Note: Descriptions are shown in the official language in which they were submitted.
lV~
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This invention relates to a method for joining
sections o~ manganese steel.
Manganese steel is used extensively in castings
; subjected to severe abrasion or impact: earth moving equipment,
grinding mills, railroad trackwork and so on, principally
because the material embodies both ductility and wear resistance.
; Large parts are economically manufactured by casting
several sections and joining them by welding. Proportions æ e
becoming enormous: in metallic mining dipper buckets ~f 25
cubic yard capacity are employed; 30 cubic yard capacities are
being planned.
The labor cost for welding becomes severe as the
castings beco~.e larger: more man hours are invol~ed, less
quality can be expected and delivery dates are retarded. This
is so in spite of the fact that it is customary to join the
parts by semiautomatic welding techniques
The cost problem of joining heavy sections of
manganese steel castings by welding ~the heavier the section
the more heat in-put) is exacerbated by the embrittlement
phenomonon encountered when cast, heat treatea manganese steel
is reheated, as will now be explained.
; Austenitic manganese steel, which is.also called
Hadfield's manganese steel after its inventor, is an extremely
.tough non-magnetic alloy in which the usual hardening trans-
formation has been suppressed by a combination of high mansanese
content and rapid cooling from a high heat treatment temperature~
It is characteri~ed by high strength, high ductility and
excellent wear resistance and is extensively used in severe
gougingj crushing, impact and grinding wear applications because
the material actually gets harder the more it is worked. ~ -
109130~i
The nominal composition contains 1.2% carbon and
12% or 13% manganese as essential elements. Commercial
products will vary within the 1.0 - 1.4% carbon and 10 - 14%
manganese ranges establlshed by AST~I Designation A128.
The as-cast structure of manganese steel contains
carbides and other transformation products that produce marked
brittleness by their continuity. The standard toughening heat
treatment involves austenitizing above 1832F to place all the
` carbides in solution, followed by rapid cooling in water to
prevent re-precipitation of the carbides.
Subsequent reheating of standard manganese steel
parts is potentially more serious than for ordinary structural
steels. Instead of the usual softening and increase in ductility,
manganese steel will become embrittled if heated enough to induce
partial transformation of the metastable austenite. As stated I -
in the Metals ~andbook (1961): "As a general rule manganese
,
steel should never be heated above 500F, either by acci~ent or
plan, unless the standard toughening treatment is to be appliedn.
Both time and temperature are involved, lower temperatures requir-
ing longer for impairment to develop. Only a few minutes are
required at the dull red heat of 1000 to 1200F to begin
embrittlement of this steel.
Since prolonged reheating of toughened manganese steel
results in embrittlement, only arc welding is currently
recommended for welding manganese steel. With a covered
electrode or semiautomatic welding, the welder can usually
control heat in-put in such a way that no area is seriously
overheated.
The problem, then, is essentially two fold. Larger
sections with iong weld seams entail high labor cost; thick
_ _ _ ___ _ ~
``-` `' ' 1091;~0~
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sections tsay two to three inches or more) involve a great
deal of heat in-put likely to produce embrittlement.
Electroslag welding is known to be more economical
than semiautomatic or manual arc welding fro~ the standpoint of
time re~uired. However, the thermal cycles involved are
discouraging to the idea of applying the process to joining
sections of manganese steel.
The foregoing explains the problems we faced in - ¦
recognizing the need to find a more acceptable way to jo~n
sections of manganese steel, particularly thick sections. The 1
objects of the invention are: to use electroslag principles to
; supplant semiautomatic arc welding (and`the other forms as well)
as a method of joining cast manganese steel sections; to produce
a wel~ of high integrity and satisfactory properties in manganese ~ -
steel parts using electroslag principles; and to attain such a
i'
weld by constantly maintaining a reserve of austenite stabilize~s
during progression o the weld. Other objects of the in~ention
are to incorporate austenite stabilizers in the weld wire and~or
. , I
consummable guide; to reduce hot tearing in the weld metal and
heat affected zone of the base metal; to enable the highest
possible welding current to be used, thereby accelerating the
process so that the base metal is exposed to high temperature
for as little time as possible; an~ to reduce the likelihood
; ~of an unacceptable e~brittlement of the base metal.
