CN1670233A - Process for producing cast pieces of spheroidal graphite with high geometrical and dimensional precision and improved mechanical properties - Google Patents

Abstract

Disclosed is a method of fabricating spheroidal graphite cast iron parts of high precision, geometrically and dimensionally, and having improved mechanical characteristics, which includes: a) preparing a mixture in the liquid state having the following composition by weight: C; Si; Mn; Ni; Cu; Mo; Mg; and iron; b) casting this liquid mixture at a certain temperature range into a mold to obtain a blank; c) extracting the blank from the mold at a temperature Ts in the limit temperatures for the austenitic range of the composition; d) shaping the blank with the finished shape and dimension at a temperature Tf in the range 1050 DEG C. to AR3 by hot plastic deformation, and cooling to ambient temperature. The cast iron is essentially bainitic, perlitic or ferritic in structure, and moulded blanks made from it have a volume more or less identical to the finished component and are shaped by hot plastic deformation using calibration in containers or closed matrices to avoid any side burrs.

Description

The method for making of the cast pieces of spheroidal of tool high precision geometrical shape size and improved mechanical properties

The present invention relates to the manufacture method of ductile cast iron casting, also relate to by implementing the resulting cast iron of this method.

Here used wording " have on geometrical shape and size high-precision and possess improved mechanical properties " is meant condition of surface, geometrical shape and the dimensional precision of spheroidal graphite cast iron part and is better than the mechanical characteristics of the prepared product of those conventional cast methods.

French Patent No.2839727 discloses a kind of special methods of making the spheroidal graphite cast iron part, and this method combines and use successively these several technology of casting, forging and thermal treatment.This method described in this patent makes the spheroidal graphite cast iron part that is obtained have extraordinary mechanical characteristics (tensile strength Rm＞1000 MPas (MPa); The ratio R p0.2/Rm of elastic limit and tensile strength＞0.68; Tension set A% is in 4% to 14% scope), and dimensional precision and the approaching traditional forging method of geometric accuracy, promptly be better than traditional precision that castmethod obtained.

Yet in the method for above-mentioned patent, all manufacturing steps are to carry out in the heat that casting is produced; This need carry out some in order to keep the intermediary operation of temperature between some manufacturing stage, because not every step all has the identical time length.This is particularly useful for casting operation and forging operation, also is applicable to the thermal treatment of forging and bainite marquenching (bainiticstaged quenching).Thereby implement this method and need a kind of special and expensive production line, promptly this method is suitable for producing in enormous quantities very much, for example in automobile making, but is not suitable for middle-size and small-size production.

In addition, many mechanical component do not need picture resulting bainite of patent FR2839727 or the so high level mechanical characteristics of austenite-ferrite structure, and this structure also is difficult to processing.

This method is applied to certain need high-ductility deformation ratio with the part that carries out punching press and handle on the time, found that this part is damaged easily when carrying out deburring (trimming), this is because graphite pebbles can produce a large amount of distortion sometimes, on the zone of part, be gathered into row then near burr (seam of flash) and burr itself, when cutting tool passed, those locational metals were torn easily.

In addition, for the part of some shape, the point that fatigue stress is fragile is positioned on the burr (flash) on the separation surface, and separation surface is usually located at the middle portion of part.

When the method among the enforcement patent FR2839727, be difficult to be controlled at the burr (flash) that certainly leads to when carrying out punching press in the chunk, therefore be difficult to the deformation rate of control cast iron at those locational deformation rates and graphite pebbles.

In addition, lower work in-process (rough part) price is also more and more sought by manufacturers, and they also need work in-process to have more and more higher precision simultaneously, i.e. its required processing is few more good more.

According to these conditions, for more competitive economically than traditional steel part forging method, particularly in the production in enormous quantities part of car category, the while, also in the part of short run processing, above-mentioned patented method need be improved.

The objective of the invention is to satisfy above-mentioned purpose and overcome described defective by proposing a kind of spheroidal graphite cast iron component working method that possesses following characteristics:

Compare with traditional forging method and with early patent FR2939727, present method has improved output capacity;

With respect to the parts that method obtained of patent FR2839727, has improved safe range of stress;

Mechanical characteristics is better than the resulting mechanical characteristics of conventional cast method; And

Dimensional precision and geometric accuracy are better than traditional casting and forging method, and are better than the method for patent FR2839727 protection theme.

