KR20120138956A

KR20120138956A - Steel material having fine crystal garin and method for manufacturing product using the same

Info

Publication number: KR20120138956A
Application number: KR1020110058410A
Authority: KR
Inventors: 이호승
Original assignee: 현대자동차주식회사
Priority date: 2011-06-16
Filing date: 2011-06-16
Publication date: 2012-12-27

Abstract

PURPOSE: A steel material having fine crystal grains and a method for manufacturing products using the same are provided to obtain desired performance without chemical heat treatment such as carburization, thereby reducing manufacturing time and costs. CONSTITUTION: A steel material having fine crystal grains is mainly composed of Fe, and the steel material comprises 0.3-0.8 wt% of C, 0.15-0.5 wt% of Si, 0.5-1.5 wt% of Mn, 0.03 wt% or less(0 is exclusive) of P, 0.01-0.1 wt% of S, 0.5-2.5 wt% of Cr, 0.02-0.1 wt% of Mo, 0.01-0.04 wt% of Nb, 0.0001-0.0005 wt% of B, 0.0002 wt% or less(0 is exclusive) of O, 0.03-0.2 wt% of Ti, and inevitable impurities. A method for manufacturing a product using the steel material comprises the steps of: cutting and hot forging the steel material, mechanically processing the hot forged steel material, processing the material with high frequency, and correcting the heat-treated material. [Reference numerals] (AA) Material cutting; (BB) Hot forging; (CC) Finish cutting; (DD) High-frequency heat treatment; (EE) Correcting

Description

Grain fine grain steel and manufacturing method using the same {STEEL MATERIAL HAVING FINE CRYSTAL GARIN AND METHOD FOR MANUFACTURING PRODUCT USING THE SAME}

The present invention has a carbon content of the medium carbon steel, the addition of Cr, Mo alloy to increase the hardenability, and the addition of Nb, B, Ti to have a fine grain in the high-frequency heat treatment of the fine grain-shaped steel materials and products using the same It relates to a manufacturing method.

At present, shaft parts used in automobile transmissions and chassis parts are subjected to carburizing heat treatment using carburizing steels such as SCr420H and SCM420H in order to satisfy high strength and high toughness. Recently, there is an urgent need for higher strength due to increased fuel economy and higher performance.

Specifically, the chemical composition of the conventional shaft component material has a low carbon of about 0.2 wt%, and Cr and Mo are added at about 1 wt%. 1 is a view showing a method of manufacturing a product using such a conventional steel material, to withstand high-strength torsional fatigue strength, in order to have internal toughness, the surface is subjected to a carburizing heat treatment having a high carbon, the core has a low carbon microstructure It was.

In addition, since the existing process uses a carburized carbon material, the agglomeration structure of ferrite + pearlite may appear. In addition, many deformations occurred after carburizing heat treatment performed at a high temperature for about 2 hours or more, and thus, the correction work after heat treatment was required several times.

Therefore, according to the conventional steel material and the product manufacturing method using the same, it takes a lot of manufacturing time to carry out the carburizing heat treatment, there was a problem that the manufacturing process is complicated by performing a step of a step. In addition, many calibrations have to be performed, resulting in increased manufacturing costs.

Therefore, a new technology for a steel material and a manufacturing method using the same may be required without satisfying the necessary performance without the chemical heat treatment such as carburizing, and thus eliminating the reclamation.

The matters described as the background art are only for the purpose of improving the understanding of the background of the present invention, and should not be taken as acknowledging that they correspond to the related art already known to those skilled in the art.

The present invention has been proposed to solve this problem, it is possible to satisfy the required performance without chemical heat treatment, such as carburization, and can be omitted according to the grain fine grain-shaped steel material that can reduce the calibration work and this Its purpose is to provide a method of manufacturing a used product.

In order to achieve the above object, the crystal grain-shaped steel material according to the present invention has Fe as a main component, C: 0.3 to 0.8 wt%, Si: 0.15 to 0.5 wt%, Mn: 0.5 to 1.5 wt%, and P: 0.03 wt% or less (0 is not included), S: 0.01 ~ 0.1 wt%, Cr: 0.5 ~ 2.5 wt%, Mo: 0.02 ~ 0.1 wt%, Nb: 0.01 ~ 0.04 wt%, B: 0.0001 ~ 0.0005 wt%, O: 0.0002 wt% or less (0 is not included), Ti: 0.03-0.2 wt% and other inevitable impurities.

