Model-Based Residual Stress Design in Multiphase Seamless Steel Tubes

Abstract

Residual stresses in quenched seamless steel tubes highly depend on the cooling conditions to which the tubes have been subjected. The design aspect of how to use controlled cooling strategies in multiphase steel tubes to achieve certain residual stress and phase configurations is discussed. In an experimentally validated finite element (FE) model considering a coupled evolution of martensite and bainite, three cooling strategies are tested for a low-alloyed 0.25 wt.% C steel tube. The strategies are (i) external cooling only, (ii) internal and external cooling for low residual stresses in a mainly martensitic tube, and (iii) internal and external cooling with low cooling rate for a mainly bainitic tube. The strategies represent design cases, where low residual stresses with different phase compositions are provoked, in order to show the potential of numerical analysis for residual stress and property design. It can be concluded that, for the investigated steel class, intense external cooling leads to a characteristic residual stress profile regardless of the dimension. A combination of external and internal cooling allows a more flexible design of residual stress and phase distribution by choosing different cooling parameters (i.e., water amount and cooling times). In general, lower cooling rates lead to lower thermal misfit strains, and thus less plasticity and lower residual stresses.

Residual Stress Evolution in Low-Alloyed Steel at Three Different Length Scales

“…The models used to describe residual stresses on three different length scales are shematically depicted in Figure 1 : (i) a macroscopic process model calculating the temperature, phase and residual stress evolution, developed in [ 9 , 10 ] (ii) a model on the mesoscopic scale describing an infinite segregation “line” (plane) and (iii) a volume element containing inclusions for calculating microscopic stresses. In the microscopic model the material properties of matrix are mixed with the precipitate properties of the volume fraction for the regions to obtain the mesoscopic properties and .…”

“…The phase transformation kinetic is combined with the concomitant changes in material properties and transformation related effects by a user defined field in ABAQUS [ 20 ]. The current phase composition is assigned to field variables and the temperature dependent data for elasticity, yield curves, thermal expansion, thermal conductivity and specific heat of the individual phases are mixed accordingly [ 9 , 10 ].…”

“…The macroscopic phase transformation model was developed to calculate the temperature, phase and residual stress evolution in seamless steel tubes during accelerated cooling [ 9 , 10 ]. In the investigated manufacturing setup, the tube moves trough a cooling equipment consisting of eight cooling baskets, which apply spray water.…”

“…The macroscopic model is briefly introduced and linked with a mesoscopic and a microscopic submodel to investigate the higher order stresses. The stress evolution on the macroscopic scale is experimentally verified and discussed in detail in [ 9 , 10 ]. The now presented work focuses on the multiscale modelling taking the macroscopic results as starting point.…”

“…This computations provide phase fraction and temperature evolution as a function of the tube’s radial position during heat treatment consisting of quenching and optional subsequent tempering. A study on how to adapt the quenching process in order to lower residual stresses is published in [ 10 ]. The model and the results are briefly introduced in this paper and linked to the stress evolution on lower length scales.…”