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Comparison of Fastener Pre-heat Treatment Normalizing and Annealing Process
by：Fortuna
2021-04-28
Green manufacturing is an important strategy for achieving sustainable development of the machinery manufacturing industry. Normalizing and annealing in the pre-heat treatment of fasteners are the two most commonly used processes, accounting for about 30% of the heat treatment of fasteners. Although these two process methods have their own different characteristics in process, they can achieve the same (or similar) process goals when dealing with low-carbon steel or medium-carbon steel materials.
According to GB/T16923-1997 'Normalizing and Annealing of Steel Parts, The technical requirements are the most the same (or similar).
1. Function
According to the low carbon steel or medium carbon steel used in the fasteners, normalizing is to heat the steel to 30～70℃ above Ac3, and then air-cooled or air-cooled to room temperature; incomplete annealing or isothermal annealing is to The steel is heated to about 30-50°C above Ac1, after holding it for a certain period of time, it is cooled to a certain temperature with the furnace and then air cooled to room temperature. They are similar or similar in that they can treat medium carbon steel and low carbon steel, and the metallographic structure obtained by the treatment is ferrite + pearlite, which can be used as a preliminary heat treatment or final heat treatment under certain circumstances. So as to achieve the purpose of refining the structure, improving the mechanical properties and cutting performance, and eliminating internal stress.
2. Process characteristics comparison
a. The grains after normalizing are smaller than the annealed ones, and more pearlite is obtained, and the mechanical properties are slightly higher than that of annealing;
b. Normalizing parts are often charged into the furnace, the heating temperature is generally slightly higher than that of annealing, and the holding time is shorter than that of annealing;
c. Normalizing can eliminate the network structure of carbides, but annealing cannot;
d. Normalizing treatment of carbon steel with lower carbon content is better than annealing, and vice versa, annealing is better than normalizing.
3. Process cost (Guide: Development direction and trend of vapor phase rust prevention technology for fasteners)
The comparison between normalizing and annealing mainly exists in the power consumption of resources, the difference in heat preservation and cooling in terms of time, and the corresponding cost difference.
The energy cost is 0.542Kw.h.Kg for normalizing and 0.580Kw.h.Kg for annealing in the domestic heat treatment industry evaluation unit consumption value. The industrial electricity cost is calculated as 0.70 yuan/Kw.h, and the average cost of annealing electric energy is calculated. The difference is 0.03 yuan/Kg.
The labor cost is about 1 yuan/Kg according to the lowest price of normalizing processing in various places in China. The labor cost of the normalizing process is about 0.32 yuan/Kg, and the labor cost of the annealing process is about 0.35 yuan/Kg, the difference is It is about 0.03 yuan/Kg.
The price difference between normalizing and annealing heat treatment in the same area in China is about 0.2 yuan/Kg. In fact, after a specific analysis of the price difference, it can be seen that the price difference is still based on the traditional heating method and the larger production batches.
4. Process evaluation
When the requirements of manufacturing fasteners and processing technology are basically the same, the normalizing process is more green than the annealing process, which is mainly reflected in the energy consumption and processing man-hours.
low temperature annealing (stress relief annealing): heating temperature Recrystallization annealing: heating temperature TR+150～250℃, holding time 0.5～1h, air cooling, recovery recrystallization process occurs, deformed grains are fine equiaxed grains, eliminating cold work hardening effect and internal stress. The annealing temperature for recrystallization of low carbon steel is 600～650℃ and the hardness is in the range of 75～90HRB.
Incomplete annealing: heating temperature Ac1+30～50℃, carbon steel is generally between 700～750℃, to refine grain, reduce hardness, improve plasticity, and remove internal stress.
Spheroidizing annealing: The heating temperature is slightly higher than Ac1, and then slowly cooled to less than 500°C after long-term heat preservation. Air cooling can spheroidize the carbides and reduce the hardness to improve the cold upsetting performance.
Normalizing: Low-carbon and medium-carbon steel heating temperature Ac3+ (50～70℃), low-carbon steel increases hardness, which is good for cutting, medium-carbon steel refines grains, and uniformly organizes stress relief.
Application examples:
Such as: 20# steel three-point welding gasket, using 850℃0.5h normalizing and 720℃3h incomplete annealing, hardness 125～165HBW is basically similar, normalizing saves production cycle and high efficiency than incomplete annealing.
SWRM15 steel single-sided rivets are normalized at 840°C for 0.5h and recrystallization annealing at 600°C for 4h. The hardness of the former is greater than 95HRB, and the hardness of the latter is 78～88HRB to meet the requirements of riveting performance.
45 steel large washers, when the hardness requirement is greater than 200HV, normalizing at 870℃ for 1h is better than incomplete annealing at 760℃ for 2.5h. The hardness can reach more than 200HV, and the productivity is significantly higher than annealing.
