CN116103562A - Production method of extra-thick rack steel plate - Google Patents

Abstract

A production method of an extra-thick rack steel plate comprises the following process steps of smelting, die casting, rolling, rapid cooling, finishing, quenching and tempering, wherein the thickness of the steel plate is 152-210 mm. The steel comprises the following chemical components, by mass, C=0.12-0.18, si=0.15-0.40, mn=1.0-1.2, P=0.006, S is less than or equal to 0.002, cr=0.8-1.5, nb=0.005-0.025, V=0.03-0.08, ni=0.8-1.5, mo=0.4-0.7, ti is less than or equal to 0.01, al=0.05-0.09, B=0.0015-0.0025 and the balance of Fe and unavoidable impurities; the invention adopts the design of low-carbon alloying components, and the yield strength of the final steel plate with 1/2 thickness is more than or equal to 690MPa, the tensile strength is more than or equal to 770MPa, the elongation is more than or equal to 16 percent, the yield ratio is less than or equal to 0.9,1/2, the transverse and longitudinal impact absorption energy is more than or equal to 100J at the transverse and longitudinal temperature of minus 60 ℃, and the production of 690 MPa-grade low-cost extra-thick rack steel is realized through QT technology. Can meet the production requirement of the rack plate with the thickness less than or equal to 210mm.

Description

Production method of extra-thick rack steel plate

Technical Field

The invention belongs to the technical field of metallurgy, and relates to a production method of a low-alloy high-strength steel plate with a strength level of 690MPa and a high toughness at a temperature of 60 ℃ below zero.

Background

With the development of wind power industry and ocean engineering industry, the demand of toothed bar steel is increasing. The toothed bar steel has the characteristics of large thickness, high strength and high toughness. After the steel plate is processed into a rack, when tooth surfaces are meshed, the stress of the core part of the original steel plate is maximum, and the core part is often required to have extremely high strength and toughness, so that the core part of the steel plate is required to be completely quenched into a martensitic structure. Since the thicker the steel sheet, the lower the actual cooling rate thereof, a large amount of alloying elements should be added to ensure that the core is capable of forming a large amount of martensitic structure at a cooling rate of 1 deg.c/s or less in the production of a rack steel sheet of 152mm or more.

In the ordinary die casting production process, the cooling speed is extremely difficult to control under the influence of the environment and the air temperature, and the too fast cooling speed is easy to cause untimely steel ingot feeding and shrinkage cavity generation; if the cooling speed is too low, harmful elements are easy to enrich, the purity of molten steel is affected, and the performance of the steel plate is reduced.

Chinese patent CN201710892107 '690 Mpa grade extra-thick rack steel and a production process thereof' discloses a production method for producing 178mm thick rack steel by adopting steel ingots, which is characterized by comprising the following chemical components in percentage by weight: 0.10 to 0.16 percent of C, 0.15 to 0.35 percent of Si, 0.95 to 1.35 percent of Mn, less than or equal to 0.015 percent of P, less than or equal to 0.010 percent of S, 0.50 to 0.60 percent of Cr, 2.30 to 2.60 percent of Ni, 0.45 to 0.55 percent of Mo, 0.03 to 0.05 percent of V, 0.07 to 0.09 percent of Al, less than or equal to 0.010 percent of Ti, 0.0010 to 0.0020 percent of B, less than or equal to 0.010 percent of N, and the balance of Fe and unavoidable impurities; the carbon equivalent Cep is 0.624-0.755, the welding sensitivity coefficient is 0.2655-0.3404, and the thickness is 152-178 mm. The patent adopts higher alloy components to compensate the problem of insufficient cooling speed of the core part of the thick steel plate, and can only produce the rack steel with the maximum thickness of 178mm under the condition of using higher Ni alloy content.

