What methods of forging heat treatment do you know?

What are the methods of heat treatment of forgings.

According to the different steel grades and process requirements, the following heat treatment methods are often used for forgings: annealing, normalizing, quenching and tempering, quenching and low-temperature tempering, quenching and aging, etc. Let's take a look at how it works

1.Annealing: The forging annealing process has various forms such as complete annealing, spheroidization annealing, low-temperature annealing and isothermal annealing, which need to be selected according to the forging material and deformation.

After the forging is annealed, the residual stress is eliminated or reduced due to the recrystallization of the grain, thereby reducing the hardness of the forging, improving its plasticity and toughness, and improving the cutting performance.

2.Normalizing: Normalizing is generally to heat the forgings to 50-70 above the GSE line, and some high-alloy steel forgings are heated to 100-150 above the GSE line, and then cooled in the air after proper insulation.

If the hardness of the forging is higher after normalizing, in order to reduce the hardness of the forging, high temperature tempering should also be carried out, and the general tempering temperature is 560-660.

3.Quenching, tempering:

Quenching is done to obtain an unbalanced structure to improve strength and hardness. Heat the steel forgings to 30-50 above the AC1 line. After heat preservation, it is quenched.

Tempering is to eliminate quenching stress and obtain a more stable structure, heat the forging to a certain temperature below the AC1 line, keep it warm for a period of time, and then air cool or fast cool.

4.Quenching, aging:

Superalloys and alloys that can be strengthened by heat treatment are often quenched after forging. Among them, quenching is to heat the alloy to an appropriate temperature, and after sufficient heat preservation, some tissue products in the alloy are dissolved into the matrix to form a uniform solid solution, and then quickly cooled to become a supersaturated solid solution, so it is also called solid solution treatment. The aim is to improve the plasticity and toughness of the alloy and to prepare it for further ageing.

Aging treatment is to put the supersaturated solid solution or the alloy deformed by cold working at room temperature or heated to a certain temperature, and keep it warm for a period of time, so that the substances previously dissolved in the matrix can be evenly dispersed and precipitated. The purpose of aging treatment is to improve the strength and hardness of the alloy.

The heat treatment of forgings is carried out according to certain heat treatment specifications, according to the forging steel grade, section size and technical requirements, etc., and with reference to the relevant manuals and information. Its contents include: heating temperature, holding time and cooling method.

Generally, it is expressed by a temperature-time curve.

The heat treatment technology of forgings mainly includes annealing, normalizing, quenching, tempering, quenching and tempering, solution treatment and aging treatment. Among them, annealing also includes incomplete annealing, complete annealing, isothermal annealing, general spheroidization annealing, isothermal spheroidization annealing, and rapid spheroidization annealing (normalizing-spheroidizing annealing); There are normal fires and two-stage normalizations. In addition, Yongxinsheng also has forging heat quenching, using part of the waste heat normalizing, using part of the waste heat quenching, using part of the waste heat isothermal annealing and high temperature tempering.

According to Yongxinsheng's many years of industry experience, 1. The structure of the heating furnace should be reasonable. The uniformity of furnace size, furnace temperature and temperature in the furnace meets the needs of heat treatment.

2. The size of the quenching groove is large enough. Fast and uniform cooling is guaranteed. In order to control the temperature of the quenching fluid, a heat exchanger should also be equipped.

3. The potentiometer should be checked regularly. The heating furnace should be equipped with a potentiometer to control the temperature and record the temperature, which should be checked and recorded by a special person.

4. Check and check the hardness of the scale. Hardness check is an integral part of heat treatment, and many steel grades often take a forging halfway through the tempering process to determine whether the temperature needs to be adjusted.

5. Check the temperature uniformity. The inspection of furnace temperature uniformity should be carried out under normal working conditions, once every six months.

6. Modulate the heat treatment system according to the chemical composition. In some superalloys or alloy steels, small changes in composition require a corresponding change in the optimal temperature for aging or tempering.

7. Keep a record. The record of the heat treatment furnace must correspond to the heat treatment furnace batch number of the forging. The batch number of the heat treatment furnace is best marked next to the melting furnace number on the forging.

The control of the heat treatment quality of forgings can be achieved through the following steps:

1.Before starting the heat treatment, the raw materials should be tested to ensure that they do not contain harmful substances.

2.When using chemical corrosives, the correct concentration and temperature should be used, and the appropriate time should be selected according to the different material requirements.

3.Use heaters and cooling devices correctly, and pay attention to the speed and time of heating and cooling.

4.Quantitative monitoring: Quantitative monitoring of the product throughout the processing process (e.g., optical microscopy, sock X-ray profile, scanning electron microscope, X-ray spectrogram, X-ray diffraction, metallographic pattern or other methods).

Post-forging heat treatment refers to the heat treatment set up in order to eliminate the defects generated in the forging process or to make other processes after forging better, such as normalizing, annealing, etc., which is used to eliminate forging stress and uniform structure.

Performance heat treatment refers to the heat treatment carried out in order to ensure the final performance of forgings.

Heating before forging of billet is an indispensable and important part of the whole forging process, which has a direct impact on improving forging productivity, ensuring forging quality, saving energy consumption and reducing product costs. The following are the purposes and requirements of forging heating:

1.Purpose of heating:

Improve the plasticity of the metal, reduce the deformation resistance of the metal, make it easy to form, and obtain good post-forging microstructure and mechanical properties of forgings.

