HB400 grade wear-resistant and corrosion-resistant steel based on continuous heat treatment production line and production method

Abstract

A HB400-grade wear-resistant and corrosion-resistant steel based on a continuous heat treatment production line has the following components (by weight): C: 0.10-0.18%, Si: no more than 0.2%, Mn: 0.2-0.9%, P ≤ 0.020%, S ≤ 0.010%, Als: 0.03-0.06%, Ti: 0.005-0.01%, and Cu: no more than 0.2%. The production method includes conventional smelting and casting into billets; heating the billets, hot rolling, and coiling; continuous uncoiling and quenching; high-speed cooling; cross-cutting to a specified length, followed by tempering; and natural cooling to room temperature. This invention achieves a simple composition, uniform product quality and performance, and reduces production costs by no less than 2%, while ensuring a product hardness of no less than 400, a yield strength of no less than 950 MPa, a tensile strength of no less than 1220 MPa, an elongation of no less than 10%, and corrosion resistance.

Description

Technical Field

[0001] The invention relates to wear-resistant steel for mechanical engineering and a production method thereof, in particular to HB400 grade wear-resistant and corrosion-resistant steel and a production method thereof. Background Art

[0002] Low-alloy, high-strength wear-resistant steel is used in machinery and equipment in metallurgy, mining, building materials, railways, electricity, coal, and other industries. With the deepening of major national strategies, the demand for wear-resistant steel in downstream industries such as commercial vehicles and construction machinery is increasing day by day. In certain corrosive environments, in addition to wear resistance, it is also required to have certain corrosion resistance. Currently, wear-resistant steel is mainly produced by the tempering heat treatment process of single steel plates, that is, after hot rolling into coils, it is cross-cut into hot-rolled plates, and then enters the heat treatment furnace for quenching and tempering to obtain the corresponding grade of wear-resistant steel products. However, the heat treatment of a single plate in the heat treatment furnace not only has low production efficiency, but also makes it difficult to ensure the uniformity of the temperature and other aspects of the steel plate when heated.

[0003] It can be seen that the existing wear-resistant steel has technical difficulties such as long production process, low production efficiency, and poor uniformity. Therefore, it is necessary to redesign the composition and process to improve product quality and production efficiency.

[0004] After searching:

[0005] The document with Chinese patent publication number CN102605234A discloses "A HB400 grade wear-resistant steel plate and its manufacturing method", whose components by weight percentage are: C: 0.08-0.24%, Si: 0.10-0.30%, Mn: 0.70-1.70%, P: ≤0.050%, S: ≤0.030%, Cr: ≤1.00%, Mo: ≤0.60%, Al: 0.01-0.10%, B: 0.0005-0.0040%, Ti: 0.005-0.06%, and satisfying: 0.15≤Cr+Mo≤1.20%, 0.011%≤Al+Ti≤0.15%, and the balance is Fe and unavoidable impurities. It is produced using the casting-controlled rolling-quenching and tempering heat treatment process, and has excellent performance. It is suitable for manufacturing easily worn equipment in engineering machinery. Its disadvantage is that since a single plate is used for the quenching and tempering heat treatment process, the production process is long, the production efficiency is low, and the performance of the head, tail and edges cannot be effectively guaranteed.

[0006] At present, when a single plate is quenched, its microstructure and mechanical properties are uneven at the head and tail. The plate shape of about 30 cm at the head and tail cannot usually be fully guaranteed. The performance indicators such as strength, hardness and plate shape quality such as flatness at the head and tail are greatly different from those of normal parts. When users use it, processing abnormalities such as component deflection and straightness deviation are prone to occur.

[0007] In order to solve this problem, during the quenching of single plates, improvements have been made through process optimization, water volume regulation and coordinated adjustment of roller speed, but it is difficult to solve the problem fundamentally. To fundamentally solve this problem, if we want to truly solve the head and tail problem, we must remove the "head and tail", but there has been no breakthrough. Summary of the Invention

[0008] The present invention aims to overcome the shortcomings of the existing technology and provide a HB400-grade wear-resistant and corrosion-resistant steel and a production method based on a continuous heat treatment production line, which has simple components and uniform product quality and performance while ensuring that the product hardness HB is not less than 400, the yield strength is not less than 950MPa, the tensile strength is not less than 1220MPa, the elongation is not less than 10%, and the product is corrosion-resistant.

[0009] Measures to achieve the above objectives:

[0010] The invention discloses an HB400 grade wear-resistant and corrosion-resistant steel based on a continuous heat treatment production line, wherein the components and weight percentage contents thereof are as follows: C: 0.10-0.18%, Si: not more than 0.2%, Mn: 0.2-0.9%, P≤0.020%, S≤0.010%, Als: 0.03-0.06%, Ti: 0.005-0.01%, Cu: not more than 0.2%, and the remainder being Fe and unavoidable impurities.

