WO2022227891A1

WO2022227891A1 - Method for preparing non-quenched and tempered steel for large-specification direct cutting

Info

Publication number: WO2022227891A1
Application number: PCT/CN2022/080600
Authority: WO
Inventors: 高华耀; 刘栋林; 江宏亮; 杜龑; 周湛; 朱康宁; 张春香
Original assignee: 江苏永钢集团有限公司
Priority date: 2021-04-27
Filing date: 2022-03-14
Publication date: 2022-11-03
Also published as: GB202213835D0; CN113134510A; CN113134510B; GB2612440B; GB2612440A

Abstract

A method for preparing non-quenched and tempered steel for large-specification direct cutting. The steel components are: 0.40-0.48％ C, 0.20-0.35％ Si, 0.80-1.30％ Mn, P≤0.020％, S≤0.035％, 0.10-0.20％ Cr, 0.05％-0.13％ V, 0.010％-0.020％ Ti, Ni≤0.025％, Mo≤0.015％, Al≤0.030％, Cu≤0.2％, 130-200ppm N, H≤2.0ppm, O≤20ppm, and the remainder is Fe and inevitable impurities. The method omits commonly used Nb while not increasing the silicon content. By means of optimizing the composition and using semi-continuous rolling technology to achieve a controlled rolling and controlled cooling process, non-quenched and tempered steel for large-specification direct cutting which has an ideal structure and comprehensive mechanical properties is finally obtained.

Description

Preparation method of non-quenched and tempered steel for large-scale direct cutting

technical field

The invention belongs to the technical field of non-quenched and tempered steel, and in particular relates to a preparation method of non-quenched and tempered steel for large-scale direct cutting.

Background technique

In the field of construction machinery, its important parts have been made of quenched and tempered steel for a long time, but the quenched and tempered steel has a long production cycle and high energy consumption, and the workpiece is easily deformed or cracked during quenching, resulting in large fluctuations in product quality, high manufacturing costs, and serious environmental pollution. , At present, the field of construction machinery often involves the manufacture of a large number of large-sized parts, but the development and application of large-scale turning non-quenched and tempered steel is not enough to meet the needs of construction machinery. As people pay more and more attention to environmental protection, processing cost, processing cycle and material stability, it is urgent to use medium and large-sized round rods for cutting rods in the machining industry, such as injection molding machine tie rods, mechanical cylinder piston rod parts, etc. Non-quenched and tempered steel is used for direct cutting instead of quenched and tempered steel, but as the specifications of non-quenched and tempered hot-rolled round steel gradually increase, the strength and toughness properties of the edge and core of the round steel section fluctuate greatly, and the grain size of the structure varies. Evenly mixed crystal phenomenon occurs.

At present, the materials used in injection molding machines on the market are mainly quenched and tempered 42CrMo and 4145H alloy structural steel. Due to the quenching and tempering process of parts, the energy consumption is increased and the environment is polluted. At the same time, the steel produces defects such as oxidation, decarburization, deformation, and cracking. It is urgent to develop new non-quenched and tempered steels to gradually replace 42CrMo, 4145H, 40Cr and other quenched and tempered steels.

Through investigation, it is found that only small-sized non-quenched and tempered steel (diameter ≤ 60mm) has been reported at present. Due to the difficulty in producing large-sized round bars, large-sized non-quenched and tempered steels are rarely reported. Therefore, it is urgent to design and obtain excellent performance. Large-size non-quenched and tempered steel for direct cutting.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the technical defects existing in the prior art, and for non-quenched and tempered steel (75-140mm in diameter) for direct cutting of large specifications, the mechanical properties and cutting performance fluctuate greatly, and it is difficult to meet the current production requirements; The invention provides a kind of non-quenched and tempered steel for direct cutting with high strength and toughness in medium and large sizes. The steel components are optimized, and the semi-continuous rolling technology is used to realize controlled rolling and controlled cooling, so that the non-quenched and tempered steel for large-size direct cutting has good mechanical properties and good mechanical properties. Processability.

