Basic of Steel

8/10/2019 Basic of Steel

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Title : Introduction to steel

Date : 13/11/2013Time : 6.30-7.30PM

Venue : Conference room


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Steel making process

Global Statistics:

According to the World Steel Association, in 2011 global

crude steel production reached a new record high at 1.527

billion metric tonnes. Of this, approximately two-thirds wasproduced using BOS plants, while EAF facilities accounted

for the remaining third

The largest steel producing countries in 2011 were China,

Japan, US, and India. China currently supplies about 45%of the world's steel. The world's largest steel producers

include Arcelor Mittal, Baosteel, POSCO and Nippon Steel.


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Iron making:

the raw inputs iron ore, coke and lime are melted in a blastfurnace.

The resulting molten iron - also referred to as 'hot metal' - stillcontains 4-4.5% carbon and other impurities that make itbrittle.

Primary Steelmaking:

differ between BOS and EAF methods.

BOS methods add recycled scrap steel to the molten iron in aconverter.

At high temperatures, oxygen is blown through the metal,which reduces the carbon content to between 0-1.5%.

EAF methods, alternatively, feed recycled steel scrap throughuse high power electric arcs (temperatures up to 1650 C) tomelt the metal and convert it to high quality steel.


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Secondary Steelmaking:

involves treating the molten steel produced from both BOS and

EAF routes to adjust the steel composition. This is done by adding or removing certain elements and/or

manipulating the temperature and production environment

Continuous Casting:

the molten steel is cast into a cooled mold causing a thin steel

shell to solidify.

The shell strand is withdrawn using guided rolls and fully

cooled and solidified.

The strand is cut into desired lengths depending on application;slabs for flat products (plate and strip), blooms for sections

(beams), billets for long products


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What is coke


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Blast furnace


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Steel finishing


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Steel finishing


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Type of steelCarbon Steels:

Carbon steelscontain trace amounts of alloying elements and account

for 90% of total steel production. Carbon steels can be furthercategorized into three groups depending on their carbon content:

Low Carbon Steels/Mild Steelscontain up to 0.3% carbon

Medium Carbon Steelscontain 0.30.6% carbon

High Carbon Steelscontain more than 0.6% carbon

Alloy Steels

Alloy steels contain alloying elements (e.g. manganese,

silicon, nickel, titanium, copper, chromium and aluminum) in varying

proportions in order to manipulate the steel's properties, such asits hardenability, corrosion resistance, strength, formability, weldability

or ductility.

Applications for alloys steel include pipelines, auto parts,

transformers, power generators and electric motors.


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Stainless Steels:

Stainless steelsgenerally contain between 10-20% chromium as the main

alloying element and are valued for high corrosion resistance. With over

11% chromium, steel is about 200 times more resistant to corrosion than

mild steel.Austenitic

non-magnetic and non heat-treatable,

generally contain 18% chromium, 8% nickel and less than 0.8% carbon.

304, 316, 316L

Ferritic

contain trace amounts of nickel, 12-17% chromium, less than 0.1%

carbon, along with other alloying elements, such as molybdenum,

aluminum or titanium.

These magnetic steels cannot be hardened with heat treatment, but canbe strengthened by cold works.

resistant to chloride stress corrosion cracking, and have high strength.

405, 409


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Martensitic:

Martensitic steels contain 11-17% chromium, less than 0.4% nickel and up to

1.2% carbon.

not as corrosion-resistant These magnetic and heat-treatable steels are used in knives, cutting tools,

as well as dental and surgical equipment and Swiss Army knife

17-4PH

Duplex Stainless Steel

having both austenite and ferrite in their microstructure

roughly twice the strength compared to austenitic stainless steels and also

improved resistance to localized corrosion.


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Element Function

Carbon (C) :

An essential alloying element in most steels.

Added to increase solid-solution strength and hardness as well as to

Increase hardenability.

Dissolves in iron to form ferrite and austenite. Combines with iron to

form a carbide (cementite-Fe3C). The carbide is a component of pearlite.

Manganese (Mn) :


Added to increase solid-solution strength and hardness as well as to increase

hardenability.

A weak carbide former (greater than iron).

Counteracts brittleness caused by sulfur (iron sulfide) through the formation of

a manganese sulfide (MnS).

High levels of manganese produce an austenitic steel with improved wear and

abrasion resistance.


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Phosphorus (P)

considered an impurity in most steels.

Can be added to low-carbon steels to increase strength and hardness.

Improves machinability of free-machining steels. Promotes temper

embrittlement. Forms an undesirable iron phosphide (Fe3P) at high phosphorus levels

(especially in cast irons)

Sulfur (S)

Usually considered an impurity in steel.

Added to special steels for improved machinability

Silicon (Si)


Added to increase solid-solution strength and hardness as well as to increase

hardenability. Is added to molten steel to remove oxygen (deoxidize).

Does not form a carbide in steels. Improves oxidation resistance.

Added to special steels to improve electrical and magnetic properties as well as

hardenability.

Increases susceptibility to decarburization. Promotes graphitization in cast irons


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Deoxidized steelDeoxidized steel :steel that has a some or all of the oxygen removed from the melt duringthe steelmaking processLiquid steels contain dissolved oxygen after their conversion frommolten iron, but the solubility of oxygen in steel decreases withtemperature.

As steel cools, excess oxygen can cause blowholes or precipitate FeO.

Types

Fully killed

steel that has been completely deoxidized by the addition of an agentbefore casting.

deoxidizing agents include aluminum, ferrosilicon and manganese.


