Druce Dunne | University of Wollongong (original) (raw)

Papers by Druce Dunne

Role of microstructure in susceptibility to hydrogen embrittlement of X70 microalloyed steel

Materials Today: Proceedings, 2015

Stellite 6 was deposited by laser cladding on a medium carbon steel substrate (MS) with energy in... more Stellite 6 was deposited by laser cladding on a medium carbon steel substrate (MS) with energy inputs of 1. kW (MS 1) and 1.8. kW (MS 1.8). The chemical compositions and microstructures of these coatings were characterized by atomic absorption spectroscopy, optical microscopy and scanning electron microscopy. The microhardness of the coatings was measured and the wear mechanism of the coatings was assessed using a pin-on-plate (reciprocating) wear testing machine. The results indicated less cracking and pore development for Stellite 6 coatings applied to the medium carbon steel substrate with the lower heat input (MS 1). Moreover, the Stellite coating for MS 1 was significantly harder than that obtained for MS 1.8. The wear test results indicated that the weight loss for MS 1 was much lower than for MS 1.8. It is concluded that the lower hardness of the coating for MS 1.8, markedly reduced the wear resistance of the Stellite 6 coating.

Advanced Materials Research, 2015

Stellite 6 was deposited by laser cladding on a martensitic stainless steel substrate with energy... more Stellite 6 was deposited by laser cladding on a martensitic stainless steel substrate with energy inputs of 1 kW (MSS-1) and 1.8 kW (MSS-1.8). The chemical compositions and microstructures of these coatings were characterized by atomic absorption spectroscopy, optical microscopy and scanning electron microscopy. The microhardness of the coatings was measured and the wear mechanism of the coatings was assessed using a pin-on-plate (reciprocating) wear testing machine. The results showed less cracking and pore development for Stellite 6 coatings applied to the MSS steel substrate with the lower heat input (MSS-1). Further, the Stellite coating for MSS-1 was significantly harder than that obtained for MSS-1.8. The wear test results indicated that the weight loss for MSS-1 was much lower than for MSS-1.8. It is concluded that the lower hardness of the coating for MSS-1.8, markedly reduced the wear resistance of the Stellite 6 coating.

Scripta Metallurgica, 1978

Recent electron microscopic studies of the martensite to austenite transformation in Fe-Pt (1) an... more Recent electron microscopic studies of the martensite to austenite transformation in Fe-Pt (1) and Fe-Ni-C (2) alloys have revealed elongated dislocation loop configurations in austenite surrounding martensite plates which had partly reverted on heating. The structure change in these alloys is b.c.t. (~' or B) ~ f.c.c. (T or F); the tetragonality of the martensite being due to partial order in the case of Fe-Pt (4) and the presence of carbon in the Fe-Ni-C alloys. The habit plane is close to (3 15 10) F in both cases and microtwins are observed in the martensite on (112) The presence of the dislocation loops has led to the

Welding in the World, 2014

Mixed microstructures of δ-ferrite, martensite and bainite are common in the weld metals produced... more Mixed microstructures of δ-ferrite, martensite and bainite are common in the weld metals produced by selfshielded arc welding (SSAW) for the purpose of hardfacing weld repair. This paper describes the development of a Schaeffler-type diagram for predicting the weld metal microstructure, thereby providing guidance on weld filler metal design to produce the optimum microstructure for industrial hardfacing applications.

Solid State Phenomena, 2017

Stellite 6 was fabricated by laser cladding on a 1050 steel (MS) substrate with laser powers of 1... more Stellite 6 was fabricated by laser cladding on a 1050 steel (MS) substrate with laser powers of 1 kW (MS-1) and 1.8 kW (MS-1.8). The chemical compositions and microstructures of the coatings were analysed by X-Ray Fluoroscense, optical microscopy and scanning electron microscopy. The microhardness of the coatings was examined and the wear mechanism of the coatings was evaluated using a ball-on-plate wear testing machine. The results indicated less cracking and pore development for Stellite 6 coatings applied to the 1050 steel substrate with the lower laser power (MS-1). Moreover, the Stellite coating for MS-1 was significantly harder than that obtained for MS-1.8. The wear test results showed that the weight loss for MS-1 was much lower than for MS-1.8. The evaluations of dilution and calculation of carbon content indicated that MS-1 has lower dilution and higher coating C content than MS-1.8. It is concluded that the lower hardness of the coating for MS-1.8, substantially reduced the wear resistance of the Stellite 6 coating and the lower hardness of the coating for MS-1.8 was due to higher level of dilution and lower coating C content. The coating-substrate couple must be considered in assessing the likely performance of the coating under service conditions.

