KR102678568B1 - Low carbon spherodial alloy steel and method of manufacturing the same - Google Patents

Abstract

The present invention provides a low-carbon nodular alloy steel that satisfies the required properties of nodular heat treatment in low-carbon alloy steel and has excellent nodular heat treatment efficiency and production time reduction effect that can reduce heat treatment time, and a manufacturing method thereof. According to one embodiment of the present invention, the method for manufacturing the low-carbon nodular alloy steel is, in weight percent, carbon (C): 0.17% to 0.23%, silicon (Si): 0.15% to 0.35%, manganese (Mn): 0.55%. % ~ 0.90%, Chromium (Cr): 0.85% ~ 1.25%, Nickel (Ni): > 0% ~ 0.25%, Copper (Cu): > 0% ~ 0.3%, Phosphorus (P): > 0% ~ 0.02 %, sulfur (S): 0.005% to 0.035%, and the balance is hot rolling a semi-finished product containing iron (Fe) and other inevitable impurities to produce a hot rolled material; Spheroidizing heat treatment of the hot rolled material at a temperature ranging from above A1 to A1+20°C; and cooling the spheroidized heat-treated hot-rolled material.

Description

Low carbon spherodial alloy steel and method of manufacturing the same}

The technical idea of the present invention relates to steel and its manufacturing method, and more specifically, to low-carbon nodular alloy steel and its manufacturing method.

Recently, cold forging applications have been gradually increasing in automotive transmission parts to reduce costs and improve forging dimensional accuracy. However, nodular heat treatment must be performed before forging to improve the formability of cold forged parts and secure the tool life of the forging mold. Nodularization heat treatment is a heat treatment method that softens the cementite contained in the pearlite structure by changing it into a spherical shape. Cold forging companies require a material that satisfies a nodular structure with more than 80% carbide and a hardness of 85 HRB or less. Meanwhile, low carbon alloy steel has low carbon activity, so nodular heat treatment takes a relatively long time, and if heat treatment is not sufficient, mold damage or part spalling may occur when manufacturing parts such as forging. Generally, batch type furnace is used for spheroidizing heat treatment, but there is a problem of very low work efficiency, such as heat treatment time for low carbon steel requiring at least 24 hours or more. In addition, in order to improve the carburizing and hardening properties of low-carbon alloy steel used as a material for transmission parts, chromium (Cr) and manganese (Mn) elements, which are cementite forming elements, are added. Since the diffusion rate of substituted chromium (Cr) and manganese (Mn) is low, the heat treatment time for nodularization of cementite is further increased.

Korean Patent Publication No. 2011-0052967

The technical problem to be achieved by the technical idea of the present invention is to provide a low-carbon nodular alloy steel that satisfies the required physical properties of nodular heat treatment in low-carbon alloy steel and has excellent nodular heat treatment efficiency and production time reduction effect that can reduce heat treatment time, and a manufacturing method thereof. .

However, these tasks are illustrative, and the technical idea of the present invention is not limited thereto.

According to one aspect of the present invention, a low-carbon nodular alloy steel and a method for manufacturing the same are provided.

According to one embodiment of the present invention, the method for manufacturing the low-carbon nodular alloy steel is, in weight percent, carbon (C): 0.17% to 0.23%, silicon (Si): 0.15% to 0.35%, manganese (Mn): 0.55%. % ~ 0.90%, Chromium (Cr): 0.85% ~ 1.25%, Nickel (Ni): > 0% ~ 0.25%, Copper (Cu): > 0% ~ 0.3%, Phosphorus (P): > 0% ~ 0.02 %, sulfur (S): 0.005% to 0.035%, and the balance is hot rolling a semi-finished product containing iron (Fe) and other inevitable impurities to produce a hot rolled material; Spheroidizing heat treatment of the hot rolled material at a temperature ranging from above A1 to A1+20°C; And it may include; cooling the spheroidized heat-treated hot-rolled material.

