Ultrahigh-strength ultrahigh-toughness and low-density dual-phase lamellar steel plate and preparation method therefor

Abstract

An ultrahigh-strength ultrahigh-toughness and low-density dual-phase lamellar steel plate is disclosed. The steel plate comprises the following alloy components in percentage by mass: 0.200-0.320% of C, 0.600-2.000% of Mn, 0.200-0.600% of Si, 2.000-4.000% of Al, 0.300-1.200% of Ni, 0.001-0.005% of B, P not greater than 0.012%, S not greater than 0.005%, and the balance of Fe and inevitable impurities. The steel plate consists of dual phases of ferrites and martensites, the ferrites are high-temperature delta ferrites, the martensites are lath martensites, the delta ferrites are distributed in the lath martensites in a lamellar mode. The steel plate has excellent mechanical properties, for example, the yield strength in the rolling direction is not less than 1000 MPa, the tensile strength is not less than 1600 MPa, the elongation is not less than 8.0%, and the average value of Charpy V-Notch impact energy at −40° C. is not less than 350J.

Claims

1. A dual-phase lamellar steel plate, comprising the following alloy components in percentage by mass: 0.200-0.320% of C, 0.600-2.000% of Mn, 0.200-0.600% of Si, 2.000-4.000% of Al, 0.300-1.200% of Ni, 0.001-0.005% of B, P not greater than 0.012%, S not greater than 0.005%, Cr not more than 0.700%, and a balance of Fe and inevitable impurities; the inevitable impurities comprise H and N, wherein H is not greater than 2.0 ppm, and N is not greater than 45 ppm; the steel plate consists of dual phases of ferrites and martensites, the ferrites are delta ferrites, the martensites are lath martensites, the delta ferrites are distributed in the lath martensites in a lamellar mode; and a volume fraction of the ferrites is not greater than 30% and is not zero.

2. The dual-phase lamellar steel plate according to claim 1, wherein a mass fraction of C, Mn and Al elements in the steel plate satisfies: 6[C]+0.8[Mn]+1≥[Al].

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic diagram showing rolling and on-line heat treatment process of steel of the present invention.

(2) FIG. 2 is a diagram showing properties of a steel plate with selected components in embodiment 1 of the present invention calculated using Thermo-calc software.

(3) FIG. 3 is a schematic diagram showing a metallographic structure of steel obtained under the preparation process condition in embodiment 2.

(4) FIG. 4 is a schematic diagram showing a scanning electron microscope structure of steel obtained under the preparation process condition in embodiment 3.

DETAILED DESCRIPTION

(5) In specific examples of the present invention, the topography of the sample is characterized by observing the microstructure topography of the sample and combining with the scanning electron microscope. To describe the present invention more clearly, the present invention is further described below in combination with the preferred embodiments. The content described below is illustrative rather than restrictive, and should not be used to limit the scope of the present invention.

Embodiment 1

(6) The steel plate of this embodiment is smelted, and the alloy components (mass percentage) of the steel plate are designed as shown in Table 1.

(7) TABLE-US-00001 TABLE 1 C Si Mn Al Ni B P S Fe 0.200 0.220 0.600 2.000 0.800 0.002 0.005 0.001 Balance

(8) The alloy components satisfy: 6[C]+0.8[Mn]+1≥[Al].

(9) A corresponding raw material is smelted and cast into a strand according to the optimal alloy components, and the strand is heated to 1200° C. and thermally insulated, is forged into a billet with a thickness of 100 mm, and is air cooled to the ambient temperature after forging.

(10) The forged billet with a thickness of 100 mm is heated to 1200° C. and thermally isolated for 60 minutes for homogenization, then is subjected to 7-pass rolling, wherein the starting rolling temperature is 1086° C., the thickness of the rolled steel plate is 12 mm, the total reduction is 88%, the finishing rolling temperature is 1033° C., and the steel plate is quenched to the ambient temperature at a cooling rate greater than 15° C./s after rolling.

(11) The mechanical properties of the final steel plate are shown in Table 2. The yield strength in the rolling direction is 1064 MPa, the tensile strength is 1658 MPa, the elongation after breaking is 10.4%, and the average value of Charpy V-Notch impact energy at −40° C. is 415.6 J. The microcosmic metallographic structure of the steel plate obtained in embodiment 1 is as shown in FIG. 3, in which the black structure is martensite, the white structure is ferrite, and the two phases are distributed in a lamellar mode.

(12) Properties of the steel plate in embodiment 1 calculated using Thermo-calc software are shown in FIG. 2.

(13) Table 2 shows mechanical properties of a steel plate sample obtained in embodiment 1.

