70
P. K. Nanavati et al.
metal develops very high hardness upon cooling. Besides this, the presence of any
residual elements in this steel, such as phosphorous, sulphur, lead, tin, copper, antimony lower melting point elements do possess the tendency to become segregate
at the grain boundaries during solidification of the weld. Due to higher hardness
of the weld metal will crack very easily. It is, therefore, very important to study
the behaviour of this material under without filler wire addition-autogenous A-TIG
process and particularly with A-TIG Process variants [7]. Many researchers have
worked on weld behaviour of P91 steel with activated TIG processes and contributed
many useful research outcomes on the effect of various activating fluxes, applied
either alone and/or in combinations, on the depth of penetration, weld bead geometries, distortions, with and without preheating, post-weld heat treatment and their
influence on microstructure and mechanical properties.
In one such study by Vora and Badheka [1], they have analysed the effect of carrier
solvent and oxide fluxes in RAFM Steel. They have made studies on Al 2 O 3 , Co 3 O 4 ,
CuO, HgO, MoO 3 , and NiO flux systems and found that Co 3 O 4 and MoO 3 fluxes
can achieve full weld penetration more than plate thickness. In contrast, other fluxes
help enhanced penetration, as compared to normal TIG but were not able to give full
weld penetration.
A study by Singh et al. [8] has used TiO 2 , SiO 2 , Cr 2 O 3 , ZnO, CaO, Fe 2 O 3 and
MnO 2 and found that B 2 O 3 , V 2 O 5 and MgO have improved the weld penetration
twice or thrice than the standard TIG welding, and the effects with B 2 O 3 , V 2 O 5 and
MgO fluxes were not reported previously.
Work by Dhandha and Badheka [9] reported the maximum depth-to-width ratio in
the case of ZnO, MnO 2 and CrO 3 as 0.95, 0.85 and 0.83, respectively, as compared to
0.29 for normal TIG. Reportedly, there is an increase in D/W aspect ratio with the flux
ZnO by 320% as compared to the conventional TIG welding process. Further work
by Dhandha and Badheka [10] reported a higher depth of penetration with MnO 2 flux
up to 231% higher compared to conventional TIG welding. The study by Vidyarthy
and Dwivedi [11] reported an increase of 200 and 300% in joint penetration obtained
with CeO 2 and MoO 3 -based flux on P91 grade 8 mm plate using A-TIG process.
A review study on FB-TIG welding process by Jayakrishnan and Chakravarthy [12]
mentioned FB-TIG as offering improved depth of penetration amongst other flux
assisted A-TIG variants owing to additional effects of a narrow flux gap that leads
to insulation effect.
The present work is slightly different from the previous work cited above in the
way that out of the two different variants of A-TIG process, i.e. FB-TIG and FZTIG as shown in Fig. 1, work on one of the variants, Flux Zone variant (FZ-TIG)
on modified 9Cr–1Mo (P91) steel, is not reported by any researcher to the best of
the author’s knowledge. So considering this “undone” work as a research gap, the
authors became curious to investigate weld behaviour of P91 steel with FZ-TIG
process, using different fluxes—TiO 2 and ZnO. As per Fig. 1, an only single type
of flux TiO 2 was used in A-TIG (on grey shaded region) and FB-TIG process (blueshaded region). While in FZ-TIG process, one of the types of flux was applied on the
centre of the weld line (on grey-shaded region), slightly away from abutting surfaces.
And another type on both sides (blue shaded region). The properties of the flux used
P. K. Nanavati et al.
metal develops very high hardness upon cooling. Besides this, the presence of any
residual elements in this steel, such as phosphorous, sulphur, lead, tin, copper, antimony lower melting point elements do possess the tendency to become segregate
at the grain boundaries during solidification of the weld. Due to higher hardness
of the weld metal will crack very easily. It is, therefore, very important to study
the behaviour of this material under without filler wire addition-autogenous A-TIG
process and particularly with A-TIG Process variants [7]. Many researchers have
worked on weld behaviour of P91 steel with activated TIG processes and contributed
many useful research outcomes on the effect of various activating fluxes, applied
either alone and/or in combinations, on the depth of penetration, weld bead geometries, distortions, with and without preheating, post-weld heat treatment and their
influence on microstructure and mechanical properties.
In one such study by Vora and Badheka [1], they have analysed the effect of carrier
solvent and oxide fluxes in RAFM Steel. They have made studies on Al 2 O 3 , Co 3 O 4 ,
CuO, HgO, MoO 3 , and NiO flux systems and found that Co 3 O 4 and MoO 3 fluxes
can achieve full weld penetration more than plate thickness. In contrast, other fluxes
help enhanced penetration, as compared to normal TIG but were not able to give full
weld penetration.
A study by Singh et al. [8] has used TiO 2 , SiO 2 , Cr 2 O 3 , ZnO, CaO, Fe 2 O 3 and
MnO 2 and found that B 2 O 3 , V 2 O 5 and MgO have improved the weld penetration
twice or thrice than the standard TIG welding, and the effects with B 2 O 3 , V 2 O 5 and
MgO fluxes were not reported previously.
Work by Dhandha and Badheka [9] reported the maximum depth-to-width ratio in
the case of ZnO, MnO 2 and CrO 3 as 0.95, 0.85 and 0.83, respectively, as compared to
0.29 for normal TIG. Reportedly, there is an increase in D/W aspect ratio with the flux
ZnO by 320% as compared to the conventional TIG welding process. Further work
by Dhandha and Badheka [10] reported a higher depth of penetration with MnO 2 flux
up to 231% higher compared to conventional TIG welding. The study by Vidyarthy
and Dwivedi [11] reported an increase of 200 and 300% in joint penetration obtained
with CeO 2 and MoO 3 -based flux on P91 grade 8 mm plate using A-TIG process.
A review study on FB-TIG welding process by Jayakrishnan and Chakravarthy [12]
mentioned FB-TIG as offering improved depth of penetration amongst other flux
assisted A-TIG variants owing to additional effects of a narrow flux gap that leads
to insulation effect.
The present work is slightly different from the previous work cited above in the
way that out of the two different variants of A-TIG process, i.e. FB-TIG and FZTIG as shown in Fig. 1, work on one of the variants, Flux Zone variant (FZ-TIG)
on modified 9Cr–1Mo (P91) steel, is not reported by any researcher to the best of
the author’s knowledge. So considering this “undone” work as a research gap, the
authors became curious to investigate weld behaviour of P91 steel with FZ-TIG
process, using different fluxes—TiO 2 and ZnO. As per Fig. 1, an only single type
of flux TiO 2 was used in A-TIG (on grey shaded region) and FB-TIG process (blueshaded region). While in FZ-TIG process, one of the types of flux was applied on the
centre of the weld line (on grey-shaded region), slightly away from abutting surfaces.
And another type on both sides (blue shaded region). The properties of the flux used