3 results listed
— Grain refinement is a unique approach to improve
physical and mechanical properties of metallic materials without
need to change their chemical compositions. Friction stir
processing (FSP), is technique for microstructural refinement of
metallic materials down to micrometer levels. In this process, a
specially designed rotating tool is plunged into the sheet to be
processed and traversed along the line of interest. The most
important advantage of process is providing weight reduction by
effectively strengthening of metals. However, applicability of this
process to thin sheets have been found difficult. In this study; thin
interstitial-free steel (IF-steel) was subjected to FSP using a
carbide-tungsten tool with the diameter of 14 mm. Ultrafine grain
structure was successfully achieved in 1.2 mm thick IF steel sheet
via position controlled processing technique and selection of the
proper tool dynamics. The microstructural evolutions were
characterized using scanning electron microscopy (SEM)
techniques. The results show that the FSP of IF-steel resulted with
the fine grains with a mean grain size of 5 µm (initial grain size
was 35 µm). FSP steel exhibited a good combination of yield
strength of 500 MPa with uniform elongation of 16%.
International Iron & Steel Symposium
UDCS
Mümün YILMAZ
Imren OZTURK YILMAZ
Onur SARAY
Friction stir processing (FSP) is a thermo-mechanical
process in which severe plastic strains are imposed by aid of
transverse movement of non-consumable rotating tool inserted
into the material. Tool friction also increases temperature of the
local deformation region. This leads occurrence of the dynamic
recrystallization leading to extensive grain refinement and
consequently improvement of strength without a considerable loss
of ductility. This improvement may be beneficial to lightweighting of the automobile bodies. However, this also requires
application of FSP to the thin metal sheets. On this point of view,
current study mainly focuses on FSP of 1.1 mm thick DP600 steel
which is widely used in body-in-white applications. SEM
investigations revealed that FSP caused both grain refinement and
morphological changes. Micro-hardness mapping of the FSP
region revealed nearly two fold increase in hardness. Similar
improvements were also detected tension tests. By selection of
proper FSP parameters, yield strength and UTS of the steel was
reached to about 720 MPa and 1050 MPa respectively. This
strength improvement was achieved with a considerably high
uniform elongation of 7%.
International Iron & Steel Symposium
UDCS
Onur SARAY
Imren OZTURK YILMAZ
Mümün YILMAZ
Friction stir processing (FSP) is a method which refines
microstructure of metals by localized plastic deformation. This
microstructural evaluation brought a remarkable increase in
mechanical properties with an acceptable loss of ductility. In the
literature there are several publications on the microstructural
and mechanical evolution of FSPed steels. However, there limited
number of studies on the effect of FSP on the microstructure and
mechanical properties of Transformation-Induced Plasticity
(TRIP) steel as a widely used material with unique properties like
excellent formability and strain hardenability. In order to close
this gap, current study is mainly concentrated on the effect of FSP
on the microstructural evolution and mechanical properties TRIP
780 steel. The microstructural evaluation was analysed scanning
electron microscopy (SEM) techniques. Mechanical properties
were investigated by microhardness test and tensile test. Results
indicated that a two-fold increase in the hardness was achieved
after FSP. Also, yield strength and UTS of the TRIP-780 steel
reached to 1280 MPa and 1475 MPa respectively. This strength
increase was also obtained with an acceptable uniform elongation
of % 9, which is concluded that a good balance of strength,
ductility and strain hardenability.
International Iron & Steel Symposium
UDCS
Imren OZTURK YILMAZ
Mümün YILMAZ
Onur SARAY