KR101882495B1 - Non-nomarlized steel composition, hot forging parts with improved strength comprising the same and method for manufacturing thereof - Google Patents

Abstract

The present invention relates to a method of manufacturing a steel structure comprising carbon (C), silicon (Si), manganese (Mn), sulfur (S), chromium (Cr), vanadium (V) Fe), a hot forged part having improved strength and a method of manufacturing the same, which comprises heating the non-tempered steel composition at a temperature in the range of 1200 to 1300 캜, heating the uncondensed steel composition Is subjected to hot forging in a temperature range of 1000 to 1200 캜, a step of trimming and piercing the hot-forged un-tempered steel composition, a step of hot-coining the trimmed and pierced non- Cooling the uncoated steel composition to a temperature of 600 DEG C, cooling the uncontrolled steel composition to a temperature of 550 to 650 DEG C in a continuous heating belt, The present invention relates to a method for manufacturing a hot forged part and a method for manufacturing the hot forged part, the hot forged part having a high strength compared to a conventional hot forged part, will be.

Description

[0001] The present invention relates to a non-tempered steel composition, a hot forged part having improved strength and a method for manufacturing the same,

The present invention relates to a non-tempered steel composition, a hot forged part having improved strength and a method of manufacturing the same, and more particularly, to a non-tempered steel composition having high strength, light weight and cost reduction by controlling a composition ratio and simplifying a process And a method of manufacturing the same.

In recent years, research has been continuing to suppress exhaust gas emissions such as carbon dioxide gas due to global warming, which is becoming a major issue. The automobile industry has been making efforts to reduce engine output and fuel consumption through lightening of high- In addition, there is an attempt to reduce the manufacturing cost by simplifying the manufacturing process.

Particularly, in the main automotive moving parts such as the connecting rod and the crankshaft, non-tempered steels are generally used. The non-tempered steels can be produced by using mechanical steels (quenching and tempering) And the crankshaft means a device for converting the reciprocating motion of the piston into a rotational motion in an internal combustion engine such as a gasoline engine or a diesel engine. The connecting rod is connected to the crank pin of the crankshaft And a rod portion integrally connecting the small end portion and the large end portion to convert the linear reciprocating motion of the piston into rotational motion.

Conventionally, vanadium (V) is added to the non-tempered steel composition to improve the strength by precipitation of vanadium carbide (VC) (Patent No. 2009-0049642), addition of niobium (No. 10-2010- 0127548), addition of vanadium and niobium complex (Publication No. 10-2010-0027887), or addition of vanadium and zirconium complex (Publication No. 10-2011-0022313). However, the fatigue strength grade And is limited to 43 kgf / mm ² or less.

FIG. 1 is a schematic view illustrating a method of manufacturing a hot forged part including a conventional non-tempered steel composition. As shown in the figure, in order to manufacture a hot forged part, a non-tempered steel composition is heated do.

Next, the heated unconditioned steel composition is subjected to hot forging comprising a buster, a blocker, and a finishing process at a temperature range of 1000 to 1200 캜.

Thereafter, the hot-forged untreated steel composition is subjected to a flashing or piercing process using trimming and punching, which is an operation of removing excess metal.

Then, the trimmed and pierced unconstrained steel composition was controlled and cooled at a cooling rate of 3 DEG C / s to 550 DEG C, and then subjected to a short blast to remove an oxide scale, ).

Thereafter, a coining process is performed in a cold (room temperature) condition for calibrating the bending and thickness dimensions, and annealing is performed in a temperature range of 550 to 650 占 폚 for 60 minutes to remove the residual stress generated during the cold coining process Annealing).

Finally, a short blast treatment is performed again to remove the blackening caused by the annealing treatment.

As described above, the fatigue strength level of the conventional non-tempered steel composition is 43 kgf / mm ² or less, which is a level that can cope with a normal engine output. However, recently, a low exhaust amount engine (GDI, TCI, T- , 7, etc.), there is a problem that it is difficult to cope with the physical properties of conventional non-tempered steel compositions.

In addition, the conventional method for manufacturing a hot forged part using a non-tempered steel composition has a problem in that the production time is prolonged due to two short blast treatments and an annealing process for removing residual stress, resulting in a decrease in productivity and a rise in cost.

In addition, there is also a problem that the coining mark remains due to the cold coining process, thereby reducing the durability of the parts due to the notch effect.