According to one embodiment of the present invention, the step of cooling the spheroidized heat-treated hot rolled material involves first cooling the hot rolled material from 550° C. to 650° C. at a cooling rate of 55° C./hour to 65° C./hour. step; and secondary cooling of the primary cooled hot rolled material by air cooling to room temperature.

According to one embodiment of the present invention, the hot rolling may be performed at a finish rolling temperature in the range of 850°C to 950°C.

According to one embodiment of the present invention, after completing the hot rolling, the hot rolled material may be cooled at a cooling rate of 0.35°C/sec to 0.45°C/sec.

According to one embodiment of the present invention, the nodularization heat treatment may be performed for 8 to 11 hours.

According to one embodiment of the present invention, the total content of the manganese and the chromium may be 1.0% by weight to 1.6% by weight.

According to one embodiment of the present invention, the low-carbon spheroidized alloy steel manufactured by the method for manufacturing the low-carbon spheroidized alloy steel may have a spheroidization rate of 80% or more and a hardness of 85 HRB or less.

According to one embodiment of the present invention, the low-carbon spheroidized alloy steel may include ferrite and spheroidized carbide.

According to one embodiment of the present invention, the spheroidizing heat treatment may be performed in a continuous heat treatment furnace or a batch heat treatment furnace.

According to the technical idea of the present invention, when applying the manufacturing method of low-carbon nodular alloy steel, the nodular heat treatment efficiency and production time reduction effect are excellent, nodular heat treatment is possible in both continuous heat treatment furnace and batch heat treatment furnace, and hardness It has excellent reduction and spheroidal tissue formation effects. The method for manufacturing low-carbon spheroidized alloy steel according to the technical idea of the present invention can reduce the spheroidizing heat treatment time in low-carbon alloy steel for transmission parts by more than 54% compared to the conventional method, and can be implemented in a continuous heat treatment furnace, and therefore can be used in a conventional batch heat treatment method. Compared to using a furnace, it can significantly contribute to improving productivity and reducing carbon dioxide emissions.

The effects of the present invention described above have been described as examples, and the scope of the present invention is not limited by these effects.

Figure 1 is a flow chart showing a method of manufacturing low-carbon nodular alloy steel according to an embodiment of the present invention.
Figure 2 is a graph showing the spheroidizing heat treatment and cooling schedule in the manufacturing method of low-carbon spheroidized alloy steel according to an embodiment of the present invention compared with the comparative example.
Figure 3 is a micrograph showing the microstructure of low-carbon spheroidized alloy steel manufactured by the method of manufacturing low-carbon spheroidized alloy steel according to an embodiment of the present invention compared with the comparative example.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. The embodiments of the present invention are provided to more completely explain the technical idea of the present invention to those skilled in the art, and the following examples may be modified into various other forms, and the embodiments of the present invention may be modified. The scope of the technical idea is not limited to the following examples. Rather, these embodiments are provided to make the present disclosure more faithful and complete and to fully convey the technical idea of the present invention to those skilled in the art. In this specification, like symbols refer to like elements throughout. Furthermore, various elements and areas in the drawings are schematically drawn. Accordingly, the technical idea of the present invention is not limited by the relative sizes or spacing drawn in the attached drawings.

The technical idea of the present invention satisfies the physical properties required for nodular heat treatment in low-carbon alloy steel for transmission parts containing manganese and chromium, and in order to maximize productivity, the time required for heat treatment in a continuous heat treatment furnace, rather than a conventional batch heat treatment furnace, is approximately 20% compared to the existing heat treatment furnace. We propose heat treatment conditions that reduce heat treatment by 54%, which can provide effects such as improving part productivity, reducing heat treatment costs, and reducing carbon dioxide emissions.

Conventional spheroidizing heat treatment of low-carbon alloy steel is a method of maintaining a temperature just below A1 for a certain period of time and then cooling. This has a limitation in that the heat treatment time for spheroidizing takes more than 24 hours because the diffusion rate of atoms is low due to the low heat treatment temperature. .

