Effect of Tempering Process on Microstructure and Mechanical Properties of Microalloyed Steels Joined by Submerged Arc Welding

Yıl 2016, Cilt: 7 Sayı: 3, 587 - 594, 01.12.2016

Hasan Karabulut Mustafa Türkmen

Öz

The main benefit of microalloyed steels is to
provide important energy and cost savings in the
manufacturing of forged components for
automotive applications. In such steels, the
strength levels and other properties achieved after
cooling from hot working temperatures are
reported to be comparable with those obtained
from conventional quenched and tempered steels.
Microalloying or the use of additions of elements
(V, Nb, and Ti) at small rates in low carbon steels
has been successfully employed for large diameter
pipelines, bridges, and other construction
applications. This has been extended to medium
carbon steels for various automotive engine and
engineering applications. The microalloying
elements produce precipitation of carbonitrides in
austenite, and the pro-eutectoid ferrite and
pearlite phases of the final microstructure in
order to obtain grain refinement and precipitation
strengthening.
Submerged arc welding (SAW) is extensively used
in industry to fabricate pressure vessels, pipelines,
marine vessels and wind turbine towers. The
extensive use of SAW is associated with certain
inherent metallurgical and process advantages
such as (a) high deposition rate (18 kg/h) and
high electrode deposition efficiency (b) low
nitrogen in weld metal (c) excellent weld bead
appearance, and (d) possibility of welding over a
wide range of thickness. In addition to high
productivity, absence of smoke, arc flash, and thus
minimum protective clothing make this process
find a prominent place in fabrication industries.
Microalloyed steel in dimension of 400x200x6 mm
was used for welding in this study. Table 1
illustrates the chemical compositions of the asreceived
metals and Oerlikon-S2 submerged arc
welding wire used for joining. Before welding,
microalloyed steels were heat treated at 100 o
C
and than the samples were centred as face to-face
with 1-mm interval, The welding process was
performed as two passes from front side and then
back side by using Oerlikon Magmaweld brand
ZD5-1000 B model submerged arc welding
machine.
In this work, microalloyed steels joined by using
submerged arc welding method under 450 A
welding current parameters. Tempering process
was performed to welded joint. Welded joints
were characterised in terms of hardness, tensile
testing before and after tempering. The results
indicated that microalloyed welded joints showed
the lower hardness, yield and tensile strenght
after tempering whereas the increase in %
elongation. While the breaking in the HAZ at the
welded joint which was not applied tempering
process on the contrary breaking was observed at
the base metal after tempering process.
It was observed that the hardness of the welded
samples S1 and S2 raised when the measurement
was carried out along the horizontal measurement
line from as-received metal to HAZ or weld metal.
The hardness measurement was also carried out
along the vertical measurement line for weld
metal obtained by two passes. It was observed
that the hardness values gradually decreases from
second weld pass to the first weld pass. This
situation shows that second weld pass applies
stress relief annealing on first weld pass and
therefore the hardness decreases accordingly
figures 5 and 6.

Anahtar Kelimeler

Microalloyed Steel, Submerged Arc Welding Method, Mechanical Properties.

Temperleme İşleminin Tozaltı Kaynak Yöntemi ile Birleştirilen Mikroalaşımlı Çeliklerin Mekanik Özelliklerine Etkisi

Öz

Bu çalışmada, mikroalaşımlı çelik malzemeler tozaltı kaynak yöntemi ile 450 A kaynak akım değeri
kullanılarak birleştirilmiştir. Kaynaklı bağlantıya temperleme işlemi uygulanmıştır. Temeperleme öncesi ve
sonrası olmak üzere numunelere sertlik ve çekme testi uygulanmıştır. Sonuç olarak, mikroalaşımlı çelik
malzeme kullanılarak yapılan kaynaklı bağlantıların temperleme sonrası daha düşük sertlik, akma ve çekme
dayanımı gösterirken buna karşın % uzamada artış gösterdiği tespit edilmiştir. Temperleme uygulanmayan
kaynaklı bağlantılarda kopma ısının tesiri altında kalan bölgesinde (ITAB) meydana gelirken temperleme
sonrası kopma ana malzemede olduğu görülmüştür.

Anahtar Kelimeler

Mikroalaşımlı çelik, Tozaltı Kaynak Yöntemi, Mekanik özellikler