Astm stp 1419 2002

STP 1419

Bearing Steel Technology

John M. Beswick, editor

ASTM Stock Number: STP1419

ASTM

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Library of Congress Cataloging-in-Publication Data

Bearing steel technology / John M. Beswick, editor.

p. cm.

"ASTM Stock Number: STP1419"

Includes bibliographical reference and index.

ISBN 0-8031-2894-0

1. Steel, Bearing-Congresses. I. Beswick, John M., 1945-

TA472 .B33 2002

672-dc21 2002071729

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Printed in Philadelphia, PA

July 2002

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Foreword

This publication, Bearing Steel Technology, contains papers presented at the symposium of the

same name held in Phoenix, AZ., on 8-10 May 2001. The symposium was sponsored by ASTM

International Committee At on Steel, Stainless Steel, and Related Alloys and its Subcommittee

A1.28 on Bearing Steels. The Symposium chairman was John M. Beswick, SKF Group Purchasing,

Engineering and Research Centre, B. V., Nieuwegein, The Netherlands.

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Contents

Overview vii

BEARING STEEL PROCESS DEVELOPMENTS

Development of 5280 Rolling Bearing Steel for Improved Performance

and Productivity--P. v. DIMITRY, P. M. MACDONOUGH, G. BECK, R. EBERHARD,

AND H.-W. ZOCK 3

Effect of Steel Making and Processing Parameters on Carbide Banding in

Commercially Produced ASTM A-295 52100 Bearing SteelhP. K. ADISHESHA 27

Ultra Clean Steel for Anti-Frictlon Bearing Applications--s. GANGULY,

I, CHAKRABARTI, M. D. MAHESHWARI, AND T. MUKHERJEE 47

STEEL TECHNOLOGY AND BEARING COMPONENT MANUFACTURE

Machinability ControI-A Topic of Great Importance to the Engineering Industry--

T. JOHANSSON AND H. SANDQVIST 71

Environmentally Friendly Bearing Steel With Reduced Hardening Distortlon--

T. B. LUND AND L. ]. PATRIK C)LUND 86

DEVELOPMENTS IN BEARING STEEL QUALITY ASSESSMENT AND CORRELATIONS WITH BEARING LIFE

Appropriate Techniques for Internal Cleanliness Assessment---G. AUCLAIR

AND P. DAGUIER I01

Influence of Hydrogen Trapped by Inclusions on Fatigue Strength of Bearing Steelh

Y. MURAKAMI AND N. N. YOKOYAMA 113

Statistical Prediction of the Maximum Inclusion Size in Bearing Steels---

G. SHI, H. v. ATKINSON, C. M. SELLARS, C. W. ANDERSON, AND L R. YATES 125

Steel Supplier Evaluation Techniques to Assure Bearing Performance--j. o. WOLFE 138

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vi CONTENTS

Study of Evaluating Method for Non-Metallic Inclusions and Development of Slag

Refining for Bearing Steel--T. NISHIKAWA, H. NAGAYAMA, S. NISHIMON, K. ASAI,

I. FUJII, AND T. SUGIMOTO

Higher Macro-Cleanliness of Bearing Steels Needs More Accurate

Measuring-Methods---D. THIERY AND C. DELHAES

Recent Evaluation Procedures of Nonmetallic Inclnsions in Bearing Steels (Statistics

of Extreme Value Method and Development of Higher Frequency Ultrasonic

Testing Method)---Y. KATO, K. SATO, K. HIRAOKA, AND Y. NURI

148

164

176

DEVELOPMENTS IN BEARING SERVICE LIFE TESTING

A New Physically Based Model for Predicting the Fatigue Life Distribution of Rolling

