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Heat treatment method of nodular iron casting and nodular iron casting obtained by heat treatment method

A heat treatment method and technology of ductile iron, applied in heat treatment equipment, quenching agent, manufacturing tools, etc., can solve problems such as uneven structure of ductile iron castings

Pending Publication Date: 2021-09-07
CRRC QISHUYAN INSTITUTE CO LTD +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0006] The main purpose of the present invention is to provide a heat treatment method for ductile iron castings and the ductile iron castings obtained therefrom, so as to solve the problem of uneven structure of ductile iron castings obtained by alloying methods in the prior art

Method used

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  • Heat treatment method of nodular iron casting and nodular iron casting obtained by heat treatment method
  • Heat treatment method of nodular iron casting and nodular iron casting obtained by heat treatment method
  • Heat treatment method of nodular iron casting and nodular iron casting obtained by heat treatment method

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0046] Non-standard ductile iron casting QT830-2, the product is a box body, the thickest wall thickness is 56mm. The technical scheme adopted is as follows:

[0047] (1) Critical temperature point and phase transition point temperature of QT830-2: Mf is 66°C; Bs is 429°C; Ac1 is 789°C; Ac3 is 845°C; the best dissolution point of carbide is 965°C.

[0048] (2) Heating and high temperature homogenization process: Put the ductile iron castings into the furnace at 30°C, heat for 8h, heat to 450°C and keep it for 2h, continue heating for 6h, heat to 800°C and keep it for 75min, continue heating for 1.5h, and heat to 980°C, keep warm for 42 minutes.

[0049] (3) In the uniform cooling stage, the ductile iron castings are cooled with the furnace for 2 hours, cooled to 880°C and kept for 60 minutes. Then immerse the ductile iron casting in a cooling tank for cooling for 89 seconds, wherein the temperature of the cooling water in the cooling tank is 85°C. Then enter the 600 ° C hea...

Embodiment 2

[0051] Non-standard ductile iron casting QT700-3, the product is a shaft, the maximum wall thickness is 81mm. The technical scheme adopted is as follows:

[0052] (1) Critical temperature point and phase transition point temperature of QT700-3: Mf is 280°C; Bs is 539°C; Ac1 is 791°C; Ac3 is 815°C; the best dissolution point of carbide is 879°C.

[0053] (2) Heating and high temperature homogenization process: Put the ductile iron castings into the furnace at 25°C, heat for 10h, heat to 600°C and keep it for 2h, continue heating for 4h, heat it to 810°C and keep it for 90min, continue heating for 1h, and heat it to 930 ℃, keep warm for 60min.

[0054] (3) In the uniform cooling stage, the ductile iron castings are cooled with the furnace for 3 hours, cooled to 840°C and kept for 90 minutes. Then immerse the ductile iron casting in a cooling tank for cooling for 210 seconds, wherein the temperature of the cooling water in the cooling tank is 90°C. Then enter the 650 ° C heati...

Embodiment 3

[0056] The difference between embodiment 3 and embodiment 1 is that the temperature of water in embodiment 3 is 80°C, and when the ductile iron casting is cooled in a water bath in a static state and a water bath in a stirring state at 80°C, the cooling curve of the cooling water is as follows image 3 ,from image 3 It can be seen from the figure that in the temperature range of 550-850 °C, the cooling rate of 80 °C water at rest is 13-17 °C / s, and the cooling rate of stirring state is 25-29 °C / s. In this temperature range, due to The cooling rate of water is uniform, which is beneficial to the uniform cooling of ductile iron castings, thereby improving the uniformity of hardness, uniformity of structure and regularity of deformation of ductile iron castings.

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Abstract

The invention provides a heat treatment method for a nodular iron casting and the nodular iron casting obtained through the heat treatment method. According to the heat treatment method, the highest heating temperature of the nodular iron casting and the heat preservation time at the temperature are controlled, so that carbide and phosphorus eutectic are eliminated; then, through staged cooling, controlling of the cooling temperature, the heat preservation time and the cooling mode, uniform cooling of the nodular iron casting, especially cooling in a liquid medium of 70-100 DEG C is effectively achieved, thermal stress in a cooling process of the nodular iron casting is reduced, the problem of non-uniform cooling of air cooling, wind cooling and fog cooling is solved, therefore, the hardness uniformity, the structure uniformity and the deformation regularity of the nodular iron casting are improved; in addition, the capacity of obtaining the high pearlite content of the core of the thick and large nodular iron casting and the low-alloy nodular iron casting is effectively improved through the cooling mode, and therefore the structure uniformity of the thick and large nodular iron casting can be improved on the basis that the alloy adding amount of the nodular iron casting is reduced.

Description

technical field [0001] The invention relates to the technical field of processing ductile iron castings, in particular to a heat treatment method for ductile iron castings and the ductile iron castings obtained therefrom. Background technique [0002] Pearlitic ductile iron is a large type of ductile iron in the GB / T 1348-2009 standard. Its matrix structure is mainly composed of ferrite + pearlite or pearlite. The commonly used grades are QT500-7, QT550-5, QT600 -3, QT700-2, etc. For ductile iron castings with ferrite and pearlite as the main structure, the mechanical performance level depends on the ratio of ferrite to pearlite, and the pearlite content is an important factor affecting the strength and fatigue properties of ductile iron castings. In order to obtain high strength and high fatigue performance, it is necessary to ensure a high pearlite content. Usually, the pearlite content in the matrix structure of pearlitic ductile iron castings is required to be no less t...

Claims

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Application Information

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IPC IPC(8): C21D5/00C21D1/60C21D1/18
CPCC21D5/00C21D1/18C21D2211/009C21D11/00C21D11/005Y02P10/20
Inventor 文超晁国强梁会雷高红梅乔建勇
Owner CRRC QISHUYAN INSTITUTE CO LTD
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