KR20190076412A - Non-heat treated steel and method of manufacturing the same - Google Patents

Abstract

According to the present invention, provided is a non-heat treated steel material comprising: 0.24-0.30 wt% of carbon (C); 0.15-0.35 wt of silicon (Si); 1.40-1.70 wt% of manganese (Mn); more than 0 and no more than 0.03 wt% of phosphorus (P); 0.04-0.07 wt% of sulfur (S); more than 0 and no more than 0.25 wt% of copper (Cu); 0.20-0.40 wt% of chromium (Cr); 0.10-0.20 wt% of vanadium (V); 0.02-0.04 wt% of aluminum (Al); 0.01-0.02 wt% of niobium (Nb); 0.010-0.025 wt% of nitrogen (N); and the remaining of iron (Fe) and inevitable impurities. Therefore, the present invention is capable of minimizing a deterioration in tension while having high strength.

Description

TECHNICAL FIELD [0001] The present invention relates to a non-tempered steel and a method of manufacturing the same.

The present invention relates to a steel material and a method of manufacturing the same, and more particularly, to a non-tempered steel material and a manufacturing method thereof.

The front axle is a component that plays a role of weight distribution, direction adjustment, driving force transmission, etc. of the vehicle. Therefore, high strength is required to withstand the load and vibration of the vehicle body. In general, however, the higher the strength, the lower the toughness. This decrease in toughness causes a reduction in the life of the front axle product.

As prior arts, Korean Patent Publication No. 2012-0063199 (published on Jun. 15, 2012, entitled "Steels Excellent in Strength and Shock Toughness and Method for Manufacturing the Same").

The present invention provides a non-tempered steel material having a high strength and minimizing toughness degradation, and a method of manufacturing the same.

The non-tempered steel according to one embodiment of the present invention is characterized by containing, by weight%, 0.24 to 0.30% of carbon (C), 0.15 to 0.35% of silicon (Si), 1.40 to 1.70% of manganese (Mn) ): More than 0 to 0.03%, sulfur (S): 0.04 to 0.07%, copper (Cu): more than 0 to 0.25%, chromium (Cr): 0.20 to 0.40%, vanadium (V) (Al): 0.02 to 0.04%, niobium (Nb): 0.01 to 0.02%, nitrogen (N): 0.010 to 0.025%, and the balance of iron (Fe) and unavoidable impurities.

The non-adjustable quality steel is fine hardness of 260 ~ 320 HV, and a tensile strength of 870 ~ 970 MPa, and yield strength of 620 ~ 700 MPa, and the elongation is more than 16%, and the impact toughness value of 80 J / cm ² be equal to or greater than have.

The non-tempered steel may be in the form of a bar.

A front axle beam according to another embodiment of the present invention includes a component made of non-tempered steel as described above.

A method for producing a non-tempered steel material according to an embodiment of the present invention includes the steps of (a) 0.24 to 0.30% carbon (C), 0.15 to 0.35% silicon (Si), 1.40 to 1.70% manganese (Mn) P: more than 0 to 0.03%, sulfur (S): 0.04 to 0.07%, Cu: more than 0 to 0.25%, chromium (Cr): 0.20 to 0.40%, vanadium (V) Providing a cast material made of 0.02-0.04% aluminum (Al), 0.01-0.02% niobium (Nb), 0.010-0.025% nitrogen (N), balance iron (Fe) and unavoidable impurities; (b) subjecting the cast material to reheating and then subjecting to a finish hot rolling at a temperature of 1150 to 1250 占 폚; And (c) air-cooling the rolled cast material.

In the method for producing a non-tempered steel, the steel material realized by performing the steps (a) to (c) has a micro hardness of 260 to 320 HV, a tensile strength of 870 to 970 MPa, a yield strength of 620 to 700 MPa, elongation of 16% or more, and impact toughness value of 80 J / cm ^{2 or} more.

According to an embodiment of the present invention, a non-tempered steel material having a high strength and minimizing toughness deterioration and a manufacturing method thereof can be realized. Of course, the scope of the present invention is not limited by these effects.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow chart illustrating a method for producing a non-tempered steel according to an embodiment of the present invention. FIG.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a non-tempered steel according to an embodiment of the present invention and a method of manufacturing the same will be described in detail. The terms used below are appropriately selected terms in consideration of functions in the present invention, and definitions of these terms should be made based on the contents throughout this specification.

According to the non-tempered steel material and the method of manufacturing the same according to an embodiment of the present invention, a non-tempered steel material having a high strength and minimizing toughness degradation and a method for manufacturing the same are secured.

