CN105039844A - Vanadium-contained TAM steel and manufacturing method thereof - Google Patents

Abstract

The invention relates to a vanadium-containing TAM steel and a manufacturing process thereof, belonging to the technical field of metal composition design and thermal processing. The invention is a vanadium-containing TAM steel, the chemical composition of which is calculated by weight percentage: C? 0.18～0.21%, Si? 1.48～1.55%, Mn1.90～2.20%, P≤0.020%, S≤0.015%, V? 0.04～0.06%, Al≤0.04%, the balance is Fe and unavoidable impurities. The present invention adopts a vanadium alloying method to add an appropriate amount of vanadium, and improves the strength and toughness of the TAM steel through the precipitation of vanadium carbides, etc., thereby improving the comprehensive mechanical properties of the vanadium-containing TAM steel, so that the steel plate has higher strength and plasticity. In particular, it has excellent resistance to hydrogen-induced delayed fracture performance. The production of the vanadium-containing TAM steel of the present invention adopts a new process—Q&P process to make the structure and performance of the steel more stable.

Description

Vanadium-containing TAM steel and its manufacturing method

technical field

The invention relates to a vanadium-containing TAM steel and a manufacturing process thereof, belonging to the technical field of metal composition design and thermal processing.

Background technique

TAM steel, also known as TRIP type annealed martensitic steel (TRIP-aided Annealed Martensite Matrix), is a kind of Q&P steel. As the third-generation AHSS (Advanced High Strength Steels) steel, Q&P (Quenching and Partitioning) steel for automobiles has natural advantages and has achieved a good match between strength and plasticity. Laboratory data shows that the strength of Q&P steel for automobiles is above 1000 MPa, and the elongation reaches 18 % or more, fully capable of meeting the requirements of bumpers (anti-collision beams), side anti-collision beams (W-type) and other components. The biggest feature of TAM steel is that it breaks through the polygonal ferrite matrix or bainite matrix structure of traditional TRIP steel, and uses the annealed lath martensite structure formed when lath martensite is reheated in the two-phase region. The flaky retained austenite between the laths has obtained excellent mechanical properties. This type of steel can also generally be strengthened by adding Nb, V and Ti, using precipitates. Vanadium is a strong carbonitride forming element, which is widely used due to its good precipitation strengthening effect and secondary precipitation during tempering. In recent years, the development of ultra-high-strength steel and the problem of hydrogen-induced delayed fracture have become increasingly prominent, and the role of vanadium in improving the resistance of ultra-high-strength steel to hydrogen-induced delayed fracture has also been extensively studied.

Among them, the reason why the transformation-induced plasticity steel (TRIP steel) has better performance than other high-strength steels is that according to the principle of alloying and phase transformation of steel, it adopts specific chemical composition and unique heat treatment process to make full use of the "phase transformation" in steel. induced martensitic effect". When the steel contains a certain amount of austenite-forming elements, it undergoes critical annealing at the temperature of the two-phase region (α+γ) and subsequent austempering of medium-temperature bainite to obtain a large amount of retained austenite. When the steel When deformation occurs under load, the retained austenite in the steel will induce martensitic transformation, resulting in a significant increase in the strength and plasticity of the steel, which is the "TRIP effect".

As for the new process of steel heat treatment - Q&P process, which is different from the traditional quenching-tempering process, in order to obtain stable retained austenite, the steel contains Si, Al (or even P) elements to hinder Fe ₃ The precipitation of C makes carbon distribute from martensite to austenite. Austenite should be rich in carbon and will not transform into martensite when it is cooled again. This provides a new and effective process for high-strength steel with toughness. At the same time, after the formation of a stable austenite film around the martensite bundles, the hydrogen-induced crack growth rate is reduced, thereby improving the resistance to hydrogen-induced delayed fracture of the steel.

Most of the research on TRIP steel in the prior art uses ordinary steel without adding vanadium, and the process only uses traditional technology. The comprehensive mechanical properties of the TRIP steel prepared by it, such as strength and plasticity, especially its resistance to hydrogen-induced delayed fracture, Neither can meet the requirements of the third generation of automotive steel.

Contents of the invention

The first technical problem to be solved by the present invention is to provide a vanadium-containing TAM steel.

Vanadium-containing TAM steel, its chemical composition is calculated by weight percentage: C0.18～0.21%, Si1.48～1.55%, Mn1.90～2.20%, P≤0.020%, S≤0.015%, V0.04～0.06 %, Al≤0.04%, the balance is Fe and unavoidable impurities.

