Low-compression-ratio blank finished center-preserving low-temperature impact steel plate and production method thereof

Abstract

The invention discloses a center-preserving low-temperature impact steel plate for a low-compression-ratio blank, which belongs to the technical field of metallurgy and comprises the following chemical components in percentage by mass: 0.05 to 0.07 percent of C, less than or equal to 0.55 percent of Si, 1.30 to 1.40 percent of Mn, less than or equal to 0.010 percent of P, less than or equal to 0.003 percent of S, 0.020 to 0.045 percent of Alt, 0.02 to 0.025 percent of Nb, 0.75 to 0.80 percent of Ni and the balance of Fe and inevitable impurities. The production method comprises the procedures of controlled rolling and heat treatment. The heat treatment process adopts a normalizing, subcritical quenching and tempering process. The steel plate is of a granular structure and ferrite composite structure, the grain size is 8.5-10.0 grade, the steel plate is good in obdurability, and the production cost is low.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy and relates to a low-compression ratio billet-finished center-preserving low-temperature impact steel plate and a production method thereof. Background Art

[0002] The development and promotion of low-temperature container steel plates has changed the situation of long-term reliance on imports for steel plates used in low-temperature equipment in my country, and has made a positive contribution to the localization of large-scale low-temperature equipment. With the rapid development of the petrochemical industry, the technical requirements for the impact of 1 / 2 thickness of steel plates are becoming more and more stringent, and higher and higher requirements are put forward for the process and performance stability of steel plates. Under the current cost control, the need for low-cost production is also increasing. For this reason, it is urgent to conduct in-depth research on the chemical composition, smelting, rolling and heat treatment process of steel plates to stabilize the organization and performance of steel plates, so as to better meet their use requirements. Summary of the invention

[0003] In order to refine the grains and obtain a production method with fine grain size and low production cost, the present invention provides a low-compression ratio billet-finished center-preserving low-temperature impact steel plate and a production method thereof.

[0004] The present invention adopts the following technical solution: A low compression ratio billet-finished center-maintaining low-temperature impact steel plate, the chemical composition and mass percentage of the steel plate are C: 0.05-0.07%, Si≤0.55%, Mn: 1.30-1.40%, P≤0.010%, S≤0.003%, Alt: 0.020-0.045%, Nb: 0.02-0.025%, Ni: 0.75-0.80%, and the balance is Fe and unavoidable impurities.

[0005] Preferably, the thickness of the steel plate continuous casting billet is 300 mm, and the thickness of the steel plate is 80 mm to 87 mm.

[0006] Preferably, the steel plate comprises granular structure + ferrite, and the grain size of the steel plate is 9.0 to 10.0.

[0007] Preferably, the steel plate yield strength R eL ≥317MPa, tensile strength R m : 445~490Mpa, elongation ≥25%, transverse impact energy at -70℃ at 1 / 2 of plate thickness ≥150J.

[0008] A method for producing a low compression ratio billet-finished steel plate with center-maintaining low-temperature impact, comprising a rolling process and a heat treatment process; The rolling process adopts a roughing mill + finishing mill Ш stage rolling process, in which the roughing mill is used in the Ⅰ stage with a starting rolling temperature of 1100-1150°C, and after removing the iron sheet, the steel is rolled to 220-260mm, in the Ⅱ stage, the finishing mill is used with a starting rolling temperature of 980-1000°C, a final rolling temperature of 950-990°C, a three-pass reduction of 20mm-40mm, and the steel is rolled to a thickness of 130-140mm, in the Ш stage, the finishing mill is used with a starting rolling temperature of 840-870°C, a final rolling temperature of 820-840°C, and a maximum reduction of 25mm.

[0009] Furthermore, in the rolling process, the red-returning temperature after rolling is 600-650°C.

[0010] Furthermore, the heat treatment process adopts normalizing + sub-temperature quenching + tempering technology.

[0011] Furthermore, the normalizing temperature is 900-930°C, the thermal insulation coefficient is 2.2-2.5min / mm, and the steel is water-cooled after leaving the furnace to return to red temperature of 600-650°C.

[0012] Furthermore, the sub-temperature quenching temperature is 850-880°C, the insulation coefficient is 1.8-2.2 min / mm, and the steel is water-cooled to room temperature after being taken out of the furnace.

[0013] Furthermore, the tempering temperature is 630-660°C, and the thermal insulation coefficient is 3.0-4.0 min / mm.

