CN107419179A - A kind of high tough microalloying contains manganese hot rolled steel plate and preparation method thereof in Al - Google Patents

Abstract

The invention discloses a high-strength and toughness micro-alloyed Al-containing medium-manganese hot-rolled steel plate and a preparation method thereof, which belong to the technical field of new-generation steel plates for automobiles. The key of the invention is to obtain a certain volume fraction of retained austenite phase through reasonable chemical composition and process design, so as to realize the control of grain size and the distribution of alloy elements. Its composition by mass percentage is: C: 0.15-0.2%, Mn: 7.6-8%, Al: 5.4-6%, Si: 0.01-0.02%, Nb: 0.02-0.04%, and the balance is Fe and unavoidable of impurities. The preparation method is as follows: a billet is prepared according to the composition ratio, and after heating and heat preservation, hot rolling is performed to obtain a hot-rolled steel plate, and after the hot-rolled steel plate is air-cooled to room temperature, post-rolling heat treatment is performed to obtain a density of 6.85-6.99g/cm ³ , The tensile strength is 940-1250MPa, the elongation is 20-40%, and the strength-plastic product is more than 30GPa%.

Description

A kind of high-strength and toughness micro-alloyed hot-rolled steel plate containing Al and medium manganese and preparation method thereof

technical field

The invention belongs to the technical field of a new generation of lightweight high-strength steel plates for automobiles, and specifically relates to the composition design and preparation method of the high-strength and toughness microalloyed Al-containing medium-manganese hot-rolled steel plates.

Background technique

In response to the increasingly tense resource shortage and environmental pollution, energy conservation, environmental protection and lightweight development have become an inevitable trend in the development of the automobile industry. At present, high-strength DP steel and TRIP steel are widely used in automobiles, but their tensile strength and formability need to be further improved. Utilizing the strengthening of martensite structure and the plasticizing mechanism of metastable retained austenite, Q&P steel has gradually realized industrial application, but its comprehensive performance cannot fully meet the needs of automobile lightweight development. Therefore, it is particularly urgent to explore the compositional design and preparation methods of a new generation of high-strength and tough automotive steels in order to obtain light-weight, high-strength and tough automotive steels with higher strength, high formability, and high cost performance.

As a new type of lightweight steel with high specific strength (ratio of strength to density), medium manganese Fe-Mn-Al-C steel has excellent strength and plasticity matching, and has a very broad application prospect. In recent years, domestic scholars have carried out a large number of new species development and research work on the medium manganese series Fe-Mn-Al-C automotive steel.

The patent application number is 201310507894.9, which discloses that the medium manganese steel with a composition system of 0.1-0.4%C+3-8%Mn can be hot-rolled, cold-rolled, and continuously annealed to obtain a steel plate with a tensile strength of 980MPa and an elongation greater than 22%; Patent application number 201610927995.5 discloses C: 0.1-0.3%, Si: 0.3-3.5%, Mn: 3.0-15.0%, Al: 1.0-3.5%, V, Ti, Nb each ≤ 0.2% of the composition system of medium manganese After hot rolling, quenching + tempering, cold rolling and annealing, the steel plate can be obtained with a yield strength of 590-970MPa, a tensile strength of 980-1440MPa, a total elongation of 30-42%, and a strong-plastic product of more than 40GPa%; the patent application number is 201610592858.0 patent discloses 0.3-0.5%C, 8-12%Mn, 1.8-3.5%Al, 0.25-0.7%V medium manganese steel through hot rolling, warm rolling, bell annealing or cold rolling, continuous annealing to obtain tensile strength The strength is 1100-1600MPa, the elongation is 35-65%, and the strong-plastic product reaches 35-65GPa%.

In summary, although medium manganese steel can obtain good strength and plasticity by adjusting the chemical composition, controlling the rolling and heat treatment process, but due to the high alloy content and the addition of Nb, V, Ti and other elements, the composition is relatively high and Generally, a relatively complicated preparation process is required. On the basis of the common medium manganese steel composition system, the present invention adds 0.02-0.04% Nb element for micro-alloying, and at the same time simplifies the preparation process to one-step solution treatment to obtain a tensile strength of 940-1250 MPa and an elongation of 20-40%. , Lightweight and high-strength automotive steel with a strong-plastic content of more than 30GPa%. It not only meets the industrial performance requirements, but also reduces the production cost and process requirements, and has important economic significance and social benefits.

