Metal heat treatment, what are the processes of metal heat treatment?

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. Therefore, it is a special process in machinery manufacturing and an important part of quality management.

In order to make the metal workpiece have the required mechanical, physical and chemical properties, in addition to the reasonable selection of materials and various forming processes, the heat treatment process is often indispensable. Steel is the most widely used material in the machinery industry, and the microstructure of steel is complex, which can be controlled by heat treatment, so the heat treatment of steel is the main content of metal heat treatment. In addition, aluminum, copper, magnesium, titanium, etc. and their alloys can also change their mechanical, physical and chemical properties through heat treatment to obtain different use properties.

The above information is from for your reference.

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Metal heat treatment is a metal heat treatment process in which the workpiece is heated as a whole and then cooled at an appropriate rate to change its surrounding metallographic mechanism and thus change the overall mechanical properties. There are four basic processes for the overall heat treatment of steel: annealing, normalizing, quenching and tempering.

annealing:Annealing is to heat the workpiece to an appropriate temperature, adopt different holding times according to the material and the size of the workpiece, and then carry out slow cooling, the purpose is to make the internal structure of the metal reach or close to the equilibrium state, or to release the internal stress generated by the previous process, to obtain good process performance and use performance, or to prepare for further quenching. Taking No. 45 steel as an example, the metallographic after annealing is austenite, and it becomes too soft after annealing, and generally 45 steel is not annealed.

Professional explanation: The heat treatment process of heating the sub-eutectic steel workpiece to 20-40 degrees above AC3 (the final temperature at which ferrite is converted into austenite when heating), holding it for a period of time, and then slowly cooling it with the furnace (or buried in sand or lime cooling) to below 500 degrees and cooling in air.

Normalization:Normalizing is to heat the workpiece to a suitable temperature and then cool it in the air, the effect of normalizing is similar to annealing, but the resulting structure is finer, often used to improve the cutting performance of the material, and sometimes used for some parts with low requirements as the final heat treatment. The metallographic after No. 45 normalizing is austenite + pearlite.

Professional explanation: the steel or steel parts are heated to the critical point AC3 (for sub-eutectic steel) or ACCM (the final temperature of the secondary cementite dissolved into austenite when heated, for per-eutectic steel) above 30 -50, and after the appropriate time of heat preservation, the heat treatment process of uniform cooling in free-flowing air is normalizing. After normalization, the sub-eutectic steel is F+S, the eutectic steel is S, and the per-eutectic steel is S+Fe3C The main difference between normalizing and complete annealing is that the cooling rate is faster, and the purpose is to normalize the steel structure, also known as normalization.

Quenching:Quenching is to heat and keep the workpiece warm, and then quickly cool it in a quenching medium such as water, oil or other inorganic salt solutions, organic aqueous solutions, etc. The rear steel becomes harder, but at the same time brittle.

In the case of No. 45 steel, it is rarely quenched alone because it is difficult to get the desired hardness. Professional explanation: The heat treatment process of cooling the steel after steel austenitization at an appropriate cooling rate, so that the workpiece can undergo martensite and other unstable microstructure transformation in all or a certain range within the cross-section.

TemperingTempering is to reduce the brittleness of steel, and the quenched steel is kept warm for a long time at an appropriate temperature higher than room temperature and lower than 650, and then cooled, this process is called tempering. Professional Explanation:

The quenched workpiece is heated to an appropriate temperature below the critical point AC1 (the starting temperature of the pearlite to austenite transition when heated) for a certain period of time, and then cooled in a manner that meets the requirements to obtain the desired structure and properties.

Metal heat treatment is to heat the metal workpiece to a suitable temperature in a certain medium, and after maintaining it at this temperature for a certain time, it is cooled at different speeds.

Tempering: The structure obtained by high temperature tempering is tempered sostenite. Tempering is generally not used alone, tempering is carried out after quenching of parts, the main purpose is to eliminate quenching stress and obtain the required structure, tempering is divided into low temperature, medium temperature and high temperature tempering according to the different tempering temperatures.