',
` 1~J9130
.
In the drawin~:
Fig. l is a dye checked section of B electroslag
weld, showing severe cracking in the weld metal and heat
affected zone of the manganese steel base metal;
'` Fig. 2 is a macro-etched section o~ an electroslag
weld showing internal cracks in the base metal;
Fig. 3 is a macro-etched section through an electroslag
weld showing crack;ng in the heat affected zone of the base mëtal
with superimposed cross weld tensile test bars;
' ~ I .
Fig. 4 is a macro-etched section through an electroslag t
weld showing hot tears at the interface between the weldment and
base metal;
j
Fig. 5 shows the results of two bend tests on electro- 1
i~ slag welds, exhibiting the effect of high aluminum in ~he base
,
.-, :
metal on hot tearing; J
Fig. 6 shows the results o~ two bend tests on electro- I
slag welas where the base metal was low in aluminum;
Fig. 7 shows damage in the base metal (bend test)
caused by welding with a current of 600 amps, relying on lo~
20 phosphorus and low aluminum in the base metal castings;
~; Fig. 8 is a perspective vie~ of a dipper bucket which
can be fabricated in accordanc~ with the present invention; and
Fig. 9 is a schematic vie-~ of an elfectroslag wel~ing
system as it may be used to practice the present invention.
~ J
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~(191~0~
Reference may be made to Fig. 8 for a consideration
of practices involved when joining sections of manganese steel
by a wela. Fig. 8 is a perspective of a manganese steel dipper !~
bucket. The middle and lower sections 10 and 12 are separate ~-
castings of manganese steel joined by a long butt weld 15. In -
use, any part of the bucket may be in tension. One advantage
of manganese steel is its inherent ductility; it will stretch
when tensioned and at the same time the tensioned area work
hardens in the localized area. As a consequence the original
yield strength of the pristine metal is increased. The adjacent
pristine metal, not stretched, is relatively weaker. On ~he
` ~ext occurence of tension, the adjacent areas of pristine ~etal
~ yield, work harden and increase in yield strength (the same
-~ pattern as before) which is to say the increase in strength is
progressive throughout a section, progressively as that section
is tensioned ~rom time to time. There is, then, a reserve of
ductility in austenitic manganese steel. In field servioe this
reserve is important in order that there will be no failure due
to unexpected, abnor~al tensioning. For this reason, high
temperature embrittlement which depreciates the reserve in
ductility cannot be tolerated.
Eowever, by our reasoning, the reserves are larse
enough to tolerate some embrittlement in the heat affected zone,
if controlled to an acceptable degree. But an additional factor
is involved, namely, to obtain a substantially unifor~ profile
of mechanical properties across the weld zone, taking into
account the indisputable fact that the base metal has to melt
as the weld metal is being deposited. ~Je fo~nd the problem of
attaining substantially matched yield strength could be resolved
in principle during electroslag ~elding by employing a weld wire
.
30~ -
` .
of a particular alloy content, assuming of course proper control
over weld par~meters.
Electroslag welding is a welding technique based on
- the generation of heat by passing an electrical current through
molten slag. Copper shoes, normally water cooled, are used
to bridge the gap (joint) of the components to be welded, thus -j -
forming a cavity to hold the molten fIux. Filler metal obtained
from a welding wire is fed into the molten flux and the Il -
resistance of the slag bath to the current flow provides the
heat to melt ~he wire and the aajacent sections of the base
metal. A guide tube is ordinarily used to feed the electrode
wire into the molten flux and this guide tube also melts and
contributes metal to the weld.
!
- The major obstacle to successful electroslag welding -
of austenitic manganese steel is the ~astly different time~
temperature relationship of an electroslag we~d as compared to
a shielded metal-arc weld.
