TY - GEN
T1 - Failure analysis of a 2.25Cr-1Mo-0.25V steel heavy wall-thickness multi-pass welded component
AU - Nevasmaa, Pekka
AU - Yli-Olli, Sanni
AU - Kortelainen, Olli
AU - Kiiski, Arto
PY - 2016
Y1 - 2016
N2 - Crack-like defects were found in a low-alloy
2.25Cr-1Mo-0.25V steel multipass welded heavy
wallthickness component prior to its usage. After
welding, the component had been subjected to local
Intermediate Stress Relief (ISR) heat treatment at
600-650°C, with the aim at removing diffusible hydrogen
and enhancing partial tempering of the weldment
microstructure before the final PWHT. The objective of
the present paper was to investigate the actual fracture
micromechanism of the discovered damage associated with
the manufacturing stage of the component, in order to
explain the inherent causes of failure. The
metallographic and fractographic studies demonstrated (i)
cracks propagating through the weld solidification
structure as quasi-cleavage fractures, (ii) the presence
of micro-cracks at thereby 'opened' solidification
boundaries, as well as (iii) occasional appearance of
ductile 'ridges' at the fracture surface; all that were
characteristic of hydrogen-induced cold cracking. In line
with this, Vickers hardness measurements revealed maximum
hardness as great as 381-382 HV and 371-378 HV in cases
of the CGHAZ and weld metal microstructures,
respectively. Furthermore, hardness traverses in the weld
thickness direction revealed higher hardness values in
the weld intermediate thickness than closer to the
surface or the root, which was ascribed to inadequacy of
the thermal effects of the ISR heat treatment. The
occurrence of hydrogen cracking was attributed to
simultaneous co-existence of several adverse factors: (i)
excessively high weldment hardness, (ii) accidentally
high initial hydrogen content of the applied SMAW
electrode and (iii) inherently high structural rigidity
and restraint of the component.
AB - Crack-like defects were found in a low-alloy
2.25Cr-1Mo-0.25V steel multipass welded heavy
wallthickness component prior to its usage. After
welding, the component had been subjected to local
Intermediate Stress Relief (ISR) heat treatment at
600-650°C, with the aim at removing diffusible hydrogen
and enhancing partial tempering of the weldment
microstructure before the final PWHT. The objective of
the present paper was to investigate the actual fracture
micromechanism of the discovered damage associated with
the manufacturing stage of the component, in order to
explain the inherent causes of failure. The
metallographic and fractographic studies demonstrated (i)
cracks propagating through the weld solidification
structure as quasi-cleavage fractures, (ii) the presence
of micro-cracks at thereby 'opened' solidification
boundaries, as well as (iii) occasional appearance of
ductile 'ridges' at the fracture surface; all that were
characteristic of hydrogen-induced cold cracking. In line
with this, Vickers hardness measurements revealed maximum
hardness as great as 381-382 HV and 371-378 HV in cases
of the CGHAZ and weld metal microstructures,
respectively. Furthermore, hardness traverses in the weld
thickness direction revealed higher hardness values in
the weld intermediate thickness than closer to the
surface or the root, which was ascribed to inadequacy of
the thermal effects of the ISR heat treatment. The
occurrence of hydrogen cracking was attributed to
simultaneous co-existence of several adverse factors: (i)
excessively high weldment hardness, (ii) accidentally
high initial hydrogen content of the applied SMAW
electrode and (iii) inherently high structural rigidity
and restraint of the component.
M3 - Conference article in proceedings
T3 - VTT Technology
BT - Baltica X
A2 - Auerkari, Pertti
PB - VTT Technical Research Centre of Finland
CY - Espoo
T2 - BALTICA X - International Conference on Life Management and Maintenance for Power Plants
Y2 - 7 June 2016 through 9 June 2016
ER -