The influence of thermomechanical processing on the corrosion behaviour and hardness of P91 and 304 stainless steel bimetallic component

ABSTRACT

The complex demands on contemporary engineering components have led to the development of advanced materials, such as functionally graded materials. A functionally graded material, P91 and 304 stainless steels (SS), were developed by WAAM and afterwards, post-processing method of thermomechanical processing is adopted. The primary objective of this approach is to enhance interfacial bonding and microstructural control between distinct base metals. The thermomechanical processing encompassed isothermal compression testing at varying deformation temperatures (800, 900, and 1000°C) and strain rates (1 and 10 s^–1). The corrosion performance of the as-built bimetallic component was compared with that of the base metals, P91 and 304 SS, by evaluating their electrochemical behaviour in a 3.5 wt% NaCl solution. Hardness results after deformation confirmed microstructural refinement, as evidenced by increasing hardness due to thermomechanical processing parameters. The corrosion results indicated that the thermomechanical processing parameters improved corrosion resistance due to the refined microstructure in the bimetallic component. Uniform corrosion dominated in the as-built condition of the bimetallic component, while pitting corrosion dominated under deformation conditions.

Keywords:
Functionally Graded Material; Hot Deformation; Microstructural Evolution; Bimetallic component

1. INTRODUCTION

Functionally graded materials, also referred to as bimetallic material in this paper, are required in typical high-temperature environments such as nuclear reactors and power generation plants [¹, ², ³]. In coal-fired plants, steam pipes, heat exchanger tubes, and steam headers operate at varying temperatures and, therefore, require different materials that are fused together to fulfil service conditions. For example, boiler superheater tubes operating at about 630°C, austenitic stainless steels such as 316 or 304H are used, while for steam headers, P91 steel is employed [³]. To satisfy the in-service requirements of this material, the integrity of the interface between the two different alloys is crucial. Defects such as porosity or cracking in the interface or inhomogeneous microstructure at various regions such as the fusion zone and the heat-affected zone would have an effect on the mechanical, oxidation, and corrosion properties of the bimetallic material [⁴, ⁵]. With an increasing demand for responsible fuel consumption and a reduction in carbon footprint, the operating temperature of plants has increased as efforts are being made to improve their efficiency [¹]. This places a higher demand on how the different processing parameters for developing functionally graded materials are scrutinised.

Additive manufacturing has recently been considered as one of the very popular routes in developing bimetallic components, involving two broad technologies: powder bed fusion and direct energy deposition (DED) [⁶, ⁷, ⁸, ⁹]. The cost advantage and high deposition rate that DED technologies have over the PBF technology have made it a technique of choice for developing functionally graded materials, particularly wire-arc-additive manufacturing (WAAM) technique [¹]. Previous studies by RANI et al. [²] and AHSAN et al. [¹⁰] on WAAM bimetallic components have reported that there is good interfacial bonding and no porosity found at the interface of P91 and austenitic stainless steels. However, an inhomogeneous microstructure between the base metals and across the interface remains a major concern. Due to different cooling rate during WAAM, microstructural evolution differs in the different regions; fusion zone, heat affected zone and base metal [¹¹, ¹², ¹³]. The difference in the microstructure can cause micro or macro galvanic cells, which accelerate the corrosion of the bimetallic component [¹⁴, ¹⁵]. The microstructural variation may cause poor mechanical properties and corrosion resistance. Consequently, efforts have been made to introduce post-processing methods such as thermomechanical processing to influence the diffusion of alloying elements and homogenise the microstructure of the bimetallic components. For instance, the metal forming process, such as hot rolling, is widely used to reduce or eliminate most metallurgical issues associated with 3D printed parts, such as inhomogeneous microstructures, coarse grain size, porosity, and distortions resulting from the thermal cycle history of layer-by-layer deposition. The technique ensures that the overall reliability of wire-arc additively manufactured parts is maintained without affecting the final desired geometry after processing [¹⁶]. Therefore, the application of metal forming is intended to enhance the overall mechanical properties of WAAM printed parts. WAAM parts are expected to deform plastically into a net-shape or near-net-shape component through subsequent metal forming operations. This approach leverages the design flexibility of metal additive manufacturing to create workpieces with optimised geometries and enhanced properties due to microstructure homogenisation.

RANI et al. [²] studied the mechanical properties of wire arc additive manufactured (WAAMed) mild steel (G3Si1) and austenitic stainless steel (SS304) bimetallic components. The hardness was observed to be higher in the 304SS (240–260 HV) than the mild steel region (160–180 HV). The drastic decrease in hardness near the interface was attributed to chromium migration from the SS304. HU et al. [¹⁷] investigated the microstructure and mechanical properties of WAAMed TP91 steel and found fluctuations in the microhardness to be minimal with corresponding average values equal to 219 HV and 216 HV. SRIDAR et al. [¹⁸] studied the interfacial characteristics and hardness properties of P91 steel and Inconel 740H bimetallic component produced by WAAM and found that intergranular cracks are found along the gradient zone due to MC carbides inducing residual stresses. It was also found that the microhardness of the gradient zone is the least as compared with the P91 and 740H regions. KUMAR et al. [¹⁹] studied the microstructure and mechanical properties of WAAMed SS304L-IN718 bimetallic and found columnar and equiaxed microstructures for SS304L and dendritic structures for IN718. The microhardness results were 215.9-231 HV for SS304L, 169.1-183 HV for interface and 240.3-253.5 HV for IN718.

