US2488513A - Production of white cast iron - Google Patents

Description

Patented Na. 15, 1949 2,438,513

UNITED STATES PATENT OFFICE 2,488,513 7 PRODUCTION OF WHITE CAST IRON Henton Morrogh, Handsworth, England, assignor to British Cast Iron Research Association, Alvechurch, England No Drawing. Application February 4, 1949, Se-

rial No. 74,709. In Great Britain February 10,

(ems-123) 6 Claims.

This invention relates to the production of white cast iron in a form specially suitable for subsequent annealing.

In white cast irons as normally produced for annealing (e. g. to give malleable cast iron) the whole of the carbon content is present as iron carbide (cementite), which gives to the white iron its hardness and brittleness.

silicon irons, however give a white cast iron in the presence of a sufiiciency of cerium r tellurium.

In relation to their. carbon content cast irons may be eutectic, hypereutectic or hypo-eutectic. The carbon content in a eutectic iron varies with the silicon and phosphorus contents, and corresponds sufiiciently accurately for present purposes'with the formula where C, P and Si stand for the percentages of carbon, phosphorus and silicon, respectively. If the percentage of carbon in the cast iron is greater than is given by this formula, the iron is said to be hypereutectic; if less, hypo-eutectic.

It is an object of the present invention to pro- In order to reduce this brittleness it is customary to subject nodules greatly facilitates the subsequent annealing process, decomposition of the cementite taking place at lower temperatures and/or in shorter times than have hitherto been found necessary.

According to the invention, therefore, cerium is added to a hypereutectic iron which on casting the cast iron to a heat treatment at high tempera- 5;; 2 5 3? 81 gaggi g???) gffi 2 82213135211 s0.08.252 tures (800 .10Q0 for lengthy fi 2.6 not more than 7% of silicon, so as to yield a white 200 hours) i order to 9 t e it- 1 cast iron in which the hypereutectic carbon is The carbon ltberated du-rmg 1s .annea mg pro' wholly or preponderantly in the form of nodular cess appears in the form of graphite nodules disgraphite.

tnbuted thmuglmut the a w decomposi' Cerium is a. powerful desulphurising agent but tion of cemfitlte by heat 15 facmtatefi by,the economic considerations make it necessary to use presence of s1l1con,,and the lower annealing times as starting material an iron already low in and/0r tempifmtiures 1 n'lentloned' phur and not to use up valuable cerium in reduc- Plicable to Whlte Irons 10h smconhigher mg the sulphur content to the required limit. Any v Silicon Content. Q V the more lfkely cerium sulphide present in the cast iron is entirely the cast iron to be grey instead of Whlte- In ineffective in the production of nodular graphite. r'ey c o the carbon is present Wholly or in If the starting material contains too much sul- Dart as flake raph t renders it useless v phur it should be pretreated with one of the for the production of malleable iron.- Even high- 5 known and cheaper desulphurising agents.

The amount of cerium to be added must be sufficient to give a white cast iron. With section sizes of one inch or less, 0.02 to 0.08% of cerium in the cast iron will be found satisfactory. (By section size is meant the diameter of the casting at its narrowest part). This is due to the more rapid cooling of the smaller sections, and a cor- I responding effect is obtained by the use of a metal duce a readily annealable white cast iron. It is a further object to produce such a cast iron from hypereutectic irons. A still further object isto produce a white cast iron in which the hypereutectic carbon (i. e. the excess of carbon over the eutectic proportion) is present in the form of nodular graphite. Other objects will appear from the following description.

I have found that the addition of cerium to a hypereutectic iron before casting results, provided the iron is low in sulphur and phosphorus, in a cast iron in which the hypereutectic carbon is wholly or preponderantly in the form of nodular or chill mould in comparison with a sand mould.

Rapid cooling of the casting also enables white iron castings to be made from iron containing the higher proportions (up to the limit of 7%) of silicon.

The smaller the section size and the greater the cooling rate, the higher may be the silicon content and the lower "the amount of cerium required.

Up to 5% of cerium may be used if desired, but owing to the cost of this metal and, as explained below, the longer time and/or higher temperatures required for annealing when much cerium is present, I prefer to limit the cerium to not more than 0.2% in the cast iron.

The annealing of castings produced according to the invention requires much less time than in the case of ordinary white cast iron. The time of heating .will vary according to the content of cerium and, as already indicated, of silicon. Longer periods and/or higher temperatures are needed according as the cerium content is higher and/or the silicon content lower.

or'all of these. The addition should be madeafter the cerium has been added and immediately before pouring the molten iron. This treatment increases the number of hypereutectic nodules and hence the rate or subsequent graphltisation. The nature of the invention will be understood from the following illustrative example, in which, as elsewhere in the description and claims, percentages are by weight.

Exampl Fifty pounds of pig iron the composition:

- Per cent Total carbon 3.80 Silicon 2.69 Manganese 0,66 Sulphur 0.030 Phosphorus 0.045 Iron, remainder was melted in a crucible furnace. To the molten metal were added first 2 /2 oz. of mischmetall and then 4 oz. of 80% ferrosilicon. The metal was poured into cold graphite chill moulds giving test bars 0.875 inch diameter. A test bar showed on analysis:

Per cent. Total carbon 3.66 Silicon 2.96 Man anese 0.60 Sulphur 0.017 Phosphorus 0.044 Cerium 0.051

Iron, remainder Ultimate tensile strength tons/sq. in..- 25.6 Ilongation at break per cent 6.5

It will be seen .that the invention provides a cast iron which can be economically annealed. It is applicable to the production not only 01' malleable cast iron but also of die-castings which are'to be annealed. For malleable cast iron a sand mould is usually employed and accordingly the silicon content should be low rather than high. For castings in dies or permanent moulds (chill castings) there is no objection to higher silicon contentv within the limit or 7% above specified.-

Iclaim:

. 1. A white cast iron containing 0.02 to 5.0% of cerium, not more than 0.02% or sulphur, less than 0.5% of phosphorus and not more than 7% or silicon. and having a carbon content greater than where P and Si stand for the percentages of phosphorus and silicon, respectively, in the cast iron, the hypereutecti carbon content being preponderantly in the form of nodular graphite.

2. A white cast iron as claimed in claim 1 which has been subjected to an annealing process.

3. Process for the production of white cast iron especially suitable for annealing, comprising adding to an iron which is hypereutectic in relation to carbon and which after casting contains not more than 0.02% of sulphur, less than 0.5% of phosphorus and not more than 7% of silicon such an amount of cerium as will result in a white iron casting containing 0.02 to 5.0% of cerium (other than that present as cerium sulphide).

4. Process 'as claimed in claim 3 in which the amount of cerium added is such as will result in a white iron casting containing 0.02 to 0.2% of cerium (other than .that present as cerium sul- Y phide) 5. Process :i'or the production of white cast iron especially suitable for annealing, comprising adding to an iron which is hypereutectic in relation to carbon and which after casting contains not more than 0.02% or sulphur, less than 0.5%

of phosphorus and not more than 7% of silicon ite, and mixtures or at least two or these substances.

I EEN'I'ON MORROGH.

No references cited.

Images