What is the difference between oil quenching and water quenching during quenching?

Water quenching has fast cooling, but with high stress, large deformation and cracking tendency. It is generally used for carbon steel with poor hardenability.

 

Oil quenching has a mild cooling effect and is generally used for alloy steels with better hardenability.

 

One, water quenching

 

Quenching with water as the quenching agent is called water quenching. The advantage is that it cools faster in the high temperature zone (550°C~650°C), but the disadvantage is that the low temperature zone (200°C~300°C) also cools faster, which is likely to cause greater tissue stress. Water quenching is to put a high-temperature object in water, then boil it to red heat, and then put it in the water. Repeatedly, the rigidity can be improved.

 

The principle of water quenching is to spray the molten material at about 1400°C from the furnace with a water stream with a certain pressure to make the total smelt suddenly solidify and break into fine particles, so that the glass structure of the molten material is fixed. It prevents the recovery of calcium fluorophosphate crystals.

 

When the content of fluorine and phosphorus in the melt is higher and the alkalinity is higher, the calcium fluorophosphate crystal recovers faster, so the water quenching pressure is higher; on the contrary, when the fluorine and phosphorus are lower and the alkalinity is lower, The recovery of calcium fluorophosphate crystals is slower, so the water quenching pressure can be lower. The finer the melt is quenched by water, the faster the cooling rate, and the higher the solubility rate of the product; on the contrary, the larger the particles, although the common surface is cold first, but the internal cooling is slower, the product solubility rate is not high. .

 

Second, quenching

 

Flame quenching is a kind of surface that uses acetylene-oxygen flame (maximum temperature up to 3100℃) or gas-oxygen flame (maximum temperature up to 2000℃) to quickly heat the surface of the workpiece, and then spray liquid (water or organic coolant) to cool the surface Quenching method. Commonly used acetylene-oxygen flame surface quenching.

 

Flame quenching began in the early 19th century. At first, it relied on the operator's experience to ensure the processing quality. With the development of technology, people have designed and manufactured special hardening machine tools for hardening the curved surfaces of crankshafts, gears and other parts, thereby expanding the application range of flame hardening. Later, a quenching machine equipped with a through-flame temperature measuring device that can automatically control the temperature appeared, which gave a new development in flame quenching.

 

Flame quenching is a local hardening process that uses combustible gas fire pinch as a heating source for austenitization. Materials that are suitable for local hardening by flame quenching must have sufficient carbon content (usually 0.4%) to be hardenable. Since this process is usually used for low-alloy steel or ordinary carbon steel with low hardenability, the quenching after heating to the phase transformation temperature is generally completed by rapid water quenching. Quenching is almost instantaneous.

 

The heating medium can be a mixture of oxygen-acetylene, oxygen-making gas, propane or any other fuel gas with an appropriate heating rate. The quenching temperature is the same as that required for furnace quenching. The depth of the flame quenching zone varies from 1/32in (0.8mm) from the surface to the entire section.

 

The steel commonly used for flame quenching is ordinary carbon steel and low alloy steel with a carbon content of 0.40 to 0.95%. High-alloy steels such as martensitic stainless steels and tool steels are sometimes locally hardened, but medium-carbon steels are used more.

 

Highly hardenable steel has a greater tendency to crack during flame quenching. By preheating the parts (approximately 300°F; 149°C) and quenching with oil or water-soluble organic liquids before quenching, the cracking tendency of low alloy steels and tool steels can be reduced. However, oil quenching has the risk of flammability, making this process not widely used.