JPH04293730A - Production of hot-dip metal coated steel sheet excellent in baking hardenability - Google Patents
Production of hot-dip metal coated steel sheet excellent in baking hardenabilityInfo
- Publication number
- JPH04293730A JPH04293730A JP8091391A JP8091391A JPH04293730A JP H04293730 A JPH04293730 A JP H04293730A JP 8091391 A JP8091391 A JP 8091391A JP 8091391 A JP8091391 A JP 8091391A JP H04293730 A JPH04293730 A JP H04293730A
- Authority
- JP
- Japan
- Prior art keywords
- steel sheet
- hot
- weight
- carbon content
- steel
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 15
- 229910000831 Steel Inorganic materials 0.000 title abstract description 43
- 239000010959 steel Substances 0.000 title abstract description 43
- 239000002184 metal Substances 0.000 title abstract 6
- 229910052751 metal Inorganic materials 0.000 title abstract 6
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 49
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 46
- 238000000137 annealing Methods 0.000 claims abstract description 36
- 239000010960 cold rolled steel Substances 0.000 claims abstract description 13
- 238000005261 decarburization Methods 0.000 claims description 28
- 229910001335 Galvanized steel Inorganic materials 0.000 claims description 10
- 239000008397 galvanized steel Substances 0.000 claims description 10
- 229910052710 silicon Inorganic materials 0.000 abstract description 5
- 229910052748 manganese Inorganic materials 0.000 abstract description 4
- 229910052698 phosphorus Inorganic materials 0.000 abstract description 4
- 229910052742 iron Inorganic materials 0.000 abstract description 3
- 229910052759 nickel Inorganic materials 0.000 abstract description 3
- 229910052717 sulfur Inorganic materials 0.000 abstract description 3
- 239000011248 coating agent Substances 0.000 abstract 2
- 238000000576 coating method Methods 0.000 abstract 2
- 230000001105 regulatory effect Effects 0.000 abstract 2
- 238000006243 chemical reaction Methods 0.000 description 11
- 238000007747 plating Methods 0.000 description 10
- 238000000034 method Methods 0.000 description 8
- 238000005275 alloying Methods 0.000 description 7
- 239000007787 solid Substances 0.000 description 7
- 238000010438 heat treatment Methods 0.000 description 6
- 239000006104 solid solution Substances 0.000 description 6
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 5
- 230000000694 effects Effects 0.000 description 5
- 239000010410 layer Substances 0.000 description 5
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 5
- 229910052725 zinc Inorganic materials 0.000 description 5
- 239000011701 zinc Substances 0.000 description 5
- 238000005246 galvanizing Methods 0.000 description 4
- 229910052758 niobium Inorganic materials 0.000 description 4
- 229910052719 titanium Inorganic materials 0.000 description 4
- 229910052804 chromium Inorganic materials 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- 239000002344 surface layer Substances 0.000 description 3
- 229910000859 α-Fe Inorganic materials 0.000 description 3
- 230000003679 aging effect Effects 0.000 description 2
- 238000013459 approach Methods 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 229910052757 nitrogen Inorganic materials 0.000 description 2
- 239000002436 steel type Substances 0.000 description 2
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 150000001721 carbon Chemical class 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000007598 dipping method Methods 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 238000010422 painting Methods 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 238000011084 recovery Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 239000007858 starting material Substances 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 230000035882 stress Effects 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000009864 tensile test Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
Landscapes
- Coating With Molten Metal (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Abstract
Description
【０００１】0001
【産業上の利用分野】本発明は、必要とする焼付け硬化
性が脱炭焼鈍により付与された溶融めっき鋼板を製造す
る方法に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing hot-dip galvanized steel sheets that have been given the necessary bake hardenability by decarburization annealing.
【０００２】0002
【従来の技術】自動車用鋼板として使用される溶融めっ
き鋼板には、パネル等の所定形状に成形した後で焼付け
塗装によって降伏強度が上昇する、いわゆる焼付け硬化
性が要求される。焼付け硬化性は、図１に示すように、
フェライト中の固溶炭素含有量によって定まる。そして
、鋼板製品において降伏点伸びの回復に起因するストレ
ッチャーストレインの発生を考慮して、３〜６ｋｇｆ／
ｍｍ２ が適正な焼付け硬化性とされている。焼付け硬
化性をこの範囲に収めるためには、図１に示した関係か
ら、固溶炭素量を４〜１１ｐｐｍに調整することが必要
とされる。2. Description of the Related Art Hot-dip galvanized steel sheets used as steel sheets for automobiles are required to have so-called bake hardenability, which means that the yield strength can be increased by baking painting after forming into a predetermined shape such as a panel. The bake hardenability is as shown in Figure 1.
