SIMP Steel Research Articles

Study on vacancy-type defects in SIMP steel induced by separate and sequential H and He ion implantation

To provide a basic understanding of the synergy effect of hydrogen and helium on structural materials for future advanced nuclear systems, the vacancy-type defects in SIMP steel induced by separate and sequential H and He implantation at room temperature was investigated using positron annihilation Doppler broadening spectroscopy (DBS) and transmission electron microscopy (TEM). The DBS results indicated that, when implanted by H and He separately, the ΔS parameter of the H-implanted sample was greater than that of He, although the damage level (that is, the displacement per atom) induced by H was lower than that induced by He. This could indicate that He is more easily trapped by vacancy than H and prefers to occupy the center of the vacancy. When sequentially co-implanted by He and H, whatever the implantation sequence, the ΔS parameter was lower than that of H-only implantation. In addition, the ΔS parameter of sequential He + H implantation was greater than that of H + He implantation when the dose of H was sufficiently high. Combined with the TEM results, the synergistic effects of He and H on vacancy-type defect evolution are discussed.

Hot Deformation Behavior of a New Nuclear Use Reduced Activation Ferritic/Martensitic Steel

The hot deformation behavior and workability of a new reduced activation ferritic/martensitic steel named SIMP steel for accelerator-driven system were studied. The flow curve and its microstructure were studied at 900–1200 °C and strain rate range of 0.001–10 s−1. The results showed that the deformation behavior of the SIMP steel during hot compression could be manifested by the Zener–Hollomon parameter in an exponent-type equation. Based on the obtained constitutive equation, the calculated flow stresses were in agreement with the experimentally measured ones, and the average activity energies QDRV and QHW for the initiation of dynamic recrystallization and the peak strain were calculated to be 476.1 kJ/mol and 462.7 kJ/mol, respectively. Furthermore, based on the processing maps and microstructure evolution, the optimum processing condition for the SIMP steel was determined to be 1050–1200 °C/0.001–0.1 s−1.

Characterization of Microstructure and Stability of Precipitation in SIMP Steel Irradiated with Energetic Fe Ions * *Supported by the Young Scientists Fund of the National Natural Science Foundation of China under Grant No 11505246, and the Major Research Plan of the National Natural Science Foundation of China under Grant No 91426301.

A type of home-made reduced activation martensitic steel, high silicon (SIMP) steel, is homogeneously irradiated with energetic Fe ions to the doses of 0.1, 0.25 and 1 displacement per atom (dpa), respectively, at 300°C and 1 dpa, at 400°C. Microstructural changes are investigated in detail by transmission electron microscopy with cross-section technique. Interstitial defects and defect clusters induced by Fe-ion irradiation are observed in all the specimens under different conditions. It is found that with increasing irradiation temperature, size of defect clusters increases while the density drops quickly. The results of element chemical mapping from the STEM images indicate that the Si element enrichment and Ta element depletion occur inside the precipitates in the matrix of SIMP steel irradiated to a dose of 1 dpa at 300°C. Correlations between the microstructure and irradiation conditions are briefly discussed.

High-Temperature Oxidation Behavior of SIMP Steel at 800 °C

In this work, the high-temperature oxidation behavior of SIMP and commercial T91 steels was investigated in air at 800 °C for up to 1008 h. The oxides formed on the two steels were characterized and analyzed by XRD, SEM and EPMA. The results showed that the weight gain and oxide thickness of SIMP steel were rather smaller than those of T91 steel, that flake-like Cr2O3 with Mn1.5Cr1.5O4 spinel particles formed on SIMP steel, while double-layer structure consisting of an outer hematite Fe2O3 layer and an inner Fe–Cr spinel layer formed on T91 steel, and that the location of the oxide layer spallation was at the inner Fe–Cr spinel after 1008 h, which led the ratio between the outer layer and the inner layer to decrease. The reason that SIMP steel exhibited better high-temperature oxidation resistance than that of T91 steel was analyzed due to the higher Cr and Si contents that could form compact and continuous oxide layer on the steel.

Corrosion resistance of self-growing TiC coating on SIMP steel in LBE at 600 °C

SIMP steel was newly developed as a candidate structural material for the accelerator driven subcritical system. The serious decarburization of SIMP steel because of the high Si content was used to successfully form a self-growing TiC coating on the surface, after the Ti deposition as a first step. This TiC layer can effectively protect the surface from the static liquid lead-bismuth eutectic (LBE) corrosion at 600 °C up to 2000 h in the low oxygen LBE. However, in the oxygen saturated LBE, the TiC coating is oxidized into porous TiO2 after only 500 h and fails to protect. Therefore, the self-growing TiC coating is desired only when the oxygen content of LBE is strictly controlled on a low level.

