CN101331242A - Low-carbon sulfur-automatic steel with good cutability - Google Patents
Low-carbon sulfur-automatic steel with good cutability Download PDFInfo
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- CN101331242A CN101331242A CNA2006800469677A CN200680046967A CN101331242A CN 101331242 A CN101331242 A CN 101331242A CN A2006800469677 A CNA2006800469677 A CN A2006800469677A CN 200680046967 A CN200680046967 A CN 200680046967A CN 101331242 A CN101331242 A CN 101331242A
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/001—Continuous casting of metals, i.e. casting in indefinite lengths of specific alloys
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/10—Supplying or treating molten metal
- B22D11/11—Treating the molten metal
- B22D11/114—Treating the molten metal by using agitating or vibrating means
- B22D11/115—Treating the molten metal by using agitating or vibrating means by using magnetic fields
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/12—Ferrous alloys, e.g. steel alloys containing tungsten, tantalum, molybdenum, vanadium, or niobium
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- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
Abstract
A low-carbon sulfur-containing free-cutting steel having excellent cuttability, characterized in that it contains 0.02-0.15 mass percent C, up to 0.004 mass percent Si (excluding 0 mass percent), 0.6-3 mass percent Mn, 0.02-0.2 mass percent P, 0.35-1 mass percent S, up to 0.005 mass percent Al (excluding 0 mass percent), 0.008-0.03 mass percent O, and 0.007-0.03 mass percent N, with the remainder being Fe and unavoidable impurities, and that the ratio of the manganese content [Mn] to the sulfur content [S], [Mn]/[S], is in the range of 3-4 and the contents satisfy the relationship (1): 10[C][Mn]<-0.94> + 1226[N]<2> <= 1.2 ...(1) (wherein [C], [Mn], and [N] represent the contents by mass percent of carbon, manganese, and nitrogen, respectively).
Description
Technical field
The present invention relates to a kind ofly not use harmful Pb, and bringing into play the low-carbon (LC) sulphur free-cutting steel of good machining surface roughness.
Background technology
Low-carbon (LC) sulphur free-cutting steel is except the hydraulic part of the wheel box of automobile, and also being used as does not have the screw what needs especially and print that smallclothes part that arbor (printer shaft) waits is used steel and general intensity.In addition, machining surface roughness, smear metal are handled property to be had when further requiring, and then adopts the lead-sulphur free-cutting steel that adds plumbous (Pb) in above-mentioned low-carbon (LC) sulphur free-cutting steel.
Contained Pb is to improving very effective elements of machinability in the free-cutting steel, but scolded to there is hazardous property in human body, in addition, on the point of the processing of the flue dust of the lead when melting and cutting swarf etc. a lot of problems are arranged also, thereby just require not add Pb (no Pb) and bring into play good machinability.
In low-carbon (LC) sulphur free-cutting steel,, also propose to have various technology up to now in order under the prerequisite of no Pb, to improve machinability.For example in patent documentation 1, propose by controlling sulfide-based inclusion improves machinability (machined surface roughness and the smear metal property handled) in size technology.Open in patent documentation 2 in addition, in order to control the size of sulfide-based inclusion, it is very important suitably to control in the steel oxygen.Propose in addition, improve the technology (for example patent documentation 3) of machinability by the oxide based inclusion in the regulation steel.In addition, in patent documentation 4, propose regulation MnS, control the technology of casting preceding free oxygen concentration and improving machinability.
On the other hand, also propose to stipulate the chemical composition of steel composition, thereby improve the technology (for example patent documentation 5～7) of machinability by suitable.
Up to now the technology of Ti Chuing all is useful on the viewpoint of the machinability that improves free-cutting steel, but on the special machined surface roughness this point in the processing that is shaped, practical situation are not obtain to be equal to the good machinability that contains the Pb steel.
In addition, as the desired characteristic of no Pb steel, except above-mentioned such machinability, productivity is good also very important.If from this viewpoint, then surface spots can not take place by the continuous metal cast process manufacturing in it, and can easily implement the rolling condition that yet necessitates.Yet continuous casting process is considered to be unfavorable for making the machinability of steel good, can also become important problem by the free-cutting steel that continuous casting process is made excellent in machinability with good productivity.
As the excellent free-cutting steel of machinability (machined surface roughness) that obtains according to surface texture and inside quality is good and yield rate is good Continuous casting process, for example also propose to have the such technology of patent documentation 8.Open in this technology, reach 100～300ppm by making the oxygen level in the steel many, containing, and contain the N of Duoing than existing, the built-up edge that is created on tool-face in the cutting can be suppressed at, the free-cutting steel of excellent in machinability can be obtained with the good connection casting of yield rate.
Yet,, take place because of (CO gas+N easily if improve oxygen and N simultaneously
2Gas) pore that causes makes the machined surface roughness deterioration of steel on the contrary.
