Quenching and Carburising - Proceedings of the Third International Seminar of the International Federation for Heat Treatment and Surface Engineering

317 Pages·1993·17.204 MB·317\317

by  Hodgeson, P. (Eds.)

QUENCHING
AND
CARBURISING
Proceedings ofthe Third International Seminar ofthe
International Federation for Heat Treatment
and Surface Engineering
Held in conjunction with the Annual Conference of
The Institute ofMetals and Materials Australasia
(The Materials Society ofIEAust)
THE INSTITUTE OF MATERIALS
Book 566
Published 1993by
The Instituteof Materials
ICarltonHouseTerrace
London SWIY 5DB
©The InstituteofMaterials 1993
Producedunderthe auspices of
The InternationalFederationfor HeatTreatment
and Surface Engineering
BritishLibraryCataloguinginPublicationData
Quenching and Carburising: Proceedings of
the 3rd International Seminar ofthe
InternationalFederationfor Heat
Treatment(Melbourne, 1991)
620.1121
ISBN 0-901716-51-0
Typeset inGreat Britain by
AldenMultimediaLtd, Northampton
PrintedinGreat Britain by
The Alden Press, OsneyMead, Oxford
Introduction
Quenching and Carburising are two ofthe most basic and widelypractised steel
heat treatmentprocesses. Each allowsthe base propertiesand performanceofthe
steel to be significantly enhanced, such that a relatively inexpensive and simple
starting material can be used for a wide range of demanding applications.
Nevertheless, thetechnologicaldevelopmentswithinthose twoprocessesare often
ignored in favour of'high tech' surface treatments.
The aim of QuenchingandCarburisingwas to reviewthe recent advancements
thathave beenmade in thesefields.Theconferencewasthe thirdbiennial seminar
of the International Federation for Heat Treatment and Surface Engineering
(IFHT) and aptly formed the centrepiece ofthe InstituteofMetals and Materials
Australasia's(IMMA)annualconference, MaterialsProcessingandPerformance.
The sessions devoted to quenching covered a range of topics from the
measurement of quench intensity, through to applications within the heat
treatment industry and the steel processing industry. The current status ofthe
application and scienceofquenching was reviewed by Professor Liscicfrom the
University of Zagreb. Contributed papers covered developments in the use of
fluidisedbedfurnaces, helium quenchinginvacuumfurnaces and theenvironmen
tal issues associated with the disposal of quenching media.
Aswithmost industrialprocessesthereisnowastrongneedforaccuratemodels
ofthequenchingprocess, and anumberofexamplesweregiven:quenchingofhigh
carbonsteels,wherethe roleofresidual stressisimportant,airmistcooling during
continuous casting, spray cooling in heat treatment and after hot rolling and gas
quenchingwithhelium. Oneimportantfeature ofsuchmodellingisthe generation
ofaccuratedatain the laboratory, and then incorporatingdifferenceswhich exist
between controlled laboratory conditions and full-scale industrial plants. It is
also apparent there there is now a degree ofcommonality between conventional
heat treatment operationsutilising controlledcooling and modern inline thermo
mechanical processing routes where the properties are generated during the
shaping ofthe final product.
Carburising currently receives less exposure in the recent technical literature
than quenching; largely because it is now an established and widely practiced
technique for surface engineering. However, there are still a number of issues
which need to be addressed, and these werecovered in the two reviewpapers by
Professors G. Krauss (Colorado School of Mines) and J. Grosch (Technical
University of Berlin), with particular emphasis on the microstructures and
toughness of the carburised steels. The contributed papers cover modelling,
mechanical properties and industrial carburising processes.
viii Introduction
Overall the conference demonstrated that there is a great deal ofknowledge
regarding many aspectsofQuenchingandCarburising, and thatthe challengeisto
apply this knowledge to control the process, and reduce the product variability.
