Back to Lean Duplex Stainless Steel
ML00147 - Aug.2018

WC Layer Detached from a Cast Lean Duplex

Macrographic aspect of the sleeve longitudinal section where the coating was applied in the external side (top of the figure). It is possible to see that the sleeve was manufactured by centrifugal casting, with elongated grains from the external side, and equiaxial grains close to the internal side (bottom of the figure). There is a weaved interface between the sleeve and the first layer of thermal spray coating, 1 mm thick; and a second layer of thermal spray coating, 0.2mm thick (almost imperceptible at this low magnification).

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Macrographic aspect of the sleeve where the was applied in the external side (top of the figure). It is possible to see that the sleeve was manufactured by , with elongated grains from the external side, and close to the internal side (bottom of the figure). There is a weaved interface between the sleeve and the first layer of , 1 mm thick; and a second layer of , 0.2mm thick (almost imperceptible at this low magnification).
M

Material

Lean Duplex Stainless Steel
  • UNS S32304
  • ALLOY 2304
Ds

Description

This centrifugally cast lean duplex , manufactured as a flanged sleeve, is responsible for sealing (at its outer diameter) an oiled system from seawater, but a was detected after five years in service. The failure is associated to the detachement of the tungsten carbide layer, applied by , and although the DSS substrate presented , perhaps associated to the preheating to apply the , the material of the substrate was not corroded.

C

Chemistry (% in weight)

Casting

0.96Si; 0.53Mn; 0.011P; 0.016S; 22.5Cr; 4.2Ni; 0.46Mo; 0.11Nb; 0.23Cu; 0.08V.

