The aim of this project was to investigate and to optimize the microstructure and wear properties of two different Fe-based hardfacing alloys which are designed for coating bimetallic barrels in plastic processing industries. The compositions of these alloys are different due to their applications. The first alloy (called alloy A) is a low chromium abrasion resistant alloy and the second one (called alloy B) is a high chromium abrasion-corrosion resistant alloy. The effect of dilution has been studied on both A and B alloys through two methods. The simulation of dilution was investigated by introducing Fe powder into the original hardfacing alloys. The obtained results were compared to the actual dilution, by performing the melting in steel crucibles. Microstructural variations have been analyzed with OM, SEM, DSC, while tribological properties were evaluated by macro and microhardness tests and by pin-on-disk wear tests. Improvement in hardness and wear properties of alloy A have been investigated by introducing vanadium as carbide forming element. This addition was performed by Fe12V powder. Based on the content of vanadium and carbon in the alloy, different morphologies of VC particles (cubic, spherical and petal-like) were identified within the microstructure. The formation of VC carbides was observed mostly in the eutectic structure. The compensation of the carbon reduction in the V-rich hardfacing alloy was performed by adding different contents of graphite. In conclusion the new compositions were optimized balancing the vanadium and graphite contents in order to produce hypereutectic structures with a fine distribution of vanadium carbides.
Lo scopo della presente ricerca è stato quello di investigare ed ottimizzare la microstruttura e le proprietà di resistenza ad usura di due differenti leghe hardfacing a base ferro utilizzate per rivestire le pareti interne di estrusori per lo stampaggio di polimeri. Nella prima fase di questo studio sono stati analizzati gli effetti della diluizione su due leghe hardfacing a base ferro (denominate A e B). Tra le due leghe di riferimento studiate, la lega A possiede elevate caratteristiche all’abrasione, mentre quella B contiene un alto tenore di Cr e di altri elementi di lega che formano carburi e boruri per garantire un’elevata resistenza ad usura e a corrosione. La simulazione della diluzione è stata realizzata, dapprima, tramite la fusione delle polveri delle leghe base in crogioli di ceramica dopo graduale aggiunta di Fe e, successivamente, attraverso la loro rifusione su un substrato metallico. L’evoluzione microstrutturale dopo diluizione è stata studiata tramite microscopia ottica (OM), elettronica (SEM), misure di calorimetria differenziale a scansione (DSC) e microdurezza, mentre la resistenza ad usura è stata analizzata attraverso prove pin-on-disc. Nell’ultima fase del presente studio, per investigare l’effetto del vanadio sulla microstruttura e sulla durezza della lega di riferimento A, sono state prodotte leghe ad alto V tramite aggiunta di polvere Fe12V. Livelli crescenti di Fe12V hanno modificato la microstruttura ipereutettica della lega base favorendo la formazione di frazione eutettica e di carburi di vanadio (VC). In particolare, per concentrazioni crescenti di vanadio e carbonio è stata osservata la presenza di VC di morfologia: cuboidale, sferoidale e petal-like, all’interno della struttura eutettica. Allo scopo di bilanciare l’aggiunta di vanadio e la riduzione di elementi interstiziali, livelli crescenti di grafite sono stati miscelati alle polveri delle leghe ad alto V. L’ottimizzazione della composizione chimica delle nuove leghe è stata realizzata considerando concentrazioni di V e C necessarie a realizzare microstrutture ipereutettiche con una distribuzione fine di carburi di vanadio.
Effect of dilution and different vanadium additions on microstructure and wear properties of Fe-based hardfacing alloys
EMAMI, ALIREZA
2014/2015
Abstract
The aim of this project was to investigate and to optimize the microstructure and wear properties of two different Fe-based hardfacing alloys which are designed for coating bimetallic barrels in plastic processing industries. The compositions of these alloys are different due to their applications. The first alloy (called alloy A) is a low chromium abrasion resistant alloy and the second one (called alloy B) is a high chromium abrasion-corrosion resistant alloy. The effect of dilution has been studied on both A and B alloys through two methods. The simulation of dilution was investigated by introducing Fe powder into the original hardfacing alloys. The obtained results were compared to the actual dilution, by performing the melting in steel crucibles. Microstructural variations have been analyzed with OM, SEM, DSC, while tribological properties were evaluated by macro and microhardness tests and by pin-on-disk wear tests. Improvement in hardness and wear properties of alloy A have been investigated by introducing vanadium as carbide forming element. This addition was performed by Fe12V powder. Based on the content of vanadium and carbon in the alloy, different morphologies of VC particles (cubic, spherical and petal-like) were identified within the microstructure. The formation of VC carbides was observed mostly in the eutectic structure. The compensation of the carbon reduction in the V-rich hardfacing alloy was performed by adding different contents of graphite. In conclusion the new compositions were optimized balancing the vanadium and graphite contents in order to produce hypereutectic structures with a fine distribution of vanadium carbides.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/101961