Carbon control in PM sintering: industrial applications and experience

Hryha, Eduard; Nyborg, Lars; Malas, Akin; Wiberg, Sören; Berg, Sigurd

doi:10.1179/0032589912z.00000000085

Cited by 20 publications

(15 citation statements)

References 5 publications

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“…Dissolution of the carbon by diffusion into the steel powder matrix chemical reaction then takes place during the subsequent heating and isothermal sintering stages. 2 The rate of carbon dissolution is determined by the graphite grade and particle size 3,4 as well as by processing conditions (sintering atmosphere, temperature profile, etc.). 2,5 The most common carbon sources are natural and synthetic graphite grades, 3,4,6 of which natural graphite currently dominates the market for PM steels.…”

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Dissolution of carbon in Cr-prealloyed PM steels: effect of carbon source

Hryha¹,

Nyborg²,

Alzati³

2015

Powder Metallurgy

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Modern water-atomised steel powder grades are characterised by the presence of two types of surface oxides: a thin iron oxide layer, covering more than 90% of the powder surface, and more thermodynamically stable particulate oxides. The development of inter-particle necks and carbon dissolution in the iron matrix both require efficient removal of the iron oxide layer. Hence, carbon reactivity strongly affects the surface oxide reduction that determines inter-particle neck development and carbon dissolution, and so microstructure development. An analysis is presented of the effect of three carbon sourcessynthetic graphite, natural graphite and carbon black -on microstructure and inter-particle neck development in Cralloyed PM steels. Metallographic and fractographic studies indicate that the most significant property of the carbon sources affecting reactivity is the carbon powder size. Carbon black shows the highest reactivity at elevated temperatures but is fully inert at temperatures below 900uC.

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confidence: 99%

Dissolution of carbon in Cr-prealloyed PM steels: effect of carbon source

Hryha¹,

Nyborg²,

Alzati³

2015

Powder Metallurgy

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“…Although this more intensive carbothermal reduction reduces the oxygen content, it also reduces carbon content in the compact. These competing effects showcase the difficulties associated with the carbon content control that will noticeably affect the mechanical properties of the final component …”

Section: Resultsmentioning

confidence: 99%

Effect of heating rate and process atmosphere on the thermodynamics and kinetics of the sintering of pre‐alloyed water‐atomized powder metallurgy steels

Hryha

Wendel

2018

J Am Ceram Soc

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During the sintering of powder metallurgy steels the full removal of the iron oxide layer is required in order to develop strong inter-particle necks. Although this iron oxide layer has low thermodynamic stability, its removal from the powder compact is a very complex process that is determined by a number of parameters such as temperature profile, sintering atmosphere, compact properties, powder properties, and additives. This paper summarizes these sintering parameters in correlation with the powder properties through the use of thermogravimetry analysis. In this work, hydrogen additions were identified as the most effective agent for the removal of the surface iron oxide during the early stages of sintering (at temperature range between~300 and 600°C). The process depends on the heating rate and a rather low activation energy of 48 kJ/mol was determined for this reaction. Carbothermal reduction plays the largest role in the oxide reduction at high temperatures where two main reactions can be distinguished. The first was the reduction of the surface oxide residue and particulates, which occurred at temperatures between 950 and 1150°C. This reaction is characterized by an activation energy of 253 kJ/mol. Second was believed to be associated with the reduction of the internal oxides, occurred at temperatures above 1150°C. This reaction is characterized by rather high activation energy of 422 kJ/mol. K E Y W O R D Salloyed sintered steels, oxide reduction, reducing agent, sintering atmosphere, surface oxide

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“…For sintering furnaces, there has been a system introduced by Linde and Höganäs AB which allows the determination and control of the sintering atmosphere (Sinterflex). The system needs some CO in the atmosphere (about 1%) and is operated not completely on-line, as it extracts some gas from the sintering atmosphere to analyse it in this extra unit (see [35][36][37]).…”

Section: Other Gas Analysing Systemsmentioning

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Reactions between ferrous powder compacts and atmospheres during sintering – an overview

Gierl‐Mayer

2020

Powder Metallurgy

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This overview paper describes the interaction of powder metallurgical iron-base alloys with the atmosphere during sintering. The methods of thermal analysis serve to clarify the processes that take place especially during the heating stage of the sintering cycle. After a discussion of the physical and chemical fundamentals of the sintering process, the methods of thermal analysis are explained. The differences between plain iron and alloyed systems are discussed in detail. Classical PM low alloy steels with alloying elements, such as Cu, Ni and Mo, react in a similar way as unalloyed carbon steels. The situation changes dramatically, when oxygen sensitive elements as chromium, manganese and even more silicon come into play. The removal of the surface oxygen is much more crucial, and there are several competing reactions, which have to be considered when these systems should be sintered in industrial scale to reach the desired mechanical and dimensional properties.

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Carbon control in PM sintering: industrial applications and experience

Cited by 20 publications

References 5 publications

Dissolution of carbon in Cr-prealloyed PM steels: effect of carbon source

Dissolution of carbon in Cr-prealloyed PM steels: effect of carbon source

Effect of heating rate and process atmosphere on the thermodynamics and kinetics of the sintering of pre‐alloyed water‐atomized powder metallurgy steels

Reactions between ferrous powder compacts and atmospheres during sintering – an overview

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