CN1840726A - Steels excellent in strength and toughness and method for making same - Google Patents

Abstract

The invention provides a steel product with high strength and tenacity, and its preparing process, wherein the steel product comprises (by weight percent) C 0.02-0.15%, Si below 1%, Mn 0.3-2.5%, P below 0.05%, S below 0.004%, Al 0.001-0.1%, Ti below 0.02%, N below 0.009%, the metal structure being one of martensite or bainite or their tempering structure.

Description

Have excellent in strength and flexible steel and manufacture method thereof

Technical field

The invention relates to and have excellent in strength and flexible steel and manufacture method thereof.

Background technology

For steel structural steel particularly, require its two specific character (strength and toughness) all excellent more.Just can satisfy above-mentioned requirements in order to add high price elements such as Ni, up to now, make the method for organizing grain refined, a lot of motions were arranged and be used about waiting by modifier treatment and control calendering.

For example, on the public clear 55-30050 communique of spy, a kind of manufacture method of obdurability steel is disclosed.This method is the iron block heating condition during by the casting condition of regulation chemical constitution, iron block and hot calender, makes AlN fine dispersion in steel, and the growth with this AlN suppresses the austenite grain obtains fine grained texture.

Adopt this method can access fine grained texture really, but AlN is the precipitate that causes iron block generation transverse crack reason when continuous casting, so be difficult to be applicable to the high efficiency like this production method of continuous casting.Open clear 57-131320 communique the spy and disclose a kind of manufacture method with high tensile steel plate of excellent low-temperature flexibility.This method has stipulated to roll be over temperature and speed of cooling afterwards.But, owing to this method need be rolled under the temperature of austenite by non-recrystallization territory to 2 phase region, so calendering efficient is very low.In addition, improve though fracture changes critical temperature, owing to separate out easily, the trend that absorption can diminish is stronger.So require absorbing at Charpy impact value can be when certain value be above, this method effective means of just can not saying so.

In addition, the spy opens flat 7-258730 communique and special opens the manufacture method that flat 7-258731 communique discloses a kind of tenacity excellent, structure Plate Steel that the sound anisotropy is few.These methods are utilized as far as possible and are made grain refining by austenitic recrystallize, and the non-recrystallization field is rolled in order to guarantee its toughness again when reducing the sound anisotropy.

Though this method is not to utilize the control rolling effect, but in order to be met practical toughness, the temperature that calendering must be over is controlled at about 900 ℃, perhaps is controlled at below 900 ℃, and the low problem of productivity that can not avoid the low temperature calendering to be brought like this.

Though above-mentioned method makes by combination processing thermal treatment and cooling and reheat dexterously and organizes grain refined, thereby guarantees needed toughness, reality is that all the productivity in industrial-scale production is all low for above-mentioned any method.

Summary of the invention

The present invention provides a kind of have excellent in strength and flexible steel and manufacture method thereof, and this method does not need to adopt and causes that control calendering that productivity descends etc. makes and organize grain refining, can produce all excellent steel of strength and toughness yet.

Main contents with excellent in strength and flexible steel and manufacture method thereof of the present invention are as follows.

1) a kind of have excellent in strength and flexible steel, it is characterized in that:

Contain: weight %, C:0.02～0.15% is discontented, below the Si:1%, Mn:0.3～2.5%, below the P:0.05%, S: less than 0.004%, sol.Al:0.001～0.1%, below the Ti:0.02%, below the N:0.009%, metal structure is one of to contain in martensite and the bainite or both tissue, or its tempered structure, the mean value of the aspect ratio of old austenite grain is below 1.5, and the mean value of the minor axis of old austenite grain is 60～700 μ m, and content and the old austenite grain minor axis dr of Ti, N, S satisfy following formula (1) or (2):

When Ti/N＜3.4,

$\mathrm{Ti}+8.1S\≤\frac{0.315}{\sqrt{\mathrm{dr}-30}}-0.011\·\·\·\·\·\left(1\right)$

When Ti/N 〉=3.4

$3.4N+8.1S\≤\frac{0.315}{\sqrt{\mathrm{dr}-30}}-0.011\·\·\·\·\·\left(2\right)$

In the formula, the symbol of element is represented the content of each element, and its unit is weight %, and the unit of dr is μ m.

2) has the big heat input of excellent in strength and flexible welding steel material, it is characterized in that: contain: weight %, C:0.02～0.15% is discontented, below the Si:1%, Mn:0.3～2.5%, below the P:0.05%, S: less than 0.004%, sol.Al:0.001～0.1%, Ti:0.004～0.02%, N:0.001～0.009%, Ti/N are 0.4～4, and metal structure is one of to contain in martensite and the bainite or both tissue, or its tempered structure, the mean value of the aspect ratio of old austenite grain is below 1.5, and the mean value of the minor axis of old austenite grain is 60～700 μ m, and Ti, N, S content and old austenite grain minor axis dr satisfy following formula (3) and (4):

$\mathrm{Ti}+8.1S\≤\frac{0.315}{\sqrt{\mathrm{dr}-30}}-0.011\·\·\·\·\·\left(3\right)$

$3.4N+8.1S\≤\frac{0.315}{\sqrt{\mathrm{dr}-30}}-0.011\·\·\·\·\·\left(4\right)$

In the formula, the symbol of element is represented the content of each element, and its unit is weight %, and the unit of dr is μ m.