Patent documentation 1: the spy opens the scope of 2003-253390 communique Patent right requirement etc.
Patent documentation 2: the spy opens the scope of flat 9-31522 communique Patent right requirement etc.
Patent documentation 3: the spy opens the scope of flat 10-158781 communique Patent right requirement etc.
Patent documentation 4: the spy opens the sharp scope that requires of 2005-23342 communique economic rights etc.
Patent documentation 5: the spy opens the scope of 2001-152281 communique Patent right requirement etc.
Patent documentation 6: the spy opens the scope of 2001-152282 communique Patent right requirement etc.
Patent documentation 7: the spy opens the scope of 2001-152283 communique Patent right requirement etc.
Patent documentation 8: the spy opens the scope of flat 5-345951 communique Patent right requirement etc.
Summary of the invention
The present invention is conceived to above-mentioned this situation and does, its purpose is, a kind of low-carbon (LC) sulphur free-cutting steel is provided, it can suppress the generation of pore, simultaneously, can not give play to good machinability (particularly machined surface roughness) even there is Pb yet, and can make with good productivity by Continuous casting process.
Can reach the low-carbon (LC) sulphur free-cutting steel so-called of the present invention of above-mentioned purpose, have following some main idea, contain:
C:0.02～0.15% (meaning of quality %, down together),
Si:0.004% following (not containing 0%),
Mn：0.6～3％、
P：0.02～0.2％、
S：0.35～1％、
Al:0.005% following (not containing 0%),
O：0.008～0.03％、
N:0.007～0.03%, surplus are Fe and unavoidable impurities, and ratio [Mn]/[S] of Mn content [Mn] and S content [S] is in 3～4 scope, and satisfy following formula (1).
10·[C]×[Mn]
-0.94+1226·[N]
2≤1.2…(1)
Wherein, [C], [Mn] and [N] represent the mass percentage content of C, Mn and N respectively.
In low-carbon (LC) sulphur free-cutting steel of the present invention, as chemical ingredients, (1) making solid solution N amount is 0.002～0.02%, (2) be suppressed at (not contain 0%) below 0.02% also useful adding up to more than a kind among Ti, Cr, Nb, V, Zr and the B, by satisfying these conditions, can further improve the characteristic of low-carbon (LC) sulphur free-cutting steel of the present invention.In addition, preferably in when casting, the induction stirring in the magnetic field by applying 100～500Gauss is made, and so can make surface texture more good.
According to the present invention, make it to satisfy the relational expression of regulation by the content of C, Mn in the control steel and N, and can suppress the generation of pore, use Continuous casting process simultaneously and also can make the good low-carbon (LC) sulphur free-cutting steel of machined surface roughness with good productivity.
Description of drawings
Fig. 1 is the graphic representation of being represented jointly that has or not with the relation of the value on the left side of (1) formula and machining surface roughness (maximum height Rz) and magnetic field.
Embodiment
The machined surface roughness of free-cutting steel depends on generation, size, shape and the homogeneity of built-up edge to a great extent.So-called built-up edge is exactly to pile up a part of being cut material is arranged on the cutter head of instrument, and the phenomenon that it in fact moves as the part (cutting edge) of instrument reduces owing to this generation movement makes the machined surface roughness.Though this built-up edge only generates under certain conditions, the common machining condition of implementing all is the condition that built-up edge generates easily.
The change of such its size of built-up edge is considered to bring fatefulue defective, but on the other hand, it also produces effect the height of life tools for the protection tool insert.Therefore, make built-up edge not have the very wise move of to say so fully, but built-up edge is stably generated, and make its size and shape homogenization.
For built-up edge is generated, and make its size and shape homogenization, importantly in being cut once shearing territory partly, secondary shearing territory, fine crack is generated in a large number.For this fine crack is generated in a large number, just need a large amount of crackles that import to generate point.And as the generation point of fine crack, known MnS is that inclusion is useful.But, be not that whole MnS is that inclusion all can generate point and work as fine crack, have only large-scale and globular (that is, width is big) MnS just can prove effective.Shear once described that MnS can extend in territory, the secondary shearing territory, but if be extended meticulously, then most of can be the same with matrix, can not become the importing point of fine crack.This shows that the MnS that need will be cut material in advance is that Control and Inclusion Removal is large-scale, spherical.
, be large-scale, the balling of inclusion in order to make MnS, the oxygen (total oxygen demand) in the general known steel can impact (for example described patent documentation 2) to this.Oxygen in the steel is many more, thinks that the sulfide diameter is big more.Therefore, be large-scale, the balling of inclusion in order to make MnS, need increase the oxygen concn in the steel to a certain extent.In addition, be that inclusion increases in order to make the MnS that becomes fine crack generation point simultaneously, need further improve Mn concentration, S concentration with respect to existing free-cutting steel (for example JIS SUM23, SUM24L).