Tempered martensite, drossite, and soxenite were obtained, respectively. Among them, the heat treatment combined with high temperature tempering after quenching is called quenching and tempering treatment, and its purpose is to obtain comprehensive mechanical properties with good strength, hardness, plasticity and toughness. Therefore, it is widely used in automobiles, tractors, machine tools, etc., such as connecting rods, bolts, gears and shafts.

After tempering, the hardness is generally HB200 330.

Annealing: The annealing process occurs in a pearlite transition, and the main purpose of annealing is to bring the internal structure of the metal to or near equilibrium in preparation for subsequent processing and final heat treatment. Stress relief annealing is an annealing process that eliminates residual stresses caused by plastic deformation processing, welding, etc., as well as within castings.

There is internal stress in the workpiece after forging, casting, welding and cutting, if it is not eliminated in time, the workpiece will be deformed in the process of processing and use, and the accuracy of the workpiece will be affected. It is important to use stress-relieving annealing to eliminate the internal stresses generated during machining. The heating temperature of the stress-relieving annealing is lower than the phase change temperature, so that no microstructure transformation occurs throughout the heat treatment process.

Internal stresses are mainly eliminated naturally by the workpiece during heat preservation and slow cooling. In order to make the stress in the workpiece more completely relieved, the heating temperature should be controlled when heating. Generally, it is fed into the furnace at a low temperature and then heated to a specified temperature at a heating rate of about 100 h.

The heating temperature of the weldment should be slightly higher than 600. The holding time depends on the situation, usually 2 4h. The upper limit of the holding time of the stress relief annealing of the casting is taken, the cooling rate is controlled at (20 50) h, and the cooling is below 300 before the furnace can be air-cooled.

Aging treatment can be divided into natural aging and artificial aging two kinds of natural aging is to place the casting in the open field for more than half a year, so that it occurs slowly, so that the residual stress is eliminated or reduced, artificial aging is to heat the casting to 550 650 for stress relief annealing, it saves time than natural aging, and the residual stress is removed more thoroughly.

Metal heat treatment is to heat and ......cool down various metals at different temperaturesDifferent materials have different thermofiber treatment processes and "temperature---time" processing process, which can optimize the performance of metal materials by changing the state of the material and metallographic structure.

Hello, metal heat treatment refers to the treatment of metal parts by annealing, tempering, normalizing, etc., with the aim of improving the metallographic structure inside the zero missing parts.

As shown in the figure: the PS** in the phase diagram of the iron-carbon alloy is the A1 line, the temperature is 727, the GS line is the A3 line, the temperature is from 912 727, it can be seen that A1 and A3 represent the temperature, as an iron-carbon alloy, the carbon content is different, and the temperature represented by A1 and A3 will be different. Heating requires superheat, which is used to be represented by C, so there are corresponding AC1, AC3 and other representations.

Cooling requires supercooling, which is used to be expressed by r, so there are corresponding representations such as ar1 and ar3.

What is the temperature above AC1 and AC3? As can be seen from the figure, it happens to be the austenite zone of steel, and the conditions for heat treatment of steel first need to be heated to the austenite zone to obtain austenite, and then by controlling the cooling rate and method, to obtain pearlite, bainite, martensite and other structures, so as to obtain different properties that we need. The heating of the steel is the first step in heat treatment.