Chinese patent CN202011054651 "a rack steel plate with low rolling compression ratio and its manufacturing method", characterized in that: 0.12 to 0.15 percent of C, 0.1 to 0.3 percent of Si, 1.0 to 1.3 percent of Mn, less than or equal to 0.02 percent of P, less than or equal to 0.01 percent of S, 0.01 to 0.03 percent of Als, 2.5 to 3.0 percent of Ni, 0.5 to 0.8 percent of Cr, 0.5 to 0.8 percent of Mo, 0.2 to 0.5 percent of Cu, 0.02 to 0.04 percent of Nb, 0.03 to 0.06 percent of V, 0.005 to 0.03 percent of Ti, 0.001 to 0.0015 percent of B, and the balance of iron and unavoidable impurities. After electroslag remelting and forging, rolling and twice heat treatment are carried out to produce the rack steel with the thickness of 260 mm. The production method produces extra thick toothed bar steel by means of electroslag remelting, forging and secondary quenching. Various performances of the ultra-thick toothed bar are ensured through more equipment and more working procedures. The segregation of the steel ingot is not fully utilized, the production cost is reduced, the method is suitable for producing rack steel with larger thickness, the energy consumption is larger, the working procedure is more complicated, and no cost advantage exists.

Chinese patent CN201910141457 "a large-thickness rack steel plate and production method thereof", characterized in that C:0.30 to 0.33 percent, si:0.20 to 0.40 percent, mn:0.55 to 0.65 percent, P is less than or equal to 0.010 percent, S is less than or equal to 0.005 percent, cr:0.85 to 0.95 percent, mo:0.50 to 0.60 percent, ni:0.60 to 0.70 percent of Al: 0.020-0.040%, and the balance of Fe and unavoidable impurities; the production method comprises the working procedures of smelting, heating, rolling, complete annealing, riser cutting, sampling and heat treatment. The high-carbon high-Mo alloy design is adopted, so that the hardenability and strength of the steel plate can be effectively improved, but the impact toughness is low, the welding sensitivity coefficient is high, the steel plate is limited in practical application, and a certain risk exists for dynamic load application of complex sea conditions.

Disclosure of Invention

The invention aims to provide a production method of a low-cost ultra-thick rack steel plate, wherein the strength grade of the produced steel is 690MPa, various impurities and inclusions in molten steel are reduced by smelting pure steel, the cooling speed of the steel ingot is controlled, the alloy cost is reduced by utilizing positive segregation of the core part of the steel plate, the toughness of the core part of the steel ingot is improved, and the production of the low-cost ultra-thick rack steel plate is realized.

The invention is realized by the following technical scheme:

the production method of the extra-thick rack steel plate comprises the following production process routes of smelting, die casting, rolling, quick cooling, finishing, quenching and tempering, wherein the thickness of the steel plate is 152-210mm, the mass percentages of the chemical components of the steel are C=0.12-0.18, si=0.15-0.40, mn=1.0-1.2, P is less than or equal to 0.006, S is less than or equal to 0.002, cr=0.8-1.5, nb=0.005-0.025, V=0.03-0.08, ni=0.8-1.5, mo=0.4-0.7, ti is less than or equal to 0.01, al=0.05-0.09, and B=0.0015-0.0025, and the balance of Fe and unavoidable impurities; the method comprises the following process steps:

(1) Smelting: adopting a BOF-LF-RH production process path, controlling P to be less than or equal to 0.01% in converter smelting, reducing the P content of molten steel to be less than 0.006% by adopting a secondary slag forming method after tapping, and adopting a deep desulfurization process in a refining LF furnace, wherein the sulfur content of a finished product is less than or equal to 0.002%; the RH furnace production adopts a deep degassing process, and the total vacuum treatment time is more than or equal to 15min; calcium treatment after RH emptying and soft blowing are carried out for more than or equal to 15 minutes;

(2) And (3) die casting: the superheat degree is controlled at 40-45 ℃, the casting speed is reduced when the ingot is cast to a riser, a heating agent is added into the riser after casting, and then the ingot mould is integrally insulated by an integral insulation cover;

