KR100759197B1 - Baf heat treating method for ultra deep drawing cold rolled steel sheet - Google Patents

Baf heat treating method for ultra deep drawing cold rolled steel sheet Download PDF

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KR100759197B1
KR100759197B1 KR1020060060694A KR20060060694A KR100759197B1 KR 100759197 B1 KR100759197 B1 KR 100759197B1 KR 1020060060694 A KR1020060060694 A KR 1020060060694A KR 20060060694 A KR20060060694 A KR 20060060694A KR 100759197 B1 KR100759197 B1 KR 100759197B1
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steel sheet
cold rolled
rolled steel
heat treatment
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Korean (ko)
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박근웅
문만빈
김효균
남궁성
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현대하이스코 주식회사
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    • C—CHEMISTRY; METALLURGY
    • C21—METALLURGY OF IRON
    • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/04—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing
    • C21D8/0447—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips to produce plates or strips for deep-drawing characterised by the heat treatment
    • C21D8/0473—Final recrystallisation annealing
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium

Abstract

A heat treatment method of a cold rolled steel sheet for extra deep drawing using a box annealing furnace is provided to increase the productivity, stabilize the quality of products, and reduce the consumption of energy by finding out an optimal batch annealing furnace heat treatment cycle, thereby expanding uses of the cold rolled steel sheet that has been heat-treated by the batch annealing furnace, and reducing annealing temperature and time of the cold rolled steel sheet. A heat treatment method of a cold rolled steel sheet for extra deep drawing using a box annealing furnace comprises performing a batch annealing furnace heat treatment process of a cold rolled steel sheet having 100 wt.% of a composition comprising 0.005 to 0.04 wt.% of C, 0.015 to 0.04 wt.% of Si, 1 to 2 wt.% of Mn, 0.2 to 0.5 wt.% of Al, 0.05 wt.% or less of N, 0.05 wt.% or less of O, 0.1 wt.% or less of P, 0.1 wt.% or less of S and the balance of Fe and inevitable impurities in an annealing heat treatment cycle having a heating maintenance temperature varied from 725 to 750 deg.C and a heating maintenance time varied from 4 to 10 hours to manufacture a cold rolled ultra-low carbon steel sheet for extra deep drawing requiring high formability.

Description

초심가공용 냉연강판의 상자소둔로를 이용한 열처리방법{BAF heat treating method for ultra deep drawing cold rolled steel sheet} BAF heat treating method for ultra deep drawing cold rolled steel sheet}

제 1도 : 본 발명의 BAF 소둔사이클Figure 1: BAF Annealing Cycle of the Present Invention

제 2도 : 본 발명 소재의 미세조직2: Microstructure of Material of the Invention

본 발명은 고성형성이 요구되는 자동차 내부 판넬류 등의 용도에 적합한 초심가공(超深加工)용 냉연강판 (cold rolled steel sheet for ultra deep drawing)의 상자소둔로를 이용한 소둔열처리 방법에 관한 발명이다. 구체적으로 말하면 상기 용도를 가진 냉연 강판의 냉간 가공성을 향상시키기 위한 목적으로 종래의 연속소둔로 내의 열처리 방법을 상자소둔로(Batch Annealing Furnace, 이하 "BAF")내에서의 최적열처리 방법 및 이에 따라 제조된 초심가공용 냉연강판에 관한 것이다.The present invention relates to an annealing heat treatment method using a box annealing furnace of a cold rolled steel sheet for ultra deep drawing, which is suitable for applications such as automotive interior panels that require high formability. Specifically, in order to improve the cold workability of the cold rolled steel sheet having the above application, the conventional heat treatment method in a continuous annealing furnace is an optimal heat treatment method in a batch annealing furnace (hereinafter referred to as "BAF") and accordingly manufactured. It relates to a cold rolled steel sheet for superlative processing.

일반적으로 소둔공정은 연속소둔라인(CAL)상의 소둔공정으로서 크게 가열(Heating)과 가열유지 또는 균열(Soaking) 및 냉각(Cooling)의 3공정으로 신속한 시간으로 일관작업 처리되고 있다. 그러나 종래의 경우 초심가공 용도의 냉연강판을 생산할 경우에는, 충분한 강조직의 연화, 재결정화가 이루어지지 못해 국부적으 로 큰 물리적 특성상의 편차발생이 심하였다. 본 발명은 종래의 실질적으로 불가능하였던 BAF 소둔공정을 취하기로 하고, 고성형성을 가진 초심가공(超深加工) 요구조건에 맞추어 가열시간과 온도, 균열시간과 그 온도 및 냉각시간과 그 온도를 각각 설정한 후 이 용도상의 조건을 충족할 수 있는 균일한 기계적 특성치를 얻는데 주력하고, 이를 실현하기 위해 초심가공이라는 가공성을 살리기 위한 최적의 BAF 소둔열처리 조건과 사이클을 설정하는데 초점을 두었다. In general, the annealing process is an annealing process on a continuous annealing line (CAL), and is generally processed in a rapid time by three processes of heating (Heating), heating maintenance, or soaking and cooling (Cooling). However, in the conventional case, when producing cold-rolled steel sheets for super-core processing, sufficient softening and recrystallization of the reinforcement fibers were not performed, causing a large variation in local physical properties. The present invention is to take the BAF annealing process, which was practically impossible, and to set the heating time and temperature, the cracking time and its temperature and cooling time and its temperature, respectively, in accordance with the requirements for superlative processing with high formability. Afterwards, the focus was on obtaining uniform mechanical properties to meet these application conditions, and to achieve this, the focus was on setting the optimum BAF annealing heat treatment conditions and cycles to take advantage of the machinability of supermachining.

