TWI391500B - Eco-friendly pb-free free-cutting steel and manufacturing method thereof - Google Patents

Description

Environmentally friendly lead-free fast cutting steel and manufacturing method thereof

The present application claims the priority of Korean Patent Application No. 2008-77067 and No. 2009-18464 filed on the Korean Intellectual Property Office on August 6, 2008 and March 4, 2009, the disclosures of which are incorporated herein by reference. The invention is incorporated by reference.

The invention relates to an environmentally friendly lead-free quick-cut steel with excellent cutting property (ie mechanical property) and a manufacturing method thereof. In particular, the present invention particularly relates to an environmentally friendly lead-free fast-cutting steel having the following characteristics: 1) adding an appropriate amount of Ti, Cr, N, or the like to form a non-metallic content and a precipitate, and 2) among other components. Having Mn/S and its ratio adjusted to 3.5 or more, 3) the total amount of oxygen (ie, all oxygen) is limited to 300 ppm or less, and 4) adjusting the amount of MnS inclusions in the direction of a wire roll steel direction Above, there are 300 to 1,000 MnS contents having an area of 5 μm ² or more per unit square mm. Thereby, the quick-cut steel of the present invention has better cutting properties (i.e., mechanical properties) and hot roll properties.

In general, a fast-cut steel refers to a steel obtained by raising the mechanical properties of a steel material (that is, generally referred to as cutting property) to a maximum value. The fast-cutting steel system is generally used as a material such as a bearing or office automatic equipment cutting part, a component that can be applied to a hydraulic component of an automatic vehicle, a printer, or the like, and a use thereof, and therefore, The demand for steel cutting continues to increase.

Quick-cut steel basically has good cutting property, especially mechanical cutting property; in addition, in the technical field, the cutting property of the steel can be improved by adding different alloying elements or forming inclusions inside. Non-metallic inclusions are particularly useful as materials for improving cutting properties, and MnS is one of the most well-known non-metallic inclusions.

The cutting properties of the fast-cut steel can be adjusted by controlling the size, composition, shape and dispersion of the MnS. In more detail, when the steel material is cut by a mechanical device such as a shelf (ie, a rack), non-metallic inclusions (such as MnS) can be used as stresses at the tip of the tool and the material of the steel material. Concentrating the source and creating voids in the interface between the non-metallic inclusions and the substrate accelerates crack formation, thereby reducing the amount of force required to operate the cut.

Therefore, in order to improve the cutting property of the quick-cut steel, basically, 1) a large amount of MnS needs to be maintained, 2) MnS must be randomly distributed, and 3) MnS needs to have a large size and is preferably spherical.

In fast-cut steel, the shape of MnS varies according to the oxygen content in the continuous casting steel liquid distributor, and can be divided into three forms: spherical (type I); strip (type II); and irregular (Type III).

It is currently known that when the MnS is closer to a spherical shape (type I), its cutting property is further improved. If the total oxygen content (T[O]) in the molten steel distributor reaches several hundred ppm high, MnS will solidify in the molten steel at high temperature and crystallize into a composite sulfide such as Mn(O) in the deoxidation process. , S). At the same time, when the MnS is closer to the strip shape (Type II), if the total oxygen content (T[O]) in the molten steel distributor is relatively low, such as tens of ppm, during solidification, the MnS in the molten steel state. It does not crystallize, but it is released along the initial interface of the particles, thus causing MnS to easily extend in the direction of the roll steel during hot rolling of the steel material, resulting in deterioration of material anisotropy.

In the solidification process of general steel except for quick-cutting steel, a strip (Type II) structure is produced, and since the strip structure causes significant deterioration of the mechanical properties of the steel, many studies attempt to reduce the content of S to several ppm. Hereinafter, in order to maintain MnS, it will not precipitate during the metallurgical process.

Finally, an MnS having an irregular shape (type III) is characterized in that when the total oxygen amount T[O] in the molten steel distributor is as low as several ppm and the molten aluminum component content is high, it is generated at a high temperature. Irregular MnS is the main MnS single inclusion, and it is currently known that irregular MnS is present in the aluminum deoxidized steel in an angular state.

In the technique of rapidly cutting steel, a polygonal ferrite (such as C, Si, Mn, S, P, Nb, O, etc.) is limited to a specific range and will be used as a fine tissue ( The area ratio of the polygonal ferrite is limited to 5% or more. However, even if a large amount of expensive alloying elements such as Nb, Mo, Zr, etc. are added, this technique cannot clearly specify the effect achieved by the ferroalloy in the fast-cut steel. In addition, although this technique limits the area ratio of polygonal ferrite to a specific range, this technique does not provide an approximate measurement method.

