FR2626896A1 - METHOD FOR MANUFACTURING A QUIET STEEL SHEET BY TITANIUM COATED WITH ZINC ALLIE - Google Patents

Abstract

Disclosed is a method for making a zinc alloy coated titanium-calmed steel sheet having excellent deep drawing ability. The process consists in adjusting the temperature of a substrate sheet made of titanium-calmed steel essentially consisting of C = <0.01%, Si <0.15%, Mn: 0.15 to 0.85%, Ti: 0.05 to 0.30%, P = <0.02%, S = <0.02%, Al = <0.05% and Fe for the rest, at a value T (degree (s) C) included in the temperature interval defined by 180 = <T = <292 - 240 XP where P% is the Ti content of the steel substrate sheet, to subject said steel sheet to zinc plating by vacuum deposition in vapor phase, then maintaining the galvanized steel sheet at a temperature of 220 to 320 degree (s) C for 1 to 50 hours, depending on the Ti content of the steel of the substrate, to alloy the deposited zinc layer and the steel of the substrate. Area of application: production of steel sheets for the automotive industry, etc.

Description

The present invention relates to a method for manufacturing a steel sheet

  cooled by titanium (Ti), coated with zinc (Zn) alloy, having excellent aptitude for deep drawing (good workability and good resistance to powder reduction), by depot

under vacuum in the vapor phase.

  A steel sheet with a metal coating.

  alloy, such as an alloy Zn-coated steel sheet, is superior to an ordinary metallized (zinc-plated) steel sheet in that continuous spot welding can

  to be easily performed, the adhesion of a thin layer of.

  Electrophoretic coating is good, corrosion resistance is better, etc., and, as a result, such sheets are widely used in the industry

  automotive and other areas.

  Conventionally, an alloy ZN-coated steel sheet is made by heat-treating a galvanized steel sheet prepared by hot dipping or electroplating. However, the hot dip coating is not suitable for a thin coating of less than 30 g / m 2, nor for single-sided metallization, and a hot-dipped metallized steel sheet-is inferior to uniformity of the thickness of the layer deposited in the longitudinal direction and the transverse direction. Electrolytic deposition is not suitable for coatings thicker than 50 g / ms because the deposit cost increases rapidly with increasing coating weight. On the other hand,

  the vacuum vapor deposition technique is advan-

  the weight of the coating can be adjusted with relative ease and that it is easy to achieve a uniform thickness. As a result, processes for producing alloy Zn coated steel sheets using the vapor phase deposition technique have been proposed and practiced (for example in JP-A-61-195,965). ). According to this method, a cold rolled steel roll is galvanized on one or both sides by vacuum vapor deposition and then heat treated to form an alloy between 250 and 350 C for 1 to 15 hours in a non-oxidizing atmosphere or weakly reducing, in a discontinuous annealing furnace. -On the other hand, to manufacture steel sheets for deep drawing, use is made of steel calmed by aluminum (A1) and steel calma by titanium (Ti). With an Al-quenched steel sheet an alloy Zn coated steel sheet can be manufactured by vacuum vapor deposition and heat treatment according to the known method described above. However, with a steel sheet calmed by Ti, there is a problem that the alloy layer formed has a lower

  resistance to powder reduction and flakes easily

is lying.

  For ordinary stamping applications

  deep, a sheet of steel calmed by Ai is sufficient

  health. However, more and more layouts

  complex have been requested recently. For these applications

  cations, it is necessary to use the steel calmed by Ti of which

  the workability and forming is better. By.

  therefore, a steel sheet coated with Zn alloyed

  killed by a sheet of steel calmed by Ti must also be

  with good resistance to powder reduction.

  The Applicant has carried out studies to determine the cause of the lower resistance to the powder reduction afforded by an alloy Zn-coated steel plate consisting of a Ti-killed steel plate, focusing on the structure of the alloy deposition layer. As a result of these studies, the Applicant has discovered that, in the case of Ti-quenched steel, highly brittle iron (Fe) and Zn intermetallic compounds are formed when the galvanized steel sheet is heated to temperatures coming out of a range of

  specific temperature, and that this temperature interval

  Specific erosion differs according to Ti content. Indeed, the temperature exceeds 320C when the Ti content is 0.05% and exceeds 260C when the Ti content is 0.3%. In addition, since a layer of brittle intermetallic compound has formed, degradation of the resistance to powder reduction is inevitable regardless of the conditions under which the metallized steel plate is treated. the Applicant has discovered that the above-mentioned problem can be solved by keeping the substrate formed by the Ti-quenched steel sheet at a fixed low temperature in relation to the Ti content during vapor-vapor deposition and by heating the metallised steel sheet in a non-oxidizing atmosphere, preferably in a batch annealing furnace for heat treatment, at a temperature within the temperature range in which the Fe content of the alloy layer formed is

  holds in a predetermined interval.

