US2272277A - Process of manufacturing steel - Google Patents

Description

stantially deoxidized. e

- Patented Feb. 10, 1942 UNITED STATES; PATENT v OFFICE 2,272,271 raoccss or morac'roama s'rnnr.

Edwin L. Ramsey and Leslie :G. Graper,

Chicago, Ill.

No Drawing. Application April 25, 1941,

4 SerialNo. 390,342 f 8 Claims. (01. 15-133) be -red short This invention relates to a new steel having improved machining properties and to a process of manufacturing such a steel.

It has been the practice, to' improve the machinability of steel, to add sulphur to the steel. The making of sulphur steel at the open-hearth is very simple in that the stick sulphuris added to the molten metal while it is being tapped into the ladle. The difllculty that arises is in rolling the steel at the blooming mill where the ingots have a tendency to crack in the rolls due to what i is called a "red short condition. The theory back of this condition is that the sulphur added to the steel forms iron sulphide which migrates to the grain boundaries in the steel. This iron sulphide has a low melting point resulting in a condition when the steel is rolled such that it will part or crack at'these grain boundaries be-.

of burning the carbon out of the steel by passing air through the molten metal, does not develop a fred short condition to the same extent as steel made in the open hearth. In this process alarge quantity of oxygen passes through the steel which probably results in the formation of a different compound from iron sulphide; hence, resulting ina steel not as red short. It has also been noticed that sulphur steel with a low carbon content usually rolls better than sulphur steel with a high carbon content. It is believed this is due to the fact that low carbon steels contain much more oxygen in solution than the higher carbon steels. It has also been found, when making sulphur additions to completely killed steel, that a small amount of sulphur will result in a red short condition when rolling. It is believed that been various processesdeveloped for the addition of sulphur by other means than as stick sulphur; f

for example, processes are known in which the sulphur is added as molybdenum sulphide and manganese sulphide.

A principal object of the present invention is to provide an improved process of manufacturing steel of improved machinability by removing from the steel inclusions and conditions resulting from manufacturing processes which reduce toollife.

A more specific object is to provide an improved manufacturingprocess for adding sulphur in an oxidized form to a killed steel such as open hearth steel.

'A still-more specific object is to obtain the proper amount of sulphurin a steel and simultaneously improve the rolling and machining properties thereof by adding sulphur as sodium 1 .sulphiteor sodium bisulphite.

Another object is to remove aluminates and silicates and otherinclusions which are apt to be detrimental to rolling or injurious to tool life by slaggingof such constituents of the steel by adding a strong base or a composition which decomposes at the temperature of molten steel to 3 provide a strong base prior to the pouring of the material into the ingots.

This invention contemplates steels having generally standard analyses or alloysteels in which the sulphur content is increased by the addition of sulphur in an oxidized form such as sodium sulphite and sodium bisulphite. Simultaneously with the addition of sulphur, it is preferable to add or have present before decomposition-of thesulphur compound, astrong base such as sodium oxide- In this respect the sodium sulphites are this is due to the fact that killed steels are sub-,

The present demand of the steel users for steels of all specifications which can be used in automatic machines and which can be machined very easily, has increased considerably, .creating a problem for the open hearth in producing these particularly suited as these chemicals when added to the molten metal decompose or break down into sodium oxide and sulphur oxide. A The molten metal picks up the sulphur, possibly as the oxide, while the sodium oxide is partially'volatilized and partially reacts with any inclusions in the metal.

of an' acid nature, such as the silicates and aluminates, forming sodium silicates and aluminates "which are very easily fiuxed andthus removed from the steel. By theuseof 'a chemical of this nature, sulphur is introduced into the steel'in a different form and at the same time some of the objectionable refractory inclusions such as silidates are removed. Steels made with the addition of these' chemicals have. been found to have sulphur bearing steels so that the steel will not.55

improved'or better physical qualities in every respect. Such steels roll much better, not exhibitwhen it isrolled. There have .55-.60 .60'.90 .04 max. 114 .07 .15.30

ing red shortness; that is, cracks and seams which must be chipped out during conditioning of the billet for further rolling to such an extent as steel made with stick sulphur; better both as to life and as to speed of out. It is believed that this better machining is due to the inclusions of the sulphur compounds being finely divided and evenly dispersed due to the fact that the sulphur is freed in the metal by decomposition of the sulphite. It is also believed that the extra tool life is due to the fact that any objectionable inclusions are removed. As inclusions such as silicates and aluminates are of a very refractory nature, such inclusions act to dull the tools very rapidly. Results which will be hereinafter set forth with the process of this invention indicate that better machinability is obtained with a smaller percentage of sulphur in the specification than has heretofore been obtained.

Although the process of this invention is particularly applicable to steels such as given in the examples to follow, other specifications which require a low sulphur content in order to obtain the desirable physical properties can be benefited by the addition of compounds which will break down into strong bases in the molten metal permitting a. fluxing of the oxide with the inclusions and therefore easily removing them from the' steel.