On the other hand, when using a conventional batch heat treatment furnace, the heat treatment was performed by maintaining the temperature just above A1 for a certain period of time and then maintaining and air cooling to below A1. However, in this case, 80% or more of carbide, which is the required standard for spheroidized heat treatment materials, was used. In order to satisfy spheroidal structure and hardness below 85 HRB, there is a limitation that the development of optimized conditions for the steel type must be preceded.

It is common to add manganese and chromium to low-carbon alloy steel used as a material for transmission parts to improve carburizing and hardening properties. The manganese and chromium are cementite forming elements, and therefore, the time required for nodularization heat treatment increases due to the influence of the manganese and chromium elements.

The technical idea of the present invention is to maintain nodular heat treatment at a temperature of A1 or higher to A1 + 20°C or lower in a low-carbon alloy steel having a total amount of manganese and chromium of 1.0% by weight to 1.6% by weight, followed by cooling at a cooling rate of about 61°C/sec. By performing the process under the following conditions, it is possible to achieve a reduction in heat treatment time and cost. Specifically, austenite + remaining cementite can be formed at a temperature of A1 or more to A1 + 20°C or less, and the remaining cementite can be sphericalized to promote grain growth. When the spheroidization heat treatment temperature exceeds A1 + 20°C, all of the cementite is dissolved in solid solution, and upon cooling, the austenite phase in which cementite is dissolved is transformed into pearlite, causing carbide agglomeration to occur, thereby achieving a spheroidization rate of 80% or more. You won't be able to do it.

Manufacturing method of low-carbon nodular alloy steel

Figure 1 is a flow chart showing a method of manufacturing low-carbon nodular alloy steel according to an embodiment of the present invention.

Referring to Figure 1, the method of manufacturing the low-carbon nodular alloy steel includes a hot-rolled material manufacturing step (S10); Nodularization heat treatment step (S20); and a cooling step (S30).

Specifically, the manufacturing method of the low-carbon nodular alloy steel is, in weight percent, carbon (C): 0.17% to 0.23%, silicon (Si): 0.15% to 0.35%, manganese (Mn): 0.55% to 0.90%, chromium ( Cr): 0.85% ~ 1.25%, Nickel (Ni): > 0% ~ 0.25%, Copper (Cu): > 0% ~ 0.3%, Phosphorus (P): > 0% ~ 0.02%, Sulfur (S): Manufacturing a hot-rolled material by hot-rolling a semi-finished product containing 0.005% to 0.035%, and the remainder containing iron (Fe) and other inevitable impurities (S10); Spheroidizing heat treatment of the hot rolled material at a temperature ranging from more than A1 to A1+20°C (S20); And a step (S30) of cooling the spheroidized heat-treated hot-rolled material.

Hereinafter, the manufacturing method of the low-carbon nodular alloy steel will be described in detail step by step.

Hot rolled material manufacturing step (S10)

The hot-rolled material manufacturing step (S10) is weight percent, carbon (C): 0.17% ~ 0.23%, silicon (Si): 0.15% ~ 0.35%, manganese (Mn): 0.55% ~ 0.90%, chromium (Cr) ): 0.85% to 1.25%, Nickel (Ni): greater than 0% to 0.25%, Copper (Cu): greater than 0% to 0.3%, Phosphorus (P): greater than 0% to 0.02%, Sulfur (S): 0.005 % to 0.035%, and the balance is a step of manufacturing hot rolled materials by hot rolling semi-finished products containing iron (Fe) and other inevitable impurities.

In the method of manufacturing low-carbon nodular alloy steel according to the present invention, the target semi-finished product may be, for example, a bloom or a slab. Blooms or slabs in a semi-finished product state can be obtained through a continuous casting process after obtaining molten steel of a predetermined composition through a steelmaking process.

Hereinafter, the alloy components included in the semi-finished product will be described in more detail.

Carbon (C): 0.17% to 0.23%

Carbon can secure strength by improving the strength of steel and forming precipitates, so as the carbon content increases, the yield strength and tensile strength can increase. If the carbon content is less than 0.17%, it may be difficult to secure strength. If the carbon content exceeds 0.23% by weight, toughness may decrease. Therefore, it is preferable that carbon is added at 0.17% to 0.23% of the total weight of the semi-finished product.