In order to achieve the above purpose, the present invention first provides a method for preparing a large-size non-quenched and tempered steel for direct cutting, which has high strength, high toughness, and excellent machining performance. The semi-continuous rolling technology is used to realize the controlled rolling and controlled cooling steps, including the following steps: step:

(1) According to the mixed materials of each component, through smelting, casting into billets; the billets are heated in a continuous heating furnace, and the high-temperature section is heated at a temperature of 1180-1240 ° C for 2-3 hours to uniformize the heating of the billets, and the heated billets are obtained;

(2) For the heated billet, turn on high-pressure water to remove phosphorus and remove the iron oxide scale on the surface of the billet. The temperature is 990～1120℃, and the deformation amount of the first 4 single passes is ≥17%;

(3) the intermediate rectangular billet obtained by rolling in the step (2) is subjected to a warm treatment, the temperature after the warm treatment is 850-920° C., and the warm-treatment time is 4 to 6 minutes;

(4) The intermediate rectangular billet after the warm treatment enters the continuous rolling mill and is rolled into a round steel bar for 5 to 9 passes. The final rolling temperature of the round steel bar is 780 to 880°C; the diameter of the round steel bar is 75°C. ~140mm;

(5) the round steel bar after continuous rolling in step (4) is discharged from the rolling mill and cooled by water penetration, and the temperature after cooling is 325-414 ° C;

(6) Slow cooling: The cooled round steel bar enters the traverse grouping system and moves to the sawing roller table for sawing. At this time, the temperature of the round steel surface is reversed to 571 ~ 590 ℃, and after sawing, it is placed on the cooling bed and enters the pit. Slow cooling, pit temperature ≤ 200℃, and then finishing and straightening process to obtain the required steel, and put into storage after testing;

The non-quenched and tempered steel for direct cutting of large size is composed of the following components by weight:

C: 0.40 to 0.48%, Si: 0.20 to 0.35%, Mn: 0.80 to 1.30%, P≤0.020%, S≤0.035%, Cr: 0.10 to 0.20%, V: 0.05% to 0.13%, Ti: 0.010% ~0.020%, Ni≤0.025%, Mo≤0.015%, Al≤0.030%, Cu≤0.2%, N: 130～200ppm, H≤2.0ppm, O≤20ppm; the balance is Fe and inevitable impurities.

Preferably, in step (1), the heating time of the soaking section is 2-3 hours.

Preferably, in step (2), the pressure of the high-pressure water for phosphorus removal is 20-30 MPa.

Preferably, in step (2), the deformation amount of the first 4 single passes is greater than or equal to 20%.

Preferably, in step (5), the specific method of the water penetration cooling is as follows: through 3-5 stages of water penetration cooling, the valve opening of each section is controlled to be 4% to 30%, and the valve opening of the water penetration cooling device is controlled by controlling the valve opening. Adjust the water flow to control the strength of the round steel cooling; adopt the alternating method of strong cooling and weak cooling, that is, the difference between the opening degrees of two adjacent valves is not less than 5%.

Ingredient Design:

For non-quenched and tempered steel products for direct cutting with medium and large diameters, it is difficult to meet the requirements due to large fluctuations in mechanical properties and machining performance. By optimizing the alloy design composition, the round bar has good mechanical properties and processing performance, which can meet the design requirements of the tie rod of the injection molding machine. Silicon mainly exists in the form of solid solution in steel, which mainly plays the role of solid solution strengthening, which can significantly increase the volume fraction of ferrite and strengthen the ferrite structure. Increasing the silicon content can shift the pearlite C curve to the left, increase the activity of carbon elements, promote the diffusion of carbon in austenite, and increase the precipitation of carbides; the silicon content of conventional non-quenched and tempered steels is less than 0.50%, but they are all prepared The small-sized non-quenched and tempered steel also contains Nb to improve performance; however, the present invention optimizes the alloy design composition, and at the same time saves the commonly used Nb under the condition of not increasing the silicon content, the design obtains a Non-quenched and tempered steel for direct cutting of medium and large diameters with excellent strength, toughness, hardness and workability.

