Soryu Submarine Steel Details - Japan Offer to Australia

A highly automated welding setup for a submarine's pressure hull. In this case a TKMS Type 214 - probably using HY-100 steel.

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For Comments of the Arrium issue see the April 8 2016 Submarine Matters article 
Arrium - Pyne's Submarine Steel Claims Don't Stack Up.


Please connect this Submarine Matters post with subsequent post Submarine Steel Strength, China and Japan, April 8, 2015.

It seemed on January 5, 2015 Japanese government and industry tried to strengthen the Soryu (build in Japan) campaign by taking the extra-ordinary step of publicising what was before a confidential negotiating point - that is Japan would assist Australian steel makers in making the steel for any Australian Soryus that are built in Japan. This may mean 10,000 tons to 20,000 tons of special submarine steel made in Australia.

Japan's Naval Steel (NS) Proof Stress Measure

A slight aside - European submarine makers may use an "EN" measure. I am advised by an Anonymous commenter that TKMS-HDW 214 hull is made of "EN" or "WL" 1.3964 (correspond to HY-80) non-magnetic steel. "EN" may mean European Naval while "WL" in German means "Werkstoff Leistungsblatt" (Material Performance Sheet of VG Standard) - see http://www.gl-group.com/infoServices/rules/pdfs/gl_ii-1-6_e.pdf .  The US uses a High Yield (HY) unit of measure. Shows how confusing and complex steel measures are! On topic - the Japanese Ministry of Defence uses a "Naval Steel (NS) measure for steel proof stress.

An excellent Japanese document http://www3.ocn.ne.jp/~y.hirama/yh_e_papers_sub_f.html  

"History of the Japanese Submarine (After WWII)" indicates the Japanese submarine steel used for the Japanese Oyashio submarine class that preceded the Soryu class. Perhaps the Soryus use the same steel as the Oyashios. The Japanese Ministry of Defence designation for the Oyashio-Soryu(?) steel is  "NS80" and also NS110. NS80 means a proof stress of 80kgf/mm2 (indicated in Japanese language document http://www.mod.go.jp/trdi/data/pdf/G/G3111C.pdf , page 4, table 4.2.1 left column, with "耐力" meaning "proof stress") NS80 converts to 113,760 lbf/in2 or HY-114. 

If also used in the Oyashios and Soryus NS110 means 110kgf/mm2 proof stress converting to 156,414 lbf/in2 or HY-156.

How this "Combination" of steels are configured is unknown. It may (?) mean:

- each hull of a double hull uses NS80 and/or NS110

- different parts along the the hull use those different grades, or

- perhaps there is a "sandwich" of the two grades.

Language and conceptual difficulties seem considerable with Australian (DSTO or Bisalloy?)  metallurgists perhaps having to frequently make NS to HY conversions using http://www.endmemo.com/sconvert/kgf_mm2ksi.php ?

In terms of depth HY-156 for the Soryu may indicate an operating depth of just over 600 metres (2,000 feet) with a "crush depth" much deeper than that.

On Materials (“HY-80” and “HY-100”, "maraging" and "composites) see BACKGROUND below.

Submarine Steel in Australia

In contrast to Oyashio-Soryu "NS" Steel the Collins class “hull is constructed from a high-tensile micro-alloy steel, developed by Swedish steel manufacturer SSAB, and improved by BHP of Australia, which was lighter and easier to weld than the HY-80 or HY-100 nickel-alloy steel used in contemporary submarine construction projects, while providing better results in explosion bulge testing" [see Yule & Woolner, The Collins Class Submarine Story, pp. 165–174].

So Japan’s (and perhaps Australia’s) future Soryus (the yet to be launched "Soryu 2s") use a steel  combination apparently beyond the capabilities of HY-80 or HY-100 used in the Collins. 

It is likely that an Australian steel maker will only contribute a portion of the steel tonnage to a pre-existing stockpile in Japan of submarine grade steel. It is highly unlikely that Japan would rely on Australia to be the sole/only source of submarine grade steel for the Soryu. Unsurprisingly Japan values its national autonomy in materials for Japanese developed weapons like the Soryu.

Australian companies approached by Japan may include BHP-Billiton and BlueScope Steel. However the main company Japan approaches is likely to be current naval steelmaker Bisalloy Steels Pty Ltd based in Port Kembla-Wollongong, New South Wales, Australia. 

In the 1980s-1990s Bisalloy supplied 8,000 tonnes of hardened steel for the Collins submarine program with research and development involvement of BHP and the Defence Science and Technology Organisation (DSTO).

Bisalloy Steels Pty Ltd (company website) has connections to Indonesia (PT Bima Bisalloy), Thailand (Bisalloy Thailand) and from July 2011 investment in the Chinese CJV - Bisalloy Jigang (Shandong) Steel Plate Co. Ltd. It would be crucial that Japanese-Australian submarine steel technology does not find its way to foreign affiliates - particularly China.

The DSTO connection is interesting because in July 2014 it was announced that Australia and Japan had agreed to jointly carry out submarine related defence research under an Agreement Between the Government of Australia and the Government of Japan Concerning the Transfer of Defence Equipment and Technology (text of the Agreement as provided by the Japanese Ministry of Foreign Affairs (MOFA)).

