Effect of Microstructure on mechanical and Charpy impact properties offerrite-martensite dual phase API X52 pipeline Steel

Year 2017, Volume: 3 Issue: 2, 33 - 36, 01.11.2017

Belkacem Boutessouna

Abstract

The microstructural changes that occur during intercritical annealing
treatment at 780°C of API X52 steel have been investigated. Three treatments
were developed to produce dual phase (DP) microstructure: Intermediate
Quenching Treatment/Air (IQ/A), Intermediate Quenching Treatment/Water (IQ/W)
and Step Quenching Treatment (SQ).The IQ/W resulted in the formation of fine and
fibrous martensite morphology uniformly distributed in the ferrite matrix.
However, the IQ/A treatment showed a spherical network of martensite along the
ferrite/ferrite grain boundaries. The SQ yielded blockly and banded martensite
and ferrite morphology. The experimental results show that API X52 (DP) steel with finely
dispersed microstructures (IQ/W) have higher Charpy impact properties and lower
ductile–brittle transition temperature (DBTT)than (DP) steel with
banded microstructures.A carefully conducted comparison of fracture surfaces of the
representative specimens obtained after IQ and SQ treatments has been studied.

Keywords

Intercritical annealing, Dual-phase steel

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