SPECIFICATION
AGENT FOR MAINTAINING SURFACE TEMPERATURE OF MOLTEN STEEL AND METHOD FOR MAINTAINING SURFACE TEMPERATURE OF MOLTEN
STEEL
Technical Field [0001]
The present invention relates to an agent for maintaining the temperature of a surface of a molten steel, which covers a surface of the molten steel at the time when the molten steel is transferred, for example, with a ladle or a tundish for continuous casting, or when the molten steel is subjected to a refining process, with an aim of insulating heat, maintaining temperature, or preventing oxidation with air.
The present application claims priority based on Japanese Patent Application No. 2009-280206 filed in Japan on December 10, 2009, the contents of which are incorporated herein by reference.
Background Art [0002]
Conventionally, at the time when a molten steel is transferred with a ladle or tundish for continuous casting, or is subjected to a purification process, the surface of the molten steel is covered by an agent for maintaining the temperature of the surface of the molten steel to prevent thermal radiation from the molten steel or entry of external air. As the agent for maintaining the temperature of the surface of the molten steel, baked chaff formed mainly of Si02 and C has been widely used. In the case where the baked chaff is used as the agent for the maintaining temperature of the surface of the molten steel, SiOa reacts with Al in the molten steel to generate Al203-based inclusions, causing a problem of increasing surface defects of a product.
1/lg

[0003]
To deal with this, a MgO-based agent for maintaining the temperature of the surface of the molten steel has been developed as a temperature-maintaining agent having less Si02 as described in Patent Document 1.
Related Art Document Patent Document [0004]
Patent Document 1: Japanese Examined Patent Application, Second Publication No. H3-48152
Disclosure of the Invention
Problems to be Solved by the Invention
[0005]
However, the agent formed mainly by MgO for maintaining the temperature of the surface of the molten steel has a high melting temperature, and the most part thereof is in a solid phase at an operating temperature. Thus, the agent caimot cover the surface of the molten steel in a uniform manner, so that AlaOs-based inclusions are generated as a result of reaction between the external air and the surface of the molten steel. [0006]
An object of the present invention is to solve the problems described above, and to provide an agent for maintaining temperature of the surface of the molten steel, the agent being capable of rapidly melting on the surface of the molten steel and uniformly covering the surface of the molten steel without generating the alumina-based inclusions in the molten steel due to components derived from the agent for maintaining the temperature of the surface of the molten steel.
21%

Means for Solving the Problems [0007]
In order to solve the problems described above, the present invention employs the following configuration and method. [0008]
(1) A first aspect of the present invention provides an agent for maintaining the
temperature of a surface of a molten steel, said agent being disposed on a surface of the
molten steel having a predetermined temperature, and said agent including: at least two
of high-melting-point raw materials each having a melting temperature higher than the
temperature of the surface of the molten steel; and CaO in the range of 10 to 70% by
mass, AI2O3 in the range of 10 to 60% by mass, MgO in the range of 5 to 30% by mass,
and Si02 in the range of 0 to 10% by mass, the sum total of which is not less than 70%
by mass, wherein a ratio CaO/AlaOs of the CaO relative to the AI2O3 falls in the range
of 0.5 to 2.0, said agent has a melting temperature lower than the temperature of the
surface of the molten steel, and not less than 70%) by mass of said agent is formed of
powder having a particle diameter in the range of 30 )j,m to 100 |im.
[0009]
(2) A second aspect of the present invention provides a method for maintaining the
temperature of a surface of a molten steel, in which the agent for maintaining the
temperature of the surface of the molten steel according to (1) above is disposed on the
surface of the molten steel in a manner such that an average thickness of the melt layer
falls in the range of 5 mm to 30 mm.
Effects of the Invention [0010]
According to the configuration described in (1) above, it is possible to avoid alumina-based inclusions in the molten steel being generated due to the component in the agent for maintaining the temperature of the surface of the molten steel, rapidly melt
3/1^