자동차 내부 판넬류에 사용되는 냉연강판은 고성형성을 필요로 하는 초심가공용(EDDQ, Extra Deep Drawing Quality) 재질이어야 하는 특성에 따라 종래에는 대부분 극저탄소강을 이용하여 연속소둔(CAL) 열처리를 행한 후 소정의 조질압연(Skin Pass Mill)을 거쳐 냉연최종강판을 생산하게 된다. 그러나 이러한 종래의 초심가공용제품은 연속소둔공정을 행하면서 소둔열처리 사이클의 정밀제어에 따른 재질관리를 하지 않으면 강도, 특히 항복강도(Y,P,) 연신율 등에, 통상 3%~10%라는 큰 편차가 발생하므로써 불량제품 생성등 안정된 제품이 얻어지지 않는데다 연속생산라인 상의 연속소둔공정 이라는 특수성 때문에 열처리시간을 비교적 짧게 진행시켜야 하는 특수한 사정이 있으므로 제품의 물리적 성질에 편차발생이 커져서 목표로 하는 재질에 맞추려면 최적의 범위를 가진 성분과 특수 합금원소가 함유된 소재로 사용해야 하는 극히 제한적인 조건하에서의 생산이라는 매우 어려운 제약조건을 내포하고 있다. 더우기 초기 생산설비 투자비가 과도하고 단위 공정이 많아 공정에 따르는 높은 고품질관리가 뒤따라야하는 실정이다.Cold rolled steel used in automobile interior panels should be an EDDQ (Extra Deep Drawing Quality) material that requires high formability.In the past, most of them have been subjected to continuous annealing (CAL) using ultra low carbon steel. The cold rolled final steel sheet is produced through a predetermined skin pass mill. However, such conventional super deep processing products have a large deviation of 3% to 10% in strength, in particular yield strength (Y, P, and elongation), unless the material is controlled according to the precise control of the annealing heat treatment cycle during the continuous annealing process. As a result of this problem, stable products such as the generation of defective products cannot be obtained, and due to the special characteristics of the continuous annealing process on the continuous production line, there is a special situation in which the heat treatment time is relatively shortened. In order to be fitted, it has very difficult constraints of production under extremely limited conditions that require the use of materials with the optimum range and special alloying elements. Moreover, due to the excessive investment of initial production equipment and the large number of unit processes, high quality control according to the process must be followed.

따라서 본 발명은 연구확인결과 고성형이 요구되는 자동차 내부 판넬류 등에 적합한 초심가공용 냉연강판은 탄소함량이 70ppm이하의 규격을 가진 극저탄소강 소재를 이용하여 단위 공정이 짧고 초기 생산설비 비용이 적게 소요되는 상자소둔(BAF)을 행하는 것이 가장 적합한 것으로 결론을 내리고 이때 열처리를 행하기 위하여 모사시험설비(Simulator)에서 주로 균열시간과 온도, 냉각시간과 온도를 고성형성의 초심가공용 요구조건으로 각각 설정한 후 이 용도에 맞는 기계적 특성치를 얻을 수 있는 최적 소둔 열처리 방안을 찾아내는데 초점을 둔 것이다. Therefore, according to the present invention, the cold rolled steel sheet for deep processing suitable for automobile interior panels requiring high molding requires short unit process and low initial production equipment cost by using ultra low carbon steel material having a carbon content of 70 ppm or less. It is concluded that it is most suitable to perform BAF which is the most suitable. In this case, in order to perform heat treatment, the crack time, temperature, cooling time, and temperature are mainly set as the requirements for the superlative processing of high formability. This paper focuses on finding the optimum annealing heat treatment method to obtain mechanical properties for this application.

