V 4 THE IEFFECT OF CHROMIUM PLATINGON THE ENDURANCE LIMIT OF 4340 STEEL

— 4 V George M. Ea le, Jr. 4

I Thesis submitted to the Graduate Faculty of the

SO

Virginia Polytechnic Institute

in candidacy for the degree of’

„ MASTER OF SCIENCE YV. in E A A

h MECHANCIAL ENGINEERING

VAPPROVED : 4 APPROVED :

T, Director of Qraduate Studies "éad of? äepartmentl 1

9;.a·g§l¤gi S €I‘Vi „l h 1952

E 1 Blacksburg,VirginiaV

In

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' TABLE OF CONTENTSC

_ SUMMARY...............................5INTRODUCTION..........................4REVIEW OF LITERATURE..................7THE INVESTIGATION.....................13

A. THE 0BJEcT.......................14A B. PREPARATION OF SPECIMENS.........17 E

· C. METHOD OF TEST...................21D. RESULTS..........................23E. GRAPHS...........................24

DISCUSSION OF RESULTS...I.............304

A. EXTRANEOUS EFFECTS...............31_B. DISCUSSION OF GRAPHS.............34C. RECOMMENDATIONS...;..............39

_ CONCLUSIONS...........................40LITERATURE CITED......................42ACKNOWLEDGMENTS.......................46

Cw

VITA..................................48. APPENDICES............................50

I. MACHINE COMPARISON TEST DATA.....51II. FATIGUE TEST DATA................52

7

;_5_.

n SUMMARY

The effect of chromium plating on the fatigue limit

of AISI 4340 Steel was determined by rotating beam fatigue

tests on five groups of specimens: 4340 steel not plated,

_plated once, plated once and baked once, plated twice,

and plated twice and baked twice.

It was found that a single chrome plating reduced the

fatigue limit 91 percent and a second chrome plating re-, duced it another 10 percent. If the steel underwent a

. 45 minute baking treatment at 825°F. after being plated

n once, the fatigue limit was restored to 99 percent of

lthat of the unplated steel. If the steel—was baked after

each of two plating baths, the fatigue limit was restored

to 95 percent of that of the unplated steel.

It also appeared that the second plating operation,

s whether followed by baking or not, introduced an un-T

certainty or scatter into the value of the fatigue limit.

It was not determined whether this scatter was due to the

second plating or to the simulated wear that the specimens

received between platings.

· T + „ „•- _

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INTRODUCTION

_T4

Locomotive side rods made of AISI 4340 steel which— had been chromium plated at the lateral faces of the

4bearing openings for increased wear resistance showed

.. failures of a fatigue type which suggested an effect on

fatigue limit due to chromium plating. Investigation4 4 disclosed a scarcity of information on the fatigue limits 4

4of steels that had been chromium plated. ,

4 4The limited literature on the subject indicated that

44 chromiu plating reduced the fatigue limit of steel and

also that a bahing process in the vicinity of 325°F. 4

4 partially restored the unplated fatigue properties. Nothing

I could be found in the literature on the effect of repeated

A4 4

plating operations. 4 4

In view of the many research possibilities, it was

4 necessary to narrow the problem down to two variables. The4

4_ two variables chosen were the use of a baking process and4 4 the number of plating operations. Fatigue limits were to

A be established for the steel used in the side rods under

five conditions: not plated, chrome plated once, chrome

. plated once and baked once, chrome plated twice, chrome

plated twice and baked twice. The twice plated specimens

were buffed down between platings to simulate wear re-

4 j ceived in actual service. p4

After a decision to use R. R. Moore type, high speed,4

rotating beam fatigue machines, the money for their

T V

purchase was appropriated by the Engineering Experiment

Station of the Virginia Polytechnic Institute, and three

· of these machines were bought. The preliminary work was

carried on at Blacksburg, Virginia, but the actual test-

ing was done in the Materials Testing Laboratory of the ·

University of Illinois at Urbana, Illinois on two of the

y machines owned by the Virginia Polytechnic Institute

~ Engineering Experiment Station.