Currently, there is insufficient information regarding the corrosion performance of WAAMed bimetallic components. Also, little is known about the influence of thermomechanical processing on the corrosion performance of WAAMed P91 and 304 SS bimetallic components, which is considered in this study. Therefore, this study is the first step towards understanding how thermomechanical processing parameters such as deformation temperatures and strain rates could influence the corrosion performance of WAAMed P91 and 304 SS bimetallic components.

2. MATERIALS AND METHODS

P91 and 304 stainless steel (304 SS) wires were deposited on a mild steel substrate using WAAM to develop a functionally graded bimetallic component. The WAAM deposition process was conducted using a custom-made WAAM rig (Figure 1a). The rig consists of an AICO Inverter welder MIG/200 GMAW machine, (AICO, Japan). A Filler wire of 1.2 mm diameter was deposited on mild steel substrate of 5 mm thick. The bimetallic structure had 15 layers (for the first material-304 SS), cooled for 20 minutes, and then another 15 layers (for second material-CrMo steel) deposited on the mild steel substrate (Figure 1b). The interpass cooling time was ~1 minute for the first and second layers. Rectangular-axial samples with dimensions of 8 × 8 × 12 mm were machined and then subjected to axisymmetric compression testing using a Gleeble® 3500 thermomechanical simulator at deformation temperatures of 800, 900, and 1000°C and strain rates of 1 and 10 s^–1 (Figure 1c). The deformation temperatures and strain rates were selected based on the optimum hot working windows for P91 and 304 stainless steel [²⁰, ²¹, ²², ²³, ²⁴, ²⁵, ²⁶]. The as-built and sectioned deformed bimetallic material samples were hot-mounted in clear resin at a temperature of 180°C and a pressure of 150 bar, ground, and polished to a mirror-like finish. After polishing, the samples were rinsed in water and air-dried. Thereafter, both the as-built and deformed bimetallic material samples were subjected to corrosion testing in a 3.5 wt% NaCl solution, using a 3-electrode electrochemical cell connected to a Gamry Interface 1010E potentiostat. A graphite rod was used as the counter electrode, while the reference electrode was Ag/AgCl in a 3M KCl solution. Open circuit potential measurement was carried out for 3600 s, while potentiodynamic polarisation scans were taken at a start potential of –0.5 V, stop potential of 1.5 V, and a scan rate of 0.16667 mV. s^–1. Electrochemical parameters such as corrosion current density, corrosion potential, and corrosion rate were determined using the polarisation resistance method described in ASTM G102-89. Scanning electron microscopy involving mainly back-scattered electron and energy-dispersive X-ray spectroscopy techniques were then performed on the corroded samples to establish the type of corrosion exhibited by the material and their underlying mechanisms. Hardness profile measurement was performed on the as-built and deformed samples using the Future Tech FM700 microhardness tester following ASTM E384-17 standard. A load of 500 gf and a dwell time of 10 s were used.

Figure 1
(a) Experimental WAAM rig set-up. (b) WAAM functionally grade material. (c) Schematic diagram of thermal cycle during hot deformation testing.

3. RESULTS

3.1. Corrosion behaviour of base metals and as-built bimetallic component

Figure 2 shows the OCP and potentiodynamic polarisation curves of as-built bimetallic component and base metals (304 SS and P91 steel) in 3.5 wt% NaCl. By comparing the OCP of the as-built P91 and 304 SS bimetallic component with the base metals (304 SS and P91 steel) in 3.5 wt% NaCl, the corrosion tendency order is: P91 > as-built bimetallic > 304 SS (Figure 2a). As seen in the potentiodynamic polarisation curves (Figure 2b), the corrosion tendency order based on Ecorr is: 304 SS > P91 > as-built bimetallic. In terms of corrosion rate, the as-built bimetallic exhibited superior performance (Table 1). The corrosion rate, which is a kinetic parameter, indicates that 304 SS corroded at a slightly slower rate compared to P91. This is expected since the chromium content in 304 SS (18 wt%) is much higher than that of P91 (9 wt%) [⁴]. Hence, a more stable and adherent chromium oxide film is expected to form on the 304 SS when compared with P91. High chromium is mainly responsible for improving corrosion resistance in many ferrous alloys, particularly stainless steels [³, ²⁷, ²⁸, ²⁹, ³⁰]. The corrosion rate of the as-built P91 and 304 SS bimetallic was found to be 10 times slower than that of the base metals (304 SS and P91 steel). The reason for this is explained further in subsequent sections.

Figure 2
Open circuit potential of P91, 304 SS and as-built P91 and 304 SS bimetallic in 3.5 wt% NaCl (a); Potentiodynamic polarisation curves of P91, 304 SS and as-built P91 and 304 SS bimetallic in 3.5 wt% NaCl (b).

