US1846140A - Free machining corrosion resisting steel - Google Patents

Description

Patented Feb. 23, 1932.

V UNITED STATES PATENT OFFICE FRANK R. PALMER, OF READING, PENNSYLVANIA, ASSIGNOR TO THE CARPENTER STEEL COMPANY, OF READING, PENNSYLVANIA, A CORPORATION OF NEW JERSEY- IREE IACHINING CORROSION BESISTING STEEL EH Drawing.

My invention consist particularly in a new and improved high chromium corrosion resisting steel having relatively free machining properties; corrosion, as herein used, c0mprehending attack by chemical reagents and oxidation or surface deterioration at elevated temperatures, and the corrosion resisting steels to which my invention relates being those in which the corrosion resistance has been imparted primarily by the element chromnnn.

Such steels are well known in the art, containing chromium from 2% to 60%, frequently modified by additions of copper, molybdeis num, silicon, tungsten and nickel; the nickel element bein often added in sufficient quantities to pro uce an austenitic non-magnetic steel, and the content aside from these elements being principally iron with suflici ent carbon to accomplish the purpose desired in each case.

In my co-pendingapplication No. 247,462 for an anti-friction and free machining corrosion resisting steel, I have fully ointed out how high chromium in steel ren ers the.

products difiicult to machine, and how the deliberate employment of abnormally high percentages of sulphur overcomes the objec' tionable efi'ect of the chromium without markedly interferin with the corrosion resisting properties. y present invention avoids some of the undesirable features of such high sulphur steel as specifically set forth in said earlier application; a mam fact being that sulphur is objectionable from a merchandizing standpoint because it has been regarded for many years as a harmful ingredient, and that this prejudiceis communicated to some extent to my high chromium corrosion re sisting steels in which commonly prohibited high percentages of sulphur are deliberately employed. My present invention rovides for producing a free machining r0 not without incurring this objection inci ent to high sulphur content.

' Furthermore, as pointed out in my prior application, the sulphur combines with various metals present in the steel to form metalsul hides which are insoluble in the solidifled steel, so that forged or rolled specimens Application filed December 7, 1929. Serial No. 412,576.

of high sulphur corrosion. resisting steel, when polished and viewed under a metallurgical microscope, reveal considerable quantities of elongated slag-like sulphide inclusions which are objectionable in that they reduce the ductility and toughness of the I metal in a direction normal to the direction of rolling or forging; whereas in my present invention, free machining qualities are imparted with decidedly less slag-like inclusions than in the case of hi h sulphur steels, constituting a very desiraile improvement.

In the periodic table of chemical elements, sulphur occurs in a group having a valence of 2 with hydrogen and a valence of 6 with oxygen, usually referred to as grou VI. This group is headed by oxygen whic is a gas, and the elements of higher atomic weight than oxygenfall intotwo groups; one group comprising metalloids and the other group comprising metals. The metalloid group consists of sulphur, selenium and tellurium with atomic weights of approximately 32, 79 and 127 respectlvely. These three metalloids are known to be closely related in many of their properties and when referred to jointly hereinai'ter will be termed group VI metalloids.

I have found that selenium and tellurium have the property, when added to high chromium corrosion resisting steel, of imparting free machining properties in like manner to sulphur, and that they at the same time avoid the principal objections to sulphur above referred to. There is no eneral prejudice against selenium and tellurium, and their use therefore does not interfere with the merchandizing of the product; microscopic examination of a series of high chromium corrosion resisting steels containing various percentages of selenium and tellurium reveals that these metalloids, like sulphur, appear to combine with a metal, forming what is 'udged to be metal-selenides or metal-tellurides which a pear very similar to metal-sulphides.

owever, the selenides and tellurides are evidently' more soluble in the solidified steel than sulphides because a iven percentage of either or both does not yie (I nearly so much slag-like inclusion as would the same percentage, of. sulphur. My examinations and tests 1W sults aimed for.