3) as above-mentioned 1) or 2) described manufacture method with excellent in strength and flexible steel, it is characterized in that: with above-mentioned 1) or 2) when the steel of described chemical constitution carries out hot-work, the minor axis of the austenite grain when hot-work finishes hot-work finishing more than 950 ℃ is 60～700 μ m, and direct quenching.

Here so-called austenite grain (following note is made the γ grain) directly is meant the old γ particle diameter in the metal structure of the steel that the hot-work postcooling obtains.Old γ grain boundary can be revealed easily owing to the corrosion in the steel that contains martensite, bainite, and particle diameter is also measured in available opticmicroscope identification.In addition, steel can be Any shape, as the shape of representing steel plate, steel pipe and shaped steel etc. are arranged.

The inventor for develop a kind of do not need the miniaturization tissue in process of production and getable tensile strength more than 400MPa and have the steel and a manufacture method thereof of excellent toughness, at the laboratory category, use has a fling at the small-sized rolling press and the heat treatment furnace of test usefulness, test under various conditions, the intensity and the toughness of gained steel disc are investigated.

At the beginning of research, be to be purpose to enhance productivity, its prerequisite is, do not adopt depend on the grain refining method that causes the inefficient control calendering of calendering or, after calendering, need the reheat treatment process with reheat quenching grain refining method.Also have, so that to improve hot worked precision work temperature as far as possible be target in order to improve productivity.But, not improving material Heating temperature and calendering precision work temperature if do not utilize the control calendering, the γ grain when calendering finishes must be thick.

If utilize the control calendering, improve toughness even have thicker γ grain also can make finally to organize miniaturization.But, owing to do not utilize the control calendering, if fully refinement γ grain then is difficult to guarantee toughness.For thin brilliant γ grain, calendering need be continued to the low temperature below 900 ℃, can not reach above-mentioned target.

In fact, under nothing control rolling condition, carried out the calendering test, changed critical temperature below-50 ℃, the γ grain need be refined to below the 40 μ m in order to ensure the ballistic fracture in the Charpy test.For this reason, or finishing calendering below 900 ℃ or 900 ℃, or beginning reheat from the α territory and make the contravariant attitude, and locking grain with AlN and NbC and grow up, then about 950 ℃, heating than the refinement that is easier to reach below the particle diameter 40 μ m down.But, if temperature surpasses 1000 ℃, because the solid solution of locking particle disappears, coarse takes place, cause the remarkable deterioration of toughness.

The inventor has carried out research repeatedly by just can produce this exploitation of steel with strength and toughness to the thinning processing that needn't carry out the γ grain in process of production, and the result draws following opinion.

(1) old γ grain becomes coarse-grained steel, though the toughness deterioration, S reduces separating out of inhibition MnS under the coarse grain state, thereby can significantly improve tansition temperature and absorb energy.But in the situation of γ grain refinement, this effect not too can be expected.

(2) detrimentally affect that too toughness had of the Ti N in the steel.By reducing N or Ti, the amount of separating out of Ti N reduces, thereby tansition temperature improves.But when the γ grain is the situation of particulate, can not get improving.

(3) as (1) (2) described with by reducing the tough property improvement effect that purification that MnS, the Ti N amount of separating out obtain accompanies, when the metal structure of steel does not contain bainite or martensite or its tempered and organizes, almost can not get.

(4) for the element of formation inclusiones such as Ca, REM, think that also thick γ grain has detrimentally affect to tansition temperature equally, so preferably with its minimizing.But, this detrimentally affect, with MnS compare with Ti N less, do not resemble from the toughness aspect reduce MnS and Ti N so important.

(5) if fully reduce the amount of separating out of MnS and Ti N, 60 μ m tansition temperatures are also just slight to rise even the γ particle diameter surpasses.And even produce the position that particle diameter surpasses 100 μ m, the rising of tansition temperature also is slight.

(6) in the condition of restriction MnS and the Ti N amount of separating out, improve intensity because of can increase hardenability by alligatoring γ grain, so if the γ grain more than 60 μ m, can enough low costs produce high-intensity steel on the contrary.In addition, owing to do not need the control calendering, can make the γ grain make homogeneous microstructure, so can stably make superior prod from the metamorphosis of perfect recrystallization state.As the roughly value of recrystallize state,, this value is being made below 1.5 in the suitable condition of the average aspect ratio of γ grain.

(7) when alligatoring γ grain, need suitably reduce MnS, Ti N according to the minor axis dr of γ grain, can limit the γ particle diameter with the formula of narrating later, can in the scope of broad, guarantee the toughness of height about the γ particle diameter.But, bring the flexible detrimentally affect if the γ particle diameter just can not be ignored its thickization above 700 μ m.

