Abstract
Welding of 13CrMoV9-10 vanadium steel requires care due to an increased susceptibility to stress relief cracking during post weld heat treatment. Previous research into the crack formation in creep-resistant steels has focused on thermal and metallurgical factors; however, little knowledge has been gathered regarding the crack formation during post weld heat treatment considering real-life restraint conditions. This work is subdivided in two parts. Part I showed that an increasing heat input during submerged arc welding under restraint led to an increasing stress level in the joint prior to the post weld heat treatment. The magnitude of stress relief cracking observed in the heat-affected zone after the post weld heat treatment is affected by the heat input. In Part II of this work, the cracks and the associated microstructure which occurred under restraint were studied. The application of a special acoustic emission analysis indicated that the cracks formed in a temperature range between 300 and 500 °C during the post weld heat treatment. The toughness in the heat-affected zone of the restrained welds was affected by the welding heat input. Microstructural analyses of all specimens revealed accelerated aging due to precipitation of carbides during post weld heat treatment under restraint.
Highlights
The creep resistant steel 13CrMoV9-10, a modified conventional low-alloyed 2.25Cr-1Mo steel with 0.25% vanadium is highly sensitive to stress relief cracking (SRC) during post weld heat treatment (PWHT)
PWHT is applied after welding und necessary to adjust the mechanical properties in the weld metal and the heat-affected zone (HAZ) as well as to reduce welding-related structural and residual stresses
That means cracking is located in the lower temperature range between 315 and 705 °C documented in the literature [6, 32]
Summary
The creep resistant steel 13CrMoV9-10, a modified conventional low-alloyed 2.25Cr-1Mo steel with 0.25% vanadium is highly sensitive to stress relief cracking (SRC) during post weld heat treatment (PWHT). PWHT is applied after welding und necessary to adjust the mechanical properties in the weld metal and the heat-affected zone (HAZ) as well as to reduce welding-related structural and residual stresses. – Almost complete dissolution of carbides and carbonitrides in the weld boundary (coarse grained HAZ) area during welding. – Separation of the dissolved elements and formation of carbides in the matrix during further PWHT. There is agreement on the origin of the crack that precipitation processes lead to differences in strength between the grain boundary regions and the interior of the grain. The crack propagation occurs along the prior austenite grain boundaries (PAGB) and leads to the typical, predominantly intergranular separation.
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