Astm stp 987 1988

STP 987

Effect of Steel Manufacturing

Processes on the Quality of

Bearing Steels

J. J. C. Hoo, editor

Q> ASTM

1916 Race Street

Philadelphia, PA 19103

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Library of Congress Cataloging-in-Publication Data

Effect of steel manufacturing processes on the quality of bearing

steels/J. J. C. Hoo, editor.

(STP; 987)

Papers from the Symposium on Effect of Steel Manufacturing

Processes on the Quality of Bearing Steels, held at Phoenix, Ariz.,

Nov. 4-6, 1986 and sponsored by the Subcommittee A01.28 on Bearing

Steels of the Committee on AOl on Steel, Stainless Steel, and

Related Alloys.

Includes bibliographies and indexes.

"ASTM publication code number (PCN) 04-987000-02."

ISBN 0-8031-0999-7

1. Steel, Bearing—Fatigue—Congresses. 2. Rolling contact—

Congresses. 3. Steel—Metallurgy—Congresses. I. Hoo, J. J. C.

II. Symposium on Effect of Steel Manufacturing Processes on the

Quality of Bearing Steels (1986: Phoenix, Ariz.) III. American

Society for Testing and Materials. Subcommittee AOl.28 on Bearing

Steels. IV. Series: ASTM special technical publication; 987.

TA473.E42 1988

620.173—dcl9

88-19876

CIP

NOTE

The Society is not responsible, as a body,

for the statements and opinions

advanced in this publication.

Peer Review Policy

Each paper published in this volume was evaluated by three peer reviewers. The authors addressed all

of the reviewers' comments to the satisfaction of both the technical editor(s) and the ASTM Committee

on Publications.

The quality of the papers in this publication reflects not only the obvious efforts of the authors and the

technical editor(s), but also the work of these peer reviewers. The ASTM Committee on Publications

acknowledges with appreciation their dedication and contribution of time and effort on behalf of ASTM.

Printed in Baltimore, MD

October 1988

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Foreword

The symposium on Effect of Steel Manufacturing Processes on the QuaUty

of Bearing Steels was presented at Phoenix, Arizona, 4-6 November 1986.

The symposium was sponsored by Committee AOl on Steel, Stainless Steel,

and Related Alloys and Subcommittee AOl.28 on Bearing Steels. J. J. C.

Hoo, General Bearing Corporation, served as chairman of the symposium

and editor of this publication.

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Contents

Overview 1

QUALITY REQUIREMENTS FOR BETTER BEARING STEELS

Selection of Rolling-Element Bearing Steels for Long-Life

Applications—ERWIN V. ZARETSKY 5

Impact of Steel Quality on Integrated Automotive Wheel Bearing

Performance—GHASSAN S. TAYEH AND HELMUT R. WOEHRLE 44

Quantitative Inclusion Ratings and Continuous Casting: User

Experience and Relatiomhips with Rolling Contact Fatigue

Life—^J. MALCOLM HAMPSHIRE AND ERNEST KING 61

Effects of Material Properties on Bearing Steel Fatigue Strength—

HANS SCHLICHT, ECKEHARD SCHREIBER, AND

OSKAR ZWIRLEIN 81

Failsafe Rating of Ball Bearing Components—AAT P. VOSKAMP

AND GRAHAM E. HOLLOX 102

The Role of Carbides in Performance of High-Alloy Bearing

Steels—PHILIP K. PEARSON AND THORN W. DICKINSON 113

Rolling Contact Fatigue Life of Various Kinds of High-Hardness

Steels and Influence of Material Factors on Rolling Contact

Fatigue Life—^N. TSUSHIMA, K. MAEDA, AND H. NAKASHIMA 132

Relationship of Melting Practice, Inclusion Type, and Size with

Fatigue Resistance of Bearing Steels—^JACQUES MONNOT,

BERNARD HERITIER, AND JEAN Y. COGNE 149

Discussion

The Distribution and Quantitative Relationship of Oxygen and

Inclusions in High-Carbon Ball Bearing Steel—

B. BOMARDELLI, G. PACCHIANI, H. HOLZNER, AND

JOSEPH J. C. HOO 166

NEW METHODS TO EVALUATE QUALITY OF BETTER BEARING STEELS

The Development of an ASTM Standard Analytical Method for

the Determination of Oxygen in Steel—

BARRY I. DIAMONDSTONE AND DEAN A. FLINCHBAUGH 191

Current Status of Round-Robin Testing of Oxygen Content in

Bearing Steels—^w. B. GREEN, JR., B. I. DIAMONDSTONE, AND

JOSEPH J. C. HOO 198

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Analysis of Microindusions in Through-Hardening Bearing

