KR950008532B1 - Continuous treatment of cold-rolled carbon manganese steel - Google Patents

Abstract

No content.

Description

Continuous Treatment of Cold Rolled Carbon Manganese Steel

1 is an illustrative view of the treatment process of the present invention.

The present invention relates to a continuous process of cold-rolled carbon manganese steel.

Today there is a group of steels characterized by improved mechanical properties that yield higher yield and tensile strengths than ordinary carbon steels. These are known as high strength low alloy steels (HSLA steel). Different kinds of HSLA steels are available, some of which are carbon-manganese steels and others that have been microalloyed by adding elements such as niobium, vanadium and titanium to improve mechanical properties. The original demand for HSLA steel has been increased by the need to improve the strength-to-weight ratio to reduce dead weight in transportation equipment. Intended for its original use, HSLA steel is used today in a wide range of applications, including vehicles, construction machinery, material handling equipment, bridges and buildings.)

Commercially available HSLA steels typically have a minimum yield strength of 275 to 345 MPa and a minimum tensile strength of 410 to 480 MPa. Mechanical and other characteristics of HSLA steels are described in the following standard specifications (Society of Automotive Engineers (SAE) J410c). Microalloyed HSLA steels have much higher strength with minimum yield strengths of 345 to 550 MPa and minimum tensile strengths of 450 to 655 MPa. These rivers are highly

Alloying elements such as niobium, vanadium, titanium, zirconium and rare earth elements are generally added in concentrations of 0.10 to 0.15% or less to achieve strength levels. The properties of microalloyed HSLA steels do not include heat treatment, as they are produced by a controlled rolling process in a continuous hot strip mill.

One of the grades of high strength low alloy steel under SAE J410c is grades 950A, B, C and C, characterized by a minimum yield strength of 345 MPa (0.2% offset), a minimum tensile strength of 480 MPa, and a minimum elongation of 22% (e.g., 5 cm test specimen). D. This material exhibits its mechanical properties when hot rolled, and then, when cooled to reduce to sheet thickness, is subjected to low temperature recovery annealing for an extended period of time to maintain the hot rolling mechanical properties.

Another grade of high-strength low-alloy steel microalloyed under SEA J410c is grade 970X, characterized by a minimum yield strength of 480 MPa (0.2% offset), a minimum tensile strength of 585 MPa, and a minimum elongation of 14% (e.g., 5 cm test specimen). . As mentioned, it exhibits its mechanical properties when hot rolled. Subsequently, when cooled and reduced to sheet thickness, these steels are also subjected to cold recovery annealing for extended periods of time to maintain controlled rolling mechanical properties. In addition to the increased cost due to the addition of the element to fine alloy, this recovery annealing may require extended time or continuous annealing required for box annealing.

It is not advantageous because of the enormous investment required for a device for continuous annealing.

Thus, there is a need for steel that can economically be manufactured from cold reinforcing sheet stock, with the desired combination of ductility and strength required for HSLA steel applications today, without the need for extended recovery annealing. Moreover, a steel is required that achieves high mechanical properties, in particular yield strength and tensile strength, without intentionally incorporating microalloys such as niobium, titanium and vanadium so as not to remarkably relate the cost of the steel.

Among the main objects of the present invention is characterized by exhibiting mechanical properties, i.e. yield strength, tensile strength and elongation in the treated state, despite the relatively low carbon content and the absence of expensive microalloys, specifications for microalloyed steel, For example, there is provided a method for treating cold refined steel compositions satisfying SAE J410c grades 950A, B, C, D and 970X. In addition, the main object of the present invention can be produced very economically in a relatively fast continuous process. SUMMARY OF THE INVENTION There is provided a method for producing cold refined steel having uniform high mechanical properties of microalloyed HSLA steel.

