After learning chemistry, you will know that the salt used as seasoning in daily life has many uses, such as?
Preservatives
And snow melting Light has many uses in life, such as the mirror we look at every day. 2. Convex mirrors placed at intersections. 3. Car rear view mirror. 4. We can see objects, and objects reflect light into our eyes. 5. Solar heater (solar cooker) 6. Periscope What are the other uses of big trees in daily life? Trees can regulate the climate and maintain ecological balance. Through photosynthesis, trees take in carbon dioxide and spit out oxygen, making the air clean and fresh. One acre of forest releases enough oxygen for 65 people to breathe.
Trees can prevent wind and sand, conserve water and soil, and absorb various dusts. One acre of forest can absorb 20-60 tons of various dusts in a year.
Woods can reduce noise pollution.
It can coordinate people's psychological state and improve interpersonal relationships.
Researchers conducted a three-year survey of 300 residents in different residential areas. The architectural structures of these residential areas are basically similar, and the social status of the residents is basically the same. The difference is that some residential areas are surrounded by trees and grass, while other residential areas are bare, truly a "desert surrounded by concrete." Residents who live in the shade have closer ties with neighbors and more harmonious interpersonal relationships. People like to go out, feel safe and have a calmer mentality. In such an environment, even violence decreases. Residents who live in the "desert" live in seclusion and prefer to stay in apartments.
Therefore, researchers believe that places with trees, flowers and plants provide people with an environment that is pleasing to the eye and is conducive to strengthening and improving interpersonal relationships. Unhappiness and frustration can be reduced through help from friends or neighbors. Increased communication between people also reduces quarrels and the use of violence. How used is electricity in daily life?
In daily life, it can be said that electricity is inseparable from home lighting, boiling water for cooking, household appliances, work, mechanical operations, vehicle communications, etc., water and electricity, power outages, etc. The water supply is also cut off, and the rural areas are making do without electricity. Now a city has both no electricity and water shortage, which can be close to paralysis; the names, chemical formulas and uses of chloride-containing compounds commonly used in daily life
Sodium chloride NaCl Needless to say, you need to eat salt
Calcium chloride GaCl2 can be used as a desiccant
Magnesium chloride MgCl2 can be used as a desiccant
Hydrogen chloride HCl and hydrochloric acid can be washed but cannot be washed away The East and West Pyramids can have many uses and unique effects. How can they be obtained and utilized in daily life?
Scientific research has found that pyramid power has many uses and unique effects: preserving freshness, reversing oxidation; improving sleep efficiency (helping deep sleep), and improving memory and thinking ability (yingkaoxue) , delaying aging and disease death (promoting self-healing), etc. Pyramid energy can be obtained through the pyramid model. However, the size of the pyramid model cannot be very large, and the time for converging wave magnetic energy is short. If ordinary materials such as plastic, ceramics, (wood) stone, concrete, etc. are used, the energy of the pyramid formed will be minimal.
Scientists have invented a real and effective pyramid model (pyramid energy generator) based on the principle of pyramid energy generation: "1. The shape of the pyramid is the basis, that is, the side inclination angle is within 50° to 54°. Hollow square pyramid; 2 Use functional materials (intelligent, wave-absorbing, hysteresis composite materials); 3 The appearance of the product must be a hollow square pyramid with sharp edges and corners, flat surface, and molded in one step." People with "weak electromagnets" only need to be in the pyramid energy field, such as placing the pyramid energy generator under the bed, under the chair, on the table, or wearing it on the head, to enjoy the benefits of the pyramid energy. The acidity and alkalinity of seasonings in our daily lives
According to the amount of elements contained in the food itself, it can be divided into alkaline foods, acidic foods, and neutral foods.
Acidic foods Animal foods other than milk.
Alkaline foods are plant foods other than whole grains.
Neutral food: oil, salt, coffee, tea, etc.
