Question

The hardenability curves for a number of steels are shown in the diagram below. Rank the steels in ascending order according to their hardenability. If the thermal properties of the steels are the same, i.e. the cooling curves (temperature versus time) at a certain distance from the quenching end are the same for all the steels, explain the difference in hardness at a distance of 30 mm from the quenched end between 5140 and 4340 by plotting schematically the C curves for each in the same continuous TTT (i.e. temperature-time-transformation) diagram and comparing the resulting microstructures. Cooling rate at 700°C (1300°F) 2 490 305 125 56 33 16.3 10 2 2 270 170 70 31 18 5.6 3.9 2.8 4340 0 8640 5140 3 2 2 3 0 4 50 mm 0 1 0 0 Distance from quenched end

Answer 1

belo ω Coolng välk 6O 100 70 4340 So 8640 3 0 40 30 l0 Distanca uhed end distan 30mm, for Sted Numbe 4340 os Stee No 514o Handness 30MRC Cat sonvn disn) Sublhacl -tese o valu Hodnessfo steel N 864 3S HR gheel NO 4140 is 43HRC

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