The present invention promptly finishes according to these opinions, because the present invention does not need by control calendering and modifier treatment thinning microstructure, so can boost productivity.

Description of drawings

What Fig. 1 represented is γ particle diameter and tough sexual intercourse.

What Fig. 2 represented is the position of taking of Charpy test sheet.

Embodiment

Below in conjunction with accompanying drawing the specific embodiment of the present invention is described.

What Fig. 1 represented is γ particle diameter and tough sexual intercourse.Use contains the steel (mouthful symbol) of Ti:0.019%, S:0.0041% and N:0.0057% and contains the steel (■) of Ti:0.006%, S:0.0009% and N:0.0015%, change all rolling temperatures and carry out hot calender, obtain the result that impact fracture changes critical temperature by Charpy test.

Can be clear that by Fig. 1,, just descend, but that shown in black box symbol among the figure if reduce the content of Ti, S and N, toughness significantly improves when particularly reducing the content of S as long as crystal grain becomes big toughness no matter how still few the content of Ti, S and N is.In addition, when the γ particle diameter is big flexible to improve effect remarkable.

Below, the reason that limits the chemical constitution of steel among the present invention (below, % represents weight %) is described.

C is the bioelement of proof strength, but if less than 0.02% just can not guarantee necessary strength.On the other hand, if surpass 0.15%, the toughness of welding heat affected zone, mother metal all can deterioration when welding.So the content of C is 0.02～0.15%.

Si has desoxydatoin to also help the intensity that improves steel plate.But, making content surpass at 1% o'clock, can bring the toughness deterioration, so 1% as the upper limit.In addition, only otherwise influence the deoxidation of steel, it is how much all out of question that Si reduces to.

Mn has the effect that improves hardenability, is the effective constituent of guaranteeing intensity.But if contain quantity not sufficient 0.3%, because the hardenability deficiency can not get intensity, toughness.On the other hand, if make content surpass at 2.5% o'clock, along with segregation increases, hardenability is too high, and the toughness of welding heat affected zone, mother metal all can deterioration during welding.So the content of Mn is 0.3～2.5%.

P exists in the steel inevitably as impurity.If surpass 0.05%, the segregation of grain boundary is not only reduced toughness, also can when welding, cause the high temperature crack, institute thinks 0.05%.

S combines with Mn, Ca or REM and forms oxysulfide, exists in the steel as inclusion.Low at hardness of steel, or the tissue occasion of refinement very, these inclusiones can not bring big detrimentally affect to toughness, if but during to a certain degree thick organizing, just must limit its content and satisfy the described formula in back.But, even satisfy formula, be 0.004% when above at content, can not avoid the flexible detrimentally affect.It is desirable to less than 0.003% more.

Al is the bioelement that is used for deoxidation, if do not contain the sol.Al more than 0.001%, and can be because the deoxidation deficiency causes the steel deterioration.But, if make content surpass 0.1%, can cause the deterioration of base metal tenacity and toughness of welded zone low, so, be the upper limit with 0.1%.

Ti normally can improve high temperature ductile element as the N in the fixing steel and quilt is contained in steel.But because Ti N causes that toughness descends, so wish not add Ti as far as possible, the scope that its toughness aspect is allowed limits with the described formula in back.But,,, also be difficult to avoid the flexible deterioration if make content surpass 0.02% even satisfy formula.

In addition, the steel that carry out big heat input welding are excessively purified, cause the excessive alligatoring of γ grain to cause the toughness deterioration sometimes.So be preferably Ti is contained more than 0.004%, and the ratio of control Ti/N is in the scope below 4.0 more than 0.4.

N is the impurity that causes that high temperature ductility descends, and usually, fixedly avoids this detrimentally affect by adding Ti with the form of Ti N.But, in the present invention, cause that toughness worsens because Ti N itself also becomes, so need to suppress the formation of Ti N.For this reason or reduce N itself, or the content of minimizing Ti.

In order to obtain excellent toughness, the scope of N content need satisfy the described formula in back.Even but satisfy formula, if N surpasses 0.009%, or because Ti N causes toughness to descend, or detrimentally affect also can not be ignored abundant fixed solid solution N to flexible because fail.In addition, if N is below 0.001%, reduce under the almost non-existent condition of MnS at S, the growth of γ grain becomes very easy.So, by the submerged arc welding method etc., when welding, at the local sometimes alligatoring γ of welding heat affected zone grain with the big heat input about 100kJ/cm.

Though steel of the present invention have the not incidental character of toughness deterioration that the alligatoring owing to the γ grain causes, but heat affected zone in big heat input welding, has Hardness Distribution, produce the big or small inhomogeneous of crystal grain, so being limited to about 300 μ m of the γ particle diameter of being allowed from the toughness face.So the occasion be welded as prerequisite with big heat input must make the Ti N that suppresses γ grain growth effect that has that contains to a certain degree, can make the N that contains more than 0.001%, also can contain some Ti simultaneously.

