When dealing with thick sections of fine grain structural steels, the welding engineer shall consider that although low cooling rate is favorable for impact toughness (especially HAZ toughness) but preheat is also required to reduce the residual stress as a result of high volume of the weld metal and reduce the risk of cracking especially on fist layers.
On one hand, a minimum preheat temperature is required (especially for fist layers) to prevent cracking and on the other hand, the heat input and interpass temperature shall be kept under a certain level to ensure coarse grain structure will not form (especially at HAZ).
Ramin Kondori
Sr. QA/QC & Welding Engineer
-----------------------------------------------------------
PG-Dip. in Welding Engineering (IWE AT 0070)
BSc. in Civil Engineering (IUT)
BGAS Painting Inspector
ASNT Level I&II
On Sat, Feb 27, 2016 at 8:21 PM, 'Shashank Vagal' via Materials & Welding <materials-welding@googlegroups.com> wrote:
--One more addition to Alan's good comment:In case of lower thicknesses, the cooling rate tends to increase and may lead to martensite formation. But it is not so slow and sustained a cooling rate as to promote grain growth/reduced ductility, as you are allowed to weld between preheat & interpass temperatures.BR,Shashank C Vagal
From: Alan Denney <alan@denney1.freeserve.co.uk>
To: materials-welding@googlegroups.com
Sent: Tuesday, 23 February 2016 2:59 AM
Subject: [MW:24358] RE: 24355] Impact Test & cooling Rate-Preheating (carbon steel)
Alan DenneyAKD Materials Consulting LtdFrom: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Mohd Siraj
Sent: 22 February 2016 09:22
To: Materials & Welding <materials-welding@googlegroups.com>
Subject: [MW:24355] Impact Test & cooling Rate-Preheating (carbon steel)Dear all,Background:impact testing is more critical for less(low)thickness than higher thickness.Reason :fine grain form during fast cooling and course grain form during slow cooling.Question is:Preheating use to lower the cooling rate for higher thickness.So lower the cooling rate means form the course grain,course grain lower the toughness.Preheating contributing to lower the toughness?--
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