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Alloy carburizing steel pretreatment method for changing network ferrites and acicular ferrites in microstructure

A technology of alloy carburizing steel and acicular ferrite, which is applied in the field of alloy carburizing steel pretreatment to change the reticular acicular ferrite in the microstructure, can solve the problems of large hardness fluctuation, coarse microstructure, and inability to Solve problems such as reasonable grain size, easy subsequent cutting, and ensure stability

Active Publication Date: 2018-03-30
刘澄 +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0013] 1. It is impossible to completely eliminate reticular and acicular ferrite, and obtain 100% massive ferrite and pearlite;
[0014] 2. The cutting performance cannot be guaranteed;
[0015] 3. The problem of coarse microstructure cannot be solved;
[0016] 4. The problem of large fluctuations in hardness cannot be solved

Method used

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  • Alloy carburizing steel pretreatment method for changing network ferrites and acicular ferrites in microstructure
  • Alloy carburizing steel pretreatment method for changing network ferrites and acicular ferrites in microstructure
  • Alloy carburizing steel pretreatment method for changing network ferrites and acicular ferrites in microstructure

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0052] Example 1: Test Part No. #1

[0053] Adopting the heat treatment process of fast cooling and slow cooling after forging and rolling, and then holding for a certain period of time (see the following processing steps), without precise control of the process steps, it can be verified that the coarse forging grains affect the microstructure of the parts after pretreatment Impact. Since no multi-stage precise control was adopted, the forging was stopped and quickly cooled to 750 degrees, then air-cooled to 600 degrees, and then placed in a holding furnace at 620 degrees for 66 minutes of heat preservation.

[0054] The specific holding temperature (and holding time) of the above process at different stages and the control range of cooling speed at different stages are as follows:

[0055] T3=750°C, T9=600°C, T10=620°C;

[0056] t3=5sec, t9=5sec, t10=66min,

[0057] v3=1.62°C / sec, v9=1.41°C / sec, v10=0.11°C / sec v11=0.15°C / sec.

[0058] Such as Image 6 As shown, what is o...

Embodiment 2

[0059] Example 2: Test Part No. #2

[0060] With a partially improved heat treatment process (see treatment steps below), without precise control of all process steps, it can be found that the influence of coarse forging grains on the microstructure is improved (reticular ferrite begins to thicken). However, there are still a considerable amount of abnormal reticular ferrite that has not had time to become massive, and there is acicular ferrite (Widmanite) inside the reticular ferrite grains (such as Figure 7 shown). The hardness is HB198, and the grain size is grade 3. It is still higher than the requirements of conventional gear blanks (HB160-190, grain size 5-8), and at the same time, the acicular ferrite (or "Widmanite") formed inside a large number of grains will cause subsequent carburization The heat-treated tissue genetics still cannot meet the customer's standard requirements.

[0061] The specific holding temperature (and holding time) of the above process at dif...

Embodiment 3

[0065] Example 3: Test Part No. #3

[0066] By adopting the high-efficiency heat treatment method of the present invention (see the following treatment steps and precise control parameters), all process steps are precisely regulated, and the adverse effects of coarse forging grains on the microstructure are completely improved. Such as Figure 8 As shown, the existence of network and acicular ferrite is completely eliminated, and 100% block ferrite and pearlite can be obtained. The hardness is HB171, and the grain size is 6 grades, which has met the customer's requirements for the microstructure and hardness of the gear blank in all aspects (HB160-190, grain size 5-8 grades). Since there is no non-equilibrium microstructure, it will not bring tissue genetic damage to the heat treatment after carburizing, so it can be used to replace the existing discontinuous heat treatment method to achieve the dual goals of organizational performance and energy saving.

[0067] The specifi...

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Abstract

The invention discloses an efficient and energy-saving pretreatment method for changing network ferrites and acicular ferrites in an alloy carburizing steel pretreatment microstructure. A forged-rolled alloy carburizing steel part is continuously subjected to primary cooling and heat insulation, at least one one-time intermediate cooling and heat insulation, and last-time cooling and heat insulation, and finally cooled to achieve a pearlite transformation temperature zone of the equilibrium phase diagram of the alloy carburizing steel part. According to the alloy carburizing steel part preheating treatment method disclosed by the invention, network proeutectoid ferrites and proeutectoid ferrites with other non-block morphologies in the alloy carburizing steel pretreatment microstructure are changed into block ferrites, so that control for the subsequent cutting machining, and carburizing and quenching deformation for the part is facilitated; and the method is simple in procedures and capable of greatly saving energy.

Description

technical field [0001] The invention belongs to the technical field of thermal processing of structural materials, in particular to an alloy carburizing steel pretreatment method for changing the reticular acicular ferrite in the microstructure. Background technique [0002] For a long time, high energy consumption and high time consumption have always been a problem in the field of thermal processing and preparation of structural materials? How to efficiently use the temperature at different stages in the thermal processing process, and reasonably solve the various microstructures and properties required in the phase transition process, so as to not only ensure and improve the quality of the product, but also reduce costs, and become green and environmentally friendly. The most important problems that the manufacturing industry needs to solve most urgently. [0003] Taking the carburized gears of automobiles as an example, at present, they have to go through several high-e...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C21D6/00
CPCC21D6/00C21D2211/005C21D2211/009
Inventor 刘澄赵振波
Owner 刘澄
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