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.
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.
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.
Submarine Steel in Australia
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 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
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?..."
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 or . 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.