KR20020053398A - A microalloyed steel with high strength bainitic structure - Google Patents

Abstract

PURPOSE: A microalloyed steel for automobile components is provided, which is able to have high strength bainitic structure without quenching-tempering treatment. CONSTITUTION: Automobile components of the present invention are manufactured by heating a bainite microalloyed steel comprising C 0.25 to 0.30 wt%, Si 0.15 to 0.35 wt%, Mn 1.6 to 2.0 wt%, P less than 0.014 wt%, S less than 0.03 wt%, Cr 0.2-0.3 wt%, V 0.15-0.2 wt%, Ni less than 0.015 wt%, Ti less than 0.015 wt% and a balance of Fe at 1250°C; and cooling at a rate of higher than 30°C/min right after hot working.

Description

A microalloyed steel with high strength bainitic structure

The present invention relates to an amorphous steel having a high-strength bainite-based structure, a manufacturing method, and a component manufactured using the same. Specifically, the main component is iron, and carbon, silicon, manganese, phosphorus, sulfur, chromium, vanadium, After manufacturing non-coated steel containing nickel and titanium through continuous casting, using non-coated steel, which can omit the heat treatment after hot processing and manufacture the final product at the same time with cooling, manufacturing method and manufactured by using the same It is about parts.

Background Art [0002] The chassis parts of a conventional automobile are made of carbon steel as a material. The carbon steel is 0.42 to 0.48% by weight, Si: 0.15 to 0.35% by weight, Mn: 0.60 to 0.90% by weight, P: 0.030% by weight or less, S: 0.03% by weight or less, and the rest is composed of an alloy composition composed of Fe. have.

In the case of manufacturing a chassis part using carbon steel, the alloy composition is heated to about 1250 ° C. and then molded using a hammer or a press, and then quenched and tempered to increase strength and toughness. This heat treatment is prepared by heating the chassis parts once molded to 800 ℃ ~ 900 ℃ and then quenched, tempering again at 400 ℃ ~ 600 ℃ ( Figure 1 ).

As a result, the manufacturing process of the product is complicated, environmental pollution can be caused by the use of coolant in the quenching process after heat treatment, and the overall cost is increased. In addition, as the performance of automobiles is gradually becoming higher in functionality and higher output, it is required to develop components of a new alloy composition having higher strength and toughness.

The present inventors, as a result of trying to solve the above problems, C: 0.25 ~ 0.30% by weight, Si: 0.15 ~ 0.35% by weight, Mn: 1.6 ~ 2.0% by weight, P: 0.014% by weight or less, S: 0.03% by weight or less , Cr: 0.2 to 0.3% by weight, V: 0.15 to 0.2% by weight, Ni: 0.015% by weight or less, Ti: 0.015% by weight or less, and the remainder was prepared by the continuous casting process alloy composition consisting of Fe, the alloy composition The present invention was completed by presenting the bainite-based non-coarse steel structure in terms of excellent mechanical strength and simplification of the product process.

An object of the present invention is to provide a high-strength bainite-based non-alloyed steel, a manufacturing method and an automotive part manufactured by using the same, the manufacturing process is simple and the mechanical strength is improved.

1 illustrates a heat treatment and cooling process used in manufacturing a conventional carbon steel hot forging,

Figure 2 shows the heat treatment and cooling process used in the manufacture of high strength bainite-based non-steel forgings of the present invention.

In order to achieve the above object, the present invention is C: 0.25-0.30 wt%, Si: 0.15-0.35 wt%, Mn: 1.6-2.0 wt%, P: less than 0.014 wt%, S: less than 0.03 wt%, Cr: It provides 0.2 to 0.3% by weight, V: 0.15 to 0.2% by weight, Ni: less than 0.015% by weight, Ti: less than 0.015% by weight, and the remainder is composed of Fe.

In addition, the present invention is produced by continuously casting the bainite-based non-alloy steel alloy composition configured in the same manner as the above, and then made of a round bar material, and at the same time cooling without heat treatment after hot processing at high temperature when manufacturing automotive parts using this material It provides a method for manufacturing the final part.

Finally, the present invention is a component manufactured through a controlled cooling process of heating the raw material of the bainite-based non-alloy steel alloy composition configured in the same manner as above to 1250 ° C and then cooling at a rate of 30 ° C / min or more at the same time as the hot working to provide.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The present invention is C: 0.25-0.30 wt%, Si: 0.15-0.35 wt%, Mn: 1.6-2.0 wt%, P: less than 0.014 wt%, S: less than 0.03 wt%, Cr: 0.2-0.3 wt%, V : 0.15 to 0.2% by weight, Ni: less than 0.015% by weight, Ti: less than 0.015% by weight, and the remainder is provided a bainite-based non-alloyed steel alloy composition.

The bainite structure is a microstructure composed of two phases of ferrite and cementite, and is generally formed when the austenite steel is quenched between a temperature below the pearlite region and a temperature above the martensite transformation start temperature. These bainite tissues exhibit high toughness compared to quenched and tempered tissues.

