(1) Melting: raw materials are melted and mixed in the electric furnace [1]

(2) Argon-oxygen decarburization (AOD)

• Reduce corrosion due to the formation of carbides, nitrides and intermetallic phases, advanced refining processes are required (shown in figure 1)
• The mixture of argon and oxygen is injected to the melted steel at 1700°C
• Argon is added to decrease the partial pressure of CO, drive the reaction forward

           Oxygen is used as reactants to remove carbides

           Decarburization: 4Cr+3O2→2Cr2O3   Cr2O3+3C→3CO+2Cr

• Reduction: remove additional oxidized elements
• Desulfurization: S+CaO=CaS+O

• Depending on “A Federal Strategy to Ensure Secure and Reliable Supplies of Critical Minerals”, presented by the United States [2]
• The list of 35 critical minerals
• Carbon, Nickel, Silicon and Molybdenum are not included in the list
• Chromium and Tungsten are on the list (The appearances of Chromium and Tungsten are shown in figure 2 and 3 respectively)
• The content of Chromium is 13%-15% & Tungsten is 2%-2.75%
• 4Cr14Ni14W2Mo can be considered as a critical material (The appearance of 4Cr14Ni14W2Mo is shown in figure 4)

1. Krivsky, W.A. The linde argon-oxygen process for stainless steel; A case study of major innovation in a basic industry. MT 4, 1439–1447 (1973).

https://doi.org/10.1007/BF02667991

2. Interior Department Final List of Critical Minerals 2018 released on 05/18/2018

           Document Citation: 83 FR 23295  Page: 23295-23296 (2 pages)

https://www.federalregister.gov/documents/2018/05/18/2018-10667/final-list-of-critical-minerals-2018

       3. The appearance of Chromium.  Accessed on: Bing images searching  https://cn.bing.com/images/search?view=detailV2&ccid=NxrEnUoB&id=FF85AECDFEF4A6D26B40D50D4B91F1F24BF3B1A2&thid=OIP.NxrEnUoBsUh2Xpi2Vy8EOgHaHa&mediaurl=https%3a%2f%2fdelachaux.com%2fwp-content%2fuploads%2f2018%2f04%2fMG_5687.jpg&exph=1024&expw=1024&q=Chromium&simid=608046164905559282&ck=316C9B7306196DEFB9828635BA706233&selectedIndex=16&ajaxhist=0

        4. The appearance of Tungsten. Accessed on: Bing images searching  https://cn.bing.com/images/search?view=detailV2&ccid=LiVUE0it&id=45B2A61D1EA2470DA49A49A515E34A85C2FB290D&thid=OIP.LiVUE0itOObDQO6xX9GoBgHaE6&mediaurl=https%3a%2f%2f3dprintingindustry.com%2fwp-content%2fuploads%2f2019%2f03%2fshutterstock_323720315.jpg&exph=664&expw=1000&q=+Tungsten&simid=608022491082982392&ck=B1138ADD1B8AF08BD17BA2C70A6088AC&selectedIndex=5&ajaxhist=0

         5. The appearance of 4Cr14Ni14W2Mo. Accessed on: Bing images searching  https://cn.bing.com/images/search?view=detailV2&ccid=Abe3SZhy&id=1A91E7815C0FDDA92B677C087EB55B5492F80901&thid=OIP.Abe3SZhyLwhqQywvHrd3_QHaJ4&mediaurl=http%3a%2f%2fimg71.ybzhan.cn%2f2%2f20190820%2f637019313910374782274.jpg&exph=1440&expw=1080&q=4Cr14Ni14W2Mo&simid=608055768377721993&ck=FEF72F76D581E2BA8006CA43F896DE9D&selectedIndex=1&ajaxhist=0