  The present invention provides a process for producing an alloy zinc coated steel sheet having excellent deep drawability, which comprises adjusting the temperature of a titanium steel sheet substantially quenched with C < 0.01%, Si <0, 15%, Mn: 0.15 to 0.85%, Ti: 0.05 to 0.30%, P 0.02%, S <0.02%, Al 0 , 05% and Pe for the remainder, a value T (pC) - in the range defined by 180- <TI <292 - (240 x P) where P (%) is the Ti-content of the substrate sheet, subjecting said steel sheet to vapor vacuum coating, and then maintaining the zinc-coated steel plate at a temperature of 220 ° to 320 ° C for 1 to 50 hours, according to Ti content, to combine the zinc layer

  deposited and the steel of the substrate.

  Throughout this description, the

  percentages (%) are by weight.

  Ti quenched steel is used to manufacture

  make a sheet of steel suitable for stamping

  - bottom is a low carbon steel (C), whose C content is normally not more than 0.01%. The silicon (Si) content should preferably be less than 0.15% because, with a Si content exceeding 0.15%,

  the adhesion of the deposition layer is unsatisfactory.

  Manganese (Mn), which is an element improving the mechanical strength of steels, should preferably be present in the range of 0.15 to 0.85%. If the Mn content is

  less than 0, t15% - we do not obtain a mechanical resistance

  satisfactory. In contrast, the mechanical strength

  nor is it improved by an excess Mn content

  0.85%. The Ti content of a Ti killed steel des-

  for deep-drawing sheet metal is usually 0.05 to 0.30%. Ti is a C-fixed member in steel and improves the workability of the steel, and it is believed that it should be employed at a level of at least about four times the C content. Fixed element also nitrogen (N) which is an impurity in steel. Therefore, Ti is included in one.

  exceeding 0,05% or more in consideration of the

  On the other hand, no advantage is obtained proportionate to the cost of manufacture if the Ti content is greater than 0.3%. The phosphorus (P, sulfur - (S) and Al may be contained as impurities at levels of <0.02%, 0.02% and <0.05%, respectively. at the current impurity contents of ordinary non-alloy steels The Ti-caloked steel sheet described above is maintained at a temperature T (C) defined according to the content P (%) in Ti by the relation 180 <T <292 (240 XP), then subjected to vacuum vapor deposition zinc plating, Zn vapor, which condenses on the surface of the steel strip, forming a layer of student

  400 C maximum temperature of the steel strip.

  If the temperature (T) of the Ti-killed steel substrate sheet exceeds the temperature defined according to the P (%) content of Ti by the relation 180 <T <292 - (240 x P) before being submitted to the deposit under vacuum in the vapor phase, the temperature of the steel sheet reaches, during the vacuum deposition in vapor phase, a value at which it forms fragile intermetallic compounds with

  because of the rise in temperature caused by the heat

  their condensation of Zn vapor. Thus, the resistance

  to the powder reduction of the formed alloy layer

is degrading.

  The upper limit of the temperature of the

  The trait differs depending on the Ti content, as described above.

  In particular, when the Ti content is 0.3%, this limit is not greater than 220 ° C. as calculated by the formula above, and when the Ti content is 0.05%, it does not exceed is not greater than 280 C. In other words, the temperature of the substrate must be adjusted so as not to exceed the upper limit defined by the

  formula above before vapor phase deposition.

  If the substrate temperature is too low, the adhesion of the deposited Zn layer is poor. The lower limit is 80 OC, which is the same as in the case of ordinary unalloyed steel

not Ti.

  * -. The vacuum vapor deposition galvanized steel strip is heat treated to form an alloy. The alloy layer formed should preferably contain 8 to 12% Fe. If the Fe content is lower

  at 6%, r-Zn remains on the surface of the

  and affects the ability to receive

  the weldability, etc., of the steel plate

  Lisée. If the Fe content exceeds 14%, the resistance to

  the reduction of the powder of the alloy layer is degraded.