..7.. E

IREVIEW OF LITERATURE

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This review is confined to literature on the

specific topic of this thesis. No attempt has been

made to cover any of the huge amount of material relating A

to phases of fatigue of metals other than the effectof chromium plating on the fatigue limit of steel. On

this particular subject little has been written. For

example, one of the leading handbooks in the field of

fatigue of metals (l)l covers the theory of fatigue and

~ all its ramifications. It covers all the known effects

in fatigue testing together with a bibliography of 914

references. However, the effect of chromium plating on

T the fatigue limit of steel is given only in one table

of comparative data taken from an unpublished report

by H. K. Cummings (2).

In this report data are given on the fatigue limits

of rotating beam fatigue specimens of SAE 6130 steel.

Group I consisted of quenched and tempered specimens,

while Group II was composed of specimens only normalized.

tli

Group I Group IINot plated 65,500 psi 33,000 psiPlated 6.00015 in. thick 38,000 psi 30,000 psiPlated 0.0045 in. thick 41,000 psi 32,000 psi

It was and still is believed that the reduction of

fatigue limit is due to residual tensile stresses set up

in the deposited material. As long ago as 1860 these

1. Numbers in parentheses refer to Literature Cited.

Istresses were reported. Not until 1929 was anything else

of importance reported when Lea (5) reported that electro-o plating did not alter the static strength of steel. The I

concept that loss in fatigue strength was due to hydrogen

embrittlement was also discussed. The following yeara(

paper by Barklie and Davies (4) gave the results of testson nickel, copper, zinc, and lead plating. The authors,

_ in 1927, found a loss of fatigue strength due to electro-

plating. They claimed the high stresses in depositedmetals plus the imposed stresses caused cracks which

then act as stress raisers at their base. They also ( e

found that residual compressive stresses in depositedmetal did not decrease the fatigue limit. Anetner(interesting discovery was that a thin lead film, as thinas ten one millionths of an inch, between nickel and steelinsulate the steel core from the effect of stressed nickel

— I deposits. ° -That some use could be made of the laboratory dis-

coveries was proven by Williams and Brown (5) who madetests on various full size crankshafts. The results of

, the tests on chromium plated crankshafts show that thepercentage reduction in fatigue limit is substantially

_the same for full size machine elements as for laboratoryspecimens.

While most of the earlier work on this subject was

n ” -10- _

reported from England, a large amount of the more recent

V work comes from this country. The next important paper

after the publication of the handbook by the Battelle

staff was by Logan (6). This paper confirmed the fact

that chromium plating reduced the endurance limit of

certain steels. It claimed that surface grinding slightlyl

increased the endurance limit. Most important was the ‘

v fact that a one hour baking at 44o°c. after chromium(Y

j plating significantly increased the rgtigue limit of 6150

_ steel. Baking temperatures less than that decreased the”

im ·endurance limit.‘

The status of knowledge of the effect is very well

summed up in an unsigned article (7) which says, "It is

we1l—known that electrodeposited coating of some metals· n on steel mmy'reduce the fatigue limit of the basis metal,

‘ and a certain amount of w¤rk has been done with the object '

of defining the conditions of deposition and subsequentItreatment designed to minimize this detrimental effect.

( There is no general solution of the pi¤b1em; the effects

are different with different metals and each metal mustbé suudied.separately.“ This paper goes on to point out

that results of Logan*s·baking experiments tend to prove‘that hydrogen embrittlement cannot be solely responsible

for the reduction in fatigue limit. y_ It is also pointed out that the microscopic cracks

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y observed in most chromium deposits and thought by some

to be responsible for the reduced fatigue limit are not

observed in all chromium deposits and these specimens

without cracks have just as large a reduction in fatigue

limit.

Ü6

That residual stresses are present in the chromiumlt

deposit is not denied, but contradictory results from A

various investigators indicate that the effects of plating

technique are not fully understood.

