1. What is heat treatment? What is heat treatment process?

Heat treatment process is a kind of thermal processing technology that uses heating and cooling methods to change the structure, properties and internal stress state of materials. It is a key link in the machinery manufacturing industry to improve the performance, service life and reliability of products. Mainly for metals, metal heat treatment is a process in which metals or alloys are heated to a certain temperature in the solid state, held at that temperature for a certain period of time, and then cooled at a certain rate. That is, through the organic combination of basic links such as heating rate, holding time, holding temperature and cooling rate, the internal structure of the metal or alloy is transformed, thereby improving the material's performance. It mainly includes: normalizing, annealing, solution heat treatment, aging treatment, quenching, tempering, carburizing, quenching and tempering, brazing, etc.

2. What is quenching and tempering heat treatment?

Quenching and tempering heat treatment refers to one of many metal heat treatment methods. Among them, metal heat treatment refers to the process method of heating, holding at temperature and cooling metals in a certain way within the solid state range to improve or change the properties and microstructure of metals. In practical applications, depending on the different purposes of heat treatment, the process of combining quenching and high-temperature tempering is often collectively referred to as quenching and tempering treatment, with the aim of endowing the workpiece with excellent comprehensive mechanical properties. Quenching and tempering treatment is widely applied to various important structural parts, especially those connecting rods, bolts, gears and shafts that operate under alternating loads. After quenching and tempering treatment, tempered sorbite structure is obtained, and its mechanical properties are all better than those of normalized sorbite structure with the same hardness. Its hardness depends on the high-temperature tempering temperature and is related to the tempering stability of the steel and the cross-sectional size of the workpiece, generally ranging from HB200 to 350.

3. What is carburizing heat treatment?

Carburizing heat treatment is generally applied to steel. It refers to a chemical heat treatment process in which steel parts are heated and held at a certain temperature in a carburizing medium to increase the carbon content on the surface layer of steel parts and form a certain carbon concentration gradient, allowing carbon atoms to penetrate the surface layer and causing a change in the carbon concentration on the surface. The principles mainly include decomposition, adsorption and diffusion. The purpose of carburizing is to endow machine parts with high surface hardness, wear resistance, as well as high contact fatigue strength and bending fatigue strength. In practical applications, carbon is classified into three types based on the different aggregation states of the carburizing agent: solid carburizing, liquid carburizing, and gas carburizing.

4. What is vacuum heat treatment?

Vacuum heat treatment is a new type of heat treatment technology that combines vacuum technology with heat treatment technology. The vacuum environment in which vacuum heat treatment takes place refers to an atmosphere environment with a pressure lower than one atmosphere, including low vacuum, medium vacuum, high vacuum and ultra-high vacuum. In fact, vacuum heat treatment also belongs to atmosphere-controlled heat treatment. Vacuum heat treatment refers to the process where all or part of the heat treatment is carried out under vacuum conditions. Vacuum heat treatment can achieve almost all the heat treatment processes that conventional heat treatment can involve, but the quality of heat treatment is greatly improved. Compared with conventional heat treatment, vacuum heat treatment can achieve no oxidation, no decarburization, no carburization, remove the phosphorus scale on the surface of the workpiece, and has the functions of degreasing and degassing, thereby achieving the effect of bright and clean surface.

5. What is heat-treated reinforcing bar?

The commonly used reinforcing bars in reinforced concrete include hot-rolled reinforcing bars, cold-drawn reinforcing bars, heat-treated reinforcing bars, etc. Generally, they can be classified into smooth reinforcing bars and deformed reinforcing bars (such as threaded reinforcing bars, crescent-shaped reinforcing bars, etc.) according to their shapes. Among them, heat-treated reinforcing bars are made by quenching and tempering the reinforcing bars rolled from oxygen top-blown converter steel or electric furnace steel. In the past, it was smooth round steel bars, but now ribbed steel bars are produced. It is not applicable to the reinforcing bars used for welding and spot welding. Heat-treated reinforcing bars are used to enhance their strength. After taking measures from aspects such as the variety and processing of steel, the strength has reached a certain level. On this basis, through the heat treatment process of steel, the mechanical properties such as the strength value of the highest strength reinforcing bars are further improved. Therefore, heat-treated reinforcing bars have high strength, require less material, have good anchoring properties, and stable prestress. They are mainly used as prestressed reinforced concrete sleepers and can also be applied to prestressed reinforced concrete slabs, crane beams and other components. Its corresponding cost and price are both higher than those of other types of steel bars.

6. What is mold heat treatment?

Mold heat treatment is mainly for rigid molds. Therefore, the mold heat treatment process refers to the specific process parameters for heating, holding and cooling of mold steel during the heating and cooling processes, which are formulated based on the laws of microstructure transformation. According to the different heating and cooling methods as well as the obtained microstructure and properties, heat treatment processes can be classified into conventional heat treatment, surface heat treatment, etc. The conventional heat treatment of die steel mainly includes annealing, normalizing, quenching and tempering. Mold heat treatment is one of the key processes in mold manufacturing, directly related to the manufacturing accuracy, mechanical properties (such as strength, etc.), service life and manufacturing cost of the mold. It is an important link to ensure the quality and service life of the mold. The correct selection of steel and reasonable heat treatment processes will play a significant role in giving full play to the potential properties of materials, reducing energy consumption, lowering costs, and improving the quality and service life of molds. At present, the fields where mold heat treatment technology is developing rapidly are vacuum heat treatment technology and surface strengthening technology of molds. According to the position and role of heat treatment in the production process of parts, mold heat treatment can be further divided into preliminary heat treatment and final heat treatment.

