CA1069314A

CA1069314A - Process for the addition of calcium to molten steel

Info

Publication number: CA1069314A
Application number: CA228,889A
Authority: CA
Inventors: Akiyoshi Mori; Katsuya Higashi; Makoto Tokuda; Minoru Fukuda; Hajime Nashiwa
Original assignee: Sumitomo Metal Industries Ltd
Current assignee: Nippon Steel Corp
Priority date: 1974-09-20
Filing date: 1975-06-09
Publication date: 1980-01-08
Also published as: IT1036958B; DE2525839A1; FR2285460A1; FR2285460B1

Abstract

Title of the Invention Process for the addition of calcium to molten steel Abstract of the Disclosure Herein disclosed is a process for the addition of calcium to molten steel at an excellent yield and effect. The process is applied to molten steel having a chemical composition of C 0,02 to 0.55%, Si less than 0.50%, Mn 0.20 to 2.50%, usual alloying elements, S less than 0.10%, total oxygen less than 100 ppm and the balance of Fe, and maintained at a temperature of 1480 to 1800°C. The process is conducted by shooting cannon balls of Ca-additive to the molten steel or by continuously feeding a wire of Ca-additive to the molten steel in an amount of 0.1 to 2.0 kg on the basis of pure calcium per tonnage of steel, whereby the calcium content of the resulting steel becomes 0,05 to 0.8 times of the sulfur-content. The resulting steel has an excellent low temperature impact characteristics.

Description

6931~

This invention relates to a process for the addition of calcium to molten steel and a Ca-additive employed therefor.
For the purpose of improving the cold workability and impact characteristics of steel products, Ti, Zr or a rare earth element has been added to molten steel to clean steel or nodularate sulfides therein. It has been also known that calcium is effective for cleaning steel or nodularating sulfides. When added to molten steel by usual processes, however, calcium is almost consumed during the passing through the slag layer on the surface of molten steel because of its strong reactivity and high vapour pressure at the metallurgical operation temperature. Hence the addition of calcium to molten steel has not been put into practical operation in view of its less effectivity and less stability than the addition of cerium and other rare earth elements.
We found that the yield and effect of Ca-addition depend largely on the sulfur and total oxygen contents of molten steel and developed an improved process for the addition of calcium.
According to one aspect of the invention there is provided a process for the addition of calcium to molten steel consisting essentially of, by weight, C: 0.02 to 0.55%, Si:
less than 0.50%, Mn: 0.20 to 2.50% and usual alloying elements, the balance being iron and inevitable amount of impurities, said process characterized in that said molten steel is main-tained at a temperature of 1480 to 1800~C and contains sulfur of less than 0.01% and oxygen in total content of less than 100 ppm, and further characterized by adding Ca-additive to said molten steel in an amount of 0.1 to 2.0 kg on the basis of pure calcium per tonnage of steel, to thereby maintain the ratio of the Ca-content of the steel after the Ca-addition to ~ - 2 -106931~ 1 .

the S-content at a value of 0.05 to 0.8.
According to another aspect of the invention there is provided a projectile containing a metallic Ca-additive for use as steel-refining agent, comprising a shell made of a ma-terial capable of being melted, decomposed or dissolved in -~ molten steel and having an outer diameter of 5 to 100 mm, a length of 100 to 800 mm, and a wall ~hickness of 0.2 to 20 m~"
; and said metallic Ca-additive contained in said shell.
The invention, at least in preferred forms, provides a practical process for Ca-addition to molten steel.
The invention, at least in preferred forms, also improves the yield and effect of Ca-addition by reducing the S-content, total oxygen content and impu~ities by treating molten steel before the addition of Ca or by slzg modifying.
It is a further advantage of this invention, at least in the preferred forms, is that it can provide Ca-addi-tives suitable for Ca-addition into molten steel.
Other advantages and features of this invention will be apparent from the following description with reference to the attached drawings, wherein: `' Fig. 1 is a graphical representation of the relation between -2a-, ~069314 ~ the desulfurization effect (in ordinate) and the ratio of CaO/SiO2 (in abscissa) of the artificial slag of this invention, when the artificial slag containing CaF2 in the order of 20 to 30% was added to molten steel in an amount of 20 kg/ton of steel.
Fig. 2 is a graphical representation of the relation between the dissolving speed of the artificial slag into molten steel (in ordinate) and the contents of A1203 and MgO of the slag (in abscissa). ~
Fig. 3 is a graphical representation of the relation ;
between the desulfurization effect of the artificial slag ~in -~
ordinate) and the added amount of the slag (in abscissa) to molten steel.
Fig. 4 shows a projectile containing a Ca-additive or "cannon ball" of this invention.
Molten steel suitable for the application of the process of this invention contains, by weight, C 0.02 to 0.55%, -~
Si of less than 0.50%, Mn 0.20 to 2.50% and usual alloying ele-ments, the balance bêing iron and inevitable amount of impuri-ties.
The lower limit of C-content is normally 0.02% in com-' mercial steel-making`processes. On the other hand, when the C-content is larger than 0.55%, the effect of Ca-addition dis-appears substantially. The Si-content falls within the range specified in the JIS and API standards for steel of hot-rolled sheets, seamless and welded pipes and tubes and preferably ranges from 0.04 to 0.40~. Abbreviations "JIS" and "API" used herein signify, respectively "Japanese Industrial Standards"
and "American Petroleum Institute". The Mn-content imparts to the mechanical strength of steel but the content of higher than

