7/31/2019 Assignment 3 Pmt

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Dewi Lestari Natalia (1006704530)

Teknik Metalurgi dan Material

Assignment 3

Question 1A. Explain how Carbon content affects the strength of steels.

Carbon content affects the strength of steel : the more cabon, so makes the steel

stronger and make lower ductility.

B. Microstructures of low carbon steels mainly consist of ferrite and pearlite.

Describe about ferrite and pearlite.

Ferrite : Body-centered cubic iron; also iron and steel alloys thathave the BCC crystal structure.

Pearlite : A two-phase microstructure found in some steels andcast irons; it results from the transformation of austenite of eutectoid

composition and consists of alternating layers (or lamellae) of -ferrite

and cementite.

C. What is the function of alloying elements in steels?

The function of alloying elements in steel are

increase hardenability,

improve strength,

improve mechanical properties (at operating temperature),

improve toughness for a given strength or hardness,

increase wear resitance,

improve magnetic properties.

D. On the basis of microstructure, briefly explain why gray cast iron is brittle? Also

describe typical applications of gray cast iron.The gray cast iron is brittle as a consequence of its

microstructure; the tips of the graphite flakes are sharp and pointed.Typical applications of gray cast iron are

engine blocks

brake drums

machine castings

E. Compare white and nodular cast iron with respect to (a) composition and heattreatment, (b) microstructure and (c) mechanical characteristics.

White Cast Iron Nodular Cast Irona) 3,4% C, heat treatable at

900C3,4% C; 0,03-0,05% Mg; heat-treatable to increase hardness

b) Pearlite in cementite Graphite speroid in a matrix of ferrite, pearlite, or both

c) Very hard but very brittle, Tough, ductile, almost like a

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wear-resistant steel

Question 2

A. Explain the stages of steel making conducted at PT. Krakatau Steel. You have to

explain the process from iron ore to semi-finished products. Please be concise and

focus on the concept and principle of each stage.Fe in terms of Fe2O3 is taking from the earth crust. % Fe in hematit devided into 2

(< 60% and >60%), Fe2O3 which % Fe < 60% is being pured, which the process are :

1. crushing and grinding iron ore

2. iron ore is cleaned in order to execute their impurities

3. separated between iron mineral and non iron mineral by magnetic separatorthe final result is consentrat (% Fe has been more than 60%).

Consentrat can be processed in blast furnace because of its small size. Consentrat must be

clotted first by agglomeration process, resulting pellet/sinter.After that, the process is reduction process, PT. Krakatau Steel uses direct reduction

reduction process.

direct reduction raw material : pellet

process : pellet is reducted direcly by CO from CH4 , in the hylsa or

midrex

the result : sponge iron (small size) or hot briket iron (big size)

electrical arc furnace (EAF)

sponge iron is raw material for steel making process in EAF. The process is happened insolid phase, so energy used is less than energy used in blast furnace. When it is used in

EAF, it can be used 100% sponge iron as bait material, because of the existance of non

metallic inclusion.Sponge iron is entered to the furnace continually after the bait material previously melt

(scrap) consumption of sponge iron in EAF, 70-90%, the remainder is return or scrapcommercial. The greater sponge iron using better steel quality will be produced.

B. Mention 3 (three) examples of engineering products made of steel.

Automotive component

Railways

Gears