Table 1
Electrochemical parameters obtained from potentiodynamic polarisation of base metals (P91 and 304 SS) and P91 and 304 SS bimetallic.

SAMPLES	ICORR (µAcm2)	ECORR (V)	CORROSION RATE (mm/yr)
304 SS	9.06511	–0.4838	0.1039
P91	32.576	–0.6731	0.3473
As-built	2.62258	–0.6772	0.0310

The SEM-BSE images of the corroded base metals (304 SS and P91 steel), and the as-built P91 and 304 SS bimetallic are presented in Figure 3. It can be seen that there are more corrosion products on the as-built P91 and 304 SS bimetallic component (Figure 3c). The corrosion products are prominent in the as-built P91 region of the bimetallic component. Figure 4 shows the EDX analysis of both 304 SS and P91 zones of the bimetallic component. It can be seen that oxygen was not detected in the 304 SS zone. The only elements found are Fe, C, Ni, and Cr, which are the essential alloying elements in the alloys (Figure 4a). The absence of detectable oxygen in the 304 SS region does not necessarily indicate the absence of a passive film. The Cr₂O₃ passive layer on stainless steels is typically nanometric in thickness and may fall below the detection depth and sensitivity of conventional EDS analysis [³¹]. However, in the P91 zone, Fe, Mn, Na, C, and O are present (Figure 4b). The presence of oxygen suggests oxides of Mn and Fe as possible corrosion products. Cr and Ni, which contribute to the corrosion resistance of ferrous alloys [³²], were not found in the P91 region. Previous reports have indicated that oxides of Cr and Fe may both be present on the surface of P91, but Fe₂O₃ is more dominant, which is less protective [³³]. Also, P91 is a tempered martensitic steel containing M₂₃C₆ and MX-type carbides which can locally deplete chromium at grain boundaries. This chromium depletion reduces the availability of chromium for passive film formation and compromises corrosion resistance [³⁴]. These observations suggest that the higher corrosion susceptibility of the P91 region might be attributed to the combined effects of lower bulk chromium content, reduced passivation capability, formation of Fe-rich oxides, and chromium depletion associated with its microstructure.

Figure 3
SEM-BSE images of corroded (a) 304 SS; (b) P91; (c) as-built P91 and 304 SS bimetallic component.

Figure 4
SEM-EDX of corroded as-built 304 SS (a) and P91 (b) bimetallic region.

3.2. Influence of deformation parameters on corrosion behaviour of as-built P91 and 304 SS bimetallic component

Figure 5 shows the OCP and potentiodynamic polarisation curves for hot-worked P91 and 304 SS bimetallic component. In terms of susceptibility to corrosion in 3.5 wt% NaCl, the hot-deformed samples all showed lower susceptibility to corrosion compared to the as-built samples, regardless of the deformation temperature and strain rate. This is depicted by the more positive OCP exhibited by the deformed P91 and 304 SS bimetallic component in Figure 5a and Figure 5c. A similar trend can be seen in the potentiodynamic polarisation curves in Figure 5b and Figure 5d, where the corrosion potential of the deformed samples at the strain rate of 1 and 10 s^–1 are all higher than that of the as-built condition. Also, the passivation currents of the deformed samples are lower than that of the as-built sample. The corrosion rates presented in Table 2 show that there are specific deformation conditions that are more favourable for enhanced corrosion performance. This indicates that the corrosion performance of the bimetallic material is sensitive to deformation conditions. For example, when deformation was carried out at the strain rate of 1 s^–1, the lowest corrosion rate was achieved at the deformation temperature of 1000°C, whereas when the strain rate increased to 10 s^–1, the lowest corrosion rate was obtained at the deformation temperature of 900°C. The trends observed in these results indicate that the microstructural evolution during deformation as well as the optimum deformation conditions for enhanced corrosion performance of P91 and 304 SS bimetallic require further investigation. The SEM images of corroded samples under all deformation conditions are shown in Figure 6, the presence of localised corrosion depicted by pits are seen on the P91 (dark region) of the bimetallic component. This differ from the uniform corrosion which is seen in the P91 region of the as-built P91 and 304 SS bimetallic.

Figure 5
Electrochemical behaviour of hot deformed P91, 304 SS and P91 and 304 SS bimetallic: (a) OCP at 1s^–1; (b) Potentiodynamic polarisation curves at 1 s^–1; (c) OCP at 10 s^–1; and (d) Potentiodynamic polarisation curves at 10 s^–1.

Table 2
Electrochemical parameters obtained from potentiodynamic polarisation curves of hot deformed P91, 304 SS and P91 and 304 SS bimetallic material.

