Note: Descriptions are shown in the official language in which they were submitted.
--\
2~76~
BAC~GROUND OF TH~ INVBNTION
FIELD OF THE INVENTION
The invention relate~ to a marten~itic stainless ~teel
article u~sd for anchoring molds and dies and to a method for
producing the ~ame.
DESCRIPTION OF THE PRIOR ART
Molds and dies used to produce part~ made from materials
such a~ pla~tic are anchored in place during operation by
frame~, holder blocks, backer~, and similar articles. The~e
articles are usually made from steel of a composition
exhibiting hlgh strength and toughness to withstand the
~tre~e~ incident to these applications and to provide
sufficient service life. The steel must al~o have good
machinability to facilitate manufacture of these articles and
must be ea~ily heat-treatable in relatively large section
sizes to the necessary hardnes~ limits.
Typical steel~ used in the manufacture of frames and
holder bloc~ are prehardened within the hardness range of
about 30 to 40 Rockwell C (HRC). Thi~ eliminates the need
for heat-treatment by the user, and avoids the distortion
normally encountered in heat-treating of machined article~.
The hardne~ range of 30 to 40 HRC i~ ~ignificant, because
2~17~
the machinability of most steels st hardnesses above 40 HRC
is reduced to a level that makes the required machinLng too
expensive for most applications. Although lowering the
hardness of the steel improves machinability, at hardnesses
below about 30 HRC the steel lacks sufficient mechanical
strength for these intended applications.
The low-alloy carbon steel~ conventionally used for the
production of holder blocks, such as the ~ulfur-bearing
modifications of AISI 4140 and AISI 5150, provide an
excellent combination of mechanical properties, in
combination with good machinability. They, however, lack
sufficient corrosion resistance to resist rusting and other
forms of corro~ion during both service and storage. This
corrosive attack reduces the operating safety, efficiency and
service life and moreover requires that the holder blocks and
frames be covered with a protective coating when they are not
in use.
A number of corrosion resistant steels have been
evaluated as replacements for the conventional low-alloy
carbon steels used in holder block applications. High
quality stainless mold steels, such as AISI Type 414, AISI
~ype 420, and tho~e disclosed in U.S. Patent No. 3,720,545
have been considered; however, they are not widely used for
holder block applications because of their cost, properties,
2~6176~
and comparatively poor machinability. To overcome the
machinabillty problem, a number of sulfur-bearing
modifications of AISI Type 420 and AISI Type 430 have been
developed. While these ~ulfur-bearing steels have relatively
good machinability, they are not well ~u$ted for this
application becau~e their inherent hardening and tempering
characteri~tics make it difficult to produce them in the
broad hardness range of 30 to 40 HRC required for holder
blocks snd especially in the narrower hardness range of 35 to
40 HRC required for high strength holder block~. In
sddition, the relatively high austenitizing temperstures used
to harden these steels, typically 1825 to 1900F, re~ult in
increased cost and contribute to con~iderable distortion of
the articles during the hardening heat-treatment. Further,
at hardnesses within the range of about 30 to 40 HRC, these
stainle~s steels exhibit a characteristic drop in toughness
and corrosion resistance that significantly detract~ from
their usefulness in these applications.
OBJECTS OF TEE INVENTION
It is a primary ob~ect of the present invention to
provide a martensitic stainless steel article which may be
used for holder blocks, frames, backers, and simllar articles
for anchoring molds and dies, having an improved combination
20~176~
of strength, toughness, corrosion resistance, and
machinability.
Another related ob~ect of the invention i8 to provide a
method for producing a martensitic stainless steel article
having these characteristics by the use of a simple hardening
and tempering heat-treatment.
