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Shanghai Shangpin Electrical Equipment Co.,Ltd (Foreign Trade Center)
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Carburizing Hardening or Induction Hardening?
Induction hardening was first applied to improve the surface hardness of parts to meet the requirements of wear resistance. After several decades of development, induction hardening has developed into the most widely used heat treatment technology, in the automotive, railway, shipbuilding, engineering machinery, machine tools and military industry, and formed a perfect technology and quality system.
Induction hardening to replace carburizing hardening is an important area of its application, based on its outstanding economic and high technical indicators, by the industry's attention. For the comparison of the two heat treatment methods, we would like to analyze the following aspects.
 
Economy
Advanced technology is the lowest cost to meet the needs of the performance, economy is the first consideration of the application of technology factors.
1. Equipment investment
Induction hardening equipment investment is relatively small. Such as medium-sized gear quenching equipment, a gear continuous furnace carburizing line investment of about 800 million, with quenching presses, spreaders and other auxiliary equipment totaling about 15 million yuan. In accordance with the same production capacity comparison, the need for two induction hardening machine, the price of each set of automatic quenching machine about 100 million, only carburizing equipment 10% to 20%. Compared with the multi-purpose furnace, a set of induction hardening machine tool production capacity with at least three multi-purpose furnace, the investment is equivalent to multi-purpose furnace (including auxiliary system) 50%.
The area of the equipment and the installation are also an important part of the cost. Carburizing equipment covers an area of large, the plant's water, electricity, gas requirements are higher, resulting in the production plant needs a larger investment, installation costs are higher. Induction hardening equipment covers an area of small, easy to install, the cost is much less.
2. Production operating costs and production rhythm
Induction hardening production operation costs low, but also its promotion of an important indicator of value. Statistics show that the energy consumption of induction hardening carburizing quenching about 20%, quenching medium consumption is about 30%, equipment maintenance and consumption of spare parts costs about 20%, the production of waste emissions are also very low.
Induction hardening for rapid heating, heating time of a few seconds to tens of seconds, the production cycle is very fast. For reducing labor costs, reduce the WIP rate has an advantage.
3. Heat treatment parts materials
Developed countries have a special induction hardening materials series, but the special material does not mean that high-cost, but to achieve better results and make adjustments. Induction hardening material selection is the most extensive, and because of its unique excellent performance can use low-cost materials to replace the higher cost of carburizing materials. Carburizing treatment of high temperature, long time, need to pay special attention to control its grain growth, so the carburizing steel must contain a certain amount of refined grain alloying elements.
4. After heat treatment
In carburizing and hardening practice, often in the follow-up grinding process appears carburized layer is worn out of the problem, the reason is that the carburized layer is relatively shallow, heat treatment deformation after partial grinding. Compared with the chemical heat treatment such as carburizing, the hardening layer of induction hardening is deeper, which brings greater flexibility to the subsequent processing and reduces the requirement of the pre-heat treatment process, so the processing cost is low and the scrap rate is low.
 