The advantages and technical effects of the present invention are:

The invention optimizes the alloy design components, and at the same time saves the commonly used Nb under the condition of not increasing the silicon content, reduces other alloy elements, and reduces the cost of raw materials; the semi-continuous rolling technology is used to produce medium and large-sized non-quenched and tempered steel, and the The large deformation of the billet and the temperature-waiting method are used to control the rolling. The cooling system is controlled by the multi-section water-penetrating pipe composite cooling system. The strong cooling-weak cooling alternate method is adopted. organization and comprehensive mechanical properties.

The invention controls the cooling rate of the ferrite-pearlite non-modulated steel after rolling, and the cooling rate in the range of 800-500°C can refine the ferrite grains, increase the proportion of pearlite and reduce the spacing between sheets; The 4 large deformations make the as-cast structure of the billet fully crush the austenite grains and refine the austenite grains. Continuous rolling adopts low temperature rolling and controlled cooling to prevent the austenite grains from crystallization and help the subsequent transformation to obtain finer grains. The ferrite and pearlite structure of the present invention realizes the high strength and toughness of medium and large-scale cutting non-quenched and tempered steel through two major process technologies of low-temperature rolling and controlled cooling, and simultaneously exerts the effects of microalloy precipitation and dispersion strengthening.

Description of drawings

1 is a metallographic picture of the steel prepared in Example 1.

2 is a picture of the grain size of the steel prepared in Example 1.

Detailed ways

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

Example 1:

The diameter of the round steel involved in this embodiment is 135mm, and its chemical composition is calculated as:

C: 0.45%, Si: 0.29%, Mn: 1.21%, P: 0.013%, S: 0.005%, Cr: 0.14%, V: 0.07%, Ti: 0.016%, Ni: 0.013%, Mo: 0.005%, Al: 0.011%, Cu: 0.21%, N: 159 ppm, H: 0.9 ppm, O: 15 ppm; the balance is Fe and inevitable impurities.

(1) According to the mixed material of each component, after smelting, it is cast into a billet; the billet is heated in a continuous heating furnace, and the high temperature section is heated at a temperature of 1180 ° C for 3 hours to uniformize the heating of the billet. In this temperature range, the alloy elements are fully solid-dissolved and the structure is complete. Austrian materialization to obtain heated billets;

(2) After the billet is descaled by high-pressure water on the roller table, the scale of the billet is removed to prevent defects such as pits and pits on the surface of the finished round steel. The dephosphorization pressure is 25MPa; the dephosphorized billet directly enters the reciprocating rolling mill (open Billet machine), after 11 rollings, the intermediate billet shape is 200*220mm, and the deformation amount of the first 4 single passes is ≥17%; the billet rolling temperature is controlled to 1005 ℃;

(3) After the intermediate billet is released from the billeting machine, the roller table is warmed and air-cooled in front of the continuous rolling mill, and the temperature is kept on the roller table to 870 ° C for 5.5 minutes, and then the intermediate billet is cut to the head and tail;

(4) The surface temperature of the intermediate rectangular billet after the warm treatment drops to 835°C and then enters the continuous rolling unit, and is rolled into a 140mm round steel after 5 passes, and the final rolling temperature is about 780°C;

(5) The round steel bar after continuous rolling in step (5) immediately enters the water-cooling system (pipe-piercing) for water-piercing cooling after the continuous rolling in step (5). The valve opening of the second stage is 10%, the valve opening of the third stage is controlled by 20%, and the valve opening of the fourth stage is controlled to 5. After the water penetration of the round steel is completed, the surface temperature is cooled to about 325°C, from the first water penetration pipe to the The time for passing the fourth section of the water pipe is 1 minute;

(6) The round steel enters the traversing marshalling system and moves to the sawing roller table for sawing. At this time, the surface of the round steel reaches an anti-red temperature of 571 °C. Straightening process, inspection and storage.