Steel

The non-tempered steel according to one embodiment of the present invention comprises 0.24 to 0.30% of carbon (C), 0.15 to 0.35% of silicon (Si), 1.40 to 1.70% of manganese (Mn) ): More than 0 to 0.03%, sulfur (S): 0.04 to 0.07%, copper (Cu): more than 0 to 0.25%, chromium (Cr): 0.20 to 0.40%, vanadium (V) (Al): 0.02 to 0.04%, niobium (Nb): 0.01 to 0.02%, nitrogen (N): 0.010 to 0.025%, and the balance of iron (Fe) and unavoidable impurities. The non-adjustable quality steel is fine hardness of 260 ~ 320 HV, and a tensile strength of 870 ~ 970 MPa, and yield strength of 620 ~ 700 MPa, and the elongation is more than 16%, and the impact toughness value of 80 J / cm ² be equal to or greater than have. The non-tempered steel may be in the form of a bar.

Hereinafter, the role and content of each component included in the non-tempered steel according to one embodiment of the present invention will be described.

Carbon (C): 0.24 to 0.30 wt%

In the present invention, carbon (C) is added to secure the strength of the steel to be produced. The carbon (C) is a main element that determines the strength and hardness of the steel. The higher the content, the higher the strength, and the tensile strength and yield point increase with increasing cold workability. It also combines with sulfur (S) to form an emulsion of carbon and increase machinability. The carbon is preferably added in an amount of 0.24 to 0.30% by weight based on the total weight of the steel according to the present invention. When carbon is added in an amount of less than 0.24% by weight, securing strength is insufficient. On the contrary, when the addition amount of carbon is more than 0.30% by weight, impact toughness is drastically lowered.

Silicon (Si): 0.15-0.35 wt%

In the present invention, silicon (Si) is added as a deoxidizer to remove oxygen in the steel, and also serves to improve the solid solution strengthening effect. The silicon is preferably added in an amount of 0.15 to 0.35% by weight based on the total weight of the steel material according to the present invention. When the addition amount of silicon is less than 0.15% by weight, deoxidation effect and solid solution strengthening effect by the addition of silicone are insufficient. On the other hand, when the content of silicon exceeds 0.35% by weight, the toughness of the steel material to be produced is deteriorated.

Manganese (Mn): 1.40 to 1.70 wt%

In the present invention, manganese (Mn) is an element that strengthens the microstructure upon air cooling after hot forging. In addition, it is an extremely effective element for improving the strength by refining bainite structure. In addition, manganese (Mn) increases sintering at high temperature to improve casting. And, manganese is combined with sulfur (S) to form MnS, thereby preventing the embrittlement of brittleness and improving cutting workability. The manganese is preferably added in an amount of 1.40 to 1.70 wt% in the steel according to the present invention. When manganese is added in an amount of less than 1.40 wt%, the effect of strengthening solubility and securing strength by manganese addition is insufficient. On the other hand, when the content of manganese exceeds 1.70% by weight, the toughness is lowered and the production cost of the steel is increased.

Phosphorus (P): more than 0 and not more than 0.03% by weight

Phosphorus (P) is added for improving cutting ability. However, if the content of phosphorus (P) is more than 0.03 wt% in the steel material according to the present invention, there is a fear of occurrence of secondary processing brittleness and surface defects due to segregation, and toughness and fatigue resistance are deteriorated. Therefore, the content of phosphorus (P) is preferably limited to a range of 0.03% by weight or less based on the total weight of the steel material according to the present invention.

Sulfur (S): 0.04 to 0.07 wt%

Sulfur (S) is added in steel to improve machinability or workability. The sulfur (S) is preferably added in an amount of 0.04 to 0.07% by weight based on the total weight of the steel according to the present invention. When the content of sulfur (S) is less than 0.04% by weight, there is a problem that the cutting property of the steel is insufficient. On the other hand, when the content of sulfur (S) exceeds 0.07% by weight, there is a fear of heat and brittleness. In addition, the MnS is elongated when it is added in excess, and the elongated MnS is located in the portion of the high frequency heat treatment and parting line during the rolling or forging process, thereby deteriorating the quality of the product. In addition, there is a problem that the hot workability is lowered, tearing is caused, and defects are caused in the surface treatment by formation of large inclusions.

Copper (Cu): more than 0 and not more than 0.25% by weight

Copper (Cu) promotes fine precipitates and contributes to the increase of strength and improves the cutting performance of the steel. Copper (Cu) is preferably added at a content ratio of 0.25% by weight or less based on the total weight of the steel material according to the present invention. If the addition amount of copper exceeds 0.25% by weight, it may be concentrated on the grain boundaries to cause surface cracking, and there is a problem that remarkable decrease in toughness and deterioration due to hot working are caused.

Cr (Cr): 0.20 to 0.40 wt%

Cr (Cr) contributes to enhancement of strength through minification of manganese (Mn) and bainite structure. The chromium (Cr) is preferably added at a content ratio of 0.20 to 0.40% by weight based on the total weight of the steel material according to the present invention. If the addition amount of chromium is less than 0.20% by weight, the effect of compensating the strength due to low carbon is insufficient. On the other hand, when the addition amount of chromium exceeds 0.40% by weight, the toughness is lowered and the workability and machinability are lowered.

