Cet ouvrage fait partie de la bibliothèque YouScribe
Obtenez un accès à la bibliothèque pour le lire en ligne
En savoir plus

Effects of tramp elements in flat and long products

De
174 pages
Mechanical working (rolling mills)
Industrial research and development
Voir plus Voir moins

Vous aimerez aussi

ISSN 1018-5593
+ *
*
*
* * *
European Commission
echnical steel research
Mechanical working (Rolling mills)
Effects of tramp elements in flat
and long products
STEEL RESEARCH I
European Commission
technical steel research
Mechanical working (Rolling mills)
Effects of tramp elements in flat
and long products
Authors
for flat products:
V. Leroy, R. D'Haeyer, J. Defourny
CRM (B)
T. Hoogendoom
Hoogovens (NL)
J. P. Birat
IRSID (F)
H. J. Grabke
MPI (D)
for long products:
W. B. Morrison, N. G. Henderson, R. D. Longbottom
British Steel (UK)
T. Laux
Arbed (L)
I. Les
Sidenor (E)
Contract No 7210-ZZ/555 + ZZ/564
Final Report
PA». ETC?, Bibltøh.
Directorate-General XII N.c.om ^rc^
Science, Research and Development
1995 CI EUR 16672 Ehi
Aç\. «q LEGAL NOTICE
Neither the European Commission nor any person acting on
behalf of the Commission is responsible for the use which might be made of the
following information
Cataloguing data can be found at the end of this publication
Luxembourg: Office for Official Publications of the European Communities, 1995
ISBN 92-827-5636-X
© ECSC-EC-EAEC, Brussels • Luxembourg, 1995
Reproduction Is authorized, except for commercial purposes, provided the source is acknowledged
w Printed in Luxembourg FOREWORD
The European Commission has funded two studies on the effects of tramp elements on the
properties of flat products and long products in order to establish what information is
available; the results of these studies are reported in this present publication.
Scrap-based steel production is of growing importance and a steadily increasing range of
grades and products is envisaged.
It is generally agreed that continued recycling of scrap could result in an increase of residual
elements in the steels produced in the coming years.
Four industries and three research centres from seven European Countries participated in the
work. Industrial and environmental aspects are addressed in relation to the concept of
sustainable development. The scientific and technical challenge faced by the sector is
significant and is somewhat illustrated by the large number of research projects undertaken,
several of which have been or are being funded through the ECS C Research Programme
"Steel".
R Tomellini
DGXII. C. 2 "Materials and Steel "
III CONTENTS
PART I - REVIEW OF THE EFFECT OF TRAMP ELEMENTS ON
LONG PRODUCT PROPERTIES
1. INTRODUCTION 1
2. SUMMARY REPORT
2.1 Surface Defects
2.2 Metallurgical Structure 2
2.3 Engineering Steels 3
2.4 Structural Sections 4
APPENDIX I INFLUENCE OF TRAMP ELEMENTS ON SURFACE
DEFECTS OF LONG PRODUCTS 5
Al.l Introduction 6
A1.2 Defect mechanism
A1.3 Internal studies in SIDENOR 12
A1.4 Conclusions
REFERENCES3
LIST OF FIGURES5
APPENDIX n INFLUENCE OF TRAMP ELEMENTS ON
METALLURGICAL STRUCTURE 3
A2.1 Introduction 36
A2.2 Embrittling elements
A2.3 Elements which enhance embrittlement
A2.4s which reducet7
A2.5 Critical residual level
A2.6 Steel microstructure 3
A2.7 Segregation8
A2.8 Conclusions9
REFERENCES
IV APPENDIX Ett THE EFFECT OF RESIDUALS ON ENGINEERING
AND WIRE ROD STEELS 51
A3.1 Introduction 52
A3.2 Mechanical properties
A3.3 Temper embrittlement3
A3.4 Machinability
A3.5 Hardenability4
A3.6 Surface hot shortness
A3.7 Decarburization 55
A3.8 Descalability
A3.9 Drawability