2.Heating requirements.

1) Under the condition of allowable temperature conductivity and internal stress of metal materials, it is heated to a predetermined temperature at a fast speed to improve efficiency and save energy.

2) Reduce the absorption of harmful gases by heated metals, such as oxygen, hydrogen, nitrogen and other gases, reduce defects such as oxidation, decarburization or hydrogen embrittlement, and improve heating quality.

3) In the low-temperature heating stage, it is necessary to prevent the excessive temperature difference between the outer layer of the metal section and the core due to improper heating, resulting in excessive thermal stress, and then superimposing other internal stresses to cause material rupture.

4) Accurately implement the given heating specifications, such as heating temperature, speed, time, and heat preservation and other heating conditions, to prevent defects such as overheating, overburning, etc.

The purpose of heating is to reduce the strength and hardness so that there is good plastic deformation.

The differences are:

Heat treatment refers to a metal thermal processing process in which materials are heated, insulated and cooled in a solid state to obtain the expected structure and properties. Metal heat treatment is one of the important processes in machinery manufacturing, compared with other processing processes, heat treatment generally does not change the shape of the workpiece and the overall chemical composition, but by changing the internal microstructure of the workpiece, or changing the chemical composition of the surface of the workpiece, giving or improving the performance of the workpiece. It is characterized by an improvement in the intrinsic quality of the workpiece, which is generally not visible to the naked eye.

Forging is a processing method that uses forging machinery to apply pressure to metal blanks to produce plastic deformation to obtain forgings with certain mechanical properties, certain shapes and sizes, and is one of the two major components of forging (forging and stamping). Through forging, the defects such as loose casting state generated by the metal in the smelting process can be eliminated, and the microstructure structure can be optimized, and at the same time, the mechanical properties of forgings are generally better than castings of the same material due to the preservation of complete metal streamlines. Forgings are mostly used for important parts with high loads and severe working conditions in related machinery, except for plates, profiles or weldments that can be rolled with simple shapes.

Casting is a metal craft that has been mastered by humans for about 6,000 years. Between about 1700 BC and 1000 BC, China had entered the heyday of bronze casting, and the craftsmanship had reached a very high level. Casting is a method of casting liquid metal into a casting cavity that is suitable for the shape of the part, and waiting for it to cool and solidify to obtain the part or blank.

Most of the materials to be cast are metals that were originally solid but heated to a liquid state (e.g., copper, iron, aluminum, tin, lead, etc.), while the materials of the casting molds can be sand, metal or even ceramics. Depending on the requirements, the methods used will vary.

Post-forging heat treatment of large forgings, also known as primary heat treatment or preparatory heat treatment, is usually carried out immediately after the forging process is completed. Its main purpose is to:

1.Eliminating forging stress, reducing the surface hardness of forgings, and improving their cutting performance are the most direct and most basic purposes of post-forging heat treatment.

2.For forgings that no longer carry out final heat treatment (or product heat treatment), the forgings should also be made to meet the various performance indicators required by the technical conditions of the product through post-forging heat treatment. Most of these forgings are forgings made of carbon steel or low-alloy steel.

3.Adjust and improve the overheating and coarse structure formed by large forgings during the forging process, reduce the inhomogeneity of the internal chemical composition and metallographic structure of large forgings, and refine the austenite grains of steel; Improve the ultrasonic flaw detection performance of forgings, eliminate grass waves, so that all kinds of internal defects in forgings can be clearly displayed, so as to prevent the transfer of unqualified forgings to the next process.

4.For all kinds of important large forgings, the first consideration must be to prevent and eliminate the white spot problem when formulating the post-forging heat treatment process. To this end, it is necessary to know the results of sampling and hydrogen determination at the riser end of the large steel ingot made of this forging, which is used by Shanxi CITIC Heavy Industry as the data of the average hydrogen content in the steel, and then the hydrogen expansion calculation of the large forging is determined to ensure that there is no white spot defect in the forging, and the arrangement is given in the heat treatment process after forging.

This is the most important and must be solved first when formulating the post-forging heat treatment process of large forgings, and it must be done effectively to avoid the forgings being scrapped due to white spots.

5.For large forgings made of molten steel that have undergone one or two vacuum treatments, if the hydrogen determination value of the ingot riser sampling is lower than the non-white point limit hydrogen content of the forging steel grade, the problem of dehydrogenation can not be considered in the formulation of the post-forging heat treatment process. However, if the forging has clear provisions on the elimination of hydrogen-induced embrittlement of steel or the value of residual hydrogen content in steel, then when formulating the post-forging heat treatment process, it is still necessary to determine the necessary dehydrogenation annealing time through hydrogen expansion calculation, and give careful arrangements to ensure that the design drawings and relevant technical documents stipulate various requirements for large forgings.

Finally, it is reported that the intermediate annealing in the forging process can make the sulfide inclusion spherical and dispersed in the steel, which is beneficial to improve the lateral properties (mainly impact toughness) of large forgings.

If the large forging is not heat-treated after forging, the India and flexibility between this section will be lost, that is, the rigidity, in order to increase its rigidity, it is generally quenched and quenched.