A method for producing a super-thick steel plate

Abstract

A method for producing a super-thick steel plate, the slab thickness is 450 mm, the slab center segregation C class is ≤2.0 level, the center porosity is ≤1.0 level, the produced steel plate thickness is 100-150 mm, and the width is 2000-4200 mm, the key process steps include that the slab is heated in a soaking furnace, the hearth temperature is 1250-1300 ℃, the slab is in the furnace for 600-750 min, the billet casting temperature is controlled to be above 1220 ℃, the high-temperature large reduction technology is adopted, and the single pass reduction of two non-expansion passes is ensured to be ≥40 mm. The normalizing process is adopted, the normalizing temperature is 880-900 ℃, the normalizing time is 1.7-2.0 times of the plate thickness mm×min / mm, the holding time after reaching the normalizing temperature is 30-50 min, and after discharging, the steel plate is air-cooled on a cooling bed, and the cooling is not allowed above 150 ℃. The steel plate center -20 ℃ Charpy V-type notch impact value KV2 is ≥47 J, the steel plate is ultrasonically detected, and meets the I level requirement of the NB / T47013.3-2015 standard.

Description

TECHNICAL FIELD

[0001] The present invention belongs to the field of metallurgy, and relates to a production method of a heavy steel plate with improved core low-temperature impact toughness. BACKGROUND

[0002] With the continuous development of continuous casting technology, the thickness of continuous casting billet can reach 450 mm. Replacing ingot with continuous casting billet for producing heavy plate has obvious advantages in cost and efficiency, but the existence of center segregation of continuous casting billet seriously affects the impact performance of the core of the steel plate, so it is necessary to study the heating, rolling and heat treatment process of the heavy plate, so as to improve the core quality of the steel plate to meet the various quality and performance requirements of the production of the heavy plate. SUMMARY

[0003] The purpose of the present invention is to provide a production method of a heavy steel plate with improved core low-temperature impact toughness, the slab thickness is 450 mm, the slab center segregation is C class ≤ 2.0 level, the center porosity is ≤ 1.0 level, the thickness of the produced steel plate is 100-150 mm, and the width is 2000-4200 mm, and the performance meets the following requirements: yield strength ReL≥320 MPa, tensile strength Rm=490-630 MPa, elongation after fracture A≥21%, and core impact energy KV2 at-20℃≥47J.

[0004] The technical scheme of the present invention is as follows:

[0005] A production method of a heavy steel plate, the slab thickness is 450 mm, the thickness of the produced steel plate is 100-150 mm, the width is 2000-4200 mm, the slab center segregation is C class ≤ 2.0 level, the center porosity is ≤ 1.0 level, and the core impact value KV2 of the steel plate at-20℃ is V-shaped notch Charpy impact value≥47J; the key process steps include:

[0006] (1) Slab heating: the slab is heated in a soaking furnace, the furnace temperature is 1250-1300℃, the slab time in the furnace is 600-750 min, and the billet casting temperature is controlled to be above 1220℃;

[0007] (2) Rolling: the one-stage opening rolling temperature is above 1180℃, the large reduction technology is adopted, the single pass reduction of two non-expansion passes is ≥40 mm, the finish rolling temperature is >920℃, and the intermediate billet thickness is ≥ the steel plate finished product thickness+40-50 mm; the two-stage opening rolling temperature is 850℃, and the finish rolling temperature is 790-820℃;

[0008] (3) Heat treatment: normalizing process is adopted, the normalizing temperature is 880-900℃, the normalizing time is 1.7-2.0 times of the plate thickness mm×min / mm, the holding time after reaching the normalizing temperature is 30-50 min, and after discharging, the steel plate is air-cooled on the cooling bed, and the cooling on the cooling bed is not allowed above 150℃.

[0009] The present application adopts slab heating + rolling + heat treatment method to produce the super-thick steel plate, and the beneficial effects are as follows: through the large reduction technique at high temperature in rough rolling, the core is deformed to further reduce the core segregation; the heat treatment adopts normalizing process, the normalizing temperature is 880-900℃, the normalizing time is 1.7-2.0 times of the plate thickness (min), the holding time after reaching the normalizing temperature is 30-50 min, and after discharging, the air cooling is carried out on the cooling bed, so as to refine the grain and improve the toughness of the steel plate.

[0010] The present application has the following creative and beneficial effects: the slab thickness is 450 mm, the heating is carried out in the soaking furnace, the temperature distribution in the furnace is uniform, the hearth temperature is set to 1250-1300℃, the furnace time is 600-750 min, the uniform heating of the slab is ensured, the high-temperature diffusion of elements is beneficial, and the heating quality of the core of the casting blank can be improved. The blank casting temperature is controlled to be above 1220℃, the one-stage rolling temperature is ensured to be above 1180℃, the large reduction technique at high temperature is adopted, the single pass reduction of two non-breadth widening passes is ≥40 mm, the core quality of the slab is further improved, the reasonable two-stage rolling and normalizing heat treatment are further carried out, the grain is further refined, the toughness of the steel plate is improved, and the mechanical properties of the 100-150 mm thick plate meet the following requirements: the yield strength ReL≥320 MPa, the tensile strength Rm=490-630 MPa, the elongation A≥21%, and the core impact energy KV2 at-20℃≥47 J.

