QUANTITATIVE PHASE ANALYSIS OF ARMOUR STEEL WELDED JOINT BY X-RAY DIFFRACTION

Yıl 2017, Sayı: 1, 36 - 40, 09.11.2017

Miroslav Cvetinov Aleksandar čabrilo Katarina Gerić Maja Stojanović Olivera Klisurić

Öz

Ultra-high tensile strength is
characteristic of armour steel and in order to preserve this strength its
welding process is of paramount importance. Austenitic filler material is
traditionally used for welding of armour steel, yet it has lower mechanical
properties than the base material, i.e. the filler material is the weakest
point of the welded joint. Moreover, due to the plastic deformation at the
crack tip austenitic filler material gets transformed into martensite during
fatigue crack propagation. An amount of austenite transformed into martensite
is directly related to crack growth resistance in the weld metal.

 

In order to quantify martensite
phase formed during the crack propagation under the effect of fatigue load, we
employed method of X-ray diffraction. Diffractograms were recorded in
Brag–Brentano θ:2θ reflection geometry on a Philips PW 1820/30 X-ray diffractometer
employing monochromatic CuKα
radiation (30 kV, 30 mA) in the range 40°-60° 2θ. For the quantitative phase analysis RIR method was subsequently
employed.

From the obtained data,
martensite to austenite ratio was calculated for the fracture surface.
Thereafter the 0.05 mm thick layer was removed from specimen surface and the
diffraction patern was recorded again. This procedure was repeated till 25% of
the martensite remained in two-phase mixture.

 

α´ martensite was detected at
distances up to 0.25 mm under the fracture surface. The greatest transformation
of austenite into α´ martensite was 55%, seen on the fracture surface. The
amount of α´ martensite declines with a distance by an average of ≈5%/0.05 mm,
in the depth perception tests. At the distance of 0.25 mm, the amount of
transformed austenite fell to 24%. 

Anahtar Kelimeler

XRD, armour steel, austenitic phase, martensite phase, welded joint, weld

Kaynakça

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