Steel is now a highly engineered material, which is still developing improved
properties at lower cost to the user. To this end it is hoped that the material
contained within this volume will enhance the application of these engineering
processes throughout the heat treatment and thermomechanical processing
industries.
The success of the conference was largely due to a small group of highly
enthusiastichardworkingpeople, most notably BruceHinton(DSTO-ARL), Bill
Sinclair(BHP Research) and the staffofthe IMMAoffice,particularlyMargaret
Kirk and Angela Krepcik. Great support was also provided by members of the
IFHT,and particularthanksisexpressedto ProfessorT. Bell,ProfessorB. Liscic
and DrJ. Naylor for their assistance during the conference organisation.
Finally, Iwouldliketothanktheauthors,many ofwhomventureddown-under
for the first time, who provided us all with the opportunity to learn, discuss and
benefit from their experiences in heat treatment research and industrial appli
cation. They have helped create a volume which, it ishoped, willservefor many
years as an important reference for those either working in the heat treatment
industry, or teaching these subjects.
Peter D. Hodgson
BHP Research - Melbourne Laboratories
Mulgrave, Victoria, Australia.
Conference Chairman
Contents
Introduction
P.D. HODGSON vii
State ofthe art in quenching 1
B. LISCIC
2 Measurement andevaluation ofthe quenching power ofquenching
media for hardening 33
J. BODIN AND S. SEGERBERG
3 Quench severity effectson the properties of selected steel alloys 55
CHARLES E. BATES,GEORGE E. TOTTEN AND KIMBERLEYB. ORSZAK
4 Use and disposal ofquenching media. Recent developments with
respect to environmental regulations 71
E.H. BURGDORF
5 Use offluidised beds for quenching in the heat treatmentfield 85
RAY W. REYNOLDSON
6 Gas quenching with helium in vacuum furnaces 107
BENOIT LHOTE AND OLIVIER DELCOURT
7 Residual stress in quenched spheres 119
D.W. BORLAND AND B.-A. HUGAAS
8 Computer simulation ofresidual stresses during quenching 127
A.K. HELLIER, M.B. MCGIRR, S.H. ALGER AND M. STEFULJI
9 A mathematical model to simulatethe thermomechanical processing
ofsteel 139
P.D. HODGSON, K.M. BROWNE, D.C. COLLINSON, T.T. PHAM AND
R.K. GIBBS
10 Measurement and characterisation of air-mist nozzles for spray
quenching heat transfer 161
M.S. JENKINS, S.R. STORY AND R.H. DAVIES
11 Investigation ofquenchingconditions and heat transfer in the
laboratory and in industry 177
s.
SEGERBERG AND J. BODIN
VI Contents
12 The design and performance ofa laboratory spray cooling unit to
simulate in-line heat treatment ofsteel 189
R.E. GLOSS, R.K. GIBBS AND P.D. HODGSON
13 Microstructure, residual stresses and fatigue ofcarburised steels 205
G. KRAUSS
14 Fundamentals ofcarburising and toughness of carburised
components 227
J. GROSCH
15 Martempering and austempering ofsteel and cast iron 251
GEORG WAHL
16 Property prediction of quenched and case hardened steelsusing a PC 267
T. RET!, M. GERGELY AND C.C. SZILVASSY
17 Effectofcarburising on mechanical properties ofsteels 281
NORIO KANETAKE
18 Heat treatment with industrial gases- Linde Carbocat and
Carboquick processes 293
ABDUL KAWSER
Index 305
1
State of the Art in Quenching
B. LISCH:
Facultyof MechanicalEngineeringandNaval Architecture, UniversityofZagreb
ABSTRACT
A survey ofactual methods (based on direct temperature measurement) for quenching
intensityevaluationinlaboratoryconditionsaswellasinworkshoppracticeisgiven,and
commented,especiallyinrelationtopossiblepredictionofmetallurgicaltransformations
and hardnessdistribution on the cross-sectionofreal workpieces.