As well as the publically stated Marine Hydrodynamics Project this Agreement may involve submarine steel and the DSTO Maritime Division. See DSTO Maritime Division Naval Architecture Project: “Structural materials and fabrication systems - Our Structural Materials and Fabrication Systems group encompasses the performance and assessment of structural materials and fabrication methodologies that may be used in naval structures or critical components within a naval platform. This includes metallurgical assessments and material assessment technologies for both initial selection as well as ensuring through life performance for fatigue.”

BACKGROUND

WHAT DO “HY-80”, “HY-100”, "Maraging" and Composite Use mean?

The English speaking world is more accustomed to talking about HY units of measure. I originally was going to limited this section to HY (high yield steel) issues - the "Harish" (on maraging) and Anonomous (on Composites) asked timely questions in Comments.

HY-80 and HY-100

See http://www.fas.org/man/dod-101/sys/ship/deep.htm:

"A submarine's hull is normally constructed of steel, or exceptionally of titanium. Special High Yield [HY] steel alloys have been developed to increase the diving depth of submarines, although the improved depth performance of these alloys imposes a price of increased fabrication challenges. These special steels are denominated by their yield stress in thousands of pounds per square inch -- thus HY-80 steel has a yield stress of 80,000 pounds per square inch [called 80 kpsi or more usually 80 ksi] [corresponding to a depth of 1,800 feet], HY-100 a a yield stress of 100,000 pounds per square inch [100 ksi][corresponding to a depth of 2,250 feet], and so on.

During World War II, American fleet submarines normally operated at a depth of 200 feet, though in emergencies they would dive to a depth of 400 feet.

Post-War American submarines, both conventional and nuclear, had improved designs and were constructed of improved materials [the equivalent of "HY-42"]. These boats had normal operating depths of some 700 feet, and a crush depth of 1100 feet.

The Thresher, the first American submarine constructed of HY-80 steel, reportedly had a normal operating depth of 1,300 feet, roughly two-thirds the crush depth limit imposed by the HY-80 steel.

The Seawolf, the first American submarine constructed of HY-100 steel, is officially claimed by the Navy to have a normal operating depth of "greater than 800 feet," and estimated here as 1,300 feet (400 metres). If there is a linear increase then the possible HY-156 for the Soryu may indicate an operating depth of just over 600 metres that is 2,000 feet.

The Soviet Alfa submarines, constructed of titanium, reportedly had an operating depth of nearly 4,000 feet.” 

An interesting February 2008 discussion of the tradeoffs of HY and other materials is here: http://www.defencetalk.com/forums/navy-maritime/steel-alloy-modern-cold-war-subs-7346/ : "I am wondering why in the newest American Seawolf Subs only HY-100 steel (Yield of 100,000 psi) is used, while there were rescue Subs in the 1960s (!) that already had HY-140 steel. Los-Angeles-Subs only have HY-80 steel alloys, what technichal reason is there to use not steel with higher yield?..."

Maraging?

See http://www.keytometals.com/page.aspx?ID=CheckArticle&site=kts&NM=99 . This paper is highly complex. Here is a conversion website for 1,000 pounds per square inch (ksi) and Mega Pascals (Mpa) http://www.convertunits.com/from/ksi/to/Mpa
Under sub-hearding "Medium-Alloy Hardenable Steels"
"There is another type of steel in this general class which is a medium-alloy quenched and tempered steel known as high-yield or HY 130/150. This type of steel is used for submarines, aerospace applications, and pressure vessels, and is normally available as plate. This steel has good notch toughness properties at 0°C and below. These types of steels have much lower carbon than the grades mentioned previously."
Under sub-heading "High-Nickel Maraging Steels" 
"This type of steel has relatively high nickel, and low carbon content. It obtains its high strength from a special heat treatment called maraging. These steels possess an extraordinary combination of ultra-high-strength and fracture toughness and at the same time are formable, weldable, and easy to heat treat. There are three basic types: the steels with 18% nickel, 20% nickel, and 25% nickel. These steels are available in sheet, forging billets, bars, strip, and plate. Some are available as tubing."

Pete's Comment - It seems HY steel (alloy) has toughness but is flexible enough to frequently experience the contractions and expansions of a submarine operating under different pressures-depths. The maraging process meanwhile provides very hard steel (alloy) but that steel is brittle. That steel is not flexible enough for multi-depth expansion and contraction. Maraging steel is particularly useful for tolerating rapid heat changes, making it useful in a submarine's engine but not for a submarine's hull.

Composite Use in Submarines

It seems that in parts of submarine exteriors, and I imagine even more so inside the sub, composities are increasingly used, to save weight and for other benefits. The pressure hulls may remain mainly HY steel or titanium (in some Russian subs?). Areas that heat up greatly may also remain steel.

A statement that probably applies more widely to other submarine makers and nuclear subs is  https://www.thyssenkrupp-marinesystems.com/en/composite-materials.html:

"Constant evolution of [TKMS-HDW subs] allowed for the intensified application of composites. Today for both HDW Class 212A and HDW Class 214 designs beside the traditional Glass-fibre Reinforced Plastics (GRP) also Carbon-Fibre Reinforced Plastics (CFRP) are used. These are used in particular when it comes to the design of large three-dimensional shapes or when outstanding transparency is required, e.g. to cover specific sonar windows."

Pete's Comment - This composite use over sonars may be to avoid steel obscuring too much of the sonar signal spectrum-spread. Also sonars are usually/always? outside the pressure hull - so steel to handle pressure is not required.

Pete