(3) Rolling: adopting two-fire cogging rolling, adopting a pit type heating furnace for initial rolling, heating at 1230-1250 ℃ and cogging thickness of 400mm, adopting a roller hearth type heating furnace for secondary heating, heating at not less than 1190 ℃, adopting two-stage rolling, adopting a low-speed large-pressure rolling mode for one-stage rolling, and then cooling to room temperature in air;

(4) Tempering: the rolled steel sheet is subjected to quenching and tempering heat treatment in a roller hearth furnace. Quenching at 900-930 ℃ for 150-200 minutes with a roller quenching machine to ensure consistent cooling of the heads and the tails of the steel plates, tempering at 600-630 ℃ for 200-300 minutes with a temperature of a tempering furnace, performing fire cutting to a fixed size after discharging the steel plates from the furnace, checking the quality of the surfaces and the fire cutting surfaces, and warehousing.

The invention adopts the design of low-carbon alloying components, and the yield strength of the final steel plate with 1/2 thickness is more than or equal to 690MPa, the tensile strength is more than or equal to 770MPa, the elongation is more than or equal to 16 percent, the yield ratio is less than or equal to 0.9,1/2, the transverse and longitudinal impact absorption energy is more than or equal to 100J at the transverse and longitudinal temperature of minus 60 ℃, and the production of 690 MPa-grade low-cost extra-thick rack steel is realized through QT technology. Can meet the production requirement of the rack plate with the thickness less than or equal to 210mm. The method is suitable for producing 152-210 mmEH690 rack steel plates, has the advantages of low production cost, excellent welding performance and good core toughness. The method has the outstanding characteristics that the positive segregation of the hardenability element in the die casting process is improved by adopting a pure steel smelting and slow cooling mode, excessive enrichment of impurity elements is avoided, the positive segregation of the hardenability element in the steel plate is fully utilized to improve the hardenability of the core part of the steel plate, thereby reducing the alloy cost and improving the performance of the steel plate.

Drawings

FIG. 1 is a structural gold phase diagram of a 210mmCCS EH690 steel plate.

Detailed Description

The following examples are provided to further illustrate the control range of the components, the preferred embodiments of the present invention, and the like:

example 1

A production method of an extra-thick rack steel plate comprises the steps of controlling P to be less than or equal to 0.009% in converter smelting, reducing the P content of molten steel to 0.004% by adopting a secondary slag forming method after tapping, and adopting a deep desulfurization process in a refining LF furnace, wherein the sulfur content of a finished product is less than or equal to 0.0015%; the RH furnace production adopts a deep degassing process, and the total vacuum treatment time is 18min; calcium treatment and soft blowing for 25 minutes after RH breaking; the die casting superheat degree is controlled at 42-44 ℃, the casting speed is reduced to 50% when the ingot is cast to a riser, 100kg of heating agent is added into the riser after casting, and then the ingot mould is integrally insulated for 72 hours by using an integral insulation cover; the rolling adopts two-fire cogging rolling, the initial rolling adopts a pit type heating furnace, the heating temperature is 1240 ℃, the cogging thickness is 403mm, the secondary heating adopts a roller hearth type heating furnace, the heating temperature is 1210 ℃, the rolling adopts two-stage rolling, the maximum rolling reduction of one stage is 48mm, and the air cooling is carried out to the room temperature after the rolling reaches the thickness of 152 mm; the rolled steel sheet is subjected to quenching and tempering heat treatment in a roller hearth furnace. Quenching at 915 ℃ for 160 minutes, quenching for 40 minutes by a roller quenching machine, cooling to room temperature, tempering at 630 ℃ for 210 minutes, performing fire cutting to a fixed size at 50 ℃ after the tempering furnace is discharged, and checking the quality of the surface and the fire cut surface and warehousing.

