WO2021036271A1 - High-temperature-resistant 400hb wear-resistant steel plate and method for production thereof - Google Patents

Abstract

Provided is a high-temperature-resistant 400HB wear-resistant steel plate, having the chemical composition: C: 0.15–0.25%, Si: 0.10–0.40%, Mn: 0.8–1.30%, Nb: 0.010–0.040%, V: 0.030–0.060%, Ti: ≤0.010%, Al: 0.03–0.06%, Ni: ≤0.1%, Cu: ≤0.1%, Cr: 0.10–0.50%, Mo: 0.50–1.00%, B: 0.001–0.005%, Ca: 0.0010–0.0050%, P: ≤0.010%, S: ≤0.0015%, O: ≤0.0015%, N: ≤0.0035%, H: ≤0.0002%, and 0.55 ≤ carbon equivalent value (CEV) ≤ 0.65, wherein CEV=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15; the remainder is Fe and inevitable impurity elements. In the production process, cooling is controlled after rolling, the grains are refined, and fine lath martensite is obtained for subsequent offline quenching. After quenching, high-temperature tempering is used, and under the combined effect of the Cr/Mo/V precipitates, the microstructure of the high-temperature performance finished steel plate is ensured to be uniform tempered sorbite, having a small grain size of ≤25 μm; the ferrite matrix is dispersed with fine and uniform precipitate, the precipitate being carbide.

Description

High temperature resistant 400HB wear-resistant steel plate and production method thereof Technical field

The invention relates to an iron-based alloy wear-resistant steel, belonging to the technical field of iron-based alloy steel.

Background technique

Wear-resistant steel plates are widely used in construction machinery, mining and transportation, road transportation, agricultural production, port power and other industries that require high strength and good wear resistance mechanical equipment, such as bulldozers, loaders, excavators, scraper conveyors, Mining dump trucks, etc. Wear-resistant steel is mainly divided into austenitic high-manganese steel and low-alloy martensitic steel. High Mn steel matrix is not high in hardness, but has the characteristics of impact hardening, showing superior wear resistance under high impact conditions; but high carbon content, poor welding performance, low wear resistance under low impact conditions, and high alloy content , Continuous casting cannot be used for mass production, resulting in high costs and low production efficiency. At present, domestic and foreign wear-resistant steel manufacturers mainly conduct research and development and continuous casting of low-alloy martensitic wear-resistant steel. This kind of wear-resistant steel mainly adjusts the hardness of the steel plate through the content of C, and adds an appropriate amount of alloy elements such as Cr/Ni/Mo. Through quenching and low temperature tempering heat treatment, the tempered martensite structure is obtained to ensure that the steel plate has a good comprehensive Mechanical behavior.

In recent years, 400HB grade wear-resistant steel plate has become the mainstream wear-resistant steel plate used in China. Domestic wear-resistant steel manufacturers have done a lot of work in low-alloy design, improvement of low-temperature impact toughness and weldability, and short-flow process design. Chinese patent CN10775543B introduces a 400HB grade wear-resistant steel plate within 30mm. This steel adopts Ni-free low-cost alloy element design to reduce production costs, and improves welding performance by controlling the carbon equivalent ≤ 0.45; after the steel plate is off-line quenched, low temperature tempering is used to eliminate the internal stress of the steel plate to ensure the hardness and wear resistance of the steel plate. Chinese patent CN104451409B uses online sub-temperature quenching method to produce 400HB wear-resistant steel, but online quenching will inevitably lead to uneven performance of the steel plate head and tail, and the application of steel plate has great limitations; Chinese patent CN103233171B publishes a NM400 grade Cracked high-strength wear-resistant steel plate and production method. This steel grade adopts a low-carbon design (C: 0.04-0.08%) to reduce crack sensitivity, but the on-line control cooling method will also cause differences in the performance of the steel plate head and tail, which affects the use range of the steel plate. Further, the above types of 400HB stage low alloy martensitic wear resistant steel plate there is a common drawback, i.e., water-cooling and tempering of the steel sheet production process will cause a significant decline in strength at high temperature hardness, thereby reducing the abrasion resistance , Affecting the popularization and use of wear-resistant steel.

