Methods to reduce costs in heat treatment processes

Thread Content

Generally, when carrying out heat treatment processes, determining the appropriate processing time, achieving an optimal heat treatment effect on the workpiece without wasting energy is a technical task. The holding time is usually calculated based on the technician’s experience and the thickness of the workpiece; in batch production, it is determined based on practical experience and by observing the color of the workpiece in the fire. This is mainly evident in carbon steel and low-alloy steel; carbon steel contains no alloying elements or carbides, so it does not require prolonged heating. The heat transfer coefficient of low-alloy steel is similar to that of carbon steel, and the cooking time required for the workpiece is mainly determined by its size. During the heat treatment of individual products, once the furnace temperature reaches the set value for the process, the workpiece has already been fully heated; there is no need to extend the holding time, which is what we refer to as \"zero\" holding time for heating. During mass production, the furnace is usually heated first; once it reaches the desired temperature, the workpieces are placed inside. After another period of time corresponding to the required processing time, a homogenization step is carried out for a certain duration, which helps to reduce the processing cycle, save energy, and lower costs. Alloy structural steel contains alloying elements, and during heat treatment it is necessary to allow the carbides to become homogeneous over a certain period of time – a longer period than in carbon steel.     In actual production, workpieces made of different materials but with roughly similar processing parameters can be processed together in the same furnace; for example, Cr12MoV, 8407, H13, 40Cr, and 42CrMo, all of which require similar quenching temperatures.      Similarly, when the tempering temperature is the same, different parts and materials can also be placed in the same furnace, with the tempering time being set to the longest duration.     Similar charging methods can significantly save energy and reduce costs.     Choosing an aqueous solution as the quenching medium helps to avoid the situation where oil quenching of large-diameter medium-carbon low-alloy steel fails to achieve the desired hardness levels, as well as the tendency to cracking that occurs with water quenching.     Water-soluble synthetic quenching fluids are suitable for quenching low- and medium-carbon steels, with the concentration being adjusted to control the cooling rate. Quenched workpieces remain shiny and are resistant to rust for a short period. They can be tempered directly without cleaning. They produce no smoke or oil fumes, are not prone to aging or deterioration, have a long service life, and are relatively inexpensive compared to oil.     The tempering process is determined by the tempering temperature of the part; usually, experience is used to take advantage of the residual heat in the furnace. The tempering temperature of the part is about 300 degrees lower than the residual heat temperature of the furnace, and once the workpiece is placed in the furnace, it quickly reaches the temperature required for the tempering process. Multiple temperings are better than a single tempering; in mass production, the microstructural properties obtained through secondary tempering are superior to those achieved with a single tempering, while costs are significantly reduced.      During production, regular maintenance and inspections of the equipment should be carried out to minimize losses resulting from shutdowns caused by electrical failures. Maintain related equipment such as trolleys and cranes to reduce losses caused by difficulties in loading and unloading from the furnace. The heat treatment process for workpieces is itself an energy-saving activity; without proper heat treatment, the service life of the parts will be very short. Extending their service life also constitutes an effort to save energy. Here are the insights of heat treatment technicians on reducing costs in heat treatment: (1) 1. Use periods when electricity prices are low to raise the temperature.   2. Load the workpiece into the furnace at high temperature.   3. Continuous operation is required to make full use of the residual heat in the furnace.   4. The furnace body is manufactured using advanced insulation materials.   5. Focus on process optimization by using normalizing instead of quenching and tempering wherever possible.  (II) 1. According to the requirements and conditions of the parts, select a higher quenching temperature as much as possible to reduce the holding time. For 40Cr round bars that have been quenched and tempered (or similar low-alloy structural steels), it is possible to directly quench them in water after they reach the desired temperature in a box furnace, without causing cracking. 2. The well-type furnace has good temperature uniformity during tempering, which allows for higher tempering temperatures and a shorter holding time. This requires extensive practical experience. However, based on the production conditions, the relationships between the loading amount per furnace, the hardness after quenching, as well as the tempering time and temperature can be determined through testing.  3. For single-piece tempering, high-temperature tempering is recommended. Tempering can be carried out directly at the furnace temperature after quenching; it is recommended that operators gain experience in such tasks over time. 4. For ordinary carburized parts for which high requirements are not imposed, the carburizing temperature can be increased to 950 degrees or higher, followed by sub-temperature quenching.  5. It is best to use all-fiber material for box furnaces, with an infrared coating applied on the inside to increase the heating speed. (III) 1. Select an appropriate material based on the working conditions of the part, including the type and magnitude of the loads, the environmental conditions, and the main failure modes.  2. Consider factors such as the structure, shape, and size of the workpiece in order to select appropriate heat treatment processes and parameters. 3. It is necessary to understand the microstructure and properties of the material after heat treatment; for example, some materials developed specifically for certain heat treatment processes exhibit improved microstructure and properties after such treatment, such as the 38CrMoAl alloy steel suitable for nitrogen treatment. 4. While ensuring performance and service life, heat treatment processes that can be simplified should be preferred as much as possible, especially materials that help save energy; for example, using non-quenched and tempered steel or low-carbon steel in place of medium-carbon quenched and tempered steel. 5. Make use of mechanical and highly automated process equipment wherever possible; this not only improves labor productivity but also facilitates control over the processing steps, ensures stable and reliable quality in heat treatment, and reduces costs. 6. Implement strict management and quality control over the materials and equipment used in heat treatment processes.