Friction Stir Welding and Processing IX: High Temperature Applications I
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Shaping and Forming Committee
Program Organizers: Yuri Hovanski, Brigham Young University; Rajiv Mishra, University of North Texas; Yutaka Sato, Tohoku University; Piyush Upadhyay, Pacific Northwest National Laboratory; David Yan, San José State University

Monday 8:30 AM
February 27, 2017
Room: 9
Location: San Diego Convention Ctr

Session Chair: Tracy Nelson, Brigham Young University; Yutaka Sato, Tohoku University


8:30 AM Introductory Comments

8:35 AM  Invited
Effect of Thermal Aging on the Corrosion and Mechanical Properties of Friction Stir Welded 250 Grade Maraging Steel: Todd Curtis1; Bharat Jasthi1; Christian Widener1; Michael West1; Brendon Kellogg1; 1South Dakota School of Mines and Technology
    The main objective of this work is to investigate the microstructure and mechanical properties of friction stir welded 250 grade Maraging steel. Successful welds were made using W-25%Re-4%HfC pin tools in forge control mode at a rotational speed of 200 RPM and a travel speed of 2 IPM. The effects of post weld aging on the mechanical properties of the welds were evaluated. Post-weld aging was performed at 800°F, 900°F and 1000°F for 1h, 5h and 15h and the mechanical properties were evaluated and compared to the parent material. Microstructural characterization was performed using optical and electron microscopy. Post-weld aging at 900°F for 15h resulted in uniform microhardness across the weld nugget and also resulted in optimized mechanical properties of the welded joints.

8:55 AM  Invited
FSW Studies to Achieve High Charpy Impact Energy in 19 mm Thick ASTM-A6 Steel: Murray Mahoney1; Russell Steel1; Dale Fleck1; Steve Larson1; Trever Davis1; 1MegaStir
    MegaStir has demonstrated the ability to FSW ASTM-A6 steel plate to a depth of 19 mm in a single pass. Weld appearance is excellent, transverse tensile strength and hardness equivalent to parent metal, and the weld nugget free of volumetric defects. However, Charpy impact results at -20°C are low. Additional weld trials were completed to understand the source of low impact energy and to provide an approach to increase Charpy impact energy values. FSW trials included a significant modification of the weld parameters to reduce heat input. Previously, weld nugget microstructures were predominantly a Widmanstätten structure and a mixture of phases. Conversely, with much lower heat input, the microstructure appears to be almost entirely proeutectoid ferrite. Very high Charpy impact energy values at -20°C were demonstrated in both ASTM-A6 steel plate (94 ft-lbf) and X-60 pipe (211 ft-lbf). These impact values are well above the program goal of 45 ft-lbf.

9:15 AM  Invited
Friction Stir Processing of 304L Stainless Steel for Crack Repair: Michael Miles1; Cameron Gunter1; Fengchao Liu1; Tracy Nelson1; 1Brigham Young University
    A dilemma facing the nuclear industry is weld repair in stainless steel components that have been irradiated over many years. When conventional fusion welding is used, the high temperatures and thermal stresses inherent in the process enhance the growth of helium bubbles, causing intergranular cracking in the heat-affected zone (HAZ). Friction stir processing (FSP) has potential as a weld repair technique for irradiated stainless steel, because it operates at much lower temperatures than fusion welding. A numerical simulation of the FSP process in 304L stainless steel was performed in order to calculate temperatures and strain rates in the stir zone. The model employed an Eulerian finite element approach, where flow stresses for the large range of strain rates and temperatures inherent in the FSP process were provided by JMatPro. Steady-state temperatures and strain rates from the model were used to predict recrystallized grain size in the processed 304L material.

9:35 AM  
Influence of Underwater Operation on Friction Stir Welding of Medium Carbon Steel: Tomoko Miyamori1; Yutaka Sato1; Hiroyuki Kokawa1; 1Tohoku University
    To secure the safety during decommissioning of nuclear power plant, the temporary repairing of the defective steel structures placed in water is required. Friction stir welding (FSW) would be effective as an underwater repairing process because the solid-state stirring of FSW can eliminate the defects through underwater operation. However, there are few systematic studies on effect of underwater FSW on microstructure and properties of steels. In this study, underwater and conventional FSWs were applied to 0.45wt% medium carbon steel at various welding parameters, and then the microstructure and hardness of the welds were examined. Underwater FSW exhibited the higher torque and Z axial load than conventional one. Underwater FSW produced defect-free stir zone consisting of bainite with ferrite and pearlite, resulting in the higher hardness than conventional process. The microstructure evolution during FSW could be explained by the cooling rate measured during welding and the continuous cooling transformation diagram.

