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The title of this research suggests the importance of manufacturing variables and their influence on the behavior of super duplex stainless steel (SDSS) alloy when exposed to corrosive aqueous environments. Studies show that SDSS alloys have many applications due to their good physical, mechanical and corrosion resistance properties. However, there are a number of cases of in-service failures of SDSS alloys, such as pitting corrosion, stress corrosion cracking and environmentally assisted cracking failures. The root cause of these failures was due to the impact of one or more manufacturing variables such as surface finish, microstructure defects or deficiencies after deformation. From this concept, a detailed study into the effect of manufacturing variables on the corrosion resistance of a UNS S39274 super duplex stainless steel has been carried out. The manufacturing variables studied are as follows: Effect of surface condition; The corrosion resistance of stainless steel components is very sensitive to the final surface condition. The effect of surface condition on the corrosion resistance was investigated by measuring the critical pitting temperature (CPT) and the pitting potential (Epit) of in-service UNS S39274 super duplex stainless steel tubular sections with three different surface roughness values of Ra =2.8, 3.2 and 3.5m. Experimental results confirmed that the surface roughness parameter Ra is a useful parameter as a general and basic guideline of surface texture but it’s not sufficient on its own to predict the likely effect of surface roughness on the in-service corrosion behaviour of SDSS materials. The manufacturer of super duplex stainless steel products should include the electrochemical corrosion evaluation such as the CPT or Epit values beside the surface roughness average value Ra and PRENs in SDSS alloy assessment. Effect of microstructure; The thermo-mechanical handling of super duplex stainless steels is an important factor in their performance. This is due to the complex nature of the material which is highly alloyed with Cr, Ni, Mo, and N. Exposure to certain temperature ranges leads to undesired secondary phases formation. The presence of intermetallic phases has been found to be harmful to super duplex stainless steel properties. A study was undertaken to evaluate the effect of thermal exposure of a solution annealed UNS S39274 super duplex stainless steel to temperatures of 850C, 1000ºC and 1300ºC on its microstructure and its localised corrosion resistance. Heat treatment at 850ºC and 1000C caused formation of intermetallics such as sigma () and chi () while at 1300C caused precipitation of secondary austenite and enlarged grains and percentage of ferrite was observed. The formation of intermetallics of sigma () and chi () had a drastic effect on the corrosion resistance of the super duplex stainless steel. Electrochemical measurements confirmed that the intermetallics affected the corrosion resistance by reducing the pitting potential by around 80% in the active direction. Evaluation of the corrosion morphology using SEM revealed depletion at the ferrite/austenite interfaces created intergranular corrosion path with preferential attack of the ferrite phase. The present results confirmed that PRENs is not suitable for corrosion assessment of SDSS after exposure to intermetallic temperature ranges. Effect of cold work; Cold work introduces metallurgical changes like dislocations and deformation bands which affect the corrosion resistance of stainless steel components. Cold work is still a complicated phenomenon for ferritic/austenitic alloys such SDSS. The effect of cold work (0%, 4%, 8%, 12% and 16% plastic strain) on the pitting corrosion behaviour of UNS S39274 SDSS was evaluated. The Ferrite phase of the material exhibits greater degrees of plastic deformation under straining providing a greater number of initiation sites than the austenite phase. The hydrogen embrittelement of the cold worked specimens was investigated after 48 hours cathodic charging in 0.1M H2SO4. Experimental results indicated that the increase in cold work caused reduction in mechanical properties such as elongation and strain to failure. The depth of embrittlement increased as the degree of cold work increased and revealed brittle surfaces of cleavage fracture mode. Manufacturer and users should consider the degree of plastic strain when cold worked SDSS components going to work in corrosive environments or hydrogen containing environments. The main conclusion of the work is that the interactions between corrosive environments and SDSS components containing one or more of the manufacturing variables evaluated must be considered if reductions in in-service life are to be avoided.