Determined by the solid solution carbon content in ferrite. Considering the occurrence of stretcher strain caused by recovery of yield point elongation in steel plate products, 3 to 6 kgf/
mm2 is considered to be an appropriate bake hardenability. In order to keep the bake hardenability within this range, it is necessary to adjust the amount of solid solute carbon to 4 to 11 ppm from the relationship shown in FIG.
【０００３】この低レベルに固溶炭素量を維持する方法
としては、製鋼段階でＣ，Ｎ，Ｓ，Ｔｉ，Ｎｂ等を厳格
に管理して極低炭素鋼を製造することが、たとえば特開
平２−１１１８４１号公報で提案されている。添加され
たＴｉ，Ｎｂ等は、鋼中に存在する余分なＣを炭化物と
して固定し、焼付け硬化性に有効な固溶炭素量を目標値
に維持する。[0003] As a method of maintaining the amount of solid solute carbon at this low level, it is possible to manufacture ultra-low carbon steel by strictly controlling C, N, S, Ti, Nb, etc. at the steel manufacturing stage, as described in, for example, Japanese Patent Laid-open Publication No. This method is proposed in Japanese Patent No. 2-111841. The added Ti, Nb, etc. fix excess C present in the steel as carbide, and maintain the amount of solid solution carbon effective for bake hardenability at a target value.
【０００４】また、自動車用鋼板として多用されている
溶融めっき鋼板にあっては、溶融めっき及び合金化処理
後の急冷のために、必要とする焼付け硬化性を得る炭素
量よりも遥かに多量の炭素がフェライトマトリックスに
固溶する。そこで、溶融亜鉛めっき後の鋼板に熱処理を
施し、過剰の炭素を析出させ、固溶炭素量を調整するこ
とが特開昭５７−７０２６９号公報で紹介されている。[0004] Furthermore, hot-dip galvanized steel sheets, which are often used as steel sheets for automobiles, contain a much larger amount of carbon than the required bake hardenability due to rapid cooling after hot-dipping and alloying. Carbon is dissolved in the ferrite matrix. Therefore, JP-A-57-70269 introduces a method of heat-treating a hot-dip galvanized steel sheet to precipitate excess carbon and adjust the amount of solid solute carbon.
【０００５】[0005]
【発明が解決しようとする課題】製鋼段階で炭素含有量
を調整する方法では、固溶炭素含有量を正確に制御する
ことが困難である。たとえば、添加されるＴｉ，Ｎｂ等
が鋼中のＣと結合する効率は製鋼条件によって変わるも
のであり、またＴｉ，Ｎｂ等はＮ，Ｓとも結合する。そ
のため、得られた鋼の固溶炭素含有量が比較的大きな幅
でばらつき、必要とする焼付け硬化性に対応する値にす
ることは、実操業上極めて困難なものとなる。[Problems to be Solved by the Invention] In the method of adjusting the carbon content at the steel manufacturing stage, it is difficult to accurately control the solid solution carbon content. For example, the efficiency with which added Ti, Nb, etc. combine with C in steel varies depending on the steel manufacturing conditions, and Ti, Nb, etc. also combine with N, S. Therefore, the solute carbon content of the obtained steel varies over a relatively large range, and it is extremely difficult in actual operation to obtain a value that corresponds to the required bake hardenability.
【０００６】また、溶融亜鉛めっき後に過剰の固溶炭素
を析出させる方法は、溶融めっきラインにポスト炉を設
置すること、或いは別途の熱処理ラインが必要となる。
そのため、設備負担及び工程の付加を招き、生産性が低
下する。[0006] Furthermore, the method of precipitating excess solid solution carbon after hot-dip galvanizing requires installing a post furnace in the hot-dip plating line or a separate heat treatment line. This results in a burden on equipment and an additional process, resulting in a decrease in productivity.
【０００７】本発明は、このような問題を解消すべく案
出されたものであり、脱炭焼鈍によって固溶炭素含有量
を調整することにより、鋼種に拘らず、必要とする焼付
け硬化性を溶融めっき鋼板に付与することを目的とする
。The present invention was devised to solve these problems, and by adjusting the solid solute carbon content through decarburization annealing, the required bake hardenability can be achieved regardless of the steel type. The purpose is to apply it to hot-dip galvanized steel sheets.
