Hot Stamping Die Treatment Methods for Hot Stamping

First of all, you have to figure out what grade of mold material you are using

The heating temperature is very delicate, the austenitizing temperature of each grade is different

There is also the speed of cooling is also to be controlled

After the cooling is also to be tempered, if you don't know how to recommend looking for a professional heat-treatment company to do

There is also material Selection, H13 is the most basic, due to the punch of copper, copper melting point is higher generally used ASSAB's QRO-90

The following is some heat treatment information for reference, the annex also has QRO-90 information

Heat Treatment Definition: Heat treatment is a metal material is placed in a certain medium heating, holding, cooling, by changing the material surface or the internal metallurgical organization, to control its properties of a metal material. , to control its properties of a metal thermal processing technology.

The development of heat treatment:

In the process of progressing from the Stone Age to the Copper Age and the Iron Age, the role of heat treatment is gradually recognized. As early as 770 to 222 B.C., the Chinese have found in production practice that the properties of copper and iron will be changed by the effects of temperature and pressurized deformation. The softening of white cast iron was an important process in the manufacture of agricultural tools. In the sixth century B.C., iron and steel weapons were gradually adopted, and in order to improve the hardness of steel, the quenching process was rapidly developed. Two swords and a halberd unearthed in Yixian Yanxiadu, Hebei Province, China, have martensite in their microstructure, indicating that they were quenched. With the development of quenching technology, people gradually found the quenching agent on the quenching quality. Pu Yuan, a Shu man of the Three Kingdoms, once made 3,000 knives for Zhuge Liang in the present-day Xiangu Valley in Shaanxi Province, and it is rumored that he sent someone to Chengdu to fetch water for quenching. This shows that China paid attention to the cooling capacity of different water qualities in ancient times, as well as the cooling capacity of oil and urine. China unearthed in the Western Han Dynasty (206 BC ~ AD 24) in the tomb of King Jing of Zhongshan sword, the heart of the carbon content of 0.15 ~ 0.4%, while the surface carbon content is up to 0.6% or more, indicating that the application of carburization process. However, at that time as a personal "craft" secret, refused to spread the word, and thus the development is very slow. 1863, British metallographers and geologists showed the steel under the microscope six different metallographic organization, proved that the steel in the heating and cooling, the internal organization of the organization will be changed, the high temperature phase of the steel in the rapid cooling when the transformation into a harder phase. phase. French Osmond established the theory of iron isotropy, as well as the British Austin first formulated the iron and carbon phase diagram for the modern heat treatment process initially laid the theoretical foundation. At the same time, people also studied the heating process in the metal heat treatment of metal protection methods to avoid the heating process of metal oxidation and decarburization, etc. 1850 ~ 1880, for the application of a variety of gases (such as hydrogen, gas, carbon monoxide, etc.) for the protection of the heating had a series of patents. 1889 ~ 1890 British Leake obtained a variety of metal bright heat treatment patents. Since the twentieth century, the development of metal physics and other new technology transplantation application, so that the metal heat treatment process has been more development. A significant progress is 1901 ~ 1925, in industrial production in the application of rotary furnace gas carburizing; 30 s dew-point potential difference meter, so that the carbon potential of the furnace atmosphere to reach a controllable, and later on the study of carbon dioxide infrared meter, oxygen probe and other further control of the furnace atmosphere of the carbon potential of the method; 60 s, the heat treatment technology using the plasma field, the development of ion nitriding, carburizing technology ; laser, electron beam technology, and the application of the metal to obtain a new surface heat treatment and chemical heat treatment methods. Heat treatment process characteristics:

Heat treatment process generally includes heating, heat preservation, cooling three processes, sometimes only heating and cooling two processes. These processes are interconnected and uninterrupted.

Heating is one of the important processes of heat treatment. Metal heat treatment of heating methods, the earliest is the use of charcoal and coal as a heat source, and the recent application of liquid and gaseous fuels. The application of electricity makes heating easy to control, and no environmental pollution. The use of these heat sources can be directly heated, but also through the molten salt or metal, to floating particles for indirect heating.

Metal heating, the workpiece is exposed to air, often oxidation, decarburization (i.e., the surface carbon content of the steel parts to reduce), which has a very negative impact on the surface properties of the heat-treated parts. Thus, the metal should usually be in a controlled atmosphere or protective atmosphere, molten salts and vacuum heating, but also available coatings or packaging methods for protective heating.