[0011] Preferably, the weight percentage of Mn is 0.20-0.60%.

[0012] Preferably, the weight percentage of Cu is 0.07-0.15%.

[0013] Furthermore, the weight percentage of added B does not exceed 0.0003%.

[0014] A method for producing HB400 grade wear-resistant and corrosion-resistant steel based on a continuous heat treatment production line, comprising the following steps:

[0015] 1) Conventional smelting and casting into billets;

[0016] 2) hot rolling and coiling the ingot after conventional heating;

[0017] 3) Continuously unwind and quench, control the quenching temperature at 850-950°C, and control the quenching time at 5-10 minutes;

[0018] 4) High-speed cooling is performed, cooling to 50-150° C. at a cooling rate of 50-100° C. / s;

[0019] 5) After cross-cutting to a fixed length, tempering is carried out, and the tempering temperature is controlled at 200-240°C and the tempering time is 20-50 minutes;

[0020] 6) Cool naturally to room temperature.

[0021] Preferably, the quenching temperature is between 865°C and 930°C.

[0022] Preferably, the temperature is cooled to 59-135° C. at a cooling rate of 58-87° C. / s.

[0023] Preferably, the tempering temperature is 205-228° C., and the tempering time is 26-40 minutes.

[0024] Functions and mechanisms of each element and main process in the present invention

[0025] C is the cheapest element to improve material strength. As the carbon content increases, the hardness and strength increase, but the plasticity, toughness and welding properties decrease. Taking all factors into consideration, the C weight percentage is 0.10-0.18%;

[0026] Si can reduce the diffusion rate of carbon in ferrite, promote the formation of ferrite, and also deteriorate the surface quality. Taking all factors into consideration, the Si weight percentage should not exceed 0.2%;

[0027] Mn significantly reduces Ar1 temperature and austenite decomposition rate, improves the stability of supercooled austenite, promotes stress release of austenite, increases the residual austenite content in the final structure, and improves cold bending performance. However, if the Mn content is too high, it will increase temper brittleness and cause severe center segregation. Taking all factors into consideration, the appropriate Mn weight percentage is 0.2-1.3%.

[0028] Als can deoxidize steel, reduce inclusion content, and also refine grains. Taking all factors into consideration, Als should be between 0.03% and 0.06%.

[0029] During the solidification process of steel, Ti can combine with N to form stable TiN, which can strongly hinder the migration of austenite grain boundaries, thereby refining the austenite grains. Taking all factors into consideration, the appropriate Ti weight percentage is 0.005-0.01%;

[0030] Cu: Adding a small amount of copper to steel can improve its atmospheric corrosion resistance, especially when combined with phosphorus. However, high copper content can increase the risk of cracking during hot working. For all other reasons, the Cu content should not exceed 0.2% by weight.

[0031] Adding a small amount of B to steel can greatly improve hardenability. However, if B is too much, it tends to be enriched at the grain boundaries, which will reduce the grain boundary binding energy, making the steel plate more prone to intergranular fracture when subjected to impact loads, and reducing the low-temperature impact energy of the steel plate. Therefore, the amount of B added in the present invention is ≤0.0003%.

[0032] P and S are harmful impurity elements in steel. P in steel tends to segregate, reducing the toughness and weldability of the steel. S tends to form plastic sulfides, causing delamination of the steel plate and deteriorating its performance. Therefore, the lower the P and S content, the better. Taking all factors into consideration, the P and S content of steel is set to 0.005% ≤ P ≤ 0.020%, and S ≤ 0.010%. The reason for a P content of not less than 0.005% is that it combines with Cu to further improve atmospheric corrosion resistance.

[0033] The reason why the present invention controls the quenching temperature at 850-950°C and the quenching time at 5-10 minutes is that under this process, a better quenched structure and quenched plate shape can be guaranteed. A lower quenching temperature will enter the two-phase region, and ferrite will eventually exist in the structure, which will reduce the strength. Too high a quenching temperature will easily cause the original austenite grains to coarsen, and the toughness will deteriorate sharply.

[0034] The present invention controls the cooling rate to 50-100°C / s and then cools to 50-150°C. This is because, at lower cooling rates, bainite may form during the cooling process. The strength of bainite differs significantly from that of martensite, ultimately affecting the strength and hardness of the quenched state. At too high a cooling rate, the cooling intensity is too high, resulting in excessive thermal stress, which can easily deteriorate the plate shape. For example, even with subsequent low-temperature tempering, a plate shape of 20-60 mm / m may not meet application requirements (less than 5 mm / m). The post-cooling temperature of 50-150°C is intended, on the one hand, to stabilize the austenite after quenching, retaining a small amount of retained austenite structure to toughen the material, and on the other hand, to maintain a certain autotempering effect, reducing the stress in the coil.