In another technique of rapidly cutting steel, a specific amount of C, Si, Mn, S, O, Bi, etc. is added, and the content of Bi inclusions per unit square mm in a section of a wire roll steel direction, And the Bi content ratio is limited to a specific value. However, although this technique limits the amount of Bi inclusions and the ratio of Bi content, in practice, the ratio is difficult to control when rapidly cutting steel. In addition, this technique is characterized in that oxygen is added in an amount of 0.005 wt% or less, but such an oxygen content is difficult to obtain a high-oxygen quick-cut steel having good cutting property to control the MnS to have a spherical shape, in other words, the first type .

In still another technique for the production of quick-cut steel, it relates to a sulfur-containing continuous casting quick-cutting steel having the same degree of cutting property as that of the fast-cut steel obtained by the conventional casting method. The sulfur-containing continuous casting quick-cutting steel is characterized in that it contains a specific content of carbon (C), manganese (Mn), phosphorus (P), sulfur (S), nitrogen (N), and oxygen (O ₂ ), and The average size of the MnS inclusions is 50 μm ² or less. However, although this technique discloses the MnS content, the particle size is rarely mentioned, and the description of the influence of the MnS profile on the cutting property is not provided.

Another technique for cutting steel is characterized in that carbon (C), manganese (Mn), phosphorus (P), sulfur (S), nitrogen (N), and oxygen (O) are used as basic components. The content of Si is limited to 0.1 wt% or less, the Al content is limited to 0.009 wt% or less, the total amount of N is in the range of 20 ppm to 150 ppm, and the oxygen-containing system is 50% or more. However, if it is considered in practical application, it is difficult to accurately measure the weight of the oxygen-containing inclusions in the fast-cut steel, and this technique is limited to an unmeasurable value in a specific range, so the technique must be effective and practical. And other issues.

In addition to the technology of fast-cutting steel, it is a manufacturing method of Bi-S-based quick-cutting steel, which makes Bi-S-based quick-cutting steel have excellent physical properties and adjusts the size of austenite particles. At a specific size to enhance high temperature ductility. In other words, the Bi-S based fast-cutting steel contains 0.05% by weight to 0.15% by weight of carbon (C), 0.5% by weight to 2.0% by weight of manganese (Mn), and 0.15% by weight to 0.40% by weight of sulfur (S). , 0.01 wt% to 0.10 wt% of phosphorus (P), 0.003 wt% to 0.020 wt% of oxygen (0), 0.03 wt% to 0.30 wt% of bismuth (Bi), 0.01 wt% or less of bismuth (Si) 0.0009% by weight or less of aluminum (Al), and an equilibrium component of Fe and unavoidable (ie, unremovable) impurities. The cross-section of the MnS-based inclusions with MnS and adsorbed with lanthanum accounts for 0.5% to 2.0% of the total cross-section of the Bi-S-based quick-cut steel, while the cross-section of the bismuth portion accounts for the total profile of the Bi-S-based quick-cut steel. 0.030% to 0.30%. However, this technique for Bi-S based quick-cutting steel does not provide a related method of how to control the composition of MnS as described in the present invention.

SUMMARY OF THE INVENTION The primary object of the present invention is to provide a fast-cut steel that avoids (or solves) problems associated with the art, or that is unresolved in the art, and which is provided by the present invention. Environmentally friendly specifications (rules) with excellent cut and hot roll characteristics, and other similar characteristics.

One aspect of the present invention provides a fast-cutting steel comprising: 0.03 wt% to 0.13 wt% of carbon (C), 0.1 wt% or less of niobium (Si), and 0.7 wt% to 2.0 wt% of manganese ( Mn), 0.05% by weight to 0.15% by weight of phosphorus (P), 0.2% by weight to 0.5% by weight of sulfur (S), 0.001% by weight to 0.01% by weight of boron (B), 0.1% by weight to 0.5% by weight Chromium (Cr), 0.003 wt% to 0.2 wt% of titanium (Ti), 0.005 wt% to 0.015 wt% of nitrogen (N), 0.03 wt% or less of oxygen (O), and iron and unavoidable impurities Balanced ingredients. On the cross section of the direction of the quick-cut steel wire roll steel, there may be 300 to 1,000 MnS contents having a particle size of 5 μm ² or more per square mm (mm ² ). Wherein, the weight ratio between Mn and S can be .