(14) TABLE-US-00002 TABLE 2 Yield Tensile Elongation −40° C. Density Strength Strength After Impact energy 7.66 1064 1658 10.4 415.6

Embodiment 2

(15) The steel plate of this embodiment is smelted, and the alloy components (mass percentage) of the steel plate are designed as shown in Table 3.

(16) TABLE-US-00003 TABLE 3 C Si Mn Al Ni B P S Fe 0.260 0.220 1.000 3.000 0.800 0.002 0.005 0.001 Balance

(17) The alloy components satisfy: 6[C]+0.8[Mn]+1≥[Al].

(18) A corresponding raw material is smelted and cast into a strand according to the optimal alloy components, and the strand is heated to 1200° C. and thermally insulated, is forged into a billet with a thickness of 100 mm, and is air cooled to the ambient temperature after forging.

(19) The forged billet with a thickness of 100 mm is heated to 1200° C. and thermally isolated for 60 minutes for homogenization, then is subjected to 7-pass rolling, wherein the starting rolling temperature is 1086° C., the thickness of the rolled steel plate is 12 mm, the total reduction is 88%, the finishing rolling temperature is 1042° C., and the steel plate is quenched to the ambient temperature at a cooling rate greater than 15° C./s after rolling.

(20) The mechanical properties of the final steel plate are shown in Table 4. The yield strength in the rolling direction is 1158 MPa, the tensile strength is 1764 MPa, the elongation after breaking is 8.9%, and the average value of Charpy V-Notch impact energy at −40° C. is 382.4 J.

(21) The scanning electron microscope structure of the steel plate obtained in embodiment 2 is as shown in FIG. 4, in which the convex structure is martensite, and the concave structure is ferrite.

(22) Table 4 shows mechanical properties of a steel plate sample obtained in embodiment 2.

(23) TABLE-US-00004 Yield Tensile Elongation Density strength strength after −40° C. (g/cm3) (MPa) (MPa) breaking (%) impact energy (J) 7.48 1158 1764 8.9 382.4

Embodiment 3

(24) The steel plate of this embodiment is smelted using a vacuum induction furnace, and the alloy components (mass percentage) of the steel plate are designed as shown in Table 5.

(25) TABLE-US-00005 TABLE 5 C Si Mn Al Ni B P S Fe 0.320 0.220 1.500 4.000 0.800 0.002 0.005 0.001 Balance

(26) The alloy components satisfy: 6[C]+0.8[Mn]+1≥[Al].

(27) A corresponding raw material is smelted and cast into a strand according to the optimal alloy components, and the strand is heated to 1200° C. and thermally insulated, is forged into a billet with a thickness of 100 mm, and is air cooled to the ambient temperature after forging.

(28) The forged billet with a thickness of 100 mm is heated to 1200° C. and thermally isolated for 60 minutes for homogenization, then is subjected to 7-pass rolling, wherein the starting rolling temperature is 1086° C., the thickness of the rolled steel plate is 12 mm, the total reduction is 88%, the finishing rolling temperature is 1037° C., and the steel plate is quenched to the ambient temperature at a cooling rate greater than 15° C./s after rolling.

(29) The mechanical properties of the final steel plate are shown in Table 6. The yield strength in the rolling direction is 1227 MPa, the tensile strength is 1851 MPa, the elongation after breaking is 8.2%, and the average value of Charpy V-Notch impact energy at −40° C. is 359.9 J. (Table 6 shows mechanical properties of a steel plate sample obtained in embodiment 3).

(30) TABLE-US-00006 TABLE 6 Yield Tensile Elongation Density strength strength after −40° C. (g/cm3) (MPa) (MPa) breaking (%) impact energy (J) 7.33 1227 1851 8.2 359.9

(31) The present invention has the characteristics that the ferrite phase area is expanded by adding the Al element, rolling deformation is realized at the two-phase area temperature, and it is known according to the calculation of Thermo-calc software that there are a ferrite phase and an austenite phases in steel within the temperature range of hot rolling deformation of the steel plate. Two-phase area rolling and on-line quenching are performed on the steel plate, and the lamellar structure obtained by rolling deformation is retained to the ambient temperature state, and a delta ferrite+martensite two-phase lamellar structure is obtained at ambient temperature, so that the steel plate has good strength and toughness.

(32) It should be noted that the above description of the specific embodiments of the present invention is only for illustrating the technical route and features of the present invention, and aims to make those skilled in the art know the content of the present invention and implement same accordingly. However, the present invention is not limited to the specific embodiments. Various changes or modifications made within the scope of the present invention shall be covered in the protection scope of the present invention.