Further, as a preferred technical solution, the chemical composition of the vanadium-containing TAM steel mentioned above is calculated by weight percentage: C0.1963%, Si1.53%, Mn2.13%, P0.0067%, S0.0056% , V0.052%, Al0.0088%, and the balance is Fe and unavoidable impurities.

The vanadium-containing TAM steel mentioned above has yield strength R _p0.2 > 500MPa, tensile strength Rm > 1050MPa, elongation after fracture A > 25%, and strong-plastic product Rm×A > 25GPa·%.

Further, as a preferred technical solution, the above-mentioned vanadium-containing TAM steel has a yield strength R _p0.2 =612MPa, a tensile strength Rm=1077MPa, an elongation after fracture A=27.1%, and a strong-plastic product Rm×A = 29.2 GPa·%.

The metallographic structure of the vanadium-containing TAM steel described above is a mixed structure of martensite matrix + retained austenite + bainite/ferrite.

In order to make full use of my country's vanadium-titanium magnetite resources, improve the strength and toughness of TAM steel, improve the comprehensive mechanical properties and excellent hydrogen-induced delayed fracture resistance of vanadium-containing TAM steel, the invention adopts a new vanadium microalloying composition design, and the slab Precipitation of vanadium-containing carbides and the like improves the strength and toughness of TAM steel. By systematically and scientifically grasping the hydrogen trap potential of various structural defects and precipitates in steel, a solution for hydrogen-storage steel materials and ultra-high-strength steel to resist hydrogen-induced delayed fracture is established, which is essential for the development of the third-generation automotive steel It provides strategic material reserve technology for the utilization of hydrogen energy in the future, promotes the sustainable development of the national economy, and provides material guarantee for maintaining national energy security. At the same time, our research in this field will be at the forefront of the world, and material design and control technology with independent intellectual property rights will be formed.

The second technical problem to be solved by the present invention is to provide a method for preparing vanadium-containing TAM steel.

The preparation method of vanadium-containing TAM steel mainly includes smelting by traditional mechanical rolling process, hot rolling, cold rolling and new process Q&P process, which specifically includes the following steps:

a. Mechanical rolling process: Smelting and casting steel billets into slabs, heating at 1150-1250°C for 70-90 minutes, then hot-rolling them into 3-5mm thick hot-rolled steel plates, and then cold-rolling them to 1- 1.5mm, the cold rolling reduction rate is 65-75%, and the ferrite + pearlite structure is obtained; among them, the hot rolling finishing temperature is 750-850°C, and the coiling temperature is 650-700°C;

b. Q&P process: heat the cold-rolled sheet obtained in step a to the austenitizing temperature of 900-920°C at 10°C/s, keep it warm for 600s, then cool it down to room temperature at 50°C/s; then heat it at 10°C/s s Reheat to annealing temperature of 760-850°C, hold for 600s, then cool down to partition temperature of 150-450°C at 50°C/s, hold for 50-200s, and finally cool down to room temperature at 50°C/s.

Further, as a more preferred technical solution, the preparation method of the above-mentioned vanadium-containing TAM steel:

In step a, the slab is preferably heated at 1200° C. for 80 minutes, then hot-rolled to form a 4 mm thick hot-rolled steel plate, and then cold-rolled to obtain a 1.2 mm cold-rolled steel plate, and the cold-rolled reduction rate is 70%; , the hot rolling finishing temperature is preferably 800°C, and the coiling temperature is preferably 670°C;

In step b, the cold-rolled sheet obtained in step a is first heated to the austenitizing temperature of 920°C at 10°C/s, kept for 600s, and then cooled to room temperature at 50°C/s; then heated again at 10°C/s to The annealing temperature is 800°C, the temperature is kept for 600s, then the temperature is lowered to the partition temperature of 400°C at 50°C/s, the temperature is kept at 200s, and finally the temperature is lowered to room temperature at 50°C/s, and the metallographic structure of the present invention is martensite matrix + retained austenite TAM steel with a mixed structure of body + bainite/ferrite.

The TAM steel prepared by the above-mentioned preferred preparation method of vanadium-containing TAM steel has yield strength R _p0.2 = 612MPa, tensile strength Rm = 1077MPa, elongation after fracture A = 27.1%, and strong plastic product Rm × A = 29.2 GPa·%.

Wherein, the hot-rolling process in step a can use a 2050 hot-rolled strip mill. Before cold-rolling on the cold-rolling mill, the hot-rolled steel plate needs to be pickled to remove surface scale and oil stains.