[0035] The reason why the present invention controls the tempering temperature at 200-240°C and the tempering time at 20-50min is that when the tempering temperature is lower than 200°C or the tempering time is lower than 20min, the tempering effect is poor and the ability to improve the plate shape and internal stress is weak. When the tempering temperature is higher than 240°C or the tempering time is higher than 50min, the supersaturated carbon in the martensite is easily precipitated, the solid solubility decreases, the strength and hardness are greatly affected, and the risk of performance mismatch is greater.

[0036] Compared with the prior art, the present invention has simple components, uniform product quality and performance, and reduces production costs by not less than 2% while ensuring that the product hardness HB is not less than 400, the yield strength is not less than 950MPa, the tensile strength is not less than 1220MPa, the elongation is not less than 10%, and the product is corrosion-resistant. DETAILED DESCRIPTION

[0037] The present invention is described in detail below:

[0038] Table 1 is a list of chemical compositions of various embodiments and comparative examples of the present invention;

[0039] Table 2 is a list of main process parameters of various embodiments and comparative examples of the present invention;

[0040] Table 3 is a table of performance test results of various embodiments of the present invention and comparative examples;

[0041] Table 4 is a table showing the corrosion resistance results of the steels of various embodiments of the present invention and comparative examples.

[0042] Each embodiment of the present invention is produced according to the following steps

[0043] 1) Conventional smelting and casting into billets;

[0044] 2) hot rolling and coiling the ingot after conventional heating;

[0045] 3) Continuously unwind and quench, control the quenching temperature at 850-950°C, and control the quenching time at 5-10 minutes;

[0046] 4) High-speed cooling is performed, cooling to 50-150° C. at a cooling rate of 50-100° C. / s;

[0047] 5) After cross-cutting to a fixed length, tempering is carried out, and the tempering temperature is controlled at 200-240°C and the tempering time is 20-50 minutes;

[0048] 6) Cool naturally to room temperature.

[0049] Table 1 Chemical composition list of various embodiments of the present invention and comparative examples (wt%)

[0050]

[0051] Table 2 List of main process parameters of various embodiments of the present invention and comparative examples

[0052]

[0053]

[0054] Table 3 Mechanical properties test results of various embodiments of the present invention and comparative examples

[0055]

[0056] To better demonstrate the corrosion resistance advantages of the steel of the present invention, the present embodiment provides two sets of comparative steel corrosion resistance results. The comparative steel is Q345 steel, as shown in Table 4. (Corrosion method: temperature 23 ± 2 ° C, 10% H2SO4 + 3.5% NaCl, full immersion for 24 hours)

[0057] Table 4 Corrosion resistance results of steels in various embodiments of the present invention and comparative examples (g / m 2 h)

[0058]

[0059]

[0060] As can be seen from Tables 1 to 3, the present invention develops a continuous quenching process and technology for HB400 grade wear-resistant steel through innovative process optimization. The mechanical properties and corrosion resistance are at the same level as those of the comparative example. However, due to continuous quenching, the process flow is shorter, the production efficiency is higher, and the production cost is reduced by no less than 2%.

[0061] This specific implementation is only the best example and is not a restrictive implementation of the technical solution of the present invention.

Claims

1. A method for producing HB400 grade wear-resistant and corrosion-resistant steel based on a continuous heat treatment production line, wherein the components and weight percentages of the steel are as follows: C: 0.11-0.18%, Si: 0.11-0.2%, Mn: 0.2-0.28%, P≤0.020%, S≤0.010%, Als: 0.05-0.06%, Ti: 0.021% or Ti: 0.022% or Ti: 0.023% or Ti: 0.026% or Ti: 0.027% or Ti: 0.028% or Ti: 0.029% or Ti: 0.031% or Ti: 0.034% or Ti: 0.035%, Cu: 0.12~0.2%, B not exceeding 0.0003%, the rest being Fe and unavoidable impurities; Production method: 1) Conventional smelting and casting into billets; 2) The slab is conventionally heated, hot rolled and coiled; 3) Continuously unwind and quench, control the quenching temperature at 850~950℃, and control the quenching time at 5~10 minutes; 4) Perform high-speed cooling, cooling to 50~150℃ at a cooling rate of 50~100℃ / s; 5) After cutting to the specified length, temper the steel. Control the tempering temperature at 200-240°C and the tempering time at 20-50 minutes. 6) Allow to cool naturally to room temperature.

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