Boron-containing ferrite-pearlite type high-toughness non-quenched and tempered steel and hot forging method

Abstract

The invention discloses boron-containing ferrite-pearlite type high-toughness non-quenched and tempered steel and a hot forging method. The non-quenched and tempered steel is prepared from, by mass, 0.28%-0.32% of C, 0.4%-0.6% of Si, 1.2%-1.5% of Mn, 0.1%-0.4% of Cr, 0.1%-0.3% of V, 0.04%-0.06% of S, 0.01%-0.03% of Ti, 0.001%-0.003% of B, 0.002%-0.006% of O, smaller than or equal to 0.01% of P, smaller than or equal to 0.005% of N and the balance Fe and inevitable impurities. A proper amount of boron element is added, and grain boundary ferrite precipitation is inhibited by means of the grain boundary segregation effect; a stable nucleation core of the intracrystalline ferrite is formed in the steel, pearlite is promoted to nucleate on the grain boundary ferrite and the intracrystalline ferrite at the same time, and the performance level of existing ferrite-pearlite non-quenched and tempered steel for hot forging is greatly improved.

Description

Technical Field

[0001] The invention belongs to the field of metal materials, and in particular relates to a boron-containing ferrite-pearlite type high-strength and tough non-quenched and tempered steel and a hot forging method. Background Art

[0002] Microalloyed non-quenched and tempered steel with ferrite-pearlite structure can be used in the field of hot forging, eliminating the post-forging heat treatment process, achieving energy conservation and consumption reduction, and is an important supporting material for the development of my country's manufacturing industry. However, the ferrite-pearlite structure after high-temperature hot forging is generally coarse, and due to the omission of the heat treatment process, the structure cannot be further refined, resulting in low toughness. Good strength-toughness matching is an important guarantee for lightweight components and service safety, so improving the toughness of ferrite-pearlite non-quenched and tempered steel is a key issue that needs to be urgently solved.

[0003] In response to the above problems, academia and industry have carried out a lot of research and practice, such as titanium microalloying, forging process control, intragranular ferrite technology, etc. Among them, intragranular ferrite technology is a more important breakthrough. It creates nucleation points inside the austenite grains so that ferrite not only precipitates at the austenite grain boundaries but also precipitates inside the austenite grains during the cooling phase transformation, thereby refining the coarse structure after hot forging and improving the toughness of non-quenched and tempered steel. However, the increase in grain boundaries caused by the precipitation of massive intragranular ferrite is relatively limited. Therefore, compared with the quenched and tempered steel with tempered troostite, the toughness of ferrite-pearlite non-quenched and tempered steel is still insufficient, and it is necessary to develop new technologies that can further refine the structure and improve the toughness.

[0004] The main way to improve the toughness of steel materials is to refine the microstructure, that is, to increase the high-angle grain boundaries in the steel. For ferrite-pearlite steel, in addition to the original austenite grain size, another key factor to consider is the size of the pearlite spherules. In the research practice of intragranular ferrite, relevant scholars found that the precipitation temperature of intragranular ferrite is lower than that of grain boundary ferrite, and it is in a "lag" state, so pearlite mainly nucleates on grain boundary ferrite. If some method can be used to lag the precipitation of grain boundary ferrite, so that the grain boundary and intragranular ferrite are in a state of simultaneous precipitation, it is expected to promote the simultaneous nucleation of pearlite on grain boundary ferrite and intragranular ferrite, increase the nucleation points of pearlite, refine the size of pearlite spherules, and improve the toughness of steel. Summary of the invention

[0005] The invention discloses a boron-containing ferrite-pearlite type high-strength and toughness non-quenched and tempered steel and a hot forging method to solve any of the above and other potential problems of the prior art.

[0006] In order to solve the above technical problems, the technical solution provided by the present invention is: a boron-containing ferrite-pearlite type high-strength and tough non-quenched and tempered steel, having the following chemical composition (mass percentage): 0.28% to 0.32% C, 0.4% to 0.6% Si, 1.2% to 1.5% Mn, 0.1% to 0.4% Cr, 0.1% to 0.3% V, 0.04% to 0.06% S, P≤0.01%, N≤0.005%, the rest is Fe and unavoidable impurities, and also contains 0.01wt% to 0.03wt% Ti, 0.002wt% to 0.006wt% O and 0.001wt% to 0.003wt% B;

[0007] Furthermore, the titanium / oxygen mass ratio in the non-quenched and tempered steel is 4-8.

[0008] Another object of the present invention is to provide a hot forging method for the non-quenched and tempered steel, the hot forging method specifically comprising the following steps:

[0009] S1) heating the boron-containing ferrite-pearlite high-strength and tough non-quenched and tempered steel billet to 1200-1300° C. and forging it into a shape;

[0010] S2) and then cooled to room temperature at a certain rate to obtain a non-quenched and tempered steel product with a tensile strength R m 850~900MPa, yield strength R p0.2 600~650MPa, elongation after fracture A is 20%~25%, and room temperature impact toughness is 40~60J / cm 2 .

