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A heat treatment method for reducing the yield ratio of low-carbon bainite bridge steel

A technology of low-carbon bainite and heat treatment method, which is applied in the field of steel plate heat treatment, can solve the problems that the yield ratio of the steel plate is not given, reduces the rolled steel plate, damages the low-temperature fracture toughness, etc., and achieves short heat treatment cycle and low oxidation burning loss , the effect of reducing the yield ratio

Active Publication Date: 2020-11-13
INST OF RES OF IRON & STEEL JIANGSU PROVINCE +2
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0003] Patent CN103667909A discloses a steel for mobile offshore platforms with a yield ratio ≤ 0.65 and its production method. The thickness of the steel plate is 8-50 mm, the composition is simple, controlled rolling and cooling are adopted, the normalizing temperature is 880-910 ° C and the furnace Time (1.3~1.6)t+0~20min normalizing process, the yield strength ratio of the steel plate obtained is ≤0.65, but the disadvantage is that the strength level of the invention is low, and the yield strength R el ≥360MPa, tensile strength R m ≥560MPa, and its -40°C impact energy is only >100J, the structure of the steel is ferrite + pearlite structure, and has obvious band structure, which will affect the anisotropy of the steel plate and damage the low temperature fracture toughness
Patent CN101328564A discloses a low yield strength ratio HT780 steel plate with excellent weldability and its manufacturing method. The invention uses low C-medium Mn-high Als-low N-(Cu+Ni+Mo+Cr) alloy-(Nb +V+Ti+B) microalloyed composition system, and through TMCP+N' (α+γ two-phase zone normalizing)+T, yield strength ≥ 650MPa, tensile strength R m ≥780MPa steel plate, but its disadvantage is that the amount of added alloy elements Cr, Cu, Ni, Mo and V is too high, which increases the cost, and the heat treatment process has many links and a long cycle, which further increases the cost and reduces the efficiency. And although its strength is high, the yield ratio ≤ 0.80 is also high
Patent CN103422027A discloses an economical low-yield point steel and its production method. Although the composition of the invention is simple and the cost is low, the disadvantage is that the strength of the steel is ≥ 225MPa, the strength index is low, and the structure is pearlite + ferrite body
After inquiry, some invention patents study how to reduce the yield strength ratio of rolled steel plates, such as CN106222548A, CN107130191A, CN101649420A and CN104046898A, etc., but there is a common deficiency that the yield strength ratio is high (the lowest ≤ 0.70) , and the yield ratio of the steel plate after heat treatment is not given

Method used

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  • A heat treatment method for reducing the yield ratio of low-carbon bainite bridge steel
  • A heat treatment method for reducing the yield ratio of low-carbon bainite bridge steel
  • A heat treatment method for reducing the yield ratio of low-carbon bainite bridge steel

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Experimental program
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Effect test

Embodiment 1

[0030] The chemical composition of the steel plate includes: C 0.10%, Si 0.20%, Mn 1.48%, Cr 0.13%, Ni 0.13%, Nb 0.020%, Ti 0.015%, Alt 0.030%, P≤0.013%, S≤ 0.005%, the rest is Fe and unavoidable impurities.

[0031] 1) Prepare a cast slab with the same chemical composition as the above-mentioned steel plate, heat the cast slab at a heating temperature of 1180°C to 1200°C, and then perform TMCP rolling to obtain a steel plate with a thickness of 20mm;

[0032]2) Put the steel plate in a heat treatment furnace, raise the temperature to 760°C at a heating rate of 480°C / min, take it out of the furnace immediately after reaching the temperature, and air cool to room temperature.

[0033] The photo of the microstructure at 500 times the longitudinal section of the steel plate at 1 / 4 is as follows: figure 1 As shown, the structure of the steel plate is a ferrite + bainite dual phase structure, wherein the volume fraction of ferrite is 33.5%, and the rest is bainite. The mechanical...

Embodiment 2

[0038] The chemical composition of the steel plate includes by weight percentage: C 0.05%, Si 0.25%, Mn 1.55%, Cr 0.20%, Ni 0.17%, Mo 0.12%, Cu 0.17%, Nb 0.030%, Ti 0.015%, Alt 0.029% , P≤0.012%, S≤0.005%, and the rest are Fe and unavoidable impurities.

