during austenite-martensite transformation in 18%Ni-M350 maraging steel

Variant selection and texture evolution of 18%Ni M350 maraging steel produced by laser-based directed energy deposition (DED) additive manufacturing (AM) technology are investigated in this study. The effects of heat treatment and AM processing parameters, including energy area density (EAD), powder feed rate, and laser power, on variant selection and texture evolution are discussed. Theoretically, 24 martensite variants tend to be formed during a cubic-to-cubic transformation based on the Kurdjumov–Sachs orientation relationship. Identifying the preference of variants in a thermo-mechanical process can pave the way for tailoring the desired product texture. Grain graph and local neighbor voting algorithms using measured electron backscatter diffraction (EBSD) were employed to reconstruct the parent austenite grain structure in this study. Even though no evidence of global variant selection is found, the variant selection tends to take place locally in small parent grains of heat-treated samples. Strong rotated Copper 112110γ and Z 111110γ components are observed in the parent austenite phase of the low EAD sample after heat treatment due to a high degree of recrystallization and second-order twins. A Goss texture 110001α in child martensite transitioned from these strong components is also observed to be strongly derived from packet 3 of this sample. This finding indicates that some low-misorientation variants of packet 3 are more energetically favorable to develop in a heat-treated M350 alloy produced by a low EAD.

Effect of ferrite morphology on pitting corrosion resistance of austenitic stainless steel weld metals

The effect of the ferrite morphology on the pitting corrosion resistance of austenitic stainless steel weld metals solidified with primary ferrite was investigated. Most of the pitting corrosion occurred at the interface between ferrite and austenite—particularly at the vermicular ferrite/austenite interface; less pitting corrosion occurred at the lacy ferrite/austenite interface. This was because a Kurdjumov–Sachs orientation relationship was established between lacy ferrite and austenite. Consequently, Cr carbide was less likely to precipitate owing to the low interfacial energy, and the lacy ferrite/austenite interface was less likely to be an initiation site of pitting corrosion.

Design of a novel (CoCrNi)84.5Al15.5 eutectic medium-entropy alloy with hierarchically nano-lamellar microstructure through additively manufactured compositionally graded materials

Eutectic medium/high-entropy alloys (E-M/HEAs) exhibit excellent castability and mechanical properties. This present work developed a novel CoCrNiAl based E-MEAs through a high-throughput method based on compositionally graded materials by laser directed energy deposition. The microstructure in the CoCrNiAlx (x ≈ 0−0.8) compositionally graded alloy changed from columnar to equiaxed with increasing Al content, and the fraction of body-centered cubic (BCC) phase increased simultaneously. Especially, a eutectic lamellar microstructure with face-centered cubic (FCC) and ordered BCC (B2) was obtained when the Al content reached 15.5 at%, and it showed a better strength-ductility combination than other reported cast eutectic alloys. The mechanical-property improvement of this novel E-MEA is related to its hierarchically nano-lamellar microstructure, in which the orientation relationship (OR) between FCC and B2 lamellae conforms to the Kurdjumov-Sachs OR, and spherical BCC and ordered FCC phases precipitate from B2 and FCC lamellae, respectively. Furthermore, the fracture mechanisms of this novel E-MEA were also investigated by in-situ tensile test and transmission electron microscope, indicating that the crack modes were closely related to the eutectic lamellar direction relative to the tensile axis, and the considerable ductility stemmed from the cooperative deformation between FCC and B2 phases caused by various deformation mechanisms.

Directed laser deposition of super duplex stainless steel: Microstructure, texture evolution, and mechanical properties

