Microstructural Evolution and Internal Friction Behavior of a Ferrite/Martensitic Steel Induced By Equal-Channel Angular Pressing

ORIGINAL RESEARCH ARTICLE Microstructural Evolution and Internal Friction Behavior of a Ferrite/Martensitic Steel Induced By Equal-Channel Angular Pressing G.J. ZHANG, Q.G. ZHANG, X.G. WANG, M. SUN, J.F. YANG, T. HAO, G. LI, H. WANG, J.G. LIU, Q.F. FANG, and X.P. WANG A newly developed equal channel angular pressing (ECAP) route BC-UD2 was applied to extrude the Fe9Cr1.5W0.7Si (in weight) ferrite/martensitic steel, and the microstructural evolution and its effect on the internal friction (IF) behavior were investigated systematically. Microstructural characterization indicates that the initial ferrite/martensitic structure was broken into a fine laminar structure with a roughly 45 deg inclination to the extrusion direction (ED), and the corresponding initial weak Goss and h111i k RD texture evolves into typical extrusion fibers b1, b2, and b3. At the same time, M23C6 and MX phases were partially dissolved after extrusion, which leads to a decrease in the Zener–Smith dragging force. Combined with the high stored energy produced by ECAP, both of them induced the decrease of recrystallization temperature and the increase of interfacial migration density during recrystallization, as revealed by the high-temperature IF behavior. In particular, the intensity variation of the recrystallization peak is also consistent with the hardness variation during annealing. The correlation between microstructure characterization results and IF behavior reflects the accuracy and reliability of the IF technique for the study of recrystallization behavior of structural materials in nuclear reactors. https://doi.org/10.1007/s11661-023-07104-x  The Minerals, Metals & Materials Society and ASM International 2023 I. G.J. ZHANG and X.G. WANG are with the Key Laboratory of Materials Physics, Institute of Solid State Physics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, P.R. China and also with the Department of Materials Science and Engineering, University of Science and Technology of China, Hefei 230026, P.R. China. Q.G. ZHANG is with the Key Laboratory of Materials Physics, Institute of Solid State Physics, Hefei Institutes of Physical Science, Chinese Academy of Sciences and also with the Institutes of Physical Science and Information Technology, Anhui University, Hefei 230601, P.R. China. M. SUN, Q.F. FANG, and X.P. WANG are with the Key Laboratory of Materials Physics, Institute of Solid State Physics, Hefei Institutes of Physical Science, Chinese Academy of Sciences. Contact e-mail: J.F. YANG is with the Key Laboratory of Materials Physics, Institute of Solid State Physics, Hefei Institutes of Physical Science, Chinese Academy of Sciences and also with the Anhui Institute of Innovation for Industrial Technology, Lu’an Branch, Lu’an 237100, P.R. China. Contact e-mail: T. HAO is with the School of Mechanical Engineering, Suzhou University of Science and Technology, Suzhou 215009, Jiangsu, P.R. China. G. LI is with the Science and Technology on Reactor Fuel and Materials Laboratory, Nuclear Power Institute of China, Chengdu 610041, P.R. China. H. WANG is with the Interdisciplinary Materials Research Center, Institute for Advanced Study, Chengdu University, Chengdu 610106, P.R. China. J.G. LIU is with the XinPengYuan (LIAOCHENG) Intelligence Technology Co., Ltd., Liaocheng 252000, P.R. China. Manuscript submitted January 9, 2023; accepted May 30, 2023. Article published online July 15, 2023 METALLURGICAL AND MATERIALS TRANSACTIONS A INTRODUCTION FERRITE/MARTENSITIC steels are of increasing interest and have prospecting applications as structural materials in the fields of nuclear reactors and power plants owing to their superior thermal conductivity, thermal expansion, and resistance to helium radiation-induced swelling and embrittlement.[1,2] For nuclear reactor systems, long-term safe operation is one of the key indicators of the service performance of fuel cladding materials (FCMs). In view of the severe service conditions such as high temperature and high neutron irradiation in nuclear reactor systems, especially lead-cooled fast reactors,[3] it is necessary to further improve the high-temperature mechanical properties and irradiation resistance of FCMs to bear the extreme service conditions.[4] Deformation-induced grain refinement of metallic materials is a well-known strategy to strengthen materials.[5] Ball milling–hot pressing (HP) sintering,[6] spark plasma sintering (SPS),[7] and severe plastic deformation (SPD) techniques are commonly used to improve their performance. However, the ball milling-HP and SPS technique is either a complex process or difficult to manufacture in large quantities.[8] The extremely high strain generated by SPD makes it very attractive for grain refinement, especially in obtaining nanocrystalline VOLUME 54A, SEPTEMBER 2023—3489 (NC) or ultrafine-grained (UFG) materials.[9] SPD techniques[10–13] include equal channel angular pressing (ECAP), high-pressure torsion (HPT), surface mechanical grinding treatment (SMGT), stacking-roller connection, and multiple forging. Among them, ECAP is a prospective one that can produce bulk NC or UFG materials without any dimensional changes.[10] This technology has been widely applied to metals and alloys, including aluminum alloy,[14] copper alloy,[15] titanium alloy,[16] magnesium alloy,[17] and so on. During ECAP, a specimen (mostly a rod) closely matched to the die size and well lubricated with the channel wall is pressed down the channel with a hydraulic press with a punch, and when the specimen passes through the intersection of the two channels, the specimen will produce a deformation similar to pure shear.[10] Different ECAP routes can change the shear plane and shear direction within the specimen, which has an important effect on grain refinement.[11] Based on the rotation of the specimen during repeated extrusion, the commonly used extrusion routes can be divided into four types according to whether the grain refinement effect is good or not, in order route A (no rotation of the sample between repetitive pressings), route BC (involves a rotation of 90 deg in the same direction between each pressing), route BA (involves alternate rotations of 90 deg between repetitive pressings), and route C (involves a rotation of 180 deg between each pressing).[10,18,19] In addition, Liang et al.[20] developed a new route BC-UD2 based on route BC by matrix transformation analysis, which is identical to route BC except that the sample is overturned upside down between alternate passes. By extruding the Mg–10Al alloy with routes BA, BC, and BC-UD2, respectively, they found that route BC-UD2 not only achieves the same grain refinement effect as routes BC and BA, but also results in more uniform particle redistribution.[20] However, this newly developed ECAP route BC-UD2 has not yet been applied to steel, particularly structural steel used for nuclear reactors, so it is not clear what kind of special micros (...truncated)