how water & oil quenching affects metal properties?

Question

(mechanical properties,tensile strength, hardness, ductility, toughness, microstructure, internal stress)

Answer 1

By controlling the rate of cooling (water is a better conductor of heat than oil is). As a heated metal cools, the molecules line up differently, giving different properties.

Answer 2

The use of oil vs. water for quenching usually is dependant on what temperatures your cooling from. Quenched metals usually, but not always increase hardness, reduce ductility, increase internal stress, depends ont eh material for the effect on tensile strength, toughness and microstructure.

Answer 3

The concept of oil vs. water quench is not a matter of thermal conductivity but boiling point. When hot steel is quenched in a liquid the surface of the steel quickly nears the boiling point of the liquid. Lower boiling point liquids remove heat more rapidly from the steel. Some specialty quenches use liquid nitrogen for more rapid cooling. Conversely, air cooling is the slowest.

The whole process is governed by the time temperature transition curve. The more quickly a steel is cooled, the more the crystal structure is frozen in place. Slower cooling allows time for growth and annealing. If steel is cooled too fast it becomes brittle (to much Martensite - the brittle phase in steel). If it is cooled slowly, it is very soft. Careful control of the time-temperature history is essential to getting the desired properties. Very low alloy steels require extremely fast cooling to be significantly hardened. The addition of alloying elements tends to stabilize the martensite so reasonable cooling rates can produce hard and strong materials.

An interesting demonstration of all this is to take a piece of piano wire from a hobby shop (high alloy steel). As is, it is very difficult to cut or bend. Take a torch and heat it to cherry red then plunge it in water. The material then is as brittle as glass. A 1/8" rod can be snapped in two by bending it with pliers. Reheat the wire but let it air cool. Now the material is soft and pliable and easily bent with pliers. This shows three states of the same material composition.

Answer 4

Metals, especially steel alloys, can be cut, pollished, etched and examined under miscrscope to determine the size of metal crystals and the composition of grain boundaries that may differ from the grains. Heating to certain temperatures allows grains to dissolve and cooling at certain rates (including hold periods) allow grains to grow. As grains grow, certain alloying agents may be pushed out of the growing crystals and ultimately form the boundary between grains. The properties of steel that you mention are obtained by soaking at high temperature and controlled cooling and perhaps sudden cooling to halt the crystalization process by quenching in oil or water. Experimentation with alloying agents and heat treatments and photomicrographs helps identify how to bring out desired characteristics including grain size, corosion resistance, ductility and stress relief, etc. Specialists in this field are called metallurgists.

Answer 5

I definitely have a diamond/gold/platinum guy's ring, which for sort of twenty years I wore devoid of removing. i think the only element you ought to be careful of is the diamond once you're in water, that's accessible (consistent with how the diamond is desperate) that over an prolonged volume of time the water could loosen the stone- yet not likely. As for the steel, platinum is risk-free in salt water and much extra apparently gold is effectively proof against sea water - it would not even tarnish, that's why that's effortless to discover real gold on the sea mattress, because it remains glittery!!! desire this enables. Si.