2.50% reduces the effect of Ca-addition. Mn is preferably .

contained in an amount from 0.75 to 1.70~ for the improvement of impact characteristics. Alloying elements may be contained in the following ranges:
Cu: 0 - 0.50%
Cr: 0 - 1.50~
Mo: 0 - 0.50%
Ni: 0 - 10.0%
Nb: 0 - 0.050%
V: 0 - 0.1%
Ti: 0 - 0.05%
It is essential to maintain the S-content at a value less than 0.010%, preferably less than 0.007% and the total ox~-gen content at-less than 100 ppm. The S-content of higher than 0.010% makes the Ca-addition ineffective and if the S~content is higher than 0.007%, the Ca-addition is less effective than the addition of cerium in improving low temperature toughness and impact characteristics of the steel products. However, when the S-content is less than 0.007%, the Ca-addition accord--ing to this invention exhibits a more significant effect than the Ce-addition with respect to the above mentioned improvement r,~
of steel products. When the total oxygen content is higher than 100 ppm, Ca will be almost consumed in the combination with oxygen due to its strong affinity with the latter with the result that sufficient effect will not be expected in cleaning or nodularating sulfides in molten steel.
At the time of the Ca-addition the temperature of molten steel is maintained at the range of 1480 to 1800C from the following reason: At a temperature lower than 1480C, in-got-making operation will become difficult and Ca-contaminates 30 will not Sufficiently float up to the surface of molten steel, thus resulting in dirty steel ingot. On the other hand, _4_ ` 1069314 if the temperature exceeds 1800C, the vapour pressure of ; molten steel becomes so high to evaporate out the Ca-ingredient of additives before the reaction with sulfides in molten steel, causing a decrease in the yield of Ca-addition and a prominent loss in ladle refractories by fusion.
Ca is~ added an an amount of 0.05 to 2.0 kg on the basis of pure Ca per tonnage of molten steel so that the Ca-content becomes 0.05 to 0.8 times of the S-content in the re-sulting steel product. Ca-addition in a net amount of Ca less 10 than 0.05 kg/ton of steel will be-insufficient to clean or nodu-larate sulfides which molten steel contains at the S-content of about 0.010%. On the other hand, Ca-addition in a net amount of Ca larger than 2.0 kg/ton of steel results in a saturated effect and therefore the addition in an excess amount makes the opera-tion uneconomical.
Pretreatments of the molten steel to be added with calcium may be provided,for the purpose of enhancing the yield and effect of Ca-addition. The pretreatments include the vacu-um degassing, inert gas-bubblir~g, aluminum deoxidizing and slag-20 modifying processes.
The molten steel is preferably of Al-killed steel and a content of acid soluble Al higher than 0.005% is preferable, because the soluble Al-content decreases the FeO content of the slag and thus results in decrease in the consumption of the slag and ladle refractories by oxidation. Further, the Ca-addition has an effect to desulfurize molten steel in the presence of Al by forming contaminates of Ca-Al-0-S system according to the following equation:
3CaO + 2Al + 3S = A12o3 + 3CaS. r 30 Accordingly, the higher the Al concentration is, the less the S-content in the molten steel becomes by ~he addition of Ca and ~

``~ 1069314 .
the more the impact characteristics of steel products are improved.
When steel product is specified not to contain Al, the molten steel should be subjected to the vacuum degassing - process before the Ca-addition in order to decrease the total oxygen content to less than 100 ppm. Al-killed steel may be also subjected to the vacuum degassing process. When Al-kil-led steel is vacuum degassed by DH process, the degassing is preferably carried out under the condition of a final vacuum ~10 degree of less than 0.5 m~ Hg in a vacuum degasser and a cir-culation ratio of higher than 1.5, with the result that the content of active oxygen becomes less than 10 ppm. ~
` The molten steel is preferably subjected to the bub- ;
bling process by-inactive gas, such as argon in order to agi-tate the molten steel to float up the remaining contaminates.
When the molten steel is contained in a ladle of 25 to 300 tons capacity, the inactive gas bubbling process is carried out under the following condition: ;
Pressure of inactive gas: 2.5 to 5.0 kg/mm gauge Feeding amount of inactive gas: 10 to 80 Nm /hr Duration time of bubbling: 20 to 40 minutes This inactive gas bubbling process, of course, may be carried out solely or in combination with the Al-deoxidizing and or vacuum degassing process.
It is preferable to effect the slag-modifying pro-cess before the Ca-addition in order to suppress the formation ,of highly oxidative slag. The slag-modifying process is car-ried out by, putting an artificial slag in an empty ladle and thereafter pouring molten steel therein. Such an artificial slag is of high basicity and comprises by weight, CaO 40 to 60%, MgO 7 to 9%, A1203 15 to 25%, SiO2 3 to 5% and CaF2 20 to 30%.