The alloy composition of the present invention controls the chemical composition to have a bainite structure. First, carbon is a basic element for determining the strength, and the carbon concentration is adjusted to 0.25-0.30 wt% to generate bainite structure and to secure proper toughness. The carbon contained in the alloy composition of the present invention is controlled to a less content than the conventional carbon steel, if the concentration of carbon is high, the decarburization occurs on the surface during cooling after melting, so that the physical properties are not desirable.

Silicon is the basic content added during steelmaking as a deoxidizer and the concentration is adjusted to 0.15 to 0.35% by weight.

Manganese is adjusted to 1.6-2.0 wt% to promote the formation of bainite tissue and to ensure adequate strength. Manganese is added as an element to improve the heat treatment ability, so that the amount of carbon is low to supplement the strength, and if the content is less than 1.0 wt%, sufficient hardening hardness cannot be obtained.

Phosphorus and sulfur when is present as impurities, in the case of phosphorus is its content exceeds 0.03 wt.% Lowers the strength by segregation on the grain boundaries of 0.03 was adjusted to less than% by weight, in the case sulfur is when it exceeds 0.03 wt%, the H ₂ S As a result it was also adjusted to less than 0.03% by weight.

Chromium is adjusted to 0.2-0.3 wt% to extend the bainite formation temperature range, and if it is out of the range, it is difficult to secure a stable bainite structure formation section.

In particular, in the alloy composition of the present invention, vanadium is adjusted to 0.05 to 0.25% by weight as the most important ferrite reinforcing element in order to produce bainite structure in non-coated steel. Vanadium is a precipitation strengthening element added to non-coarse steel to control the physical properties of the alloy composition of the present invention, the hardness of which can be maximized to 373 (HV).

Titanium is added as an element to refine the crystal grains and inhibits crystal growth, especially at high temperatures. If the content is less than 0.01% by weight, the micronization effect is weak, and if it exceeds 0.03% by weight, there is a problem that the micronization effect is saturated, so that the concentration is adjusted to 0.015% by weight or less to achieve grain refinement.

In addition, the present invention, the present invention is C: 0.25-0.30 wt%, Si: 0.15-0.35 wt%, Mn: 1.6-2.0 wt%, P: less than 0.014 wt%, S: less than 0.03 wt%, Cr: It provides 0.2 to 0.3% by weight, V: 0.15 to 0.2% by weight, Ni: less than 0.015% by weight, Ti: less than 0.015% by weight and the remainder is made of Fe bainite-based non-alloy steel alloy composition.

The bainite-based non-alloyed steel alloy composition of the present invention is prepared by melting in a melting furnace at 1200 ° C. and then injecting it into a mold to adjust the cooling rate after molding to at least 30 ° C./min and hot working ( FIG. 2 ).

The metallization of the non-coated steel alloy composition is determined by the cooling rate after hot working. The present invention is to control the cooling rate to 30 ℃ / min or more, and to cool to room temperature, thereby producing an amorphous steel alloy composition having a bainite-based structure.

The alloy made of the composition of the present invention can not only obtain the bainite-based non-alloyed steel with improved mechanical strength without omitting the quenching-tempering heat treatment, but also shorten the manufacturing process, thereby reducing production costs and preventing environmental pollution.

According to the embodiment of the present invention, it can be seen that the mechanical strength and hardness, including tensile strength, are much superior to that of the carbon steel alloy composition subjected to the conventional quenching-tempering heat treatment.

Finally, the present invention is C: 0.25-0.30 wt%, Si: 0.15-0.35 wt%, Mn: 1.6-2.0 wt%, P: less than 0.014 wt%, S: less than 0.03 wt%, Cr: 0.2-0.3 wt% %, V: 0.15-0.2% by weight, Ni: less than 0.015% by weight, Ti: less than 0.015% by weight, and the remainder is heated to 1250 ° C after heating the bainite based crude steel raw material to 1250 ° C and 30 ° C / It provides a manufactured part through a controlled cooling process that cools at a speed of min or more.

By producing the same bainite-based non-alloyed steel alloy composition as described above according to the production method of the present invention, a low-arm connector as a component for a passenger car was manufactured. Loam connector manufactured according to the present invention is improved in tensile strength, yield strength, fatigue strength, elongation and hardness compared to the components made of conventional carbon steel.

Hereinafter, the present invention will be described in detail by way of examples.

However, the following examples are merely to illustrate the invention, but the content of the present invention is not limited to the following examples.

<Example 1>

The present invention according to the chemical composition of the test piece heat-treating step of the Table 1, high-strength bay Fig nitro-based non-adjustable vaginal cavity alloy composition consisting of a component according to the heat treatment step to prepare a.

First, the heated raw material was molded into a press by heating the bainite-based non-alloyed steel alloy composition to 1250 ° C. and then hot working.

Finally, the hot worked alloy composition was cooled at a rate of 30 ° C./min or more.