Apart from the widely used immersion quenching technique, the fundamental and
latest developments of other quenching techniques such as spray quenching, gas
quenching in vacuum furnaces and hot salt bath quenching are briefly described.
Informationabout 'intensivequenching' isgiven, and the prospects offurther develop
ments in the fieldofquenchingoutlined.
1 INTRODUCTION
Quenching has a historical background centuries old, and has always played an
importantrolein the manufactureofmetallic products. Certainly,the technology
ofquenchinghas changedaswellas the kindofworkpiecesbeingquenched:from
axes and swords to gears and automotive components and, as the latest
development, to a gas turbine blade that has been quenched in a hot isostatic
pressing (HIP) quenching unitin argon under 2000barsofpressure.\Even more
important is the fact that simultaneously quenching has changed from an
empirical skill to a scientifically founded and controlled process which now
belongsto thearea of'intelligentprocessing'of'materials.lThisisthegoaltowhich
wearestriving, andhopefullybythebeginningofanewmilleniumwewillbemuch
closertoitthanwearetoday,because inpresentworkshoppracticewestillhaveto
rely on practicalexperience.
Fora long periodin the recent historyofquenching, besideswater, oilwas the
main quenching medium. Correspondingly, manufacturers and suppliers of
quenching oils have played the main role in the development of quenching
technology and related testing methods and specifications.
Nowadays the assortment of quenchants in use ismuch broader. There are at
least seven groups of quenching media having different chemical and physical
2 Quenching and Carburising
propertiesand, ofcourse, different quenchingintensities. They are (indescending
order ofquenching intensities):
• Water solutions ofinorganic substances.
• Plainwater.
• Polymer solutions in water.
• Quenching oils of different grades.
• Hot salt baths.
• Fluidised beds.
• Pressurised and circulated gases (N2, He, Ar).
In spray quenching techniques water, water-oil emulsions, polymer solutions in
water or water-air mixtures are used.
One has to take into account that with each of above mentioned groups of
quenchants verymanydifferent quenchingintensitiescan be realised. On the one
hand this is due to different substances and their concentration, and to different
quenching parameters (bath temperature, agitation rate, pressure) on the other.
This situationcallsfor a universallyapplicablemethodfor testing andevaluation
of quenching intensity and makes the selection of optimum quenchant and
quenching conditions both from the technological and economical point ofview
an important consideration.
Followingmodernproductionconceptssuchas'justintimemanufacturing'and
'total quality control', when reproducibility of results becomes necessary, heat
treatment processes and relevant equipment have become fully automated and
CNC controlled. Ofall heat treatment operations quenching (especially immer
sion quenching) is still the least controlled. Even in a fully automated and CNC
controlled sealed batch furnace, where temperature-time cycles as well as the
atmosphere can be automatically changed according to the requirements at the
time, quenching intensity depends on the quenchant and quenching conditions
selectedand nothingmuch can bedone duringquenchingtochangethe quenching
intensity in order to obtain optimum structures, hardness and residual stresses.
This is unfortunately so, because with immersion quenching the only quenching
parameterwhichcan bechangedinthecourseofquenchingisthe rate ofagitation
ofthe quenchant. This possibility is also limited to workpieces ofbigger cross
sections (where the quenchingitselflastslonger), andcallsfor an adequatesensor
which will automatically change the speed ofthe agitation pump exactly at the
momentwhen acertaintemperaturehas been reached at the relevant pointin the
cross-section of the workpieces treated. The best possible conditions for a fully
automated CNC control of the quenching intensity exist with water-air spray
quenching.'
In order to predict the microstructure, the distribution of hardness (strength)
andresidualstressesafterquenchingaswellas to optimisethe hardeningprocess,
computer modelling is performed. The benefits of such optimised production
process are as follows:"
- Reducing scrap or rework rate.
State ofthe Art in Quenching 3
- Reducing trial and errorin developing process parameters for new parts.
- Allowing tightertolerancesto beachievedviabettercontroloftheheat-treating
process.