Heating temperature is one of the important process parameters of the heat treatment process, the selection and control of the heating temperature, is to ensure the quality of heat treatment of the main issues. Heating temperature varies with the metal material being treated and the purpose of heat treatment, but generally are heated above the phase transition temperature to obtain high temperature organization. In addition, the transformation requires a certain amount of time, so when the surface of the metal workpiece to achieve the required heating temperature, but also have to be maintained at this temperature for a certain period of time, so that the internal and external temperatures are consistent, so that the microstructure transformation is complete, which is known as the holding time. The use of high energy density heating and surface heat treatment, the heating rate is extremely fast, there is generally no holding time, while the chemical heat treatment of the holding time is often longer.

Cooling is also an indispensable step in the heat treatment process, cooling methods due to different processes, mainly to control the cooling rate. General annealing cooling rate is the slowest, normalizing the cooling rate is faster, quenching the cooling rate is faster. But also because of the different types of steel and have different requirements, such as air-hardened steel can be quenched with the same cooling rate as normalizing.

Process classification

Metal heat treatment process can be broadly divided into the overall heat treatment, surface heat treatment and chemical heat treatment of three categories. According to the heating medium, heating temperature and cooling methods, each category can be distinguished into a number of different heat treatment processes. The same metal using different heat treatment processes, can obtain different organizations, thus having different properties. Iron and steel is the most widely used metal in industry, and steel microstructure is also the most complex, so there are many kinds of steel heat treatment process.

The overall heat treatment is the overall heating of the workpiece, and then cooled at an appropriate rate, to obtain the required metallurgical organization, in order to change its overall mechanical properties of the metal heat treatment process. Steel overall heat treatment roughly annealing, normalizing, quenching and tempering four basic processes.

Process means

Annealing is the workpiece is heated to the appropriate temperature, according to the material and the size of the workpiece using different holding time, and then slowly cooled, the purpose is to make the internal organization of the metal to achieve or close to equilibrium, to obtain a good process performance and use of the performance, or further quenching of the organization for the preparation.

Normalizing is to heat the workpiece to the appropriate temperature after cooling in the air, the effect of normalizing similar to annealing, only to get a finer organization, often used to improve the cutting performance of the material, but also sometimes used for some of the less demanding parts as the final heat treatment.

Quenching is the workpiece is heated and insulated, in water, oil or other inorganic salts, organic aqueous solutions and other quenching media, rapid cooling. After quenching the steel parts become hard, but at the same time become brittle, in order to eliminate the brittleness in a timely manner, generally need to be tempered in a timely manner.

In order to reduce the brittleness of steel parts, the quenched steel parts at a suitable temperature higher than room temperature and lower than 650 ℃ for a long period of insulation, and then cooled, this process is called tempering.

Annealing, normalizing, quenching, tempering is the overall heat treatment of the "four fires", of which the quenching and tempering close relationship, often used in conjunction with each other, indispensable.

"Four fires" with the heating temperature and cooling mode of different, and evolved a different heat treatment process. In order to obtain a certain degree of strength and toughness, the quenching and tempering at high temperatures combined with the process, known as tempering. After certain alloys are quenched to form a supersaturated solid solution, they are held at room temperature or at a slightly higher appropriate temperature for a longer period of time in order to improve the hardness, strength, or electrical magnetism of the alloy. Such a heat treatment process is called aging treatment.

The pressure processing deformation and heat treatment effectively and closely combined to carry out, so that the workpiece to obtain a very good strength, toughness with the method known as deformation heat treatment; in a negative atmosphere or vacuum heat treatment known as vacuum heat treatment, which not only can make the workpiece does not oxidize, do not decarburize, keep the surface of the workpiece after treatment is smooth and clean to improve the performance of the workpiece, but also through the osmotic agent for chemical heat treatment.

Surface heat treatment is only heating the surface layer of the workpiece to change the mechanical properties of the surface layer of the metal heat treatment process. In order to only heat the surface layer of the workpiece without excessive heat transfer into the workpiece, the use of the heat source must have a high energy density, that is, in the unit area of the workpiece to give a larger heat energy, so that the surface layer of the workpiece or localized can be a short period of time or instantaneous to reach a high temperature. Surface heat treatment of the main methods of flame quenching and induction heating heat treatment, commonly used heat sources such as oxyacetylene or oxypropane flame, induction current, laser and electron beam.