Another aspect of the present invention provides a method for fabricating a fast-cutting steel, comprising: introducing oxygen into a reforming furnace at a supersonic rate to transform and metallize the molten metal, and when free Oxygen is stopped at 400 ppm to 1,000 ppm; oxygen is discharged in a non-deoxidized state to complete the molten metal into the ladle; from the ladle to the refining furnace (LF) to heat the molten steel, and then Performing LF metallurgy until the free oxygen density in the metal melt ranges from 100 ppm to 200 ppm; the molten steel is continuously cast using a steel blank so that the time point is equal to 10% to 50% of the duration of the metallurgical chain The density of free oxygen is from 50 ppm to 150 ppm; and the steel embryo is maintained in a heating furnace at 1,200 ° C to 1,350 ° C for 2 to 5 hours to roll the steel blank to form a wire. Among them, in the continuous casting process, the molten steel can be made into a piece of steel, which can be formed into a steel embryo by rolling through the steel blank, and in this process, the method of manufacturing the quick-cut steel can further include: The steel is maintained in a furnace at a temperature of 1,250 ° C or above for 4 to 10 hours to roll the steel to form a steel embryo.

The quick-cut steel may include: 0.03 wt% to 0.13 wt% of carbon (C), 0.1 wt% or less of niobium (Si), 0.7 wt% to 2.0 wt% of manganese (Mn), 0.05 wt% to 0.15 wt. % phosphorus (P), 0.2 wt% to 0.5 wt% sulfur (S), 0.001 wt% to 0.01 wt% boron (B), 0.1 wt% to 0.5 wt% chromium (Cr), 0.003 wt% to 0.2 wt% of titanium (Ti), 0.005 wt% to 0.015 wt% of nitrogen (N), 0.03 wt% or less of oxygen (O), and an equilibrium component of iron and unavoidable impurities. On the cross section in the direction of the wire roll steel, there may be 300 to 1,000 MnS contents having a particle size of 5 μm ² or more per square mm (mm ² ). In particular, the continuous casting process can be performed using a magnetic stirrer or a light press device, or simultaneously using the electromagnetic stirrer and the light pressure device, and the weight ratio between Mn and S can be .

In order to achieve the above object, the inventors of the present invention have made a fast-cutting steel which is 1) adding an appropriate amount of Ti, Cr, N, or the like to form a non-metallic content and a precipitate, and 2) controlling Mn/S, The ratio of the other components is 3.5 or more, 3) the total amount of oxygen is limited to 300 ppm or less, and 4) the amount of the MnS inclusion is adjusted so as to be in the section of the direction of the roll steel of the wire. There are 300 to 1,000 MnS contents having an area of 5 μm ² or more.

The MnS inclusion type in the fast-cut steel is shown in Fig. 1. At the same time, by limiting the technical characteristics of Ti, Cr, and N, etc., when the solidification is performed, a large amount (e.g., precipitation) can be precipitated at the particle interface. A fine precipitate of (Cr,Ti)S group or (Cr,Ti)N group in the range of 0.1 μm to 5 μm, as shown in FIG. 2 . Thereby, it can reach 1) prevent the processing of difficult areas during mechanical operation to improve the cutting property; and 2) improve the fracture toughness of the steel material to prevent the build-up edge (BUE) and overcome the blade chip generation. To improve the performance of fast cutting steel. Therefore, the use time of the appliance and the surface hardness can be extended.

Next, the composition of the fast-cut steel will be described in further detail.

Carbon (C): 0.03 wt% to 0.13 wt%

Carbon is an element that forms carbides to increase the strength and hardness of the material. The carbon system is present as a part of pearlite in the fast-cut steel, which is used to prevent the generation of BUE in the appliance when cutting the steel material. If the carbon (C) content is less than 0.03 w%, the hardness of the material cannot be increased to a desired level, and the effect of limiting the generation of BUE cannot be achieved. At the same time, if the carbon (C) content exceeds 13w%, the hardness of the material will increase greatly, which in turn will shorten the use time of the appliance. Therefore, in one embodiment of the invention, the carbon (C) content is limited to the range of 0.03 w% to 0.13 w%.

矽(Si): 0.1wt% or less

Germanium (Si) is one of the elements in the material because it is present in pig iron or a reducing agent. In addition to the formation of oxides, so-called SiO ₂ , yttrium (Si) is mostly solid-soluted, so it is known that yttrium does not significantly affect the mechanical properties of the fast-cut steel. However, the inventors of the present invention have found that in the high-oxygen quick-cut steel, if the cerium (Si) content exceeds 0.1 w%, SiO ₂ is generated, which causes the life of the appliance to be greatly shortened when the steel is quickly cut by mechanical operation. Therefore, the present invention does not mainly use bismuth (Si). However, if considering the feasibility, bismuth (Si) is still inevitable in iron alloys, iron ore, and the like, so in one embodiment of the present invention, bismuth (Si) in the fast-cut steel The content is adjusted to 0.1% or less.