The mostcritical informationrelatingto the hardeningprocess isthe rate ofheat
transferfrom the workpiece to the quenching medium.
2 IMMERSION QUENCHING
Although quenching techniques, especially in recent decades, have become more
and more diversified, immersion quenching stillconstitutes the largestpart ofall
quenching processes.
Immersionquenchingismostly performedinevaporablequenchantslikeoilsor
water solutions, exhibitingthe three knownstages ofcooling, i.e.vapourblanket
stage, boiling stage and convection stage. It is a non-stationary heat transfer
process thatcan be described using the following equation, the left sideofwhich
being Fourier's differential equation givingthe heatflowfrom the interiorto the
surface oftheworkpiece, whiletheright sideisNewton'sequationforheattransfer
from the workpiece surface to the ambience:
aT
q = - A.-a= oc (TN - Tamb) (1)
XN
where:
q= heat fluxdensity, W m-2
A.=thermalconductivity within the workpiece, W/mK,
aT
a = temperature gradient normal to the surface of the workpiece, Kjm,
XN
oc=interfacial heat transfer coefficient,W m-2 K,
TN= surface temperature ofthe workpiece, K,
Tamb= ambienttemperature,i.e.temperatureofthequenchant,K.
Inthe caseofquenchingrealpartsthere aremanyfactorswhichinfluencethisheat
transfer/metallurgical transformation process:
(a) Factors depending on the workpieceitself:
alloy grade (transformation characteristics);
mass ofthe workpiece (sizeof the critical cross-section);
geometry (volume/surface ratio);
surface roughness andcondition;
load arrangement and density.*
(b) Quenchant characteristics:
density (molecular weight);
viscosity;
specificheat;
thermal conductivity ofthe fluid;
boiling temperature;
4 Quenching and Carburising
Leidenfrost-temperature (transition temperature between the vapour
blanket and the boiling stage);
wetting property ofthe liquid.
(c) Factors depending on quenching facility:
Bath temperature;*
Agitation rate;*
Flow direction;
Concentration of the solution (ifapplicable).*
Of all these influencing factors listed, only a few can be changed in the heat
treatment shop. They are marked with a * and are usually called technological
parameters of quenching.
Takinginto account the simultaneous influence ofso many factors during the
quenching process, one logically wants to know what 'cooling power' or
'quenching intensity' will result in each specific case. There are actually three
different reasonswhywewantto have aspreciseandcompleteinformationofthe
quenchingintensity, as possible, namely:
I. Checking the specific characteristics of the quenchant (e.g. for mutual
comparison, monitoring ofdeterioration or development ofnew grades of
quenchants).
II. Selectionofoptimumquenchantand technologicalquenchingparametersfor
the specifiedalloy and workpieces.
III. Computer modelling ofresulting properties.
On the other hand many methods exist for measuring and evaluatingquenching
intensityandonehas to know whichmethodshouldbeappliedinthecasesofI,II
or III.
The IFHT Committee on Scientificand Technological Aspects of Quenching,
established in 1978, has, from its very beginning, distinguished between a
laboratory methodfor testingofthe coolingpower ofa quenchingmedium, anda
practical method for the measurement ofthe quenching intensity in the quench
tank, assuming that laboratory testing is carried out in a small quantity of
quenchingmediumwithoutagitation, whilepracticaltestinginvolves all relevant
technological parameters.
2.1 EVALUATION OF THE QUENCHING INTENSITY BY COOLING
CURVES
Ofallmethodsfor testingquenchingintensity,thosemeasuringthetemperatureas
afunction of time (cooling curve) at a specifiedpointwithin the test specimen are
mostly used. It seems also to be generally accepted to use test specimens of
cylindrical shape, but unfortunately there is no general agreement as yet on
specimen size, material and position of the thermocouple tip. In order to
standardizeworld-widethe laboratory methodfor testing ofindustrial quenching
oilsthe IFHT Committee on Scientificand Technological Aspects ofQuenching