Welding Metallurgy

The iron carbon phase diagram

The transformation diagramThe transformation diagram express the dynamic transformation carried out during cooling at different cooling rates.

TTT-TRANSFORMATION DIAGRAM

Heat Affected Zone Welding Concerns

Formation of HAZ

Effect of temperature gradient onweld microstructure

Classification of HAZ sections:

Section 1: (fusion zone) is a mixed section between filler metal and parent metal.Section 2 : ( overheated section) the metal was overheated to a high degree which lead to grain coarsening, the most brittle region (1100 C – solidus line )

Classification of HAZ sections:Section 3: ( normalized section) the temperature didn’t exceed 1100 C

(900-1100 C) the metal in this section has improved mechanical

properties compared to parent metal.

Section 4: (incomplete recrystallization section). Incomplete

recrystallization of the metal occurred, since it was heated

to temperature between Ac1 and Ac3.

Section 5: (recrystallization section), no structure changes occur in

the metal, (500 C – Ac1).Section 6: (blue shortness section), no structure changes occur in the metal. If the parent metal for example low carbon steel contains gases in the ranges ( O2 > 0.005%, N2 >0.005% and H2> 0.0005) the impact value considerably reduces. ( 100 –500 C)

Common types of stainless steels

Steel Typical welding Practical___________composition problems Solution___________

Austenitic 18%Cr-8%Ni Solidification Maintaining 4-10%ferriteStainless 22%Cr-20%Ni cracking in weld phase in weld metalSteels 22%Cr-12%Ni metal Keep C/ √Si ≥ 0.22 in

fully austenitic weld metal

Martensitic 12-16%Cr Hydrogen-induced Preheat 200-400 º C andStainless 0.3%C cracking in HAZ post heat at 750 º C

Ferritic 16-30%Cr Low toughness in Preheat 200 º CStainless 0.1%C grain coarsened

Steels HAZ

Schaeffler DAIGRAM

The Shaeffler Diagram

Sigma Phase embrittlement

Embrittlement by grain coarsened 475C embrittlement

Hot cracking

Cold cracking

Two dissimilar materials A&B are welded together. They are in the form of plates. The thickness of each plate is 10 mm. The chromium equivalent of the used electrode is 26 with ferrite number equals 10. The chemical composition of the two base metals A and

B are as follows -:

Elements (Wt%)

AlloysCr Ni C Mn Si

A2 1 0.03 0.5 1.3

B14 22 0.1 2 1.5

BA10

2mm

x x

60˚

From the Schaeffler diagram, and the shown joint design answer the following questionsName the located alloys.Get the dilution of the electrode material.Calculate the distance X shown in the joint design.

)Note: The fused areas from the two base metals A and B are equal and they are in the triangle form.(

4-Draw a diagram showing the metallurgical changes in HAZ of butt welded steel plates, what are the mechanical and structural properties of each section.

-Draw the schaeffler diagram and locate the following stainless steel alloys.

Element C Mn Si Cr Ni Others

AISI 312 0.25 2.01 .5 24-26 19-22---

AISI 310 0.08 2.0 1.0 18-20 8.0-10.5---

AISI 308 0.08 2.0 1.0 19-21 10-12---

-Name the situated alloys and determine their ferrite numbers-Discuss the weldability of the above alloys and choose their suitable electrode materials in case of SMAW Process