Oxidation and tensile behavior of ferritic/martensitic steels after exposure to lead-bismuth eutectic

Two ferritic/martensitic steels, T91 steel and newly developed SIMP steel, were subject to tensile test after being oxidized in the liquid lead-bismuth eutectic (LBE) at 873K for 500h, 1000h and 2000h. Tensile tests were also carried out on the steels only thermally aged at 873K. The result shows that thermal aging has no effect. Exposure to LBE at 873K leads to a slight decrease in strength, but a large decrease in elongation when tested at 873K. When tested at 873K after 2000h exposure, the tensile strength of T91 decreases slightly, and elongation from 39% to 21%. For SIMP, the decreases are slightly and from 44% to 28%, for tensile strength and elongation, respectively. The room temperature strength has slightly larger percentage reductions after the LBE exposure, but the elongation changes little.

High Temperature Oxidation Behavior of SIMP Steel and T91 Steel at 800

Oxidation behavior of two ferrite/martensite(F/M) steels, namely a novel 9%-12% Cr modified F/M steel(SIMP steel) and a commercial T91 steel were comparatively studied in air at 800 oC. The oxide scales formed on the two steels were characterized by XRD, SEM and EPMA. The results show that the oxide scale formed on SIMP steel is single- layer composed of Cr_2O_3 and Mn_(1.5)Cr_(1.5)O_4 spinel particles,and Si was enriched at the interface between the chromia scale and matrix; while the oxide scale formed on T91 steel has a double layered structure with an outer hematite Fe_2O_3 layer and an inner Fe-Cr spinel layer. The SIMP steel has better high temperature oxidation resistance than T91 steel, which may be due to the higher content of Cr and Si beneficial to the formation of the compact oxide scale on the SIMP steel.

Effects of temperature and strain rate on the tensile behaviors of SIMP steel in static lead bismuth eutectic

In order to assess the susceptibility of candidate structural materials to liquid metal embrittlement, this work investigated the tensile behaviors of ferritic-martensitic steel in static lead bismuth eutectic (LBE). The tensile tests were carried out in static lead bismuth eutectic under different temperatures and strain rates. Pronounced liquid metal embrittlement phenomenon is observed between 200 °C and 450 °C. Total elongation is reduced greatly due to the liquid metal embrittlement in LBE environment. The range of ductility trough is larger under slow strain rate tensile (SSRT) test.

High Temperature Oxidation Behavior of SIMP Steel

The oxidation behavior of two ferrite/martensite (F/M) steels, including a novel 9–12 % Cr modified F/M steel named SIMP steel and a commercial T91 steel, were studied in air at 700 °C for up to 1,000 h. The oxides formed on the two steels were characterized and analyzed by XRD, XPS, SEM and EPMA. The results showed that the oxide formed on SIMP steel was single-layer including flake-like Cr2O3 with Mn1.5Cr1.5O4 spinel particles, while the oxide on T91 steel exhibited a double layers structure consisting of an outer hematite Fe2O3 layer and an inner Fe–Cr spinel layer. The reason why the SIMP steel showed better high temperature oxidation resistance than T91 steel was analyzed to be due to the higher Cr and Si contents that could form compact and continuous oxide layer on the steel. Based on all the results, a kinetic model describing nucleation, growth and degradation of the oxide scale formed on surfaces of the two steels was proposed.

Oxidation behavior of ferritic/martensitic steels in stagnant liquid LBE saturated by oxygen at 600 °C

Ferritic/martensitic (F/M) steels are primary candidates for application as cladding and structural materials in the Generation IV Nuclear Reactor, especially accelerator driven sub-critical system (ADS). The compatibility of F/M steels with liquid lead-bismuth eutectic (LBE) is a critical issue for development of ADS using liquid LBE as the coolant. In this work, the corrosion tests of two F/M steels, including a novel 9–12 Cr modified F/M steel named SIMP steel and a commercial T91 steel, were conducted in the static oxygen-saturated liquid LBE at 600°C up to 1000h, the microstructure of the oxide scale formed on these two steels was analyzed, the relationship between the microstructure and the oxidation behavior was studied, and the reason why the SIMP steel showed better oxidation resistance compared to T91 steel was analyzed. The results of this study confirmed that the oxidation behavior of the F/M steels in liquid metals is influenced by their alloying elements and microstructures.