[0011] Furthermore, the cooling rate in S2) is 0.1-0.5°C / s.

[0012] Furthermore, the non-quenched and tempered steel after the hot forging method has ferrite and pearlite, the volume fraction of ferrite is 15% to 25%, and the average size of pearlite nodules is less than 30 μm.

[0013] Furthermore, the pearlite of the non-quenched and tempered steel treated by the hot forging method nucleates simultaneously on the grain boundary ferrite and the intragranular ferrite, and the nucleation core of the intragranular ferrite is MnS-Ti2O3 composite particles.

[0014] Based on the above technical ideas, the present invention proposes to add an appropriate amount of boron element to ferrite-pearlite non-quenched and tempered steel, and use its grain boundary segregation effect to inhibit the precipitation of grain boundary ferrite; and through reasonable chemical composition design, a stable nucleation core of intracrystalline ferrite is formed in the steel, and the simultaneous nucleation of pearlite on grain boundary ferrite and intracrystalline ferrite is promoted; a ferrite-pearlite high-strength and tough non-quenched and tempered steel for hot forging is obtained.

[0015] The technical points of the present invention are specifically described as follows:

[0016] (1) The non-quenched and tempered steel has a low carbon content (0.28wt% to 0.32wt%) and a high manganese content (1.2wt% to 1.5wt%), which can obtain a suitable ratio of ferrite and pearlite, fully refine the pearlite lamellae, and improve strength and toughness.

[0017] (2) The non-quenched and tempered steel contains an appropriate amount of boron (0.001wt% to 0.003wt%), which can inhibit and delay the precipitation of grain boundary ferrite during the cooling phase transformation process, so that the precipitation of intragranular ferrite is no longer delayed, promote the simultaneous nucleation of pearlite on grain boundary ferrite and intragranular ferrite, refine the pearlite spheroids, and improve the toughness of the steel.

[0018] (3) The non-quenched and tempered steel also contains appropriate amounts of manganese, sulfur, titanium and oxygen elements, which can form MnS-Ti2O3 composite particles, which are the nucleation cores of intragranular ferrite. The present invention does not use the common MnS-VN composite particles, which are the nucleation cores of intragranular ferrite in medium carbon non-quenched and tempered steel, because the formation of MnS-VN composite particles requires the addition of more than 0.001wt% of nitrogen to the steel, which will lead to the formation of boron nitride and consume the solid solution boron in the steel, reducing its inhibitory effect on the precipitation of grain boundary ferrite.

[0019] Beneficial effects of the present invention:

[0020] (1) Excellent strength-toughness matching can be obtained. After hot forging at high temperature (1200-1300℃), its tensile strength R m 850~900MPa, yield strength R p0.2 600~650MPa, elongation after fracture A is 20%~25%, and room temperature impact toughness is 40~60J / cm 2 , greatly improving the performance level of existing ferrite-pearlite non-quenched and tempered steel for hot forging, and promoting its promotion and application in high-end products.

[0021] (2) Compared with conventional ferrite-pearlite non-quenched and tempered steel for hot forging, the elements such as titanium, boron, and oxygen added in the present invention hardly increase the production cost, thus having significant economic advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The present invention discloses a stress-strain curve of a tensile specimen of a boron-containing ferrite-pearlite high-strength and tough non-quenched and tempered steel for hot forging after high-temperature hot forging.

[0023] Figure 2 The optical microscope photograph of the microstructure of the boron-containing ferrite-pearlite type high-strength and tough non-quenched and tempered steel for hot forging of the present invention.

[0024] Figure 3The optical microscope photograph is of pearlite nucleation on intragranular ferrite during cooling of a boron-containing ferrite-pearlite type high-strength and tough non-quenched and tempered steel for hot forging according to the present invention. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further described below in conjunction with embodiments.

[0026] The invention discloses a boron-containing ferrite-pearlite type high-strength and tough non-quenched and tempered steel, wherein the chemical elements mass percentages thereof are: 0.28%-0.32% C, 0.4%-0.6% Si, 1.2%-1.5% Mn, 0.1%-0.4% Cr, 0.1%-0.3% V, 0.04%-0.06% S, 0.01%-0.03% Ti, 0.001%-0.003% B, 0.002%-0.006% O, P≤0.01%, N≤0.005%, and the rest are Fe and unavoidable impurities.

[0027] The tensile strength R of the boron-containing ferrite-pearlite high-strength and tough non-quenched and tempered steel for hot forging after high temperature (1200-1300° C.) hot forging is m 850~900MPa, yield strength R p0.2 600~650MPa, elongation after fracture A is 20%~25%, and room temperature impact toughness is 40~60J / cm 2 .

