Impact Energy (ft-lb) #2 Hardness (HR.) Heat Treatment | #1 Annealing Normalizin

Question

Impact Energy (ft-lb) #2 Hardness (HR.) Heat Treatment | #1 Annealing Normalizing 95 Polymer Q.117123120 Water Q. Tempered 1 Average | #1 #2 #4 Average 2 .5 105 100 11.7 11.49.16 9.16 15.5 20.819.2 21.7 19.54 19.54 20.227.823.7 28.227.5227.52 35.3 28.434.636.4 34.34 34.34 56 56 56 86 80 83 1. Explain the results and analyze the plots for trends. (Hint: In the plot of HRC vs. Impact Energy, 5 there should be a clear trend for all of the samp7) First point furthest to the left is annealing To the right of it is normalizing, then polymer Quenching, Water Q. and Tempered Hardnes vs Impact Energy 150 100 0 10 2 30 40 Average Hardness

Explanation / Answer

In annealing of steel, say, the specimen is heated above upper critical temperature for hypoeutectoid steel and lower critical temperature for hyper eutectoid steel and then cooled in a furnace. Here the product will be tougher and ductile. Hence obviously the hardness and impact resistance is lowest.

But in normalizing, it's heated above upper critical temperature and cooled in air, resulting in a finer grains. As suggested by Hall-perch relation if grain size reduces strength increases and hardness also. This is the reason for this trend.

However in water quenching the rate if cooling is every high, hence hardest material is obtained.

Forging quenching is done on forged products to increase the hardness. This is good for better depth of hardening in impact testing. It's evident from results

Tempering is done to reduce the hardness and increase toughness of a quenched material by heating at a temperature of about 300 to 500 degree Celsius. So hardness of tempered is less than quenched one.

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