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Heat treatment method of steel plate with large thickness

A heat treatment method and large thickness technology, applied in heat treatment furnaces, heat treatment equipment, heat treatment process control, etc., can solve the problems of increasing the risk of cracking, deterioration of mechanical properties, increase of residual stress, etc., to suppress the growth of ferrite. , Small difference in mechanical properties, the effect of increasing yield strength

Inactive Publication Date: 2014-01-29
WUYANG IRON & STEEL +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, if the accelerated cooling process is not appropriate, the steel plate is prone to abnormal structure, increased residual stress, and poor mechanical properties.
For example: (1) The cooling time of extra-thick steel plate in water is short, and the core of the steel plate cannot be cooled thoroughly, resulting in uneven structure between the surface and the core; The speed is faster, and the abnormal structure of bainite or even martensite is prone to appear. The temperature of steel plate reddening is low, and this abnormal structure cannot be decomposed, resulting in poor plasticity and toughness of the steel plate, which is also not conducive to subsequent machining. The temperature difference in the core is large, the residual stress increases, and the risk of cracking increases

Method used

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Examples

Experimental program
Comparison scheme
Effect test

Embodiment 1

[0016] Steel type: S355J2+N; thickness specification: 240mm, normalizing in the external machine furnace, normalizing temperature 910±10℃, thermal insulation coefficient 2.0min / mm (thickness of steel plate), furnace charging temperature 350℃, heating rate at 110℃ / h. After the steel plate comes out of the bottom furnace, enter the water in time. After entering the water for 1.5 minutes, it will be air-cooled for 6 minutes. The red temperature of the steel plate will be 690°C. Properties: Yield strength 405MPa, strength 575 MPa, elongation 29%, -40°C impact energy average 166 joules; performance at half thickness: 390MPa, strength 560 MPa, elongation 27%, -40°C impact energy average 126 joules. The entire thickness of the steel plate is composed of ferrite + pearlite structure, and the ferrite grain size reaches 8.5 grades.

Embodiment 2

[0018] Steel type: Q460C; thickness specification: 400mm, normalized in an external furnace, the normalizing temperature is 900±10°C, the thermal insulation coefficient is 1.8min / mm (thickness of the steel plate), the furnace charging temperature is 300°C, and the heating rate is 90°C / h. After the steel plate comes out of the bottom furnace, enter water in time. After entering the water for 3 minutes, it will be air-cooled for 10 minutes. The temperature of the steel plate is 720°C. The properties of the quarter thickness of the steel plate: yield strength 430 MPa, strength 600 MPa, elongation 26%, impact energy at 0°C average 118 joules; properties of half thickness: 420 MPa, strength 583 MPa, elongation 24%, The average impact energy at 0°C is 106 joules. The entire thickness of the steel plate is composed of ferrite + pearlite structure, and the ferrite grain size reaches 8.0 grades.

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Abstract

The present invention relates to a heat treatment method of a steel plate with large thickness. The method includes the following steps: (1) heating: heating and normalizing the steel plate with large thickness in an external mechanical furnace, a car bottom furnace or a pit furnace; (2) heating rate: a charging temperature lower than 400 DEG C, and a temperature rising speed at 80-120 DEG C / h; (3) insulation time: after heating to a process temperature, insulating for 1.8-2.0min / mm (thickness of the steel plate) to ensure fully austenitization and homogenization of the entire plate; and (4) cooling process: employing a water-air-water-air clearance circulating cooling technology. The present invention employs time-sharing temperature control and cooling control on the steel plate with large thickness after normalizing to realize consistent steel plate core with surface tissue and avoid abnormal tissue generating on the surface (cooling rate control); the rapid cooling increases nucleation rate of pearlite, inhibits the growth of ferrite, and refines changed tissue. Therefore, the steel plate with large thickness produced by the method of the invention has the following advantages: (1) greatly improved mechanical performance; (2) little mechanical property difference between plate positions with different thickness; and (3) fine and uniform tissue at steel plate positions with different thickness.

Description

technical field [0001] The invention relates to a heat treatment method for large-thickness steel plates, in particular to a normalizing process for low-alloy large-thickness steel plates and a method for accelerated cooling after normalizing, and belongs to the technical field of heat treatment for wide and thick steel plates. Background technique [0002] In recent years, with the rapid development of large-scale equipment industries such as wind power, hydropower, nuclear power, and offshore platform engineering, the market demand for steel plates with large thickness and single weight is increasing. Especially for large single-weight steel plates with a thickness of more than 200mm, domestically produced steel plates cannot meet market demand in terms of production capacity or performance. Many are produced by forging, but the forging surface has a large machining allowance and high cost. [0003] Normalizing can refine the grain, homogenize the structure, and have excel...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): C21D9/52C21D1/28C21D11/00
Inventor 吴涛赵文忠李建立韦明叶建军宋向前孔祥丽高大伟桑德广张亚丽张仪杰
Owner WUYANG IRON & STEEL