Microstructure and texture evolution of directed-laser deposited super-duplex stainless-steel, in the as-received block, were characterized using light and electron microscopies and electron backscattered diffraction. Mechanical properties in different directions were studied. Local FCC-depleted and FCC-rich zones and extensive precipitation of oxides were detected at the matrix wherein the different types of reformed austenite were surrounded by the elongated coarse ferrite. A vertical gradient of austenite content, caused by overall change in cooling rate, generated a waning hardness distribution along the building direction. The texture of austenite across the different deposition layers was not as intense as that of the ferrite. A dominant ⟨001⟩ ⫽ND fibre, embedding strong Cube {001}⟨100⟩, was calculated for ferrite on the layer away from the bottom while the Goss {011}⟨100⟩ appeared in the layer near the building substrate due to the considerable epitaxially developed grains. The less intensified multi-component texture of austenite at the layer near the substrate changed to ⟨011⟩ ⫽ND fibre adorned by Rotated-Goss and Goss components at the upper layers where an incomplete fibre {001}⟨uvw⟩ with a major Rotated-Cube was also partially inherited from the parent phase. The inter-phase boundaries obeying Kurdjumov-Sachs orientation relationship were predominantly formed at all layers. A slight increase of Σ3 coincidence site lattice interfaces was observed in austenite across the build direction. The possible mechanical anisotropy was depressed due to complex and multi-component transformation texture of the austenite. The material showed brittleness corresponding to significantly high tensile strength and low impact toughness.

Revealing the phase-transformation path in a FeCoNiSnx eutectic high entropy alloy system by crystallographic orientation relationships

High entropy alloys are the focus of current research. An accurate description of their phase-transformation path, however, is a challenge when their phase constituent and transformation process are complex. In this study, a FeCoNiSnx eutectic high entropy alloy (EHEA) system was investigated and a novel FeCoNiSn EHEA composed of BCC + HCP phases was reported. The transition from the hypoeutectic to the fully eutectic and then to the hypereutectic microstructure with the Sn addition was characterized by the electron backscatter diffraction (EBSD) technology, and the phase-transformation path was clarified by crystallographic orientation relationships. The studies reveal that the primary phase of FeCoNiSnx (x = 0.2, 0.4) is FCC structure, and a further Sn addition induces an obvious phase-transformation from FCC to BCC in both the primary phase and eutectic lamellar, which satisfies the Kurdjumov-Sachs (K-S) or Nishiyama-Wasserman (N-W) variant orientation relationship. The mechanical results confirm that the phase structure and microstructure transition caused by Sn addition do significantly improve the strength and hardness of FeCoNiSnx EHEAs, but have serious adverse effects on plasticity. This study would be of significance to understanding the phase-transformation process in HEAs and preparing the HEAs with aimed mechanical properties.

A microstructure-based three-scale homogenization model for predicting the elasto-viscoplastic behavior of duplex stainless steels

A new microstructure-informed three-scale homogenization scheme for elasto-viscoplastic heterogeneous materials is developed. It is applied to predict the mechanical behavior of cast duplex austenitic-ferritic (AF) steels, which are widely used in primary loop of pressurized water reactors (PWR). At the first scale (microscale), the elasto-viscoplastic behavior of single crystals for both phases is modeled using linear elasticity and a viscoplastic crystal plasticity model. An “affine” type formulation based on the first moments of stresses is applied to the inelastic non-linear part of the deformation. Then, at the second scale (mesoscale), an EBSD-informed two-phase austenite/ferrite laminate structure (LS) model is developed with {110}-type habit planes (HP) in ferrite and a Kurdjumov-Sachs orientation relationship (KS-OR) between both phases. At the third scale (macroscale), the model considers a single ferritic primary grain as an aggregate of spherical two-phase laminate structure domains corresponding to the 24 KS-OR variants. The elasto-viscoplastic self-consistent scheme (EVPSC) is used through the Translated Fields (TF) method to obtain the effective behavior at this scale. The TF-EVPSC scheme is also used for an ensemble of primary ferritic grains to identify materials parameters from experimental tensile curves corresponding to as received and aged specimen. From EBSD measurements, the crystallographic data are thoroughly analyzed to physically feed the three-scale model. The results are discussed in terms of stress/strain responses in ferrite and austenite, which are correlated to the different KS-OR variants and HP orientations. The effect of primary ferritic grain crystallographic orientation and aging is also studied regarding monotonic and cyclic tests to study the possible origins of backstress in this material.