Bearings--R. FOUGI~RES, G. LORMAND, A. VINCENT, D. NELIAS, G. DUDRAGNE,

D. G1RODIN, G. BAUDRY, AND P. DAGUIER 197

Estimation of Rolling Bearing Life Under Contaminated Lubrication---

H. TANAKA AND N. TSUSHIMA 213

Rolling Contact Fatigue Under Water-Inf'dtrated Lubrication--v. MATSUMOTO,

Y. ~, AND M. OOHORI 226

Microstructural Optimisation of Bearing Steels for Operation Under Contaminated

Lubrication by Using the Experimental Method of Dented Surfaces--

H.-J. BOI.-IMER AND R. EBERHARD 244

Rolling Contact Fatigue Tests to Investigate Surface Initiated Damage and

Tolerance to Surface Dents--D. GIRODIN, F. VILLE, R. GUERS, AND G. DUDRAGNE 263

BEARING METALLURGY DEVELOPMENTS FOR IMPROVED SERV1CE LIFE

Development of Long Life Rolling Bearings for Use in the Extreme Conditions--

M. SHIBATA, M. GOTO, A. OHTA, AND K. TODA

The Effect of V, Ai and N on the Fatigue Life of a Carbonitrided Bearings---

S. J. YOO, S. W. CHOI, S. K. HAN, J. S. LEE, B. J. JUNG, B. H. SONG, AND C. N. PARK

Development of a New Material for Guide Roll Bearings for Continuous Casting

Machine---K. YAMAMURA AND M. OOHORI

Improved Bearing Steel for Applications Involving Debris, Higher Loads and

Temperatures--P. DAGUIER, G. BAUDRY, J. BELLUS, G. AUCLAIR, J. ROFI~S-VERNIS,

G. DUDRAGNE, D. GIRODIN, AND G. JACOB

The Effect of Bearing Steel Composition and Microstructure on Debris Dented

Rolling Element Bearing Performance--D. CARLSON, R. PITSKO, A. J. CHIDESTER,

AND J. R. IMUNDO

285

297

309

320

330

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CONTENTS vii

DEVELOPMENTS IN HIGH ALLOY STEEL FOR IMPROVED HIGH TEMPERATURE AND ENHANCED

CORROSION RESISTANCE PROPERTIES

Wear and Corrosion Resistant PM Tool Steels for Advanced Bearing Applieation--

A. KAJINIC, R. B. DIXON, AND B. A. HANN

A Comparison of the Mechanical and Physical Properties of Contemporary

and New Alloys for Aerospace Bearing Applications--M. A. RAGEN,

D. L. ANTHONY, AND R. F. SPITZER

Progress in the Evaluation of CSS-42LTM: A High Performance Bearing Alloy--

C. M. TOMASELLO, H. 1. BURRER, R. A. KNEPPER, S. BALLIETT, AND J. L. MALONEY

Duplex Hardening for Aerospace Bearing Steels--E. STREIT AND W. TROJAFIN

Carburizable High Speed Steel Alioys---D. W. HETZNER

The Development of Bearing Steels with Long Life and High Corrosion

Resistance--s. TANAKA, K. YAMAMURA, AND M. OOHORI

349

362

375

386

399

414

MICROSTRUCTURAL CHANGE AND ITS RELATIONSHIP WITH BEARING FATIGUE AND

LWE TIME PREDICTION

Local Elasto-Plastic Properties of Bearing Steels Determined by Nano-Indentation

Measurements--A. VINCENT, H. ELGHAZAL, G. LORMAND, A. HAMEL,

AND D. GIRODIN

Microstructural Stability and Bearing Performance---A. P. VOSKAMP

427

443

MATERIAL FACTORS IN BEARING LIFE CALCULATIONS

A Physically Based Endurance Limit Model for Through Hardened and Surface

Hardened Bearing Steels---A. VINCENT, R. FOUGI~RES, G. LORMAND, G. DUDRAGNE,

AND D. GIRODIN

Fatigue Limit Stress--A New and Superior Criterion for Life Rating of Rolling

Bearing Materials--T. A. HARRIS

Application of a New Physically Based Model to Determine the Influence

of Inclusion Population and Loading Conditions on the Distribution

of Bearing Lives--G. LORMAND, D. PIOT, A. VINCENT, G. BAUDRY, P. DAGUIER,

D. GIRODIN, AND G. DUDRAGNE

Rolling Bearing Material Quality Fatigue Testing--Material Quality Life Factors--

