A low-alloyed bainitic steel, its preparation method and application

Abstract

The present invention relates to a low-alloyed bainitic steel, which is prepared from alloy components and micro-alloyed alloying elements; the alloy components are: C, Si, Mn, V, Ti, Fe; or C, Si, Al, Mn, V, Ti, Fe; the micro-alloyed alloying elements include: V and / or Ti. This low-alloyed bainitic steel is a medium-carbon carbide-free bainitic steel micro-alloyed with vanadium and titanium, which not only reduces the number of alloying elements, but also has excellent strength, toughness and weldability.

Description

Technical Field

[0001] The present invention relates to the technical field of steel preparation, and particularly to a low-alloyed bainitic steel and its preparation method and application. Background Art

[0002] Bainitic steel is widely used in many fields such as transportation, construction, and national defense due to its good mechanical properties and service performance. A variety of alloying elements are often added to bainitic steel. For example, in currently commonly used bainitic steel, the alloy content is as high as 10%, and the types of alloying elements are up to six or more. The addition of alloying elements does improve the performance to a certain extent. However, with the development of society, the consumption of steel materials has been increasing year by year, and raw material shortages, energy shortages, etc. have become prominent problems faced by the whole world. The high alloying of steel materials not only leads to the development of materials relying on resources, but also makes the recycling and reuse of materials more difficult. Therefore, it is necessary to design low-alloyed steel in high-strength and high-toughness bainitic steel.

[0003] However, the purpose of adding relatively expensive metals such as Cr, Ni, and Mo to bainitic steel is to improve the comprehensive performance of bainitic steel. For example, with the increase of Ni content, the toughness and hardness of the steel will be improved. This is because with the increase of Ni content, it is more conducive to the formation of a finer microstructure and the formation of lower bainite. The Cr element can also form CrC precipitates by combining with the C element. The precipitates fix the grain boundaries of austenite, inhibit the growth of grains, refine the austenite grains, and thus improve the material strength. In low-carbon bainitic steel, the Mo element can improve the strength of the steel through transformation strengthening, mainly because the Mo element increases the driving force for carbon diffusion, promotes the bainite transformation rate, and obtains more bainite tissue. Therefore, how to enable bainitic steel to obtain good performance under the premise of low alloying is an urgent problem to be solved. Summary of the Invention

[0004] In view of the above problems, the present invention provides a low-alloyed bainitic steel, which is a medium-carbon carbide-free bainitic steel microalloyed with vanadium and titanium. It not only reduces the number of alloying elements, but also has excellent strength, toughness, and weldability.

[0005] To achieve the above object, the present invention provides a low-alloyed bainitic steel, which is prepared from alloy components and microalloyed alloying elements;

[0006] The alloy components are: C, Si, Mn, V, Ti, Fe;

[0007] Or C, Si, Al, Mn, V, Ti, Fe;

[0008] The microalloyed alloying elements include: V and / or Ti.

[0009] In the process of studying the above technical problems, the present inventor found that microalloying is a good method to improve the performance - cost ratio of steel, and can obtain steel with excellent mechanical properties at a relatively low cost. Steel materials need to be welded in many field applications. The level of carbon content determines the quality of welding performance. Therefore, medium - low carbon microalloyed bainitic steel not only has good welding performance, but also has excellent mechanical properties. Microalloyed bainitic steel has excellent strength, toughness and weldability, and the cooling conditions for obtaining bainite structure after austenitization are relatively loose.

[0010] At the same time, considering the rich reserves of titanomagnetite in China, Ti and V microalloying is more cost - saving. Among them, V is the most suitable and effective additive because it has a strong and easily controllable precipitation strengthening effect. This is mainly because V has a high solubility in austenite at relatively high temperatures required for forging steel. Element Ti is an important additive for steel microalloying. Its functions include pre - precipitation strengthening, inhibiting the growth of austenite grains during heating, and forming acicular ferrite. Ti can refine the austenite grain size. Since the compound formed by Ti and N is very stable in the austenite phase, it can not only improve strength but also toughness, and at the same time can achieve the light weight of steel structures. Therefore, the present inventor proposed to prepare low - alloyed bainitic steel by microalloying with the above raw materials. This low - alloyed bainitic steel not only reduces the number of alloying elements, but also has excellent strength, toughness and weldability.

