JPS62161938A - Cold-rolled steel sheet having superior workability and chemical conversion treating property and its production - Google Patents

Abstract

PURPOSE:To improve workability as well as chemical conversion treating property by subjecting a rolled steel sheet in which amounts of C, Mn, Al, Ti, Nb, etc., are specified to annealing at a prescribed temp. so as to allow unrecrystallized structure to remain. CONSTITUTION:A steel containing, by weight, <=0.006% C, <=0.5% Mn, <=0.05% Al, <=0.006% N, <=0.05% P, and 0.001-0.1% Ti and/or Nb is refined. The rolled sheet of this steel is subjected to continuous annealing at a temp. between recovery temp. and final recrystallization temp., so that unrecrystallized structure of 5-30% area ratio in sectional structure is allowed to remain.

Description

【発明の詳細な説明】 （産業上の利用分野） 連続焼鈍による極低炭素冷延鋼板の化成処理性・加工性
の兼備に関してこの明細書には、焼鈍条件の適合による
化成処理性及び加工性の改善に係る開発研究の成果につ
いて以下に述べる。Detailed Description of the Invention (Industrial Application Field) Regarding the combination of chemical conversion treatability and workability of ultra-low carbon cold rolled steel sheets by continuous annealing, this specification describes the combination of chemical conversion treatability and workability by adapting annealing conditions. The following describes the results of development research related to the improvement of

近年、冷延鋼板の焼鈍方法は、省エネルギー又は納期短
縮などの要請をみたすため、箱焼鈍法から連続焼鈍法へ
と変遷してきた。また、一般に冷延鋼板に用いられる鋼
は低炭素Ａ１キルド鋼である。In recent years, the annealing method for cold-rolled steel sheets has changed from a box annealing method to a continuous annealing method in order to meet the demands for energy conservation and shortened delivery times. Further, the steel generally used for cold rolled steel sheets is low carbon A1 killed steel.

連続焼鈍法によりプレス成形性の良好な冷延鋼板を製造
するには、再結晶焼鈍後、３００〜５００℃の温度域で
３〜１０分過時効処理を行ない、耐時効性の改善を行な
う必要があり、さらに耐時効性、絞り性を向上させるた
めＴｉ　、Ｎｂ　、Ｂのごとき炭窒化物形成元素の添加
も行われていた。In order to produce cold rolled steel sheets with good press formability using the continuous annealing method, it is necessary to perform overaging treatment for 3 to 10 minutes at a temperature range of 300 to 500 °C after recrystallization annealing to improve aging resistance. Furthermore, carbonitride-forming elements such as Ti, Nb, and B have been added to improve aging resistance and drawability.

一方プレス成形性を向上させるために固溶Ｃ１Ｎを数１
ｏｐｐｍの水準にまで低下させた極低炭素鋼を素材とす
る方法が、近年採用されるようになってきたが、このよ
うな極低炭素鋼を素材とした場合でも、絞り性、耐時効
性は若干の改善にとどまり、とくに深絞り性の良好なあ
るいは完全非時効性の冷延［ｉを製造するのは一般に困
難であって、それらの特性を改善するためやはり炭窒化
物形成元素の添加が必要とされる。On the other hand, in order to improve press formability, solid solution C1N is added to
In recent years, a method of using ultra-low carbon steel that has been reduced to the oppm level as a material has been adopted, but even when such ultra-low carbon steel is used as a material, it has poor drawability and aging resistance. However, it is generally difficult to produce cold-rolled products with good deep drawability or complete non-aging property, and in order to improve these properties, it is still necessary to add carbonitride-forming elements. is required.

しかもこのような極低炭素冷延鋼板にあっては、上掲の
低炭素鋼素材に比べてプレス成形後、塗装下地処理とし
て施されるりん酸亜鉛による化成処理において、りん酸
塩の被膜結晶が粗大化したり、りん酸塩結晶が析出しな
い部分、すなわち、スケが発生し、その結果塗装後の耐
食性が劣るところにおいて、この種冷延鋼板の重要な使
途たる自動車用鋼板として致命的な欠点が指摘される。Furthermore, compared to the above-mentioned low-carbon steel materials, ultra-low carbon cold-rolled steel sheets like this are coated with phosphate crystals during chemical conversion treatment with zinc phosphate, which is applied as a base treatment for painting after press forming. This is a fatal drawback for steel sheets for automobiles, which is an important use of this type of cold-rolled steel sheet, in areas where phosphate crystals become coarse or where phosphate crystals do not precipitate. is pointed out.