Almen (8), in the most recent paper on the subject,l

mentions a special procedure of nickel plating whichleft‘

the plating with residual compressive stresses. In tests

the compressive stressed, nickel plated steel had a

fatigue limit equal to the unplated steel while the

tensile stressed, nickel plated steel showed a reduction’ I

of fatigue limit of 55 percent.

l_

It was also found that mechanical prestressing was

effective. For this test shot peening was used although

surfact rolling would probably have the same effect.r Chrome plated steel showed a reduction of fatigue limit

of 19.1 percent from the unplated steel. Shot peened steel

showed an increase of 10.6 percent whereas steel, shot~

peened and then chrome plated, showed an increase in fatigue

limit of 8.5 percent compard to the fatigue limit of un-

plated and unpeened steel.

g A A -12-

A general reference on fatigue testing which was '

A most helpful in setting up this investigation was the

A‘.S.T.M. Manual on Fatigue Testing (9).

J “

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A. THE OBJECT 4

Fatigue failures of side rods made of AISI 4540‘ nsteel on Norfolk and Western Railway Class Jsteamlocomotiveshave occurred during the past three years

which have led the Research and Test Department of that _ , Vrailroad to recommend the discontinuance of the practice

of hard chromiu plating portions of these rods. It had _l

been the practice for several years to hard chromium

plate these rods on the lateral faces at the bearing open- ·

_ ings to secure increased wear,resistance. Plating was}

_1

applied about .010 inches to .015 inches thick, directly

.d'pon the base metal, all other portions of the rod being

sr·"hlocked off. After the rod had been in service and the,1

p ^ plating worn down by normal wear, the faces were replated

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without removing the old plating. Plating practiceedid'

not include a low temperature heating or baking cycle to

reduce the tendenqy of hydrogen embrittlement which, it(y is thought, sometimes occurs in this process (10, ll).

The staff of the Mechanical Department of theV

,Norfo1k and Western Railway Company felt the problem was·„

to investigate the effect on fatigue strength of chromium

plating heat treated AISI 4540 steel (12).

.A search of the literature revealed that chromium (

plating reduced the fatigue limits of all steels which‘

had been tested after chromium plating, so it was

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reasonable to assume that the same would happen with AISI( 4540 steel. Investigators at the Bureau of Standards dis-

covered that a high temperature baking cycle after chromium

plating had a restoring effect on the fatigue limit of two

particular steels (6). However nothing was found in the

literature on the effect of more than one plating process

on the fatigue limit. °

5 In view of these facts the decision was made toinvestigate:

l. The percentage of reduction in fatigue limit of4 AISI 4540 steel due to chromium plating.

l

2. The effect of a baking cycle after chromium

plating on the fatigue limit of AISI 4540 steel.

5. The effect of a second plating after the first

A had worn down on the fatigue limit of AISI 4540 steel.

The three stated objectives could be accomplished by _

the testing of five different categories of specimens.

·The five categories and some comments on each follow:

p 1. Heat treated AISI 4540 steel without chromium

“plating or baking.

H Although two unpublished fatigue limit curves (15) H

were available from Timken Roller Bearing Co., manufact-

_ urers of the steel, there was a difference of tenpercentin

the fatigue limit of the two heats. For that reason it

was felt necessary to establish a fatigue limit for the

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"i

particular heat from which all the specimens would come.

y 2. The same heat treated steel with a chromiumT

plating and no other treatment.

This would provide an answer for the first of the cobjectives.

3. The same heat treated steel with a chromiumÜ

plating and a baking cycle at 825°F.

This would provide an answer for the second cf the’”

objectives.i

4. The same heat treated steel with a chromiumi

w plating, no baking cycle but buffed down to simulatei wear that would be received in service. Then a second

chromium plating on top of the first.

This would provide an answer to the third of the

w objectives. T

5. The same as the last previous category but with

a baking cycle after each plating operation.

This would provide a further answer to the second

and third objentives. .

· ‘ -17-

B. PREPARATION OF SPECIMENSIn order to get results that could be considered

significant, it was necessary to eliminate as manyA

variables as possible. The first requirement was that

the steel of all the specimens be as similar as possible.I

That meant that all the spe¤1me¤S should be made from

steel produced in the same heat. Dr. 0. J. Horger of the

· Timken Roller Bearing Compan arranged to supply 30 feetof 5/8 inch diameter, hot rolled, round, AISI 4340 steel

in multiples of five inch lengths.— This steel was sent to the Roanoke Shops of the

‘ Norfolk and Western Railway Company where it was allheat treated at the same time. The heat treatment con-

sisted of the following:

Normalized at l650°F., one hour at heat.