For this purpose, the present invention relates to a low carbon manganese steel composition which is not microalloyed and to a method of heat treatment thereof. One steel composition within the scope of the present invention has carbon between 0.04 and 0.15 weight percent and manganese between 0.25 and 0.70 weight percent. Microalloy elements such as niobium, titanium and vanadium are added to the steel composition to achieve improved mechanical properties. Cold-refined steel in the range of the desired sheet thickness, for example 0.078 to 0.236 mm, is continuously passed through three heating stages. The first stage is a preheating stage that raises the temperature of the cold rolled sheet to a temperature range of about 371.l to 537.8 ° C. The steel is then heated to a temperature range of 885 to 940.5 ° C., quenched to a temperature range of 343.3 to 398.9 ° C. and then cooled to room temperature. Another steel composition within the scope of the present invention has 0.11 to 0.18% by weight of carbon and 1.20 to 1.40% by weight of manganese. Such steels also have a desired sheet thickness, for example from 0.078 to

Cold refined in the range of 0.236 mm and passed through three heating stages continuously. The first stage is a preheating stage for raising the temperature of the cold rolled sheet to a temperature range of about 371 to 537.8 ° C. Thereafter, the steel is heated to a temperature range of 815.5 to 857.2 ° C.,

It is quenched to a temperature range of 455 to 510.0 ° C and then cooled to room temperature.

을 연속해서 통과시키고 이어서 3개의 가열 스테이지를 통과시킨다.The heat treatment in both cases is carried out continuously at a line speed of 50 to 300 ft / min, thereby providing continuous length of steel with the desired gauge and width.

Are passed continuously and then three heating stages.

One of the presently preferred steel compositions is about 0.10 to 0.15% by weight of carbon and about

0.25 to 0.70 wt.% Manganese and the remainder are steels consisting of iron and common residues from the deoxidation process. When treated according to the first heat treatment schedule described above, the treated steel shall have a minimum yield strength of 345 MPa, a minimum tensile strength of 480 MPa, and a minimum elongation of 22% as specified for grades 950A, B, C, and D of the SAE J410c specification. Exceed. Another low carbon composition containing from about 0.04% to 0.07% by weight of carbon and from about 0.25% to 0.4% by weight of manganese is treated with the method of the present invention, with a minimum yield strength of 345 MPa, a minimum tensile strength of 410 MPa and a relative strength of 28%. It shows high elongation.

Another presently preferred highlight is a steel consisting of about 0.11 to 0.18 weight percent carbon and about 1.20 to 1.40 weight percent manganese and the remainder conventional residues from iron and deoxidation processes. When treated according to the second heat treatment schedule described above, the treated steel exceeds the minimum yield strength of 480 MPa and the minimum elongation of 14% of the minimum tensile strength limit of 585 MPa specified for class 970X of SAE J410c specification.

The method of the present invention for treating steels with relatively low carbon and manganese contents specified and containing no microalloy produces a cold refining product having mechanical properties that meet or slightly exceed the HSLA steel specification for microalloy steels. Let's do it. Accordingly, the present invention has the high mechanical properties of some of the commercially available microalloyed high strength low alloy steels, but can be obtained as a low carbon steel that is not microalloyed and cold refined, and is economical and cold refined in the absence of a microalloy agent. Characterized by a continuous treatment process of the product.

The carbon-manganese steel composition treated by the process of the present invention in some cases contains about 0.04 to 0.15% by weight of carbon and 0.25 to 0.70% by weight of manganese, and in other cases about

0.1 to 0.18 wt% carbon and 1.20 to l.40 wt% manganese. These steels are kllling, preferably aluminum calming and casting continuously to achieve uniformity of mechanical properties. As a result, such a composition may contain residual silicon and aluminum from the deoxidation process. Such steels may also be silicon soothing steels or semi-settling steels.

In FIG. 1, hot rolled coils of steel, which can be pickled and oiled, are refined through a series of cold rolling processes, for example from 0.078 to

It is made of a sheet 10 having a desired refined thickness of the order of 0.236 mm. The cold rolled and refined sheet 100 is then passed over the mill 11 and placed in a preheating bath 12 which may be an applied lead bath maintained at a temperature range of 371.1 to 537.8 ° C. The lead bath can be heated in various ways, for example with natural gas or electricity. Unlike lead baths, other media may be used that can provide a liquid bath with a temperature range of 37 l. 1 to 537.8 C. Thereafter, the material is lifted to the top of the bath and passed over the elevated rolling mill 14. The material is then passed through a second molten lead bath 16 which is a quench bath.