본 발명은 일반 범용으로 사용되고 있는 극저탄소(70ppm 이하)의 강판을 소재로 이용하여 초심가공(YP: 12.0kg.mm2이상, 16.5kg/mm2 이하, El.:47% 이상)이 가능하도록 가열유지온도와 유지시간 즉, 균열온도와 균열시간을 각각 설정하여 BAF 소둔열처리를 행한 후 가공성평가를 거쳐 최종 자동차 내부 판넬류 용도의 초심가공용 자동차 냉연강판의 생산이 가능한 최적의 BAF 소둔열처리 사이클을 찾아내므로써, BAF 냉연강판 제품의 용도확대와 적정 소재 선택에 따른 소둔온도 및 시간을 단축시켜 최적 소둔사이클을 확보하여 생산성 증가, 품질의 안정화 및 에너지 절감을 이루는데 그 목적이 있다. The present invention uses ultra low carbon (70ppm or less) steel sheet used as a general purpose as a material for ultra-deep processing (YP: 12.0kg.mm 2 or more, 16.5kg / mm 2 or less, El .: 47% or more) After setting the heating holding temperature and the holding time, that is, the cracking temperature and the cracking time, BAF annealing heat treatment is performed to evaluate the workability, and then the final automotive interior panel. By finding the optimal BAF annealing heat treatment cycle for the production of automotive cold rolled steel for super-critical processing, we increase the use of BAF cold rolled steel products and shorten the annealing temperature and time according to the selection of the appropriate material to secure the optimum annealing cycle to increase productivity. The purpose is to achieve stabilization of quality and energy saving.

본 발명자들은 일반 범용으로 사용되고 있는 극저탄소 탄소함량(70ppm 이하의 규격)의 강판을 소재로 이용하여 전술한 바와 같이 균열온도와 균열시간 조건을 초심가공(YP: 12.0~16.5kg/mm2)이 가능하도록 설정하여 상자소둔로(BAF)에서 열처리를 행한 후 가공성평가를 거쳐 최종 자동차 내부 판넬류 용도의 초심가공용 자동차 냉연강판의 생산이 가능한 BAF 소둔열처리 사이클 방안을 제공하는데 연구의 역점을 두었다. 즉, 본 발명은 고성형이 요구되는 초심가공 용도의 냉연강판 제품에 대하여 기계적 특성치와 성형가공성을 향상시키기 위한 목적으로 진행되는 상자소둔(Batch Annealing Furnace, 이하 BAF) 열처리의 균열온도와 균열시간을 각각 변화시키는 특성을 갖는 최적열처리 사이클 방안을 제공하는데 그 요지가 있다.The inventors of the present invention, using the steel sheet of the ultra-low carbon content (70ppm or less) used as a general purpose as a material as described above for the initial processing (YP: 12.0 ~ 16.5kg / mm 2 ) crack temperature and crack time conditions The research was focused on providing a BAF annealing heat treatment cycle method that can be used to produce a cold rolled steel sheet for automotive cores for the final automotive interior panels after heat treatment in a BAF annealing furnace. That is, the present invention relates to the cracking temperature and the cracking time of the heat treatment of annealing (Batch Annealing Furnace, BAF), which is carried out for the purpose of improving the mechanical properties and the formability of the cold rolled steel sheet products for super-machining applications requiring high molding. There is a need to provide an optimal heat treatment cycle scheme with varying characteristics.

BAF에서 진행할 수 있는 열처리로 일례를 들면 종형(Bell type) BAF이다. 이러한 BAF에서 진행시겨야 할 소둔공정은 간단히 말하면 ① 강판적재 → ② 분위기 균질화(pursing) → ③ 가열(heating) → ④ 균열(soaking) → ⑤ 냉각(cooling) → ⑥ 취출 등의 제반과정이고 이러한 과정에서 진행되는 강재 조직의 재질측면상의 특성은 1단계인 회복(recovery), 2단계인 재결정(recrystallization), 3단계인 결정립성장(grain growth)으로 구성된다. 본 발명에서는 소둔 공정 중 초심가공용 강판의 기계적 특성을 만족시킬 수 있는 균열과정의 온도와 시간의 최적화 조건에 대한 소둔 사이클 방안에 대하여 중점적으로 나타내고자 한다.An example of a heat treatment furnace that can be carried out in BAF is a bell type BAF. The annealing process to be carried out in this BAF is simply a process of ① steel sheet loading → ② atmosphere homogenization → ③ heating → ④ soaking → ⑤ cooling → ⑥ take-out The characteristics of the material structure of the steel structure proceeded from are composed of the first stage of recovery, the second stage of recrystallization, and the third stage of grain growth. In the present invention, we will focus on the annealing cycle scheme for the optimization conditions of temperature and time of the crack process that can satisfy the mechanical properties of the super-core steel sheet during the annealing process.

