Tensile Properties, Structural Alloys

The mechanical properties of low- or medium-carbon structural steels can be improved considerably by small alloy additions. For example, 1% of chromium will raise the yield point of 0.2% carbon steel from about 280MN/m to 390MN/m. This has led to the development of a range of so-called low-alloy steels with high tensile properties. A typical example is grade 817M40 (En 24), which contains 0.4% C, 0.2% Si, 0.6%, Mn, 1.2%, Cr, 0.3% Mo and 1.5% Ni. 

Main uses ofNa alloys. Hypoeutectic Al-Si alloys (from 5 mass% Si to the eutectic) through the so-called modification (structural modification of the normally occurring eutectic) achieve somewhat higher tensile properties and improved ductility. Modification is obtained by the addition of elements such as Na (or Sr, Ca, Sb) and results in a finer lamellar or fibrous eutectic. Phosphorus, which reacts with sodium, interferes with the modification mechanism. Sodium can be used as the reductant of several chlorides in the preparation of metals such as Ti (Hunter process), Zr, Hf, Nb, Ta. 

Fu] Fu, W., Furuhara, T., Maki, T., Effect of Mn and Si Addition on Microstracture and Tensile Properties of Cold-rolled and Annealed Pearlite in Eutectoid Fe-C Alloys , ISU Int., 44, 171-178 (2004) (Crys. Structure, Experimental, Meehan. Prop., Morphology, Phys. Prop., 32)... 

The tensile properties of the 7000 series aluminum alloys were determined as a function of temperature from 78° to 423°F. Partial embrittlement, as determined by notch/unnotched tensile ratios, was experienced by all the alloys at cryogenic temperatures however, 7079-T6 sheet material was found to retain sufficient toughness for structural applications to-320 F. The low temperature... 

Tensile properties at room temperatureforaTi-25AI-16Nb alloy lath structures as function of cooling rate (p) and equiaxed structures (a2 + P) as a function of primary, equiaxed o2 volume fraclion. 

These alloys contain 3-12 wt% Mg. Strength increases with increasing Mg content (Fig. 3.1-33). Above about 7 wt% Mg, the alloy has to be heat-treated to homogenise the structure and thus obtain good tensile properties. With Mg contents of up to 5 wt%. Si additions of up to 1 wt% are possible, and these lead mainly to improvements in the casting properties. The addition of Si causes hardening due to the formation of Mg2Si. 

Alloys of antimony, tin, and arsenic offer hmited improvement in mechanical properties, but the usefulness of lead is limited primarily because of its poor structural qualities. It has a low melting point and a high coefficient of expansion, and it is a veiy ductile material that will creep under a tensile stress as low as 1 MPa (145 IbFin"). 

Nickel normally crystallises in the f.c.c. structure it undergoes a magnetic transformation at 357°C and is ferromagnetic below that temperature. In all the alloys shown in Table 4.21 the f.c.c. (austenitic) structure is substantially retained, and in consequence most of the alloys possess the combination of properties required of materials for widespread industrial acceptability, i.e. tensile strength, ductility, impact strength, hardness, hot and cold workability, machinability and fabrication. 

Beryllium is a light metal (s.g. 1 -85) with a hexagonal close-packed structure (axial ratio 1 568). The most notable of its mechanical properties is its low ductility at room temperature. Deformation at room temperature is restricted to slip on the basal plane, which takes place only to a very limited extent. Consequently, at room temperature beryllium is by normal standards a brittle metal, exhibiting only about 2 to 4% tensile elongation. Mechanical deformation increases this by the development of preferred orientation, but only in the direction of working and at the expense of ductility in other directions. Ductility also increases very markedly at temperatures above about 300°C with alternative slip on the 1010 prismatic planes. In consequence, all mechanical working of beryllium is carried out at elevated temperatures. It has not yet been resolved whether the brittleness of beryllium is fundamental or results from small amounts of impurities. Beryllium is a very poor solvent for other metals and, to date, it has not been possible to overcome the brittleness problem by alloying. 

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