; With a metal arcr the temperature of the fusion~
zone is relatively high instantaneously but it cools rapialy
and only a very small a~ount of metal is at a high temperature
relative to the weld. In electroslag welding, however, the ~1
temperature of the flux pool (3,000 - 4,000F) is much lower
than the temperature of a welding arc but the ~ass of the slag !
pool and molten weld metal at a high temperature is relati~ely
- large. Since a larger area of the base metal is heated in
electroslag welding, both the heating and cooling rates of
- the metal in the heat affected zone (HAZ) are much slower in
co~parison to arc welding. This thermal feature of electroslag
welding can be very beneficial when welding carbon and alloy
3~ s~eel$~ In these steels, the slow cooling rate considerably
. ~ ~
1(~91;~0~
reduces the risk of cracks developing in the heat affected
zone of the weldment. However, this characteristic thermal
cycle associated with electroslag welding adversely affects
the properties of austenitic manganese steel for reasons
explained above.
In the first attempt to join manganese steel I~
sections by the electroslag process, three weldments were
made, one 2" section and two 4" sections, using an experimental
welding wire. Otherw~ise, welding parameters were mainly b~sed
on experience with other steels. The base metal for two o~
the weldments cons;isted of standard manganese steel ana for
the third weld a grade of manga~ese steel con~aining molybaenum
was used (AST~-A-128, Grade E-l). This particular grade is krown
to offer better resistance to heat embrittlement than the
regular grade of manganese steel.
Nonetheless, all three welding tests were unsuccessul
d7~e to severe cracking in both the weld deposit and the heat
affected zone of the base metal - see Fig. 1. Microstruc~ural
.
examination revealed severe embrittlement of the weld and base
metal and evidence of incipient melting in the base metal. In
addition, large metallic inclusions were found in the weld,
suspected as being unfused portions of the carbon steel suide
tube normally recommended for electroslag wel2ing.
. The abnormal structure resulted in spite of the fact
that the welding wire contained a relatively large amoun~ of
nic~el, normally considered helpful in avoidins e~brittlement
of manganese steel. The nominal analysis for the wire was
0.92C, 20.8Mn, and 3.2Mi.
As will be evident from Fig. 1, extensive cracks ,~- -
are revealed at the ~nterface between the weld metal and ~he
10~13~
weld. CracXs were persistent throughout the cross-sectiOn
and were not confined to the exposed end surfaces. Heat
damage, as evidenced by a continuous grain boundary carbide
network, was observed in the base metal up to an inch from
~ interface. -¦
-; Analysis showed that melting of the base metal
contri~uted nearly fifty percent of the weld metal, a
considerable dilution. Realization of this large dilution
factor, coupled with the immense heat input, coula be viewed
as causing catastrophic instability of austenite in the
- critical area. It was therefore reasoned that modifications
in both the weld wire and guide tube conceivably co~ld be
relied on to preserve austenitic stability, provided heat
input could be reduced.
', The heat input was reduced by:
a. ~educing the root gap from 1-1~4"
to 3~4"; -
b. Liniting the electrical parameters
to 400 amps and 38 volts; and
c. Using a smaller diameter wire ~1/16
instead of 3/32~) since a thinner
wire would provide increased
deposition rate for a gi~en amperase.
The base metal was further modified to provide improved
heat resisting properties, the nominal chemical analysis being:
C% Mn~O Mo~ Si~ P%
0.80 14.00 1.20 0.5 .05 max.
This chemical analysis still ~alls within ASTM
specification A-128, Grade E-l,
1~9.130
. .
To compensate for the tremendous dilution by the
melting base metal, to introduce austenite stabilizers and -
in a further effort to reduce heat input, a sta;nless steel
guide tube (SAE 304: 18Cr, 9Ni3 was com~ined with a welding .
wire having the following nominal analysis: O.9C, 18Mn, 7Cr, .