Steels—STEVEN LANE 211

Measurement of Extremely Low Inclusion Contents by Image

Analysis—GEORGE F. VANDER VOORT 226

Inclusion Assessment in Steel Using the New Jernkontoret

Inclusion Chart II for Quantitative Measurements—

STIG JOHANSSON 250

NEW PROCESSES TO PRODUCE BETTER BEARING STEELS

The Ladle Refining Process for Bearing-Quality Steels—

JEFFREY A. ODAR AND DAVID J. FECICH 263

Quality of High-Carbon Chromium Bearing Steel Produced in the

Electric Arc Furnace—Ladle Furnace—^RH Vacuum

Degassing Vessel—^Vertical Continuous Caster—

TOSHIKAZU UESUGI AND KAZUICHI TSUBOTA 278

New Developments in the Production and Testing of Bearing

Steels—PAUL GERHARD DRESSEL, KARL-JOSEF KREMER,

HORST SPITZER, HANS VOGE, AND LUDWIG WEBER 293

Oxygen Content, Oxidic Microindusions, and Fatigue Properties

of Rolling Bearing Steels—^THORE LUND AND JAN AKESSON 308

The Effects of Ladle Refining, With and Without Vacuum, on

Bearing Steel Quality—D. A. WHITTAKER 331

Fatigue Life of High-Carbon Chromium Ball Bearing Steel

Produced by Electric Furnace Vacuum Slag Cleaner—Ladle

Furnace—RH Degassing—Curved Continuous Caster—

KENTCHI KUMAGAI, YATUKA TAKATA, TADAMASA YAMADA,

AND KOHICHI MORI 348

Properties of Through-Hardening Bearing Steels Produced by

BOF Blowing Metallurgy and by Electric Arc Furnace with

Ladle Metallurgy—RUDOLF BAUM, KURT BOHNKE,

TILMAN BOECKERS, AND HARALD KLEMP 360

Ladle Refining: An Integral Part of Bearing Steel Manufacture—

I. OWEN DA VIES, MICHAEL A. CLARKE, AND DAVID DULIEU 375

Author Index 391

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STP987-EB/Oct. 1988

Overview

The fatigue life of rolling bearings has experienced a significant increase in the past several

years. The improvement is attributed to the lowering of oxygen content in the bearing steels to

the level of less than 10 parts per million by weight. This accomplishment is the direct result

of new ladle degassing practices adopted in the steel making processes. Associated with this

progress the methods used to evaluate the quality of bearing steels have been also improved,

refined, and in many instances newly developed.

It is very timely for the American Society for Testing and Materials Committee AOl,

Subcommittee AOl.28 on Bearing Steels to sponsor an international symposium on the theme

of effect of steel manufacturing processes on the quahty of bearing steels. The symposium was

held on 4 to 6 Nov. 1986 in Phoenix, Arizona. This is the third symposium sponsored by

ASTM Subcommittee AOl.28 since May 1974 on bearing steels. We have set up a target that

for every five to six years we will provide a forum for bearing steel producers and users to get

together to present their latest research results, the newest state of the art, and to discuss the

direction for future development. The response from the scientific and engineering community

in the world has been very enthusiastic. This symposium in Phoenix received papers from

Canada, France, Grermany, Italy, Japan, Netherlands, Sweden, United Kingdom, and the

United States. Almost all the major rolling bearing and bearing steel manufacturers in the

developed countries participated. We are extremely gratified for both the quaUty and quantity

of the papers received.

This book has collected 22 papers presented at the symposium. It is divided into three

sections. In the first section there are nine papers discussing quality requirements for better

bearing steels. In this section the phenomenal improvement in rolling bearing fatigue life

in recent several years is unambiguously shown in facts and figures obtained both in laboratories and in the field. The significant contribution of a new quantitative metallographical

method, the SAM method, adopted by ASTM AOl.28 to assess the nonmetallic inclusion

content in bearing steels is also clearly demonstrated. This method is detailed in Supplementary

Requirement S2 of ASTM Standard Specification for High-Carbon Ball and Roller Bearing

Steel (A 295-84). It has proved once more how an improved test method can stimulate the

progress of manufacturing processes. Since the rating of nonmetallic inclusions was the major

theme of the first bearing steel symposium held in Boston, Massachusetts in 1974 and ASTM

STP 575, Bearing Steels: The Rating of Nonmetallic Inclusion was the first book published

anywhere dedicated entirely to that subject, we proudly feel that the symposium has become

an integral part of that progress. The second bearing steel symposium was held in Phoenix,

Arizona in 1981 and was published as ASTM STP 771, Rolling Contact Fatigue Testing of

Bearing Steels.

