FIG. 82.—An obsolete method.
Give the steel a chance to heat properly, mix a little common sense with "your 30 years experience on the other fellows steel." Remember that high-carbon steel hardens at a lower heat than low-carbon steel, and quench when at the right heat in the two above ways, and 99 per cent of the trouble will vanish.
When a die flies to pieces in quenching, don't rush to the superintendent with a "poor-steel" story, but find out first why it broke so that the salesman who sold it will not be able to harden piece after piece from the same bar satisfactorily. If you find a "cold short," commonly called "a pipe," you can lay the blame on the steelmaker. If it is a case of overheating and quenching when too hot, you will find a coarse grain with many bright spots like crystals to the hardening depth. If uneven heating is the cause, you will find a wider margin of hardening depth on one side than on the other, or find the coarse grain from over-heating on one side while on the other you will find a close grain, which may be just right. If you find any other faults than a "pipe," or are not able to harden deep enough, then take the blame like a man and send for information. The different steel salesmen are good fellows and most of them know a thing or two about their own business.
For much work a cooling bath at from 50 to 75°F. is very good both for small hobs, dies, cutter plates or plungers. Some work will harden best in a barrel of brine, but in running cold water, splendid results will be obtained. Cutter plates should always be dipped corner first and if any have stripper holes, they should first be plugged with asbestos or fire clay cement.
In general it may be said that the best hardening temperature for carbon steel is the lowest temperature at which it will harden properly.
CARBON IN TOOL STEEL
Carbon tool steel, or "tool steel" as it is commonly called, usually contains from 80 to 125 points (or from 0.80 to 1.25 per cent) of carbon, and none of the alloys which go to make up the high speed steels. This was formerly known also as crucible or "cast" steel, or crucible cast steel, from the way in which it was made. This was before the days of steel castings. The advent of these caused so much confusion that the term was soon dropped. When we say "tool steel," we nearly always refer to carbon-tool steel, high-speed steel being usually designated by that name.
For many purposes carbon-steel cutters are still found best, although where a large amount of material is to be removed at a rapid rate, it has given way to high-speed steels.