[0014] The composition and process design ideas of the present invention are as follows: 1. By strengthening the heating before rolling and controlling the rolling process, increasing the rolling reduction, increasing the austenite shape and nucleation points, and controlling the red-return temperature, redistributing the carbon element and solidifying, increasing the intragranular phase boundaries and the nucleation points of the grain boundaries during the later heat treatment to obtain a refined matrix structure.

[0015] 2. After the first high-temperature normalizing, the steel plate is poured with water to return to red. After the composition is homogenized, the carbides at the segregation are fixed by pouring water to return to redistribution, so as to achieve the purpose of redistribution of carbon elements and reduce the central segregation at 1 / 2 of the plate thickness. Then, the low-temperature quenching process is adopted to refine the grains, reduce the original grain size during the austenite transformation process, adjust the matrix structure, and improve the comprehensive performance of the steel plate.

[0016] The beneficial effects of the present invention are embodied in: The present invention refines the grains by controlling the rolling and heat treatment processes, thereby obtaining a production method with fine grains and low production costs. The obtained steel plate has good strength and toughness and is suitable for the production of 80-87 mm steel plates. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a 100× metallographic structure steel plate at 1 / 2 of the plate thickness of Example 1 of the present invention; Figure 2 This is a 200× metallographic structure steel plate at 1 / 2 of the plate thickness in Example 1 of the present invention. DETAILED DESCRIPTION

[0018] The present invention is further described in detail below with reference to the embodiments. Example 1

[0019] This embodiment provides a method for producing a low compression ratio billet-shaped steel plate with center-maintained low-temperature impact, including controlled rolling and heat treatment processes. The control parameters of each process are as follows: Controlled rolling process: adopting Ш stage rolling process, the starting rolling temperature of stage Ⅰ is 1100℃ and rolled to 220mm; the starting rolling temperature of stage Ⅱ is 980℃, the final rolling temperature is 950℃, the maximum pass reduction is 40mm, and the steel thickness is 135mm; the starting rolling temperature of stage Ш is 860℃, the final rolling temperature is 840℃, the maximum pass reduction is 20-25mm, and the water cooling after rolling returns to red at 600℃.

[0020] Heat treatment process: normalizing process, normalizing temperature is 910℃, insulation coefficient is 2.5min / mm, the steel plate is poured with water to return to red to 650℃ after being taken out of the furnace; quenching process, quenching temperature is 870℃, insulation is 1.8min / mm, and the steel plate is water-cooled to room temperature after being taken out of the furnace; tempering process, tempering temperature is 640℃, insulation is 3.0min / mm.

[0021] The thickness of the low compression ratio billet-formed steel plate with center-protected low-temperature impact is 80 mm, and its metallographic structure is as follows: Figure 1 and Figure 2 As shown in the figure, it can be seen that the structure of the steel plate in this embodiment is granular structure + ferrite, the internal structure is uniform and refined, and the grain size reaches level 9.5.

[0022] The chemical composition and mass percentage of a low compression ratio billet-finished steel plate with center-protected low-temperature impact in this embodiment are shown in Table 1, and its mechanical properties are shown in Tables 2 and 3. Figure 1 , 200× metallographic structure steel plate at 1 / 2 thickness is shown in Figure 2 . Example 2

[0023] Controlled rolling process: adopting Ш stage rolling process, the starting rolling temperature of stage Ⅰ is 1120℃ and rolled to 230mm; the starting rolling temperature of stage Ⅱ is 990℃, the final rolling temperature is 980℃, the maximum pass reduction is 40cm, and the steel thickness is 135mm; the starting rolling temperature of stage Ш is 840℃, the final rolling temperature is 838℃, the maximum pass reduction is 25cm, and the water cooling after rolling returns to 630℃.

[0024] Heat treatment process: normalizing process, normalizing temperature is 900℃, insulation coefficient is 2.2min / mm, the steel plate is poured with water to return to red at 630℃ after being taken out of the furnace; quenching process, quenching temperature is 850℃, insulation coefficient is 2.2min / mm, and the steel plate is water-cooled to room temperature after being taken out of the furnace; tempering process, tempering temperature is 645℃, insulation coefficient is 4.0min / mm.

[0025] The thickness of the low compression ratio billet-finished steel plate with center-protected low-temperature impact is 84 mm, and its metallographic structure is as follows: Figure 1 As shown in the figure, it can be seen that the structure of the steel plate in this embodiment is granular structure + ferrite, the internal structure is uniform and refined, and the grain size reaches level 10.0.