The second section of this book contains five papers dealing with new methods to evaluate

the quality of better bearing steels. Attention should be paid to papers discussing the analytical

method for the determination of oxygen in steel, and the latest round-robin tests conducted

jointly by ASTM Subcommittees A 1.28 and E03.01 on Ferrous Metals. Again we are proud

to show the world that ASTM has taken a leading role in the standardization of a new test

method that has become very important in its application. It is equally significant that papers

in this section do not respond to the papers in the first section of this book in that there is an

urgent need to develop a practical and meaningful test method for the evaluation of macroinclusions in bearing steels. This is no doubt an indication to the scientists and engineers of a

future research subject.

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2 EFFECT OF STEEL MANUFACTURING PROCESSES

The third section of this book has eight papers covering the new processes to produce better

bearing steels. We designed the sequence of the papers in this book in such way so that the

readers can appreciate what the quality requirements of good bearing steels are, and how they

are tested before reading the new manufacturing methods. Judgment must be made on sound

and thorough understandings. Only after good bearing steel is defined can the reader judge

how good a new manufacturing method is. All eight papers in this section are presented by

leading specialty steel manufacturers in the world.

Both rolling bearings and bearing steel industries are highly competitive. Many research

results are tightly guarded as trade secrets. Moreover, because bearing steel fatigue testing

is very time consuming and usually a set of good comparative tests lasts several years, the

academic institutions have shown little interests in taking up the research. We feel this book

adds valuable information to the science and technology of bearing steels.

Joseph J. C. Hoo

General Bearing Corporation,

Blauvelt, NY 10913; symposium chairman

and editor.

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Quality Requirements for

Better Bearing Steels

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Erwin V. Zaretsky^

Selection of Rolling-Element Bearing Steels

for Long-Life Applications

REFERENCE: Zaretsky, E. V., "Selection of Rolling-Element Bearing Steels for Long-life

Applications," Effect of Steel Manufacturing Processes on the Quality of Bearing Steels, ASTM

STP 987, J. J. C. Hoo, Ed., American Society for Testing and Materials, Philadelphia, 1988,

pp. 5^3.

ABSTRACT: Nearly four decades of research in bearing steel metallurgy a,nd processing has

resulted in improvements in bearing life by a factor of 100 over that obtained in the early 1940s.

For critical applications such as aircraft, these improvements have resulted in longer-lived, more

reliable commercial aircraft engines. Material factors such as hardness, retained austenite, grain

size and carbide size, number, and area can influence roUing-element fatigue life. Bearing steel

processing such as double-vacuum melting can have a greater effect on bearing life than material

chemistry. The selection and specification of a bearing steel is dependent on the integration of all

these considerations into the bearing design and application. The paper reviews rolUng-element

fatigue data and analysis, which can enable the engineer or metallurgist to select a rolling-element

bearing steel for critical applications where long Ufe is required.

KEY WORDS: bearing steel, carbide, fatigue, grain, hardness, lubricant, retained austenite,

rolling element, vacuum

Through the use of improved technology, rolling-element bearing life and reliabihty have

increased dramatically over the past four decades. A chart showing the major advances contributing to these hfe improvements is shown in Fig. 1 [7]. The major reason for these advances

has been the rapidly increasing requirements of aircraft jet engines from the early 1950s to the

present.

Starting in the early 1940s, new developments in the making of bearing steels began. The

improved steelmaking developments were primarily initiated by the acceptance of a comprehensive material specification for AMS 6440 and AISI 52100 steel (A, Fig. 1). New heat-treatment equipment became available in 1941 which incorporated improved temperature controls

and recorders. The use of neutral atmospheres during heat treatment eliminated, for all practical purposes, surface decarburization (B, Fig. 1),

As the requirement for bearing steel increased, large electric arc furnaces were installed

which produced larger size billets. These larger billets necessitated working the material to

reduce the billets to size for tubing or individual forgings. The working of the bearing steel

refines the steel grain and carbide size and reduces the size of the materials inclusions and

segregates (C, Fig. 1). This trend toward larger furnace size has continued to this time [/].

Major advances in melting practice evolved over a period between 1952 and the early 1970s.

Immersion thermocouples, introduced in 1952 (D, Fig. 1), permitted better control of steel

melting [/].

Some significant manufacturing process changes were made in the 1950s. Shoegrinding (E,

Fig. 1) was introduced about 1953. This method improved race surface quality and tolerance.

'Chief engineer for structures. National Aeronautics and Space Administration, Lewis Research Center,

Cleveland, OH 44135.