In addition, the manufacturing method of the product using the grain-like micro-grain steel material, hot forging step for cutting the material and hot forging; A machining step of mechanically processing the hot forged material; Heat treatment step of high frequency heat treatment of the processed material; And a calibration step of calibrating the heat treated material.

Here, in the heat treatment step may be water cooled after heating for 5 seconds at a frequency of 30kHz.

In the calibration step, the calibration may be performed 5 to 10 times with a load of 150 kgf using a three-point bending calibrator.

In particular, the product may be applied as a shaft used in a vehicle transmission or a chassis part.

According to the grain-fine grained steel material having a structure as described above and the manufacturing method of the product using the same, since the use of the fine-grained high-frequency steel has an increase in strength of about 15% compared to the existing carburizing heat treatment products.

In addition, compared to the existing carburizing heat treatment, it is possible to reduce the cost in manufacturing by using a high frequency heat treatment. And, heat treatment time is shortened, environmentally friendly and no emissions of harmful gases. In particular, the number of corrections is reduced in favor of the shaft bending deformation.

1 is a view showing a method of manufacturing a product using a conventional steel material.
Figure 2 is a view showing a method of manufacturing a product using a grain-fine grained steel material according to an embodiment of the present invention.

Hereinafter, with reference to the accompanying drawings looks at with respect to the fine grain-shaped steel material and the manufacturing method of the product using the same according to a preferred embodiment of the present invention.

The technical significance of the components for each composition of the grain-like micro-grained steel as described above is as follows.

For C it contains 0.3 to 0.8 wt%. This is because carbon is a basic element that increases strength in steel, and at least 0.3 wt% of carbon is required for high frequency heat treatment, and more than 0.8 wt% of the carbon may cause workability degradation and toughness degradation. Therefore, carbon needs to be in the range of 0.3 to 0.8 wt%.

Si and silicon are elements used for deoxidation and increase the strength and hardenability of the steel. The high frequency heat treatment material does not heat treatment other than the surface portion, so silicon requires a content of at least 0.15 wt%. However, if the silicon content is more than 0.5 wt%, cold forging is lowered, so the silicon needs to be within the range of 0.15 to 0.5 wt%.

Mn and manganese are elements that enhance the strength and hardenability of the steel. The Mn and manganese are at least 0.5 wt% to increase the hardness of the core without heat treatment, and 1.5 wt% or less to maintain cold forging.

If P and phosphorus are high in content, the brittleness becomes strong during forging, so it is 0.03 wt% or less.

S and sulfur are brittle if the content is high, so 0.1 wt% or less, but when the addition of a small amount of MnS compound to improve the processability, 0.01 wt% or more needs to be within the 0.01 ~ 0.1 wt% range.

Cr and chromium are important elements for strength and hardenability, and the effect is small at less than 0.5 wt%. However, if the Cr content is more than 2.5 wt%, there is a possibility of excessive increase in the amount of retained austenite or chromium carbide. Therefore, the chromium needs to be in the range of 0.4 to 2.5 wt%.

Mo and molybdenum have a material strength improvement effect and hardenability effect when added at 0.02 wt% or higher, and the range is set to 0.02 to 0.1 wt% when added at 0.1 wt% or higher, so that workability may be reduced due to increase in material hardness.

Nb and niobium are elements that combine with carbon and nitrogen in steel to form niobium carbonitride to maintain fine grains, and have an effect even in a trace amount of 0.01 wt% or more. However, when contained in 0.04 wt% or more, since workability may deteriorate, it is necessary to make it within 0.01 to 0.04 wt%.

B, boron is a high-strength element having a high hardenability as an element capable of obtaining high hardenability with addition of a small amount of elements, and serves to increase toughness. The effect can be obtained even in a trace amount of more than 0.0001 wt%, and if the addition is more than 0.0005 wt%, the effect does not increase any more, so it needs to be within the range of 0.0001 to 0.0005 wt%.

O and oxygen play a role of lowering the fatigue strength and toughness of the steel even in a trace amount of 0.0002 wt% or more, so it is necessary to be within 0.0002 wt% or less.