A. GABELLI, S. IOANNIDES, J. BESWICK, G. DE WIT, H. KROCK, B. KORENHOF,

AND A. KERRIGAN

Author Index

Subject Index

459

474

493

509

527

529

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Overview

This ASTM International Special Technical Publication represents the work of numerous rolling

bearing experts who presented papers at the 6 th International Symposium on Bearing Steels, held in

Phoenix, 8-10 May, 2001. The almost traditional five-yearly cycle for the ASTM International bearing steel symposia resulted in the Phoenix location being selected for the thir d time in association

with the ASTM International A1 committee week and the A1.28 subcommittee for beating steel

meetings. The remit for the subcommittee A1.28 on bearing steels is to have jurisdiction over the

standards for steels commonly used for ball and roller bearings. This subcommittee is responsible for

preparing, reviewing and maintaining these standards and assuring that they reflect current technology. Currently the A1.28 subcommittee is faced with many challenges, not the least of which is to

keep the ASTM International specifications aligned with steel making processes changes. In addition,

vindication of the current specifications in light of the economic pressure within the industry is an increasing requirement. It is generally recognized that many of the steel quality assessment methods

and related specification limits, used within the industry, were developed for steel making methods,

either obsolete or inappropriate to current methods or product functional requirements. Resistance to

change is always present and product liability considerations, together with the related risk of litigation, place a high burden material, on engineers responsible for major specification changes.

However the preparation and application of state-of-the-art, ASTM International bearing steel assessment methods and related acceptance limits (specifications) provides a professional forum for the

introduction of progressive changes. Cross border joint-ventures or mergers are becoming increasingly common, within the rolling bearing industry, which adds to the requirement for up to date, state

of the art bearing steel specifications.

The rolling beating industry is truly global and bearing steels and rolling bearings are manufactured, and, or assembled in all industrialized countries. Some of the largest bearing steel producers

have manufacturing facilities in more than one country and all of the largest rolling bearing producers have manufacturing plants located world-wide. The rolling bearing industry statistics are:

9 Rolling bearings are a 20 billion U.S. dollar global business and rolling bearings are produced in

17 countries

9 Approximately 500 rolling bearings are produced, per second, by about 30 manufactures

9 More than 55 steel producers manufacture bearing steels

9 In the Year 2000, 2.6 million tons of 1C-1.5Cr bearing steel was produced which represents

about 0.5% of current global steel production

9 Currently 37 different bearing steels are specified by ASTM International

The rolling bearing industry is characterized as investment intensive with a relatively low return on

capital employed. In addition, the industry is highly competitive with, as previously shown, in excess

of 55 beating steel producers, about the same number of component producers and about 30 rolling

bearing manufactures.

The economic use of materials and heat treatments can be identified as a key success factor for

profitable rolling bearing manufacture. It therefore is appropriate to pursue an ASTM International

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X OVERVIEW

symposium in which the state-of-the-art in bearing steel technology is reviewed. Such a review can

provide a platform'for the bearing steel purchasers and bearing users to analyze beating industry

trends and develop economic acquisition strategies.

