Impact energy Vs Structure

[EmaD FaRaHanI]

Dear Friends,

Consider we have a mild-steel, cooling fast from welding temperature, we must have a fine grain structure with martensite formation.

Hypothetically, considering that we want to use this structure. I was wondering what is the relation between the impact energy and the structure? will it be decreased due to martensite formation? or increased due to fine grain? I understand that we don't use the martensite state of structures and we need to quench and tempering them.

Thanks,

Emad

[Kannayeram Gnanapandithan]

u have given answer also

THANKS & BEST REGARDS,

KG.PANDITHAN, BE, IWE,  CSWIP 3.1,

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[Vinoth kanna ramachandran]

Dear sir,

Greetings for the day 

Mild steel - BCC structure (body centred cubic ) 

Austenite stainless steel - FCC structure (face centered cubic) 

Martensite - FCT structure  ( face centred tetragonal )

coarse grain means - less FCT crystals , fine grain means - More FCT crystals. 

Tetragonal structure can't absorb more impact energy , due to its crystal structure , since it prevents its movement . if it's fine grain , still more difficulty to absorb energy . 

That's why FCC crystals have better impact properties than any other in the steel family .Fine Grain FCC - greater impact energy absorption.

Regards

Vinoth kanna

QC- welding & piping inspector 

Manifa Project

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On Thu, Mar 25, 2021 at 8:43 AM EmaD FaRaHanI <emad.f...@gmail.com> wrote:

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[sunil kaushik]

What is the difference between BCT and FCT structure?

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[Vinoth kanna ramachandran]

Hi 

Greetings 

When carbon steel (BCC) - cools rapidly it forms BCT -martensite . 

When Austenitic Stainless steel (FCC) - Rapid cool may form FCT martensite . Based on CCT AND TTT diagrams.  

Regards 

Vinoth kanna 

9787954338

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[Vinay Thattey]

The martensite phase essentially consists of a metastable iron phase oversaturated in carbon. Since the more carbon a steel has, the harder and more brittle it is, a martensitic steel is very hard and brittle.  Because the cooling rate is so sudden, carbon does not have enough time for diffusion. Yes ,impact energy absorbing capacity will decrease..

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[George Dilintas]

Martensite formation depends also on the chemical composition and not only on the cooling rate.

The last weld bead has not a fine grain structure. It has more a dendritic structure.

Fine grain martensite will give low impact energy

Fine grain ferrite will give better impact energy.

Residual stresses also affect impact energy in a negative way.

In the mild steel the PWHT is to relief the residual stresses and not to temper the martensite.

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Dr. Georgios Dilintas,

Dipl. Ing. In Aeronautic and Space Engineering

Ph.D in Mechanics of Solids - Computational Mechanics

A.I.S, A.N.I, IRCA Lead Auditor

Welding, Stress Analysis, Corrosion, QA/QC, Failure Analysis, Risk Analysis