CN111647800A

CN111647800A - Preparation method of hot-rolled round steel capable of being directly cut

Info

Publication number: CN111647800A
Application number: CN202010360301.0A
Authority: CN
Inventors: 冀鸰; 高助忠; 郑亚明
Original assignee: Jiangsu Taifu Pipe Technology Co ltd; Jingjiang Special Steel Co Ltd
Current assignee: Jiangsu Taifu Pipe Technology Co ltd; Jingjiang Special Steel Co Ltd
Priority date: 2020-04-30
Filing date: 2020-04-30
Publication date: 2020-09-11
Anticipated expiration: 2040-04-30
Also published as: CN111647800B

Abstract

The invention relates to a preparation method of hot-rolled round steel capable of being directly cut, wherein a steel billet is heated before rolling to enable a structure to be completely austenitized, the steel billet is descaled after being taken out of a furnace, first air cooling is carried out after two descales to wait for temperature, the steel billet is warmed to 1050-; then, carrying out secondary air cooling on the intermediate billet to be warmed up, warming the intermediate billet to be at the initial temperature of 800-920 ℃ for continuous rolling, continuously rolling the intermediate billet into round steel by using a continuous rolling mill after the intermediate billet is warmed up for the second time, wherein the final rolling temperature is not less than 780 ℃; and (3) when the temperature of the round steel after hot rolling is lower than Ar3, comprehensively cooling the round steel by adopting spray and air cooling, cooling to 600 ℃, and then naturally cooling to obtain the microstructure of fine lamellar pearlite and a small amount of ferrite.

Description

Preparation method of hot-rolled round steel capable of being directly cut

Technical Field

The invention relates to a preparation method of hot-rolled round steel capable of being directly cut without tempering.

Background

The hot rolled round steel for direct cutting is widely used for replacing quenched and tempered steel such as 45, 40Cr, 42CrMo and the like to produce a pull rod of an injection molding machine, a piston rod of an oil cylinder of an engineering vehicle and other various rod parts. Compared with the traditional quenched and tempered steel, the production process omits the heat treatment link after rolling, so that the production period is shorter, the production cost is lower, and the production purposes of energy saving, cost reduction, emission reduction and efficiency improvement are achieved. However, the hot rolled round steel generally needs to be warmed during rolling so as to realize low-temperature rolling; in addition, in order to ensure higher strength and toughness, higher content of grain refining elements such as Nb, V and the like are required to be added into the components, the requirement on toughness is higher, and special measures such as spray cooling, even water penetration forced cooling and the like are further required to be matched in the preparation method. Either the addition of alloy or the addition of forced cooling offsets the cost advantage of eliminating temper.

Based on the above situation, those skilled in the art still try to find the best match between the element components and the controlled rolling and controlled cooling process, and obtain a more economic and reasonable preparation method on the premise of ensuring the toughness.

Patent document No. CN1730703A discloses a non-quenched and tempered high-quality carbon structural steel and a manufacturing method thereof, and provides a non-quenched and tempered carbon structural steel which is added with trace micro-alloying elements on the basis of the main chemical components of No. 45 steel and a manufacturing method thereof, and solves the problem that the strength of the non-quenched and tempered steel is surplus and the toughness is insufficient by combining the element composite micro-alloying effect and the corresponding controlled rolling and controlled cooling process. Chemical components: 0.42 to 0.50 percent of C, 0.17 to 0.37 percent of Si, 0.50 to 0.80 percent of Mn, 0.03 to 0.30 percent of V, 0.005 to 0.040 percent of Ti, 0.005 to 0.020 percent of N, 0.005 to 0.050 percent of Al, less than or equal to 0.035 percent of S, less than or equal to 0.035 percent of P, and the balance of Fe. The preparation method comprises the steps of controlled rolling and controlled cooling: the soaking temperature of the billet in the heating furnace is 1130-1280 ℃, the initial rolling temperature is 1050-1200 ℃, the final rolling temperature is 850-1050 ℃, and the cooling speed of the rolled material is 20-110 ℃/min. The manufacturing method needs to add Ti, V and Nb with higher contents, has higher material cost, can predict the difficulty of casting the billet, and is difficult to meet the strength requirement of yield strength of more than 500 MPa.