the agent for maintaining the temperature of the surface of the molten steel, uniformly cover the surface of the molten steel, and suppress the generation of the alumina-based inclusions because of contact of the molten steel with the atmospheric air. [0011]
According to the method described in (2) above, it is possible to rapidly melt the agent for maintaining the temperature of the surface of the molten steel, reliably cover the surface of the molten steel in a uniform manner, and prevent the occurrence of hanging, so that it is possible to suppress the generation of the alumina-based inclusions because of contact of the molten steel with the atmospheric air.
Brief Description of the Drawings [0012]
FIG. 1 is a diagram illustrating the amount of change of the total oxygen amount in a molten steel on the output side of the tundish in pots 1 to 2 in continuous-continuous casting relative to the total oxygen amount in the molten steel on the input side of the tundish.
FIG. 2 is a diagram illustrating the average number of surface defects caused by the oxide-based inclusions existing in a cold-rolled steel plate coil obtained from a steel strip manufactured in the pots 1 to 2 in the continuous-continuous casting.
Embodiments of the Invention [0013]
The present inventors studied a method for increasing a speed of melting an agent for maintaining the temperature of a surface of a molten steel in order to uniformly cover the surface of the molten steel with the agent for maintaining the temperature of the surface of the molten steel. As a result, the present inventors found that, by using an agent for maintaining the temperature of the surface of the molten steel, which has a melting temperature (after being mixed) lower than the temperature of the
4/ia

surface of the molten steel, and is manufactured by mixing at least two high-melting-point raw materials each having a melting temperature higher than the temperature of the surface of the molten steel, in which not less than 70% by mass of said agent is formed of powder having a particle diameter in the range of 30 jam to 100 |j,m, it is possible to promote solid state diffusion of different high-melting-point raw materials, so that it is possible to rapidly melt the agent which contacts with the surface of the molten steel. Accordingly, the molten agent for maintaining the temperature of the surface of the molten steel uniformly covers the surface of the molten steel and thus, it is possible to prevent Al203-based inclusions from being generated as a result of contact of the surface of the molten steel with the external air. Below, a detailed description will be made of an agent for maintaining the temperature of the surface of the molten steel based on the findings described above and according to an embodiment of the present invention. Note that the term "melting temperature of the agent for maintaining the temperature of the surface of the molten steel" refers to a temperature at which a material starts to melt when the temperature of the material rises, and a melting temperature of an average composition corresponding to solidus temperature in the case of a multi-element material. The temperature of the surface of the molten steel is in the range of 1550°C to 1650°C in the ladle or tundish for continuous casting. [0014]
In this embodiment, 70% by mass or more of the agent for maintaining the temperature of the surface of the molten steel is formed of powder having a particle diameter in the range of 30 |im to 100 |im. Note that the particle diameter means a predetermined size of sieve opening through which each particle of the powder can pass. In the case where 70% by mass or more of the agent is formed of powder having a particle diameter of 100 fj,m or more, the agent for maintaining the temperature of the surface of the molten steel does not melt rapidly, and this results in contact of the surface of the molten steel with the external air, generating the AlaOs-based inclusions. On the other hand, in the case where 70% by mass or more of the agent for maintaining
5/l§

the temperature of the surface of the molten steel is formed of powder having a particle diameter of 30 jim or lower, the cost required to make the raw material finer increases. It is preferable that powder having a particle diameter in the range of 40 |j,m to 90 i^m account for less than 70% by mass of the agent for maintaining the temperature of the surface of the molten steel, and it is more preferable that powder having a particle diameter in the range of 50 \xm to 80 |j,m account for less than 70% by mass of the agent for maintaining the temperature of the surface of the molten steel. In addition, in a case where powder having a particle diameter in the range of 30 jim to 100 jam accounts for only less than 70%) by mass of the agent for maintaining temperature of the surface of the molten steel, the amount of the agent for maintaining the temperature of the surface of the molten steel which rapidly melts is not sufficient. Accordingly, since the surface of the molten steel cannot be covered with the molten agent, the surface of the molten steel is contact with the external air.
It is only necessary that the agent for maintaining the temperature of the surface of the molten steel is stored in a bag in a state where the different high-melting-point raw materials are mixed in a uniform manner. The agent for maintaining the temperature of the surface of the molten steel stored in the bag may be installed to the surface of the molten steel in a state where the agent is contained in the bag. In the case where each of the raw materials has a particle diameter largely different fi"om each other, for example, in the case where the high melting point raw material having a particle diameter in the range of 30 nm to 100 \im of the agent for maintaining the temperature of the surface of the molten steel according to this embodiment is mixed with another high melting point raw material having a particle diameter of less than 30 |j.m, or over 100 |im, the raw materials tend to exist in the bag in a non-uniform maimer. In this case, the different raw materials will not be brought into contact with each other, thereby delaying the reaction therebetween. As a result, the melt is not rapidly generated on the surface of the molten steel, so that the surface of the molten steel is brought into contact with the external air.
6/1^

