How many types of annealing

The longer the water explosion time, the higher the hardness. Compared with traditional quenching and tempering and low temperature annealing, boiling water quenching is superior. Please send us your inquiry about the customization of other furnace types or related questions about vacuum furnace.

We will reply you immediately. Thank you. Downloads All documents in the overview. Request Send us a message. All Rights Reserved. CN RU. Toggle navigation. A new rapid softening process — water annealing Water quenching is a common hardening method for carbon steel heat treatment, which is well known, but water annealing is rare. Fast spheroidizing annealing After high-speed steel is forged, slow cooling followed by reheating annealing process is adopted in general units. Diffusion work usually requires a second pass, which is effected as a complete annealing operation or an alloy normalizing pass.

The full annealing procedure generally suits most applications and steels, but then there are the high and low carbon variants to consider. Think of the contrasting procedures as material and application-specific options. For example, tool or bearing steel parts should be spheroid annealed so that they gain carbide hardened-strength. For residual stress control, the temperatures change, fine-tuned annealing curves are initiated, and grain structures homogenize or develop application-specific properties.

Isothermal Annealing On taking the temperature of a steel workpiece to its critical transformative temperature, similar to the full annealing process, the alloy is forcibly cooled.

This is a process for high carbon and alloy steel in order to improve their machinability. A heat treatment process in which ingots, castings, or blanks are heated to a temperature slightly below critical temperature for a long time and then cooled slowly to eliminate chemical inhomogeneity.

Thus to eliminate dendritic segregation and regional segregation during solidification of the ingot, and to homogenize the composition and structure. Diffusion annealing for some high quality alloy steel and alloy castings and ingot with serious segregation. De-stressed annealing does not change the metal structure. Recrystallization annealing, also known as intermediate annealing, is a heat treatment process that heats the cold-deformed metal above the recrystallization temperature for a certain period of time, so that the deformed grain can be converted into the uniform equiaxed grain to eliminate the processing hardening and residual stress.

Recrystallization must occur at first with a certain amount of cold plastic deformation and then at a certain temperature. The lowest temperature at which recrystallization occurs is called the lowest recrystallization temperature. Your email address will not be published. A full anneal is accomplished by heating the steel above the upper critical temperature, transforming the microstructure to completely austenite. The furnace is turned off, and the temperature allowed to drop.

Typically, this can take 30 hours or more depending on the alloy. Isothermal annealing or process annealing, is slightly different from a full anneal, but produces a similar microstructure. The austenite transforms to ferrite and pearlite. The part is then withdrawn from the furnace, and allowed to air cool in some convenient manner. The advantage of an isothermal anneal over a process anneal is predominately shorter time.

A full anneal will require about 30 hours, but an isothermal anneal will require approximately four hours, depending on the alloy. This is shown in Figure 3. Normalizing is a similar process to full annealing, but with some important differences.

After complete transformation to austenite generally soaked at temperature for one hour per inch or 25 mm of thickness , the part is withdrawn from the furnace and allowed to air cool.

These processes are typically performed on weldments, forgings or castings. The forging process as well as welding and casting occurs at elevated temperatures, where grain coarsening can occur. This means that forgings can have a large variability in the grain size. Depending on how the forging or weldment is cooled from the forging or welding temperature, the microstructure will be mixed, and exhibit large variability in hardness.

There are also large residual stresses thermal and transformational that can result in distortion. The purpose of normalizing is produce a fine-grained and uniform microstructure — typically fine grains of fine pearlite. The largest difference between full annealing and normalizing, is the lamellar spacing of the resulting pearlite.

Very coarse pearlite is very soft. Fine grained pearlite is harder, and somewhat easier to machine. The resulting hardness is in the upper HRB range. However, for steels with high hardenability, a fast air cool can result in a mixed microstructure containing significant quantities of bainite, and possibly martensite for very high hardenability steels.

The resulting hardness is also greater. Spheroidizing or a spheroidizing anneal is a process where the lamella of pearlite consisting of iron carbide or Fe 3 C is transformed to spheres of iron carbide.

The resulting matrix is now ferrite with spheres of cementite, instead of pearlite, which is a matrix of ferrite with lamella of cementite. Below the lower critical temperature, the diffusion of carbon is slow, so long times are required to spheroidize the cementite lamella.

The primary reason for spheroidizing is to produce a very ductile steel suitable for deep forming, or forming in complex shapes.