Associated Images
Macroscopic aspect of the outer diameter of the flanged sleeve presenting adhered products at the surface. The flanged sleeve was manufactured by centrifugal casting in a lean duplex stainless steel and it was externally coated by thermal spray (TS) in a position of sealing. After 5 years in service the system suffered leakage.
569
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - Aspect Before AnalysisDf - External Surface
Detail of the external surface of the sleeve where the surface coating was detached, creating a lack of sealing condition.
67
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - Surface AspectDf - External Surface
General view of the 10" diameter flanged sleeve, 1/2" wall thickness, manufactured by centrifugal casting of lean duplex stainless steel (DSS), Alloy 2304 (without Mo), with an external coating applied by thermal spray (TS). The sleeve is assembled in a shaft. The internal environment is oil and a seal box is assembled in the external side that is wet with seawater.
56
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - Aspect Before AnalysisDf - General View
Longitudinal slice of the flanged sleeve, 180 mm long, in a macrography presenting the 1/2" tubular wall thickness where the sealing was applied. The external surface of the sleeve (seawater wet) is in the left side of the figure and the internal surface (oiled) is in the right side. The flange is to the top of the figure.
52
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - Longitudinal Section AspectDf - General View
Macrographic aspect of the sleeve longitudinal section where the coating was applied in the external side (top of the figure). It is possible to see that the sleeve was manufactured by centrifugal casting, with elongated grains from the external side, and equiaxial grains close to the internal side (bottom of the figure). There is a weaved interface between the sleeve and the first layer of thermal spray coating, 1 mm thick; and a second layer of thermal spray coating, 0.2mm thick (almost imperceptible at this low magnification).
49
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - NaOH Electrolytic Etched MacroDf - Coating Layer
Micrography of a longitudinal section of the sleeve, at the external surface where there are two layers of coating. The electrolytic etch evidenced the duplex stainless steel substrate (bottom of the figure) and the weave interface of the substrate and the first thermal spray layer, about 1 mm thick, in a stainless steel. The surface layer, of tugnsten carbide, about 0.2 mm thick, is black and not clearly visible in this figure.
50
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - NaOH Electrolytic Etched MicroDf - External Surface
Micrography of a longitudinal section of the sleeve close to the external surface, evidencing a tugnsten carbide thermal spray layer, thickness about 0.2 mm, at the sleeve outer diameter (OD), black due to the etch (top of the figure). This WC layer was deposited over a stainless steel layer disposed in several layers, non etched.
42
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - NaOH Electrolytic Etched MicroDf - Thermal Spray Layer
Micrographic detail of the interface between the two thermal spray layers, the first one in stainless steel (bottom of the figure) and the second one, at the surface,in tungsten carbide (top of the figure). The micrographic sample is etched and that is why the WC is dark (black) and the stainless steel is light (non etched).
41
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - NaOH Electrolytic Etched MicroDf - Thermal Spray Layer
Micrographic detail by scanning electron microscopy of the interface between the two thermal spray layers, the first one in stainless steel (bottom of the figure) and the second one, at the surface,in tungsten carbide (top of the figure). The composition of the first layer is similar to the base metal (lean duplex) and the composition of the second layer is WC in a Co matrix.
16
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - Electrolytic Etch Micrography by SEMDf - Thermal Spray Layer
Micrographic detail of the first thermal spray layer, in stainless steel with the same composition of the base metal (lean duplex).
16
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - Electrolytic Etch Micrography by SEMDf - Thermal Spray Layer
Micrography of the longitudinal section of the sleeve, at the interface between the substrate and the first thermal spray layer. The substrate (bottom of the figure) shows a ferritic-austenitic microstructure and detrimental phases that look like sigma. The thermal spray layer (top of the figure) presents the non-etched stainless steel, disposed in layers, with oxides (gray) and voids (black). The substrate is deformed in a thin layer at the interface.
38
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - NaOH Electrolytic Etched MicroDf - Close to the External Surface
Micrographic detail of the interface between the substrate and the first thermal spray layer. The substrate (bottom of the figure) shows a ferritic-austenitic microstructure and detrimental phases that look like sigma at the delta and gamma interface. The thermal spray layer (top of the figure) presents the non-etched stainless steel, disposed in layers, with oxides (gray) and voids (black). The substrate is deformed in a thin layer at the interface.
34
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - NaOH Electrolytic Etched MicroDf - Sigma
Micrography of the longitudinal section of the cast sleeve in the middle of the thickness. The microstructure is coarse, austenitic ferritic.
34
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - NaOH Electrolytic Etched MicroDf - In the Center of the Thickness
Micrography of the longitudinal section of the cast sleeve in the middle of the thickness. The microstructure is duplex, austenitic and ferritic. The etch presents different colours for the phases. The yellow is associated to detrimental phases, like sigma, at the ferritic phase (ligh blue) and the white phase is the austenite.
36
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - NaOH Electrolytic Etched MicroDf - Duplex structure
Micrographic detail of the longitudinal section of the cast sleeve in the middle of the thickness. The microstructure is duplex, austenitic and ferritic. The etch presents different colours for the phases. The yellow is associated to detrimental phases, like sigma, at the ferritic phase (ligh blue) and the white phase is the austenite.
30
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - NaOH Electrolytic Etched MicroDf - Sigma
Micrographic detail, by scanning electron microscopy, of the duplex, austenitic and ferritic, structure with sigma phase.
16
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - Electrolytic Etch Micrography by SEMDf - Sigma
General view of the 10" diameter flanged sleeve, with the external coating applied by thermal spray (TS), and the sealing rings of the seal box assembled at the sleeve external surface. It is important to observe that the internal surface of the sleeve presents no corrosion spots.
23
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - Aspect Before AnalysisDf - General View
Micrography of the longitudinal section of the cast sleeve, close to the internal diameter (ID). The microstructure is coarse, austenitic ferritic, and presents the same microstructure, ferritic and austenitic, all through the thickness.
21
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - NaOH Electrolytic Etched MicroDf - Internal Surface
Micrography of the longitudinal section of the cast sleeve at the ID. The microstructure is duplex, austenitic and ferritic. The etch presents different colours for the phases. The yellow is associated to detrimental phases, like sigma, at the ferritic phase (ligh blue) and the white phase is the austenite.
21
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - NaOH Electrolytic Etched MicroDf - Duplex structure
Micrographic detail of the longitudinal section of the cast sleeve at the ID. The microstructure is duplex, austenitic and ferritic. The etch presents different colours for the phases. The yellow is associated to detrimental phases, like sigma, at the ferritic phase (ligh blue) and the white phase is the austenite. No evidences of corrosion. The environment in this position is non corrosive, oil.
19
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - NaOH Electrolytic Etched MicroDf - Sigma
General view of the 10" diameter flanged sleeve, with the sealing rings of the seal box assembled at the sleeve external surface. The right side of the figure shows the surface region where the a lack of seal was identified, with adhered products.
23
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - Aspect Before AnalysisDf - External Surface
Macroscopic aspect of the OD surface of the sleeve (top of the figure), and a macrography of a longitudinal section (bottom of the figure). In the right side of the figure it is possible to see that the lack of sealing is associated to the detachment of the thermal spray surface layer.
26
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - Surface AspectDf - Longitudinal Section
Macrography of a longitudinal section showing the region where the surface layer was detached (top of the figure), creating a lack of sealing condition.
23
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - NaOH Electrolytic Etched MacroDf - Thermal Spray Layer
Micrography of a longitudinal section of the sleeve, in a region where the two layers applied by thermal spray are sound, not detached. The grey layer (200 micros) is the tugnsten carbide; and the white layer (1000 microns) is a stainless steel. The substrate is white in the bottom of the figure.
24
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - As polished micrographyDf - Thermal Spray Layer
Micrography of a longitudinal section of the sleeve, in a region where the surface layer starts detachment. This grey layer is the tugnsten carbide; and the white layer (1000 microns) is a stainless steel. In this case the first TS layer is sound. The substrate is white in the bottom of the figure.
20
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - As polished micrographyDf - Layer Detachment
Micrography of a longitudinal section of the sleeve, in a region where the surface layer was completely removed. In this position only the stainless steel layer is at the surface. That is why the sealing condition was lost. The substrate is white in the bottom of the figure.
19
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - As polished micrographyDf - Layer Detachment
Micrographic detail of a longitudinal section of the sleeve, in a region where the WC (tungsten carbibe) surface layer was degradated and partially removed.
17
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - As polished micrographyDf - Layer Detachment
Micrographic detail of the WC (tungsten carbibe) surface layer, degradated and partially removed.
16
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - As polished micrographyDf - Layer Detachment
Micrography of a longitudinal section of the sleeve, in a region where the surface layer was completely removed. In this position only the stainless steel layer, that is porous and full of oxides, is at the surface. That is why the sealing condition was lost.
17
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - As polished micrographyDf - Thermal Spray Layer
Micrographic detail of the sleeve in a region where the surface layer was completely removed. In this position only the stainless steel layer, that is porous and full of oxides, is at the surface.
16
VIEW
ML00147 / Aug.2018
WC Layer Detached from a Cast Lean Duplex
M - Lean Duplex Stainless SteelP - Centrifugal CastingAp - ShipCd - Lack of Sealing
Cm - As polished micrographyDf - Thermal Spray Layer