رفتار یک لوله‌ی فولاد زنگ نزن دوفازی با جوش‌کاری محیطی تحت فشار خارجی

Behavior of a girth-welded duplex stainless steel pipe underexternal pressure

رفتار یک لوله‌ی فولاد زنگ نزن دوفازی با جوش‌کاری محیطی تحت فشار خارجی

ABSTRACT

This study attempts to investigate the effects that external pressure has on the residual stress behavior in a girth-welded duplex stainless steel pipe. At first, FE simulation of the pipe girth welding is performed to identify the weld-induced residual stresses and depressions using sequentially coupled three-dimensional (3-D) thermo-mechanical FE formulation. Then, 3-D elastic–plastic FE analysis is carried out to evaluate the residual stress redistributions in the girth-welded pipe under external pressure. The residual stresses and plastic strains obtained from the thermo-mechanical FE simulation are employed as the initial condition for the analysis. The FE analysis results show that the hoop compressive stresses induced by the external pressure significantly alter the hoop residual stresses in the course of the mechanical loading, i.e. the hoop residual stress distributions on both surfaces of the pipe weld shift downward considerably, whilst the axial residual stresses are little affected by the superimposed external pressure.

 

نقش آستنیت در چقرمگی جوش فولاد زنگ‌نزن سوپردوفازی

Role of Austenite in Weld Toughness of Super Duplex Stainless Steel

نقش آستنیت در چقرمگی جوش فولاد زنگ‌نزن سوپردوفازی

ABSTRACT

Microstructure control for welding super duplex stainless steel SAF2507 was carried out on a welded joint by GTA welding. The toughness of the bond region in the heat-affected zone (HAZ) of the advanced SAF2507 stainless steel was much lower than that of the base metal. The microstructure of the bond region for the as-welded sample was examined and the extreme grain growth of ferrite and the lowering of the amount of austenite phase were observed. In order to improve the toughness of the bond region, microstructure control was carried out using a cooling rate control process during welding. Various cooling times from 1 673 K to 1 073 K in the bond region were selected, which corresponded to the heat input from 1 kJ/mm to 6 kJ/mm. For the ferrite grain growth, the cooling time from 1 673 K to 1 473 K, that is,
t16-14 was controlled using a Gleeble simulator. The ferrite grain size increased with increasing cooling time
t16-14. For austenite phase reformation, the cooling time from 1 473 K to 1 073 K,
t14-10 was selected, since austenite phase reformation occurs within that temperature range. The amount of austenite increased with increasing
t14-10. Increasing the cooling rate caused both ferrite grain growth and an increase of the austenite phase. Improvement of the toughness was accomplished up to 60 s in the cooling time from 1 473 K to 1 073 K, however hardly any change in toughness was accomplished at the cooling time of 120 s, because the slow cooling rate caused both ferrite grain growth and an increase of the austenite phase.

 

اثر ارتعاش مکانیکی روی ریزساختار ماده‎ی جوشکاری

Studies on the Effect of Mechanical Vibration on 

the Microstructure of the Weld Metal

تحقیقات در مورد اثر ارتعاش مکانیکی روی ریزساختار ماده‎ی جوشکاری

ABSTRACT

The solidification process in the weld metal produces solidification structure. The solidification process depends on the thermal gradient, solidification speed and the alloy content. These structures can be planar, cellular, columnar dendritic and equiaxed dendritic. The solidification process may change from planar to cellular, columnar dendritic and equiaxed dendritic across the weld metal zone as shown in fig.1. Three grains are shown to grow epitaxially from the fusion line. A short distance away from the fusion line, solidification changes to the cellular mode. Further away from the fusion line, the solidification changes to columnar dendritic mode. Near the weld centre line equiaxed dendrites nucleate and grow, blocking off the columnar dendrites. Each one of these structures would affect the hot cracking susceptibility in greater or smaller extent.