Remaining questions are based on the ironIron Carbide phase

Remaining questions are based on the iron-Iron Carbide phase diagram T FeaC 0.02 a+ Fesc Figure 5- Steel phase diagram. 13. What is the maximum carbon content in Austenite? (3) 2.ll 14. What is the eutectoid temperature of Steel? 15. What constituent of steel always contains 0.77 wt% carbon? (3) C)? (6) 16. What are the relative proportions of constituents in 4140 steel (0.4% 17. What is the purpose of adding alloying elements like nickel, chromium, molybdenum and boron to steels? (5)

Solution

1. What constituent of steel always contains .77wt% C

If you look at the phase diagram, the .77 mark is at the eutectoid miniumum.

The tie line from L to R across this fulcrum passes from ferrite to Fe3C on the right. So the two phases in equilibrium at theis balance of ,77C are Ferrite and Fe3C, in other words Pearlite or Bainite depending on quench time.

2)What are the relative proportions of Austenite in .4 %C

You need to locate .4% and draw a vertical to the temperature at which you quenched it, then draw a tie line across. On the way you may hit ferrit and the field with austeniste and Fe3C.Or if you are above ferrite temp, you are in austenite only. Once you have the correct temp line, apply lever rule.

3) These components change the gamma field (austenite ) and expand it so you have more room to get a ductile and creep resistant alloy. Each element affects the alloy in a different way.