Patent document No. CN 109295391a discloses a high strength and toughness non-quenched and tempered steel and a preparation method thereof, the components of which are: c: 0.23-0.27%; si: 0.22-0.35%; mn: 1.81-1.90%; cr: 0.50-0.55%; s: 0.0450.06 percent; p: less than or equal to 0.02 percent; v: 0.11-0.14%; n: 0.025-0.040 percent, and the balance of iron and inevitable impurities, and is formed by adopting a forging mode, wherein the initial forging temperature is higher than 1150 ℃, the final forging temperature is 840-1000 ℃, the carbon content of the product is low, the product contains higher alloys of Mn, Cr and V, the element cost is very high, and the efficiency is obviously lower than that of a hot rolling forming process by adopting the forging process, so that the method cannot be suitable for mass delivery.

Patent document No. CN 109759779a discloses a non-quenched and tempered steel motor shaft and a processing method thereof, belonging to non-quenched and tempered round steel, and the element components are C: 0.46-0.55%, Si: 0.20-0.60%, Mn: 1.20-1.60%, Cr: 0.00-0.30%, Al: 0.010-0.030%, Ni: 0.10-0.30%, Cu: 0.00-0.20%, P: 0.000 to 0.030%, S: 0.020-0.050%, V: 0.050 to 0.250%, Nb: 0.020-0.050%, Ti: 0.010-0.030%, B: 0.0005-0.0030%, N: 0.012-0.020%, and the balance Fe. The non-tempered steel is processed by adopting temperature-controlled hot pressure and is cooled at a controlled speed, namely the temperature of final rolling or final forging is controlled to be 780-850 ℃, and the cooling speed after rolling is controlled to be 3-5 ℃/s, so that higher strength and toughness are obtained. Because of the adoption of high contents of Mn, Ni, V, Nb, Ti and B, the element cost is particularly high.

Patent application CN 201711100874 discloses a non-quenched and tempered steel and a preparation method thereof, wherein the non-quenched and tempered steel comprises the following components in percentage by weight: 0.46-0.55%, Si: 0.20-0.60%, Mn: 1.20-1.60%, Cr: 0.00-0.30%, Al: 0.010-0.030%, Ni: 0.10-0.30%, Cu: 0.00-0.20%, P: 0.000 to 0.030%, S: 0.020-0.050%, V: 0.050 to 0.250%, Nb: 0.020-0.050%, Ti: 0.010-0.030%, B: 0.0005-0.0030, N: 0.012-0.020%, and the balance Fe, the product of the patent application contains higher alloys of Mn, V, Nb, Ti and B, the material cost is high, and the production efficiency is low because the temperature needs to be raised to 780-.

Disclosure of Invention

The invention aims to provide a preparation method of directly-cutting hot-rolled round steel, which combines the design of element components and a forming process to finally prepare the directly-cutting round steel without heat treatment, wherein the yield strength of the round steel reaches more than 450MPa, the elongation is more than 15%, the U-shaped impact energy at room temperature is more than 27J, and the round steel can be used as a processing material of a part of rod parts in the market.

The technical scheme of the invention is that the preparation method of the hot-rolled round steel capable of being directly cut comprises the following steps

(1) Designing element components: c is calculated according to the mass percentage: 0.35 to 0.50%, Si: 0.15 to 0.60%, Mn: 0.50-1.80%, Cr: 0.00-0.35%, S: 0.003-0.060%, Al: 0.006-0.060%, N: 0.0050-0.020%, and the balance Fe and inevitable impurity elements. The ranges of the elements are set as follows

C: the pearlite proportion and the strength and the hardness of the whole section are increased, but the plasticity and the toughness are reduced, and the content of the pearlite is controlled to be 0.35-0.50%.

Si: is a deoxidizing element in steel and improves the strength of steel in a solid solution strengthening mode. When the Si content is less than 0.15%, the deoxidation effect is poor, and when the Si content is higher, the toughness is reduced. The Si content of the invention is controlled to be 0.15-0.60%.

Mn: is an element for improving the hardenability of steel, and plays a role in solid solution strengthening to improve the strength of steel. However, Mn is easy to promote the segregation of harmful elements P to grain boundaries and cause hydrogen-induced intergranular fracture, and excessively high Mn can reduce the impact toughness of steel, and the Mn content is controlled to be 0.50-1.80%.