① Acidic foods
Foods containing more minerals such as sulfur, phosphorus, and chlorine have acidic final metabolites in the body, such as meat, eggs, fish and other animal foods and Legumes and cereals, etc. Appropriate combination with alkaline foods can help maintain the acid-base balance in the body.
② Alkaline foods
Foods containing more minerals such as potassium, sodium, calcium, and magnesium often have alkaline final metabolites in the body, such as vegetables, Fruits, dairy, soybeans and fungi foods, etc. Appropriate combination with alkaline foods can help maintain the acid-base balance in the body.
Speaking of alkaline foods, we have to mention the glacier water in the Pamir Plateau, which is very helpful to people.
What are alkaline foods:
Strongly acidic foods: beef, pork, chicken, tuna, oysters, halibut, cheese, rice, wheat, bread, alcohol, peanuts, walnuts , thin sausage, sugar, biscuits, sugar, beer, etc.
Weakly acidic foods: ham, eggs, lobster, octopus, squid, buckwheat, butter, peas, eels, river fish, chocolate, green onions, hollow noodles, fried tofu, etc.
Strongly alkaline foods: tea, cabbage, persimmons, cucumbers, carrots, spinach, cabbage, lettuce, taro, kelp, citrus, figs, watermelon, grapes, raisins, strawberries, millet, coffee, wine etc.
Weakly alkaline foods: tofu, peas, soybeans, mung beans, bamboo shoots, potatoes, shiitake mushrooms, mushrooms, rapeseed, pumpkin, tofu, celery, sweet potatoes, lotus root, onions, eggplants, pumpkins, radishes, milk, Apples, pears, bananas, cherries and more.
There are also some foods that taste sour, so people mistakenly regard them as acidic foods, such as wild plants, tomatoes, vinegar, etc. In fact, these foods are typical alkaline foods.
Certain dried fruits (coconut, apricots, chestnuts) produce alkaline ash, while others (such as peanuts, walnuts) produce acidic ash. Corn and lentils are acidic foods.
Alkaline foods are mainly divided into: 1. Vegetables and fruits; 2. Seaweeds; 3. Nuts; 4. Sprouted cereals and beans. Avoid or reduce the intake of the following acidic foods: 1. Starches; 2. Animal foods; 3. Sweets; 4. Refined processed foods (such as white bread, etc.); 5. Fried foods or butter; 6. Beans (Such as peanuts, etc.)
Alkaline foods such as beans (soybeans, kidney beans, red beans), vegetables (radish, rape, tomatoes), sea vegetables (kelp, seaweed, green algae), fruits (oranges, grass) Lemon, banana, grape) and fresh fruit juice without added sugar. Note: Food with added sugar or fried food will turn alkaline into acidic.
Strongly alkaline food: grapes, tea, wine, kelp , citrus, persimmon, cucumber, carrot.
Moderately alkaline foods: soybeans, tomatoes, bananas, strawberries, egg whites, prunes, lemons, spinach, etc.
Weakly alkaline foods: red beans, apples, cabbage, tofu, cabbage, rape, pears, potatoes.
Alkaline food recommendations
1. Apple. Fruits are the easiest to digest among foods and are the best internal cleansers. Among fruits, apples are known as the best alkaline food. They can improve acidic physique and maintain the body's acid-base balance. Eating apples can quickly neutralize excess acidic substances in the body, thereby enhancing physical strength and disease resistance. In addition to neutralizing the acid-base balance, research and analysis also show that eating apples regularly is beneficial to weight loss. This is because apples increase the feeling of fullness. Eating them before meals can reduce food intake and achieve the purpose of weight loss.
2. Vegetables: Almost all vegetables, especially green leafy vegetables, are alkaline foods. They are rich in vitamins and minerals, which can add nutrients to the body. The large amount of fiber in vegetables can also improve the body's digestive function and maintain gastrointestinal health. Therefore, they are very suitable for using them to neutralize a large amount of acidic foods such as meat and starch in the body, and help the food be digested and excreted in time.