Heated in salt bath (slightly decarburizing) to

l550°F., one hour at heat.Quenched in oil spray. .

‘ Tempered at ll00°F. for two hours.w Air cooled.

J The steel was also machined at the Roanoke ShopsI

where each piece was first rough turned using a carbon

«~ steel tool. All specimens were prepared by the same_

machinist. The specimens were then finished on anv automatic lathe, which operates from a profile template,

_‘

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thus producing the same radius and diameter for each

specimen. The finish machining was done at 246 RPM with

0.006 inch feed. A high speed tool was used without a

coolant. T

The ends or shoulders of the specimen were then

ground with a Norton No. 57A60-KSVBE wheel at a speed of

6000 surface feet per minute. During the grinding opera- -

tion, the specimen was revolved counter to the direction 4of the grinding wheel on centers at 480 RPM, and a coolant

was used. Next the.center portion of the specimen was t. ground with a Norton No. 32A46-KSVBE wheel which was con-

toured·to the desired radius of that portion of the.specimen. The specimen was turned on centers at 480 RPM

counter to the direction of the grinding wheel. The 4.

speed of the grinding wheel was 5,000 surface feet per

minute and a coolant was used.x

The polishing operation was done with a No. 180

Behr-Manning sending belt on an inflated wheel, followed

by polishing with a No. 240 belt._ The final polishing

was done with No. 000 metallurgical polishing paper in’

the longitudinal direction. _

The plating operations were performed in the Plating

Shop of the Roanoke Shops. A11 portions but the center

or test portion of the specimens were blocked off so·that

no chromium would bedeposited on the parts of the spec- _

imens that fit into the chucks of the machines. The

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processing given the specimens was the same as that ‘

wgiven the actual side rods of locomotives and consistedof the following (14):

The specimen was first placed in a tank and washed

in petroleum spirits, after which it was moved to the

alkali tank where it was rinsed in cold water. The stop-off lacquer was then applied to the parts not to be plated,

and the specimen placed in a rack. This was followed by

a dip in the electro cleaner tank with reverse polarity at

six volts, and than a cold water rinse. Next it went into T

the acid dip tank, and another rinsing in cold water.After this, the specimen was placed in the chromium plat-

T ing tank where it was etched with reversed polarity of ·‘«

six volts for one minute.

In this tank, a lead anode was used as the positive

electrode, and the specimen as the negative electrode.The anode material was a 7 percent tin - 95 percent lead·

alloy. The lead anode acts as a conductor for the chro-

mium in the solution, and the deposit is made on the

article from the solution itself. The solution was 250

grams of chromic acid per liter and 2.5 grams·of sulphate

radical per liter. The solution was kept at a constantItemperature of l5l°F. The voltage was six volts withthe amperage 25 amperes per square inch, or a total amper-

‘ age of five amperes. The time in the plating bath was two

u

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hours which gave a deposit of hard chromium platingt approximately 0.003 inches thick.

p After removal from the plating tank, the specimenwas placed in the reclaim tank to remove excess chromicacid. Next came a hot water rinse after which the stop-

W off lacquer was removed.A Those specimens which were to be plated a second

time were buffed down to simulate wear received in actualservice by the side rods. They were then plated a second

time in a manner similar to the first plating with one· exception. The amperage in the plating tank was begun

at;one ampere per square inch and gradually increasedip

to 2.5 amperes per square inch.

The baked specimens were baked in an oven at 825°F.nfor45 minutes, then air cooled.

af

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METHOD OF TEST

The specimens were wrapped to exclude moistureuntil ready for use. When a specimen was to be tested,

h it was removed from its wrapping and the two ends whichwere.to be inserted into the chucks of the bearinghousings were lubricated with Lubriplate No. 150 AApgrease. This was done to prevent fretting corrosion

I. which would other wise occur. The ends of the specimenswere then inserted in the bearing housings and firmly

' fastened. Care was taken never to touch the specimen I

with the bare hand.•

The whole unit of housings and specimen was then

placed in position on the machine, and the final connect-ions made. The machine was started with no load on the

specimen. After the machine was up to speed, the load.A was applied in small increments. When the desired load

had been applied, the revolution counter was read for

the initial reading. The whole procedure from startingof the machine to reading of the revolution counter

usually took less than one minute.