SUMMARY OF THF INVENTION
It has been determined in accordance with the invention
that a martensitic stainle~s ~teel article having an improved
combination of strength, toughne~s, corrosion resistance, and
machinability may be produced by controlling carbon and
nitrogen to achieve the desired hardness. Sulfur is
controlled in accordance with carbon plu~ nitrogen to
maintain a drill machinability rating equal to or greater
*L~\Css ~,
than 100 (when compared to a commercial ~ronbe-- hold0r block
~ 4;~\
steel). For this purpose, sulfur must be increased with
increases in the carbon and nitrogen content. Chromium, and
also nickel, are present for maintaining corroslon
resistance. Molybdenum is also added for corro~ion
resistance and specifically to counteract the adverse effects
of increased sulfur in this regard. Consequently, molybdenum
is increased with increased sulfur contents.
In accordance with the invention, a martensitic
stainless steel article, which may be used for holder blocks,
2~176~
frames, backers, and similar articles for anchoring mold~ and
dies, is of a composition within the limits set forth in
Table 1.
_ g ~t ~ 2 ~ ~ ~0~76~i
9 ~11 9 9 8 ~ S
o 8 o _ 8 8 N 8
¦ O O O N O O _ _ _ O
8 ~n _ 8.
~ ~ - x ~j ~ 8 ~
8 8 o o o o 8 0 8 ~ 8
O O O N O O _ _ _ O
8 N O
9 9 8 9 ~ 8 ~ ~ _ ~ y
8 8 o 8 o _ 8 8 . N 8
~ O O O N O O -- N _ O -- 1~
Vl g o ~" ~
o 9 9 9 ~li 9 9
a~ 8 g o 8 o o o 8 . ''7 8
_ O O O N O O _ ~ -- O _ a~
1~1 ~ ~ N 8 ~ ~
a~ 9 ii _ 9 0 9 N o o
o ~0 10 o 8 o o o N 8
_ O ~ O O;; O O _ _ _ O _ a~ `D
o 9 ~ O ~ o _ j;
_ o o o 8 o o 8 g 8 N g a
o 1~ O O O N O O _ _ _ O _ ~3
2c~ ~ g
C~ V~ O ~N 8 ~ r~
~ 9 ~ 9 ~ 9 ~ g ~ ~ Ue
i~ ~ o o o 8 o _ 8 8 j N 8
o _ 8, ~ r~
~ ~i 9 9 o 9 ~ o ~
o o o o o o 8 g "' 8
_ O O O N O O _ N O
_ g N 8 ~ 8
~ 9 9 ~ 9 9 0 o
m 8 g o ~ o o 8 8 . N g
O O O ~ O O -- _ -- O
_
1~
.
20S176~
The article is characterized by a hardness within the
range of 30 to 40 HRC, preferably 35 to 40 HRC for higher
strength application~.
In accordance with the method of the invention, stsel in
accordance with the compoqition limits set forth in Table I
is austenitized at a temperature within the range of 1500 to
1750F for about l hour per inch of thickness and either oil
quenched or air cooled to achieve a martensitic structure.
Thereafter, the article can be tempered or stress-relieved at
a te~perature between about 500 and 850F for about 1 hour
per inch of thickness and for a minimum of 2 hours. After
these heat treatments, the articles will exhibit a hardness
within the range of 30 to 40 HRC, preferably 35 to 40 HRC for
high strength application~, and a drill machinability rating
equal to or greater than 100.
Preferably, the article after tempering in addition
exhibits a corrosion rate in inches per year of less than 9
when tested in accordance with the procedure disclosed
hereinafter.