Alkaline foods contain more metal elements such as sodium, potassium, calcium, and magnesium. It does not mean that something sour is sour food. You should know one thing: all sour fruits and soy products are alkaline foods, not acidic foods. Alkaline foods are considered to be foods with beauty effects.
Tofu, milk, celery, potatoes, bamboo shoots, mushrooms, carrots, kelp, mung beans, bananas, watermelons, strawberries, etc. and most vegetables and fruits are alkaline.
The "acidity and alkalinity" of food will affect body posture and skin fitness.
It has been determined that weakly alkaline foods include: tofu, peas, soybeans, mung beans, rape, celery, sweet potatoes, lotus roots, onions, eggplants, pumpkins, cucumbers, mushrooms, radishes, milk, etc. Alkaline foods include: spinach, cabbage, cabbage, lettuce, carrots, bamboo shoots, potatoes, kelp, citrus, watermelon, grapes, bananas, strawberries, millet, persimmons, coffee, wine, etc. There are also some foods that taste sour, so people mistakenly regard them as acidic foods, such as wild plants, tomatoes, vinegar, etc. In fact, these foods are typical alkaline foods.
Eat more alkaline foods. Studies have found that eating more alkaline foods can keep the blood weakly alkaline, reduce acidic substances such as lactic acid and urea in the blood, and prevent them from depositing on the wall of the blood vessels, thus softening the blood vessels, so some people call it alkaline. Food is a "cleanser of blood and blood vessels." The acidity and alkalinity mentioned here is not the nature of the food itself, but the nature of the elements left in the body after the food is digested and absorbed. Common acidic elements include nitrogen, carbon, sulfur, etc.; common alkaline elements include potassium, sodium, calcium, magnesium, etc. Some foods have a very sour taste, such as tomatoes and oranges, but they are all highly alkaline foods, because the final element they metabolize in the body is potassium.
What is acidic or alkaline food? The so-called acidic food or alkaline food does not refer to food that tastes sour or salty, but refers to food in which cations or anions are dominant after digestion, absorption and metabolism. . That is to say, a certain food is an alkaline food if the cations such as potassium, sodium, calcium, and magnesium that are produced after metabolism are dominant; and the food that is dominated by anions such as phosphorus, chlorine, and sulfur after metabolism is an acidic food. Although lemons, tangerines, star fruits, etc. taste sour, after metabolism, the organic acids turn into water and carbon dioxide. The latter is exhaled from the body through the lungs. The remaining cations dominate and are still alkaline foods. Similarly, meat Although food, fish, eggs and rice noodles have no sour taste, they produce more anions after metabolism and are still acidic foods. Therefore, acidic or alkaline foods cannot be distinguished from the taste of the food. There are chemicals in our daily life. And what impact do chemicals have on daily life?
Chemicals are everywhere in life, such as plastics, edible medicines, cosmetics, lithium-ion batteries, various batteries, and adhesives used for furniture bonding. Agents, etc. In short, science is to advance human living standards and make life better. Types, properties, and uses of alloys in daily life
A brief description
Metal heat treatment is to heat metal workpieces in a certain medium to a suitable temperature, and at this temperature A process in which the material is kept for a certain period of time and then cooled at different speeds.
Metal heat treatment is one of the important processes in mechanical manufacturing. Compared with other processing processes, heat treatment generally does not change the shape and overall chemical composition of the workpiece, but changes the internal microstructure of the workpiece. Or change the chemical composition of the workpiece surface to give or improve the performance of the workpiece. Its characteristic is to improve the intrinsic quality of the workpiece, which is generally not visible to the naked eye.
In order to make metal workpieces have the required mechanical properties, physical properties and chemical properties, in addition to the reasonable selection of materials and various forming processes, heat treatment processes are often indispensable. Steel is the most widely used material in the mechanical industry. The microstructure of steel is complex and can be controlled through heat treatment. Therefore, 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 performance properties.
