Dissertation > Excellent graduate degree dissertation topics show

Researchs on Effect of Al Element on Microstructures and Properties of Heat-resistant Casting Alloy HP40

Author: LiuZhiYuan
Tutor: HaoYuan；LaPeiQing；LiKeXiong
School: Lanzhou University of Technology
Course: Materials Processing Engineering
Keywords: HP40 alloy Ni3Al FeNiAl mechanical properties oxidation resistance
CLC: TG136.1
Type: PhD thesis
Year: 2008
Downloads: 171
Quote: 1
Read: Download Dissertation

Abstract


HP40 alloy has been extensively used for high temperature alloy tubes such as ethylene cracking furnace tubes and steam reformer tubes.During running the material is often destroyed by coking and carburization,high temperature oxidation,squirm invalidation and so on.Therefore we attempt to develop HP40 steel with Al element in displacement of Ni to improve elevated temperature mechanical properties,oxidation resistance and coking & carbonization resistance as well as decrease cost of the steel.By vacuum arc melting furnace in copper mold cooling with water,HP40 steel with 5-20 wt.%Al in displacement of Ni were prepared.Microstructures,mechanical properties,oxidation resistance of the steels were investigated.The results showed that the matrix of the steels transformed fromγ-Fe solution to a-Fe solution phase and lots of FeNiAl phase appeared in the microstructure with further increased Al content.The FeNiAl phase shape changed from sphere to dendrites.Yield strength and hardness of the alloys were improved markedly by Al element.With increased Al content, brittleness of the alloys was increased.The oxide film on the surface of the alloys mainly consisted of Al2O3,thus the oxidation resistance was increased.When Al content was 5 and 10wt%,the oxidation resistance was the best.But when Al content further increaseed,the oxidation resistance was decreased.Due to increase of the alloy’s oxide film thickness,the film was broken off easily and the oxidation resistance was decreased.Then,HP40 based steels with 2.5-15 wt.%Al in displacement of Ni were prepared by frequency inductive furnace melting at atomosphere.Microstructures,mechanical properties,oxidation resistance of the steels were also investigated.Because of different cooling conditions,the microstructures of the alloys made by frequency inductive furnace were different from that of made by vacuum arc melting furnace observably.The Al element was all dissolved in the matrix of the alloy with 2.5 wt.%Al.There were a few particles of Ni3Al precipitated in theγmatrix of the alloy with 5 wt.%Al.When the Al element added above 7.5wt.%,the FeNiAl phase solidified directly from the melting body.The matrix of the steels transformed fromγ-Fe solution to a-Fe solution phase and the amount of FeNiAl phase in the alloys increased with further increased Al content.Their shape changed from grain to dendrite.When the Al element was added up to15wt.%,the eutectic structure was made from FeCrNiAl and carbide.The room temperature and high temperature mechanical properties of the alloy with 2.5 wt.%Al were not increased.The alloy with 5 wt.%Al had the best room temperature and high temperature mechanicai properties.The mechanical properties of the alloys with 7.5,10 wt.%Al were lower than the HP40.The ductilities of the alloys decreased with further increased Al content.The high-temperature oxidation resistance of the alloys with 2.5-10wt.%Al at 1200℃for 30h in air was studied by using weight gain method.Experiment results indicated that addition of aluminum element had improved high temperature oxidation resistance of the alloys.The alloys’ oxidation behaviour was approximately parabolaic. The oxidation speed was decreased with time.The phases of the oxidation film varied with aluminum content.The oxidation film of the alloy with 5 wt.%Al was more compacted.With increased Al content,the oxidation film became very thick and flaked off when outside force processed.Influence of heattreatment on the microstructure of HP40 alloys with 5-10wt.%Al was studied by solution with two-step aging treatment.The results showed that the precipitation phases of as-cast alloys were changed.The Ni3Al phase shape of 5wt.%Al became bigger from particle to strip,and the shape of 7.5,10wt.%Al became homogeneous and small from block to strip and particle.Between the solution temperature 1180℃and 1220℃,the upper temperature was more reasonable for optimizeing microstructure.The weldability of HP40 and the alloy with Al 5wt.%was investigated.The mechanical properties of welded joint were same to that of HP40.The welded joint had excellent high-temperature mechanical properties.The alloy with 5 wt.%Al had good weldability.

Related Dissertations

  1. Reactive Hot-Pressing and Mechanical Properties of （ZrB2-ZrO2）/BN Composites,TB332
  2. Research on Welding Characteristics of CO2 Laser-GMA Hybrid Welding for Ultra-Low Carbon Bainitic Steel,TG456.7
  3. Microstructure and Mechanical Properties of Mg-Zn-Y-Zr Alloys,TG146.22
  4. Study on the Recycling of Post-Consumer Polyester Textiles,X791
  5. Fabricationand Properties of SiC-AlN Multiphase Ceramics Prepared by Gelcasting,TQ174.62
  6. Synthesis of Polysulfones and Modification for Epoxy Adhesives,TQ433.437
  7. Solid Oxide Fuel Cell ferrite connect the material properties of,TM911.4
  8. Structure and Characterization of Room Temperature Self-crosslinked Acrylonitrile-butadiene-styrene,TQ325.2
  9. Studies of Plasma Spray Metal-Ceramic Compounds Coatings on Q245r Steels,TG174.44
  10. The Research on Extrusion Parameters Through the Plate Billet of Magnesium Alloy,TG379
  11. Modification of Talc Powder and Its Reinforcing and Toughening on Recycled Polypropylene,TQ325.14
  12. Effect of Adding ZrO 2 Nanopowder on Microstructure and Mechanical Properties of Carbon Steel,TB383.1
  13. Preparation of Surface-functionalized Graphene and Its Influence on the Mechanical Properties of Nanocomposite Materials,TB332
  14. Preperation of Low Friction and Wear Resistant High-Purity Alumina Ceramic,TQ174.1
  15. The Study of Forming Process and Properties of PTT/PET Skin-Core Composite Monofilament with Large Diameter,TQ340.64
  16. Fe 3 O 4 , carbon nanotubes and graphene reinforced regenerated cellulose membrane research,TB383.1
  17. Titanium sponge reactor temperature oxidation resistant coating Preparation and Mechanism,TG174.442
  18. Extrusion Mg-Al-Zn-Y alloys Low Cycle Fatigue Behavior,TG379
  19. ZA35 alloy elements Zr on Microstructure and Properties,TG131
  20. Boron nitride fiber reinforced ceramic matrix composites through the waves and Properties,TB332
  21. Strain hardening austenitic stainless steel 022Cr17Ni12Mo2 low cycle fatigue properties of,TG115.57

CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > The alloy learn with a variety of properties of alloys > Special arts and crafts nature of the alloy > Casting alloys
© 2012 www.DissertationTopic.Net  Mobile