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» Kinetics of phase transformations during tempering of tool steels of a different chromium content
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JERZY PACYNA  PIOTR BAŁA JANUSZ KRAWCZYK
During heating as-quenched martensite, the tempering (of unalloyed,
medium and high carbon steels) takes place in three distinct
but overlapping stages: precipitation of ε carbide, transformation
of the retained austenite into lower bainite and precipitation of cementite.
In steels containing alloying elements contributing to an
effect of secondary hardening (V, Mo, W) a fourth stage (transformation)
occurs: precipitation of MC and M2C-type alloy carbides,
that nucleate independently [1÷4].
The first transformation occurs in the temperature range of
100÷200°C. Metastable ε carbide (Fe2.4C) with hexagonal crystal
structure precipitates from the supersaturated martensite [5÷8].
Precipitation of highly dispersed ε carbide is believed to enhance
strengthening in steel [2, 4].
The second transformation takes place during tempering in the
temperature range of 200÷320°C and this is a transformation of the
retained austenite. As the result of this transformation, a non-homogeneous
mixture consisting of supersaturated ferrite and cementite,
i.e. lower bainite forms [1, 2, 4].
Cementite is formed during the third transformation occurring
during tempering in the temperature range of 200÷420°C. This
results in further decarbonization of the matrix and dissolution of
metastable ε carbides allowing for the recovery of the steel matrix
[4, 7]. The mechanism of the nucleation of cementite is, however,
not fully understood yet. According to Ref. [4] precipitating cementite
nucleates independently or in situ on ε carbide particles. Whereas
according to Ref. [5] cementite nucleates independently, mainly on
grain boundaries of former austenite or on subgrain boundaries of
the newly formed cell structure.
Above 400°C diffusion of alloying elements such as V, Mo and
W takes place. Then, the cementite gradually dissolves to make the
nucleation of MC and M2C carbides coherent with the alloy matrix
possible. This leads to an [...]
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INŻYNIERIA MATERIAŁOWA 2010/3
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» Kinetics of phase transformations of undercooled austenite in tool steels of a different chromium content
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JANUSZ KRAWCZYK JERZY PACYNA PIOTR BAŁA TERESA SKRZYPEK ADAM KOKOSZA
The chemical composition and microstructure of hypereutectoid
steel influences its most important properties, such as: heat fatigue
resistance, resistance to oxidation and mechanical properties [1],
which in consequence determines functionality qualities of tools
produced of this steel. Depending on the material used certain surface
defects can generate, which eliminate tools from further exploitation
[2]. A retained austenite can also play a significant role.
Retained austenite being a metastable phase, appears to be the main
reason for spalling of indigenous rolls [2]. Hypereutectoid cementite
and changes in a matrix influence tribological properties [3, 4].
Spectroscopic methods can be used for the analysis of such changes,
e.g. for characteristics of cementite precipitates [5]. Possibilities
of applying hypereutectoid steels for tools production can also
be determined by means of the CCT diagrams. E.g. the effect of
hot deformation on phase transformation kinetics of undercooled
austenite was considered in the reference [6]. The knowledge mentioned
above, allows to design hypereutectoid steels (e.g. of a bainitic
matrix) or to estimate possible effects when elements made of
this steel (intended to be of a pearlitic matrix) enter into a bainitic
zone at cooling [7]. The chemical composition analysis of this type
of steel requires also a broad estimation of alloy carbides being
formed in it [8], including the role of a continuous network of secondary
cementite [9, 10]. Thus, a carbon content in those steels can
be optimised with regard to the mechanical properties [11] and its
influence on the microstructure of a steel matrix can be determined
[12]. An interlamellar distance in pearlite substantially influences
functional qualities of steel [13]. The austenitizing temperature [14]
and the cooling rate [15] are decisive when considering the steel
microstructure. Vanadium carbides, especially their influence on
grain sizes, are[...]
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INŻYNIERIA MATERIAŁOWA 2010/3
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» Nowe materiały i nowe technologie obróbki cieplnej dla hutnictwa w ofercie AGH
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JERZY PACYNA JANUSZ KRAWCZYK PIOTR BAŁA ADAM KOKOSZA ROBERT DĄBROWSKI EDYTA ROŻNIATA
W pracy opisano nowe materiały i nowe technologie znajdujące się w ofercie Wydziału Inżynierii Metali i Informatyki Przemysłowej
AGH dla hutnictwa polskiego i światowego. Zamieszczone oferty podzielono na dwie grupy. Pierwsza grupa to oferty ostatnio wdrożone.
Druga natomiast to oferty, nad którymi nadal trwają prace w AGH, lecz ich rezultaty w postaci nowych materiałów i nowych
technologii wkrótce zostaną przedłożone wybranym firmom do wykorzystania.
This paper content an offer of the new materials and new technologies of heat treatment for Polish metallurgical industry. The offer
was divided on the two groups. First one - a new materials and new technologies, which were recently implemented. The second
group content a new materials and new technologies, on which we are still working, however in near future they will be submit for
metallurgical companies to use it in practice.
Słowa kluczowe: produkty stalowe, nowe technologie, szyny kolejowe, walce hutnicze, wały siłowni wiatrowych
Keywords: steel products, new technologies, railway track, mill rolls, wind power plant shafts.Wprowadzenie. Wydział Inżynierii Metali
i Informatyki Przemysłowej legitymuje się blisko
90-letnią tradycją współpracy z hutnictwem polskim
a także z hutnictwem światowym. Mimo zachodzących
w ostatnim dziesięcioleciu, na skalę do
niedawna niewyobrażalną, zmian strukturalnych
i własnościowych w hutnictwie polskim oraz degradacji
jakości produktu oferowanego w sensie gatunkowym
przez huty działające na terenie Polski,
Akademia Górniczo‑Hutnicza, ze swymi trzema
wydziałami o profilu hutniczym, bezustannie oferuje
temu hutnictwu nowe materiały o unikatowych
własnościach i nowe technologie, konkurencyjne
pod względem ekonomicznym i ekologicznym.
Ponieważ większość produkcji hut działających na
obszarze naszego kraju, ogranicza się do stali niestopowych,
głównie do gatunku S235JR (dawniej
St3S), dlatego opracowywane w AGH nowe materiały
i nowe technologie s[...]
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HUTNIK - WIADOMOŚCI HUTNICZE 2010/4
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