Excellence in maritime manufacturing – award-winning project develops enhanced shipbuilding steel


Today @AuManufacturing’s editorial series Excellence in maritime manufacturing looks at collaborative R&D on tougher shipbuilding steel in Australia.

A project to understand what contributes to tougher shipbuilding steel in cold water conditions, as well as new techniques to produce it, has earned a High Commendation award at this week’s Indo Pacific Awards.

The work between BlueScope Steel, DMTC, Defence Science and Technology Group (DSTG) and University of Wollongong came out of material qualification tests by DSTG for the Hunter Class frigate program.

DSTG sourced DH36 plate steel from around the world, encountering “a fair bit of discrepancy” across suppliers when tested at low temperatures — an important design consideration given the extremes of weather and operating conditions in which the Royal Australian Navy deploys. 

(DH36 grade is a high-tensile steel, used for ship and offshore applications. DH refers to its minimum toughness requirement at – 20 degrees Celsius, and 36 to minimum yield stress 355 Mpa and ultimate tensile strength between 490 and 620 Mpa.)

“DSTG found a fair bit of discrepancy between the performance of steel from different steel makers from across the globe” explains Miles Kenyon, Head of Maritime Strategy at DMTC.

“Whilst all met the material performance qualification requirements for DH36, DSTG really wanted to understand why some steels perform better than others, especially in that low temperature range.”

Chris Killmore, Manager Hot Rolled Product Development at BlueScope Steel, adds that “testing it in extreme conditions which may be experienced in a naval application” could also possibly explain the variation across suppliers.

Testing included Charpy impact tests, dynamic tear tests and high strain rate tests, with DSTG recording inconsistent performance under blast conditions across the steels. This was attributed to different inclusions, steel making practices and processing conditions. 

Developing an Australian solution would improve the toughness as well as ductility of the steel. Killmore says this came down to fine-grained steels (to resist cracks propagating) with “internal cleanness”. This then needed to be translated into steelmaking and rolling processes.

Air Warfare Destroyer, NUSHIP Brisbane

Air Warfare Destroyer, NUSHIP Brisbane (ABIS Tara Byrne)

“They wanted better survivability, but how does that translate into what I need to do?” he adds. 

“And then how do I devise a plan on how to tailor our steelmaking and rolling processes to achieve that performance?”

Killmore says Bluescope’s DH36 recipe was specifically modified, with the main change to considerably enhance the steel cleanness levels through “additional specialised secondary steelmaking refining processes.”

As a key input to the collaborative project, University of Wollongong analysis is credited with understanding the effect of inclusions on microstructure and how that relates to low temperature toughness.

The steel rolling schedule was also redesigned, with different temperatures contributing to the required grain sizes.

The R&D has flowed on to other DMTC projects, says Kenyon, including a welding and productivity improvement project with BAE Systems Maritime Australia, which leads the Hunter class program, and the enhanced steel characteristics used in life of type capability assessment work, involving modelling and simulation of shipbuilding steel under blast and ballistic conditions.

The enhanced steel is under consideration by BAE Systems Maritime Australia for the shipbuilding program, with the plate offered to other end users as well.

“The main thing for Bluescope is to demonstrate our domestic steel manufacturing capability and also our ability to supply sovereign capability for defence applications and provide support for the defence sector,” says Killmore.

“Volumes mightn’t be large compared to our big [production runs] here, but it’s still very important that we supply this sovereign capability to the country and also support the defence effort.” 

@AuManufacturing’s editorial series Excellence in maritime manufacturing is brought to you with the support of BAE Systems Australia.

Main picture: Bluescope

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