BRIFP D~SCRIPTION OF THF DRAMINGS
Figure 1 is a graph showing the relationship between
tempering temperature and hardness for a commercial stainless
2~617~
holder block steel of the composition, in weight percont,
0.32% carbon, 1.33% mangane~e, 0.32% ~ilicon, 0.097% sulfur,
0.50% nickel, 16.8% chromium, 0.04% molybdenum, Q.034%
nitrogen and balance iron and incidental impurities;
Figure 2 is a graph showing the relationship between
tempering temperature and hardness for the two indicated
holder block steels in accordance with the invention;
Figure 3 is a graph showing the relation~hip between the
hardness of holder block steel~ in accordance with the
invention in the a~-hardened condition in relation to the
carbon plu8 nitrogen content thereof;
Figure 4 is a graph showing the relationship between the
drill machinability of holder block steels in accordance with
the invention with re~pect to a parameter relating to the
hardness and sulfur contents thereof; and
Figure 5 is a ~eries of photograph~ comparing the
corrosion resi~tance of three holder block ~teel~ in
accordance with the invention with two holder block steels of
compositions outside the scope of the invention.
DBTAI~BD DESCRIPTION OF TH~ PXBFERRED EM~ODI~ENTS
Stainles~ steel holder blocks are generally made by hot
rolling or forging an ingot to slab or billet that i~
subsequently heat-treated to the desired final hardne~ and
2~76a
then sawed and machined into blocks of the required shapes
and dimensions. Less commonly, the holder blocks are cut and
rough machined from fully annealed slabs or billets, heat-
treated separately to the desired hardnes~, ~nd then machined
to f~nal shape. The hardness typical of ~tandard holder
block applicatLons ranges from about 30 to 35 HRC, wheress
that for high strength holder block applications ranges from
about 35 to 40 HRC. In order to attain these hardnesses
without undue cost or difficulty, it is essential that the
steel used in the holder block be readily heat-treatable to
the required hardnesa levels. With stainless steels typical
of those now used in corrosion resistant holder blocks, such
as that tested to obtain the data presented in Figure 1, the
tempering temperatures required to produce hardnesses in the
range of about 30 to 40 HRC and especially in the range of
about 35 to 40 HRC are quite critical in that s1ight
differences in temperature result in a larqe difference in
hardness. Thus, very close control of the tempering
operstion is needed with these steels to obtain the
hardnesse~ requ~red for holder block applications. Further,
such steel~ when tempered to hardnesses in the range of about
30 to 40 HRC exhibit relatively low notch toughness and
corrosion resistance.
In comparison, with the holder block steels of this
invention it is possible to obtain an improved combination of
2~6~76~
corrosion resistance and toughne~ and the hardnesse~ needed
for this application with a simple heat-treatment. Figure 2
shows that steel holder blocks produced in accordance with
the invention and within the composition limit~ g$ven in
Table I provide the desired hardnesse- in both the as-
hardened condition and when tempered or ~tress-relieved over
a broad range of temperatures. For example, a ~teel holder
block made from Heat V1056 containing 0.043% carbon plu8
nitrogen schieve~ a hardness well within the range needed for
standard holder blocks (30 to 35 HRC) in the as-hardened
condition and also when tempered or stress relieved at
temperatures up to about 850F. Similarly, a holder block
made from Heat V1020 with 0.0~9~ carbon plu8 nitrogen
achieves a hardness well within the range 35 to 40 HRC needed
for high strength holder blocks in the as-hardened condition
and also when tempered or stress relieved over a wide range
of temperaturea. Also, in contrast to ~t~inle~s ~teel~ of
the type now used in corrosion res$stant holder blocks, which
are normally austenitized from temperatures between about
1825 to 1900F, steel holder blocks produced within the scope
of the invention can be austeniti2ed from temperatures as low
as about 1550F, which achieves considerable energy savings
in heat-treatment.
With respect to the chemical composition of the steels
used in the holder blocks of this invention, it is necessary
_ 10 --
2061765
within the composition ranges given in Table I to control
their overall composition so that the holder block~ will be
substantially fully martensitic in the as-hardened condition.
To obtain a substantially fully martensitic structure in the
as-hardened condition, it is necessary that the composition
of the steelY be balanced with respect to the austQnite
forming elements, such as carbon, nitrogen, nickel, and
manganese, and the ferrite forming elements, such as
chromium, molybdenum, and ~ilicon, to minimize the formation
of delta ferrite. Large amount-q of delt~ ferrite are
detrimental in the steel from the ~tandpoint of reducing the
hardne6s and toughness of holder blocks made therefrom.
