This process leaves the piece harder than does the quenching in water-annealing; the decrease in hardness due to water-annealing is the difference between the effects of the two operations. Let two pieces of the same bar be heated exactly the same for water-annealing; let one be quenched in water, and the other be allowed to cool in the air in a dry place. Then the superior softness of the air-cooled piece will show that the so-called water-annealing furnishes no exception to the rule.
There is one extremely important matter connected with cooling that should be noted carefully.
It is a common practice among steel-workers when they get a part of a piece of steel too hot to partially quench that part, and then go on with their heating; or if they are in a hurry to get out a big day’s work, or if the weather is hot, and a pile of red-hot bars is uncomfortable, to dash water over the pile and hurry the cooling.
This practice means checks in the steel, hundreds of them.
A bar breaks and has this appearance. The dark spot is the check; it did not show in the bar, no inspector could see it, but it broke the bar. Any one can prove this to his own satisfaction in a few minutes. Take a bar of convenient size, about one inch by one eighth; heat it carefully to an even medium orange color and quench it completely; then snip it with a hand-hammer over the edge of an anvil, snipping away until satisfied that it is sound steel. There are no checks.
Now beat a similar length of the same bar in the same way, and pass it through the stream from the bosh-pipe, or submerge it for a moment in the bosh, not long enough to produce more than the slightest trace of a change in the color; then put it back in the fire and bring it gently to the uniform color used before, and quench it completely. Now when it is snipped over the anvil it will show numerous checks, dozens of them.
In this experiment the complete submersion for a moment may not produce checks at every trial, because the complete submersion permits practically uniform cooling, which if continued to complete cooling would be simply the ordinary hardening process. Still it will produce checks in the majority of cases, indicating that starting the changes, strains, or whatever they are of the quenching process and then stopping them suddenly while the steel is in the plastic condition does cause disintegration, so that the operation is dangerous and should not be tolerated. Passing the hot steel through a stream of water or dashing water over it must cause different rates of cooling, and necessarily produce local strains resulting in checks. These latter ways of injuring, therefore, rarely fail to produce the ruinous checks.
If this positive destruction is produced in this way, in steel containing enough carbon to harden it is clear that similar, although not so pronounced, results will be produced in the mildest steels when they are treated in the same manner.
The rule, then, should be: Never allow water to come in contact with hot steel, and never allow hot steel to be laid down upon a damp floor.