Effect of Deformation Heating on Microstructure Evolution During Hot Forging of Ti-6Al-4V

Mykola Kulakov,Salaheddin Rahimi,S Lee Semiatin

doi:10.1007/s11661-021-06493-1

Mykola Kulakov, Salaheddin Rahimi + Show 1 more

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https://doi.org/10.1007/s11661-021-06493-1

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Abstract

The effect of deformation heating on microstructure evolution during hot forging of Ti-6Al-4V was established. For this purpose, right-circular cylinders of Ti-6Al-4V with an equiaxed-α preform microstructure were preheated to a temperature between 1148 K (875 °C) and 1223 K (950 °C), and compressed to a 60-pct. height reduction in a screw press, yielding average true strain rates of ~ 5 to 20 s−1. Thermocouple measurements and corroborating finite-element-method (FEM) simulations quantified substantial deformation-heating-induced temperature increases. For all preheat temperatures, the heating transient led to an exposure above the equilibriumβ transus temperature. Despite such temperature excursions, the volume fraction of equiaxed primary α in each forged billet was only slightly lower than that in the corresponding preheated condition. The source of such observations was rationalized on the basis of the (hypothesized) solute-concentration fields that develop during the heating and cooling transients experienced in high-rate deformation processing.

Highlights

HIGH-INTEGRITY structural components are often fabricated via thermomechanical processes consisting of a series of bulk-forming operations and intermediate and final heat treatments
In conventional processes using these types of equipment, the workpiece is preheated to a high temperature and shaped between dies that are at room temperature or a slightly elevated temperature
The key results of this investigation consisted of measured temperature transients during hot forging and observations of the resulting evolution of microstructure in the Ti-6Al-4V billets

Summary

Introduction

HIGH-INTEGRITY structural components are often fabricated via thermomechanical processes consisting of a series of bulk-forming operations and intermediate and final heat treatments. The starting stock is usually manufactured from large ingots that are worked in hydraulic presses or slabbing mills to produce semi-finished wrought products with a uniform, recrystallized grain structure. Sections of the mill product are cut and shaped by closed-die forging. Such forging operations are usually conducted using a variety of types of equipment including hydraulic, mechanical, screw presses or forging hammers, each with its own ram-position-versus-time characteristics.[1,2] In conventional processes using these types of equipment, the workpiece is preheated to a high temperature and shaped between dies that are at room temperature or a slightly elevated temperature.

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