（従来の技術） 特開昭５９−７４２５９号公報には、極低炭素鋼又はＴ
ｉ　、Ｎｂ　、Ｚｒを添加したスタビライズド鋼の表面
に、片面当り２〜１００μｍでＣ，’Ｍｎ、Ｓ。(Prior art) Japanese Patent Application Laid-open No. 59-74259 discloses ultra-low carbon steel or T
C, 'Mn, S at 2 to 100 μm per side on the surface of stabilized steel added with i, Nb, and Zr.

Ｐの１種又は２種以上から成る濃化層を有するようにし
て加工性、およびりん酸塩処理性を改良することが開示
されている。しかし、箱焼鈍法ならばともかく、連続焼
鈍法のように短時間で焼鈍過程が終了する方法では、鋼
板表面にＣ，Ｍｎ　、Ｓ。It is disclosed that the processability and phosphate treatment properties are improved by having a concentrated layer consisting of one or more types of P. However, unlike the box annealing method, when the annealing process is completed in a short time, such as the continuous annealing method, C, Mn, and S are deposited on the surface of the steel sheet.

Ｐ等の濃化層を形成させるのは技術的にかなり困難であ
る。なお同号公報にはクラッド法（熱延に先立って極低
炭素材の鋼片と所定のＣ，Ｍｎ、Ｐ。It is technically quite difficult to form a layer enriched with P or the like. The same publication describes a cladding method (prior to hot rolling, a steel billet of ultra-low carbon material and predetermined C, Mn, and P are coated).

Ｓの化学成分を有する素材の鋼片とを圧接し、加熱圧延
する方法）や浸透法（焼鈍時の雰囲気ガスで浸炭させる
方法、又は焼鈍後、中性塩浴中で浸漬処理を行なう方法
）により表面濃化層を形成させることに言及されている
が、製造工程が繁雑化し製造日数の長期化、製造コスト
の上昇などの不利を招く欠点がある。A method of press-welding a steel piece with a material having a chemical composition of S and hot rolling) or an infiltration method (a method of carburizing with atmospheric gas during annealing, or a method of performing immersion treatment in a neutral salt bath after annealing) Although it is mentioned that a surface concentration layer is formed by the method, there are drawbacks such as the production process becomes complicated, the number of production days becomes longer, and the production cost increases.

（発明が解決しようとする問題点） 従来の技術につき上掲したような表面濃化層の形成のご
とき手間をかける不利なく、連続焼鈍工程操作に配慮を
加えるだけで極低炭素鋼、とくに炭窒化物形成元素を添
加した場合にも、プレス成形に何らの支障を与えずして
その後の塗装下地処理のためのりん酸塩によるような化
成処理性にすぐれる冷延鋼板とその有利な製造方法を与
えることがこの発明の目的である。(Problems to be Solved by the Invention) Ultra-low carbon steel, especially carbon steel, can be produced by simply adding consideration to the operation of the continuous annealing process, without the disadvantage of requiring time and effort such as the formation of a surface enriched layer as described above with respect to the conventional technology. A cold-rolled steel sheet that has excellent chemical conversion treatment properties such as phosphate for subsequent painting base treatment without causing any hindrance to press forming even when nitride-forming elements are added, and advantageous production thereof. It is an object of this invention to provide a method.