Comparative Example 1

A specimen was prepared in accordance with the thermal process of Figure 1 as a chemical component is carbon steel alloy composition consisting of components shown in Table 1 according to a conventional heat treatment process.

Carbon steel (S45C) was purchased, and the carbon steel alloy composition having the following composition was heated to 1250 ° C., and then molded in a press and allowed to cool in air.

Next, the molten metal was heated to 850 ° C. and then quenched, and further heated to 500 ° C. and then quenched.

weight% C Si Mn P S Cr V N Ti Fe Example 1 0.25 0.15 1.6 Less than 0.014 Less than 0.03 0.2 0.15 Less than 0.015 Less than 0.015 Remainder Comparative Example 1 0.42 0.15 0.60 Less than 0.03 Less than 0.03 - - - - Remainder

Experimental Example 1 Mechanical Strength Comparison

The mechanical strengths of the specimens prepared in Example 1 and Comparative Example 1 were compared as follows.

(1) tensile strength (kgf / mm ² )

Tensile strength was measured using a universal tensile tester after processing the KS No. 4 tensile test specimen in the prototype-vehicle connector low-arm connector and the results are shown in Table 2 .

(2) yield strength (yield strenth, kgf / mm ² )

Yield strength was expressed as the yield strength of 0.2% PROOF STRESS measured after the tensile test specimen and the results are shown in Table 2 .

(3) fatigue strength (kgf / mm ² )

Fatigue strength was measured using a rotary bending fatigue tester and the results are shown in Table 2 .

(4) elongation (%)

Elongation was measured by attaching an extender-extensionometer to the center of the specimen during the tensile test. The results are shown in Table 2 .

(5) Hardness (HV)

Hardness was measured using a Vickers hardness tester (load: 300 gf) and the results are shown in Table 2 .

Tensile strength (kgf / mm ² ) Yield strength (kgf / mm ² ) Fatigue Strength (kgf / mm ² ) Elongation (%) Hardness (HV) Example 1 121 81 44 16 373 Comparative Example 1 82 55 38 23 210

As shown in Table 2 , the specimen prepared by the manufacturing method of the present invention of Example 1 compared to the specimen prepared by the prior art of Comparative Example 1, even if the additional heat treatment step omitted the concentration of carbon By adjusting to 0.25-0.30% by weight, it was possible to produce bainite tissue and ensure proper toughness, and by adjusting the concentration of manganese to 1.6-2.0% by weight, it was possible to promote the production of bainite tissue and to secure proper strength. Grain refinement could be achieved by adjusting the titanium to 0.015% by weight.

As described above, the manufacturing method of the high strength bainite-based non-manufactured steel manufactured according to the present invention shortens the heat treatment process during the manufacturing process as compared to the existing carbon steel, thereby reducing the production lead time and reducing the production cost. Reduces wastewater and air pollution In addition, the loam connector for automobile parts manufactured according to the manufacturing method of the present invention has significantly improved tensile strength, yield strength, fatigue strength, elongation and hardness, compared to parts manufactured with conventional carbon steel. In addition, by using the alloy adjusted to the carbon concentration of 0.25-0.30% by weight to improve the tensile strength, yield strength, hardness and elongation to increase the mechanical strength overall by 10% or more to lighten the product.

Claims (3)

In the non-coated steel alloy composition, C: 0.25-0.30 wt%, Si: 0.15-0.35 wt%, Mn: 1.6-2.0 wt%, P: less than 0.014 wt%, S: less than 0.03 wt%, Cr: 0.2-0.3 A bainite-based non-alloyed steel alloy composition, comprising:% by weight, V: 0.15 to 0.2% by weight, Ni: less than 0.015% by weight, Ti: less than 0.015% by weight. In the method for producing an amorphous steel alloy composition, C: 0.25 to 0.30% by weight, Si: 0.15 to 0.35% by weight, Mn: 1.6 to 2.0% by weight, P: less than 0.014% by weight, S: less than 0.03% by weight, Cr: 0.2-0.3% by weight, V: 0.15-0.2% by weight, Ni: less than 0.015% by weight, Ti: less than 0.015% by weight, and the remainder of the bainite-based non-alloyed steel alloy composition composed of Fe is melted and cooled simultaneously with hot working Method for producing a high strength bainite-based non-alloy steel alloy composition, characterized in that consisting of a step. C: 0.25-0.30 wt%, Si: 0.15-0.35 wt%, Mn: 1.6-2.0 wt%, P: less than 0.014 wt%, S: less than 0.03 wt%, Cr: 0.2-0.3 wt%, V: 0.15- The raw material of the bainite-based non-alloyed steel alloy composition composed of 0.2 wt%, less than 0.015 wt% of Ni, and less than 0.015 wt% of Ti, and the remainder was heated at 1250 ° C and at the same time hot-worked at 30 ° C / min or more Automotive parts, which are manufactured through a controlled cooling process to cool by.