Determination of Nitrogen in Duplex Stainless Steels by EPMA

 We describe the quantitative determination of low nitrogen contents (< 1 %wt) in highly-alloyed, duplex stainless steels by EPMA using a calibration curve. Five monophasic stainless steels with various nitrogen concentrations were used for the calibration curve, namely, three highly alloyed steels prepared in the laboratory, with nitrogen contents 0.066, 0.565 and 1.016 %wt and two industrial alloys with nitrogen concentrations 0.174 %wt and 0.023 %wt. For these samples, the plot of nitrogen X-ray intensities versus nitrogen contents exhibited an acceptable linear relationship. Average nitrogen contents of the analysed duplex alloys were found to vary in the range < 0.045–0.07 %wt in ferrite and 0.52–0.77 %wt in austenite. These results suggest that the nitrogen solubility limit in ferrite has been reached; on the other hand, nitrogen solubility in austenite increases due to the high manganese and low nickel contents.     

Extraction-spectrophotometric determination of chromium with Nitrotetrazolium Blue

The interaction of Cr(VI) and Nitrotetrazolium Blue has been examined. A 12 NTB (CrO₃Cl)₂ ion-associate is formed and is extractable into 1,2-dichloroethane. The optimum conditions have been established. The molar absorptivity at 260 nm was (8.2 ± 0.06) × 10⁴L mol^–1cm^–1. Beer's law was obeyed in the range 0.01–0.4 g ml^–1 Cr(VI). A sensitive and selective method for determination of micro-quantities of Cr(VI) in soils and steels is suggested.     

光电直读光谱法测定高锰不锈钢中硫量的改进

使用Spectro Lab M8光电直读光谱仪所提供的Fe-30不锈钢分析程序测定高锰不锈钢中硫量时,所得测定值均偏低。为此,改用高锰不锈钢国家光谱标准样品和内控样品,重新确定了干扰元素(特别是锰)的基体校正模式及测定硫元素的回归分析曲线。通过7个不同含锰量的不锈钢标准样品的分析验证,证明采用经过改进的方法所得测定值均与认定值一致,其绝对误差值均小于JIS标准的允许差。     

Microscale deformation of a tempered martensite ferritic steel: Modelling and experimental study of grain and sub-grain interactions

In this paper, a finite-element modelling framework is presented with explicit representation of polycrystalline microstructure for a tempered martensite ferritic steel. A miniature notched specimen was manufactured from P91 steel with a 20,000 h service history and tested at room temperature under three point bending. Deformation at the microscale is quantified by electron back scattered diffraction (EBSD) before and after mechanical loading. A representative volume element was developed, based on the initial EBSD scan, and a crystal plasticity model used to account for slip-based inelastic deformation in the material. The model showed excellent correlation with the experimental data when the relevant comparisons were made.     

Finite element and experimental method for analyzing the effects of martensite morphologies on the formability of DP steels

Abstract

In this article, we investigated the effect of martensite morphology on the mechanical properties and formability of dual phase steels. At first, three heat treatment cycles were subjected to a low-carbon steel to produce ferrite–martensite microstructure with martensite morphology of blocky-shaped, continuous, and fibrous. Tensile tests were then carried out so as to study mechanical properties, particularly the strength and strain hardening behavior of dual phase steels. In order to study the formability of dual phase samples, Forming Limit Diagram was obtained experimentally and numerically. Experimental forming limit diagram was obtained using Nakazima forming test, while Finite Element Method was utilized to numerically predict the forming limit diagram. The results indicated that the dual phase samples with fibrous martensite morphology had the highest tensile properties and strain rate hardening out of the three different microstructures. Blocky-shaped martensite morphology, on the other hand, had the worst mechanical properties. The study of the strain hardening behavior of dual phase sample by Kocks–Mecking-type plots, evinced two stages of strain hardening for all specimens with different microstructures: stages III and IV. The forming limit diagram of dual phase steels also proved that samples with fibrous martensite morphology had the best formability compared to other two microstructures. The simulated forming limit diagram manifested that there is a good agreement between experimental results and those obtained by FEM.     