Manganese (Mn): 0.7 wt% to 2.0 wt%

Manganese (Mn) is one of the necessary alloying elements for forming a non-metallic inclusion MnS to provide mechanical properties of the steel material. When the addition amount of manganese (Mn) is 0.7 w% or more, it is ensured that the MnS inclusion has an effective crystallinity, and the effect of reducing the surface defects of the steel during the hot roll can be achieved. If the manganese (Mn) content exceeds 2.0 w%, the hardness of the steel material will decrease, and the use time of the appliance will also be shortened. When the content of manganese (Mn) ranges from 0.7 w% to 2.0 w%, part of the manganese combines with oxygen to form MnO, which can be used as a core for MnS formation in the solidification process to accelerate the formation of spherical MnS inclusions.

Phosphorus (P): 0.05wt% to 0.15wt%

Phosphorus (P) is one of the elements used to suppress the easy formation of BUE at the front end of the cutting instrument. If the phosphorus (P) content is less than 0.05w%, the effect of inhibiting the formation of BUE is hardly produced. If the phosphorus (P) content exceeds 0.15w%, the BUE suppression effect is good, but the hardness of the steel material is increased, and the cutting tool is shortened. Service life. Therefore, in one embodiment of the present invention, the content of phosphorus (P) is limited to the range of 0.05% by weight to 0.15% by weight.

Sulfur (S): 0.2wt% to 0.5wt%

In fast-cut steel, sulfur is used to form MnS inclusions during solidification. As described above, MnS is used to improve the mechanical properties of the steel material, thereby reducing the wear of the cutting tool and increasing the surface hardness of the working member. Therefore, MnS is one of the most important components in the present invention. Based on the above purpose, the amount of sulfur (S) added is 0.2% by weight or more. However, the inventors of the present invention have experimentally shown that if the amount of sulfur (S) added is excessive, it causes a network (like a net) FeS to precipitate on the particle interface. FeS is very fragile and has a low melting point, which tends to cause a significant deterioration in the characteristics of the heat roller. At the same time, if the sulfur content exceeds its requirements, it will lead to an increase in surface defects of the steel material, and at the same time, the hardness and ductility of the steel material are significantly deteriorated. Therefore, the sulfur (S) content must not exceed 0.5% by weight.

Boron (B): 0.001 wt% to 0.01 wt%

Boron (B) is used to increase the quenching characteristics of steel materials. Therefore, in the present invention, 10 ppm to 100 ppm of boron (B) is added. If the amount of boron (B) added is not less than 10 ppm, it may be difficult to appropriately increase the quenching characteristics. However, if the amount of boron (B) added exceeds 100 ppm, the quenching characteristics may be sufficiently improved, but the high temperature ductility may be deteriorated and the hot roll may not be performed. Process. Therefore, the boron (B) content should have the above limitations.

Chromium (Cr): 0.1wt% to 0.5wt%

Chromium (Cr) is one of the elements that can enlarge the austenite region. In other words, chromium is an essential component and is a cheap general alloying element. At the same time, even if the chromium content is large, the carbide formed by chromium does not cause material extraction. The addition of Cr forms a larger (Cr,Mn)S based non-metallic inclusion of particles. In addition, the addition of Cr prevents deformation of the non-metallic inclusions, and the inclusions can be evenly distributed in the material during the rolling step. In one embodiment of the present invention, the addition of chromium enhances the mechanical properties, and the inventors of the present invention have experimentally confirmed that when the amount of chromium added is less than 0.1%, the effect of improving mechanical properties cannot be produced, but when the amount of chromium is added Above 0.5% by weight, the mechanical properties reach an upper limit and will not continue to increase. Therefore, the content of chromium (Cr) is limited to the range of 0.1 wt% to 0.5 wt%. Preferably, the amount of chromium (Cr) added may be from 0.1% by weight to 0.5% by weight.

Titanium (Ti): 0.003 wt% to 0.2 wt%

Titanium (Ti) and oxygen (O), nitrogen (N), carbon (C), sulfur (S), hydrogen (H), and similar elements can exhibit excellent affinity, especially when titanium is used Deoxygenation, denitrification, desulfurization, and similar reactions. In addition, titanium (Ti) is easy to form carbides and smelt out particles. Related experiments of the present invention confirmed that the addition of more than 0.003 wt% of titanium (Ti), the smelting of the particles can greatly improve the mechanical properties. In addition, the addition of Ti enhances the hardenability to prevent BUE formation, thereby improving mechanical properties. However, if the titanium (Ti) content exceeds 0.2% by weight, the effect of improving the mechanical properties has reached an upper limit, and the service life of the cutting device is shortened due to the formation of TiO ₂ in the material. Therefore, the titanium (Ti) content should be limited to the range of 0.003 wt% to 0.2 wt%, preferably 0.008 wt% to 0.15 wt%.

Nitrogen (N): 0.005 wt% to 0.015 wt%

Nitrogen is one of the elements that affects the BUE formation and the surface roughness of the cut in the cutting instrument. If the nitrogen (N) content is less than 0.005 wt%, BUE generation is increased and surface roughness is deteriorated. When the nitrogen content is increased, the BUE production is reduced, but when the nitrogen (N) content exceeds 0.015 wt%, the surface defects of the rapidly-cut steel which is die-casting are increased, which causes another disadvantage. Therefore, in the present invention, the nitrogen (N) content is limited to the range of 0.005 wt% to 0.015 wt%.