  As a means of heating, it is possible to use a

  discontinuous annealing furnace. In the processing of

  alloying by means of an annealing annealing furnace, the steel sheets are generally heated in a non-oxidizing atmosphere in order to avoid oxidation of the steel strip (or sheet). The heating can be carried out with a strip in the form of a roll or a roll

tight, a loose roll.

  The temperature and the heating time may vary depending on the deposition weight and the average Pe content considered, but the heating temperature must be 30 ° C lower than the alloy forming temperature for a zinc-free steel sheet. The upper limit of the heating temperature differs depending on the Ti content. This limit is 2800C when the Ti content is

  0.3% and 320 ° C when the Ti content is 0.05%.

  If the heating temperature exceeds the upper limit

  As noted above, the powder reduction resistance is degraded as a fragile alloy layer is formed. In contrast, if the temperature of

  * heating is below the temperature range

  As described above, the deposited Zn layer does not mix well. Application of heat for less than one hour does not completely raise the temperature of the substrate and satisfactory heating can not be achieved. In contrast, a heating of a duration

  greater than 50 hours lowers productivity.

  It is possible to drive the heating in continuous mode by means of an annealing furnace installed in a continuous metallization furnace, but the heating conditions then differ from those applied in the case of a batch annealing furnace. The use of a batch annealing furnace is preferred because the

  temperature adjustment is easy.

  The rate of rise in temperature and the rate of cooling are not particularly

  limited and these conditions are determined in

  ration of the operating characteristics of ovens

  & discontinuous annealing of current industrial type.

  In the accompanying drawings: FIG. 1 is a diagram showing the temperature and Ti content ranges of the substrate sheet between which no fragile Fe-Zn intermetallic compounds are formed at the interface of the substrate. steel and the deposited layer when the substrate is galvanized by vacuum vapor deposition; and FIG. 2 is a diagram showing the temperature and treatment time intervals between the limits of which the average Fe content of the

  Allied layer can be set from 8 to 12.0%.

  The invention will now be described more

  particularly by means of examples, comparative examples

and experimental results.

  The Applicant galvanized ordinary Ti-killed steel strips containing 0.05 to 0.3% Ti, by vacuum vapor deposition at various substrate temperatures using a vacuum vapor deposition apparatus. working in continuous mode such as

  described in Nisshin Giho No. 51.t1954, 1984.

  The other operating conditions were as follows; Steel strip: Ti steeled steel strips 0.8 mm thick and 1200 mm wide Scroll speed: 80 m / min Pressure in the deposition chamber: 1.33 Pa (0.01 Torr) Alloy Formation Temperature: 270 C The relationship between the Ti content of the steel substrates and the temperature of the substrates was thus determined to obtain an alloy layer containing no intermetallic compounds. The results are represented on the

figure 1.

  Figure i shows the temperature intervals

  the substrate and the Ti content of the steel of the

  between Fe-Zn intermetallic compounds at the interface of the substrate and the deposited layer. In the drawing, the solid line a represents the upper limit of the temperatures below which no fragile Fe-Zn intermetallic compounds are formed. This line is expressed

  by the relation T = -240P + 292 (tC), where T is the temperature

  The size of the C and P substrate is the Ti content in%.

  The solid line b represents the lower limit of the temperatures above which the adhesion of the deposition layer is satisfactory. This temperature is

  constant at 180 C, regardless of the Ti content.

  It has been maintained at various temperatures and

  different durations the prepainted galvanized

  as described above (not yet subjected to alloy forming treatment), and the Fe content of the formed alloy layers was determined. It has been found that there is a relationship between the

  Ti and the upper limit of temperatures. The results

  States are shown in Figure 2.

  Figure 2 is a diagram that shows the

  temperature intervals and heat treatment times

  between the limits of which the average Fe content of the alloy layer can be adjusted from 8 to 12.0%.

  drawing, the area surrounded by the lines in inter-

  Broken is the region in which the Fe content of the alloy layer formed fits between 8% and 12%. As

  this appears on this figure, the band can be heated

  fairy up to 320 0C when the Ti content is 0.05%

  and up to 280 C when the t content is 0.3%.

  From this figure, those skilled in the art will be able to determine the upper temperature limit for Ti contents between 0.05% and 0.3%. The Fe content of the alloy layer of the Ti-steel plate is between 8% and 12% when the galvanized steel sheet is heated to between 220 and 3200C depending on the content.

in Ti.

