Question

QUESTION 9 a) Heat treatment schedule for three (3) thin samples of plain carbon steel containing different carbon concentration is summarized in Table Q9(a). Determine and sketch the resultant microstructure for each steel. Distinguish steel 1 from steel 3 with reference to their mechanical properties. Table 29(a) Steel wt% C Heating temperature Soaking time (°C) (minutes) Cooling process 1 0.5 950 60 Furnace cooled 2 0.8 800 60 Air cooled 3 1.2 850 60 Furnace cooled (6 marks) b) List four (4) mechanisms in which a metal can be strengthened by hindering the motion of dislocations. Briefly explain why metallic alloy is usually harder and stronger than pure metal from the standpoint of the mechanism that causes resistance to dislocation motion (6 marks) QUESTION 10 a) Heat treatment schedule for two (2) thin samples of 0.2 wt%C steel is summarized in Table Q10(a). Distinguish steel 1 from steel 2 from the stand point of their microstructure and mechanical properties and propose the steel which should be chosen in applications requiring good wear resistance. CO2/PO2/04 (6 marks) Table Q10(a) Heating Steel temperature Heating environment Soaking time Cooling process (°C) (minutes) 950 Normal 60 Furnace cooled Carbon rich 950 60 (Pack in charcoal) Furnace cooled 1 2 b) Excellent combinations of hardness, strength, and toughness are obtained from tempered martensite. One heat treatment facility austenitized an eutectoid steel at 850°C, held for 45 min and finally allowed the steel to cooled in normal air. Do you think the required tempered martensite structure was produced? If not, propose in detail a heat treatment that can be employed for the steel. CO2/PO2/04 (6 marks)

Its a thermal treatment of metallic materials from material science questions

Answer 1

Solution 9 (a) Microstructure Steel 1 : o.swt %. c heated groc & soak time 60min I cooley furnace cooled d slow co since cooling promotes pearlite formation caybon ontent less than entectoid composition there fore at room temperature pheses formed pearlite + poroentectad ferrite where pearlite = Ferozite t cementite. cora cementite + ferrite e? pearlite proeutectoid ferrite steel 2 0.8 wt %C heated 800°c soal time 60 mia د\ air cooled since carbon content is eand to entectoid composition, therefore at room temperature phase formed pearlite consist alternate layers of cementite and ferrite. Micro structure ferrite othing of pearlite cementite

steel 3: 1.2 wtf.ca heated 850°c soak time 60mis cooling since is more furnace cooled carton content than entectoid composition, therefore at room temperature phases formed are pearlite & proeutectoid cementite microstructure cementite pearlite forrit proentectoid cementite

from steel 3 Compared to steel 1 steel 1 forite is softer And steel 3 is softer than steel 3 is harder than steel 1. Reason is that and cementite phase is harder . Rn steal 1 amount ferrite phase is more than steel has more amount 3: But steel 2 has of amentite than steel 1 of 1 2 Age precipitation har 3 work 4 (6) Fowy mechanis ons for strengthening by henderry the motion of dislocations Solute solution hardeni soning hardening cold worki working hardening Grain size redretion. Metallic allog is handey and and stronger than metal based on resistance to dislocation motion : if dislocations easily move across the and grams then the material gets gram boundary no hinderance to because there is deformed easily dislocation motion due to which crack on any defect ecsity propagates pure Basically

In case but in cannot pass easily voida metallic solute atoms filled the voids of metal due to which the dislocations of pure metals present so diskications ooss easily and exacle propagates. That's strungth and hendress is compared to more why In metallic alloys metals. pure