Chemical heat treatment is by changing the chemical composition of the surface layer of the workpiece, organization and properties of the metal heat treatment process. Chemical heat treatment differs from surface heat treatment in that the former changes the chemical composition of the surface layer of the workpiece. Chemical heat treatment is placed on the workpiece containing carbon, salt media or other alloying elements in the medium (gas, liquid, solid) in the heating, insulation for a longer period of time, so that the surface layer of the workpiece infiltration of carbon, nitrogen, boron and chromium and other elements. After infiltration of elements, and sometimes other heat treatment processes such as quenching and tempering. The main methods of chemical heat treatment are carburizing, nitriding, metal penetration.

Heat treatment is one of the important processes in the manufacturing process of mechanical parts and molds. Generally speaking, it can ensure and improve the various properties of the workpiece , such as wear resistance, corrosion resistance. Can also improve the organization of the blank and stress state, in order to facilitate a variety of cold and hot processing.

For example, white cast iron after a long time annealing treatment can be obtained malleable cast iron, improve plasticity; gears with the correct heat treatment process, service life than the non-heat treatment of the gear can be doubled or dozens of times to improve; in addition, inexpensive carbon steel through the infiltration of certain alloying elements with some of the price of the performance of alloy steels can be used instead of some heat-resistant steel, stainless steel; molds and dies are almost all need to be After heat treatment can be used.

Supplementary means

One, the type of annealing

Annealing is the workpiece is heated to the appropriate temperature, maintained for a certain period of time, and then slowly cooled heat treatment process.

There are many types of steel annealing process, according to the heating temperature can be divided into two categories: one is at the critical temperature (Ac1 or Ac3) above the annealing, also known as the phase change recrystallization annealing, including complete annealing, incomplete annealing, spheroidal annealing and diffusion annealing (homogenization annealing), etc.; the other is below the critical temperature of the annealing, including recrystallization annealing and de-stressing annealing, etc.. According to the cooling method, annealing can be divided into isothermal annealing and continuous cooling annealing.

1. Complete annealing and isothermal annealing

Complete annealing, also known as recrystallization annealing, generally referred to as annealing, it is the steel piece or steel heated to 20 ~ 30 ℃ above the Ac3, holding time is long enough to make the organization completely austenitized and then slowly cooled to obtain nearly balanced organization of the heat treatment process. This annealing is mainly used for sub **** precipitation composition of various carbon and alloy steel castings, forgings and hot rolled profiles, and sometimes also used for welded structures. Generally often as a number of not heavy workpiece final heat treatment, or as a pre-heat treatment of certain workpieces.

2. spheroidal annealing

Spheroidal annealing is mainly used for over **** analysis of carbon steel and alloy tool steel (such as the manufacture of cutting edge tools, gauges, molds and dies used in the steel). Its main purpose is to reduce the hardness, improve the machinability, and prepare for future quenching.

3. Stress relief annealing

Stress relief annealing, also known as low-temperature annealing (or high-temperature tempering), this annealing is mainly used to eliminate the castings, forgings, weldments, hot-rolled parts, cold-drawn parts, such as residual stress. If these stresses are not eliminated, will cause steel after a certain period of time, or in the subsequent cutting process to produce deformation or cracks.

4. Incomplete annealing is the steel is heated to Ac1 ~ Ac3 (sub***ysis steel) or Ac1 ~ ACcm (over***ysis steel) between the heat preservation and slow cooling to obtain nearly equilibrium organization of the heat treatment process.

Two, quenching, the most commonly used cooling medium is brine, water and oil. Salt water quenching of the workpiece, easy to get high hardness and smooth surface, not easy to produce quenching not hard soft spot, but it is easy to make the workpiece deformation is serious, and even cracking. The use of oil as a quenching medium is only suitable for the stability of the supercooled austenite is relatively large in some alloy steel or small size of carbon steel workpiece quenching.

Three, the purpose of steel tempering

1. Reduce brittleness, eliminate or reduce internal stress, there is a great deal of internal stress and brittleness after quenching of steel, such as tempering in a timely manner will often lead to deformation or even cracking of steel parts.

2. Obtain the required mechanical properties of the workpiece, the workpiece after quenching high hardness and brittleness, in order to meet the requirements of different properties of a variety of workpieces, can be adjusted through the appropriate tempering of the coordination of the hardness, reduce the brittleness, and get the required toughness, plasticity.