The rotating beam fatigue testing machine was run

at approximately 10,000 revolutions per minute. The

test was run until either the specimen broke, or enoughcycles of stress had been completed that it was felt that

the specimen would not break thereafter. Steel usually

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will not break if it has undergone more than ten millioncycles without failure. At this time the revolutioncounter was again read for the final reading, the differ-ence being the number of cycles of stress repetition.

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D. RESULTS

The object of fatigue testing is usually to estab-”

lish fatigue limits. Fatigue limits are best illustratedby plotting a "stress versus number of cycles of repeti-tion of stress" curve or, as it is commonly called, an

u"S-N" curve. The results of this investigation are given

nu

as "S-N" curves plotted on semi—logarithmic paper. Thesecurves are shown on pages 24 through 29. "

' The values of fatigue limits for AISI 4540 steel

r „under the specified methods of treatment were:_ Not chrome plated 75,000 p.s.i.. Chrome plated once 57,500 p.s.i.° Chrome plated once, baked once 72,500 p.s.i.

r Chrome plated twice 50,500 p.s.i.Chrome plated twice, baked twice 69,500 p.s.i.

V ZF V g -______ 1

4

I 1 5, 4 V_______=; * *

V'—r···r—

r ·1 4.;; 7,

4

X-

. _

n.,

*

O

‘VÄ°—°ÄÄÄ*ÄÄ°Ä—7”'T'°"?’? . . , , ~;—r~¢« Q 7-——--—— --— --...... -,_,__, _Q V 1 ÄÄÄÄÄÄ_VÄÜÄÄÄÄTfÄ77 2QQQfT Ä ·Ä Y Ä J QQ QÄÄÄYÄÄQ ‘ 7Q:ÄYÄ

..;5()..

DISCUSSION Q__E'_ BESULTS

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A. EXTRANEOUS EFFECTS(

There are a number of extraneous effects that couldbe introduced into fatigue results. It is important toexplain the precautions taken to try to avoid these.

- The first is the speed of test. Since these testswere run at speeds in the neighborhood of 10,000 revolu-

‘ ‘tions per minute, there might be a question as to the_effect this high speed would have on the results. Severalinvestigators (15, 16) have shown that test speeds from1800 to 12,000 rpm have no significant effect (less than (

5 percent) on the fatigue limits of steels.' The second is the effect of size of specimens on

g' _ the fatigue limit. Much research has been done on this

question, but Dolan and Hanley (17) investigated this

h, effect on the same steel as was used in these tests,(1.e., 4540 steel. On the basis of their conclusions

x the maximum variation in fatigue limits due to the( · different sizes of specimens used in this test, 0.500

inches and 0.260 inches, is 500 psi. Since fatigue(limits can not be considered accurate to less than500 psi in most cases, this variation would not seriouslyaffect the results.

Another possible question might arise due to the

p time it took to load the specimen. The literature on

"understressing" and "coaxing“ (18, 19) indicate that no

i-52- 4

effect due to these causes is noticeable at less thanA _a hundred thousand cycles. 4The maximum number of cyclesA ’ that could have possibly occurred in this investigationbefore a specimen was fully loaded was 25,000.

Since two machines were used in these tests, it wasfelt desirable to check the machines, one against the

.other, in regard to induced stress versus applied load.A

This was done by attaching an SR-4 paper-bonded wire. resistance strain gage to an unplated specimen at its t

I N- minimum diameter. The specimen was placed in the machine,_ ,4

A_ load applied, and the strains read on a strain indicator.