As we progressed from the Stone Age to the Bronze Age and Iron Age, the role of heat treatment gradually became recognized. As early as 770 BC to 222 BC, the Chinese discovered in production practice that the properties of copper and iron will change due to the influence of temperature and pressure deformation. The softening treatment of white cast iron is an important process for manufacturing agricultural tools.
In the sixth century BC, steel weapons were gradually adopted. In order to improve the hardness of steel, the quenching process was rapidly developed. Two swords and a halberd unearthed from Yanxiadu, Yixian County, Hebei Province, China, have martensite in their microstructure, indicating that they have been quenched.
With the development of quenching technology, people gradually discovered the impact of refrigerant on quenching quality. Pu Yuan, a native of Shu in the Three Kingdoms, once made 3,000 knives for Zhuge Liang in Xiegu, Shaanxi today. According to legend, he sent people to Chengdu to get water for quenching. This shows that China paid attention to the cooling capabilities of different water qualities in ancient times, and also paid attention to the cooling capabilities of oil and urine. The sword unearthed in China from the tomb of King Jing in Zhongshan during the Western Han Dynasty (206 BC to AD 24) has a carbon content of 0.15 to 0.4% in the heart, but a carbon content of more than 0.6% on the surface, indicating that the carburizing process has been applied. But at that time, as a secret of personal "craft", it was not allowed to be disclosed, so its development was very slow.
In 1863, British metallographers and geologists demonstrated six different metallographic structures of steel under a microscope, proving that the internal structure of steel will change when it is heated and cooled. The phase changes to a harder phase during rapid cooling. The allotropy theory of iron established by the Frenchman Osmond and the iron-carbon phase diagram first formulated by the British Austin laid the initial theoretical foundation for modern heat treatment technology. At the same time, people have also studied methods to protect metals during the heating process of metal heat treatment to avoid oxidation and decarburization of metals during the heating process.
From 1850 to 1880, there were a series of patents for the application of various gases (such as hydrogen, coal gas, carbon monoxide, etc.) for protective heating. From 1889 to 1890, the British man Lake obtained patents for bright heat treatment of various metals.
Since the 20th century, the development of metal physics and the transplantation and application of other new technologies have enabled greater development of metal heat treatment processes. A significant development was the application of rotary drum furnaces for gas carburizing in industrial production from 1901 to 1925. In the 1930s, a dew point potentiometer appeared to control the carbon potential of the atmosphere in the furnace. Later, a carbon dioxide infrared meter was developed. , oxygen probes and other methods to further control the carbon potential of the furnace atmosphere; in the 1960s, heat treatment technology used the role of plasma fields to develop ion nitriding and carburizing processes; the application of laser and electron beam technology gave metals new Surface heat treatment and chemical heat treatment methods.
2. Metal heat treatment process
The heat treatment process generally includes three processes: heating, insulation, and cooling. Sometimes there are only two processes: heating and cooling. These processes are interconnected and cannot be interrupted.
Heating is one of the important steps in heat treatment. There are many heating methods for metal heat treatment. The first was to use charcoal and coal as the heat source, and then to use liquid and gaseous fuels. The application of electricity makes heating easy to control and has no environmental pollution. These heat sources can be used for direct heating, or indirect heating through molten salt or metal, or even floating particles.
When metal is heated, the workpiece is exposed to the air, and oxidation and decarburization often occur (that is, the carbon content on the surface of the steel part is reduced), which has a very negative impact on the surface properties of the parts after heat treatment. Therefore, metals should usually be heated in a controlled atmosphere or protective atmosphere, in molten salt, and in a vacuum. Protective heating can also be carried out by coating or packaging methods.
Heating temperature is one of the important process parameters of the heat treatment process. Selecting and controlling the heating temperature is the main issue to ensure the quality of heat treatment. The heating temperature varies with the metal material being processed and the purpose of the heat treatment, but it is generally heated to above the phase transformation temperature to obtain the required structure. In addition, the transformation requires a certain amount of time, so when the surface of the metal workpiece reaches the required heating temperature, it must be maintained at this temperature for a certain period of time to make the internal and external temperatures consistent and the microstructure transformation to be complete. This period of time is called the holding time. When high-energy-density heating and surface heat treatment are used, the heating speed is extremely fast, and generally there is no holding time or the holding time is very short, while the holding time of chemical heat treatment is often longer.