. 6Ni. The guide tube, it was reasoned, would melt at a - - --
temperature lower than the carbon steel guiae initially used;
the nickel-chromium content in both the guida tube and weld.. , .- .,
wire would impart heat resistance (resistance to embrittlement ~ :
of the weld metal) and would continuously contribute austenite
. . - . ( . .
stabilizers in the form-of nicXel, manganese and carbo~ during
. the progression o' the weld.
These modifications in the ~uide tube and wel~ wire
were determined as responsible for establishîng mechanical
proper.ies across the weld satisfactorily matching those of
a standard manganese steel tY.S. 50-55000; El. 30-34~ as will
. be evident from data obtained from this successful experimental
wela set forth in Ta~le 1:
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l(J9i3~6
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: TABLE 1
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Automatic ~elding of Man~anese Steel
; 2" Section Test Weld
. Base Metal
Heat C~ Mn% Si% Mo~ P%
2-001 0.8214.02` 0.44 1.25 0.028 ~ ,~
2-020 0.8114.10 0.51 1.22 0.020 J
: Wire Composition
Experimental formulation AN 4 cal~ulated
~ composition:
: C~ Mn~ Cr% - Ni%
0.932 18.77 7.67 6.39
(Calculated to provide a weld composition of
0.80%C, 14.04%~, 4.01~Cr, 3.52%Ni) .
~ , . . I
Actual Weld Analysis: ¦
C% ~ Mn% Si~ Cr% Mo% Ni% P%
Burn 1 0.81 15.70 0.36 4.12 0.52 3.40 0.022
Burn 2 0.82 15.80 0.40 4.13 0.50 3.46 0.021
Burn 3 0.79 15.70 0.36 3.92 0.55 3.45 0.022
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Cross-~eld Tensile Properties
. , I
Sample . -
No. Y.S T.S. El.~ R.A.%
AT-484-A 54,999102,000 33.5 44.9
AT-484-E 50,000104,000 34.0 35.0
When givin~ the analysis (chemistrv) of the base metal,
wire ana weld it is understood the remainder or balance (percent
by weight) is substantially iron, that is, iron diminished by
incidental impurities.
--
lO9i3Q~i
. ~ .
Based on the successful trial weld, pilot production
was instituted. ~owever, upon sectioning the initial pilot
welds internal cracks were found in the heat affected zone of
". ,
the base metal (HAZ zone); a typical example is shown in Fig. 2.
Cross weld tensile tests (.505" dia. bars) on the
weld shown in Fig. 2 exhibited zero ductility, Fig. 3 and
TabIe 2, but microstructural examination did not reveal any -
., ., - .-. - ~
obvious structural embrittlement i~ the base metal ~AZ which
would account for cracking. These microstructural obser~atlons ¦--
were confirmed by taking smaller tensile samples (.242" di~. bars) ¦
from crack-free regions of the heat affected zone and ~he weld
J
metal. The tensile tests exhibited very good ductility values
~see Table 2) which clearly ruled out the possibility of a heat
embrittled microstructure as the cause of the cracking, ~er~fying
that we were stabilizing the austenite in the weld by means of ~ ;
nickel in ~oth the weld wire and guide tube, and by molybaenum
; in the base metal. I
TABLE 2
,. ., . - ~
Cross Weld Tensile Tests (.505" Dia. Bars)
Lab. No. Y~S. (PSI) T.S. (PSI) El.% - R.A.
AU-665-1 37,200 37,900 0 2.3
AU-605-2 36,600 38,~00 0 2.3
Results of Tensile Tests Wlth Small Dia. Test Bars (.252" Dia.~ ~
~ab.No. Location Y.S. (PSI) T.S. (PSI) El.~ R.A.~ i
., ~ I
AU-665-A2 Weld* 59,160 112,500 38.0 37.0
AU-665-Bl H.A.Z.** 57,000 107,800 36.0 36.4
*Tensile bar taken from all-weld metal.
**Tensile bar taken through fusion zone on the fine
grained side of the weld.
!,
.