Oxygen (O): 0.03 wt% or less

Oxygen (O) is used to form fine MnO in the initial step of solidifying molten steel in a mold during die casting, and MnO is used as a crystal nucleation point of MnS crystal. Here, the oxygen referred to is the total amount of oxygen (T.[O]) present in the die-cast steel (i.e., cast plate). As described above, when the oxygen content is several tens ppm or less, when the molten steel solidifies, the MnS in the second type or the third type may precipitate, and the type of MnS causes the cutting property of the quick-cut steel. (ie mechanical properties) deterioration. In the present invention, in order to have optimum cutting properties, the main object is to produce a type I MnS crystal, so-called spherical MnS. The experimental results show that when the oxygen content is increased, spherical MnS can be effectively crystallized, but if the oxygen content exceeds 0.03 wt%, surface defects such as pinholes, pores, or similar pores are greatly increased. Therefore, the upper limit of the oxygen content must be limited.

Weight ratio of manganese (Mn) to sulfur (S):

In addition to adjusting the component content, in order to make the fast-cut steel have better ductility at high temperatures, it is necessary to control the ratio between manganese (Mn) and sulfur (S) so that the Mn/S ratio is 3.5 or more by weight. This ratio is to prevent the FeS from being brittle due to the mixing of manganese (Mn) and sulfur (S), and it is necessary to ensure that the Mn content is above a certain value. In particular, if the ratio of manganese (Mn) and sulfur (S) is less than 3.5, the characteristics of the hot roll are deteriorated, and it is difficult to obtain the fast-cut steel to be obtained by the present invention.

Further, on a section in the direction of a wire roll steel, there are 300 to 1,000 MnS having a particle size of 5 μm ² or more per square mm (mm ² ).

The cutting properties (ie, mechanical properties) of the fast-cut steel vary with the size and distribution of the non-metallic inclusions in the steel. In general, when the MnS particles are large and the MnS content is large, the steel material has better cutting properties. The evaluation results of the optical microscope measurement and the cutting property test by the inventors of the present invention show that, in the cross section of the direction of the roll steel (i.e., the L direction), there are 300 to 1,000 particle sizes per square mm (mm ² ) exceeding 5 μm ^{2 .} In the case of MnS, the cutting property of the steel material is optimal. When there are less than 300 MnS, the use time of the appliance is shortened due to poor cutting property, and the surface roughness of the processing region is also deteriorated. At the same time, if the number of MnS exceeds 1,000, the service life of the appliance can be increased, but the workability of the steel is deteriorated (poor). Therefore, the amount of MnS is preferably controlled within the range of 300 to 1,000.

Next, referring to Fig. 3, a method of producing a quick-cut steel comprising the above alloy composition, which is applicable to the present invention, will be described in detail.

Transformation and metallurgy chain:

First, oxygen is introduced into the molten metal in the reformer at a supersonic rate to remove impurities such as C, Si, Mn, P, etc. contained in the molten metal by air or slag. In the conversion and metallurgical chain process, oxygen blowing is stopped when the free oxygen conversion range contained in the metal melt is in the range of 400 ppm to 1,000 ppm. If the oxygen is less than 400 ppm, the carbon content in the metal melt may exceed the composition range of the present invention, resulting in difficulty in controlling the carbon component. At the same time, if the oxygen exceeds 1,000 ppm, it may cause excessive corrosion of a refractory appliance such as a reformer, a steel drum, or the like.

Discharge non-deoxidized steel:

The oxygen melt is blown to the metal melt to be (discharged) into the ladle in a non-deoxidized state, and if necessary, a secondary material such as a ferroalloy or a similar product may be added during the discharge operation. The addition of a suitable range of ferroalloys or by-products can form molten steel or slag.

Refining furnace (LF) heating:

When the discharge is over, the ladle is transferred to the LF to heat the molten steel. As for the heating process of the metal melt, the temperature of the molten steel is raised by passing an arc through the carbon electrode rod formed in the LF. During the heating process, if necessary, iron alloy or other auxiliary materials may be added, or the molten steel test sample may be taken out according to the use conditions, or the oxygen density of the molten steel may be measured. When the molten steel is heated, the oxygen compound in the slag or the oxygen in the air can be decomposed by the arc and passed into the molten metal to increase the oxygen density of the molten steel. In LF, the LF refining operation is terminated, preferably when the free oxygen density in the molten metal is in the range of 100 ppm to 200 ppm. If the LF refining operation is stopped when the free oxygen density is less than 100 ppm, it may be difficult to form the desired MnS. Conversely, if the LF refining operation is stopped when the free oxygen density exceeds 200 ppm, it may be difficult to predict the molten metal in the next step. The composition changes, and it is difficult to control the composition of the molten metal. Therefore, the time point at which the LF refining operation is stopped by the free oxygen density control should be controlled in the range of 100 ppm to 200 ppm.