Prominent role of reversed austenite on corrosion property of super 13Cr martensitic stainless steel

The microstructure and corrosion property of super 13Cr martensitic stainless steel (S13CrMSS) processed by quenching, one-step tempering and two-step tempering were investigated by XRD, SEM, EBSD and TEM-EDS analysis. It has been found that volume fraction of the reversed austenite in the sample treated by two-step tempering treatment was 13.5 vol. % up to the maximum. The reversed austenite almost always nucleated and distributed in martensite laths boundary during tempering and the diffusion of Ni, Mn and C promoted its growth. Enrichment of such elements as Ni, Mn, C and the ultrafine size of the reversed austenite were considered to be the main factor that accounted for the stability of the reversed austenite. At the same time, martensite and reversed austenite satisfy the (1 1¯ 1)γ // (011)α' and [011]γ // [1¯1¯ 1]α' Kurdjumov-Sachs (K–S) orientation relationship. Potentiodynamic polarization curves and electrochemical impedance spectroscopy indicated that two-step tempered specimen exhibited a higher pitting potential, lower corrosion current density, thicker passivation film and superior pitting resistance than the quenching specimen (without reversed austenite) as well as one-step tempering specimen (3.6 vol.%). It has been confirmed that the reversed austenite has a beneficial effect on the corrosion property of S13CrMSS.

Relationship between Microstructure, Mechanical Properties and Creep Behavior of a Cr-Rich Ferritic Stainless Steel Produced by Laser Powder Bed Fusion

Additive manufacturing (AM) techniques such as laser powder bed fusion (L-PBF) are rapidly growing due to the inherent design freedom and possibilities to produce components not available with other techniques. This could be utilized in, e.g., the design of new types of heat exchangers in ferritic stainless steels often used for high-temperature applications. Ferritic stainless steels are, however, difficult to weld and could therefore imply obstacles when produced by AM. When establishing the AM-produced alloy in new applications, it is therefore important to increase the understanding of the mechanical properties and high-temperature creep resistance in relation to the unique microstructure and printability. In this study, we have investigated the microstructure of Cr-rich SS446 ferritic stainless steel produced by L-PBF by microscopical and crystallographic techniques. The properties were compared to the conventionally produced tubes. The rapid cooling and reheating during the application of the subsequent powder layers during L-PBF introduces an intriguing microstructure consisting of a ferritic matrix with precipitation of austenite showing a Kurdjumov–Sachs orientation relationship. Characteristic dislocation networks were observed in the L-PBF samples and contributed to the good mechanical properties in the as-built state (more than twice the yield strength of the conventionally produced tube). Furthermore, the creep resistance at 800 °C was superior to the conventionally produced component, suggesting that L-PBF-produced SS446 possesses many advantages regarding production as compared to the conventional route.

Effect of repeated laser scanning on the microstructure evolution of carbon-bearing martensitic steel manufactured by laser powder bed fusion: Quenching-partitioning drives carbon-stabilized austenite formation

Carbon-bearing martensitic steels have gained interest for their use in aerospace and defense applications due to their ultra-high strength and reasonable ductility. In addition, additive manufacturing (AM) is an effective manufacturing process for a high degree of control over geometry. Microstructure evolution during additive manufacturing should be importantly considered because it is closely related to the formation of defects, mechanical properties, and conditions of post-heat treatments. This study investigated the microstructure evolution of carbon-bearing martensitic steel during laser powder bed fusion (LPBF) to identify the effect of rapid solidification, solid-state transformation, and in-situ heat treatments on the formation of the as-built microstructure. As a result of investigation of a reconstructed prior austenite map by the Kurdjumov-Sachs orientation relationship, it was confirmed that the austenite is generated mainly at the columnar, martensite block, and lath boundaries. A Scheil-Gulliver model represented that carbon and molybdenum are segregated to the columnar boundary, and this could be the main reason why austenite showed high fraction at room temperature. The carbon concentration in the austenite is much higher than that of the martensite interior, which is significantly caused by carbon partitioning derived by repeated laser scanning. A constrained carbon equilibrium model was used to estimate the final fraction of austenite, and the results showed that the characteristics of the as-built microstructure can be reasonably estimated. The microstructural evolution mechanism introduced here is expected to allow successful LPBF of carbon-bearing martensitic steels.