: -6-.... " . . .. , .-.

";: 1069314 The artificial slag of this composition is prepared from the -~ slag which forms at the final stage of steel-refining in the electric furnace.
As shown in Fig. 1, the desulfurization effect (which is represented by a ratio to the maximum desulfuriza-tion degree achieved in the all test) begins to increase at a CaO/SiO2 ratio of 8 and converges to the maximum at a CaO/SiO2 ratio of 20. This experiment was conducted maintaining the content of CaF2 at 20 to 30%. The desulfurization effect be-comes also the saturated point when the slag contains 40 to60% of CaO. Al203 and ~gO are contained in order to lower the melting point of the artificial slag and the dissolving speed of the slag into molten steel, as shown in Fig. 2.
It is preferable to control the size distribution of the artificial slag as follows:
Larger than 8 mesh ........... .3 - 17%
- 8 - 12 mesh .................. lO - 16%
12 - 20 mesh ................. 15 - 20%
20 - 32 mesh ................. ll - 22%
32 - 48 mesh ................. 10 - 30%
48 - 60 mesh ................. .2 - 5%
60 - lOO mesh ................ .6 - 8%
` lOO - 150 mesh ................ .1 - 5%
150 - 200 mesh ................ .Less than 3%
Smaller than 200 mesh ......... .Less than 11%

" .
i The slag-modifying process is also effective for the desulfurization of molten steel and the desulfurization effect becomes significant at the addition of the slag of 5 kg/ton of steel and becomes to a saturated point at 20 kg/ton as shown in Fig. 3. The artificial slag may have a chemical .
;:

composition of CaO 55 to 70%, A1203 10 to 25~ and CaF2 3 to 14~.
This invention provides a method for the addition of calcium, wherein calcium is not consumed during the pas-sing through the slag layer but at a sufficient depth in molten steel.
According to an embodiment of this invention, Ca-addition is carried out by shooting cannon balls of Ca-addi-tive at an initial shooting velocity of 20 to 100 m/sec from a launcher into molten steel in a ladle of 25 to 300 tons ca-pacity. Such a ladle is 1 to 7 meter in height. At an ini-tial shooting velocity lower than 20 m/sec, the cannon balls of Ca-additive cannot penetrate into molten steel with a suf-ficient depth, so that the cannon balls float upwards to the slag layer before it has been completely dissolved, with the result that the effect and yield of Ca-addition is decreased.
On the other hand, an initial velocity higher than 100 m/sec is unfavorable since the cannon balls will collide against and damage the refractories of the bottom part of the ladle.
The projectile containing a Ca-additive suitable for use in the method described in the above has a diameter of 5 to 100 mm, preferably 25 to 50 mm, a length of 100 to 800 mm and comprises a shell and Ca-additive contained therein. The shell of the projectile is composed of any one selected from the following materials:
Aluminum of a thickness 0.5 to 20 mm Iron of a thickness 0.2 to 15 mm Copper of a thickness 0.2 to 15 mm Organic màterial of a thickness 0.2 to 20 mm Fire-proof paper of a thickness 1.0 to 20 mm Ca-ad-ditives contained in the projectile include '~ -8-~069314 metallic Ca and Ca-alloys such as Ca-Si or Ca-Ba-Si alloy.
Representative compositions of the Ca-additive are shown in the following:
i) Ca ........... More than 40% :
Si ........... More than 40%
Ba ........... Less than 20%
ii) Ca ........... More than 40~
Mg ........... More than 10~ -Si ........... Less than 10%
Other ingredients: Coating material of high molecular organic compound iii) Ca .......... More than 25%
Mg ........... More than 7%
Rare earth elements ... More than 15%

~'1 ' ;`
' ," ~

.

~, ~ .

-8a-iO69314 Al .,........ More than 20 Si .......... More than 20%
iv) Ca ...... ~... 25 - 35%
Mg .......... 5 - 15%
Rare earth elements ,,,, 10 - 20%
Si ..,,,.,,,, More than 10% ~r~jeC~- ~e or A Fig, 4 illustrates an example of the~ c~a~-~ll according to this invention, ~he cannon ball 10 consists of a tip 11 made of a metal such as iron having a higher density than the materials of the other portion5 a mid portion 12 of the shcll made of the above- ~A;' mentioned materials and Ca-additive contained therein~ and rudders 13 attached to the end portion of the cannon ball lO for stabilizing the flying direction, As mentioned above, the tip portion is prefer- ~-ably made of a material of higher density in order to maintain the posture of the cannon ball 10 perpendicular t~ the surface of the -molten steel when the cannon ball is shot from a launoher~
: Aooording to another embodiment of this invention~ Ca-addition is performed by continuously feading Ca-additive in the form of a wire at a velocity of 10 to 100 m/seo into molten steel in a ladle ,i -having a capacity of 25 to 300 tons, ~he wire of Ca-additive accord-, . .
, - - ing to this invention consists of a hollow cylindrical shell having ,~, an outer diame-ter of 5 to 100 mm~ preferably 25 to 5C mm and Ca-additive ¢ontained therein, The material of the hollow cylindrical shell and its thickness are the same as in the case of the Ca-additive of cannon ball type~ ~ecallse of the same reasons as in the case of the cannon ball type, tha feeding velocity of the wire is limited to the range of 10 to 100 m/sec, The following examples are included merely to aid in the undar-standing of the invention, and variations may be made by those skilled in the art without departing the spirit and scope of the invention, .