Example 2

A production method of an extra-thick rack steel plate comprises the steps of controlling P to be less than or equal to 0.010% in converter smelting, reducing the P content of molten steel to be 0.005% by adopting a secondary slag forming method after tapping, and adopting a deep desulfurization process in a refining LF furnace, wherein the sulfur content of a finished product is less than or equal to 0.0012%; the RH furnace production adopts a deep degassing process, and the total vacuum treatment time is 20min; calcium treatment and soft blowing for 28 minutes after RH breaking; the die casting superheat degree is controlled at 43-45 ℃, the casting speed is reduced to 50% when the ingot is cast to a riser, 120kg of heating agent is put into the riser after casting, and then the ingot mould is integrally insulated for 72 hours by using an integral insulation cover; the rolling adopts two-fire cogging rolling, the initial rolling adopts a pit type heating furnace with the heating temperature of 1247 ℃ and the cogging thickness of 410mm, the secondary heating adopts a roller hearth type heating furnace with the heating temperature of 1205 ℃ and adopts two-stage rolling, the maximum rolling reduction of one stage is 47mm, and the air cooling is carried out to the room temperature after the rolling reaches the thickness of 178 mm; the rolled steel sheet is subjected to quenching and tempering heat treatment in a roller hearth furnace. Quenching at 925 ℃ for 180 minutes with a roller quenching machine, cooling to room temperature at 635 ℃ with a tempering temperature for 240 minutes, and performing fire cutting to a fixed size at 60 ℃ after the tempering furnace is discharged from the furnace, and checking the quality of the surface and the fire cut surface and warehousing.

Example 3

The P content of the molten steel is reduced to 0.004% by adopting a secondary slag forming method after tapping, the sulfur content of a finished product is less than or equal to 0.0013% by adopting a deep desulfurization process in a refining LF furnace; adopting an RH furnace deep degassing technology to produce, and carrying out vacuum treatment for 20min; calcium treatment and soft blowing for 32 minutes after RH breaking; the degree of superheat of die casting is controlled at 41-43 ℃, the casting speed is reduced to 40% when the ingot is cast to a riser, 140kg of heating agent is added into the riser after casting, and then the ingot mould is integrally insulated for 75 hours by using an integral insulation cover; the rolling adopts two-fire cogging rolling, the initial rolling adopts a pit type heating furnace with the heating temperature of 1237 ℃ and the cogging thickness of 408mm, the secondary heating adopts a roller hearth type heating furnace with the heating temperature of 1200 ℃, the two-stage rolling is adopted, the maximum rolling reduction of one stage is 49mm, and the air cooling is carried out to the room temperature after the rolling reaches the thickness of 178 mm; the rolled steel sheet is subjected to quenching and tempering heat treatment in a roller hearth furnace. Quenching at 923 ℃ for 185 minutes, quenching by a roller quenching machine for 45 minutes, cooling to room temperature, tempering at 634 ℃ for 243 minutes, and performing fire cutting to a fixed size at 60 ℃ after the tempering furnace is discharged from the furnace, and checking the quality of the surface and the fire cut surface and warehousing.

Example 4

The P content of the molten steel is reduced to 0.004% by adopting a secondary slag forming method after tapping, the sulfur content of a finished product is less than or equal to 0.0010% by adopting a deep desulfurization process in a refining LF furnace; the RH furnace production adopts a deep degassing process, and the total vacuum treatment time is 22min; calcium treatment and soft blowing for 27 minutes after RH breaking; the degree of superheat of die casting is controlled at 43-45 ℃, the casting speed is reduced to 40% when the ingot is cast to a riser, 140kg of heating agent is added into the riser after casting, and then the ingot mould is integrally insulated for 72 hours by using an integral insulation cover; the rolling adopts two-fire cogging rolling, the initial rolling adopts a pit type heating furnace with the heating temperature of 1249 ℃ and the cogging thickness of 445mm, the secondary heating adopts a roller hearth type heating furnace with the heating temperature of 1220 ℃, the two-stage rolling is adopted, the maximum rolling reduction of one stage is 46mm, and the air cooling is carried out to the room temperature after the rolling reaches the thickness of 210 mm; the rolled steel sheet is subjected to quenching and tempering heat treatment in a roller hearth furnace. Quenching at 930 ℃ for 200 minutes with a roller quenching machine, cooling to room temperature for 50 minutes, tempering at 630 ℃ for 300 minutes with a tempering furnace, and performing fire cutting to a fixed size at 60 ℃ after the tempering furnace is discharged from the furnace, and checking the quality of the surface and the fire cut surface and warehousing.