On the other hand, for the steel that do not need to weld, and the steel that can only carry out the following little heat input welding of 40kJ/cm, in economic institute allowed band, can reduce N as far as possible.

Steel of the present invention except that above-mentioned element, can contain the following element that is useful on raising hardenability and intensity as required.

Cr is to improving the useful element of hardenability, though only can guarantee the hardenability of bottom line necessity with above-mentioned bioelement, when steel are the steel pipe etc. of wall thickness, uses for further assurance hardenability.If the content of Cr is more than 0.02%, so the effect of the temper softening impedance that also can be improved except that hardenability it is desirable to more than 0.02%.But, so can not avoid the toughness of weld part will be below 1.5% if surpass 1.5%.

Mo is when steel are the steel pipe etc. of wall thickness, for further improving the element that hardenability and temper softening impedance preferably contain.But, can not get these effects, so it is desirable to make the Mo that contains more than 0.02% if contain quantity not sufficient 0.02%.But if surpass 1%, the remarkable deterioration of toughness meeting of weld part is limited to 1% so be preferably.

B is particularly useful to the hardenability and the intensity that improve the γ grain boundary.Content is better below 0.003%.

Nb is with necessary interpolation element in the steel of so-called control calendering manufacturing, but in the present invention, does not utilize the control calendering substantially, so be not must element.But it is effective to further raising intensity, can be many as if making content, when under the high temperature more than 1000 ℃, finishing calendering, separate out damage tolerance widely by reinforcement.So must make content below 0.015%.Be more preferably below 0.01%.

V has the effect of separating out raising intensity by reinforcement, and is smaller to the flexible influence, effective to improving intensity.If content more than 0.01%, improves the effect of hardenability in addition except that the temper softening opposing, it is desirable to more than 0.01%.But if surpass 0.15% toughness deterioration greatly, so the upper limit is being advisable below 0.15%.

Cu can improve intensity and solidity to corrosion effectively, so when needs further when high-yield strength and high anti-corrosion, can make and contain Cu.If content more than 0.05%, can improve hardenability, so it is desirable to more than 0.05% in direct quenching.Even add but surpass 1.5%, also do not see the improvement of the performance that conforms to the cost increase, so the upper limit is relatively good below 1.5%.

Ni has the flexible effect of the matrix (parent) of the steel that improves solid solution condition, contains Ni so can make in the time need stably obtaining excellent more toughness.If content is also reaching the effect that improves hardenability more than 0.05%, so it is desirable to more than 0.05%.But, can not obtain improving if surpass 4%, so the upper limit is advisable 4% with the corresponding flexible of the increase of cost of alloy.

S in Ca and the steel is reflected in the molten steel and generates hydrosulfate.This hydrosulfate is different with MnS etc., is not to extend to rolling direction by rolling processing, but also is spherical after calendering.So will suppress with the front end of the inclusion after extending etc. serve as the weld cracking or the hydrogen induced cracking (HIC) (HIC:Hydrogen Induced Cracking) of cracking starting point, can make in the occasion of inhibition weld cracking or HIC and to contain.If content is also having the effect that improves toughness of welded zone more than 0.0002%, so comparatively desirable more than 0.0002%.But,, cause that base metal tenacity reduces because degree of cleaning reduce if surpass 0.004%.

REM helps the refinement of tissue and the fixing of S of welding heat affected zone, but can become inclusion degree of cleaning is reduced.But, owing to add the formed inclusion of REM, and smaller to the influence of toughness deterioration, so even contain below 0.004%, the degree that base metal tenacity reduces is an allowed band.

Below, metal structure and old austenite grain are described.

1) metal structure

In order to make tensile strength more than 450MPa, the metal structure of steel need contain in bainite and the abnormal at low temperatures martensite that generates one or both and contain, or their tempered structure, other contain ferrite, pearl layer iron.Such tissue can from the quenching in γ territory, carry out tempering and obtain as required by after carrying out hot calender.

2) aspect ratio of old γ grain

Why the mean value with the aspect ratio of old γ grain fixes on below 1.5, is in order to prevent the reduction of anisotropic minimizing and intensity.Accept processing and contain the γ grain of transposition in inside, from the transposition α of intragranular also product nucleus mutually, so hardenability reduces strength degradation.In order to prevent this phenomenon, need make the abundant recrystallize of γ grain (carried out the γ grain of recrystallize, aspect ratio is near 1) back remetaboly.If the mean value of the aspect ratio of old γ grain can prevent strength degradation below 1.5.

In addition, the mean value of aspect ratio is to select to observe the test portion that the orientation cutting opticmicroscope of the face that the γ grain extends is most used, fibrous tissue is manifested, and by the old γ grain of picture processing instrumentation, major diameter and likening to of minor axis during with each γ grain approximate ellipsoidal are mean value.