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This master thesis is written to examine the influence of different low carbon steel sheet materials on the GMAW welding process. During welding the properties of the base material influence the productivity of the welding process. The purpose of this thesis is to examine how the choice of material and welding speed affect the welding process and the productivity. A literature survey was performed to describe the welding technique and the differences in manufacturing for the sheet materials as well as the effect of alloying and welding on the sheet material. Defects in the weld and methods used to determine them are explained. Test pieces of the different sheet materials were welded with the GMAW process and examined. The result shows that there is a variation in the welding process regarding weld penetration. Measurements also show that welding speed and gap have little influence on the hardness of the weld and heat-affected zone and that the S355MC is more likely to suffer from a narrower toe transition radius than S355NL and S355MC Si. This and the higher area in the Y2 region for the S355MC could indicate a stronger inward flow in the weld pool during welding possibly a result of surface active agents such as oxygen and sulphur. / Denna uppsats skrevs för att undersöka hur olika lågt legerade kolstål påverkar svetsprocessen för gasmetallbågsvetsning. Under svetsning påverkar materialets egenskaper produktiviteten för svetsprocessen. Syftet med denna uppsats är att undersöka hur svetshastighet och materialval påverkar svetsprocessen och produktivitet. En litteraturstudie genomfördes för att beskriva svetsprocessen och olikheter i tillverkningen av de olika plåtkvaliteterna samt hur olika legeringsämnen påverkar plåtkvaliteten. Dessutom beskrivs Svetsdefekter samt metoder för detektering av svetsdefekter förklaras. Testbitar av de olika plåtkvaliteterna svetsa samman genom gasmetallbågsvetsning och undersöks sedan. Resultatet visar på att variationer i svetsprocessen förekommer vid mätning av inträningen. Resultat visar även på att svetshastigheten och förekomsten av en spalt har liten inverkan på hårdheten i svetsen eller den värmepåverkade zonen samt att S355MC i större utsträckning lider av en snävare övergångsradie an S355NL och S355MC Si. Detta tillsammans med en större area i Y2 regionen av svetsen tyder på att S355MC kan leda av ett starkare inåtgående flöde i smältan vilken kan påverkas av ytaktiva ämnen som syre och svavel.

Gerdau Manitoba Mill (Gerdau) at Selkirk, Manitoba is one of the biggest energy consumers in the province of Manitoba. This research analysis undertaken at Gerdau evaluated opportunities for energy efficiency, including the following six areas: 1) recovering waste heat to preheat billets, 2) upgrading the charge end in the reheat furnace, 3) recovering waste heat to preheat combustion air in the ladle preheater, 4) replacing direct-fired natural gas heaters with indirect-fired natural gas heaters, 5) Oxyfuel combustion, and 6) “tap to tap time” control in the eccentric bottom tapping (EBT) furnace in the melt shop. As part of this research, end-user distribution was analyzed and energy losses were assessed. An end-use analysis found that the melt shop that includes the EBT furnace is the biggest consumer of electricity consumption (kWh) and electric demand (kVa), which accounted for 68.7% and 73.6 % respectively. The 2010 delay time in the power-off time of EBT furnace at Gerdau was found to be 762.3 hr/yr. Further research to analyze the cause of each downtime at Gerdau is recommended to determine how these unplanned downtime can be reduced in the EBT furnace. The reheat furnace is the biggest natural gas consumer at Gerdau with 437,563 MCF in 2010. Flue gas losses from the reheat furnace are the biggest energy losses in the gross heat distribution with 26,874,657 Btu/hr. Energy losses from hearth and roof by heat transmission are the biggest energy losses in the net heat distribution during operation, which accounted for 8.9%. The average thermal efficiency in the reheat furnace at Gerdau is 58.9% ± 3.6%. Compared to peak capacity, idle and partial operations of the reheat furnace and idling were found to be less efficient. The opportunities that are considered feasible and recommended to Gerdau are: 1) recovering waste heat to preheat billets, 2) upgrading the charge end in the reheat furnace, 3) recovering waste heat to preheat combustion air in the ladle preheater, 4) replacing direct-fired natural gas heaters with indirect-fired natural gas heaters. These are both good for the environment, reducing fuel use and emissions and providing a good payback period and annual savings. Many opportunities are available for reducing energy as provided in Table A, which shows emissions reductions, costs, energy savings and payback. Oxyfuel combustion is not deemed feasible without considering productivity improvement as oxygen cost is more than natural gas saving. A number of incentive programs, including those from Manitoba Hydro, are applicable to Gerdau. However, a number of barriers to accessing these, particularly as regards tax incentive programs, should be explored to see if these barriers can be overcome.

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