Neodymium-Rich Precipitate Phases in a High-Chromium Ferritic/Martensitic Steel

Yinzhong Shen,Xiaoling Zhou,Zhongxia Shang 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.3

Neodymium being considered as nitride forming element has been used in a design of advanced ferritic/martensitic (FM) steels for fossil fired power plants at service temperatures of 630 °C to 650 °C to effectively improve the creep strength of the steels. To fully understand the characteristics of neodymium precipitates in high-Cr FM steels, precipitate phases in an 11Cr FM steel with 0.03 wt% addition of Nd have been investigated by transmission electron microscopy. Three neodymium phases with a face-centered cubic crystal structure and different composition were observed in the steel. They consisted of neodymium carbonitride with an average lattice parameter of 1.0836 nm, Nd-rich carbonitride mainly containing Mn, and Nd-rich MN nitride mainly containing Mn and Co. Other three Nd-rich and Nd-containing phases, which appear to be Nd-Co-Cr/Nd-rich intermetallic compounds and Cr-Fe-rich nitride containing Nd, were also detected in the steel. Nd-relevant precipitates were found to be minor phases compared with M23C6 and Nb/V/Ta-rich MX phases in the steel. The content of Nd in other precipitate phases was very low. Most of added Nd is considered to be present as solid solution in the matrix of the steel.

Ar Ion Irradiation Hardening of High-Cr Ferritic/Martensitic Steels at 700 °C

Yinzhong Shen,Jun Zhu,Xi Huang 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.2

High-Cr ferritic/martensitic (FM) steels are being considered for applications as fuel cladding or core structures for Generation-IV reactors. Because high temperatures approaching 923-973 K (650-700 °C) are envisioned in the designs of Generation IV reactors, irradiation response of high-Cr FM steels at the high temperatures requires investigations. Response of two high-Cr FM steels P92 and 11Cr to irradiation at 973 K (700 °C) was investigated through Ar ion irradiation in combination with damage simulations, nanoindentation measurements and microstructure analyses. Irradiation hardening occurred in both steels after Ar ion irradiation at 973 K (700 °C) to 10 dpa, providing the first evidence that irradiation hardening can occur at a high irradiation temperature of 973 K (700 °C) in high-Cr FM steels. Argon bubbles with a very high number density and an average diameter of about 2.6-3 nm formed in the two steels after the irradiation. The irradiation hardening occurred in the two steels is attributed to the formation of these high-number-density fine argon bubbles produced by the irradiation homogeneously distributed in the matrix. Difference in the magnitude of irradiation hardening between the two steels was also discussed.

M5C2 Carbide Precipitates in a High-Cr Martensitic Steel

Yinzhong Shen,Bo Ji,Xiaoling Zhou 대한금속·재료학회 2014 METALS AND MATERIALS International Vol.20 No.3

The precipitate phases in an advanced 11% Cr martensitic steel, expected to be used at 650 °C, have beeninvestigated to understand the effect of precipitates on the creep-rupture strength of the steel. M23C6 andMX precipitates were dominant phases in this steel. Needle-like precipitates with a typical length of 180nm and width of 20 nm; and metallic-element compositions of 53-74Fe, 16-26Cr, 3-18Ta, 2-8W, and 2-4Co(at%); were observed mainly within the martensite laths of the normalized-and-tempered steel. The needle-likeprecipitates have been identified as monoclinic carbide M5C2, which is not known to have been reported previouslyin high chromium steels, or in heat-resistant steels those have been normalized-and-tempered. Thisindicates that the formation of M5C2 carbides can occur in heat-resistant steels produced under appropriatetempering conditions, and that this does not require long-term isothermal aging or creep testing, in all cases.

Irradiation-Induced Hardening and Softening of CLAM Steel Under Fe Ion Irradiation

Qingshan Li,Yinzhong Shen,Xi Huang,Zhiqiang Xu,Jun Zhu 대한금속·재료학회 2017 METALS AND MATERIALS International Vol.23 No.6

The irradiation-induced hardening and softening of CLAM steel irradiated with 3.5 MeV Fe13+ions at temperaturesof 300 °C and 550 °C were investigated by nanoindentation tests in combination with microstructures. Irradiation-induced hardening occurred in the steel irradiated at 300 °C to doses of 0.46 dpa, 0.94 dpa, and 2.79 dpa. The hardening occurred at 300 °C is mainly attributed to the formation of irradiation-produced dislocation loopsand a network of tangled dislocations in the irradiated steel samples. Significant hardening was found in the steelirradiated at 550 °C to 0.38 dpa. On the contrary, irradiation-induced softening occurred in the steel irradiated at550 °C to both 0.76 dpa and 2.75 dpa. Irradiation-produced dislocation loops are not dominant effect on the irradiationhardening of the steel samples irradiated at 550 °C. The hardening and softening of the irradiated steel wereexplained in terms of the irradiation-produced defects and recovery process occurred during the irradiation.

Effect of irradiation temperature on the nanoindentation behavior of P92 steel with thermomechanical treatment

Huang Xi,Shen Yinzhong,Li Qingshan,Li Xiaoyan,Zhan Zixiong,Li Guang,Li Zhenhe 한국원자력학회 2022 Nuclear Engineering and Technology Vol.54 No.7

The nanoindentation behavior of P92 steel with thermomechanical treatment under 3.5 MeV Fe13þ ion irradiation at room temperature, 400 and 700 C was investigated. Pop-in behavior is observed for all the samples with and without irradiation at room temperature, while the temperature dependence of pop-in behavior is only observed in irradiated samples. The average load and penetration depth at the onset of pop-in increase as the irradiation temperature increases, in line with the results of the maximum shear stress. Irradiation induced hardening is exhibited for all irradiated samples, but there is a significant reduction in the hardness of sample irradiated at 700 C in comparison to the samples irradiated at room temperature and 400 C. The ratio of hardness to elastic modulus for all samples decreases with increasing penetration depth except for samples at 700 C. With the increasing of irradiation temperature, the ratio of the irreversible work to the total work gradually decreases. In contrast, it increases for samples without irradiation

Effect of δ-Ferrite Evolution and High-Temperature Annealing on Mechanical Properties of 11Cr3W3Co Ferritic/Martensitic Steel

Zhongxia Shang,Yinzhong Shen,Bo Ji,Lanting Zhang 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.2

An 11Cr3W3Co ferritic/martensitic steel was annealed at 1100 °C for different time to gradually dissolve δ-ferrite, and then conducted tensile, hardness, and short-term creep tests in combination with microstructural characterization to study the effect of δ-ferrite on the mechanical properties of high-Cr ferritic/martensitic steels. The amount of δ-ferrite gradually decreased to a minimum value with increasing annealing time up to 10 h, and then tended to an ascending tendency when annealed for 15 and 20 h. Accordingly the tensile strength at 300 and 650 °C, and Vickers hardness of the steel had an increase and a decrease tendency when δ-ferrite amount decreased down to its minimum value and increased again, respectively. The short-term creep property at 210 MPa at 650 °C of the steel exhibited a serious degradation as annealing time gradually increased to 15 h. The morphology and orientation of δ-ferrite grains seriously affected the short-term creep property of the steel. δ-ferrite with a continuously bamboo-like shape parallel to loading direction effectively improved the short-term creep property of the steel at high temperature, while δ-ferrite with a granular or block shape seriously damaged the short-term creep property of the steel. These findings have also been discussed.