QTR Operation 27.09.10.ppt

8/10/2019 QTR Operation 27.09.10.ppt

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Operation in QTB


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Process inQ.T.B.

Principle

A Thermo-mechanical Metallurgical Process of Quenched Tempered Bar

Heated bar surface is quenched (hardened) by flowing stream of water

Hardened surface is tempered by flowing heat flux from bar core


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Philosophy Behind Process

Cost-EffectivenessBillet Cost

2000 Tk /T lower compared with Low Alloy Steel3000 Tk/T lower compared with Micro- alloyed Steel

Property-EffectivenessYield Strength

Increased by 150 MPa

Ductility

Good value

Welding Ability

Improved through reduction of alloying elements

Mechanical PropertyBetter uniformity and repeatability


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IststageSurface quenching by means of

water spraying in QTB.

Result: martensite and bainite at the outersurface.

Theory behind Operation

3rd stageSlow cooling of cores results ferrite and pearlite

2ndstageFlowingresidual heat from core temper crudemartensite And to some extent bainite

TEMPERINGSTAGE

Austenite

::

Austenite

Martensite

200 C

400 C

600 C

800 C

BAR SURFACE

BAR CORE

MIDDLERADIUS

QUENCHINGSTAGE

COOLINGFINAL

TEMPERING

TEMPERATURE

Bainite

Tempered Bainite

Bainite

Ferrite + Pearlite


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tempered martensite

mixed bainitic products

ferrite-pearlite

TEMPEREDMARTENSITE

MIXEDBAINITE

PEARLITE-FERRITE

Microstructure

TemperedmartensiteDepth 0,8 to 2,0 mm,

Hardness 280 - 300 HV

Mix bainiteDepth 1,2 to 2,8 mm

Hardness 220 - 240 HV

Ferrite and pearliteHardness 190 - 210 H

Distribution of hardness, strength and ductility prove its superiority


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Comparison among Rolling Processes

C

% C

1100

1000

910

800

700

6000.86 2.10

Austenite

Primary Ferriteand Pearlite

Thermo Mechanical

Rolling

Conventional

Rolling

Primary / Pro-

eutectoidFerrite +

Stable

Austenite

Austenite

Ferrite


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QTB Parts

Consists of

Water box

Water system.

Pneumatic system

Hydraulic system

Electric system/Automation

laying head

finishing block

valves benches

water quenching boxes


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Box type, Main body of QTB Process

Q.T.B.

Troll ey type, adry roller table and by-pass water treatment for producing sections

Welded, with top cover and containing one or more treating line/s.

Types

What it is

F ixed type, fixed foundation for production of bars.


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0 10 20 30 40 50 60

600

650

700

750

800

850

900

950

1,0001,050

1,100

TEMPERATURE(C)

1waterbox

2waterbox

3waterbox

laying

head

minimum temperature during water cooling = 600C

max temperature difference at laying headbetween surface and core = 100C

max finishing temperature = 1100C (for 5.5 - 6 mm)

min re-equalizing time1.5 x W.C. time

min coiling temperature800C (for 5.5 - 6 mm)

FINAL STEEL GRADE

(AISI)

LAYINGTEMPERATURE

(C)

COOLINGMODE

Low Carbon 1008 880 - 920 slow

1012 880 - 900 slow

Medium Carbon 1038 840 - 850 slow1038 860 - 880 fast

Temperature Profile in QTB Process


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Composed of:

Cooler

Stripper

Dryer

Material flow

Cooling Chambers Strippers Dryer

Water Box Treatment Line


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Water supplyline

Spraying of cold water in same direction of bar at rate higher than critical cooling rate for MS bar

Cooler

Main body (green) with a bottom inlet hole and top plane

Consists of

What it does

Final guiding pipe (purple and grey) with second locking point.

Internal element (grey) ensured in position by locking nut (orange).


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Material flow

Water supplyline

Opposite directional water flow relative to bar breaks down the water wall of bar.

Contact

PlaneWater or

CompressedAir supply

Gap

AdjustingPlane

Stripper

Main body (green & purple) with a bottom inlet hole and Top plane for locking purposes.

What it Does

Internal element (grey), screwed in to the main body, locked in position by

the locking nut (black)

Internal element is adjustable according to the different products and water requirement

Composed of


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Main body (green & purple) with a bottom inlet hole and Top plane for locking purposes.

Material flow

Water supplyline

Air supplyline

Gap AdjustingPlane

Water or

Compressed

Air supply

Contact

Plane

Dryer

Compressed air is oppositely directed to bar movement

Drying water and steam from the bar.

What it does

Composed of

Internal element (grey) locked in position by the locking nut (black).


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Use as system back up for QTB process

By Pass Pipe

What it does


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QTB Water System

W.T.P. Booster pumps

Distribution benchDelivery line

Compressed Water

Water

Compressed

Water

How it works


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Pneumatic System

Dryer

Air feeder Feeding lines

Actuators of FCV,

On/off valves.

Air Air

Air

How it works


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Electrical System

Flow rate close loop control

Temperature close loop control

Interlocking

Sequence controlReadings

-

-

-

-

Display of main variables

Alarm displayLine set-up

CONTROL PANEL

-

-

PLC

T T

SIGNALS FROM

PYROMETERS

M

PUMPS UNIT

IPIP

PIFTPT

VALVE BENCH

electropneumatic

PLC

How it works


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Conclusion

Steel Grade

Typical

Steel

Natural Cooling QTB Process

YS

(N/mm2)

UTS

(N/mm2)

EL

(%)

YS

(N/mm2)

UTS

(N/mm2)

EL

(%)

Low Carbon QTB 400 ------ ------- ----- > 400 > 500 > 17

Low Carbon QTB 500 ----- ------- ------ > 500 > 600 >14

Yield Strength, increased by 150 MPa

Good valuesof ductility

Better uniformity and repeatability of mechanical properties

Improved Welding ability through reduction of alloying elements


19/19

Thank You

All

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QTR Operation 27.09.10.ppt