According to present inventors' research, distinguish that also the solid solution N in the steel also is related to the generation of fine crack to a great extent, by suitably adjusting its amount, can realize the free-cutting steel that machinability is good.Once shear in territory, the secondary shearing territory aforesaid, if the position is slightly different, then temperature contrast is very big.And, a certain amount of if solid solution N exists, then because the temperature of each position can cause being out of shape the impedance difference.Because this difference can become the generation point of fine crack,, guaranteeing on the solid solution N effectively so the fixing composition of solid solution N promptly, is controlled at Ti, Cr, Nb, V, Zr, the B that generates the composition of nitride easily below the specified amount.
By above-mentioned 2 such phenomenons, promptly (1) MnS is large-scale, the balling of inclusion, (2) increase of solid solution N etc., discovery can make built-up edge stably generate, and make its size and the shape homogenization, as a result of be that the machined surface roughness in the shaping processing of steel improves epoch-makingly, can give play to the characteristic that is equal to the Pb free-cutting steel.
In free-cutting steel of the present invention, need also suitably to stipulate that its chemical ingredients forms, limit as the scope of C, Si, Mn, P, S, Al, O and the N of its basal component and the reasons are as follows.
[C：0.02～0.15％]
C in addition by adding, also has the effect that improves the machined surface roughness guaranteeing on the intensity of steel it is indispensable element more than specified amount.In order to bring into play such effect, need make it to contain more than 0.02%.Yet if contain superfluously, reduce the life tools during machining, the machinability variation, and in addition, the flaw that the CO gas in the time of also will bringing out because of casting causes takes place.From this viewpoint, C content is being advisable below 0.15%.Also have, the preferred lower limit of C content is 0.05%, and preferred upper limit is 0.12%.
[Si:0.004% following (not containing 0%)]
Si is guaranteeing that by solution strengthening aspect the intensity be effective elements, but it works as reductor basically and generates SiO
2And, though this SiO
2Cause inclusion to become MnO-SiO
2-MnS system still surpasses 0.004% as if Si, then the SiO in this inclusion
2Concentration uprises, and can not guarantee the O concentration among the MnS, thereby makes machined surface roughness deterioration.From this viewpoint, need make Si content is below 0.004%, to be preferably below 0.003%.
[Mn：0.6～3％]
Mn improves hardenability, promotes the generation of bainite structure, has the effect that the machinability of making improves.In addition, also be effective elements in intensity aspect guaranteeing.In addition, it combines with S and forms MnS, perhaps combine with O and generates MnO, and generation MnO-MnS complex inclusion has the effect of the machinability of making raising thus.In order to bring into play these effects, needing Mn content is more than 0.6%, but if surpass 3%, then intensity excessively rises, and machinability reduces.Also have, the preferred lower limit of Mn content is 1%, and preferred upper limit is 2%.
[P：0.02～0.2％]
P is bringing into play the effect that the machined surface roughness is improved.In addition, owing to make the crack propagation in the smear metal easy easily, so it also has the effect that the smear metal of making property handled significantly improves.In order to bring into play such effect, need P content to be at least more than 0.02%.Yet if P content surplus, the hot workability deterioration therefore need be for below 0.2%.Also have, the preferred lower limit of P content is 0.05%, and preferred upper limit is 0.15%.
[S：0.35～1％]
S is combined into MnS with Mn in steel, stress raiser when becoming machining, and it cuts apart smear metal easily, is the useful element that is used to improve machinability.In order to bring into play this effect, S content need be for more than 0.35%.Yet, surpass 1% if S content is superfluous, cause the reduction of hot workability, preferred upper limit is 0.8%.
[Total.Al:0.005% following (not containing 0%)]
Al the intensity of utilizing solution strengthening to bring guarantee with deoxidation on be useful element, but its reductor as brute force works and forms oxide compound (Al
2O
3).Because this Al
2O
3Cause inclusion to become MnO-Al
2O
3-MnS system still surpasses 0.005% as if Al content, then the Al in this inclusion
2O
3Concentration uprises, and can not guarantee the oxygen concn among the MnS, and the machined surface roughness is worsened.Also have, preferred upper limit is 0.003%, more preferably below 0.001%.
[O：0.008～0.03％]
O combines with Mn and generates MnO.In addition, MnO contains S in a large number, can form the MnO-MnS complex inclusion.And, because this MnO-MnS complex inclusion is difficult to by rolling extension, thereby exist, so when machining, play a role as stress raiser relatively to accept the globular state.Therefore, O can add energetically, but it is little to be lower than 0.008% o'clock its effect, on the other hand, makes it to contain if surpass 0.03%, then can make the subsurface defect that generation causes because of CO gas in the steel ingot.Thus, needing O content (total oxygen demand) is 0.008～0.03% scope.