Example 2:

The diameter of the round steel involved in this embodiment is 100mm, and its chemical composition is calculated as:

C: 0.41%, Si: 0.30%, Mn: 1.20%, P: 0.010%, S: 0.002%, Cr: 0.16%, V: 0.07%, Ti: 0.014%, Ni: 0.019%, Mo: 0.006%, Al: 0.012%, Cu: 0.21%, N: 143 ppm, H: 1.1 ppm, O: 10 ppm; the balance is Fe and inevitable impurities.

(1) According to the mixed materials of each component, after smelting, casting into billets; the billets are heated in a continuous heating furnace, and the high temperature section is heated at a temperature of 1160 ° C for 1 hour to uniformize the heating of the billets. In this temperature range, the alloying elements are fully solid-dissolved and the structure is complete. Austrian materialization to obtain heated billets;

(2) The billet is descaled by high-pressure water on the roller table to remove the scale of the billet, and the dephosphorization pressure is 25MPa; the dephosphorized billet directly enters the reciprocating mill, and is rolled into an intermediate billet of 150*180mm after 11 passes. The first 4 The deformation amount of a single pass is ≥20%; the billet rolling temperature is controlled to 995 ℃;

(3) After the intermediate billet is out of the billeting machine, the roller table is warmed and air-cooled in front of the continuous rolling mill, and the temperature is kept on the roller table to 865 ° C for 5 minutes, and then the intermediate billet is cut to the head and tail;

(4) The surface temperature of the intermediate rectangular billet after the warm treatment drops to 840°C and then enters the continuous rolling unit, and is rolled into a 100mm round steel after 7 passes, and the final rolling temperature is about 775°C;

(5) The round steel bar after continuous rolling in step (5) immediately enters the water-cooling system (pipe-piercing) for water-piercing cooling after the continuous rolling in step (5). The valve opening of the second stage is 10%, the valve opening of the third stage is controlled by 20%, and the valve opening of the fourth stage is controlled by 10%. The time until the fourth section of the water pipe is pierced is 0.7 minutes;

(6) The round steel enters the traversing marshalling system and moves to the sawing roller table for sawing. At this time, the surface of the round steel reaches an anti-red temperature of 585 °C. Straightening process, inspection and storage.

Example 3:

The diameter of the round steel involved in this embodiment is 75mm, and its chemical composition is calculated as:

C: 0.42%, Si: 0.29%, Mn: 1.20%, P: 0.011%, S: 0.004%, Cr: 0.15%, V: 0.07%, Ti: 0.015%, Ni: 0.017%, Mo: 0.004%, Al: 0.012%, Cu: 0.20%, N: 149 ppm, H: 1.2 ppm, O: 14 ppm; the balance is Fe and inevitable impurities.

(1) According to the mixed materials of each component, through smelting, casting into billets; the billets are heated in a continuous heating furnace, and the high temperature section is heated at a temperature of 1240 ° C for 3 hours to uniformize the heating of the billets. In this temperature range, the alloying elements are fully solid-dissolved and the structure is complete. Austrian materialization to obtain heated billets;

(2) The billet is descaled by high-pressure water on the roller table to remove the scale of the billet, and the dephosphorization pressure is 20MPa; the dephosphorized billet directly enters the reciprocating mill, and is rolled into an intermediate billet shape of 150*180mm after 11 passes. The first 4 The deformation amount of a single pass is ≥20%; the billet rolling temperature is controlled to 990℃;

(3) After the intermediate billet is released from the billeting machine, the roller table is warmed and air-cooled in front of the continuous rolling mill, and the temperature is kept on the roller table to 870 ° C for 5 minutes, and then the intermediate billet is cut to the head and tail;