The hardness of the ~teels used in the holder blocks of
the invention in the as-hsrdened condition i8 primarily a
function of the carbon plus nitrogen content. To obtain the
desired hardnesses within the range of 30 to 40 HRC, it is
therefore necessary to control the carbon and nitrogen
contents within the rangeq indicated in Table I. With a
carbon plu8 nitrogen content that is too low, the holder
blocks will not achieve the minimum desired strength and
hardness; with a carbon plu~ nitrogen content that is too
high, the holder blocks will exceed the de~ired maximum
hardness and exhibit unacceptable machinab$1ity.
Manganese is a desirable element in the steels used in
the holder blocks. Manganese imparts hardenability and, in
-- 11 --
2~1765
combination with sulfur, is al~o present for purposes of
improvinq machinability through the formation of manganese
sulfide. Also, manganese is an austenite forming element and
can be used to partially replace nickel in the ~teel for
composition balance and to thereby redùce steel costs.
Silicon is used in steelmaking for deoxidation and
increasing chromium recovery. It al80 slightly improves
corrosion resistance, but is a ferrite forming element and
thus increases the amount of costly nickel or manganese
needed to obtain a fully martensitic structure.
Nickel is required within the indicsted ranges to obtain
the desired austenite-ferrite balance and to thereby obtain a
substantially fully martensitic structure in the holder
blocks. It also improves corrosion resi~tance; but ~8 a
costly element, and for this reason is not desirable above
the indicated ranges.
Chromium is essential for corro~ion re~istance, but
above the indicated amounts increases the amount of nickel,
manganese, and other austenite forming elements that are
required to be present to avoid the formation of delta
ferrite and to obtain a substantially fully martensitic
structure ln the holder blocks.
Molybdenum is an expensive alloying element, but in
small amounts and together with chromium has a very
2 ~ ~ ~ 7 6 ~
beneficial affect on the corro~ion resistance of the holder
block~, and a minimum of about 0.25~ is neces~ary for
reducing the adverse effect~ of ~ulfur on this property.
Consequently, molybdenum generally should be increased in the
pre~ence of increa~ed ~ulfur for this purpo~e.
Sulfur i~ used for improving machinability, but
decreases notch toughness and corrosion resistance. When
high toughne~s and corrosion resistance are required in the
holder blocks of the invention, ~ulfur should be limited to
about 0.10~; but when greater machinability is desired, it
can be increased to about 0.25% without lowering toughnesg
and corrosion resi~tance to unacceptable levels. Molybdenum
should be incres~ed w$th increased sulfur to maintain
corrosion resistance at the desired level.
Copper is a common re~idual element in stainle~s steel
melting, and i~ useful for controlling the austenite-ferrite
balance. However, in amount~ greater than about 1.0~ it can
have an undesirable hardening effect during tempering of the
holder blocks.
To demonstrate the principle~ of the invention, a serie~
of experiment~l holder block steels were made and sub~ected
to a variety of mechan~cal and corrosion tests. The chemical
compositions of the experimental holder block steels and of a
commercial ~tainless holder block steel (Alloy 90-45)
included for comparison are given in Table II.
- 13 -
206176~
_ ~
_ O N~O~O~gg~
jNN~ 2 ~ ~ N~oo
2 _ _ N~oN~NN~s
.~ ~ NNNNNNNNN~
O ._ ~ n
~ NNNN_NNN_O
_
,0 _ O ` O O ~~ O ~ - æ. 8.