A committee comprising representatives from bearing steel makers, "commercial" bearing manufacturers, aerospace bearing manufacturers, and the ASTM International symposium operations staff

organized the 6 th International Symposium on Bearing Steels, and the members of organization committee were as follows:

John Beswick,

Dorothy Fitzpatrick

James Carosiello

Jeff Fuller,

Ronald Spitzer

Paul Dimitry

SKF Group Purchasing, Nieuwegein, The Netherlands

ASTM, Conshohocken, PA

The Timken Company, Canton, OH

Brenco, Petersburg, VA

MRC Bearings, Jamestown, NY

Macsteel, Jacksson, MI

This symposium, being the 6 tb in the series, was significant in that it enjoyed the best ever attendance and attracted 190 attendees from eleven nations. In addition, the event enjoyed a significant

level of sponsorship from the following companies:

Aichi Steel Company MRC Beatings Saarstahl

Ascometal-Lucchini Group Nedstaal B.V. SKF AB

Aubert & Duval Nippon Steel Corporation SNR Roulements

Brenco NSK Ltd The Timken Company

Crucible Compaction NTN Corporation Timken Latrobe

FAG Ovako Steel The Torrington Company

Macsteel Sanyo Special Steel VSG

The global nature of the industry attracted 42 presentations at the symposium and the symposium

program was divided into the nine technical sessions over three days, The presenters had the following affiliations:

9 Rolling bearing producers 17

9 Bearing steel producers 15

9 University and R&D institutes 8

9 Rolling bearing ulcers 2

The broad goal of the symposium, and this book, was, and is to bring clarity into what is important

in respect of rolling bearing steel technologies and the relevant disciplines are described in nine sections in this book. The 34 papers that were accepted for publication have been peer reviewed by 46

rolling bearing technology practitioners from 8 nationalities.

Bearing Steel Process Developments

In this section the global bearing steel making technologies were reviewed, at the symposium, and

bearing steel purchasers find the potential price reduction due to the use of billet casting, of rolling

beating steels, very attractive. The reduced cost in billet casting and/or "hot charging" is primary due

to the elimination of the rolling operations and/or reduction of the post casting thermal treatments

such as the ingot or blooms "soak". In support of the technical information on this subject a paper was

given describing a billet casting friendly steel grade. Another paper provided hitherto never published

data on the relative segregation levels for ingot and continuously cast 1C-1.5Cr, bearing steel and the

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OVERVIEW xi

effect of steel making processing parameters and soaking practice on the bearing steel segregation

properties.

Steel Technology and Bearing Component Manufacture

For the first time at the ASTM International bearing steel symposia, a session was included on the

roiling bearing component manufacturing aspects of bearing steel technologies. In one paper, the

machinability parameters in bearing steels were reviewed and relevant testing methodologies described. In another paper, a modernistic steel technologies related to improved environmental aspects

of the hardening heat treatment process was described. It was generally agreed that future ASTM

International bearing steel symposia would benefit from having more papers on the bearing manufacturing aspects of bearing steel technologies.

Developments in Bearing Steel Quality Assessment and Correlation's with Bearing Life

The bearing steel industry is highly dependent upon the availability of clean steel making methods

and the related techniques to assess steel cleanliness were reviewed. The use of statistics of extreme

values (SEV) and a new method based on generalized Pareto distribution (GPD), when using optical

microscopy, were presented. These technologies are being accepted as relevant methods for the new

generation of rolling bearing steel specifications and the methods will be seriously considered in future ASTM International bearing steel specifications.

The attractiveness in the use of ultrasonic techniques, for internal cleanliness assessment, was covered in some papers. The use of an ultrasonic method was advocated at the first ASTM International

beating steel symposium in 1974, and it is significant that currently, all the top level bearing steel

technologists are now applying advanced ultrasonic testing competencies in support of their product

integrity guarantees.

Developments in Bearing Service Life Testing

Rolling bearing service life, as opposed to "pure" rolling contact fatigue life testing, was covered

in some papers. Rolling bearing life tests for improved service life under hard particle contaminant

in the lubricant, water ingress and dented raceways due to artificial indentations, were described. The

challenges and opportunities in effective integration of bearing metallurgy, tribology and mechanical

testing to perform meaningful service life tests were adequately demonstrated in these papers.

Bearing Metallurgy Developments for Improved Service Life

The technologies pertaining to new alloys, heat treatments and microstructure control for improved

served life and extreme conditions were described in a number of presentations at the symposium.