[0011] BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 、 Figure 2 、 Figure 3 The figure is the full-thickness hot pickling figure of the steel plate of example 1, the rolling state sample core metallographic figure, and the core sample figure after heat treatment.

[0013] Figure 4 、 Figure 5 、 Figure 6 The figure is the full-thickness hot pickling figure of the steel plate of example 2, the rolling state sample core metallographic figure, and the core sample figure after heat treatment. DETAILED DESCRIPTION

[0014] Example 1:

[0015] ​A method for producing extra-thick steel plates with improved low-temperature impact toughness of the core is disclosed. The slab, numbered 1#, exhibits low-magnification center segregation of grade C 1.5 and center porosity of grade 1.0, with a thickness of 450 mm. Production is carried out in a soaking furnace for 650 min at a tapping temperature of 1220℃. The first-stage rolling temperature is 1190℃, employing a large reduction technique with a reduction of 40 / 43 mm, resulting in an intermediate slab thickness of 140 mm. The second-stage rolling temperature is 850℃, with a final rolling temperature of 825℃, producing a finished product with a thickness of 140 mm and a width of 2460 mm. A full-thickness rolled sample is taken from the steel plate at 1 / 4 of its width and subjected to hot pickling to obtain the product shown in the attached figure. Figure 1 As shown, metallographic analysis is attached. Figure 2 The core segregation was relatively dispersed. The steel plate was normalized at 895℃ for 255 min and held for 40 min. Samples were taken at 1 / 4 of the steel plate width for metallographic analysis and -20℃ impact performance testing. The metallographic analysis is shown in Figure 3. The mechanical properties of the steel plate and the low-temperature impact test of the core are shown in Table 1. The steel plate was subjected to ultrasonic testing, which met the Class I requirements of NB / T47013.3-2015 standard.

[0016] Example 2:

[0017] A method for producing extra-thick steel plates with improved low-temperature impact toughness in the core area. Slab number 2#, from the same heat as slab 1#, with a thickness of 450mm, is produced in a walking beam furnace for 480 minutes. The slab tapping temperature is 1200℃. The first-stage rolling temperature is 1180℃, employing a large reduction technique with a reduction of 41 / 43mm, resulting in an intermediate slab thickness of 140mm. The second-stage rolling temperature is 850℃, and the final rolling temperature is 828℃, producing a finished product with a thickness of 140mm and a width of 2460mm. A full-thickness rolled sample is taken from the steel plate at 1 / 4 of its width and subjected to hot pickling to obtain the product shown in the attached figure. Figure 4 As shown, metallographic analysis is attached. Figure 5 The segregation in the core area was relatively concentrated. The steel plate was normalized at 893℃ for 260 minutes and held for 42 minutes. Samples were taken from one-quarter of the plate's width for metallographic analysis and -20℃ impact testing. Metallographic analysis results are attached. Figure 6 The mechanical properties of the steel plate and the low-temperature impact test of the core are shown in Table 1. The steel plate was subjected to ultrasonic testing and met the Class II requirements of NB / T47013.3-2015 standard.

[0018] Appendix Figures 1-6As shown, the same furnace 450mm slab, the macrostructure of the slab is center segregation C class 1.5 level, center loose 1.0 level, using 2 pieces of soaking pit and step furnace respectively, in the case of similar heating and rolling process, the steel plate produced by the application is obviously improved in macro and micro analysis of the core segregation; through the mechanical property test, the core low temperature impact toughness is greater than or equal to 47J, and the steel plate can meet the requirements of the NB / T47013.3-2015 standard level I through ultrasonic flaw detection.

[0019] Table 1 mechanical property test results of each embodiment steel

[0020]

Claims

1. A method of producing a super-thick steel plate, the slab thickness being 450 mm, the steel plate thickness being 100-150 mm, and the width being 2000-4200 mm, characterized by: The slab center segregation C class is ≤2.0, the center porosity is ≤1.0, and the steel plate core -20℃ Charpy V-type notch impact value KV2 is ≥47J; The key process steps include: (1) Slab heating: the slab is heated in a soaking furnace, the hearth temperature is 1250-1300℃, the slab time in the furnace is 600-750min, and the billet casting temperature is controlled above 1220℃; (2) Rolling: the one-stage opening rolling temperature is above 1180℃, the large reduction technology is adopted, the single pass reduction of two non-expansion passes is ≥40mm, the finish rolling temperature is >920℃, and the intermediate slab thickness is ≥ the steel plate finished product thickness+40-50mm; the two-stage opening rolling temperature is 850℃, and the finish rolling temperature is 790-820℃; (3) Heat treatment: the normalizing process is adopted, the normalizing temperature is 880-900℃, the normalizing time is 1.7-2.0 times of the plate thickness mm×min / mm, the holding time after reaching the normalizing temperature is 30-50min, and after discharging, the air cooling is performed on the cooling bed, and the cooling is not allowed above 150℃.

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