The chemical composition control of each smelting example is shown in Table 1, and the detection performance of the steel is shown in Table 2.

TABLE 1 chemical composition (wt%) of example steel

Table 2 example steel test properties

As can be seen from Table 2, the strength and toughness of 152-210mm can be produced by the method disclosed by the invention, and the strength and toughness of the EH690 rack steel core part meet the requirements of toughness and hardness. The steel plates with various thicknesses have stable performance and compact core. Because the steel plate fully utilizes segregation of the hardenability elements, the whole carbon equivalent of the steel plate is lower, a large amount of Ni elements are saved, and the welding of the steel plate is facilitated.

As can be seen from fig. 1, after the steel plate is quenched and tempered, the structure is a tempered rope solid and a small amount of bainite, the structure is fine and uniform, and the requirement of the toothed bar on the toughness of the core part is met.

Claims (1)

1. The production method of the ultra-thick rack steel plate comprises the following process routes of smelting, die casting, rolling, rapid cooling, finishing, quenching and tempering, wherein the thickness of the steel plate is 152-210mm, and the production method is characterized in that: the steel comprises the following chemical components, by mass, C=0.12-0.18, si=0.15-0.40, mn=1.0-1.2, P=0.006, S is less than or equal to 0.002, cr=0.8-1.5, nb=0.005-0.025, V=0.03-0.08, ni=0.8-1.5, mo=0.4-0.7, ti is less than or equal to 0.01, al=0.05-0.09, B=0.0015-0.0025 and the balance of Fe and unavoidable impurities; the yield strength of the final steel plate with the thickness of 1/2 is more than or equal to 690MPa, the tensile strength is more than or equal to 770MPa, the elongation is more than or equal to 16%, the yield ratio is less than or equal to 0.9,1/2, and the transverse and longitudinal impact absorption energy at-60 ℃ is more than or equal to 100J; the method comprises the following process steps:

(1) Smelting: adopting a BOF-LF-RH production process path, controlling P to be less than or equal to 0.01% in converter smelting, reducing the P content of molten steel to be less than 0.006% by adopting a secondary slag forming method after tapping, and adopting a deep desulfurization process in a refining LF furnace, wherein the sulfur content of a finished product is less than or equal to 0.002%; the RH furnace production adopts a deep degassing process, and the total vacuum treatment time is more than or equal to 15min; calcium treatment after RH emptying and soft blowing are carried out for more than or equal to 15 minutes;

(2) And (3) die casting: the superheat degree is controlled at 40-45 ℃, the casting speed is reduced when the ingot is cast to a riser, a heating agent is added into the riser after casting, and then the ingot mould is integrally insulated by an integral insulation cover;

(3) Rolling: adopting two-fire cogging rolling, adopting a pit type heating furnace for initial rolling, heating at 1230-1250 ℃ and cogging thickness of 400mm, adopting a roller hearth type heating furnace for secondary heating, heating at not less than 1190 ℃, adopting two-stage rolling, adopting a low-speed large-pressure rolling mode for one-stage rolling, and then cooling to room temperature in air;

(4) Tempering: the rolled steel sheet is subjected to quenching and tempering heat treatment in a roller hearth furnace. Quenching at 900-930 ℃ for 150-200 minutes with a roller quenching machine to ensure consistent cooling of the heads and the tails of the steel plates, tempering at 600-630 ℃ for 200-300 minutes with a temperature of a tempering furnace, performing fire cutting to a fixed size after discharging the steel plates from the furnace, checking the quality of the surfaces and the fire cutting surfaces, and warehousing.

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