The effects of aging and straining on the internal friction of hydrogen charged 1020 steel at low temperatures

THE

EFFECTS

OF

AGING

HYDROGEN

AND

CHARGED L.

C.

STRAINING

ON

1020 STEEL

WEINERt

and

AT M.

THE

INTERNAL

LOW

FRICTION

OF

TEMPERATURES*

GENSAMERt

It has been found that aging at room temperature or previous straining of hydrogen charged 1020 steel causes an internal friction peak at 105°K to appear, reach a maximum, decrease and finally disappear. This peak has been explained by a model which involves the dragging along of hydrogen atmospheres by oscillating dislocations. In addition another peak at 50°K has been observed which is apparently due to stress-induced diffusion of interstitial hgdrogen. LES EFFETS

DU VIEILLISSEMENT

TURES

LES

SUR

VALEURS

DE

ET DE LA DEFORMATION FRICTION

INTERNE

DUN

AUX ACIER

BASSES TEMPERA1020 CHARGE

EN

HYDROGENE Pour un acier 1020 charge en hydrogene, les auteurs ont trouve que le vieillissement B temperature ambiante, ou une deformation prealable, provoque it 105°K un pit de friction interne qui apparait, atteint un maximum deoroit, puis disparait. Ce pit est explique par un modele oti les atmospheres d’hydrogene sont attirees par des dislocations oscillantes. En outre, ils ont observe un autre pie It 50”K, provoque vraisemblablement par la diffusion de l’hydrogene interstitiel sous l’effet des tensions. DER EINFLUSS

VON ALTERUNG

UND VERFORMUNG

WASSERSTOFFBELADENEN

1020 STAHL

AUF DIE INNERE

BEI TIEFEN

REIBUNG

VON

TEMPERATUREN

Es wurde gefunden, dass eine Alterung bei Raumtemperatur oder eine vorherige Verformung von wasserstoffbeladenem 1020 Stahl ein Maximum der inneren R&bung entstehen und wieder verschwinden l&s&. Da4 Maximum wurde in einem Model1 erklart, in dem oszillierende Versetzungen ihre Wasserstoffatmosphiiren mitnehmen. Ausserdem wurde ein anderes Maximum bei 50’K beobachtet, das anscheinend von einer spannungserzwungenenDiffusion von Wasserstoff auf Zwischengitterplatzen herrtihrt.

INTRODUCTION

An internal

friction

temperature,

peak had been observed(l)

as

well

as

stability and versatility.

at

to

improve

mechanical

The bell jar was replaced by

about 105“K, in 1020 steel that had been pickled or had been annealed in hydrogen at high temperature

a double walled, evacuated

and pressure.

nitrogen or liquid helium was used as a coolant, introduced into the system through a transfer tube

An internal friction

peak in hydrogen

charged iron and steel in this temperature

range has

also been Manning.@’

hydrogen

observed

by

Another

peak

Maringer, at

50°K

Marsh in

and

stainless-steel jacket which

was sealed to the base with an O-ring.

and flushed directly

on the specimen,

Either liquid

For tempera-

tures below that of liquid nitrogen an outer jacket was

charged steel has been observed in this laboratory, which has also been observed by Heller.c3) It seems

also used so that the double walled evacuated

likely

nitrogen.

that

the

stress-induced

interstitial

diffusion

Temperature

study was to learn more about the 105°K peak.

’ in. from the point of least thickness. i?i

The low frequency, vibrating reed type of internal friction apparatus used was described in the initial investigation;(l) measurements

it has been modified to to be made down to liquid

permit helium

* Received May 13, 1957. 7 Columbia University, New York 27, New York. ACTA

METALLURGICA,

VOL.