_ O O O O O O O O
__ 2i S ~ I a!; ¢l
. _o~NO~N~o~
_ ~ _ o 8 o o o
2~6~6~
Ingots of the experimental holder block steels were hot
worked from a reheating temperature of about 2150F to bar
stock from which samples were taken for metallographic
evaluation and testing. Except for those samples used to
determine attainable hardne~s, all the test ~ample~ were
austenitized at 1550F, air cooled to room temperature, and
then tempered for two hour~ at 550F. None of the
experLmental holder block steels were found to contain any
delta ferrite after this heat-treatment. The samples of the
commercial stainless holder block steel were received in the
prehardened condition at a hardness of 33 HRC. In order to
test this material at a higher hardness of 38 ERC, samples of
the commercial holder block steel were austenitized at
1850F, oil quenched to room temperature and then tempered
for 2 hours at 975F.
Several tests were conducted to compare the advantages
of the holder block steels of the invention with those of a
commercial stainle~s holder block steel and to demonstrate
the significance of their composition. Tests were conducted
to illustrate the effects of steel composition on attainable
hardnes~, notch toughness, tensile strength, machinability,
and corrosion re~istance.
The attainable hardnesses of the experimental holder
block steels in the as-hardened condition are plotted in
2~176~
Figure 3 as a function of their carbon plus nitrogen
contents. The specimens for these tests were austenitized
for 15 minutes at 1600F and then air cooled to room
temperature. Allowing for some normal scatter in the results
of the hardness tests, Figure 3 shows that the attainable
hardnes~ of the steels used in the holder blocks of the
invention has a strong relationship with their carbon plus
nitrogen contents. To obtain the hardnesses needed for
holder block applications (30 ~o 40 HRC), Figure 3 shows that
the carbon plus nitrogen contents of the holder blocks of the
invention must be controlled in a range between about 0.02 to
O.09%. Further, to obtain the hardness typical of standard
holder blocks (30 to 35 HRC) and of high strength holder
blocks (35 to 40 HRC), the carbon plu8 nitrogen content of
the steels used in the holder blocks of the invention must be
controlled from about 0.02 to 0.06% and from about 0.06 to
0.09%, respectively.
The results of the notch toughness and tension tests
conducted on the experimental holder block steels and on the
commercial stainless holder block steel are given in
Table III.
- 16 -
2~76
o Q~
y
U .~ ~ ~ ~ o ~ I ~ ~ ~
~ .... _ . o
~ _ _ _ ~ ~
V- V~ o~ ~ ` ~ ~
~ ~ C
.o ~ o ~ o o ~ o ' 2L
2 ~ ~ n 0 ~ ~ ~ J
o ~ 3
.
c ~ V o o ~ o 4 o o o ~n e ,.
~ ~ ~ 2
~ O O ~ g g ~ a o
~C, ~ O
o o o o o o o o o O, 1"~
__ _ _ ~ - ~
~ 8~ ~0 0~ 0~ o ~, æ o . ~ -
_ _ _
2~176a
These test results show that the notch impact toughness of
the ~teels u~ed in the holder blocks of this invention, as
measured in the Charpy V-notch impact test, are clearly
superior to those of a commercial stainles~ steel typically
used in this application (Alloy 90-45). The advantage in
toughnes~ i8 particularly great for those experimental steels
containing les~ than about 0.10~ sulfur, as can be qeen by
comparing the notch toughnes~ values of Alloy V1033 (30.6 ft-
lb) with those of the commercial stainless holder block steel
(5.0 ft-lb). Above sulfur levels of about 0.10%, the impact
properties of the steels u~ed in the holder blocks of the
invention are still ~ignificantly better than that of the
commercial stainle~s holder block steel. For example, the
notch toughness of Alloy V1055 with 0.20% sulfur i8 15.0 ft-
lb in the longitudinal direction; whereas, that of the
commercial stainless holder block steel (Alloy 90-45) with
0.09% sulfur is only 5.0 ft-lb.
The tensile properties of the steels used in the holder
blocks of this invention are largely a function of their
hardness and are at least comparable to tho~e of the
commercial stainless holder block steel at the same hardneqs.
