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The effect of Ce on hot ductility of Cu-As bearing steel in the temperature ranging from 700 to 1100 °C was investigated using Gleeble-3800 thermal-mechanical simulator. The hot ductility evaluation and fracture morphology observation showed that the hot ductility was obviously improved as Ce content increased from 0 to 0.0290 wt%. Detailed, the upper limit temperature of the ductility trough was decreased from 1057 to 765 °C, and the temperature corresponding to the minimum reduction of area was decreased from 850 to 750 °C. The fracture morphology was overall transformed from the dominantly intergraular brittle failure to the ductile failure characterized by the large and deep dimples. Analysis of metallographic, inclusions and grain boundary elements suggested that increasing Ce content inhibited the proeutectoid ferrite formation, which enhanced hot ductility of the steel bearing Cu and As. Moreover, the competitive grain boundary segregation of the solute Ce and As in steel with 0.0022 wt% Ce without arsenious rare earth inclusions decreased the quantity of As distributed at grain boundaries and thereby improved the hot ductility. When the Ce content reached 0.0290 wt%, a large number of arsenious rare earth inclusions were formed, and the grain boundary segregation of As was further decreased As, which was more beneficial to hot ductility than that with the lower Ce content in austenite single phase region. [ABSTRACT FROM AUTHOR]

The significant influence of the welding heat input on the microstructural evolution, precipitation behavior and resultant properties of the coarse grained heat affected zone (CGHAZ) in low carbon Nb-V-Ti-N quaternary microalloyed steel was comparatively studied on a Gleeble 3800 thermomechanical simulator. Metallographic investigations revealed that the dominant microstructure transformed from lath bainite (LB) at heat input of 50 kJ/cm to intragranular acicular ferrite (IAF) at 100 kJ/cm, to IAF and intragranular polygonal ferrite (IPF) at 150 kJ/cm and to IPF, IAF and grain boundary ferrite (GBF) at 200 kJ/cm. In addition, Ti- and Nb-enriched submicron-scale precipitates promoted IAF and IPF nucleation with an orientation relationship 01 1 − MC / / 1 − 11 Ferrite and effectively pinned grain boundaries; V-enriched nanoscale precipitates acted as obstacles for dislocation movement, consequently improving CGHAZ performance. Moreover, the impact absorbed energy at 20 °C and −20 °C first increased from 216 ± 4.3J and 58 ± 2.7J to 219 ± 3.7J and 64 ± 3.0J, respectively, and then decreased to 184 ± 7.5J and 45 ± 2.1J, respectively, when the heat input increased from 50 kJ/cm to 200 kJ/cm. The maximum value was obtained at heat input of 100 kJ/cm, which was primarily attributed to the largest amount of high angle grain boundaries originating from IAF. The microhardness slightly reduced as heat input increased from 50 kJ/cm to 100 kJ/cm and did not obviously decrease as heat input varied from 100 to 200 kJ/cm, which was directly related to the microstructure constituents and nanoscale precipitates. Furthermore, the optimal heat input to obtain a good combination of strength and toughness was 100 kJ/cm, and Nb-V-Ti-N microalloyed steel was suitable for high heat input welding. • The low carbon Nb-V-Ti-N microalloyed steel is suitable for high heat input welding. • The optimum welding heat input is 100 kJ/cm to obtain a strengthened and toughened CGHAZ. • The submicron Nb- and Ti-enriched particles promote intragranular ferrite nucleation and pin grain boundary. • The orientation relationship between nucleation site and the induced ferrite grain is 01 1 − MC / / 1 − 11 Ferrite. • The nanoscale V-enriched precipitates act as obstacles for dislocation movement. [ABSTRACT FROM AUTHOR]