Questo sito utilizza cookie di terze parti per inviarti pubblicità in linea con le tue preferenze. Se vuoi saperne di più clicca QUI 
Chiudendo questo banner, scorrendo questa pagina, cliccando su un link o proseguendo la navigazione in altra maniera, acconsenti all'uso dei cookie. OK

Mechanical Properties of High Density Low Alloyed PM Steels: Effect of Sintering and Secondary Heat Treatments

Nowadays sintered components are widely used for different applications. One of the biggest end user is the automotive industry. The growth of the PM Industry in recent years can to a very large extent be explained by the shaping ability of PM processes.
In this work the mechanical properties of two main low alloyed PM steel groups were studied as a function of density, sintering temperature and microstructure (modified by carbon content and either heat or thermochemical treatment). The former group is based on the Fe-Mo-(Ni) system, widely used in the industry today and the latter is based on Astaloy CrL prealloyed powder based on the Fe-Cr system. Astaloy CrL was designed as complement or replacement to powders based on common Fe-Mo-Ni-Cu systems used for medium-to-high strength applications.
The purpose of this study was to check how the mechanical properties (tensile, impact and fatigue resistance) of materials are influenced by the processing conditions investigated, through their effect on density, porosity and microstructure.
Different methods to obtain high density, such as warm compaction and high velocity compaction were used, the results in any case were compared to convectional (cold) compacted materials.
Generally, the sintering during this project was carried out in 90%N2/10%H2 atmosphere at 1120 (belt furnace) and 1250ºC (batch furnace) for 30 min. Some additional high temperature sintering tests were carried out in an industrial vacuum furnace, with different cooling rate.
Experiments with different secondary heat treatments, such as through hardening, steam oxidation and carburizing, subjected to improve the material’s performance were carried out.

Mostra/Nascondi contenuto.
Theoretical Remarks _________________________________________________________________________________________________________________ Preface Powder metallurgy (PM) parts are often used in structural parts because of the low production cost in large scale series. This economic benefit is granted by a near net shape and low raw material loss. Historically, PM has been used to produce simple geometry parts, addressed to low stressed applications. Research and development in manufacturing has broadened the use of PM to produce complicated parts used for highly stressed applications. Large-scale production of ferrous structural components by the powder metallurgical manufacturing technique goes back to the late 1930s. The main reason this technique came into technical use was that it provided a simple and easily automated shaping method with very low material losses for the production of parts with high demands on dimensional accuracy [1]. The components were mainly produced from plain iron powder which meant that any higher demands on mechanical properties were not fulfilled. The strength of the material corresponded to that of soft iron which is reduced by the influence of the porosity, this being an inevitable consequence of the process. There are several ways to improve desired properties with iron-based sintered materials. The most important parameters of influence are: • Density and porosity • Sintering conditions • Alloying elements/methods • Heat-treating conditions These parameters should be controlled within the as closest possible limits, because even small variations may cause unacceptably wide scatter of dimensional changes during sintering and thus spoil the dimensional stability of the sintered parts. 1 Table of contents

Tesi di Dottorato

Dipartimento: DIMTI

Autore: Vanya Stoyanova Contatta »

Composta da 204 pagine.

 

Questa tesi ha raggiunto 241 click dal 30/01/2009.

 

Consultata integralmente una volta.

Disponibile in PDF, la consultazione è esclusivamente in formato digitale.