Research on Fabrication Procedure of Spherical Pressure Hull Made from Titanium Alloy for Deep
Submergence Research
Vehicle (2 nd Report)
by Michimasa Endo, Member Kimio Yokota, Member
Ryoichiro Sasano, Member Tsutomu Toyohara, Member
Genta Takano, Member Ken-ichi Yasui
Takashi Nishimura
Summary
Following "Shinkai 2000", as Japanese deep research project, a 6000 m class deep submergence
research vehicle is under planning. For the research vehicle of this class, from the maneuverability
and operationability, of utmost importance is the reduction of weight. As for a pressure hull, which
houses crew members, the authors have carried out a series of research for the application of
titanium alloy (Ti-6 Al-4 V ELI) considering the strengthweight ratio, and anti-corrosion capability
against sea water. In the 1 st report, the authors have made a full scale model of the pressure hull of
Ti-6 Al-4 V ELI for the 6000 m class submersible to establish the manufacturing procedure. In this
report, by disassembling the model, the authors have investigated the material characteristics for
the application of a deep submergence research vehicle. The research covered the fields of
mechanical properties, fracture toughness, fatigue strength, stress corrosion cracking, hardness
distribution, microstructure, and residual stress. As a result, 6 Al-4 V titanium alloy was confirmed
to be one of the most effective material for the pressure hull of a deep submergence research
vehicle.
1 Introduction
Japan's deep-sea submersible research vessel pro following "Shinkai 2000". The pressure
hull of a 6,000m class submersible research vessel being planned as a project High-strength
steel (10Ni-8Co steel) and titanium alloy (Ti-6 Al-4V ELI)1) to 6). For titanium alloys, they are
applied to pressure shells. If it is considered for use, it will be the largest in Japan.
Investigations from the aspect of processing and processing are necessary, and the authors
A full-scale model is manufactured according to the same processing steps as in The
method was established and the results were reported in the first report. as a result, Ultrathick titanium alloy sheet manufacturing technology, hot forming of titanium alloy hemisphere
Shape technology, titanium alloy hemisphere and global heat treatment technology,
hemisphere 3D machining technology, electron beam melting of ultra-thick titanium alloy
Contact technology, titanium alloy Nondestructive inspection technology for materials and
welds It was possible to establish a working method such as 7). In this report, This full-scale
model was dismantled and the material properties of each part and residual stress
investigated. As a result, Ti-6 Al-4V ELI titanium alloy. The prospect of a material that can be
used sufficiently for pressure-resistant spherical shells was obtained, and the results are
reported.
2 Full-scale model production 7)
Figure 1 shows the shape of the full-scale model. Real large model Simulates the pressure hull of an
actual machine with a thickness of 2 mm and a finished plate thickness of 70 mm 6A l-4V ELI
titanium alloy on N hemisphere and equatorial ring. In the N hemisphere, the through-hole
hardware required for the pressure-resistant shell was used. (Diameter: 500 mm) 2 pieces, wire
penetration hardware (diameter: 800 mm) 1 And one hatch opening (diameter 500 mm) were
installed. The S hemisphere is economical except for the equatorial ring that is welded to the N
hemisphere. Pure titanium (JIS class 3) was used from the viewpoint. N hemisphere material is
rolled from a 9-ton ingot and has a thickness of 115 mm by hot rolling and STOA processing. Was.
The material of the equator ring and through hardware is 5 tonnes Manufactured by forging from
Ngot and STOA processing. N Electron beam welding is used to weld the hemisphere material and
the through metal material After stress relief annealing, precision machining was performed by
three-dimensional machining. gave.
Welding of the N hemisphere and the equatorial ring was also performed by electron beam. Welding
was performed and PWHT was implemented to remove residual stress. After the application, the
equatorial part was finished to a perfect sphere. It is possible to produce a spherical shell with a
sphericity of almost 1.003 7). Fig. 2 shows these fabrication procedures.
3 Disassembly test procedure for titanium alloy pressureresistant shell