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1

Influence of cooling rates on properties of pre-alloyed PM materials

Dobrzański L. A., Musztyfaga M.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 37, nr 1

28-35

EN

Purpose: The paper focuses on microstructural and mechanical properties of pre-alloyed Astaloy CrL and CrM sintered steels with high addition of carbon. Design/methodology/approach: The main objective of the present work was to establish the effect of cooling rates on the microstructure and properties such as: Charpy impact test, microhardness, wear resistance (disk on disk test) were evaluated depending on chemical composition. Compacts containing low amounts of chromium, molybdenum and high amount of graphite were sintered in a vacuum furnace at 1120şC in vacuum atmosphere and rapidly cooled in nitrogen with two different rates. Then compacts were tempered in vacuum, and cooled in nitrogen. Obtained samples were analysed by light optical microscopy (LOM) for microstructure observation and scanning electron microscopy (SEM) with EDS for chemical composition. Findings: Sinter hardening is a cost-effective process that consists of sintering and heat treatment in one step, so it minimizes the number of processing steps. It is known that the cooling rate following sintering greatly affect material microstructure, which determine the final properties of sinter-hardened materials. The objective was to understand how sintering conditions influence the development of microstructures and thereby control mechanical properties of materials. Practical implications: Changing the amount of graphite element and cooling rates, will affect the amount of ferrite, perlite, martensite and bainite in the microstructure. Further tests should be carried out in order to examine different cooling rates. Originality/value: Sinter-hardening of CrL and CrM pre-alloyed powders with addition of graphite was investigated to study cooling mechanism.

2

Effect of cooling rates on sinter-hardened steels

Dobrzański L. A., Musztyfaga M.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 37, nr 2

630-638

EN

Purpose: Purpose of this paper was to evaluate the differences between rapid, medium and low cooling rates on three systems and also to study cooling mechanism of known materials. Design/methodology/approach: Two different systems have been tested in order to investigate how the cooling rates influence on the microstructure and properties. The powders used in the present invention are pre-alloyed iron-base powders containing low amounts of chromium and molybdenum. The amount of graphite that was admixed to the iron-base powder was 0.6% and lubricant 0.75%. The amount of graphite which is mixed with the iron-base powder is 0.6% and lubricant is 0.75%. Green compact were sintered in a vacuum furnace at 1120şC for 30 minutes in vacuum atmosphere and rapidly cooled in nitrogen with three different rates: rapid cooling (7şC/s) and medium cooling (1.6şC/s), slow cooling (0.3şC/s). Next the samples were tempered in vacuum in the same furnace at 200şC for 60 minutes and then were cooled to room temperature in nitrogen, with the exception of slow cooling cycle. Findings: The effect of cooling and applied sintering were studied in terms of mechanical properties, hardness and wear resistance. The results achieved after the investigation sinter-hardened steels with low carbon content proved that applied process of sintering and different cooling rates brought expected outcome. Practical implications: According to the powders characteristic, the applied rapid and medium cooling rate seems to be a good compromise for mechanical properties and microstructure, nevertheless further tests should be carried out in order to examine different cooling rates. Originality/value: The effect of cooling rates on mechanical properties of pre-alloyed Astaloy CrL and CrM powders was investigated.

3

Characteristic of vacuum sintered stainless steels

Brytan Z., Dobrzański L. A., Actis Grande M., Rosso M.

Journal of Achievements in Materials and Manufacturing Engineering

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2009

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Vol. 33, nr 2

126-134

EN

Purpose: In the present study duplex stainless steels were sintered in vacuum. using rapid cooling form the mixture of prealloyed and alloying element powders The purpose of this paper was to describe the obtained microstructures after sintering as well as the main mechanical properties of sintered stainless steels. Design/methodology/approach: In presented work duplex stainless steels were obtained through powder metallurgy starting from austenitic 316L or ferritic 410L prealloyed stainless steels powders by controlled addition of alloying elements powder. Prepared mixes were sintered in a vacuum furnace in 1250°C for 1h. After sintering rapid cooling (6°C/s) using nitrogen under pressure was applied. Sintered compositions were subjected to structural examinations by scanning and optical microscopy and EDS analysis as well as X-ray analysis. Mechanical properties were studied through tensile tests and Charpy impact test. Findings: It was demonstrated that austenitic-ferritic microstructures with regular arrangement of both phases and absence of precipitates can be obtained with properly designed powder mix composition as well as sintering cycle with rapid cooling rate. Obtained sintered duplex stainless steels shows good mechanical properties which depends on phases ratio in the microstructure and elements partitioning (Cr/Ni) between phases. Research limitations/implications: Basing on alloys characteristics applied cooling rate and powder mix composition seems to be a good compromise to obtain balanced sintered duplex stainless steel microstructures. Practical implications: Mechanical properties of obtained sintered duplex stainless steels structures are rather promising, especially with the aim of extending their field of possible applications. Originality/value: The utilization of vacuum sintering process with rapid cooling after sintering combined with use of elemental powders added to a stainless steel base powder shows its advantages in terms of good microstructural homogeneity.