【０００８】[0008]
【課題を解決するための手段】本発明の製造方法は、そ
の目的を達成するため、Ｃ：０．０３〜０．３０重量％
，Ｓｉ：０．８０重量％以下，Ｍｎ：０．６０〜２．０
重量％，Ｐ：０．１重量％以下，Ｓ：０．０１０重量％
以下，Ａｌ：０．０２０〜０．０７９重量％を含有する
冷延鋼板に対し、１０〜３０ｐｐｍの範囲で目標焼付け
硬化性に対応する炭素含有量に低下させる脱炭焼鈍を施
した後、溶融めっきすることを特徴とする。[Means for Solving the Problems] In order to achieve the object, the manufacturing method of the present invention provides C: 0.03 to 0.30% by weight.
, Si: 0.80% by weight or less, Mn: 0.60 to 2.0
Weight%, P: 0.1% by weight or less, S: 0.010% by weight
Hereinafter, a cold-rolled steel sheet containing Al: 0.020-0.079% by weight is subjected to decarburization annealing to reduce the carbon content to a target bake hardenability in the range of 10-30 ppm, and then melted. Characterized by plating.
【０００９】脱炭焼鈍された冷延鋼板のうち、高Ｍｎ，
Ｓｉ，Ｃｒ，Ｐ鋼のように合金元素Ｍｎ，Ｓｉ，Ｃｒ，
Ｐ等が濃縮され易い鋼種にあっては、溶融亜鉛に対する
濡れ性及び合金化の反応速度を向上させるために、予め
Ｆｅ，Ｆｅ−Ｂ，Ｎｉ等のプレめっきを冷延鋼板に施し
ておくことが好ましい。Among the decarburized annealed cold rolled steel sheets, high Mn,
Alloying elements Mn, Si, Cr, like Si, Cr, P steel
For steel types where P etc. are easily concentrated, pre-plating with Fe, Fe-B, Ni etc. should be applied to the cold rolled steel sheet in advance in order to improve the wettability to molten zinc and the reaction rate of alloying. is preferred.
【００１０】0010
【作 用】本発明者等の研究により、溶融めっき鋼板
の焼付け硬化性は、炭素含有量との間に図２に示した関
係を持っていることが判った。この炭素含有量は、固溶
炭素含有量の測定と異なり、比較的容易に求めることが
できる。そして、脱炭焼鈍時の焼鈍時間や加熱温度等の
条件を変えることによって、炭素含有量を目標値に調整
することが容易に行われる。脱炭焼鈍による炭素含有量
の制御は、製鋼段階における成分調整に比較して、鋼種
による制約を受けることなく、必要とする焼付硬度に対
応する炭素含有量に高精度で一致させることができる。[Function] Through research conducted by the present inventors, it has been found that the bake hardenability of hot-dip galvanized steel sheets has the relationship shown in FIG. 2 with the carbon content. This carbon content can be determined relatively easily, unlike the measurement of solid solution carbon content. By changing conditions such as annealing time and heating temperature during decarburization annealing, the carbon content can be easily adjusted to a target value. Controlling the carbon content through decarburization annealing is not limited by the type of steel and can match the carbon content corresponding to the required baking hardness with high precision compared to component adjustment at the steelmaking stage.
【００１１】炭素含有量を１０〜３０ｐｐｍに下げるこ
とは、オープンコイル焼鈍により十分可能である。そこ
で、オープンコイル焼鈍設備を使用し、冷延鋼板を６０
０℃以上の高温に加熱することにより、脱炭焼鈍を行う
。[0011] It is fully possible to reduce the carbon content to 10 to 30 ppm by open coil annealing. Therefore, using open coil annealing equipment, cold-rolled steel sheets were
Decarburization annealing is performed by heating to a high temperature of 0° C. or higher.
【００１２】焼鈍雰囲気は、水蒸気を混入したＡＸガス
を使用する。水蒸気の混入量は、脱炭反応を円滑に行わ
せる上から、雰囲気の露点が２０〜６０℃の範囲に維持
されるように調整することが好ましい。露点が２０℃よ
り低い乾燥雰囲気では、Ｃ＋Ｈ２ Ｏ→ＣＯ＋Ｈ２ の
脱炭反応速度が小さく、長時間の高温加熱が必要とされ
る。
その結果、鋼板表面にＳｉ，Ｃｒ，Ｍｎ，Ｐ等が濃縮し
、溶融亜鉛めっき工程において溶融亜鉛の付着や合金化
反応を阻害する。また、露点が６０℃を超えるとき、２
Ｈ２ Ｏ→２Ｈ２ ＋Ｏ２ の分解反応で生じた酸素に
より鋼板表面が酸化し易くなる。[0012] For the annealing atmosphere, AX gas mixed with water vapor is used. The amount of water vapor mixed is preferably adjusted so that the dew point of the atmosphere is maintained in the range of 20 to 60° C. in order to smoothly carry out the decarburization reaction. In a dry atmosphere with a dew point lower than 20° C., the decarburization reaction rate of C+H2O→CO+H2 is slow, and long-term high-temperature heating is required. As a result, Si, Cr, Mn, P, etc. are concentrated on the surface of the steel sheet, inhibiting adhesion of molten zinc and alloying reaction in the hot-dip galvanizing process. Also, when the dew point exceeds 60℃, 2
The surface of the steel sheet becomes easily oxidized due to oxygen generated by the decomposition reaction of H2O→2H2 +O2.