In molten steel, O (Total Oxygen) generates MnO, and in addition, MnO contains S in a large number, can form the MnO-MnS complex inclusion.In process of setting, with these MnO-MnS complex inclusions serve as nuclear separate out MnS, in casting sheet (the casting sheet that obtains by continuous casting), based on the MnO-MnS complex inclusion generation of MnS thereafter.This casting sheet is thereafter after heating, be carried out split rolling method, rod rolling (or bar steel is rolling), but it is many more to contain O based on the MnO-MnS complex inclusion of MnS, then be difficult to more extend, in end article (casting material and bar steel), become large-scale, globular MnS by split rolling method, rod rolling (or bar steel is rolling).
When considering so mechanism, O (Total Oxygen) is high more good more, though therefore have lower value, in fact also has higher limit.Its reason is described.O (Total Oxygen) is made of oxygen that exists as oxide compound and the molten oxygen (free oxygen) of depositing that is dissolved in the molten iron.As the oxygen that oxide compound exists, promptly the O among the MnO is very useful oxygen, but free oxygen (O) in process of setting with molten iron in carbon (C) reaction, become CO gas [C+O=CO (gas)], if it is not eliminated well, then can become pore.In addition in the present invention, because also improve N, so in process of setting, the oxygen solubility in temperature reduction and the molten steel reduces, and generates N+N=N
2(gas) reaction forms pore.That is, the first portion of pore is CO (gas)+N
2(gas).
Therefore, purport of the present invention is to make this CO (gas)+N
2(gas) growing amount is in the scope that pore does not take place, and makes free oxygen (O) and nitrogen (N) maximum.In addition, even pore takes place, the induction stirring by carrying out in the mold of continuous casting also can discharge pore, therefore except composition, utilizes induction stirring that room for improvement is also arranged.
Under these imagination, free oxygen (O) is no matter by what decision, and the result of its investigation is distinguished that it is mainly determined by Mn content [Mn] and S content [S].Therefore, can pass through the generating capacity of [C], [Mn] and [S] control CO (gas), aforementioned (1) formula according to wherein having added [N] can make CO (gas)+N
2(gas) generating capacity is made clear, thereby can control pore (details aftermentioned).
Also have, from this viewpoint of subsurface defect that prevents that CO gas from causing, though the free oxygen in the molten steel (O) also can be different according to [C] and [N] or induction stirring condition, preferably be controlled at general below 0.0050% about.Also have, the preferred lower limit of the O content (total oxygen demand) in the steel is 0.01%, and preferred upper limit is 0.03%.
[N：0.007～0.03％]
N is the element that the growing amount for built-up edge impacts, and its content can bring the machined surface roughness with influence.When N content was lower than 0.007%, the growing amount of built-up edge was too much, made machined surface roughness deterioration.In addition, N has the character of segregation on the easy dislocation in tissue, and segregation and make the mother metal embrittlement on the dispiration is propagated the crackle of generation easily when cutting, thus also can high chip fracture (smear metal processing).Yet if N content becomes superfluous and surpasses 0.03%, bubbling (blow hole) when casting constitutes the subsurface defect and the surface spots of ingot casting easily, so it need be suppressed at below 0.03%.Also have, N content preferred lower limit is 0.005%, and preferred upper limit is 0.025%.
In low-carbon (LC) sulphur free-cutting steel of the present invention, only regulation chemical ingredients composition can't be reached purpose of the present invention in the above described manner, also need the ratio of Mn content [Mn] and S content [S] is controlled in the suitable scope, and make it to satisfy the relation of aforementioned (1) formula.These scopes limit and the reasons are as follows.
([Mn]/[S]：3～4)
[Mn]/[S] is the important factor that the crackle during to hot-work etc. exerts an influence, if lack ([Mn]/[S]＜3) with respect to S content Mn, then FeS generates easily, and this becomes the reason of thermal crack.This is when the value of [Mn]/[S] is in 3～4 scope, guarantee to have with respect to S, so Mn of the abundant amount that needs, can not generate FeS, performance can be prevented the effect that thermal crack is such, still, if [Mn]/[S]＞4 this effect is saturated, and the free oxygen (O) by [Mn] and [S] decision reduces, and goes through this machined surface roughness deterioration.
(10·[C]×[Mn]
-0.94+1226·[N]
2≤1.2)
Prevent to guarantee to exist side by side for pore is generated, and need satisfy above-mentioned relation with machinability.If the value on its left side (10[C] * [Mn]
-0.94+ 1226[N]
2) must surpass 1.2 greatly, then pore will generate.The preferred value on its left side is below 1.1, more preferably below 0.9.
