Effect of process variables on formation of dynamic strain induced ultrafine ferrite during hot torsion testing

Ultrafine grain sizes were produced using hot torsion testing of a 0.11C-1.68Mn-0.20Si (wt-%) steel, with ultrafine ferrite (&lt;1 &micro;m) nucleating intragranularly during testing by dynamic strain induced transformation. A systematic study was made of the effect of isothermal deformation temperature, strain level, strain rate, and accelerated cooling during deformation on the formation of ultrafine ferrite by this process. Decreasing the isothermal testing temperature below the Ae3 temperature led to a greater driving force for ferrite nucleation and thus more extensive nucleation during testing; the formation of Widmanst&auml;tten ferrite prior to, or early during, deformation imposed a lower temperature limit. Increasing the strain above that where ferrite first began 0.8 at 675C and a strain rate of 3 s&macr;1 increased the intragranular nucleation of ferrite. Strain rate appeared to have little effect on the amount of ferrite formed. However, slower strain rates led to extensive polygonisation of the ferrite formed because more time was available for ferrite recovery. Accelerated cooling during deformation followed by air cooling to room temperature led to a uniform microstructure consisting of very fine ferrite grains and fine spherical carbides located in the grain boundaries regions. Air cooling after isothermal testing led to carbide bands and a larger ferrite grain size.<br /

The detection of oil in water by near infrared pulsed photoacoustic spectroscopy

An experimentally based study to investigate near infrared laser photoacoustic spectroscopy as a technique to measure oil pollution is described. Photoacoustic spectroscopy is shown to be well suited to the application of monitoring oil in water in a pipeline. The role of the physical parameters important to photoacoustic generation is shown to lead to an effective amplification of differences in the optical absorption coefficients for many hydrocarbons and alcohols in water. This amplification is typically an order of magnitude and persists at low concentrations of arialyte, such that a Nd:YAG source (2 mJ pulses) yields a 7.2 % increase in the photoacoustic signal magnitude for a 500 mg/I oil in water sample compared to distilled water, corresponding to a detection limit of 4 mg/I. Using a 904 nm diode laser as a source for photoacoustic generation, a detection limit of 400 mg/1 of oil is demonstrated. In addition there is found to be no discernible effect on the magnitude of the photoacoustic signal caused by the presence of optically scattering particles. The design and development of a photoacoustic instrument to measure oil in water is described, and the performance of such an instrument is compared to that of the competing technology

Dynamic adjustment of ferrite grains during dynamic strain induced transformation

The dynamic adjustment of ferrite grains formed during \u27dynamic strain induced transformation (DSIT)\u27 is an important feature of this mechanism that has not been addressed previously. A novel experimental method was applied to follow the effect of deformation at different stages on ferrite formed initially through DSIT. It is shown that while the continuous dynamic recrystallisation (CDRX) appears to be an acceptable mechanism for re-refinement of coarser grain size (i.e. d&alpha;&gt;2dDSIT), it cannot explain the steady state grain size for finer ferrite grains (i.e. d&alpha;&lt;2dDSIT). Other potential mechanisms involved in this phenomenon are examined.<br /

The formation of ultrafine grained steel microstructures through thermomechanical processing.

The formation of ultrafine grained steels is an area of intense research around the World. There are a number of methods to produce grain sizes of approximately 1 &micro;m, ranging from extreme thermal and deformation cycles to more typical thermomechanical processes. This paper reviews the status of the production of ultrafine grained steels through relatively simple thermomechanical processing. It is shown that this requires deformation within the Ae3 to Ar3 temperature range for a given alloy. The formation of ultrafine ferrite involves a dynamic transformation of a significant volume fraction of the austenite to ferrite. This dynamic strain induced transformation arises from the introduction of additional intragranular nucleation sites. It is possible that the deformation also hinders the growth or coarsening of the ferrite and may also lead to dynamic recrystallization of the ferrite. The most likely commercial exploitation of ultrafine ferrite would appear to rely on the formation of a critical volume fraction of dynamic strain induced ferrite followed by controlled cooling to ensure this is maintained to room temperature and to also form other secondary phases, such as martensite, bainite and/or retained austenite to improve the formability.<br /

The static, dynamic and metadynamic recrystallisation of a medium carbon steel

Grain refinement during and after hot isothermal deformation of a medium carbon steel has been investigated. The average austenite grain size decreased with an increase in strain for the hot deformed and recrystallised material, with refinement extending beyond the strain for the peak stress. A window of strain that corresponds to transition from classical static to metadynamic recrystallisation was observed in respect to the recrystallised material. Within this post-dynamic transition window the strain at which strain independent softening occurs was different for different volume fractions of the recrystallised material. This led to a new terminology corresponding to initiation of strain independent softening. For the alloy of this study, strain independent softening for the start of post-deformation recrystallisation occurred near the strain to the peak stress. The strain corresponding to complete metadynamic recrystallisation, which was defined as when all levels of recrystallisation were strain independent, was much greater than the strain for the peak stress. <br /

Von Schönheit im Garten : das Schöne gemeinsam hervorbringen und entdecken

Gartenkunst war jahrhundertelang das Privileg einer kleinen Schicht, der es vorbehalten war, kunstvolle Gärten anlegen zu lassen. Die Mehrzahl der Menschen hingegen war damit beschäftigt, Obst und Gemüse anzubauen. Dies änderte sich grundlegend erst mit der modernen Konsumgesellschaft nach dem Zweiten Weltkrieg. Als Phänomen des Wohlstands begann sich das Meer der Einfamilienhäuser mit im Verhältnis kleinen Gärten auszubreiten, von denen heute viele durch „Amateurgärtner“ angelegt werden

Kleines Haus, grosser Garten, gesundes Alter

In Wädenswil pflegen drei Frauen aus drei Generationen ihren Garten. Er ist ein Gegenbild zur alles überwältigenden Konsum- und Wegwerfgesellschaft

Microstructure evolution of TI-SN-NB alloy prepared by mechanical alloying

In the present study, Ti-16Sn-4Nb alloy was prepared by mechanical alloying (MA). Optical microscopy, scanning electron microscopy combined with energy dispersive X-ray analysis (SEM-EDX), and X-ray diffraction analysis (XRD) were used to characterise the phase transformation and the microstructure evolution. Results indicated that ball milling to 8 h led to the formation of a supersaturated hcp &alpha;-Ti and partial amorphous phase due to the solid solution of Sn and Nb into Ti lattice. The microstructure of the bulk sintered Ti-16Sn-4Nb alloy samples made from the powders at shorter ball milling times, i.e. 20 min- 2 h, exhibited a primary &alpha; surrounded by a Widmanst&auml;tten structure (transformed &beta;); while in the samples made from the powders at longer ball milling times, i.e. 5- 10 h, the alloy evolved to a microstructure with a disordered and fine &beta; phase dispersed homogeneously within the &alpha; matrix. These results contribute to the understanding of the microstructure evolution in alloys of this type prepared by powder metallurgy.<br /