Thickness difference control method for cold-rolled ultrahigh-strength steel plate with tensile strength larger than or equal to 800 MPa

Abstract

The invention discloses a method for controlling the thickness difference of a cold-rolled ultrahigh-strength steel plate with the tensile strength larger than or equal to 800 MPa. The method comprises the steps that in the steel coil transportation process, a hot coil saddle bears a steel coil, and heat insulation treatment is conducted between the hot coil saddle and the steel coil, so that the direct contact time between the hot coil saddle and the steel coil does not exceed the set time. According to the thickness difference control method for the cold-rolled ultrahigh-strength steel plate with the tensile strength larger than or equal to 800 MPa, the thermal insulation pad is additionally arranged on the hot rolling saddle, the situation that the time of direct contact between the hot rolling saddle and the steel coil exceeds the set time in the transportation process is avoided, the thickness difference amplitude and length are effectively reduced, and the product percent of pass is increased.

Description

Technical Field

[0001] The invention belongs to the technical field of cold-rolled ultra-high-strength steel plate manufacturing methods, and specifically relates to a thickness difference control method for cold-rolled ultra-high-strength steel plates with a tensile strength of ≥800MPa. Background Art

[0002] Cold-rolled or galvanized ultra-high-strength steel plates with a tensile strength of ≥800MPa are widely used in automotive body structural parts and connectors, and are an important means of lightweighting automobiles. Cold-rolled or galvanized ultra-high-strength steel plates usually use different ratios of elements such as C, Si, Al, Mn, Cr, Mo, Nb, Ti, etc. to obtain high-strength characteristics. The production processes involved include steelmaking, continuous casting, hot rolling, cold rolling, annealing or galvanizing. Due to the high alloy content and strong hardenability, the difference in the cooling process after hot rolling coiling can easily lead to differences in phase transformation structure, which is manifested as differences in hot coil strength. The main factor for the difference in the cooling process is whether the hot coil contacts the saddle during the cooling process. Since the heat exchange forms in the contact saddle area and the non-contact saddle area are heat conduction and heat radiation, respectively, and the cooling rate in the heat conduction area is faster, the phase transformation is mainly hard phase bainite or even martensite phase transformation, resulting in a significant increase in the hot coil strength in this area. When the hot coil is coiled at a higher temperature, thinner and closer to the saddle, the periodic thickness difference phenomenon will be more obvious during cold rolling, which will significantly reduce the cold rolling efficiency and product qualification rate.

[0003] The Chinese patent with application number 202010823443.6 discloses a production process of a three-layer composite aluminum plate for cookers, including a composite aluminum plate, which is composed of a pure aluminum plate with a thickness of 25%, a 3003 aluminum alloy plate with a thickness of 50%, and a pure aluminum plate with a thickness of 25%. The function is to retain the high strength of the aluminum alloy and the high elongation characteristics of the pure aluminum material, and to retain the advantages of the aluminum alloy such as high thermal conductivity, low cost and rust resistance. On the other hand, it is to eliminate the harmful effects of human intake caused by the Mn element added to the 3003 alloy. This patent is a production process for a three-layer "sandwich" composite aluminum plate for cookers, which is significantly different from the materials, production processes and problems solved by this patent.

[0004] The patent document with publication number WO 2019 / 242565A1 discloses a method for manufacturing cold-rolled or galvanized dual-phase steel plates above 980MPa. The method solves manufacturing problems such as edge cracking after cold rolling and drastic fluctuations in thickness after cold rolling by designing a heat source or heat insulation process with or without a heat source after hot rolling coiling, thereby obtaining good cold rolling manufacturability. The measure is to artificially create a closed space with relatively uniform temperature with or without a heat source, slow down the temperature drop rate of the hot coil, and decompose the hard phase structure through "self-tempering" during the insulation process, so as to obtain a hot coil raw material with relatively uniform structure and strength, realize cold rolling manufacturability, and avoid defects such as edge cracking after cold rolling and drastic fluctuations in thickness after cold rolling.

[0005] It is desirable to provide an improved method for controlling the thickness difference of cold-rolled ultra-high-strength steel plates with a tensile strength ≥ 800 MPa, particularly with regard to how to improve the cold rolling efficiency and product qualification rate. Summary of the invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a method for controlling the thickness difference of a cold-rolled ultra-high strength steel plate with a tensile strength ≥ 800 MPa, the purpose of which is to improve the product qualification rate.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is: a method for controlling the thickness difference of a cold-rolled ultra-high-strength steel plate with a tensile strength ≥ 800MPa, comprising:

[0008] During the transportation of the steel coils, the hot coil saddle carries the steel coils, and the hot coil saddle and the steel coils are subjected to temperature insulation treatment so that the direct contact time between the hot coil saddle and the steel coils does not exceed the set time.

[0009] The heat insulation treatment between the hot coil saddle and the steel coil comprises: arranging a heat insulation pad between the hot coil saddle and the steel coil.

[0010] A plurality of the thermal insulation pads are provided.

[0011] The thermal insulation pad comprises an outer shell and a core arranged inside the outer shell, and the core is made of a refractory material with a low thermal conductivity.