위 BAF소둔 공정의 각각의 과정에 대하여 상세히 설명한다. 먼저 강판을 로내부의 처리용량과 강종별, 두께별 그리고 소둔 사이클에 맞추어 적재하고 로외곽부를 차폐(shielding)한 후 대부분 상온의 분위기가스를 로(furnace) 처리공간(inner-cover)에 흡입시켜 환원성 분위기를 형성시키면서 퍼징(pursing)을 행한 다. 여기서 분위기가스로는 보통 질소가스(N2) 또는 수소가스(H2)를 많이 사용한다. 분위기가스의 퍼징은 처리공간 내의 산화성 분위기를 제거하여 구상화 소둔 처리 후의 강판의 산화물 형성방지와 탈탄방지 효과를 위해 행해지는 전처리 공정으로서, 퍼징을 거치면 소둔 후의 강판표면이 미려해지고 깨끗한 특성을 얻을 수 있다.Each process of the above BAF annealing process will be described in detail. First, the steel sheet is loaded according to the processing capacity, steel type, thickness, and annealing cycle in the furnace, and the outside of the furnace is shielded. Most of the ambient gas is sucked into the furnace-cover. Purging is performed while forming a reducing atmosphere. Atmospheric gas is usually used a lot of nitrogen gas (N 2 ) or hydrogen gas (H 2 ). Purging the atmospheric gas is a pretreatment step to remove the oxidizing atmosphere in the processing space to prevent oxide formation and decarburization of the steel sheet after the spheroidizing annealing treatment. .

다음, 가열장치를 장착 후 가동시켜 적정 가열속도로 목표로 하는 유지온도까지 가열한 다음 상기 용도에 적합한 가열유지온도와 가열유지시간을 각각 설정하여 균열시킨다. 이후 가열장치를 분리해내고 냉각팬과 냉각수가 부착된 냉각장치를 장착후 가동시켜 탈취 온도까지 냉각시키며 마지막으로 소재를 탈 이동시킨다.Next, the heating apparatus is mounted and operated to heat up to a target holding temperature at an appropriate heating rate, and then cracked by setting a heating holding temperature and a heating holding time suitable for the purpose. After the heating device is removed, the cooling fan and cooling water attached to the cooling device is mounted and operated to cool down to the deodorizing temperature, and finally the material is moved.

상술한 BAF 소둔공정을 통하여 생산되는 열처리 된 냉연강판은 가열유지온도와 가열유지시간에 따라 요구되는 재질특성이 상이하게 나타나는데, 본 발명에서는 초심가공용 냉연강판의 용도에 적합한 소둔 유지시간과 온도 조건에 주안점을 두면서 극 저탄소 (규격상 탄소함량 70ppm이하)의 강판을 소재로 이용하여 가열유지(균열)온도와 가열유지(균열)시간 조건을 초심가공(YP: 12.0~16.5kg/mm2, El.:47% 이상)이 가능하도록 각각 표 1의 화학성분범위, 균열온도범위, 균열시간범위 등의 BAF소둔조건을 설정하였다. 여기에서, Y.P. 16.5kg/mm2를 초과할 경우 초심가공이 불가능해진다. 또한 Y.P. 12kg/mm2를 밑돌게 되면 가공시 소정의 강도가 확보되지못하고, 아울러 연신율 47%미만으로 되기 쉬우며 연신율 47%미만으로 될 경우 가공부분의 국부파열, 파손이 일어나기 쉽다. 몰론 그외에도 불균일 가공이 일어나기 쉽다. 항복강도(Y.P.)와 연신율을 이와 같이 특별히 한정하는 이유는 강도유지와 가공성, 용접성 때문이며, 특히 자동차판넬용 강판 등의 제품의 경우에는 가공성, 용접성에 있어 불균일, 편차를 최저로 줄이기 위함이다.The heat-treated cold rolled steel sheet produced through the above-described BAF annealing process has a different material characteristic depending on the heating holding temperature and the heating holding time. In the present invention, the annealing holding time and temperature conditions suitable for the use of the cold rolled steel sheet for deep processing are used. With a focus on ultra-low carbon (standard carbon content of 70ppm or less) steel sheets as materials, heating processing (cracking) temperature and heating maintenance (cracking) time conditions are considered as the first (YP: 12.0 ~ 16.5kg / mm 2 , El. : 47% or more), BAF annealing conditions such as chemical composition range, crack temperature range and crack time range of Table 1 were set. In this case, when the YP exceeds 16.5kg / mm 2 , super-machining becomes impossible. In addition, if the YP 12kg / mm 2 is less than the predetermined strength is not secured during processing, and less than 47% elongation tends to be less, and less than 47% elongation is likely to cause local rupture, breakage. Of course, other than non-uniform processing is likely to occur. The reason why the yield strength (YP) and the elongation are specifically limited is because of the maintenance of strength, workability and weldability. In particular, in the case of products such as steel sheets for automobile panels, in order to minimize unevenness and variation in workability and weldability.