10693~4 - Exampl~ 1 Al-killed steels of-the chemioal oompositions shown in Table 1 .
were prepared for the use ! as the material of high strength line pipe~
in the arctio sites, Additions of Ca, Ti, Zr and Ce were made res-pectively to the steel at the molten state, The resulting steels were rolled to plate of 11 mm in thickness under the same low temperature - . controlled condition, . Table 1 _ lolement incor-Sa~ToPl~ . Chemical composi tion, ~O by ~ 3ight tive addition, -~
C Si Mn S V Nb Al ~al. ~O bY w~i~ht .
1* 0,05 0 35 i.25 0.005 0.075 0,015 0,029 Fe non non 2* 0.05 0.37 1,27 0,005 o.o8 0,024 G.030 Fe Ti Tis 0.06 . 3* 0,048 0.38 1.29 0~005 o.o8 0.027 G.043Fe Ce Ce. 0.034 4* 0,049 0.37 1,32 0.005 0.075 0.024 0.047 Fe Ca Ces 0.070 . 5* 0.05 o~35 1,26 0.005 o.o85 0.019 0,036Fe Zr Zrs 0 10 6 0,048 0,33 1,45 0.005 0.08 0.027 0,034Fe Ce-Ca .
7 0,058 0,34 1,29 0.005 0.07 0,027 0.030Fe Ca Cas 0,0029 ô 0.060 0.26 1,23 0.005 0.09 0,027 0.035Fe Oa Ca, G.00Z~

, ,~ ~
The mark * exhibits that the addition was made out of the SCOpl3 of this invention, :~
Mechanical properties of the thus rolled steel samples were determined and shown in ~able 2, ~...

lablo 2. Mechanical properties Tensil~ properties Charpy properties aoross the rolled direction Yield TerlRile ~otal 50% fraoture Shelf Absorption stres~, strength elonga-. transition energy~ energy at Sample ~ ~ 2 tion~ % temperature, kg,m- 80C
No, kg/mm kg~fmm C kf,m 1* 51,2 56.7 34.o - 90 14.9 4.5 2* 55.7 61.2 28.0 - 48 15.7 0,9

- 3* 53,3 58,8 33.0 - 82 11.3 3,4

4* 53.4 5O.o 34.0 - 65 12,3 1.4

5* 52,4 57,4 3~,o - 57 12,0 o,g

6 56,5 59,2 33,0 -107 21,3 11,6

7 54~5 58,8 35,o -120 22,8 13,1

8 53,3 61,3 35.2 _ 92 21,5 14,0 As seen from-Table 2, all of the s.teel samples exhibit.~he 15 mechanical properties largely exceeding the values requirad for the line pipa matarials, Particularly, Samples ~Jos, 6 to 8 e:x:hibit values ~: of shelf energy about twice higher than those of Samples Nos, 1 to 5, Fracture transition temperature of Samples ~os, 6 to 8 is also oxcel-.. . . .
lently 10N as compared with Samples ~os, 1 to 5. ~amely9 at the sulfur-level of o,o5%, the Ca-addition according to this invention is promi-nently effective for the improvement of the absorption shelf anargy characteristic whioh cannot be achleved by the conventional addition of such.as ~i, Zr and.Ce, E~ample 2 Samples of molten steel each having the~chemical oomposition shown i~ ~able 3 were prepared by a high frequency induction furnace and added with Ca-additive, The resulting steel samples were rolled to 17 mm thick under the same low temperatura controlled condition, 10693~4 :
T ble 3 Sample S-leve-, Chamical composition~ ~o by weight Amount of Ca-~o, ~ C Si. M~ S Nb Bl Ce additive~
g/ton

9 0,0~ 0,11 0,~ 1.29 0,005 0,0240.025 - 150

10* 0,005 0,11 ~,33 1,32 0,005 0,022 0.034

11~ 0,005 0.10 0.31 1,31 0.005 G.024 0.035 0.015 - `
~2* 0.005 0,10 0,35 1,32 O.Q06 0.019 0.044 - 80 13 '0.007 -9 0,29 1,40 0.007 G.0250.041 - 150 . 14* '7 0.10 0,32 1.37 0.007 0.0~1 0,030 - - ~:
15* 0,010 0,11 0.30 1,26 0.011 0.018 0.033 - - -`
^~
16* 0.010 0.10 0.31 1,33 O.G10 G.022 0.035 0.025 - ~
17* 0.010 0,09 0,34 1,32 0.010 0,021 0~034 - 8C :
18* 0.010 0,10 0,35 1,30 0.011 O.Gl9 0O030 - 150 19* 0.015 0.10 0,29 1,30 0.016 0,024 0.025 20* G.015 0.11 .0,30 1,28 0.016 00022G.o28 - 150 ~he mark * exhibits the control sample which was tested in order to determine the standards of the e~feot of this invention, Although there is no indication of the total oxygen content of the steel samples~ all of the samples were Al-killed stee]. and the total oxygen content thereof was less than 100 ppm, .
Mechanical proportios of ths thus rolled sbe~l samples are ~hown in Table 4, .