9:55 AM  Invited
Friction Stir Welding of Steel-two Innovative Welding Methods: Hidetoshi Fujii1; 1Osaka University
    Based on the principle of FSW, two innovative welding methods for steels were developed. The first is to weld below the A1 temperature. A high carbon steel is generally difficult to weld due to martensite formation which causes cracks during the welding. Using this method, carbon steels, even including hypereutectoid steel, can be welded without any pre- or post-heat treatment, independent of the carbon content. In the second method, the welding temperature exceeds the A1 temperature. In this case, brittle martensite is generally formed. However, it was found that the austenite can be significantly stabilized by utilizing the severe plastic deformation during the FSW. Using this method, martensite is not formed because austenite is retained even after the welding. Due to the retained austenite, the welded steel has extraordinary properties, namely, over 1000MPa strength and 50% elongation for a typical steel due to the artificial TRIP effect.

10:15 AM Break

10:30 AM  Invited
High Temperature Properties and Microstructures of ODS and RAFM Alloys FSW: Wei Tang1; Xinghua Yu1; David Hoelzer1; Zhili Feng1; 1Oak Ridge National Lab
    Oxide dispersion strengthened (ODS) steels and reduced-activation ferritic/martensitic (RAFM) steels are two primary structural material candidates to safely sustain the extremely hostile environment inside the fusion reactor. Joining them without largely degrade their high temperature properties is a major challenge. Solid phase friction stir welding (FSW) was used to join ODS alloy 14YWT, RAFM alloys 9Cr and F82H. FSW parameters were compared, joint microstructures were characterized by optical and electronic microscopes, tensile creep-rupture tests were performed using a Gleeble system, and local deformations at different metallurgical zones were recorded by digital image correlation technology. Results showed unique material flow pattern in dissimilar FSW, stir zone (SZ) and heat affected zone (HAZ) grain sizes and hardness were affected by FSW heat input, nano-scaled strengthening particles aggregation was observed in ODS alloy SZ, and RAFM SZ high temperature creep resistance was better than that of the HAZ and base metal.

10:50 AM  
Feasibility of Iridium Containing Nickel Base Superalloy Tool to Friction Stir Spot Welding of High Strength Steel: Kunihiro Tanaka1; Tatsuya Nakazawa1; Koichi Sakairi1; Yutaka Sato2; Hiroyuki Kokawa2; Toshihiro Omori2; Kiyohito Ishida2; 1Tanaka Kikinzoku Kogyo K.K.; 2Tohoku University
    The authors developed a Ir-containing Ni base superalloy tool, strengthened by γ’ precipitation, for friction stir welding (FSW) of steels and titanium alloys. The Ir-containing Ni base superalloy tool exhibited the acceptable performance during FSW of 304 stainless steel and Ti-6Al-4V. In this study, feasibility of Ir-containing Ni base superalloy tool to friction stir spot welding (FSSW) of high strength steel was examined. FSSW was conducted on the lapped sheets of DP590 steel with thickness of 1.2 mm. The Ir-containing Ni base superalloy tool with 1.2mm long probe successfully produced the spot welds on DP590 steel without macroscopic deformation. Even after 600 FSSW trials, the tool shape was hardly changed, confirming that severe wear did not occur on the Ir-containing Ni base superalloy tool.

11:10 AM  
Effect of Friction Stir Processing on Microstructure and Mechanical Properties of Cast Eglin Steel (ES-1): Vedavyas Tungala1; Matthew Carl1; Amit Arora2; Marcus Young1; Rajiv Mishra1; Kyu Cho3; Raymond Brennan3; 1University of North Texas; 2Indian Institute of Technology, Gandhinagar; 3Army Research Laboratory
    Eglin steel (ES-1) is an ultra-high-strength steel developed for various demanding applications. It is a low cost alternative to 4340 steel in which nickel-cobalt additions are replaced by large tungsten additions, achieving comparable strength and ductility. The effect of friction stir processing (FSP) on the microstructure and mechanical properties on this steel was studied. FSP was successfully carried out on Eglin steel using PcBN tool under various processing conditions. The processing conditions were selected to vary peak temperature and cooling rate, and that influenced the resultant martensitic and bainitic microstructure. The volume fractions of various phases in the weld nugget were evaluated using Synchrotron high energy diffraction studies and were correlated with the observed mechanical properties. 3D temperature modelling was carried out to predict the various thermal cycles within the processed region. Initial results after FSP showed a tensile strength above 2 GPa with 9% ductility

11:30 AM  
Friction Stir Processing of 2507 Super Duplex Stainless Steel: Microstructure and Corrosion Behaviour: M.K. Mishra1; G. Gunasekaran2; A.G. Rao2; B.P. Kashyap1; N. Prabhu1; 1Indian Institute of Technology Bombay; 2Naval Materials Research Laboratory
    Friction stir processing (FSP) has been shown to be effective in the microstructural modification. In this study, 2507 super duplex stainless steel was subjected to multipass FSP and the processed samples were investigated. Refinement in grain size of both ferrite and austenite was observed in the stir zone of the processed samples. Increased number of passes led to further reduction in grain size. Anodic polarization studies in 3.5 wt. % NaCl solution showed that the processed samples possessed improved corrosion resistance. The Mott-Schottky analysis confirmed that the charge carrier density in the passive oxide layer is decreased with decreasing grain size.