CN114480988B - A kind of multi-phase composite high-strength high-toughness low-density steel and its preparation method - Google Patents

Abstract

The invention discloses multiphase composite high-strength high-toughness low-density steel and a preparation method thereof, belonging to the technical field of metal materials and metallurgy. The multiphase composite high-strength high-toughness low-density steel comprises the following chemical components in percentage by mass: 1.05-1.10wt.% C, 27.0-28.0wt.% Mn, 10.3-11.0wt.% Al, 3.0-3.5wt.% Cr, 0-3.6wt.% Ni, 0.02-0.04wt.% Nb, S less than or equal to 0.01%, P less than or equal to 0.005%, and the balance Fe and unavoidable impurities. The preparation method comprises the steps of smelting according to the component proportion, casting, forging into a square billet after homogenization treatment, performing multi-pass hot rolling and water cooling after homogenization treatment, and performing solid solution treatment to obtain the steel. The invention obtains the multiphase composite high-strength high-toughness low-density steel with low cost and high efficiency and the preparation method thereof by selecting the components and the contents of microalloying elements and a preparation mode.

Description

A kind of multi-phase composite high-strength high-toughness low-density steel and its preparation method

technical field

The invention belongs to the technical field of metal materials and metallurgy, and relates to a multi-phase composite high-strength, high-toughness and low-density steel and a preparation method thereof.

Background technique

Usually, the design scheme of high-strength low-density steel is to obtain an austenite matrix and dispersed nano-scale κ carbides through a reasonable ratio of Mn, Al, and C alloying elements, followed by solid solution or aging treatment. However, κ carbides have a great influence on the properties of low-density steels. Although they can increase the strength, they will also increase the brittleness of the material.

At present, although there are low-density steels obtained by adding alloy elements and mediating preparation methods, the obtained low-density steels not only have higher density, but also have low elongation, and the phase structure is mostly precipitation strengthening phases, which cannot be well matched. Therefore, The existing high-strength low-density steel has poor plasticity and toughness, and the phase structure in the microstructure is unreasonable.

For example: Chinese patent CN 106244927 A discloses a low-density ultra-high-strength steel, which precipitates fine and dispersed NbMoC phases by compounding Nb and Mo, and cooperates with κ-carbides for precipitation strengthening. The tensile strength reaches more than 1350 MPa and the elongation reaches Above 10%, the density is 6.8-7.0g/cm ³ ; the organizational structure is austenite matrix, κ-carbide and NbMoC phase, which cannot greatly increase the elongation and further reduce the steel density.

Chinese patent CN 107841691 A discloses a 750MPa-level ultra-high-strength Fe-Mn-Al-C light-weight cast steel. From its examples, it can be seen that the tensile strength of the cast steel is 756-768MPa, and the yield strength is 713 -731MPa, the elongation after fracture is 15.03-20.05%, and the density is 6.84-6.95g/cm ³ ; among them, the alloy elements are complex and the cost is high. Although it has undergone solution treatment and aging treatment, the structure is cast structure with high density and lower elongation after breakage.

Chinese patent CN 109628850 A discloses a multi-purpose all-austenitic low-density steel. The density of the steel is 7.0-7.4g/cm ³ , the structure type is full-austenite + nanoscale VC and MoC precipitates, and the steel is resistant to The tensile strength can reach 1300MPa, the yield strength can reach 1100MPa, the elongation can reach 25%, the area reduction rate can reach 45%, and the V-notch low temperature impact toughness at -40°C can reach 35J; although the tensile strength and yield strength are relatively high, but Low-temperature impact toughness is not high, and the cost of vanadium and molybdenum elements in the phase structure is high, and the content of aluminum element is low, which cannot play a good role in reducing cost, density and improving plastic toughness.

Contents of the invention

The technical problem solved by the present invention is that the density reduction range of the existing austenitic low-density steel is not large, the selection of microalloying element components is complicated, and the cost is high; The ingredients are not well controlled.

In order to solve the above technical problems, the present invention provides the following technical solutions:

A multi-phase composite high-strength, high-toughness and low-density steel, the chemical composition of the multi-phase composite high-strength, high-toughness and low-density steel is: 1.05-1.10wt.%C, 27.0-28.0wt.%Mn, 10.3-11.0 wt.%Al, 3.0-3.5wt.%Cr, 0-3.6wt.%Ni, 0.02-0.04wt.%Nb, S≤0.01%, P≤0.005%, the balance is Fe and unavoidable impurities.

