To form metals into various shapes, they must possess excellent mechanical and physical properties. Therefore, metals need to undergo a series of structured production procedures. Heat treatment is one of the most critical production processes in metal casting technology.
As we all know, metals have an extremely wide range of applications. From essential automotive parts to agricultural components, they can be manufactured into diverse forms. However, when metals are shaped, their internal particles interact with each other, which changes their mechanical properties. Heat treatment is the core method to maintain the desired properties of metals.
Like other foundries, Zhaoyuqi has also developed various heat treatment process technologies. This article will introduce the different heat treatment processes adopted by Zhaoyuqi. Additionally, we will discuss why heat treatment is necessary for metal casting and how it modifies the mechanical and physical properties of metals.
The controlled process of heating and cooling metals is generally referred to as heat treatment. Technically, this controlled heating and cooling process does not alter the original shape of the metal, but it changes its physical and mechanical properties. Therefore, the term "heat treatment" specifically refers to heating and cooling processes whose primary purpose is to modify the properties of metals.
As the name implies, heat treatment involves extreme temperature conditions and is sometimes also called metal cold treatment (here, "cold treatment" refers to a special process within the broad scope of heat treatment, not treatment at room temperature). Depending on specific requirements, the heat treatment process can either strengthen or soften metals. The most common heat treatment techniques include annealing, normalizing, quenching, and tempering.
Furthermore, heat treatment can enhance the strength of metals, facilitate more efficient subsequent machining, and improve the formability of metals. Moreover, the cooling stage of the heat treatment process can restore the ductility of metals. In some manufacturing processes, enterprises prefer to use heat treatment as an initial production step, and the production of Zhaoyuqi's products is a typical example.
Zhaoyuqi is one of the most renowned stainless steel casting companies worldwide. We commit to meeting all strength specifications required by customers. In terms of heat treatment procedures, we adopt the most advanced technologies to ensure the optimal quality of stainless steel castings. Therefore, we warmly welcome customers to inquire about quotations regarding any metal properties required for their specific applications.
The basic principle of heat treatment for steel consists of three stages: heating, holding (soaking), and cooling. Process parameters are usually adjusted according to customer requirements to ensure quality while controlling costs. The specific process is as follows:
Heating → Holding → Cooling
During the heat treatment process, heating is the most energy-consuming stage. Radiation heating, induction heating, and salt bath heating are the three most commonly used heating methods at present. The production team of Zhaoyuqi selects a specific heating method based on actual requirements to ensure that the heating process is fast and uniform, while achieving precise control and cost savings.
The holding process refers to the heat preservation operation that brings cast steel to an austenitized state. Austenitization is a heat treatment process for steel that enhances material performance. The holding temperature for this process is usually controlled near a specific reference temperature.
Holding (also known as heat insulation) is one of the most crucial stages in heat treatment. During this stage, operators must ensure that the temperature of the casting's surface and core remains consistent, while also maintaining the uniformity of the casting's internal structure.
Different cooling rates cause different metallographic structure changes in metals and help achieve specific performance indicators. Sometimes, increasing the cooling rate can help metals form an ideal organizational structure and restore grain integrity, thereby enabling metals to obtain better mechanical properties.
All components produced by Zhaoyuqi undergo heat treatment, thus possessing excellent hardness and ultra-high durability. Thanks to their outstanding durability, Zhaoyuqi's components occupy a leading position in the steel component market. Our success stems from our commitment to product quality—from heat treatment processes to investment casting and sand casting, high-standard production procedures are adopted in every link.
The heat treatment process has a crucial impact on the overall quality of castings. It not only improves the strength of metals, reduces brittleness but also enhances the toughness of steel. In addition to these, heat treatment also offers the following significant advantages:
Relieves internal stress in metals and improves machinability;
Endows metals with wear-resistant properties;
Enhances the electrical and magnetic properties of metals;
Makes Zhaoyuqi's components harder and more robust, ultimately extending their service life.
As mentioned earlier, the basic heat treatment process includes three stages: heating, holding, and cooling. However, heat treatment can be divided into various types based on differences in holding temperature and cooling time.
According to different processing procedures, the seven most commonly used heat treatment processes at Zhaoyuqi are: annealing, normalizing, quenching, tempering, solution and aging treatment, precipitation strengthening treatment, and stress relief treatment.
