Materials technology

Past exam questions

Name

Date

Question 1

Rimmed steel often possess little or even no deoxidizing agent used on it during the casting process which allows CO evolving from the ingot

Semi-killed is a deoxidized form of steel . However , the remaining CO2 results into porosity from blow holes distributed across the ingot

Capped steel unlike the rimmed steel , involves capping of the ingot as solidification takes place . This is mainly a result of adding deoxidizing agent . It cleanliness decreases as carbon content increases .Killed steel involves complete de-oxidation of an

agent prior to casting . No gases are thus evolved during solidification . They exhibit high level of chemical homogeneity as well as freedom in relation to gas porosity

Rimmed Killed

Low quality usually used for making steels sheets , wires and tubes . High quality used for making automotive , aircraft and marine engines

Least homogenous form of steel due to segregation effects . No segregation effect hence most homogenous

Good surface quality Poor surface quality

Has low yields and high costs Has high yields reduced costs

Poor formability characteristics Good formability characteristics Segregation effects

Segregation effect relate to the chemical composition non-uniformity . In rolled plates the extent to which centerline segregation occurs is increased centerline segregation resulting to decreased grain size and randomized crystalline distribution and orientation

The high yield strength possessed by cast irons calls for application of large plastic deformations during its processing . This results into change in grain size and orientations to that f directional dependency thus its anisotropic properties

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