13 - q+t steels & welding q+t steels

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08/06/2004Istituto Italiano della saldaturaENTE MORALE

WELDABILITY OF LOW ALLOYED

QUENCHED AND TEMPERD

STEELS


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Weldability of Q+T steels

Istituto Italiano della saldaturaENTE MORALE

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Introduction QUENCHED AND TEMPERED steels

are designed especially for welded

construction and fabrication.

They are furnished from steel producers

in the heat treated condition

Yield strengths range from 350 to 1000

MPa) depending on

their chemical composition

Thickness

type of heat treatment.

The heat treatment for most of these

steels consists of austenitizing,

quenching, and tempering.

A few are given a precipitation-

hardening (i.e., aging) treatment

following hot rolling or some other

thermal treatment.


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Metallurgy The carbon content of quenched and tempered steels generally does not

exceed 0.22% for good weldability.

The other alloying elements are carefully selected to provide the most

economically heat-treated steel with the desired properties and acceptable

weldability:

Microalloyng elements (Al, Ti, V, Ti, Zr, Nb)

Quenching elements (Cr, Mo, Cu, Ni)

Small quantities of Boron, 5 to10 ppm, in order to reduce grain size.


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Chemical composition EN 10137-2


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Tensile properties EN 10137-2


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Toughness EN 10137-2


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Chemical composition EN 10028-6


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Tensile properties EN 10028-6


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Toughness properties - EN 10028-6


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ASTM designations

f Q


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Commercial designations

T1 (grades T1, T1A, T1B e T1C)

US Steel patented, is classified

as

ASTM A514 structural

ASTM A517 pressure equipment

HY

US Navy specification

used for submarines

Good toughness properties at

low temperature

USS Skipjack, 1965

W ld bilit f Q T t l


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Chemical composition

W ld bilit f Q T t l


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Weldability

Cold cracking

The metallurgical structure is anon-equilibrium structure

Hydrogen must be as low as

possible

Preheat temperature must be

properly selected Hot cracking

Susceptivity is generally low

Some phenomena may occur

depending on Ni content

Lamellar tearing

The heat treatment generally

guarantees good properties

W ld bilit f Q+T t l


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Weldability

To obtain the same

properties of the materialafter welding:

Low heat input

Low preheat temperature

Low interpass temperature

W ld bilit f Q+T t l


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Weldability - PWHT

The mechanical properties of thewelded steel or the weld metal itselfmay be adversely affected by astress relief.

The alloying elements can causeadverse effects when the weldment

is postweld heat- treated: A PWHT in the temperature range of

510 to 650 C, with slow cooling speeds,may decrease the toughness of the weldmetal and the HAZ.

Reheat cracking can occur whenweldments of many high-strength steelsare heated above about 510 C.Intergranular cracking may take pIace inthe coarse-grained region of the weldHAZ.

31,83,3 VMoCrCS

The precipitation of carbides during stressrelaxation at elevated temperature alters thedelicate balance between resistance to grainboundary sliding and resistance to deformationwithin the coarse grains in the HAZ.

CS Is a Reheat Cracking parameter proposedby Nakamura Reference value is 0



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Weldability - PWHT

With any of the quenched and tempered steels, a postweld

stress-relief heat treatment should be used only afterassurance that worthwhile benefits can be achieved and

possible harmful effects can be tolerated. Stress relief is

desirable for some applications when:

Dimensional stability must be maintained during close tolerance

machining,

The weld is susceptible to stress corrosion after cold forming or

welding.

If postweld stress relief is required, the temperature must

not exceed that used for tempering the steel. A temperatureabout 30 to 60C lower than the tempering temperature is

desirable to avoid lowering the strength of the steel.



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Weldability Temper Beads



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Filler Metals- MMAW: EN 757



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Filler Metals- MMAW: EN 757



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Filler Metals GMAW: EN 12564



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Filler Metals - MMAW: EN 757



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13 - q+t steels & welding q+t steels

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