3. Stabilize the size of the workpiece

4. For annealing is difficult to soften certain alloy steels, in the quenching (or normalizing) is often used after high-temperature tempering, so that the steel carbide appropriate aggregation, the hardness will be reduced, in order to facilitate cutting and processing.

Supplementary concepts

1. annealing: refers to the metal material heated to the appropriate temperature, maintained for a certain period of time, and then slowly cooled heat treatment process. Common annealing processes are: recrystallization annealing, stress relief annealing, spheroidization annealing, complete annealing and so on. The purpose of annealing: mainly to reduce the hardness of the metal material, improve plasticity, in order to facilitate cutting or pressure machining, reduce residual stress, improve the organization and composition of the homogenization, or for the latter heat treatment to make the organization ready.

2. Normalizing: refers to the steel or steel heated to or (steel on the critical point of temperature) above, 30 ~ 50 ℃ to maintain the appropriate time, cooling in still air heat treatment process. The purpose of normalizing: mainly to improve the mechanical properties of low carbon steel, improve the cutting and machinability, grain refinement, eliminate organizational defects, for the organization of the latter heat treatment to prepare for the preparation of the organization.

3. quenching: refers to the steel heated to Ac3 or Ac1 (steel under the critical point of temperature) above a certain temperature, keep a certain time, and then with the appropriate cooling rate, to obtain martensite (or bainite) organization of the heat treatment process. Common quenching processes include salt bath quenching, martensitic graded quenching, bainitic isothermal quenching, surface quenching and localized quenching. The purpose of quenching: so that the steel parts to obtain the required martensitic organization, improve the hardness of the workpiece, strength and abrasion resistance, for the latter heat treatment to make good preparation for the organization and so on.

4. Tempering: refers to the steel hardened, then heated to a temperature below Ac1, holding time, and then cooled to room temperature heat treatment process. Common tempering process: low-temperature tempering, medium-temperature tempering, high-temperature tempering and multiple tempering.

The purpose of tempering: mainly to eliminate the stresses generated in the quenching of steel parts, so that the steel has a high hardness and wear resistance, and has the required plasticity and toughness.

5. Tempering: refers to the steel or steel for quenching and tempering at high temperatures of the composite heat treatment process. Used in the tempering treatment of steel called tempered steel. It generally refers to medium carbon structural steel and medium carbon alloy structural steel.

6. Carburizing: Carburizing is the process of infiltrating carbon atoms into the surface layer of steel. Also is to make low carbon steel workpiece with high carbon steel surface layer, and then after quenching and low temperature tempering, so that the surface layer of the workpiece with high hardness and wear resistance, while the center part of the workpiece still maintains the toughness and plasticity of low carbon steel.

Vacuum method

Because operations such as heating and cooling of metal workpieces require a dozen or even dozens of actions to complete. These actions within the vacuum heat treatment furnace, the operator can not approach, so the degree of automation of the vacuum heat treatment furnace requirements are high. At the same time, some actions, such as heating and holding the end of the metal workpiece quenching process shall be six or seven actions and to be completed within 15 seconds. Such agile conditions to complete many actions, it is easy to cause the operator's nervousness and constitute misoperation. Therefore, only a high degree of automation can be accurate, timely coordination in accordance with the program.

Metal parts for vacuum heat treatment are in the closed vacuum furnace, strict vacuum seal is well known. Therefore, to obtain and adhere to the original air leakage rate of the furnace, to ensure that the vacuum furnace working vacuum, to ensure the quality of parts vacuum heat treatment has a very major significance. So a key issue of vacuum heat treatment furnace is to have a reliable vacuum sealing structure. In order to ensure the vacuum performance of the vacuum furnace, vacuum heat treatment furnace structure design must follow a basic principle, that is, the furnace body to use gas-tight welding, while the furnace body as little as possible to open or not open the hole, less or avoid the use of dynamic sealing structure, in order to minimize the opportunity for vacuum leakage. Installed in the vacuum furnace body parts, accessories, such as water-cooled electrodes, thermocouple export device must also be designed to seal the structure.

Most heating and insulation materials can only be used under vacuum. Vacuum heat treatment furnace heating and insulation lining is in the vacuum and high temperature work, and thus these materials put forward high temperature resistance, radiation results good, small thermal conductivity requirements. The requirements for oxidation resistance are not high. Therefore, the vacuum heat treatment furnace widely used tantalum, tungsten, molybdenum and graphite for heating and thermal insulation materials. These materials in the atmospheric state is very easy to oxidize, therefore, ordinary heat treatment furnace can not use these heating and insulation materials.