Vanadium (V): 0.10 to 0.20 wt%

Vanadium (V) plays a role in improving the strength by precipitation strengthening. The vanadium is preferably added in an amount of 0.10 to 0.20% by weight based on the total weight of the steel material. If the addition amount of vanadium is less than 0.10 wt%, the precipitation strengthening effect is insufficient. On the contrary, when the addition amount of vanadium exceeds 0.20% by weight, the workability may be greatly lowered.

Aluminum (Al): 0.02 to 0.04 wt%

Aluminum (Al) provides an excellent deoxidizing effect and also contributes to particle refinement by bonding with nitrogen (N). The aluminum is preferably added in an amount of 0.02 to 0.04% by weight based on the total weight of the steel material. When the addition amount of aluminum is less than 0.02 wt%, the effect of adding aluminum is insufficient. If the added amount of aluminum exceeds 0.04% by weight, clogging of the nozzle may occur during casting and toughness of the steel may be lowered.

Niobium (Nb): 0.01 to 0.02 wt%

Niobium (Nb) precipitates as fine carbonitride during hot rolling, thereby reducing both recrystallization and grain growth, thereby finer austenite grains, thereby improving both strength and toughness. The niobium is preferably added in an amount of 0.01 to 0.02% by weight based on the total weight of the steel sheet according to the present invention. If the addition amount of niobium is less than 0.01% by weight, the effect of adding niobium can not be exhibited properly. On the other hand, if the amount of niobium exceeds 0.02% by weight, the niobium exists in a solid state in the ferrite, and there is a risk that the impact toughness of the steel sheet is lowered. When the addition amount of niobium exceeds 0.02% by weight, the weldability of the post-welded steel sheet can be impaired.

Nitrogen (N): 0.010 to 0.025 wt%

Nitrogen (N) contributes to the enhancement of strength by precipitation strengthening and the formation of nitride by bonding with aluminum or the like, thereby contributing to the improvement of mechanical properties due to refinement of austenite grain size. The nitrogen is preferably contained in an amount of 0.010 to 0.025% by weight (100 to 250 ppm) of the total weight of the steel material. When the content of nitrogen is less than 0.010 wt%, the effect of nitride formation is insufficient. On the contrary, when the content of nitrogen exceeds 0.025 wt%, it may cause clogging of the nozzle during casting and may interfere with hot stripping.

The non-tempered steel according to one embodiment of the present invention is made by refining the crystal grains by adding 0.02 to 0.04% of aluminum (Al), 0.01 to 0.02% of niobium (Nb) and 0.010 to 0.025% of nitrogen (N) Thereby improving the strength.

Manufacturing method of non-tempered steel

A method for producing a non-tempered steel material according to an embodiment of the present invention will be described in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow chart illustrating a method for producing a non-tempered steel according to an embodiment of the present invention. FIG.

(A) 0.24 to 0.30% carbon, 0.15 to 0.35% silicon, and 1.40 to 1.70 manganese (Mn) in weight percent based on the total weight of the steel. (Cu): more than 0 and not more than 0.25%, chromium (Cr): 0.20 to 0.40%, vanadium (V): 0.10%, phosphorus (P): more than 0 and not more than 0.03% (Fe) and unavoidable impurities, in a range of 0.01 to 0.02% of aluminum (Al), 0.02 to 0.04% of aluminum (Al), 0.01 to 0.02% of niobium (Nb), 0.010 to 0.025% of nitrogen (S100); (b) a step (S200) of finishing hot rolling at a temperature of 1150 to 1250 占 폚 after reheating the cast material; (c) cooling the rolled cast material (S300).

According to the method for producing a non-tempered steel described above, it is possible to produce a non-tempered steel having a microhardness of 260 to 320 HV, a tensile strength of 870 to 970 MPa, a yield strength of 620 to 700 MPa, an elongation of 16% J / cm < ² >. The non-tempered steel may be in the form of a bar. That is, it has been confirmed that a combination of high strength and toughness can be ensured by changing the components and the manufacturing conditions for the steel sheet, and the process conditions with low manufacturing cost can be realized.

Experimental Example

Hereinafter, preferred examples of the present invention will be described in order to facilitate understanding of the present invention. It should be understood, however, that the following examples are intended to aid in the understanding of the present invention and are not intended to limit the scope of the present invention.