In the heating stage, the material is heated to a temperature range of 885 to 940.5 ° C. depending on the composition. In the quench stage, the material is quenched to a temperature range of 343.3 to 510. ° C., depending on the composition. That is, the low manganese composition is heated to a temperature range of 885 to 940.5 ° C. and quenched to a temperature range of 343.3 to 398.9 ° C., while the high manganese composition is heated to a temperature range of 815.5 to 857.2 ° C. and a temperature range of 426.7 to 510. ° C. Quench with Heating of the material in the heating stage is carried out by resistance heating. That is, the preheating bath 12 and the quench bath 16 are grounded quench baths that are maintained at a voltage of about 90 volts (V) and a current of 8000 amperes (A). As a result, the sheet material 100 passing through the preheating bath and the quenching bath shunts the current and thus is resistance heated. The length, current and rate of movement of the material through the heating stage are adjusted to treat the material in the heating stage at the desired processing temperature. The protective atmosphere is maintained at the heating stage by wrapping the sheet material 10 in an atmospheric housing 18 flushing with the protective exothermic gas. This gas prevents oxidation of the sheet material when passing from the preheating bath 12 to the quench bath 16. Unlike resistance heating, the material 10 may be heated by conduction, infrared, and other heating means such as gas heating.

물 탱크(downstream water tank)를 통과시키거나 물 분무하여(나타내지 않음) 온도를 약 65.5℃로 강하시킨다. 그러나, 강의 모든 변형은 물질이 급냉 욕(16)을 떠나는 시간으로 완결된다. 냉각시킨 후, 물질을 선적용으로 코일링(coiling) 시키거나 공지된 기술 또는 공지된 기술의 조합, 예를 를면, 산 및/또는 연마세척, 페인팅, 도금, 플래트닝(flattening), 인장 레벨링(tension leveling) 등으로 계속해서 가공한다.The quench bath 16 is also a lead bath that can be heated to the desired temperature using means such as electric anti-immersion heating or radiant gas tubes. After quenching, a charcoal runway 22 containing ignited charcoal designed to prevent lead from the quench bath is drawn out of the sheet material while placing the material on the mill 20 in a vertical direction in the quench bath 16. Pass it through. Now the sheet material at a temperature of about 260 ° C.

Pass the water tank (downstream water tank) or spray water (not shown) to bring the temperature down to about 65.5 ° C. However, all deformation of the steel is completed by the time the material leaves the quench bath 16. After cooling, the material is coiled for shipment or a combination of known or known techniques such as, for example, acid and / or abrasive cleaning, painting, plating, flattening, tensile leveling ( tension leveling).

The sheet material is subsequently passed through preheating, heating and quench stages. Representative line speeds are between 15 and 100 m / min. The preheating, heating and quench stages are approximately 3 to 8 meters in length. As a result, the material is heated or quenched very rapidly at each stage, for example, only 6-15 seconds at a linear speed of 30 m / min.

Representative apparatus for carrying out such heating are described in US Pat. Nos. 2,224,988 and 2,304,225 to Wood et al. Again, in addition to molten lead, heating and quenching media can be used for both preheating and quenching baths. Can be.

A relatively short cycle time in the preheating, heating and quenching stages has been found to refine the particles, resulting in increased strength. That is, in the preheating mill heating stage, the strain introduced into the material from the cold rolling recrystallizes the ferrite into a fine grain structure. Short cycle times limit particle growth to keep the particle size small, typically 0.01 mm or less, often 0.003 to 0.004 mm and finer. In addition, a small amount of austenite is formed at the edge of the particle during heating and locks the particle edge out of motion, thus limiting particle growth again to produce high strength levels. At the same time, carbides in pearlite are constructed and defects are eliminated to increase the ductility of the steel. During quenching, the carbide precipitates to introduce ductility and eliminate the potential for subsequent strain aging.