~ 12 -~able 4. Mechanical proporties ~onsile properties Charpy propertios across the rolled direction Yield Tensilo Total 5010 fracture Shelf Absorption Sample stress 9 strength, elonga- .transition energy energy 3t 5 ~No. kg/mm2 kg/mm tion~ % temPerOature 9 - 80 C :.
. . ~
9 47~856~4 40~0 ~ 100 19~2 12~4 10* 48~756~6 38~o ~ 81 1~5 3~2 `
11* 47~957~0 39~ ~ 79 11~0 2,5

12* 48~656~9 38~0 ~ 83 10~0 3~

13 49~256~4 39~0 ~ 103 17~8 12~3

14* 49~2- 57~8 37~5 - 84 9~2 3,2

15* 46~357~1 35~ - 85 ~2 3~0

16* 47~256~6 36~0 ~ 86 11~2 3~3 j 15 17* 48~357~1 35~5 ~ 78 7~9 1~7 18* 48~657~4 36~0 ~ 88 10~6 3~8 -19* 47~355~9 33~0 ~ 80 5~ 8 ;~
i 20* 47~256~1 33~5 - 83 7~2 3~2 As is readily seen from Table 4 ~ the Ca-addition according to ~ ~;
this invention (Samples Nos. 9 and 13) remarkably improved the impact oharacteristics. At the same S-level of O.G05 %, Sample ~To 9 e2hibited a larger absorption energy at -80'C than that of Sample No 12~ Namely~
the Ca-addition in a net amount of less than 100 g/ton of steel did not improve the impact proparties across the rolling direction 4t the S-level of 0 010 %, the C3-addition in a net amount of higher than 100 g/ton of steel (Sample No 18) was lfss effective than the Ce-addition (Sample No 16) E~ample 3 :~ Steel samples were prepared of the chemical composition 3S
shown in llable 5 Ca was added to Samples ~Tos 21 and 25, and Ce w~s 1~6931~

added to Sample No, 24, ~heroafter~ each samplos w3s hot rolled at a finishing temperatur~ of 800C and a ooiling temporature of 570 C, thereby obtaining a steel sheet of 6,0 mm thickness.
Table 5, Chemical composition , I No, I Cchem oal colnpositiTn9 ~o b I ~b I Al ~ddition 21 0,10 0,22 1,26 1 -4 GoO37 0.021 Ca. in 150 g/ton 22* ¦ 0.11 0,29 ~ 0,004 0,030 0.029 non -23* o,11 O,25 1,25 0.013 0.031 0.039 non - 24* 0,11 0,26 1,21 O ,011 0.027 o ,045 Ce o rated after th~
_ addition _ 25* 0,10 0,25 1,32 0.011 0.047 0.014 Cao in 150 g/ton The mark * signifies the control samples.
' ~he following Table 6 shows the meehanical properties of the resulting sheets which were determined across the roiling direction, ~, 15 ~~ 6. ~
!~ensile properties ~otc~ Charpy properties elonga- across the rolled sYield ~ensile Total 'tion~ direction ';'`samplo 'stress~ strength~ el g 50~ fracture ~bsorption ,,, kg/mm k / 2 tlon~ ~ t~nsition energy at .4 ' ' temperature~ C, C kg,m ' , 21 49,9 58,5 32,0 22,1 - 92 9,2 ;~ 22* 46,8 56,5 32.0 20,2 - 73 5.~
23* 52,2 60,5 28,5 8,o ~ 7 2,2 ~-24* 48,5 57,6 30,5 16,4 - 77 4,8 25* 49,4_ 58,9 30,0 15.8 - 75 4.1 Charpy tests were conduct,ed by means of half subsi~ed test pioces. ~lotch e10ngation tests were cenducted using test ', pieoes of the same shape as the test pieces fOr the tensile test according JIS ~o, 5 and cut with V-notches of l mm on the both sides of the centor. The gauge length of the notch elongation te~t was 25 mm, - ~06931~

A9 se~n from Table 6~ r~markabl3 improvementa in notch elonga-tion and oharpy propertios were aohievod by the Ca-addition of this -.
invention, E~ample 4 Molten steel was prepared having a ohemical oomposition of C 0.05~0~ Si 0.33%, Mn 1.46~o~-P 0.016%9 S 0.005~/0, Cu o,o6~0, Cr 0,02%7 ~b 0.023%~ sol, Ai o.o38% and the ~alano~ being iron.. ~he samples of bhis molten steel were respe¢tively maintained at temperatures as shown in ~able 7 and were added with Ca-additives of oannon ball type under the following conditiono Ca-ingredient of the additlve; single substance of Ca Size of the additive; 40 mm in outer diameter and 250 mm in length Initial velocity of shooting; 50 m/seo N:et amount of added Ca3 200 g/ton of steel -.
Ca-oontent of the steel after tha addition7 0.0031~o . Ca/S ratio of the steal after tha addition9 o.6 . Miorooleanlinass test for tha non-matallic inclusions in steal was oonducted in aocordance with JIS and the obtainad rasults are shown ~.-,, .
in Table 7.

