Note: Descriptions are shown in the official language in which they were submitted.
122~
BP~CKGROUND OF THE INVENTION
_ _ _ _ _
The present invention relates to a
work-hardenable austenitic manganese (Hadfield type) steel
having an elongation at rupture of 10 percent to 80
percent, and to a method for the production thereof.
Work-hardenable austenitic manganese steels
have a wide range of application in the form of castings,
forgings and rolled material. This wide use is due, in
particular, to its high inherent ductility and satisfactory
work-hardening ability. Uses range from castings for
crushing hard materials to shell-proof objects. The
valuable properties of manganese steel reside in the
combina~ion of the above-mentioned properties of
work-hardening and ductility. Work~hardening takes place
whenever manganese steel is subjected to mechanical stress,
for example, by shock or impact which converts the
austenite in the surface layer partly to an
epsilon martensite. Measurements of work-hardening reveal
an increase of between 200 and 550 in Brinell hardness.
Thus, castings, forgings and the like increase in hardness
during use, if they are subjected to mechanical stress.
However, since such objects are also subjected to abrasion,
the surface layer is constantly being removed, leaving
austenite at the surface. This austenite is again
~f.
conver-ted by renewed mechanical stress. The alloy located
below the surface layer is highly ductile, and manganese
steels can therefore withstand high mechanical impact
stress without any danger of rupture, even in the case of
objects having thin walls.
ln the case of objects to be made of manganese
steel, it is essential that a preliminary mold or
ingot-casting be produced in order to predetermine the
properties of objects made therefrom. If the casting has
an unduly coarse structure, the object will have low
ductility. In the cases of large castings, it is known
that grain-size varies over the cross-section. At the
outside is a thin, relatively fine-grained edge zone,
followed by a zone consisting of coarse columnar crystals,
followed, in turn, by the globulitic structure at the
center of the casting. Although the steel is essentially
austenitic and work-hardenable over its entire
cross-section, great differences arise in its mechanical
properties, especially in its ductility, as a result of
these structural differences.
In order to achieve the most uniform ductility
possible over the entire cross-section, it has already been
proposed that the casting temperature be kept as low as
possible, for example at 1410C, since increasing
super-cooling should cause the number of nuclei to grow and
produce a finer grain-size. These low casting
temperatures, however, cause major production problems.
For instance, ~-shuts occur in the casting and the
rheological pxoperties of the molten metal are such that
the mold is no longer accurately filled, especially at the
edges. Furthermore, the molten metal solidifies, during
casting, on the lining of the ladle, leading to ladle
skulls or skins which must be removed and reprocessed.
During actual casting, the plug may stick in the outlet,
which means that pouring must be interrupted. It will
easily be gathered from the foregoing that the economic
disadvantages to be incurred for a non-reproducible
refining of the grain are so serious that this
low-temperature-casting process has not been able to gain
acceptance.
Another method of refining the grain involves a
specific heat-treatment, the casting being annealed for 8
to 12 hours at a temperature of between 500C and 600C,
whereby a large proportion of the austenite is converted
into pearlite. This is followed by austenitizing-annealing
at a temperature of between 970C and 1110C. This double
structural change is supposed to produce a finer grain, but
it also causes the product to become extremely brittle
during the heat-treatment, so that it ruptures without any
2~
deformation even under low mechanical stress. Another
major disadvantage is that the process re~uires a
considerable amount of energy.
Fox these reasons, attempts have already been
made to achieve grain refining by adding further alloying
elements, for example chromium, titanium, zirconium and
nitrogen, in amounts of at least 0.1 percent or 0.2 percent
by weight. Although at low casting temperatures, these
additions or additives do refine the grain, they
substantially impair mechanical properties, especially
elongation and notch-impact strength.
Manganese steels ~Hadfield type) usually have a
carbon content of 0.7 percent to 1.7 percent by weight,
with a manganese content of between 5 percent by weight and
18 percent by weight. A carbon : manganese ratio of
between 1 : 4 and 1 : 14 is also essential if the
properties of manganese steels are to be maintained. At
lower ratios, austenitic steel is no longer present, the
steel can no longer be work-hardened, and toughness is also
impaired. At higher ratios, the austenite is too stable,
again there is no work-hardening, and the desired
properties are also not obtained.
i
s
~ - 5 -
122~
A phosp~orus content in excess of 0.1 percent
by weight produces an extreme decline in toughness, so
that, as is known, a particularly low phosphorus content
must be sought.