Cooling is also an indispensable step in the heat treatment process. The cooling methods vary depending on the process, mainly controlling the cooling rate. Generally, annealing has the slowest cooling rate, normalizing has a faster cooling rate, and quenching has a faster cooling rate. However, there are different requirements due to different steel types. For example, air-hardened steel can be hardened at the same cooling rate as normalizing.
Metal heat treatment processes can be roughly divided into overall heat treatment, surface heat treatment, local heat treatment and chemical heat treatment. Depending on the heating medium, heating temperature and cooling method, each category can be divided into several different heat treatment processes.
Using different heat treatment processes, the same metal can obtain different structures and thus have different properties. Steel is the most widely used metal in industry, and the microstructure of steel is also the most complex, so there are many types of steel heat treatment processes.
Integral heat treatment is a metal heat treatment process that heats the workpiece as a whole and then cools it at an appropriate speed to change its overall mechanical properties. The overall heat treatment of steel generally includes four basic processes: annealing, normalizing, quenching and tempering.
Annealing is to heat the workpiece to an appropriate temperature, adopt different holding times according to the material and workpiece size, and then slowly cool it. The purpose is to make the internal structure of the metal reach or approach an equilibrium state and obtain good process performance and Use properties, or prepare the tissue for further quenching. Normalizing is to heat the workpiece to a suitable temperature and then cool it in the air. The effect of normalizing is similar to that of annealing, except that the obtained structure is finer. It is often used to improve the cutting performance of materials, and is sometimes used for parts with low requirements. as final heat treatment.
Quenching is to heat and maintain the workpiece and then quickly cool it in a quenching medium such as water, oil or other inorganic salts, organic aqueous solutions. After quenching, the steel becomes hard but at the same time becomes brittle. In order to reduce the brittleness of steel parts, the quenched steel parts are kept for a long time at an appropriate temperature above room temperature and below 710°C, and then cooled. This process is called tempering. Annealing, normalizing, quenching, and tempering are the "four fires" in overall heat treatment. Among them, quenching and tempering are closely related and are often used together. One is indispensable.
The "Four Fires" have evolved different heat treatment processes with different heating temperatures and cooling methods. In order to obtain a certain strength and toughness, the process of combining quenching and high-temperature tempering is called quenching and tempering. After some alloys are quenched to form a supersaturated solid solution, they are kept at room temperature or a slightly higher temperature for a longer period of time to improve the hardness, strength or electromagnetic properties of the alloy. This heat treatment process is called aging treatment. The method of effectively and closely combining pressure processing deformation and heat treatment to obtain good strength and toughness of the workpiece is called deformation heat treatment; heat treatment performed in a negative pressure atmosphere or vacuum is called vacuum heat treatment, which not only enables The workpiece will not be oxidized or decarburized, and the surface of the treated workpiece will be kept smooth and clean, improving the performance of the workpiece. It can also be chemically heat treated by penetrating agent.
Surface heat treatment is a metal heat treatment process that only heats the surface layer of the workpiece to change the mechanical properties of the surface layer. In order to only heat the surface of the workpiece without transferring too much heat into the interior of the workpiece, the heat source used must have a high energy density, that is, a large amount of heat energy is given to the workpiece per unit area, so that the surface or part of the workpiece can be heated for a short or instant. reach high temperatures. The main methods of surface heat treatment include laser heat treatment, flame quenching and induction heating heat treatment. Commonly used heat sources include flames such as oxyacetylene or oxypropane, induced current, laser and electron beams.
