Numerical assessment of large hexagonal seamless steel tube extrusion feasibility

Denis Sornin,Dylan Habans,Katia Mocellin,Patrick Olier,Pierre Montmitonnet

doi:10.25518/esaform21.3605

Abstract

The study assesses feasibility of hot extrusion of a large seamless hexagonal 9%Cr-1%Mo steel tube. The manufacturing chain starts from a pierced cylindrical billet, hot extruded and to be further cold drawn in several passes. Preliminary industrial tests have shown thickness reduction in extrusion limited by a huge initial force peak (+25 %) reaching the press capacity. To understand this force peak, thermomechanical numerical simulation (ForgeNxt®) of the furnace-press transfer and extrusion stages is carried out. Constitutive model at high temperature, high strain and strain rate has been selected from literature. Surface properties, namely Heat Transfer Coefficient (HTC) and friction coefficient, have been made space- and time-dependent to represent glass lubrication. Numerical results are qualitatively compared to industrial experimental values to evaluate the prediction of the model. It suggests that the difficult start of the glass melting and flow along a cooled die affects the force peak. Practical improvements are suggested on this basis, together with possible refinements of the simulation for more precision and insight into extruded tube quality.

Highlights

In 2010, CEA revived studies on Fast Sodium Reactors (SFRs)
The manufacturing chain starts from a pierced cylindrical billet, hot extruded and to be further cold drawn in several passes
The billet is compressed inside the container until it fills the container-needle gap, a force peak Fpeak is observed at the Numerical assessment of large hexagonal seamless steel tube extrusion feasibility beginning of the extrusion, and the measured force drops to a relatively stable steady-state value Fss

Summary

Introduction

In 2010, CEA revived studies on Fast Sodium Reactors (SFRs). The main goal was to build a demonstrator, first called ASTRID. In 2018, ASTRID’s capacity was reduced from the original, commercial 600 MWe to a 150 MWe research model (150 MWe SFR) In this framework, many studies started to ensure that the industrial base was able to produce the structural elements of the reactor’s core, including the hexagonal wrapper steel tube containing the nuclear fuel claddings [1]. Numerical assessment of large hexagonal seamless steel tube extrusion feasibility curve (Fig. 2) shows a force Fpeak at 2200 tons, around 25% more than the steady extrusion pressure (Fss) and very close to the capacity of the press. This is what restricts a decrease of semi-product thickness. Friction coefficient and heat transfer coefficient (HTC) were used as varying parameters and were eventually found non-uniform if the peak amplitude is to be recovered

Model construction

Lubrication in hot extrusion

Tools and billet thermomechanical properties

Conclusion