Prakt. Met. Sonderband 50 (2016) 217
ungen mit Hilfe MONITORING OF PHASE TRANSFORMATIONS IN STEELS BY
Pe IN-SITU ELECTRICAL RESISTANCE MEASUREMENTS
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M. Bruncko', P. Kirbis'?, I. Anzel!
smiBig einfache » University of Maribor, Faculty of Mechanical Engineering, Slovenia
nlagig erzeugter Metal Ravne d.o.o., Koroska cesta 14, SI-2390 Ravne na Koroskem, Slovenia
rritischen Matrix
lachenanteil die ABSTRACT
This paper deals with the problem of non-destructive monitoring and characterization of phase
. transformations in steels. Determination of critical temperatures and phase transformations is of
g der Methodik crucial importance for better understanding of kinetics and mechanisms of heat treatments of steels.
konnten bereits The goal of our research work was to find out the use of electrical resistance measurements for
zeleitet werden. monitoring of microstructural changes in steels. For this purpose, several steel grades were thermal
kstofftechnik der cycled and monitored by electrical resistance changes during heating and cooling. The results
obtained with a novel measurement method were compared with metallographic analysis of
microstructural changes during the heat treatment procedures.
d-metal deposits. 1. INTRODUCTION
3, No. 28, 1-69.
Electrical resistance has to date been applied in the study of various physical phenomena including
plastic deformation [1], recovery and recrystallization kinetics [2], precipitation reactions [3] and
ures in the light phase transformations [4-5]. The determination of critical temperatures and phase transformation
85 (IX-1377-85) kinetics is of essential importance in many industrial processes. There exist a variety of
measurements techniques that fulfill this purpose. Most widely used and well understood are
Materials Science dilatometry [6] and differential scanning calorimetry (DSC) [7]. Their physical basis being the
measurements of volume change and release of latent heat respectively. One additional means for
, monitoring the phase transformations in steel is by in situ measurements of changes in electrical
einflussung des resistance. High temperature diffusional transformations generate small amounts of heat and
ufithrung; DVS- produce very little distortions. On the other hand, they are always accompanied by considerable
changes in electrical resistivity, due to partitioning of solutes. The latter are known to exert a
: profound effect as they act as point defects [8]. Therefore, it is proposed that electrical resistance
of the multi pass measurements would be a particularly suitable method for such investigations. On the other hand,
al heat treatment diffusionless phase transitions are detectable as well due to the variations in specific electrical
19, 282-292 resistivity which is dependent on the crystal structure. Known data can therefore be enriched and
ce of martensite- different information obtained through this method. Electrical resistance measurements also offer
als Science and the advantage of being applicable to a wide variety of specimen geometries. For instance, thin
sheets and small diameter wires cannot be studied using dilatometry.
The aim of this paper is to outline the use of electrical resistance measurements for monitoring of
‚gasschweißen im microstructural changes in steels. It is of interest what information can be obtained and the possible
und Schneiden, advantages that the method presents. For this purpose, a variety of different steels were thermally
cycled and the changes in electrical resistance during heating and cooling monitored “in situ” with
the use of a specially designed measuring cell. Results were presented in the form of diagrams in
ıkterisierung von conjunction with metallographic analysis. The critical temperatures were determent with the use of
+ = Praktische the well-established tangent method.