Example I

Cold refined 5 cm butterfly of 0.2 cm material using the apparatus described in FIG. 1 ×

을 열처리한다. 특성의 균일성을 위하여 강을 알루미늄 진정시키면 조성물은 탄소 0.10%, 망간 0.40%, 규소 0.012% 밋 알루미늄 0.057%, 주조하기 전에 강의 탈산공정으로부터 잔류하는 규소 및 알루미늄 성분을 함유한다. 스트

물질은 33m/min의 속도로 이동한다. 예비가열 욕 중의 납하에서 스트

의 길이는 3m이고, 급냉 욕중에서는 6m이며 가열 스테이지에서는 7.3m이다. 압연기(14)는 납 욕 위의 2.4m 위치에 있다. 광학 고온도계(optical pyrometer)를 사용하어 스트

온도를 측정한다. 처리 스케쥴 및 생성되는 기계적 특성을 표 1에 나타내었다.0.11 cm thick steel

Heat treatment. Aluminum calming of the steel for uniformity of properties causes the composition to contain 0.10% carbon, 0.40% manganese, 0.012% silicon 0.057% silicon, and the silicon and aluminum components remaining from the deoxidation of the steel prior to casting. Stri

The material travels at a speed of 33 m / min. Strip under lead during preheating bath

The length of is 3m, 6m in the quench bath and 7.3m in the heating stage. The rolling mill 14 is at 2.4 m above the lead bath. Test using an optical pyrometer

Measure the temperature. The treatment schedule and the resulting mechanical properties are shown in Table 1.

TABLE 1

As can be seen from Table 1, the mechanical properties resulting from the process exceed the minimum mechanical properties specified for grades 950A, B, C and D (yield strength: 345 MPa, tensile strength 480 MPa, elongation 22%).

A second similar steel composition is carried out using the same process conditions. The composition contains 0.04 / 0.06% carbon and 0.25 / 0.35% manganese. The treatment schedule and the resulting mechanical properties are shown in Table 2.

TABLE 2

The material is characterized by lower tensile strength than the previous examples but with good elongation and is therefore expected to have a high formability.

Example II

을 열처리한다. 특성의 균일성을 위하여 강을 알루미늄 진정시키면 조성물은 탄소 0.14%, 망간 1.33%, 규소 0.22% 및 알루미늄 0.019%, 주조하기 전에 강의 탈산공정으로부터 잔류하는 규소 및 알루미늄 성분을 함유한다. 스트

물질은 33m/mim의 속도로 이동한다. 스트

의 길이는 예비가열 욕 중의 납하에서는 3m이고, 급냉 욕중에서는 6m이며 가열 스테이지에서는 7.3m이다. 압연기(l4)는 납 욕 위의 2.4m 위치에 있다. 광학 고온도계를 사용하여 스트

온도를 측정한다. 처리 스케쥴 및 생성되는 기계적 특성을 표 3에 나타내었다.5 cm butterfly x 11 cm thick steel strip cold-refined from a 0.2 cm material using the apparatus described in FIG.

Heat treatment. Aluminum calming of the steel for uniformity of properties results in the composition containing 0.14% carbon, 1.33% manganese, 0.22% silicon and 0.019% aluminum, the silicon and aluminum components remaining from the deoxidation of the steel prior to casting. Stri

The material travels at a speed of 33m / mim. Stri

The length of is 3m in lead in preheating bath, 6m in quench bath and 7.3m in heating stage. The rolling mill l4 is at 2.4 m above the lead bath. Using an optical pyrometer

Measure the temperature. The treatment schedule and the resulting mechanical properties are shown in Table 3.

TABLE 3

As can be seen from Table 3, the mechanical properties resulting from the treatment process exceed the minimum mechanical properties specified for grade 970X (yield strength: 480 MPa, tensile strength: 585 MPa, elongation: 14%). Both samples show good ductility with high intensity levels.

The method of the present invention is applicable to a range of steel compositions within the range of the above-described composition. As shown in the specific embodiments described above, the process provides a low carbon high manganese cold refining steel combined to the desired degree of strength and ductility characterized by commercially available microalloyed and hot rolled high strength low alloy steels.

Claims (3)

(1) pre-heating cold-refined steel having a composition of about 0.04 to 0.14% by weight carbon and 0.25 to 1.33% by weight manganese to a temperature range of 371.1 to 537.8 ° C., (2) the steel to 815.5 to Heating the steel described above to a temperature range of 940.5 ° C. and (3) quenching the steel to a temperature range of 343.3 to 510 ° C. without adding a microalloy agent for the purpose of achieving improved mechanical properties. How to process continuously. The method of claim 1, wherein the material is preheated through a molten lead bath with each step less than about 15 seconds and heated to a resistive heating stage. The method of claim 1, wherein the material is aluminum calm sheet or strip.

How to be.

Images