阅读说明：本技术 合金化热浸镀锌钢板的制造方法和连续热浸镀锌装置 (The manufacturing method and continuous hot-dipping galvanizing device of alloyed hot-dip galvanized steel plate ) 是由 武田玄太郎 牧水洋一 铃木克一 姫井善正 高桥秀行 于 2018-02-19 设计创作，主要内容包括：本发明提供一种合金化热浸镀锌钢板的制造方法,其对Si含量为0.2质量％以上的钢板实施热浸镀锌时,镀覆密合性高,可得到良好的镀覆外观,并且即使其后连续地对Si含量低于0.2质量％的钢板实施热浸镀锌时,通过迅速地切换均热带内气氛的露点而还能够抑制拾取缺陷的产生。本发明中,当通过均热带的钢板为含有0.2质量％以上的Si的钢种时,向均热带供给干燥气体和加湿气体这两者,此时,在均热带中,从通板速度V和均热带输出侧的目标温度T考虑来确定均热带后段,上述加湿气体仅从多个加湿气体供给口中的位于上述均热带后段的加湿气体供给口供给。(The present invention provides a kind of manufacturing method of alloyed hot-dip galvanized steel plate, when it implements galvanizing by dipping to the steel plate that Si content is 0.2 mass % or more, plating adaptation is high, good plating appearance can be obtained, and even if the generation for picking up defect can also be inhibited and promptly switching the dew point of atmosphere in soaking zone when continuously the steel plate to Si content lower than 0.2 mass % implements galvanizing by dipping thereafter.In the present invention, when being the steel grade of the Si containing 0.2 mass % or more by the steel plate of soaking zone, to both soaking zone supply dry gas and humidification gas, at this time, in soaking zone, considered from the target temperature T of plate speed V and soaking zone outlet side to determine that soaking zone back segment, above-mentioned humidification gas are only supplied from the humidification gas supply port positioned at above-mentioned soaking zone back segment in multiple humidification gas supply ports.)

1. a kind of manufacturing method of alloyed hot-dip galvanized steel plate, which is characterized in that be the conjunction using continuous hot-dipping galvanizing device The manufacturing method of aurification hot-dip galvanized steel sheet, the continuous hot-dipping galvanizing device have: being arranged successively and be provided with heating tape, soaking The vertical annealing furnace of band and cooling zone, the hot-dip galvanizing device positioned at the downstream of the cooling zone, and, it is located at the hot-dip The alloying equipment in the downstream of zinc equipment,

With process below:

In the inside of the annealing furnace, steel plate is carried out according to the sequence of the heating tape, the soaking zone and the cooling zone Conveying, anneals to the steel plate, at this point, the steel plate is repeatedly formed by conveying in above-below direction in the inside of each band The process of multiple passages,

Using the hot-dip galvanizing device, implement the process of galvanizing by dipping to the steel plate being discharged from the cooling zone,

Using the alloying equipment, it will be applied to the zinc-plated process for carrying out heating alloying of the steel plate,

Also, it is more configured with reproducibility or non-oxidizing humidification gas is supplied into the soaking zone in the soaking zone A humidification gas supply port and at least one is done by reproducibility or non-oxidizing dry gas are supplied into the soaking zone Dry gas supply port,

When being the steel grade of the Si containing 0.2 mass % or more by the steel plate of the soaking zone, by the dry gas It is supplied with both the humidification gas to the soaking zone,

At this point, in the soaking zone, will than with sheet steel sections corresponding to the L that is determined in a manner of meeting following formula (1), most The definition space of the passage of one upstream of passage corresponding to upstream position closer to the cooling zone side is soaking zone back segment, The humidification gas is only from the humidification gas supply port positioned at the soaking zone back segment in the multiple humidification gas supply port Supply,

≤ 2.5 (1) 1.0≤10100L/V exp { ﹣ 14560/ (T+273.15) }

L: the steel plate length started from soaking zone outlet side, unit m,

V: plate speed, unit m/s,

T: the target temperature of soaking zone outlet side, unit are DEG C.

2. the manufacturing method of alloyed hot-dip galvanized steel plate according to claim 1, wherein when by the soaking zone When the steel plate is the steel grade of the Si containing 0.2 mass % or more, controls from the dew point for being located at the soaking zone back segment and measure mouth The dew point for the furnace gas taken is 25 DEG C~0 DEG C of ﹣.

3. a kind of continuous hot-dipping galvanizing device, which is characterized in that be to carry out hot-dip galvanized steel sheet of any of claims 1 or 2 The continuous hot-dipping galvanizing device of manufacturing method, has:

It is arranged successively the annealing furnace for being provided with heating tape, soaking zone and cooling zone,

Hot-dip galvanizing device positioned at the downstream of the cooling zone,

Alloying equipment positioned at the downstream of the hot-dip galvanizing device, and,

Be configured at the soaking zone, by reproducibility or non-oxidizing supplied into the soaking zone multiple of humidification gas plus Humid gas supply mouth and at least one the drying gas for supplying reproducibility or non-oxidizing dry gas into the soaking zone Body supply mouth,

It is the multiple humidification gas supply port have each independently can control it is described humidification gas supply and blocking and The regulating valve of gas flow.

Technical field

The present invention relates to have: being arranged successively and is provided with the annealing furnace of heating tape, soaking zone and cooling zone, positioned at above-mentioned cold But the continuous hot dipping of the hot-dip galvanizing device in the downstream of band and the alloying equipment positioned at the downstream of above-mentioned hot-dip galvanizing device Galvanizing rig, and, use the manufacturing method of the alloyed hot-dip galvanized steel plate of the device.

Background technique

In recent years, (high to the high-tensile steel of the lightness for facilitating structural body etc. in fields such as automobile, household electrical appliances, building materials Strength steel sheet) demand it is more and more.As high strength steel, for example, as it is known that by alloing in steel to manufacture expansion containing Si The good steel plate of permeability, remnants γ's easy to form can manufacture the good steel plate of ductility and containing Si, Al.

But alloy is manufactured as base material in the high-tensile steel that will contain a large amount of (especially 0.2 mass % or more) Si When changing hot-dip galvanized steel sheet, have the following problems.Alloyed hot-dip galvanized steel plate is by reducing atmosphere or non-oxidizing gas After base material steel plate is carried out heating anneal with 600~900 DEG C or so of temperature in atmosphere, galvanizing by dipping processing is carried out to the steel plate, Further by it is zinc-plated carry out heating alloying and manufacture.

Wherein, the Si in steel is easily oxidizable element, even if in usually used reducing atmosphere or non-oxidizing atmosphere Also it can be selectively oxidized, in the surface enrichment of steel plate, form oxide.The melting when oxide can be reduced to plating The wetability of zinc generates not plating.Therefore, as the increase of Si concentration in steel, wetability sharply decline, plating does not take place frequently.Separately Outside, even if the case where being not up to not plating, also there is the problem of plating adaptation difference.Moreover, if the Si in steel is by selective oxygen Change in the surface enrichment of steel plate, then can also generate significant alloying delay in the alloying process after galvanizing by dipping, deposits The problem of obviously hindering productivity.

For such problems, a kind of manufacturing method of alloyed hot-dip galvanized steel plate is recorded in patent document 1, it is special Sign is, comprising: in the inside of annealing furnace, according to the heating tape, soaking zone and cooling zone for including direct-fired heating furnace (DFF) Sequentially-fed steel plate, the process annealed to above-mentioned steel plate；Galvanizing by dipping is implemented to the steel plate being discharged from above-mentioned cooling zone Process；By the zinc-plated process for carrying out heating alloying, the mixed gas of humidification gas and dry gas is supplied to soaking zone and is done Pathogenic dryness body, Xiang Shangshu cooling zone supply dry gas, also, the humidification gas for making the volume Vr of soaking zone, supplying to soaking zone Gas flow Qrw and containing moisture Wr, to soaking zone supply dry gas gas flow Qrd, Xiang Shangshu cooling zone supply The mean temperature Tr of the inside of the gas flow Qcd and above-mentioned soaking zone for the dry gas given meets defined relationship.The skill Art be by heating tape using direct-fired heating furnace make surface of steel plate oxidation sufficiently carry out after, make soaking zone generally than normal The high dew point of the dew point of rule method and carry out the internal oxidation of Si sufficiently, to inhibit the surface enrichment of Si and reduce alloying The technology of temperature.According to this method, even if implementing alloyed hot-dip zinc-coated feelings to the steel plate of the Si containing 0.2 mass % or more Under condition, plating adaptation is also high, can obtain good plating appearance, and by reducing alloying temperature, is able to suppress drawing Stretch the decline of intensity.

Summary of the invention

However, being only conceived in the method documented by patent document 1 to the height that Si content is 0.2 mass % or more Power steel plate implements that good plating appearance can be obtained when galvanizing by dipping, absolutely not considers followed by make Si content lower than 0.2 The steel plate (hereinafter, being known as " general steel plate " in the present specification) of quality % leads to the case where plate.However, if steel grade changes, Required annealing temperature (soaking zone outlet side temperature), soaking zone dew point can also change.Therefore, if as patent document 4 In the logical plate for the high-tensile steel that Si content is 0.2 mass % or more, humidification gas is supplied to the entirety of soaking zone, it will be equal Tropical whole dew point control then switches to thereafter most suitable Si content lower than 0.2 matter at uniform high dew point in soaking zone The low dew point for measuring the general steel plate of % needs the time.Therefore, general steel plate (the i.e. steel plate annealed before dew point sufficiently switches The front end portion of coil) it generates and picks up (pick up) defect, it needs to cut the front end portion in subsequent handling, leads to qualification Rate declines, and there are also rooms for improvement in this respect for the method recorded in patent document 1.

Therefore, for the present invention in view of the above subject, its purpose is to provide real to the steel plate that Si content is 0.2 mass % or more When heat application zinc immersion, plating adaptation is high, good plating appearance can be obtained, and even if be continuously lower than to Si content thereafter When the steel plate of 0.2 mass % implements galvanizing by dipping, pickup is able to suppress and promptly switching in soaking zone the dew point of atmosphere The manufacturing method and continuous hot-dipping galvanizing device of the alloyed hot-dip galvanized steel plate of the generation of defect.

The present invention is directed to realize following targets simultaneously: (A) leads to plate in the high-tensile steel that Si content is 0.2 mass % or more When, inhibit Si oxide to be enriched in surface of steel plate and realizes good adaptation；(B) thereafter, it is lower than 0.2 mass % in Si content General steel plate when continuously leading to plate, inhibit the generation for picking up defect and promptly switching the dew point of atmosphere in soaking zone.And And by the research of the inventors of the present invention, learn to realize (A), be not necessarily required to the whole supply humidification gas of soaking zone and High dew point only becomes the back segment supply humidification gas of the soaking zone of the highest temperature from especially steel plate.By only to back segment Supply humidification gas, and the not entirety of soaking zone, thus when logical plate does not need the steel grade of supply humidification gas, it can be rapid Make low dew point in soaking zone, realizes the target of (B).Moreover, obtaining following opinions by the research of the inventors of the present invention: from logical The target temperature T of plate speed V and soaking zone outlet side considers that humidification gas should be supplied in the logical plate of high-tensile steel to determine The range of soaking zone back segment be important, thus, it is possible to realize (A) and (B) simultaneously.

The purport composition of the invention completed based on above-mentioned opinion is as follows.

[1] a kind of manufacturing method of alloyed hot-dip galvanized steel plate, which is characterized in that be using continuous hot-dipping galvanizing device Alloyed hot-dip galvanized steel plate manufacturing method, above-mentioned continuous hot-dipping galvanizing device has: be arranged successively be provided with heating tape, The vertical annealing furnace of soaking zone and cooling zone, the hot-dip galvanizing device positioned at the downstream of above-mentioned cooling zone, and it is located at above-mentioned heat The alloying equipment in the downstream of dip galvanising equipment,

The manufacturing method of above-mentioned alloyed hot-dip galvanized steel plate has process below:

In the inside of above-mentioned annealing furnace, according to the sequentially-fed steel of above-mentioned heating tape, above-mentioned soaking zone and above-mentioned cooling zone Plate anneals to above-mentioned steel plate, at this point, above-mentioned steel plate is repeatedly formed more by conveying in above-below direction in the inside of each band The process of a passage,

Using above-mentioned hot-dip galvanizing device, implement the process of galvanizing by dipping to the steel plate being discharged from above-mentioned cooling zone,

Using above-mentioned alloying equipment, it will be applied to the zinc-plated process for carrying out heating alloying of above-mentioned steel plate,

Also, reproducibility or non-oxidizing humidification gas are stated supply in soaking zone upwards by configuration in above-mentioned soaking zone Multiple humidification gas supply ports and at least one for supplying reproducibility or non-oxidizing dry gas into above-mentioned soaking zone Dry gas supply mouth,

When being the steel grade of the Si containing 0.2 mass % or more by the above-mentioned steel plate of above-mentioned soaking zone, by above-mentioned drying Both gas and above-mentioned humidification gas are supplied to above-mentioned soaking zone,

At this point, in above-mentioned soaking zone, will sheet steel sections corresponding with the L determined in a manner of meeting following formula (1), most The definition space of the passage of one upstream of passage corresponding to upstream position closer to above-mentioned cooling zone side is soaking zone back segment, Above-mentioned humidification gas is only from the humidification gas supply port positioned at above-mentioned soaking zone back segment in above-mentioned multiple humidification gas supply ports Supply.

≤ 2.5 (1) 1.0≤10100L/V exp { ﹣ 14560/ (T+273.15) }

L [m]: the steel plate length started from soaking zone outlet side

V [m/s]: plate speed

T [DEG C]: the target temperature of soaking zone outlet side

[2] manufacturing method of the alloyed hot-dip galvanized steel plate according to above-mentioned [1], wherein when passing through above-mentioned soaking The above-mentioned steel plate of band be the Si containing 0.2 mass % or more steel grade when, control for from be located at above-mentioned soaking zone back segment dew point The dew point for the furnace gas that measurement mouth is taken is -25 DEG C~0 DEG C.

[3] a kind of continuous hot-dipping galvanizing device, which is characterized in that be to carry out electro-galvanized steel described in above-mentioned [1] or [2] The continuous hot-dipping galvanizing device of the manufacturing method of plate, has:

It is arranged successively the annealing furnace for being provided with heating tape, soaking zone and cooling zone,

Hot-dip galvanizing device positioned at the downstream of above-mentioned cooling zone,

Alloying equipment positioned at the downstream of above-mentioned hot-dip galvanizing device,

Be configured at above-mentioned soaking zone, reproducibility or non-oxidizing humidification gas stated upwards supplied in soaking zone it is more A humidification gas supply port and at least one is done by reproducibility or non-oxidizing dry gas are supplied into above-mentioned soaking zone Dry gas supply port,

Above-mentioned multiple humidification gas supply ports have each independently the supply that can control above-mentioned humidification gas and block with And the regulating valve of gas flow.

The manufacturing method and continuous hot-dipping galvanizing device of alloyed hot-dip galvanized steel plate according to the present invention, to Si content When implementing galvanizing by dipping for the steel plate of 0.2 mass % or more, plating adaptation is high, good plating appearance can be obtained, and i.e. When the steel plate for being continuously lower than 0.2 mass % to Si content thereafter being made to implement galvanizing by dipping, by promptly switching gas in soaking zone The dew point of atmosphere and can also inhibit pick up defect generation.

Detailed description of the invention

Fig. 1 is the signal for indicating the composition of continuous hot-dipping galvanizing device 100 used in an embodiment of the invention Figure.

Fig. 2 is the schematic diagram for indicating the system of the supply of the soaking zone 12 humidification gas into Fig. 1 and dry gas.

Specific embodiment

Firstly, referring to Fig.1 to making in the manufacturing method of the alloyed hot-dip galvanized steel plate of an embodiment of the invention The composition of continuous hot-dipping galvanizing device 100 is illustrated.Continuous hot-dipping galvanizing device 100 has: being arranged successively and is provided with The vertical annealing furnace 20 of heating tape 10, soaking zone 12 and cooling zone 14,16, the steel plate positioned at cooling zone 16 lead to plate direction downstream Galvanizing by dipping as hot-dip galvanizing device bathes 22, and the alloying for leading to plate direction downstream positioned at the steel plate of galvanizing by dipping bath 22 is set Standby 23.Cooling zone includes the 1st cooling zone 14 (chilling band) and the 2nd cooling zone 16 (removing cold belt) in present embodiment.It is cooling with the 2nd The front end of furnace nose 18 with 16 connections is impregnated in galvanizing by dipping bath 22, and annealing furnace 20 is connect with galvanizing by dipping bath 22.

Steel plate P is imported in heating tape 10 by the steel plate introducing port of the lower part from heating tape 10.In each band 10,12,14,16 Upper and lower part configures 1 or more hearth roll.Using hearth roll as starting point by steel plate P fold-back 180 degree when, in the rule of annealing furnace 20 The inside of fixed band, steel plate P repeatedly form multiple passages by conveying in above-below direction.Showing in Fig. 1 has 2 in heating tape 10 A passage, the example for having 10 passages in soaking zone 12, having 2 passages in the 1st cooling zone 14, having 2 passages in the 2nd cooling zone 16 Son, but road number is not limited thereto, and can suitably be set according to treatment conditions.In addition, in the hearth roll of a part, no Steel plate P is turned back and turns to it for right angle, keeps steel plate P mobile to next band.It, can be in this way, in the inside of annealing furnace 20 According to the sequentially-fed steel plate P of heating tape 10, soaking zone 12 and cooling zone 14,16, anneal to steel plate P.

Each band 10,12,14,16 is vertical heater, and height is not particularly limited, and can be 20~40m or so.In addition, The length (left and right directions in Fig. 1) of each band can be suitably determined according to the road number in each band, for example, if it is 2 roads Secondary heating tape 10 can be then 0.8~2m or so, can be left for 10~20m if it is the soaking zone 12 of 10 passages The right side can be respectively 0.8~2m or so if it is the 1st cooling zone 14 and the 2nd cooling zone 16 of 2 passages.

In annealing furnace 20, adjacent band via by the top of respective band each other or the interconnecting part that is connected to each other of lower part and Connection.In the present embodiment, heating tape 10 and soaking zone 12 are via the furnace throat (necking down that the lower part of respective band is connected to each other Portion) and be connected to.Soaking zone 12 and the 1st cooling zone 14 are connected to via the furnace throat that the lower part of respective band is connected to each other.1st is cold But band 14 and the 2nd cooling zone 16 are connected to via the furnace throat that the lower part of respective band is connected to each other.The height of each furnace throat can be with It suitably sets, but from the viewpoint of the independence of atmosphere for improving each band, the height of preferably each furnace throat is low as far as possible.Annealing furnace Gas in 20 flows to upstream from the downstream of furnace, the steel plate introducing port discharge from the lower part of heating tape 10.

(heating tape)

In the present embodiment, radiant tube (RT) can be used in heating tape 10 or electric heater carrys out indirect heating steel plate P. The mean temperature of the inside of heating tape 10 is preferably 700~900 DEG C.Gas from soaking zone 12 flows into the same of heating tape 10 When, separately reducibility gas or non-oxidizing gas are supplied to heating tape 10.As reducibility gas, usually using H₂- N₂It is mixed Gas is closed, such as can be enumerated with H₂: 1~20 volume % and remainder is by N₂The composition constituted with inevitable impurity Gas (dew point: 60 DEG C of ﹣ or so).In addition, can enumerate has by N as non-oxidizing gas₂It is constituted with inevitable impurity Composition gas (dew point: 60 DEG C of ﹣ or so).The gas supply of heating tape 10 is not particularly limited, but is preferably thrown with equalization Enter the mode in heating tape, from short transverse 2 more than, at length direction 1 more than input port supply.It is supplied to heating tape The flow of gas is measured using the gas flowmeter (not shown) for being set to piping, is not particularly limited, and can be 10~100 (Nm³/ hr) left and right.

(soaking zone)

In present embodiment, soaking zone 12 can be used that radiant tube is (not shown) to carry out indirect heating steel plate as heating mechanism P.The mean temperature of the inside of soaking zone 12 is preferably 700~1000 DEG C.

Reducibility gas or non-oxidizing gas are supplied to soaking zone 12.As reducibility gas, usually using H₂- N₂ Mixed gas, such as can enumerate with H₂: 1~20 volume % and remainder is by N₂The composition constituted with inevitable impurity Gas (dew point: 60 DEG C of ﹣ or so).In addition, can enumerate has by N as non-oxidizing gas₂With inevitable impurity structure At composition gas (dew point: 60 DEG C of ﹣ or so).

In the present embodiment, to soaking zone 12 supply reducibility gas or non-oxidizing gas be humidification gas and This two kinds of forms of dry gas.Herein, " dry gas " refers to that dew point is 50 DEG C or so of 60 DEG C~﹣ of ﹣ of above-mentioned reducibility gas Or non-oxidizing gas, it is the gas of no humidified device humidification.On the other hand, " humidification gas ", which refers to, utilizes humidification dress It sets and humidifies dew point to 0~30 DEG C of gas.

Fig. 2 is the schematic diagram for indicating to supply the system of humidification gas and dry gas to soaking zone 12.Gas is humidified by adding Humid gas supply mouth 44A~E, humidification gas supply port 45A~E and humidification these three systems of gas supply port 46A~E supply. In Fig. 2, above-mentioned reducibility gas or non-oxidizing gas (dry gas) utilize dry gas distributor 24, a part of quilt It send to humidifier 26, remainder, by dry gas piping 30, is supplied with the state of dry gas via dry gas Mouth 32A, 32B, 32C, 32D are supplied into soaking zone 12.

The position of dry gas supply mouth and number are not particularly limited, it may be considered that various conditions suitably determine.But It is that preferably the length direction along soaking zone configures multiple dry gas supply mouths in identical height and position, and preferably in soaking The length direction of band equably configures.

The gas that humidified device 26 humidifies is assigned to by the piping 40 of humidification gas by humidification gas distributing device 39 Above three system, via the piping 43 of each humidification gas, via humidification gas supply port 44A~E, humidification gas supply port 45A~E and humidification gas supply port 46A~E are supplied into soaking zone 12.

Humidification gas supply port position sum number be not particularly limited, it may be considered that various conditions and suitably determine.But It is that preferably the length direction along soaking zone configures multiple humidification gas supply ports in identical height and position, and preferably in soaking The length direction of band equably configures.In addition, along soaking zone length direction humidification gas supply port column preferably along equal The up and down direction in the torrid zone 12 is divided into more than two-part region is respectively set at 1.Thereby, it is possible to equably control soaking zone 12 Whole dew point.Symbol 41 is humidification gas flowmeter, and symbol 42 is humidification gas dew point instrument.

In humidifier 26, there is the humidification module with fluorine system or polyimides system hollow-fibre membrane or flat membrane etc., In the circulating inside dry gas of film, follow the pure water for being adjusted to predetermined temperature in circulation constant temperature sink 28 Ring.Fluorine system or polyimides system hollow-fibre membrane or flat membrane are the one kind for the amberplex for having affinity with hydrone.Such as Fruit is poor in the inner and outer of hollow-fibre membrane generation moisture concentration, then generates the power for making concentration difference equalization, moisture is with this Power penetrates a Fang Yidong of the film to low moisture concentration as driving force.Dry gas temperature is according to season or 1 day temperature change And change, but can sufficiently have in the humidifier and carry out heat through the gas of film and the contact area of water via vapor Exchange, therefore no matter dry gas temperature is higher than circulating water temperature or low, dry gas become humidification to set water temperature phase The gas of same dew point is able to carry out high-precision dew point control.The dew point for humidifying gas can be any in the range of 5~50 DEG C Control.If the dew point for humidifying gas is higher than piping temperature, condensation, the water of condensation are possible to be directly immersed in furnace in piping It is interior, therefore humidify gas piping and be heated thermal protection to humidification gas dew point or more and external air temperature or more.

Here, in manufacture with the Si containing 0.2 mass % or more at the high-tensile steel being grouped as when, in order to make Dew point in the torrid zone rises, and also supplies humidification gas to soaking zone 12 on the basis of dry gas.In contrast, contain in manufacture Si It is only dry to the supply of soaking zone 12 when amount is lower than steel plate (such as general steel plate of tensile strength 270MPa or so) of 0.2 mass % Pathogenic dryness body, without supplying mixed gas.

Present embodiment is characterized in that: when the high-tensile steel that Si content is 0.2 mass % or more leads to plate, humidifier Body only becomes the back segment supply of the soaking zone of the highest temperature from steel plate, moreover, from the target temperature of plate speed V and soaking zone outlet side Degree T considers and determines the range of soaking zone back segment.Hereinafter, being illustrated to the technical meaning constituted using such feature.It answers Explanation is given, in order to control the supply of such humidification gas, in the present embodiment, as shown in Fig. 2, all humidification gas Supply mouth has the regulating valve 50 of the supply/blocking and gas flow that can control humidification gas each independently.

The steel billet temperature of heating tape outlet side is set as lower by 300 than the steel billet temperature of soaking zone outlet side (annealing temperature) ~500 DEG C or so.For example, making the steel billet temperature of heating tape outlet side when the steel billet temperature of soaking zone outlet side is 850 DEG C 350~550 DEG C or so, steel plate is heated 300~500 DEG C by the leading portion in soaking zone.On the other hand, the Si added in steel is 700 DEG C or more at a high temperature of, it is obvious in surface of steel plate enrichment.In order to inhibit the surface enrichment, steel plate can be made to become the equal of the highest temperature The dew point in the region of tropical back segment is 25~0 DEG C of ﹣, it is known that Si promotes the oxide inside steel plate to be formed, and has raising plating close Conjunction property, the effect for promoting alloying reaction.Further, it was found that should supply the range of the soaking zone back segment of humidification gas can be based on down Formula (1) determines.

≤ 2.5 (1) 1.0≤10100L/V exp { ﹣ 14560/ (T+273.15) }

L [m]: the steel plate length started from soaking zone outlet side

V [m/s]: plate speed

T [DEG C]: the target temperature of soaking zone outlet side

Wherein, the target temperature T of plate speed V and soaking zone outlet side is in the height that Si content is 0.2 mass % or more Power steel plate predefines when leading to plate.In general, considering that the thickness etc. of steel plate determines plate speed V from the range of 1.0~2.0m/s, examine Consider steel plate at the target temperature T for determining soaking zone outlet side from 750~900 DEG C of range such as being grouped as.It should be noted that " The target temperature of tropical outlet side " refers to the target temperature of the steel plate of the soaking zone outlet side set in the material control of steel plate Degree controls temperature in soaking zone in such a way that the steel billet temperature measured by radiation thermometer becomes the target temperature.

Therefore, the target temperature T of predetermined plate speed V and soaking zone outlet side is substituted into formula (1), to meet formula (1) mode determines the steel plate length L started from soaking zone outlet side.Referring to Fig. 2, the steel plate that will be started from soaking zone outlet side Length L is set as from the lower part hearth roll 49E of the soaking zone outlet side positioned at most downstream in the lower part hearth roll 49 of soaking zone The steel plate length of calculation.Moreover, by one of passage corresponding to sheet steel sections corresponding with determining L, upstream-most position The definition space of the passage of trip closer to cooling zone side is soaking zone back segment.Referring to Fig. 2, by P₁It indicates from the outlet side of soaking zone The length of calculation is the upstream-most position of the sheet steel sections of L.It will be with upstream-most position P₁Corresponding passage (is the 5th in Fig. 2 It is secondary) the passage (in Fig. 2 be the 4th passage) of a upstream set closer to the downstream side of cooling zone side, i.e. uniform temperature zone length, direction For soaking zone back segment 12B.It should be noted that will compared with upstream-most position P₁The passage of one upstream of corresponding passage (is in Fig. 2 4th passage) closer to the upstream side of heating tape side, i.e. uniform temperature zone length, direction it is set as soaking zone leading portion 12A.Moreover, in this reality It applies in mode, humidification gas is only from the humidification gas supply port positioned at soaking zone back segment 12B in multiple humidification gas supply ports (in Fig. 2, upper section is humidification gas supply port 44C~E, and middle section is humidification gas supply port 45C~E, and lower section is that humidification gas supplies Give mouth 46C~E) supply.In this way, (A) is able to suppress Si when the high-tensile steel that Si content is 0.2 mass % or more leads to plate Oxide is enriched in surface of steel plate and realizes good adaptation, also, (B) is general lower than 0.2 mass % in Si content thereafter When logical steel plate continuously leads to plate, the generation for picking up defect is able to suppress and promptly switching the dew point of atmosphere in soaking zone.It answers Explanation is given, according to the definition of above-mentioned soaking zone back segment, for the sheet steel sections for being L with the length started from soaking zone outlet side Upstream-most position P₁In corresponding passage, to the surface of the steel plate of the passage and back side supply humidification gas.

1.0 or more the value for making the second side in formula (1) is internal oxidation in order to ensure reaching the Si of necessary bottom line Necessary condition.Therefore, in the case that the value on the second side is lower than 1.0, in the high-tensile steel that Si content is 0.2 mass % or more When logical plate, the internal oxidation of Si is unable to fully carry out, and cannot get plating adaptation height and good plating appearance.In addition, alloy Change temperature and becomes high temperature, tensile strength decline.As a result, in the present embodiment, make 1.0 or more the value on the second side.

On the other hand, it shown below the value 2.5 on the second side to carry out the switching of the atmosphere in soaking zone rapidly Necessary condition.Therefore, in the case that the value on the second side is greater than 2.5, ordinary steel is being switched to from the high-tensile steel for being added to Si When plate, dew point change expends the time, and the surface defects such as pickup are generated when manufacturing general steel plate.Even if in addition, making the second side Value is greater than 2.5 and lengthens and increase humidification region, and plating adaptation, alloying reaction facilitation effect also reach saturation.As a result, at this In embodiment, make 2.5 or less the value on the second side.

In actual operation, it such as can carry out as follows.For example, in the case where plate speed V=2.0m/s, soaking zone At T=750 DEG C of the target temperature of outlet side, meet formula (1) from soaking zone outlet side start steel plate length be 301m≤L≤ 750m at T=800 DEG C of the target temperature of soaking zone outlet side, meets the steel plate length of formula (1) started from soaking zone outlet side For 155m≤L≤387m.Therefore, want in operation in the case where keeping plate speed 2.0m/s constant, to meet 301m≤L The mode of≤387m, such as L=301m is made to set soaking zone back segment.In this way, no matter the target temperature T of soaking zone outlet side is 750 DEG C or 800 DEG C, the operation for meeting formula (1) can be carried out, therefore do not need significantly in addition to changing target temperature T The change of operating condition.

In addition, in the case where plate speed V=1.0m/s, at T=750 DEG C of the target temperature of soaking zone outlet side, meet The steel plate length of formula (1) started from soaking zone outlet side is 151m≤L≤375m.Carrying out plate speed=2.0m/ as a result, S, after the operation (the L range for meeting formula (1) is the operation of 155~387m) of T=800 DEG C of the target temperature of soaking zone outlet side, When wanting to carry out the target temperature of soaking zone outlet side being changed to T=750 DEG C of operation, if making plate speed 1.0m/ S is then capable of fixing as L=155m or more.That is, it is not necessary to expand soaking zone back segment, therefore switch fast from atmosphere From the viewpoint of for preferably.

The flow of the humidification gas supplied into soaking zone 12 is not particularly limited as long as control as described above, substantially Maintain 100~400 (Nm³/ hr) in the range of.In addition, the flow of the dry gas supplied into soaking zone 12 is not special Limit, with Si containing 0.2 mass % or more at the high-tensile steel being grouped as logical plate when, substantially maintain 10~ 300(Nm³/ hr) in the range of, in steel plate of the Si content lower than 0.2 mass %, (such as tensile strength 270MPa's or so is common Steel plate) logical plate when, maintain 200~600 (Nm³/ hr) in the range of.

(cooling zone)

In present embodiment, steel plate P is cooled in cooling zone 14,16.Steel plate P is cooled to 480 in the 1st cooling zone 14~ 530 DEG C or so, 470~500 DEG C or so are cooled in the 2nd cooling zone 16.

It is also supplied with above-mentioned reducibility gas or non-oxidizing gas to cooling zone 14,16, but is only supplied dry gas herein Body.The supply of the dry gas carried out to cooling zone 14,16 is not particularly limited, preferably in the mode in impartial investment cooling zone More than from short transverse 2, at longitudinal direction 2 more than input port supply.The conjunction of the dry gas supplied to cooling zone 14,16 Meter gas flow is not particularly limited using the gas flowmeter for being set to piping measurement (not shown), can be 200~1000 (Nm³/ hr) left and right.

(galvanizing by dipping bath)

Galvanizing by dipping bath 22 can be used, galvanizing by dipping is implemented to the steel plate P being discharged from the 2nd cooling zone 16.Galvanizing by dipping It can carry out according to conventional methods.

(alloying equipment)

Alloying equipment 23 can be used and carry out heating alloying to the zinc-plated of steel plate P is applied to.Alloying Treatment can be with It carries out according to conventional methods.According to the present embodiment, since alloying temperature not will become high temperature, so being able to suppress manufacture The tensile strength of alloyed hot-dip galvanized steel plate declines.

(steel plate at be grouped as)

The steel plate P of object as annealing and galvanizing by dipping processing is not particularly limited, but for containing 0.2 mass % with On Si at the steel plate being grouped as, i.e. high tension steel in the case where, can advantageously obtain effect of the invention.Hereinafter, right The preferred of steel plate is illustrated at being grouped as.The all quality % of unit indicated in the following description by %.

C by formed as structure of steel retained austenite layer, the equal and easy raising processability of martensite, it is advantageous to It is 0.025% or more, not special provision lower limit in the present invention.On the other hand, if it exceeds 0.3%, then weldability deteriorates, therefore C amount is preferably 0.3% or less.

Si is to obtain the effective element of good material to steel is strengthened, and 0.2% or more is added in high-tensile steel.Si When lower than 0.2%, high intensity needs the alloying element of high price in order to obtain.On the other hand, if it exceeds 2.5%, then can inhibit Oxide scale film in oxidation processes is formed.In addition, alloying temperature also becomes high temperature, it is difficult to obtain desired mechanical special Property.Therefore, Si amount is preferably 2.5% or less.

Mn is to the effective element of the high intensity of steel.In order to ensure the tensile strength of 590MPa or more, preferably comprise 0.5% or more.On the other hand, if it exceeds 3.0%, then it is difficult to ensure that weldability, plating adaptation, strength ductile are flat sometimes Weighing apparatus.Therefore, Mn amount is preferably 0.5~3.0%.When tensile strength is 270~440MPa, suitably added with 1.5% or less.

P be to the effective element of the high intensity of steel, but due to postpone zinc and steel alloying reaction, so adding In the case where the steel of 0.2% or more Si, in addition preferably 0.03% according to intensity hereinafter, can suitably add.

Though influence of the S to hardness of steel is few, oxide scale film formation when to hot rolling cold rolling has an impact, therefore preferably 0.005% or less.

It should be noted that on the basis of above-mentioned element, such as can also arbitrarily add the elements such as Cr, Mo, Ti, Nb, V, B In a kind or two or more, other than remainder be Fe and inevitable impurity.