The relation of following formula (1) is to try to achieve when carrying out various experimental machine, and its fact is described.Molten be stored in carbon (C) in the molten steel, oxygen [
Free oxygen (O): say that correctly so-called free oxygen is an oxygen activity] and nitrogen (N), when solidifying, at first owing to solid-liquid distributes microsegregation takes place, in the hydraulic fluid side multiviscosisty.In addition, C+O=CO (gas), N=1/2 N take place in (C) in the liquid, (O) and (N) the solution degree minimizing owing to temperature reduces therefrom
2(gas) reaction is preponderated as if this site pressure, then the hydraulic fluid side bubbling in molten steel.The pressure at so-called this position mainly is the interfacial energy/bubble diameter of normal atmosphere+molten steel static pressure+liquids and gases, and the molten steel static pressure is little, takes place easily near meniscus (meniscus).The composition of this gas (bubble) is CO (gas).If this gas (bubble) is owing to density difference floats, and from molten steel to breaking away from atmosphere, then can be not remaining on the sheet as pore in casting, still,, then can become the defective of casting sheet as pore if its crystallization that is solidified etc. capture.
Because above-mentioned mechanism is inferred, so the generation of pore is considered to exist with ... carbon concentration [C], free oxygen concentration [O] and nitrogen concentration [N].Therefore, on thermodynamics, think and to represent with following formula (2)～(7).
CO(gas)＝[C]+[O] …(2)
K
CO＝(a
C·a
o)/P
CO＝f
C[C]·f
O[O])/P
CO …(3)
logK
CO＝-1160/T-2.003 …(4)
C
C L＝C
C 0/{1-(1-k
C)f} …(5)
C
O L＝C
O 0/{1-(1-k
O)f} …(6)
P
CO＝(f
C·f
o·C
C 0·C
O 0)/
[{1-(1-k
C)f}{1-(1-k
O)f}K
CO] …(7)
At first, consider following formula (2) (when the right side proceeds to a left side).(2) the reactivity coefficient K of formula
COShown in (3) formula, be subjected to the activity quotient (f of C
C), the activity quotient (f of C content [C], O
O), O content [O], CO dividing potential drop (P
CO) about.This numerical value is by about (4) formula.At this T is absolute temperature.In addition, C content [C], O content [O] are the concentration of microsegregation, therefore adopt the formula of Sheil to try to achieve as (5) formula and (6) formula.At this, C
C 0, C
O 0C content [C], the O concentration [O] of molten steel before expression is cast respectively, that be the initial stage, C
C L, C
O LC content [C], the O concentration [O] of liquid phase of (solid phase, liquid phase coexisting state) during expression is solidified respectively is microsegregation and the concentration of multiviscosisty.If with its substitution following formula (3), then CO dividing potential drop (P
CO) represent by (7) formula.Also have, f is a solid rate, k
C, k
OThe equilibrium distribution coefficient of representing C and O respectively.
On the other hand, same shown in following (8) formula～(12) formula about N.
1/2N
2(gas)＝[N] …(8)
C
N L＝C
N o/{1-(1-k
N)f} …(11)
That is the reactivity coefficient K of following formula (8),
N2Can represent that thermodynamics numerical value is represented by (10) formula by (9) formula.In addition, the N concentration [N] of the molten steel side during microsegregation can be represented by (11) formula, if with its substitution (9) formula, then N
2Dividing potential drop (P
N2) represent by (12) formula.
(7) formula of so inferring and the dividing potential drop of (12) formula and (P
CO+ P
N2) as shown in the formula shown in (13), when surpassing the interfacial energy of external pressure (normal atmosphere)+molten steel static pressure+liquids and gases/bubble diameter, then form pore.
P
g≥P
a+ρLgh+2σ/r …(13)
P
a: external pressure
ρ Lgh: fluid pressure
σ: the interfacial energy of liquids and gases
R: bubble diameter
According to method of calculation, for (the P that calculates with this physical property meaning
CO+ P
N2) the generation frequency of checking pore, its result as can be known, if (P
CO+ P
N2) surpass 1.2atm, then pore takes place.
Present inventors study and make (P
CO+ P
N2) exponentiate.Though can measure simply by on-line analysis, [O] needs to use the free oxygen meter to measure [C] and [N].In addition, by measuring, error is also very big.Therefore, as can be known, it was by Mn concentration [Mn] and S concentration (S content) [S] decision when what research free oxygen concentration [O] determined by.Also this is because in molten steel, O becomes oxide compound-sulfide of MnO-MnS as can be known.Thus, the relational expression that has or not clearly serve as reasons [C], [Mn], [S] and [N] of the generation of pore is represented.On the other hand, because [Mn] and [S] has the relation of [Mn]/[S]=3～4, so if also consider this relation, then having or not substantially of the generation of clear and definite pore represented by the relational expression that has of [C], [Mn] and [N].
Under this imagination, P
COBased on described (7) formula, proportional with [C] and [O], but at this because [O] and [Mn] have relation, so, try to achieve P experimentally according to the data of the right of (7) formula and [Mn] etc.