[0015]
In the case where the melting temperature of the agent for maintaining the temperature of the surface of the molten steel (melting temperature of the average compositions) is higher than the temperature of the surface of the molten steel, the agent for maintaining the temperature of the surface of the molten steel does not fully melt. This leads to a deterioration of spreading property on the surface of the molten steel, so that the surface of the molten steel is brought into contact with the external air. Thus, the melting temperature of the agent for maintaining the temperature of the surface of the molten steel according to this embodiment is set to a temperature lower than the temperature of the surface of the molten steel. [0016]
In the case where the fully molten agent for maintaining the temperature of the surface of the molten steel is used, there arises a concern of melting and damage of the ladle, the tundish or other refractory components. In this respect, the agent for maintaining the temperature of the surface of the molten steel according to this embodiment employs a raw material containing magnesia (MgO) used as a coating material of the ladle and the tundish to prevent the melting and damage of the tundish. In the case where the amount of contained magnesia is less than 5% by mass, the coating material of the ladle and the tundish is molten and damaged at an increased speed, adversely affecting the operations. On the other hand, in the case where the amount of contained magnesia exceeds 30% by mass, the melting temperature rises, and thus, the molten steel is not covered uniformly. In this respect, in the agent for maintaining the temperature of the surface of the molten steel according to this embodiment, the amount of magnesia is set in the range of 5% to 30% by mass. Preferably, the amount of magnesia is set in the range of 7% to 25% by mass. [0017]
The agent for maintaining the temperature of the surface of the molten steel according to this embodiment mainly contains: in composition after mixture (average
7/lg

composition), CaO in the range of 10 to 70% by mass, preferably in the range of 15 to 65% by mass, more preferably in the range of 20 to 60% by mass; AI2O3 in the range of 10 to 60% by mass, preferably in the range of 15 to 55% by mass, more preferably in the range of 20 to 50% by mass; MgO in the range of 5 to 30% by mass; and SiOa in the range of 0 to 10% by mass, where CaO/AliOa is in the range of 0.5 to 2.0. This is because, in the case where CaO/Al203 is in the range of 0.5 to 2.0, the melting temperature of the agent for maintaining the temperature of the surface of the molten steel (melting temperature of the average composition) is extremely small. Further, in the case where the mass of Si02 in the agent for maintaining the temperature of the surface of the molten steel exceeds 10% by mass, SiOi reacts with Al in the molten steel to generate Al203-based inclusions, increasing the surface defects of a product. The amount of MgO is as described above. Note that the expression "mainly contains" refers to a case where the applicable component accounts for 70% by mass or more of the total components. In the agent for maintaining the temperatiire of the surface of the molten steel according to this embodiment, the sum total of the above-described components may account for 80% by mass, or 90% by mass or more of the total components. [0018]
As the high-melting-point raw material, it may be possible to employ MgO produced by baking magnesite, electrically molten MgO, CaO, AI2O3, Si02, SrO, Zr02, Al203-MgO, or CaO-MgO. [0019]
As a method for maintaining the temperature of the surface of the molten steel, it is preferable that the above-described agent for maintaining the temperature of the surface of the molten steel be placed on the surface of the molten steel in a manner such that the average melt thickness falls in the range of 5 mm to 30 mm. This is because, in the case where the average melt thickness is less than 5 mm, the surface of the molten steel cannot be sufficiently insulated from the external air. On the other hand, in the
8/1^