Silicon (Si): 0.15% to 0.35%

Silicone is used as a deoxidizing agent in steelmaking, and has a deoxidizing effect and improves strength and hardenability. If the silicon content is less than 0.15%, the effect of addition is minimal. If the silicon content exceeds 0.35%, processability such as cold forging may be reduced, or it may be difficult to secure the target strength. Therefore, it is preferable that silicone is added at 0.15% to 0.35% of the total weight of the semi-finished product.

Manganese (Mn): 0.55% to 0.90%

Manganese is an element that improves hardenability and strength. If the manganese content is less than 0.55%, the effect of addition is minimal. If the manganese content exceeds 0.90%, the amount of MnS-based inclusions produced increases, and brittleness may increase or toughness may decrease during forging. Therefore, manganese is preferably added at 0.55% to 0.90% of the total weight of the semi-finished product.

Chromium (Cr): 0.85% to 1.25%

Chromium is an element that improves fatigue strength, has a cementite stabilizing effect, increases hardenability, and improves strength. If the chromium content is less than 0.85%, the effect of addition is minimal. If the chromium content exceeds 1.25%, toughness may decrease or machinability may decrease. Therefore, it is desirable to add chromium in an amount of 0.85% to 1.25% of the total weight of the semi-finished product.

Nickel (Ni): >0% to 0.25%

Nickel is an element that refines the structure of steel and increases hardenability. If the nickel content exceeds 0.25%, toughness is improved, but machinability is reduced, the effect of increasing hardenability due to an increase in the addition amount is minimal, and production costs may only increase. Therefore, it is preferable that nickel is added in an amount exceeding 0% to 0.25% of the total weight of the semi-finished product.

Copper (Cu): >0% to 0.3%

Copper is an effective element in increasing the strength and improving toughness of steel materials, but if the addition amount is high, it may be concentrated at grain boundaries and cause surface cracks, so the upper limit is limited. If the copper content exceeds 0.3%, surface cracking may occur during forging. Therefore, it is preferable that copper is added in an amount exceeding 0% to 0.3% of the total weight of the semi-finished product.

Phosphorus (P): >0% ~ 0.02%

When adding a large amount of phosphorus, there is a risk of secondary processing embrittlement and surface defects due to segregation, so the upper limit is limited. If the phosphorus content exceeds 0.02%, secondary processing embrittlement may occur or surface defects may occur due to phosphorus segregation. Therefore, it is desirable to add phosphorus in an amount exceeding 0% to 0.02% of the total weight of the semi-finished product.

Sulfur (S): 0.005% ~ 0.035%

Sulfur is added to improve machinability, but its range is limited because there is a risk of red embrittlement. If the sulfur content is less than 0.005%, the effect is minimal. If the sulfur content exceeds 0.035%, red heat embrittlement may occur. Therefore, it is desirable to add sulfur in an amount of 0.005% to 0.035% of the total weight of the semi-finished product.

The total content of the manganese and the chromium may be 1.0% by weight to 1.6% by weight.

The remaining ingredient of the semi-finished product is iron (Fe). However, in the normal manufacturing process, unintended impurities may inevitably be introduced from raw materials or the surrounding environment, so this cannot be ruled out. Since these impurities are known to anyone skilled in the normal manufacturing process, all of them are not specifically mentioned in this specification.

By hot rolling the semi-finished product, a hot rolled material can be manufactured. To perform the hot rolling, the semi-finished product may be reheated at a reheating temperature of 1,180°C to 1,220°C. The hot rolling may be performed continuously through width rolling, rough rolling, and finishing rolling. The hot rolling may be performed at a finish rolling temperature ranging from 850°C to 950°C. After the hot rolling is completed, the hot rolled material may be cooled from 600°C to room temperature (25°C) at a cooling rate of 0.35°C/sec to 0.45°C/sec.