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EFFECT OF STEEL MANUFACTURING PROCESSES

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ZARETSKY ON SELECTION OF ROLLING-ELEMENT BEARING STEELS 7

With this grinding method, it is practically impossible to grind eccentricity and face ranout into

the bearing race. Also, the transverse radii of the races, controlled by the grinding wheel

dresser, are more consistent [/].

The vacuum degassing and vacuum melting processes were introduced to the bearing industry in the late 1950s. Consumable-electrode vacuum melting (CVM) was one such process (F,

Fig. 1). Vacuum melting releases entrapped gasses and reduces the quantity and alters the type

of inclusions and trace elements present in the steel.

In order to assure clean steel with the vacuum-melting processes, nondestructive testing,

using eddy current and ultrasonic methods, was applied to billets, bars, and tubing (G, Fig. 1).

This assured the quahty of the steel for the bearing manufacturing process.

In rolling-element bearings, the elastically deformed rolling-element surfaces are separated

by a thin lubricant film referred to as an elastohydrodynamic (EHD) film [2]. The concept of

EHD lubrication, while recognized in 1949 [J], was further recognized as a significant factor

in affecting bearing fatigue life and wear (H, Fig. 1). By controlling the EHD film thickness

through lubricant selection and control of operating conditions together with the improvements in surface finish, roUing-element bearings were able to operate at higher temperatures

and for longer times [4].

In the 1960s, argon atmosphere protection of the molten steel during teeming was introduced (I, Fig. 1). Drastic improvement in micro- and macroscopic homogeneity and cleanliness with a resultant improvement in fatigue was realized [/].

Prior to the 1950s, as-ground races were hand poUshed to improve finish and appearance.

Overly aggressive polishing could create a thin layer of plastically displaced or smeared material which was softer and more prone to fatigue failure. This manual process was replaced by

mechanized honing in which all parts are smoothed in a more uniform manner (J, Fig. 1).

In 1958, the National Aeronautics and Space Administration (NASA) published its results

of controlled fiber or grain on the effect of bearing life [5,(5]. Controlled fiber can be obtained

by forging to shape the raceway of angular-contact ball bearings. Forged raceways with

controlled fiber orientation was introduced in 1963 (I, Fig. 1). This innovation improved the

life of angular-contact ball bearings.

Work performed by NASA beginning in the late 1950s on material hardness effiects culminated with the discovery of the differential hardness principle or controlled hardness (J, Fig.

I) [7]. Prior to this time, significant variations between roUing-element and race hardnesses

could result in significant reduction in bearing Ufe.

Combining improved surface finishes obtained by honing, improved lubricants whose selection was based upon EHD principles, controlled fiber and hardness, consumable-electrode

vacuum melted (CEVM) AISI M-50 steel, as well as improved nondestructive inspection

of the steel billet, relative bearing Ufe of approximately 13 times the 1940 standard was

achieved in 1975 [4]. The NASA research culminated by using, for the first time, vacuuminduction melted, vacuum-arc remelted (VIM-VAR) AISI M-50 (K, Fig. 1) demonstrating lives in excess of 100 times the 1940 standard at speeds to three million DN [8]. The

improvement in lives with the VIM-VAR process was accompanied by improved product

consistency by reducing human element variability through better process controls and audits

(L, Fig. 1) [/].

In 1983, Bamberger [P] at General Electric Co. developed a significantly improved AISI

M-50 steel which he called M-50NiL. This new steel was capable of being case-hardened and

exhibited lives in excess of through hardened VIM-VAR AISI M-50 (M, Fig. 1).

The steel technology for long-Ufe bearing application, over the last 20 years, has reached a

20-fold increase in life potential. The object of this paper is to review roUing-element fatigue

data and analysis which can enable the engineer or metallurgist to select and specify a rollingelement bearing steel for critical application where long life is required.

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8 EFFECT OF STEEL MANUFACTURING PROCESSES

Material Cleanliness

Rolling-element fatigue is a mode of failure that occurs in rolling-element bearings such as

ball and roller bearings. It is a cyclic-dependent phenomenon resulting from repeated stresses

under rolling-contact conditions. Fatigue can be affected by many variables, such as rolling

speed, load, material, sliding within the contact zone, temperature, contact geometry, and type

of lubricant. The fatigue failure manifests itself initially as a pit which, in general, is limited in

depth to the zone of resolved maximum shearing stresses and in diameter to the width of the

contact area (Fig. 2).

Research performed by Bear, Butler, Carter, and Anderson [5,6,10] substantiated the early

findings of Jones [11] that one mode of roUing-element fatigue is due to nonmetallic inclusions.