【００１３】焼鈍温度は、脱炭反応開始温度６００℃以
上、好ましくは７００〜８００℃に設定する。この焼鈍
温度が６００℃より低いとき、脱炭反応が進行しないか
、長時間の脱炭が必要となる。また、８００℃を超える
焼鈍温度では、脱炭反応の進行状態を予測することが困
難になり、炭素含有量を目標レベルに制御することが難
しくなる。[0013] The annealing temperature is set at a decarburization reaction starting temperature of 600°C or higher, preferably 700 to 800°C. When this annealing temperature is lower than 600°C, the decarburization reaction does not proceed or a long time decarburization is required. Further, at an annealing temperature exceeding 800° C., it becomes difficult to predict the progress of the decarburization reaction, and it becomes difficult to control the carbon content to a target level.
【００１４】炭素含有量１０〜３０ｐｐｍまで脱炭する
ための時間は、鋼板の初期炭素量，板厚，表面積等によ
って変わる。たとえば、初期炭素含有量が０．１４重量
％の冷延鋼板を温度７４０℃のＡＸガス雰囲気で脱炭す
るとき、鋼板表面積Ｓに応じて焼鈍時間ｔが次式（１）
及び（２）のように変わることが実験的に求められた。The time required to decarburize the steel sheet to a carbon content of 10 to 30 ppm varies depending on the initial carbon content, sheet thickness, surface area, etc. of the steel sheet. For example, when decarburizing a cold-rolled steel plate with an initial carbon content of 0.14% by weight in an AX gas atmosphere at a temperature of 740°C, the annealing time t is determined by the following formula (1) depending on the steel plate surface area S.
It has been experimentally determined that the following changes occur: and (2).
【００１５】Ｓ≦１．５×１０９ ｍｍ２ の場合、脱
炭反応が鋼中のＣの拡散速度に律速されて、焼鈍時間ｔ
は、式（１）で表される。
ｔ＝１．３０８×（Ｇ＋０．０４９５）２＋Ａ
×Ｇ２ ・・・・・（１）When S≦1.5×109 mm2, the decarburization reaction is rate-limited by the diffusion rate of C in the steel, and the annealing time t
is expressed by equation (1). t=1.308×(G+0.0495)2+A
×G2・・・・・・(1)
【００１６】また、鋼板
表面積Ｓが１．５×１０９ ｍｍ２を超えて大きな場合
、雰囲気ガスの供給速度に律速される段階及び鋼中のＣ
の拡散速度に律速される段階を経る。そして、焼鈍時間
ｔは、式（２）で表される。
ｔ＝１．３０８×（Ｇ＋０．０４９５）２＋Ａ
×Ｇ２ ＋９．８×１０
−１０ ×Ｓ−１．３８ ・・・・・（２）
[0016] In addition, when the surface area S of the steel sheet is larger than 1.5 x 109 mm2, the carbon in the steel is
It passes through a stage determined by the rate of diffusion. The annealing time t is expressed by equation (2). t=1.308×(G+0.0495)2+A
×G2 +9.8×10
-10 ×S-1.38 (2)
【００１７】ただし、これらの式（１）及び（２）にお
いて、ｔは脱炭時間（時）、Ｇは板厚（ｍｍ）、Ａは４
．０〜１０．０の定数、Ｓは焼鈍される鋼板の表面積（
ｍｍ２）を表す。定数Ａは、目標とする脱炭後の炭素量
に基づいて定められ、１０．０に近くなるに従って脱炭
後の炭素量が１０ｐｐｍに近付く。そこで、目標炭素量
に応じた定数Ａを決定し、式（１）又は（２）に従って
定められた焼鈍時間で焼鈍を行うとき、必要とする焼付
け硬化性に対応した炭素含有量の焼鈍材が得られる。However, in these equations (1) and (2), t is the decarburization time (hours), G is the plate thickness (mm), and A is 4
．． A constant from 0 to 10.0, S is the surface area of the steel plate to be annealed (
mm2). The constant A is determined based on the target amount of carbon after decarburization, and as the constant A approaches 10.0, the amount of carbon after decarburization approaches 10 ppm. Therefore, when determining the constant A according to the target carbon content and performing annealing for the annealing time determined according to formula (1) or (2), the annealed material with the carbon content corresponding to the required bake hardenability is obtained. can get.