AST~ A 128/64 describes four different kinds of
manganese steel, with the carbon content varying between
0.7 percent by weight and 1.45 percent by weight and the
manganese content between 11 percent by weight and 14
percent by weight. The carbon content is varied to alter
the degree of work-hardening, and this may also be
influenced ky the addition of chromium in amounts of
between 1.5 percent by weight and 2.5 percent by weight.
Coarse carbide precipitations are to be avoided by adding
up to 2.5 percent by weight of molybdenum. An addition of
up to 4.0 percent by weight of nickel is intended to
stabilize the austenite, thus preventing the formation of
pearlite in thick-walled castings.
Also known is manganese steel containing about
5 percent by weight of manganese. Although such steels
have little toughness, they have high resistance to wear.
1~2~i;6~
OBJECTS OF THE INVENTION
_
It is an important object of the present
invention to provide a work-hardenable austenitic manganese
steel having an eiongation at rupture of 10 percent to 80
percent, -the most uniform possible structure over the
entire cross-section, and a particularly fine grain size,
with no impairment of mechanical properties.
DETAILED DESCRIPTION OF THE INVENTION
r: . _ _ _ __ _____
The work-hardenable austenitic manganese steel
according to the invention, having an elongation at rupture
of 10 percent to 80 percent, measured according to L = 5 d
or L = 10 d, and the following content in percent by
weight:
0.7 to 1.7 C
5.0 to 18.0 Mn
0 to 3.0 Cr
0 to 4.0 Ni
0 to 2.5 Mo
0.1 to 0.9 Si
up to 0.1 P
1~:%~
and with the proviso that the carbon : manganese ratio be
between ~ : 4 and 1 : 14, comprises, as micro-alloying
elements, up to 0.20 percent of titanium, up to 0.05
percent of zirconium and up to 0.05 percent of vanadium,
with the proviso that the sum of micro-alloying elements be
between 0.002 percent and 0.25 percent by weight.
It came as a complete surprise to find that
such small additions of alloying elements refine the grain
and simultaneously maintain or increase mechanical
properties. It has been found that at high furnace
temperaturesr such as 1600C, additions of 0.1 percent by
weight or more of the alloying elements result in
impairment of the aforesaid mechanical properties, while at
lower furnace temperatures such as 1480C the addition of
0.25 percent by weight or more of the alloying elements
results in such impairment. No precise explanation for this
has as yet been found. Zirconium and vanadium are
particularly effective at high casting temperatures.
A still finer grain size is obtained by also
adding 0.002 percent by weight to 0.008 percent by weight
of boron to the manganese steel.
-- 8
~2~0
Particularly satisfactory grain refinement is
obtained by usiny only 0 01 percent by weight to 0.025
percent by weight of titanium as a micro-alloying el.ement.
If the manganese steel contains from 0.01
percent by weight to 0.05 percent by weigh~ of aluminum,
the titanium content can be particularly accurately
maintained.
The production of a manganese-steel casting
according to the invention, by melting a charge in an
electric furnace and adding to the molten metal
lime-containing and slag-forming additives, adjusting to
the desired analysis, raising the charge to a tapping
temperature of 1450C to 1600C, deoxidizing with an
element having an affinity for oxygen, and tapping into the
casting ladle, consists mainly in that the content of the
micro-alloying elements titanium, zirconium and vanadium is
adjusted in the casting ladle, the melt being poured at a
temperature of between 1420C and 1520C, the casting being
cooled down and then heated again to an austenitizing
temperature of 980C to 1150, and being then quenched.
Adding the micro-alloying elements in the ladle
ensures that the content of the said elements is
reproducible. A particular high degree of toughness is
~22~6~
obtained by heating the casting to an austenitizing
temperature of 980C to 1150C, followed by quenching.
If after being heated to 1030C to 1150C, the
casting is cooled to a temperature of 980C to 1000C and
is quenched after the temperature in the casting has
equalized, this substantially reduces the tendency oE the
casting to crack. Manganese steel has lower
heat-conductivity than other steels (only one sixth that of
iron), and particular attention must therefore be paid to
temperature equalization.
Even in the case of large cross-sections,
reliable dissolution of grain-boundary carbides may be
achieved, with low power-consumption, by a solution
heat-treatment at a temperature of between 1080C and
1100C, after which the temperature is lowered to 980C to
1000C and is equalized. The casting is then quenched.
A casting having particular low internal stress
may be obtained by heating it to the austenitizing
temperature and then subjecting it alternatingly to
coolants of different heat-conductivity. Particularly
suitable coolants for this purpose are water and air.
