1、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
2、 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 repre
3、sents 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 tempera
4、ture 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 grain
5、s 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 i
6、f 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 brig
7、hten 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 cri
8、tical 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 m
9、ay 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 austenit
10、e, 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 s
11、teel 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 ov
12、er 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
13、 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 particu
14、larly 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 b
15、egin 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
16、 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 forging. My last heats are always at critical. When the blade is finally shaped, I cycle the blade just above critical and down
17、 to almost black heat at least three times, cooling between by moving it back and forth in the air gently. Hardening You have a lot of options when it comes to hardening carbon steel. Even the slightest change in alloy content can make a remarkable difference in the hardening characteristics of the
18、steel, so I would again encourage you to study the steels you will be using. The transformation temperatures and times are described using a chart that shows the Ae1 line, the temperature at which austenite begins to form and the Msline, the temperature at which martensite starts to form from austen
19、ite.The time line at the bottom of the chart is in seconds and side bars give temperature. This is called an S curve chart and it is very useful in determining the quench speeds for each steel. The top curve of the S is known as the nose of the curve. When quenching from critical, the temperature of the steel must drop below the nose of the curve within a precise amount of time in order for the steel to harden to martensite. In this case, it must get below 900F in under five seconds to form martensite. Marquenching