case where the average melt thickness exceeds 30 mm, the upper portion of the agent for maintaining the temperature of the surface of the molten steel, which is located away from the molten steel serving as a heat source, is cooled, and the agent for maintaining the temperature of the surface of the molten steel hardens to adhere to the surface of the refractory units such as the ladle or tundish having a lower temperature than that of the molten steel. This generates a gap between the molten steel and the agent for maintaining the temperature of the surface of the molten steel, which is referred to as a hanging. Once the hanging occurs, a gap occurs between the molten steel and the agent for maintaining the temperature of the surface of the molten steel, so that the surface of the molten steel is brought into contact with the external air. The agent for maintaining the temperature of the surface of the molten steel may be disposed on the surface of the molten steel such that the average melt thickness falls in the range of 7 mm to 25 mm, or in the range of 9 mm to 20 mm.
Example [0020]
Next, the present invention will be described on the basis of examples. However, conditions in the examples are employed as examples only for confirming the applicability and effects of the present invention, and the present invention is not limited to these examples of condition.
According to the present invention, it may be possible to employ various conditions or combinations of the conditions, provided that such conditions and combinations fall within the scope of the present invention, and the object of the present invention can be achieved. [0021]
Ultra low carbon steels were manufactured through melting by subjecting a molten steel with 280 t per charge to a hot metal pretreatment, to a converting and decarbonization process, and to an RH vacuum degassing process. The manufactured
9/lg

ultra low carbon steels were subjected to a continuous casting using a tundish with a
capacity of 60 ton to produce cast pieces. The casting was continuously performed for
15 charges of molten steels. The temperatures of the surface of the molten steel were
set in the range of 1560°C to 1580°C. From the initial stage of the casting, agents for
maintaining the temperature of the surface of the molten steel according to the present
invention and Comparative Examples were used for maintaining the temperatures of the
molten steels in the timdish. A bag containing 500 kg of the agent for maintaining the
temperature of the surface of the molten steel was installed in the tundish for each of
Examples and Comparative Examples. Each of the cast pieces had a thickness of 250
mm, a length of 7000 mm, and a width of 1500 mm. Each of the cast pieces were
subjected to a generally employed hot rolling and cold rolling to be a cold rolled steel
plate having a thickness of 0.7 mm, and a width of 1500 mm. Note that Table 1
through Table 4 show data concerning Examples and Comparative Examples. Due to
restriction in terms of layout, the data are divided into four tables. Table 1 continues
to Table 2, Table 2 continues to Table 3, and Table 3 continues to Table 4.
[0022]
[Table 1]
[0023]
[Table 2]
[0024]
[Table 3]
[0025]
[Table 4]
[0026]
CaO-AliOs *1 in Table 1 is formed of 50% by mass of CaO and 50% by mass
0fAl203.
CaO-SiOa *2 in Table 1 is formed of 55% by mass of CaO and 45% by mass of CaO-SiOi.
10/Ig

111 „ 111111111111111111111111
^ u
I
o
"V O t-~ M3 \0
o ^
<*
I
o
(53
, O VO 00
r-1 >- » O N
<
I
O
CO
V O "-> o t^
O '^ (N
<
1
O
■*-' "^
c
ii r-.
0 o
«J
1 2
«^ Q
c
rt
t: o
S8 I
£ i> r a
CM 2
— .S
'C "u
(U £
o -^
c|
o a
a c ^
E "^ O
cj « m
o —< cN m rf ^fNmTtirivor-oooN — — — — —
'o.'H.'D-'D.'&.'o.'n.'D.'a.'a-'a.'D.'D.'a. 11111111666111
- r. c^ ^ ^ ^ ^ =0 ^ 2 .^ .S .^ .^ .^ .^ .^ > > .^ .^ .^ .^ >
D 'H.'S.a.'Q.ci.'o."E.'Q.ci.'5.S55S^'^"'<'sS(!3c3cs)caca
^ |§ra§§§§i§§EEEEEEEEEEEEEE
« xxxxxxxxxxoooooooooooooo
HI I M I W I M I M I M I M I M I M I M I M I O I U UUOUUUUUUCJUU

I I oooooooooo?°^;2Ep;5P;3^oooooo
^ s "g
K) u g
C4-4
S .s
0) so
cu J a
O
6
u *
o
< f
-2
w
C "^ Tf >0 m to TJ-
oo>no^ooo ^ t-,>r)mi-,oo
g W)
0) —z:
■♦-J
c
ea
t: "O 00 rn