[0011] In one embodiment, the low - alloyed bainitic steel is prepared from the following raw materials by mass percentage:

[0012]

[0013] The dosages of V and Ti are not both 0 at the same time.

[0014] In one embodiment, the low - alloyed bainitic steel is prepared from the following raw materials by mass percentage:

[0015]

[0016] The dosages of V and Ti are not both 0 at the same time.

[0017] In one embodiment, the low - alloyed bainitic steel is prepared from the following raw materials by mass percentage:

[0018]

[0019] Elements Ti and V can also be added in appropriate amounts and mixed, which has the effect of enhancing each other.

[0020] In one embodiment, the mass percentage of the alloy in the low-alloyed bainitic steel is ≤ 5%.

[0021] In one embodiment, the preparation method of the low-alloyed bainitic steel comprises the following steps: preparing an ingot; preparing an initial mixed structure; heating, holding, cooling, holding, heating, holding, and tempering the initial mixed structure to obtain the low-alloyed bainitic steel;

[0022] The step of preparing the initial mixed structure comprises: subjecting the ingot to solution treatment, holding, performing hot rolling deformation to precipitate the second phase of the micro-alloyed alloying elements, and air cooling to obtain the initial mixed structure.

[0023] In the above method, through the hot rolling deformation process, the precipitation strengthening of V and Ti micro-alloying is beneficial to improving the properties of the bainitic steel. This process is combined with the above specific metal elements and the dosage of the metal elements, and finally the prepared low-alloyed bainitic steel has its properties unaffected and maintained at a relatively high level on the premise of reducing the types and total amount of the alloy.

[0024] The present invention also provides a preparation method of the low-alloyed bainitic steel, comprising the following steps:

[0025] Preparing an ingot: weighing raw materials and forging to obtain an ingot;

[0026] Preparing an initial mixed structure: subjecting the ingot to solution treatment, holding, performing hot rolling deformation to precipitate the second phase of the micro-alloyed alloying elements, and air cooling to obtain the initial mixed structure;

[0027] Preparing the low-alloyed bainitic steel: heating, holding, cooling, holding, heating, holding, and tempering the initial mixed structure to obtain the low-alloyed bainitic steel.

[0028] In the above preparation method, the key to preparing the initial mixed structure is to achieve precipitation strengthening by precipitating the second phase of V and Ti through the hot rolling deformation method. The precipitation strengthening plays a dominant role in improving the properties of the bainitic steel; at the same time, the V or Ti elements dissolved in the matrix have an impact on the bainite phase transformation characteristics and can also make the components more uniform. Therefore, solid solution strengthening is also beneficial to the properties of the bainitic steel.

[0029] In one embodiment, in the step of preparing the initial mixed structure, the temperature of the solution treatment is 1100 ± 100 °C; the holding time is 2 - 4 h.

[0030] In one embodiment, in the step of preparing the initial mixed structure, the initial temperature of the hot rolling deformation is ≥ 950 °C, the final rolling temperature is ≥ 860 °C, and the rolling deformation amount is 15 - 40%.

[0031] In one embodiment, the initial mixed structure includes bainite and martensite.

[0032] In one embodiment, the step of preparing the low-alloy bainitic steel includes: heating the initial mixed structure to 890 - 980 °C, holding for heat preservation to fully austenitize the initial mixed structure, cooling to 290 - 360 °C, holding for heat preservation to obtain a bainitic structure, and performing tempering treatment.