7. What is metal heat treatment? What is heat treatment of metals?

Metal heat treatment is one of the important processes in mechanical manufacturing. Compared with other processing techniques, metal heat treatment generally does not change the shape or overall chemical composition of the workpiece, but rather endows or improves the service performance of the workpiece by altering its internal microstructure or the chemical composition of its surface. Its characteristic is to improve the intrinsic quality of the workpiece, which is generally not visible to the naked eye. Metal heat treatment processes can be generally classified into three major categories: overall heat treatment, surface heat treatment and chemical heat treatment. According to the differences in heating medium, heating temperature and cooling method, each major category can be further divided into several different heat treatment processes. The same metal, when subjected to different heat treatment processes, can obtain different structures and thus possess different properties.

8. What is welding heat treatment?

Before, during or after welding, the entire or part of the welded workpiece is heated to a certain temperature, held at that temperature for a certain period of time, and then cooled at an appropriate rate to improve the welding process performance and mechanical properties of the workpiece. This is a process method for improving the metallographic structure of the welded joint. Usually, during the welding process, uneven temperature distribution of the welded parts and thermal expansion and contraction of the weld metal occur. Therefore, residual stress is bound to be generated along with the welding construction.

9. What is post-weld heat treatment?

Post-weld heat treatment is a heat treatment process carried out to improve the microstructure and properties of the welded joint or eliminate welding residual stress. This treatment process includes quenching, tempering, quenching and tempering, annealing and normalizing. It can not only reduce residual stress, but also adjust the mechanical properties of the welded joint, improve the metallographic structure of the heat-affected zone of the weld metal, enhance the impact toughness and fracture toughness of the welded joint, increase the resistance to stress corrosion, and improve the stability of the structure. However, the influence of post-weld heat treatment on the tensile strength and creep limit of metals is related to the temperature of heat treatment and the holding time. Moreover, the influence of post-weld heat treatment on the impact toughness of the weld metal varies with different steel types.

10. What is pipeline heat treatment?

As most of the pipeline quality accidents that have occurred are due to mistakes in the heat treatment process of pipeline welds, currently, pipeline heat treatment mainly refers to the heat treatment of pipeline welds. The quality control of the heat treatment process plays a very important role in ensuring the welding quality of pressure pipeline projects. Therefore, pipeline heat treatment refers to three parts: preheating before welding, post-heat treatment and post-weld heat treatment. Among them, preheating before welding is an important means to improve the metal welding process performance of the welded parts, preventing the welded parts from cooling too quickly during welding and causing cracks. Post-heat treatment can provide a guarantee for preventing the formation of cold cracks. Post-heat treatment provides conditions for the escape of dissolved hydrogen in the weld seam and is sometimes also called dehydrogenation treatment. Post-weld heat treatment is a fundamental method for improving the metallographic structure and mechanical properties of welded joints and eliminating or reducing welding residual stress.

11. What is solution heat treatment?

Solid solution heat treatment refers to a heat treatment process in which an alloy is heated to a high-temperature single-phase region and held at a constant temperature to allow the excess phase to fully dissolve into the solid solution, followed by rapid cooling to obtain a supersaturated solid solution. The main purpose is to improve the plasticity and toughness of steel and alloys, prepare for precipitation hardening treatment, fully dissolve various phases in the alloy, strengthen the solid solution, and enhance toughness and corrosion resistance, eliminate stress and soften, so as to facilitate further processing or forming. Solution heat treatment is aimed at dissolving the carbides within the matrix to obtain a uniform supersaturated solid solution, which facilitates the re-precipitation of fine and evenly distributed carbides during aging, and at the same time eliminates the stress generated by cold and hot working, causing recrystallization of the alloy. Secondly, solution treatment is aimed at achieving an appropriate grain size to ensure the high-temperature creep resistance of the alloy. The temperature range for solution treatment is approximately between 980 and 1250℃. The selection is mainly based on the phase precipitation and dissolution laws in each alloy and the application requirements to ensure the necessary precipitation conditions for the main strengthening phase and a certain grain size.

12. What is heat treatment of steel?

Heat treatment of steel refers to the process of heating, holding at temperature and cooling solid metals in an appropriate way to obtain the desired microstructure and properties. Heat treatment of steel can not only improve its microstructure and properties, but also enhance its processing performance. More importantly, it is the key process that endows the final performance of the parts. Many parts cannot be used directly after being processed and formed; instead, they must undergo heat treatment before they can be used. Moreover, there are many heat treatment methods for steel. According to the type of process, process name and the method used to achieve heat treatment, they can be roughly divided into overall heat treatment and surface heat treatment. Overall 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 obtain the required metallographic structure and change its overall mechanical properties. There are roughly four basic processes: annealing, normalizing, quenching and tempering. Surface heat treatment mainly includes surface quenching, carburizing, nitriding and carbo-nitriding treatment processes.

13. What is surface heat treatment?

Surface heat treatment refers to a metal heat treatment process that alters the mechanical properties of the surface layer by heating or cooling the surface of steel parts. Surface hardening is the main content of surface heat treatment. Its purpose is to obtain a high-hardness surface layer and a favorable internal stress distribution to enhance the wear resistance and fatigue resistance of the workpiece. It is a metal heat treatment process that strengthens the surface of the workpiece. It is widely used in parts that require both high wear resistance, fatigue strength and large impact load on the surface layer, as well as good plasticity and toughness as a whole, such as crankshafts, camshafts, transmission gears, etc. Surface heat treatment is divided into two major categories: surface quenching and chemical heat treatment.

14. What materials can be heat-treated?

Generally speaking, metal raw materials, especially rigid materials, can all undergo heat treatment. The selection of heat treatment processes should be based on different uses to choose different heat treatments. Generally, when making steel structures, the steel used does not need to undergo heat treatment. However, if bar stock is used to make bearings, heat treatment must be carried out.