1(~9i.30~;
- Since the cracks were always located in the coarser
grains, further test blocks of base metal were produced with
a controlled fine grain structure to determine whether grain
size and cracking were related. Additional weldments ~rere
produced with these fine grain blocks. Upon sectioning,
internal cracks were again revealed, except now the cracks
... - . I
were present on both sides of the fusion zone; an example is
shown in Fig. 4.
It will be noted from Table 1 that the amount of
phosphorus in the base metal involving the successful
experimental weld was 0.028 and 0.020. On the other hand it
was found that pilot welds, Fig. 3, was performed on a base
having 0.~38 phosphorus.
Based on the above, it was suspected that ~he poor
high te~perature strength of manganese steel was the problem
- and high temperature tearing was occuring.
Mhen an electroslag weld solidifies, there is
considerable contraction and both the weld ~eposit and super- !
heated base metal must possess sufficient strength to withstand
the high strain generated by the hindered contraction, other~ise
hot tears will result. Contraction is hindered by the mass of
the parts being joined. .
In thP case of manganese steel, higher than norma} -
strains can be generated during solidification of the electroslag
weld due to the high coefficient of thermal expansion of manganese
steel ~deemed to be 1-1~2 times that of ferritic steels). In
addition, much steeper temperature gradients will exist causing
a higher strain concentration because of the low thermal
conductivity of manganese steel (about one-sixth that of pure
iron).
12
~` 109i30~i
This situation is further aggravated due to the
relatively poor high temperature strengths of manganese steel
especially as the phosphorus content increases. In manganese
steel castings with phosphorus contents above 0.06%, phosphide
eutectic envelopes can be observea at the grain boundaries which
drastically reduce the high temperature ductility of the steel.
~- It has been postulated that at elevated temperatures the eutectic
is either soft or completely molten ana if a stress i5 applied
whi~e in this temperature range the grains can easily separate
wherever the envelop~ exists. Even below .06% phosphorus,
.
where the phosphide eutectic is not visible with an optical
microscope, the propertie~ o~ ~anganese steel are adversely
affected by phosphorus.
Since the aegree of hindexed contraction and the
te~perature gradients are more severe with an electroslag weld,
increased susceptibility to hot tearing (and a lower tolerance
for phosphorus) can be e~pected in the heat affected zone.
Therefore, after specifying an upper limit for
phosphorus of 0.025 to 0.035 in the base metal, three additional
20 welds were produced on a pilot scale, using the stainless steel
guide tube and the weld wire identi~ied in Table 1. All three
welds were tear-free and excellent ductility values were - -
obtained as shown by Table 3:
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13
-` lO9i3Q~;
~:: . TABLE 3
'
`~ ~UTO!~ATIC ~LDING OF MANGANESE STEEL
Test Welds No's 49, 50 and 51
I. Base Metal:
Heat No. C% Mn% Si% Cr~ Mo% P~ Al~
74-018 0.79 13.20 0.52 0.64 1.02 ~029 .OgO
._'.;''J- -'
- II. ~Jeldin Parameters: -
Thickness of Test Plate: 2"
Number of Electrodes : 1 -
Ocillation Distance : 1.5n
Root Gap : 3/4"
~lectrode Wire : 1/16~ Dia.
Electrode Guide Type : 304 SS
Current : 400 Amps
Voltage -: 37.5 Volts
III. Cross-Weld Tensile Properties t.505" Dia.~ -
Yield Tensile
SampleStrength Strength
No. ~PSI) ~PSI) El.% R.A.~ -
49-A S6,640 101,300 25.0 32.9
-B 56,400 105,700 26.0 26.5
50-A 54,600 113,200 35.0 37.0
~, -B 58,200 110,800 31.0 28.9
51-A 56,750 117,740 37.5 38.2
-B S6,880 117,200 37.0 35.0
-C 56,400 114,500 37.0 37.7
Two additional welds.were produce~ at a hi~her
; amperage ~450 instead of 400 amps) but both exhibited tears
in the ~AZ of the base metal. Thus, it was concluded that 2"
section manganese steel plates could be successfully joined ~ith
the electroslag process by operating at 400 amps using a base
metal containing a restricted amount of phosphorus.
