Effects of N and B on continuous cooling transformation diagrams of Mo–V–Ti micro-alloyed steels

Effects of the single addition of nitrogen (N) and boron (B) and the combined addition of N and B on continuous cooling transformation (CCT) diagrams and properties of the three Mo–V–Ti micro-alloyed steels were investigated by means of a combined method of dilatometry and metallography. Microstructures observed in continuous cooled specimens were composed of pearlite (P), quasi-polygonal ferrite (QPF), granular bainite (GB), acicular ferrite (AF), lath-like bainite (LB) and martensite (M) depending on the cooling rates and transformation temperatures. Single addition of 12?ppm B effectively reduced the formation of QPF and broadened the cooling rate region for LB and M. Added N makes the action of B invalid and the QPF region was prominently broadened, and even though the cooling rate is higher than 50°C?s^?1, it cannot obtain full bainite.     

Surface composition of the steel powders pre-alloyed with manganese

The determination of the surface oxide layer composition is vital to facilitate the adjustment of the sintering conditions for sufficient removal of the surface oxides for providing strong metal bonding between the metal particles during sintering. To systematically investigate the composition, morphology and thickness of the surface oxide the influence of manganese content from 0.3 to 1.8 wt.% on the surface products composition in the case of water atomized steel powder was evaluated. Analysis of the powder surfaces by X-ray photoelectron spectroscopy and high-resolution scanning electron microscopy in combination with X-ray microanalysis showed that powder particles in all cases are covered by heterogeneous oxide layer, composed of particulate features of thermodynamically stable oxides (Cr-Mn-Si) and homogeneous iron surface oxide layer in between. For increasing alloying content the fraction of stable oxide cations in the surface layer increases linearly, whereas the thickness of the iron oxide layer decreases. Moreover, from the investigation of the sintering and degassing behavior by thermal analysis coupled with mass-spectrometry (TG/DTA + MS), three different stages of carbothermal reduction process were observed and their correlation with surface oxides composition was established during sintering in argon.     

核反应堆压力容器模拟钢中富Cu原子团簇的析出与嵌入原子势计算

利用原子探针层析技术(APT)和热处理时效方法,研究了合金元素Ni对核反应堆压力容器模拟钢中富Cu原子团簇析出的影响.实验结果表明,添加合金元素Ni(0.84wt%)的样品中析出富Cu原子团簇的数量密度高于不添加Ni的样品,富Cu原子团簇内以及团簇和基体界面处都有Ni元素的富集现象,这说明合金元素Ni会促使富Cu原子团簇的析出.从多体势的角度出发,利用嵌入原子势理论,基于纯金属元素Fe,Cu,Ni的多体势参数,建立了Fe-Cu二元和Fe-Cu-Ni三元体系的嵌入原子多体势.计算结果表明,当模拟合金中存在1at%Ni时有利于富Cu原子团簇的析出,这与实验结果相符.     

Zur Bestimmung der Beteiligung radioaktiv markierter Schmierstoffbestandteile an der Schichtbildung auf Reibkörpern)

Bei Untersuchungen zum Gleitverschleiß von Stahl mit einer Stift-Scheibe-Apparatur wurde als Modellschmierstoff Hexadecan mit Additiven, insbesondere Zn-Dicyclohexyldithiophosphat (ZnDTP), verwendet. Zur Bestimmung der Bildung festhaftender Schichten von Schmierstoffbestandteilen mit ⁶⁵ZnDTP, ZnDTP(¹⁴C) und Hexadecan (¹⁴C) in der Reibspur und außerhalb erwies sich bei Markierung mit ¹⁴C die Messung mit und ohne Abdcckung der Reibspur, mit dem γ, ß-Strahler ⁶³Zn die photometrische Auswertung der Autoradiographien als am besten geeignet. Die visuelle Beurteilung der Autoradiographien ergibt vor allem Aussagcn zur Gleichmäßigkeit der Schichten. ZnDTP (1% in Hexadecan) bildet z. B. ußerhalb der Reibspur etwa cine Monoschicht aus, in der Gleitspur dickere Schichten.     

Einsatzmögliclikeiten der energiedispersiven Pulverdiffraktometrie zur Phasenanalyse metallurgischer und geologischer Proben

Die energiedispersive Pulverdiffraktometrie ermöglicht die zerstörungsfreie quantitative Bestimmung der α- und γ-Phase in Eisen bei im Vergleich zum winkeldispersiven Verfahren geringeren Meßzeiten. Bei der Untersuchung geologischer Proben liegt der Vorteil vor allem in der Möglichkeit, in kurzer Zeit qualitative Übersichtsanalysen anzufertigen. Die vergleichsweise geringere Separierbarkeit führt auf Grund der großen Liniendichte zu Komplikationen. In diesem Fall erfordert die quantitative Phasenanalyse den Einsatz von Spektren-Entfaltungsprogrammen. Fūr die Laboranalytik von Vorteil ist die Tatsache, daß mit der gleichen Meßanordnung auch eine Vielelementanalyse durchgeführt werden kann.     

