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 hardness

Date: 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 Sangamnerkar

09724738118

--
To post to this group, send email to materials-welding@googlegroups.com
To unsubscribe from this group, send email to materials-welding+unsubscribe@googlegroups.com
For more options, visit this group's bolg at http://materials-welding.blogspot.com/
http://www.linkedin.com/groups/MaterialsWelding-122787?home=&gid=122787&trk=anet_ug_hm
 
The views expressed/exchnaged in this group are members personel views and meant for educational purposes only, Users must take their own decisions w.r.t. applicable code/standard/contract documents.
---
You received this message because you are subscribed to the Google Groups "Materials & Welding" group.
To unsubscribe from this group and stop receiving emails from it, send an email to materials-welding+unsubscribe@googlegroups.com.
For more options, visit https://groups.google.com/groups/opt_out.
 
 
--
To post to this group, send email to materials-welding@googlegroups.com
To unsubscribe from this group, send email to materials-welding+unsubscribe@googlegroups.com
For more options, visit this group's bolg at http://materials-welding.blogspot.com/
http://www.linkedin.com/groups/MaterialsWelding-122787?home=&gid=122787&trk=anet_ug_hm
 
The views expressed/exchnaged in this group are members personel views and meant for educational purposes only, Users must take their own decisions w.r.t. applicable code/standard/contract documents.
---
You received this message because you are subscribed to the Google Groups "Materials & Welding" group.
To unsubscribe from this group and stop receiving emails from it, send an email to materials-welding+unsubscribe@googlegroups.com.
For more options, visit https://groups.google.com/groups/opt_out.
 
 

--
Hrushikesh H Sangamnerkar

09724738118

--
To post to this group, send email to materials-welding@googlegroups.com
To unsubscribe from this group, send email to materials-welding+unsubscribe@googlegroups.com
For more options, visit this group's bolg at http://materials-welding.blogspot.com/
http://www.linkedin.com/groups/MaterialsWelding-122787?home=&gid=122787&trk=anet_ug_hm
 
The views expressed/exchnaged in this group are members personel views and meant for educational purposes only, Users must take their own decisions w.r.t. applicable code/standard/contract documents.
---
You received this message because you are subscribed to the Google Groups "Materials & Welding" group.
To unsubscribe from this group and stop receiving emails from it, send an email to materials-welding+unsubscribe@googlegroups.com.
For more options, visit https://groups.google.com/groups/opt_out.