US2837422A - Addition agents for the treatment of molten cast iron - Google Patents

Description

United States ADDITION AGENTS FOR THE TREATMENT OF MOLTEN CAST IRON No Drawing. Application August 15, 1956 Serial No. 604,073

Claims priority, application Germany August 27, 1955 11 Claims. c1. 75-134 The present invention relates to an improved article of manufacture comprising an addition agent for the treatment of molten cast iron, and, more particularly, to an improved article of manufacture comprising an addition agent containing magnesium, calcium, iron and silicon with magnesium and calcium within critical ratios and ice " stantially devoid of the disadvantages of prior addition being especially useful for the treatment of molten cast iron to produce spheroidal or spherulitic cast iron.

It is well known in the art of cast iron that various addition agents have been proposed for the purpose of deoxidizing, desulfurizing, degasifying and otherwise refining or purifying the melt under treatment. In recent years, special addition agents have been used for treating molten cast iron, especially of a gray iron composition, to produce a new type of cast iron containing graphite in a spherical, spheroidal or spherulitic form and called by various names such as ductile iron, nodular iron, etc. (See, for instance, U. S. Patents Nos. 2,485,760 and 2,488,511.) These special addition agents contained magnesium and/or cerium when used on an industrial scale for the production of commercial castings in iron foundries. Various proposals have been made to provide the cast iron art with addition agents which could be manufactured, sold, handled and used on an industrial. scale safely, easily and practically- Such proposals have included addition agents composed of magnesium, calcium and silicon and containing other elements, especially metals such as copper, nickel and/or iron. (See, for instance, U. S. Patents Nos. 2,555,014; 2,582,079 and 2,563,- 859; Italian Patent No. 469,164 and Japanese patent application Publication No. Sho 28-2207/53.) Very wide 1 limits have been proposed for the constituents of the aforesaid proposed addition agents, ranging from low to high magnesium and calcium contents or including relatively high iron contents in excess of 30%. All such addition agents had disadvantages of one kind or another. Although attempts were made to overcome. the disadvantages of such proposed addition agents, none, as far as is known, was entirely successful when carried into practice commercially on an industrial scale. I

It has now been discovered that the usual violence of the reaction of magnesium-calcium-iron-silicon addition agents with magnesium contents between about 17% to about and the ensuing magnesium losses can be considerably decreased provided magnesium and calcium are present in certain proportions. It has been found that when the magnesium-calcium proportion lies within a range of 4:1 to 9:1, new results are obtained including calming the violence of the reaction and decreasing the magnesium losses.

It is an object of the present invention to provide an improved article of manufacture comprising an addition tent is at least high enough to bind not agent for the treatment of moltencast iron which is subagents.

Another object of the invention is'to provide an improved article of manufacture comprising an addition agent containing magnesium, calcium, iron and silicon with magnesium and calcium within critical ratios and being especially useful for the treatment of molten cast iron to produce spheroidal and spherulitic cast iron.

The invention also contemplates providing a novel addition agent for molten cast iron comprising magnesium, calcium, silicon and iron within special percentages and having magnesium and calcium in such special proportions as to come within critical ratios.

It is a further object of the invention to provide a novel addition agent for molten cast iron composed essentially of magnesium, calcium, silicon and iron with magnesium not higher than 50%, silicon at least 35% but not exceeding 60% and iron up to 30% and having a magnesiumcalcium ratio within 4:1 and 9: 1.

The invention further contemplates providing an improved article of manufacture comprising an addition agent for the treatment of molten cast iron comprising magnesium, calcium, and silicon iron including at least a sufiicient amount to bind the magnesium, calcium and iron in the form of silicides, and having a magnesiumcalcium ratio within 4:1 to 9:1 to assure a retarding of the velocity of the reaction, to produce a more quiescent reaction and to decrease the loss of magnesium.