[0033] The present invention also provides the application of the low-alloy bainitic steel in the preparation of building materials, transportation equipment or defense equipment.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] A low-alloy bainitic steel, a preparation method and an application thereof according to the present invention. The low-alloy bainitic steel is a medium-carbon carbide-free bainitic steel microalloyed with vanadium and titanium, which not only reduces the number of alloying elements, but also has excellent strength, toughness and weldability. Detailed implementation manners

[0036] To facilitate the understanding of the present invention, the present invention will be described more comprehensively below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, these embodiments are provided to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0038] Source:

[0039] Unless otherwise specified, the reagents, materials and equipment used in this embodiment are all commercially available; unless otherwise specified, the experimental methods are all conventional experimental methods in this field.

[0040] The raw materials and dosages of each embodiment of the present invention are shown in the following table:

[0041] Table 1 Raw materials and dosages of each embodiment (wt.%)

[0042] Example C Si Al Mn Cr Ni Mo V Ti 1 0.24 1.5 0.5 1.5 1.1 0.2 0.3 / / 2 0.24 0.9 0.7 2.9 / / / 0.1 / 3 0.23 0.5 1.2 3 / / / / 0.1 4 0.32 1.5 0.5 1.6 1.1 0.5 0.4 / / 5 0.33 0.5 1.1 2.5 / / / 0.11 / 6 0.253 1.061 0.46 2.164 / / / / / 7 0.247 1.037 0.474 2.146 / / / / 0.05 8 0.238 1.069 0.463 2.127 / / / 0.08 0.05 9 0.252 1.071 0.489 2.128 / / / 0.08 / 10 0.38 1.5 0.07 1.3 1.1 / 0.3 / / 11 0.37 1.5 / 2.2 / / / 0.072 / 12 0.39 1.5 / 2.1 / / / 0.12 /

[0043] Example 1

[0044] A bainitic steel and a preparation method thereof.

[0045] Preparation of ingot: Weigh the raw materials according to Table 1, with the balance being Fe, and forge to obtain the ingot;

[0046] Preparation of initial mixed structure: Subject the refined ingot to solution treatment at 1100 ± 100 °C, hold for 2 - 4 h, perform hot rolling deformation, with the initial temperature of hot rolling deformation ≥ 950 °C, the final rolling temperature ≥ 860 °C, and the rolling deformation amount being 15 - 40%; air cool to obtain the initial mixed structure;

[0047] Preparation of low-alloyed bainite steel: Heat the initial mixed structure to 890 - 980 °C, perform the second heat preservation operation to obtain complete austenite; cool to 290 - 360 °C, perform the third heat preservation, and bainite phase transformation occurs to obtain bainite structure; heat up to 290 - 360 °C again, perform the fourth heat preservation, and carry out tempering treatment.

[0048] Example 2

[0049] It is basically the same as Example 1, except that the raw materials and their dosages are different.

[0050] Example 3

[0051] It is basically the same as Example 1, except that the raw materials and their dosages are different.

[0052] Example 4

[0053] It is basically the same as Example 1, except that the raw materials and their dosages are different.

[0054] Example 5

[0055] It is basically the same as Example 1, except that the raw materials and their dosages are different.

[0056] Example 6

[0057] It is basically the same as Example 1, except that the raw materials and their dosages are different.

[0058] Example 7

[0059] It is basically the same as Example 1, except that the raw materials and their dosages are different.

[0060] Example 8

[0061] It is basically the same as Example 1, except that the raw materials and their dosages are different.

[0062] Example 9

[0063] It is basically the same as Example 1, except that the raw materials and their dosages are different.

[0064] Example 10

[0065] Basically the same as Example 1, except that the raw materials and dosages are different.

[0066] Example 11

[0067] Basically the same as Example 1, except that the raw materials and dosages are different.

[0068] Example 12

[0069] Basically the same as Example 1, except that the raw materials and dosages are different.

[0070] Experimental Example

[0071] I. After heat-treating the bainitic steel prepared in each example, the hardness, impact and tensile properties of the steel were detected. The specific detection methods were as follows: Rockwell hardness: GB / T 230.1-2009; Impact: GB / T 229-2020; Tensile: GB / T 228.1-2010.

[0072] II. Detection results.