This was done for each machine. These data (see Appendix I)

4 showed that the machines were similar, the maximu varia-tion in stress being 150 psi. at 15,160 psi., or a varia-

, A tion of less than 0.9 percent.A _ Considering the extraneous effects as well as the

“ difficulty of fitting a curve to experimental points andA

the statistical deviation that can be present when a

4 fatigue limit is established with relatively few points,·

AJa,safe estimate would be that the fatigue curves obtained

4 in this investigation are accurate to the nearest 1,000 psi.This does not imply that large machine elements, such as

4 the driving rods of locomotives, would show the same,fatigue limits. On the contrary, Horger, Buckwater and

Neifert (20) have shown that fatigue limits are much lower

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for large diameter shafts or axles than for small

circular specimens. However, Williams and Brown (5)

have shown that the percentage loss in fatigue strength

of chromium plated machine elements is substanticalLy‘_

H the same as in laboratory specimens•

When the fatigue limits obtained are viewed closely,_ it can be seen that a number of interesting phenomena

are present in some of the graphs.

u

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B. DISCUSSION OF GRAPHS

GRÄPH l: AISI 4540 Steel, Not Plated, Not Baked.

This curve is a well-fitted curve, and well with-7 v_ in the scatter band to be expected from this type of

steel. Tests by the steel manufacturer (15) show that

the fatigue limits of steel from two consecutive heats

varied by 7,000 psi. The fatigue limit in this category

was found to be 75,000 psi. This is somewhat below the

fatigue limits found by the manufacturer. The difference

might well be due to variations in heat treatment.

GRAPH 2: AISI 4540 Steel, Plated Once, Not Baked.(

This curve, with the exception of one point, is a

well-fitted curve. It appears within the expectation of

normal scatter. The exceptional point which failed after

228,000 cycles at a stress of 58,000 psi, might be ex-

plained in one of two ways. This specimen was run almost

two months after the first specimens of the group, and

more than a month after the last previous specimen which

ran out at the same stress. It is possible that there is

an aging effect due to the chromium plating process, al-

though no mention of such has been found in the literature.

The second possibility is that of a "freak" specimen.

These "freaks" occur quite frequently in steels such as

this. This curve gives a fatigue limit of 57,500 psi.

This is a reduction of over 2l percent from that of the

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unplated steel.A GRAPH 3: AISI 4340 Steel, Plated Once, Baked Once.

_4

This also is a well—fitted curve with all points butone fitting it very well. This one point, No. B-12, againthe last point run, falls considerably above the curve.It was stopped unbroken at 4,600,000 cycles, which is nota large enough number of cycles to say that it probablynever would have broken. In fact, the machine was stoppedbecause of excessive vibration caused by excessive de-formation but not fracture, of the specimen. The point is 5probably an unsound one. The fatigue limit was thereforeestablished at 72,500 psi. which is a reduction of less

· than one percent from the value for the unplated steel.Another way of stating this would be that the fatigue 4

limit was reduced only three percent as much as it wouldhave been if the steel had not been baked.GRAPH 4: AISI 4340 Steel, Plated Twice, Not Baked.

This set of data is peculiar. The points at the higherstresses seem reasonably regular, but at lower stresses theyare scattered. The scatter is large, giving a dispersion

T band wider than usually found in this type of steel. Itß

was finally decided to draw the fatigue limit at 50,500 psi.The irregularity of the points, if not due to normal

scatter, might be due to any or all of three causes. Onecondition, about which nothing is known, is the effect of

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a second plating on the-fatigue limit of steel. It ispossible that this second plating, in addition to reducing

fthe fatigue limit, also introduces excessive scatter. An-other possibility is that the irregularity is due to thesimulated wear, that is, the buffing operation betweenplatings.

The third possible cause is an aging effect due tochromium plating which would further reduce the strength1of the steel as the time after plating increases. Thereis insufficient evidence to make a definite conclusion in

4

this regard, but the facts should be pointed out. Thefirst twelve specimens, C-1 through C-12, were shippedfrom Roanoke October lst and were tested during the periodthree weeks to one month after shipment. The last sevenspecimens were shipped March 19th and were tested duringthe period eight to ten days after shipment. Since bothgroups were sent by themselves and were not held up wait-

ing for other groups to be finished, it is safe to assumethat the.time between the last plating and shipment wasapproximately the same in both cases. There was then a

'difference in age of about two weeks at the time of test.All of the first twelve older specimens failed, nine ofthem at stresses between 51,000 and 55,000 psi. Of the

Wsix tested specimens in the younger group, five ran out

at these same stresses an one failed at 55,000 psi.

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This evidence is not conclusive because of the possibility

of other variables being present, but it must be considered.