- Table 7 _ _ Temperature of Cleanliness Degree d(~o) :~
. Sample .moltenisteel at the Steel added with Ca I Steal withou the ~o, ¦ tiDe of Ca-~ddition addition '. . 26 iower than 1480 C 0 090 0 225 with large 0.090 - 0,185 27 1480 ~ 1600 C 0.050-0,115, Fairo.o6s- 0.15G

28 1600 - 1700 C 0.018~0 .oko, Good 0.025 ~ 0.090 29 l 1700 ~ 18G0 C lo.025~0.080, Fair l 0,025 ~ 0,120 _ At temperatures of molten steel below 1480 C, the effect of Ca-addition is too fluctuant to put the Ca-addition into practice, ` `

: 5 . :
~ .

Example 5 Sampl~s were prepared from molten stee]. oonsisting of C 0,O9qo~
Si 0.28%~ Mo 1 .30~o~ P o .017%, s o .oo6%, cu o .02~o, U 0 .03%~ sol. Al G .041,%
and the balance of i.ron.~: Samples of th~ molton'stool w~r~-rc.speotivoly ~ 5 maintained at temperatures shown in Table 8 and the Ca-addition was con-ducted by feeding thereto a wire of Ca-additive under the following oondition~
Ca-ingredient~ Ca alloy consisting of Ca 33%~ Si. 50% and the balance of Fe. , . :
~ `' .
10Size of wireo 35 mm in diameter .

Feeding velocity of wire: 35 m/sec ' Net amount of added Cao 250 g/ton of steel -~ Ca/S ratio o~ the steel after the additiong 0.5 ~ 1.5. :.

Miorocleanliness test for the non-metallic inclusions in steal :~

~as conducted on each sample in aocordance with the method of JIS and the results are shown in Table 8, _able 8 -:.
.. . _ . -- . .
. ~emperature of molten ~
Sample steel at the ~ime of Clean].iness degree d (%) . o. Ca-addition .

. 2030 ~elow 1480 C 0.090 ~ 0.225 with large deviation 31 1480 ~ 1600~C 0.050 ~ 0,115 Fair ;

32 1600 ~ 1700 C 0.018 ~ o.o60 Good . .

. 33 1700 ~ 1800 C 0.025 ~ o.o80 Fair .
_ _ . '.
~
Samples of molten steel were prepared of a chemical composition . shown in ~able 9 and some of the samples were subjected to the vacuum degassing by D~ method under the condition shown in ~able 10, wheraby reducing the active o~ygen amount aO to less than 1 ppm~ ~he active oxygen amount ln the molten steel was determin.~d by an oxygen probe in accordance with the solid zirconia eleotrode m~thod.

( -` " 1069314 ~able 9_ Chemio~l compo~ition of the molten steel . _ . _._ , _ ~ Si Mn P S Cu Cr Nb Sol.Al O(aO)ppm degassin6 0.0~ 0,05 0.60 0.015 o.oo6 0,02 0.02 Traoe Trace .70 ;
~fter va uu 0.06 0.30 1,35 0.019 0.006 0.02 0.03 0.024 ~race Tra¢e -.

Table 10 Conditions of the vacuum degassing . _ ~ :
~empsrature of the molten steel before vaouum degassing 1670 C . ~ ~.
Temperature of the molten steel after vacuum degassing 1635 C .
. Degree of vacuum finally achieved 0,2 mm Hg .
Mean amount of sucked. steel per stroke i 13,3 tons ~,-; Number of times of suction 43 times Ratio of sucked steel amount to the whole amount 3.3 Durir~ the vacuum degassing, the samples of molten steel were `~
added with tha following alloys ` 15 Low-carbon Si-Mn alloys 10 kg/ton Low-carbon Fe-Mn alloy: 3 kg/ton ~.
Fe-Nb. 0,4 kg/ton . .
Thereafter~ samples of the molten ateel were added with Ca under the following conditionO ~-Ca additive; cannon ball comprising a shell of iron au Ca ~:~
-element oontained therein, - Initial shooting velocity; 50 m/sec Net amount of addad Ca; 270.g/ton of ste~
- Meohanica]. properties of each samples are shown in Table 11, .

. .;.

... .

