A1 Journal article (refereed), original research

Effect of Heat Input and Undermatched Filler Wire on the Microstructure and Mechanical Properties of Dissimilar S700MC/S960QC High-Strength Steels


Open Access publication

Publication Details
Authors: Njock Bayock Francois, Kah Paul, Mvola Belinga, Layus Pavel
Publisher: MDPI
Publication year: 2019
Language: English
Related Journal or Series Information: Metals
Volume number: 9
Issue number: 8
eISSN: 2075-4701
JUFO-Level of this publication: 1
Open Access: Open Access publication

Abstract

The effect of heat input on the microstructure and mechanical
properties of dissimilar S700MC/S960QC high-strength steels (HSS) using
undermatched filler material was evaluated. Experiments were performed
using the gas metal arc welding process to weld three samples, which had
three different heat input values (i.e., 15 kJ/cm, 7 kJ/cm, and 10
kJ/cm). The cooling continuous temperature (CCT) diagrams,
macro-hardness values, microstructure formations, alloy element
compositions, and tensile test analyses were performed with the aim of
providing valuable information for improving the strength of the
heat-affected zone (HAZ) of both materials. Micro-hardness measurement
was conducted using the Vickers hardness test and microstructural
evaluation by scanning electron microscopy and energy-dispersive X-ray
spectroscopy. The mechanical properties were characterized by tensile
testing. Dissimilar welded samples (S700MC/S960QC) with a cooling rate
of 10 °C/s (15 kJ/cm) showed a lower than average hardness (210 HV5) in
the HAZ of S700MC than S960QC. This hardness was 18% lower compared to
the value of the base material (BM). The best microstructure formation
was obtained using a heat input of 10 kJ/cm, which led to the formation
of bainite (B, 60% volume fraction), ferrite (F, 25% volume fraction),
and retained austenite (RA, 10%) in the final microstructure of S700MC,
and B (55%), martensite (M, 45%), and RA (10%), which developed at the
end of the transformation of S960QC. The results showed the presence of
1.3 Ni, 0.4 Mo, and 1.6 Mn in the fine-grain heat-affected zone of
S700MC. The formation of a higher carbide content at a lower cooling
rate reduced both the hardness and strength.


Last updated on 2020-20-03 at 10:03