【００１８】脱炭焼鈍が施された鋼板は、炭素含有量が
低下していることから優れた加工性を呈する。たとえば
、この鋼板をプレス成形するとき、プレス型に対する馴
染が良く、プレス型から外したときのスプリングバック
がないため、形状特性の良好な製品となる。そして、プ
レス成形後に焼付け塗装した状態では、高い降伏強度が
得られる。しかも、鋼種の如何によらず脱炭焼鈍で所定
の焼付け硬化性が付与されるため、汎用性の高い製法で
ある。[0018] A steel plate subjected to decarburization annealing exhibits excellent workability due to its reduced carbon content. For example, when this steel plate is press-formed, it conforms well to the press die and has no spring back when removed from the press die, resulting in a product with good shape characteristics. In addition, high yield strength can be obtained in a state where the product is baked and painted after press forming. In addition, the decarburization annealing imparts a predetermined bake hardenability regardless of the type of steel, so it is a highly versatile manufacturing method.
【００１９】本発明で使用される冷延鋼板に含まれるＭ
ｎは、強度，遅時効性及び適度の焼付け硬化性を与える
ために有効な元素であり、その作用を得るため０．６０
〜２．０重量％の範囲で添加される。Ｍｎ含有量が０．
６０重量％未満であると所望の遅時効性及び適度の焼付
け硬化性を確保することができず、また２．０重量％を
超えると製鋼が困難になると共に溶接性も劣化し易い。
なお、Ｍｎ強化鋼にあっては脱炭焼鈍時にＭｎが酸化さ
れ易いため、焼鈍時のガスクリーニングを省略すること
が好ましい。M contained in the cold rolled steel sheet used in the present invention
n is an element effective for imparting strength, slow aging properties, and appropriate bake hardenability, and in order to obtain these effects, 0.60
It is added in a range of 2.0% by weight. Mn content is 0.
If it is less than 60% by weight, desired slow aging properties and appropriate bake hardenability cannot be ensured, and if it exceeds 2.0% by weight, steel manufacturing becomes difficult and weldability tends to deteriorate. In addition, in Mn-strengthened steel, since Mn is easily oxidized during decarburization annealing, it is preferable to omit gas cleaning during annealing.
【００２０】Ｃは、脱炭焼鈍によって１０〜３０ｐｐｍ
まで下げられる元素であるが、当初のＣ含有量が多すぎ
ると長時間の脱炭が必要となり、しかも長時間の脱炭に
伴ってＭｎが濃縮した表面層が形成され易くなる。しか
し、Ｃ含有量が低い鋼板を出発材料として使用すること
は、本発明に従った脱炭焼鈍の効果を薄めると共に、製
鋼に特殊な工程が必要とされる。この点で、脱炭焼鈍前
の冷延鋼板の炭素含有量を、０．０３〜０．３０重量％
としている。[0020] C is reduced to 10 to 30 ppm by decarburization annealing.
However, if the initial C content is too high, a long time decarburization is required, and moreover, a surface layer enriched with Mn is likely to be formed as a result of the long decarburization. However, using a steel plate with a low C content as a starting material weakens the effect of decarburization annealing according to the present invention and requires special steps for steel manufacturing. In this regard, the carbon content of the cold rolled steel sheet before decarburization annealing is set to 0.03 to 0.30% by weight.
It is said that
【００２１】Ｓｉは、鋼の強度を向上させる上で有効な
元素であるが、化成処理性やめっき付着性等を劣化させ
易い。そこで、Ｓｉの上限を０．８０重量％に規定した
。焼付け硬化性を改善するためＰを使用することも知ら
れているが、Ｐの含有によって溶接性が低下し易い。
そこで、本発明においては、Ｍｎ含有量を前述のように
規定することにより焼付け硬化性を確保し、Ｐ含有量を
０．１０重量％以下に抑えることによってＰに起因する
欠陥を回避している。[0021]Si is an effective element in improving the strength of steel, but tends to deteriorate chemical conversion properties, plating adhesion, etc. Therefore, the upper limit of Si was set at 0.80% by weight. It is also known to use P to improve bake hardenability, but the presence of P tends to reduce weldability. Therefore, in the present invention, baking hardenability is ensured by specifying the Mn content as described above, and defects caused by P are avoided by suppressing the P content to 0.10% by weight or less. .