(4) The surface temperature of the intermediate rectangular billet after the warm treatment drops to 850°C and then enters the continuous rolling unit, and is rolled into a 75mm round steel after 9 passes, and the final rolling temperature is about 775°C;

(5) The round steel bar after continuous rolling in step (5) immediately enters the water-cooling system (pipe-piercing) for cooling, and uses three-stage water-piercing pipes for water-piercing, controlling the opening of the first stage valve by 20%, and controlling The valve opening of the second stage is 10%, and the valve opening of the third stage is controlled to 4%. After the water penetration of the round steel is completed, the surface temperature is cooled to about 414°C, and the time from entering the first water penetration pipe to the third water penetration pipe is 0.5 minute;

(6) The round steel enters the traversing marshalling system and moves to the sawing roller table for sawing. At this time, the surface of the round steel reaches an anti-red temperature of 590 °C. Straightening process, inspection and storage.

The present examples 1 to 3 mainly replace the production method of ordinary quenched and tempered 40Cr and 45 steel for straight cutting non-quenched and tempered steel. The bar is cooled by water through 3 to 5 stages; Cooling, after continuous rolling, the temperature of the bar is relatively high. The strong cooling method is used to quickly cool the bar. Due to the transfer of heat from high to low, the heat from the core of the round steel is gradually transferred to the surface. Transfer more to the surface while avoiding thermal stress caused by the large temperature gradient of the round steel. After strong cooling, weak cooling is adopted, so that more time is reserved for heat transfer to the core during the cooling process. After weak cooling, the surface temperature increases and is used again. The surface temperature of the round steel is taken away by strong cooling; such strong cooling-weak cooling-strong cooling is repeated alternately, and finally the core temperature and the surface temperature tend to be consistent, thereby ensuring the uniformity of the structure and mechanical properties of the round steel.

The present invention designs a forming process, using molten iron and scrap steel as raw materials (82%-85% of molten iron is used, and the balance is scrap steel); in the specific operation process, it can be divided into continuous multiple processes. After the first billet enters the continuous rolling step, The second billet can enter the billet rolling step, and then after the second billet enters the continuous rolling step, the third billet can enter the billet rolling step, and so on; this continuous production process method meets the requirements of continuous casting billets - The process requirements for the warm rolling in the middle of the intermediate billet can offset the time waste caused by the warm rolling, ensure that the production capacity of the warm rolling is similar to that of the normal rolling, and improve the production efficiency of the warm rolling.

For the non-quenched and tempered steel prepared in Example 1 above, the metallographic photo of the core magnified by 500 times is ferrite and pearlite (as shown in Figure 1), and the actual grain size according to GB/T 6394 standard (100 times as shown in Figure 2) The rating is 9 to 10, the grain size is uniform and fine, the grade difference from the core to the edge is not more than 1.5, the mechanical properties from the core to the edge are uniform and the fluctuation range is small, which meets the general machining requirements, and the hardness from the core to the edge is poor. ≤30HBW, which can effectively avoid adverse effects on tool processing when the hardness changes greatly.

The mechanical property data of the above-mentioned Examples 1-3 are shown in Table 1 below.

Table 1 Mechanical property data of Examples 1 to 3

From the values of yield strength, tensile strength, elongation, elongation, impact value and surface hardness in Table 1, it can be seen that the yield strength is not less than 740MPa and the tensile strength is not less than 930MPa, achieving both strength and plastic toughness; The invention obtains a non-quenched and tempered steel for direct cutting of medium and large diameters with excellent strength, toughness, hardness and workability.

The invention optimizes the alloy design components, and at the same time saves the commonly used Nb without increasing the silicon content; combined with the optimization of micro-alloying elements such as V and Ti, the cost of raw materials is reduced, and the micro-alloy is added at the same time to form composite carbide precipitation. , The carbide precipitation size is small and the precipitation temperature is wide. It has a pin rolling effect on the austenite grains, which can effectively prevent the austenite grains from growing during the heating process, and can delay the recrystallization process during rolling. Improve and increase the toughness of the material , so that the strength and toughness of the steel have been greatly improved.