.~
-- 10 -
~2X156~
If a casting is removed from the mold at a
temperature of between 800C and 1000C, is then placed in
a heat-treatment furnace in which the temperature of the
casting is equalized, and then is immediately raised to the
austeniti~ing temperature, this provides a particularly
energy-saving process and at the same time prevents high
stresses from building up in the casting and avoids
pearlitizing.
The invention is explained hereinafter in
greater detail by reference to the following examples:
Example 1:
15 t of manganese steel of the following
composition were melted in an arc-furnace:
1.21 percent by weight of carbon; 12.3 percent
by weight of manganese; 0.47 percent by weight of silicon;
0.023 percent by weight of phosphorus; 0.45 percent by
weight of chromium, and traces of nickel and molybdenum.
The melt was covered with a slag consistiny of 90 percent
by weight of limestone and 10 percent by weight of calcium
fluoride, after which the melt was adjusted to a tapping
temperature of 1520C. Final deoxidizing was then carried
out with metallic aluminum. After deoxidizing, the melt
~2~5~C)
was tapped into the casting ladle, where the measured
temperature was 1460C. The melt was poured into a basic
sand casting mold Imagnesite). The casting obtained was a
tumbler having a gross weight of 14 t and a net weight of
11 t had walls between 60 mm and 180 mm in thickness. The
castin~ was allowed to cool to room temperature, was
removed from the mold, and then was heated slowly to
1050C. After a holding period of four hours, the tumbler
was quenched in water. The casting thus obtained exhibited
cracks which had to be closed by welding with the same type
of material. The metallographic tests showed an extreme
transcrystallite zone with an adjacent globulitic zone.
Test pieces from the said globulitic zone showed 8.4
percent elongation, as measured according to L = 10 d.
Tensile strength was 623 N/mm .
The procedure was the same as in Example 1,
titanium in the form of ferro-titanium being added in the
casting ladle. The casting ladle was moved to the mold and
pouring was carried out at 1460C. ~he casting was cooled
and then heated to 1100C, being held at this temperature
for four hours. The temperature of the furnace was then
lowered to 1000C. Temperature-equalization was obtained
in the casting after one hour, after which the casting was
- 12 -
~2~ 3
cooled by alternating immersion in a bath of water The
tumbler thus obtained was free from cracks. Metallographic
investigation revealed a completely uniform fine-grained
structure, except at the edge zone which was
microcrystalline. The average titanium-content of the
casting was 0.02 percent by weight. Samples taken from the
center and edge or the casting showed almost identical
mechanical properties, the tensile strength being 820 and
830 N/mm , respectively, and the elongation 40 percent
and 43 percent, respectively.
Example 3:
For the purpose of producing a 180 Kg
drop-forged striking hammer, with trunnions, for a
rock-crushing mill, an ingot similar to that in Example 2
was cast. This ingot was divided and the parts were
converted into striking hammers at a forging temperature of
1050C. In the vicinity of the trunnions, these hammers
exhibited a completely fine structure which was maintained
even after solution heat-treatment and quenching. A hammer
produced with the alloy according to Example 1 showed
coarse-grained crystals in the vicinity of the trunnions,
resulting in some micro-cracks.
X~i6~3
Example 4:
10 t of manganese steel of the ~ollowing
composition were melted in an arc-furnace:
1.0 percent by weight of carbon; 5.2 percent by
weight of manganese; 0.4 percent by weight of silicon; 1.7
percent by weight of chromium; 1.0 percent by weight of
molybdenum, and 0.03 percent by weight of phosphorus. The
melt was covered with a slag consisting of 90 percent by
weight of limestone and 10 percent by weight of calcium
fluoride, and the melt was adjusted to a tapping
temperature of 1490C. Final deoxidizing was then carried
out with metallic aluminum. After deoxidizlng, the melt
was tapped into the casting ladle where the measured
temperature was 1430C. Ferro-titanium and a
zircon-vanadium alloy were added to the melt in the casting
ladle. During the casting of plates for ball-mills, a
temperature of 1430C was maintained. The plates obtained
had walls 80 mm in thic~ness. They were removed from the
mold at a temperature of 850C and were held for two hours
in a heat-treatment furnace adjusted to a temperature of
850C until the temperature had equalized. Thereafter, the
said plates were heated to 1100C and were then cooled.
Metallographic investigation revealed a completely uniform
fine-grained structure except for the edge-zone, which was
- 14 -
.5~
microcrystalline. The average content of titanium,
vanadium and zirconium was 0.03 percent by weight. The
mechanical properties of samples taken from the edges and
centers were almost identical, the tensile strength being
850 and 835 N/mm2~ respectively, and the elongation 45
percent and 48 percent, respectively.