SAMPLES	ICORR (µAcm2)	ECORR (V)	CORROSION RATE (mm/yr)
As-built	2.62258	–0.6772	0.0310
Deformation at 1 s –1
P91 and 304SS at 800 ℃	0.00008667	–0.1826	0.000001025
P91 and 304SS at 900 ℃	5.17774	–0.5043	0.06125
P91 and 304SS at 1000 ℃	0.000052	–0.1595	0.000000615
Deformation at 10 s –1
P91 and 304SS at 800 ℃	1.83525	–0.5869	0.02171
P91 and 304SS at 900 ℃	0.000065	–0.3015	0.00000077
P91 and 304SS at 1000 ℃	8.04829	–0.538	0.0952

Figure 6
SEM-BSE images of corroded P91 (dark region) and 304 SS (white region) bimetallic (a) 800°C/10 s^–1; (b) 900°C/10 s^–1; (c) 1000°C/10 s^–1; (d) 800°C/1 s^–1; (e) 900°C/1s^–1; and (f) 1000°C/1 s^–1.

3.3. Hardness profile of P91 and 304 SS bimetallic in as-built and deformation conditions

The hardness of the P91 and 304 SS base metals was compared with the P91 and 304 SS bimetallic in the as-built condition. Figure 7 shows that the P91 region of as-built bimetallic component has a similar hardness as the base metals (P91 and 304 SS), while the 304 SS region of as-built bimetallic component has a lower hardness than the base metals. As expected, the base metal of P91 had a higher hardness values compared to 304 SS (base metal), owing to fine MC/MX carbides [³⁵]. Strengthening in 304 SS is primarily governed by solid-solution strengthening from Cr and Ni alloying elements and its high work-hardening capability [³⁶]. The hardness profile of the deformed P91 and 304 SS bimetallic is compared with the as-built P91 and 304 SS bimetallic in Figure 8. The hardness of all the deformed samples was higher than that of the as-built sample. The profile also shows that at 800°C/1 s^–1 and 1000°C/1 s^–1, hardness at the 304 SS region are higher than the as-built 304 SS region, but closer at the P91 region of deformed bimetallic. At 900°C/10 s^–1 and 1000°C/10 s^–1, the difference in hardness between the P91 and 304 SS regions is closer, whereas hardness is higher in the 304 SS region at 800°C/10 s^–1 than the 304 SS region of the as-built and at 900°C/10 s^–1 and 1000°C/10 s^–1. This result suggests that the thermomechanical treatment may have resulted in a more homogeneous and refined microstructure in the deformed P91 and 304 SS bimetallic. It is clear from Figure 8 that the interface between the P91 and 304 SS bimetallic under as-built and deformation conditions had the lowest hardness value. The low hardness value can be due to the depletion of MC/MX carbides and Cr-rich M₂₃C₆ that would promote hardening. Further characterisation of the interface is required to determine possible phenomenon that might have taken place in this region.

Figure 7
Hardness of base metals (P91 and 304 SS) and the P91 and 304 SS bimetallic.

Figure 8
Hardness profile of P91 and 304 SS bimetallic component (a) 1 s^–1; and (b) 10 s^–1.

4. DISCUSSION

This study seeks to answer the question of whether thermomechanical processing parameters influence the corrosion behaviour of P91 and 304 SS bimetallic component. To answer this question, the corrosion performance of the individual alloys was evaluated in 3.5 wt% NaCl. The results were then compared with the P91 and 304 SS bimetallic component. The OCP potential curves indicated that the susceptibility of 304 SS to corrosion in 3.5 wt% NaCl is lower when compared to P91 and the bimetallic counterpart owing to higher chromium content, which would allow for a compact and protective oxide layer on the surface of the alloy. The corrosion resistance of stainless steel is dependent on the composition and structure of the passive film formed on the metal surface [³⁷, ³⁸]. The OCP reflects thermodynamic tendencies, whereas corrosion rate represents kinetic metal dissolution. While OCP is a valid parameter that can provide insights into the stability of the oxide film formed on the surface of alloys, the corrosion rate remains an important parameter that allows for an estimation of the service life of materials under corrosive conditions. From the corrosion rate results, the as-built bimetallic component has a corrosion rate that is 10 times lower than the base metals. To gain further insights into the observed trend, the SEM images of the corroded surface were analysed. The bimetallic component had more corrosion product on the P91 region than in the 304 SS region. This corrosion product has been reported to retard the corrosion rate of P91 immersed in sodium sulphate or nitrate salts [³, ³³]. CHAO et al. [³³] reported that the corrosion rate of P91 may be higher at the initial period of immersion in Na₂SO₄ environment during which the corrosion products, such as oxides of Fe, Cr, and Fe-Cr spinel, are building up, but the corrosion rate is reduced significantly when the corrosion product has reached a critical amount. A similar phenomenon may be at play in the 3.5 wt% NaCl environment. The higher corrosion rate seen in P91 when immersed in 3.5 wt% NaCl may be due to lower bulk chromium content, reduced passivation capability, formation of Fe-rich oxides, and chromium depletion associated with its microstructure.

