Study On Creep Damage And Life Estimation Of Stainless Steel Welded Joints

As an important material processing technology, welding technique is widely used in variety of industry. With the development of economic construction and industry, the need for the welded unit safety becomes more and more higher, the service environment in which the welded unit operates becomes more and more austere, especially at high temperature. The quality of welded joint has a great influence to the safety of the engineering unit. In engineering practice, creep damage often occurs at the fusion zone and HAZ of welded parts working at high temperature, which results in enormously economic loss and people casualties. So it is very significant to study the creep behavior of welded joints operating at high temperature.In the view of the mesoscopic and nanoscopic structure, this paper expound the mechanism of creep damage of 0Cr18Ni9 stainless steel welded joint On the base of creep tests, cavity diameter is measured with grid transparency overlaid on fractograph. Average cavity diameter and its error are calculated using data measured, cavity size distribution is plotted, the relationship of D-σand D-T are obtained. Creep damage level is predicted by cavity size distribution. The data measured are analyzed with mathematical method, and the function of D-σand D-T is obtained. Curve of D-σand D-T are fitted with creep data using MATLAB language. Based on the growth rule of cavity size, the function of D-σ and D - T are proposed as the temperature and working load change.The results show that the cavity occurs at the intersection of three grain boundary or grain-boundary step, which leads creep generation. These cavities grow and coalesce under stresses and cavity current. When cavity coalescence takes place on the same or adjacent grain-boundary, the micro-cracks are formed. Micro-cracks become to macro-cracks. When the macro-crack size is greater than the critical crack size, the fracture phenomenon happens. During the research of creep damage, average cavity size is seen an indicator of creep damage level. Cavity diameter size increases as the temperature and stress increase. The effect of temperature cavity size is more obvious than that of stress.