KR20130110615A - Bar steel for shaft and method of manufacturing the same - Google Patents

Abstract

PURPOSE: An iron bar for a shaft and a manufacturing method thereof are provided to add a grinding process removing surface defects of a half-finished slab so that an excellent surface quality is obtained. CONSTITUTION: A method for manufacturing an iron bar for a shaft includes the following steps of: forming molten steel comprising 0.36-0.39 wt% of C, 0.1-0.4 wt% of Si, 0.7-1.1 wt% of Mn, 0.035 wt% or less of P, 0.03 wt% or less of S, 0.03-0.06 wt% of Ti, 0.0008-0.0050 wt% of B, and the rest of Fe and unavoidable impurities; grinding the surface of a slab; reheating the slab at a temperature of 1100-1250°C and hot-rolling the reheated slab; and cooling the hot-rolled slab at a temperature of 500-600°C. [Reference numerals] (AA) Start; (BB) End; (S110) Casting; (S120) Grinding; (S130) Hot-rolling; (S140) Cooling

Description

TECHNICAL FIELD [0001] The present invention relates to a shaft for a shaft,

The present invention relates to a shaft steel bar and a method of manufacturing the same, and more particularly, to a shaft steel bar having excellent surface characteristics that can be used by pulling a bar having a length of 20 to 40 mm by grinding a cast steel in a semi-finished product state, .

In the case of parts for automotive shafts, the raw material is used by drawing wire materials with a diameter of 15 mm or less, which have almost no surface defects, in order to prevent defects such as cracks on the product surface. On the other hand, when a rod having a diameter of 20 mm or more is used as a shaft component for an automatic head, the surface is used by being peeled.

At this time, there is a problem that the cost of the material is relatively high, whereas the surface quality of the wire is good. On the other hand, in the case of the bar, there is a favorable aspect in terms of manufacturing cost compared with the wire, but the bad quality of the surface quality is a disadvantage, and it is urgent to solve it.

Related prior arts are Korean Patent Registration No. 10-0398375 (2003.12.18 publication), which discloses a method of manufacturing non-coarse steel wire for high frequency quenching.

An object of the present invention is to provide a method for manufacturing a shaft steel rod having excellent surface characteristics that can be used by drawing a rod having a diameter of 20 to 40 mm by grinding a cast steel in a semi-finished product state.

Another object of the present invention is to provide a process for producing a polypropylene having a tensile strength (TS) of 800 to 950 MPa, a yield strength (YS) of 650 to 750 MPa, an elongation (EL) of 15 to 25% and an impact value of 5 J / Can be satisfied.

Steel bar manufacturing method for a shaft according to an embodiment of the present invention for achieving the above object is (a) wt%, C: 0.36 ~ 0.39%, Si: 0.1 ~ 0.4%, Mn: 0.7 ~ 1.1%, P: 0.035 Forming a molten metal composed of% or less, S: 0.03% or less, Ti: 0.03 to 0.06%, B: 0.0008 to 0.0050% and the remaining iron (Fe) and other unavoidable impurities, and then casting the cast into a semi-finished slab; (b) grinding the surface of the cast steel; (c) reheating the grinding-treated cast slab at 1100 to 1250 占 폚, followed by hot rolling; And (d) cooling the hot-rolled steel slab to 500 to 600 ° C.

Steel bar for the shaft according to an embodiment of the present invention for achieving the above another object by weight, C: 0.36 ~ 0.39%, Si: 0.1 ~ 0.4%, Mn: 0.7 ~ 1.1%, P: 0.035% or less, S : 0.03% or less, Ti: 0.03 ~ 0.06%, B: 0.0008 ~ 0.0050% and the remaining iron (Fe) and other unavoidable impurities, tensile strength (TS): 800 ~ 950MPa and yield strength (YS): 650 ~ It has a 750MPa, the average diameter is 20 ~ 40mm, it is ground in a semi-finished state is characterized by having a surface defect of 0.05mm or less.