Characterizing local distribution of microstructural features and its correlation with microhardness in resistance spot welded ultra-low-carbon steel: Experimental and finite element characterization

This study investigated the influence of microstructural features on the heterogeneous distribution of hardness in resistance spot welded (RSWed) 340BH steel. The microstructure and texture across the weld region was investigated using optical microscopic and electron backscattered diffraction (EBSD) techniques. Finite element analysis (FEA) was used to simulate the RSW process, which helped in predicting the nugget dimensions as well as the cooling rate in different weld regions. Rapid cooling in the fusion zone (FZ) led to the formation of martensite with typical packet and block substructures. Numerical reconstruction of the prior austenite grain (PAG) was employed to understand the orientation relationship between martensite and austenite. The results showed that child laths obey a Kurdjumov-Sachs orientation relationship (K-S OR) with respect to the austenite matrix with a slight deviation (~3° angular deviation) from a conventional K-S OR. Moreover, microhardness was measured across the weld zone. An increase in the hardness was observed throughout the weld zones. The hardness increase in the heat-affected zone (HAZ) was due to a finer (smaller) grain size and an increase in the dislocation density, whereas in the FZ, the improvement in hardness was attributed to the phase change during the solidification process. The microhardness of martensite formed during RSW was strongly dependent on the block size according to the Hall-Petch relationship. • A heterogeneous distribution of microstructure and hardness in RSWed 340BH steel was characterized using EBSD and FEA. • Lower ZHP values and fast kinetics of dynamic recrystallization resulted in fine structure of ferrite grains in ICHAZ. • FZ hardness was mainly driven by martensite formation, while grain size distribution and dislocation density were mainly responsible for higher hardness in HAZ. • The block size in the martensite substructure followed Hall-Petch type relationship with microhardness of lath martensite.

Advantageous Implications of Reversed Austenite for the Tensile Properties of Super 13Cr Martensitic Stainless Steel.

The advantageous implications of the microstructure and volume fraction of reversed austenite for the tensile properties of super 13Cr martensitic stainless steel (13Cr SMSS) in an experiment with quenching and double-step tempering treatment in the temperature range of 550-750 °C were investigated. The results show that, with increases in one-step tempering temperature, the content of reversed austenite was enhanced considerably from 0.9% to 13.3%. The reversed austenite distributed in the martensitic lath boundary conformed to the (11¯1)γ//(011)α' and [011]γ//[1¯1¯1]α' Kurdjumov-Sachs orientation relationship with the matrix. When tempered at 675 °C for 3 h for the first stage and 600 °C for 2 h for the second stage, the maximum volume fraction of reversed austenite was approximately 13.3%, achieving uniform elongation of 10.4% and total elongation of 27.2%. Moreover, the product of strength and elongation (PSE) was 23.5 GPa·% higher than other samples. The outstanding combination of high strength and commendable plasticity was due to the phase transformation of the reversed austenite into secondary martensite during tensile straining. The reversed austenite consumed the plastic energy at the tip of the microcrack and made the crack tip blunt, which hindered the further propagation of the crack, consequently increasing the total elongation and improving toughness.

Hierarchical eutectic structure and superior mechanical property in low cobalt content AlCo0.2CrFeNi2.1 alloy by laser metal deposition

The fabrication of AlCo 0.2 CrFeNi 2.1 high entropy alloy via laser metal deposition (LMD) was motivated and implemented by the demand for overcoming the strength-ductility trade-off of the as-cast alloys due to the Co concentration. The microstructure features of AlCo 0.2 CrFeNi 2.1 alloy were characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and electron back-scattered diffraction. The mechanical properties were evaluated by a tensile test at room temperature. The synergy of reduced Co content and LMD process led to the formation of hierarchical eutectic microstructures consisting of columnar grains, eutectic colonies, alternately arranged fcc(L1 2 )+B2 lamellae, and coherent Cr-rich nanoprecipitates in B2. The growth direction of those eutectic structures was found to be mainly parallel to the building direction (BD). The fcc(L1 2 )/B2 eutectics agreed well with the Kurdjumov–Sachs orientation relationship of {110} B2 //{111}L1 2 , and< 111 > B2 //< 110 >L1 2 . The LMD fabricated AlCo 0.2 CrFeNi 2.1 exhibited anisotropic mechanical properties when stretched in BD and transverse direction (TD). An excellent combination of the ultimate tensile strength (1246 MPa) and ductility (17.1%) was achieved in the BD, better than the as-cast counterpart. The elevated mechanical properties could be attributed to the high cooling rate solidification induced microstructural refinement. The same interlamellar spacing in BD and TD embraced a nearly equal ability to block dislocation movement and gave rise to the similar yield tensile strength. The differences in grain/colony size induced boundary strengthening in BD and TD were evaluated to account for the remarkable changes in ultimate tensile strength as well as ductility. • High entropy alloy AlCo 0.2 CrFeNi 2.1 was made by laser metal deposition(LMD). • Excellent combination of strength and ductility was achieved with less Co content. • LMD overrode chemical composition to affect strength-ductility trade-off. • Refined microstructure by LMD caused better property than casting. • Interlamellar spacing contributed to yield strength, grain/colony size affected ultimate strength.