Chinese patent CN103205650B introduces a heat-resistant and wear-resistant steel plate and its manufacturing method. The steel plate is different from the conventional wear-resistant steel plate. On the basis of Cr/Ni/Mo, the rare earth element La/Ce/Nd is added to refine the grain, strengthen the grain boundary to improve the strength and toughness, and increase the tempering stability of the steel plate by adding W element And thermal strength, the steel plate is tempered in the range of 400-600℃ to ensure that the steel plate has high hardness and good wear resistance in the range of 300-600℃. However, the addition of rare earth elements and W elements increases the cost and requires certain improvements to the conventional smelting process. The addition of alloying elements in the invention is relatively high, resulting in too high carbon equivalent; in 10 examples, the carbon equivalent of Examples 4-10 is 0.75-0.94; the carbon equivalent of Examples 1-3 is 0.57-0.65, but the Mn content is as high as 1.65-2.00 , It is easy to cause central segregation and cutting cracks; the high carbon equivalent design greatly limits the welding performance of the steel plate; this invention uses Ti/V composite, and the content is relatively high, the Ti content is up to 0.08, and the V content is up to 0.1, which has exceeded The conventional microalloying range has a certain influence on the toughness of the steel plate. Therefore, this invention does not study the low-temperature impact toughness of wear-resistant steel.

With the enlargement of wear-resistant equipment and the further complication of operating conditions, it is imperative to develop low-cost wear-resistant steel plates with excellent impact toughness that can be used under high temperature conditions.

Summary of the invention

The purpose of the present invention is to provide a low-cost, high-temperature resistant 400HB wear-resistant steel plate with excellent low-temperature impact performance and a manufacturing method thereof. The microstructure of the low-alloy wear-resistant steel plate is fine tempered sorbite (completely different from the traditional martensite structure); the surface Brinell hardness is 370-430HB; the 600℃ tensile strength is ≥1000MPa, and the elongation is ≥10% , Charpy V-type impact energy at -40℃≥30J, showing good low-temperature toughness and strength.

The technical solution adopted by the present invention to solve the above problems is: a high temperature resistant 400HB wear-resistant steel plate, the chemical composition is calculated by mass percentage of C: 0.15 to 0.25%, Si: 0.10 to 0.40%, Mn: 0.8 to 1.30%, Nb ：0.010～0.040%, V: 0.030～0.060%, Ti: ≤0.010%, Al: 0.03～0.06%, Ni: ≤0.1%, Cu: ≤0.1%, Cr: 0.10～0.50%, Mo: 0.50～1.00 %, B: 0.001～0.005%, Ca: 0.0010～0.0050%, P: ≤0.010%, S: ≤0.0015%, O: ≤0.0015%, N: ≤0.0035%, H: ≤0.0002%, and carbon equivalent 0.55 ≤CEV≤0.65, the balance is Fe and unavoidable impurity elements.

Further, the microstructure of the above-mentioned finished steel sheet is uniform tempered sorbite, with fine grains: the size is ≤25um, fine and uniform precipitates are dispersed on the ferrite matrix, and the precipitates are carbides. Based on this, for the wear-resistant steel of the present invention with a thickness of 4-30mm, the surface Brinell hardness is 370-430HB; the tensile strength at 600°C is ≥1000MPa, the elongation is ≥10%, and the Charpy V-type impact energy at -40°C is ≥30J.

The reasons for limiting the steel composition in the present invention are explained as follows:

C: The carbon content determines the hardness of the steel sheet. Low carbon content, low hardness, good toughness, and excellent weldability; high carbon content, complete quenched martensite transformation, high strength, high hardness, and good wear resistance, but the steel plate has reduced plastic toughness and poor weldability. Based on the steel plate hardness, wear resistance and weldability requirements, the carbon content in the present invention is controlled to 0.15-0.25% (low carbon design).

Si: Silicon is dissolved in ferrite and austenite to improve strength and hardness. Too high a content will deteriorate the toughness of the martensitic steel, and at the same time the surface quality will decrease, so it is controlled between 0.10% and 0.40% (low content of Si).