The present invention adopts a vanadium alloying method to add an appropriate amount of vanadium, and improves the strength and toughness of the TAM steel through the precipitation of vanadium carbides, etc., thereby improving the comprehensive mechanical properties of the vanadium-containing TAM steel, so that the steel plate has higher strength and plasticity. In particular, it has excellent resistance to hydrogen-induced delayed fracture performance. Compared with the common production method, the production process of the vanadium-containing TAM steel of the present invention adds an intermediate annealing process, so that the structure and performance of the steel are more stable.

Detailed ways

Vanadium-containing TAM steel, its chemical composition is calculated by weight percentage: C0.18～0.21%, Si1.48～1.55%, Mn1.90～2.20%, P≤0.020%, S≤0.015%, V0.04～0.06 %, Al≤0.04%, the balance is Fe and unavoidable impurities.

Further, as a preferred technical solution, the chemical composition of the vanadium-containing TAM steel mentioned above is calculated by weight percentage: C0.1963%, Si1.53%, Mn2.13%, P0.0067%, S0.0056% , V0.052%, Al0.0088%, and the balance is Fe and unavoidable impurities.

The vanadium-containing TAM steel mentioned above has yield strength R _p0.2 > 500MPa, tensile strength Rm > 1050MPa, elongation after fracture A > 25%, and strong-plastic product Rm×A > 25GPa·%.

Further, as a preferred technical solution, the above-mentioned vanadium-containing TAM steel has a yield strength R _p0.2 =612MPa, a tensile strength Rm=1077MPa, an elongation after fracture A=27.1%, and a strong-plastic product Rm×A = 29.2 GPa·%.

The metallographic structure of the vanadium-containing TAM steel described above is a mixed structure of martensite matrix + retained austenite + bainite/ferrite.

In order to make full use of my country's vanadium-titanium magnetite resources, improve the strength and toughness of TAM steel, improve the comprehensive mechanical properties and excellent hydrogen-induced delayed fracture resistance of vanadium-containing TAM steel, the invention adopts a new vanadium microalloying composition design, and the slab Precipitation of vanadium-containing carbides and the like improves the strength and toughness of TAM steel. By systematically and scientifically grasping the hydrogen trap potential of various structural defects and precipitates in steel, a solution for hydrogen-storage steel materials and ultra-high-strength steel to resist hydrogen-induced delayed fracture is established, which is essential for the development of the third-generation automotive steel It provides strategic material reserve technology for the utilization of hydrogen energy in the future, promotes the sustainable development of the national economy, and provides material guarantee for maintaining national energy security. At the same time, our research in this field will be at the forefront of the world, and material design and control technology with independent intellectual property rights will be formed.

The preparation method of vanadium-containing TAM steel comprises the following steps:

a. Mechanical rolling process: Smelting and casting steel billets into slabs, heating at 1150-1250°C for 70-90 minutes, then hot-rolling them into 3-5mm thick hot-rolled steel plates, and then cold-rolling them to 1- 1.5mm, the cold rolling reduction rate is 65-75%, and the ferrite + pearlite structure is obtained; among them, the hot rolling finishing temperature is 750-850°C, and the coiling temperature is 650-700°C;

b. Q&P process: heat the cold-rolled sheet obtained in step a to the austenitizing temperature of 900-920°C at 10°C/s, keep it warm for 600s, then cool it down to room temperature at 50°C/s; then heat it at 10°C/s s Reheat to annealing temperature of 760-850°C, hold for 600s, then cool down to partition temperature of 150-450°C at 50°C/s, hold for 50-200s, and finally cool down to room temperature at 50°C/s.

Further, as a more preferred technical solution, the preparation method of the above-mentioned vanadium-containing TAM steel:

In step a, the slab is preferably heated at 1200° C. for 80 minutes, then hot-rolled to form a 4 mm thick hot-rolled steel plate, and then cold-rolled to obtain a 1.2 mm cold-rolled steel plate, and the cold-rolled reduction rate is 70%; , the hot rolling finishing temperature is preferably 800°C, and the coiling temperature is preferably 670°C;

In step b, the cold-rolled sheet obtained in step a is first heated to the austenitizing temperature of 920°C at 10°C/s, kept for 600s, and then cooled to room temperature at 50°C/s; then heated again at 10°C/s to The annealing temperature is 800°C, the temperature is kept for 600s, then the temperature is lowered to the partition temperature of 400°C at 50°C/s, the temperature is kept at 200s, and finally the temperature is lowered to room temperature at 50°C/s, and the metallographic structure of the present invention is martensite matrix + retained austenite TAM steel with a mixed structure of body + bainite/ferrite.