Effect of Carbon Content on Variant Pairing in Bainitic Low Alloy Steel

Variant pairing in bainite was evaluated in four different commercial low alloy steels with medium to high carbon content. The steels investigated were austempered in the temperature range 275 °C to 450 °C to obtain a bainitic microstructure. It was found that the V1–V6 is the most frequent variant pairing at lower temperature, while it gradually decreases towards intermediate temperatures, and at the highest austempering temperatures the variant pairing with low misorientation boundaries such as V1–V4 and V1–V8 is the most frequent. The preferred variant pairing is the least pronounced after austempering of steels with higher carbon contents at intermediate temperature. Nonetheless, a continuous increase of variant pairing within the same Bain group was observed with increasing austempering temperature for all steels. Furthermore, it was observed that the deviation from the theoretical Kurdjumov–Sachs orientation relationship increases with increasing austempering temperature for all steels.

Formation of Widmanstätten Ferrite and Grain Boundary Ferrite in a Hypereutectoid Pearlitic Steel

Accompanied by the formation of pearlite, Widmanstätten ferrite (WF), grain boundary ferrite and cementite are often found to nucleate at the prior austenite grain boundary during isothermal heat treatment. A hypereutectoid pearlitic steel transformed isothermally at temperatures ranging from 607 to 707 °C was investigated to clarify the evolution of different phases. At 607 °C, WF grains, which had a Kurdjumov–Sachs orientation relationship with the remaining austenite, were found to be aligned with the grain boundary. At 707 °C, lath WF grains, which were arranged parallel to each other, were at a certain angle to the grain boundary. The formation of pearlite showed two-stage kinetics in the dilatometer curve, and the grain boundary’s abnormal structure was suppressed.

Effect of Zr on the microstructure and mechanical properties of 12Cr ferritic/martensitic steels

The effect of Zr in the range of 0–∼1.36 wt.% on the microstructure and mechanical properties of 12Cr ferritic/martensitic steels was investigated. The steels were prepared by melting and hot rolling, then normalized at 1050 °C for 30 min and tempered at 760 °C for 90 min. The steels with 0–∼0.11 wt.% Zr had a mixture of martensite and ferrite, while the steels with ∼1.36 wt.% Zr showed fully ferrite. The area fraction of the ferrite phase in steels increases as an increase in the Zr content, which indicates that Zr is a ferrite forming alloy element in steels. The precipitates in steels with 0–∼0.11 wt.% Zr were mainly distributed along martensitic lath boundary and ferritic/martensitic interface. The coarser precipitates distributed at the ferrite/martensite interface were M23C6 carbides and obey Kurdjumov-Sachs orientation relationship, namely (110)α-Fe//(111)M23C6 and [-111]α-Fe//[011]M23C6. There were two kinds of precipitates in the steels containing ∼1.36 wt.% Zr. The coarser precipitates, which distributed randomly, were Zr-rich (Fe, Zr) compounds. The Laves phases found in smaller precipitates were distributed at the grain boundary. Tensile tests showed that the strength decreased and the ductility increased as an increase in the Zr content. The steels with 0–∼0.11 wt.% Zr demonstrated a superior strength balance, of which the tensile strength and elongation at room temperature were 750–830 MPa and 19%–22%, respectively. At the elevated temperature (600 °C), the tensile strength of the steels decreased to 390–450 MPa and the elongation of steels increased to 27%–34%.

