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Thermal treatment method for inhibiting and eliminating banded structure in low-alloy and heatproof steel tube

A heat treatment method and banded structure technology, which is applied in heat treatment equipment, manufacturing tools, quenching agents, etc., can solve problems such as molding and other process difficulties, achieve versatility and effectiveness, broad application prospects, and eliminate banded structures Effect

Active Publication Date: 2014-03-12
TIANJIN STEEL PIPE MFG CO LTD
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  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, when the cooling rate is very high, the supercooled austenite will transform into bainite or martensite. Although the band structure is eliminated, it changes the ferrite pearlite structure expected to be obtained by the steel, which is for the subsequent Machining, molding and other processes bring great difficulties, so the cooling rate should be strictly controlled

Method used

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  • Thermal treatment method for inhibiting and eliminating banded structure in low-alloy and heatproof steel tube
  • Thermal treatment method for inhibiting and eliminating banded structure in low-alloy and heatproof steel tube
  • Thermal treatment method for inhibiting and eliminating banded structure in low-alloy and heatproof steel tube

Examples

Experimental program
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Effect test

Embodiment 1

[0033] Cut a certain length of SA-210Gr.C pipe, the pipe size (outer diameter × wall thickness) is 57 × 7mm, grade the banded structure of the rolled pipe as 4.5, and then machine it into a cylindrical sample. The sample was heated to 880°C at a heating rate of 30°C / min by a thermal expansion tester, and kept warm for 8 minutes. Then rapid cooling to 620°C was performed by spraying high-velocity nitrogen gas to the sample at 20°C / S, and then the sample was air-cooled to room temperature.

[0034] The sample treated above was sawed along the axial direction, then inlaid with resin, ground, polished and chemically etched. The metallographic structure was observed under an optical microscope, and the banded structure was graded according to the national standard GB / T13299-91. The rating result is 1.5, such as Figure 5a As shown, it can be seen that the banding is significantly reduced. Microhardness testing was carried out on the sample, and the Vickers hardness value was 172,...

Embodiment 2

[0036] Cut a certain length of SA-210Gr.C pipe, the pipe size (outer diameter × wall thickness) is 51 × 7mm, grade the banded structure of the rolled pipe as 4.5, and then machine it into a cylindrical sample. The sample was heated to 890°C at a heating rate of 40°C / min by a thermal expansion tester, and kept warm for 8 minutes. Then rapid cooling was performed to 630°C by spraying high-velocity nitrogen gas to the sample at 50°C / S, and then the sample was air-cooled to room temperature.

[0037] The sample treated above was sawed along the axial direction, then inlaid with resin, ground, polished and chemically etched. The metallographic structure was observed under an optical microscope, and the banded structure was graded according to the national standard GB / T13299-91. The rating result is level 0, such as Figure 5b As shown, it can be seen that the banding is completely eliminated. Microhardness testing was carried out on the sample, and the measured hardness value was...

Embodiment 3

[0039] Cut a certain length of SA-210Gr.C pipe, the pipe size (outer diameter × wall thickness) is 57 × 4mm, grade the banded structure of the as-rolled pipe to grade 5, and then machine it into a cylindrical sample. The sample is heated to 910°C by a thermal expansion tester at a heating rate of 50°C / min, and kept warm for 8 minutes. Then rapid cooling to 600 °C was performed by spraying high-velocity nitrogen gas to the sample at 100 °C / S, and then the sample was air-cooled to room temperature.

[0040] The sample treated above was sawed along the axial direction, then inlaid with resin, ground, polished and chemically etched. The metallographic structure was observed under an optical microscope, and the band structure was graded according to the national standard GB / T13299-91. The rating result is level 0, such as Figure 5c As shown, it can be seen that no band-like structure was formed in the sample. Microhardness testing was carried out on the sample, and the measured ...

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Abstract

The invention provides a thermal treatment method for inhibiting and eliminating a banded structure in a low-alloy and heatproof steel tube. The method comprises the following steps: sampling low-alloy and heatproof steel tubes which are subjected to smelting and rolling, performing metallographic structure observation and grading the banded structure; machining the low-alloy and heatproof steel tubes which are rolled in a thermal mode to manufacture a cylindrical sample with the diameter of 3mm and the length of 12mm, and welding a K-type thermocouple in a central position along the length direction of the cylindrical sample; heating at a warming speed from the temperature of 20-50 DEG C to 880-910 DEG C and performing heat preservation for 8 minutes to ensure that the cylindrical sample structure is completely austenitized; cooling the cylindrical sample at the cooling speed of 20-100 DEG C / S by jetting nitrogen at a high speed; performing air cooling on the cylindrical sample till reaching the room temperature. The method has the beneficial effects that by using the thermal treatment method, the structure after thermal treatment is a ferrite pearlite, and the banded structure formed in the hot-rolling formation process can be effectively eliminated, and the increase of the production cost is avoided, so that the method is an economic and effective treatment method.

Description

technical field [0001] The invention belongs to the technical field of hot rolling production of low-alloy steel pipes, and in particular relates to a heat treatment method for suppressing and eliminating band structures in low-alloy heat-resistant steel pipes. Background technique [0002] After the low-alloy steel is deformed by hot rolling, it is easy to form a banded structure during the cooling process. The so-called banded structure refers to the microstructure in which proeutectoid ferrite and pearlite are stacked on each other in bands along the rolling direction. The formation of the banded structure makes the performance of the steel parallel to the rolling direction and the mechanical properties perpendicular to the rolling direction significantly different, that is, the latter performance is significantly lower than the former, so the banded structure is considered to be a harmful structure. Banding in rolled steel needs to be strictly controlled. Low-alloy hea...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): C21D8/10C21D6/00C21D1/613
Inventor 刘源卢居桂许磊磊赵庆权王国亮何彪曹金荣肖功业
Owner TIANJIN STEEL PIPE MFG CO LTD
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