（問題点を解決するための手段） この発明は、結晶粒内にある無数の転位が優先核生成サ
イトとなり得ることの知見に由来するものでＣ：　　０
．００６ｗｔ％以下、Ｍｎ　：　　０．５ｗｔ％以下、
Δｉ：　　０，０５ｗｔ％以下、Ｎ　：　　０．００６
ｗｔ％以下、ｐ　：　　０．０５ｗｔ％以下を含みかつ
、窒化物、硫化物は不算入としたＴｉ及び／又はＮｂの
合計ｏ、ｏｏｉ〜０，１００ｗｔ％を含有し、残部は鉄
及び不可避的不純物の組成から成り、断面組織面積率に
て５〜３０％の未再結晶組織を有することを特徴とする
化成処理性、加工性の良好な冷延鋼板、ならびにＣ：０
．００６ｗｔ％以下、Ｍｎ　：　　０．５ｗｔ％以下Ａ
ｌ：０．０５ｗｔ％以下、Ｎ　：　　０．００６ｗｔ％
以下、Ｐ：０．０５ｗｔ％以下のほか、窒化物、硫化物
は不算入としたＴ１及び／又はＮｂの合計ｏ、ｏｏｉ〜
ｏ、ｉｏ。(Means for Solving the Problems) This invention originates from the knowledge that countless dislocations within a crystal grain can serve as preferential nucleation sites, and C: 0
．． 006wt% or less, Mn: 0.5wt% or less,
Δi: 0.05wt% or less, N: 0.006
wt% or less, p: Contains a total of o, ooi ~ 0,100 wt% of Ti and/or Nb, including 0.05 wt% or less and excluding nitrides and sulfides, the remainder being iron and unavoidable A cold-rolled steel sheet with good chemical conversion treatability and workability, characterized by having a composition of impurities and having an unrecrystallized structure with a cross-sectional structure area ratio of 5 to 30%, and C: 0
．． 006wt% or less, Mn: 0.5wt% or less A
L: 0.05wt% or less, N: 0.006wt%
Hereinafter, in addition to P: 0.05 wt% or less, the total of T1 and/or Nb excluding nitrides and sulfides o, ooi ~
o,io.

Ｗ【％を含有し、残部は鉄および不可避的不純物とから
成る極低炭素鋼板を圧延したのち、連続焼鈍法で回復温
度以上、再結晶終了温度未満の温度で短時間焼鈍し、断
面組織面積率にて５〜３０％の未再結晶組織を残存させ
ることを特徴とする化成処理性、加工性の良好な冷延鋼
板の製造方法である。After rolling an ultra-low carbon steel plate containing W[%] and the balance being iron and unavoidable impurities, it is annealed for a short time using a continuous annealing method at a temperature above the recovery temperature and below the recrystallization completion temperature, and the cross-sectional structure area is This is a method for producing a cold-rolled steel sheet with good chemical conversion treatment properties and workability, which is characterized by leaving 5 to 30% of unrecrystallized structure.

以下、この発明の基礎となった実験についてまず説明す
る。Hereinafter, the experiments that formed the basis of this invention will first be explained.

表１に示すような化学組成の鋼を溶製俊、熱間圧延によ
り熱延板とし、脱スケール後、冷間圧延により板厚をｏ
、ａｍｍとした。Steel with the chemical composition shown in Table 1 is melted and hot-rolled to form a hot-rolled plate, and after descaling, the plate thickness is reduced to o by cold rolling.
, amm.

ｊ） １−。j) 1-.

巨 次いで、第１図に示すヒートサイクルで焼鈍温度を種々
に変えて鋼板の未再結晶組織率を変化させた。Next, the annealing temperature was varied in the heat cycle shown in FIG. 1 to change the unrecrystallized microstructure ratio of the steel sheet.

何れの場合も焼鈍後、０．８％の調質圧延を施し、鋼板
の材質（全伸び）、ならびに化成処理性を調べた。その
結果を第２図に示し、ここに、化成処理性　　：市販の
化成処理液に２分浸漬酸素還元電流値：ＮａＯＨ溶液（
Ｄ　Ｈ＝１１．８）中で測定 によるものとした。In each case, after annealing, 0.8% temper rolling was performed, and the material quality (total elongation) and chemical conversion treatability of the steel sheets were examined. The results are shown in Figure 2, where chemical conversion property: immersion in a commercially available chemical treatment solution for 2 minutes;
D H = 11.8).

第２図に示す８鋼（Ａ）、（Ｂ）及び（Ｃ）鋼は未再結
晶組織率が５〜３０％の範囲内において化成処理性を示
すりん酸塩結晶の粒度、ならびにＮ　ａ　ＯＨ（１）　
Ｈ＝　１１．８）　溶液中テａｌ定シタＭ素’Ａ１元電
流値は良好であった。すなわち、未再結晶組織率が５％
以上の鋼板のりん酸塩結晶粒は細かく、かつ酸素還元電
流値は低く、化成処理性にすぐれたりん酸塩被膜が形成
された。また、全伸びは未再結晶組織率が３０％以内に
おいて加工性を損なわない程度の伸びであることが知見
された。Steels 8 (A), (B), and (C) shown in Figure 2 have a grain size of phosphate crystals that exhibit chemical conversion treatability within the range of unrecrystallized microstructure ratio of 5 to 30%, and N a OH (1)
H = 11.8) The constant current value of the element M'A1 in solution was good. That is, the unrecrystallized structure rate is 5%.
The phosphate crystal grains of the above steel sheets were fine, the oxygen reduction current value was low, and a phosphate film with excellent chemical conversion properties was formed. It was also found that the total elongation was such that workability was not impaired when the unrecrystallized structure ratio was within 30%.