Cr: carbide forming elements increase the hardness of the material and prevent the crystal grains from growing, but the ductility and toughness are reduced and the manufacturing cost is improved due to the excessively high addition of Cr, so that the Cr content is controlled to be 0.00-0.35 percent.

Al: al and N are combined to generate AlN, so that excessive growth of austenite grain size during heating and deformation of a continuous casting billet is prevented, and the content of Al is controlled to be 0.006-0.060%.

N: n can promote the precipitation of Al fine nitrides and play a role in refining grains in the heating and deformation processes, and the content of N is controlled to be 0.0050-0.020 percent in the invention.

S: s and Mn form strip-shaped sulfide inclusions, and the cutting performance of steel is improved. The invention controls the content of S to be 0.003 to 0.060 percent.

(2) Designing a molding process: the method comprises the steps of smelting molten steel according to element component design, casting the molten steel into a steel billet, heating the steel billet after slow cooling to enable the structure to be completely austenitized, removing scale after discharging, removing the scale by adopting high-pressure water, starting first air cooling after the scale is removed to wait for the temperature, heating the steel billet to 1050 and 950 ℃ of the initial temperature of cogging rolling, waiting for the temperature of the hot steel billet on a roller way of a cogging mill, turning the steel billet by 180 degrees by using the cogging mill in the temperature waiting process, namely adjusting the surface up and down, uniformly cooling the two sides of the square billet, and avoiding overlarge local temperature drop. After the temperature is reached for the first time, roughly rolling the steel billet into an intermediate billet by using a cogging mill (a reciprocating mill), wherein the finish rolling temperature is 1000-; and then carrying out secondary air cooling on the intermediate billet to be warmed up, warming the intermediate billet to the initial temperature of 800-920 ℃ for continuous rolling, and continuously rolling the intermediate billet into round steel by using a continuous rolling mill after the intermediate billet is warmed up for the second time, wherein the final rolling temperature is more than or equal to 780 ℃.

The final rolling temperature of cogging rolling is controlled to be 1000-plus 950 ℃, deformed austenite grains are fully recrystallized when the temperature is waited for the second time of air cooling, meanwhile, Al nitrides are fully precipitated in the process of the second time of waiting for temperature (the precipitation temperature of AlN is about 1000-plus 900 ℃), and the AlN precipitated in the process of waiting for temperature plays a role in pinning the grain boundary of AlN when the continuous rolling deformation is carried out later, so that the grain growth is inhibited, and the structure is refined.

(3) And (3) a cooling process: and (3) when the temperature of the round steel after hot rolling is lower than the starting temperature Ar3 of the transformation from austenite to ferrite, comprehensively cooling the round steel by adopting spray cooling and air cooling, and naturally cooling after cooling to 600 ℃ to obtain the microstructure of fine lamellar pearlite and a small amount of ferrite. The cooling is accelerated through spray cooling and air cooling, the transformation interval from austenite to ferrite is shortened, the structure enters a pseudo-pearlite transformation area as fast as possible, the effect of reducing interlayer spacing of pearlite slices while inhibiting ferrite precipitation is achieved, and high-proportion fine lamellar pearlite is obtained so as to improve the strength and hardness of the material. The round steel can obtain strength, elongation and impact toughness after being rolled off line, and can be directly used for being processed into cutting parts.

Optionally, the molten steel smelting at least comprises primary smelting and LF furnace refining. Wherein the primary smelting is to smelt the alloy raw material blocks and molten iron in a converter or an electric furnace. More reasonably, the molten steel smelting also comprises smelting, LF furnace refining and vacuum degassing treatment.

Optionally, the steel billet is a continuous casting square billet, the superheat degree of molten steel casting is designed to be 15-30 ℃ during continuous casting, and the continuous casting square billet is placed into a pit for slow cooling after being formed.

Preferably, the reheating temperature of the billet is 1150-1220 ℃, and the temperature is kept in the temperature range to ensure that alloy elements are fully dissolved in solid solution and the structure is fully austenitized.

Preferably, the descaling comprises two times, and the steel billet is subjected to twice high-pressure water descaling in a way of going back and forth once on the roller way, so that the surface oxide skin is removed, the temperature drop of the continuous casting billet is accelerated, and the time for waiting for temperature of the first air cooling is reduced.