The spheroidal graphite cast iron part that obtains in this way has enough sizes and geometric accuracy, in some cases, can save the preprocessing step of reference plane.

For this reason, the present invention proposes a kind of being manufactured on and have high-precision on geometrical shape and the size and possess the method for the spheroidal graphite cast iron part of improved mechanical properties, this method comprises the following steps:

A) mixture of a kind of liquid state of preparation, it has the following component of calculating by weight: 3% to 4% C; 1.7% to 3% Si; 0.1% to 0.7% Mn; 0 to 4% Ni; 0 to 1.5% Cu; 0 to 0.5% Mo; Have the residual Mg composition that adapts with part thickness, in 0.025% to 0.080% scope; Remaining in iron and the preparation process with impurity; These impurity can be content less than 0.015% S and content less than 0.10% P especially;

B) be cast to when the mixture of these liquid states is in temperature is 1350 ℃ to 1550 ℃ scopes in the mould to obtain a required part blank, the shape of this blank is near the shape of part;

C) when temperature is Ts described blank is deviate from from mould, this temperature T s is between solidus and AR3, and wherein solidus and AR3 represent the ultimate temperature of the austenitic range of described composition;

D) when being Tf, temperature blank is carried out moulding by pyroplastic deformation, this temperature T f at 1050 ℃ between the AR3, directly in the heat of casting or with temperature, keep Tm=Tf+20 ℃ to 50 ℃ to reach 10 minutes to 60 minutes long time, thus the part that can obtain to have its net shape and size;

E) described part is directly quenched in the formed heat under a temperature T b, this temperature is between 260 ℃ to 420 ℃ and be in the bainite scope, and this part is kept Tb temperature for some time tb, and time tb is in 60 minutes to 180 minutes scope; And

F) the described part of cooling is to envrionment temperature;

The method is characterized in that the volume that equals part by the volume of the molded blank that obtains substantially, and the operation of carrying out moulding by thermoplastic distortion is a calibration operation in unopened container or mould, this operation can so that to calibrated mo(u)lded piece do not have horizontal burr.

This method of implementing the inventive method can obtain being substantially the spheroidal graphite cast iron of bainite structure, thereby makes part have extraordinary mechanical characteristics, but safe range of stress is greater than the resulting safe range of stress of the method for utilizing patent FR2839727.

Here the wording of using " basic bainite " is meant the structure that is made of at least 50% bainite.

In another embodiment of the inventive method, after the calibration operation of the calibration molded part that obtains not to be with horizontal burr by pyroplastic deformation, the described molded part of having calibrated can be cooled to envrionment temperature by cooling air mode, control mode or quenching, so that part has required mechanical characteristics; This has replaced bainitic hardening.This embodiment of the present invention makes can obtain a kind of spheroidal graphite cast iron structure that is made of the ferrite and/or the perlite of different ratios; This structure is basic for ferritic or substantially for pearlitic, perhaps ferrite-pearlite.

Here and hereinafter employed wording " basic ferrite " and " basic perlite " be meant the structure that constitutes by at least 50% ferrite or at least 50% perlite respectively.

The mechanical characteristics that part obtained, particularly safe range of stress, although it is good unlike the result who adopts patent FR2839727 method, than only good by the spheroidal graphite cast iron of casting, this is owing to compacting and drawing hardening effect that calibration operation obtained.

In described preceding two embodiments of the inventive method, with blank stripping operation c) and pyroplastic deformation operation d) between, perhaps at blank demoulding c) and the additional operation that blank is remained on the temperature T m between, add one by cutting or some other methods the intermediate steps of separating casting head (rising head, skewed slot) from the blank, to obtain the independent blank that a volume equals required calibration foundry goods volume substantially.

This intermediate steps attempts to remove all dead heads from the casting blank, and is same, if necessary, can also improve its shape and volume, thinks that next step calibration operation prepares.This step can also comprise the step that cleans described blank, for example, utilizes scratch brushing or other method, to remove any oxide compound or the residue that is produced in the casting step before carrying out calibration operation.

In another embodiment of the inventive method, after the step of casting blank, and before the calibration steps by pyroplastic deformation in container or mould, described blank is cooled to temperature to be lower than to deviate from from mould after the AR3, and then heat described blank and its temperature is remained in AC3 to the 1050 ℃ of scope, and continue for some time of 10 minutes to 90 minutes, to guarantee in described blank, having height uniform temperature and chemical composition.