The use of steels alloyed with silicon to improve the service life, particularly for elevated temperature demanding applications, was a reoccurring theme in new roiling bearing steel developments.

Developments in High Alloy Steel for Improved High Temperature and Enhanced Corrosion

Resistance Properties

The rolling bearing industry, particularly aerospace, demands for high temperature and corrosion

resistance was addressed in some papers. The advantages of powder metallurgy for the creation of

microstructures, not possible by conventional melting, to give elevated wear and corrosion resistant

rolling bearing properties were presented. In addition, the relative properties of contemporary and

new alloys for aerospace, as well as carburized and nitrogen alloyed steels were covered.

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xii OVERVIEW

Microstructural Changes and its Relationships with Bearing Life and Life Time Predictions

The material physics aspects associated with the Hertzian contact cycle process in rolling bearing

contacts were presented in some papers at the symposium. The well known aspects of microstructure

change in the Herzian contact zones of rolling bearing was treated in one paper, presented at the symposium, using a thermo-mechanical response model for the prediction bearing rolling contact fatigue

life.

Material Factors in Bearing Life Calculations

Material factoring of rolling bearing life is known to be difficult, and at times emotive, when comparing different bearing steel and roiling bearing producer manufacturing philosophies. Eminent

North American and Western European workers in the field of rolling bearing life modeling presented

papers on the subject. The development of rolling bearing life endurance models were reviewed and

new physically based endurance limit model, for life estimates on surface and through hardened

rolling bearings were presented, as well as advanced testing and a modeling information on steel quality, life factors.

Bearing User Future Requirements

The future user requirements in respect of roiling bearing steel technologies were presented by representatives from prime user segments. The aerospace--aircraft engine rolling bearing steel requirements were reiterated as being improved service life for the rolling elements and cages in conditions

of corrosion and lubricant contaminate, as well as "slow and graceful spall propagation rates when

the bearing starts to faiL"

The high demands in the earthmoving industrial equipment, manufacturing segment were presented and the steel and rolling bearing technologist were challenged with an industry wish list of requirements for society and industry standards for basic parameters tests, and the ability to determine

value of the enhancement in specific applications, and the ability to quantitatively rate suppliers enhanced product against other suppliers' products.

In the relatively short time, which has elapsed between the symposium, and the publication of this

book, quite significant changes have occurred within the bearing steel and the rolling bearing manufacturing industries. The global economic down turn has necessitated cutbacks in the rolling bearing

steel technology budgets resulting in some producer R&D facilities being downsized. These changes

require increased diligence within the bearing steel technology fraternity in order to retain a competitive posture within the context of an ever increasingly price sensitive steel supply and bearing sales

markets.

The ASTM International standardization committees, together with the ASTM International symposium and publications staff, have an important role to play to sustain growth within the rolling bearing industry. The ASTM International symposia are a neutral forum to address the "added value" relationship in rolling bearing steel technologies. Bearing steel technologies and purchasing managers,

interested in utilizing the global bearing steel supply market opportunities, will benefit from a closer

look at the information and wisdom contained in this publication.

John M. Beswick

SKF Engineering & Research Centre B. V.

3430DT Nieuwegein, The Netherlands

Symposium Chairman and STP Editor

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Bearing Steel Process Developments

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P. V. Dimitry, l P. J. McDonough, l G. Beck, 2 R. Eberhard, 2 and H-W. Zock 3

Development of 5280 Rolling Bearing Steel for Improved Performance and

Productivity

Reference: Dimitry, P. V., McDonough, P. J., Beck, G., Eberhard, R., and H-W. Zock, "Development of

5280 Rolling Bearing Steel for Improved Performance and Productivity," Bearing Steel Technology,

ASTM STP 1419, J. M. Beswick, Ed., American Society for Testing and Materials International, West

Conshohocken, PA, 2002.