. . . ~ . . , .. ~ , :,. ., ;, , , .. ... ~ -~06~314 ~

?able 11 Meohanioal ~ropertias - ~Chemioal oomposition Sample No. aO(ppm) C(G~o) Mn(%) S(%) Sol.Al('~o) Ca(ppm) . .
34~ Ca-addition after Trace 0 o81 35 0.006 ~race 25 ~acuum degassing 35, Ca-addition after Trace 071 41 o.oo6 ~race 18 vacuum degassing 36, Ca-addition without 8 07 1 370 006 Traoe 5 vaouum degassing 37. No Ca-addition 21 0.07 1,380.005 0.038 ~raoe ' :.
Absorption en~rgy at -40 C measured by 2 mm~ full Sample ~o. sized Charpy test a kg.m V~-40 (L)VE_40 (C ) VEO (Z )V~s (C ) o .
34 30 30 1?.7- 115 C
3S 30 30 10,8- 105'C
_ _ ,' :-36 28,3 22,5 2,3 - 60C-37 26,0 11,8 o,8- 55 C
_ - , ~hu symbol 1~30 ~ exhibits the amount of aotive oxygen in E
the stael In the impaot tests9 L was det rmined along the rolling dirootion9 C across the rolling direction and Z along ths direction p~rpendicular to the rolled surface ~, . ~ ;, From these results~ it can be seen that the low temporature ~` 20 impact characteristics were markedly improved in Samples Nos, 34 and 35 wherein the vacuum degassing had been performed before tne Ca-addition as compared with Samples Nos. 36 an~ 31 wherein vacuum dogas-- . :
sin6 had not been porformed~ thus the vacuum degassing enhanced the effect of Ca-addition.
~xample 7 A ladle was charged with molten steel having a chemical com-position of C c.o8~O~ Si 0.30G/~o~ Un 1.41~o~ P O.O18JO~ S o.oo8a/o~ Cu O.G2 ; Cr 0.03G~o~ Nb 0.023~10~ V o.o6~0~ Sol Al 0.027¦o, the balance of Fe. ~he ., .
molten steel was stirrad by blowing argon gas thereto for 2C 9 30 9 40 - 30 or 50 minutes under the following conditio-n-.~-1(~69314 ~lo~ing press~ro: 3,5 kg/cm2 Flow rat~ of argon~ 35 Nm3/hr ~hereafte~J Ca-~ddition was made to steel s~mples which had been su~jected to the gas bubbling under the above oondition and to steel sample which had not been subjacted thereto, Condition of Ca-addi-i;ion Additive. cannon ball type ~flmperature of molten steel. 1630C ;
Initial shooting vclooityO 50 m/seo Net amount of added Cas 270 g/ton of steel Ratio of Ca/So 0,33 Mechanical properties and oleanliness of the resulting steal samples are shown in Table 12, ~;
Table 12 -~
Sample Duration time of Yield index of Cleanliness Low temp,~rature No; gas blowing(min) Ca-addition index i-mpact proparty _ _ 38 0.5 0~7 0.7 39 20 0,8 0,9 0,8 4 3 0,95 1-.0 o,85 41 4 1,0 1,0 1,0 . ..
, 42 5 1.0 1,0 1,0 ~ ;~
Note l. nYield index of Ca-addition" is represented by a ratio of the yiold of added Ca of a particular case to tha maximum yiald of ;; addod C3 in the pr~sant ~xample, ~, Note 2s "Cleanliness index" is represa~ted by a ratio of the claanli-~ ness of a particular casd to tha maximum cleanliness in the`. 25 present Example, ~ote 3O "Low temperature impact property" is reprasantad by a ratio of the value of absorption energy in the C-diraction at -40C
i~ for 2 mm V-notohed specimen of a partioular sample to a value of 30 kg,m, It is readily seen from ~able 12 that the yield and effact of Ca-addition are remarkably enhanced by the gas bubbling, . .
.:': -- 19 -- - :
~: .
.. :, .

(~ 1069~14 Examplo 8 Molten æteel was prepared ha~ing a ohemioal composition of C G.07 to O C9%, Si 0,28 to 0.33~o~ Mn 1 33 to 1 41,~ P 0 011 to 0 023%~ -S 0.004 to 0.007%, Nb 0 020 to 0,021~o~ Cu 0 02%, Cr 0,02 to 0 03%, sol Al 0 018 to 0 045% and the balance of Fe On the other hand, artifi¢ial slag having a composition of CaO 45a~0~ MgO 7%, A1203 20~, SiO2 3~ and CaF2 25~ was put in a ladle in an amount of 5.0~ 10 0, 20,0 or 30 kg/ton of steel ~hereafter, tho -ladle ~s oharged with molten steel of the above composition and the Ca-addition was made therato unde~ the same condition. ~able 13 shows the yield of Ca-addition~ the cleanliness degree and the impact pro-perty of the resulting steel Table 13 .
~mount of the Yield index Cleanliness Low temperature -~
; Sample artificial slag of degree of impact property at No (kg/ton of steel) Ca-addition the steel(% oDc ,' 43 0 0.5 o.G55 0.7 44 5.0 1 0.7 0.045 o.85 10.0 0.8 0.038 0.95 . 46 20.0 1,0 0 027 i~oo 47 30.0 1 0 0.03~ 1.00 I _ ' ~ote: '~he yield index oE Ca-addition" is represanted by a ratio of the yield of a particular sample to maximum value of the yield of Ga-additions in this Example. The low bemparatura impact ~` property is represented by a ratio of absorption energy in C-direction for full si~ed specimen of a particular sample ;. to the maximum value in this Example.
,~ 25 '~