A3.10 Fonnability 56
A3.11 Heat treatment
A3.12 Conclusions6
REFERENCES7
APPENDIX IV INFLUENCE OF TRAMP ELEMENTS ON THE
PROPERTIES OF STRUCTURAL SECTIONS AND THEIR
WELDABILTTY 61
A4.1 Introduction and definition of tramp elements2
A4.2 Steel grades
A4.3 Effects of tramp elements on product quality
A4.4s of elements in structural steels3
A4.5 Tramp elements and the welding operation4
A4.6 Effects of copper on weldability5
A4.7 Effect of other residual elements on weldability 6
A4.8 Conclusion 66
REFERENCES
V PART H - TRAMP ELEMENTS IN FLAT PRODUCTS
1. INTRODUCTION 75
2. DISCUSSION6
2.1 About surface defects of flat products 7
2.2t interface segregation of tramp elements and end user's properties . 78
2.3 About the influence of tramp elements on weldability 82
2.4 Actual levels of tramp elements in steel 84
2.5 Anticipated nitrogen levels for EAF steels
3. CONCLUSIONS AND RECOMMENDATIONS7
APPENDIX I THE INFLUENCE OF TRAMP ELEMENTS ON
SURFACE DEFECTS OF FLAT PRODUCTS 89
APPENDIX II INTERFACIAL SEGREGATION OF Sn AND Sb,
INFLUENCES ON END USER'S PROPERTIES 95
1. Introduction 9
2. Interfacial segregation of Sn and Sb on and in iron and steels8
3. Effects of interfacial segregation of Sn and Sb on steel properties 101
4. Conclusions 104
REFERENCES6
FIGURES Ill
APPENDKm THE INFLUENCE OF TRAMP ELEMENTS
UPON THE WELDABILITY OF STRUCTURAL STEELS,
A LITERATURE SURVEY 121
1. Introduction 12
2. Steels of interest2
3. Basic aspects of a welding operation and links with the tramp elements .. 12
4. Analysis of the relevant data6
5. Conclusions and guidelines for a future research
work9
TABLES 130
LITERATURE8
FIGURES 143
APPENDIX IV ACTUAL LE VELS IN TRAMP ELEMENTS AND IN
NITROGEN OBTAINED BY EAF STEELMAKING 15
REFERENCES 15
FIGURE 160
VI REVIEW OF THE EFFECT OF TRAMP ELEMENTS ON LONG PRODUCT PROPERTIES
1. INTRODUCTION
It is anticipated that in the future there will be an increased usage of low grade scrap in steelmaking. This
situation arises due to the increase in steel production by the electric arc furnace route which uses greater
amounts of scrap and from environmental issues leading to legislation which will require more recycling of
all materials including steel based.
It is of concern to steelmakers (both EAF and BOS) that increased levels of tramp elements could cause a
deterioration in surface quality and mechanical properties of certain steel grades. The tramp elements
which tend to remain as residuals in steel and thus potentially cause problems are copper, nickel, cobalt,
antimony, arsenic, tungsten, molybdenum, tin and chromium, although it should be noted that some of
these elements can be added deliberately to specific grades.
There is a need to quantify the deterious effects of tramp elements on various steel grades so that if
necessary, steps can be taken within the recycling strategy to limit these effects when they arise. A
multinational Mega project has started which includes a study of tramp elements on properties and in
support of this project a review of relevant published and unpublished data was planned. The present
report presents the results of a review dealing with long products and complements one on flat products
co-ordinated by CRM.
The study has been divided into four tasks shared by Acenor, British Steel and Arbed.
1. Influence of tramp elements on surface defects.
2.e of tramp elements on metallurgical structure (segregation, grain boundaries,
precipitation, etc).
3. Influence of tramp elements on end user properties for engineering steels including free
cutting, alloy steels and wire rod.
