formaiblity of friction stir process low carbon steel used in ship building

1. FORMABILITY OF FRICTION STIR PROCESSED
LOW CARBON STEELS USED IN SHIPBUILDING
A research on

2. CONTENT
 abstract
 Introduction
 Experimental procedure
 Results and discussion
• Microstructure
• Uniaxial tensile behavior
• Formability behavior under biaxial loading
 conclusion

3. ABSTRACT
 Friction stir process decreased the ferritic grain size in
the processed zone from 25µm to about 3µm, which also
caused a remarkable increase in strength values without
considerable decrease in formability under uniaxial
loading.
 Fsp reduced considerably the roughness of the free
surface.
 The FG microstructure provides a good balance between
strength and formability

4. INTRODUCTION
 Low carbon steel sheets/plates have been widely used in
transportation industries due to their high availability
good formability and excellent weld ability. But they
have a draw back that they have low strength, hardness
and fatigue due to their low carbon content.
 Grain refinement, advanced thermo-mechanical process
and classical severe plastic deformation methods are
used to produced steel with inferior ductility and limited
formability.

5. INTRODUCTION
 Friction Stir Processing (FSP) is a novel surface
modifying technique that provides micro structural
modification and control in the near surface layer of
metal components.
 FSP provides the ability to thermo mechanically process
selective locations on the structure’s surface and to some
considerable depth to enhance specific properties
 FSP was developed based on the basic concepts of
Friction Stir Welding (solid state welding process), but
FSP is used to modify the local microstructure and
doesn’t join metals together

6. INTRODUCTION
FSP have been successfully applied to several type of steel
including:
 Ultra low carbon steel
 Low carbon steels
 High carbon steels
 Medium carbon steels
 Dual phase steels
 Stainless steel
 High strength low alloy steels

7. EXPERIMENTAL PROCEDURE
FSP was performed using a WC tool
having a convex shoulder with the
diameter of 18mm
and a cylindrical pin with the diameter
and the length of 8mm and 3mm,
respectively. FSP was conducted with
a tool rotation of 635rpm and a traverse
speed of 45mm/min.

8. EXPERIMENTAL PROCEDURE
Rotating tool provides
 Continuous heating of work piece
 Plasticizing metal
 Transporting metal from the leading face of pin to its
trailing edge.

9.  Microstructure:
A remarkable refinement in the microstructure occurred
especially inside the stir zone. After FSP the average
grain size inside the ferritic phase decreased from 25µm
down to 3.0µm.
 Uniaxial tensile behavior:
during deformation about 14% uniform elongation
indicates this low increase in dislocation density. Which
causes a remarkable increase in strength but not a
considerable change in ductility.
RESULTS AND DISCUSSION

10. RESULTS AND DISCUSSION
 Formability behavior under biaxial loading:
No considerable changes are seen on stretch deformation
behavior under biaxial loading of the base steel sample.
FSPed conditions exhibit several deformation stages under
biaxial stresses.

11. CONCLUSION
The main results and conclusions of this study can be
summarized as follows:
 FSP decrease the ferritic grain size of the steel 25µm
down to 3µm, and the grain are separated by high angle
boundaries with increase dislocation density.
 FSPed steel sample can be considerably deformed under
biaxial loading.
 A considerable improvement in the surface quality of the
stretched steel samples was achieved by grain refinement
via FSP.