[0026] The chemical composition and mass percentage of a low compression ratio billet-finished center-maintained low-temperature impact steel plate of this embodiment are shown in Table 1, and its mechanical properties are shown in Tables 2 and 3. Example 3

[0027] Controlled rolling process: adopting Ш stage rolling process, the starting rolling temperature of stage Ⅰ is 1150℃ and rolled to 260mm; the starting rolling temperature of stage Ⅱ is 990℃, the final rolling temperature is 970℃, the maximum pass reduction is 40cm, and the steel thickness is 140mm; the starting rolling temperature of stage Ш is 856℃, the final rolling temperature is 838℃, the maximum pass reduction is 25cm, and the water cooling after rolling returns to 650℃.

[0028] Heat treatment process: normalizing process, normalizing temperature is 910℃, insulation coefficient is 2.2min / mm, the steel plate is poured with water to return to red at 630℃ after being taken out of the furnace; quenching process, quenching temperature is 880℃, insulation coefficient is 2.0min / mm, and the steel plate is water-cooled to room temperature after being taken out of the furnace; tempering process, tempering temperature is 645℃, insulation coefficient is 3.5min / mm.

[0029] The thickness of the low compression ratio billet-finished center-maintained low-temperature impact steel plate of this embodiment is 84 mm, and the grain size reaches level 9.5.

[0030] The chemical composition and mass percentage of a low compression ratio billet-finished center-maintained low-temperature impact steel plate of this embodiment are shown in Table 1, and its mechanical properties are shown in Tables 2 and 3. Example 4

[0031] Controlled rolling process: adopting Ш stage rolling process, the starting rolling temperature of stage Ⅰ is 1130℃ and rolled to 240mm; the starting rolling temperature of stage Ⅱ is 995℃, the final rolling temperature is 987℃, the maximum pass reduction is 40cm, and the steel thickness is 135mm; the starting rolling temperature of stage Ш is 865℃, the final rolling temperature is 820℃, the maximum pass reduction is 20cm, and the water cooling after rolling returns to 650℃.

[0032] Heat treatment process: normalizing process, normalizing temperature is 930℃, insulation coefficient is 2.2min / mm, the steel plate is poured with water to return to red to 650℃ after being taken out of the furnace; quenching process, quenching temperature is 880℃, insulation coefficient is 2.0min / mm, and the steel plate is water-cooled to room temperature after being taken out of the furnace; tempering process, tempering temperature is 645℃, insulation coefficient is 3.5min / mm.

[0033] The thickness of the low compression ratio billet-finished center-maintained low-temperature impact steel plate in this embodiment is 85 mm, and the grain size reaches level 9.5.

[0034] The chemical composition and mass percentage of a low compression ratio billet-finished center-maintained low-temperature impact steel plate of this embodiment are shown in Table 1, and its mechanical properties are shown in Tables 2 and 3. Example 5

[0035] Controlled rolling process: adopting Ш stage rolling process, the starting rolling temperature of stage Ⅰ is 1100℃ and rolled to 220mm; the starting rolling temperature of stage Ⅱ is 980℃, the final rolling temperature is 960℃, the maximum pass reduction is 40cm, and the steel thickness is 140mm; the starting rolling temperature of stage Ш is 867℃, the final rolling temperature is 840℃, the maximum pass reduction is 20cm, and the water cooling after rolling returns to 600℃.

[0036] Heat treatment process: normalizing process, normalizing temperature is 910℃, insulation coefficient is 2.2min / mm, the steel plate is poured with water to return to red at 630℃ after being taken out of the furnace; quenching process, quenching temperature is 880℃, insulation coefficient is 2.0min / mm, and the steel plate is water-cooled to room temperature after being taken out of the furnace; tempering process, tempering temperature is 645℃, insulation coefficient is 3.5min / mm.

[0037] The thickness of the low compression ratio billet-finished center-maintained low-temperature impact steel plate in this embodiment is 87 mm, and the grain size reaches level 9.0.

[0038] The chemical composition and mass percentage of a low compression ratio billet-finished center-maintained low-temperature impact steel plate of this embodiment are shown in Table 1, and its mechanical properties are shown in Tables 2 and 3. Example 6

[0039] Controlled rolling process: adopting Ш stage rolling process, the starting rolling temperature of stage Ⅰ is 1100℃ and rolled to 230mm; the starting rolling temperature of stage Ⅱ is 1000℃, the final rolling temperature is 990℃, the maximum pass reduction is 40cm and the steel thickness is 140mm; the starting rolling temperature of stage Ш is 870℃, the final rolling temperature is 840℃, the maximum pass reduction is 25cm, and the water cooling after rolling returns to 600℃.