また、以上の実験で得られたりん酸塩結晶は、たとえば
特開昭５９−　７４２５９号公報に開示されているりん
酸塩結晶と比較し、同等あるいはそれより小さなりん酸
塩結晶粒であり、良好な化成処理性を示すことが判明し
た。Furthermore, the phosphate crystals obtained in the above experiment are phosphate crystal grains that are equivalent to or smaller than, for example, the phosphate crystals disclosed in JP-A-59-74259; It was found that it exhibited good chemical conversion treatment properties.

（作用） 以上の鋼（Ａ）、（Ｂ）及び（Ｃ）で化成処理性の良好
な冷延鋼板を得られた理由については、定かではないが
、鋼板組織内に残存する転位が化成処理性向上に何らか
の寄与をしているためと考えられる。(Effect) The reason why cold-rolled steel sheets with good chemical conversion treatability were obtained from the steels (A), (B), and (C) described above is not clear, but dislocations remaining in the steel sheet structure cause chemical conversion treatment. This is thought to be due to some contribution to sexual improvement.

すなわち、一般に化成処理時には粒界がりん酸塩結晶の
優先核生成サイトとなり易く、そのためりん酸塩結晶は
粒界より核生成し、成長する。よって極低炭素鋼のよう
な結晶粒の大きな鋼板では結晶粒１個をりん酸塩結晶で
覆うことになるため必然的にりん酸塩結晶も粗大化する
。これに対し、鋼板中の転位密度が高い場合、粒内に存
在する無数の転位が優先核生成サイトとなり、きわめて
多数の緻密なりん酸塩結晶が生成し、化成処理性を良好
とならしめたものと推定される。That is, in general, grain boundaries tend to become preferential nucleation sites for phosphate crystals during chemical conversion treatment, and therefore phosphate crystals nucleate and grow from grain boundaries. Therefore, in a steel plate with large crystal grains such as ultra-low carbon steel, each crystal grain is covered with phosphate crystals, so the phosphate crystals inevitably become coarse. On the other hand, when the dislocation density in the steel sheet is high, the numerous dislocations existing within the grains become preferential nucleation sites, and a large number of dense phosphate crystals are formed, resulting in good chemical conversion treatment properties. It is estimated that

次に本発明において、鋼組成、製造条件を限定した理由
について以下に述べる。Next, the reason for limiting the steel composition and manufacturing conditions in the present invention will be described below.

Ｃの含有量の上限を０．００６％とした理由は、０．０
０６％を越えると結晶粒は細かく、固溶Ｃ量が多くなる
ことから加工性、耐時効性を著しく損なうことがらであ
る。The reason why the upper limit of the C content was set to 0.006% is that 0.0
If it exceeds 0.6%, the crystal grains will be fine and the amount of solid solute C will increase, which will significantly impair workability and aging resistance.

ｎ １ｙｌｎは、熱間割れの原因となるＳを固定するのに有
効な元素であり、製鋼工程で添加する必要があるが、０
．５％超の含有は材質を硬化させ、延性を低下させるこ
とから、上限を０．５％とした。n 1yln is an effective element for fixing S, which causes hot cracking, and needs to be added during the steelmaking process, but 0
．． Since a content of more than 5% hardens the material and reduces ductility, the upper limit was set at 0.5%.

八ぶ ＡＡは製鋼時の脱酸剤として、また固溶ＮをＡＡＮとし
て固定する効果もあることから、ＡＡの添加は必要であ
る。しかし、あまり多聞の添加は溶鋼コストを上昇させ
ることから、本発明では０．０５％以下とした。The addition of AA is necessary because Yabu AA acts as a deoxidizing agent during steel manufacturing and also has the effect of fixing solid solution N as AAN. However, adding too much increases the cost of molten steel, so in the present invention it is set at 0.05% or less.

