Professional knowledge for quenching, recovery, positive fire, annealing

1. Quench

 

▼ Inductor heating quenching

 

1. What is quenching?

The quenching of the steel is to heat the steel to the critical temperature AC3 (Assembly steel) or AC1 (over -common steel) above the temperature, and heat the heat for a period of time to make all or part of the auscularization of the Octobicuration, and then the cold at the critical cooling speed Quickly cold to the thermal treatment process of martensite (or bell) transition below MS (or temperature near MS). Usually, the solid -soluble treatment of aluminum alloy, copper alloy, titanium alloy, tempered glass and other materials is called quenching with the heat treatment process with a fast cooling process.

2. The purpose of quenching:

 

1) Improve the mechanical properties of metal materials or parts. For example: Improving the hardness and abrasion resistance of tools, bearing, etc., improve the elastic limit of spring, and improve the comprehensive mechanical properties of the shaft parts.

 

2) Improve the material performance or chemical performance of certain special steel. Such as improving the corrosion resistance of stainless steel, increasing the permanent magneticity of magnetic steel.

 

When cooling and cooling, in addition to the reasonable quenching medium, there must also be correct quenching methods. Commonly used quenching methods, mainly monoclinal quenching, double liquid quenching, grading quenching, equal temperature quenching, local quenching, etc.

 

3. Steel workpiece has the following characteristics after quenching:

 

① Organized an unbalanced (unstable) tissue such as martensite, bale, and residual austenite.

 

② Exist large internal stress.

 

③ The mechanical performance cannot meet the requirements. Therefore, the steel workpiece generally needs to be recovered after quenching

 

2.Recovery

▼ Fire recovery

 

1. What is the fire?

 

The ignition is to heat the quenching metal material or parts to a certain temperature. After the heat preservation for a certain period of time, the heat treatment process in a certain way is a kind of operation after the quenching. A process, thus referring to the joint process of quenching and recovery.

 

2. The main purpose of quenching and recovery is:

 

1) Reduce the internal stress and reduce the brittleness. There are great stress and brittleness in quenching parts. If not recovered in time, it will often cause deformation or even cracking.

 

2) Adjust the mechanical performance of the workpiece. After the workpiece is quenched, the hardness is high and the brittleness is high. In order to meet the different performance requirements of various workpieces, it can be adjusted by ignition, hardness, strength, plasticity and toughness.

 

3) Stable workpiece size. By igniting, the gold phase organization can stabilize to ensure that it will no longer deform during the future use process.

 

4) Improve the cutting performance of certain alloy steel.

 

3. The role of recovery is:

 

① Improve the stability of the tissue so that the workpiece will no longer occur during the use of the workpiece, so that the geometric size and performance of the workpiece are stable.

 

② Eliminate internal stress to improve the performance of the workpiece and stabilize the geometric size of the workpiece.

 

③ Adjust the mechanical performance of steel to meet the requirements of the use.

 

The reason why recovery has these effects is that when the temperature is increased, the atomic activity capacity is enhanced. The atoms of iron, carbon and other alloying elements in steel can spread quickly to achieve the rearranging and combination of atoms, so as to make it unstable The unbalanced organization has gradually transformed into a stable balanced organization. The elimination of internal stress is also related to the decrease in metal strength when the temperature is elevated. Generally, when steel is recovered, the hardness and strength decreases and the plasticity is improved. The higher the fire temperature, the greater the changes in these mechanical properties. For some alloy steels with high alloy elements, when a certain temperature range recovered, some small metal compounds are precipitated to increase the strength and hardness. This phenomenon is called secondary sclerosis.

 

Requirement requirements: Different workpieces should be returned at different temperatures to meet the requirements in use.

 

① The knife, bearings, carburizing quenching parts, and surface quenching parts are usually recovered at low temperature below 250 ° C. After low temperature recovery, the hardness changes greatly, the internal stress decreases, and the toughness is slightly improved.

 

② The spring is warmed at 350 ～ 500 ℃, which can obtain higher elasticity and necessary toughness.

 

③ The parts of medium -carbon structure steel are usually recovered at 500-600 ° C to obtain a good coordination of suitable strength and toughness.

 

When the steel recovered around 300 ° C, it often increases its brittleness. This phenomenon is called the first type of ignition brittleness. Generally, it should not be recovered in this temperature range. Some medium -carbon alloy structure steel is easy to turn crispy if it is cold to room temperature after high temperature recovery. This phenomenon is called the second category of ignition brittleness. Adding molybdenum in steel, or cooling in oil or water when recovered, can prevent the second type of crispness. The second type of fire crispy steel is newly heated to the original ignition temperature, and this brittleness can be eliminated.

 

In production, it is often based on the requirements of workpieces. According to the different heating temperature, the ignition was divided into low temperature recovery, the medium temperature recovered, and the high temperature recovered. The combination of quenching and subsequent high temperature recovery is called quality adjustment, that is, while having high strength, it has good plastic toughness.

 

1) Low temperature recovery: 150-250 ° C, M return, reducing the internal stress and brittleness, improving plastic toughness, and high hardness and abrasion resistance. Used to make quantities, tools and rolling bearings.

 

2) Medium temperature recovery: 350-500 ° C, T to return, it has high elasticity, a certain plasticity and hardness. Used to make spring, forging models, etc.

 

3) High temperature recovery: 500-650 ° C, S back, have good comprehensive mechanical properties. Used to make gears, crankshafts, etc.

