Low Temperature Brittle Fracture Susceptibility In Welding of F70 Grade Forging

Welsch, Markus T. (BRUCK Forging) | Bruch, Dominik (BRUCK Forging) | Akselsen, Odd M. (SINTEF Materials and Chemistry) | Østby, Erling (SINTEF Materials and Chemistry)

OnePetro 

ABSTRACT

For steel application at low temperatures their brittle fracture resistance is of vital importance. The present investigation addresses the susceptibility to brittle fracture of forgings of F70 grade. To evaluate the mechanical properties after welding, weld thermal simulation tests with different cooling times were performed. Both CTOD testing with shallow and deep cracks was carried out for coarse grained (CGHAZ) and intercritically reheated coarse grained heat affected zone (ICCGHAZ) to identify possible influence of microstructure and eventual constraint effects. In addition Charpy-V notch and hardness tests of CGHAZ and ICCGHAZ were carried out. The results are discussed in terms of crack position, microstructure and constraint and compared to the base material results.



INTRODUCTION

Forgings are widely used in offshore applications such as piping components (e. g. flanges or T-pieces) or structural parts in oil and gas exploration. They can be found in both, welded and non-welded conditions. With the expansion of the oil and gas recovering area in the arctic region, resistance to brittle fracture at low temperatures is of great importance for all components, regardless of their manufacturing process. Since forgings generally have larger wall thicknesses than e.g. tubes, it is more difficult to realize the required properties over the entire cross-section. At the same time a good weldability of the parts has to be provided. In a former paper (Welsch, Bruch and Østby, 2011) the base material properties of forged materials for arctic application were addressed. From the two investigated material grades, namely ASTM A694 F65 and F70, the F70 showed improved properties in all types of tests, especially in fracture toughness (CTOD) testing. In terms of arctic application not only the base materials properties but furthermore the weldability of the grades is of high importance. The higher alloying content of the F70 compared to the F65 leads to a higher carbon equivalent (CE-L).