About the ~ame mechanical properties and notch toughne~s are
obtained for the higher manganese and lower nickel containing
experimental holder block steels ~Alloys V1022 and V1055) a~
- 18 -
206176~
for the comparable steels with higher nickel and lower
manganese (Alloys V1020 and V1056). Thus, when it i9
de~irable to reduce cost, manganese csn be used to replace
psrt of the nickel in the steels used in the holder blocks of
this invention.
The re~ult~ of drill machinability tests conducted on
the experiment~l steel~ used in the holder blocks of the
invention and on a commercial st~inless holder block steel
are given in Table IV and in Figure 4. The machinability
indexes given in this table and figure were obtained by
comparing the times re~uired to drill holes of the same size
and depth in the experimental steels and in the commercial
stainless holder block steel at a hardness of 33.0 HRC and by
multiplying the ratios of these time~ by 100. Indexes
greater than 100 indicate that the drill machinability of the
test specimen i~ greater than that of the commercial
stainless holder block steel. Because the hardness and
sulfur content of these steels are known to influence
machinability, a parameter based on these factors [Rockwell C
hardnes~ -100 (% S)] wa~ derived and used to compare the
drill machinability of the test materials.
-- 19 --
2~176~
8 ?~
I - ~ ~ Z Z, ~ i
ll L ~! C æ _ O o ". æ ~ ~ N 8 ~
~ ~ 1~ -- C
~ 0 ~ ~ ~ ~7 o, ~7 o. o, ~ 0 ~
1~ -- 0 N N æ N N Ir~ N _ _ N l!e
~ ~ '
~ ~ ~ O. O. ~ ~ O. In 0. O, O. In ~
S~ ~i -- N ~ ~ O
~ ~ O ~ ~ o O O N _ ~ g ~ ~
_ O O O O O O O O O O O ~
O
'~ I ~ ~ O ~ O O O 0 50~ ~o ~N N
_ O O O O O O O O O O O
~ 1~ O~ ~ N O _ ~ tl ~ ~U
3 ~ 8 o ~ o o o ~ ~ ~ _
20~7~
Analysis of the drill machinability test data using the
rQlationship derived between the above parameter and the
machinability index indicate~ that to provide machinability
at lea~t equivalent to that of the commercial stainless
holder block steel at a hardness of 33 HRC, the steels used
in the holder blocks of this invention must contain at least
0.05% sulfur. Likewise, to provide machinability at least
comparable to that of the commercial ~tainless holdor block
steel at a hardness of 33 HRC, the holder block steels of the
invention at a hardness of 38 HRC mu~t contain at least 0.10
sulfur. These result~, in combination with those of the
notch toughness tests reported in Table III, indicate that at
sulfur levels between about 0.05 and 0.10% the steels used in
the holder blocks of the invention afford substantially
better notch toughne~s and machinability superior to that
provided by current stainles~ holder block ~teels. They also
indicate that at sulfur contents between about 0.10 and
0.25~, the steels used in the holdor block~ of this invention
provide substantially better machinability and notch
toughness superior to that of current stainless holder block
~teel~.
Two tests were used to compare the corrosion re~istance
of the steels used in the holder blocks of this invention to
that of a typical commercial stainless holder block ~teel,
20~176a
the composition of which iQ given in Table II. In one test,
the weight 1088 and resulting corro-~ion rates were determined
for specimenQ immerQed for three hours at ambient temperature
in a dilute solution of aqua-regia containing 5% nitric acid
and 1% hydrochloric acid by volume. This test is described
in the literature (E. A. Oldfield, "Corrosion of Cutlery~,
Corrosion Technology, June, 1958, pp. 187-189) and is
particularly useful for comparing the effects of composition
and heat treatment on the corroQion re~istance of marten~itic
stainless steels. The term corrosion rate in inche~ per
year~ as used herein rafer~ to the corrosion rate exhibited
by an alloy article sub~ected to this test procedure. The~e
tests were conducted on specimen that were passivated and
not passivated prior to testing in a solution of 20% nitric
acid containing 3% by weight of potas~ium chromate at 120F
for 1/2 hour. The other test was a salt spray test in which
~pecimens were exposed for three hours at 90F to vapors
generated from an aqueous solution containing 2.5% by weight
of sodium chloride. In this latter test, material
performance was ran~ed visually by estimating the percentage
of the surface area thst was affected by corrosion. The
results of the corro~ion tests are summarized in Table V.