Mn: Increase the stability of austenite, reduce the critical cooling rate of martensite transformation during quenching, and strongly improve the hardenability of steel. When the manganese content is low, the above effects are not significant, and the strength and toughness of the steel plate are low. If it is too high, it will tend to coarsen the crystal grains, and will cause segregation of the continuous casting billet to form MnS, poor toughness and reduced weldability. Therefore, the present invention takes into account the comprehensive addition of alloys, and limits the addition of manganese to 0.80 to 1.30. %In the range.

Nb/V/Ti: It is a strong forming element of C and N compounds, which can pin the austenite grain boundary, inhibit the growth of austenite grains during heating, and is used in rolling and tempering. Precipitating during the process significantly improves the strength and toughness of the steel. Due to the strong affinity between Ti and N, it is easy to preferentially precipitate micron TiN particles during the solidification process; TiN is hard and has sharp corners, is not easy to deform, and is detrimental to the low-temperature impact performance of the steel plate; therefore, the present invention strictly limits the Ti element content and controls Ti The content is less than or equal to 0.010%. The invention adopts the Nb/V composite method, and mainly controls the crystal grain size through the solid solution and deformation induced precipitation of Nb; through the high temperature tempering precipitation of V, the strength and hardness of the steel at high temperature are improved, and the tempering stability is increased. The present invention stipulates that the content of niobium should be between 0.010% and 0.040%; the content of vanadium should be between 0.030% and 0.060%.

Al: A strong deoxidizing element, and at the same time, it has a strong affinity with N, which can eliminate the aging sensitivity caused by the N element. The precipitation of the N compound has the effect of refining the austenite grains and protects the hardenability of the B element. In the present invention, it is stipulated that the Al content should be between 0.030% and 0.060%.

Ni, Cu: The most commonly used elements that effectively improve the low-temperature toughness of steel. However, due to the high price and poor economy, the present invention limits the addition amount of Ni and Cu, reduces the dependence on the effects of these two elements, and greatly improves the cost competitiveness of the invention steel.

Cr: Reduces the critical cooling rate for martensite transformation and improves hardenability. Cr can also form a variety of carbides in steel, improve the strength, hardness and wear resistance of steel, and improve the high temperature tempering resistance of steel. Excessive Cr content will reduce the weldability of the steel plate. Therefore, the chromium content in the present invention is controlled at 0.10 to 0.50%.

Mo: An element that greatly improves the hardenability of steel, is conducive to the formation of full martensite during quenching, and improves the impact toughness of the steel plate. Mo is a strong carbide forming element at the same time. By affecting the diffusion rate of C, the size of precipitated carbides is refined, and the high temperature tempering resistance is improved, so that the steel plate can maintain a certain strength, hardness and wear resistance in the medium and high temperature range. In the present invention, the content of Mo is controlled at 0.50-1.00%.

B: In the present invention, 0.001-0.005% of a trace amount of B is added, and its main purpose is to improve the hardenability of the steel sheet, thereby reducing the addition amount of other precious metals and reducing the cost. More than 0.005% of B is prone to segregation and the formation of borides, which severely deteriorates the toughness of the steel plate and reduces the hardenability.

Ca: Ca treatment is usually used for inclusion denaturation treatment, changing the elongated inclusions such as MnS into spherical inclusions such as CaS, reducing the anisotropy of the steel plate and improving the comprehensive performance of the steel plate. The invention controls the content of Ca from 0.0010% to 0.0050%.

P: Harmful element, which has an adverse effect on the plasticity and toughness of the material. The present invention pursues ultra-pure steel and strictly controls the content of P≤0.01%.

S: Harmful elements in steel, adversely affecting material plasticity and toughness. S content is high, it is easy to form long inclusions such as MnS, resulting in anisotropy of the steel plate, and it is prone to delamination and cracking. The present invention requires S: ≤0.0015%.

O, N, H: harmful gas elements, high content, many inclusions, easy to produce white spots, greatly reducing the plasticity and toughness of the steel plate, resulting in delayed cutting cracks. The present invention strictly controls the content of O to not more than 0.0015%; the content of N to not more than 0.0035%; and the content of H to be less than or equal to 0.0002%.