CO=10[C] [Mn]
-0.94On the other hand, P
N2Based on preceding formula (12) since with [N]
2Proportional, thus according to the right of (12) formula multiply by 2 and the data of [N] etc., try to achieve P experimentally
N2=1226[N]
2
And, if P
CO+ P
N2(=10[C] * [Mn]
-0.94+ 1226[N]
2) become big, then pore takes place, and surface spots produces, but not only pore takes place certainly, simultaneously the machined surface roughness is also impacted.About
CO+ P
N2With the relation of machined surface roughness, shown in Figure 1 as described later, no matter having or not of surface spots as can be known, in the machined surface roughness, its threshold value all is about 1.2.
In low-carbon (LC) sulphur free-cutting steel of the present invention, except that mentioned component, constitute by iron basically, but beyond this, also can contain trace ingredients, contain such composition and be also contained in the technical scope of the present invention.In addition, in low-carbon (LC) sulphur free-cutting steel of the present invention, contain unavoidable impurities (for example Cu, Sn, Ni etc.), but it is allowed to contain under the degree of not damaging effect of the present invention.
In low-carbon (LC) sulphur free-cutting steel of the present invention, as required, (1) make solid solution N amount be 0.002～0.02% and (2) be suppressed at adding up to more than a kind among Ti, Cr, Nb, V, Zr and the B that (not contain 0%) 0.02% below also useful, its scope qualification be the reasons are as follows.
[solid solution N amount: 0.002～0.02%]
As above-mentioned, the solid solution N in the steel is related to the generation of fine crack, by suitably adjusting its amount, can realize the free-cutting steel that machinability is good.In order to bring into play such effect, the amount of the solid solution N in the steel can be guaranteed more than 0.002%, but if surpass 0.02%, then surface spots increases.
[among Ti, Cr, Nb, V, Zr and the B more than a kind: add up to (not contain 0%) below 0.02%]
These elements are the compositions of giving birth to nitride with the N be combined into, if its amount is many, then solid solution N amount reduces, thereby can not guarantee the requirement of solid solution N.Thus, these one-tenth subtotalings are suppressed at below 0.02% and are advisable.
When making low-carbon (LC) sulphur free-cutting steel of the present invention, basically according to the continuous casting manufactured, but its concrete manufacturing step for example gets final product in the following manner.At first, reduce C, make C concentration, produce the high situation of free oxygen (the molten oxygen of depositing) in the molten steel below 0.04% with converter.At this moment free oxygen is preferably more than the 500ppm.Secondly, when this molten steel of tapping, add the alloy of Fe-Mn alloy and Fe-S alloy etc.Though these alloys contain Si and Al as impurity, owing to add them in the hyperoxia molten steel when converter tapping, cause Si and Al oxidized and become SiO
2And Al
2O
3, in addition when thereafter molten steel is handled, it floats and separates and enter into slag, reduces and becomes aimed concn thereby remain in Si in the steel and Al.In this is handled, importantly when converter tapping, add more than 70% of the Fe-Mn alloy that is used for the composition adjustment and adds and Fe-S alloy etc., reducing Al, Si, and when handling, molten steel adds remaining below 30%.By following step like this, can make Si below 0.004%.
Preferably the stirring in the magnetic field by applying regulation is made when this casts.Above-mentioned such induction stirring, be from being reduced in the pore that generates when solidifying to prevent flaw, the good viewpoint of surface texture is set out carries out, but and with such induction stirring, exceedingly useful on the generation inhibition of large-scale, the balling of MnS and pore is existed side by side.When carrying out such induction stirring, the magnetic field that applies is to be advisable about 100～500Gauss.When the intensity in magnetic field is lower than 100Gauss, can not bring into play the effect of induction stirring, if surpass 500Gauss, then connect the molten steel flow speed aggravation in the casting mold, can be involved in mould rack etc., casting difficulty itself.
Below, enumerate embodiment and be described more specifically the present invention, but the present invention is not subjected to the restriction of following embodiment certainly, in meeting the scope of preceding, aim after stating, also can be changed enforcement, these all are included in the technical scope of the present invention.
Embodiment
The molten steel treatment facility that uses the converter of induction furnace, 100t of 3t scale and ladle etc. to constitute makes the content of Si, Mn, S, Al, N etc., the various molten steel of melting.At this moment, by Fe-Mn alloy and Si concentration in the Fe-S alloy and the Al change in concentration that makes interpolation, adjust for Si and Al.Before the molten steel that will so obtain is cast in the mold of regulation, use free oxygen detector (trade(brand)name " HYOP10A-C150 " ヘ レ ウ ス エ レ Network ト ロ Na イ ト society system) to measure, as free oxygen concentration.
In addition, carrying out the cross section is the first bundle steel billet continuous casting of 300mm * 430mm or during with 3t scale induction furnace, use that (sectional dimension is 300mm * 430mm), molten steel is cast with just pricking the mold that steel billet casting sheet is the cast iron that designs of same speed of cooling.At this moment, as required mold is applied magnetic field and carries out induction stirring.