4.e of tramp elements on properties of structural beams, rails etc including weldability.
These reports appear as Appendices 1 to 4 in this document.
The following brief report summarises the main details contained in the appendices.
2. SUMMARY REPORT
2.1 Surface Defects
Copper is the key element related to surface defects. Copper enrichment occurs due to surface scaling and
above a certain temperature forms a liquid phase which causes surface cracking (hot shortness). This
liquid phase is formed when the solubility limit of Cu in austenite is exceeded.
2.1.1 The Effect of Various Elements in Copper Cracking
There is evidence that during oxidation of the surface S is associated with Cu and therefore at least some of
the enriched Cu may be rendered harmless by the formation of cuprous sulphide.
An addition of Ni at a Ni:Cu ratio of 2:1 is generally considered to guarantee freedom from surface
cracking due to Cu. In practice ratios of 1:1 have been found to prevent hot shortness but the critical ratio
is dependent on reheating temperature. The normal explanation for this beneficial effect of Ni is that it
increases the solubility of Cu in austenite. Sn has a powerful detrimental effect on surface cracking by Cu which has been explained by its lowering of
Cu solubility in austenite by a factor up to three. Only small amounts of Sn are required to exert a major
influence e.g. the addition of 0.05% Sn to a steel containing 0.22% Cu had a marked effect on the cracking
index of this steel which did not exhibit cracking in the absence of Sn.
Sb could potentially be a problem since it has a similar effect to Sn on Cu solubility in austenite.
As has a small beneficial effect and in this context is not considered as a harmful tramp element.
2.1.2 Heating Conditions
Residual element enrichment depends on the balance between build-up due to oxidation and diffusion back
into the parent steel. Since increased temperature affects diffusion rate more than scaling rate high
soaking temperature is probably beneficial in reducing Cu build-up.
Another potential way of removing the Cu-rich phase is by occlusion in the scale followed by descaling.
Increased furnace temperature and oxygen content aid oxidation and removal of Cu by occlusion. The
oxygen content at which peak cracking occurs tends to be lower the higher the temperature.
Water vapour in the furnace atmosphere increases the oxidation rate without promoting occlusion and
thus the water content of thee should be reduced to minimise cracking.
2.1.3 Combined Effects
Heating at around 1100°C optimises Cu enrichment but if the steel contains less than about 0.2% Cu with
no other significant amounts of residuals present no cracking will occur.
A number of formulae have been suggested to obtain a 'Cu equivalent' from the combined effects of Cu and
other elements. It is proposed that a suitable Cu equivalent is Cu +10 Sb+5 Sn+2 As - Ni.
2.2 Metallurgical Structure
Of particular concern is the segregation of tramp elements to the grain boundaries of low alloy steels
which, under certain heat treatment conditions, causes severe embrittlement. Such grain boundary
embrittlement affects properties such as stress corrosion cracking, hydrogen embrittlement, creep
rupture, stress relief cracking and fatigue crack growth at high temperature.
2.2.1 Embrittling Elements
Embrittlement occurs by Bi, S, Sb, Se, Sn, Te, As, Ge, P and Si and is related to the amount of element
segregated to the grain boundaries. This in turn is inversely related to the solubility limit in Fe. Grain
boundary enrichment is much higher in alloy steels than in Fe by an order to magnitude and therefore
they are much more likely to be embrittled than plain C steels.
2.2.2 Elements which Enhance Embrittlement
Significant grain boundary embrittlement will only occur in the presence of certain alloying elements Ni,
Cr or Mn and these must be at a level greater than 1%. This has been explained by an attractive
interaction between the residual element and the alloying element leading to co-segregation. Both P and
Sb interact more strongly with Ni than with Mn or Cr.
2.2.3 Elements Which Reduce Embrittlement
Theoretically by replacing the embrittling elements in the grain boundary by elements with a relatively
small atom size it should be possible to improve properties. Although this can occur to a limited extent it is
not a practical solution.