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Developing an Appropriate Heat Treatment Protocol for Additively Manufactured Alloy 718 for Oil and Gas Applications

Additive manufacturing (AM) is a transformative technology that has opened areas of design space that were previously inaccessible by enabling the production of complex, three-dimensional parts and intricate geometries that were impractical to produce via traditional manufacturing methods. However, the extreme thermo-mechanical conditions in the AM build process (e.g., cooling rates ranging from 103 K/s
to 106 K/s and repeated heating/cooling cycles) generate deleterious microstructures with high residual stresses, and extreme compositional gradients.

Product Number: 51323-18793-SG
Author: M.R. Stoudt, M.E. Williams, J.S. Zuback, K.W. Moon, C.E. Campbell, C.R. Beauchamp, M. Yunovich
Publication Date: 2023
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$20.00
$20.00

The combination of strength, corrosion resistance, and excellent weldability makes Alloy 718 an attractive alloy for additive manufacturing (AM) applications, but the AM build process generates large compositional and microstructural heterogeneities. The formation of the δ-phase is of particular importance within the petroleum and natural gas (PNG) industries and a reduced Nb content is one method currently in use to control δ-phase growth in wrought IN718. However, it is not clear how effective that strategy will be in AM components as the growth kinetics of δ -phase are exceptionally sensitive to the build parameters used in the AM processing. Since the API 6ACRA treatment protocol used for wrought Alloy 718 does not produce the same properties in AM 718, a refined post-build heat treatment is required to relieve residual stresses and produce uniform microstructures and properties. An integrated computational materials engineering (ICME) framework was adopted for this work to develop
an effective heat treatment protocol for AM-processed IN718 that consistently achieves the requisite performance metrics while minimizing the δ-phase growth. for oil and gas industry applications. The results revealed that even though the wrought heat treatment does not completely remove all the AM solidification microstructure, it was sufficient to precipitate γ’ to achieve the 1035 MPa (150 ksi) strength level. Precipitation of γ’’, which governs the 850 MPa (120 ksi) strength level, is far more difficult to achieve without significant co-precipitation of the δ-phase.

The combination of strength, corrosion resistance, and excellent weldability makes Alloy 718 an attractive alloy for additive manufacturing (AM) applications, but the AM build process generates large compositional and microstructural heterogeneities. The formation of the δ-phase is of particular importance within the petroleum and natural gas (PNG) industries and a reduced Nb content is one method currently in use to control δ-phase growth in wrought IN718. However, it is not clear how effective that strategy will be in AM components as the growth kinetics of δ -phase are exceptionally sensitive to the build parameters used in the AM processing. Since the API 6ACRA treatment protocol used for wrought Alloy 718 does not produce the same properties in AM 718, a refined post-build heat treatment is required to relieve residual stresses and produce uniform microstructures and properties. An integrated computational materials engineering (ICME) framework was adopted for this work to develop
an effective heat treatment protocol for AM-processed IN718 that consistently achieves the requisite performance metrics while minimizing the δ-phase growth. for oil and gas industry applications. The results revealed that even though the wrought heat treatment does not completely remove all the AM solidification microstructure, it was sufficient to precipitate γ’ to achieve the 1035 MPa (150 ksi) strength level. Precipitation of γ’’, which governs the 850 MPa (120 ksi) strength level, is far more difficult to achieve without significant co-precipitation of the δ-phase.

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Picture for Statistics to Compare Alloy 718 Properties from Additive Manufactured and Newer Mill-Produced Bar Stocks
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Statistics to Compare Alloy 718 Properties from Additive Manufactured and Newer Mill-Produced Bar Stocks

Product Number: 51319-12948-SG
Author: Manuel Marya
Publication Date: 2019
$20.00

Alloy 718 is a common oilfield material for permanent and service equipment in need of high-mechanical ratings and resistance to corrosion especially environmentally-assisted cracking in sour gas wells. In past decade Alloy 718 production from traditional and newer mills has greatly increased in response to global demands; independently yet driven by similar market growth additive manufacturing (AM) has expanded beyond rapid prototyping to become an industrial production process namely in the aerospace. Today 718 bar stocks as per API6CRA are produced by over a dozen mills worldwide;similarly 718 powder products are increasingly offered by both traditional and newer mills with intents to servea multitude ofAM technologies. Due to the rise of new economic forces in the O&G there are today needs for evaluating (ultimately qualifying) newer 718 producing mills as well as 718 powders in combination with various AM technologies. Due to concerns overraw-material properties a study was conducted to analyze 718 materials from these various origins utilizing (1) mill cert big-data analyses (2) third-party recertified mechanical test data (3) a multitude of sour service test results outside the traditional NACE MR0175/ISO15156 operational service limits among others. The later raw-material test implemented in the early 2010s for screening and qualification purposes aims at quantitatively comparing 718 production heats of various origins and with additive manufacturing also generating interests since the early 2010sthe same tests have also beenextended to determine how layer-by-layer deposited materials compare to bar stock materials.