[0039] 1) Prepare a cast slab with the same chemical composition as the above-mentioned steel plate, heat the cast slab at a heating temperature of 1180°C to 1200°C, and then perform TMCP rolling to obtain a steel plate with a thickness of 30mm;

[0040] 2) Put the steel plate in the heat treatment furnace, raise the temperature to 770°C at a heating rate of 415°C / min, take it out of the furnace immediately after reaching the temperature, and cool it to room temperature in air.

[0041] The photo of the microstructure at 500 times the longitudinal section of the steel plate at 1 / 4 is as follows: image 3 As shown, the structure of the steel plate is a ferrite + bainite dual phase structure, wherein the volume fraction of fer...

Embodiment 3

[0046] The chemical composition of the steel plate includes by weight percentage: C 0.05%, Si 0.15%, Mn 1.58%, Cr 0.30%, Ni 0.40%, Mo 0.15%, Cu 0.30%, Nb 0.045%, Ti 0.013%, Alt 0.020% , P≤0.010%, S≤0.003%, and the rest are Fe and unavoidable impurities.

[0047] 1) Prepare a cast slab with the same chemical composition as the above-mentioned steel plate, heat the cast slab at a heating temperature of 1180°C to 1200°C, and then perform TMCP rolling to obtain a steel plate with a thickness of 16mm;

[0048] 2) Put the steel plate in the heat treatment furnace, raise the temperature to 780°C at a heating rate of 520°C / min, take it out of the furnace immediately after reaching the temperature, and air cool to room temperature.

[0049] The photo of the microstructure at 500 times the longitudinal section of the steel plate at 1 / 4 is as follows: Figure 5 As shown, the structure of the steel plate is a ferrite + bainite dual phase structure, wherein the volume fraction of ferrite ...

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Abstract

The invention provides a heat treatment method for reducing the yield ratio of a low-carbon bainitic bridge steel. After controlled rolling and controlled cooling, heat treatment is carried out on thelow-carbon bainitic bridge steel billet with the thickness less than or equal to 30 mm; the heat treatment process comprises the following steps that a steel plate is heated up to 760-800 DEG C in aheat treatment furnace at the heating rate of 310 DEG C / min-520 DEG C / min, the steel plate is immediately discharged out of the furnace after the temperature is reached, and air cooling is carried outto room temperature. The tissue of the steel plate obtained after heat treatment is a ferrite and bainite complex phase structure, the yield strength Rp0.2 is 390 MPa-540 MPa, the extension strengthRm is larger than or equal to 630 MPa, the percentage elongation after fracture is larger than or equal to 22%, the yield ratio (Rp0.2 / Rm) is 0.60-0.65, and the charpy impact absorption power is larger than 210 J at 40 DEG C below zero. The method is short in period and low in cost.

Description

technical field [0001] The invention belongs to the technical field of steel plate heat treatment, and relates to a heat treatment method for reducing the yield ratio of low-carbon bainite bridge steel. Background technique [0002] In recent years, the low-carbon bainitic bridge steel produced by the TMCP process has developed rapidly and has gradually become an important direction for the development of bridge steel in the future. However, with the increase of its strength level, the yield strength of low-carbon bainitic bridge steel Ratio control has increasingly become a difficult problem in the industry, especially for steel plates with a thickness specification of ≤30mm. Due to large rolling deformation and rapid temperature drop, the yield ratio of as-rolled steel plates often exceeds the standard range, and in order to eliminate the steel plate during rolling and The internal stress generated during the cooling process ensures the safety performance and service life ...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): C21D6/00C21D8/02C21D1/28C22C38/02C22C38/04C22C38/06C22C38/42C22C38/44C22C38/48C22C38/50C22C38/58
CPCC21D1/28C21D6/004C21D6/005C21D6/008C21D8/0205C21D8/0273C21D2211/002C21D2211/005C22C38/02C22C38/04C22C38/06C22C38/42C22C38/44C22C38/48C22C38/50C22C38/58
Inventor 邵伟杨浩镇凡曲锦波
Owner INST OF RES OF IRON & STEEL JIANGSU PROVINCE
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