【００２２】Ｓは、鋼中に含まれる不純物元素であって
、焼付け硬化性に有効な作用を呈する。しかし、Ｓ含有
量が多量になると赤熱脆性による表面疵が発生し易くな
るので、上限を０．０１０重量％に設定した。S is an impurity element contained in steel and has an effective effect on bake hardenability. However, if the S content becomes large, surface flaws due to red heat brittleness are likely to occur, so the upper limit was set at 0.010% by weight.
【００２３】Ａｌは、脱酸剤として使用される元素であ
り、十分な脱酸を行うために０．０２０重量％以上が必
要である。しかし、多量のＡｌ含有量は鋼の表面性状の
悪影響を及ぼすので、その上限を０．０７９重量％に設
定した。Al is an element used as a deoxidizer, and 0.020% by weight or more is required for sufficient deoxidation. However, since a large amount of Al content adversely affects the surface properties of steel, the upper limit was set at 0.079% by weight.
【００２４】強度向上元素として使用されるＳｉ，Ｍｎ
は鋼板表面に濃縮し、溶融亜鉛に対する濡れ性や溶融亜
鉛めっき層の合金化反応等が劣る表面層を形成し易い。
そこで、脱炭焼鈍された鋼板を溶融亜鉛めっきする場合
、予めＦｅ，Ｆｅ−Ｂ，Ｎｉ等のプレめっき層を形成し
ておくことが好ましい。このプレめっき層は、Ｓｉ，Ｍ
ｎ等が濃縮した表面層の影響を受けることなく溶融亜鉛
を付着させ、且つ合金化反応を促進させる。このような
作用を発揮させるため、目付け量１〜２０ｇ／ｍ２ で
プレめっき層を形成することが良い。Si, Mn used as strength improving elements
tends to concentrate on the surface of the steel sheet, forming a surface layer with poor wettability to molten zinc and poor alloying reaction of the hot-dip galvanized layer. Therefore, when hot-dip galvanizing a decarburized and annealed steel sheet, it is preferable to form a pre-plating layer of Fe, Fe-B, Ni, etc. in advance. This pre-plating layer is made of Si, M
Molten zinc is allowed to adhere without being affected by the surface layer enriched with n, etc., and the alloying reaction is promoted. In order to exhibit such an effect, it is preferable to form a pre-plating layer with a basis weight of 1 to 20 g/m2.
【００２５】[0025]
【実施例】実施例１：表１に示した成分を含有する板厚
０．８ｍｍの冷延鋼板を、Ｎ２：２２容量％，Ｈ２：６
７容量％，Ｈ２ Ｏ：１１容量％の雰囲気で、７４０℃
に加熱するオープンコイル焼鈍を施した後、溶融亜鉛め
っきを行った。めっき後の成分変化を、表１に併せて示
す。[Example] Example 1: A cold-rolled steel plate with a thickness of 0.8 mm containing the components shown in Table 1 was prepared with N2: 22% by volume and H2: 6% by volume.
7% by volume, H2O: 11% by volume atmosphere, 740°C
After open-coil annealing, hot-dip galvanizing was performed. Table 1 also shows the changes in components after plating.
【００２６】[0026]
【表１】[Table 1]
【００２７】このように焼鈍された鋼板の炭素含有量は
、焼鈍時間が長くなるにつれて低下している。そこで、
焼鈍時間を調整することによって炭素含有量を低下させ
た溶融めっき鋼板の焼付け硬化性を測定し、炭素含有量
との関係を調べたところ、図２に示す関係があることが
判った。なお、焼付け硬化性は、１７０℃×２０分の熱
処理前後の引張り試験における降伏応力の差で表した。The carbon content of the steel sheet thus annealed decreases as the annealing time increases. Therefore,
The bake hardenability of a hot-dip galvanized steel sheet whose carbon content was lowered by adjusting the annealing time was measured, and the relationship with the carbon content was investigated, and it was found that the relationship shown in FIG. 2 was found. The bake hardenability was expressed as the difference in yield stress in a tensile test before and after heat treatment at 170° C. for 20 minutes.