CEV: The present invention adopts the carbon equivalent formula CEV=C+Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15; the carbon equivalent has a greater impact on the strength and weldability of steel. CEV has high strength and high strength, but the weldability is reduced; the present invention controls 0.54≤CEV≤0.65.

The present invention also provides a method for preparing the above-mentioned high-temperature resistant 400HB wear-resistant steel plate. The specific process is as follows:

Smelting process: It is smelted by converter method, then sent to LF refining furnace for refining, and undergoes VD or RH vacuum treatment. After the molten steel is degassed, a trace amount of Ca treatment is carried out to control the Ca content of 0.001 to 0.005%. After the treatment, the molten steel is softly stirred, and the stirring time is not less than 10 minutes to ensure that the steel sulfides and oxides are completely denatured and fully floated and removed. The total level of inclusion control A, B, C, D is less than or equal to 2.5.

Continuous casting process: In order to control the internal looseness and segregation of the steel plate, low superheat pouring, full argon gas protection pouring, and dynamic light reduction control are carried out. The superheat of molten steel is controlled at 5-20℃, the center segregation is not higher than C1.0, and the center porosity is not higher than 1.0.

Heating rolling process: The casting billet is put into a walking heating furnace and heated to 1150-1250°C. When the temperature of the core reaches the surface temperature, the heat preservation time is not less than 30min, so that the alloy elements in the steel are fully dissolved to form a solid solution. Ensure the uniformity of the composition and performance of the final product. After the steel billet is discharged from the furnace, it is subjected to a two-stage controlled rolling of rough rolling + finishing rolling after high-pressure water descaling treatment to refine the grains and improve the strength and toughness. The opening temperature of rough rolling is between 1000-1100°C. The thickness to be warmed is ≥3H, where H is the thickness of the finished product. The finish rolling temperature is between 850-950℃. After the rolling is completed, the steel plate is passed through the ACC unit for accelerated cooling. The final cooling temperature is controlled at 600-750°C, and the cooling rate is required to be ≥6°C/s. The grains are refined, and fine martensite slats are obtained for subsequent offline quenching. Low-temperature impact toughness provides a good foundation.

Quenching heat treatment process: After rolling, the steel plate is subjected to offline quenching treatment. The quenching temperature is 880-930℃, and the holding time is 30-60min after the furnace temperature reaches high temperature. In order to ensure the uniformity of the steel plate, the temperature control accuracy is ±10℃ to ensure that a uniform quenched martensite structure is obtained.

Tempering heat treatment process: After the steel plate is quenched, it needs to be tempered at a high temperature at 500-600℃. After the core of the steel plate reaches temperature, the tempering time is 30-90min. The steel plate obtains a stable high-temperature tempered sorbite structure to ensure high-temperature strength and excellent low-temperature impact toughness.

Compared with the prior art, the present invention has the following characteristics and advantages:

The chemical composition design uses a combination of alloy elements such as Cr/Mo/V, which is similar to the traditional one, but the addition of the noble metal elements Ni, Cu, rare earth elements and W is eliminated, which greatly reduces the alloy cost of the steel plate; Nb/V composite is used instead of V/ Ti compound refines the grains, increases the high temperature tempering strength, and improves the low temperature impact toughness of the steel plate. The low carbon equivalent of steel plate is controlled to 0.54≤CEV≤0.65 to ensure the hardness of the steel plate while ensuring that the steel plate has good welding performance.

In terms of production technology, the present invention controls cooling after rolling, the final cooling temperature is controlled at 600-750°C, the cooling rate is required to be ≥6°C/s, the crystal grains are refined, and fine martensite slats are obtained for subsequent offline quenching. Low-temperature impact toughness provides a good foundation. After quenching, high-temperature tempering is used to replace the low-temperature tempering process of conventional wear-resistant plates. The tempering temperature is 500-600℃. Under the combined action of Cr/Mo/V precipitates, the high-temperature performance of the steel plate is guaranteed.