 

3.Positive fire

▼ Steel in the state of fire

 

1. What is positive fire?

 

Positive fire is a heat treatment that improves steel toughness. After heating the steel component to the AC3 temperature above 30 to 50 ° C, the heat preservation is air -cooled for a period of time. The main feature is that the cooling speed is faster than the annealing and below quenching. When the fire can be flickered in a slightly cooling, the crystal grains of the steel can be meticulous. The cracking tendency of components. After some low -alloy hot -rolled steel plates, low -alloy steel forging and casting parts are treated with the fire, the comprehensive mechanical properties of the material can be greatly improved, and the cutting performance is also improved.

2. Positive fire has the following purpose and purpose:

① Analysis of steel for Asian Communities, the positive fire is used to eliminate the overheating crude crystal tissue and Wei's tissue of casting, forging, and welded parts.

 

② For the analysis of the co -analysis steel, the positive fire can eliminate the mesh two -time carburizing body and refine the pearl light body, which not only improves the mechanical properties, but also helps future ballization annealing.

 

③ For low -carbon deep -rushing thin steel plates, the positive fire can eliminate the free carburizing body of the crystal world to improve its deep -rushing performance.

 

④ For low-carbon steel and low-carbon low alloy steel, positive fires can be used to obtain more fine piece of pearl light tissue to increase hardness to HB140-190, avoid the "sticky knife" phenomenon during cutting, improve cutting processability Essence For medium -carbon steel, it is more economical and convenient to use the fire to use the fire and annealing.

 

⑤ For ordinary medium -carbon structured steels, under the occasion of low mechanical performance, it is possible to replace the quenching and high temperature recovery with a positive fire.

 

⑥ High temperature positive fire (150 to 200 ° C above AC3) can reduce the analysis of the composition of the casting and forging due to high diffusion speed at high temperature. After high -temperature positive fire, the rough grains can be refined by the subsequent low -temperature positive fire.

 

⑦ For some low and medium -carbon alloy steels used for steam turbines and boilers, positive fires are often used to obtain the bellite tissue, and then redeemed at high temperatures. It has good creep resistance at 400-550 ° C.

 

In addition to the steel parts and steel, the positive fire is also widely used in the heat treatment of the ball and ink cast iron, so that it can obtain the pearlite substrate and increase the strength of the ball and cast iron.

 

Due to the characteristics of air cooling, the environmental temperature, stacking method, airflow and workpiece size affect the tissue and performance of the positive fire. Positive fire organizations can also be used as a classification method of alloy steel. After heating to 900 ° C according to a sample with a diameter of 25 mm, the tissue obtained by empty cold is divided into pearl steel, glywede steel, martensite steel, and Austeenne steel.

 

4.Annealing

▼ Gas Antimading Furnace

 

1. What is annealing?

 

The annealing is to slowly heated the metal to a certain temperature, keep enough time, and then treat a metal heat treatment process with a suitable speed cooling. The heating heat treatment is divided into completely annealing, incomplete annealing and exfoliating. The mechanical properties of annealing materials can be tested with stretching tests, and hardness tests can be used to detect. Many steels are supplied by annealing heat treatment state. Steel hardness detection can use the Lowl hardness meter to test HRB hardness. For thinner steel plates, steel bands, and thin -walled steel pipes, the surface of the Loos hardness can be used to detect HRT hardness. Essence

2. The purpose of annealing is:

 

① Improve or eliminate various tissue defects and residual stress caused by steel in the process of casting, forging, rolling, and welding to prevent workpieces from deforming and cracking.

 

② Soft chemicals for cutting processing.

 

③ Fine grains and improve the organization to improve the mechanical performance of workpieces.

 

④ Prepare for the final thermal treatment (quenching and recovery).

 

3. The commonly used annealing process is:

 

① completely annealing. It is used to refine the thick and heated tissue that occurs after the casting, forging and welding of medium and low carbon steels. Heat the workpiece to the temperature of all sides of the austenite 30-50 ° C for the temperature of the austenitic, and the heat preservation for a period of time, and then slowly cool it with the furnace. During the cooling process, the austenite changes again, which can make the tissue of steel thinner. Essence

 

② Ballization annealing. It is used to reduce the high hardness of tool steel and bearing steel for forging. Heating the workpiece to the steel starts to form the temperature above 20 to 40 ° C. After the heat preservation, the chip -shaped carburizing body in the pearl body becomes spherical after the cooling process, thereby reducing the hardness.

 

③ Waiting for warming. It is used to reduce the high hardness of alloy structure steels with higher nickel and chromium content for cutting processing. Generally, it is cooled to the most unstable temperature of the austenite at a faster speed. When the preservation of the appropriate time, the austenitic transforms into a Totheon or a Corpox, and the hardness can be reduced.

 

④ Crystallize annealing. It is used to eliminate the hardening phenomenon of metal wires, thin plates in the process of cold pulling and cold rolling (rising hardness and decreased plasticity). The heating temperature is generally 50-150 ° C below the temperature of the ganglin to form the temperature of the austenite. Only in this way can the processing hardening effect be eliminated to soften the metal.

 

⑤ Graphite annealing. It is used to make the cast iron containing a large amount of carbon into a metastic cast iron with good plasticity. The process operation is to heat the casting to about 950 ° C. After the heat preservation, it is appropriately cooled to make the carburizing body decompose to form a flocculent graphite.

 

⑥ Swallowing and annealing. It is used to make alloy casting chemical composition evenly and improve its use performance. The method is to heat the casting to as high as possible without melting, and keep warm for a long time. The diffusion of various elements in the alloy is evenly distributed and slowly cold.

 

⑦ Remove stress annealing. It is used to eliminate the internal stress of steel castings and welded parts. After the steel products are heated, it begins to form 100 ℃ below the temperature of the austenite. After the heat preservation, it can be cooled in the air to eliminate the internal stress.