Strengthening of a thin austenitic stainless steel coil by cold wavy rolling with no magnetic and dimensional changes

A comparison of the effects of wavy rolling and cold rolling on microstructure variation, phase evolution, tensile and magnetic properties of a thin coil of Fe-18.47Cr-8.10Ni-0.94Mn austenitic stainless steel was made at room temperature. Wavy rolling led to strengthening with no change in magnetic property and thickness, unlike the conventional cold rolling that changed all these properties by deformation induced martensitic transformation, in addition to substructure evolution. The yield strength of 413 MPa and magnetic saturation 3.7 emu/g under mill-annealed condition increased, respectively, to 1208 MPa and 11.8 emu/g, upon four cycles of wavy rolling. While the maximum yield strength of 1790 MPa could be achieved by combining this stage of four cycles of wavy rolling with subsequent 50% conventional cold rolling, the magnetic saturation increased to 73.3 emu/g by deformation induced martensitic transformation caused by the latter.     

Oriented sulphides induced by electric current in medium carbon steel

Oriented sulphides parallel to the electric current direction have been experimentally observed when a pulsed electric current is passed through medium carbon steels with MnS inclusions. Two different configurations of sulphides occur after the application of the electric current: namely, oriented elongated ellipsoidal particles and oriented chain-like particles composed of two or three small spherical sulphides. Theoretical analysis indicates that this phenomenon is associated with minimization of the electrical resistance of the material.     

Measuring grain-boundary segregation in nanocrystalline alloys: direct validation of statistical techniques using atom probe tomography

Atom probe tomography (APT) is used to investigate grain-boundary segregation of W solute atoms in nanocrystalline Ni. For the heat-treated specimens used here, the grain structure can be observed in the APT data, enabling direct composition analyses across individual grain boundaries. These direct measurements are used to validate methods proposed in earlier work, which determine the average segregation state in nanocrystalline materials through statistical analysis of the solute distribution, without knowledge of the boundary positions. Good agreement is demonstrated between the two experimental techniques.     

Nanoindentation measurements on deformation-induced α’-martensite in a metastable austenitic high-alloy CrMnNi steel

The hardness of deformation-induced α’- martensite and parent austenitic matrix in high-alloy CrMnNi steel was investigated by nanoindentation measurements inside scanning electron microscope using picoindenter. After the indentation, the microstructure was investigated by electron backscattered diffraction measurements. The hardness values for α’-martensite are only 24% higher than those of austenite. Thus, the increase in strength during the formation of deformation-induced α’-martensite is rather caused by the small grain size of α’-nuclei resulting in a dynamic Hall–Petch effect than by its “intrinsic” hardness.     

Positron lifetime study of an Al-1.7at.% Mg-1.1at.% Cu alloy

The behaviour of vacancies during isothermal ageing following quenching of an Al-1.7at.% Mg-1.1at.% Cu alloy has been studied by positron annihilation lifetime spectroscopy. The positron lifetime parameters vary in parallel with the Vickers hardness of the alloy, suggesting simultaneous migration of vacancies and changes in the size and concentration of vacancies containing clusters and dislocation loops. The results also explain the long hardness plateau observed previously in ageing experiments carried out between 100 and 240°C in terms of a continuous growth of Mg-Cu-vacancy clusters during ageing. The vacancy concentration of the clusters increases gradually until the setting in of the cluster Guinier-Preston-Bagaryatsky zone transformation.     

Creep strengthening by lath boundaries in 9Cr ferritic heat-resistant steel

The interactions between dislocations and lath boundaries in Grade 91 steel were observed by an in situ transmission electron microscopy tensile test at 973 K. Dislocations glided slowly and bowed out in a martensite lath interior. The ends of the dislocation were connected to the lath boundaries. In a tempered specimen, the pinning stress caused by the lath boundary was estimated to be >70 MPa with a lath width of 0.4 μm. In crept specimens, lath coarsening reduced the pinning effect.     

Microstructures and strengthening mechanisms in high-carbon titanium-microalloyed interstitial-free steels

We report the mechanical properties and microstructures of titanium-microalloyed interstitial-free (IF) steels with different carbon contents smelted and rolled in the laboratory. The results show an increase of yield strength and tensile strength with carbon content, which are enhanced with lower coiling temperature (CT). Microstructure analysis reveals that the ferrite grain size varies from 11 to 23?μm, while the average size of TiC as the main second-phase particle ranges from 10 to 35?nm. The sample with 80?ppm carbon and 853?K CT reaches a mechanical strength close to that of high-strength IF steels. The increase of yield strength is mainly attributed to both grain-refining and precipitation strengthening.     

Microstructures and tensile properties of 304 steel with dual nanocrystalline and microcrystalline austenite content prepared by aluminothermic reaction casting

The microstructures of 304 stainless steels with different amounts of nanocrystalline and microcrystalline austenite prepared by an aluminothermic reaction casting, without and with annealing at 1073?K for 8?h, have been investigated by X-ray diffraction, an electron probe micro-analyser, a transmission electron microscope and a scanning electron microscope. The steels, both without and with annealing, consisted of different dual nanocrystalline and microcrystalline austenite combinations and a little nanocrystalline δ ferrite, while the average grain size of the nanocrystalline austenite increased from 19 to 26?nm and volume fraction of the microcrystalline austenite increased from 17 to 30% after annealing. The tensile strength of the steel was dramatically increased from 500 to 1000?MPa and the tensile elongation ratio increased from 8 to 12% after annealing. However, the tensile strength was decreased to 600?MPa and the tensile elongation ratio increased from 12 to 22% after an annealing at 1273?K. The combination of dual nanocrystalline and microcrystalline austenite obtained after the annealing at 1073?K results in the best tensile properties.     

A combination of Al diffusion and surface nanocrystallization of carbon steel for enhanced corrosion resistance

Surface nanocrystallization is beneficial to the corrosion resistance of passive alloys, but generally has a negative effect on the corrosion behavior of non-passive alloys due to the enhanced surface reactivity. In this study, a combination of Al diffusion treatment and surface nanocrystallization was applied to carbon steel with the aim of exploring an alternative approach to improve the corrosion resistance of non-passive carbon steel. The surface nanocrystallization was achieved by sandblasting and subsequent recovery treatment. The former resulted in severe plastic deformation, while the latter turned high-density dislocation cells into nano-sized grains. The present study demonstrates that the combined Al diffusion and nanocrystallization generated a nanocrystalline Al-containing surface layer on the carbon steel with its surface grain diameter in the range of 10–300 nm. The corrosion resistance of the treated steel was evaluated. It is demonstrated that treated specimens possess increased resistance to corrosion with higher surface electron stability. Surface microstructure of the treated specimens was examined using SEM, AFM, and EDS in order to elucidate the mechanism responsible for the improved corrosion resistance.     

The infrared absorption spectra of diamonds expected to contain voidites

Abstract

The infrared spectra of several type Ia diamond crystals expected to contain voidites have been examined in the wavenumber range 4000–2700 cm^?1. The absence of any absorption which could possibly be attributable to the stretching of N─H bonds makes unlikely recent suggestions that the voidites may contain a solid phase of NH₃.