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Semi-killed

I. mostly deoxidized steel, but the carbon monoxide left leaves

blowhole type porosity distributed throughout the ingot.

Rimmed

I. has little to no deoxidizing agent added to it during casting

which causes carbon monoxide to evolve rapidly from the ingot

II. causes small blow holes in the surface that are later closed upin the hot rolling process

Capped

I. starts as rimmed steel but part way through the solidification

the ingot is capped

II. done by literally covering the ingot mold or by adding a

deoxidizing agent


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Formal Classi f icat ion Sys tems

The American Iron and Steel Institute (AISI) and Society of

Automotive Engineers (SAE) System.

In the four- or five-digit code designation, the last two or three

digits represent the carbon content (three digits for steels with

a carbon content of 1.00% and above), and the first two digitsrepresent the compositional class.

example of AISI/SAE 1040, the 10 represents the class of

plain carbon steels, and the 40 represents the carbon contentof 0.40% C.


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The American Society for Testing and Materials (ASTM)

System.

not based on composition but on the steel product and

application.

devised a system of specifications that contain composition,

mechanical properties, and other required characteristics of

steels and cast irons.

The American Society of Mechanical Engineers (ASME) deviseda similar system, but it is generally limited to boiler and heat

exchanger steels and other materials that are covered by the

boiler code specifications.


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The Unified Numbering System (UNS).

1. Created because of the confusion of different systems

2. The system fully incorporates the AISI/SAE system.

3. G: carbon and alloy steels. F: cast irons D:steels with specificmechanical properties. S: heat- and corrosion resistant steels.

T: for tool steels. H: for steels with enhanced hardenability.

European Standards (ENs)

Prepared and issued by CEN (European Committee and

Standardization) E.g. EN 10025-2004 ; standard for structural steel


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MILL CERT


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TYPE OF INSPECTION Refer EN 10204 : 2004


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Material identification

Heat Number/ Ladle number/Cast number

1. An identification number that is stamped on a material plate after it

is removed from the ladle and rolled at a steel mill.

2. The only way to trace a steel plate back to its Mill Cert

3. similar to a lot number, which is used to identify production runs ofany other product for quality control purposes.


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Type of chemical analysisLadle/heat analysis

1. chemical analysis obtained from a sample taken during

pouring of steel.

2. Ladle analysis is representative of the heat of steel and is

reported to the purchase

Product/check analysis

1. analysis of the metal after it has been rolled or forged into

semi-finished or finished forms. It is not a check on the ladle

analysis, but is a check against the chemistry ordered.

2. Check analysis of known heats is justified only where a highdegree of uniformity of composition is essential


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Charpy impact test To determine the resistance of a material against shocks. The

resistance does decrease with decreasing temperature.

There are 2 types of Charpy tests:

1. U-notch, called Charpy U

2. V-notch, called Charpy V.


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Hardness test Hardness definition: resistance to local penetration to

scratching, to machining, to wear or abrasion, and to yielding. Type of hardness test:

Brinell

Rockwell

Vickers

Refer ASTM E140 for

Hardness conversion


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Stress strain diagram

Yield strength: max stress/load can be applied without

permanent deformation.

Tensile strength (UTS): max stress/load can be sustained by the

specimen.


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Tensile test (ASTM A370)


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Material compliance


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Material traceability

General Requirement All the material must have physical traceability from the steel

manufacturer except for the subdivided material.

All the data (HN, grade, Manufacturer) for the subdividedmaterial must be transferred on the material (refer ASTM A6for more detail)


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Special project requirement Any special requirement for the material, purchaser will trigger

the supplier for the specification needed.

Example ASME BPV requirement

1. for all the plate for pressure vessel, the requirement must

comply with the purchase specification (refer below) provided by

purchaser


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COMMON ISSUE IN MILL

CERT


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1. No cert and heat number

Cert number

not

available

HN number not

available


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2. No mechanical data

Please dont provide

material without

mechanical data

(basic YS, TS, EL)


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3. Unclear mill cert


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4. Company logo and name not visible.

Manufacturer??


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5. Different units used in part description

mm and inch in one item

dimension


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MVR contains:

Project detail

Material grade (spec and actual)

Purchase dimension Mechanical properties (spec and

actual)

Chemical properties (spec and actual)


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WHY MVR IMPORTANT

Make sure the material comply with customer spec-green light to

purchaser to purchase the material

Make sure qc personnel receive correct material-heat number must

tally between material, mill cert received and MVR.


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Spec comparison

Either using customer MS or standard industrial spec.

For customer MS, all the chemical and mechanical properties

must comply with the spec.

Any value less or exceed from the spec it will be rejected.

Purchasing will liaise with project personnel if the need to raise a

concession/deviation

For customer spec that using standard industrial spec, the mill

cert will review base the mentioned spec.

Any value that less or exceed the standard, it will be rejected

unless got some tolerance for that.


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FLOW

CHARTmill cert receive from Purchasing

Dept.

JO internal raise by

engineering

MVR approved

MVR

no

Purchasing Dept. will source other material

Purchasing Dept. Ask project to

raise a waiver

yes

Waiver approved

yes

PSL, drawing and BOM received

Send to Purchasing Dept. to purchase the

material

no


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Thank you


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Reference

DNV 2.7-1

EN 10204-2004

Steel Metallurgy for the Non-Metallurgist by John D. Verhoeven

Mechanical Metallurgy by George E. Dieter]

wikipedia

Engineering Handbook

Basic of Steel

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