The TAM steel prepared by the above-mentioned preferred preparation method of vanadium-containing TAM steel has yield strength R _p0.2 = 612MPa, tensile strength Rm = 1077MPa, elongation after fracture A = 27.1%, and strong plastic product Rm × A = 29.2 GPa·%.

Wherein, the hot-rolling process in step a can use a 2050 hot-rolled strip mill. Before cold-rolling on the cold-rolling mill, the hot-rolled steel plate needs to be pickled to remove surface scale and oil stains.

The specific implementation of the present invention will be further described below in conjunction with the examples, and the present invention is not limited to the scope of the examples.

Example 1

The composition percentage of each component of vanadium-containing TAM steel of the present invention is shown in Table 1 with reference to:

Table 1 Composition percentage of vanadium-containing TAM steel

According to the composition percentages of vanadium-containing TAM steel in Table 1, traditional mechanical rolling process smelting, hot rolling, cold rolling and new process Q&P process are carried out. The specific process parameters of the traditional mechanical rolling process are shown in Table 2:

Table 2 The specific process parameters of the mechanical rolling process

The specific process parameters of the new process Q&P process are shown in Table 3:

Table 3 Q&P process specific process parameters

According to the composition percentages of the vanadium-containing TAM steel in Table 1 and the mechanical rolling process in Table 2 and the Q&P process in Table 3, the mechanical properties of the TAM steel produced are shown in Table 4:

Table 4 Mechanical properties of vanadium-containing TAM steel

serial number Yield strength/MPa Tensile strength/MPa elongation after break Strong Plastic Product/GMa·% 1 612 1077 27.1% 29.2 2 668 1243 26.1% 32.4 3 687 1098 25.3% 27.8 4 669 1026 25.9% 26.6 5 654 1203 26.7% 30.5

Claims (7)

1. Vanadium-containing TAM steel, characterized in that: its chemical composition is: C0.18～0.21%, Si1.48～1.55%, Mn1.90～2.20%, P≤0.020%, S≤0.015%, V0.04～0.06%, Al≤0.04%, the balance is Fe and unavoidable impurities. 2. The vanadium-containing TAM steel according to claim 1, characterized in that: its chemical composition is calculated by weight percentage: C0.1963%, Si1.53%, Mn2.13%, P0.0067%, S0.0056% , V0.052%, Al0.0088%, and the balance is Fe and unavoidable impurities. 3. According to the described vanadium-containing TAM steel according to claim 1 or 2, it is characterized in that: the yield strength R _p0.2 of steel > 500MPa, the tensile strength Rm > 1050MPa, the elongation after fracture A > 25%, the strong plastic product Rm ×A>25GPa·%. 4. The vanadium-containing TAM steel according to claim 3, characterized in that: yield strength R _p0.2 of the steel = 612MPa, tensile strength Rm = 1077MPa, elongation after fracture A = 27.1%, strong plastic product Rm × A = 29.2 GPa·%. 5. The method for preparing vanadium-containing TAM steel according to any one of claims 1 to 4, characterized in that: comprising the following steps: a. Mechanical rolling process: steel is smelted and cast into a slab, heated at 1150-1250°C for 70-90 minutes, hot-rolled to obtain a 3-5mm thick hot-rolled steel plate, and then cold-rolled to obtain a 1-1.5mm thick cold-rolled steel plate Steel plate; among them, the hot rolling finishing temperature is 750-850°C, the coiling temperature is 650-700°C, and the cold rolling reduction rate is 65-75%; b. Q&P process: heat the cold-rolled sheet obtained in step a to the austenitizing temperature of 900-920°C at 10°C/s, keep it warm for 600s, then cool it down to room temperature at 50°C/s; then heat it at 10°C/s s Reheat to annealing temperature of 760-850°C, hold for 600s, then cool down to partition temperature of 150-450°C at 50°C/s, hold for 50-200s, and finally cool down to room temperature at 50°C/s. 6. according to the preparation method of the described vanadium-containing TAM steel of claim 5, it is characterized in that: after the slab is heated at 1200 ℃ for 80min in a step, then hot-rolled and rolled into 4mm thick hot-rolled steel plate, then through cold rolling A 1.2 mm thick cold-rolled steel plate was obtained; wherein, the hot-rolling finishing temperature was 800° C., the coiling temperature was 670° C., and the cold-rolling reduction rate was 70%. 7. The method for preparing vanadium-containing TAM steel according to claim 5, characterized in that: in step b, the austenitization temperature is 920°C; the annealing temperature is 800°C; the partition temperature is 400°C, and the partition temperature is kept for 200s.