Distortion In Tube and Pipe Products: Microstructural and Computational Evidence

Current industrial practices often involve extensive methods for re-straightening quenched and tempered carbon steel tube and pipe products.  Relying heavily on these “after-the-fact” methods is inherently problematic; therefore the more desirable option is to eliminate straightness issues at the outset.  During quench and temper operations, there are several aspects of the process which can allow the formation of non-uniform microstructures in the product.  For example, incomplete austenite transformation can leave regions of retained ferrite which constrain the product as the surrounding austenite undergoes the FCC to BCT martensite transformation.  Further, non-uniform quenching and inadequate tempering can compound these distortion effects, and in extreme cases, the restraightening process can introduce more residual stresses into the work piece.

 The current study examines the effects of variations in phase volume fractions formed or altered during the austenitizing, quenching, and tempering stages on the final product dimensions.  Quench and temper experiments, as well as calculations and modeling, have been used to characterize the compounding effects of incomplete austenite transformation paired with non-uniform quenching of tubular products.  Simulations have been carried out using SolidWorks Simulation, and experimental pieces have been examined using traditional metallography as well as micro- and macro-hardness measurements.  As expected, we have found strong correlations between microstructure (from both incomplete austenite transformation and incomplete martensite transformation) and the distortion of the product.  Methods to prevent both of these issues are discussed.