Chemical heat treatment is a metal heat treatment process that changes the chemical composition, structure and properties of the surface layer of the workpiece. The difference between chemical heat treatment and surface heat treatment is that the latter changes the chemical composition of the surface layer of the workpiece. Chemical heat treatment is to heat the workpiece in a medium (gas, liquid, solid) containing carbon, nitrogen or other alloying elements, and keep it warm for a long time, so that the surface of the workpiece can penetrate into elements such as carbon, nitrogen, boron and chromium. After the elements are infiltrated, other heat treatment processes such as quenching and tempering are sometimes performed. The main methods of chemical heat treatment include carburizing, nitriding, metal infiltration, composite infiltration, etc.
Heat treatment is one of the important processes in the manufacturing process of mechanical parts and tools and molds. Generally speaking, it can ensure and improve various properties of the workpiece, such as wear resistance, corrosion resistance, etc. It can also improve the structure and stress state of the blank to facilitate various cold and hot processing.
For example, white cast iron can be annealed for a long time to obtain malleable cast iron, which improves plasticity; using the correct heat treatment process for gears, the service life can be doubled or dozens of times longer than gears without heat treatment; in addition, Cheap carbon steel has certain properties of expensive alloy steel by being infiltrated with certain alloying elements, and can replace some heat-resistant steel and stainless steel; almost all tools and molds need to be heat treated before they can be used.
3. Classification of Steel
Steel is an alloy with iron and carbon as its main components. Its carbon content is generally less than 2.11%. Steel is an extremely important metal material in economic construction. Steel is divided into two categories according to its chemical composition: carbon steel (carbon steel for short) and alloy steel.
Carbon steel is an alloy obtained by smelting pig iron. In addition to iron and carbon as its main components, it also contains a small amount of manganese, silicon, sulfur, phosphorus and other impurities. Carbon steel has certain mechanical properties, good process properties, and is cheap. Therefore, carbon steel has been widely used. However, with the rapid development of modern industry and science and technology, the performance of carbon steel can no longer fully meet the needs, so various alloy steels have been developed. Alloy steel is a multi-component alloy obtained by purposely adding certain elements (called alloying elements) to carbon steel. Compared with carbon steel, the performance of alloy steel has been significantly improved, so it is increasingly used.
Due to the wide variety of steel materials, steel materials must be classified in order to facilitate production, storage, selection and research. According to the use, chemical composition and quality of steel, steel can be divided into many categories:
(1). Classification by use
According to the use of steel, it can be divided into three categories: structural steel, tool steel, and special performance steel.
1. Structural steel:
(1). Steel used as various machine parts. It includes carburized steel, quenched and tempered steel, spring steel and rolling bearing steel.
(2). Steel used in engineering structures. It includes A, B, special steel and ordinary low alloy steel in carbon steel.
2. Tool steel: Steel used to make various tools. According to different uses of tools, they can be divided into cutting tool steel, mold steel and measuring tool steel.
3. Special performance steel: It is steel with special physical and chemical properties. It can be divided into stainless steel, heat-resistant steel, wear-resistant steel, magnetic steel, etc.
(2). Classification by chemical composition
According to the chemical composition of steel, it can be divided into two categories: carbon steel and alloy steel.
Carbon steel: According to the carbon content, it can be divided into low carbon steel (carbon content ≤ 0.25%); medium carbon steel (0.25% < carbon content < 0.6%); high carbon steel ( Carbon content ≥0.6%).
Alloy steel: According to the alloying element content, it can be divided into low alloy steel (total alloying element content ≤ 5%); medium alloy steel (total alloying element content = 5%--10%); high alloy Steel (total alloying element content >10%). In addition, according to the main alloying elements contained in steel, it can also be divided into manganese steel, chromium steel, chromium-nickel steel, chromium-manganese-titanium steel, etc.
(3). Classification by quality
According to the content of harmful impurities phosphorus and sulfur in steel, it can be divided into ordinary steel (phosphorus content ≤ 0.045%, sulfur content ≤ 0.055%; or phosphorus and sulfur content both ≤ 0.050%) ; High-quality steel (phosphorus and sulfur content, sulfur content ≤0.030%).