3) the average minor axis of old γ grain

In the present invention,, do not make the machining at low temperature of structure refinement, so old γ grain is a coarse grain in order to enhance productivity.In addition, because coarse, the minimizing of Ti, N and S brings unusual effect to toughness and intensity.The average minor axis of old γ grain is if less than 60 μ m just can not get desired intensity and toughness.And on the other hand, if surpass 700 μ m again too alligatoring cause the toughness deterioration.

4) relational expression of Ti, N, S and old γ grain minor axis

When the less than 3.4, if then the content of Ti and S is too much for discontented foot formula (1), thereby the quantitative change of Ti N and MnS causes the toughness deterioration to the content of Ti and N more than Ti/N.This formula is the formula that sums up by test of many times, according to the minor axis regulation Ti of old γ grain and the appropriate amount of S.

Ti/N＜3.4 o'clock,

$\mathrm{Ti}+8.1S\≤\frac{0.315}{\sqrt{\mathrm{dr}-30}}-0.011\·\·\·\·\·\left(1\right)$

In addition, at the content of Ti and N than Ti/N 3.4 when above, promptly the content of N than Ti after a little while, if then the content of N and S is too much for discontented foot formula (2), thereby the amount of Ti N and MnS increases and causes the toughness deterioration.

When Ti/N 〉=3.4

$3.4N+8.1S\≤\frac{0.315}{\sqrt{\mathrm{dr}-30}}-0.011\·\·\·\·\·\left(2\right)$

If during as big heat input welding, the scope of Ti/N is 0.4～4 at steel of the present invention, and discontented foot formula (3) and (4), the γ grain toughness deterioration of this part of alligatoring too in the heat affected zone of weld part.That is, when carrying out big heat input welding, need the amount of Ti and N more a little, Ti N and MnS are grown up separating out the grain that suppresses the heat affected zone to a certain degree.

$\mathrm{Ti}+8.1S\≤\frac{0.315}{\sqrt{\mathrm{dr}-30}}-0.011\·\·\·\·\·\left(3\right)$

$3.4N+8.1S\≤\frac{0.315}{\sqrt{\mathrm{dr}-30}}-0.011\·\·\·\·\·(4)$

In the formula, the symbol of element is represented the content of each element, and its unit is weight %, and the unit of dr is μ m.

Below, the manufacture method of steel of the present invention is described.

When the steel of the above-mentioned chemical constitution of hot-work, the minor axis of austenite grain is 60～700 μ m when by the control hot processing temperature hot-work being finished, and finishes hot-work direct quenching and can obtain the excellent more steel of strength and toughness.

The minor axis of the austenite grain when hot-work finishes is the hot processing temperature of 60～700 μ m, the degree of finish according to chemical constitution during and different with hot-work, substantially, to guarantee more than 950 ℃ being standard.In addition, as long as old γ particle diameter is no more than 700 μ m, no matter the many height of precision work temperature all can obtain good performance, but actual production line is difficult to guarantee that the precision work temperature is above 1150 ℃.In addition, such temperature can be because the generation of incrustation scale increases the loss of steel.From this angle, be limited to about 1150 ℃ on the precision work temperature is substantial.

Though there is no need to proceed to cryogenic hot calender in order to ensure toughness, if carry out depressing more than 30% at the temperature field below 900 ℃, the effect of refinement with the control calendering of γ grain appears sometimes, thus the situation that intensity descends greatly.Because this character can become the unsettled reason of mass discrepancy, so must avoid processing at low temperatures when steel product batch is produced.

For fear of this detrimentally affect, be lower than 60 μ m in order not make old γ particle diameter, in addition, for make the γ grain at not processed hardened state by water-cooled, must control hot calender end temp.The cooling of the quench treatment after being used to process also need not be a water-cooled, but wishes that at least the bainite of the tissue after the metamorphosis or martensite are fibrous tissue and account for area more than 40%, need corresponding therewith speed of cooling.Its cooling conditions can be inferred by CCT figure.

[embodiment]

In the vacuum melting stove, melting has the circular steel ingot 150kg of 16 kinds of chemical constitutions shown in the table 1.In addition, in real machine 250t converter, melting has the steel of 10 kinds of chemical constitutions shown in the table 2, and is continuously cast into the iron block that thickness is 150～300mm.

Table 1 (remainder: Fe and unavoidable impurities)

