Question 3. (4 4-3-11 points) the year 1907 Irelend, the J.P.Morgan was in the r

Question

Question 3. (4 4-3-11 points) the year 1907 Irelend, the J.P.Morgan was in the room One day you entered the elevator in the Engineering building and experienced a time travel to chairman of White Star line, J.Bruce Ismay and the person who wants to invest on this big ship where you suddenly arrived from 2018. The ship was just about to begin to construct at Be universe, you cannot change the fate of the iceberg collision, but you are design and process of the material. For your reference the figure below shows a plot of the impact Charpy test versus temperature for two different orientations for the Titanic hull steel, as well as modern lfast. Due to the rule of the allowed to suggest engineering solution to the energy measured by the A36 steel, which is similar to AISI 1018 steel. (a) Both the Titanic steel and the A36 steel have the same chemical composition, but why do they have different ductile to brittle temperature (DBTT)? (b) The steel material which they have in Belfast is the best you can get at that time so your option to change the performance of the material will be the heat treatment or pre-treatment (including machining) of the material. What process and heat treatment are you going to suggest? (c) Finer grain size usually increases the yield strength of the material. Show how the grain refinement decreases the DBTT using the Yoffee diagram. Brittle / Ductile Transition Curves 140 190 A36 Stee 120 163 136 100 106 Titanic Long 60 81 Titanic Trans 54 40 27 20 100 200 100 Temperature c

Explanation / Answer

(A) The ductile behaviour of the steel is largely dependent upon the variation of temperature and microstructure of the steels which is controlled during the forming process. The microstructure of A36 steel is oriented uniformly which gives it a better ductile behaviour as the grains can deform in the direction of applied load. For, the case of titanic steel the grain size is not uniformly distributed which reduces its ductility during the variation of temperature. The titanic steel also contained a increased amount of sulphur in it which adds to its brittle nature.

(B) To improve the performance of the steel a finer grain size can be used to resembling the properties of much finer pearlite with smaller and less numerous rare doped-earth MnS particles. This microstructure is very much similar to that produced in High speed mills followed by quench and normalization treatment of grain structure.

(C) Decrease in grain size results in both increase in yield strength and fracture strength which results in decrease in transition temperature. With the increase in yield strength the brittle nature of the material increases at the lower temperature as shown by the yoffee diagram.

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