Water-cooling device: vacuum heat treatment furnace shell, furnace cover, electric heating elements, water-cooled electrodes, the middle of the vacuum insulation door and other components, are in a vacuum, under the state of heat work. In this extremely unfavorable conditions of work, it must be ensured that the structure of the components are not deformed, not damaged, the vacuum seal is not overheated, not burned. Therefore, each component should be set according to different circumstances of water-cooling devices to ensure that the vacuum heat treatment furnace can operate normally and have sufficient utilization life.

Using low voltage and high current: vacuum container, when the vacuum vacuum degree of a few torr a lxlo-1 torr range, the vacuum container of the energized conductor in the higher voltage, will produce glow discharge phenomenon. In the vacuum heat treatment furnace, serious arc discharge will burn the electric heating element, insulation layer, causing major accidents and losses. Therefore, the vacuum heat treatment furnace electric heating element working voltage is generally not more than 80 a 100 volts. At the same time in the electric heating element structure design to take effective methods, such as try to avoid the tip of the parts, electrode spacing between the electrodes can not be too small, in order to prevent the generation of glow discharge or arc discharge.

Tempering

According to the different performance requirements of the workpiece, according to the different tempering temperatures, can be divided into the following types of tempering:

(a) low-temperature tempering (150-250 degrees)

Low-temperature tempering of tempered martensite for the resulting organization. Its purpose is to maintain the high hardness and high wear resistance of quenched steel under the premise of reducing its quenching internal stress and brittleness, so as to avoid chipping or premature damage during use. It is mainly used for a variety of high-carbon cutting tools, gauges, cold-drawn dies, rolling bearings and carburized parts, etc., after tempering hardness is generally HRC58-64.

(ii) medium temperature tempering (250-500 degrees)

Medium-temperature tempering of tempered quenched steel organization for the tempered quenched. Its purpose is to obtain high yield strength, elastic limit and high toughness. Therefore, it is mainly used for a variety of springs and hot work mold treatment, tempering hardness is generally HRC35-50.

(C) high temperature tempering (500-650 degrees)

High-temperature tempering of the organization for the tempered Sohnite. It is customary to quenching and high temperature tempering combination of heat treatment known as tempering treatment, its purpose is to obtain strength, hardness and plasticity, toughness are better overall mechanical properties. Therefore, widely used in automobiles, tractors, machine tools and other important structural parts, such as connecting rods, bolts, gears and shafts. Tempered hardness is generally HB200-330.

Deformation prevention

The cause of deformation of precision and complex molds is often complex, but we only need to grasp the law of deformation, analyze the reasons for its generation, the use of different methods of prevention of deformation of the mold is able to reduce, but also able to control. Generally speaking, the heat treatment of precision complex mold deformation can take the following methods of prevention.

(1) reasonable material selection. Precision complex molds should be selected material good microdeformation mold steel (such as air quenching steel), the carbide segregation of serious mold steel should be reasonable forging and tempering heat treatment, the larger and can not be forged mold steel can be solid solution double refinement heat treatment.

(2) mold structure design should be reasonable, thickness should not be too disparate, the shape should be symmetrical, for the deformation of the mold to grasp the law of deformation, reserved machining allowances for large, precise and complex molds can be used in a combination of structures.

(3) precision complex molds should be pre-heat treatment to eliminate residual stresses generated during machining.

(4) a reasonable choice of heating temperature, control the heating rate, for precision complex molds can be taken slowly heating, preheating and other balanced heating methods to reduce mold heat treatment deformation.

(5) under the premise of ensuring the hardness of the mold, try to use pre-cooling, graded cooling quenching or temperature quenching process.

(6) for precision and complex molds, under the conditions permit, try to use vacuum heating quenching and deep cooling after quenching.

(7) for some precision and complex molds can be used pre-heat treatment, aging heat treatment, tempering nitriding heat treatment to control the accuracy of the mold.

(8) in the repair of mold sand holes, pores, wear and other defects, the use of cold welding machine and other thermal impact of the repair equipment to avoid deformation in the repair process.

In addition, the correct heat treatment process operation (such as plugging holes, tied holes, mechanical fixation, suitable heating methods, the correct choice of the cooling direction of the mold and the direction of movement in the cooling medium, etc.) and reasonable tempering heat treatment process is also an effective measure to reduce the deformation of precision complex molds.

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