Effect of multiple repairs in 690 MPa steel on the mechanical properties

 

Brief Description

Objectives

Australia’s Collins class submarines are fabricated using a minimum 690MPa yield strength steel (BIS812EMA). There has been extensive research on the weldability of this steel (Hakansson, 2002, Ritter et al, 1986, Dixon, 1994) and as a result effective procedures for primary fabrication have been developed. As discussed by these authors the operating envelope is bounded by the need to avoid Hydrogen Assisted Cold Cracking (HACC) at low heat inputs and degradation of parent metal properties at higher heat inputs. In practice submarines may  be subject to corrosion and/or mechanical damage during service, and welding is one of the most efficient methods to repair the damage; either by overlaying or replacement of damaged sections. In addition it may be necessary to remove and replace sections of material for maintenance purposes and again re-welding is required. The object of the proposed work is to determine the effect of multiple weld on the material properties of the parent plate including the development of possible alternative welding procedures which minimise the damage to parent plate properties whilst ensuring that HACC is avoided.  In addition the effect of re-welding to deposit multiple layers of weld metal pads previously deposited needs to be assessed. The project will aim to provide objective quality evidence to quantify the effect of multiple welds on the mechanical properties of the BIS 812 EMA base metal.  This will enable structural integrity engineers to determine how many times one can weld at a given location.  

Scope of the work

An HDR student will be registered for a PhD at UOW with a 3 year scholarship from ITTC. Although the content of the UOW research is ‘generic’ for security and IP reasons it is required that the student is an Australian permanent resident or citizen to allow access to ASC and DSTO. The HDR research will focus on the effect of multiple thermal cycles on damage in HSLA steels and the possible ameliorating effect of alternative low heat input welding procedures. The student will initially conduct a comprehensive analysis of the extensive literature on HSLA steels and their weldability. The student will investigate the effects of welding procedures (heat input, preheat temperature) on the microstructure of HAZ and weld metal

Which SEA program would benefit and how? Final outcome and impact (eg TRL increase?)

Collins sustainment programs and all future builds could benefit from the results of this program.