GRAPH 5: AISI 4540 Steel, Plated Twice, Baked Twice.

In this curve the scatter characteristic of the

previous set of data is even more evident. There is a

break and a runout at 75,000 psi. stress. At 71,000 psi.stress there is a break and two runouts. In view of the

inconsistent data the fatigue limit was placed below the

lowest value of stress at which there was a break regardless

of the number of runouts at that stress, a value of 69,500 psi.

This means that the fatigue limit of this steel plated twice

and baked after each plating is 95 percent of that of the

unplated steel.

The peculiarity of excessive scatter which occurs in4 this curve does not seem to be a result of an aging factor

because the break and the runout at 75,000 psi. were both

run on the same day, and the break and one runout at

70,000 psi. were run within two days of each other.

The scatter might have been caused by the buffing

operation between the first and second platings. However

since all plated specimens were buffed after the plating,

it seems probable that some scatter would have appeared

in the single plated groups if this were the cause.

The only other plausible cause is the second platingvontop of the first. Just what is the basic cause of

_ -38- (

this phenomenon is not apparent from the informationcurrently available.

(

GRAPH 6: Comparative Plot of All DataThis is a plot of all the previous graphs put on one

page to show better the relationships between the varioussets of data. All data are tabulated in Appendix II.

The percentage of reduction in fatigue limit found inthis investigation agrees quite closely to those found bymost previous investigators, the most recent of which,Almen (8) found a reduction of 19.1 percent for one plating.

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C. RECOMMENDATIONS

This investigation has revealed the need for more

information in several categories. It is recommended that

an attempt be made to investigate the scatter found in the

twice plated groups. The possibility of an aging effect

should be thoroughly covered.ß

r . A second recommendation is that tests be conducted to

see if mechanical prestressing by surface rolling would

have the same effect on fatigue limit as was evident in the

A shot peening experiments.A A third recommendation is to investigate the effect of

keeping the specimen in compression or tension during the

actual electroplating. In fact, there is still a great

deal of work to be done before the mechanics of effect ofl

electroplating on the fatigue limit of metals is thoroughly

understood.

..4Q..

‘CONCLUSIONS

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1. The percentage of reduction in fatigue limit of AISI .

L ° 4540 steel due to one chromium plating was 21 percent,based on the fatigue limit of unplated AISI 4540 steel.

2. The effect of a 45 minute baking at 825°F. after·

chromium plating on the fatigue limit of AISI 4540 steelwas to restore the fatigue limit almost to the value of

U

that obtained with the unplated steel. For specimens _plated once and baked once, the fatigue limit was 99 per-1cent of the fatigue limit of the unplated steel. For _ ”

fspecimens plated twice and baked twice, the fatigue limitwas 95 percent of the fatigue limit of the unplated steel.

i5._ The effect on the fatigue limit of AISI 4540 steel of

_ a second plating after the first had been worn down, was

L a further reduction. The reduction in fatigue limit was~5lpercent, based on the fatigue limit of the unplated

steel, and_l2 percent based on the fatigue limit of thesteel chromium plated once.

u

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LITERATURE CITED

-45-

1. "Prevention of the Failure of Metals Under RepeatedStress", by the staff of Battelle Memorial Institute,John Wiley and Sons, New York, 1946.V

2. H. K. Cummings, "Case Hardening and Chromium PlatingData", Unpublished Report to Bureau of Aeronautics,U. S. Navy Department.

s 5. F. C. Lea, "Penetration of Hydrogen into Metal Cathodes7

Iand Its Effect upon Tensile Properties and TheirResistance to Repeated Stresses with a Note ontheEffects

of Non-electrolytic Baths and Nickel Platingon the Properties", Proceedings, Royal Society (London),Vol. 125A, 1929, pp. 171-185. p

4. R. H. D. Barklie and H. J. Davies, "The Effects ofSurface Conditions and Electrodeposited Metals on theResistance of Materials to Repeated Stresses",Proceedings, Institute of Mechanical Engineers, 1950

(Part I, pp. 751-750.