Abstract: A new optimized steel analysis has been developed m which the carbon and

chromium are reduced and the manganese increased to improve the solidification during

continuous easting. The aim of this new grade is a steel far more suitable for continuous casting

than 52100 (100Cr6).

The bearing steel 52100 (100Cr6) has a proven track record throughout the world as the

high carbon material of choice. With the increased production from the continuous casting

process and the efficieneies of direct rolling, in combination with higher stress conditions for

bearings, certain weaknesses have been recognized with the grade 52100 (100Cr6). Due to the

high productivity rates of modem continuous easters, the long homogenizing cycles to minimize

carbide segregation in 52100 are no longer practical. Without these long homogenizing cycles

the result is more pronounced forms of segregation and adverse carbide distributions. These

disadvantages can result in restricted mechanical and thermo-mechanieal physical properties

leading to difficulties m conventional and induction heat treatments.

The new grade under development can be classified 5280 (80CrMn4) and has been

evaluated from both the steel production aspects as well as metallurgical behavior. With regard

to the decisive properties ofmicrostructure, life and processing the 5280 (80CrMn4) was

equivalent to or better than the 52100 (100Cr6) steel. Continuous casting improved significantly;

porosity, cracks or cavities were not present. The carbon segregation index was reduced.

Carbide distributions measured according to SEP 1520 were at a minimum level, without

excessive soaking prior to direct rolling. Heat treatment response was slightly modified to lower

quenching temperatures, tempering at 220~ and 240~ resulted in the same values for hardness

and retained austenite as in the case of 52100 (100Cr6). After martensitic heat treatment the

hardness stabilization in 5280 (80CrMn4) required no process change from 52100 (100Cr6) to

achieve the same degree of stabilization.

Mechanical properties of tensile strength, impact bending and notch impact strength;

wear resistance and rotating bending strength were evaluated with direct comparisons to 52100

(100Cr6). Rolling contact fatigue tests were carried out on angular contact ball beatings of t3qoe

7205B where the inner rings were the test specimens. Test conditions were selected m such a

way that it would be possible to make comparisons with 52100 (100Cr6) under diverse t3qoes of

stress. The fatigue life of the 5280 (80CrMn4) was equivalent to the 52100 (100Cr6) base

data.

Keywords: through-hardening bearing steel, rolling contact fatigue, mechanical properties

1 Mgr. Technical Service and Product Development and Mgr. Quality Assurance and Metallurgy,

MACSTEEL |One Jackson Sq. #500, Jackson, M149201

2 Mgr. Laboratory and Research Engineer, FAG OEM land Handel AG, D-97419 Schweinfurt, Germany

3 Director Research, New Materials Bayreuth Inc.

Copyright9 by ASTM lntcrnational www.astm.org

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4 BEARING STEEL TECHNOLOGY

Introduction

The use of 52100 for high carbon bearing applications is the standard material by

which all other steel compositions are judged. In the production of high carbon steel with

modern continuous casting machines the main difficulties are low productivity, heavy

segregation and difficult processing. The aim of this project was to develop new rolling

bearing steel with equivalent or better properties than possible with 52100. The

introduction of 5280 is a significant steel composition to meet the bearing industry needs

while reducing the difficulty in continuous casting 52100.

Steel Production Efficiency

Improved Chemical Analysis

The basis for the new chemistry was to reduce carbon, increase the Mn:Si ratio

and lower the chromium content. The new chemistry must develop equivalent hardness

and hardenability, less carbide segregation, and rolling bearing performance

characteristics similar to 52100. The steel analysis to improve, among other factors, the

segregation susceptibility during solidification and therefore the properties is presented

below.

Chemical composition:

Carbon Manganese Silicon Chromium

0.78% 0.78% 0.24% 0.82%

Steelmaking/Manufacturing Properties

The new grade 5280 was evaluated for steelmaking and manufacturing properties.