In addition, according to the type of smelting furnace, steel is divided into open-hearth steel (acidic open-hearth furnace, alkaline open-hearth furnace), air converter steel (acid converter, alkaline converter, oxygen top-blown converter steel) and Electric furnace steel. According to the degree of deoxidation during smelting, steel is divided into boiling steel (incomplete deoxidation), killed steel (relatively complete deoxidation) and semi-killed steel.
When steel mills name steel products, they often combine the three classification methods of use, composition, and quality. For example, steel is called ordinary carbon structural steel, high-quality carbon structural steel, carbon tool steel, advanced high-quality carbon tool steel, alloy structural steel, alloy tool steel, etc. All ≤0.040%); high-grade high-quality steel (phosphorus content ≤0.035%,
Mechanical properties of four metal materials
The properties of metal materials are generally divided into two categories: process performance and use performance. Category. The so-called process performance refers to the performance of metal materials under specified cold and hot processing conditions during the processing and manufacturing of mechanical parts. The quality of the process performance of metal materials determines its adaptability to processing and forming during the manufacturing process. Ability. Due to different processing conditions, the required process properties are also different, such as casting performance, weldability, forgeability, heat treatment performance, cutting processability, etc. The so-called service performance refers to the performance of metal materials under the conditions of use. The performance includes mechanical properties, physical properties, chemical properties, etc. The performance of metal materials determines its use range and service life.
In the machinery manufacturing industry, general mechanical parts. They are all used in normal temperature, normal pressure and non-strongly corrosive media, and during use, each mechanical part will bear the effects of different loads. The performance of metal materials in resisting damage under load is called mechanical properties (or. (called mechanical properties). The mechanical properties of metal materials are the main basis for the design and material selection of parts.
Depending on the nature of the applied load (such as tension, compression, torsion, impact, cyclic load, etc.), the mechanical properties required for metal materials will also be different. Commonly used mechanical properties include: strength, plasticity, hardness, toughness, multiple impact resistance and fatigue limit, etc. Each mechanical property is discussed separately below.
1. Strength
Strength refers to the resistance of metal materials to damage (excessive plastic deformation or fracture) under static load. Since the load acts in the form of tension, compression, bending, shearing, etc., the strength is also divided into tensile strength, compressive strength, flexural strength, shear strength, etc. There is often a certain relationship between various strengths. In use, tensile strength is generally used as the most basic strength index.
2. Plasticity
Plasticity refers to the ability of a metal material to undergo plastic deformation (permanent deformation) without destruction under load.
3. Hardness
Hardness is a measure of how hard or soft a metal material is. At present, the most commonly used method for measuring hardness in production is the indentation hardness method, which uses an indenter of a certain geometric shape to press into the surface of the metal material being tested under a certain load, and the hardness value is measured based on the degree of indentation.
Commonly used methods include Brinell hardness (HB), Rockwell hardness (HRA, HRB, HRC) and Vickers hardness (HV).
4. Fatigue
The strength, plasticity, and hardness discussed previously are all mechanical performance indicators of metal under static load. In fact, many machine parts are operated under cyclic loading, and fatigue will occur in the parts under such conditions.
5. Impact toughness
The load acting on the machine part at a very high speed is called impact load, and the ability of metal to resist damage under the action of impact load is called impact toughness.
Five Annealing--Quenching--Tempering
(1). Types of annealing
1. Complete annealing and isothermal annealing
Complete annealing is also called recrystallization annealing, generally referred to as annealing. This kind of annealing is mainly used for castings, forgings and various carbon steels and alloy steels with sub-element analysis components. Hot-rolled profiles are sometimes used in welded structures. It is generally used as the final heat treatment of some unimportant workpieces, or as the pre-heat treatment of some workpieces.