	Mark	C	Si	Mn	P	S	Al	Ti	N	Other	Ti/N
												Embodiment
	1 2 3 4 5 6 7 8	0.096 0.137 0.036 0.061 0.095 0.050 0.049 0.052	0.30 0.19 0.16 0.19 0.18 0.16 0.32 0.10	1.35 1.26 2.21 1.43 0.91 0.78 1.07 1.34	0.009 0.009 0.011 0.010 0.012 0.009 0.011 0.010	34 12 16 12 7 5 5 8	0.021 0.023 0.023 0.026 0.028 0.029 0.025 0.024	0.005 0.006 0.017 0.004 0.006 0.001 0.002 0.008	14 14 40 6 10 5 22 20	B：8，Ca：2，Mg：3 Ca：2，Mg：4 Ca：2，Mg：2 Cr：0.10，Mo：0.29，Ca：2，Mg：3 Ni：0.48，Cr：0.15，Mo：0.61，Ca：2，Mg：2 Ni：0.19，Cr：0.99，Mo：0.14，Ca：2，Mg：3 Cu：1.21，Ni：0.78，Ca：2，Mg：4，REM：6 Nb：0.010，V：0.029，Ca：2，Mg：4	6.40 4.11 4.25 7.02 5.57 1.82 3.17 3.87
												Comparative example	9 10 11 12 13 * 14 15 * 16 *	0.100 0.138 0.037 0.061 0.099 0.051 0.051 0.048	0.29 0.20 0.15 0.19 0.20 0.15 0.30 0.10	1.31 1.26 2.18 1.38 0.92 0.79 1.08 1.34	0.010 0.010 0.010 0.010 0.011 0.008 0.010 0.010	51 * 58 * 19 8 19 22 9 26	0.026 0.026 0.028 0.027 0.026 0.026 0.027 0.025	0.009 0.029 * 0.025 * 0.002 0.004 0.021 * 0.011 0.010	33 30 69 98 * 11 45 32 19	B：8，Ca：2，Mg：3 Ca：2，Mg：3 Ca：2，Mg：41 Cr：0.10，Mo：0.31，Ca：2，Mg：3 Ni：0.50，Cr：0.15，Mo：0.63，Ca：2，Mg：2 Ni：0.19，Cr：1.05，Mo：0.15，Ca：48，Mg：3 Cu：1.23，Ni：0.78，Ca：2，Mg：4，REM：43 Nb：0.022，V：0.049，Ca：2，Mg：3	2.76 9.56 3.68 0.22 4.00 40.35 3.37 5.50

(S, N, B, Ca, Mg, the unit of REM is ppm, other are weight %,

* be illustrated in outside the specialized range of the present invention.Mark 13,15,16 relational expressions (with reference to table 3) for discontented unabridged version invention.)

Table 2 (remainder: Fe and unavoidable impurities)

	Mark	C	Si	Mn	P	S	Al	Ti	N	Other	Ti/N
												Embodiment	17 18 19 20 21	0.072 0.118 0.082 0.073 0.048	0.32 0.28 0.24 0.20 0.11	1.49 0.52 1.10 1.42 1.31	0.011 0.010 0.009 0.008 0.010	12 12 5 10 14	0.027 0.024 0.024 0.028 0.028	0.011 0.007 0.006 0.012 0.007	40 19 24 33 23	Cu：0.31，Ni：0.35 Cr：0.10，Mo：0.10，Nb：0.06，Ca：2，Mg：3 V：0.110，Ca：2，Mg：3，REM：10	2.75 3.62 3.01 3.69 3.07
Comparative example	22 23 24 25 26	0.068 0.124 0.077 0.071 0.050	0.32 0.28 0.25 0.19 0.11	1.45 0.50 1.18 1.38 1.26	0.009 0.008 0.010 0.011 0.010	29 8 9 8 8	0.024 0.028 0.027 0.024 0.026	0.006 0.010 0.002** 0.002** 0.001**	9 100* 6 54 9	Cu：0.31，Ni：0.34 Cr：0.10，Mo：0.10，Nb：0.004，Ca：2，Mg：3 V：0.106，Mg：2，REM：49	6.44 0.98 3.05 0.36 * 3.05

(S, N, B, Ca, Mg, the unit of REM is ppm, other are weight %,

* be illustrated in outside the specialized range of the present invention.* during as big heat input steel outside specialized range of the present invention.)

As shown in table 3 steel ingot is forged into the slab of 120～170mm thickness, after 1180～1270 ℃ of heating, making thickness through hot calender is that 25～50mm heat is prolonged steel plate.

In addition, the iron block of continuous casting is shown in 1200～1250 ℃ of heating by table 4 after, to make thickness be that 25～40mm heat is prolonged steel plate through hot calender.Carry out shrend and a part is quenched-tempering heat treatment by shown in table 3 and the table 4 these heat being prolonged steel plate.

