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Heat treatment process for refining M-A island in granular bainite structure of low-carbon low alloy steel

A granular bainite and low-alloy steel technology, applied in the field of heat treatment of iron and steel materials, can solve problems such as difficulty in uniform dispersion and precipitation of carbides, reduction in strength, mismatch of strength and toughness of components, etc., to eliminate tissue heredity and inhibit growth speed Effect

Active Publication Date: 2019-06-04
INST OF METAL RESEARCH - CHINESE ACAD OF SCI
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  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

It not only deteriorates the low-temperature impact toughness of non-quenched and tempered low-carbon and low-alloy bainitic steel components, but also brings difficulties to the uniform dispersion and precipitation of carbides in the structure of quenched and tempered granular bainitic steel components during subsequent high-temperature tempering treatment, which leads to The strength and toughness of its components do not match, etc.
[0003] In order to solve the problems of poor strength-toughness matching of low-carbon and low-alloy bainite steels or the low impact toughness of materials due to the coarse M-A islands in the granular bainite structure, some literatures reported that the critical zone heat treatment process was used to improve the low-temperature impact of steel parts. Toughness, but due to the lack of precise control of the critical zone treatment temperature and initial microstructure, the ferrite content in the microstructure after critical zone treatment is relatively high, and the ferrite morphology is mainly block
Although it can improve the low-temperature impact toughness of related components to a certain extent, it will significantly reduce its strength and greatly reduce the high-temperature durability of the material. It is not suitable for some components that have special requirements for the high-temperature performance of the material.

Method used

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  • Heat treatment process for refining M-A island in granular bainite structure of low-carbon low alloy steel
  • Heat treatment process for refining M-A island in granular bainite structure of low-carbon low alloy steel
  • Heat treatment process for refining M-A island in granular bainite structure of low-carbon low alloy steel

Examples

Experimental program
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Effect test

Embodiment 1

[0032] This implementation is to manufacture a Ni-Cr-Mo series low-alloy steel thick slab for racks on an offshore platform. First, the steel plate is sampled for chemical composition analysis. The test results are: 0.15C (weight percentage, the same below), 0.20Si, 1.5Ni, 1.20Cr, 0.45Mo, 0.005V, 0.005P, 0.002S, Fe balance. The Ac3 and Ac1 of this steel measured by thermal expansion are 857°C and 752°C respectively. According to the test results of the critical phase transition point of steel, the new / old heat treatment process is specifically formulated as follows:

[0033] (1) For the conventional treatment process, the rolled slab is subjected to austenitic treatment at 900°C x 8h, and then directly air-cooled and normalized;

[0034] (2) For the new heat treatment process, that is, on the basis of normalizing, the slab is tempered at 650°C, and the tempering holding time is about 2h, and it is cooled to room temperature by air cooling; then the steel plate is 830°C. Heat...

Embodiment 2

[0037] This implementation is to manufacture low-carbon and low-alloy -2.25Cr1Mo0.25V steel thick plates for a large-scale hydrogenation reactor. The specific implementation process is as follows:

[0038] (1) First, analyze the chemical composition of the thick plate samples. The test results are: 0.15C (weight percentage, the same below), 0.05Si, 2.46Cr, 1.01Mo, 0.28V, 0.15Ni, 0.006P, 0.002S, Fe amount, the result meets the requirements of relevant standards for the chemical composition of 2.25Cr-1Mo-0.25V steel, and belongs to the scope of application of the present invention. Take a φ3x10mm round bar on a rolled thick plate, and use the thermal expansion method to measure the Ac3 and Ac1 of the material to be 886°C and 776°C, respectively.

[0039] (2) After the slab is forged, the post-forging heat treatment (that is, normalizing treatment + tempering treatment) that needs to be carried out after forging. Therefore, in the subsequent performance heat treatment process, t...

Embodiment 3

[0042] In this embodiment, the heat treatment of complex thick-walled castings of G18CrMo2-6 steel low-pressure cylinders for nuclear power is taken as an example. The specific process is as follows:

[0043] (1) This embodiment is a large thick-walled casting made of G18CrMo2-6 steel with a maximum wall thickness of 400 mm. Firstly, the main chemical composition of the steel piece in this embodiment is detected to be 0.18C (weight percentage, the same below), 0.67Cr, 0.69Mo, 0.48Ni, 0.73Mn, and Fe balance, which is in line with the scope of low-carbon low-alloy steel applicable to the present invention. The phase transition critical points Ac1 and Ac3 of the material measured by thermal expansion are: 762°C and 883°C respectively;

[0044] (2) Similar to Example 1, this example also first carries out normalizing treatment to the casting, but the difference from Example 2 is that the normalizing austenitization temperature of this example is 960°C, the heat preservation is 20 ...

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Abstract

The invention belongs to the field of heat treatment of steel materials, and particularly discloses a heat treatment process for refining an M-A island in a granular bainite structure of low-carbon low alloy steel. The heat treatment process is suitable for solving the problem of low impact toughness or fluctuation caused by a coarse martensite / austenite island structure (referred to as M-A island) contained in a microstructure of low-carbon low alloy granular bainite steel after heat treatment. After conventional quenching (normalizing), one-pass tempering treatment is performed to obtain a uniformly dispersed Mn-rich carbide or Cr-rich carbide; and then austenitizing in a two-phase region is performed at a temperature slightly lower than Ac3, the ferrite content is controlled to be lessthan 10%, and then quenching (normalizing) in a conventional cooling mode is performed. The purpose that a film-like or acicular ferrite formed through quenching (normalizing) treatment in the two-phase region controls the content, size, carbon concentration and distribution position of the M-A island in the granular bainite structure, particularly fines the size of the M-A island in the structureis achieved.

Description

technical field [0001] The invention belongs to the field of heat treatment of iron and steel materials, in particular to a heat treatment process for refining M-A islands in the granular bainite structure of low-carbon and low-alloy steel. Background technique [0002] Low-carbon low-alloy bainitic steel is often used in petroleum, chemical, bridge, marine engineering and other fields due to its good strength and toughness, good processing performance and high cost performance. Because in actual industrial production, low-carbon low-alloy steel components (especially thick and large cross-section components) always undergo phase transformation during continuous cooling rather than isothermal process, they often obtain all or a certain amount of granular bainite structure at room temperature . When the thermal processing process is improper or the hardenability of the material is not enough, the M-A islands in the granular bainite structure are relatively coarse, and they a...

Claims

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Application Information

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IPC IPC(8): C21D1/18C21D1/28C21D6/00C22C38/58C22C38/44C22C38/46C22C38/48C22C38/54C22C38/50
Inventor 王培蒋中华李殿中李依依
Owner INST OF METAL RESEARCH - CHINESE ACAD OF SCI
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