By adding a grinding process to remove surface flaws in a semi-finished product, excellent surface quality can be ensured in the product state after hot rolling. In particular, the product with the surface defect in the surface defect inspection step can be screened, so that it is possible to select and pull out only the bar with almost no surface defects, and also to remove the surface defect material at the final inspection stage after the drawing. Since the screen can be sorted, it is possible to manufacture a material having almost no surface defects with a surface flaw of 0.05 mm or less in the process for finally manufacturing the shaft parts.

In addition, since the present invention can manufacture a shaft component using a bar made of a steel which is less expensive than a wire rod, a cost saving effect can be expected. In addition, the present invention is advantageous in terms of cost because it can apply a drawing process with little loss of material in place of a filling process with a large loss of material.

1 is a flowchart showing a method of manufacturing a shaft steel bar according to an embodiment of the present invention.
FIG. 2 is a photograph showing a shaft manufactured using a rod for a shaft according to an embodiment of the present invention. FIG.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. It should be understood, however, that the invention is not limited to the disclosed embodiments, but is capable of many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, To fully disclose the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

Hereinafter, a shaft steel bar according to a preferred embodiment of the present invention and a method of manufacturing the same will be described in detail with reference to the accompanying drawings.

Shaft bar

The rod for a shaft according to the present invention has a tensile strength (TS) of 800 to 950 MPa, a yield strength (YS) of 650 to 750 MPa, an elongation (EL) of 15 to 25% and an impact value of 5 J / .

To this end, the steel bar for the shaft according to the present invention in weight%, C: 0.36 ~ 0.39%, Si: 0.1 ~ 0.4%, Mn: 0.7 ~ 1.1%, P: 0.035% or less, S: 0.03% or less, Ti: 0.03 to 0.06%, B: 0.0008 to 0.0050%, and the remaining iron (Fe) and other unavoidable impurities.

Hereinafter, the role and content of each component contained in the shaft steel bar according to the present invention will be described.

Carbon (C)

Carbon (C) is added to secure the strength. In addition, the carbon (C) is a major element that determines the strength and hardness of the steel, the higher the content, the strength increases, and combines with sulfur (S) to form a carbohydrate to increase the machinability.

The carbon (C) is preferably added in a content ratio of 0.36 to 0.39% by weight based on the total weight of the shaft steel bars according to the present invention. When the content of carbon (C) is less than 0.36% by weight, it may be difficult to secure sufficient strength. Conversely, when the content of carbon (C) exceeds 0.39% by weight, it is advantageous in securing strength but it is difficult to secure toughness.

Silicon (Si)

Silicon (Si) is added as a deoxidizer for removing oxygen in the steel and also serves to enhance the solid solution strengthening effect.

The silicon (Si) is preferably added at a content ratio of 0.1 to 0.4% by weight based on the total weight of the shaft steel bars according to the present invention. When the content of silicon (Si) is less than 0.1% by weight, the deoxidation effect and the solid solution strengthening effect due to the addition of silicon are insufficient. On the contrary, when the content of silicon (Si) exceeds 0.4% by weight, the toughness is lowered.

Manganese (Mn)

In the present invention, manganese (Mn) is a very effective element for improving the strength by refining bainite structure. In addition, manganese (Mn) increases the plasticity at high temperatures to improve castability. And manganese (Mn) is combined with sulfur (S) to form MnS to prevent red brittleness and improve the machinability.

The manganese (Mn) is preferably added at a content ratio of 0.7 to 1.1% by weight based on the total weight of the shaft steel bars according to the present invention. When the content of manganese (Mn) is less than 0.7% by weight, the effect of strengthening solubility and securing strength due to the addition of manganese is insufficient. On the other hand, when the content of manganese exceeds 1.1% by weight, the toughness is lowered and the manufacturing cost is increased.