The role of each chemical element in steel is as follows:

C: Carbon is an austenite forming and stabilizing element, which not only acts as interstitial solid solution strengthening, but also forms κ carbides with Mn and Al elements in steel, which has a great influence on the strength and toughness of steel; The C content is 1.05-1.10%.

Mn: Manganese is the main alloying element of Fe-Mn-Al-C low-density steel. Manganese is an element that expands the austenite phase region. Its addition can reduce the Ms point. The Mn element also affects the stacking fault energy of the Fe-Mn-Al-C low-density steel and controls the deformation mechanism of the steel. But too high Mn content can cause component segregation, form band structure, and when Mn content exceeds 30%, can form β-Mn harmful phase, make mechanical property and weldability decline; The present invention sets the content of Mn as 27.0- 28.0%.

Al: Aluminum is a ferrite forming element, which can increase the temperature _of A3 and increase the stacking fault energy of Fe-Mn-Al-C low-density steel, thereby improving the strength of Fe-Mn-Al-C low-density steel plasticity. The addition of aluminum will reduce the density of the steel. For every 1% Al added, the density of the steel will decrease by 0.1g/cm ³ . An appropriate amount of aluminum can significantly improve the thermal deformation resistance of the steel, delay dynamic recrystallization, and make the austenite grains in the Refinement is obtained after dynamic recrystallization; the present invention sets the Al content at 10.3-11.0%.

Cr: Chromium is an element that reduces the austenite phase zone, increases stacking fault energy, reduces Ms points, and improves corrosion resistance; a small amount of chromium can improve low-temperature impact toughness. The addition of chromium can also control the precipitation of κ carbides and reduce the size and content of κ carbides; the present invention sets the content of Cr to be 3.0-3.5%.

Ni: Nickel is an austenite forming element, which not only improves the corrosion resistance of steel, but also improves the toughness of steel. Ni and Al are easy to form NiAl(B ₂ ) phase, which not only can refine grain but also has strong precipitation strengthening effect; the content of Ni is set at 0-3.6% in the present invention.

Nb: Niobium is a strong carbide forming element, which can refine grains and improve strength and toughness, and can also increase the elastic modulus of steel; the content of Nb is set at 0.02-0.04% in the present invention.

P, S: Phosphorus and sulfur are unfavorable elements for steel formation. Sulfur exists in steel in the form of sulfide intercalations such as FeS and MnS. The sulfide is usually released in the grain boundary and will melt when the temperature reaches its melting point, which will lead to cracking when the steel is thermally deformed during rolling and forging . Phosphorus will seriously affect the cold deformation ability of steel, and with the increase of phosphorus content, its influence will be sharply intensified, and cold and brittle phenomenon will appear; the present invention sets the content of P and S as S≤0.01%, P≤0.005%.

Preferably, the multi-phase composite high-strength, high-toughness and low-density steel has a density ≤ 6.6g/cm ³ , a yield strength of 585-910MPa, a tensile strength of 880-1100MPa, and an elongation of 42-68%. V-notch impact energy>50J.

Preferably, the structure of the multi-phase composite high-strength, high-toughness and low-density steel is an austenite matrix and κ carbide, δ ferrite, NiAl phase and NbC precipitated phase; the content of κ carbide is less than 3%, and the δ ferrite The +NiAl phases are all of BCC structure, the content of which is 3%-11% detected by XRD, and the content of NbC is less than 0.1%.

The preparation method of described multiphase composite high-strength high-toughness low-density steel, described preparation method comprises the steps:

S1, smelting: Proportioning and weighing according to the chemical composition content of the required multi-phase composite high-strength, high-toughness and low-density steel, using a vacuum induction furnace to fully smelt evenly, and casting to obtain an ingot;

S2. The first homogenization treatment: performing high-temperature homogenization treatment on the ingot in the step S1;

S3, hot forging: forging the ingot processed in step S2 into a billet;

S4, the second homogenization treatment: performing high-temperature homogenization treatment on the billet in the step S3;

S5, multi-pass hot rolling: performing multi-pass hot rolling on the billet in the step S4, and water cooling to room temperature to obtain a hot-rolled plate;

S6, solution treatment: after solution treatment of the hot-rolled plate in the step S5, water-cool to room temperature to obtain a finished multi-phase composite high-strength, high-toughness and low-density steel.