Contents of the invention

The purpose of the present invention is to provide a preparation method of high-strength micro-alloyed Al-containing medium-manganese hot-rolled steel plate, which adopts the design concept of combining composition and structure control, and obtains fine grains, ferrite + austenite through solid solution treatment. body duplex organization. On the basis of further optimizing and narrowing the content of carbon and manganese in medium-manganese steel, the addition of microalloy strengthening element Nb makes the steel have a higher volume fraction and stable retained austenite, and at the same time adjusts the element distribution in austenite, Reduce the content of C and Mn in the austenite, so that the retained austenite has sufficient stability to ensure that the austenite phase will undergo TRIP (transformation induced plasticity) or TWIP (twin induced plasticity) effect during the deformation process of the steel plate, Thereby, a light-weight, high-strength, high-toughness automotive steel plate with high strength and excellent plasticity is finally obtained.

In order to achieve the above object, the present invention designs a light-weight, high-strength and tough microalloyed Fe-Mn-Al-C steel, whose chemical composition is: C: 0.15-0.2%, Mn: 7.6-8.0%, Al: 5.4- 6.0%, Si: 0.01-0.02%, Nb: 0.02-0.04%, and the balance is Fe and unavoidable impurities. The density of the steel used in the experiment is 6.85-6.99g/cm ³ , which is 11.1-12.8% lower than that of pure iron.

Medium manganese Fe-Mn-Al series low-density steel has high Al content and low Mn content, and the structure at room temperature is generally based on ferrite; by precisely controlling the content of Mn, Al, and C elements in the steel to adjust the austenitic The volume fraction and grain size of the body; the microalloying element Nb can stabilize the ferrite and can effectively pin the grain boundary. At the same time, the solute Nb can delay the phase transformation from austenite to ferrite.

The preparation method of the above-mentioned high-strength and toughness micro-alloyed Al-containing medium-manganese hot-rolled steel plate is as follows:

(1) Smelting according to the above-mentioned chemical composition, obtaining the molten steel with the above-mentioned chemical composition by smelting in a converter, an electric furnace or an induction furnace, then adopting die casting to produce an ingot and forging the ingot into a slab;

(2) The billet is heated to 1200°C and held for 2 hours, which is conducive to the diffusion of alloying elements and provides a uniform original structure for subsequent rolling;

(3) The prepared slab is hot-rolled. The process is that the starting rolling temperature is 1100-1150°C, and the finishing rolling temperature is 850-900°C. It is hot-rolled into a thin plate with a thickness of 3mm after 6 passes, and coiled after rolling. Air cool to room temperature;

(4) Rapidly heat the hot-rolled steel plate to 700-1000° C. for solution treatment, keep it warm for 0.5-1 hour, and then water-quench to room temperature.

The invention provides a high-strength and toughness micro-alloyed Al-containing medium-manganese hot-rolled steel. Through optimized alloy composition and solid solution process design, the content of retained austenite in the hot-rolled steel structure is greatly increased and at the same time, the content of residual austenite is precisely adjusted. Mechanical stability of retained austenite. The addition of trace Nb elements can increase the volume fraction of austenite, refine the austenite grains, and adjust the distribution of C, Mn and other elements in the austenite. While improving the tensile strength of the steel plate, it has matching plasticity. The tensile strength is 940-1250MPa, the elongation is 20-40%, and the strong-plastic product is more than 30GPa%. At the same time, compared with the cold-rolled annealed steel widely used at present, the preparation process of hot-rolled + solution treatment adopted in the present invention is greatly simplified, which improves the feasibility of industrialization and reduces the production cost at the same time, and is suitable for steel for automobiles Lightweight development needs at this stage and in the future.

Description of drawings

Fig. 1 is the XRD image of the retained austenite content of lightweight, high-strength and toughness microalloyed Fe-Mn-Al-C steel prepared by Examples 1, 2, 4 and 6 of the present invention;

Fig. 2 is the SEM morphology image of the lightweight high-strength toughness microalloyed Fe-Mn-Al-C steel prepared by Examples 1, 2, 4 and 6 of the present invention: wherein:

(a) is the SEM morphology image of the high-strength and toughness microalloyed hot-rolled steel containing Al in the embodiment 1;

(b) is the SEM morphology image of the high-strength and toughness microalloyed hot-rolled steel containing Al in the embodiment 2;

(c) is the SEM image of the high-strength and toughness microalloyed hot-rolled Al-containing manganese steel of embodiment 4;

(d) is the SEM image of the high-strength and toughness microalloyed hot-rolled steel containing Al and manganese in Example 6;

Fig. 3 is the stress-strain curve image of the high-strength and toughness microalloyed Al-containing medium-manganese hot-rolled steel prepared by Examples 1, 2, 3, 4, 5 and 6 of the present invention;

Fig. 4 is the SEM morphology image of the Nb-containing precipitates of the high-strength and toughness microalloyed Al-containing medium-manganese hot-rolled steel prepared in Example 1 of the present invention;

Figure 5 is the TEM morphology image and diffraction spot of Nb-containing precipitates in the high-strength and toughness micro-alloyed Al-containing medium-manganese hot-rolled steel prepared in Example 1 of the present invention