In terms of product performance, the steel plate structure of the present invention is different from the tempered martensite of the conventional wear-resistant steel plate. It is tempered sorbite. The structure not only maintains high strength at high temperature, the tensile strength at 600°C is ≥1000MPa, and it is extended Rate A≥10%; at the same time, the low-temperature impact toughness is excellent, and the low-temperature Charpy impact toughness at -40℃ is ≥30J. The steel plate has a hardness of 370-430HB at 300-600℃ and has good wear resistance.

The high-temperature resistant 400HB wear-resistant steel plate of the present invention has excellent comprehensive performance and good weldability. Compared with existing steel grades, it has obvious advantages in high-temperature environments. At the same time, it adopts conventional low-alloy design and simple process; it is an inevitable trend for the development of social economy and steel industry. .

Description of the drawings

Fig. 1 is a SEM electron microscope scanning picture (2000X) of a typical structure of the product steel of Example 1 of the present invention.

detailed description

The present invention will be further described in detail below in conjunction with the embodiments of the drawings.

The production process of the high temperature resistant and wear resistant steel of the present invention is: converter steelmaking -> LF refining -> VD or RH high vacuum degassing -> continuous casting -> heating -> rolling -> quenching -> high temperature tempering

The production method of the high-temperature resistant and wear-resistant steel plate of embodiment 1-2 of the present invention includes the following steps:

(1) Smelting: use electric furnace or converter to smelt, then send it to LF refining furnace for refining, and go through VD or RH vacuum treatment. After the molten steel is degassed, carry out a small amount of Ca treatment to control the Ca content of 0.001 to 0.005%. After the treatment, the molten steel is softly stirred for no less than 10 minutes to ensure that the steel grade sulfide and oxides are completely denatured and fully floated and removed. The composition control of molten steel is shown in Table 1.

(2) Continuous casting: Cast the molten steel into a continuous casting billet with a thickness of 150mm. The casting temperature is controlled at 5-25°C above the liquidus line. Dynamic soft reduction is implemented during the casting process. The continuous casting process parameters are shown in Table 2.

(3) Rolling: Put the continuous casting billet obtained in step (2) into a walking-type heating furnace and heat it to 1200°C. After the core reaches the temperature, it will start to keep warm for 60 minutes. After the billet is discharged from the furnace, it is subjected to a two-stage controlled rolling of rough rolling + finishing rolling after high-pressure water descaling treatment. The opening temperature of rough rolling is between 1000-1100℃, and the thickness after temperature is ≥3.0H; the opening temperature of finishing rolling is between 850-950℃, after the rolling is completed, ACC rapid cooling is adopted, and the final cooling temperature is 600-750℃, cooling Speed ≥6℃/s. The specific relevant process parameters are shown in Table 3.

(4) Quenching: The quenching temperature of the steel plate is about 900℃, the holding time is 30-60min, and water quenching.

(5) High temperature tempering: the quenched steel plate enters the tempering furnace for high temperature tempering, the tempering temperature is 500-600℃, and the holding time is 30-90min.

See Table 1 to Table 4 for specific ingredients and process parameters. The corresponding performance of each example model is shown in Table 5.

Figure 1 shows a photo of the microstructure of the test steel in Example 1. The microstructure of the finished steel plate is uniform tempered sorbite, with fine grains, size ≤25um, and fine and uniform precipitates dispersed on the ferrite matrix. It can be seen that through the controlled rolling and controlled cooling process control and the selection of appropriate quenching process parameters, the original austenite grains are fully refined, and uniformly dispersed carbides are precipitated through appropriate high temperature tempering to ensure the high temperature hardness, strength and excellent quality of the steel plate. Low temperature impact toughness.

Table 1 The chemical composition of the wear-resistant steel plate of the embodiment (wt%)

Table 2 Continuous casting process control

Example	Overheating degree ℃	Center segregation	Loose center
1	20	C1.0	0.5
2	15	C0.5	0.5

Table 3 Rolling process control

Table 4 Heat treatment process control

table 5

The invention adopts high-cleanliness steelmaking and continuous casting process, controlled rolling and controlled cooling, off-line quenching, and high temperature tempering. It is controlled from the perspectives of chemical composition design, base material structure, inclusions, center segregation, quenching and tempering temperature and time. , To ensure the mechanical properties of the steel plate under high temperature conditions, provide the feasibility for the high temperature use of engineering equipment, and have the advantages and prospects of mass production and application.