Take a sample from the chilling portion of the near surface of the casting sheet (perhaps ingot casting) that obtains, implement chemical analysis, measure to become to be grouped into.Its result is presented in the following table 1.
For the casting sheet that obtains, after heating in 1 hour, carry out split rolling method (sectional dimension: 155mm * 155mm), be rolled down to thereafter with 1250 ℃
And carry out pickling, become
Frotton for cutting test.At this moment, rollingly implement down at 1000 ℃, be cooled to 500 ℃ by forcing cooling from 800 ℃, its average cooling rate is about 1.5 ℃/second.In addition, the mensuration utilization of steel temperature radiation thermometer carries out.
Measure solid solution N amount for each steel plate according to following method, and carry out cutting test with following condition.In addition, the metewand of the surface spots of the evaluation of the machined surface after the cutting test and steel billet is as follows.
(mensuration of solid solution N)
Solid solution N tries to achieve according to the difference of total N (rare gas element heat of fusion conductivity method) and compound N (with 10% methyl ethyl diketone (acetylacetone)+1% tetramethyl ammonium chloride (tetramethyl ammonia chloride)+dissolve with methanol solution extraction, with 1 μ m strainer extraction → with indophenols (indophenol) extinction photometer).
(cutting test condition)
Instrument: high speed tool steel SKH4A
Cutting speed: 100m/ branch
Give: 0.01mm/rev
Depth of cut: 0.5mm
Machining oil: the not water-soluble machining fluid of chlorine system
Length of cut: 500m
(metewand)
Machined surface is estimated: based on JIS B 0601 (2001), according to maximum height Rz evaluation table surface roughness.
Surface spots is estimated: for the steel billet of split rolling method (sectional dimension: 155mm * 155mm), the investigation surface spots, with seeing the flaw detection of defect device automatically, flawless average evaluation is " zero ", confirm flaw but can be enough hand remove be evaluated as " △ ", be evaluated as " * " with what hand still can not be removed.
Cutting test result is presented in the following table 2 with the value on the left side of (1) formula, the intensity in magnetic field etc.
[table 2]
| Experiment N 0. | The value on the left side (1) | Magnetic field (Gau ss) | Solid solution N (quality %) | Machining surface roughness Rz (um) | The surface is by indefectible | Remarks |
| 1 | 1.293 | - | 0.0052 | 45 | × | Comparative example |
| 2 | 1.320 | - | 0.0138 | 46 | × | Comparative example |
| 3 | 1.298 | - | 0.0162 | 43 | × | Comparative example |
| 4 | 1.292 | - | 0.0183 | 40 | × | Comparative example |
| 5 | 1.260 | - | 0.0198 | 43 | × | Comparative example |
| 6 | 0.734 | 100 | 0.0036 | 17 | ○ | Reference example |
| 7 | 1.092 | - | 0.0140 | 28 | △ | |
| 8 | 1.023 | - | 0.0130 | 27 | △ | Embodiment |
| 9 | 1.174 | - | 0.0190 | 29 | △ | Embodiment |
| 10 | 1.057 | 100 | 0.0120 | 18 | ○ | Embodiment |
| 11 | 0.875 | 100 | 0.0090 | 17 | ○ | Embodiment |
| 12 | 0.833 | 100 | 0.0155 | 16 | ○ | Embodiment |
| 13 | 0.688 | 100 | 0.0113 | 17 | ○ | Embodiment |
| 14 | 0.697 | 100 | 0.0120 | 21 | ○ | Embodiment |
| 15 | 0.589 | 100 | 0.0080 | 25 | ○ | Embodiment |
| 16 | 1.076 | 500 | 0.0128 | 20 | ○ | Embodiment |
| 17 | 0.770 | 500 | 0.0101 | 16 | ○ | Embodiment |
| 18 | 0.888 | 500 | 0.0120 | 17 | ○ | Embodiment |
| 19 | 0.881 | 500 | 0.0125 | 19 | ○ | |
| 20 | 1.013 | 500 | 0.0181 | 23 | ○ | Embodiment |
| 21 | 0.980 | 500 | 0.0113 | 26 | ○ | Embodiment |
By these results as can be known, in satisfying (test No.7～21) of regulation important document of the present invention, (maximum height Rz) is fine for the machining surface roughness, can give play to good machinability.Particularly applied in (test No.10～21) of induction stirring, the surface spots that is caused by pore also is lowered as can be known.
With respect to this, in (test No.1～5) of any one important document that shortcoming the present invention stipulates, a certain as can be known deterioration in characteristics.
In addition, based on The above results, the relation of the value on the left side of (1) formula and machining surface roughness (maximum height Rz) was presented among Fig. 1 with having or not of magnetic field.