Fig. 6 is the EDS energy spectrum of the Nb-containing precipitates of the high-strength and toughness microalloyed Al-containing medium-manganese hot-rolled steel prepared in Example 1 of the present invention

Fig. 7 is an EPMA morphology diagram of C and Mn partitioning of the high-strength and toughness microalloyed Al-containing medium-manganese hot-rolled steel prepared in Example 4 of the present invention,

in:

(a) for the high strength and toughness microalloying containing Al medium manganese hot-rolled steel prepared by embodiment 4 selected area SEM topography figure;

(b) is the high-strength and toughness microalloying containing Al middle manganese hot-rolled steel selected region C element distribution diagram prepared in embodiment 4;

(c) is the Mn element distribution diagram of the selected region of the high-strength and toughness microalloyed Al-containing manganese hot-rolled steel prepared in Example 4;

detailed description

The present invention will be described in further detail below in conjunction with specific embodiments.

Example 1

The chemical composition and mass percentage of the steel are as follows: C: 0.15%, Mn: 7.87%, Al: 5.91%, Nb: 0.03%, Si: 0.02%, and the remainder is Fe and unavoidable impurities. The steel ingot is smelted in a vacuum induction furnace, the steel ingot is heated to 1200°C for 2 hours, and then forged into a billet.

Heat the steel billet to 1200°C for 2 hours, and hot-roll it into a thin plate with a thickness of 3mm through 6 passes. The final rolling temperature is 850-900°C, and then air-cool to room temperature.

Heat the hot-rolled steel plate to 700°C in a heating furnace, keep it warm for 1 h, and water quench to room temperature.

Relevant performance tests were carried out on the high-strength and toughness micro-alloyed Al-containing medium-manganese hot-rolled steel obtained in this example. The XRD characterization results are shown in Figure 1; the SEM morphology image is shown in Figure 2(a); according to GB/T228-2002 "Metal material room temperature tensile test method" processes the heat-treated steel plate into a tensile sample, and the stress-strain curve is shown in Figure 3; the SEM high-magnification image containing Nb precipitates, the TEM transmission image and the selected diffraction spot and EDS energy spectrum results These are shown in Figures 4, 5 and 6, respectively.

Example 2

The chemical composition and mass percentage of the steel are as follows: C: 0.18%, Mn: 7.58%, Al: 5.98%, Nb: 0.02%, Si: 0.02%, and the remainder is Fe and unavoidable impurities. The steel ingot is smelted in a vacuum induction furnace, the steel ingot is heated to 1200°C for 2 hours, and then forged into a billet.

Heat the steel billet to 1200°C for 2 hours, and hot-roll it into a thin plate with a thickness of 3mm through 6 passes. The final rolling temperature is 850-900°C, and then air-cool to room temperature.

Heat the hot-rolled steel plate to 800° C. in a heating furnace, keep it warm for 1 hour, and water-quench to room temperature.

Relevant performance tests were carried out on the high-strength and toughness micro-alloyed Al-containing medium-manganese hot-rolled steel prepared in this example. The XRD characterization results are shown in Figure 1; the SEM morphology image is shown in Figure 2(b); the stress-strain curve is shown in Figure 3 shown.

Example 3

The chemical composition and mass percentage of steel are as follows: C: 0.15%, Mn: 7.87%, Al: 5.91%, Nb: 0.01%, Si: 0.01%, and the remainder is Fe and unavoidable impurities. The steel ingot is smelted in a vacuum induction furnace, the steel ingot is heated to 1200°C for 2 hours, and then forged into a billet.

Heat the steel billet to 1200°C for 2 hours, and hot-roll it into a thin plate with a thickness of 3mm through 6 passes. The final rolling temperature is 850-900°C, and then air-cool to room temperature.

Heat the hot-rolled steel plate to 850°C in a heating furnace, keep it warm for 1 h, and water quench to room temperature.

Relevant performance tests were carried out on the high-strength and toughness micro-alloyed Al-containing medium-manganese hot-rolled steel prepared in this example, and the stress-strain curve is shown in Figure 3.

Example 4

The chemical composition and mass percentage of the steel are as follows: C: 0.21%, Mn: 7.78%, Al: 5.90%, Nb: 0.04%, Si: 0.01%, and the remainder is Fe and unavoidable impurities. The steel ingot is smelted in a vacuum induction furnace, the steel ingot is heated to 1200°C for 2 hours, and then forged into a billet.

Heat the steel billet to 1200°C for 2 hours, and hot-roll it into a thin plate with a thickness of 3mm through 6 passes. The final rolling temperature is 850-900°C, and then air-cool to room temperature.