표 1은 본 발명소재의 화학성분계를 나타낸 것이다. C : 5~40ppm, 중량%(0.005~0.04중량%) 그 중에서도 열처리 안된 소재로서의 냉연강판 소재(A)는 탄소함량을 20~40(30±10)ppm, 중량%(0.02~0.04중량%)을 가지며 Si는 15~40ppm, Mn은 1000~2000ppm, P는 100ppm 이하, S는 100ppm 이하, Al은 200~500ppm, N은 50ppm 이하, Ｏ는 50ppm 이하, 나머지는 Fe 및 불가피 불순물로 구성되는 성분조성을 갖는다. 소재(B)는 탄소함량을 5~15ppm으로 설정하고, Si는 15~40ppm, Mn은 1000~2000ppm, P는 100ppm 이하, S는 100ppm 이하, Al은 200~500ppm, N은 50ppm 이하, O는 50ppm 이하, 나머지는 Fe 및 불가피 불순물로 구성되는 성분조성을 갖는다. 어느 경우이든 성분조성 총합계 100중량%로 구성된다. 여기에서 Al은 N와 결합하여 AlN의 형태로 N을 제거하기 위함이며, Ｏ또한 같은 원리에 의해 제거하기 위한 것이다. Mn은 단순히 강도향상을 목적으로 한 첨가성분이며, 본 발명소재에서 가장 중요한 것은 탄소함량이다.Table 1 shows the chemical composition of the present invention. C: 5 to 40 ppm, weight% (0.005 to 0.04 weight%) Among them, cold rolled steel material (A) as an unheated material has a carbon content of 20 to 40 (30 ± 10) ppm, weight% (0.02 to 0.04 weight%) Si is 15 ~ 40ppm, Mn is 1000 ~ 2000ppm, P is 100ppm or less, S is 100ppm or less, Al is 200 ~ 500ppm, N is 50ppm or less, O is 50ppm or less, and the rest is composed of Fe and unavoidable impurities Has a composition. Material (B) is set to 5 to 15 ppm of carbon, Si is 15 to 40 ppm, Mn is 1000 to 2000 ppm, P is 100 ppm or less, S is 100 ppm or less, Al is 200-500 ppm, N is 50 ppm or less, O is 50 ppm or less, and the rest have a component composition which consists of Fe and an unavoidable impurity. In either case, the total composition is 100% by weight. Here Al is to remove N in the form of AlN in combination with N, O is to remove by the same principle. Mn is simply an additive component for the purpose of improving strength, and the most important thing in the present invention is carbon content.

[표 1] 본 발명 소재의 화학성분계 설정범위 [ Table 1 ] Chemical composition range of the present invention

Figure 112006047201813-pat00001
Figure 112006047201813-pat00001

여기에서, 본 발명은 상기 열처리 안된 냉연강판 소재의 초심가공(超深加工)보증을 하기 위해 우선, 탄소함량의 범위를 70ppm이하, 그 중에서도 표 1에서와 같이 5~40ppm(0.005~0.04중량%)으로 설정하였다. 그 중에서도 특히 초심가공을 중요시하는 경우에는 초심가공보증을 위해 탄소함량을 10±5ppm(5~15ppm)으로 설정하였다. 이와 같이 탄소함량을 매우 좁은 범위로 낮게 설정하는 이유는 특히, 탄소함량이 가공성, 용접성 등에 미치는 영향이 가장 커서 15ppm이하로 제어하면 가공성, 용접성이 보증되며, 그러나 5ppm미만으로 함유되면 Y.P.등의 소정의 강도가 얻어지지 아니하고, 40ppm을 초과하면 연신율 확보에 어려움은 물론 Y.P. 연신율, 인장강도 등에 편차가 심히 발생하기 쉬워지므로 이를 위하여 본 발명은 이들 요구조건을 안정적으로 소정의 용도에 적합한 소둔사이클의 적용을 위해 BAF 시뮬레이터(Simulator) 장치를 사용하여 실제 현장의 BAF와 동일한 분위기 및 가열조건, 유지조건, 냉각조건으로 처리를 행하였다.
본 발명에서는 특히, 초심가공 기계적 특성치가 가능하고 성형 가공성 및 용접성을 확보하기 위해 탄소함량 범위를 상술한 바와 같이 선정하고 소둔사이클 조건은 유지온도 범위를 725~750℃로 설정하고 가열유지시간을 4시간 이상, 10시간 이하로 설정하였다. 가열유지시간을 4시간 미만으로 하게 되면 균열효과가 생기지 않는다. 또한 10시간 초과하게 되면 물리적 특성의 편차가 심히 발생하며 생산성 저하와 에너지소모 과다, 로내강판의 소착방지가 일어나기 쉽다. 또한, 725℃미만인 경우 균열이 충분하게 되지 못하여 국부적으로 온도편차가 발생하기 쉽고 이에 따라 가열유지시간이 오히려 길어지며, 특히 충분한 조직상의 재결정화가 균일히 잘 이루어지기 어렵다. 반대로 750℃를 초과하면, 단시간에 지나치게 재결정화가 진행되어 연화되기 쉬우므로 항복강도, 경도가 소정치 이하로 저하되거나 분균일하게 되기 쉽다.
소둔처리를 행한 후 소재의 기계적 특성 평가는 인장시험 및 미세조직, 경도시험을 실시하여 상기 요구 용도에 만족하는 결과치와 대비확인하여 도 2에서와 같이 현미경 조직상 등축정조직이 뚜렷하면 이는 본 발명목적을 달성하게 되므로 상기 소둔사이클 조건을 최적화 방안으로 제시하였다.In the present invention, in order to guarantee the super-deep processing of the cold rolled steel sheet material which has not been heat-treated, first, the carbon content is in the range of 70 ppm or less, and among them, 5 to 40 ppm (0.005 to 0.04 weight%), as shown in Table 1 below. Set to. In particular, when the initial processing is important, the carbon content was set to 10 ± 5ppm (5 ~ 15ppm) for the initial processing guarantee. The reason for setting the carbon content low in a very narrow range is that the carbon content has the greatest influence on workability, weldability, etc., and therefore, when controlled to 15 ppm or less, workability and weldability are guaranteed, but when it is contained below 5 ppm, a predetermined amount such as YP is required. If the strength is not obtained and exceeds 40ppm, it is difficult to secure the elongation, as well as the deviation of YP elongation, tensile strength, and the like easily occurs. For this purpose, the present invention stably applies these annealing cycles to these requirements stably. For this purpose, the BAF simulator was used in the same atmosphere, heating conditions, holding conditions, and cooling conditions as the actual BAF.
In the present invention, in particular, the ultra-high mechanical properties are possible, and in order to secure the formability and weldability, the carbon content range is selected as described above, and the annealing cycle condition is set at a holding temperature range of 725 to 750 ° C. and a heating holding time of 4 It set to time or more and 10 hours or less. If the heating holding time is less than 4 hours, there is no cracking effect. In addition, when more than 10 hours, physical property deviations occur severely, and productivity deterioration, excessive energy consumption, and prevention of seizure of the inner steel sheet are likely to occur. In addition, if the temperature is less than 725 ° C cracks are not enough to cause a local temperature deviation and accordingly the heating holding time is rather long, in particular, it is difficult to uniformly recrystallize a sufficient texture. On the contrary, when it exceeds 750 degreeC, recrystallization advances too much easily in a short time, and it is easy to soften, and yield strength and hardness fall below predetermined value, or it is easy to become uniform.
Evaluation of the mechanical properties of the material after the annealing treatment is carried out in a tensile test, microstructure, hardness test to check the results and satisfactory to meet the requirements, if the equiaxed crystal structure in the microscopic structure as shown in Figure 2 is clear, this invention Since the objective is achieved, the annealing cycle condition is proposed as an optimization method.