Blowing and continuous casting:

The molten steel material which has been heated to complete the LF refining operation is transferred to a continuous casting apparatus and continuously cast of molten steel. At the beginning of continuous casting, the density of free oxygen in the molten steel is first measured to ensure in advance whether the cast fast-cut steel has good cutting properties. The free oxygen density is measured when passing 10% to 50% of the total casting time, where the free oxygen density needs to be between 50 ppm and 150 ppm. If the free oxygen density is measured before 10% of the casting time, it is difficult to obtain the accurate free oxygen density due to the influence of the steel liquid distributor refractory material, the steel liquid distributor insulation material, or the like, and vice versa. Measuring the free oxygen density after 50% of the time may miss the opportunity to control the oxygen density. In addition, experiments have shown that when the measured free oxygen density is less than 50ppm, the cutting property is poor, and when the measured free oxygen density exceeds 150ppm, how much will result in the cast steel (ie, steel embryo) There are pinholes or stomata in the increase. In the fast-cutting steel die casting process, the preferred cast steel parts can be produced using a mold electromagnetic stirrer (mold EMS) or a light pressure device. The use of the mold EMS helps to produce spherical MnS inclusions with larger particle sizes, while the use of a light pressure device is more conducive to reducing center segregation and surface defects of the steel surface, such as pinholes. Or blow holes. In the continuous casting process of the quick-cutting steel, the continuous casting process can basically use 300mm x 400mm, 400mm x 500mm, etc., or steel slabs of 120mm x 120mm, 160mm x 160mm. In this embodiment, if a block steel is used in the continuous casting process, a steel blank roll rolling process, that is, a so-called fast-cut steel blank process can be used; however, if a steel blank is used in the roll rolling process, The rolling process of the wire roll can be omitted and the rolling process of the wire roll can be performed.

Rolled steel into a steel embryo:

In the continuous casting process, if the block steel is cast instead of the steel die casting, an additional process of rolling the block steel into a steel blank is required. When using a 300mm x 400mm or 400mm x 500mm fast steel roll to roll into a 120mm x 120mm or 160mm x 160mm steel blank, it is generally called steel blank rolling or steel blanking. At the same time, it is the most in the steel roll rolling process. It is important to keep the steel temperature and the furnace heating time. If the steel is rolled at a low temperature, the surface of the resulting steel blank will be severely damaged. Therefore, in one embodiment of the invention, the furnace temperature is limited to 1,250 ° C or above and maintained for four to ten hours. It has been experimentally confirmed that when the steel temperature is lower than 1,250 ° C, if the steel embryo is too long in the heating furnace, the surface properties of the obtained steel embryo will be deteriorated; however, even if the temperature of the steel block is maintained at 1,250 ° C or above, If the heating time maintained by the furnace is less than four hours, the surface properties of the steel blank will also deteriorate. At the same time, when the block steel is maintained in the heating furnace for more than ten hours, and the temperature of the bulk steel is maintained at 1,250 ° C or above, the yield is greatly reduced, but if it is four to ten hours, the steel embryo having the same surface properties can be obtained. Therefore, the heating time maintained by the furnace must be limited to four to ten hours.

Rolled wire:

When the quick-cut steel is cast by a steel blank, or when the fast-cut steel is cast in one piece of steel and then the steel is rolled in a steel block to form a steel blank, the steel is subjected to a rolling process to form a steel roll. Wire. In the process of making wire for quick-cut steel and steel, the most important factors are the furnace temperature and the continuous heating time. In order to obtain a fast-cut steel having good surface properties, the temperature of the steel preform is preferably maintained in a heating furnace at 1,200 ° C to 1,350 ° C for two to five hours. When the temperature of the steel is lower than 1,200 ° C, the surface properties of the wire are not easily obtained, and when the temperature of the steel exceeds 1,350 ° C, it is difficult to obtain a relatively good surface property of the wire. At the same time, if the continuous heating time in the heating furnace is less than two hours, it is difficult to obtain a good wire surface property, and it is difficult to maintain the heating time for more than five hours even in the heating furnace compared to the maintenance heating time of two to five hours. Achieved with better wire surface properties.

Next, the present invention will be described in more detail by way of the following examples.

[Example 1]

In the present embodiment, the steel compositions of the examples and comparative examples listed in the following Table 1 were produced using a 200 kg high frequency air induction melting furnace. Here, the comparative example is the most widely used lead-free quick-cut steel, and both the examples and the comparative examples were manufactured by the same experimental equipment and manufacturing method, and the dimensions were 230 mm x 230 mm x 350 mm.