[0073] 1. Comparing Example 1 and Example 2, without adding Cr, Ni, and Mo in the alloying elements, appropriately increasing the content of Mn element, and adding a small amount of V element in the microalloying, the obtained properties are shown in the following table. The strength is slightly increased and the toughness is significantly improved.

[0074] 2. Comparing Example 1 and Example 3, without adding Cr, Ni, and Mo in the alloying elements, appropriately increasing the content of Mn element, and adding a small amount of Ti element in the microalloying, the obtained properties are shown in the following table. The strength is hardly reduced and the toughness is significantly improved.

[0075] Table 2 Hardness, impact and tensile properties of the tested steel after heat treatment

[0076]

[0077] 3. Comparing Example 4 and Example 5, without adding Cr, Ni, and Mo in the alloying elements, appropriately increasing the content of Mn element, and adding a small amount of V element in the microalloying, the obtained properties are shown in the following table. Both the strength and the impact energy are increased.

[0078] Table 3 Hardness, impact and tensile properties of the tested steel after heat treatment

[0079]

[0080] 4. Comparing Example 6 with Example 7, 8, and 9, adding a small amount of single V, Ti element or composite alloying elements in the microalloying, the obtained properties are shown in the following table. The impact absorption energy has a certain increase and the strength is increased by about 40 MPa.

[0081] Table 4 Hardness, impact and tensile properties of the tested steel after heat treatment

[0082]

[0083] 5. Compared with Example 10, in Examples 11 and 12, Cr, Mo, and Al are no longer added to the alloy composition, and steel design compositions with different V contents are added. A small amount of single V is added in microalloying, and the obtained properties are shown in the following table. With the increase of V, both the impact absorption work and strength are improved.

[0084] Table 6 Hardness, impact and tensile properties of the tested steel after heat treatment

[0085]

[0086] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0087] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A low-alloyed bainitic steel, characterized in that, Prepared from raw materials with the following mass percentages: The amounts of V and Ti are not both 0 at the same time. The preparation method of the low-alloyed bainitic steel comprises the following steps: preparing an ingot; preparing an initial mixed structure; heating the initial mixed structure, holding the temperature, cooling, holding the temperature, heating, holding the temperature, and tempering to obtain the low-alloyed bainitic steel. The step of preparing the initial mixed structure comprises: subjecting the ingot to solution treatment, holding the temperature, performing hot rolling deformation to precipitate the second phase of the microalloyed alloying elements, and air cooling to obtain the initial mixed structure; the initial temperature of the hot rolling deformation is ≥950 °C, the finish rolling temperature is ≥860 °C, and the rolling deformation amount is 15-40%.

2. The preparation method of the low-alloyed bainitic steel according to claim 1, characterized in that Comprises the following steps: Preparing an ingot: weighing raw materials and forging to obtain an ingot. Preparing the initial mixed structure: subjecting the ingot to solution treatment, holding the temperature, performing hot rolling deformation to precipitate the second phase of the microalloyed alloying elements, and air cooling to obtain the initial mixed structure; the initial temperature of the hot rolling deformation is ≥950 °C, the finish rolling temperature is ≥860 °C, and the rolling deformation amount is 15-40%. Preparing the low-alloyed bainitic steel: heating the initial mixed structure, holding the temperature, cooling, holding the temperature, heating, holding the temperature, and tempering to obtain the low-alloyed bainitic steel.

3. The preparation method according to claim 2, characterized in that, In the step of preparing the initial mixed structure, the temperature of the solution treatment is 1100±100 °C; the holding time is 2-4 h.

4. The preparation method according to claim 2, characterized in that, The initial mixed structure comprises bainite and martensite.

5. The preparation method according to claim 2, characterized in that, The step of preparing the low-alloyed bainitic steel comprises: heating the initial mixed structure to 890-980 °C, holding the temperature to completely austenitize the initial mixed structure, cooling to 290-360 °C, holding the temperature to obtain a bainite structure, and performing tempering treatment.

6. Application of the low-alloyed bainitic steel according to claim 1 in the preparation of building materials, transportation equipment or defense equipment.

Images