Among the further objects of the present invention is the'provision of an improved addition agent containing special amounts of magnesium, calcium, silicon and iron, having a magnesium-calcium ratio of 4:1 to 9:1, and including a small amount of cerium or cerium mischmetal.

Other objects and advantages will become apparent from the following description.

Generally speaking, the present invention contemplates the provision of improved addition agents for the treatment of molten cast iron for the production of spheroidal or spherulitic cast iron Which have approximately the following composition:

The iron content is not to exceed 30%. The silicon cononly the calcium but also the magnesium and iron in the form of silicides. As a general rule, an excess of silicon is to be desired. The magnesium-calcium proportions are carefully controlled so as to be within a special ratio of 4:1 to 9:1. When the magnesium-calcium ratio lies within the range of the aforesaid special ratios, the calcium content, which is present in the form of silicides, has the elfect of retarding the velocity with which the novel addition agent dissolves in the iron. By producing a more quiescent reaction, the loss of magnesium is greatly decreased. In this manner, the desirable combination of favorable properties of the novel addition agents is secured.

For magnesium contents up to 40%, the ratio of magnesium to calcium must be between 4:1 to 7:1; whereas for magnesium contents over 40%, the calcium content is to be 6 to 10% and the magnesium-calcium ratio is to be within the aforesaid range. Within these limits, the following novel addition agents have been successful in practice and have produced satisfactory results:

The balance is mainly or principally iron but not eXy ceeding 30%. The most useful among the novel addition agents having the aforesaid special ratios of magne sium to calcium are as follows:

Element: Range, percent Magnesium 25-35 Calcium 3.6-7 Silicon 35-60 Iron Up to 30 However, the following addition agents are also advantageous Element: Range, percent Magnesium 25-35 Calcium 2.8- Silicon 35 -60 Iron Up to 30 In the latter addition agents, it is preferred to have the ratio of magnesium to calcium between 71.1 and 9:1.

The minimum amount of calcium when the magnesium content exceeds 40% is about 6%. In these improved addition agents, the iron content particularly should be kept low. When the magnesium content exceeds 42%, a calcium content of only 6% does not provide the preferred ratio of MgzCa=7 :1. It has been found, however, that when magnesium contents are higher, the novel addition agents with calcium contents below the aforesaid proportion are still advantageous. The violence of the reaction of these addition agents is somewhat greater and the corresponding percentage magnesium recovery is a little lower. However, in view of their high absolute magnesium. contents, these improved addition agents. are still useful for effecting the introduction of magnesium into molten cast iron.

When the specified conditions relating to the silicon content are not observed, the advantages that can be gained by the presence of calcium will be only partly secured. Moreover, iron contents beyond 30% in these addition agents likewise. decrease the magnesium re.- covery. Only when the quantity of silicon is at least sufiicient to bind the calcium, magnesium and iron in the form of their silicides and the iron content does not under any circumstances exceed 30%, will the introduction of the magnesium by meansof these improved addition agents produce a quiet and steady. eaction and provide a'high magnesium recovery.

When the calcium content is raised beyond the limits hereinbefore set forth and outside the specified magnesium-calcium proportions, the resultant reaction will be too sluggish and unduly increase the temperature loss of the iron bath. The magnesium recovery decreases and the residues of the addition agents will be found remaining in and clogging. the plungcrused for introducing the agents into the bath of molten iron. Such residues make it impossible for the'plunger to be used again. When calcium contents are upward of 10%, such residues remain in major quantity in the plunger after every treatment. For instance, addition agents containing to 30% magnesium, 14 to% calcium, 40 to 50% silicon, and 4 to 14% give low magnesium recoveries. Only in-one test of a series, did the recovery even. reach whereas in other cases the magnesium yields were even substantially lower.

