Technology and market study on continuous casting rolls

University essay from Luleå/Tillämpad fysik, maskin- och materialteknik

Abstract: This Master’s Thesis consists of two separate and independent studies: One
metallurgical study and one industrial buying behaviour study. Both studies
concern continuous casting rolls.

Metallurgical Study:
The first objective of this study was to investigate two continuous casting
rolls, consisting of different steel tubes with different martensitic
stainless steel weld overlays. The second objective was to evaluate the
methods employed in the study.

The weld overlaps are clearly the weakest points of the weld overlay. They
are sensitive to corrosion attacks, mainly due to sensitisation. The delta
ferrite present in the welded overlay of both rolls is a preferential site
for the corrosion attacks and the delta ferrite content depends primarily on
the chemical composition of the weld overlay. The welding temperature may
also have some influence on the delta ferrite content, but this has not been
observed in this study. Both rolls have similar surface hardness. Roll no. 2
has more generalized corrosion attacks than roll no. 1. This is due to a
higher delta ferrite content in roll no. 2 than in roll no. 1.

The methods employed during the study proved to be adequate. In any future
study, on condition that the visual inspection, diameter measurements,
ultrasonic testing and surface hardness measurements show that all positions
on the roll are similar, it will be sufficient to cut a bead and overlap
sample from only one position.

The rolls were investigated using macro etching, optical microscopy, Vickers
hardness testing, ultrasonic testing ICP-OES analysis of nickel and chromium
content and carbon content analysis by wet chemical method. Delta ferrite
content was also calculated theoretically using a Schaeffler – DeLong diagram
and a semi-empirical model.

Industrial Buying Behaviour Study:
The aim of this study is to investigate the industrial buying behaviour in
slab casting steelworks in Western Europe when buying roll-lines. Case
studies have been conducted at four steelworks belonging to different
companies. Data was collected through personal interviews with people from
production, maintenance and purchasing department and intermediate level
management.

A test consisting of a smaller amount of rolls is always performed before
buying any larger quantities of rolls. Even though the test order has
relatively low economic value, compared to a full-scale order, it is during
this process that the relationships are established between the buying and
the selling company. Findings show that the industrial buying behaviour of
steelworks in Western Europe agrees well with the theory in this field. The
buying process follows the steps in the buygrid model with only a few
exceptions. The decision-making power lays in the intermediate level
management, even though approval is required from upper level management. The
most important factors affecting the buying behaviour are the relationship
between the buyer and the seller, service-life and life cycle cost of the
roll-line.

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