When the bimetallic component was subjected to different deformation conditions, the deformed samples showed a significant reduction in corrosion rate. The corrosion potential also increased to more positive values. This indicates that deformation improved the corrosion performance of the bimetallic component in 3.5 wt% NaCl. This marked improvement may be ascribed to a more homogeneous and refined microstructural constituents in the deformed bimetallic component. Deformation can reduce diffusion distance [³⁹, ⁴⁰] and allow faster Cr diffusion from 304 SS towards the P91 region. Figure 9 shows evidence of microstructural refinement in the deformed samples, particularly in the 304 SS region. The hardness profile provided additional insights into how reduced corrosion rates in the deformed samples may be linked to refinement in the microstructure of the bimetallic component. The difference between the hardness of base metals, is quite obvious, and in the as-built condition, the P91 region has higher hardness than 304 SS in the bimetallic material.

Figure 9
Optical images of (a) as-built P91 and 304 SS bimetallic with coarser microstructure; (b) P91 region after deformation (900°C/10 s^–1); and (c) 304 SS region showing finer microstructure after deformation (900°C/10 s^–1).

Contrarily, in the deformed condition, the hardness of all the deformed samples was higher than that of the as-built sample. Only marginal differences are observed between the hardness of the P91 region and the 304 SS region of the deformed bimetallic component at 900°C/10 s^–1 and 1000°C/10 s^–1. This observation may be attributed to the reduced diffusion distance during high-temperature deformation, and a more refined grain may have formed [³⁹, ⁴⁰]. Moreover, the deformation temperature influences material hardness. Higher deformation temperature caused higher hardness since diffusion increases at higher deformation temperatures [⁴¹, ⁴²]. The corresponding increase in hardness at deformation temperatures indicates that grain refinement in the deformed bimetallic component occurred. The observed microstructural changes, although needing further analysis, would have a definite influence on the observed corrosion results presented on WAAM-processed P91 and 304 SS in this study.

There are specific deformation conditions that reduce the corrosion rate in deformed bimetallic components significantly. For example, deformation at 800 and 1000°C at a 1s^–1 strain rate and 900°C at a 10 s^–1 strain rate (Figure 9). While the reason for this may be linked to the microstructural evolution, there is a need for the optimisation of microstructure for enhanced mechanical properties and corrosion performance for this specific bimetallic component. The corrosion products obtained for the deformed bimetallic condition showed that pitting corrosion was dominant rather than uniform corrosion that was observed in the as-built bimetallic material. This pitting corrosion is predominant in the P91 region of the bimetallic component, and these pits are covered by corrosion products. In this study, pitting is observed under all deformation conditions, and the lower corrosion rate may be due to the covering of the pits by oxides that retarded the rate at which corrosion was occurring. It is quite clear that the contribution of the P91 region to the corrosion performance of the bimetallic component is quite significant, and should there be any improvement required, more research focus would be on the P91 region of the bimetallic component.

5. CONCLUSIONS

Electrochemical techniques, scanning electron microscopy, and hardness profile measurements were used to assess the influence of thermomechanical processing on the corrosion performance of P91 and 304 SS bimetallic material in 3.5 wt% NaCl. The bimetallic component was developed using WAAM. From the results, the following conclusions were drawn:

• The P91 region of the bimetallic material is more susceptible to corrosion in 3.5 wt% NaCl.

• Thermomechanical processing improved corrosion performance in the bimetallic material by reducing the corrosion rate significantly, especially when deformation was performed at 800 and 1000°C, at 1 s^–1; and 900°C, at 10 s^–1.

• Improvement in corrosion performance of the bimetallic material under deformation conditions was ascribed to microstructural refinement.

• Hardness profile confirmed that microstructural refinement in deformed samples occurred due to the increasing hardness.

Further work will involve establishing quantitative correlations between corrosion performance and the deformation regimes of the bimetallic component, with optimum conditions identified using processing maps and validated through detailed microstructural analysis. This will provide a robust framework for tailoring deformation parameters to enhance corrosion resistance. In addition, future studies will investigate in detail the diffusion of alloying elements during deformation of WAAM-processed P91/304 stainless steel bimetallic materials.

DATA AVAILABILITY

Data available upon request.