  In Figure 2, the area surrounded by solid lines is the known region for AI quenched steel. Indeed, the sloping line lying on the side

  lower left is known to those skilled in the art.

  EXAMPLES AND COMPARATIVE EXAMPLES Ti-calened steel strips, as described above, containing 0.05% and 0.3% of Ti were zinded on both sides by vacuum vapor deposition.

  under the various conditions shown in Table 1.

  The rolls of steel sheets thus galvanized are heat-treated to effect alloy formation in a batch annealing furnace under an atmosphere composed of 3.% H2 and 97% N2 and having a dew point (PR). is -25 ° C, observing the temperature and time conditions indicated on the

table 1.

  The surface state and the reduction resistance are determined in. powder of the alloy Zn-coated steel sheets thus produced. the powder reduction resistance is evaluated by bending test pieces at 180 with a radius of curvature of 3 times the thickness of the sheet.

  (folding 6 layers) and observing if it occurs -

  or not peeling of the deposit layers inside.

  The results are summarized in Table 1.

  The terms used in Table 1 have the meanings

  following statements concerning the surface condition: Good: Homogeneous stirring sTest

form.

Zn remaining: there remains Rn-Zn.

  Concerning the resistance to the reduction in powder: Good: no reduction in powder has had bad places: it occurred a reduction in

powder.

  Bad adhesion: the deposition layer -

flakes easily.

  Values marked with an asterisk are outside the conditions defined by the scope of this

invention.

  As is apparent from the results given, the products of the present invention have a good surface state and good resistance to powder reduction, whereas the products of the Comparative Examples are inferior due to the existence of non-alloyed Zn or the formation of intermetallic compounds, in particular in the following manner: ## EQU1 ## where: ## STR1 ## , OB1 OZn0, 0C'0, 01101cl JI oo09 gas is 081 011 0810 01 / 01Il II Ge. 9 O 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 si si si si si si si si si si si si si si si si si si 01 01 01 01 01 01 01 01 01 01 01 11 11 11 11 11 11 11 11 11 q: .--: J i OIC OIC Fr8g 081 081 8O'a 01/01 9 r- TI 01 F8r8 0gu 081. 90'O O1101 OS QZ2 ks81 081 0DB allai O OS QZS solo jar 01/01 E i : '[I 012 F8T 081 084 CO'O 0O1 / 0 Z UaWoq uoq 1 0ot Ir81 08t 08Z soo' OtJOIt Oldwaxa = :: d - - -r - T ipnod0u3! N (<moaq (0D) (Do) U0) ) Do (g + tdOFz -) (Pplod us%) (IaJ3) I uol, ap; lu; hgjU1 [pI eHPIvp I1 dp uq.de Ilrgqno np Jgrqn, np; e.1qnu np tQsP the P -onpv el uollairlol lUollsjuo lp 'miqno np a2JnupqdmO oeanlrîuodwe! op tual opp

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Table 1 (2)

  Limlite Sup4rleue Temperature.Temperature Time of Resettlement

  P4lds of Temperature Ti Content Temperature of Formation Substrate Formation Background Reduced

  Substrate Deposition Test of the Substrate Substrate After Alloy Slag Deposition Lion State in g / im) (wt%) (-240P + 92Z) C ('C) (OC) (CC) (hours) surfaced powder xicample t8 l0 / 10 0.30 220 22 224 220 o50 good good 19 50 / 50th e, es 280 180 20 '2R0 1 50150' 0.0 280 law zoo 320 1 21 50151 0.05 280 150 2zo 320 SD JI

22 50150 0.05 280 180 200 220 15 I.

  23 5e150 0.05 280 10 20o 220 s 24 50150 0.05 280 280 300 2f0 t 50150 o, 06 280 280 300 320 1 J * I 26 n015s 0.05,280 2.80 300 320 5D to 27 50/50 0, 05 280 280 300 0.e II

28 50/50 0.05 280 '280 300 220 50

  29 50'S50 0.30 220 180 2O0 280 3 I I

50 [50 0.30 220 18 Me 200 50.