Preferably, the temperature of the first homogenization treatment in the step 2 is 1100-1150°C, and the time is 11-13h.

Preferably, the forging temperature in step 3 is the homogenization treatment temperature in step 2, and the final forging temperature is >950°C.

Preferably, the temperature of the second homogenization treatment in the step 4 is 1180-1200°C, and the time is 2-4h.

Preferably, the multi-pass hot rolling in step 5 is 5-7 hot rolling passes, the starting rolling temperature is 1130-1180°C, the finishing rolling temperature is ≥950°C, and the cumulative reduction is 65-80%.

Preferably, the solution treatment temperature in step 6 is 1000°C, and the time is 0.5-2h.

The above technical solutions provided by the embodiments of the present invention have at least the following beneficial effects:

In the above scheme, the present invention obtains a low-cost and high-efficiency multi-phase composite high-strength high-toughness low-density steel and its preparation method through the selection of microalloying element composition and content and the preparation method.

The phase structure obtained by the invention is an austenite matrix, kappa carbide, delta ferrite, NiAl phase and NbC precipitated phase.

The invention refines the austenite grains through the three phases of delta ferrite, NbC and NiAl, improves the work hardening ability, and improves the comprehensive mechanical properties of the steel.

The density of the low-density steel of the present invention is ≤6.6g/cm ³ , the yield strength is 585-910MPa, the tensile strength is 880-1100MPa, the elongation is 42-68%, and the V-notch impact energy at -40°C is greater than 50J; Not only the weight loss effect is obvious, but also the strength and toughness are improved synergistically.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings that need to be used in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those skilled in the art, other drawings can also be obtained based on these drawings without creative effort.

Fig. 1 is the structural diagram of the multiphase composite high-strength, high-toughness and low-density steel of Example 1 of the present invention after solid solution for 0.5h; wherein: (a) is a metallographic structure diagram, (b) is a κ carbide morphology diagram, ( c) is the NbC transmission topography;

Fig. 2 is the engineering stress-strain curve figure of embodiment 2 of the present invention and embodiment 4 after solid solution 1h at 1000 ℃;

Fig. 3 is a strain hardening curve of Example 2 and Example 4 of the present invention after solid solution at 1000° C. for 1 hour.

detailed description

In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will describe in detail with reference to the drawings and specific embodiments. It should be noted that the technical features or combinations of technical features described in the following embodiments should not be considered isolated, and they can be combined with each other to achieve better technical effects. In the drawings of the following embodiments, the same reference numerals appearing in each drawing represent the same features or components, which can be applied in different embodiments.

Example 1

A multi-phase composite high-strength, high-toughness and low-density steel, the chemical composition of the multi-phase composite high-strength, high-toughness and low-density steel is: 1.10wt.%C, 27.0wt.%Mn, 11.0wt.%Al, 3.0wt.% wt.%Cr, 3.6wt.%Ni, 0.02wt.%Nb, 0.01wt.%S, 0.003wt.%P, the balance being Fe and unavoidable impurities.

The preparation method of described multiphase composite high-strength high-toughness low-density steel, described preparation method comprises the steps:

S1, smelting: Proportioning and weighing according to the chemical composition content of the required multi-phase composite high-strength, high-toughness and low-density steel, using a vacuum induction furnace to fully smelt evenly, and casting to obtain an ingot;

S2, the first homogenization treatment: the ingot in the step S1 is subjected to a high-temperature homogenization treatment with a temperature of 1150° C. and a time of 13 hours;

S3. Hot forging: forging the ingot processed in the step S2 into a billet, and the final forging temperature is >950°C;

S4, the second homogenization treatment: the billet in the step S3 is subjected to a high-temperature homogenization treatment with a temperature of 1190° C. and a time of 3 h;

S5, multi-pass hot rolling: the billet in the step S4 is hot-rolled for 6 passes, water-cooled to room temperature, the starting rolling temperature is 1150°C, the finishing rolling temperature is ≥950°C, and the cumulative reduction is 70%, to obtain hot rolled plate;

S6. Solution treatment: the hot-rolled sheet in the step S5 is subjected to a solution treatment at a temperature of 1000° C. for 0.5 h, and then water-cooled to room temperature to obtain a finished multi-phase composite high-strength, high-toughness and low-density steel.

