i

STEEL.— Mechanical Properties. 881

require close study and much further investigationin order to clear up the mystery that surrounds them.

Copper .—Small quantities of copper are occa-sionally found in steel, generally derived from thespiegeleisen. Some steel made at Harrisburg frompig iron, smelted from ore containing a considerablequantity of copper pyrites, was found to have asmuch as -5 per cent, of copper, and yet is stated tohave rolled well; but the general opinion of metal-lurgists is that copper induces red shortness in steelin about the same proportion as sulphur does.

Tungsten alloys with iron much in the same way thatmanganese does. The properties of this alloy havebeen successfully studied by Mushet, who has suc-ceeded in introducing it commercially under the nameof Mushet’s “special steel.” The analysis of specialsteel in Table XIV a is by Pattinson and Stead.

TABLE XIVa.

Iron, .

Combined carbon.

Silicon,.

Sulphur,.

Ferro

Manganese.

ManganSilicon Risen.

Special Steel.

8-25

6‘62

0*093

trace.

0*145

85*50

66 752-6510-20trace.0-18520-50

;87-00

•62

•21

•03

•10

•73

nil.

11*40

Manganese, .

Titanium,.

Tungsten r .

100-608

100-285 100-09

Heeren found 873 per cent, and Willis 1275per cent, tungsten in other samples. It is ex-tremely hard, breaking with a conchoidal fracturelike that of hardened steel, and has a very fine grain.It can only be forged at a moderate heat, and absorbsheat much more slowly than ordinary steel, so thatit should be raised in temperature very gradually.It is so hard that it needs no tempering, and thustools for turning and planing need only to be groundafter coming from the smith. Hackney states thattool steel containing IT per cent, tungsten madeexcellent turning tools and punches. Dr. WernerSiemens has shown that tungsten steel is twice aspowerful in retaining permanent magnetism as thebest ordinary steel.

Chromium readily alloys with iron, producing a fineclose grained steel, somewhat similar in many of itsproperties to tungsten steel. The finest steel forpurposes of tools and cutlery, however, appears afterall to be the old carbon steel; and the maximum ofhardness and toughness combined is to be obtainedonly by selecting material as free as possible from allforeign elements, except carbon.

Sir J. Whitworth has succeeded in condensingfluid steel by the application of enormous pressure,so as to obliterate the blow holes usually contained,and has thereby produced a material having greatstrength, which is suitable for many special purposes.The material is of great utility for guns, linings ofcylinders, &c., and the operations, though extremelydifficult, have been devised with great skill; but theprocess is a very costly one, and the utmost that canbe done is to entirely destroy all blow holes. Ifthese can be prevented by improving the metal-lurgical processes, without at the same time pro-

VOL. II.

ducing a weaker metal absolutely, it would appearthat compression would be needless. The specificgravity of the east-metal should indicate whetherthe blow holes have been thoroughly obliterated, andit is curious that some of the samples of solid caststeel from Terre Noire show quite as high a specificgravity as Whitworth’s compressed steel. Accordingto Dr. Percy the specific gravity of Whitworth’ssteel is 7-84, while the Terre Noire cast metal hasa density of 7'8 to 7-9. It must be admitted, how-ever, that the elasticity of the annealed cast metalof Terre Noire is not equal to that of Whitworth’ssteel of the same tensile strength; but there is greathope that even this defect may be overcome, andthat metallurgy will not be outdone by mechanics.

Mechanical Properties of Steel. —The resistanceto crushing strain, tensile strain, elasticity, resistanceto bulging stress, and other mechanical properties ofsteel, vary mainly according to the chemical composi-tion of the material; but they also vary with themode of treatment which the material has under-gone. Very elaborate experiments have been madefrom time to time to elucidate this subject; but weare still wanting a perfectly systematized set ofresults, accompanied at the same time with a com-plete history of the processes the material has gonethrough, together with careful chemical and physicalanalyses of the material. Great expectations wereformed of the value of the results that would followfrom the investigations of the committee of expertsappointed recently by the United States ; and it willbe a great pity if their labours are cut short forwant of funds. D. Kirkaldy has undoubtedly mademore mechanical tests of steel than any other man,and he has shown great skill in designing theapparatus for carrying these out, and indomitableperseverance in checking all his results personallywith the greatest care; but the mass of results whichhe has accumulated requires much sifting, and hismechanical tests have unfortunately rarely beenaccompanied with any chemical or physical examina-tion of the materials. They are therefore, like manyothers, of little use to the investigator, and seldomhelp us to elucidate principles.

An extremely interesting series of experimentswith steel for shipbuilding purposes was made byJ. Barba, chief constructor for the French navy,and reported in Engineering for 1875. One ofthe chief subjects of discussion, in reference to theextended use of steel for constructive purposes, hasbeen the relative effects of punching and drilling uponsteel plates, and Barba thus sums up his results.

“The following conclusions may be deduced fromthe preceding experiments on plates from -275 to•472 inches thick:—

“ 1. That the effects of punching and shearing areentirely local, and extend over a limited zone, lessthan ‘04 inch in width on the edge of the sidesheared, or of the hole punched.

“ 2. That no cracks exist in parts so changed.

“ 3. That tempering destroys the effect of shearingand of punching, by restoring the metal to thecondition in which it would have been if the opera-111