2. Spheroidizing annealing
Spheroidizing annealing is mainly used for carbon steel and alloy tool steel that have been analyzed (such as steel types used in the manufacture of cutting tools, measuring tools, and molds). Its main purpose is to reduce hardness, improve machinability, and prepare for subsequent quenching.
3. Stress relief annealing
Stress relief annealing is also called low-temperature annealing (or high-temperature tempering). This kind of annealing is mainly used to eliminate residual stress in castings, forgings, welding parts, hot-rolled parts, cold-drawn parts, etc. If these stresses are not eliminated, it will cause the steel parts to deform or crack after a certain period of time or during subsequent cutting processes.
(2). Quenching
The main methods used to improve hardness are heating, heat preservation, and rapid cooling. The most commonly used cooling media are brine, water and oil. The workpiece quenched in salt water is easy to obtain high hardness and smooth surface, and is not prone to soft spots that are not hardened, but it is easy to cause serious deformation of the workpiece and even cracking. The use of oil as the quenching medium is only suitable for quenching some alloy steels or small-sized carbon steel workpieces where the stability of supercooled austenite is relatively large.
(3). Tempering
1. Reduce brittleness and eliminate or reduce internal stress. After quenching, steel parts will have great internal stress and brittleness. If they are not tempered in time, the steel parts will often deform or even crack.
2. Obtain the required mechanical properties of the workpiece. After quenching, the workpiece has high hardness and high brittleness. In order to meet the different performance requirements of various workpieces, the hardness can be adjusted through appropriate tempering, reducing the brittleness and obtaining the required toughness. Plasticity.
3. Stable workpiece size
4. For some alloy steels that are difficult to soften by annealing, high-temperature tempering is often used after quenching (or normalizing) to properly gather carbides in the steel and reduce the hardness to facilitate cutting.
6. Selection of commonly used furnace types
The furnace type should be determined according to different process requirements and the type of workpiece
1. For those that cannot be produced in batches, have unequal sizes of workpieces, and have many types, and require versatility and versatility in the process, box-type furnaces can be used.
2. When heating long shafts, long screw rods, pipes and other workpieces, deep well electric furnaces can be used.
3. For small batches of carburized parts, a well-type gas carburizing furnace can be used.
4. For the production of large quantities of automobile, tractor gear and other parts, a continuous carburizing production line or a box-type multi-purpose furnace can be selected.
5. When heating stamping sheet blanks for mass production, it is best to use rolling furnaces and roller hearth furnaces.
6. For batches of finalized parts, push rod or conveyor belt resistance furnaces (push rod furnaces or cast belt furnaces) can be used for production
7. Small mechanical parts such as screws, nuts, etc. can choose vibrating bottom furnace or mesh belt furnace.
8. The internal spiral rotary tube furnace can be used for heat treatment of steel balls and rollers.
9. Push rod furnaces can be used for mass production of non-ferrous metal ingots, while air circulation heating furnaces can be used for small non-ferrous metal parts and materials. How to limit salt intake in daily life
Salt is an important substance for the human body to maintain volume balance. Excessive intake of salt can increase the concentration of sodium in tissue fluid and circulating blood. The fluid and circulating blood volume increases, aggravating the peripheral resistance of small blood vessels and the pressure on the walls of large blood vessels. In addition, diabetic patients are more likely to have high blood pressure than normal people. Once hypertension occurs, it is particularly likely to be complicated by kidney disease, retinopathy and arteriosclerosis. Excessive sodium intake is also one of the causes of high blood pressure. In order to prevent and control high blood pressure and reduce diabetic vascular disease, salt intake should be reduced as much as possible. The daily salt consumption is best controlled within 6 grams. How to calculate salt intake: record the day the salt was purchased and the weight of the salt (for example, 500 grams). After the salt to be purchased is used up, calculate how long the salt has been used (for example, 30 days), and then calculate the average number of people eating per day (for example, 3 people), and you can calculate the average salt consumption per person per day (for example, 3 people). Such as 500÷30÷3=5.6 grams). If salt intake is excessive, it should be appropriately limited.