The density of the hot-rolled sheet prepared in the step S5 is 6.5g/cm ³ , the yield strength is 910MPa, the tensile strength is 1100MPa, the elongation is 42%, and the V-notch impact energy at -40°C is 30J; the step The yield strength of the finished multiphase composite high-strength high-toughness low-density steel prepared by S6 is 829MPa, the tensile strength is 1091MPa, the elongation is 44%, and the V-notch impact energy at -40°C is 57J.

The metallographic structure and intragranular κ carbides in this example are shown in (a) and (b) in Figure 1, respectively, and the NbC transmission morphology is shown in (c) in Figure 1, and the size of κ carbides < 1nm, the content is less than 3%, the δ ferrite + NiAl phase is BCC structure, the total content is 10.5% by XRD, the δ ferrite size is 20-50μm, the B ₂ phase size is 0.5-5μm, and the NbC size 20-100nm, the content is less than 0.1%.

Table 1 below shows the quantitative analysis results of EPMA elements of delta ferrite, austenite and NiAl phase. The delta ferrite and NiAl phases of the BCC structure are rich in Ni and Al elements and poor in Mn, Cr and C elements. That is to say, the addition of Ni element introduces NiAl strengthening phase, while Cr element is segregated in austenite to inhibit the precipitation of κ carbide and stabilize the austenite matrix.

Table 1

mn al Ni Cr C Fe Delta ferrite 21.7 13.7 7.9 2.3 0.5 margin Austenitic 28.1 9.5 3.1 3.2 1.6 margin NiAl phase 21.5 13.5 8.4 2.6 0.7 margin

Example 2

A multi-phase composite high-strength, high-toughness and low-density steel, the chemical composition of the multi-phase composite high-strength, high-toughness and low-density steel is: 1.08wt.%C, 27.5wt.%Mn, 10.7wt.%Al, 3.3 wt.%Cr, 1.6wt.%Ni, 0.025wt.%Nb, 0.01wt.%S, 0.003wt.%P, the balance is Fe and unavoidable impurities.

The preparation method of described multiphase composite high-strength high-toughness low-density steel, described preparation method comprises the steps:

S1, smelting: Proportioning and weighing according to the chemical composition content of the required multi-phase composite high-strength, high-toughness and low-density steel, using a vacuum induction furnace to fully smelt evenly, and casting to obtain an ingot;

S2, the first homogenization treatment: the ingot in the step S1 is subjected to a high-temperature homogenization treatment with a temperature of 1120° C. and a time of 11 hours;

S3. Hot forging: forging the ingot processed in the step S2 into a billet, and the final forging temperature is >950°C;

S4, the second homogenization treatment: the billet in the step S3 is subjected to a high-temperature homogenization treatment with a temperature of 1185° C. and a time of 2 h;

S5, multi-pass hot rolling: the billet in the step S4 is hot-rolled for 7 passes, water-cooled to room temperature, the starting rolling temperature is 1140°C, the finishing rolling temperature is ≥950°C, and the cumulative reduction is 72%, to obtain hot rolled plate;

S6. Solution treatment: the hot-rolled sheet in the step S5 is subjected to a solution treatment at a temperature of 1000° C. for 1 hour, and then water-cooled to room temperature to obtain a finished multi-phase composite high-strength, high-toughness and low-density steel.

The density of the hot-rolled sheet prepared in the step S5 is 6.5g/cm ³ , the yield strength is 904MPa, the tensile strength is 1053MPa, the elongation is 45%, and the V-notch impact energy at -40°C is 36J; the step The yield strength of the finished multiphase composite high-strength high-toughness low-density steel prepared in S6 is 755MPa, the tensile strength is 1013MPa, the elongation is 50%, and the V-notch impact energy at -40°C is 51J.

Example 3

A multi-phase composite high-strength, high-toughness and low-density steel, the chemical composition of the multi-phase composite high-strength, high-toughness and low-density steel is: 1.08wt.%C, 27.3wt.%Mn, 10.5wt.%Al, 3.2 wt.%Cr, 3.2wt.%Ni, 0.04wt.%Nb, 0.005wt.%S, 0.004wt.%P, and the balance is Fe and unavoidable impurities.