C Si Mn P S Cu Cr V Al Nb N Comparative Example 0.24 0.24 1.49 0.018 0.055 0.05 0.26 0.13 0.005 0.002 0.0056 Example 0.27 0.30 1.51 0.014 0.054 0.05 0.25 0.13 0.027 0.016 0.0122

Microhardness (HV) Tensile Strength (MPa) Yield strength (MPa) Elongation Impact (J / cm2) Comparative Example 250 858 609 18% 70.0 Example 277 896 655 16.9% 88.2

Table 1 shows the composition (unit: wt%) of the steel material according to the experimental example of the present invention. In the case of the comparative example, hot rolling was carried out at 1240 占 폚, and in the case of the embodiment, at 1190 占 폚. After hot rolling, it was subjected to air cooling treatment.

Table 2 shows the physical properties of the steel according to the experimental example of the present invention.

The steel material according to the comparative example of the present invention contains 0.24% by weight of carbon (C), 0.24% by weight of silicon (Si), 1.49% by weight of manganese (Mn) ): 0.018%, sulfur (S): 0.055%, copper (Cu): 0.05%, chromium (Cr): 0.26%, vanadium (V): 0.13%, aluminum (Al) 0.002%, nitrogen (N): 0.00056%, and the balance of iron (Fe). That is, the steel according to the comparative example of the present invention does not satisfy the range of 0.02 to 0.04% of aluminum (Al), does not satisfy the range of 0.01 to 0.02% of niobium (Nb) % Range. The steel material according to the comparative example of the present invention having such a composition had a microhardness of 250 HV, a tensile strength of 858 MPa, a yield strength of 609 MPa, an elongation of 18% and an impact toughness value of 70 J / cm ² Respectively.

On the contrary, the steel material according to the embodiment of the present invention contains 0.27% of carbon, 0.30% of silicon, 1.51% of manganese (Mn), 0.014% of phosphorus (P) (Al): 0.027%, Niobium (Nb): 0.016%, nitrogen (N): 0.054%, copper (Cu): 0.05%, chromium (Cr): 0.25% ): 0.0122%, and the balance of iron (Fe). That is, the steel material according to the embodiment of the present invention is characterized in that aluminum (Al) is in a range of 0.02 to 0.04%, niobium (Nb) is in a range of 0.01 to 0.02%, nitrogen (N) is in a range of 0.010 to 0.025% . The steel material according to the embodiment of the present invention having such a composition had a microhardness of 277 HV, a tensile strength of 896 MPa, a yield strength of 655 MPa, an elongation of 16.9% and an impact toughness value of 88.2 J / cm ² Respectively. It can be seen that the steel according to the above-mentioned Comparative Examples has higher microhardness, tensile strength and yield strength, and impact toughness characteristics are further improved. By adding aluminum, niobium and nitrogen to the comparative example, it is possible to make the crystal grains finer and form fine precipitates to improve the strength.

It is to be understood that the invention includes various modifications and equivalent embodiments that can be derived from the disclosed embodiments as well as those of ordinary skill in the art to which the present invention pertains. Accordingly, the technical scope of the present invention should be defined by the following claims.

Claims (6)

(P): more than 0 and not more than 0.03%, sulfur (S): not more than 0.10% 0.04 to 0.07%, Cu: more than 0 to 0.25%, chromium (Cr): 0.20 to 0.40%, vanadium (V): 0.10 to 0.20%, aluminum (Al): 0.02 to 0.04%, niobium (Nb) : 0.01 to 0.02%, nitrogen (N): 0.010 to 0.025%, balance of iron (Fe) and unavoidable impurities,
Non-tempered steel.
The method according to claim 1,
The steel has a microhardness of 260 to 320 HV, a tensile strength of 870 to 970 MPa, a yield strength of 620 to 700 MPa, an elongation of 16% or more, and an impact toughness value of 80 J / cm ² or more doing,
Non-tempered steel.
The method according to claim 1,
Characterized in that the steel material is in the shape of a bar.
Non-tempered steel.
A front axle beam comprising a component made of said non-tempered steel according to any one of claims 1 to 3.
(P): more than 0 to 0.03%, sulfur (S): 0.04% or less, and more preferably, 0.04 to 0.15% (Al): 0.02 to 0.04%, niobium (Nb): 0.07 to 0.07%, copper: more than 0 to 0.25%, chromium (Cr): 0.20 to 0.40%, vanadium (V) 0.01 to 0.02% of nitrogen (N), 0.010 to 0.025% of nitrogen (N), the balance of iron (Fe) and unavoidable impurities;
(b) subjecting the cast material to reheating and then subjecting to a finish hot rolling at a temperature of 1150 to 1250 占 폚; And
(c) air-cooling the rolled casting material;
Of the non-tempered steel.
6. The method of claim 5,
The steel material realized by performing the steps (a) to (c) has a microhardness of 260 to 320 HV, a tensile strength of 870 to 970 MPa, a yield strength of 620 to 700 MPa, an elongation of 16% , And an impact toughness value of 80 J / cm < ² > or more.
(JP) METHOD FOR MANUFACTURING COATED STEEL.

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