6. BIBLIOGRAPHY

• ^[1] KRSTEVSKA, A., POSER, M.B., ZDRAVESKI, F., “Weldability between steel type 304H and steel type P91 for high temperature applications”, Društvo Za Unapređivanje Zavarivanja U Srbiji, v. 100, pp. 128–136, 2021.
• ^[2] RANI, K.U., KUMAR, R., MAHAPATRA, M.M., et al, “Wire arc additive manufactured mild steel and austenitic stainless-steel components: microstructure, mechanical properties and residual stresses”, Materials (Basel), v. 15, n. 20, pp. 7094, 2022. doi: https://doi.org/10.3390/ma15207094. PubMed PMID: 36295161.
  » https://doi.org/10.3390/ma15207094
• ^[3] LI, N., TARIQ, N.U.H., HAN, B., et al, “Study of corrosion performance and mechanisms of P91, 304SS and IN625 alloys in molten nitrate salts used for thermal energy storage system”, Metals, v. 13, n. 4, pp. 806, 2023. doi: https://doi.org/10.3390/met13040806.
  » https://doi.org/10.3390/met13040806
• ^[4] BRITTO, J.G., SULBIHAR, A.D., DINESH, K.L., et al, “Microstructural studies of P91 and SS304L dissimilar welding”, Materials Today: Proceedings, v. 47, pp. 4571–4577, 2021. doi: https://doi.org/10.1016/j.matpr.2021.05.434.
  » https://doi.org/10.1016/j.matpr.2021.05.434
• ^[5] ZOU, Y., LIU, K., XU, Z., et al, “Weld solidification cracking of austenitic stainless steels: mechanisms, testing methods, and controlling factors and strategies”, Journal of Materials Science, v. 61, n. 4, pp. 2067–2121, 2026. doi: https://doi.org/10.1007/s10853-025-11954-8.
  » https://doi.org/10.1007/s10853-025-11954-8
• ^[6] LESUFI, M., AKINWAMIDE, S.O., MAKOANA, W., et al, “Nanoindentation and corrosion behaviour of 410 stainless steel fabricated via additive manufacturing”, Transactions of the Indian Institute of Metals, v. 76, n. 3, pp. 695–702, 2023. doi: https://doi.org/10.1007/s12666-022-02736-w.
  » https://doi.org/10.1007/s12666-022-02736-w
• ^[7] KLENAM, D.E.P., BAMISAYE, O.S., WILLIAMS, I.E., et al, “Global perspective and African outlook on additive manufacturing research − an overview”, Manufacturing Review, v. 9, pp. 1–37, 2022. doi: https://doi.org/10.1051/mfreview/2022033.
  » https://doi.org/10.1051/mfreview/2022033
• ^[8] AFROUZIAN, A., GRODEN, C.J., FIELD, D.P., et al, “Additive manufacturing of Ti-Ni bimetallic structures”, Materials & Design, v. 215, pp. 110461, 2022. doi: https://doi.org/10.1016/j.matdes.2022.110461. PubMed PMID: 35370339.
  » https://doi.org/10.1016/j.matdes.2022.110461
• ^[9] WU, B., QIU, Z., PAN, Z., et al, “Enhanced interface strength in steel-nickel bimetallic component fabricated using wire arc additive manufacturing with interweaving deposition strategy”, Journal of Materials Science and Technology, v. 52, pp. 226–234, 2020. doi: https://doi.org/10.1016/j.jmst.2020.04.019.
  » https://doi.org/10.1016/j.jmst.2020.04.019
• ^[10] AHSAN, R.U., NEWAZ, A., TANVIR, M., et al, “Fabrication of bimetallic additively manufactured structure (BAMS) of low carbon steel and 316L austenitic stainless steel with wire arc additive manufacturing”, Rapid Prototype Journal, v. 3, pp. 519–530, 2020.
• ^[11] LI, W., CAO, R., ZHU, W., et al, “Microstructure evolution and impact toughness variation for high strength steel multi-pass weld metals with various cooling rates”, Journal of Manufacturing Processes, v. 65, pp. 245–257, 2021. doi: https://doi.org/10.1016/j.jmapro.2021.03.027.
  » https://doi.org/10.1016/j.jmapro.2021.03.027
• ^[12] WILLIAMS, I., MALEDI, N., BAMISAYE, O.S., et al, “Microstructure, hardness, and wear behaviour of laser-cladded Inconel 625 and 718 powders on Hadfield steel”, Proceedings of the Institution of Mechanical Engineers. Proceedings Part L, Journal of Materials: Design and Applications, pp. 1–16, 2025. doi: https://doi.org/10.1177/14644207251362598.
  » https://doi.org/10.1177/14644207251362598
• ^[13] MEI, Y., LIU, Y., LIU, C., et al, “Effect of base metal and welding speed on fusion zone microstructure and HAZ hot-cracking of electron-beam welded Inconel 718”, Materials & Design, v. 89, pp. 964–977, 2016. doi: https://doi.org/10.1016/j.matdes.2015.10.082.
  » https://doi.org/10.1016/j.matdes.2015.10.082
• ^[14] RAHIMI, E., RAFSANJANI-ABBASI, A., IMANI, A., et al, “Insights into galvanic corrosion behavior of Ti-Cu dissimilar joint: Effect of microstructure and volta potential”, Materials (Basel), v. 11, n. 10, pp. 1820, 2018. doi: https://doi.org/10.3390/ma11101820. PubMed PMID: 30257472.