The preparation method of described multiphase composite high-strength high-toughness low-density steel, described preparation method comprises the steps:

S1, smelting: Proportioning and weighing according to the chemical composition content of the required multi-phase composite high-strength, high-toughness and low-density steel, using a vacuum induction furnace to fully smelt evenly, and casting to obtain an ingot;

S2, the first homogenization treatment: the ingot in the step S1 is subjected to a high-temperature homogenization treatment with a temperature of 1140° C. and a time of 11 hours;

S3. Hot forging: forging the ingot processed in the step S2 into a billet, and the final forging temperature is >950°C;

S4, the second homogenization treatment: the billet in the step S3 is subjected to a high-temperature homogenization treatment with a temperature of 1200 ° C and a time of 2.5 h;

S5, multi-pass hot rolling: the billet in the step S4 is hot-rolled for 5 passes, water-cooled to room temperature, the starting rolling temperature is 1135°C, the finishing rolling temperature is ≥950°C, and the cumulative reduction is 68%, to obtain hot rolled plate;

S6. Solution treatment: the hot-rolled sheet in the step S5 is subjected to a solution treatment at a temperature of 1000° C. for 2 hours, and then water-cooled to room temperature to obtain a finished multiphase composite high-strength, high-toughness and low-density steel.

The density of the hot-rolled sheet prepared in the step S5 is 6.55g/cm ³ , the yield strength is 920MPa, the tensile strength is 1150MPa, the elongation is 43%, and the V-notch impact energy at -40°C is 33J; the step The yield strength of the finished multiphase composite high-strength high-toughness low-density steel prepared in S6 is 748MPa, the tensile strength is 1085MPa, the elongation is 48%, and the V-notch impact energy at -40°C is 55J.

Example 4

A multi-phase composite high-strength, high-toughness and low-density steel, the chemical composition of the multi-phase composite high-strength, high-toughness and low-density steel is: 1.05wt.%C, 28.0wt.%Mn, 10.3wt.%Al, 3.2 wt.%Cr, 0%Ni, 0.04wt.%Nb, 0.01wt.%S, 0.005wt.%P, and the balance is Fe and unavoidable impurities.

The preparation method of described multiphase composite high-strength high-toughness low-density steel, described preparation method comprises the steps:

S1, smelting: Proportioning and weighing according to the chemical composition content of the required multi-phase composite high-strength, high-toughness and low-density steel, using a vacuum induction furnace to fully smelt evenly, and casting to obtain an ingot;

S2, the first homogenization treatment: the ingot in the step S1 is subjected to a high-temperature homogenization treatment with a temperature of 1100° C. and a time of 11 hours;

S3. Hot forging: forging the ingot processed in the step S2 into a billet, and the final forging temperature is >950°C;

S4, the second homogenization treatment: the billet in the step S3 is subjected to a high-temperature homogenization treatment with a temperature of 1180° C. and a time of 4 h;

S5, multi-pass hot rolling: the billet in the step S4 is hot-rolled for 5 passes, water-cooled to room temperature, the starting rolling temperature is 1180°C, the finishing rolling temperature is ≥950°C, and the cumulative reduction is 65%, to obtain hot rolled plate;

S6. Solution treatment: the hot-rolled sheet in the step S5 is subjected to a solution treatment at a temperature of 1000° C. for 1 hour, and then water-cooled to room temperature to obtain a finished multi-phase composite high-strength, high-toughness and low-density steel.

The density of the hot-rolled sheet prepared in the step S5 is 6.56g/cm ³ , the yield strength is 690MPa, the tensile strength is 965MPa, the elongation is 52%, and the V-notch impact energy at -40°C is 62J; the step The yield strength of the finished multiphase composite high-strength high-toughness low-density steel prepared in S6 is 585MPa, the tensile strength is 880MPa, the elongation is 68%, and the V-notch impact energy at -40°C is 80J.

As shown in Figures 2 and 3, the comparison of the engineering stress-strain curves and strain hardening curves of Example 2 and Example 4 shows that the presence of NiAl phase makes the strength significantly improved, and at the same time increases the strain hardening rate.

