Thanks for your answer.
I'm actually working with prof Balasubramaniam on P-indian iron.
About Mn, may I ask a question on this part of your mail:
"You have stated that you have found inclusions containing 30% MnO. This
should not be taken to mean that the ore originally had manganese in that
much amount. Since iron oxide gets reduced first, the unreduced part would
get enriched in manganese resulting in high manganese in inclusions. But,
like you have observed, hardly any manganese has ever been found - and here
I speak from my Indian experience only - in any of the "bloomery" iron of
ancient India."
Of course the reduction of Fe-oxide provokes an increase of the non reduced
compounds content in the slag inclusions. But, in this case this value of
30% is nevertheless relatively high compared to "usual" values observed in
Mn containing slags from the bloomery process (about several % to 10%)
PhD
-----Message d'origine-----
De : Arch-Metals Group [mailto:[log in to unmask]] De la part de Dr.
K.K. Prasad
Envoyé : lundi 16 mai 2005 11:31
À : [log in to unmask]
Objet : Re: Manganese in bloomery process
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Dr. Krishna Kant Prasad (DGM, RDCIS, SAIL),
2C/E Bel-Air Complex,
Jokhiram Durgadutt Lane,
Main Road, Ranchi-834001,
Jharkhand State, India
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May 16, 2005
Dear Philippe,
I do not have direct answer to the questions you have raised, but I would
like to comment on some of the related and, I think, relevant issues.
You have stated that in the thermodynamic conditions of the shaft furnace,
manganese oxide cannot be reduced into metallic manganese. While literally
that statement is true, manganese has an opportunity to appear dissolved in
metallic iron (the two form a near ideal solid solution at low manganese
concentration) and therefore minor manganese reduction is feasible. Kinetic
factors are probably responsible for preventing this reduction process.
You have stated that you have found inclusions containing 30% MnO. This
should not be taken to mean that the ore originally had manganese in that
much amount. Since iron oxide gets reduced first, the unreduced part would
get enriched in manganese resulting in high manganese in inclusions. But,
like you have observed, hardly any manganese has ever been found - and here
I speak from my Indian experience only - in any of the "bloomery" iron of
ancient India.
India has many iron based ancient monuments with remarkable properties. The
most famous of these is the Iron Pillar of Delhi. Iron for all these
monuments and artifacts were extracted by the bloomery method (we prefer to
call it the mud- or clay-shaft process). Some of the indigenous people in
Chhattisgarh and Jharkhand States are still practicing this technique.
Studies of the products made by these people, as well as study of ancient
heritage (Delhi Pillar being one), have revealed some points of importance.
1. It was easy to make very low carbon wrought iron by such a process. While
higher carbon iron could be attempted, control of carbon was found
difficult. Large variation of carbon between subsequent heats was observed.
2. All the samples examined by us as well as those reported in literature
contained either no manganese or in traces only. One of the many reported
investigations on the Delhi Iron Pillar was carried out (in either 50's or
60's) in BISRA laboratories.
3. As there was no control over phosphorous in the process, high phosphorous
in the iron ore led to high phosphorous wrought iron. Probably such an ore
was deliberately chosen for the Delhi Pillar.
4. The Iron Pillar of Delhi was probably made by making high carbon 'blooms'
successively one over the other, and beating the freshly formed 'bloom' on
to the older layer - while keeping a split hollow cylindrical stone die
around. This way the bloom layers could be effectively welded to each outer,
but left the surface extremely rough. The erect iron mass was then taken
down, heated and rotated on a manually driven stone lathe and forged between
stone dies - much like the modern forging of railroad axles. During this
forging process the surface got heavily decarburised while the interior
remained relatively high in carbon.
5. Studies conducted by Prof. Balasubramaniam of IIT Kanpur have indicated
that a combination of extremely low mangenese and high phosphorous has
contributed to the excellent corrosion resistance of the Iron Pillar. Too
much carburisation would have had an adverse effect on this property.
On the whole, from the Indian experience, it can be concluded that since
manganese was never picked up during the bloomery process, its effect on
carburising the metal was never of any importance. As to why manganese was
not reduced - I can do no better than hold kinetic factors responsible.
Krishnakant Prasad
----- Original Message -----
From: "dillmann" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Sunday, May 15, 2005 3:00 PM
Subject: Manganese in bloomery process
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>
>
> Dear all,
>
> For several month, I'm analysing ferrous artefacts coming from direct
> process and that are made from an ore containing high levels of Manganese
(a
> 14th c. forge in the French Pyrenees). The slag inclusions contain up to
> 30mass% of MnO and Mn is not detectable in the metal (<100ppm). Indeed,
the
> metal is highly carburised (over eutectoid).
>
> Several authors talk about the carburising role of Mn and, indeed, several
> historical zones of producing steel were associated with high Mn ores
> (Italian alps, Pyrenees...)
> Nevertheless, I have several questions about the exact metallurgical role
of
> this element in the carburising process during bloomery operating chain.
> Indeed, in the thermodynamic conditions of the shaft furnace, the MnO
oxide
> can not be reduced into metallic Mn. Thus, this element can not play a
role
> in the metal. Moreover, even if this element were in the iron, it seems
that
> the influence of Mn on the diffusion coefficient of carbon is not proved.
>
> So, I ask the questions: does anyone study the exact role of manganese on
> the carburisation of iron in the direct process. Does Mn play a role
indeed?
> Can you help me?
>
> Best regards
>
> Philippe Dillmann
>
>
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