The steel was heated in a 1,300 ° C heating furnace and then rolled into a metal plate having a thickness of 30 mm using a trial rolling mill. Next, the metal plate was cut into a square having a size of 30 mm x 30 mm, and then processed on a shelf (i.e., a rack) to form a ring bar (strip) having a diameter of 25 mm. Then, a 25 mm diameter ring rod was subjected to a cutting evaluation test on a CNC shelf to measure the time characteristics of the appliance and the surface roughness of the cut surface. The cutting evaluation test was carried out under the conditions of a cutting rate of 100 m/min, a cutting depth of 1.0 mm, and a rotational speed of 0.1 mm/rev, and was carried out without using lubricating oil and maintaining a dry state.

The experiment of the service life characteristics of the appliance is to measure the side wear related to the cutting time (usually used in the test), and the surface roughness test uses the surface roughness related to the cutting time. The units of side wear and surface roughness are (m), respectively, and the smaller the value, the higher the surface characteristics. Fig. 4 is a view showing the results of an experimental example of the use time of the apparatus of the embodiment and the comparative example of the present invention. It is worth noting that the experimental examples of the present invention have the same length of service life as the comparative examples. Meanwhile, in FIG. 5, it can be found that the experimental examples of the present invention have the same degree of surface characteristics as the conventional lead-free quick-cut steel in the same time interval, and are even better than the conventional lead-free quick-cut steel.

It can be determined from experiments that the surface roughness and the service life of the fast-cut steel containing a predetermined content of Cr, Ti, and N instead of Pb are the same as or better than the lead-free fast-cut steel (harmful to the human body). For example, if the high oxygen-containing quick-cut steel having 0.2% by weight to 0.5% by weight of sulfur contains 0.1% by weight to 0.5% by weight of chromium, 0.003% by weight to 0.2% by weight of titanium, and 0.005% by weight to 0.015% by weight. % of nitrogen, when the molten steel solidifies, a large amount of (Cr, Mn) S-based, (Cr, Ti) S-based, and (Cr, Ti) N-based fine particles having a size of 1 μm are precipitated on the particle interface. Precipitate, and such a precipitate can prevent the steel material from being difficult to operate during the mechanical operation of the component, and can achieve the purpose of reducing the fracture characteristics of the steel material and other similar purposes, thereby limiting BUE generation and improving the fragmentation phenomenon.

[Embodiment 2]

The continuous-cut steel block with a size of 300mm x 400mm is made into a steel piece with a size of 160mm x 160mm through a rolling mill roll, and then the steel is passed through a wire roll to a diameter of 25mm. Wire rod. The steel and steel embryos are heated and cooled under the conditions of generally fast-rolling steel rolling. The test sample was taken out from the rolled wire, and the total oxygen amount was measured by an N/O analyzer, and the area and shape of the MnS were observed through an optical microscope. At the same time, the wire rolled by the wire is subjected to a cold rolling drawing process to obtain a ring rod (ie, a cold drawn (CD) strip), and the cutting test is performed using a CNC shelf under the same conditions to measure the instrument. Use time characteristics. Table 2 below shows the total oxygen content (ppm) of the wire obtained by the experiment, the area per unit square millimeter (mm ² ) of 5 (the number of MnS of m2 or more, and the time of use. In Table 2, the time of use of the appliance) Indicates the relative number of parts that can be cut using a single cutting tool.

In Table 2, when the total oxygen content of the wire is in the range of 300 ppm and the number of MnS per unit area is in the range of 300 to 1,000 (Experimental Examples 6 to 9), the service life of the appliance is 5,000 or more, or more than the user's The standards required for the use of fast-cut steel parts are high. Meanwhile, even if the total oxygen amount is still within the range described in the present invention, as in Comparative Examples 2 and 3, when the number of MnS per unit area is less than 300, the service life of the appliance cannot exceed the standard required for the user to use the fast-cut steel part. 5,000 times. The reason for this phenomenon is that there is less MnS with a relatively large area, which leads to fragmentation, which results in a relatively small application range. Meanwhile, in Comparative Examples 4 and 5, the number of MnS per unit area is within the scope of the present invention, and the service life of the cutting tool also exceeds the reference value of 5,000 times, but by the steel casting (ie, cast steel steel, Or the recovery of the block to the CD strip is less than 80%. It is worth noting that the factor causing this phenomenon is that the total oxygen content is too high, exceeding 300 ppm, which is the main factor causing pinholes and blowholes on the surface of the steel casting, thus failing to improve the steel blank process and the wire roll rolling process. . Therefore, too high a total amount of oxygen causes a large amount of surface defects, a low recovery rate, and an increase in cost, which makes it difficult to achieve the object of the present invention.