Example 5

A multi-phase composite high-strength, high-toughness and low-density steel, the chemical composition of the multi-phase composite high-strength, high-toughness and low-density steel is: 1.06wt.%C, 27.7wt.%Mn, 10.4wt.%Al, 3.1 wt.%Cr, 0.5wt.%Ni, 0.035wt.%Nb, 0.01wt.%S, 0.004wt.%P, and the balance is Fe and unavoidable impurities.

The preparation method of described multiphase composite high-strength high-toughness low-density steel, described preparation method comprises the steps:

S1, smelting: Proportioning and weighing according to the chemical composition content of the required multi-phase composite high-strength, high-toughness and low-density steel, using a vacuum induction furnace to fully smelt evenly, and casting to obtain an ingot;

S2, the first homogenization treatment: the ingot in the step S1 is subjected to a high-temperature homogenization treatment with a temperature of 1150° C. and a time of 13 hours;

S3. Hot forging: forging the ingot processed in the step S2 into a billet, and the final forging temperature is >950°C;

S4, the second homogenization treatment: the billet in the step S3 is subjected to a high-temperature homogenization treatment with a temperature of 1200°C and a time of 2-4h;

S5, multi-pass hot rolling: the billet in the step S4 is hot-rolled for 7 passes, water-cooled to room temperature, the starting rolling temperature is 1130°C, the finishing rolling temperature is ≥950°C, and the cumulative reduction is 80%, to obtain hot rolled plate;

S6. Solution treatment: the hot-rolled sheet in the step S5 is subjected to a solution treatment at a temperature of 1000° C. for 0.5 h, and then water-cooled to room temperature to obtain a finished multi-phase composite high-strength, high-toughness and low-density steel.

The density of the hot-rolled sheet prepared in the step S5 is 6.56g/cm ³ , the yield strength is 700MPa, the tensile strength is 980MPa, the elongation is 58%, and the V-notch impact energy at -40°C is 67J; the step The yield strength of the finished multiphase composite high-strength high-toughness low-density steel prepared by S6 is 580MPa, the tensile strength is 895MPa, the elongation is 60%, and the V-notch impact energy at -40°C is 86J.

Example 6

A multi-phase composite high-strength, high-toughness and low-density steel, the chemical composition of the multi-phase composite high-strength, high-toughness and low-density steel is: 1.07wt.%C, 27.1wt.%Mn, 10.4wt.%Al, 3.0wt.% wt.%Cr, 0.9wt.%Ni, 0.03wt.%Nb, 0.01wt.%S, 0.003wt.%P, and the balance is Fe and unavoidable impurities.

The preparation method of described multiphase composite high-strength high-toughness low-density steel, described preparation method comprises the steps:

S1, smelting: Proportioning and weighing according to the chemical composition content of the required multi-phase composite high-strength, high-toughness and low-density steel, using a vacuum induction furnace to fully smelt evenly, and casting to obtain an ingot;

S2, the first homogenization treatment: the ingot in the step S1 is subjected to a high-temperature homogenization treatment with a temperature of 1123° C. and a time of 12.5 hours;

S3. Hot forging: forging the ingot processed in the step S2 into a billet, and the final forging temperature is >950°C;

S4, the second homogenization treatment: the billet in the step S3 is subjected to a high-temperature homogenization treatment with a temperature of 1195° C. and a time of 2.8 hours;

S5, multi-pass hot rolling: the billet in the step S4 is hot-rolled for 6 passes, water-cooled to room temperature, the starting rolling temperature is 1160°C, the finishing rolling temperature is ≥950°C, and the cumulative reduction is 73%, to obtain hot rolled plate;

S6. Solution treatment: the hot-rolled sheet in the step S5 is subjected to a solution treatment at a temperature of 1000° C. for 2 hours, and then water-cooled to room temperature to obtain a finished multiphase composite high-strength, high-toughness and low-density steel.

The density of the hot-rolled sheet prepared in the step S5 is 6.55g/cm ³ , the yield strength is 670MPa, the tensile strength is 940MPa, the elongation is 48%, and the V-notch impact energy at -40°C is 56J; the step The yield strength of the finished multiphase composite high-strength high-toughness low-density steel prepared in S6 is 560MPa, the tensile strength is 840MPa, the elongation is 63%, and the V-notch impact energy at -40°C is 85J.

