60 100 80 50 50 40 -: PERCENTAGE MARTENSTE, Me, % 30 10 15 20 25 30 35 40 45 50
ID: 2248076 • Letter: 6
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60 100 80 50 50 40 -: PERCENTAGE MARTENSTE, Me, % 30 10 15 20 25 30 35 40 45 50 Distance from Quenched End, d, mmm 170 70 31 18 5,6 3.9 2.8 Cooling Rate Re, C. imen is the le-shown in PROBLEM 5. Using the figure titled: AISI 4140 Hardenability Range determine and state why a range is more appropriate than a single curve. the variable Justify this answer by hypothesizing what the is always the position of the measured and plotted AISI 4140 set of dato alues is your the same table specimen indicates about its composition.Explanation / Answer
The Jominy End Quench Test ASTM A 255 measures Hardenability of steels. Hardenability is a measure of the capacity of a steel to be hardened in depth when quenched from its austenitizing temperature. Hardenability of a steel should not be confused with the hardness of a steel. The Hardness of a steel refers to its ability to resist deformation when a load is applied, whereas hardenability refers to its ability to be hardened to a particular depth under a particular set of conditions. Information gained from this test is necessary in selecting the proper combination of alloy steel and heat treatment to minimize thermal stresses and distortion when manufacturing components of various sizes.
To perform the Jominy Test: First, a sample specimen cylinder either 100mm in length and 25mm in diameter, or alternatively, 102mm by 25.4mm is obtained. Second, the steel sample is normalized to eliminate differences in microstructure due to previous forging, and then it is austenitised. This is usually at a temperature of 800 to 900°C. Next, the specimen is rapidly transferred to the test machine, where it is held vertically and sprayed with a controlled flow of water onto one end of the sample. This cools the specimen from one end, simulating the effect of quenching a larger steel component in water. Because the cooling rate decreases as one moves further from the quenched end, you can measure the effects of a wide range of cooling rates from vary rapid at the quenched end to air cooled at the far end.
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