An example will be given of a steel manufactured by the process of this invention. The particular heat was to be made to the following specification:

Mn P1105. Sui Si].

dition of .020 points of sulphur by means of thesodium bisulphite. This heat rolled very well in the blooming mill and in the merchant mill. A portion of the heat was rolled into round bars which-were later machined from about 1 "'to 1" round, as is common practice.- The bars were machined at the rate of 85 lineal feet per hour as compared to about 69 lineal feet per hour on bars of the other heats having the same ladle analysis except for the additional sulphur. It was also found that the tool life for the treated steel was approximately three times as long as for the untreated steel: that is, about .nine bars per tool were turned as compared with one to three bars per tool with the untreated steel.

As another example of the practice of this method, a heat was made having the following analysis:

0 Mn Phos. Bu]. Bil.

In order to check the sulphur distributionthroughout an ingot when making a sodium bisulphite addition to a 26" mold, 6.6 poundsof sodium bisulphite were added to the first ingot of this heat. The ingot weight was 9500 pounds: the sulphur recovery was about 70%. The first and second ingots were spotted and samples were taken for sulphur analysis, the second ingot being taken to give a comparison between the first ingot and the balance of the heat. The sulphur analyzed as follows:

There was practicallyv no slag formation at the top of the second or untreated ingot. In the first ingot there was an appreciable slag formed at the top of the ingot. This resulted from the breaking up of sodium bisulphite into sodium oxide and sulphur dioxide. The sodium oxide volatilized to someextent but unites to a considerable degree with the acid reaction products-oi the deoxidation process utilized in killing open hearth steels. A sample of the slag formed at the top of the ingot analyzed as follows:

FeO 3.24

MnO 5.55

SlO2 36.14 A1203 28.77

Lime Nil Sul 1.27 NaaO 21.15

Heat No. 65.504 with sodium bi-sulphite Impact Percent Percent Elastic Tensile elongation reduction Feet Pounds 119. 900 107. 380 23. o 44. 0 1a 21 150, 900 107. 030 23. 0 44. 0 17 17 68.920 107.030 23.0 44.0 I 17 17 Heat No. 73,843 with stick sulphur Pe ce t Pe t Impact I ll rcen Elastic Tensile elongation reduction N Feet Pounds Analysis of heats 0 Mn P1108. Sul. 80.

Under the microscope at 2,000 diameters the inclusions in the bisulphite heat up red smaller and-of a very irregular shape, while in .t e other heat they look larger and with a smoother edge.

Applicants have defined specific examples of the addition of sulphur as-a sodium bisulphite 'to steels of a specified composition. Other bi- 2,272,277 sulphitesof the alkali metal group have substantially'the same chemical properties in so far as the practicing of this invention is concerned. In so far as the use of a sulphite or bisulphite for obtaining free sulphur dioxide at a relatively low temperature is a part of the invention, other metal sulphites may be used, it being only necessary to obtain the results of the invention that the metallic sulphite decompose at the temperature of the fused metal being treated to' give oif sulphur dioxide. It is to be understood that the process of the invention can be practiced simultaneously withotherprocesses for impartproved machinability comprising adding to a v molten mass of steel a metallic sulphite which decomposes at the temperature of said molten v mass to give up a substantial proportion of the 'sulphur as sulphur dioxide.

2. A process of manufacturing a steel of improved machinability comprising adding to a molten mass of steel a sodium sulphite..

3. A process of manufacturing a steel of 'improved machinabilitycomprising adding to a molten mass of steel sodium bisulphite.

4. A process 01' manufacturing a steel of improved machinability comprising adding to a molten mass of steel before cooling in an ingot mold a sodium sul'phite in amounts ranging from 1 to 5 pounds per ton of steel.

5. A process of manufacturing a steel of improved machinability'comprising adding to molten steel before cooling in an ingot mold having an initial sulphur content of .030 to .070 a sodium sulphite in amounts ranging from 2 to 5 pounds per ton of steel.

6. A process of manufacturing a steel of improved machinability comprising adding to the ladle'during tapping from the furnace and before pouring into an ingot mold, a steel having a composition of carbon .55, manganese .75, phosphorus .016, sulphur .020, silicon .019, sodium bisulphite at the rate of approximately 3 pounds per ton thereby increasing-the sulphur content from .020 to .046 .whereby certain im-- purities as silicates and aluminates are fluxed by the decomposition of the bisulphite into sodium oxide and sulphur dioxide and rise as a slag to the surface of the metal in the ingot.

7. A process of manufacturing a steel of improved machinability comprising adding to' a molten mass of steel an alkali metal sulphite.

8. A process of manufacturing a steel of improved rolling and machining properties which comprises adding to a molten mass of steel a metallic sulphite which decomposes at the temperature of the molten mass to provide widely dispersed sulphur inclusions in the hardened metal.

4 EDWIN L. RAMSEY. LESLIE G. GRAPER.