These inclusions act as stress raisers similar to notches in tension and compression specimens

or in rotating beam specimens. Incipient cracks emanate from these inclusions, and enlarge and

propagate under repeated stresses, forming a network of cracks which form into a fatigue spall

or pit. In general, the cracks propagate below the rolling-contact surface approximately 45 deg

to the normal; that is, they appear to be in the plane of maximimi shearing stress (Fig. 3).

Carter [10] made a qualitative generalization that the location of an inclusion with respect to

the maximum shearing stress is of prime importance. Based on observations of inclusions in

AISI 52100 and AISI M-1 steels. Carter concluded that

1. Inclusion location is of primary importance.

2. Size and orientation are also important.

CS-67890

FIG. 2—Fatigue crack emanating from an inclusion.

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ZARETSKY ON SELECTION OF ROLLING-ELEMENT BEARING STEELS 9

3. The oxides and larger carbides are more harmful than the softer sulfide inclusions.

4. Inclusions, carbides, and irregular matrix conditions appear slightly less harmful to

fatigue life in AISI 52100 than in AISI M-1.

Carter's conclusions were substantiated by Johnson and Sewell [12], whose results are

summarized in Fig. 4. They show that as the total number of alumina and silicates increase,

fatigue life decreases. However, they indicate that the increase in sulfides may have a positive

effect upon fatigue life. In addition to inclusions, material defects such as microcracks, trace

elements, or unusual carbide formations present in the material can contribute to failure. An

attempt was made by NASA in the early 1960s to manufacture 12.7-mm (0.5-in.) diameter

AISI 52100 steel balls with increased sulfur content. This effort resulted in balls having incipient cracks in their matrices.

One method for increasing rolUng-element reliability and load capacity is to eliminate or

reduce nonmetallic inclusions, entrapped gases, and trace elements. Improvements in steelmaking processing, namely melting in a vacuum, can achieve this. These vacuum-melting

techniques include vacuum induction melting (VIM) and CVM or vacuum-arc melting (VAR),

as well as vacuum degassing.

It is possible with any of these melt techniques to produce material with a lower inclusion

content than air-melted material, particularly those inclusions which are generally considered

to be more injurious, such as oxides, silicates, and aluminates. These inclusions in part are the

result of standard air melt deoxidation practice which involves the use of silicon and aluminum. Exposing the melt to a vacuum permits deoxidation to be performed effectively by

the carbon. The products formed when using carbon as a deoxidizer are gaseous and thus

FIG, 3—Typical fatigue spall in bearing race.

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10 EFFECT OF STEEL MANUFACTURING PROCESSES

30 r —

0 I I I I I I

RELATIVE ALUMINA + SILICATE CONTENT

30 [—

1 2 3 1 5 6 7

RELATIVE SULFIDE CONTENT

FIG. 4—Relationship between life and inclusion content.

are drawn off in the vacuum. Further, these techniques permit extremely close control of

chemistry and also permit production of variations in chemical analysis which was at one time

impractical.

Fatigue tests of 6309-size deep-groove ball bearings made from two heats of AISIM-50 steel

produced by the CVM process resulted in an average 10% life (L,o) of 4.2 times the catalog life

of 10 milhon revolutions. Additional fatigue tests of the same type of bearings made from a

single heat of air-melted AISI M-50 steel resulted in a life of only 0.4 times the catalog rating

[13].

The improvement in life of bearings made of vacuum-melted steels does not appear to be

commensurate with the improvement in cleanliness. This, of course, supports the long-held

theory that cleanliness is not the only factor involved in bearing fatigue. Even in exceptionally

clean materials, nonmetallics are present to some degree and, depending on the magnitude and

location in relation to the contact stresses, can be the nucleus of fatigue cracks as previously

discussed. A single heat of primary air-melted AISI 52100 steel was processed through five

successive consumable-electrode vacuum remelting cycles. Groups of 6309-size bearing innerraces were machined from material taken from the air-melt ingot and the first, second, and fifth

remelt ingots for evaluation; they were then heat treated and manufactured as a single lot to

avoid group variables. With each remelt, a progressive reduction of nonmetallic content occurred. Endurance results, summarized in Fig. 5, show that the Ljo life appears to increase for

successive remelting with the fifth remelt material reaching a life approximately four times that

of the air melt group [14\.

Based upon the above, it becomes apparent that significant increases in rolling-element

fatigue life, and thus bearing life and reliability, can be achieved through the use of successive

remelting of the bearing steel. Recognizing this fact, Bamberger, Zaretsky, and Signer [8\ had

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