金属的热处理外文翻译

附录 1

英文及翻译

Heat Treating of metals

Heating

For this discussion, I will take you through the hardening process that I use on a

high carbon steel blade, but first a few asides. When you place the steel in the fire it

begins to gain heat. The steel will begin to give off visible color just above 900F it

will continue to pick up color until it reaches a point where it seems to hang. It is still

gaining heat, but it is undergoing an internal transformation from its cold structure

into a metastable condition called austenite. This point at which it seems to hang is

called decalescence and it represents the bottom of the critical temperature. It usually

begins around 1335F

In carbon steel depending on the carbon content. Once it passes through this

point, the crystal structure of the steel changes as the ferrite reacts with some of the

carbide and begins to pool into austenite. As the temperature increases more of the

austenite will begin to form in other places and continue until it reaches a point 10 or

15 degrees above the critical temperature where all of the ferrite should be consumed.

At this point the steel should consist of austenite and undissolved carbides. The

austenite grains start from a small nucleus and continue to grow until they impinge on

other growing grains. The initial grain size is established at this point and if the excess

carbide is in large quantities it will maintain this size with little increase, pinned by

the carbide.

You can see this transformation if you watch the steel carefully and bring the

steel up slowly. The Japanese talked about watching the shadows on the blade and

quenching when the shadows turned to liquid. If you take the blade out of the fire at

this point and watch the colors drop, you will notice a point where the steel will

brighten even as it is cooling. On a tapered cross section like a knife blade it will

appear to travel up from the edge to the spine of the blade. This is call recalescenceand represents the transformation from austenite back to pearlite. After I

am done forging a blade, I cycle the blade just above critical and down to dark heat at

least three times. I watch for these two points to establish critical in my mind and to

set up a very fine grain pearlite structure in the steel.

After reaching critical temperature, the steel should be fully austenized, but the

carbides will continue to dissolve. It may be necessary to soak at temperature to fully

dissolve all the carbides. In some steels it may be necessary to continue to raise the

temperature for this to be accomplished especially in the presence of alloying

elements that retard the transformation.

Once the steel is above critical and austenite, it may be quenched and hardened.

The structure of the steel can be established by carefully controlling the time it takes

the steel drop from critical through the various temperature sensitive points.

Transformations on Cooling

Annealing, normalizing, quenching

The structure and hardness of the steel is established by the rate of cooling from

the austenitic condition. If brought down slowly the steel will be annealed and soft.

The structure will be mostly ferrite and cementite, carbides. This can be done in a

temperature controlled furnace by dropping the temperature through a known rate

over a set period of time dependent on the type of steel. Another method is to preheat

a heavy bar of low carbon to the same temperature as critical for the steel and bury

both of them together in vermiculite. It will slow the cooling rate down so that the

blade will still be hot to the touch the next day. For most of the carbon steels this will

be enough to anneal the piece.

If allowed to air cool it will be normalized, a tougher condition comprised of fine

pearlite and carbides. Blades can be prepared for heat treatment in either normalized

or annealed states. Another treatment that is particularly effective for workability and

for dimensional stability is called sphereodizing. With the steel in a normalized condition you reheat, usually in salt to inhibit oxidization, to a temperature just below

lower critical, 1300F and hold for at least an hour. What occurs is that the carbides

will begin to aglomulate or pool into larger more evenly spaced particles in a ferrite

matrix. It makes handfinishing much easier.

It is important to precondition your blades not only because it helps workability,

but also to stress relieve the steel after forging. This will reduce chances of cracking

and warping in the quench. It is helpful to think of the forging stage as the beginning

of the heat treatment and to pay careful attention to the heats especially in the final