5, DECEMBER

welded

individually

with

to the specimen

each

wire

approximately

The specimens were the same as those used and described previously.(i) The steel was annealed ‘at 850°C for one half-hour, then air cooled, The machined specimens

were subsequently

annealed

at 5OOV for

2 hr. Hydrogen charging was carried out by two methods: (a) at 600 lb/in2 at 500°C for 20 hr, followed by 2 hr at 6OO”C, and (b) cathodically, using an electrolyte consisting

1957

thermocouple,

were made with

a

PROCEDURE

copper-constant

measurements

peak is this lower one rather than that observed at 105°K. The objective of the continuation of this

EXPERIMENTAL

jacket

and the base of the apparatus were immersed in liquid

692

of 4 per cent H,SO,

with one or two

L.

C.

WEINER

AND

M.

GENSAMER:

FRICTION

OF

1020

STEEL

OQ87-

3Q3755Q-

90

&I 1

80

90

100 110 120 Tempemture

130

100 110 120 Temperature

lJO

FIG. 2. Internal friction of hydrogen charged and strained 1020 steel aged for various times at room temperature (frequency of 20 c/s).

140

lK

FIG. 1. Internal friction of hydrogen charged 1020 steel aged for various times at room temperature (frequency of 20 c/s).

and, as expected,

drops of CS,, a current density of 2 mA/in2 and a time

disappear,

of 24 hr.

straining accelerates the entire process.

causes the peak to appear immediately Aging at 300°K

It was established

the same results;

that both methods gave

the majority

of observations

were

Another

were copper plated to help retain the hydrogen,

50’K

one half-hour

the internal

friction

measure-

ments were started. Copper plating blank specimens produced no measureable effect on internal friction.

Hatfield

Lecture.c4)

which decreased 100°K

a frequency

of 20 c/s of a charged specimen that had

been aged for various times at room temperature. peak is present immediately

No

HelleiJ3) found a peak at about

With

peak.

the

of internal friction

further

peak disappeared Behavior

aging

entirely,

this

iron by K&t5) and

and Hahn,c6) in which a 250°C peak

expense

of

the

2O”C, stress-induced

diffusion of interstitial nitrogen peak.

after charging but with

aging at room temperature, 300”K, a peak appears between 100 and 110°K and reaches its maximum after 4 days aging time. peak to disappear.

Further

aging causes the

The width of the peak indicates

that it is not associated with a single time of relaxation. Other specimens gave peaks at slightly different temperatures,

all lying between 95 and 115°K.

Internal friction measurements were made on other specimens that were strained in tension after charging and plating. Because of the shape of the specimens it was difficult to estimate the actual amount of strain. Fig. 2 presents the internal friction of a strained specimen upon immediate testing as well as after aging 1 and 2 days at room temperature. Straining

Temperature FIG.

lower

leaving only

similar to this has also

with cold worked

KGster, Bangert at

in

with aging, while another at about

appeared.

temperature

rises

Clearly,

(Fig. 3), referred to by Bain in the

been observed

Fig. 1 shows a sequence of internal friction runs at

1 day caused the peak to

on the initial measurement

the 100°K RESULTS

for only

at about 115’K

is also increased.

peak at about 50°K has been observed

this laboratory

and

the background

with a decrease in background.

made with specimens charged at high temperature and pressure. Immediately after charging, the specimens within

!I (

‘K

3. Internal friction of hydrogen charged unaged 1020 steel (frequency 20 c/s).

ACTA

694

METALLURGICA,

DISCUSSION

VOL.

5,

to immobilize

1957

the dislocations

at a given stress level.

a charged specimen

not only increases the

According to Wert’s empirical relationship,(‘) the relaxation processes associated with the 50 and 105°K

Straining

peaks

hydrogen diffusion to the dislocations become quite small, but also increases the rate of that diffusion.

should

have

an activation

energy

of about

3000 Cal/mole and 6000 Cal/mole, respectively. and Tompkins’@

Stross

and Geller and Sunc9) found that the

activation

energy

interstitial

diffusion

at higher

temperatures

of hydrogen

100 and 2900 Cal/mole,

for

the

in iron was 3050 &

respectively.