Phosphorus (P)

Phosphorus (P) is added to improve machinability. However, when the content of phosphorus (P) exceeds 0.035 wt% in the shaft steel bar according to the present invention, there is a problem that toughness and fatigue resistance are deteriorated. Therefore, in the present invention, the content of phosphorus (P) was limited to 0.035% by weight or less of the total weight of the steel bar for the shaft.

Sulfur (S)

Sulfur (S) is added to improve machinability or processability.

However, when the content of sulfur (S) in the shaft steel bar according to the present invention is more than 0.03% by weight, not only center segregation but also micro segregation is formed, which adversely affects the material and may deteriorate the weldability. Therefore, in the present invention, the content of sulfur (S) was limited to 0.03% by weight or less of the total weight of the steel bar for the shaft.

Titanium (Ti)

Titanium (Ti) is a strong carbonitride-forming element that precipitates solid carbon and solid nitrogen to improve non-vitrification and processability. In particular, titanium (Ti) prevents Boron (B) from being precipitated as a nitride precipitate, and boron is present in a solid state in the steel so that boron serves to improve the hardenability of the steel.

The titanium (Ti) is preferably added at a content ratio of 0.03 to 0.06% by weight based on the total weight of the shaft for a shaft according to the present invention. If the content of titanium (Ti) is less than 0.03% by weight, there is a problem that age hardening occurs due to the solid solution carbon and the solid solution nitrogen remaining without precipitation. On the contrary, when the content of titanium (Ti) exceeds 0.06% by weight, the performance is deteriorated and the manufacturing cost is increased without any additional effect.

Boron (B)

Boron (B) is a strong incipient element, which plays a role in blocking segregation of phosphorus (P) and improving strength. If segregation of phosphorus (P) occurs, secondary processing brittleness may occur, so boron (B) is added to block segregation of phosphorus (P) to increase resistance to process embrittlement.

The boron (B) is preferably added in a content ratio of 0.0008 to 0.0050% by weight based on the total weight of the steel sheet according to the present invention. When the content of boron (B) is less than 0.0008% by weight, the amount of boron (B) is insufficient, so that the above effect can not be exhibited properly. On the other hand, if the boron (B) content is over 0.0050 wt%, the formation of boron oxide may cause a problem of deteriorating the surface quality of the steel sheet.

Manufacturing method of shaft steel for shaft

1 is a flowchart showing a method of manufacturing a shaft steel bar according to an embodiment of the present invention.

Referring to FIG. 1, the illustrated method of manufacturing a shaft for a shaft may include a casting step S110, a grinding step S120, a hot rolling step S130, and a cooling step S140.

casting

In the casting step (S110), in weight%, C: 0.36 to 0.39%, Si: 0.1 to 0.4%, Mn: 0.7 to 1.1%, P: 0.035% or less, S: 0.03% or less, Ti: 0.03 to 0.06%, B: A molten metal composed of 0.0008 to 0.0050% and the remaining iron (Fe) and other unavoidable impurities is formed and cast into a cast product in a semi-finished state. At this time, the billet or bloom is referred to as a semi-finished billet.

Grinding

In the grinding step (S120), the surface of the cast steel in the semi-finished product having the above composition is grinded. At this time, the grinding process is carried out for the purpose of physically removing surface flaws existing on the surface of the slab in the semi-finished product state by using a grinder. By this grinding process, the surface of the cast steel in the semi-finished product state can be transformed into a smooth state. As a result, the surface quality can be improved in the product state after hot rolling, which will be described later. Such a grinding process can be performed for about 10 seconds or more, but it is not necessarily limited thereto.

Hot rolling

In the hot rolling step (S130), the grinding-treated cast steel is reheated at 1100 to 1250 DEG C and hot-rolled. At this time, reheating is carried out for the purpose of reusing segregated components in casting.

In this step, when the reheating temperature is lower than 1150 占 폚, the temperature is too low to increase the rolling load. On the other hand, when the reheating temperature is higher than 1250 占 폚, the austenite grains are coarsened and it is difficult to secure the strength of the steel to be produced.

