Ing.de los materiales
(a) Transition temperatures defined by the mean of the absorbed energies are: 0.30% Mn: mean energy = 2 + (130 + 2)/2 = 68 J; T =27oC 0.39% Mn: mean energy = 5 + (135 + 5)/2 = 75 J; T = 10oC 1.01% Mn: mean energy = 5 + (135 + 5)/2 = 75 J; T = 0oC 1.55% Mn: mean energy = 15 + (140 + 15)/2 = 92.5 J; T = −12oC (b)Transition temperatures defined by 50 J are: 0.30% Mn: T = 15oC 0.39% Mn: T = −5oC 1.01% Mn: T = −15oC 1.55% Mn: T = −45oC
Increasing the manganese increases the toughness andreduces the transition temperature; manganese is therefore a desirable alloying element for improving the impact properties of the steel. If the part is to be used at 25oC, we wouldwant at least 1.0% Mn in the steel based on the mean absorbed energy criterion or 0.36% Mn based on the 50 J criterion. 7.2- A 1.5-cm-diameter metal bar with a 3-cm gage length issubjected to a tensile test. The following measurements are made.
Determine the strain hardening coefficient for the metal. Is the metal most likely to be FCC, BCC, or HCP? Explain.t = Ktn
ln 143 = ln K + n ln 0.2 ln 249 = ln K + n ln 0.6 (4.962 − 5.517) = n(−1.609 + 0.511)
n = 0.51 A strain hardening coefficient of 0.51 is typical of FCC metals.
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