[0012] The core is made of ceramic fiber blanket material.

[0013] The content of aluminum oxide in the ceramic fiber blanket material is less than 1%.

[0014] The outer shell is made of steel material.

[0015] The outer shell is made of a steel material with a thickness of 0.5 to 2.0 mm.

[0016] The thickness difference control method of cold-rolled ultra-high-strength steel plate with a tensile strength of ≥800 MPa also includes:

[0017] When hot coiling, the temperature is set at 500-570°C.

[0018] The thickness difference control method of cold-rolled ultra-high strength steel plate with a tensile strength of ≥800MPa of the present invention adds a thermal insulation pad to the hot coil saddle to prevent the direct contact time between the hot coil saddle and the steel coil from exceeding the set time during transportation, effectively reducing the thickness difference amplitude and length, and improving the product qualification rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] This specification includes the following drawings, which show the following contents:

[0020] Figure 1 It is a side view of the hot coil saddle;

[0021] Figure 2 It is a top view of the hot coil saddle;

[0022] Figure 3 This is a comparison chart of the effects of the experimental groups;

[0023] Figure 4 This is a comparison chart of the thickness fluctuation control effect of 0.78mm 800MPa grade cold-rolled dual-phase steel hard coil before and after the application of the method;

[0024] Marked in the figure: 1. hot coil saddle; 2. thermal insulation pad. DETAILED DESCRIPTION

[0025] The specific implementation methods of the present invention are further explained in detail below by describing the embodiments with reference to the accompanying drawings, with the aim of helping those skilled in the art to have a more complete, accurate and in-depth understanding of the inventive concept and technical solution of the present invention and facilitating their implementation.

[0026] The present invention provides a method for controlling thickness difference of a cold-rolled ultra-high-strength steel plate with a tensile strength ≥ 800 MPa, comprising:

[0027] During the transportation of the steel coil, the hot coil saddle 1 carries the steel coil, and the hot coil saddle 1 and the steel coil are insulated so that the direct contact time between the hot coil saddle 1 and the steel coil does not exceed the set time. By performing the insulation treatment between the hot coil saddle 1 and the steel coil, the cooling rate of the contact saddle area on the steel coil is reduced, and the hot coil structure and strength are uniform, which has the characteristics of easy implementation and easy maintenance.

[0028] Specifically, the thickness difference control method of cold-rolled ultra-high strength steel plate with tensile strength ≥800MPa provided by the present invention has no specific restrictions on the alloy composition of the steel plate, which usually contains C, Si, Mn, Cr, Mo, Nb, Ti, etc., and the rest is Fe and impurity elements.

[0029] The process path for preparing hot-rolled steel plates is hot rolling, coiling, saddle transportation and storage, natural cooling, and then cold rolling, and then continuous annealing and hot-dip galvanizing to obtain cold-rolled, galvanized ultra-high-strength steel plates.

[0030] like Figure 1 and Figure 2 As shown, the heat insulation treatment between the hot coil saddle 1 and the steel coil includes: arranging a heat insulation pad 2 between the hot coil saddle 1 and the steel coil so that the direct contact time between the hot coil saddle 1 and the steel coil does not exceed a set time. Exemplarily, the set time can be 10 minutes.

[0031] Preferably, a plurality of insulation pads 2 are provided. The insulation pads 2 are laid on the bearing surface of the hot coil saddle 1 to prevent the hot coil saddle 1 from directly contacting the steel coil for more than 10 minutes during transportation. The insulation pads 2 are installed and maintained offline.

[0032] Preferably, the thermal insulation pad 2 comprises an outer shell and a core arranged inside the outer shell, and the core is made of a refractory material with low thermal conductivity.

[0033] Preferably, the core is made of ceramic fiber blanket material. The aluminum oxide content in the ceramic fiber blanket material is less than 1%, and the main chemical components of the ceramic fiber blanket material are alkaline earth metal oxides such as calcium oxide and magnesium oxide and silicon dioxide, and the ceramic fiber blanket has the characteristics of being degradable in the human body; the thickness in the natural state is 30mm to 100mm, and the ceramic fiber blanket material has high temperature resistance, and the ceramic fiber blanket material can withstand temperatures exceeding 800°C.

[0034] In the outer shell, the ceramic fiber blanket material is in a compressed state, and the steel outer shell ensures the durability of the insulation pad 2. The hot coil saddle 1 is made of metal. During the transportation of the steel coil, the insulation pad 2 can reduce the cooling rate of the steel coil in the contact saddle area, reduce the strength, and eliminate the thickness difference of cold-rolled or galvanized ultra-high strength steel cold-rolled.

[0035] Preferably, the outer shell is made of steel material. The thickness of the outer shell is 0.5-2.0 mm, such as conventional steel plate or stainless steel plate. When the steel outer shell is damaged, the insulation pad 2 needs to be replaced in time.