Phase transformation behavior of Ti–40Al–8Nb alloys with a submicron (ω0+γ) microstructure during tempering at 1000 °C

In this work, the phase transformation behavior of Ti–40Al–8Nb (at. %) alloys with a submicron (ω0+γ) microstructure during tempering at 1000 °C was investigated, and special attention was paid on the ω0-assisted α2 nucleation. Results indicated that the ω0+γ→B2→α2 transformation dominated the precipitation of α2 phase. The ω0 and γ phases first dissolved into the B2 phase within a short time, and then the B2→α2 transformation occurred. The α2 phase could nucleate in the interior of B2 matrix and precipitate at the B2/γ interfaces by following the Burgers orientation relationships (ORs), <11–20>α2//<111>B2 and (0001)α2//{110}B2. With the increase of isothermal holding time, the γ phase reprecipitated through two phase transition routes, including B2→γ and α2→γ transformations by following the Kurdjumov-Sachs ORs, <111>B2//<110>γ and {110}B2//{111}γ, and Blackburn ORs, i.e., (0001)α2//{111}γ and <11–20>α2//<011>γ, respectively. Finally, a (α2+γ+B2) microstructure was obtained after isothermal holding at 1000 °C for 300 min.

Non-cube-on-cube orientation relationship between M23C6 and austenite in an austenitic stainless steel

Crystallographic orientation relationship between M23C6 carbides and austenite in the lightweight high carbon stainless steel Fe−17Cr−9Ni−6Mn−4Al−0.42C (wt.%) was investigated by diffraction analysis in scanning and transmission electron microscopes. Electron backscatter diffraction analysis in SEM indicated the existence of an orientation relationship approximated by the Kurdjumov-Sachs (K-S) orientation relationship between the M23C6 carbides induced by aging and the austenitic matrix. The observation of an orientation relationship deviating from the commonly reported cube-on-cube orientation relationship was explained by the formation of M23C6 carbides via M7C3 carbides as an intermediate phase.

The Effect of Cooling Rate on the Microstructure Evolution and Mechanical Properties of Ti-Microalloyed Steel Plates.

Ti-bearing microalloyed steel plates with a thickness of 40 mm were subjected to ultra-fast cooling (UFC) and traditional accelerate cooling after hot-rolling, aiming to investigate the effect of cooling rate on the microstructure and mechanical properties homogeneity, and thus obtain thick plates with superior and homogeneous mechanical properties. Yield strength, tensile strength, and elongation were 642 MPa, 740 MPa, 19.2% and 592 MPa, 720 MPa and 16.7%, respectively, in the surface and mid-thickness of the steel with ultra-fast cooling, while in the steel with traditional accelerate cooling, 535 MPa, 645 MPa, 23.4% and 485 MPa, 608 MPa, 16.2% were obtained in the surface and mid-thickness of the plate. The yield strength has been greatly improved after UFC, for the refinement of grain and precipitates produced by UFC. In addition, the equivalent grain size and precipitates size in the thick plate with UFC are homogeneous in the thickness direction, leading to uniform mechanical properties. The crystallographic characteristics of different precipitates have been studied. The precipitates formed in the austenite deformation stage obey Kurdjumov–Sachs orientation relationship with the ferrite matrix, while the fine precipitates formed in the ferrite obey [112]MC//[110]α and // orientation relationship with the ferrite matrix.

Crystalline characteristics of a dual-phase precipitation hardening stainless steel in quenched solid solution and aging treatments

This study investigated the development of the microstructures and aging reactions in a new dual-phase (allotriomorphic δ + γ) 17–4 precipitation-hardened (PH) stainless steel (SS) alloy. The 17–4 PH alloy, a martensitic stainless steel containing Cu (3–5 wt.%), was subjected to solid solution treatment followed by quenching using oil, H2O, or liquid N2. The microstructures of the steel specimens were primarily composed of lath martensite and allotriomorphic δ-ferrite. X-ray diffraction analysis indicated that the structures consisted entirely of bcc phase peaks. During aging at 560 and 600 °C, the local microstrain was released because of the tempering of the lath martensite and the formation of reverted austenite, resulting in a shift in the kernel's average misorientation distribution toward lower angles. The misorientation associated with the martensite boundaries ranged from 10° to 20° and from 47° to 57° in the packets. In the blocks, it ranged from 50° to 60°. The F1-ferrite approximately followed the Kurdjumov–Sachs orientation relationship with A1-austenite and A2-austenite.