Metal Science, 1982

ABSTRACT Cold rolling an Fe–1V–0·23C alloy contaInIng ?1 vol.-% of fine interphase V4C3 particles... more ABSTRACT Cold rolling an Fe–1V–0·23C alloy contaInIng ?1 vol.-% of fine interphase V4C3 particles results in the formation of shear bands at rolling reductions greater than 20%. Although in general the dislocation distribution is homogenized by the presence of the particles, the shear bands provide potent sites for nucleation of recrystallization on subsequent annealing. In 60% cold-rolled samples, annealing at 706°C resulted in the onset of recrystallization within 15 min, but the recrystallization process was still incomplete after 1000 h. This is consistent with the exhaustion of shear-band and grain-boundary sites at a relatively small volume fraction of recrystallized grains, and the severe retardation of both nucleation and growth rates by the precipitate dispersion. The low rate of recrystallization is associated with the pinning effect of the V4C3 precipitates on boundaries of both recrystallized grains and subgrains. Coarsening of the pinning particles controls the rate of migration of the recrystallizing interfaces. Recovery is shown to occur simultaneously and competitively with recrystallization, and to reduce progressively the driving force for recrystallization.

Stellite 6 was deposited by laser cladding on a martensitic stainless steel substrate with laser ... more Stellite 6 was deposited by laser cladding on a martensitic stainless steel substrate with laser powers of 1 kW (MSS-1) and 1.8 kW (MSS-1.8). The chemical compositions and microstructures of these coatings were characterized by atomic absorption spectroscopy, optical microscopy and scanning electron microscopy. The microhardness of the coatings was measured and the wear mechanism of the coatings was examined using a pin-on-plate (reciprocating) wear testing machine. The results showed less cracking and pore development for Stellite 6 coatings applied to the MSS substrate with the lower laser power (MSS-1). Further, the Stellite coating for MSS-1 was significantly harder than that obtained for MSS-1.8. The wear test results showed that the weight loss for MSS-1 was much lower than for MSS-1.8. The measurements of dilution and coating C content showed that MSS-1 possesses lower dilution and higher coating C content than MSS-1.8. It is concluded that the lower hardness of the coating f...

The mean free path of the ferrite crystals in the different regions of multipass weld metals prod... more The mean free path of the ferrite crystals in the different regions of multipass weld metals produced via flux cored arc welding has been investigated for varying heat input, shielding gas, welding technique, and welding position. The mean free path describes the average separation of boundaries between ferrite grains or crystals, regardless of the morphology of the ferrite, and it has been measured in the present work as the mean linear intercept length between boundaries. This quantity has been determined in an attempt to correlate weld metal microstructure quantitatively with mechanical properties, specifically tensile strength and toughness. The weld metal subzones for characterisation of mean free path included the solidified weld metal and the grain coarsened, grain refined, and intercritical regions. Seventeen testplates welded using three different consumables were examined. Using the volume fraction of each subzone obtained via linear intercept measurements, the overall ave...

Materials Science and Engineering: A, 2017

This paper investigates the effects of accelerated creep testing of a temperbead (TB) repair weld... more This paper investigates the effects of accelerated creep testing of a temperbead (TB) repair weld for a P22 pressure vessel component that was produced without post-weld heattreatment (PWHT). The mechanical properties of the "cold" (non-PWHT) weld metal were superior to those of aged parent metal and the original fabrication welds for all tests, with the notable exception of creep performance. The creep performance of the TB repair weld material was inferior to that of the aged parent metal, due to the metastability of the weld metal microstructure relative to restoration processes occurring at the "accelerated" temperatures used for testing. It is concluded that the test conditions induced structural changes that are unlikely to occur under the actual service conditions and resulted in a creep life assessment that was highly conservative. The reported results are relevant to the security and integrity of non-PWHT repair welding of high-energy piping components.