Ti and titanium react with nitrogen and carbon in the steel to form nitrides and nitride carbides to prevent grain growth. When 0.03 wt% or more is contained, the effect of nitride / nitride production can be seen. When 0.2 wt% or more is contained, the coarsened titanium nitride carbide may occur when the workability decreases due to the increase in strength. It is necessary to set it as -0.2 wt%.

On the other hand, the production method of the product using the grain-like grain-shaped steel material, hot forging step for cutting the material and hot forging; A machining step of mechanically processing the hot forged material; Heat treatment step of high frequency heat treatment of the processed material; And a calibration step of calibrating the heat treated material.

That is, according to the grain-fine grained steel material of the present invention can have a fine grain during high frequency heat treatment, it does not perform a separate carburizing heat treatment, saving production time and cost, and also because the carburizing treatment is not necessary, so as to unnecessarily do.

Figure 2 is a view showing a method of manufacturing a product using a grain-like microcrystalline steel material according to an embodiment of the present invention, when producing a product using a grain-like grain-shaped steel material by such a process, fine grains generated high-frequency steel As a result, the strength increase of about 15% compared to the existing carburizing heat treatment products.

On the other hand, in the heat treatment step may be water-cooled after heating for 5 seconds at a frequency of 30kHz. In the calibration step, the calibration may be performed 5 to 10 times with a load of 150 kgf using a three-point bending calibrator. In the conventional case, the degree of deformation of the material is severe due to the carburizing process (which was inevitably generated even if the roughening process was performed), and thus the increase of the effect was remarkably large compared to the fact that the calibration work had to be performed 15 times or more. .

In particular, when the product is applied as a shaft used in a vehicle transmission or chassis parts, it can be said that the effect is excellent in terms of deterioration of deformation, increase in strength, and maintenance of workability.

Tables 1 to 3 below are test results comparing the properties of shaft products using a conventional shaft product and the grain-shaped microscopic steel material of the present invention.

The hardness measurement in the test was measured using the KS B 0811 measuring method, the depth of the effective hardened layer was measured using the KS D 0215 measuring method, the average grain is measured using the KS D 0205 measuring method. Looking at the test results, it can be seen that according to the present invention the surface hardness is further improved and the grains are also finer.

In the case of the calibration, it was calibrated with a 150kgf load using a three-point bending calibrator, it can be seen as normal when the average is 50㎛ or less. As can be seen from the test results, the present invention can be seen that the number of corrections and the amount of correction is significantly reduced.

In the case of the test, the fatigue test was conducted using a hydraulic torsion fatigue tester, and the fatigue strength point was seen to withstand 10 million cycles. As can be seen from the results of this test, it can be seen that the fatigue strength at the limit endurance point is increased according to the present invention.

While the present invention has been particularly shown and described with reference to specific embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the following claims It will be apparent to those of ordinary skill in the art.

Claims

Fe is the main component, C: 0.3-0.8 wt%, Si: 0.15-0.5 wt%, Mn: 0.5-1.5 wt%, P: 0.03 wt% or less (0 is not included), S: 0.01-0.1 wt%, Cr: 0.5 ~ 2.5 wt%, Mo: 0.02 ~ 0.1 wt%, Nb: 0.01 ~ 0.04 wt%, B: 0.0001 ~ 0.0005 wt%, O: 0.0002 wt% or less (0 is not included), Ti: 0.03 ~ 0.2 wt Grain fine grained steel material having a composition containing% and other unavoidable impurities.

As a method of manufacturing a product using the grain-fine grained steel of claim 1,
A hot forging step of cutting the material and hot forging;
A machining step of mechanically processing the hot forged material;
Heat treatment step of high frequency heat treatment of the processed material; And
Method for producing a product using a grain-like fine grained steel material comprising a; correcting step of correcting the heat-treated material.

The method according to claim 2,
In the heat treatment step is a method of manufacturing a product using a grain-fine grain shaped steel material, characterized in that the water is cooled after heating for 5 seconds at a frequency of 30kHz.

The method according to claim 2,
In the calibration step using a three-point bending calibrator, a method of manufacturing a product using a grain-fine grain-shaped steel material, characterized in that for performing 5 to 10 times the calibration with a load of 150kgf.

The method according to claim 2,
The product is a manufacturing method of a product using a grain-fine grain-shaped steel material, characterized in that the shaft used in a vehicle transmission or chassis parts.