【００２８】図２に示した関係を図１の固溶炭素量と焼
付け硬化性との関係と比較すると、必要とする焼付け硬
化性３〜６ｋｇｆ／ｍｍ２ を得るための炭素含有量は
、高Ｃ側で且つより広範囲となっている。これは、鋼中
のＣが全てフリーカーボンとなっておらず、一部炭化物
を形成していることに起因すると考えられる。特に、本
発明で使用される鋼種が炭化物形成元素であるＭｎを比
較的多量に含有していることから、炭化物として消費さ
れるＣ量が多いことに由来すると考えられる。そして、
必要とする焼付け硬化性を得るための炭素含有量が高Ｃ
側で広範囲となっているので、焼鈍条件に対する制御精
度が緩和され、製造が容易になる。Comparing the relationship shown in FIG. 2 with the relationship between solid solution carbon content and bake hardenability shown in FIG. 1, the carbon content to obtain the required bake hardenability of 3 to 6 kgf/mm2 is It is wider and wider. This is thought to be due to the fact that not all of the C in the steel is free carbon, but some of it forms carbides. In particular, since the steel used in the present invention contains a relatively large amount of Mn, which is a carbide-forming element, it is thought that this is because the amount of C consumed as carbide is large. and,
High carbon content to obtain the required bake hardenability
Since the side width is wide, the control accuracy for annealing conditions is relaxed and manufacturing becomes easier.
【００２９】これら焼鈍−めっき材について各種機械的
性質を調べたところ、降伏強度，引張り強度及び硬度は
、共に１００ｐｐｍ以下の炭素量が低い段階で著しい増
加がみられ、炭素含有量が２００ｐｐｍを超える段階で
は増加が緩やかであった。また、伸び及びランクフォー
ド値に関しては、逆の傾向がみられた。これは、フェラ
イト相中へのＣの固溶限が２００ｐｐｍであり、２００
ｐｐｍを超えるＣがＭｎ炭化物として粒界に析出してい
るためであると考えられる。When various mechanical properties of these annealed and plated materials were investigated, it was found that the yield strength, tensile strength, and hardness all significantly increased at a low carbon content of 100 ppm or less, and when the carbon content exceeded 200 ppm. At this stage, the increase was gradual. In addition, the opposite trend was observed for elongation and Lankford value. This means that the solid solubility limit of C in the ferrite phase is 200 ppm, and 200 ppm
This is considered to be because more than ppm of C is precipitated at grain boundaries as Mn carbide.
【００３０】表２は、５時間２分の脱炭焼鈍を行った合
金化溶融亜鉛めっき鋼板のトップ及びボトムについての
Ｃ方向の試験結果を示す。表２から明らかなように、脱
炭焼鈍後の合金化溶融亜鉛めっき鋼板は、自動車用車体
としての必要特性、特に焼付け硬化性を備えていること
が判る。Table 2 shows the test results in the C direction for the top and bottom alloyed hot-dip galvanized steel sheets that were subjected to decarburization annealing for 5 hours and 2 minutes. As is clear from Table 2, it can be seen that the alloyed hot-dip galvanized steel sheet after decarburization annealing has the necessary properties as an automobile body, especially bake hardenability.
【００３１】[0031]
【表２】[Table 2]
【００３２】実施例２：実施例１と同じ板厚０．８ｍｍ
の冷延鋼板を、７４０℃に６時間加熱するオープンコイ
ル焼鈍により脱炭した後、目付け量６ｇ／ｍ２ でＦｅ
−Ｂプレめっきを施した。そして、還元性雰囲気で４６
０℃に予熱し、Ａｌ：０．１０重量％を含有する同じ温
度に保持された溶融亜鉛浴にラインスピード１２０ｍ／
分で導入した後、５１０℃に１３秒間加熱する合金化処
理を施した。Example 2: Same plate thickness as Example 1, 0.8 mm
After decarburizing cold-rolled steel sheets by open coil annealing at 740°C for 6 hours, Fe
-B pre-plating was applied. Then, in a reducing atmosphere, 46
A line speed of 120 m/min was added to a molten zinc bath preheated to 0°C and kept at the same temperature containing 0.10 wt% Al.
After introducing the alloy for 1 minute, alloying treatment was performed by heating it to 510° C. for 13 seconds.
【００３３】得られた合金化溶融亜鉛めっき層は、Ｆｅ
含有量が９．６重量％であり、焼けムラがなく密着性に
優れたものであった。また、下地の炭素含有量は２０ｐ
ｐｍに低下されており、焼付け硬化性は４ｋｇｆ／ｍｍ
２ であった。The obtained alloyed hot-dip galvanized layer is made of Fe.