Heat the hot-rolled steel plate to 900°C in a heating furnace, keep it warm for 1 h, and water quench to room temperature.

Relevant performance tests were carried out on the high-strength and toughness micro-alloyed Al-containing medium-manganese hot-rolled steel prepared in this example. The XRD characterization results are shown in Figure 1; the SEM morphology image is shown in Figure 2(c); the stress-strain curve is shown in Figure 3 Figure 7(a) shows the SEM topography of the selected area measured by EPMA, the C element distribution in the selected area is shown in Figure 7(b), and the Mn element distribution in the selected area is shown in Figure 7(c) Show.

Example 5

The chemical composition and mass percentage of the steel are as follows: C: 0.18%, Mn: 7.82%, Al: 5.56%, Nb: 0.02%, Si: 0.02%, and the remainder is Fe and unavoidable impurities. The steel ingot is smelted in a vacuum induction furnace, the steel ingot is heated to 1200°C for 2 hours, and then forged into a billet.

Heat the steel billet to 1200°C for 2 hours, and hot-roll it into a thin plate with a thickness of 3mm through 6 passes. The final rolling temperature is 850-900°C, and then air-cool to room temperature.

Heat the hot-rolled steel plate to 950°C in a heating furnace, keep it warm for 1 h, and water quench to room temperature.

Relevant performance tests were carried out on the high-strength and toughness micro-alloyed Al-containing medium-manganese hot-rolled steel prepared in this example, and the stress-strain curve is shown in Figure 3.

Example 6

The chemical composition and mass percentage of steel are as follows: C: 0.20%, Mn: 7.84%, Al: 5.69%, Nb: 0.02%, Si: 0.02%, and the remainder is Fe and unavoidable impurities. The steel ingot is smelted in a vacuum induction furnace, the steel ingot is heated to 1200°C for 2 hours, and then forged into a billet.

Heat the steel billet to 1200°C for 2 hours, and hot-roll it into a thin plate with a thickness of 3mm through 6 passes. The final rolling temperature is 850-900°C, and then air-cool to room temperature.

Heat the hot-rolled steel plate to 1000° C. in a heating furnace, keep it warm for 1 hour, and water-quench to room temperature.

Relevant performance tests were carried out on the high-strength and toughness micro-alloyed Al-containing medium-manganese hot-rolled steel prepared in this example. The XRD characterization results are shown in Figure 1; the SEM morphology image is shown in Figure 2(d); the stress-strain curve is shown in Figure 3 shown.

Claims (5)

1. A high-strength micro-alloyed Al-containing medium-manganese hot-rolled steel plate, characterized in that the chemical composition ratio of the steel plate is: C: 0.15-0.20%, Mn: 7.6-8.0%, Al: 5.4-6.0%, Si : 0.01 to 0.02%, Nb: 0.02 to 0.04%, and the balance is Fe and unavoidable impurities. 2. the preparation method of high-strength and toughness microalloying containing Al medium manganese hot rolled steel plate as claimed in claim 1, comprises smelting, forging, hot rolling, solid solution treatment, it is characterized in that, concrete steps are as follows: (1) smelting according to the chemical composition described in claim 1, and forging the cast blank into a slab; (2) Hot-rolling the slab prepared in step (1), the process is to heat the steel billet to 1200° C., keep it warm for 2 hours, hot-roll it into a thin plate with a thickness of 3 mm through 6 passes, and coil it and cool it to room temperature after rolling; (3) The hot-rolled plate is subjected to heat treatment after rolling, and the steel plate is rapidly heated to 700-1000° C. by using a solution treatment process, kept for 0.5-1 hour, and then water-quenched to room temperature. 3. The preparation method of the high-strength and toughness microalloyed Al-containing medium-manganese hot-rolled steel sheet according to claim 2, characterized in that, the hot-rolling start-rolling temperature in step (2) is 1050-1150° C., and the finish-rolling temperature is 850～900℃. 4. The method for preparing high-strength and toughness microalloyed Al-containing medium-manganese hot-rolled steel sheet according to claim 2, characterized in that the quenching temperature of the hot-rolled sheet in step (3) is 900° C., and the holding time is 1 h. 5. A kind of high-strength and toughness micro-alloyed Al-containing medium-manganese hot-rolled steel plate as claimed in claim 1, characterized in that, after heat treatment, the steel plate presents a two-phase structure mainly composed of δ-ferrite+austenite, and the austenite The volume fraction of tenite is higher than 34%, the grain size of austenite is 5-16 μm, the content of Mn in austenite is 8.65-9.47%, and the content of C is 0.92-1.01%. The Al hot-rolled medium-manganese steel plate has a density of 6.85-6.99g/cm ³ , a tensile strength of 940-1250MPa, an elongation of 20-40%, and a strong-plastic product of more than 30GPa%.