The most known and main alloy in the history of a civilization is all the known steel. Its basis - iron which was and will remain a basis for the vast majority of structural materials, and the new alloys including alloyed will still be developed.
Instruction
1. The majority of the information about stalyakh is supplied by the chart of a state iron-carbon, more precisely - its left bottom corner to 2.14% From (carbon), presented in figure 1. It is possible to determine temperature of melting and hardening by it staly and chugun, intervals of temperatures at mechanical and heat treatment and some more process parameters. Such charts are constructed practically for all significant alloys. During creation alloyed staly also threefold charts are used.
2. These charts of a state receive quasistatic (very slow) heating and cooling of the studied solid solutions at their most various concentration. Phase transformations proceed at a constant temperature and therefore temperature curves for some time form isothermal sites. Among metallurgists and metallurgists of all countries there is a secret agreement according to which typical points on the chart iron-carbon are designated by the same letters. It should be noted that such approach does not exist at designation of steel grades therefore at the solution of tasks in metallurgy there can periodically be difficulties.
3. Metallurgists most of all are interested in those sites of the chart where solid alloy iron-carbon, actually, and is called steel. Here temperatures preceding liquid state of alloy are considered. First of all, it is necessary to deal with the main phases designated on the chart. Ferrite – solid solution of carbon in iron with a cubic face-centered lattice (GCK). Austenite – high-temperature ferrite. It has an objemocentrirovanny lattice (OCK). Tsementit – carbide of iron (Fe3C). Perlite is called the ferrito-tsementitny structure. There are also subtleties, such as primary and secondary tsementit which should be lowered here, as well as ledeburit.
4. To analyze a state became at different temperatures, carry out the vertical corresponding to the concentration of carbon chosen by you on the chart. So, at 0.4%C, after cooling the IE lines are lower and up to SE structure of steel austenite. Further, up to evtektoidny temperature of 768 °C that corresponds to the PSK line we have a state austenite + tsementit also up to room temperature – ferrite + perlite. Thus, the main temperature for the technologist – 768 °C. The majority medium-carbon staly is alloyed in one percent of chrome that lowers its temperature, approximately, to 720 °C.
5. On the chart of a state there is no such important phase of steel as martensite. Actually it is metastable austenite which did not manage to turn into perlite owing to the high speed of cooling of steel (training). Martensite has considerable hardness and at the room temperature metastabilen is purely conditional as for transition to perlite it just lacks internal energy. However at such transformation in steel there is high internal tension that can lead to formation of cracks. These processes bring up one more question for the technologist – the correct spending vacation of the tempered steel which removes internal stress, raises a cold brittleness threshold, but also diminishes hardness. Solving such problem, it is necessary to make the choice between losses and acquisitions.
6. For determination of temperature of heating when training the chart of a state are simply invaluable. It turns out that at concentration of carbon below those that there correspond to a point P charts, not alloyed steel "is not heated". Throughout all PSK line (and you need no more than 2.14% of carbon) is the temperature of approximately equal 780 °C. Overheating over evtektoidny is admissible, but it is worth to remember that it will cause growth of grain of austenite and other after training. Which consequence will be only negative.