Calculation

of

the diffusion rate, D, from internal friction measurernents(lO) gives 2.8 x 10-l’ cm2/sec.

cal/mole.(9)

expected

at 50°K

obtained

However,

friction

this value

observations when

is off at

cm2/sec at 105”K.(s)

by

seven

with

an

105”K(8)

and

These observa-

tions strongly indicate that the 50°K peak is due to the stress-induced

diffusion

of interstitial

hydrogen,

but

that the 105°K peak has its origin in another process. K8f5) and Koster et uZ.(@ attribute the 250°C peak to the dragging along of nitrogen and perhaps carbon atoms with oscillating be assumed

dislocations.

that the 105°K

dislocation

the

by oscillating

In charged and unaged specimens, the density is comparatively small, and

because of the large distances between the dislocations it is possible that it takes some time for hydrogen diffuse

to and start saturation

Hydrogen virtually

atmospheres non-existent

around dislocations

appearance

of the

105°K

decrease the amount of hydrogen induced

interstitial

would be

aging at room temperature, can take place, resulting in

partial saturation of the dislocations the

to

of the dislocations.

and the 105°K peak would not

appear as yet. With diffusion of hydrogen

diffusion

by hydrogen and

peak.

This

should

available for stress-

and a decrease

of the

50°K peak. These concomitant processes should continue until the 50°K peak disappears and the 105°K

peak reaches a maximum.

would

decrease

with further

and dissolution

of hydrides,

but there is no

evidence to support this. CONCLUSIONS

Aging

or

straining

causes

the

105°K

internal

friction peak in hydrogen charged 1020 steel to appear, reach a maximum,

decrease and finally disappear.

In

addition, another peak, at 50”K, apparently due to stress-induced diffusion of interstitial hydrogen, has also

been

observed.

The

105°K

peak

has

been

explained by a model similar to one proposed for peaks associated with nitrogen and carbon in cold worked iron, and involves the dragging along hydrogen atmospheres by oscillating dislocations.

of

Similarly it may

peak results from

dragging along of hydrogen atmospheres dislocations.

of the peak through saturation.

It is possible, of course, to imagine that these effects

Geller

energy of of D from

compared

D = 4.3 x 1O-9 cm2/sec 1tF

from

using an activation

magnitude

D = 2.2 x

disappearance

immedi-

an aging time of only 1 day at is enough to bring about the

solution

cm2/sec

of

Apparently temperature

could be produced by such a process as strain-induced

and Sun’s observations internal

should be accomplished

observa-

5.6 x lo-l6

the

ately. room

partial saturation

and the peak should be observable

obtained

an activation energy of 3050 + 100 and in reasonable agreement with

orders

quickly

cm2/sec at 50’K

tions using cal/mole,(8)

2900

Therefore

density so that the distances necessary for

from Stross and Tompkins’

agreement with 4.9 x 10-l’ by extrapolation

This is in excellent

dislocation

The 105°K

aging and finally

peak dis-

appear upon achieving a sufficient degree of saturation

ACKNOWLEDGMENTS The authors are indebted to Dr. John 0. Brittain for his assistance in designing the present apparatus as well as direction of some of the early experimentation reported in this paper, to Mr. Henry Nowotny for carrying out the *internal friction measurements in this study, and to Drs R. E. Maringer and W. R. Heller for stimulating discussion and comments. This research was sponsored by the Office of Naval Research. REFERENCES 1. L. C. CHANGand M. GENSAMER Acta Met. 1,484 (1953). 2. R. E. MARIN~ER, L. L. MARSH and G. R. MANNING Private communication. 3. W. R. HELLER Private communication. 4. E. C. BAIN J. Iron St. Inst. 181, 206 (1955). 5. T. S. K& Trans. Amer. Inst. Min. (Metall.) Engrs. 176, 448 (1948). 6. W. KBSTER, L. BANGERTand R. HAHN Arch. Eisenhiittenw. 25, 669 (1954). 7. C. A. WERT and J. A. MARX Acta Met. 1, 113 (1953). 8. T. M. STROSSand F. C. TOMPKINS J. Chem. Sot. 230 (1956). 21, 423 9. W. GELLER and T. SUN Arch. Eisenhiittenw. (1950). 10. C. A. WERT Phys. Rev. 70, 601 (1950).