Nodularization heat treatment step (S20)

The spheroidizing heat treatment step (S20) is a step of spheroidizing heat treatment of the hot rolled material. The spheroidizing heat treatment is performed by heating the hot-rolled material to a temperature above A1 and then cracking and maintaining it at a temperature ranging from above A1 to A1+20°C. In the above spheroidizing heat treatment, when cracking is maintained at a temperature below A1, the effect of promoting spheroidization is reduced, the heat treatment time is delayed, and when cracking is maintained at a temperature exceeding A1+20°C, heat treatment costs may increase. . The A1 temperature may vary depending on the type of the hot rolled material, and may be, for example, 700°C to 730°C. The temperature of the spheroidizing heat treatment may be in the range of 700°C to 750°C.

The nodularization heat treatment may be performed for 8 to 11 hours. If the spheroidization heat treatment time is less than 8 hours, the spheroidization ratio may decrease and fall short of the target value of 80%, and if it exceeds 11 hours, the heat treatment cost may increase without further spheroidization effect.

Conventional spheroidization heat treatment is performed by a method of holding the temperature just below A1 for a long time and then cooling it, or by heating it at a temperature just above A1 and then cooling it to a temperature below A1. However, it takes a considerable amount of time to decompose and spheroidize cementite, so heat treatment usually takes more than 24 hours, and as the spheroidization heat treatment is performed in a batch type heating furnace, there are problems with increased production speed and cost.

The spheroidizing heat treatment may be performed in a continuous heat treatment furnace or a batch heat treatment furnace. In particular, the present invention has excellent spheroidizing heat treatment efficiency, making it possible to shorten the heat treatment time and prevent an increase in heat treatment costs even when the spheroidizing heat treatment is performed in a continuous heat treatment furnace.

Cooling step (S30)

The cooling step (S30) is a step of cooling the spheroidized heat-treated hot rolled material. The cooling step (S30) includes first cooling the hot rolled material to 550°C to 650°C at a cooling rate of 55°C/hour to 65°C/hour; And it may include the step of secondary cooling the primary cooled hot rolled material by air cooling to room temperature.

The primary cooling step may be performed with ronin.

In the secondary cooling step, the primary cooled hot rolled material may be cooled to a temperature of 0°C to 40°C at a cooling rate of 100°C/hour to 200°C/hour.

Through the cooling, the target hardness of the low-carbon nodular alloy steel can be secured.

Subsequently, the low-carbon nodular alloy steel can form a cold forging material by undergoing correction, cutting, and cold forging.

When applying the manufacturing method of low-carbon nodular alloy steel according to the present invention, nodular heat treatment efficiency and production time reduction effect are excellent, nodular heat treatment is possible in a continuous heat treatment furnace, and hardness reduction and nodular structure formation efficiency are excellent, and batch type Productivity improvement and cost reduction effects can be superior to performing heat treatment in a heat treatment furnace.

Low-carbon nodular alloy steel manufactured by the manufacturing method of low-carbon nodular alloy steel

The low-carbon nodular alloy steel manufactured by the method for producing the low-carbon nodular alloy steel has, in weight percent, carbon (C): 0.17% to 0.23%, silicon (Si): 0.15% to 0.35%, and manganese (Mn): 0.55% to 0.55%. 0.90%, Chromium (Cr): 0.85% ~ 1.25%, Nickel (Ni): > 0% ~ 0.25%, Copper (Cu): > 0% ~ 0.3%, Phosphorus (P): > 0% ~ 0.02%, Sulfur (S): 0.005% to 0.035%, and the balance may include iron (Fe) and other inevitable impurities.

The components included in the low-carbon spheroidized alloy steel are the same as described above, so detailed description thereof will be omitted.

The low-carbon nodular alloy steel may have a nodularity rate of 80% or more, for example, a nodularity rate of 80% to 99%, and a hardness of 85 HRB or less, for example, 78 to 85 HRB. The spheroidization rate refers to the fraction (volume %) of the spheroidized carbide with respect to the total carbide formed in the low-carbon spheroidized alloy steel.

