Nanoscale austenite reversion through partitioning, segregation, and kinetic freezing: Example of a ductile 2 GPa Fe-Cr-C steel

Austenite reversion during tempering of a Fe-13.6Cr-0.44C (wt.%) martensite results in an ultrahigh strength ferritic stainless steel with excellent ductility. The austenite reversion mechanism is coupled to the kinetic freezing of carbon during low-temperature partitioning at the interfaces between martensite and retained austenite and to carbon segregation at martensite-martensite grain boundaries. An advantage of austenite reversion is its scalability, i.e., changing tempering time and temperature tailors the desired strength-ductility profiles (e.g. tempering at 400{\deg}C for 1 min. produces a 2 GPa ultimate tensile strength (UTS) and 14% elongation while 30 min. at 400{\deg}C results in a UTS of ~ 1.75 GPa with an elongation of 23%). The austenite reversion process, carbide precipitation, and carbon segregation have been characterized by XRD, EBSD, TEM, and atom probe tomography (APT) in order to develop the structure-property relationships that control the material's strength and ductility.Comment: in press Acta Materialia 201

Microstructures of nickel-base alloy dissimilar metal welds

Dissimilar metal welds (DMWs) between low-alloy steels (LAS), stainless steels (SS) and nickel-base alloys are very important in the design of conventional and nuclear power plants (NPPs). They help to reach better performances for high temperature environment but they can promote premature failure of components. Failure is often related to cracking in the heat affected zone of base materials. In this study, a literature review was conducted concerning the behavior of Inconel Ni-base alloys and LAS in DMWs for nuclear applications. It was centered on the metallurgical changes occurring with post-weld heat treatment (PWHT) at the interface of ferritic/austenitic DMWs, on the weldability of Inconel filler metals and on the narrow-gap welding (NGW) technique emerging in the NPP design. The aim was to characterize a NGW present in modern pressurized water reactor (PWR) design, which uses an Inconel filler metal to join the reactor pressure vessel nozzle to its safe-end. In addition, the behavior of Alloy 690 was studied. Eight samples were characterized. A narrow-gap Alloy 52 mock-up manufactured in the SINI project was studied in the as-welded condition and after PWHT. It showed that PWHT resulted in increased carbon depletion in the LAS side and in an extensive chromium carbide precipitation in the weld metal. It was responsible for a sharp hardness peak in the weld metal. Samples from EPRI (Electric Power Research Institute) were characterized for ENVIS project, showing different weld configurations involving Alloy 690 as base metal and Inconel 52, 152 and 52M as filler metals. Differences in the behavior of the filler metals were observed. Higher hardness was found in Inconel 52M, followed by Inconel 152 and 52, respectively. Inconel 152 showed different behavior than Inconel 52 concerning carbon migration. The microstructure of Alloy 690 was characterized and was found to correspond to the literature review

Study guide on “Technology of Structural materials and Material Science” Part 3

Study guide on have been approved at the meeting of building mechanics department (minutes No 1 from 25 August 2016) The Study guide on have been approved by the Mechanical Engineering Faculty methodological committee (minutes No 1 from 29 August 2016)“Technology of Structural materials and Material Science” is one of the basic technical disciplines in the syllabus for “Engineering mechanics” field of study. During the implementation of laboratory work considerable attention is given to the educational and experimental work for the study of materials that are used in different branches of an industry; methods of treatment and external environments The study of the theory and practice of different methods of materials strengthening is to provide a high reliability and longevity of the machine’s details, devices, tools etc. After every practical class and lab activities in the laboratory, students will fill the laboratory report. The content of the laboratory class corresponds with the syllabus of the course “Technology of Structural materials and Material Science” for students of the “Engineering mechanics” field of study. The purpose of this manual is to provide guidelines for the students in preparation for independent laboratory work and to project its results in the laboratory reports

Notes and laboratory reports on “Electrical and Structural Materials” Part 2 “Structural materials”

The notes and laboratory reports have been approved at the meeting of structural mechanics department (minutes № 5 from 15 January 2018) The notes and laboratory reports have been approved by methodological committee of the faculty of engineering of machines, structures and technologies (minutes № 5 from 18 January 2018

Effect of heat treatment on wear properties of plain carbon steel

A study was made of the effect of heat treatment upon the wear resistance of low and high carbon steels as determined by the ball on a plate wear-testing machine (diamond indenter) under combined action of rolling and sliding friction under pressures. Total ten samples of the steel (5 samples each from low carbon and high carbon range) were subjected to five different heat treatments i.e. annealing, normalizing, oil quenching, water delay quenching and water quenching heated to a temperature of 960¢ªC. One from each heat treated types was prepared for microstructural and hardness studies. The hardness of the five different heat treated samples was measured by Vickers hardness testing machine. Optical microscopies to study the microstructure and Scanning electron microscopic analysis of wear surface have been done

Heat treatment, microstructure and properties of 75Cr1 steel, for use in heavy loaded elements

This study aims to optimize the heat treatment of tool steel 75Cr1 which is used for heavy loaded elements in transmissions. A salt bath was used to quench and temper the steel at different temperatures. Mechanical tests and microstructural characterization were done to define the heat treatment parameters corresponding to the optimal performance of the elements. Optical microscopy, electron back scatter diffraction and x-ray diffraction were used to characterize the microstructure, while tensile tests and toughness tests were employed to determine the mechanical properties after different heat treatments. It was found that the yield strength decreases with increasing annealing temperature and that the toughness decreases with increasing annealing time and temperature. The changes of the mechanical properties are discussed in relation with the thermal treatment and the corresponding microstructures