In summary, in the experimental example of the present invention, the sulfur-free quick-cut steel can be easily produced by using a steel making process or a continuous casting process, and since a large amount of spherical MnS crystals are formed in the steel making process, cutting property can be provided (ie, Mechanical properties) Environmentally-friendly, fast-cut steel with greatly improved and superior hot workability (ie, hot roll characteristics).

The present invention has been described with reference to the preferred embodiments thereof, and modifications and modifications may be made without departing from the scope of the invention.

The above-mentioned embodiments are merely examples for convenience of description, and the scope of the claims is intended to be limited to the above embodiments.

The above and other aspects, features, and other advantages of the present invention will become more apparent from the accompanying drawings and detailed description.

Figure 1 is a photomicrograph of the inclusion of MnS.

Figure 2 is a photomicrograph of the coexistence of Cr, Ti, N, and S-based precipitates in a high oxygen-containing fast-cut steel with MnS inclusions.

3 is a schematic view showing a manufacturing process of an environmentally friendly lead-free quick-cut steel according to an experimental example of the present invention.

Fig. 4 is a graph showing the comparison of the service life of an experimental example and a comparative example satisfying the conditions of the embodiment of the present invention.

Fig. 5 is a comparison of surface roughness of an experimental example and a comparative example satisfying the conditions of the examples of the present invention.

Claims (8)

A fast-cutting steel comprising: 0.03 wt% to 0.13 wt% of carbon (C), 0.1 wt% or less of niobium, 0.7 wt% to 2.0 wt% of manganese (Mn), and 0.05 wt% to 0.15 wt% of phosphorus (P), 0.2 wt% to 0.5 wt% sulfur (S), 0.001 wt% to 0.01 wt% boron (B), 0.1 wt% to 0.5 wt% chromium (Cr), 0.003 wt% to 0.2 wt% Titanium (Ti), 0.005 wt% to 0.015 wt% nitrogen (N), 0.03 wt% or less oxygen (O), and an equilibrium component of iron and unavoidable impurities, wherein (Cr, Ti) S-based precipitate And (Cr,Ti)S-based and (Cr,Ti)N-based fine precipitates are present in the particle interface of the fast-cut steel, and have a particle size ranging from 0.1 μm to 5 μm. The fast-cutting steel according to the first aspect of the invention, wherein the MnS content of the mixture of 300 to 1,000 particles having a particle size of 5 μm ² or more per square millimeter (mm ² ) in a cross section of the wire direction of the wire rod Things. The fast-cutting steel according to claim 1, wherein the weight ratio between Mn and S is Mn/S. 3.5. A method for fabricating a fast-cutting steel, the method comprising: introducing oxygen into a reforming furnace at a supersonic rate to transform the metal melt, and when the free oxygen is between 400 ppm and 1,000 ppm Oxygen blowing is stopped; the non-deoxygenated oxygen is blown to complete the molten metal into the ladle; the ladle is transferred to the refining furnace (LF) to heat the molten steel, and then the LF chain is smelted until The free oxygen density in the metal melt ranges from 100 ppm to 200 ppm; The molten steel is continuously cast using a steel blank such that the density of free oxygen is from 50 ppm to 150 ppm when the time point is equal to 10% to 50% of the duration of the metallurgical chain; and the steel embryo is maintained at 1,200 ° C to 1,350 In a heating oven of °C for 2 to 5 hours, the steel blank is rolled to form a wire, wherein the fast-cut steel contains 0.03 wt% to 0.13 wt% of carbon (C), 0.1 wt% or less ( Si), 0.7 wt% to 2.0 wt% of manganese (Mn), 0.05 wt% to 0.15 wt% of phosphorus (P), 0.2 wt% to 0.5 wt% of sulfur (S), 0.001 wt% to 0.01 wt% Boron (B), 0.1 wt% to 0.5 wt% chromium (Cr), 0.003 wt% to 0.2 wt% titanium (Ti), 0.005 wt% to 0.015 wt% nitrogen (N), 0.03 wt% or less Oxygen (O), and the balance of iron and inevitable impurities. The method of claim 4, wherein the MnS content having a particle size of 5 μm ² or more per square millimeter (mm ² ) in a cross section of a wire roll steel direction. The method of claim 4, wherein the continuous casting process comprises: molding the molten steel to form a piece of steel; and maintaining the piece of steel in a heating furnace at a temperature of 1,250 ° C or higher 5 to 10 In an hour, the piece of steel is rolled to form a steel blank. The method of claim 4, wherein the continuous casting process is performed by using a magnetic stirrer or a light press device or simultaneously using the electromagnetic stirrer and the light press device. The method of claim 4, wherein the weight ratio between Mn and S is Mn/S 3.5.