According to statistics, the cost difference between normalizing and annealing processes is 0.2 yuan/Kg～0.45 yuan/Kg. If the normalizing process is properly selected instead of the annealing process, it can help fastener companies to achieve green manufacturing at the same time. Comes considerable economic benefits.
In short, with the development of the fastener industry and the promotion of advanced technology, energy saving and consumption reduction will be in the first place, and the green characteristics of the normalizing process will be more obvious and prominent compared to the annealing process.
More related stamping hardware machinery industry news:
According to GB/T16923-1997 'Normalizing and Annealing of Steel Parts, The technical requirements are the most the same (or similar).
1. Function
According to the low carbon steel or medium carbon steel used in the fasteners, normalizing is to heat the steel to 30～70℃ above Ac3, and then air-cooled or air-cooled to room temperature; incomplete annealing or isothermal annealing is to The steel is heated to about 30-50°C above Ac1, after holding it for a certain period of time, it is cooled to a certain temperature with the furnace and then air cooled to room temperature. They are similar or similar in that they can treat medium carbon steel and low carbon steel, and the metallographic structure obtained by the treatment is ferrite + pearlite, which can be used as a preliminary heat treatment or final heat treatment under certain circumstances. So as to achieve the purpose of refining the structure, improving the mechanical properties and cutting performance, and eliminating internal stress.
2. Process characteristics comparison
a. The grains after normalizing are smaller than the annealed ones, and more pearlite is obtained, and the mechanical properties are slightly higher than that of annealing;
b. Normalizing parts are often charged into the furnace, the heating temperature is generally slightly higher than that of annealing, and the holding time is shorter than that of annealing;
c. Normalizing can eliminate the network structure of carbides, but annealing cannot;
d. Normalizing treatment of carbon steel with lower carbon content is better than annealing, and vice versa, annealing is better than normalizing.
3. Process cost (Guide: Development direction and trend of vapor phase rust prevention technology for fasteners)
The comparison between normalizing and annealing mainly exists in the power consumption of resources, the difference in heat preservation and cooling in terms of time, and the corresponding cost difference.
The energy cost is 0.542Kw.h.Kg for normalizing and 0.580Kw.h.Kg for annealing in the domestic heat treatment industry evaluation unit consumption value. The industrial electricity cost is calculated as 0.70 yuan/Kw.h, and the average cost of annealing electric energy is calculated. The difference is 0.03 yuan/Kg.
The labor cost is about 1 yuan/Kg according to the lowest price of normalizing processing in various places in China. The labor cost of the normalizing process is about 0.32 yuan/Kg, and the labor cost of the annealing process is about 0.35 yuan/Kg, the difference is It is about 0.03 yuan/Kg.
The price difference between normalizing and annealing heat treatment in the same area in China is about 0.2 yuan/Kg. In fact, after a specific analysis of the price difference, it can be seen that the price difference is still based on the traditional heating method and the larger production batches.
4. Process evaluation
When the requirements of manufacturing fasteners and processing technology are basically the same, the normalizing process is more green than the annealing process, which is mainly reflected in the energy consumption and processing man-hours.
low temperature annealing (stress relief annealing): heating temperature
Incomplete annealing: heating temperature Ac1+30～50℃, carbon steel is generally between 700～750℃, to refine grain, reduce hardness, improve plasticity, and remove internal stress.
Spheroidizing annealing: The heating temperature is slightly higher than Ac1, and then slowly cooled to less than 500°C after long-term heat preservation. Air cooling can spheroidize the carbides and reduce the hardness to improve the cold upsetting performance.
Normalizing: Low-carbon and medium-carbon steel heating temperature Ac3+ (50～70℃), low-carbon steel increases hardness, which is good for cutting, medium-carbon steel refines grains, and uniformly organizes stress relief.
Application examples:
Such as: 20# steel three-point welding gasket, using 850℃0.5h normalizing and 720℃3h incomplete annealing, hardness 125～165HBW is basically similar, normalizing saves production cycle and high efficiency than incomplete annealing.
SWRM15 steel single-sided rivets are normalized at 840°C for 0.5h and recrystallization annealing at 600°C for 4h. The hardness of the former is greater than 95HRB, and the hardness of the latter is 78～88HRB to meet the requirements of riveting performance.
45 steel large washers, when the hardness requirement is greater than 200HV, normalizing at 870℃ for 1h is better than incomplete annealing at 760℃ for 2.5h. The hardness can reach more than 200HV, and the productivity is significantly higher than annealing.
According to statistics, the cost difference between normalizing and annealing processes is 0.2 yuan/Kg～0.45 yuan/Kg. If the normalizing process is properly selected instead of the annealing process, it can help fastener companies to achieve green manufacturing at the same time. Comes considerable economic benefits.
In short, with the development of the fastener industry and the promotion of advanced technology, energy saving and consumption reduction will be in the first place, and the green characteristics of the normalizing process will be more obvious and prominent compared to the annealing process.
More related stamping hardware machinery industry news:
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