In the production of fasteners, in order to facilitate cold heading, the disk is usually drawn and spheroidized. The quality of the spheroidizing annealing will directly affect the quality of the final product. So, as a fastener manufacturer, how to choose a suitable spheroidizing annealing furnace?
Element 1: We need to understand the purpose of spheroidizing annealing:
1. Improve the properties of mechanical materials, reduce the hardness and strength of materials, and improve cold workability;
2. The workpiece is forged at a lower energy and is easy to cut;
3. Reduce mold loss;
4. Avoid splitting and twisting of the workpiece.Element 2: We need to understand the relationship between cold heading performance and spheroidizing quality
1. Deformation resistance:
It is related to the hardness value and tensile strength of the material.
Hardness value deformation resistance
The lower the lower the lower2, deformation energy:
Related to the metallographic structure of the material, such as complete annealing, the normalized tissue deformation is worse than the spheroidized structure. In the spheroidized group, the higher the spheroidization ratio of cementite (Fe3C), the better the deformation energy; and the cementite (Fe3C) is finely dispersed in the ferrite structure, and its deformation energy is the most good.Element 3: We need to understand several indicators that the disk element usually pays attention to after spheroidizing annealing:
1. Surface oxidation 2, surface decarburization;
3. Hardness and hardness uniformity;
4, spheroidization rate 5, metallographic organizationNext, let's analyze the impact of the above indicators on fastener production one by one:
Surface oxidation and decarburization:
Oxidation of the surface of the material causes loss of material (magnification of the machining allowance), which increases production costs (material loss, extended rust removal time). When the surface decarburization is severe, the strength level of the product is lowered, and even waste products are generated.
The key to solving surface oxidation and decarburization is precise control of the furnace atmosphere! Only by precisely controlling the oxygen potential in the atmosphere of the furnace can it be oxidized and slightly decarburized; if it is simply introduced into some gases and cannot be precisely controlled, it will not help solve the problem of surface decarburization and oxidation.
The national standard for surface decarburization is 15 ‰ D. Generally, the surface decarburization can be controlled within 8 ‰ D. When high requirements, the decarburization should be controlled within 0.05 mm or even 0.03 mm.Hardness and hardness uniformity:
When the metal material is subjected to cold heading or cold extrusion, a suitable hardness is required in order to obtain higher yield and lower mold loss. Of course, we need the hardness uniformity (hardness difference) of the same batch of materials at the same time, and control it within the smallest possible range; otherwise, the high and low hardness will seriously affect the production efficiency and result in the yield. Low, the mold life is shortened.
The appropriate hardness and hardness uniformity depends mainly on the uniformity of temperature; and the uniformity of temperature depends firstly on the structure of the spheroidizing furnace: the optimal design of the furnace cover, the furnace shell, the convection bucket, the diversion seat and the convection fan. It can meet the requirements of fluid mechanics; secondly, the choice of protective atmosphere, such as the use of highly reactive reducing gases, accelerates the heat transfer on the metal surface.
Generally, the hardness difference is controlled at 3-5 HRB to meet the production requirements. When the demand is high, the hardness difference should be controlled within 3HRB.Spheroidization rate and metallographic organization
After the steel is rolled and forged, it is air-cooled. The resulting structure is lamellar pearlite and reticulated cementite. This kind of structure is hard and brittle, which is not only difficult to cut, but also easily deformed and cracked during the subsequent quenching process. The spheroidized annealing results in a spherical pearlite structure in which the cementite is spherical particles dispersed in the ferrite matrix. Compared with the flaky pearlite, it has low hardness, is easy to be cut, and is quenched. When heated, austenite grains are not easily grown, and the tendency of deformation and cracking of the workpiece during cooling is small. Therefore, when the formed part has a large amount of deformation, the material needs to have a higher level of spheroidization rate and a good metallographic structure. Otherwise, it will cause problems such as difficulty in forming parts and low qualification rate.
The spheroidization rate and the quality of the metallographic structure are related to the structure and annealing process of the spheroidizing furnace; in terms of structure, there must be a good atmosphere circulation system, a forced cooling device capable of program control, and a high efficiency capable of controlling the heating rate. The heating device; the annealing process should be designed according to the material of the material, the manufacturer of the material, the use, etc., such as the heating rate and the cooling rate.
Usually the spheroidization rate is controlled at 4.5-6 (according to Japanese JIS G3539 standard, the highest level is 6)In addition to the above technical indicators, when choosing a spheroidizing annealing furnace, we also need to put forward some requirements for the spheroidizing annealing furnace itself:
1. Sealing performance (how much pressure can be maintained in 48 hours of production?)
2. Energy-saving measures (surface temperature rise, heating efficiency, waste heat utilization, energy consumption)
3, intelligent (heat treatment expert system, remote control, process curve recording, fault alarm, atmosphere control, air-fuel ratio automatic adjustment)
4. Quality and brand of materials used in the manufacture of spheroidizing furnacesIn a nutshell, the quality of spheroidizing annealing is closely related to the structure of the furnace, atmosphere control, automatic control, and annealing process design. In actual production, the reasons for the above analysis are not generated separately, but will interact. Therefore, when selecting a spheroidizing annealing furnace, you can refer to the above points for comparison selection.
Attached: Â
Haiyan Huachen exports spheroidizing annealing furnace loading and transportation in Algeria
brief introduction:
Heating method: electricity, oil, gas (natural gas) heatingFeatures: a composite of well and bell-type furnaces, with a simple operation of the pit furnace and excellent quality of the bell-type furnace
Protective atmosphere: nitrogen, methanol decomposition gas
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