Chrome-nickel Steel





Forging heat of chrome-nickel steel depends

very largely on the percentage of each element contained in the

steel. Steel containing from 1/2 to 1 per cent chromium and from

1-1/2 to 3-1/2 per cent nickel, with a carbon content equal to

the chromium, should be heated very slowly and uniformly to

approximately 1,600 deg. F., or salmon color. After forging, reheat

the steel to about 1,450 deg. and cool slowly so as to remove forging

strains. Do not attempt to harden the steel before such annealing.



A great deal of steel is constantly being spoiled by carelessness

in the forging operation. The billets may be perfectly sound, but

even if the steel is heated to a good forging heat, and is hammered

too lightly, a poor forging results. A proper blow will cause the

edges and ends to bulge slightly outwards--the inner-most parts

of the steel seem to flow faster than the surface. Light blows

will work the surface out faster; the edges and ends will curve

inwards. This condition in extreme cases leaves a seam in the axis

of the forging.



Steel which is heated quickly and forging begun before uniform

heat has penetrated to its center will open up seams because the

cooler central portion is not able to flow with the hot metal

surrounding it. Uniform heating is absolutely necessary for the

best results.



Figure 16 shows a sound forging. The bars in Fig. 17 were burst

by improper forging, while the die, Fig. 18, burst from a piped

center.



Figure 19 shows a piece forged with a hammer too light for the size

of the work. This gives an appearance similar to case-hardening,

the refining effect of the blows reaching but a short distance

from the surface.



While it is impossible to accurately rate the capacity of steam

hammers with respect to the size of work they should handle, on

account of the greatly varying conditions, a few notes from the

experience of the Bement works of the Niles-Bement-Pond Company

will be of service.









For making an occasional forging of a given size, a smaller hammer

may be used than if we are manufacturing this same piece in large

quantities. If we have a 6-in. piece to forge, such as a pinion or

a short shaft, a hammer of about 1,100-lb. capacity would answer

very nicely. But should the general work be as large as this, it

would be very much better to use a 1,500-lb. hammer. If, on the

other hand, we wish to forge 6-in. axles economically, it would

be necessary to use a 7,000- or 8,000-lb. hammer. The following

table will be found convenient for reference for the proper size

of hammer to be used on different classes of general blacksmith

work, although it will be understood that it is necessary to modify

these to suit conditions, as has already been indicated.









Diameter of stock Size of hammer

3-1/2 in. 250 to 350 lb.

4 in. 350 to 600 lb.

4-1/2 in. 600 to 800 lb.

5 in. 800 to 1,000 lb.

6 in. 1,100 to 1,500 lb.



Steam hammers are always rated by the weight of the ram, and the

attached parts, which include the piston and rod, nothing being

added on account of the steam pressure behind the piston. This makes

it a little difficult to compare them with plain drop or tilting

hammers, which are also rated in the same way.






Steam hammers are usually operated at pressures varying from 75

to 100 lb. of steam per square inch, and may also be operated by

compressed air at about the same pressures. It is cheaper, however,

in the case of compressed air to use pressures from 60 to 80 lb.

instead of going higher.



Forgings must, however, be made from sound billets if satisfactory

results are to be secured. Figure 20 shows three cross-sections

of which A is sound, B is badly piped and C is worthless.





Case-hardening Treatments For Various Steels Chromium facebooktwittergoogle_plusredditpinterestlinkedinmail

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