[0028] Embodiment 1:

[0029] A boron-containing ferrite-pearlite type high-strength and tough non-quenched and tempered steel for hot forging has the following chemical composition (mass percentage): 0.28% C, 0.4% Si, 1.2% Mn, 0.1% Cr, 0.1% V, 0.04% S, 0.01% Ti, 0.001% B, 0.002% O, 0.006% P, 0.003% N, and the rest is Fe and unavoidable impurities.

[0030] The large bars are prepared by using the conventional bar production process of steel enterprises.

[0031] The above-mentioned boron-containing ferrite-pearlite high-strength and tough non-quenched and tempered steel for hot forging is heated to 1250°C, hot forged by conventional process, and cooled to room temperature, and the cooling rate in the phase transformation zone is 0.1-0.5°C / s.

[0032] Mechanical properties of the obtained boron-containing ferrite-pearlite high-strength and tough non-quenched and tempered steel for hot forging: tensile strength R m The yield strength R is 866MPa. p0.2 The elongation after fracture is 24.6%, and the room temperature impact toughness is 42 J / cm 2 .

[0033] Embodiment 2:

[0034] A boron-containing ferrite-pearlite type high-strength and tough non-quenched and tempered steel for hot forging has the following chemical composition (mass percentage): 0.32% C, 0.6% Si, 1.5% Mn, 0.4% Cr, 0.3% V, 0.06% S, 0.03% Ti, 0.003% B, 0.006% O, 0.008% P, 0.004% N, and the rest is Fe and unavoidable impurities.

[0035] The large bars are prepared by using the conventional bar production process of steel enterprises.

[0036] The above-mentioned boron-containing ferrite-pearlite high-strength and tough non-quenched and tempered steel for hot forging is heated to 1250°C, hot forged by conventional process, and cooled to room temperature, and the cooling rate in the phase transformation zone is 0.1-0.5°C / s.

[0037] Mechanical properties of the obtained boron-containing ferrite-pearlite high-strength and tough non-quenched and tempered steel for hot forging: tensile strength R m The yield strength R is 895MPa. p0.2 The elongation after fracture is 20.6%, and the room temperature impact toughness is 58 J / cm 2 .

[0038] Embodiment 3:

[0039] A boron-containing ferrite-pearlite type high-strength and tough non-quenched and tempered steel for hot forging has the following chemical composition (mass percentage): 0.29% C, 0.52% Si, 1.31% Mn, 0.32% Cr, 0.21% V, 0.055% S, 0.02% Ti, 0.002% B, 0.004% O, 0.007% P, 0.003% N, and the rest is Fe and unavoidable impurities.

[0040] The large bars are prepared by using the conventional bar production process of steel enterprises.

[0041] The above-mentioned boron-containing ferrite-pearlite high-strength and tough non-quenched and tempered steel for hot forging is heated to 1250°C, hot forged by conventional process, and cooled to room temperature, and the cooling rate in the phase transformation zone is 0.1-0.5°C / s.

[0042] Mechanical properties of the obtained boron-containing ferrite-pearlite high-strength and tough non-quenched and tempered steel for hot forging: tensile strength R m The yield strength R is 876MPa. p0.2 The elongation after fracture is 22.1%, and the room temperature impact toughness is 51 J / cm 2 .

[0043] Embodiment 4:

[0044] A boron-containing ferrite-pearlite type high-strength and tough non-quenched and tempered steel for hot forging has the following chemical composition (mass percentage): 0.31% C, 0.55% Si, 1.36% Mn, 0.36% Cr, 0.14% V, 0.047% S, 0.02% Ti, 0.002% B, 0.004% O, 0.005% P, 0.002% N, and the rest is Fe and unavoidable impurities.

[0045] The large bars are prepared by using the conventional bar production process of steel enterprises.

[0046] The above-mentioned boron-containing ferrite-pearlite high-strength and tough non-quenched and tempered steel for hot forging is heated to 1250°C, hot forged by conventional process, and cooled to room temperature, and the cooling rate in the phase transformation zone is 0.1-0.5°C / s.

[0047] Mechanical properties of the obtained boron-containing ferrite-pearlite high-strength and tough non-quenched and tempered steel for hot forging: tensile strength R m The yield strength R is 887MPa. p0.2 The elongation after fracture is 21.6%, and the room temperature impact toughness is 53 J / cm 2 .