,
,
14
~ 0913~6
A small test sample of S/64" diameter weld wire
was produced with a lower carbon content to provide 0.60% C
instead of 0.80% in the weld. This change was made in order
to lower the yield strength of the weld deposit to more closely
match the yield strength of the base metal; also a lower yield
strength would help to reduce the tearins susceptibility by
allowing easier deformation of the weld during cooling and -
thus promoting a better distri~ution of induced strain across
the total weld joint.
For the initial weld trial with the lower strength
ire r low phosphorus tand low aluminum for reason~ explained
below) were used and the electrica~ parameters were maintained
at 400 amps and 38 volts. A vexy good wela was produced with
excellent cross-weld tensile properties.
! In order to determine whether higher amperages could
be tolerated with the combination of lo~Jer strength wire, low
phosphorus and low aluminum, a weld was produced at 500 amps.
This weld again provided excellent results and it was thereore
concluded the lower strength wire was also acceptable. ~ater
- 20 tests with a 3/32- diameter wire gave equally good results,
3/32a diameter wire being easier to produce than a 5/64" wire.
,
Further experiments established it woula not be
.
; ~ necessary to oscillate the weld wire while producing the weld,
but these s~me experiments revealed that high residual aluminum
in the base metal (0.100%~ was producing an effect.
Thus, when some tears were found in the HAZ of the
base metal, the only noticeable difference between this and
previous tear-fxee welds was a high residual aluminum content
.100%?. This fact, together with other inaications that
' ' , . :, .
9130~
aluminum could be affecting results, prompted production of
a heat of test blocks with both low phosphorus (.026~) ana
` low aluminum (.020~).
Seve~al weldments were producea using these low
aluminum test blocks ~no oscillation) and these welds were
found to be tear-free and exhibited good cross-weld tensile
- properties.
In order to study the influence of aluminum in ~ore
detail, a series of test block (base metal) heats was produce~
at three different aluminum levels: high aluminum (analyzed
at ~.14%), low aluminum (.031~) and zero aluminum (~.01%).
All the test heats contained less than .03~ phosphorus and
the 3/32" diameter wire at 400 amps and 38 volts was used for
each weld.
! Upon sectioning the ~Jelds; tears were observed in
the ~Z of the welds produced with high aluminum test blocks.
~Jo tears could be observed in the ~Jelds produced with the low
or zero aluminum test bloc~s. Bend tests were performed on
` each wela and the results are sho~m in Figs. 5 and 6. Tensile
data on low and zero aluminum welds are shown in Table 4:
TABLE 4
Cross-Weld Tensile Test Results
~leld No. Y.S. (PSI) T.S. (PSI) El.~ R.A.
71-A 53,160 99,800 30.5 36.3
-B 51,960 103,300 35.0 35.0
-C 5~,~80 100,600 30.0 35.4
72-A 56,760 110,700 39.0 39.8
-B 56,400 115,000 43.0 42.2
~ ' , '
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1~J9130~ -
Another weld was produced with the low aluminum,
low phosphorus test blocks but in this case the current was
raised to 600 amps to determine if higher amperages could-be
tolerated. Reasonably good bend test results were obtained
but some small tears were evident in the base ~see Fig. 7).
The above data confirms that aluminum does influence the hot
tearing tendency.
Good manganese electroslag wel~s can be produced
under the foll~wing conditions:
a. Not more than about 0.035% phosphorua
in the base metal;
b. Using only small amounts of aluminum
for deoxidation of the castings,`so
the residual aluminum after deoxidation
' is not more than about 0.05 - O.OÇ~;
.,
; c. Using the lower strength wire; and ~ ~
.. - .
d. Maintaining a maximum current of 5Q0 amps.
