A small correction please!
It should read as ......... "consists of a serious of graded structures in the base metal
From: c sridhar <sridhar305@yahoo.com>
To: "materials-welding@googlegroups.com" <materials-welding@googlegroups.com>
Sent: Thursday, 21 March 2013 3:21 PM
Subject: Re: [MW:17181] HAZ hardness
Mr. Hrushikesh
HAZ is subjected to complex thermal cycle (sudden heating followed by rapid cooling) in
which all temperatures from melting range of the steel down to mere warming are involved
and therefore consists of a serious of graded structures in the weld bead.
There are 4 regions at HAZ area.,
Region 1, lies in contact with fusion line, heated high into the austenite temperature range
and is therefore extremely coarse-grained. It is normally a high hardness zone and if cooling
rate is high, can readily transform into brittle martensite. This is a dangerous area of HAZ and
potential zone to form cracks.
Region 2, with slightly less heat (compared to to region.1) and fully- austenitic range. Normally
fine grained, of moderate hardness and not likely to transform to martensite.
Region 3, with slightly less heat (compared to reg.2) but, more than base metal, i.e. partially
into austenite range and acquires a mixed structure. a small amount of martensite may form if
the cooling rate is rapid. This zone is not very hard and yet may be brittle if martensite is present.
Region 4, nearer to base metal, was not heated high enough to form martensite, but the welding
heat has served to temper the metal to a soft condition.
HAZ micro structure is determined by composition of steel and welding thermal cycle. Higher the
Carbon content, harder will be the zone. Similarly higher content of alloying elements like, Cr, Ni,
Mo, V etc., will increase the harden-ability, enabling a rapid formation of a hardened HAZ .
The thickness factor also affects cooling rate of, resulting in a change in the structure.
So, higher HAZ hardness is a indication of presence of a martensite structure and potential
Cracking zone.
In general cracking rarely occurs, if HAZ hardness is 250 HV or less. It becomes critical if reaches
350 HV for Rutile coated electrodes and as if it approaches 450 HV for Low Hydrogen / basic
coated electrodes.
A well baked Low Hydrogen Electrode along with pr-heat / PWHT will help to reduce the fusion line
hardness from 420 HV to 350 HV with pr-heat and to <200 HV with pr-heat & PWHT and helps to
avoid formation of cracking.
C Sridhar.
From: Hrushikesh Sangamnerkar <hrushi612@gmail.com>
To: materials-welding@googlegroups.com
Sent: Wednesday, 20 March 2013 7:14 PM
Subject: Re: [MW:17164] HAZ hardness
--
Hrushikesh H Sangamnerkar --
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It should read as ......... "consists of a serious of graded structures in the base metal
adjacent to weld bead" and not in the weld bead.
thanks,
sridhar
From: c sridhar <sridhar305@yahoo.com>
To: "materials-welding@googlegroups.com" <materials-welding@googlegroups.com>
Sent: Thursday, 21 March 2013 3:21 PM
Subject: Re: [MW:17181] HAZ hardness
Mr. Hrushikesh
HAZ is subjected to complex thermal cycle (sudden heating followed by rapid cooling) in
which all temperatures from melting range of the steel down to mere warming are involved
and therefore consists of a serious of graded structures in the weld bead.
There are 4 regions at HAZ area.,
Region 1, lies in contact with fusion line, heated high into the austenite temperature range
and is therefore extremely coarse-grained. It is normally a high hardness zone and if cooling
rate is high, can readily transform into brittle martensite. This is a dangerous area of HAZ and
potential zone to form cracks.
Region 2, with slightly less heat (compared to to region.1) and fully- austenitic range. Normally
fine grained, of moderate hardness and not likely to transform to martensite.
Region 3, with slightly less heat (compared to reg.2) but, more than base metal, i.e. partially
into austenite range and acquires a mixed structure. a small amount of martensite may form if
the cooling rate is rapid. This zone is not very hard and yet may be brittle if martensite is present.
Region 4, nearer to base metal, was not heated high enough to form martensite, but the welding
heat has served to temper the metal to a soft condition.
HAZ micro structure is determined by composition of steel and welding thermal cycle. Higher the
Carbon content, harder will be the zone. Similarly higher content of alloying elements like, Cr, Ni,
Mo, V etc., will increase the harden-ability, enabling a rapid formation of a hardened HAZ .
The thickness factor also affects cooling rate of, resulting in a change in the structure.
So, higher HAZ hardness is a indication of presence of a martensite structure and potential
Cracking zone.
In general cracking rarely occurs, if HAZ hardness is 250 HV or less. It becomes critical if reaches
350 HV for Rutile coated electrodes and as if it approaches 450 HV for Low Hydrogen / basic
coated electrodes.
A well baked Low Hydrogen Electrode along with pr-heat / PWHT will help to reduce the fusion line
hardness from 420 HV to 350 HV with pr-heat and to <200 HV with pr-heat & PWHT and helps to
avoid formation of cracking.
C Sridhar.
From: Hrushikesh Sangamnerkar <hrushi612@gmail.com>
To: materials-welding@googlegroups.com
Sent: Wednesday, 20 March 2013 7:14 PM
Subject: Re: [MW:17164] HAZ hardness
Dear all,
I completely agree your point that variation in grain structure affects the hardness. But the thing is that in welding HAZ is subjected to repeatative number of heat cycles which results in grain coarsening of HAZ. So, are coarse grain responsible for high hardness of HAZ?
Thanks and regards,
On Tue, Mar 19, 2013 at 6:27 PM, paragpan@gmail.com <paragpan@gmail.com> wrote:
Dear Hrushikesh,
It is due to the distortion of grain structure occurred during welding in the HAZ area due to heat transfer from the molten weld metal to the base metal.
Regards,
PARAG
Sent from my HTC----- Reply message -----
From: "Hrushikesh Sangamnerkar" <hrushi612@gmail.com>
To: <materials-welding@googlegroups.com>
Subject: [MW:17145] HAZ hardnessDate: Mon, Mar 18, 2013 10:50 PM
--Dear sir,Why is the Hardness of HAZ higher than that of Weld?Thanks and Regards,
Hrushikesh H Sangamnerkar09724738118
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Hrushikesh H Sangamnerkar
09724738118
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