  $ 1 n0150 0.30 2201 80 200 220 50 I 32 50150 0.30 22P0 180 z00 220 1S 3 5/0150 0.30 220 220 240 2f0 3

34 50/50 0.30Q 220 220 240 260 50

  50150 0.30 220 220 240 220 15 good good 0% 3: o

Table I (3)

  Temperature Limit Temperature Temptrature Time of llxtmence

  Polde of temperature Min temperature TI Temperature of formation substrate formation h reduction

  Bem substrate deposition of the substrate substrate aprta alloying deposit of the alloy stat in (gm) (% min weight) (-2401P +) 2) C CoC (OC) (= a (hours) Surface powder Example 30 50650 0.30 220 220 240 220 50 good good

37 1001100 0.05 280 180 220 280 I

  38 l00 / 100.05 280 180 220 320 i 39 100/100 0.05 280 180 z20 320 50 [1001100 S0.05 280 180n 220 220 5 I 41 100/1100 0.05 280 380 220 220 5s

  42 100/100 o, 280 280 280 280 1. [.

43 100100 D0.05 280 280 320 320

  44 1001100 0 ', 0 280 28e 320 320 50 1001100 / 0,05 280 280 320 '20 Il 1 46 100/1100 0,05 280 280 320 220 0se I

47 100/100 0.30 220 18O 220 250 3 I

48 100/100 0.30 220 180 220 260 50

49 1001100,, 30 220 180 220 220 15

  1001100 0, n0 220 180 220 220 50 s 1001100 0,30 22n 220 260 t00 3 52 100/100 0,30o 220 * 20 260 260 50 + 53 il00o / 100 030 2S20 220 260 g0 15 good good you CN 0% N Iffl Quua04nmlo..uZos O oz9.08 ocl. doj 0I c '.' 0 P'O 1 ae! LAautouoq: T * 0l Oz?, 00Z Ota 0'O 09 / 06gl aupAnwmt ozq My DlP OgOz ul SIS auquq uz4S * a OZZ 40E DZ OJ '0 OGOl fa IValUluoq U * Z009E 00Z OtI) 0Z9 sOg0 'DOSlû9 0lpA' otum oauoz a DDDt DZZ 'O * n O /, DaAulu antuoq0z e1tz18 z. 'O * / i ba09E0 0 9 UauuUI alaaa OZEoz u0E you 091 OE DeSo 0 / S0 Zl +> An Uluoqe' * ga t 1 09t * ZS 'OS / OS 0111 ouuoq amesa. uzOS.oe00e 09 OZ OSE GD00 09/01 8 * ajMAnIuuuoqx T 0SC OE DOI 0E o0'0 08109 IT apmlnim: uoq0 Oaz #te * 0.C Ot Z 0 '/ 09a lo auuhiWenO paDa uz0 0> 9E to91 Q091. OSEa O'O 109 6 auuoq; maa uq aç * lOUoz DOZ gO'o 001îiB ampinuwuioq Ion T 'DSúiiZ o, 008. OI / OT eU amapAnuuoq OZ 08Z 929..2 081 se' bigà 3 i m iua tlpw :. _unp ampAnuio s: a.r Uz0g. 0fx 9I, 0I D8; ## EQU1 ## where ## EQU1 ## ## EQU1 ##, ## EQU0000 ##, ## EQU1 ##, ## EQU1 ##, ## EQU1 ##, ## EQU1 ## where: ## EQU2 ## where ## EQU1 ## os) <o) (o.). o.C; oz * gKo9t-) ('ppd ua, 3) (muiI / :) sa * u0o ap; tb BuJI [urnp a0B.jUOP; gdp 8ada j4sqnm. p'v.awqn. ###################################################################################################################################################################################- .md [uaL ae; W1dmL a..zgnopdne; lmil (j) I nwalqUL

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Claims (1)

CLAIM   A process for producing an alloy zinc-coated steel sheet having excellent deep drawability, characterized by adjusting the temperature of a steel substrate sheet   calmed by titanium essentially consisting of.   C <0.01%, Si <0.15%, Mn: 0.15 to 0.85%, Ti: 0.05 to 0.30%, P <0.02%, S g 0, Gf 2%, Ai <0.05% and Fe for the rest,   at a value T (C) within the temp range $ -   defined by 180 <T <292 - (240 x P) where P (%) is   the Ti content of the steel substrate plate, and   said steel sheet is galvanized by vacuum vapor phase deposition, and then the galvanized plate is maintained at a temperature of 220 to 320 ° C for 1 to 50 hours, depending on the Ti content of the substrate steel, to combine   the deposited zinc layer and the steel of the substrate.