실시예Example

이하에, 본 발명을 일실시예를 들어 구체적으로 설명한다.EMBODIMENT OF THE INVENTION Below, this invention is concretely demonstrated to an Example.

도 1은 본 발명의 BAF 소둔 사이클을 일실시예로 나타낸 것이다. 먼저 탄소함량이 21ppm 항복강도 16.5kg/mm2의 전술한 냉연강판 소재(A)와 탄소함량 8ppm 항복강도(Y.P.) 14kg/mm2의 소재(B)로 나누어 그 최적의 초심가공용 냉연강판의 소둔 사이클 조건을 가열유지온도 범위를 보다 효과적으로 제어하기 위하여 두 가지 온도범위로 나누어 각각 (가)조건 725~740℃, (나)조건 735~750℃의 범위를 갖는 목표 가열유지온도(균열온도)에서 5±0.5시간(hr.) 가열유지시간(균열시간)의 소둔사이클로 한 것을 나타낸 것이다. 5-0.5시간 미만인 경우 균열효과가 서서히 감소되고, 5+0.5시간 초과시에는 Y.P.등 물리적 특성에 있어 편차가 서서히 나타나기 시작한다. 다만 여기에서 승온 및 냉각 조건은 기존 조건과 동일하게 적용할 수 있다. 그리고 가열 및 냉각의 전체 열처리 사이클의 각 단계별 온도범위는 도1에 나타낸 바와 같았으며 보열유지온도에 따라 '가' 및 '나' 조건으로 구분하여 각각 나타내었다.1 illustrates the BAF annealing cycle of the present invention in one embodiment. First, annealing of the cold rolled steel sheet for optimal super-deep processing is divided into the above-described cold rolled steel sheet material (A) having 21 ppm yield strength of 16.5 kg / mm 2 and the carbon material having 8 ppm yield strength (YP) of 14 kg / mm 2 . To better control the heating and holding temperature range, the cycle conditions are divided into two temperature ranges, respectively, at the target heating holding temperature (cracking temperature) having the range of (A) conditions 725 to 740 ° C and (B) condition 735 to 750 ° C. It shows the annealing cycle of 5 ± 0.5 hours (hr.) Heating holding time (cracking time). If it is less than 5-0.5 hours, the cracking effect is gradually decreased, and if it is more than 5 + 0.5 hours, the variation in physical properties such as YP starts to appear slowly. However, the temperature rising and cooling conditions may be applied in the same manner as the existing conditions. In addition, the temperature range of each step of the entire heat treatment cycle of heating and cooling was as shown in FIG. 1, and is divided into 'A' and 'B' conditions according to the holding temperature.

