Effects of Ultrasonic Treatment during the Solidification Process on the Structure Formation of Low Carbon Steel
This paper studied effects of ultrasonic treatment during the solidification process on structure formation of low carbon steel. Results showed that with ultrasonic treatment grains were refined and the steel ingot avoided the cast widmanstatten structure. When ultrasonic treatment was employed, pearlite was broken and the average length of pearlite was decreased from 550 mm to 140 mm. The corresponding aspect ratio was reduced from 12 to 1. At high magnification the treated pearlite was cloud-like, rather than plate-like, as normal. Ultrasonic treatment also can remove the gas from low carbon steel. These phenomena of low carbon steel generated by ultrasonic treatment were explained. [doi:10.2320/matertrans.M2011091]
The Formation of Intragranular Acicular Ferrite in Simulated Heat-affected Zone
The preferential conditions of intragranular acicular ferrite (IAF) in heat-affected zone were studied by adding sulfur and calcium into a Ti-killed steel. Sulfur and calcium addition refined the austenite grain due to the increase in the number density of inclusions. An intermediate austenite grain favored the formation of IAF due to the prevention of Widmanstatten ferrite and polygonal ferrite. The inclusions changed from Ti-oxides dominant to Ti-oxysulfides dominant and Ti-Ca-oxysulfides dominant due to small addition of sulfur and calcium. The nucleation potential of inclusions was found to increase in the sequence of Ti-oxides, Ti-oxysulfides, and Ti-Ca-oxysulfides. This phenomenon could be attributed to the increase of the lattice disregistry between inclusions and ferrite matix or the decrease of strain field around inclusions. Both effects prevented the transformation of austenite to ferrite at elevated temperatures, thereby promoting the formation of IAF. The highest volume fraction of IAF was, therefore, obtained at an intermediate sulfur content with small amount of calcium due to the achievement of optimum nucleation potential and grain size.
"Flying Triangulation" - a new optical 3D sensor enabling the acquisition of surfaces by freehand motion
In order to obtain complete 3D surface information of an object it is often necessary to acquire many partial 3D views. For this purpose, the sensor has to be moved (e.g. for the acquisition of sculptures or rooms). Further, in many cases a motion of the object relative to the sensor is unintended but inevitable (e.g. for medical applications such as intraoral measurements of teeth). Nearly all existing optical 3D sensors either lack an easy handling or require a standstill during the acquisition of a single partial 3D view, since usually multiple camera shots have to be taken for this purpose. This makes such measurements elaborate or even impossible.