Ferritic stainless steel (FSS) is one of the high-temperature materials, used in many industries for sustainable applications such as power plants, automotive, offshore and chemical industries. ...Joining these materials is challenging due to the formation of an intermetallic and the grain growth with high-heat-input welding methods. Laser beam welding (LBW) that uses a low heat input was used successfully to join AISI 409 FSS tubes. In this work the welding speed and focal distance were varied as per a two-factor, three-level face-centred central composite design (FCCCD) to join AISI 409 FSS. A numerical model was developed to correlate the relationship between the ultimate tensile strength (UTS) and LBW process parameters. The validation of the developed model was carried out using the analysis of variance. Both welding speed and focal distance have a significant effect on determining the UTS. The optimised process parameters provided for a better UTS as reported in this paper.
The aim of our study was to investigate how different thermal conditions affect the transformation temperatures of two hot-work steels with high thermal conductivity. We focused on two conditions: ...soft annealing, and quenching and tempering. Soft annealing results in a ferritic steel matrix with spherical carbides, while quenching and tempering result in a fully hardened and tempered martensitic matrix with secondary and tempering carbides. We analysed samples using a simultaneous thermal analysis (STA) and differential scanning calorimetry (DSC) to determine the transformation temperatures. Controlled heating and cooling allowed us to observe the energy changes associated with the phase transformations. The equilibrium temperatures were calculated using the CALPHAD method. Our study investigated the influence of thermal conditions on different transformation temperatures, including solidus/liquidus temperatures, austenite solid transformation temperatures (A1 and A3), austenite solidification temperatures and bainite and/or martensite transformation temperatures. A DSC analysis was used to quantitatively measure the transformation temperatures and energy absorption during the endothermic processes (austenite solid transformation and melting) and to study the energy release during the exothermic processes (solidification and transformation). The results showed that soft annealing reduced the solidification interval and the solidus temperature, while energy absorption increased during melting. Conversely, quenching and tempering reduced the austenite solid transformation temperatures and energy release during solidification, including δ-ferrite solidification.
PDF