Experiment example

Below, preferred experimental examples are presented to aid understanding of the present invention. However, the following experimental examples are only intended to aid understanding of the present invention, and the present invention is not limited by the following experimental examples. Any information not described here can be technically inferred by anyone skilled in the art, so description thereof will be omitted.

By weight, carbon (C): 0.17% to 0.23%, silicon (Si): 0.15% to 0.35%, manganese (Mn): 0.55% to 0.90%, chromium (Cr): 0.85% to 1.25%, nickel ( Ni): more than 0% to 0.25%, copper (Cu): more than 0% to 0.3%, phosphorus (P): more than 0% to 0.02%, sulfur (S): 0.005% to 0.035%, and the balance is iron ( The semi-finished product containing Fe) and other inevitable impurities was hot rolled at the finish rolling temperature to produce a hot rolled material. Next, the hot rolled material was subjected to spheroidizing heat treatment, and then the spheroidizing heat treated hot rolling material was cooled to produce low carbon spheroidizing alloy steel.

The hot rolled material had a hardness of 89 HRB and had a microstructure of a mixture of ferrite and pearlite. The A1 temperature was 724°C.

Figure 2 is a graph showing the spheroidizing heat treatment and cooling schedule in the manufacturing method of low-carbon spheroidized alloy steel according to an embodiment of the present invention compared with the comparative example.

Referring to FIG. 2, in the case of Comparative Example 1, the hot-rolled material was cracked and held at 760°C for 5 hours to perform spheroidizing heat treatment, cooled at a cooling rate of 69°C/hour for 2.5 hours, and then air cooled. Therefore, the holding time in the heat treatment furnace was 7.5 hours, which is the sum of 5 hours and 2.5 hours.

In the case of Comparative Example 2, the hot-rolled material was cracked and held at 750°C for 11 hours to perform spheroidizing heat treatment, cooled for 2.5 hours at a cooling rate of 65°C/hour, and then air-cooled. Therefore, the holding time in the heat treatment furnace was 13.5 hours, which is the sum of 11 hours and 2.5 hours. Comparative Example 2 is the case where the holding time in the heat treatment furnace is the longest.

In the case of Comparative Example 3, the hot-rolled material was cracked and held at 750°C for 8.5 hours to perform spheroidizing heat treatment, cooled at a cooling rate of 65°C/hour for 2.5 hours, and then air-cooled. Therefore, the holding time in the heat treatment furnace was 11 hours, which is the sum of 8.5 hours and 2.5 hours.

In Example 1, the hot-rolled material was cracked and held at 740°C for 8.5 hours to perform spheroidizing heat treatment, cooled at a cooling rate of 61°C/hour for 2.5 hours, and then air-cooled. Therefore, the holding time in the heat treatment furnace was 11 hours, which is the sum of 8.5 hours and 2.5 hours.

In Example 2, the hot-rolled material was cracked and held at 740°C for 11 hours to perform spheroidizing heat treatment, cooled at a cooling rate of 61°C/hour for 2.5 hours, and then air-cooled. Therefore, the holding time in the heat treatment furnace was 13.5 hours, which is the sum of 11 hours and 2.5 hours.

Comparative Example 1, Comparative Example 2, Comparative Example 3, Example 1, and Example 2 were performed in batch heat treatment.

Example 3 had the same process conditions as Example 1 and was performed in a continuous heat treatment furnace. In the case of Example 3, the hot-rolled material was cracked and held at 740°C for 8.5 hours to perform spheroidizing heat treatment, cooled at a cooling rate of 61°C/hour for 2.5 hours, and then air-cooled. Therefore, the holding time in the heat treatment furnace was 11 hours, which is the sum of 8.5 hours and 2.5 hours.

Figure 3 is a micrograph showing the microstructure of low-carbon spheroidized alloy steel manufactured by the method of manufacturing low-carbon spheroidized alloy steel according to an embodiment of the present invention compared with the comparative example.

Referring to FIG. 3, carbide agglomeration was observed in all comparative examples, as indicated by the red dotted circle.