' ~ - 20- - ~

:

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the addition of calcium to molten steel consisting essentially of, by weight, C: 0.02 to 0.55%
Si: less than 0.50%
Mn: 0.20 to 2.50%
and usual alloying elements, the balance being iron and in-evitable amount of impurities, said process characterized in that said, molten steel is maintained at a temperature of 1480 to 1800°C and contains sulfur of less than 0.01% and oxygen in total content of less than 100 ppm, and further characterized by adding Ca-additive to said molten steel in an amount of 0.1 to 2.0 kg on the basis of pure calcium per tonnage of steel, to thereby maintain the ratio of the Ca-content of the steel after the Ca-addition to the S-content at a value of 0.05 to 0.8.

2. A process as claimed in Claim 1 and said steel consis-ting essentially of, by weight:
C: 0.02 - 0.55%, Si: Less than 0.50%
Mn: 0.20 - 2.50%
Cu: 0 - 0.50%
Cr: 0 - 1.50%
Mo: 0 - 0.50%
Ni: 0 - 10%
Nb: 0 - 0.050%
V: 0 - 0.1%
Ti: 0 - 0.05%
and the balance of Fe and inevitable amount of impurities.

3. A process as claimed in Claim 1, wherein said molten steel is Al-killed to thereby contain soluble aluminum in an amount of 0.005 to 0.085% by weight before the Ca-addition.

4. A process as claimed in Claim 1, further comprising the step of, in advance of the Ca-addition, subjecting said molten steel to inactive gas bubbling in a ladle of a capacity from 25 to 300 tons for 20 to 40 minutes under the following condition:
Blowing pressure of inert gas: 2.5 to 5.0 kg/cM2 Feeding rate of inert gas: 10 to 80 Nm3/hr, thereby floating and separating the contaminants in the molten steel

5. A process as claimed in Claim 1, further comprising the step of, in advance of the Ca-addition, modifying the chemical property of the slag on said molten steel by adding to said molten steal artificial slag in an amount of 5.0 to 20.0 kg/ton of the steel, said artificial slag consisting of, by weights CaO: 40 to 60%
MgO: 7 to 9%
A1203: 15 to 25%
SiO2 : 3 to 5%
CaF2: 20 to 30%

6. A process as claimed in Claim 1, further comprising the step of, in advance of the Ca-addition, modifying the chemical property of the slag on said molten steel by adding to said molten steel artificial slag in an amount of 5.0 to 20.0 kg/ton of the steel, said artificial slag consisting of, by weight:
CaO: 55 to 70%
A1203: 10 to 25%
CaF2: 3 to 14%

7. A process as claimed in Claim 1, further comprising the step of, in advance of the Ca-addition, subjecting said molten steel to the vacuum degassing process to thereby decrease the total oxygen con-tent to less than 10 ppm.

8. A process as claimed in Claim 7, wherein the vacuum degassing process is conducted by DH method under the follow-ing conditions;
Degree of vacuum finally achieved in a vacuum degas-ser: less than 0.5 mm Hg Ratio of the amount of circulated molten steel to the whole amount of molten steel to be treated: higher than 1.5.

9. A process as claimed in Claim 1, wherein the Ca-addi-tion is conducted by shooting projectiles containing Ca-addi-tive at an initial shooting velocity of 20 to 100 m/sec to the molten steel contained in a ladle having a capacity of 25 to 300 tons and a depth of 1.0 to 7.0 m, said projectile being 5 to 100 mm in diameter and 100 to 800 mm in length.

10. A process as claimed in Claim 1, wherein the Ca-addi-tion is conducted by continuously feeding a wire of Ca-additve at a feeding velocity of 10 to 100 m/sec into the molten steel contained in a ladle having a capacity of 25 to 300 tons and a depth of 1.0 to 7.0 m, said wire being 5 to 100 mm in diameter.

11. A projectile containing a metallic Ca-additive for use as steel-refining agent! comprising a shell made of a ma-terial capable of being melted, decomposed or dissolved in molten steel and having an outer diameter of 5 to 100 mm, a length of 100 to 800 mm, and a wall thickness of 0.2 to 20 mm, and said metallic Ca-additive contained in said shell.

12. Ca-additive as claimed in Claim 11, wherein said Ca-ingredient is at least one selected from the group consisting of metallic Ca, Ca-Si alloy and Ca-Ba-Al alloy.

13. Ca-additive as claimed in Claim 11, wherein the ma-terial of said shell is one selected from Al, Fe, Cu and fire-proof paper and has the following thicknesses:
Al ... 0.5 to 20 mm Fe . . . 0. 2 to 15 mm Cu . . . 0. 2 to 15 mm Fire-proof paper . . . 1.0 to 20 mm