Cooling Optimization of a Large Duplex Forged Bar and Subsequent Improvement in Impact Toughness over Its Thickness

Abstract

The machining of a central axial hole in a duplex stainless steel 2205 bar is sufficient to optimize cooling and thus to achieve the toughness requirements of the most demanding international standards. The cooling rates are obtained by finite element methodology simulation. The increased cooling rate in the central zone of the bar is directly related to the improvement of the Charpy impact toughness. Microstructure at different bar locations is characterized by optical microscopy, scanning electron microscopy, and energy‐dispersive X‐ray spectrometry. In the absence of sigma phase precipitation, an austenite spacing over 45 μ provokes a decrease in absorbed energy close to 40 J. Moreover, the pierced bar complies with the international standards requirements in tensile with yield strength higher than 450 MPa and Rockwell hardness lower than 31 (HRC) over the section and along the bar. Finally, the resistance to pitting corrosion required is also satisfactory due to the absence of chromium nitrides.