ＮはＣと同様、結晶粒を微細にし加工性を低下させる上
、耐時効性も劣化させてしまうことから、Ｎの含有口は
０．００６％以下とする必要がある。Like C, N makes crystal grains finer and reduces workability, as well as deteriorating aging resistance. Therefore, the N content needs to be 0.006% or less.

Ｐは化成処理性を向上させる元素であるが、０．０５％
越の含有は材質を硬化させ加工性を劣化させることから
、上限を０．０５％とした。P is an element that improves chemical conversion treatment properties, but at 0.05%
The upper limit was set at 0.05% since the content of nitrate hardens the material and deteriorates workability.

Ｔｉ　、　Ｎｂ 窒化物、硫化物については不算入としたＴｉもしくはＮ
ｂを１種または２種の合計で、０．００１〜０、１００
％とした理由は、０．００１％未満では加工性を向上さ
せることは困難であり、また０、　１００％越では再結
晶温度を著しく上昇させ、溶鋼コストのみならず製造コ
ストも高くなることからひある。Ti, Nb Nitride and sulfide are not included in Ti or N.
The total of one or two types of b is 0.001 to 0, 100
% is because it is difficult to improve workability if it is less than 0.001%, and if it exceeds 0 or 100%, the recrystallization temperature will increase significantly, increasing not only the molten steel cost but also the manufacturing cost. There is.

未再結晶組織 未再結晶組織の存在は化成処理性を向上させるが、５％
未満の残存では効果はなく、また３０％越の残存では加
工性が著しく劣化することから、本発明ではその残存量
を５〜３０％の範囲内とした。Non-recrystallized structure The presence of non-recrystallized structure improves chemical conversion properties, but 5%
If less than 30% remains, there is no effect, and if more than 30% remains, workability deteriorates significantly, so in the present invention, the remaining amount is set within the range of 5 to 30%.

連続焼鈍 箱焼鈍法よりも連続焼鈍法が未再結晶組織の残存最を制
御しやすく、また連続焼鈍法は短時間で焼鈍工程が完了
することから、本発明では連続焼鈍法を採用した。しか
し、ヒートサイクル（加熱条件、焼鈍温度、均熱時間、
冷却条件）は、とくに規定するものではない。Continuous annealing The continuous annealing method is easier to control the remaining unrecrystallized structure than the box annealing method, and the continuous annealing method completes the annealing process in a short time, so the continuous annealing method was adopted in the present invention. However, heat cycle (heating conditions, annealing temperature, soaking time,
Cooling conditions) are not particularly specified.

（実施例） 次に実施例を以下に述べる。(Example) Next, examples will be described below.

表２に示す組成の鋼を溶製後、熱間圧延により板厚３．
２ｍｍとし、脱スケール後、冷間圧延により板厚０．７
ｍｍの冷延板とし、第３図に示したような焼鈍を行なっ
た。After melting steel with the composition shown in Table 2, it is hot rolled to a thickness of 3.
After descaling, the plate thickness was 0.7 mm by cold rolling.
A cold-rolled sheet with a thickness of 1 mm was prepared and annealed as shown in FIG.

すなわち、（７％Ｈ２＋Ｎ２　）雰囲気において、平均
加熱速度１５℃／Ｓで加熱し種々の温度に３０ｓ保持侵
、平均１０℃／Ｓの冷却速度で３００℃まで冷却し、そ
の後室温まで空冷した。That is, in a (7% H 2 + N 2 ) atmosphere, it was heated at an average heating rate of 15°C/S, held at various temperatures for 30 seconds, cooled to 300°C at an average cooling rate of 10°C/S, and then air cooled to room temperature.

次いで０．８％の調質圧延を施し、市販の化成処理液（
ｐＨ＝３）に２分間浸漬した後、鋼板表面のりん酸塩結
晶の大きさとＮａ　ＯＨ溶液（ｐ　Ｈ＝１２）中での酸
素還元電流、ならびにＪ　１８５号試片による機械的特
性をそれぞれ調べ、これらの結果を表３に示した。Next, 0.8% temper rolling was performed and a commercially available chemical conversion treatment liquid (
The size of phosphate crystals on the surface of the steel sheet, the oxygen reduction current in NaOH solution (pH = 12), and the mechanical properties using J 185 specimen were investigated. , these results are shown in Table 3.

