Date of Award

10-30-2020

Publication Type

Master Thesis

Degree Name

M.A.Sc.

Department

Mechanical, Automotive, and Materials Engineering

Keywords

Carbides, Characterization, Mechanical Testing, Tool Steel, Trimming

Supervisor

Daniel E. Green

Supervisor

Ahmet T. Alpas

Rights

info:eu-repo/semantics/embargoedAccess

Abstract

Tool steels with increased wear-resistance are being developed for use in trimming operations to improve tool life and final part quality. This study investigates Uddeholm Carmo and Caldie, tool steels exhibiting microstructures with small, evenly distributed carbides. The microstructure and mechanical properties of these steels are compared to D2,a conventional tool steel with much larger bands of carbides. Tests were conducted using miniature tensile, shear compression, and compression specimens. Digital image correlation (DIC) strain measurements were used to develop flow curves. Material characterization and analysis of fracture surfaces were carried out using SEM. Trimming trials were conducted with D2, Carmo, and TiCN PVD coated Caldie. The profiles of the trim edges were captured using optical profilometry. Carmo and Caldie showed increased fracture stresses and strains compared to the conventional D2. In Caldie, there was as much as 169% and 281% increase in stress and strain respectively in tension compared to D2. This resulted in a reduction in material loss on the trim edge. The fracture surfaces revealed a primarily brittle fracture in D2, with the cleavage fracture of the large primary carbides being the dominant mode of fracture in all of the tests conducted. Carmo and Caldie fractured with dimples composed of local quasi-cleavage fracture as its dominant fracture mode. It can be concluded that the smaller, more evenly dispersed carbides in Carmo and Caldie improved their mechanical properties and had a positive effect on the fracture toughness and wear resistance.

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