[0048] The present invention discloses a high-strength and tough non-quenched and tempered steel containing boron ferrite-pearlite for hot forging. The non-quenched and tempered steel has a low carbon content (0.28wt% to 0.32wt%) and a high manganese content (1.2wt% to 1.5wt%), which can obtain a suitable ratio of ferrite and pearlite, and fully refine the pearlite lamellae to improve strength and toughness; the non-quenched and tempered steel contains an appropriate amount of boron element (0.001wt% to 0.003wt%), which can inhibit and delay the precipitation of grain boundary ferrite during the cooling phase transformation process, so that the precipitation of intracrystalline ferrite is no longer delayed, and promotes the simultaneous precipitation of pearlite on the grain boundary ferrite and intracrystalline ferrite. Nucleation, refinement of pearlite nodules, and improvement of steel toughness; the non-quenched and tempered steel also contains appropriate amounts of manganese, sulfur, titanium, and oxygen elements, which can form MnS-Ti2O3 composite particles, the nucleation core of intracrystalline ferrite. The present invention does not use the common MnS-VN composite particles, the nucleation core of intracrystalline ferrite in medium-carbon non-quenched and tempered steel, because the formation of MnS-VN composite particles requires the addition of more than 0.001wt% of nitrogen to the steel, which will lead to the formation of boron nitride and consume the solid-solution boron in the steel, reducing its inhibitory effect on the precipitation of grain boundary ferrite. The invented boron-containing ferrite-pearlite type high-strength and tough non-quenched and tempered steel for hot forging has a tensile strength R after high-temperature (1200-1300℃) hot forging. m 850~900MPa, yield strength R p0.2600~650MPa, elongation after fracture A is 20%~25%, and room temperature impact toughness is 40~60J / cm 2 .

[0049] The above is a detailed introduction to a boron-containing ferrite-pearlite type high-strength and tough non-quenched and tempered steel for hot forging and its preparation provided in the embodiments of the present application. The description of the above embodiments is only used to help understand the method and its core idea of ​​the present application; at the same time, for those skilled in the art, according to the idea of ​​the present application, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

[0050] For example, certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that hardware manufacturers may use different nouns to refer to the same component. This specification and claims do not use differences in names as a way to distinguish components, but use differences in the functions of components as the criteria for distinction. As mentioned throughout the specification and claims, "including" and "comprising" are open-ended terms, so they should be interpreted as "including / including but not limited to". "Approximately" means that within an acceptable error range, those skilled in the art can solve the technical problem within a certain error range and basically achieve the technical effect. The subsequent description of the specification is a preferred embodiment of the present application, but the description is for the purpose of illustrating the general principles of the present application, and is not used to limit the scope of the present application. The scope of protection of the present application shall be determined by the definition of the attached claims.

[0051] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a product or system including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such a product or system. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the product or system including the elements.

[0052] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0053] The above description shows and describes several preferred embodiments of the present application, but as mentioned above, it should be understood that the present application is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the application concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art do not deviate from the spirit and scope of the present application, and should be within the scope of protection of the claims attached to the present application.

Claims

1. A boron-containing ferrite-pearlite type high-strength and tough non-quenched and tempered steel, characterized in that: The mass percentage of each component of the non-quenched and tempered steel is: 0.28%-0.32% C, 0.4%-0.6% Si, 1.2%-1.5% Mn, 0.1%-0.4% Cr, 0.1%-0.3% V, 0.04%-0.06% S, 0.01%-0.03% Ti, 0.001%-0.003% B, 0.002%-0.006% O, P≤0.01%, N≤0.005%, and the rest is Fe and unavoidable impurities.

2. The non-quenched and tempered steel according to claim 1, characterized in that: The titanium / oxygen mass ratio in the non-quenched and tempered steel is 4-8.

3. A hot forging method for non-quenched and tempered steel according to any one of claims 1 to 2, characterized in that: The hot forging method specifically comprises the following steps: S1) heating the boron-containing ferrite-pearlite high-strength and tough non-quenched and tempered steel billet to 1200-1300° C. and forging it into a shape; S2) and then cooled to room temperature at a certain rate to obtain a non-quenched and tempered steel product.

4. The hot forging method according to claim 3, characterized in that: The cooling rate in S2) is 0.1-0.5°C / s.

5. The hot forging method according to claim 3, characterized in that: The tensile strength R of the non-quenched and tempered steel after the hot forging method is m 850~900MPa, yield strength R p0.2 600~650MPa, elongation after fracture A is 20%~25%, and room temperature impact toughness is 40~60J / cm 2 .

6. The hot forging method according to claim 3, characterized in that: The non-quenched and tempered steel treated by the hot forging method has ferrite and pearlite, the volume fraction of ferrite is 15% to 25%, and the average size of pearlite nodules is less than 30 μm.

7. The hot forging method according to claim 6, characterized in that: The pearlite of the non-quenched and tempered steel treated by the hot forging method is nucleated simultaneously on the grain boundary ferrite and the intracrystalline ferrite, and the intracrystalline ferrite nucleation core is MnS-Ti2O3 composite particles.

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