Preferably, the front and rear steel billets are continuously operated in the forming process, and when the former steel billet is subjected to the second temperature waiting, the adjacent rear steel billet is subjected to the first temperature waiting before the descaling and the cogging. The working hours are saved when the device is produced in batch.

Compared with the prior art, the invention has the advantages that:

1. the traditional Nb and V microalloying elements are not added, the raw material cost is low, the recrystallization of austenite after deformation is delayed through low-temperature cogging and low-temperature continuous rolling at the rolling temperature which is obviously lower than that of the conventional rolling process, fine austenite grains are obtained, so that the sizes of ferrite and pearlite grains precipitated subsequently are fine, the fine lamellar pearlite with thin carbide sheets and fine space between sheets is obtained through rapid cooling below Ar3, and finally the strength and toughness of the material are equivalent to those of microalloyed steel.

2. The traditional Nb and V microalloying elements are not added, the raw material cost is lower, high-temperature solid solution is not needed, the blank reheating temperature is low, the energy is saved, the emission is reduced, the subsequent temperature waiting and cooling time is shortened, and the production rhythm is improved.

3. And the two-time high-pressure water descaling is adopted, so that the descaling effect is better, the accelerated cooling of the continuous casting billet is facilitated, the first temperature waiting time is shortened, and the production rhythm is improved.

4. Two sections of temperature waiting are adopted, so that the adverse effects of uneven performance or corner cracks caused by overlarge temperature drop of local corners and the like due to overlong first temperature waiting time are reduced, and the burning loss of high-temperature steel billets to equipment parts such as roller ways, bearings and the like is reduced.

5. Two sections of temperature waiting are adopted, the second temperature waiting of the previous steel billet and the first temperature waiting of the next steel billet can be synchronously carried out, the accumulated temperature waiting time during batch production is shortened, and the production rhythm is improved.

Drawings

FIG. 1 is a typical structure of hot-rolled round steel produced by the preparation method of the application, which is magnified by 100 times;

fig. 2 shows a typical structure of hot-rolled round steel produced by the preparation method of the present application, which is enlarged by 200 times.

Detailed Description

The present invention is described in further detail below with reference to examples, which are intended to be illustrative and not to be construed as limiting the invention.

Example 1

The diameter of the round steel related to the embodiment is 60mm, and the round steel comprises the following chemical components in percentage by mass: c: 0.45%, Si: 0.25%, Mn: 0.60%, Cr: 0.15%, Al: 0.025%, S: 0.015%, N: 0.0050%, and the balance of iron and inevitable impurity elements.

The round steel is sequentially subjected to electric furnace smelting and LF refining to produce molten steel; pouring molten steel into a 250 x 250mm continuous casting square billet by adopting low superheat degree full-process argon protection at 15-30 ℃, and slowly cooling the continuous casting billet in a pit for 32 hours; heating the continuous casting slab to 1170 ℃, preserving heat for 3 hours and discharging; returning the original path after the first descaling by high-pressure water, and performing second descaling by high-pressure water; and then, waiting for temperature on a material turning roller way of the reciprocating cogging mill, turning the material by using a material turning machine during the temperature waiting period, turning the material by 180 degrees, adjusting the surface up and down, and uniformly cooling to avoid overlarge temperature drop of the contact part between the lower part of the blank and the roller way. After the surface temperature of the blank is reduced to 980 ℃, rolling the blank into an intermediate blank with the specification of 135 x 145mm by a reciprocating rolling mill; the intermediate billet is heated on a roller way of a continuous rolling mill, and meanwhile, the next continuous casting billet is discharged from the furnace for secondary descaling and heated on a reversing roller way of a reciprocating rolling mill; after the surface temperature of the first intermediate billet is reduced to 840 ℃, the first intermediate billet enters a continuous rolling unit, an austenite single-phase region is rolled into 60mm round steel, the final rolling temperature is 830 ℃, and meanwhile, the next continuous casting billet enters a reciprocating rolling mill for cogging; sawing round steel, putting the round steel on a cooling bed, cooling the round steel to 600 ℃ by adopting a spray cooling and air cooling mode at 720 ℃, and then naturally cooling the round steel by air to obtain a mixed structure of fine lamellar pearlite and a small amount of ferrite, wherein the typical structure is shown in a figure 1 and a figure 2; then, the steel is subjected to the processes of off-line stacking cooling, straightening and finishing and then is put into storage; the round steel is directly processed into parts with required shapes.