5. C. G. Williams and J. S. Brown, "Fatigue Strengthof Crankshafts", Engineering, Vol. 154, Nos. 5992 and ‘

5995, July 17 and 24, 1942, pp. 58-59 and 78-79.6. H. L. Logan, "The Effects of Chromium Plating on the

Endurance Limit of Steels Used in Aircraft", U. S.National Bureau of Standards Journal of Research,

(1Mo1. 45, No. 2, August 1949, pp. 101-110.

. 7. "Fatigue Limits of Chromium-Plated Steels", The

(-44-

Engineer (London), Vol. 189 Part I, No. 4908, Feb. 24,1950, pp. 241.

R 8. J. 0. Almen, "Fatigue Loss and Gain by Electroplating",Product Engineering, Vol. 21, No. 6, June 1951.

9. "Manual on Fatigue Testing", by Committee E-9 onFatigue, American Society for Testing Materials,

Special Technical Publication No. 91, 1949.10. Metallurgical Report No. 115, Research and Test

Department, Norfolk and Western Railway Company,

December 15, 1949, unpublished.11. Metallurgical Report No. 117, Research and Test

.Department, Norfolk and Western Railway Company,.

March 7, 1950, unpublished.

12. Correspondence, C. E. Pond, Assistant to Superintendent

· Motive Power, Norfolk and Western Railway Company, to

author, November 7, 1950.

15. Fatigue Test Data, 4540 Steel, Heats 10802 and 10805,.

Timken Roller Bearing Company, Canton, Ohio, January

1944,unpublished.14.T. R. Boggess, "Electroplating of Wearing Parts",

Railway Mechanical and Electrical Engineer, Vol. 124,. No. 6, June 1950, pp. 555-556.

15. T. T. Oberg and J. B. Johnson, "Fatigue Properties of

Metals Used in Aircraft Construction at 5450 and 10,600

Cycles", Proceedings, American Society for Testing

-45-

Materials, Vol. 57 Part II, 1957, pp. 195-205.16. P. K. Roos, D. C. Lemmon, J. T. Ranson: "Influence of

Type of Machine, Range of Speed, and Specimen Shape onFatigue Test Data", American Society for TestingMaterials Bulletin No. 158, May 1949, pp. 65-67.

17. T. J. Dolan and B. C. Hanley, "The Effect of Size ofy Specimen on the Flexural Fatigue Strength of SAE 4540

Steel", United States Air Force, Air Materiel Command,Technical Report No. 5726, 1948.

18. J. B. Kommers, "Understressing and Overstressing inIron and Steel", Engineering News-Record, Vol. 114,

‘April 18, 1955, pp. 550-551. r19. F. E. Richart Jr. and N. M. Newmark, "An Hypothesis

'forthe Determination of Accumulative Damage in

Fatigue", Proceedings, American Society for TestingMaterials, Vol. 48, 1948, pp. 767-800. «

20. 0. J. Horger, T. V. Buckwater, H. R. Neifert, "Fatigue‘ Strength of 5} inch Diameter Shafts as Related to

1

Design of Large Parts", Journal of Applied Mechanics,American Society of Mechanical Engineers, Vol. 12,

No. 5, pp. Al49—A155.

-46-A

ACKNOWLEDGMENTS

—————————————————————————————————————————————————*———""*——————*———’*—"——————"—“1

-47-

The author wishes to acknowledge his indebtedness tothe following members of his Thesis Committee for their

„, pguidance and assistance:I

Professor J. B. Jones, Head of Department.of MechanicalEngineering, Virginia Polytechnic Institute.

C Mr. C. E. Pond, Assistant to Superintendent Motives

Power, Norfolk and Western Railway Company.I Professor J. P. Mahanay, Department of Mechanical

Engineering, Virginia Polytechnic Institute.Special acknowledgment is expressed to the Norfolk

and Western Railway Company and to Mr. G. E. Baumgardner,Assistant Research Engineer of that company, for thepreparation of the specimens.

d

The author also wishes to express his gratitude to l

the Timken Roller Bearing Compan and to Dr. L. J. Horger,Chief Engineer, Railway Division of that company, for the

T donation of the steel from which the specimens were made.dThe author is indebted to the Department of

Theoretical and Applied Mechanics, University of Illinois, U

for the use of their-facilities during most of this· investigation. ~ l I

4-46- 4

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