Annealing refers to the process in heat treatment where metals are heated above the critical point or recrystallization temperature, followed by slow cooling in a heat treatment furnace. This method typically involves holding the steel in the heat treatment furnace for several hours.
Generally, annealing can be divided into four types based on the composition of the steel and actual requirements: full annealing, spheroidizing annealing, isothermal annealing, and stress relief annealing. Through annealing, the strength and flexibility of steel can be improved, and internal stress can be eliminated.
Normalizing is very similar to annealing in terms of heat treatment principles; the only difference lies in the cooling method: annealing involves slow cooling inside the heat treatment furnace, while normalizing involves cooling in the air outside the furnace.
The normalizing process requires heating the steel to a temperature 30-50°C above AC3 (the upper critical point of hypoeutectoid steel) or ACM (the upper critical point of hypereutectoid steel). Here, AC3 and ACM are specific temperature critical points for different types of steel, which need to be determined based on the steel's composition.
Therefore, products treated by normalizing will exhibit different performance characteristics after cooling in different environments (such as air environments with different temperatures and humidity levels).
Similar to other heat treatment methods, quenching also involves heating and cooling metals in a heat treatment furnace, but the process is relatively simpler. During quenching, the heating temperature of the metal needs to be controlled between the recrystallization temperature and the melting point.
Depending on specific application scenarios, different quenching media are used for steel quenching. Air, oil, water, and brine are the most commonly used media in this process.
Zhaoyuqi adopts modern technology for quenching. Quenching can significantly increase the hardness of steel, but it also increases its brittleness; however, it can enhance the steel's ability to withstand vibration and wear. Since steel is extremely sensitive to the process parameters of quenching, operators must strictly control every link to avoid errors.
After the quenching process, metals usually need to undergo tempering. The tempering process involves further heating the metal to below the recrystallization temperature and holding it for several hours. Through tempering, the internal stress of the metal (or steel) can be reduced, and its flexibility can be improved. Generally, all steel casting tools need to undergo tempering.
In addition, tempering can be divided into three types: low-temperature tempering, medium-temperature tempering, and high-temperature tempering. Among these, the process of high-temperature tempering after quenching is usually referred to as "modulating treatment" (a combined process of quenching + high-temperature tempering).
The four heat treatment processes mentioned earlier are applicable to various types of metals. Solution and aging treatment specifically refer to the process of dissolving carbides and other precipitates in metals into a solid solution to obtain a single-phase organizational structure. This process is most commonly used for the treatment of stainless steel and manganese steel. However, the following three heat treatment processes are specifically designed for stainless steel.
When stainless steel and manganese steel undergo solution treatment, the required temperature usually ranges from 1000°C to 1250°C. The specific temperature range needs to be adjusted based on the carbon content in the steel.
Precipitation hardening stainless steel (referred to as PH stainless steel for short) is a type of high-tensile-strength stainless steel commonly used in the petroleum, natural gas, and aerospace industries. The application of such stainless steel usually requires its tensile strength to reach 850 MPa to 1700 MPa, which needs to be achieved through precipitation strengthening treatment.
During the precipitation strengthening treatment process, a certain amount of elements such as copper, molybdenum, aluminum, and titanium are added to achieve precipitation hardening (i.e., reaching the PH state). Martensitic stainless steel and austenitic stainless steel are the most common types of materials that adopt this heat treatment process.
As the name suggests, stress relief treatment technology is mainly used to eliminate internal stress generated in metals during casting, quenching, and machining processes, thereby helping to stabilize the structure of castings. The treatment temperature for this process is usually controlled between 100°C and 200°C, which is lower than AC1 (the lower critical point of steel). Before placing the casting into the heat treatment furnace for cooling, it needs to be held at this temperature for a short period.
Castings made of carbon steel, low-alloy steel, and high-alloy steel are most suitable for this stress relief heat treatment method.
Heat treatment is an indispensable basic step in both investment casting and sand casting processes. According to different product requirements, Zhaoyuqi adopts specific heat treatment processes. A well-designed heat treatment process can ensure that steel possesses excellent strength, durability, and flexibility. To accurately achieve various heat treatment effects, Zhaoyuqi continuously introduces the latest technologies to provide customers with product solutions that meet diverse needs.
Professional technical research and development team to provide customers with the best solution.
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