Temperatures above AC1 and AC3 are matched with austenitization temperatures! We know that the austenite region on the diagram has a temperature range, in order to get the austenite muxun, the heating temperature is higher or lower, but it must be heated to the austenitization temperature above AC1 and AC3. Similarly, the principle of heat treatment tells us that the heating temperature is high, the austenitization process is fast, saving time and electricity, but the austenite grains are easy to be coarse, resulting in the back cooling structure is also coarse, the performance is not good, the heating temperature is low, the austenitization process is slow, time-consuming, the production efficiency is low, and the cost is high, but the austenite grains are small, resulting in the back cooling organization is small, and the performance is good, so the temperature is not high, and it is not suitable if it is low, which needs to be weighed, therefore, AC1, AC3 The actual temperature of the above needs to be determined according to the actual situation of the part size, structure, technical requirements, furnace capacity, furnace size, power, heating method, heating medium, process adopted, etc.

For example, eutectic steel, if it is normalizing, ACM+20 40 is generally used, AC1+30 50 is generally used for quenching, alloy steel is often used for upper limit temperature, carbon steel or manganese steel is used for lower limit temperature, and so on, the temperature needs to be adjusted according to the specific situation, and this is precisely the technology and charm of heat treatment.

1. Fill-in-the-blank questions (30 points, 1 point for each blank).

1. Body-centered cubic lattice face-centered cubic lattice.

2. Nucleation grows.

3. The interstitial solid solution is specialized, and the replacement is a solid solution.

4. Point defects, line defects, and surface defects.

5. Annealing and tempering.

6. Strength and plasticity.

7. Interstitial phases and interstitial compounds.

8. Structural steel and tool steel.

9. Strength, hardness, plasticity, toughness, fatigue.

10、p、b、m

11. Hardenability.

12. Ferrite, austenite, cementite, pearlite.

2. Explanation of terms.

No explanation 2. Multiple choice questions (30 points, 2 points each).

1. Can't answer.

2. The c lattice is deformed.

3. A quenching + high temperature fire.

4. A quenching + low temperature tempering.

5. C austenite grains are coarse.

6. The equipment is simple.

7. High strength and high wear resistance.

3. True/False Questions (20 points, 2 points for each question).

1、y2、y

3、n4、y

5、n6、y

7、n8、y

9、y10、n

5. Short-answer questions (10 points, 5 points each).

1. Briefly describe the purpose of tempering.

Eliminate quenching stress, stabilize structure, stabilize size, and achieve the desired performance.

2. What is surface chemistry such as treatment? What are the processes?

Decomposition, absorption, diffusion.

You are too picky, there are so many questions, you don't even add a point, and you can solve it yourself if you don't answer.

First of all, the sentence "Relative Mass Fraction of Pearlite, Secondary Cementite and Layenite in Equilibrium Structure" means that pearlite and secondary cementite refer to the precipitation of primary crystalline austenite, and do not include pearlite and secondary cementite in low-temperature Laistenite. Otherwise, you won't ask about the relative content of leas, and you can see that pearlite, secondary cementite and leesite are juxtaposed. If it is included, the question will say that w( of the relative mass fraction of the total pearlite and secondary cementite in the room temperature equilibrium structure of the subeutectic white iron.

The law of leverage can be used to calculate the relative content of primary crystalline austenite and high-temperature leastenite.

2. After the content of the primary crystalline austenite is determined, you can calculate the relative content of the precipitated secondary cementite, because the secondary cementite is the maximum content of austenite (from the place, that is, point E) precipitated, you can also calculate or check the book, because the book has calculated the content of the maximum secondary cementite is.

3. After the primary crystalline austenite precipitates the secondary cementite, the rest will be transformed into pearlite, minus the content of the secondary cementite, and the rest is the content of pearlite.

The following calculations: 1. Leasel content:

WA=(WLD=Leas content has been calculated).

2. Secondary cementite content:

WFE3CII = primary crystalline austenite x austenite contains the maximum percentage content of secondary cementite =

That is, the relative content of secondary cementite is.

3. Pearlite content:

The primary crystalline austenite minus the content of secondary cementite, and what remains is the content of pearlite.

wp=。The relative mass fractions of pearlite, secondary cementite and lydeon in the room temperature equilibrium structure of subeutectic white iron of w(, respectively: .