On the other hand, in this step, hot rolling is preferably performed at a finish hot rolling temperature of 800 to 840 캜. If the finish hot rolling temperature is less than 800 ° C, the microstructure may be unevenly distributed, which may act as a factor for hindering the workability. On the other hand, when the final hot rolling temperature (FDT) exceeds 840 DEG C, a large amount of cooling water is required due to a large deviation from the cooling end temperature to be described later, and the brittleness of the steel sheet is increased.

Cooling

In the cooling step (S140), the hot-rolled cast steel is cooled to 500 to 600 占 폚.

At this stage, when the cooling end temperature is less than 500 ° C, a large amount of low-temperature transformed structure is formed and the toughness is rapidly lowered. On the other hand, when the cooling end temperature exceeds 600 ° C, there is a problem that the strength is insufficient due to the coarse microstructure formation.

On the other hand, in this step, the cooling rate is preferably 5 to 50 ° C / sec. If the cooling rate is less than 5 DEG C / sec, it may be difficult to secure strength. On the other hand, when the cooling rate exceeds 50 DEG C / sec, there is a problem that the structure is weakened and the toughness is rapidly lowered.

After the cooling step (S140), air cooling may proceed to room temperature.

The shaft steel bars manufactured in the above-described processes (S110 to S140) can grind excellent-surface characteristics by grinding the semi-finished steel products. Through this, it is possible to draw a bar having an average diameter of 20 to 40mm, and to select the surface defects again in the final inspection step after drawing, so that the surface defects in the process for manufacturing the shaft-like parts are finally 0.05 It may be possible to produce a material having mm or less. This makes it possible to produce a shaft-like component by pulling out a bar having an average diameter of 20 to 40 mm without performing peeling processing.

Also, the rod for a shaft manufactured by the above process satisfies a tensile strength (TS) of 800 to 950 MPa, a yield strength (YS) of 650 to 750 MPa, an elongation (EL) of 15 to 25% and an impact value of 5 J / .

Although not shown in the drawings, the method for manufacturing a shaft steel bar according to the present invention may further include a surface defect inspection step (not shown), a drawing / machining step (not shown), and a high frequency heat treatment step (not shown).

In the surface defect inspection step, surface defects of the bar are inspected. This surface defect inspection step may be performed visually or by using an inspection apparatus. For example, in the surface defect inspection step, materials having a surface flaw of 0.05 mm or less and materials having a surface flaw of more than 0.05 mm are classified. If the surface flaw of the steel bar is 0.05 mm or less, the subsequent process is performed. On the contrary, if the surface flaw of the steel bar is 0.05 mm or more, the process may be performed by separately sorting and discarding or by additionally peeling. Can proceed.

In the drawing / machining step, the bar is drawn and processed into a uniform shape. In this drawing / machining step, to produce the compressive residual stresses on the surface of the bar, the drawing is performed in accordance with the dimensions of the final product, followed by cutting to a proper size and cutting to produce the final product shape.

In the high-frequency heat treatment step, high-frequency heat treatment is applied to the processed steel bars. By such high-frequency heat treatment, strength and toughness suitable for the final product can be ensured.

As described above, the shaft steel bar according to the embodiment of the present invention can provide excellent surface quality in the product state after hot rolling by adding a grinding process to remove surface flaws on the semi-finished product. In particular, products with surface defects in the surface defect inspection step can be screened, so that it is possible to select and pull out only steel bars having almost no surface defects, and also to remove the surface defects in the final inspection stage after drawing. Since the screen can be sorted, it is possible to manufacture a material having almost no surface defects with a surface flaw of 0.05 mm or less in the process for finally manufacturing the shaft parts.

Example

Hereinafter, the configuration and operation of the present invention through the preferred embodiment of the present invention will be described in more detail. It is to be understood, however, that the same is by way of illustration and example only and is not to be construed in a limiting sense.