含Nb微合金钢应变诱导析出的模拟

基于物理冶金原理建立了微合金钢在热轧过程中流变应力、回复、再结晶和析出模型，模拟了含Nb微合金钢Nb（C,N）析出动力学，并利用Thermo-Calc软件计算了不同条件下析出粒子形核驱动力和元素平衡含量值，同时考虑了回复和再结晶对析出的影响.计算结果表明，该模型对含Nb微合金钢在不同热轧形变条件下模拟结果与实验结果符合较好，因此可以有效预测在不同热轧形变条件下析出粒子体积分数和析出粒子尺寸. 关键词： 微合金钢 位错密度 回复 再结晶     

Fissile core and Tritium-Breeding Blanket: structural materials and their requirements

High radiation resistant structural materials for fusion and fission nuclear power plants are a key issue for the development of both types of reactors. Selection criteria, elements of metallurgy of the selected materials, and the major issues as they are revealed by the results of the present development programmes, are presented. At low temperature (300 °C) ferritic/martensitic steels are suffering from He-embrittlement, associated with possible hardening due to α/α^′ unmixing. The kinetics of hardening and embrittlement versus dose, especially saturation with dose, are still open key issues, difficult to settle on the basis of a purely experimental programme. Important progress is still to be made in mastering the initial microstructure, inclusion cleanness and joining techniques of oxide dispersion strengthened steels for higher heat resistance. Physics modeling as presented in this issue should promote guidance to the understanding of the mechanisms involved, provide solutions to master the initial microstructure and phase stability, and mitigate the in-service property degradation. To cite this article: J.-L. Boutard et al., C. R. Physique 9 (2008).     

Influence of CrN surface compound on the initial stages of high temperature oxidation of ferritic stainless steel

Segregation phenomena and formation of surface compounds on Fe-17Cr (ferritic stainless steel) were studied at temperatures up to 800 °C upon annealing and kinetically controlled oxidation by photoelectron spectroscopy and inelastic electron background analysis. The results revealed the formation of a chromium nitride surface compound during annealing in ultrahigh vacuum at temperatures exceeding 527 °C. Surface enrichment of P, As, and other trace elements became more prominent at higher temperatures approaching 800 °C. It was found that nitrogen was buried below the surface oxide layer during oxygen exposure, yet it had little effect on the rate of oxidation. However, the formation of CrN surface compound promoted the selective oxidation of Cr initially, which is of great importance in processing and application environments involving high temperature and controlled atmosphere conditions.     

Vacancy-solute complexes and their clusters in iron

In this contribution, several vacancy-solute complexes in iron are investigated theoretically from the viewpoint of positron annihilation. In particular, V-Si, V-P, V-Cr, V-Mn, V-Ni, V-Cu and V-Mo complexes are examined. In addition, nano-sized vacancy-Cu clusters in the Fe matrix are also studied. We concentrate on positron lifetimes and coincidence Doppler broadening profiles that bring complementary information about the studied complexes and their clusters. Positron calculations are carried out using the atomic superposition method employing realistic atomic configurations obtained recently using an ab initio pseudopotential method (vacancy-solute complexes) and Monte Carlo/molecular dynamics methods (vacancy-Cu clusters). The main aim of this study is to predict as to what extent such defects are detectable and differentiable using positron annihilation techniques. The results obtained are discussed in the context of experimental data available in the literature.     

On-line electrolytic dissolution of alloys in flow-injection analysis. Part 3. Multi-elemental analysis of stainless steels by inductively coupled plasma atomic emission spectrometry

The simultaneous determination of chromium, nickel, manganese, silicon and iron in stainless steels was achieved by inductively coupled plasma atomic emission spectrometry (ICP-AES) after on-line electrodissolution using an improved flow-through electrolytic cell. The solution containing the electrodissolved ions was impelled by an air carrier stream in a flow-injection manifold towards a mixing-dilution chamber. From this chamber, the diluted and homogenized solution was aspirated and nebulized into the ICP torch. A quantification procedure is proposed for direct solid analysis without the use of certified reference materials. Under the proposed electrolysis conditions, up to 60 solid samples can be analysed per hour. Results obtained for alloying elements in austenitic and ferritic stainless steels were in good agreement with the certified values.