표 2는 본 발명의 기계적 특성치를 나타낸 것이다. 소재(A)의 최적 소둔 사이클에 대한 기계적 특성치를 비교하여 나타내어 보면, 초심가공용 냉연강판 보증범위(YP: 12.0kg/mm2이상, 16.5kg/mm2 이하, El.:47% 이상)를 만족시키는 사이클의 조건은 725℃ 내지 750℃의 범위를 갖는 유지온도와 5±0.5hr의 가열유지시간이며 항복강도(YP), 인장강도(TS), 연신율(El.), 가공경화지수(n), 소성이방성계수(r-bar) 값은 표에 나타낸 바와 같다. 다음으로 소재(B) 최적 소둔 사이클에 대한 기계적 특성치를 비교하여 나타내어 보면, 초심가공용 냉연강판 보증범위를 만족시키는 사이클의 조건은 도 1에서와 같이 725~740℃ 또는 735~750℃의 균열온도 범위에서 4~10hr. 균열하는 것으로 그중에서도 이들 온도범위에서 5±0.5시간(4.5~5.5hr)의 가열유지(균열)가 생산성을 고려할 때 양호한 것으로 나타났다. 이때의 항복강도(YP), 인장강도(TS), 연신율(El.), 가공경화지수(n), 소성이방성계수(r-bar) 값은 표 2에 나타낸 바와 같았다. 여기에서 균열시간을 5±0.5hr.(4.5~5.5hr)로 한 것은 극히 미세한 조정으로서 다수의 실험과 시험조업결과 상기 (가)조건, (나)조건 모두 물리적 성질의 편차가 극히 적은 결과에 의한 초심가공성 보증이 가능한 범위로 판명되었다.Table 2 shows the mechanical properties of the present invention. When expressed as compared to the mechanical characteristic value of the optimal annealing cycle of the material (A), the cold-rolled steel sheet for processing original intention warranty range satisfying (YP 12.0kg / mm 2 or more, 16.5kg / mm 2 or less, or more El.:47%) The conditions of the cycle were 725 ℃ to 750 ℃, holding temperature and heating holding time of 5 ± 0.5hr, yield strength (YP), tensile strength (TS), elongation (El.), Work hardening index (n) The plastic anisotropy (r-bar) values are shown in the table. Next, by comparing the mechanical characteristics of the optimum annealing cycle of the material (B), the cycle conditions satisfying the cold-rolled steel sheet warranty range for deep processing is 725 ~ 740 ℃ or 735 ~ 750 ℃ crack temperature range as shown in FIG. In 4 ~ 10hr. Among these, cracking showed that 5 ± 0.5 hours (4.5 ~ 5.5hr) of heat holding (cracking) in these temperature ranges was good considering productivity. Yield strength (YP), tensile strength (TS), elongation (El.), Work hardening index (n) and plastic anisotropy coefficient (r-bar) at this time were as shown in Table 2. The crack time of 5 ± 0.5hr. (4.5 ~ 5.5hr) is extremely fine adjustment, and the results of many experiments and tests have resulted in extremely small variations in physical properties in both (a) and (b) conditions. It is proved to be possible to guarantee the superlative workability.

[표 2] 발명 소재의 기계적 특성치

Figure 112007048706017-pat00005
Table 2: mechanical property values of the invention Material
Figure 112007048706017-pat00005

도 2는 본 발명제품의 미세조직을 나타낸 것으로, 소재 (A)와 (B) 모두 소둔 사이클 조건에 따라 본 발명의 목적에 부합되는 극저탄소강(탄소범위: 70ppm 이하)이 갖는 전형적인 등축정(Equi-Axed Grain) 조직특성을 나타내고 있음을 알 수 있다. 따라서, 종래에 제품특성 편차가 커서 실질적으로 불가능하였던 BAF 소둔열처리도 도 2에서와 같이 본 발명에 의해서 종래와 동일한 정도의 조직이 얻어지게 되었음을 이로써 확인할 수 있었다.Figure 2 shows the microstructure of the product of the present invention, both the material (A) and (B) is a typical isoaxial crystal of ultra-low carbon steel (carbon range: 70ppm or less) in accordance with the object of the present invention according to the annealing cycle conditions ( Equi-Axed Grain) It can be seen that it shows the tissue characteristics. Therefore, the BAF annealing heat treatment, which was largely impossible due to the large variation in product characteristics, was confirmed by the present invention as shown in FIG.