Example 2

The diameter of the round steel related to the embodiment is 60mm, and the round steel comprises the following chemical components in percentage by mass: c: 0.45%, Si: 0.30%, Mn: 1.55%, Cr: 0.20%, Al: 0.030%, S: 0.028%, N: 0.0080%, and the balance of iron and inevitable impurity elements.

The round steel is sequentially subjected to electric furnace smelting and LF refining to produce molten steel; pouring molten steel into a 300 x 340mm continuous casting square billet by adopting low superheat degree full-process argon protection at 15-30 ℃, and slowly cooling the continuous casting billet in a pit for 32 hours; heating the continuous casting slab to 1180 ℃, preserving heat for 3 hours and discharging; returning the original path after the first descaling by high-pressure water, and performing second descaling by high-pressure water; and then, waiting for temperature on a material turning roller way of the reciprocating cogging mill, turning the material by using a material turning machine during the temperature waiting period, turning the material by 180 degrees, adjusting the surface up and down, and uniformly cooling to avoid overlarge temperature drop of the contact part between the lower part of the blank and the roller way. After the surface temperature of the blank is reduced to 1000 ℃, rolling the blank into a 135 × 145mm intermediate blank by a reciprocating rolling mill; the intermediate billet is heated on a roller way of a continuous rolling mill, and meanwhile, the next continuous casting billet is discharged from the furnace for secondary descaling and heated on a reversing roller way of a reciprocating rolling mill; after the surface temperature of the first intermediate billet is reduced to 860 ℃, the first intermediate billet enters a continuous rolling mill set, an austenite single-phase region is rolled into 60mm round steel, the final rolling temperature is 850 ℃, and meanwhile, the next continuous casting billet enters a reciprocating rolling mill for cogging; sawing the round steel, putting the round steel on a cooling bed, cooling the round steel to 600 ℃ by adopting a spray cooling and air cooling mode after the temperature of the round steel is reduced to 730 ℃, and then naturally cooling the round steel by air to obtain a mixed structure of fine lamellar pearlite and a small amount of ferrite; then, the steel is subjected to the processes of off-line stacking cooling, straightening and finishing and then is put into storage; the round steel is directly processed into parts with required shapes.

Example 3

The diameter of the round steel related to the embodiment is 60mm, and the round steel comprises the following chemical components in percentage by mass: c: 0.36%, Si: 0.30%, Mn: 1.35%, Cr: 0.20%, Al: 0.025%, S: 0.035%, N: 0.0120% of iron and the balance of inevitable impurity elements.

The round steel is sequentially subjected to converter smelting and LF refining to produce molten steel; pouring molten steel into a 300 x 340mm continuous casting square billet by adopting low superheat degree full-process argon protection at 15-30 ℃, and slowly cooling the continuous casting billet in a pit for 32 hours; heating the continuous casting slab to 1180 ℃, preserving heat for 3 hours and discharging; returning the original path after primary descaling by high-pressure water, and performing secondary descaling by high-pressure water; then, the temperature is waited on a material turning roller way of the reciprocating type cogging mill, and the material is turned by the material turning machine during the waiting period, so that the temperature drop at the contact part of the lower part of the blank and the roller way is avoided to be overlarge; reducing the surface temperature of the blank to 1020 ℃, and then rolling the blank into a 135 × 145mm intermediate blank by a reciprocating rolling mill; the intermediate billet is heated on a roller way of a continuous rolling mill, and meanwhile, the next continuous casting billet is discharged from the furnace for secondary descaling and heated on a reversing roller way of a reciprocating rolling mill; after the surface temperature of the first intermediate billet is reduced to 900 ℃, the first intermediate billet enters a continuous rolling mill set, an austenite single-phase region is rolled into 60mm round steel, and the final rolling temperature is 880 ℃; simultaneously, the next continuous casting billet enters a reciprocating rolling mill for cogging; sawing the round steel, putting the round steel on a cooling bed, cooling the round steel to 600 ℃ by adopting a spray cooling and air cooling mode when the temperature reaches 740 ℃, and then naturally cooling the round steel to obtain a mixed structure of fine lamellar pearlite and a small amount of ferrite; then, the steel is subjected to the processes of off-line stacking cooling, straightening and finishing and then is put into storage; the round steel is directly processed into parts with required shapes.

