Mechanical Behavior And Microstructure Analysis Of 11Cr3W3Co Steel

High chromium ferritic martensitic steel is considered as one of the best candidate materials for the Generation IV reactors because of its low coefficient of the thermal expansion,high thermal conductivity,excellent high temperature anti-neutron irradiation capability,high temperature strength and corrosion resistance.11Cr3W3Co F/M steel is a new type of high chromium ferritic martensitic steel,and its operating temperature is up to 650?.But in the temperature where the future Generation IV reactor operates,the 11Cr3W3Co F/M steel is susceptible to dynamic strain aging?DSA?.So it is very important and very significant to investigate the serrated flow behavior of 11Cr3W3Co F/M steel.On the other hand,the precipitated phase has an important impact on the creep properties.So it is necessary to investigate the precipitation with the tempering temperature.In this paper,there are two parts in this research.In the first research part,the serrated flow behavior of 11Cr3W3Co F/M steel is investigated.In the other part,the precipitation is investgated under the different tempering temperature.Through tensile tests,the serrated flow behavior of the 11Cr3W3Co F/M steel with standard heat treatment was investigated at the strain rates of 2×10^-5 s^-12×10^-44 s^-1 at temperatures ranging from room temperature to 700?.At intermediate temperature of 285³25?,the apparent activation energy of 124 KJ/mol measured for normal serrated flow indicated that diffusion of substitutional atoms such as chromium is responsible for dynamic strain aging?DSA?.Abnormal serrated flow was also observed at intermediate temperatures of 325³65?as a result of the faster diffusion of solute atoms which may decline the effect of DSA as well as the diffusion of substitutional atoms from the dislocation line to finely dispersed carbides which resulted in the depletion of chromium atoms at dislocation.At high temperature,the rapid decrease in flow stress values and increase in ductility with increase in temperature indicated the dominance of dynamic recovery.The mechanical properties evolution of 11Cr3W3Co ferritic/martensitic steel and heat treatment was investigated.The results showed that the strength of the 11Cr3W3Co steels decreased with the increase of the tempering temperature,and a significant secondary hardening appeared in the steel tempered at 550?.When the tempering temperature was beyond 550?,the strength decreased rapidly.A lot of?ferrite was found in the 11Cr3W3Co steels after different heat treatment,and M₂₃C₆ carbides film at the?ferrite boundaries was found in high tempering temperature.At the same time,the phase of MX was found under the tempering temperature of 250?;at the temperature of550?,the secondary hardening was found,which may be due to the precipitation of a large number of fine W₂C carbides.With increase in tempering temperature dislocation substructures within the grains and the decrease of dislocation density made stress/strength values and ductility rapidly decreased.