その結果、この発明の方法によって製造された鋼板の化
成処理性改善により、りん酸塩結晶は小さく密に分布し
、酸素還元電流は比較例よりもはるかに小さい値であっ
た。また、加工性、とくに、伸びは本発明鋼であれば３
０％以上の値を得ることができた。As a result, due to the improved chemical conversion properties of the steel sheet manufactured by the method of the present invention, the phosphate crystals were small and densely distributed, and the oxygen reduction current was much smaller than that of the comparative example. In addition, the workability, especially the elongation of the steel of the present invention, is 3.
We were able to obtain a value of 0% or more.

（発明の効果） この発明は鋼板組織を完全に再結晶させず、転位密度の
高い鋼板を製造する方法であり、この発明によれば炭窒
化物形成元素を添加した鋼板でも、化成処理性の良好な
冷延鋼板を製造することが可能である。(Effect of the invention) This invention is a method for manufacturing a steel sheet with high dislocation density without completely recrystallizing the steel sheet structure. It is possible to produce good cold rolled steel sheets.

【図面の簡単な説明】[Brief explanation of drawings]

第１図は連続焼鈍のヒートサイクルを示す図面。 第２図はりん酸塩平均結晶粒径、酸素還元電流、および
全伸びと未再結晶組織率の関係を示す図面。 第３図は連続焼鈍のヒートサイクルを示す図面。 第１図 第３図FIG. 1 is a diagram showing a heat cycle of continuous annealing. FIG. 2 is a diagram showing the relationship between phosphate average crystal grain size, oxygen reduction current, total elongation, and unrecrystallized structure ratio. FIG. 3 is a diagram showing a heat cycle of continuous annealing. Figure 1 Figure 3

Claims (1)

【特許請求の範囲】 １、Ｃ：０．００６ｗｔ％以下、Ｍｎ：０．５ｗｔ％以
下、Ａｌ：０．０５ｗｔ％以下、Ｎ：０．００６ｗｔ％
以下、Ｐ：０．０５ｗｔ％以下を含みかつ、窒化物、硫
化物は不算入としたＴｉ及び／又はＮｂの合計０．００
１〜０．１００ｗｔ％を含有し、残部は鉄及び不可避的
不純物の組成から成り、断面組織面積率にて５〜３０％
の未再結晶組織を有することを特徴とする化成処理性、
加工性の良好な冷延鋼板。 ２、Ｃ：０．００６ｗｔ％以下、Ｍｎ：０．５ｗｔ％以
下Ａｌ：０．０５ｗｔ％以下、Ｎ：０．００６ｗｔ％以
下、Ｐ：０．０５ｗｔ％以下のほか、窒化物、硫化物は
不算入としたＴｉ及び／又はＮｂの合計０．００１〜０
．１００ｗｔ％を含有し、残部は鉄及び不可避的不純物
の組成から成る極低炭素鋼板を圧延したのち、連続焼鈍
法で回復温度以上再結晶終了温度未満の温度で短時間焼
鈍し、断面組織面積率にて５〜３０％の未再結晶組織を
残存させることを特徴とする化成処理性、加工性の良好
な冷延鋼板の製造方法。[Claims] 1. C: 0.006wt% or less, Mn: 0.5wt% or less, Al: 0.05wt% or less, N: 0.006wt%
Below, the total amount of Ti and/or Nb is 0.00, including P: 0.05 wt% or less and excluding nitrides and sulfides.
Contains 1 to 0.100 wt%, the remainder consists of iron and unavoidable impurities, and has a cross-sectional structure area ratio of 5 to 30%.
Chemical conversion treatability characterized by having an unrecrystallized structure of
Cold rolled steel sheet with good workability. 2. In addition to C: 0.006wt% or less, Mn: 0.5wt% or less, Al: 0.05wt% or less, N: 0.006wt% or less, P: 0.05wt% or less, nitrides and sulfides are free. Total amount of Ti and/or Nb included: 0.001 to 0
．． After rolling an ultra-low carbon steel sheet containing 100wt% and the remainder consisting of iron and unavoidable impurities, it is annealed for a short time using a continuous annealing method at a temperature above the recovery temperature and below the recrystallization completion temperature to reduce the cross-sectional structure area ratio. A method for producing a cold-rolled steel sheet with good chemical conversion treatment properties and workability, characterized in that 5 to 30% of unrecrystallized structure remains in the steel sheet.