The significance of Ti in promoting the nucleation of MX-type carbides and further refine the MX carbides is currently unknown. Thus, we study here by high resolution transmission electron microscopy (HRTEM) and electron back scattered diffraction (EBSD), the determining role of titanium on the orientation of grains, texture, deformation and fracture of low activation martensitic steel with different Ti-content and determine the phase diagram. Strengthening mechanisms played by grain boundary and nanosized precipitates are discussed in detail. As the Ti content increased from 0.02 to 0.10 wt%, grain size of the LAM steels decreased significantly from 12 μm to 7 μm, accompanied by an increase in the volume fraction of MX carbide from 0.2 to 0.3% and decrease in the volume fraction of M23C6 carbide from 3.5 to 1.2%. Yield strength (σy) decreased with increasing Ti-addition. At room temperature, σy decreased slightly from 630 MPa to 590 MPa while it decreased from 315 MPa to 260 MPa at 600 °C for 0.02 and 0.10 wt % LAM steels. In contrast, elongation significantly increased from 37% to 47% at 600 °C with increase of Ti content. Boundary strengthening and MX-type carbide strengthening increased while M23C6 strengthening decreased greatly with increasing Ti-addition, which promoted the precipitation of fine MX-type and depressed M23C6. Excessive Ti-addition retarded the precipitation of large M23C6 carbides, which was responsible for significantly increasing elongation of 0.10 wt % Ti LAM steel, especially at 600 °C.

Strengthening a fine-grained low activation martensitic steel by nanosized carbides

This review summarizes the strengthening mechanisms of reduced activation ferritic/martensitic (RAFM) steels High-angle grain boundaries, subgrain boundaries, nano-sized M23C6, and MX carbide precipitates effectively hinder dislocation motion and increase high-temperature strength M23C6 carbides are easily coarsened under high temperatures, thereby weakening their ability to block dislocations Creep properties are improved through the reduction of M23C6 carbides Thus, the loss of strength must be compensated by other strengthening mechanisms This review also outlines the recent progress in the development of RAFM steels Oxide dispersion-strengthened steels prevent M23C6 precipitation by reducing C content to increase creep life and introduce a high density of nano-sized oxide precipitates to offset the reduced strength Severe plastic deformation methods can substantially refine subgrains and MX carbides in the steel The thermal deformation strengthening of RAFM steels mainly relies on thermo-mechanical treatment to increase the MX carbide and subgrain boundaries This procedure increases the creep life of TMT(thermo-mechanical treatment) 9Cr-1W-006Ta steel by ∼20 times compared with those of F82H and Eurofer 97 steels under 550°C/260 MPa

Strengthening mechanisms of reduced activation ferritic/martensitic steels: A review

Here the tensile behavior of a 9Cr-1.7W-0.1C reduced activated ferritic-martensitic steel over the temperature region from room temperature (RT) to 600 °C was studied. The variation of the dislocation distribution under the interplay mechanism of dislocations with solute atoms and lath boundaries was found to be the main reason for the decreasing of plasticity in the intermediate temperature zone. Temperature and strain rate were confirmed to affect the interaction intensity of this dynamic strain aging (DSA) phenomenon on the tensile deformation behavior through changing the extent of dislocation pile-up on the lath boundaries. The variation of average rate of crack propagation in the fibrous region was determined to be related to the DSA effect on the dislocation mobility.

Mechanical properties and tensile deformation behavior of a reduced activated ferritic-martensitic (RAFM) steel at elevated temperatures

Effects of Ti and Ta addition on microstructure stability and tensile properties of reduced activation ferritic/martensitic steel for nuclear fusion reactors

Review on niobium application in microalloyed steel

Effects of tantalum content on the microstructure and mechanical properties of low-carbon RAFM steel

The RAFM (reduced activation ferritic/martensitic) steels containing different tantalum contents (0 wt. %, 0.027 wt. %, 0.073 wt. %) were designed and cast. Differential scanning calorimetry and optical microscopy were employed to explore the influence of tantalum content on the austenitic transformation of RAFM steels. The austenitic transformation kinetics was described by a phase-transformation model. The model, involving site saturation nucleation, diffusion-controlled growth and impingement correction, was established based on the classical Johnson-Mehl-Avrami-Kolmogorov model. The phase-transformation kinetics parameters, including D0 (pre-exponential factor for diffusion) and Qd (activation energy for diffusion), were calculated by fitting the experimental data and the kinetic model. The results indicated that the average grain size is decreased with the increase of tantalum. The values of Ac1 and Ac3 (onset and finish temperature of austenitic transformation, respectively) are increased by increasing the tantalum content. The increase of tantalum caused the decrease of D0. However, Qd is increased with the increase of tantalum. In addition, as a carbides forming element, tantalum would reduce the carbon diffusion coefficient and slow down the austenitic transformation rate.

Effects of tantalum on austenitic transformation kinetics of RAFM steel

Thermal simulation on double-pass welding of a high Cr ferritic steel

The invention discloses a corrosive and application thereof in low-activation ferrite heat resistant steel treatment. The corrosive is composed of water, picric acid, sodium dodecyl sulfate and fatty alcohol ether sodium sulfate, the water serves as a solvent, the picric acid serves as an oxidizing agent, and the sodium dodecyl sulfate and the fatty alcohol ether sodium sulfate serve as surface active agents. When the corrosive is used, the prepared corrosive is heated till the temperature is 60-70 DEG C through a heat-collecting type constant-temperature heating magnetic force stirrer, and the polished low-activation ferrite heat resistant steel samples for nuclear power is placed into the corrosive and then taken out after heat preservation is conducted for 2-4 min. According to the corrosive, the prior austenite crystal boundary of the low-activation ferrite heat resistant steel samples for nuclear power can be clearly displayed, grain size rating can be conducted under 500 times, and the effect is good.

Corrosive and application thereof in low-activation ferrite heat resistant steel treatment

The invention discloses a delta-ferrite content control method of low-activity ferrite heat resistant steel for nuclear power A low-activity ferrite heat resistant steel sample for nuclear power is heated to reach a normalization temperature of 1000-1100 DEG C for insulation 200-800 s, and then, is cooled in air; and the delta-ferrite content in a matrix structure is controlled through reasonably controlling the normalization temperature and time of the low-activity ferrite heat resistant steel for nuclear power After treatment by the method, the delta-ferrite content in the low-activity ferrite heat resistant steel matrix structure for nuclear power is obviously reduced

Delta-ferrite content control method of low-activity ferrite heat resistant steel for nuclear power

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