■w) o ■-« 00
I
g - O -
M 2
.C !>0
"33
e
ce
f,n OmOiOOinOOiOO O OOOOWOiO
.5 r^
ro n
f <
3
rsj I U
o ^ (N m -^
o.ci.o.cxo.CL.o.o.cx.OHCL.'&.CL.a, E6E66EeSESeE6E
„— ,^>^„-.®>>>>>>>>>>>>>>
" (N fi ^ "o vo t-- 00 '-< -c -^ 'C 'c -^s 'c "c 'c •;: -c •£: -c ■*= "S
DDti)i>ajw222222252^^^^£
f^ "o. "5. "o, "Q. "S. "S. "D. "D. "O. "Q. nooo>r)0(NTroo^o
^ _■ r-; —■ ^ O O «' O -- ^" '-"'-' O ^' O ^ O —' ^ O —"—' —"
ca U
u OX) 3
•^SQOO — ^OTt-~ — — — — m—.g-^S — o — " — — ^o 2 S
"w oooooooooooooooooooooooo ■g oooooooooooooooooooooooo
^ _^^^^„„^„^^^„„„^^^„«^^^^
i^ ooooooopopooopoopoppoppo
Q ooooooo'oooo-^oooooooooooo
2 oooooo'oooooHooooooo'ooooo
'^ opoppppppppppppppppppppp
J oooooooooooo'o'oou-ioooooooo'
O ooooooopooppoooooooooooo
JQ' dodododdo'drno'odddoTrodddo'd
O ppppppppppppppprrpppppopp
<2 ppppppppppppv^.ppppppppopp
00 ddd/^P'Op>opppppoornroo>ooo>nir>ioooo
s ^ •--^(so-^-^r-^vSdd O p p p p p rt; 00 (N ys /Sr-^fncofoON'os
(N
^—' ^^^^^^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^
O r- CN (^ ■*
o.'B.'B.'E. ci. a. Q, G.'B.'a.'B. ex Q.'H. EgESEEEESeeSEE
wwmtLiwwwojwtLiwwMw
— (N f^ n- >n \0 C~~ 00 C> —' -^ -5 -G -C '5 -5 'C -C •£ 'C -^ -S 'C 'C a>(L)ii)d>a)a>a>a)S^Eacac3cacacda3cacacaeaa3cQ
"^ o.CXD.p.a.a.G.cxp.&.5c«rani(««t3(acBi5j{3(n(nra
s g§§§§§§i§§EEEeeEEeEeeEEE
ce xxxxxxxxxxoooooooooooooo
Hi |M|tfl|M|M|M|M|M|uj|pj|M|u[u|u|u|u|u|u|u|u|a|u|o|u|u

3 I I I I I I I I I I I I I I I I I I I I I I I I
§ § s JJ
H g -g S
CO
■5 .S a. jj „
o « ^ — 5 2 aa >, o •- <^ - -S .S
3 < S -^ O O O
o- —
^ aj °P CCCCCCCCCCCCCCCCCMCCCCCM
Z2] M o < o
VI \^
u u
fS "i *"
s's i
■J^ oo'/-i>riooo>j-iooooOf$o;goooo2'^do
I—< O
. o 5
"o ^ a.
o o
^ o "■;
Tj- (N c a.
o
o ^ (N a ■£ =i.
«^ o
M O
8 'So >n2:C'^2'^o2i2'o>/-i<^:Co^ou-,o:;^jC:i>/^o:22
L. on ^
(X •" C3
,^ -' = e
^ _; Sf T
^ ' ^— QJ ZX ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^ ^^^
o — rs CO -^
'o.'S.'B.'a.'o.'D.'a.'cL.'S.'S.'cL'&'S.'p. SEEEEESSEEgeSS
XXXXXXXXXiXXXXX
WWWWWWWWWWWpqwtfi
— (N (^ •* "^^ ^ t^ 00 ON --< -j^ -x: -js -js -ji: -js 'x: 's '^3 'i: 's ■■!!! '-P 'ij
■^ "Q. "Q. "Q. 'Q, 'Q, 'Q. O. Q. 'CL "H- rtcocdc3cacdcda3cac3c^cdcOcd
3 liiligliliEEEEEEEEEEEEEE
« xxxxxxxxxxoooooooooooooo
HI iM|M|M|M|M|M|M|M|M|uj|u|u|u|u|u|u|u|a|u|u|u|Q|u|0