The content was 9.6% by weight, and there was no uneven burning and excellent adhesion. In addition, the carbon content of the base is 20p
pm, and the bake hardenability is 4kgf/mm.
It was 2.
【００３４】[0034]
【発明の効果】以上に説明したように、本発明において
は、脱炭焼鈍により鋼中の炭素含有量を１０〜３０ｐｐ
ｍに低下させ、必要とする焼付け硬化性を溶融めっき鋼
板に付与している。この方法によるとき、製鋼段階で厳
格な成分調整をする必要がなく、安価な製造コストで焼
付け硬化性に優れた製品を得ることができる。また、溶
融めっき後の固溶炭素量調整のためのポスト炉を必要と
しないため、新たな設備負担を招くこともない。Effects of the Invention As explained above, in the present invention, the carbon content in steel can be reduced to 10 to 30 pp by decarburization annealing.
m, giving the necessary bake hardenability to the hot-dip plated steel sheet. When this method is used, there is no need to strictly adjust the composition at the steel manufacturing stage, and a product with excellent bake hardenability can be obtained at low manufacturing cost. Furthermore, since a post furnace for adjusting the amount of solid solute carbon after hot-dip plating is not required, no new equipment burden is incurred.
【図１】 従来知られている固溶炭素量と焼付け硬化
性との関係を表したグラフ[Figure 1] Graph showing the conventionally known relationship between the amount of solid solute carbon and bake hardenability
Claims (1)
：０．８０重量％以下，Ｍｎ：０．６０〜２．０重量％
，Ｐ：０．１重量％以下，Ｓ：０．０１０重量％以下，
Ａｌ：０．０２０〜０．０７９重量％を含有する冷延鋼
板に対し、１０〜３０ｐｐｍの範囲で目標焼付け硬化性
に対応する炭素含有量に低下させる脱炭焼鈍を施した後
、溶融めっきすることを特徴とする焼付け硬化性に優れ
た溶融めっき鋼板の製造方法。[Claim 1] C: 0.03 to 0.30% by weight, Si
: 0.80% by weight or less, Mn: 0.60 to 2.0% by weight
, P: 0.1% by weight or less, S: 0.010% by weight or less,
A cold rolled steel sheet containing Al: 0.020 to 0.079 wt% is subjected to decarburization annealing to reduce the carbon content to a target bake hardenability in the range of 10 to 30 ppm, and then hot-dipped. A method for producing a hot-dip galvanized steel sheet with excellent bake hardenability.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP3080913A JP2540089B2 (en) | 1991-03-19 | 1991-03-19 | Method for producing hot-dip galvanized steel sheet having excellent bake hardenability |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP3080913A JP2540089B2 (en) | 1991-03-19 | 1991-03-19 | Method for producing hot-dip galvanized steel sheet having excellent bake hardenability |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH04293730A true JPH04293730A (en) | 1992-10-19 |
| JP2540089B2 JP2540089B2 (en) | 1996-10-02 |
Family
ID=13731633
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP3080913A Expired - Lifetime JP2540089B2 (en) | 1991-03-19 | 1991-03-19 | Method for producing hot-dip galvanized steel sheet having excellent bake hardenability |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2540089B2 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1149928A1 (en) * | 1999-11-08 | 2001-10-31 | Kawasaki Steel Corporation | Hot dip galvanized steel plate excellent in balance of strength and ductility and in adhesiveness between steel and plating layer |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5852433A (en) * | 1981-09-19 | 1983-03-28 | Sumitomo Metal Ind Ltd | Production of thermally hardenable thin steel sheet |
-
1991
- 1991-03-19 JP JP3080913A patent/JP2540089B2/en not_active Expired - Lifetime
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5852433A (en) * | 1981-09-19 | 1983-03-28 | Sumitomo Metal Ind Ltd | Production of thermally hardenable thin steel sheet |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1149928A1 (en) * | 1999-11-08 | 2001-10-31 | Kawasaki Steel Corporation | Hot dip galvanized steel plate excellent in balance of strength and ductility and in adhesiveness between steel and plating layer |
| EP1149928A4 (en) * | 1999-11-08 | 2002-06-05 | Kawasaki Steel Co | Hot dip galvanized steel plate excellent in balance of strength and ductility and in adhesiveness between steel and plating layer |
| US6558815B1 (en) | 1999-11-08 | 2003-05-06 | Kawasaki Steel Corporation | Hot dip Galvanized steel plate excellent in balance of strength and ductility and in adhesiveness between steel and plating layer |
Also Published As
| Publication number | Publication date |
|---|---|
| JP2540089B2 (en) | 1996-10-02 |
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