Details that are not described herein will be omitted since those skilled in the art can sufficiently infer technically.

1. Preparation of specimens

Table 1 shows the component compositions for the specimens according to Examples 1 and 2 and Comparative Examples 1 and 2. At this time, the specimens having compositions according to Examples 1 and 2 were melted in a vacuum induction melting furnace (VIM), cast into billets, and then subjected to grinding treatment for 30 seconds. Thereafter, after reheating at 1200 ° C, the product was subjected to finish hot rolling so as to have a bar shape of 30 mm diameter at 830 ° C, and then water-cooled to 570 ° C. On the other hand, the specimens having compositions according to Comparative Examples 1 and 2 were melted in a vacuum induction melting furnace (VIM), cast into billets, reheated at 1200 ° C and finally subjected to finish hot rolling at 830 ° C to have a rod shape having a diameter of 30 mm, And water-cooled to 570 ° C.

TABLE 1 (% by weight)

2. Evaluation of mechanical properties

Table 2 shows the mechanical property results for the specimens according to Examples 1 and 2 and Comparative Examples 1 and 2.

[Table 2]

(TS): 800 to 950 MPa, yield strength (YS): 650 to 750 MPa, and elongation (EL) corresponding to the target values for the specimens prepared according to Examples 1 and 2, ): 15 to 25% and the impact value: 5 J / cm < 2 > or less.

On the other hand, most of the alloy components are added in a similar amount as in Example 1, but carbon (C), sulfur (S) and titanium (Ti) are added in excess of the content range shown in the present invention, In the case of the specimens prepared according to Comparative Examples 1 and 2 which were not conducted, the tensile strength TS and the yield strength YS satisfied or exceeded the target value, while the elongation (EL) Value is not satisfied. In particular, in the case of the specimens prepared according to Comparative Examples 1 and 2, it can be confirmed that the surface groove is out of the target value, which is believed to be due to not performing the grinding treatment.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. Such changes and modifications are intended to fall within the scope of the present invention unless they depart from the scope of the present invention. Accordingly, the scope of the present invention should be determined by the following claims.

S110: Casting step
S120: Grinding step
S130: Hot rolling step
S140: cooling step

Claims (6)

(a) By weight, C: 0.36 to 0.39%, Si: 0.1 to 0.4%, Mn: 0.7 to 1.1%, P: 0.035% or less, S: 0.03% or less, Ti: 0.03 to 0.06%, B: 0.0008 Forming a molten metal composed of ˜0.0050% and the remaining iron (Fe) and other unavoidable impurities, and then casting the cast into a semi-finished product;
(b) grinding the surface of the cast steel;
(c) reheating the grinding-treated cast slab at 1100 to 1250 占 폚, followed by hot rolling; And
(d) cooling the hot-rolled cast steel to 500 to 600 占 폚.
The method of claim 1,
After the step (c)
Wherein the cast steel has a bar shape having an average diameter of 20 to 40 mm.
The method of claim 1,
In the step (c)
And the finish hot rolling temperature is 800 to 840 占 폚.
The method of claim 1,
After the step (d)
(e) inspecting the surface defects of the bar steel,
(f) drawing the bar steel, drawing it, and subjecting it to high-frequency heat treatment.
By weight%, C: 0.36 to 0.39%, Si: 0.1 to 0.4%, Mn: 0.7 to 1.1%, P: 0.035% or less, S: 0.03% or less, Ti: 0.03 to 0.06%, B: 0.0008 to 0.0050% And the remaining iron (Fe) and other unavoidable impurities,
Tensile strength (TS): 800 ~ 950MPa and Yield strength (YS): 650 ~ 750MPa, the average diameter is 20 ~ 40mm, grinding for the semi-finished state, characterized in that the surface has a surface defect of 0.05mm or less Steel bar.
The method of claim 5,
The bar-
An elongation (EL) of 15 to 25% and an impact value of 5 J / cm < 2 > or less.

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