Photographs of five of the specimens sub~ected to the salt
spray test are shown in Figure S.
206~7~5
~ ~y
_ } ~ SS ii
,, D 2 ~ o o o ~ o ~ ~o
Y ~`
D N 1' ~ ~ N ~ ~
~:3 ~ _
1~ 1~ ~ ~ ~ .-
lô ~ 8 N -- ~E -- Y
O O O O O O O O O _ y
O Y
.. ~ o ~ 8 ~ e ~
_ o
~ J 0 ~0 0 g 0~ 0 0 0 C O
_ ,, ~,,,,, æ ~ ~
_ _
206~7~5
The result~ of the dilute aqua-regia and the salt spray
tests clearly show that the steels used in holder blocks of
this invention have substantially better corrosion resistance
than a steel typical of that now uQed in stainless steel
holder block~. This is evidenced by the great difference in
the corrosion rates exhibited in the dilute aqua-regia te~t
by Alloys V1033 (4.3 inches/year) and V1021 (5.5 inchesJ
year), whose compo~itionQ are within the scope of the
invention, and Alloy 90-45 (14.1 inches/year) which is
representative of the steel~ now used in stainless steel
holder blocks. The great advantage of the s~eels used in the
holder blocks of this invention is also exhibited in the salt
spray test, a~ can be seen by comparing the percent affected
area for these same alloys. The results of the corrosion
tests also demonstrate the importance of maintaining the
molybdenum content of the steels used in the holder blocks of
this invention above about 0.25. In this regard, note, for
example, the relatively poor performance of Alloy V1087,
which except for a very low molybdenum content has a
composition within the scope of the invention, a~ compared to
the good performance of Alloys V1003 and V1009, which contain
about 0.32~ molybdenum and whose compo~itions are within the
scope of the invention.
The relative corrosion reQistance of three of the
experimental holder block steel~ (Alloy~ Y1009, V1020, and
- 24 -
2~617~
Vl020) and of two steel~ (Alloy~ V1087 and 90-45) out~ide the
~cope of the invention is further illustrated in ~igure 5.
As can be ~een, Alloy~ V1009, V1020, and V1021, havinq
compositions within the ~cope of the invention, ~how
considerably better corro~ion re~i~tance in the salt spray
te~t than do Alloy~ V1087 and 90-45. The composition of
Alloy V1087 i9 similar to that of Alloy~ V1009 and V1020,
except that it contain~ lesY than 0.01~ molybdenum. This
again demonstrates the importance of maintaining a minimum of
about 0.25% molybdenum in the steels used in the holder
block~ of this invention. ~lloy 90-4S iQ typical of the
steels currently used in stainless steel holder blocks, and
its comparatively poor performance again demon~trates that
the steels used in the holder blocks of thi~ invention have
substantially better corro~ion resistance.
The re~ults of the corro~ion test~ together with those
of the mechanical property tests in ~able III and of the
machinability te~ts in Table IV clearly ~how that the
corrosion re~istant holder block ~teel~ of the invention
provide a substantially better combination of notch
toughne~, m~chinability, and corrosion re~i~tance than
afforded by conventional stainless steel holder blocks.
Further, the steel~ u~ed in the holder block~ of the
invention have the advantaqe of being hardenable to the
hardnesse~ needed for this application with a ~imple heat-
tre~tment.
- 25 -