reveal no notable difference between the behavior of selenium and tellurium insofar as they are used to achieve the objects of this invention. They apparently can be variedly used with ordinary judgment, either llldlVldually, or jointly, and with or without sulphur, so as to satisfactorily achieve the stated re- 1 have further discovered that it is not necessary to use as much selenium or tellurium, singly or jointly, as would be necessary in the case-of sulphur alone to secure satisfactory machining properties. As pointed out in said a plication, No. 247,462 sulphur has little e ect on the machining properties of high chromium corrosion resisting steel, particularly when the chromium exceeds 10.00%, until the sulphur exceeds .15% by weight of the mass; whereas I have obtained very satisfactory machining properties by usin onl about .07 of selenium or tellurium, t oug I have found the optimum percentage of these new metalloids to be about .20% by weight. 'So far as I am aware neither selenium nor tellurium have been heretofore used in any ferrous alloy for the present stated purpose,'or any other.

Hi h hromium corrosion re'sistin steels, as now commonly employed, contain a ut .20 to .50% mangane'se. In my prior a plication No. 247,462, I have pointed out t at hot h following type compositions:

malleability may be preserved in high. sulphur corrosion resisting-steels by increasing the manganese percentage above this norma range or by the addition of a metal like zircomum, in order to prevent the formation of a preponderance of iron-sulphide with resultant red shortness. In my present invention,

- since tellurium and 'selemumilsingly or jointly, need not be added in suc large percentages as sulphur, and also presuma ly because 0 their partial solubility in the steel base, the need for s ial alloy additions to secure hot malleabilityis not so vital. Neverthe less, I prefer, 1n the interests of good steel making practice, to use increased manganese or a metal like zirconium in conjunction with the metalloids noted. Y

My invention -is fully embodied inhigh chromium corrosion resisting steels of the Carbon Chromlumfiulphur Zirconium Selenium Tellurium I have carefully compared steels of the above type compositions with steels. of the following type compositions Carbon Chromium Sulphur Zirconium Selenium Tellurlum Steels (a). and ((1) do not machine satisfactorily with the usual machine shop practice because the chips tend to all and adhere to the tools, producing a con 'tion frequentrosion resisting steels containing minor per-' centages of other alloys such assilicon, copper, molybdenum and tungsten; and with nickel additions even suflicient to produce an austenitic product, the application of my mvention produces markedimprovement in machining properties.

Steels within the scope of this invention can readily be made in a crucible pot furnace by compounding the corrosion resisting base analysis steel in accordance with usual crucible steel meltin practice and adding metallic selenium or te lurium or both, just before pouring the metal fromthe crucible. Both metalloids are quite volatile and should be added in stick form-rather than as a powder, and losses can be reduced by thrusting the metalloids beneath the surface of the molten steel on the end of a rod. In any case an excess of metalloid ranging from'2 to 10 times the residual quantity requiredshould be allowed for volatilization, the exact excess necessary varying according to the individual melters mani ulations in adding the metal loids. These improved free machining steels can also .be made in the electric furnace but.

the selenium andtellurium should be added in the ladle with due provision forloss.

It-is to be understood from the above description, that my present invention is a further development of the invention specifical- 1y set forth in my said prior. application 50-, r1al No. 247,462, t being based-on determination of the fact that the elements selenium and tellurium, of the recognized periodic group VI, may be used individually or jointly to replace wholly or in partthe sulphur of said group, and with stated advantages over use of sulphur alone as previously described; the essential desired. effect of free machining bemg apparently always secured,with and incidental to resulting reduction .of high frictional quality in the alloy; and such main desired effect being secured-by an actual content in the. alloyof between 03% and 2.00%,

of the group VI metalloids.

WhatI claim is:

1. As a composition of matter an alloy steel containing chromium between 4% and 60% and the elements selenium and tellurium of a total percentage between .03%' and 2%, and characterized by relatively free machining quality.

2. As a composition of matter, an alloy I steel containing chromium between 4% and 60% and selenium between 03% and 2%, and