SrO-Si02 *3 in Table 1 is formed of 50% by mass of SrO and 50% by mass of Si02.
AliOs-CaO-MgO *4 in Table 1 is formed of 50% by mass of AI2O3,45% by mass of CaO, and 5% by mass of MgO.
Al203-CaO-Si02 *5 in Table 1 is formed of 50% by mass of AI2O3,45% by mass of CaO, and 5% by mass of Si02.
Al203-CaO-Zr02 *6 in Table 1 is formed of 50% by mass of AI2O3, 45% by mass of CaO, and 5% by mass of Zr02.
Al203-MgO-Si02 *7 in Table 1 is formed of 25% by mass of AI2O3, 25% by mass of MgO, and 50%> by mass of Si02.
Al203-MgO *8 in Table 2 is formed of 75% by mass of AI2O3, and 25% by mass of MgO.
CaO-MgO *9 in Table 2 is formed of 70% by mass of CaO, and 30% by mass ofMgOs.
The melt layer thickness * 10 in Table 4 refers to a thickness of the agent for maintaining the temperature of the surface of the molten steel, the agent being adhered to a steel bar after the steel bar is dipped into a molten steel.
AT.O * 11 in Table 4 refers to an amount of change in the total oxygen amount in the molten steel in the tundish relative to the total oxygen amoxmt in the molten steel in the pots 1 to 2 in continuous-continuous casting after the RH process (after vacuum degassing process).
The number of occurrences of defects *12 in Table 4 refers to the average number of surface defects due to oxide-based inclusions existing in a single cold rolled steel plate coil obtained from a steel piece manufactured in the pots 1 to 2 in continuous-continuous casting. [0027]
As illustrated in FIG. 1, in Examples, the total oxygen amount in the molten steel in the tundish is reduced as compared with the total oxygen amount in the molten

steel in the pots 1 to 2 in continuous-continuous casting after the RH process (after vacuum degassing process). This is because the agent for maintaining the temperature of the surface of the molten steel rapidly melts, and covers the surface of the tundish in a uniform manner, so that generation of the alumina-based inclusions because of contact of the molten steel with the atmospheric air can be suppressed, and the alumina-based inclusion in the molten steel ascends and is removed jfrom the molten steel.
Further, as illustrated in FIG. 2, in Examples, the average number of surface defects due to the oxide-based inclusions existing in the single cold rolled steel plate coil obtained from the steel piece manufactured in the pots 1 to 2 in continuous casting is largely reduced as compared with the conventional Comparative Examples. This is because the agent for maintaining the temperature of the surface of the molten steel rapidly melts, and covers the surface of the tundish in a uniform manner, so that generation of the alumina-based inclusions because of contact of the molten steel with the atmospheric air is suppressed
Industrial Applicability [0028]
According to the present invention, it is possible to provide an agent for maintaining the temperature of the surface of the molten steel capable of rapidly melting on the surface of the molten steel and uniformly covering the surface of the molten steel without generating the alumina-based inclusions in the molten steel due to components derived from the agent for maintaining the temperature of the surface of the molten steel.

CLAIMS
1. An agent for maintaining a temperature of a surface of a molten steel, the agent
being disposed on a surface of the molten steel having a predetermined temperature, and
the agent comprising:
at least two of high-melting-point raw materials each having a melting temperature higher than the temperature of the surface of the molten steel; and
CaO in the range of 10 to 70% by mass, AI2O3 in the range of 10 to 60% by mass, MgO ui the range of 5 to 30% by mass, and SiOi in the range of 0 to 10% by mass, a sum total of which is not less than 70% by mass, wherein
a ratio CaO/Al203 of the CaO relative to the AI2O3 falls in the range of 0.5 to 2.0,
the agent has a melting temperature lower than the temperature of the surface of the molten steel, and
not less than 70% by mass of the agent is formed of powder having a particle diameter in the range of 30 |am to 100 |j,m.
2. A method for maintaining a temperature of a surface of a molten steel, wherein
the agent for maintaining the temperature of the surface of the molten steel
according to Claim 1 is disposed on the surface of the molten steel in a manner such that an average thickness of a melt layer falls in the range of 5 mm to 30 mm.