In the above scheme, the present invention obtains a low-cost and high-efficiency multi-phase composite high-strength high-toughness low-density steel and its preparation method through the selection of microalloying element composition and content and the preparation method.

The phase structure obtained by the invention is an austenite matrix, kappa carbide, delta ferrite, NiAl phase and NbC precipitated phase.

The invention refines the austenite grains through the three phases of delta ferrite, NbC and NiAl, improves the work hardening ability, and improves the comprehensive mechanical properties of the steel.

The density of the low-density steel of the present invention is ≤6.4g/cm ³ , the yield strength is 585-910MPa, the tensile strength is 880-1100MPa, the elongation is 42-68%, and the V-notch impact energy at -40°C is greater than 50J; Not only the weight loss effect is obvious, but also the strength and toughness are improved synergistically.

The above description is a preferred embodiment of the present invention. It should be pointed out that for those skilled in the art, some improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications It should also be regarded as the protection scope of the present invention.

Claims (7)

1. The multiphase composite high-strength high-toughness low-density steel is characterized by comprising the following chemical components in percentage by mass: 1.05-1.10wt.% C, 27.0-28.0wt.% Mn, 10.3-11.0wt.% Al, 3.0-3.5wt.% Cr, 0-3.6wt.% Ni, 0.02-0.04wt.% Nb, S less than or equal to 0.01%, P less than or equal to 0.005%, and the balance Fe and unavoidable impurities;

the density of the multi-phase composite high-strength high-toughness low-density steel is less than or equal to 6.56g/cm ³ The yield strength is 585-910MPa, the tensile strength is 880-1100MPa, the elongation is 42-68%, and the impact energy of a V-shaped notch at the temperature of minus 40 ℃ is more than 50J;

the structure of the multiphase composite high-strength high-toughness low-density steel is an austenite matrix, kappa carbide, delta ferrite, a NiAl phase and an NbC precipitated phase; wherein: the content of kappa carbide is less than 3 percent, delta ferrite and NiAl phases are BCC structures, the content of the beta ferrite and the NiAl phases is 3 to 11 percent by XRD detection, and the content of NbC is less than 0.1 percent.

2. Method for the preparation of a multi-phase composite high strength high toughness low density steel according to claim 1, characterized in that it comprises the following steps:

s1, smelting: weighing the chemical components according to the required chemical component content of the multiphase composite high-strength high-toughness low-density steel in proportion, fully and uniformly smelting by adopting a vacuum induction furnace, and casting to obtain a cast ingot;

s2, first homogenization treatment: performing high-temperature homogenization treatment on the cast ingot in the step S1;

s3, hot forging: forging the cast ingot processed in the step S2 into a square billet;

s4, second homogenization treatment: performing high-temperature homogenization treatment on the square billet in the step S3;

s5, multi-pass hot rolling: carrying out multi-pass hot rolling on the square billet obtained in the step S4, and cooling the square billet to room temperature by water to obtain a hot rolled plate;

s6, solution treatment: and (5) carrying out solution treatment on the hot rolled plate in the step S5, and then cooling the hot rolled plate to room temperature by water to obtain the finished product of the multiphase composite high-strength high-toughness low-density steel.

3. The method for preparing the multi-phase composite high-strength high-toughness low-density steel according to claim 2, wherein the temperature of the first homogenization treatment in the step 2 is 1100-1150 ℃ and the time is 11-13h.

4. The method for producing a multi-phase composite high strength high toughness low density steel according to claim 3, wherein the forging temperature in step 3 is the homogenization treatment temperature in step 2, and the finish forging temperature is > 950 ℃.

5. The method for preparing the multi-phase composite high-strength high-toughness low-density steel as claimed in claim 2, wherein the temperature of the second homogenization treatment in the step 4 is 1180-1200 ℃ for 2-4h.

6. The method for preparing the multiphase composite high-strength high-toughness low-density steel as claimed in claim 2, wherein the multi-pass hot rolling in the step 5 is 5-7 passes of hot rolling, the initial rolling temperature is 1130-1180 ℃, the final rolling temperature is not less than 950 ℃, and the accumulated reduction is 65-80%.

7. The method for preparing the multi-phase composite high-strength high-toughness low-density steel according to claim 2, wherein the solution treatment temperature in the step 6 is 1000 ℃ and the time is 0.5-2h.

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