[0036] Preferably, the thickness difference control method of the cold-rolled ultra-high-strength steel plate with a tensile strength ≥ 800 MPa of the present invention further includes:

[0037] When the hot coil is coiled, the temperature is set to 500-570°C. For example, the hot coil coiling temperature can be set to 500°C, 530°C, 540°C, 550°C, 560°C or 570°C to avoid the risk of excessive cold rolling load caused by too low coiling temperature and color difference of coating caused by too high coiling temperature. After the hot coil is coiled, the steel coil is transported.

[0038] By adopting the method of the present invention, a thermal insulation pad 2 is added to the hot coil saddle 1 to effectively reduce the thickness difference amplitude and length. Taking the specific implementation case below as an example, when the target thickness of cold rolling is 0.78 mm, the length of the cold rolled coil with a post-rolling fluctuation amplitude ≥30 μm is reduced from 170 m to 0 m, and the comprehensive yield rate is expected to be increased by 5%.

[0039] Example

[0040] This embodiment is a production example of 800MPa grade cold-rolled galvanized dual-phase steel with a hot-rolled coil of 2.2mm and a cold-rolled thickness specification of 0.78mm.

[0041] 1. In this embodiment, the test coil adopts a temperature process system in which the hot rolling final rolling target temperature is 890±20°C and the coiling temperature is 550±20°C.

[0042] 2. In this embodiment, the steel coil is transported to the hot coil saddle 1 equipped with the insulation pad 2 within a time range of <5 minutes after the hot rolling line is completed, and the steel coil runs on the hot coil saddle 1 equipped with the insulation pad 2 for more than 20 minutes, and then the steel coil is placed in the hot rolling warehouse for natural cooling. The effect achieved is that the fluctuation of the mechanical properties of the outer ring of the steel coil is significantly reduced, and the performance fluctuation during cold rolling is effectively avoided.

[0043] 3. In this embodiment, the industrial production line comparison verification results show that when the coiling temperature is set to 650°C, the maximum difference in yield strength of the outer 7 layers of the hot coil is 208MPa, when the coiling temperature is set to 550°C, the maximum difference in yield strength of the outer 7 layers of the hot coil is 104MPa, and when the coiling temperature is set to 550°C and the insulation pad 2 is applied, the maximum difference in yield strength of the outer 7 layers of the hot coil is 34MPa.

[0044] 4. The method involved in the present invention has been successfully applied to cold-rolled and galvanized high-strength steel strip products. Industrial production verification shows that the cold-rolled thickness deviation of the invention group can be controlled within the range of <30μm.

[0045] Table 1 Verification effect comparison

[0046] Experimental Group Coil temperature,℃ Is the insulation pad 2 in use? Cold rolling length with thickness deviation > 30μm, m Comparison group 1 650 Not put into use ＞600 Comparison group 2 550 Not put into use ＞170 Invention Group 550 Commissioning 0

[0047] The present invention is described above by way of example in conjunction with the accompanying drawings. Obviously, the specific implementation of the present invention is not limited to the above-mentioned methods. As long as various non-substantial improvements are made using the method concept and technical solution of the present invention; or the above concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A method for controlling thickness difference of cold-rolled ultra-high strength steel plates with a tensile strength ≥ 800 MPa, characterized in that: include: During the transportation of the steel coils, the hot coil saddle carries the steel coils, and the hot coil saddle and the steel coils are subjected to temperature insulation treatment so that the direct contact time between the hot coil saddle and the steel coils does not exceed the set time.

2. The method for controlling thickness difference of cold-rolled ultra-high strength steel plate with tensile strength ≥ 800 MPa according to claim 1, characterized in that: The heat insulation treatment between the hot coil saddle and the steel coil comprises: arranging a heat insulation pad between the hot coil saddle and the steel coil.

3. The method for controlling thickness difference of cold-rolled ultra-high strength steel plate with tensile strength ≥ 800 MPa according to claim 2, characterized in that: A plurality of the thermal insulation pads are provided.

4. The method for controlling thickness difference of cold-rolled ultra-high strength steel plate with tensile strength ≥ 800 MPa according to claim 2, characterized in that: The thermal insulation pad comprises an outer shell and a core arranged inside the outer shell, and the core is made of a refractory material with a low thermal conductivity.

5. The method for controlling thickness difference of cold-rolled ultra-high strength steel plate with tensile strength ≥ 800 MPa according to claim 4, characterized in that: The core is made of ceramic fiber blanket material.

6. The method for controlling thickness difference of cold-rolled ultra-high strength steel plate with tensile strength ≥ 800 MPa according to claim 5, characterized in that: The content of aluminum oxide in the ceramic fiber blanket material is less than 1%.

7. The method for controlling thickness difference of cold-rolled ultra-high strength steel plate with tensile strength ≥ 800 MPa according to any one of claims 4 to 6, characterized in that: The outer shell is made of steel material.

8. The method for controlling thickness difference of cold-rolled ultra-high strength steel plate with tensile strength ≥ 800 MPa according to claim 7, characterized in that: The outer shell is made of a steel material with a thickness of 0.5 to 2.0 mm.

9. The method for controlling thickness difference of cold-rolled ultra-high strength steel plate with tensile strength ≥ 800 MPa according to any one of claims 1 to 8, characterized in that: Also includes: When hot coiling, the temperature is set at 500-570°C.

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