Technical indicators
Carburizing quenching in the surface of the formation of high carbon content of the martensite layer, high hardness, high carbide content, high wear resistance, and the heart is low-carbon martensite, the surface compressive stress, parts Overall toughness. These characteristics make carburizing and quenching widely used in gears and other parts requiring high wear resistance, high fatigue strength and high contact fatigue strength. Induction hardening has the characteristics of rapid heating and rapid cooling, which greatly improves the grain size of the material, and obtains the high toughness index and high performance index.
1. Wear resistance
Carburizing quenching parts with high wear resistance, is due to its surface hardness and carbide. Induction hardening can be achieved at low carbon content of high hardness, wear resistance and its microstructure related.
20CrMnTiH3 carburizing quenching and 45 steel induction quenching made of standard wear samples, hardness 62 ~ 62.5HRC, in the M-200 wear test machine on the test, the grinding parts for the T10 quenching. After 1.6 million wear and tear, carburizing sample weight loss 4.0mg, induction hardening weight loss 2.1mg. What is the mechanism of induction hardened specimens with higher wear resistance, is worth studying.
2. Intensity
It is generally believed that the strength is related to the hardness, and the same hardness can give the same strength. For specific parts, but also with which parameters are linked? We tested 20CrMnTiH3 carburizing hardening and 45 steel, 40CrH, 40MnBH induction hardened standard dumbbell tensile specimens were tested, the effective part of the diameter of 20mm, the measured tensile strength of 819MPa, 1184MPa, 1364MPa, 1369MPa, several carbon steel samples after induction hardening strength was significantly higher than carburizing parts.
Two process results compared. Carburizing quenching sample surface for the high-carbon martensite, infiltration layer 1.25mm, hardness 62 ~ 63HRC, the heart of low-carbon martensite, hardness 32HRC. Induction hardening specimen surface for the middle carbon martensite, hardened layer depth of 3.6mm, hardness 62HRC, heart for the tempered sorbite, hardness 26HRC. Can be found in two ways to get the depth of the surface hardened layer is quite different, induction hardening to get deeper hardening layer, resulting in greater part strength. Therefore, to discuss what kind of strengthening process is better, not only from the micro-perspective, but also from the macro side.
3. Fatigue strength
Carburizing quenching and induction hardening parts after the surface has been effectively enhanced and the formation of a large residual compressive stress, have a high fatigue strength.
Selection of modulus 2.5 gear parts were studied, respectively, using 20CrMnTiH3 carburizing quenching, carburizing depth of 1.2mm; 45 steel, 42CrMo induction hardening, tooth root quenching depth of 2.0mm. Hardness are 61 ~ 63HRC, after grinding through the heat treatment. The test was carried out on a fatigue tester according to the loading pattern shown in Fig. The fatigue limit pressures of three kinds of gears with different materials and heat treatments are 18.50kN, 20.30kN and 28.88kN respectively. 42CrMo induction hardening gear fatigue strength is higher than 20CrMnTiH3 carburizing quenching 56%, with significant advantages. Analysis of its mechanism, need from the hardened layer organization, the surface compressive stress level, heart tissue and hardness and so on.
4. Contact fatigue strength
For gear parts, tooth contact fatigue failure is the main form of failure. Light-load gear on the contact fatigue requirements are relatively low, and induction hardening can replace the specific heavy-duty gear carburizing quenching, the indicator is necessary to assess the content. Our research in this area is not deep enough.
5. Quenching deformation
Carburizing process temperature is high, a long time, quenching deformation. Subsequent grinding procedures will be the highest intensity, the maximum compressive stress surface of the surface thin, resulting in lower part strength. Gear carburizing quenching more and more pressure quenching technology, the purpose is to reduce the quenching deformation. Induction hardening deformation is relatively small, and because the quenching layer thickness, grinding on the hardening depth of the impact is relatively small.
 
Induction Hardening Limitations
Induction hardening process has its special application limitations, which is related to the objective law of the magnetic field distribution, specific analysis of specific parts.
1. Complex cross-section parts
Such as a transmission gear shaft, including multiple gears, multiple steps and bearing bits, using induction hardening process more difficult, cost point of view is not appropriate. There are some hardened area contains sharp parts, induction hardening is very difficult, should use carburizing or other chemical heat treatment.
2. Thin-walled parts
Carburizing hardening can be a thin layer of hardened, low hardness to ensure toughness of the heart. Induction hardening may be due to quenching embrittlement.
3. Small parts
Induction hardening Each part requires loading and unloading, heating, cooling and other steps, for small parts do not have the economy. Carburizing quenching furnace can be installed in bulk, high yield and low cost.
4. One-piece production
Induction hardening requires the production of different parts for different sensors, for small batch production does not have the economic advantage.
 
Some Suggestions on Induction Hardening to Replace Carburizing
In general, the heavy-duty gear induction hardening alternative carburizing hardening research also need to do a lot of work, other parts need to improve the wear resistance and strength can use the appropriate combination of induction hardening process materials substitution.
Induction heat treatment selection. After carburizing the surface of the material for the high-carbon layer, high carbide content, beneficial to wear resistance. Induction heat treatment materials for medium carbon steel and medium carbon alloy steel, wear-resistant parts in alternative carburizing material selection can choose high carbon materials, such as a camshaft using 80 # steel manufacturing, in order to obtain the required performance.
Induction hardened parts require less than carburizing quenching materials, often not be taken seriously. Selection process not only to consider whether it can be quenched to the required hardness and quenching depth, but also on the chemical composition of materials, grain size, impurity and other indicators to be taken seriously, these factors on the performance of parts also have a great impact, Steel is highly treated with induction hardened steel.
Attention to pre-heat treatment. Induction hardening of the heating time is short, too late to homogenize the alloy composition, you need to do the preparatory heat treatment. Induction hardening is usually surface hardening, the heart of the organization and other indicators in the preparatory heat treatment process to ensure.

Shiyan Hengjin induction is professional in the induction hardening solutions. The induction hardening equipment developed and applied in the automotive, railway, shipbuilding, engineering machinery, machine tools and military industries and other fields, induction hardening equipment helps industrial customers to save investment costs and improve production efficiency.


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