Table 3

	Mark	Old γ grain minor axis	Aspect ratio	Ti/N	Formula 1 left side	Formula 1 the right	Sotck thinkness mm	Blank heating temperature ℃	End product thickness mm	Calendering end temp ℃	Thermal treatment	Tempering temperature ℃	Yield strength MPa	Tensile strength Mpa	Tansition temperature vTrs ℃
																Embodiment	1 2 3 4 5 6 7 8	62 72 69 61 210 67 310 57	1.1 1.2 1.2 1.0 1.1 1.2 1.1 1.5	6.40 4.11 4.25 7.02 5.57 1.82 3.17 3.87	0.032 0.015 0.026 0.012 0.009 0.005 0.006 0.013	0.045 0.037 0.039 0.045 0.012 0.041 0.008 0.049	300 200 150 300 150 150 120 200	1250 1200 1270 1180 1250 1210 1270 1270	25 25 40 20 35 40 50 35	990 1080 1100 1000 1110 1070 1150 1070	Shrend water-cooled to 500 a ℃ sealing hardening hardening is chilled to 500 ℃ of sealings and is chilled to 500 ℃ of sealing hardening and quenches	600 - 600 600 - - 600 600	473 437 485 530 506 501 477 518	563 534 570 608 586 581 560 595	-73 -97 -59 -107 -91 -82 -54 -92
Comparative example	9 * 10 * 11 * 12 * 13 14 * 15 16	59 73 58 67 188 77 250 57 *	1.2 1.3 1.1 1.2 1.0 1.3 1.1 1.4	2.76 9.56 3.68 0.22 4.00 40.35 3.37 5.50	0.050 0.057 0.039 0.008 0.019 0.033 0.018 0.015	0.047 ** 0.037 ** 0.049 0.040 0.014 ** 0.035 0.010 ** 0.028 **	300 200 150 300 150 150 120 200	1250 1200 1270 1180 1250 1210 1250 1270	25 25 40 20 35 40 50 35	990 1090 1110 990 1110 1070 1140 1060	Shrend water-cooled to 500 a ℃ sealing hardening hardening is chilled to 500 ℃ of sealings and is chilled to 500 ℃ of sealing hardening and quenches	600 - 600 600 - - 600 600	479 426 481 504 506 499 475 544	569 528 574 580 584 580 566 618	-45 -26 -16 -20 -18 -29 22 -10

(* is illustrated in outside the specialized range of the present invention.* in the mark hurdle is expressed as being grouped into outside specialized range of the present invention.The relational expression of * unabridged version invention with thumb down.)

Table 4

	Mark	Old γ grain minor axis	Aspect ratio	Ti/N	Formula 1 left side	Formula 1 the right	Sotck thinkness mm	Blank heating temperature ℃	End product thickness mm	Calendering end temp ℃	Thermal treatment	Tempering temperature ℃	Yield strength MPa	Tensile strength Mpa	Tansition temperature vTrs ℃	VTrs ℃ of seam tansition temperature
																	Embodiment	17 18 19 20 21	80 63 144 73 53	1.0 1.1 1.2 1.2 1.2	2.75 3.62 3.01 3.69 3.07	0.021 0.016 0.010 0.019 0.018	0.034 0.044 0.018 0.037 0.055	300 300 200 200 150	1250 1200 1250 1230 1250	30 25 30 40 40	1090 1060 1150 1050 990	Shrend water-cooled to 500 a ℃ sealing hardening hardening is quenched	600 - 600 600 600	410 398 415 427 465	518 511 520 527 559	-89 -87 -77 -73 -70	-64 -50 -56 -50 -44
Comparative example	22 23 * 24 * 25 * 26 *	87 39 70 144 51	1.2 1.1 1.1 1.2 1.2	6.44 * 0.98 3.05 0.36 * 3.05	0.026 0.016 0.010 0.009 0.007	0.031 0.095 0.039 0.018 0.057	300 300 200 200 150	1250 1200 1250 1230 1250	30 25 30 40 40	1090 1060 1150 1050 990	Shrend water-cooled to 500 a ℃ sealing hardening hardening is quenched	600 - 600 600 600	428 397 415 428 458	526 510 518 523 553	-99 -25 -126 -104 -51	-43 -39 -36 -34 -22

(* is illustrated in outside the specialized range of the present invention.* in the mark hurdle is expressed as being grouped into outside specialized range of the present invention.)

Produce JIS4 Charpy test sheet, pole tension test sheet from prolonging steel plate, as Charpy impact test, tension test through heat treated each heat.

In addition, the heat of mark 17～26 is prolonged steel plate, carried out the making of the welding joint of submerged arc welding, and carried out Charpy impact test.Welding is two sides one deck welding of V forging welding groove, and the welding heat input is 70kj/cm to the steel of the following thickness of 30mm, and the steel that surpass 30mm thickness are 100kj/cm.

What Fig. 2 represented is the position of taking of Charpy test sheet.Shown in same figure, on the section after the test of test film 1 (notch portion), welding metal portion 1 and welding heat affected zone 2 almost respectively are half.

Each experimental result of the common expression of table 3 and table 4.Can be clear that by table 3,, in example of the present invention, show below-50 ℃, can be used for the sufficient toughness of any purposes although thick as the result's who finishes calendering through 990 ℃～1100 ℃ high temperature down γ grain.And, because composition or contain minor N b, or contain Nb hardly, and unfavorable to guaranteeing intensity, however,, can obtain surpassing 400 to 500MPa yield point strength owing to strengthened hardenability by the alligatoring of γ grain.

In table 4, except that the mechanical characteristics that shows mother metal, also show the result of simulation thermal cycling test.

