Results of computer simulations of long term service exposure for weldments of the CSN 15 128/P91 and SK3STC/P91 steels are presented and compared with corresponding results of phase and composition experiments. The welded material P91 (EU designation: X10CrMoVNb 9 -1) represents progressive chromium steel alloyed with molybdenum, vanadium, carbon, and nitrogen. The CSN 15 128 (13CrMoV 2 -5) material is low alloy Cr -Mo -V steel. The SK3STC alloy (12CrMo 10 -10) represents the consumable electrode material. The stability of the weldment microstructure is investigated at elevated temperatures (500 -700°C). The simulation method is based on the Calphad approach complemented with the theory of multicomponent bulk diffusion, local conditions of phase equilibrium, and the assumption that diffusion is the process that controls the rate of phase transformation. Signi cant phase pro les, concentration pro les, and phase transformation processes in the diffusion affected zone are simulated, investigated, and compared with experimental results. The potentially deleterious carbon depleted region inside each weld joint is discussed. The method described can be used to predict microstructure instability in weld joints. STWJ/374Keywords: low alloy steel, kinetic simulation Dr Sopous fek is in the Faculty

In the present paper, steels that are mostly used in technical practice as base materials, filler metals and consumable electrodes in the design of dissimilar weld joints are studied. These steels differ mainly in the content of Cr, Mo, V, W and N. It is explained and emphasised in the present paper that the effect of thermodynamics, diffusion and phase transformations on the stability of dissimilar weld joints that are exposed to temperatures of over y500uC cannot be underrated during operation. For all the materials under study the carbon activity at 600uC is given as calculated by the CALPHAD method, and a correlation is shown to exist between the carbon activity and the total chromium content. This correlation can be used as a most general alternative in the selection of filler metals or consumable electrodes in the design of dissimilar weld joints. The primary goal of the present paper is, however, to present a more sophisticated alternative based on a mutual comparison of the temperature dependence of the carbon activities of the base alloys, filler metals and consumable electrodes under consideration. This alternative is suitable for routine engineering purposes. Attention is also drawn to the currently most advanced alternative, which enables the prediction of the redistribution of elements and phases after prolonged exposure.

The present paper addresses the issue of carbon and nitrogen redistribution in weld joints between creep resistant chromium steels. The redistribution of carbon and nitrogen was measured using the wave dispersive X-ray method. The conditions of the long term diffusion annealing process were: temperature 575, 625, and 700°C; and time 10, 100, 1000, and 5000 h. It was ascertained that carbon and nitrogen diffused from the low alloy steels to the high alloy steel P91. The carbon diffusion coefficients in the individual steels in 15128/P91 and SK3STC/P91 weld joints, the ratio between the thermodynamic activity coefficients of carbon in the joints, the diffusion interaction parameters βCr C, and their temperature dependencies were estimated from carbon concentration curves. The present paper also contains a microstructure analysis of decarburised and carburised zones in the weld joints studied.

Aluminum and titanium alloys are among the most important and the most frequently used construction materials due to their physical and mechanical properties. Especially in the automotive and aerospace industry these materials allow to reduce the weight of structure which leads to reducing fuel consumption and environment pollution. These materials are often used together which leads to problems with junction between these materials. In addition to the mechanical joints, there is an effort to produce quality welded joints. Series of works focused to welding of Al/Ti joints by conventional and nonconventional welding methods were published [1, 4, 5, 6, 7]. By reduction of dimensions of molten material is possible to reduce the amount of emerging intermetallic phases and welding defects. Electron beam welding appears as suitable method for welding Al/Ti joints because it allows production of very narrow welds. The benefit is also necessity to perform electron beam welding in vacuum which is required for decrease energy losses of incident beam and simultaneously prevents reaction of molten metal with ambient atmosphere. This paper is focused to determine of appropriate parameters for electron beam welding of heterogeneous welds of titanium alloy Ti-6Al-4V and aluminum alloy 6061. Metallographic evaluation, analysis of chemical and phase composition were performed on the test welds for purpose to describing present phases. On the selected welds was evaluated the influence of intermetallic phases on the mechanical properties. The obtained results will be used for further experiments focused to optimize the process of electron beam welding of Al/Ti alloys.

No abstract