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Testing of Residual Straisn in Stainless Steel - Zirconium Transition Joint Tube by Neutron Diffraction Method M.Vrana, P.Lukas, P.Micula Nuclear Physics Institute, 25068 ReZ, Czech Republic V.L.Aksenov, A.M.Balagurov, V.V.Sumin. Frank Laboratory of Neutron Physics. JINR, 141980 Dubna, Russia. Contact

Key words: residual strains, neutron diffraction, bimetallic joint, texture.

Bimetallic stainless steels - Zr (Ti) joints have important applications in chemical, nuclear, etc. industries.

The coefficient of linear expansion (CLE) of stainless steels is two times greater than for Zr. So strong stresses arise in the tight joint of these two metals.

In this work we studied the transition joint tube performed by diffusion welding. A scheme of the tube is on Fig.1. The steel end of tube transits to Zr-end through some steps the high of which is 2 mm.

Fig 1: Scheme of the joint tube and a scan region

As NDT of the residual strains we choose the high-resolution neutron diffraction method [1]. The accuracy of determination of the (111) austenite reflection was e =Dd/d=1.0*10^-4 . All e -data will be later in unit without 10^-4. Optimized gauge volume was 1.5*1.5*4 mm ³ .

From residual strains point of view, the most interested place of the tube is a region around the first Zr-step (Fig.1). In accordance of this we measured axial and radial maps across the first Zr-step and the hook strain along the line in front of Zr-edge (y=2, Fig.1).

To take account the surface effects [2] we measured etalons cut from the steel end of the tube. The etalon measurements were subtracted from the measurements across the tube.

Discussion

The axial strain map is showed in Fig.2. The outward part of the tube is more compressive than the inside one which is tensile in the depth ca 10 mm. Some increase of compression was measured in depth 15 mm in front of the second Zr-step.

Fig 2: The map of the axial strains of the stainless steel - Zr joint tube

Fig 3: The map of the radial strains of the stainless steel - Zr joint tube

The radial strains have a quite different map (Fig.3). For this strains the outward region has a strong compression down to -9.0. The middle part of the wall is in the equilibrium state. The inside region is under compression, also, but more weak. The compression increases strongly in front of the second Zr-step down to -8.0.

The hoop strains Fig.4) were measured only along a line perpendicular to axis of the tube in front of the beginning of the first Zr-step (Fig.1,y=2) and showed a variable, moderate compression ca -2.0.

Fig 4: The hoop strain along the line with y=2

Analysis of the width (111)-reflection for axial direction showed an increase it in the outward region due to mechanical treatment at tube preparation. The integral intensities of these reflections have a maximum in the middle of the wall, which is caused, probably, by a texture of the tube.

Resume: creation of the compressive strains in the outward and inside region of the steel part of tube must improve corrosion and mechanical resistance the joint tube.

References

1. M. Vrana, P.Lukas, P. Micula, J.Kulda. Nuclear Inst.& Meth. In Phys. Research.
2. D.Q.Wang, and L.Edwards. 15 Int. Conf. On Residual Stresses.V2, p.628.

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