What is the allowable contact stress number, sac, in MPa,  for ductile iron  ASTM A536,  60-40-18 annealed?

1600 Question 4. An austenitized 4340 standard steel bar is cooled at different rates (see Figure 2). 0.41 C,0.87 Mn, 0.28 Si, L.83 Ni. 0.72 Cr, 0.20 Mo 12.7 mm 4340 25 mm 800 mm 19 mm Austenitized at 1550F (843 C) Grain size: ASTM No.7 Acy: 1390'F (754 C) Ac: 1330'F (721'C) Predict what will be the constituents in the 1400 Va in. microstructure of the bar at 200°C for the 6.3 mm 700 76 mm following cooling rates: 1200 9.5 mm Cooling curves from 1550'F (843 C) at indicated distances from quenched end mm 600 (a) 5°C/s (51-mm from the quenched end of a Jominy bar) (b) 8°C/s (19.0-mm from the quenched end of a Jominy bar) (c) 50°C/s (9.5-mm from åe quenched end of a Jominy bar) E 1000 |500 800 400 Transformed 600 No% 300 M+A 400 200 200 100 1000 10 20 50 100 200 500 Cooling time (s) Figure 2 Temperature (F) Temperature (C)