[0040] Heat treatment process: normalizing process, normalizing temperature is 920℃, insulation coefficient is 2.2min / mm, the steel plate is poured with water to return to red at 600℃ after being taken out of the furnace; quenching process, quenching temperature is 880℃, insulation coefficient is 2.0min / mm, and the steel plate is water-cooled to room temperature after being taken out of the furnace; tempering process, tempering temperature is 635℃, insulation coefficient is 3.5min / mm.

[0041] The thickness of the low compression ratio billet-finished center-maintained low-temperature impact steel plate of this embodiment is 87 mm, and the grain size reaches grade 9.0.

[0042] The chemical composition and mass percentage of a low compression ratio billet-finished center-maintained low-temperature impact steel plate of this embodiment are shown in Table 1, and its mechanical properties are shown in Tables 2 and 3.

[0043] Table 1. Chemical composition and mass percentage (wt%) of the steel plates in each example

[0044] Note: In Table 1, the balance is Fe and unavoidable impurities.

[0045] Table 2. Tensile mechanical properties of steel plates in various examples

[0046] Table 3. Impact mechanical properties of steel plates in various examples

[0047] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A low compression ratio billet-finished steel plate with center preservation and low temperature impact, characterized in that: The chemical composition and mass percentage of the steel plate are C: 0.05-0.07%, Si≤0.55%, Mn: 1.30-1.40%, P≤0.010%, S≤0.003%, Alt: 0.020-0.035%, Nb: 0.02-0.25%, Ni: 0.75-0.80%, and the balance is Fe and unavoidable impurities.

2. The low compression ratio billet-finished center-keeping low-temperature impact steel plate according to claim 1, characterized in that: The thickness of the steel plate continuous casting billet is 300 mm, and the thickness of the steel plate is 80 mm to 87 mm.

3. The low compression ratio billet-finished center-keeping low-temperature impact steel plate according to claim 2, characterized in that: The steel plate has a granular structure + ferrite, and the grain size of the steel plate is 9.0 to 10.

0.

4. A low compression ratio billet-finished center-keeping low-temperature impact steel plate according to any one of claims 1 to 3, characterized in that: The steel plate yield strength R eL ≥317MPa, tensile strength R m : 445~490Mpa, elongation ≥25%, transverse impact energy at -70℃ at 1 / 2 of plate thickness ≥150J.

5. The method for producing a low compression ratio billet-formed steel plate with center preservation and low temperature impact according to claims 1-4, characterized in that: It includes rolling process and heat treatment process; The rolling process adopts a roughing mill + finishing mill Ш stage rolling process, in which the roughing mill is used in the Ⅰ stage with a starting rolling temperature of 1100-1150°C, and after removing the iron sheet, the slab is rolled down to 220-260mm, in the Ⅱ stage, the finishing mill is used with a starting rolling temperature of 980-1000°C, a final rolling temperature of 950-990°C, a three-pass reduction of 20mm-40mm, and the steel is rolled to a thickness of 130-140mm, in the Ш stage, the finishing mill is used with a starting rolling temperature of 840-870°C, a final rolling temperature of 820-840°C, and a maximum reduction of 25mm.

6. The method for producing a low compression ratio billet-finished steel plate with center-maintained low-temperature impact according to claim 5, characterized in that: In the rolling process, the red-returning temperature after rolling is 600-650°C.

7. The method for producing a low compression ratio billet-finished steel plate with center preservation and low temperature impact as claimed in claim 5, characterized in that: The heat treatment process adopts normalizing + sub-temperature quenching + tempering process.

8. The method for producing a low compression ratio billet-finished steel plate with center-maintained low-temperature impact according to claim 7, characterized in that: The normalizing temperature is 900-930℃, the insulation coefficient is 2.2-2.5min / mm, and the steel is water-cooled after leaving the furnace to return to red temperature of 600-650℃.

9. The method for producing a low compression ratio billet-finished steel plate with center-maintained low-temperature impact according to claim 7, characterized in that: The sub-temperature quenching temperature is 850-880℃, the insulation coefficient is 1.8-2.2min / mm, and it is water-cooled to room temperature after being taken out of the furnace.

10. The method for producing a low compression ratio billet-finished steel plate with center preservation and low temperature impact according to claim 7, characterized in that: The tempering temperature is 630-650℃, and the thermal insulation coefficient is 3.0-4.0min / mm.

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