Mechanical work and recrystallization in Alumina-Forming alloys Kevin Slezak, Nisrit Pandey, Lizeth Ortiz, Dr. Benjamin Church Department of Materials Science and Engineering

Introduction Workpiece Boring Tool Feed Figure 1: Sketch of a boring Process In the petrochemical industry, hydrocarbons are cracked at very high temperatures to produce ethylene gas and other products. Steel alloys used need both superior corrosion and creep resistance as well as coking resistance. A series of alumina-forming alloys produced via centrifugal casting process were received as sections of pipe, which are perceived to have increased oxidation resistance Following horizontal centrifugal casting, the cast tubes were pull-bored to machine the inner diameter. This production process used is identical to that used to produce production tubes for ethylene service. The project involves the analysis of the near-surface hardness and understanding if the boring is imparting cold work that would potentially provide the means for recrystallization near the ID of the tube.

Coking HP-Nb Alloy AFA Heat Treatment at 850 °C in a C2H6 Environment Figure 2: Carbon deposition in inner-diameter of a traditional chromia former and alumina former HP-Nb Alloy AFA Heat Treatment at 850 °C in a C2H6 Environment HP-Nb Alloy shows a thick layer of carbon compared to Alumina Forming Alloy (AFA)

Figure 3: Alumina Formers have significantly less amount of carbon deposited to the surface of the inner diameter Coking Atmosphere: H2 – C2H6 (10:1) at 950 °C.

Materials Preparation ID   OD 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 Materials: Chromia G2535 – A Chromia Forming Alloy Alumina G3610 – An Alumina Forming Alloy 3 samples from each of the above materials (6 total) Sample 1: No Heat-Treatment Sample 2: 500 °C 1 hr in Ar-H2 (5% H2) atmosphere Cooled normally Sample 3: 1000 °C 1 hr in Ar-H2 (5% H2) atmosphere Cooled normally Figure 4: Nanoindentation Setup

Nanoindentation Figure 5: Nanoindentation Results detecting a cold worked and recrystallized region

Conclusion Alumina formers show better coking resistance based on gain in mass after exposure. They have a higher surface hardness due to cold working, which may result in superior mechanical properties. Further testing is required to determine crystallization temperature and its influence on properties for energy applications.