  » https://doi.org/10.3390/ma11101820
• ^[15] LI, X., SAARIO, T., IKÄLÄINEN, T., et al, “Corrosion behavior of additively manufactured M300-CuCr1Zr by multi-material laser-based powder bed fusion”, Electrochimica Acta, v. 507, pp. 145199, 2024. doi: https://doi.org/10.1016/j.electacta.2024.145199.
  » https://doi.org/10.1016/j.electacta.2024.145199
• ^[16] ROSADO, P.M., SAMPAIO, R.F., MEDEIROS, J.M., et al, “Hybrid wire-arc additive manufacturing of sheet metal components with three-dimensional features”, Progress in Additive Manufacturing, v. 11, pp. 3789–3800, 2026. doi: https://doi.org/10.1007/s40964-026-01549-3.
  » https://doi.org/10.1007/s40964-026-01549-3
• ^[17] HU, R., GUO, C., YING, M., et al, “Microstructure properties of TP91 (9Cr-1Mo-V-Nb) steel produced by wire arc additive manufacturing”, Transactions of the Indian Institute of Metals, v. 75, n. 12, pp. 3213–3222, 2022. doi: https://doi.org/10.1007/s12666-022-02717-z.
  » https://doi.org/10.1007/s12666-022-02717-z
• ^[18] SRIDAR, S., KLECKA, M.A., XIONG, W., “Interfacial characteristics of P91 steel-Inconel 740H bimetallic structure fabricated using wire-arc additive manufacturing”, Journal of Materials Processing Technology, v. 300, pp. 117396, 2022. doi: https://doi.org/10.1016/j.jmatprotec.2021.117396.
  » https://doi.org/10.1016/j.jmatprotec.2021.117396
• ^[19] KUMAR, K.D.V., KARPAGARAJ, A., LOGANATHAN, T.G., “Mechanical and metallurgical properties of SS304L-IN718 bimetallic wall deposited using cold metal transfer”, Journal of Materials Engineering and Performance, v. 34, n. 24, pp. 30280–30293, 2025. doi: https://doi.org/10.1007/s11665-025-11439-4.
  » https://doi.org/10.1007/s11665-025-11439-4
• ^[20] DUAN, H., GAO, Y., LIU, Y., et al, “A modified Johnson-cook model for 304 stainless steel”, Applied Physics. A, Materials Science & Processing, v. 131, n. 3, pp. 176, 2025. doi: https://doi.org/10.1007/s00339-025-08276-6.
  » https://doi.org/10.1007/s00339-025-08276-6
• ^[21] NKHOMA, R.K.C., SIYASIYA, C.W., STUMPF, W.E., “Hot workability of AISI 321 and AISI 304 austenitic stainless steels”, Journal of Alloys and Compounds, v. 595, pp. 103–112, 2014. doi: https://doi.org/10.1016/j.jallcom.2014.01.157.
  » https://doi.org/10.1016/j.jallcom.2014.01.157
• ^[22] OBIKO, J., MXOLISI, B., NICHOLUS, M., “Hot workability of AISI 304 stainless steel: constitutive and ANN modelling”, International Journal on Interactive Design and Manufacturing, pp. 1–15, 2025.
• ^[23] BABU, K.A., MOZUMDER, Y.H., SAHA, R., et al, “Hot-workability of super-304H exhibiting continuous to discontinuous dynamic recrystallization transition”, Materials Science and Engineering A, v. 734, pp. 269–280, 2018. doi: https://doi.org/10.1016/j.msea.2018.07.104.
  » https://doi.org/10.1016/j.msea.2018.07.104
• ^[24] MAUBE, S., OBIKO, J., VAN DER MERWE, J., et al, “Comparative study on hot metal flow behavior of virgin and rejuvenated heat treatment creep exhausted P91 steel”, Applied Sciences (Basel, Switzerland), v. 13, n. 7, pp. 4449, 2023. doi: https://doi.org/10.3390/app13074449.
  » https://doi.org/10.3390/app13074449
• ^[25] SHAH, N.S., CHAKRAVARTTY, J.K., SARKAR, A., “Comparative study on hot deformation behavior of P91, RAFM-CLAM and Low C RAFM-CLAM steels by processing maps”, Fusion Engineering and Design, v. 138, pp. 109–118, 2018. doi: https://doi.org/10.1016/j.fusengdes.2018.11.010.
  » https://doi.org/10.1016/j.fusengdes.2018.11.010
• ^[26] OBIKO, J., WHITEFIELD, D., BODUNRIN, M., “Hot workability of two P92 creep resistant steels: constitutive analysis”, International Journal of Advanced Manufacturing Technology, v. 129, n. 3-4, pp. 1503–1512, 2023. doi: https://doi.org/10.1007/s00170-023-12402-0.
  » https://doi.org/10.1007/s00170-023-12402-0
• ^[27] RÖTTGER, A., BOES, J., THEISEN, W., et al, “Microstructure and mechanical properties of 316L austenitic stainless steel processed by different SLM devices”, International Journal of Advanced Manufacturing Technology, v. 108, n. 3, pp. 769–783, 2020. doi: https://doi.org/10.1007/s00170-020-05371-1.
  » https://doi.org/10.1007/s00170-020-05371-1