It is an object of the present invention to solve the above-mentioned problems, and an object of the present invention is to provide a non-tempered steel composition which is improved in strength, light in weight and cost reduced by additionally adding vanadium (V) and titanium (Ti) And a method for manufacturing the same.

In order to achieve the above object, the non-tempered steel composition of the present invention comprises carbon, silicon, manganese, sulfur, chromium, vanadium and nitrogen, , And further comprises titanium (Ti) and the balance iron (Fe).

In an embodiment of the present invention, titanium (Ti) is preferably 0.01 to 0.2% by weight based on the total weight of the composition.

In one embodiment of the present invention, the non-tempered steel composition comprises 0.30 to 0.55 wt% of carbon (C), 0.8 to 1.2 wt% of silicon (Si), 0.8 to 1.20 wt% of manganese (Mn) (V) and 0.005 to 0.020% by weight of nitrogen (N), more preferably not more than 0.10% by weight, more than 0% by weight and less than 0.2% by weight of chromium (Cr)

In order to achieve still another object, the hot forged part of the present invention is characterized by being a hot forged part having improved strength including the non-tempered steel composition.

According to another aspect of the present invention, there is provided a method of manufacturing a hot forged part, the method including the steps of heating the non-tempered steel composition at a temperature in the range of 1200 to 1300 캜, heating the un- A step of subjecting the non-tempered steel composition subjected to the hot forging treatment to a trimming and a piercing treatment, a step of subjecting the non-tempered steel composition subjected to the trimming and piercing treatment to a hot coining treatment Cooling the uncoated steel composition subjected to the hot coining treatment to 600 ° C; keeping the controlled cooled unconstrained steel composition in a temperature range of 550 to 650 ° C on a continuous heating belt; Blast-treating the composition of the present invention.

In addition, the step of performing hot coining according to an embodiment of the present invention is preferably performed by hot coining in a temperature range of 800 to 1000 ° C.

Further, in the control cooling step according to an embodiment of the present invention, the cooling rate is preferably 3 DEG C / sec.

Further, in the embodiment of the present invention, it is preferable that the warming step is maintained warm for 20 minutes or more until the residual stress is removed.

The advantage of the present invention having the above-described structure is that the durability is improved and the weight of the component is reduced as compared with the conventional non-tempered steel composition, so that the present invention can be applied to harsh conditions such as a high output engine.

Further, according to the present invention, the shot blast process is omitted after cooling and the residual stress relief heat treatment process is shortened to simplify the entire process, thereby shortening the process time and reducing the cost.

In addition, unlike the conventional cold coining process, there is an advantage in that the durability of parts due to the notch effect is not lowered because the coining marks are hardly left.

1 is a schematic view showing a method of manufacturing a hot forged part including a conventional non-tempered steel composition.
FIG. 2 is a schematic view showing a method of manufacturing a hot forged part having improved strength including the non-tempered steel composition of the present invention.
3 is a graph showing fatigue strength according to the rotational speeds of Examples 1, 3 and Comparative Example 2. FIG.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

In one aspect, the present invention relates to a method of manufacturing a semiconductor device including at least one selected from the group consisting of carbon (C), silicon (Si), manganese (Mn), sulfur (S), chromium (Cr), vanadium (V) Iron (Fe) which is a non-welded steel composition.

Name of material C Si Mn S Cr V N Ti Fe Invention 0.30
~ 0.55 0.8
~ 1.2 0.8
~ 1.20 0.06
~ 0.10 0.2
Below 0.20
~ 0.35 0.005
~ 0.020 0.01
~ 0.2 Rem.

Table 1 shows the composition of the non-tempered steel composition according to the present invention.

As shown in Table 1, in the non-tempered steel composition according to the present invention,

(Si), 0.8 to 1.2 wt% of silicon (Si), 0.8 to 1.20 wt% of manganese (Mn), 0.06 wt% or more of sulfur (S), 0.10 wt% or less of chromium (Cr) (V) of from 0.20 to 0.35% by weight and nitrogen (N) of from 0.005 to 0.020% by weight,

0.01 to 0.2% by weight of titanium (Ti) and the balance iron (Fe).

At this time, the carbon (C) is preferably at least 0.30% by weight in order to increase the strength and hardness of the material and to obtain the desired mechanical strength as an element essential for the deposition of the carbide by the fine alloy element, It is preferably 0.55% by weight or less.