Electric furnace melting and secondary refining operations improved with better control

of lower carbon and chromium. The 4:1 Mn/Si ratio for 5280 (vs. <2:1 for 52100) was

considered an improvement for continuous casting and slag control. Steel cleanliness

evaluations for microscopic and macroscopic were equivalent with 52100.

Continuous Casting Properties

This experimental material was rotary cast into a 205mm billet. The casting rate

for 5280 was increased by +15% compared to 52100, due to lower %C and %Cr contents.

Carbon segregation index was 1.13 max. and no porosity was observed.

Rolling Mill Properties

The experimental billets were direct charged from the rotary continuous caster at

95013(3 into a gas fired furnace, held 45 minutes and direct rolled into 55ram bars

having a reduction ratio of about 14:1. Steel grade 52100 is rarely direct rolled.

Generally a long heating cycle is required to allow soaking time at temperature for carbon

diffusion. Thus primary carbides can breakdown into diffused carbides that slowly begin

to fade into a homogenous structure. Soaking times can be as long as 24 hours and

higher soaking temperatures, to reduce diffusion time, can lead to melting of primary

carbides resulting in porosity. Decarburization is a further negative from this practice of

long heating time prior to rolling. The experience with 5280 was to direct charge and roll

within one hour to final dimension with 0.47mm decarburization.

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DIMITRY ET AL. ON 5280 ROLLING BEARING STEEL 5

Comparative Study 5280 to 52100

Metallurgical Test Results

The following material inspections were performed on 12 bars randomly selected

from a 50 ton heat of 5280, produced by EAF melting, ladle refining, vacuum degassing,

rotary continuous casting, and directly charged and rolled to 55 mm by 6400 mm long

bar. The microscopic cleanliness of the heat was (acc. to DIN 50602) K1 = 1.6 and there

were no internal defects such as cavities, pores or cracks.

The blue fracture test on 12 coupons revealed 2 defects of 0.7rnm and 0.1mm length by

20 ~tm in width. The limiting value of 2.5 mm/dm 2 was observed.

The carbide formation (acc. To SEP 1520) is 5.1, 6.0 and 7.1 at a maximum value.

Figure 1 shows comparative photomicrographs of 5280 and 52100 at surface, mid-radius

and core locations at 100x and 500x.

Heat Treatment

Soft Annealing

The standard 52100 (100Cr6) annealing program for rolling bearing steel when

applied to the 5280 material resulted in a hardness of 198 HB and a structure of lamellar

pearlite (>80%) with small amounts of spheroidized carbide. This microstructure was

optimized by means of decreasing the annealing temperature in the high temperature

range from 800~ to 760~ then cooling down to 700~ for 7 hours. The result was a

hardness of 180-190HB and a general spheroidization according to CG 2.0-2.2 with a

slight lamellar share in the core area.

Hardness-austenitizing-respo_nse / microstructure, retained austenite

To develop suitable heat treatments, a hardness austenitizing response was

prepared and the microstructure and retained austenite were analyzed. Figure 2 provides

the results as compared with 52100. The hardness required is reached at lower quenching

temperatures in the case of 5280 than with 52100. This is due to the reduction of

chromium content. Hardness is the same though, after tempering at 180~

The metallographic evaluation of the martensite structure shows that austenitising at

about 820~176 is possible with a retained austenite content 9-15%. Figure 3

illustrates the martensite structure.

Tempering behavior

Hardness and retained austenite reaction to tempering was tested. In order to

maintain the SO or S1 dimensional stabilization 52100 is tempered at 220~ or at 240~

resulting in a mean value of hardness 60.5 HRC and 60 HRC for the SO and S1

respectively. The corresponding retained austenite measured was 6 5% and 6 2%

respectively.

Figure 4 provides the tempering diagram of 5280 in which hardness and retained

austenite are indicated. With tempering temperatures of 220~ and 240~ the same

values for hardness and retained austenite are achieved as in the case of 52100. It is

therefore assured that after martensitic hardening of 5280, stabilization does not require a

change in procedure.

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