ABSTRACT
The effects of and heat treatment on mechanical of duplex stainless steel were investigated. The stainless-steel rod of 8mm diameter was cut into length of 100.2mm; they were further cut into two equal parts with the two faces beveled to have a 60° grooved angle,
leaving a root and face gap of 2mm. The rods were then joined together using GMAW and SMAW processes using steel coated electrode and bare wire (E308L-16 and Nertalic 50).
After welding, some specimens passed through stress relief and quenching heat treatment (in neem oil and gear oil (85W90)) and some samples served as standards for comparison and analysis. Tensile, Charpy impact and hardness tests were carried out.
The results of the studies show that welding and heat treatment really affect the mechanical properties of the alloy, the control strength was 811.47MN/m2 while that of gas metal arc welding (GMAW) it ranged from 177.07 to 257.32MN/m2 and for shield metal arc welding (SMAW) from 452.23 to 678.98MN/m2.
The control impact energy was 162.70J, while that of the gas metal arc welding (GMAW) ranged from 38.64J to 56.20J and for shield metal arc welding (SMAW) ranged from 148.70 to 156.02J.
It was also noted that shield metal arc welding (SMAW) gives better results close to the as received than the gas metal arc welding (GMAW) process and heat treatment improved the mechanical properties of the alloy after welding.
The research also showed that the stress relief gives better strength (A3 =331MN/m2 and B3 =665MN/m2 ) compared to those that were quenched in lubricating oil (A2 =329MN/m2 and B2 =601MN/m2 ),
and neem oil (A1 =222MN/m2 and B1 =566MN/m2 ), while those that were quenched in lubricating oil and neem oil had higher toughness.
INTRODUCTION
Duplex stainless steels were first produced by Avesta Jernverk in the year 1929 with an alloy called 453E (25%Cr-5%Ni). Another record of the earliest production of duplex stainless steel products dates back to 1933 through an alloying error at J.
Holtzer Company, France. An 18%Cr-9%Ni-2.5%Mo austenitic stainless steel grade was made to a 20%Cr-8%Ni-2.5%Mo composition containing a high volume of ferrite in an austenitic matrix.
This two-phase material was then studied and it was found that when it was properly solution heat treated, the alloy was not sensitive to intergranular corrosion (IGC) in various corrosive environments; a significant advantage compared to fully [Gunn, 1997].
However the development of duplex alloys suffered from many problems such as corrosion, ductility and welding. The real rapid development occurred in the 1970s with improved chemistry analysis capability and the introduction of the argon-oxygendecarburization (AOD) refining process.
The control of alloy chemistry and the removal of oxygen and sulfur were significantly improved in the early 1970s; the 22%Cr commercial grade duplex was developed in Germany and Sweden. It was claimed that this grade of duplex was not sensitive to IGC upon welding due to balanced chemistry [Charles, 1991].
In the 1980s, higher alloyed duplex stainless steel (DSS) grades were produced, and developed into super DSS. They were made to withstand more aggressive environments,
but also bearing higher risk of due to the higher alloying element content. In the making of super DSS, Cr and Ni forming elements are balanced and more nitrogen is added.
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