. Railway mechanical engineer . fficult to establish an exact sched-ule of temperatures for the various requirements in carboncontent but if we carbonize at a certain temperature, for acertain depth at least, the case will have the amount of carbonthe chart indicates. Such depth is sometimes so slight as tomake it difficult to get a chemical analysis, but photomicro-graphs often prove such values in quite a convincing manner. After steel has been carbonized its heat treatment must begoverned by the nature of the service that it will be obligedto render. If a hyper-eutectoid case has been estab
. Railway mechanical engineer . fficult to establish an exact sched-ule of temperatures for the various requirements in carboncontent but if we carbonize at a certain temperature, for acertain depth at least, the case will have the amount of carbonthe chart indicates. Such depth is sometimes so slight as tomake it difficult to get a chemical analysis, but photomicro-graphs often prove such values in quite a convincing manner. After steel has been carbonized its heat treatment must begoverned by the nature of the service that it will be obligedto render. If a hyper-eutectoid case has been established andthe requirement is for extreme hardness without the need ofany particular toughness in the sharp edges or the lightersections of the material, the quench for the case should be atthe critical temperature of approximately per cent car-bon steel, without any subsequent draw; but if the wear towhich the parts are to be subjected is abrasive in charactersuch as gears, or dies, the parts should be given a draw of 1800. 5olid Line = Furnace Line = Box Temp. 800 10 2 3 4 5 6 7 8Hours of Operation Fig. 2—Curves Showing Comparative Temperatures Inside andOutside of Boxes During Carbonizing Operations approximately 400 deg. F.; the exact temperature of the drawcan only be determined when the scleroscope or Brinell hard-ness requirement is known. It is a matter usually for the op-erator himself to determine by test, since there are alwaysvariations in steel, and in conditions within the shop thatmake it impossible to establish exact rules for hardeningsteel that may be followed successfully by all steel treaters. A single quench for carbonized parts always should beavoided where it is economically possible, and never shouldbe chanced where the carbonizing temperature exceeds 1,650deg. F. (if quenching from the pot is necessary) for suchpractice results so often in the absolute loss of parts so treated,that the chance of avoiding trouble is too small to be wort
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectrailroadengineering
