Method for reducing breakage of scale on surface of S355 series medium and thick plate

Abstract

The invention discloses a method for reducing breakage of scale on the surface of an S355-series medium-thickness plate. The method comprises the following steps that S1, a blank is prepared from 0.16%-0.18% of C, 1.2%-1.3% of Mn, smaller than or equal to 0.02% of P, smaller than or equal to 0.005% of S, 0.15%-0.25% of Si, smaller than or equal to 0.02% of Nb, smaller than or equal to 0.1% of Ni, smaller than or equal to 0.15% of Cr, smaller than or equal to 0.1% of Cu, smaller than or equal to 0.08% of Mo, smaller than or equal to 0.01% of V, smaller than or equal to 0.02% of Ti, smaller than or equal to 0.004% of Ca and the balance Fe and inevitable impurities; s2, heating is conducted, specifically, the heating temperature is 1150 + / -20 DEG C, the in-furnace time is 7.3-16 mm / min, and the staying time of a plate blank in a soaking section is longer than or equal to 20 min; and S3, rolling: rolling the blank by adopting a single-stand steckel mill, carrying out high-pressure water double-pump descaling by adopting a descaling box before rolling, then transporting the blank to the front of the rolling mill through a roller way, starting a rough rolling stage, carrying out rough rolling at the initial rolling temperature of about 1030-1050 DEG C, carrying out fine descaling on a rolled piece by adopting a rolling mill in the first and second passes of the rough rolling stage, and carrying out fine descaling on the rolled piece in the second pass of the rough rolling stage. After the rough rolling stage is completed, the thickness of the intermediate billet is 1.8 times or more than 1.8 times of the thickness of a finished product; and the initial rolling temperature in the finish rolling stage is smaller than or equal to 970 DEG C, and the rolled piece is subjected to finish descaling in the first pass and the last but one pass in the finish rolling stage.

Description

Technical Field

[0001] The invention relates to a method for reducing the breakage of iron oxide scale on the surface of S355 series medium and thick plates. Background Art

[0002] During the production process of hot-rolled steel plates, due to improper heating temperature, rolling process, descaling, cooling, etc., the iron oxide scale on the surface of the steel plate will be broken and fall off in a large area, especially for steel plates with a thickness of ≥16mm. Due to the high cooling rate, the iron oxide scale on the surface of the steel plate is severely broken. This kind of steel plate with broken iron oxide scale will peel off in a large area during the process of wind turbine tower winding, and even be pressed into the steel plate matrix, causing surface defects of the steel plate, bringing major losses such as rescue and construction delays to downstream customers, and causing huge negative impacts on the image and reputation of the company. Therefore, it is necessary to develop a new process method to improve the density of the iron oxide scale and reduce the breakage and shedding of the iron oxide scale of wind tower steel. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a method for reducing the crushing of iron oxide scale on the surface of S355 series medium and thick plates in view of the shortcomings of the above-mentioned prior art. By optimizing the component design, heating, rolling process and optimizing the distribution of descaling passes, the crushing of iron oxide scale on the surface of thick medium and thick plates for wind power is reduced without changing the equipment capacity and sacrificing the rolling efficiency.

[0004] The technical solution of the present invention to solve the above technical problems is: a method for reducing the crushing of iron oxide scale on the surface of S355 series medium and thick plates, comprising the following steps: S1 billet composition: C: 0.16~0.18%, Mn: Mn: 1.2~1.3%, P≤0.02%, S≤0.005%, Si: 0.15~0.25%, Nb≤0.02%, Ni≤0.1%, Cr≤0.15%, Cu≤0.1%, Mo≤0.08%, V≤0.01%, Ti≤0.02%, Ca≤0.004% and the rest are Fe and unavoidable impurities; S2 heating: heating temperature is 1150±20℃, furnace time is 7.3-16mm / min, and the slab stays in the soaking zone for ≥20min; S3 rolling: a single-frame furnace coil mill is used to roll the billet. Before rolling, a descaling box is used for high-pressure water double pump descaling. The billet is then transported to the front of the rolling mill by rollers to start the rough rolling stage. The starting temperature of the rough rolling is about 1030~1050℃. In the first and second passes of the rough rolling stage, the mill uses fine descaling to descale the rolled piece. After the rough rolling stage is completed, the thickness of the intermediate billet must be guaranteed to be 1.8 times or more of the thickness of the finished product; the starting temperature of the finishing rolling stage is ≤970℃, and the first and second to last passes of the finishing rolling stage are used to finely descale the rolled piece.

[0005] The present invention further defines the scheme: Preferably, the specifications of the medium and thick plates are: blank thickness 150-220 mm, blank width 1600-3300 mm, and blank length ≤17600 mm.

[0006] Preferably, the S1 billet composition is: C: 0.17%, Mn: 1.43%, P: 0.0:14%, S: 0.0023%, Si: 0.20%, Nb: 0.012%, Ni: 0.02%, Cr: 0.036%, Cu: 0.019%, Mo: 0.001%, V: 0.002%, Ti: 0.005%, Ca: 0.001%, and the rest is Fe and unavoidable impurities.

[0007] Preferably, the air-fuel ratio of the heating furnace in S2 is 1.3-1.8, and the residual oxygen is less than 5%.

[0008] Preferably, before the S4 rolling, a descaling box is used to perform high-pressure water double-pump descaling, and the descaling pressure is ≥20MPa.

[0009] The beneficial effects of the present invention are as follows: the present invention effectively reduces the crushing of iron oxide scale on the surface of S355 series medium and thick plates through a series of measures such as component design, heating, rolling process and optimization of descaling pass distribution. Without changing the equipment capacity and sacrificing the rolling efficiency, the crushing of iron oxide scale on the surface of thick medium and thick plates for wind power generation is reduced, and the crushing rate is reduced from 100% to less than 10%, thereby improving the aesthetics of the steel plate surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 The surface effect diagram of the steel plate before and after the implementation of Example 1 DETAILED DESCRIPTION Example

[0011] This embodiment provides a method for reducing the breakage of iron oxide scale on the surface of S355 series medium and thick plates, comprising the following steps: S1 billet composition: C: 0.17%, Mn: 1.43%, P: 0.0:14%, S: 0.0023%, Si: 0.20%, Nb: 0.012%, Ni: 0.02%, Cr: 0.036%, Cu: 0.019%, Mo: 0.001%, V: 0.002%, Ti: 0.005%, Ca: 0.001%, the rest is Fe and unavoidable impurities; S2 material design: the blank size is 150mm×3050mm×11632mm; S3 heating: heating temperature 1154℃, furnace time 144min, soaking zone residence time 38min, heating furnace air-fuel ratio reduced to 1.3, residual oxygen 3%; S4 rolling: After leaving the furnace, a descaling box is used to perform one pass of high-pressure water double pump descaling, with a descaling pressure of 22.3MPa. The billet is then transported to the front of the rolling mill by rollers to start the rough rolling stage. The rough rolling start temperature is about 1052℃. The rolling mill fine descaling is used to descale the rolled piece in the 1st and 2nd passes of the rough rolling stage. After the rough rolling stage is completed, the thickness of the intermediate billet is 1.8 times the thickness of the finished product. The start rolling temperature of the finishing rolling stage is about 880℃. The first and second to last passes of the finishing rolling stage are used to finely descale the rolled piece. The surface quality of the finished product is significantly improved compared with that before optimization, as shown in the attached figure. Figure 1 Through long-term tests, the crushing of iron oxide scale on the surface of S355 series steel plates before and after the implementation of this technology is shown in the following table. The crushing rate has been reduced from 100% to below 10%, and the implementation effect is significant.

[0012] Order thickness Iron oxide is not broken Iron oxide scale crushing Crushing rate ≥16-<20mm 44 1 2.2% ≥20-<30mm 206 3 1.4% ≥30mm 78 3 3.7% total 328 7 2.09% In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. A method for reducing the crushing of iron oxide scale on the surface of S355 series medium and thick plates, characterized by: The following steps are involved: S1 billet composition: C: 0.16~0.18%, Mn: Mn: 1.2~1.3%, P≤0.02%, S≤0.005%, Si: 0.15~0.25%, Nb≤0.02%, Ni≤0.1%, Cr≤0.15%, Cu≤0.1%, Mo≤0.08%, V≤0.01%, Ti≤0.02%, Ca≤0.004% and the rest are Fe and unavoidable impurities; S2 heating: heating temperature is 1150±20℃, furnace time is 7.3-16mm / min, and the slab stays in the soaking zone for ≥20min; S3 rolling: a single-frame furnace coil mill is used to roll the billet. Before rolling, a descaling box is used for high-pressure water double pump descaling. The billet is then transported to the front of the rolling mill by rollers to start the rough rolling stage. The starting temperature of the rough rolling is about 1030~1050℃. In the first and second passes of the rough rolling stage, the mill uses fine descaling to descale the rolled piece. After the rough rolling stage is completed, the thickness of the intermediate billet must be guaranteed to be 1.8 times or more of the thickness of the finished product; the starting temperature of the finishing rolling stage is ≤970℃, and the first and second to last passes of the finishing rolling stage are used to finely descale the rolled piece.

2. The method for reducing the crushing of iron oxide scale on the surface of S355 series medium and thick plates according to claim 1, characterized in that: The specifications of the medium and thick plates are: blank thickness 150-220mm, blank width 1600-3300mm, and blank length ≤17600mm.

3. The method for reducing the crushing of iron oxide scale on the surface of S355 series medium and thick plates according to claim 1, characterized in that: The S1 billet composition is: C: 0.17%, Mn: 1.43%, P: 0.0:14%, S: 0.0023%, Si: 0.20%, Nb: 0.012%, Ni: 0.02%, Cr: 0.036%, Cu: 0.019%, Mo: 0.001%, V: 0.002%, Ti: 0.005%, Ca: 0.001%, and the rest is Fe and unavoidable impurities.

4. The method for reducing the crushing of iron oxide scale on the surface of S355 series medium and thick plates according to claim 1, characterized in that: The air-fuel ratio of the heating furnace in S2 is 1.3-1.8, and the residual oxygen is less than 5%.

5. The method for reducing the crushing of iron oxide scale on the surface of S355 series medium and thick plates according to claim 1, characterized in that: Before the S4 rolling, a descaling box is used to perform high-pressure water double pump descaling, and the descaling pressure is ≥20MPa.

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