When addition agents of the pure magnesium-ironsilicon type, which include no calcium, were introduced in molten iron the reaction took su-ch'a violent course that the major proportion of the magnesium vapor formed. failed to dissolve and was oxidized. The magnesium yield then sank to values around and below 30%.

iron are insufficiently utilizedand In carrying the invention into practice, it is preferred to use improved addition agents having the following composition:

Element: Range, percent Magnesium 17 to 40 Calcium 2.8 to 8 Silicon 35 to 60 Iron Up to 30 When the magnesium-calcium ratio is maintained within the limits specified herein, the magnesium recoveries rise to 50% and sometimes even higher.

The best addition agent embodying the present invention has the following composition:

Element: Range, percent Magnesium 25 to 35 Calcium 2.8 to 7 Silicon 35 to 60 Iron Up to 30 The magnesium-calcium ratio is adjusted between 4:1 and 9:1 and is preferably controlled with a ratio of about 7:1 to about 9:1 which is especially advantageous. Plant scale. tests in foundries have shown that when sulphur-rich iron (about 007% to about 0.12%) is treated with a magnesium-containing addition agent at a temperature between about 1450" C. and about 1500 C., the spheroidal or spherulitic graphite precipitation occurs with about 35% to 44% recovery when the magnesium-calcium ratiowas 7:1 to 9:1, whereas it occurs with about 30% to 38% recovery when the magnesium-calcium ratio was 4-: 1 to 7: 1.

Alternatively, the calcium content can be adjusted to 2.8% to 5%, provided the magnesium-calcium ratio is adjusted to between-7 :1 and 9: 1-.

For the purpose of giving those skilled in the art a better understanding ofthe invention and/or a better appreciation of the advantages thereof, a number of illustrative examples will be given.

Tests wereperformed under controlled conditions with experimental melts each weighing about 8 kilograms. Thev melts had a gray cast iron composition containing relatively low sulfur (about 0.01% to about 0.015%). The. molten-cast iron was treated at about 1520 C. with improved addition agents having compositions given in thefollowing table. The MgzCa ratios and the magnesium recoveries are likewise given in this table as follows:

Table I Percentage Magnesium, Calcium, Silicon, Iron Mg: Ca Magnesium percent percent percent percent Ratio Recovery 17. 3 3. 2 54. 8 Hal. 5. 4:1 48 21. 2 3. 3 48. 2 Bal; 6. 4:1 50 30. 3 5. 8 54. 2 Hal. 5. 2:1 45 34. 9 GI 51 40. 0 Hal. 5. 4:1 48 38. 2 6. 5 38.0 Dal; 5:9:1 40 32. 4 3. 9. 61.0 Bal. 8 3:1 49 31. 1 4.0 v 58.0 13:11. 7. 8: 1 52 43.0 10.0 42.0 Bal; 4.0:1- 32 48.0 3.0 V 40.0 Bal. 6.0:1 34

The following table contains the results obtained under ordinary operational conditions using about 11 kilograms of the improved. addition agent embodying the present invention and adding it to a melt ofmolten cast iron weighing about 800 kilograms and having a composition suitable for the production ofspheroidal or spherulitic cast iron, such as one having the following composition:

Percent C 3.4-3.7 Si 2.0-2.4

P 0.06-0.08 ,S 0.07-0.10 Ti 0.03-0.04

Fe Balance Table II Addition Agent Mg in Mg: Ca Treatment Iron Mg Re- Melt Ratio Temperaas-Oast, covery, N0. Mg, Ca, 81, Fe, ture, 0. Percent Percent Percent Percent Percent Percent The sulfur content of melts Nos. 1 to 5 was 0.084%, of melts Nos. 6 to 10 was 0.083% and of melts Nos. 11 to 16 was 0.085%.

By way of comparison, the following table gives'the results obtained in a number of tests carried out with similarly composed addition agents in which the proportions were outside the ranges contemplated by the present The improved addition agents embodying the present invention may also contain up to 2% cerium or cerium mischmetal. As is known, such additions compensate the inhibiting eifect of certain trace or subversive elements, such as titanium, lead, tin, arsenic, bismuth upon the spheroidal precipitation of the graphite.

