Alloys ductility values

Vacuum annealing leads to a higher ductility and impact toughness of alloy T110. Its multistage heat treatment provides the best combination of strength and ductility values. Annealing at 750°C is the simplest type of heat treatment and provides the required level of mechanical properties. 

Many austenitic stainless steels display a maximum in hydrogen embrittlement susceptibility at a temperature near 200 K and, like the ferritic alloys, are less susceptible at elevated temperature. The former behavior is illustrated in Fig. 3.7, which shows that the relative ductility of several austenitic stainless steels is lowest between 200 and 250 K [11] (a relative ductility value of 1 implies no hydrogen embrittlement). One effect of low temperature is to promote strain-induced martensite in metastable austenitic stainless steels, which enables hydrogen embrittlement. While a maximum in hydrogen embrittlement at moderately low temperatures is common for austenitic stainless steels, it is not a universal trend at least one alloy shows a minimum near room temperature [41, 42]. 

EFFECT OF COPPER. Elimination of copper, as in T448, results in an alloy of very low austenite stability, even much lower than the alloy containing 15 manganese. Apparently at these compositions, copper is a very strong austenite stabilizer. Again, the decreased austenite stability results in lower ductility values at all test temperatures. 

EFFECT OF CHROMIUM. The addition of chromium apparently results in an alloy of somewhat increased stability. The austenite stability measurements indicate that the addition of 2 chromium (5 total, T453) results in an alloy of somewhat higher stability than the addition of 2 manganese (19 total, T450), especially at room temperature and 77 K. At 20 K the results are not clear. Ductility values are about the same, with a higher ductility at room temperature, falling off more rapidly at low temperatures to approximately the same elongations at 20 K. 

Nitrogen (0.10 ) was added to alloy T451 (0.08 carbon) in an attempt to stabilize the austenite further. As shown in Table II, this addition approximately doubled the austenite stability. Ductility values remained almost identical at all test temperatures. Yield strengths increased, particularly at low temperatures. At 20"K the yield strength increased from 89,900 psi (T451) to 125,000 psi (T452). 

In snmmary, for the eutectoid alloy snbjected to the specified isothermal heat treatment, tensile strength and ductility values are approximately 1125 MPa and 42% RA, respectively. 

The formation of an alumina scale generally needs at least 5 wt% in alloys such as Ee-Cr or Ni-Cr. Over this aluminium content, the mechanical properties, mainly the alloy ductility, are poor, leading to machinability problems. Below this aluminium content, it is not possible to form a covering alumina scale, despite a favourable value for the free enthalpy of formation (-1238 kJ.moE at 1100°C [19]). These alloys generally contain enough chromium (typically around 20 wt%) to allow the growth of chromia layers. But, as the... 

Titanium alloys should be melted and cast under carefully controlled and optimum conditions. The higher elongation values of titanium castings reflect the superior ductihty of titanium. Ductile clasp arms of titanium castings can withstand relatively large bending adjustments without fracture. 

The hydrogen effect on ductility and the flow stress will be considered first on the example of non-alloyed titanium. The Ti - H phase diagram is given in Fig. 1, and Fig. 2 shows the temperature dependence of ductility of Ti-a H alloys, A , for several X values. Tensile tests were run at a rate e 10" s . Ductility of the commercial... 

Adsorption-induced brittle fracture. This model is based on the hypothesis that adsorption of environmental species lowers the interatomic bond strength and the stress required for cleavage. This model of chemical adsorption can explain the fact that a certain alloy is susceptible to specific ions. An important factor in support of this mechanism is the existence of a critical potential below which the SCC does not occur in some systems, and this model underlines the relation between the potential value and the capacity of adsorption of the aggressive ion. It also explains the preventive action of SCC for some systems by cathodic protection. This model may interpret the rupture of plastic materials or glass. It is referred to as the stress-sorption model, and similar mechanisms have been proposed for HE and LME. In this model, the crack should propagate in a continuous way at a rate determined by the arrival of the embrittling species at the crack tip. The model does not explain how the crack maintains a sharp tip in a normally ductile material.156... 

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