An Incremental Physically-Based Model of P91 Steel Flow Behaviour for the Numerical Analysis of Hot-Working Processes

et al. 2021

Metals

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The evolution of the microstructure changes during hot deformation of high-chromium content of stainless steels (martensitic stainless steels) is reviewed. The microstructural changes taking place under high-temperature conditions and the associated mechanical behaviors are presented. During the continuous dynamic recrystallization (cDRX), the new grains nucleate and growth in materials with high stacking fault energies (SFE). On the other hand, new ultrafine grains could be produced in stainless steel material irrespective of the SFE employing high deformation and temperatures. The gradual transformation results from the dislocation of sub-boundaries created at low strains into ultrafine grains with high angle boundaries at large strains. There is limited information about flow stress and monitoring microstructure changes during the hot forming of martensitic stainless steels. For this reason, continuous dynamic recrystallization (cDRX) is still not entirely understood for these types of metals. Recent studies of the deformation behavior of martensitic stainless steels under thermomechanical conditions investigated the relationship between the microstructural changes and mechanical properties. In this review, grain formation under thermomechanical conditions and dynamic recrystallization behavior of this type of steel during the deformation phase is discussed.

Section: Hot Formability Of Mssmentioning

confidence: 99%

Review on Dynamic Recrystallization of Martensitic Stainless Steels during Hot Deformation: Part I—Experimental Study

Derazkola

et al. 2021

Metals

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“…The material of the billet is a P91 steel, which was characterised experimentally by means of compression tests, performed at a temperature range of 900-1270 • C and at strain rates in the range of 0.005-10 s −1 [27]. The behaviour was defined as elasto-viscoplastic according to Hansel-Spittel model, given byσ…”

Section: Thermo-mechanical Properties Of the Materialsmentioning

confidence: 99%

Analysis of Wall Thickness Eccentricity in the Rotary Tube Piercing Process Using a Strain Correlated FE Model

Barco³

et al. 2020

Metals

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The wall thickness eccentricity is one of the most important weaknesses that appears in seamless tubes production, since this imperfection is subsequently transferred downstream through the manufacturing stages until the final product. For this reason, in this article a finite element model of the rotary tube piercing (RTP) process is developed aimed at analysing the wall thickness eccentricity imperfection. Experimental data extracted from the industrial process is used for the validation of the model, including operational process variables like power consumption and process velocity, and deformation variables as elongation and longitudinal torsion, originated by axial and shear strain respectively. The cause of longitudinal torsion is also analysed. The two most important conclusions derived from this study are: (I) the longitudinal torsion of the tube is a crucial parameter for the correct model validation, and (II) the combined effect between the uneven temperature distribution of the billet and the plug bending deformation is identified as the major cause of the wall thickness eccentricity flaw.

“…From Equation ( 11 ), Jonas et al [ 55 ] defined a relation of proportionality between the flow stress

and the dislocation density

. On this basis, the model has been proposed as an step-by-step incremental constitutive formulation, suitable for its implementation in finite element codes [ 56 ]. The flow stress during the work-hardening and DRV transient,

, is given by

with

where j is the step number (

the saturation stress,

the yield stress and

the initial work-hardening rate, which is determined according to

where

and

are material constants.…”

Section: Theoretical Background Of the Constitutive Modelmentioning

confidence: 99%

“…The methodology followed for the determination of all the material parameters involved in the constitutive model is available in [ 56 ]. The values of these material parameters are provided in Table 1 , presenting an average absolute relative error (AARE) of approximately 4% with respect to the experimental data.…”

Section: Theoretical Background Of the Constitutive Modelmentioning

confidence: 99%

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Application of an Incremental Constitutive Model for the FE Analysis of Material Dynamic Restoration in the Rotary Tube Piercing Process

Barco³

et al. 2020

Materials

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In the numerical simulation of hot forming processes, the correct description of material flow stress is very important for the accuracy of the results. For complex manufacturing processes, such as the rotary tube piercing (RTP), constitutive laws based on both power and exponential mathematical expressions are commonly used due to its inherent simplicity, despite the limitations that this approach involves, namely, the use of accumulated strain as a state parameter. In this paper, a constitutive model of the P91 steel derived from the evolution of dislocation density with strain, which takes into account the mechanisms of dynamic recovery (DRV) and dynamic recrystallization (DRX), is proposed for the finite element (FE) analysis of the RTP process. The material model is developed in an incremental manner to allow its implementation in the FE code FORGE®. The success of this implementation is confirmed by the good correlation between results of the simulation and experimental measurements of the manufactured tube (elongation, twist angle, mean wall thickness and eccentricity). In addition, this incremental model allows addressing how the restoring mechanisms of DRV and DRV occur during the RTP process. The analysis puts into evidence that DRV and DRX prevail over each other cyclically, following an alternating sequence during the material processing, due mainly to the effect of the strain rate on the material.