삭제delete

본 발명에서와 같이 고성형성이 요구되는 자동차 내부 판넬류 등의 용도에 적합한 초심가공용 냉연강판 제품에 대하여 기계적특성치와 성형가공성을 만족시키기 위한 목적으로 진행되는 상자소둔(Batch Annealing Furnace, 이하 BAF) 열처리의 최적열처리 사이클 방안으로 얻어지는 주요 효과는 종래의 연속소둔열처리 공정에 한하여 생산해온 제품을 BAF 소둔열처리 공정으로 대체 생산을 가능하게 하므로써 저렴한 설비투자를 통한 경제적 잇점과 원가경쟁력을 확보하였음은 물론 종래의 자동차 소재의 초심가공용 제품상 가장 큰 단점이었던 소정항복강도(Y.P.) 및 연신율의 큰 편차발생을 줄일 수 있게 되었으며 소재 가공성 향상과 사이클 단축에 따른 생산능력(Capability of products)도 증대시킬 수 있게 되어 생산원가와 에너지 소모율을 낮출 수 있게 된 것이다. 다음으로 기존 소둔사이클이 갖는 기술적인 한계를 극복하여 더욱 진보된 소둔가열사이클을 독자적으로 확보할 수 있는 계기를 제공할 수 있게 되었다.Batch Annealing Furnace (BAF) heat treatment for the purpose of satisfying the mechanical properties and molding processability for the super-core cold-rolled steel sheet products suitable for the use such as automotive interior panels that require high formability as in the present invention The main effect obtained by the optimal heat treatment cycle method is that it is possible to substitute the BAF annealing heat treatment process for the products produced only in the conventional continuous annealing heat treatment process, thereby securing economic advantages and cost competitiveness through low-cost investment. It is possible to reduce the occurrence of large deviation of the predetermined yield strength (YP) and elongation, which is the biggest shortcoming in the product for the deep processing of automotive materials, and to improve the processability of the material and increase the capacity of products by shortening the cycle. Lowering the cost and energy consumption . Next, by overcoming the technical limitations of the existing annealing cycle, it is possible to provide an opportunity to independently secure a more advanced annealing heating cycle.

Claims (3)

고성형이 요구되는 초심가공 용도의 극저탄소강의 냉연강판 제품을 제조하기 위하여 C: 5~40ppm(이하 중량%), Si: 15~40ppm, Mn: 1000~2000ppm, Al: 200~500ppm, N: 50ppm이하, Ｏ: 50ppm이하, P: 100ppm이하, S: 100ppm이하 나머지는 Fe 및 불가피 불순물로 이루어져 총계 100중량%를 구성하는 화학성분 조성을 갖는 냉연강판을 상자소둔(Batch Annealing Furnace, 이하 BAF)열처리의 가열유지온도 725℃~750℃ 가열유지시간을 4시간~10시간의 범위 내에서 각각 변화시키는 소둔열처리사이클을 갖는 것을 특징으로 하는 초심가공용 냉연강판의 상자소둔로(BAF)를 이용한 열처리방법 C: 5 ~ 40ppm (hereinafter by weight), Si: 15 ~ 40ppm, Mn: 1000 ~ 2000ppm, Al: 200 ~ 500ppm, N: 50ppm or less, O: 50ppm or less, P: 100ppm or less, S: 100ppm or less Bannet Annealing Furnace (BAF) heat treatment having a chemical composition comprising 100% by weight of Fe and unavoidable impurities Heat treatment method using a box annealing furnace (BAF) of cold-rolled steel sheet for deep processing, characterized in that it has an annealing heat treatment cycle for varying the heating holding temperature of 725 ℃ ~ 750 ℃ heating holding time within the range of 4 hours to 10 hours 삭제delete 삭제delete
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KR101039984B1 (en) 2008-10-02 2011-06-09 현대하이스코 주식회사 Batch annealing furnace heat trearment conditions for high strength steel
KR101063582B1 (en) 2009-03-26 2011-09-07 현대하이스코 주식회사 Box Annealing Heat Treatment of High Tensile Strength Steel Sheet
CN102912232A (en) * 2012-11-16 2013-02-06 内蒙古包钢钢联股份有限公司 Ultra-deep-draw Ti-IF steel cold rolling and annealing process

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JPS5732330A (en) 1980-08-06 1982-02-22 Nippon Steel Corp Production of high strength cold rolled steel plate of superior quench hardenability and formability
JPS5743932A (en) 1980-08-28 1982-03-12 Sumitomo Metal Ind Ltd Production of high strength cold rolled steel strip excellent in press formability and bake hardenability
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JPS566709A (en) 1979-06-28 1981-01-23 Sumitomo Metal Ind Ltd Manufacture of cold rolled steel sheet possessing excellent press formability and baking hardenability
JPS5713123A (en) 1980-06-23 1982-01-23 Nippon Steel Corp Production of cold rolled steel plate for deep drawing
JPS5732330A (en) 1980-08-06 1982-02-22 Nippon Steel Corp Production of high strength cold rolled steel plate of superior quench hardenability and formability
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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR101039984B1 (en) 2008-10-02 2011-06-09 현대하이스코 주식회사 Batch annealing furnace heat trearment conditions for high strength steel
KR101063582B1 (en) 2009-03-26 2011-09-07 현대하이스코 주식회사 Box Annealing Heat Treatment of High Tensile Strength Steel Sheet
CN102912232A (en) * 2012-11-16 2013-02-06 内蒙古包钢钢联股份有限公司 Ultra-deep-draw Ti-IF steel cold rolling and annealing process

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