The silicon (Si) is preferably at least 0.8% by weight for strengthening the ferrite matrix structure as a stabilizing element for facilitating breakage of the connecting rod large end portion, and is preferably 1.2% by weight or less in consideration of the possibility of component removal .

The manganese (Mn) is a deoxidation or desulfurizing agent which produces manganese sulfide (MnS) inclusion and prevents an increase in toughness. In order to obtain a desired mechanical strength, the manganese (Mn) preferably has a content of not less than 0.8 wt% It is preferably 1.20% by weight or less.

The sulfur (S) is an element which bonds with manganese (Mn) to produce manganese sulfide (MnS) inclusions and improves the workability. In order to improve the workability of the high strength steel, it is preferably more than 0.06% by weight, Considering the defect, it is preferably 0.10% by weight or less.

In addition, the chromium (Cr) is an element which improves the incombustibility and increases the strength. It is preferably more than 0% by weight, and is preferably 0.2% by weight or less in view of the cost and economical efficiency of the expensive furnace material.

The vanadium (V) is an element for increasing the strength of a material by precipitating fine vanadium carbonitrides (VCN). In order to obtain a desired fatigue strength, vanadium (V) is preferably not less than 0.20 wt% By weight or less is preferable.

The nitrogen (N) is an element which binds with vanadium (V) and binds to vanadium carbonitrides (VCN) and titanium (Ti) to precipitate titanium carbonitride (TiCN) Or more, and it is preferably 0.020% by weight or less in consideration of the strength reduction and saturation of the effect due to the addition.

The titanium (Ti) is an element which increases the yield strength and the fatigue strength due to grain refinement by producing titanium carbonitride (TiCN). It is preferably 0.01% by weight or more for the purpose of generating sufficient fine precipitates, 0.2% by weight or less is preferable.

In another aspect, the present invention relates to a hot-forged part having improved strength comprising the composition and a method of manufacturing the same.

Forging refers to a process of finely grinding a crystal by applying a static or dynamic pressure in a state in which a plastic is flowed well to a metal to uniformize the texture and to shape it into a predetermined shape, Heating and forging are referred to as hot forging, and automobile connecting rods and crank shafts are typical hot forged parts including a non-tempered steel composition.

FIG. 2 is a schematic view showing a method of manufacturing a hot forged part having improved strength including the non-tempered steel composition of the present invention.

As shown in the figure, the non-tempered steel composition is first heated in a temperature range of 1200 to 1300 ° C as in the conventional method of manufacturing a hot forged part using a non-tempered steel composition.

Then, the heated unconditioned steel composition is subjected to a buster process at a temperature range of 1000 to 1200 ° C, a broker process using a broker-die to make an approximate shape, A hot forging process comprising a finisher process using a finisher-die is performed.

Thereafter, the non-tempered steel composition subjected to the hot forging treatment is subjected to a piercing treatment such as trimming and punching, which is an operation of removing extra metal formed as a thin thin plate on the outer surface of a flash or the like.

Unlike the conventional control cooling process, the coining process is performed first. The coining is a process of applying pressure to the front or a part of the forged product in order to obtain a more precise tolerance and a smooth surface. The bending and thickness dimensions For the calibration.

At this time, in order to prevent the occurrence of the notch effect by the coining process by the coining process, it is preferable to perform the coining process at a temperature of 800 占 폚 or more and 1000 占 폚 or less to obtain a sufficient effect by the coining process.

Next, in order to obtain the desired strength and other physical properties, the uncoated steel composition subjected to the coining treatment is controlled and cooled to 600 ° C. In order to minimize the formation of bainite and convert it into a ferrite-pearlite structure, s. < / RTI > That is, if the cooling rate is excessively low, bainite is generated, and if it is quenched, martensite is generated, and it is necessary to appropriately adjust it.

Thereafter, it is warmed to a temperature range of 550 to 650 ° C in a continuous heating belt covered with a cover to remove residual stress generated in the hot coining and cooling process, at least until the residual stress is removed in the temperature range It is desirable to keep warm for 20 minutes or more.

Thereafter, the surface of the non-tempered steel composition maintained in the warm state is shot blasted to smooth the surface.

That is, in the method of manufacturing a hot forged part including a conventional non-tempered steel composition, a separate shot blasting process is omitted after control cooling, and residual stress is reduced due to hot coining rather than cold coining, The time required for the stress relief heat treatment process is shortened, and as a result, the manufacturing cost is reduced.