Example 5:
The procedure was as in Example 2, but boron as
well as tltanium were added in the casting ladle. The
temperature pattern was as in Example 2. The casting had
an average titanium content of 0.02 percent by weight and
an average boron content of 0.005 percent by weight. In
the case of samples taken from similar locations,
micrographs showed 50 grains in the samples containing
titanium only and an average of 60 grains in samples also
containing boron, the reduction in average grain-size being
from 0.02 mm to 0.017 mm.
Example 6:
500 kg of manganese steel of the following
composition were melted in an induction furnace:
122i56~
1.35 percent by weight of carbon; 17.2 percent
by weight of manganese; traces of nickel and chromium, and
0.02 percent by weight of phosphorus. The melt was covered
with a slag consisting of 90 percent by weight of limestone
and 10 percent by weight of calcium fluoride and was
adjusted to a tapping temperature of 1600C. Final
deoxidizing was carried out with metallic aluminum, after
which the melt was tapped into the casting ladle and
titanium was added. Round bars 110 mm in diameter were
then cast at 1520C. Upon cooling, the bars were removed
from the molds, were heated to 1030C, and were held at
this temperature for five hours. The furnace-temperature
was then lowered to 980C, at which it was held for an hour
and a half. The bars were then quenched in a bath of
water.
The melts were repeated with varying titanium
contents, the mechanical values given in the following
table being measured on test-pieces taken from the centers
and edge-zones:
~156~
cer.ter test-pieces edge test-pieces
tensile elongation tensile elongation
% by weight streng~h at rupture streng~h at rupture
of titanium N/mm % N/mm %
- 650 12 710 22
0.2 550 7.8 710 22
0.1 580 9~2 705 21
0.04 790 42 810 45
0.02 ~12 50 ~25 55
0.01 815 52 830 58
As may be gathered from the table, the addltion
of 0.1 percent by weight of titanium at the indicated high
furnace temperature produced impairment of mechanical
properties and also a relatively large difference between
edge and center test-pieces. With a titanium content of
less than 0.05 percent by weight, the properties of edge
and center test-pieces are almost identical and there is an
increase in mechanical properties as compared with
non-micro-alloy manganese steel.
Tensile strength and elongation at rupture were
determined in accordance with DIN 5 D 145/1975.
Example 7:
500 kg of manganese steel of the following
composition were melted in an induction furnace:
- 17 -
~:2~S~
1.35 percent by weight of carbon; 17.2 percent
by weight of manganese; -traces of nickel and chromium, and
0,02 percent by weight of phosphorus. The melt was covered
with slag. The temperature of the melt rose to a
temperature or 1480C at most. For final deoxidation
metallic aluminum was added, whereafter the melt was -tapped
into the casting ladle and 0.2 percent by weight titanium
were added. Round bars 110 mm in diameter were then cast at
1440C. Upon cooling, the bars were removed from the
molds, heated to 1030C and held at this temperature for
five hours. The furnace temperature was then lowered to
980C and held there for an hour and a half. The bars were
subsequently quenched in a bath of water.
Example ~:
500 kg of manganese steel of the following
composition were melted in an induction furnace:
1.24 percent by weight of carbon, 0.52 percent
by weight of silicon, 12.57 percent by weight of manganese,
0.13 percent by weight of nickel, 0.42 percent by weight of
chromium, 0.027 percent by weight of phosphorus and 0.008
percent by weight of sulfur. The melt was covered with
slag and adjusted to a tapping temperature of 1470C. For
fina~l deoxidation metallic aluminum was added whereafter
- 18 -
~2~i5~
the melt was tapped into the casting ladle and 0.05 percent
by weight of titanium was added. The melt temperature was
kept always below 1490C. Round bars 110 mm in diameter
were then cast at 1440C. Upon cooling, the bars were
removed from the molds, heated to 1030C and held at this
temperature for five hours. The furnace temperature was
then lowered to 980C, and held there one hour and a half.
The bars were then quenched in a bath of water.
Example 9
500 kg of manganese steel were melted in an
induction furnace. The procedure was basically the same as
in Example 8, however, 0.10 percent by weight of titanium
was added into the casting ladle.
_xample 10:
500 kg of manganese steel were melted in an
induction furnace. mhe procedure was basically the same as
in Example 8, however, 0.18 percent by weight of titanium
was added into the casting ladle.
-- 19 --
~ ~215~
Example 11-
._
500 kg of manganese steel of the same
composition as in ~xample 10 were melted in an induction
furnace and cast from the casting ladle at a casting
temperature of 1460C.