Embodiment 17～21 also shows good welding heat affected zone toughness.But, the mark 22,24,25 in the comparative example, though toughness after heat treatment also is good, the toughness that the reason that excessively purifies owing to steel makes heat affected zone is deterioration greatly.

The forged material of the chemical ingredients of mark 1～8 in the his-and-hers watches 1 has carried out hot calender under temperature lower below 900 ℃.Rolling condition and heat-treat condition are represented with table 5.From carried out each test same as described above through heat treated steel plate.Its result is also represented by table 5.

Table 5

	Mark	Old γ grain minor axis	Aspect ratio	Sotck thinkness mm	Blank heating temperature ℃	End product thickness mm	Calendering end temp ℃	Thermal treatment	Tempering temperature ℃	Yield strength MPa	Tensile strength Mpa	Tansition temperature vTrs ℃
													Comparative example	1 2 3 4 5 6 7 8	30 * 28 * 27 * 31 * 36 * 32 * 35 * 35 *	2.2 1.9 2.1 2.2 1.7 1.9 1.8 2.0	300 200 150 300 200 150 300 200	1250 1200 1270 1180 1200 1210 1250 1270	25 25 40 20 35 40 50 35	810 830 780 800 840 830 850 880	Shrend water-cooled to 500 a ℃ sealing hardening hardening is chilled to 500 ℃ of sealings and is chilled to 500 ℃ of sealing hardening and quenches	600 - 600 600 - - 600 600	378 337 382 435 409 399 377 445	492 478 498 533 517 511 493 542	-92 -100 -73 -125 -96 -96 -71 -98

(* is illustrated in outside the specialized range of the present invention.)

Though carry out refinement by low temperature calendering, how much toughness makes moderate progress, with table 3 more as can be known, intensity descends greatly.Consider that as if just guaranteed sufficient toughness from stage the precision work of such low temperature calendering just damages intensity and do not have sharp point at table 3.On the contrary, the steel that also quenches through the high temperature reheat from table 4 now illustrates the phenomenon of good intensity and toughness and considers, steel with the decline of the excessive temperature in calender line shown in the table 5, before water-cooled, in process furnace, be heated to more than 1000 ℃ again, and make abundant recrystallize, and make after the alligatoring of γ grain water-cooled again, can obtain good performance.

[invention effect]

Adopt the present invention, can produce high strength and have the steel of excellent toughness, alloy addition level is few, and the sustainable high productivity of keeping.This means to strengthen new installation, just can increase the turnout of high-performance steel, be highly profitable aspect the steel production.

Claims (3)

1. one kind has excellent in strength and flexible steel, it is characterized in that: contain: weight %, C:0.02～0.15% is discontented, below the Si:1%, Mn:0.3～2.5%, below the P:0.05%, S: less than 0.004%, sol.Al:0.001～0.1% is below the Ti:0.02%, below the N:0.009%, metal structure is one of to contain in martensite and the bainite or both tissue, or its tempered structure, and the mean value of the aspect ratio of old austenite grain is below 1.5, the mean value of the minor axis of old austenite grain is 60～700 μ m, and Ti, N, S content and old austenite grain minor axis dr satisfy following formula (1) or following formula (2):

When Ti/N＜3.4,

$\mathrm{Ti}+8.1S\≤\frac{0.315}{\sqrt{\mathrm{dr}-30}}-0.011---\left(1\right)$

When Ti/N 〉=3.4

$3.4N+8.1S\≤\frac{0.315}{\sqrt{\mathrm{dr}-30}}-0.011---\left(2\right)$

In the formula, the symbol of element is represented the content of each element, and its unit is weight %, and the unit of dr is μ m.

2. one kind has excellent in strength and the big heat input of flexible welding steel material, it is characterized in that: contain: weight %, C:0.02～0.15% is discontented, below the Si:1%, Mn:0.3～2.5%, below the P:0.05%, S: less than 0.004%, sol.Al:0.001～0.1%, Ti:0.004～0.02%, N:0.001～0.009%, Ti/N are 0.4～4, and metal structure is one of to contain in martensite and the bainite or both tissue, or its tempered structure, the mean value of the aspect ratio of old austenite grain is below 1.5, and the mean value of the minor axis of old austenite grain is 60～700 μ m, and Ti, N, S content and old austenite grain minor axis dr satisfy following formula (3) and (4):

$\mathrm{Ti}+8.1S\≤\frac{0.315}{\sqrt{\mathrm{dr}-30}}-0.011---\left(3\right)$

$3.4N+8.1S\≤\frac{0.315}{\sqrt{\mathrm{dr}-30}}-0.011---\left(4\right)$

In the formula, the symbol of element is represented the content of each element, and its unit is weight %, and the unit of dr is μ m.

3. make the manufacture method described in claim 1 or 2 for one kind with excellent in strength and flexible steel, it is characterized in that: when requiring the steel of the chemical constitution described in 1 or 2 to carry out hot-work aforesaid right, the minor axis of the austenite grain when hot-work makes that finishing more than 950 ℃ hot-work finishes is 60～700 μ m, and direct quenching.

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