• ^[28] YU, Y., SHIRONITA, S., SOUMA, K., et al, “Effect of chromium content on the corrosion resistance of ferritic stainless steels in sulfuric acid solution”, Heliyon, v. 4, n. 11, pp. e00958, 2018. doi: https://doi.org/10.1016/j.heliyon.2018.e00958. PubMed PMID: 30839865.
  » https://doi.org/10.1016/j.heliyon.2018.e00958
• ^[29] FRANCIS, R., Corrosion performance of metals for the marine environment, Boca Raton, CRC Press, 2012. EFC 63.
• ^[30] MALIK, S., RADWAN, A.B., AL-QAHTANI, N., et al, “Focused review on factors affecting martensitic stainless steels and super martensitic stainless steel passive film in the oil and gas field”, Journal of Solid State Electrochemistry, v. 28, n. 10, pp. 3533–3557, 2024. doi: https://doi.org/10.1007/s10008-024-05984-6.
  » https://doi.org/10.1007/s10008-024-05984-6
• ^[31] OLSSON, C.O.A., LANDOLT, D., “Passive films on stainless steels–chemistry, structure and growth”, Electrochimica Acta, v. 48, n. 9, pp. 1093–1104, 2003. doi: https://doi.org/10.1016/S0013-4686(02)00841-1.
  » https://doi.org/10.1016/S0013-4686(02)00841-1
• ^[32] WANG, D., ZHONG, Q., YANG, J., et al, “Effects of Cr and Ni on the microstructure and corrosion resistance of high-strength low alloy steel”, Journal of Materials Research and Technology, v. 23, pp. 36–52, 2023. doi: https://doi.org/10.1016/j.jmrt.2022.12.191.
  » https://doi.org/10.1016/j.jmrt.2022.12.191
• ^[33] CHAO, F., YI, X., JUN, W., et al, “The corrosion behaviour of T/P91 steel under the atmosphere environment in Hunan province”, MATEC Web of Conferences, v. 175, pp. 1–4, 2018.
• ^[34] NISHAD, S.K.N., DWIVEDI, D.K., “Role of Cr-precipitates and diffusible hydrogen on SCC of SS304-P91 dissimilar steel welds under boiling MgCl2 solution”, Electrochimica Acta, v. 553, pp. 148310, 2026. doi: https://doi.org/10.1016/j.electacta.2026.148310.
  » https://doi.org/10.1016/j.electacta.2026.148310
• ^[35] ABE, F., KERN, T.U., VISWANATHAN, R., Creep-resistant steels, Cambridge, Woodhead Publishing, 2008. doi: https://doi.org/10.1533/9781845694012.
  » https://doi.org/10.1533/9781845694012
• ^[36] DAVIS, J.R. (ed), ASM specialty handbook: stainless steels, Veldhoven, ASM International, 1994.
• ^[37] PESQUEIRA, C.M., LUIZ, L.A., ANDRADE, J., et al, “The effect of chloride, sulfate, and ammonium ions on the semiconducting behavior and corrosion resistance of AISI 304 stainless steel passive film”, Matéria (Rio de Janeiro), v. 28, n. 4, pp. 1–10, 2023. doi: https://doi.org/10.1590/1517-7076-rmat-2023-0139.
  » https://doi.org/10.1590/1517-7076-rmat-2023-0139
• ^[38] LIMA, B.F.V.A., MEDEIROS, J.L.B., SOUZA, J., et al, “Evaluation of the behavior of austenitic stainless steel AISI 304 in different soils with acid PH”, Matéria (Rio de Janeiro), v. 29, n. 4, pp. 1–7, 2024. doi: https://doi.org/10.1590/1517-7076-rmat-2024-0513.
  » https://doi.org/10.1590/1517-7076-rmat-2024-0513
• ^[39] BODUNRIN, M.O., CHOWN, L.H., VAN DER MERWE, J.W., et al, “Microstructural evolution during hot forming of Ti-6Al-4V alloy with complex initial microstructure”, International Journal of Advanced Manufacturing Technology, v. 104, pp. 3017–3026, 2019. doi: https://doi.org/10.1007/s00170-019-04162-7.
  » https://doi.org/10.1007/s00170-019-04162-7
• ^[40] KOIKE, J., SHIMOYAMA, Y., OHNUMA, I., et al, “Stress-induced phase transformation during superplastic deformation in two-phase Ti–Al–Fe alloy”, Acta Materialia, v. 48, n. 9, pp. 2059–2069, 2000. doi: https://doi.org/10.1016/S1359-6454(00)00049-5.
  » https://doi.org/10.1016/S1359-6454(00)00049-5
• ^[41] ZHOU, Y., LIN, X., KANG, N., et al, “Hot deformation induced microstructural evolution in local-heterogeneous wire + arc additive manufactured 2219 Al alloy”, Journal of Alloys and Compounds, v. 865, pp. 158949, 2021. doi: https://doi.org/10.1016/j.jallcom.2021.158949.
  » https://doi.org/10.1016/j.jallcom.2021.158949
• ^[42] WANG, Y.T., LI, J.B., XIN, Y.C., et al, “Hot deformation behavior and hardness of a CoCrFeMnNi high-entropy alloy with high content of carbon”, Acta Metallurgica Sinica, v. 32, n. 8, pp. 932–943, 2019. doi: https://doi.org/10.1007/s40195-019-00916-0.
  » https://doi.org/10.1007/s40195-019-00916-0

Publication Dates

• Publication in this collection
  18 May 2026
• Date of issue
  2026

History

• Received
  09 Nov 2025
• Accepted
  15 Mar 2026