Although the preferred embodiments of the present invention are described in detail above, it should be clearly understood that for those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (5)

1. A high temperature resistant 400HB wear-resistant steel plate, characterized in that the chemical composition is C: 0.15 to 0.25%, Si: 0.10 to 0.40%, Mn: 0.8 to 1.30%, Nb: 0.010 to 0.040%, V: 0.030～0.060%, Ti: ≤0.010%, Al: 0.03～0.06%, Ni: ≤0.1%, Cu: ≤0.1%, Cr: 0.10～0.50%, Mo: 0.50～1.00%, B: 0.001～0.005% , Ca: 0.0010～0.0050%, P: ≤0.010%, S: ≤0.0015%, O: ≤0.0015%, N: ≤0.0035%, H: ≤0.0002%, and 0.55≤Carbon equivalent CEV≤0.65, CEV=C +Mn/6+(Cr+Mo+V)/5+(Ni+Cu)/15, the balance is Fe and inevitable impurity elements.
2. The high temperature resistant 400HB wear-resistant steel plate according to claim 1, characterized in that: the microstructure of the finished steel plate is uniform tempered sorbite, and the crystal grains are fine: the size is less than or equal to 25um, and the ferrite matrix is dispersed with fine and uniform Precipitates, which are carbides.
3. The high temperature resistant 400HB wear-resistant steel plate according to claim 2, characterized in that: the thickness is 4-30mm; the surface Brinell hardness is 370-430HB; the tensile strength at 600°C is ≥1000MPa, the elongation is ≥10%, and the summer temperature is -40°C. The impact energy is greater than or equal to 30J than the V type.
4. A method for producing high temperature resistant 400HB wear-resistant steel plate, which is characterized in that it comprises the following main steps

   (1) Molten steel smelting: using converter smelting, then sending it to LF refining furnace for refining, and undergoing VD or RH vacuum treatment. After the molten steel is degassed, a trace amount of Ca treatment is carried out, and the Ca content is controlled to be 0.001 to 0.005%. After the treatment, the molten steel is softly stirred , The stirring time is not less than 10 minutes, to ensure that the steel sulfide and oxide are completely denatured and fully floated and removed; the vacuum treatment must control the total level of inclusions A, B, C, and D ≤ 2.5;

   (2) Casting billet: casting molten steel into a billet, the center segregation of the billet is not higher than C1.0, and the center porosity is not higher than 1.0;

   (3) Heating rolling: the billet is heated to 1150-1250°C, and the heat preservation is started when the core temperature reaches the surface temperature, and the holding time is not less than 30min; after the billet is released from the furnace, it is subjected to two-stage control rolling of rough rolling + finishing rolling after descaling , To refine the grains, improve the strength and toughness: the opening temperature of rough rolling is between 1000-1100℃, the thickness after temperature is ≥3H, H is the thickness of the finished product; the opening temperature of finishing rolling is between 850-950℃; the rolling is completed After that, the steel plate is cooled by ACC unit to accelerate the cooling, the final cooling temperature is controlled at 600-750℃, and the cooling rate is required to be ≥6℃/s;

   (4) Quenching heat treatment: After rolling, the steel plate is subjected to offline quenching treatment, the quenching temperature is 880-930℃, and the holding time after the furnace temperature reaches the temperature is 30-60min, to obtain a uniform quenched martensite structure;

   (5) Tempering heat treatment: After the steel plate is quenched, it needs to be tempered at a high temperature at 500-600℃. After the core of the steel plate reaches temperature, it is tempered for 30-90min to obtain a stable high-temperature tempered sorbite structure.
5. The method for producing a high-temperature resistant 400HB wear-resistant steel plate according to claim 4, characterized in that: in step (4), fine martensite slats are obtained after quenching.

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