In Comparative Examples 1 to 3, a structure in which carbides were aggregated in the ferrite matrix was observed. Hardness was measured at 76 HRB for Comparative Example 1 and 78 HRB for Comparative Examples 2 and 3.

In Examples 1 to 3, spheroidized carbides were observed in the ferrite matrix, and no structure in which carbides were agglomerated was observed. The hardness was measured at 79 HRB for Example 1, 78 HRB for Example 2, and 82.7 HRB for Example 3.

According to the method for manufacturing low-carbon nodular alloy steel according to the technical idea of the present invention, nodular heat treatment is performed at 740 ° C. for 8.5 hours at a temperature just above A1, and furnace cooling is performed for 2.5 hours at a cooling rate of 61 ° C. / hour, thereby maintaining the heat treatment furnace. By shortening the time to 11 hours, low-carbon nodular alloy steel can be manufactured while reducing the time required by more than 54% compared to the conventional method, which requires more than 24 hours of heat treatment time. In addition, the low-carbon nodular alloy steel manufactured by the above manufacturing method has a hardness of 85 HRB or less and a ferrite and carbide nodular structure of more than 80%, thereby satisfying the desired physical property conditions. On the other hand, in the case of the comparative example, the spheroidizing heat treatment was performed at a temperature higher than 740°C, and the maintenance time in the heat treatment furnace took a long time, so economic feasibility was low, and also the phenomenon of carbide agglomeration occurred and hardness decreased. .

In addition, the method for manufacturing low-carbon nodular alloy steel according to the technical idea of the present invention is applicable not only to the batch heat treatment process but also to the continuous heat treatment process with excellent mass productivity.

The technical idea of the present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes are possible without departing from the technical idea of the present invention. It will be clear to those skilled in the art.

Claims (9)

By weight, carbon (C): 0.17% to 0.23%, silicon (Si): 0.15% to 0.35%, manganese (Mn): 0.55% to 0.90%, chromium (Cr): 0.85% to 1.25%, nickel ( Ni): more than 0% to 0.25%, copper (Cu): more than 0% to 0.3%, phosphorus (P): more than 0% to 0.02%, sulfur (S): 0.005% to 0.035%, and the balance is iron ( Hot rolling a semi-finished product containing Fe) and other inevitable impurities to produce a hot rolled material;
Spheroidizing heat treatment of the hot rolled material at a temperature ranging from 700°C to 740°C; and
It includes; cooling the spheroidized heat-treated hot rolled material,
The step of cooling the spheroidized heat-treated hot rolled material,
Primary cooling the hot rolled material to 550°C to 650°C at a cooling rate of 55°C/hour to 65°C/hour; and
Including, secondary cooling the primary cooled hot rolled material by air cooling to room temperature.
Manufacturing method of low-carbon nodular alloy steel. delete According to claim 1,
The hot rolling is performed at a finish rolling temperature in the range of 850°C to 950°C.
Manufacturing method of low-carbon nodular alloy steel. According to claim 1,
After completing the hot rolling and before performing the spheroidizing heat treatment, the hot rolled material is cooled at a cooling rate of 0.35 ° C/sec to 0.45 ° C/sec.
Manufacturing method of low-carbon nodular alloy steel. According to claim 1,
The nodularization heat treatment is performed for 8 to 11 hours,
Manufacturing method of low-carbon nodular alloy steel. According to claim 1,
The total content of the manganese and the chromium is 1.0% by weight to 1.6% by weight,
Manufacturing method of low-carbon nodular alloy steel. According to claim 1,
The low-carbon spheroidized alloy steel manufactured by the method for manufacturing the low-carbon spheroidized alloy steel has a spheroidization rate of 80% or more and a hardness of 85 HRB or less.
Manufacturing method of low-carbon nodular alloy steel. According to claim 7,
The low-carbon spheroidized alloy steel includes ferrite and spheroidized carbide,
Manufacturing method of low-carbon nodular alloy steel. According to claim 1,
The spheroidizing heat treatment is performed in a continuous heat treatment furnace or a batch heat treatment furnace,
Manufacturing method of low-carbon nodular alloy steel.

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