Example 12:
500 kg of manganese steel of the same
composition as in Example 9 were melted in an induction
furnace and tapped into the casting ladle at a tapping
temperature of 1550.
Example ~3:
500 kg of manganese steel of the following
composition were melted in an induction furnace:
1.24 percent by weight of carbon, 0.52 percent
by weight of silicon, 12.57 percent by weight of manganese,
0.13 percent by weight of nickel/ 0.42 percent by weight of
chromium, 0.027 percent by weight of phosphorus and 0.008
percent by weight of sulfur. The melt was covered with
slag and adjusted to a tapping temperature of 1550C. For
- 20 -
~L~2~S~
final deoxidation ~etallic aluminum was added and
thereafter O.G5 percent by weight of vanadium.
Subsequently the melt was tapped into the casting ladle and
0.10 percent by weight of titanium was added. The melt
temperat~lre was kept always below 1490C. Round bars llo
mm in diameter were then cast at 1440C. Upon cooling, the
bars were removed from the molds, heated to 1030C and held
at this temperature for five hours. The furnace
temperature was then lowered to 980C and held there for
one hour and a half. The bars were then quenched in a bath
of water.
Example 14:
500 kg of manganese steel having the same
composition as in Example 13 were melted in an induction
furnace and the procedures were the same as in Example 13
with the exception of the tapping temperature of the
furnace being adjusted to 1520C.
Example 15:
500 kg of manganese steel having the same
composition as in Example 13 were melted in an induction
furnace and the procedures were the same as in Example 13
with the exception of the tapping temperature of the
furnace being adjusted to 1520C and with the further
1~21~
exception that the bars were cast at a casting temperature
o~ 1475C.
Example 16:
500 kg of manganese steel were melted in an
induction ~urnace as in Example 8 wlth the exception that
the maxinlum temperature of the melt was 1500C, that 0.035
percent by weight of vanadium was added in the furnace and
that 0.08 percent by weight of titanium were added in the
casting ladle.
Example 17:
500 kg of manganese steel of the following
composition were melted in an induction furnace:
1.24 percent by weight of carbon, 0.52 percent
by weight of silicon 12.57 percent by weight of manganese,
0.13 percent by weight of nickel, 0.42 percent by weight cf
chromium, 0.027 percent by weight of phosphorus, and 0.008
percent by weight of sulfur. At first, however, only 90
percent by weight of the required manganese content were
added in the furnace and the melt was heated to a
temperature of 1620C. Thereafter the melt was cooled by
argon ~lushing to a temperature of 1520C and the remaining
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~Z~5~
10 percent by weight of the total manganese content was
added. The melt was covered with slag and adjusted to a
tapping temperature of 1470C. For final deoxidation
metallic aluminum was added and thereafter 0.035 percent by
weight of vanaclium. The melt was then tapped into the
casting ladle and 0.08 percent by weight of titanium was
added. The melt temperature was kept always below 1490C.
Round bars 110 mm in diameter were then cast at a casting
temperature of 1460C. Upon cooling, the bars were removed
from the molds, heated to 1030C and held at this
temperature for five hours. The furnace temperature was
then lowered to 980C and held there for one hour and a
half. The bars were then quenched in a bath of water.
Example 18:
500 kg of manganese steel of the composition as
in Example 17 were melted with the same procedures as in
Example 17 with the exception that the vanadium was added
into the casting ladle and not in the induction furnace.
The grain size of the vanadium was in the range of 1/8 to
1/4 inch.
- 23 -
~;~2~5SO
Example 19:
500 kg of manganese steel of the composition as
in Example 9, with the exception that in addition to the
titanium there was added 0.02 percent by weiyht of
~irconium, were melted in an induction furnace under the
same procedures as in Example 9.
In the following table the tensile strength and
the elongation at rupture are shown for center test pieces
and edge test pieces in accordance with examples with
examples 7-19.
TABLE
center test-pieces edge test-pieces
tensile elongation tensile elongation
Example stren~th at rupture stren~th at rupture
N/mm % N/mm %
7 770 41 783 43
8 80S 45 815 47
9 800 44 813 49
801 43 812 48
11 805 41 811 46
12 650 12 690 20
13 648 1~ 695 20
14 810 42 815 44
805 40 812 44
16 813 44 820 46
17 795 42 803 45
1~ 794 43 804 45
19 805 45 810 48
- 24 -
~2%~56~
As shown by the table a synergisti.c effect
occurs with respect to the titanium content and the
temperature program or excursion of the melt ! 50 that an
improvement in properties only can be obtained when
distinct values for the ti-tanium and vanadium content are
observed as well as distinct values of the different
temperatures.
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