" The process in practice is shown schematically in
Fig. 9~ The two sections of base metal are separated and the
sides are closed by a pair of mQlds such as graphite or water
cooled copper shoes. The guide and weld wire are disposed in
., .
the gap betwe2n the base metal sections. The weld wire andjor
guide tube is used as an electrode! while grounding the base
metal sections to establish an electrical couple. In the course
of perfecting the weld the weld wire is fed at an appro~riate
rate. ~ continuous slag cover is maintainea by adding flux
from time to time~
109130~;
P~ATE OF WELD ~ETAL DEPOSIT; CO~POSITE GUIDE TUBE
Having determined the effect of phosphorus and
aluminum, the preference for molybdenum in the base metal and
the chemistry for the weld were, welds were tried on a
production scale. Two conclusions emerged: (l? embrittlement
and tearing are a function of the rate at which weld metal is -
deposited; and t2) a composite guide, characterized by a copper
guide tube inside a stainless steel sleeve, is re~uired fo~
long welds.
Considering first the requirement of a composite guide
it was found that in the instance of long seams of the character
shown ~t lS in Fig. 8 the stainless steel guide tube distorted.
A bent guide tube results in erratic arc behavior and
uncontrolled weld metal deposit. It was reasoned that
distortion was caused by prolonged exposure of the guide tube
to high te~perature. The problem was further complicated by
~he fact that stainless steel was desirable as a guide not
only because of its compatability with the chemistry of the
weld wire, developed after considerable thought and experiments,
but also because of its role in maintaining the austent~c
character of the weld deposit.
Nonetheless the in~tial use of a carbon steel guide~
was reevaluated. It was ruled out because a minimum diameter
of 1/2" was required for an eisht foot weld seam ~nd a diameter
of that size would virtually monopolize a 3t4" gap bet~een
` sections to be welded, causing arcing.
If the stainless steel guide could be insulate~ from
the effect of the electrical current this would diminish t~e
1~
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lO9i30f;
distortion problem. This ~as achieved by a decision to use
a stainless steel tube as an external supporting sleeve for
a copper guide tube, the weld wire in turn bein~ centered in
co p,~e r
the ee~er guide tube. Copper is much weaker structurally
than steel but its electrical conductivity and thermal
conductivity are vastly superior. Also, copper does not
adversely effect the achievement of austenite; indeed copper
encourages austenitic stability. '-
The composite guiae thus developea (e.g. a 1/4"
; 10 diameter copper guide tube inside a 3/8" stainless steel
support sleeve) performed admirably. The copper tube employe~
as the electrode easily carried the current and its structural~
. .
~eakness ~Jas obviated by the steel sheath.
The proposition of controlling the rate of deposit
ithin limits, and verification of the effect of phosphorus
" and aluminum, emerged during a trial run of ~elds on a
: production basis~ The data are set forth in Table 5.
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.19 ''
lOgl3~
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q e~ ~ q ~ 1~ Ul ~ q N N N N N .~ I ~I C N
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--21--
.
osl~nt,; .,
Based on the d~ta in Table S, the upner limit of
0.03S% phos~horus is verified and aluminum should be lLmi~ed
to 0.05 to 0.06%, nominal. The electrical parameters m~y ~e
~ariea and the gap adjusted for optimum conditions as long as
the rate of deposit is in the range of 0.6 to 0.9 inches per
;~ minute. A slo~Jer speed incxeases the chance ~or embrittlement;
a higher speed encourages hot tears because of the ther~al
gradient being too steep, even though embrittle~ent may not
; occur. The smaller the gap the faster the rate o~ aepos;tr
and vice versa, other conditions being equal. Therefore, tlith
a given electrical rate, the gap is adjusted and a feed rate
~or the wire is selected, which will result in a weld metal
de~osit t?ithin ~he limit o about 0.6 to 0.9 inches per minute~
Evidence shows that moly~den~m when incor orated in
the base metal may be as low as a nomiIIal v~lue OL 0. ~ to 0.6
; This application is a division of copending Canadian
application Serial No. 256,363, filed July 6, 1976.
.. . .
'' ' - ' , ' ';
22