In addition, since the coining marks are hardly left by hot coining, there is no problem of durability degradation of parts due to the notch phenomenon.

Hereinafter, the present invention will be described in more detail with reference to Examples. It is to be understood by those skilled in the art that these embodiments are merely illustrative of the present invention and that the scope of the present invention is not construed as being limited by these embodiments.

division
Chemical composition (% by weight) Mechanical Properties (MPa) C Si Mn S Cr V Ti N Fe YS TS fatigue Comparative Example 1 0.7 0.2 0.5 0.06 0.12 0.03 - 0.008 Rem. 540 920 343 Comparative Example 2 0.38 0.71 1.00 0.06 0.12 0.26 - 0.012 Rem. 712 964 441 Example 1 0.37 0.95 1.00 0.07 0.12 0.27 0.08 0.011 Rem. 842 1061 519 Example 2 0.67 1.0 0.81 0.08 0.13 0.14 0.01 0.012 Rem. 656 1077 412 Example 3 0.43 1.1 0.8 0.09 0.10 0.32 0.04 0.015 Rem. 849 1124 570 Example 4 0.42 0.9 0.8 0.09 0.10 0.27 - 0.015 Rem. 726 978 451

(YS: Yield Strength, TS: Tensile Strength)

Table 2 is a table showing the mechanical properties of a non-tempered steel composition and a method of manufacturing hot forged parts including the same.

Specifically, Comparative Example 1 and Comparative Example 2 show mechanical properties of a conventional non-tempered steel composition and a hot forged part including the same,

Example 2 shows the mechanical properties of a non-tempered steel composition containing titanium (Ti) but not satisfying the composition ratio of the present invention and a method of manufacturing a hot forged part including the same.

Example 4 shows the mechanical properties of the non-tempered steel composition without the addition of titanium (Ti) and the method of manufacturing the hot forged part including the same, although the composition ratio of the non-tempered steel composition of the present invention is satisfactory.

Examples 1 and 3 show the mechanical properties of the unconstrained steel composition of the present invention and the method of manufacturing the hot forged part including the same, wherein the yield strength, the tensile strength, and the fatigue strength are both excellent . ≪ / RTI >

Fig. 3 is a graph showing fatigue strengths according to the rotational speeds of Examples 1, 3 and Comparative Example 2. As shown in Fig. 3, the fatigue strengths of Examples 1 and 3 were higher than those of Comparative Example 2 .

As described above, the non-tempered steel composition of the present invention, the hot forged part having improved strength, and the manufacturing method thereof have tensile strength of 10%, yield strength of 20% and fatigue strength of 15% By adjusting the composition ratio, the weight is reduced by 15% (based on 1.6L diesel engine: 0.33kg / unit). By simplifying the manufacturing process, manufacturing costs can be reduced and it can be used for hot forging parts such as connecting rods and crankshafts. have.

Claims (8)

(Si), 0.8 to 1.2 wt% of silicon (Si), 0.8 to 1.20 wt% of manganese (Mn), 0.06 wt% or more of sulfur (S), 0.10 wt% or less of chromium (Cr) (V), 0.005 to 0.020 wt% of nitrogen (N), 0.01 to 0.2 wt% of titanium (Ti), and the balance iron (Fe).
delete delete An improved strength hot forged part comprising the non-tempered steel composition of claim 1.
(C), silicon (Si), manganese (Mn), sulfur (S), chromium (Cr), vanadium (V), nitrogen (N), titanium Heating the vaginal composition at a temperature ranging from 1200 to 1300 캜;
Hot forging the heated uncondensed steel composition at a temperature in the range of 1000 to 1200 캜;
Treating the hot-forged untreated steel composition by trimming and piercing;
Subjecting the non-tempered steel composition subjected to the trimming and piercing treatment to a hot coining treatment;
Cooling the uncoated steel composition subjected to hot coining to 600 ° C;
Maintaining the controlled-cooled un-tempered steel composition in a continuous heating belt at a temperature ranging from 550 to 650 캜;
Blast-treating the non-tempered steel composition that is kept warm; And the strength of the hot forged part is improved.
6. The method of claim 5, wherein the hot coining step comprises hot coining at a temperature ranging from 800 to 1000 < 0 > C.
The method of manufacturing a hot forged part according to claim 5, wherein the controlled cooling step has a cooling rate of 3 DEG C / sec.
6. The method of claim 5, wherein the warming step is maintained warm for at least 20 minutes until the residual stress is removed.

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