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Method for thinning crystalline grain of large low alloy cast

A low-alloy and casting technology, which is applied in the fields of refining the grain size of large-scale low-alloy castings and controlling the grain size of large-scale low-alloy castings, can solve the problems of difficulty in realizing large-scale castings, burning deformation of castings, and difficulty in practical operation, and achieves cost-effectiveness. Inexpensive, avoid burning and deformation of castings, and improve competitiveness

Active Publication Date: 2012-08-29
INST OF METAL RESEARCH - CHINESE ACAD OF SCI
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0004] However, even with multiple cycles of heat treatment, there are still many problems in the actual production operation of large low-alloy castings. On the one hand, due to the large size of large castings, multiple cycles of austenitization process consume a lot of energy and cause castings to burn The deformation is serious, which makes the actual operation very difficult; on the other hand, multiple cycles of austenitization treatment often require rapid heating of the casting to cause a large number of nucleation during austenitization, and at the same time require short-term heat preservation to reduce austenite crystals. However, these requirements are almost difficult to achieve in the production process of large castings

Method used

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  • Method for thinning crystalline grain of large low alloy cast
  • Method for thinning crystalline grain of large low alloy cast
  • Method for thinning crystalline grain of large low alloy cast

Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0035] figure 1 It is a three-dimensional modeling drawing of a large casting made of 35CrNiMo. The entire casting is about 5000mm long, 1900mm wide, with a maximum wall thickness of about 600mm and a gross weight of about 50 tons. Castings not only have strict requirements on the conventional mechanical properties of materials, but also require that the overall grain size of castings should not be thicker than ASTM 7.5 grade.

[0036] figure 2 From the CCT diagram of the 35CrNiMo material used for this casting, it can be seen that the A3 point temperature of this steel type is 806 °C. After austenitization, if the cooling rate is between 0.02°C / s and 0.5°C / s, bainite transformation occurs; when the cooling rate is greater than 0.5°C / s, martensitic transformation occurs; the cooling rate is less than Pearlite phase transformation occurs at 0.02°C / s.

[0037] On the basis of accurately measuring the thermophysical parameters of the relevant materials and the surface heat tr...

Embodiment 2

[0042] The difference from Example 1 is:

[0043] A large casting made of 55NiCrMoV has a length of about 4000mm, a width of about 1500mm, a maximum wall thickness of about 400mm, and a gross weight of about 30 tons. Castings not only have strict requirements on the conventional mechanical properties of materials, but also require that the overall grain size of castings should not be thicker than ASTM 7.5 grade.

[0044] A 3 Above 30-80°C (this embodiment is A 3 For the austenitizing treatment above 40°C), the cooling method is furnace cooling. At this time, the grain size of the material is about 35.16 μm, and the grain size is 6.2. Then carry out tempering treatment, the tempering temperature of this embodiment is 630 ℃, and the holding time is calculated by increasing 1.5-2 hours for every increase of 25mm in effective wall thickness;

[0045] The second austenitizing temperature is at A 3 Above 30-50°C (this embodiment is A 3 Above 30°C), oil cooling is used to contro...

Embodiment 3

[0047] The difference from Example 1 is:

[0048] A large casting made of 42CrMo has a length of about 4500mm, a width of about 1700mm, a maximum wall thickness of about 450mm, and a gross weight of about 40 tons. Castings not only have strict requirements on the conventional mechanical properties of materials, but also require that the overall grain size of castings should not be thicker than ASTM 7.5 grade.

[0049] A 3 Above 30-80°C (this embodiment is A 3 For the austenitizing treatment above 60°C), the cooling method is air cooling. At this time, the grain size of the material is about 30.84 μm, and the grain size is 6.8 grade. Then carry out tempering treatment, the tempering temperature of this embodiment is 680 ℃, and the holding time is calculated by increasing 1.5-2 hours for every increase of 25mm in effective wall thickness;

[0050] The second austenitizing temperature is at A 3 Above 30-50°C (this embodiment is A 3 Above 50°C), the oil-cooled sample is used ...

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Abstract

The invention relates to a method for thinning a crystalline grain of a large low alloy cast based on computer simulation, material continuous cooling transformation curve measurement and material phase change mode control, and belongs to the field of steel and iron metallurgy. The method comprises the steps as follows: firstly, measuring a continuous cooling curve of a related cast material and determining the critical cooling rate of the material with martensite, bainite and pearlite phase change; secondly, building a corresponding cast model, and determining the cooling rate of the parts of the cast under different cooling mediums by a way of computer simulation; and lastly, heating the cast to be A3<+> (30-80 DEG C) for austenitizing at first, slowly cooling to be room temperature, enabling the cast to be subjected to diffusion or semi-diffusion phase change, after that, heating the cast to be A3<+> (30-50 DEG C) for austenitizing, selecting a proper cooling way according to simulation calculation, enabling the cast to be subjected to bainite phase change, and thinning the crystalline grain of the cast to be below the ASTM (American Society for Testing Material) standard crystalline grain size 7.5 through the semi-diffusion bainite phase change.

Description

technical field [0001] The invention relates to a method for controlling the grain size of large-scale low-alloy castings, in particular to a method for refining the grain size of large-scale low-alloy castings based on computer simulation, measurement of material continuous cooling transition curves and material phase transition mode control, and belongs to the field of iron and steel metallurgy . Background technique [0002] Large-scale castings are important structural components in power station equipment, large-scale metallurgy, and mining equipment. With the enlargement of major engineering equipment and the extreme service environment, the size of related castings is gradually increasing and the performance requirements are becoming more and more stringent. Therefore, in order to improve the performance of large castings, optimizing the casting process of castings to reduce internal defects, optimizing casting materials and microstructure has become an important dir...

Claims

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Application Information

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IPC IPC(8): C21D6/00
Inventor 王培叶中飞李殿中李依依
Owner INST OF METAL RESEARCH - CHINESE ACAD OF SCI
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