23.10 Tempering is a heat treatment applied to hardened steels that is best defined as which of the following (one correct answe
r): (a) heating and soaking at a temperature above the austenitizing level followed by rapid cooling, (b) heating and soaking at a temperature above the austenitizing level followed by slow cooling, (c) heating and soaking at a temperature below the austenitizing level followed by rapid cooling, or (d) heating and soaking at a temperature below the austenitizing level followed by slow cooling,?
The correct answer is (a), heating and soaking at a temperature above the austenitizing level followed by rapid cooling.
Explanation:
Tempering is a heat treatment that is performed to change microstructure of steel <em>and increase it's hardness.</em>
It is done by heating above the austenitizing level, because for this heat treatment it's necesary to heat the steel to get <em>austenite structure</em> that is the <em>alotropic form of gamma iron.</em>
The procedure of tempering, continues with rapid cooling, because this way you get the microstructure with the best hardness properties, that is <em>martensite.</em>
The burning of the sun is not chemical combustion. It is nuclear fusion. This combustion releases energy which we experience as the heat and light given off by the flame.