Orientation relationship in various 9%Cr ferritic/martensitic steels–EBSD comparison between Nishiyama–Wassermann,Kurdjumov–Sachs and Greninger–Troiano

EBSD measurements were carried out on four different martensitic steels (T91, P92, EM10 and Eurofer) in various metallurgical conditions (nine different microstructural states). The usual orientation relationships (ORs) between the parent austenitic phase and the resulting martensite in martensitic steels are those of Nishiyama–Wassermann (NW) and Kurjumov–Sachs (KS). The present study first proposes a methodology based on the combined analysis of the misorientation distribution, the pole figures (PFs) and the angle/axis pairs. This methodology leads to the conclusion that neither NW nor KS relationships are able to account for all the features observed whatever the material under study. A third OR proposed by Greninger and Troiano (GT) proves to describe the relationship between austenite and ferrite in all four different martensitic steels much more accurately.     

Autoradiography of Light Elements in Austenite Steels tested in Liquid Metals

The multielement autoradiography has been used to investigate the redistribution of boron, carbon, oxygen, sodium and phosphorus in an austenitic chromium-nickel steel exposed to a flow of sodium. Under all experimental conditions, the steel samples became impoverished with respect to boron, carbon and phosphorus and this phenomenon became more pronounced with the increases in both the temperature from 923 to 1073 K and the time of the experiment from 500 to 8000 h. The sodium and oxygen penetration of the steel was intercrystalline by character, oxygen being approximately 10 μm ahead of sodium. The redistribution of boron and carbon in the steel samples with and without boron has been investigated after the exposure to lithium and data of the steel penetration by lithium have been obtained. Lithium penetration followed the grain boundaries of steel.     

Application of 35S as a Radioactive Tracer for a Determination of the Composition and the Structure of Dispersion Coatings,Containing MoS2

A method is proposed for the determination of the content and distribution of MoS₂ in Ni-P-MoS₂, coatings deposited on a steel using ³⁵S as a radioactive tracer. ³⁵S is isolated and measured as BaSO₄. At the same time this approach gives the possibility to perform an autoradiographic investigation which enlarges the metallographic data.     

Computer Progamming for Matrix Effect Correction in X-Ray Fluorescence Spectrometry

Interelement effects can be of great significance in the outcome of the analytical results from X-ray fluorescence technique. In an attempt to obtain rapid and accurate quantitative analysis a simple mathematical correction computer program is described with the aid of three different practical examples, namely steel 1, steel 2 and standard rock samples. The approach described in this study requires a minimum number of standards and can be run in any personal computer. The analytical values obtained by utilizing this program are within the accuracy level accepted by conventional techniques.

Störungseffekte von Elementen untereinander bei der Ausgabe von analytischen Ergebnissen durch die Röntgenfluoreszenzanalyse können von groβer Bedeutung sein. Es wird der Versuch unternommen, durch ein Computerprogramm zu schnellen und genauen quantitativen Analyseresultaten zu gelangen. Seine Anwendbarkeit wird an drei verschiedenen praktischen Beispielen, ncmlich Stahl I, Stahl II und eine Standardgesteinsprobe, gezeigt. Die vorgeschlagene Methode benötigt ein Minimum an Standards und kann mit jedem Personalcomputer ausgeführt werden. Die Analyseniwerte unter Verwendung dieses Programms liegen innerhalb der Genauigkeitsgrenzen konventioneller Verfahren.     

Complex unloading behavior: Nature of the deformation and its consistent constitutive representation

Complex (nonlinear) unloading behavior following plastic straining has been reported as a significant challenge to accurate springback prediction. More fundamentally, the nature of the unloading deformation has not been resolved, being variously attributed to nonlinear/reduced modulus elasticity or to inelastic/“microplastic” effects. Unloading-and-reloading experiments following tensile deformation showed that a special component of strain, deemed here “Quasi-Plastic-Elastic” (“QPE”) strain, has four characteristics. (1) It is recoverable, like elastic deformation. (2) It dissipates work, like plastic deformation. (3) It is rate-independent, in the strain rate range 10⁻⁴-10⁻²/s, contrary to some models of anelasticity to which the unloading modulus effect has been attributed. (4) To first order, the evolution of plastic properties occurs during QPE deformation. These characteristics are as expected for a mechanism of dislocation pile-up and relaxation. A consistent, general, continuum constitutive model was derived incorporating elastic, plastic, and QPE deformation. Using some aspects of two-yield-function approaches with unique modifications to incorporate QPE, the model was implemented in a finite element program with parameters determined for dual-phase steel and applied to draw-bend springback. Significant differences were found compared with standard simulations or ones incorporating modulus reduction. The proposed constitutive approach can be used with a variety of elastic and plastic models to treat the nonlinear unloading and reloading of metals consistently for general three-dimensional problems.