The simple treatment of a molten pig iron containing 0.12% of titanium with magnesium fails to induce an adequate formation of spheroidal graphite. However, by using an improved addition agent embodying the present invention and containing 29.4% magnesium, 5.1% calcium, 56% silicon and the balance iron to which cerium mischmetal has been added in such amount that the measured quantities therein were only 0.20% lanthanum and 0.28% cerium, 90% of the graphite was produced in the iron in the spheroidal form.

Apart from iron, the novel addition agents may contain impurities that have been introduced, for instance, in the basic materials, such as the ferro-silicon, the silicocalcium, an-d/ or magnesium scrap, used in the production of the addition agents.

In all cases hereinbefore referred to, the addition agents were introduced into the molten iron in the as-cast condition by means of a plunger. The improved addition agents may, however, be employed in the form of pressed shapes, sintered shapes, or in any other convenient and suitable form.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

We claim:

1. As a new article of manufacture, an improved addition agent for treating molten cast iron containing the following:

30-50% magnesium 28-10% calcium At least silicon Up to 30% iron 35 the quantity of silicon contained in the addition agent being at least sufiicient to combine-with the magnesium, calcium, and iron as silicides and the ratio of magnesium to calcium ranging between 4:1 and 9: 1.

2. As a new article of manufacture, an improved the following:

30 to 40% magnesium 28-10% calcium At least 35% silicon Up to 30% iron 30-50% magnesium 2.8-8% calcium 35-60% silicon 25-40% magnesium 3.6-8% calcium 35-60% silicon and the balance consisting mainly of iron but not sub stantially exceeding 30%, the quantity of silicon contained in the addition agent being at least sufficient to combine with the magnesium, calcium, and iron as silicides, and the ratio of magnesium to calcium ranging between 4:1 and 7:1.

addition agent for treating molten cast iron containing 7 5. As a new article of manufacture, an improved addition agent for treating molten cast iron containing the following:

30-40% magnesium 2.8-% calcium 3560% silicon and the balance consisting mainly of iron but not substantially exceeding 30%, the quantity of silicon contained in the addition agent being at least sufiicient to combine with the magnesium, calcium, and iron as silicides and the ratio of magnesium to calcium ranging between 7:1 and 9:1.

6. The improved article of manufacture of the character set forth in claim 1 in which the magnesium content is not more than 40% and the calcium content is at least 5%.

7. The improved article of manufacture of the character set forth in claim 1 which contains up to about 2% cerium.

8. The improved article of manufacture of the character set forth in claim 1 which contains up to about 2% of mischmetal.

9. The improved article of manufacture of the character set forth in claim 1 which contains up to about 2% of lanthanides.

10. As a new article of manufacture, an improved addition agent for treating molten cast iron containing at last and not more than magnesium, at least 5% and not more than 10% calcium, about 3560% silicon, and the balance consisting mainly of iron but not substantially exceeding 30%, the quantity of silicon contained in the addition agent being at least sufiicient to combine with the magnesium, calcium, and iron as silicides and the ratio of magnesium to calcium ranging between 4:1 and 9:1.

11. As a new article of manufacture, an improved addition agent for treating molten cast iron containing about 17% and up to about 30% magnesium, about 1.9% to about 5.5% calcium, at least about 35% and up to about silicon, and the balance consisting mainly of iron but not substantially exceeding 30%, the quantity of silicon contained in the addition agent being at least sufficient to combine with the magnesium, calcium, and iron as silicides and the ratio of magnesium. to calcium ranging between 5,5:l and 9:1.

References Cited in the file of this patent UNITED STATES PATENTS 2,762,705 Spear et al. Sept. 11, 1956 FOREIGN PATENTS 730,712 Great Britain May 25, 1955

Claims (1)

1. AS A NEW ARTICLE OF MANUFACTURE, AN IMPROVED ADDITION AGENT FOR TREATING MOLTEN CAST IRON CONTAINING THE FOLLOWING: