CN105408511B

CN105408511B - The ferrite-group stainless steel of the excellent corrosion resistance of weld part

Info

Publication number: CN105408511B
Application number: CN201480041182.5A
Authority: CN
Inventors: 吉野正崇; 太田裕树
Original assignee: NKK Corp
Current assignee: JFE Engineering Corp
Priority date: 2013-07-29
Filing date: 2014-07-16
Publication date: 2018-09-07
Anticipated expiration: 2034-07-16
Also published as: TWI526547B; JPWO2015015735A1; CN105408511A; WO2015015735A1; TW201512425A; MY160981A; KR101809812B1; US20160168673A1; KR20160014685A; JP5700182B1

Abstract

The present invention provides the ferrite-group stainless steel of the excellent corrosion resistance of weld part.A kind of ferrite-group stainless steel, which is characterized in that in terms of quality %, contain C：0.001~0.025%, Si：0.05~0.30%, Mn：0.35~2.0%, P：0.05% or less, S：0.01% or less, Al：0.05~0.80%, N：0.001~0.025%, Cr：16.0~20.0%, Ti：0.12~0.50%, Nb：0.002~0.050%, Cu：0.30~0.80%, Ni：0.05% less than 0.50%, V：0.01~0.50%, and meet following formula (1), surplus is made of Fe and inevitable impurity.0.50 25 × C+18 of ＜ × N+Ni+0.11 × Mn+0.46 × Cu (1).It should be noted that the symbol of element in formula refers to the content (quality %) of each element.

Description

The ferrite-group stainless steel of the excellent corrosion resistance of weld part

Technical field

The present invention relates to invade to the carbon of weld seam and nitrogen when being not easy because being welded from welding object material or from air The nitrogen of intrusion and the ferrite-group stainless steel that the reduction of corrosion resistance occurs.

Background technology

Compared with austenite stainless steel, ferrite-group stainless steel can ensure corrosion resistance with few Ni amounts.Ni is valence The element of lattice costliness, therefore, compared with austenite stainless steel, ferrite-group stainless steel can be manufactured with low cost.Separately Outside, compared with austenite stainless steel, ferrite-group stainless steel is high with thermal conductivity, coefficient of thermal expansion is small and is not susceptible to answer The excellent characteristic such as power corrosion cracking.Therefore, ferrite-group stainless steel is applied to automobile exhaust system member, roof or door and window The pipe devices material such as equal construction materials, cooking apparatus or water tank, heat accumulation water pot etc. is extensive on the way.

When making these works, in most cases by austenite stainless steel, particularly SUS304 (18%Cr-8% Ni) (JIS G 4305) etc. is applied in combination with ferrite-group stainless steel.As the welding method of such stainless steel, generally use TIG weld.In this case, also require that there is good corrosion resistance same as base material portion to weld part.

For such project, it is proposed that following method：It, will by adding the Ti or Nb big with the affinity ratio Cr of C and N C and N is fixed in the form of the carbonitride of Ti or Nb, is inhibited the generation of Cr carbonitrides and is inhibited the generation being sensitized, it is ensured that is good Good corrosion resistance.For example, Patent Document 1 discloses improve ferrite-group stainless steel by compound addition Ti and Nb Resistance to grain boundary corrosion resistance steel.In addition, Patent Document 2 discloses improve resistance to grain boundary corrosion by adding Nb Steel.

But any one invention is required for the Mo of addition 0.3 mass % or more.Mo is that the corrosion resistance of base material is made to improve Element.But Mo is strong ferrite generating elements, and therefore, in the case of the Mo added with 0.3 mass %, weld part The generation of ferritic phase be promoted, to encourage the sensitization of weld part, therefore the corrosion-resistant of sufficient weld part cannot be obtained Property.In addition, being required to the Nb of addition 0.1 mass % or more.But when being welded to the steel containing a large amount of Nb, it is dissolved Nb The problems such as weld part is generated in the form of coarse Nb precipitates, will produce weld crack sometimes.In view of manufacturing, practicability When, the corrosion resistance of weld part is obtained by only adding the carbonitrides such as Nb, Ti generation element can not say it is Best strategy.

Existing technical literature

Patent document

Patent document 1：Japanese Unexamined Patent Publication 2007-270290 bulletins

Patent document 2：Japanese Unexamined Patent Publication 2010-202916 bulletins

Invention content

Problem to be solved by the invention

Therefore, the purpose of the present invention is to provide the iron without excessively adding Ti, Nb, weld part excellent corrosion resistance Plain system stainless steel.

The method for solving problem

To solve the above-mentioned problems, the present inventor to that can inhibit the skill of the reduction of the corrosion resistance of weld part back and forth Art has made intensive studies.First, inventor using 16~20 mass %Cr draw points to for obtaining the resistance to of sufficient weld part The degree of the permitted sensitization of corrosivity has been systematically carried out investigation.Itself as a result, it has been found that, the corrosion resistant of the weld part caused by being sensitized The reduction of corrosion the ferritic phase coated by Cr carbonitrides crystal boundary clad ratio (about crystal boundary clad ratio, reference implementation example Assay method) more than 40% when become apparent.

Then, the method for the crystal boundary clad ratio for the ferritic phase that the present inventor is coated reduction by Cr carbonitrides carries out Research.Itself as a result, it has been found that, so that austenite phase is stabilized for improving by adding The corrosion resistance of weld part is extremely effective.

It finds, keeps austenite phase stabilized by adding Mn and Cu, iron when welding can be inhibited The generation of ferritic phase, also, by the C more than solid solubility limit with ferritic phase contained and N to be solid-solution in solid solubility limit overwhelming The state that ground is more than in the austenite phase of ferritic phase is stabilized, and thus, it is possible to prevent from causing because generating Cr carbonitrides Sensitization, the corrosion resistance of weld part significantly improves.

It is moreover found that since C and N being solid-solubilized in austenite phase, with previous C and N merely with Ti, Nb etc. Immobilization compare, can prevent from being sensitized under more C and N amounts.Inventor is for can be obtained the steel of said effect It is investigated to component system, it is found that said effect meets by the content of austenite phase stabilized C, N, Ni, Mn and Cu Following formula obtains in the case of (1).

0.50 25 × C+18 of ＜ × N+Ni+0.11 × Mn+0.46 × Cu (1)

It should be noted that the symbol of element in formula refers to the content (quality %) of each element.

In addition, this effect can be applied in combination with the immobilization of the C and N of the addition using Ti, Nb as the prior art, Therefore, the corrosion-resistant of especially excellent weld part compared with existing steel can be obtained if even if Ti, Nb need not be added excessively Property.

The present invention is completed based on above-mentioned opinion, and purport is as described below.

[1] a kind of ferrite-group stainless steel of the excellent corrosion resistance of weld part, which is characterized in that in terms of quality %, contain There is C：0.001~0.025%, Si：0.05~0.30%, Mn：0.35~2.0%, P：0.05% or less, S：0.01% or less, Al：0.05~0.80%, N：0.001~0.025%, Cr：16.0~20.0%, Ti：0.12~0.50%, Nb：0.002~ 0.050%, Cu：0.30~0.80%, Ni：0.05% less than 0.50%, V：0.01~0.50%, and meet following Formula (1), surplus are made of Fe and inevitable impurity.

0.50 25 × C+18 of ＜ × N+Ni+0.11 × Mn+0.46 × Cu (1)

Wherein, the symbol of element in formula refers to the content (quality %) of each element.

[2] ferrite-group stainless steel of the excellent corrosion resistance of the weld part as described in [1], which is characterized in that with matter % meters are measured, also contains and is selected from Zr：0.01~0.50%, W：0.01~0.20%, REM：0.001~0.10%, Co：0.01~ 0.20%, B：0.0002~0.010%, Sb：One or more of 0.05~0.30%.

Invention effect

According to the present invention it is possible to obtain invading under welding condition as base material from welding object material even if in C and N Also the ferrite-group stainless steel with excellent corrosion resistance.

Specific implementation mode

The restriction reason of each constitutive requirements of the present invention is illustrated below.

1. about at being grouped as and metal structure

First, illustrating at the reasons why being grouped as to the steel of the regulation present invention.It should be noted that ingredient % is Refer to quality %.

C：0.001~0.025%

C is the element inevitably contained.The C amounts the high, intensity more improves, more few, processability more improves.It is terrible To sufficient intensity, need containing 0.001% or more.But content, when being more than 0.025%, the reduction of processability becomes notable, And it is easy the reduction (sensitization) that locality Cr caused by the precipitation of reason Cr carbide lacks and occur corrosion resistance.Therefore, C Amount is set as 0.001~0.025% range.But it is although more lower more excellent from C amounts from the viewpoint of corrosion resistance and processability When selecting, but C amounts being made extremely to reduce, refining spends the time, not preferred in manufacture.It is therefore preferable that for 0.003~0.018% Range.More preferably 0.005~0.012% range.

Si：0.05~0.30%

Corrosion resistance effective elements of the Si to raising weld part.The effect in order to obtain is needed containing 0.05% or more, Content more at most its effect is bigger.But Si contents, when being more than 0.30%, formability, the toughness of weld part reduce, therefore unexcellent Choosing.Therefore, Si amounts are set as 0.05~0.30% range.Preferably 0.05~0.25% range.Further preferably 0.08~0.20% range.

Mn：0.35~2.0%

Mn is especially important element in the present invention.Mn is as the effective element of deoxidier, and with by Ovshinsky The effect of phase stabilizer.By the Mn containing specified amount, the generation of ferritic phase when welding can be inhibited, by will be with iron States of the C and the N more than solid solubility limit of ferritic phase contained to be solid-solution in the solid solubility limit austenite phase bigger than ferritic phase It is stabilized, shows the effect for preventing from being sensitized because caused by generating Cr carbonitrides, the corrosion resistance of weld part improves. These effects in order to obtain are needed containing 0.35% or more Mn.But Mn contents are when being more than 2.0%, the excessive hard of base material Change, ductility reduction, and the reduction of the toughness caused by the hardening of weld part is generated in weld part, therefore not preferably.Cause This, Mn amounts are set as 0.35~2.0% range.Preferably 0.50~1.5% range.Further preferably 0.75~ 1.25% range.

P：0.05% or less

P is the element inevitably contained in steel, excessive containing that weldability can be made to reduce, and easy tos produce crystal boundary corruption Erosion.The tendency is becoming notable more than 0.05% when containing.Therefore, P amounts are set as 0.05% or less.Preferably 0.03% with Under.

S：0.01% or less

The element that S and P also inevitably contains in steel, containing more than 0.01% can be such that corrosion resistance drops It is low.Therefore, S amounts are set as 0.01% or less.Preferably 0.008% or less.

Al：0.05~0.80%

Al and Si also makes the element that the corrosion resistance of weld part improves.The affinity ratio Cr's and N of Al and N is affine Power is strong, therefore, in the case of N has been mixed into weld part, N is made to be precipitated in the form of Al nitride rather than with Cr nitride Form is precipitated, and has the effect of inhibiting sensitization.In addition, Al is also for element useful for the deoxidation in steel making working procedure.This A little effects obtain sometimes in 0.05% or more contain.But when containing having more than 0.80% Al, ferrite crystal grain coarsening adds Work, manufacturing reduce.Therefore, Al amounts are set as 0.05~0.80% range.Preferably 0.10~0.60% range.Into One step is preferably 0.15~0.50% range.

N：0.001~0.025%

N and C is also in the element inevitably contained in steel.N content height then intensity improve, more few then processability more It improves.Sufficient intensity in order to obtain, 0.001% or more contain is appropriate.But content extends when being more than 0.025% Property significantly reduce, and the reduction of corrosion resistance can occur because encouraging the precipitation of Cr nitride, therefore not preferably.Therefore, N amounts It is set as 0.001~0.025% range.From the viewpoint of corrosion resistance, the N the low the more preferred.However, it is desirable to increase refining Time reduces N amounts, leads to the reduction of manufacturing.It is therefore preferable that being set as 0.003~0.025% range.More preferably 0.003~0.015% range.Further preferably 0.003~0.010% range.

Cr：16.0~20.0%

Cr is for ensuring that the most important element of the corrosion resistance of stainless steel.When Cr contents are less than 16.0%, welded in reason Oxidation caused by connecing makes the weld seam and its surrounding of the Cr reductions on surface layer, cannot obtain sufficient corrosion resistance.In addition, because of welding When be sensitized further being encouraged caused by the welding object material or the mixed N of air, therefore not preferably.On the other hand, Cr When content is more than 20.0%, toughness reduces, the deoxygenated skin after annealing reduces, therefore not preferably.Therefore, Cr amounts are set as 16.0%~20.0% range.Preferably 16.5%~19.0% range.Further preferably 17.0~18.5% model It encloses.

Ti：0.12~0.50%

Ti be preferentially with C and N in conjunction with and it is corrosion-resistant caused by being sensitized caused by inhibiting the precipitation of reason Cr carbonitrides The element of the reduction of property.Its effect is obtained by 0.12% or more contain.But content generates thick when being more than 0.50% Big Ti carbonitrides cause surface defect, therefore not preferably.Therefore, Ti amounts are set as 0.12~0.50% range.It is preferred that For 0.15~0.40% range.Further preferably 0.20~0.35% range.

Nb：0.002~0.050%

Nb be preferentially with C and N in conjunction with and it is corrosion-resistant caused by being sensitized caused by inhibiting the precipitation of reason Cr carbonitrides The element of the reduction of property.In addition, Nb also has the crystallization particle diameter miniaturization for making weld part, the toughness and bendability for improving weld part Effect.These effects obtain when containing 0.002% or more.On the other hand, Nb is also to make the raised element of recrystallization temperature, When content is more than 0.050%, required annealing temperature high temperature is recrystallized, therefore, in moving back using high speed cold-reduced sheet annealed wire In firer's sequence, annealing becomes inadequate, and the reduction of processability occurs due to non-recrystallization crystal grain and recrystal grain are mixed, Therefore not preferably.Therefore, Nb amounts are set as 0.002~0.050% range.Preferably 0.010~0.045% range.Into One step is preferably 0.015~0.040% range.

Cu：0.30~0.80%

Cu is the element for making corrosion resistance improve, and is for improving in aqueous solution or being attached with mother when faintly acid water droplet The particularly effective element of the corrosion resistance of material and weld part.In addition, it is strong austenite forming element that Cu is same as Ni, there is suppression The generation of the ferritic phase of weld part processed inhibits the effect being sensitized caused by the precipitation of Cr carbonitrides.These effects containing It is obtained when having 0.30% or more.When on the other hand, containing 0.80% Cu is had more than, hot-workability reduces, therefore not preferably.Cause This, Cu amounts are set as 0.30~0.80% range.Preferably 0.30~0.60% range.Further preferably 0.35~ 0.50% range.

Ni：0.05% less than 0.50%

Ni is the element for making the corrosion resistance of stainless steel improve, be cannot be formed passivation envelope and active dissolution occurs Inhibit the element of the progress of corrosion in corrosive environment.In addition, Ni is strong austenite forming element, there is the iron for inhibiting weld part Ferritic generates, inhibits the effect being sensitized caused by the precipitation of Cr carbonitrides.These effects contain by 0.05% or more And it obtains.But when containing 0.50% or more Ni, processability reduces, and in addition to this, stress corrosion opening cracking maleate sensitivity becomes strong. In addition, Ni is expensive element, therefore leads to the increase of manufacturing cost, therefore not preferably.Therefore, Ni amounts are set as 0.05% or less and less than 0.50% range.Preferably 0.10~0.30% range.Further preferably 0.15~ 0.25% range.

V：0.01~0.50%

V is the element for making corrosion resistance, processability improve, and is had in the case of being mixed into N in weld part by being tied with N It closes to inhibit the effect of the generation of Cr nitride, the sensitization for reducing weld part.The effect is obtained by 0.01% or more by containing It arrives.But content, when being more than 0.50%, processability reduces, therefore not preferably.Therefore, V amounts are set as 0.01~0.50% model It encloses.Preferably 0.05~0.30% range.Further preferably 0.08~0.20% range.

0.50 25 × C+18 of ＜ × N+Ni+0.11 × Mn+0.46 × Cu (1)

In order to make the C and N of weld part be solid-solubilized in austenite phase and immobilization, need raw in cools tissue after welding At austenite phase.In order to generate austenite phase in cooling procedure after welding, need to meet above-mentioned formula (1).The right side in formula (1) In the case of side is 0.50 below, the stabilisation of austenite phase becomes inadequate, and cannot be generated for will be of the invention in weld part The austenite phase of the solid solution C of offer and the degree of solid solution being effectively fixed of N.Therefore, it is set greater than 0.5 on the right of formula (1). Preferably 0.60 or more.More preferably 0.70 or more.

It is the basic chemical composition of the present invention above, surplus is made of Fe and inevitable impurity.It should be noted that As inevitable impurity, Ca can be allowed：0.0020% or less.

In addition, on the basis of above-mentioned basis, the purpose of sensitization and raising corrosion resistance etc. for inhibition weld seam, Following element can also be contained.

Zr：0.01~0.50%

Zr have the effect of with C and N in conjunction with and inhibit be sensitized.The effect is obtained by 0.01% or more contain.But It is that when content is more than 0.50%, processability reduces.In addition, Zr is expensive element, therefore, excessively addition can cause to make This increase is caused, therefore not preferably.Therefore, containing Zr, it is preferably set to 0.01~0.50% range.More Preferably 0.10~0.35% range.

W：0.01~0.20%

W is same as Mo to have the effect of that corrosion resistance is made to improve.The effect is obtained by 0.01% or more contain.But It is that when content is more than 0.20%, intensity increases, and leads to the reduction of the manufacturing caused by increase of rolling loads etc., therefore not It is preferred that.Therefore, containing W, it is preferably set to 0.01~0.20% range.More preferably 0.05~0.15% Range.

REM：0.001~0.10%

REM has the effect of that inoxidizability is made to improve, for inhibiting closely to weld back by inhibiting the formation of oxide skin The formation in the scarce regions Cr of the lower section of heat color is effective.The effect in order to obtain, needs containing 0.001% or more.But contain When amount is more than 0.10%, the reduction of the manufacturings such as pickling can be made.In addition, it is expensive element that REM is same as Zr, therefore, Excessively containing the increase that can lead to manufacturing cost, therefore not preferably.Therefore, it containing REM, is preferably set to 0.001~0.10% range.More preferably 0.010~0.08% range.

Co：0.01~0.20%

Co is the element for making toughness improve.The effect is obtained by 0.01% or more contain.On the other hand, content is super When 0.20%, manufacturing can be made to reduce.Therefore, containing Co, it is preferably set to 0.01~0.20% range. More preferably 0.05~0.15% range.

B：0.0002~0.010%

B is the element for improving secondary processing brittleness, and effect is obtained by 0.0002% or more contain.But contain When amount is more than 0.010%, the reduction of the ductility caused by excessive solution strengthening can be induced.Therefore, containing B the case where Under, it is preferably set to 0.0002~0.010% range.More preferably 0.0010~0.0075% range.

Sb：0.05~0.30%

Sb is same as Al to be had the effect of capturing from the mixed N of air when the gas shield of TIG weld is insufficient, is being answered It is particularly effective element in the case of for the structure with the complicated shape for being difficult to carry out sufficient gas shield.Its Effect is obtained by 0.05% or more contain.But content generates nonmetallic folder when being more than 0.30% in steel making working procedure Sundries, surface texture are deteriorated.In addition, making the degraded toughness of hot rolled plate.Therefore, it containing Sb, is preferably set to 0.05~0.30% range.More preferably 0.05~0.15% range.

2. about manufacturing condition

Then, the preferable production process of steel of the present invention is illustrated.The molten steel of mentioned component composition is utilized into converter, electricity Method well known to stove, vacuum fusion stove etc. carries out melting, and steel former material (steel billet) is made by continuous metal cast process or ingot casting-cogging method. Hot rolling is carried out after the steel billet is heated 1~24 hour at 1100~1250 DEG C or without heating and in the state of casting It is lower directly to carry out hot rolling, to which hot rolled plate be made.

In general, the hot rolled plate that hot rolled plate is implemented 1~10 minute at 800~1100 DEG C is annealed.It should be noted that root According to purposes, hot rolled plate annealing can also be omitted.Then, after hot rolled plate pickling, cold-reduced sheet is made by cold rolling, then, is implemented Recrystallization annealing, pickling, to which product be made.

From the viewpoint of extensibility, bendability, press formability and shape, cold rolling is preferably with 50% or more reduction ratio It carries out.Recrystallization annealing about cold-reduced sheet, it is however generally that, in the Surface Finishing of JIS G0203, No.2B finished goods In the case of, from the viewpoint for obtaining good mechanical performance and from the aspect of pickling, preferably at 800~950 DEG C into Row.In addition, the component at the position for further requirement gloss, it is effective to carry out BA annealing (bright annealing) in finishing 's.It should be noted that in order to further increase surface texture after cold rolling and after processing, it is possible to implement grinding etc..

Embodiment 1

Hereinafter, being illustrated in more details to the present invention based on embodiment.

By the melting in 50kg small size vacuum melting furnaces of the stainless steel with chemical composition shown in table 1.By these blooms After being heated 1 hour at 1150 DEG C, implements hot rolling and the hot rolled plate of 3.5mm thickness is made.Then, to these hot rollings at 950 DEG C After plate implements hot rolled plate annealing in 1 minute, bead is carried out to surface, then, in 80 DEG C of temperature, 20 mass % sulfuric acid solutions Middle dipping impregnates 60 after 120 seconds in the mixed acid for 55 DEG C of temperature being made of 15 mass % nitric acid and 3 mass % hydrofluoric acid Second, pickling is thus carried out, deoxygenated skin is carried out.

In turn, it is cold-rolled to plate thickness 0.8mm, in weak reducing atmosphere (hydrogen：5 volume %, nitrogen：95 volume %, dew point：- 40 DEG C) in 900 DEG C carry out recrystallization annealing in 1 minute, obtain cold rolled annealed plate.By the cold rolled annealed plate temperature 50 C, Cathodic pickling is carried out in the mix acid liquor being made of 15 mass % nitric acid and 0.5 mass % hydrochloric acid, is thus carried out at deoxygenated skin Reason, obtains cold-rolling pickling annealed sheet.

It should be noted that table 1-1, table 1-2 are continuous a series of table.

The cold-reduced sheet of use production and commercially available austenite stainless steel SUS304 (C：0.07 mass %, N：0.05 matter Measure %, Cr：18.2 mass %, Ni：8.2 mass %) plate thickness be 0.8mm cold-reduced sheet, carry out docking TIG weld (butt TIG welding) (cold-reduced sheet of the invention：Base material, welding object material：SUS304).Welding current is set as 90A, welding Speed is set as 60cm/ minutes, and for protective gas, the nitrogen comprising 8 volume %, the oxygen of 2 volume % were used with 15L/ minutes The Ar gases of gas.The width of the weld seam of obtained surface side is about 3mm.

The test film for including weld seam for cutting making, carries out following experiments.

1. the pitting potential of base material and weld part is tested

Test film after cold rolled annealed and the test film after welding cut the test film of 20mm square, make residual 10mm The aspect of measure of square and the test film coated with sealing material.For the test film after welding, with the side comprising weld seam Formula cuts test film, keeps remaining the state because of the tempering colour (oxide film thereon) that welding generates.For these test films, 30 DEG C 3.5 mass %NaCl solution in measure base material and weld part pitting potential.When measurement, without test film grinding, Passivation Treatment, but assay method in addition to this is according to JIS G 0577 (2005).

By the pitting potential of base material：The pitting potential of 150mV or more, weld part：0mV or more is set as qualified.

2. neutral salt spray cyclic test

The test film of the 100mm square comprising weld seam is cut from the test film after welding, is made of #600 sand paper to surface Be ground the test film for end face portion being sealed after finishing, for neutral salt spray cycle examination specified in JIS H8502 It tests.In neutral salt spray cyclic test, 5 mass %NaCl solution spraying (35 DEG C, 2 hours) → dry (60 DEG C, 4 hours, phase To humidity 20~30%) → (moistness) (40 DEG C, 2 hours, 95% or more relative humidity) is soaked as a cycle.It will be real Apply 15 cycle the experiment after from base material or weld part there is a situation where corrode be set as qualification.

3. the crystal boundary clad ratio of the ferritic phase coated by Cr carbonitrides measures

Metal structure observation test film, mirror ultrafinish are cut in the right angle orientation of the weld seam of test film after welding Afterwards, so that metal structure and precipitate is shown by using the etching of picrate aqueous acid, carry out using scanning electron The identification of phases of the structure observation and precipitate of microscope and energy dispersion type X-ray optical spectroscopy, measures the ferritic phase of welding seam part The crystal boundary clad ratio coated by Cr carbonitrides.

About crystal boundary clad ratio, the crystal boundary that the crystal grain in captured macrograph is measured using image analysis apparatus is long Degree, and the direction parallel with the crystal boundary of Cr carbonitrides being precipitated on crystal boundary is measured using same image analysis apparatus Diameter passes through crystal boundary clad ratio (%)=(total of the diameter in the direction parallel with the crystal boundary of Cr carbonitrides on crystal boundary) ÷ The formula of (total of the crystal boundary length of crystal grain) × 100 calculates.

The situation that the crystal boundary clad ratio of the ferritic phase coated by Cr carbonitrides is 40% or less is set as qualified.

4. mechanical property is evaluated

From made cold rolled annealed plate, JIS 13B tension test sheets are parallelly cut with rolling direction, according to JIS Z2241 carries out tension test, measures elongation at break.

Elongation at break is set as qualified for 25% or more.

5. surface quality is evaluated

Detect by an unaided eye cold rolled annealed rear, after deoxygenated skin surface of steel plate, is confirmed whether have deoxygenated skin bad and line The surface defects such as shape defect.

No oxide skin is remained and surface defect, has obtained the case where good appearance and is set as qualified benchmark.

Test result is shown in Table 2.

Steel No.1~20 for meeting the important document of the present invention are that the pitting potential of base material is the spot corrosion of 150mV or more, weld seam Current potential is 0mV or more, also, not because neutral salt spray cyclic test generates corrosion, even if stainless with austenite Steel is implemented also to have obtained sufficient corrosion resistance in the case of welding.In addition, steel No.1~20 weld after by Cr carbonitrides The crystal boundary clad ratio of the ferritic phase of cladding is 40% hereinafter, having obtained defined anti-sensitization effect.In addition, based on examination is stretched The elongation at break tested is 25% or more, has obtained good processing characteristics, and surface defect is also not observed.

On the other hand, for Cr amounts are more than the steel No.21 of the scope of the present invention, the toughness of the steel plate after hot rolling is notable It reduces, the manufacturing process after cannot implementing cannot evaluate characteristic.

For steel No.22 of the Cr amounts less than the scope of the present invention, it cannot get sufficient pitting potential, in addition, in Property brine spray cyclic test in, from base material and weld part generate corrosion, defined corrosion resistance cannot be obtained.

For steel No.23 of the Mn amounts less than the scope of the present invention, although having been obtained for base material sufficient corrosion-resistant Property, but sufficient corrosion resistance cannot be obtained for weld part.

On the other hand, for Mn amounts or Al amounts are more than the steel No.24 and 25 of the scope of the present invention, although being advised Fixed base material and corrosion resistance at welded part, but make ductility reduction because of steel plate hardening, it is special that defined machinery cannot be obtained Property.

For Ti amounts are more than the steel No.26 of the scope of the present invention, although having obtained defined corrosion resistance and machinery Characteristic, but surface defect is produced because largely generating coarse Ti systems field trash, defined surface texture cannot be obtained.

Although the content for meeting the scope of the present invention but austenite stabilizer element for the content of each element is less than formula (1) for steel No.27~30 of range, defined base material corrosion resistance and mechanical property have been obtained.But it is not advised The pitting potential of fixed welding seam part and the corrosion resistance of weld part.The fractography of the weld part of No.27~30 is examined It examines, as a result confirms, be precipitated in ferritic phase grain boundaries and 50% or more Cr extremely large amount of in this way is calculated as with crystal boundary clad ratio Carbonitride.Think for steel No.27~30, austenite stabilizer element is insufficient, therefore, raw in cooling after welding At ferritic phase, generation of the Cr carbonitrides on crystal boundary cannot be inhibited, significant sensitization as a result occurs, cannot be obtained defined The corrosion resistance of weld part.

It can be seen from the above result that according to the present invention it is possible to obtaining without being excessively added Ti, Nb and with excellent corrosion-resistant The ferrite-group stainless steel of property, mechanical property and surface texture.

Industrial availability

The ferrite-group stainless steel obtained in the present invention is suitably applied the purposes for the making that structure is carried out by welding In, in structure materials such as automobile exhaust system material, door and window or ventilation opening, pipeline etc. such as muffler.

Claims

1. a kind of ferrite-group stainless steel, which is characterized in that in terms of quality %, contain C：0.001~0.025%, Si：0.05~ 0.25%, Mn：0.38~2.0%, P：0.05% or less, S：0.01% or less, Al：0.10~0.80%, N：0.001~ 0.025%, Cr：16.0~20.0%, Ti：0.12~0.50%, Nb：0.002~0.050%, Cu：0.30~0.80%, Ni： 0.05% less than 0.50%, V：0.01~0.50%, and meet following formula (1), surplus is by Fe and inevitably Impurity is constituted,

0.50 25 × C+18 of ＜ × N+Ni+0.11 × Mn+0.46 × Cu (1)

Wherein, the symbol of element in formula refers to the quality % contents of each element.

2. ferrite-group stainless steel as described in claim 1, which is characterized in that in terms of quality %, also contain and be selected from Zr：0.01 ~0.50%, W：0.01~0.20%, REM：0.001~0.10%, Co：0.01~0.20%, B：0.0002~0.010%, Sb：One or more of 0.05~0.30%.