Combined with semi-continuous rolling, controlled rolling and controlled cooling technology, and 4 large deformations in front of the billet machine, the as-cast structure of the billet is fully crushed and austenite grains are refined; continuous rolling adopts low-temperature rolling to prevent austenite. The crystal grains are crystallizing, which is helpful for the subsequent phase transformation to obtain finer ferrite and pearlite structures. Further combining the metallographic pictures and grain size pictures of the present invention, it can be seen that the present invention realizes large-diameter direct cutting non-ferrous metals. High strength and toughness of quenched and tempered steel.

Explanation: The above embodiments are only used to illustrate the present invention rather than limit the technical solutions described in the present invention; therefore, although this specification has described the present invention in detail with reference to the above-mentioned embodiments, those of ordinary skill in the art should It should be understood that the present invention can still be modified or equivalently replaced; and all technical solutions and improvements that do not depart from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

A preparation method of non-quenched and tempered steel for large-scale direct cutting, characterized in that it comprises the following steps:

(1) According to the mixed materials of each component, through smelting, casting into billets; the billets are heated in a continuous heating furnace, and the high-temperature section is heated at a temperature of 1180-1240 ° C for 2-3 hours to uniformize the heating of the billets, and the heated billets are obtained;

(2) For the heated billet, turn on high-pressure water to remove phosphorus and remove the iron oxide scale on the surface of the billet. The temperature is 990～1120℃, and the deformation amount of the first 4 single passes is ≥17%;

(3) the intermediate rectangular billet obtained by rolling in the step (2) is subjected to a warm treatment, the temperature after the warm treatment is 850-920° C., and the warm-treatment time is 4 to 6 minutes;

(4) The intermediate rectangular billet after the warm treatment enters the continuous rolling mill and is rolled into a round steel bar for 5 to 9 passes. The final rolling temperature of the round steel bar is 780 to 880°C; the diameter of the round steel bar is 100°C. ~140mm;

(5) The round steel bar after continuous rolling in step (4) is discharged from the rolling mill and cooled by water penetration, and the temperature after cooling is 325-414 ° C; the specific method of water penetration cooling is: water penetration through 3-5 sections Cooling, control the valve opening of each section to be 4% to 30%, and adjust the water flow by controlling the valve opening of the water cooling device to control the strength of the round steel cooling; the alternating method of strong cooling and weak cooling is adopted, that is, adjacent The difference between the opening degrees of the two valves is not less than 5%;

(6) Slow cooling: The cooled round steel bar enters the traversing marshalling system and moves to the sawing roller table for sawing. At this time, the surface of the round steel returns to a red temperature of 571-590 °C, and after sawing, it is placed on a cooling bed and enters the pit. Slow cooling, pit temperature ≤ 200℃, and then finishing and straightening process to obtain the required steel, and put into storage after testing;

The non-quenched and tempered steel for direct cutting of large size is composed of the following components by weight:

C: 0.40 to 0.48%, Si: 0.20 to 0.35%, Mn: 0.80 to 1.30%, P≤0.020%, S≤0.035%, Cr: 0.10 to 0.20%, V: 0.05% to 0.13%, Ti: 0.010% ~0.020%, Ni≤0.025%, Mo≤0.015%, Al≤0.030%, Cu≤0.2%, N: 130～200ppm, H≤2.0ppm, O≤20ppm; the balance is Fe and inevitable impurities.
The method for preparing non-quenched and tempered steel for large-scale direct cutting according to claim 1, wherein in step (1), the heating time of the soaking section is 2-3 hours.
The method for preparing large-size non-quenched and tempered steel for direct cutting according to claim 1, wherein in step (2), the pressure of the high-pressure water for phosphorus removal is 20-30 MPa.
The method for preparing non-quenched and tempered steel for large-size direct cutting according to claim 1, characterized in that, in step (3), the first four single-pass deformations are ≥ 20%.