Materials Science Forum, 2014

The effect of phases and steel processing on hydrogen uptake (diffusible and residual), surface a... more The effect of phases and steel processing on hydrogen uptake (diffusible and residual), surface and internal damage were evaluated using optical and scanning electron microscopy. The results have shown the fastest formation of blisters in ferrite-pearlite microstructure of strip, followed by equaixed ferrite-pearlite microstructure in normalised condition, then by ferrite-bainite microstructure. No blistering was observed in heat affected zone samples for up to 24 hrs charging. Analysis of hydrogen-induced cracking using electron back scattering diffraction has revealed that crack propagation has predominantly intragranular character without a clear preference on {001}, {110}, {112} and {123} planes and is independent of the steel microstructure and prior processing.

This paper presents a three-dimensional finite element model of the heat flow during tandem pulse... more This paper presents a three-dimensional finite element model of the heat flow during tandem pulsed laser welding. Model predictions of fusion zone and heat-affected zone dimensions are compared with experimental measurements. When two beams from the same laser are used in tandem to weld a material, it is the intensity distribution of the composite processing beam which is important. This is similar to being able to select the mode of the laser beam, as the relative intensities, spacing and spot size of the two beams can be varied. The potential benefits such a scheme may produce over single beam laser processing are: the possibility of removing potential contaminants to the weld with a minor beam ahead of the main welding beam; the ability to control the heating and cooling rates of the workpiece by employing a minor beam to effectively preheat or postheat the weld; and the modification of the speed and penetration characteristics of single beam laser welding with the same total power. Experiments using a pulsed Nd:YAG laser to produce bead-on-plate welds in AISI 1006 steel were performed to compare with theory. The results suggest that the cooling rates associated with single beam laser welding can be reduced by introducing a minor preheat beam.This paper presents a three-dimensional finite element model of the heat flow during tandem pulsed laser welding. Model predictions of fusion zone and heat-affected zone dimensions are compared with experimental measurements. When two beams from the same laser are used in tandem to weld a material, it is the intensity distribution of the composite processing beam which is important. This is similar to being able to select the mode of the laser beam, as the relative intensities, spacing and spot size of the two beams can be varied. The potential benefits such a scheme may produce over single beam laser processing are: the possibility of removing potential contaminants to the weld with a minor beam ahead of the main welding beam; the ability to control the heating and cooling rates of the workpiece by employing a minor beam to effectively preheat or postheat the weld; and the modification of the speed and penetration characteristics of single beam laser welding with the same total power. Experiments using a...

Stellite 6 coatings were deposited using laser cladding, high velocity oxygen fuel (HVOF)

Materials Science and Technology

Materials Science Forum

Welding of low carbon martensitic steels with yield strengths above 690 MPa requires careful atte... more Welding of low carbon martensitic steels with yield strengths above 690 MPa requires careful attention to the welding procedure to avoid hydrogen assisted cold cracking (HACC) and to minimise degradation of the mechanical properties of the weldment. Investigations of the microstructural and hardness gradients in the heat affected zone (HAZ) of these types of steels revealed that the peak hardness does not occur in the grain coarsened heat affected zone (GCHAZ) adjacent to the fusion boundary, as normally observed for ferritic steels, but is displaced towards the grain refined region (GRHAZ). This phenomenon, referred to as the displaced hardness peak (DHP) effect, is considered to arise when the hardenability of the steel is sufficiently high to produce the same microstructure in the both the GC and GR heat affected zones, but the enhanced structural refinement of the GRHAZ increases the hardness and strength above that of the GCHAZ. Implications relative to the susceptibility of th...

Materials Science Forum, 1991