As a comparison, the inventors of the present application additionally performed three sets of comparative experiments: in the comparative example 1, the rolling is started within the range of 1050-; the comparative examples 2 and 3 adopt temperature-controlled rolling, the initial rolling temperature is 1050-1200 ℃, the final rolling temperature is 850-1050 ℃, compared with the comparative example 1, the alloy elements in the examples 1-3 are similar in composition, but the yield strength and the tensile strength are higher, compared with the comparative examples 2 and 3, the element components do not contain precious micro-alloy elements Ti, V and Nb, but the mechanical properties such as strength, elongation, impact toughness and the like are equivalent due to the adoption of the lower initial rolling temperature and the lower continuous rolling temperature and the adoption of the composite forced cooling of spraying and air cooling below the Ar3 line, the temperature is kept in sections, the rhythm of batch production is faster, the production efficiency is improved, and the production advantages are achieved.

TABLE 1 comparison of the compositions (wt%) of the round steels of the examples and comparative examples

TABLE 2 comparison of the properties of the round steels of the examples and the comparative examples

Claims

1. A preparation method of hot-rolled round steel capable of being directly cut is characterized by comprising the following steps: comprises that

(1) Designing element components: c is calculated according to the mass percentage: 0.35 to 0.50%, Si: 0.15 to 0.60%, Mn: 0.50-1.80%, Cr: 0.00-0.35%, S: 0.003-0.060%, Al: 0.006-0.060%, N: 0.0050-0.020%, and the balance Fe and inevitable impurity elements;

(2) designing a molding process: smelting molten steel according to the element component design, casting the molten steel into a steel blank, heating the steel blank after slow cooling to enable the structure to be completely austenized, removing scale after discharging, removing the scale by adopting high-pressure water, starting first air cooling to wait for the temperature after removing the scale, heating the steel blank to 1050-; then, carrying out secondary air cooling on the intermediate billet to be warmed up, warming the intermediate billet to be at the initial temperature of 800-920 ℃ for continuous rolling, continuously rolling the intermediate billet into round steel by using a continuous rolling mill after the intermediate billet is warmed up for the second time, wherein the final rolling temperature is not less than 780 ℃;

(3) and (3) a cooling process: and (3) when the temperature of the round steel after hot rolling is lower than the starting temperature Ar3 of the transformation from austenite to ferrite, comprehensively cooling the round steel by adopting spray cooling and air cooling, and naturally cooling after cooling to 600 ℃ to obtain the microstructure of fine lamellar pearlite and a small amount of ferrite.

2. The method of producing directly machinable hot-rolled round steel according to claim 1, characterized in that: the molten steel smelting at least comprises primary smelting and LF furnace refining.

3. The method of producing directly machinable hot-rolled round steel according to claim 2, characterized in that: the primary smelting is to smelt the alloy raw material blocks and molten iron in a converter or an electric furnace.

4. The method of producing directly machinable hot-rolled round steel according to claim 2, characterized in that: the steel billet is a continuous casting square billet, the superheat degree of molten steel casting is designed to be 15-30 ℃ during continuous casting, and the continuous casting square billet is placed into a pit for slow cooling after being formed.

5. The method of producing directly machinable hot-rolled round steel according to claim 2, characterized in that: the reheating temperature of the billet is 1150-1220 ℃, and the temperature is kept in the temperature range to ensure that alloy elements are fully dissolved in solid solution and the structure is completely austenitized.

6. The method of producing directly machinable hot-rolled round steel according to claim 1, characterized in that: the descaling comprises two times of high-pressure water descaling, wherein the steel billet is subjected to twice high-pressure water descaling by going and returning once on a roller way, so that oxide scales are fully removed and the temperature is reduced quickly.

7. The method of producing directly machinable hot-rolled round steel according to claim 1, characterized in that: and continuously operating the front steel billet and the rear steel billet in the forming process, and when the temperature of the front steel billet is kept for the second time, carrying out the descaling and the first temperature keeping before cogging on the adjacent rear steel billet.