Claims (4)
1. the low-carbon (LC) sulphur free-cutting steel of an excellent in machinability is characterized in that, contains:
C:0.02～0.15 quality %,
Si:0.004 quality % following but do not contain 0 quality %,
Mn:0.6～3 quality %,
P:0.02～0.2 quality %,
S:0.35～1 quality %,
Al:0.005 quality % following but do not contain 0 quality %,
0:0.008～0.03 quality %,
N:0.007～0.03 quality %,
Surplus is Fe and unavoidable impurities,
And ratio [Mn]/[S] of Mn content [Mn] and S content [S] is in 3～4 scope, and satisfies (1) formula, should (1) formula be:
10·[C]×[Mn]
-0.94+1226·[N]
2≤1.2…(1)
And, in should (1) formula should [C], should [Mn] and should [N] represent the content of representing with mass percent of C, Mn and N respectively.
2. low-carbon (LC) sulphur free-cutting steel according to claim 1 is characterized in that, solid solution N amount is 0.002～0.02 quality %.
3. low-carbon (LC) sulphur free-cutting steel according to claim 2 is characterized in that, the total content of element more than a kind that will select from Ti, Cr, Nb, V, Zr and B is suppressed at below the 0.02 quality %.
4. according to each described low-carbon (LC) sulphur free-cutting steel in the claim 1～3, it is characterized in that, form by the induction stirring manufacturing that when casting, applies the magnetic field of 100～500Gauss.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP363816/2005 | 2005-12-16 | ||
| JP2005363816A JP4203068B2 (en) | 2005-12-16 | 2005-12-16 | Low-carbon sulfur free-cutting steel with excellent machinability |
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| CN101331242A true CN101331242A (en) | 2008-12-24 |
Family
ID=38162701
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|---|---|
| US (2) | US20090169414A1 (en) |
| EP (1) | EP1964939B1 (en) |
| JP (1) | JP4203068B2 (en) |
| KR (1) | KR101033073B1 (en) |
| CN (1) | CN101331242A (en) |
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| CN104451458A (en) * | 2014-12-01 | 2015-03-25 | 杭州钢铁集团公司 | Free-cutting steel and production method thereof and application of free-cutting steel in manufacturing keys |
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| JP2009106967A (en) * | 2007-10-30 | 2009-05-21 | Sumitomo Metal Ind Ltd | Continuous casting method for steel |
| KR101253806B1 (en) * | 2009-07-01 | 2013-04-12 | 주식회사 포스코 | High sulfur free cutting steel having excellent machinability and method for manufacturing the same |
| HUP1300336A2 (en) * | 2013-05-27 | 2014-11-28 | Astra Mining Hungary Kft | Method for production of steel microalloyed with super clean sulfur and controlled sulfur addition affecting metalurgical characteristics |
| CN115386800B (en) * | 2022-08-30 | 2023-10-20 | 鞍钢股份有限公司 | Low-carbon high-manganese-sulfur environment-friendly free-cutting steel and manufacturing method thereof |
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| JP2922105B2 (en) * | 1993-12-21 | 1999-07-19 | 新日本製鐵株式会社 | Low-carbon sulfur-based free-cutting steel with excellent machinability |
| JPH10158781A (en) * | 1996-12-02 | 1998-06-16 | Kobe Steel Ltd | Free cutting steel excellent in cemented carbide tool life |
| JP3687370B2 (en) * | 1998-11-25 | 2005-08-24 | 住友金属工業株式会社 | Free-cutting steel |
| DE60318745T2 (en) * | 2002-11-15 | 2009-01-15 | Nippon Steel Corp. | STEEL WITH EXCELLENT CUT-OUTPUT AND MANUFACTURING METHOD THEREFOR |
| JP4034700B2 (en) * | 2003-06-30 | 2008-01-16 | 株式会社神戸製鋼所 | Manufacturing method of high S free cutting steel with excellent machinability and high S free cutting steel |
| JP4441360B2 (en) * | 2003-12-01 | 2010-03-31 | 株式会社神戸製鋼所 | Low carbon composite free-cutting steel with excellent finish surface roughness |
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| CN104451458A (en) * | 2014-12-01 | 2015-03-25 | 杭州钢铁集团公司 | Free-cutting steel and production method thereof and application of free-cutting steel in manufacturing keys |
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| TW200738892A (en) | 2007-10-16 |
| US20120121454A1 (en) | 2012-05-17 |
| EP1964939B1 (en) | 2018-05-16 |
| JP4203068B2 (en) | 2008-12-24 |
| KR20080068750A (en) | 2008-07-23 |
| EP1964939A4 (en) | 2009-11-18 |
| TWI326714B (en) | 2010-07-01 |
| WO2007069386A1 (en) | 2007-06-21 |
| US20090169414A1 (en) | 2009-07-02 |
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