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Caballero, F.; Miller, M.; Garcia-Mateo, C.; Capdevila, C.; Garcia de Andrés, C.
doi: 10.1007/s11837-008-0159-zpmid: N/A
An innovative design procedure based on phase transformation theory alone has been successfully applied to design steels with a microstructure consisting of a mixture of bainitic ferrite, retained austenite, and some martensite. An increase in the amount of bainitic ferrite is needed in order to avoid the presence of large regions of untransformed austenite, which under stress decompose to brittle martensite. The design procedure addresses this diffi culty by adjusting the T′o curve to greater carbon concentrations with the use of substitutional solutes such as manganese and chromium. The concepts of bainite transformation theory can be exploited even further to design steels with strength in excess of 2.5 GPa and considerable toughness.
doi: 10.1007/s11837-008-0160-6pmid: N/A
Among high-strength steels, transformation hardening steels such as dual-phase (DP) steel and transformation-induced plasticity (TRIP) steel offer a superior relationship between tensile strength (TS) and elongation (El) on a commercial scale. As demand has grown for lighter-weight automobiles, so also has the demand for higher TS, lower yield ratio, and higher hole expansion ratio grown. Recently DP steel has been developed with precipitation hardening and grain refining by TiC. A new TRIP steel composed of 5Mn-2Si and control-rolled with niobium addition suggests the formation of retained austenite (γ R ) as much as 30% and TS × El = 3,000 kgf/mm2·%.
doi: 10.1007/s11837-008-0161-5pmid: N/A
Fluid systems in a variety of industries use tube fittings to readily install leak-free connections. Robust tube-fitting performance depends on adequate differential hardness, the gripping element on the tube, and a guided plastic deformation of the tube-gripping components. Low-temperature carburization technology hardens the surface of austenitic stainless steels. Since 1999, this treatment has been applied to the ferrules of the Swagelok tube fitting, ensuring tube grip, gas-tight seal, and vibration resistance in hundreds of millions of fluid system connections around the world. The process involves activation of the surface followed by a gas-phase treatment, performed at temperatures low enough to avoid the formation of carbides, for a sufficient time to allow carbon diffusion to occur. The result is a hardened conformal case on the treated parts without distortion or change to dimension. The treated case remains austenite (with verified carbon concentrations over 12 atomic percent at the surface) and retains its ductility. This paper will discuss the design features and performance characteristics of tube fittings enabled by low-temperature carburization.
Gröbner, Joachim; Janz, Andres; Kozlov, Artem; Mirković, Djordje; Schmid-Fetzer, Rainer
doi: 10.1007/s11837-008-0163-3pmid: N/A
In this paper an overview of the most relevant phase diagrams is given comprising the unconventional alloying elements Sn, Ca, and Sr, in reasonable combinations with Al and Mn in Mg alloys as a basis for advanced applications. The focus is on magnesium-rich partial projections of the liquidus surface of five ternary systems, relevant to technological applications for lightweight materials. All phase diagrams are calculated from a coherent thermodynamic multicomponent database for magnesium alloys. These calculations are validated by key samples in the pertinent subsystems, including extensive ternary assessments and also quaternary work. Isothermal sections of magnesium-rich phase diagrams of alloys with constant aluminum and manganese content at 500°C and 550°C are given for the two five-component systems: Mg-Al-Mn-Ca-Sr and Mg-Al-Mn-Ca-Sn.
Liu, Ming; Uggowitzer, Peter; Schmutz, Patrik; Atrens, Andrej
doi: 10.1007/s11837-008-0164-2pmid: N/A
The factors determining corrosion are reviewed in this paper, with an emphasis on iron tolerance limit and the production of high-purity castings. To understand the iron impurity tolerance limit, magnesium phase diagrams were calculated using the Pandat software package. Calculated phase diagrams can explain the iron tolerance limit and the production of high-purity castings by means of control of melt conditions; this is significant for the production of quality castings from recycled magnesium. Based on the new insight, the influence of the microstructure on corrosion of magnesium alloys is reviewed.
Shang, ShunLi; Zhang, Hui; Ganeshan, Swetha; Liu, Zi-Kui
doi: 10.1007/s11837-008-0165-1pmid: N/A
The available thermodynamic databases for magnesium alloys are discussed in this paper. Of particular interest are the features of a magnesium database developed by the authors with 19 elements: Mg-Al-Ca-Ce-Cu-Fe-KLa-Li-Mn-Na-Nd-Pr-Si-Sn-Sr-Y-Zn-Zr. Using this database, two applications are presented. One is the phase evolution in AZ61 magnesium alloy including the variations of phase fractions, alloying compositions, and partition coefficients of alloying elements as a function of temperature (or solid fraction). The other is to understand sodium-induced high-temperature embrittlement in the Al-Mg alloy, which is ascribed to the formation of a liquid phase due to the presence of sodium traces.
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