In this embodiment method of the present invention, comprise that removing rising head, polishing and possible deburr and the casting blank precision work process of shot peening becomes easier, because it carries out at ambient temperature; Because molded and calibration operation separately carries out, and has simplified the enforcement of this method.

In this embodiment of the inventive method, the precision work step can also comprise grinding and/or cutting operation, obtaining a blank volume that equals the part volume substantially, and/or a blank volume that is designed to finely tune described blank shapes.

In each embodiment of the inventive method, the viscous deformation rate in the calibration operation process is limited wittingly, and smooth with the transition of avoiding producing graphite pebbles, wherein the smooth graphite pebbles of transition is along the flow direction orientation of metal.

Utilize a volume to be substantially equal to the blank of the part volume that will obtain, and utilize close die to remove horizontal burr, can eliminate owing to graphite pebbles is subjected to the more weak zone of fatigue stress that bigger distortion produces.

In addition, no longer need to cut away the step of burr, and eliminated tearing of on these zones, might taking place.

In each embodiment of the inventive method, the concrete shape of the casting blank of part is to be determined by the net shape of part, with the deformation rate scope of all parts in the calibration operation process that guarantees this blank is 1% to maximum 20%, and can guide wire in this operating process, flow along a direction, this is favourable to its mechanical characteristics, particularly the fatigue stress in the part time job process.

Further feature according to each embodiment of the inventive method:

Calibration operation in unopened container or mould, be by at least two tool room punching presses or impact this blank or implement at the moving part and/or the drift of mould or cutter inner slide, particularly can obtain the multiaxis viscous deformation of this blank by utilizing;

The volume of casting blank equals to calibrate the volume of foundry goods, and maximum allowance is in 0 to+6% scope;

On the blank corresponding to the unnecessary volume in the tolerance range, in calibration operation, be directed in the recess of excess metal, described recess or be in the one or more blind holes or through hole on the part to be processed, be in the one or more cavitys that are used for this purpose, described cavity is positioned on the parts in the zone that can not influence the geometric accuracy of calibrating foundry goods.

The mould of blank of being used to cast is preferably a permanent mold, and this permanent mold is made of at least two metals half parts that are coated with releasing agent, but also can be mould volatile, that made by sand or other material.

In the embodiment of the inventive method, comprise with air cooling mode, controllable manner or quenching mode coming the calibration foundry goods is cooled off, cooling is in free air, the air of agitating or airtight medium or carries out in the atmosphere that this depends on environment.

Wording used herein " is cooled off under control mode " and be meant that cooling is to carry out under a speed setting and control, thereby can make part obtain predefined, a needed structure.When with free way, controllable manner, perhaps when quenching structure that can not directly obtain being scheduled to and required, can also after the step of calibration foundry goods, add the heat treatment step of annealing, to adjust described calibration THE STRUCTURE OF CASTINGS and/or mechanical characteristics.

The present invention also provides and used the inventive method to be prepared and the spheroidal graphite cast iron of moulding, its structure or be basic bainite, or pearlitic substantially, perhaps ferritic substantially, or constitute by the ferrite of various ratios and perlite.

Preferably, during calibration operation, cast iron is subjected to the viscous deformation of the ratio of a restricted and inclusive, thereby can limit the planarization of graphite pebbles.Preferably, the deformation rate of this blank all parts in the calibration operation process arrives in the scope of maximum 20% 1%, metal flow in the calibration operation process is bootable to help the particularly direction of the work fatigue stress of this part of its mechanical characteristics to one thereby can make, and limits the distortion of graphite pebbles in this way.

The present invention also provides a kind of any embodiment of utilizing the inventive method to be prepared the cast iron part that is made of spheroidal graphite cast iron with moulding.

The present invention is specially adapted to, but is not limited to, and makes the mechanical component of motor car engine, for example other moving parts on connecting rod or the engine.

This lighter than forged steel by spheroidal graphite cast iron component weight molded and thermoplastic distortion calibration, mechanical characteristics is similar to even is better than forged steel, and condition of surface that it provides and size and geometric accuracy all are better than tradition forging in enormous quantities or castmethod.

The present invention is than steel saving in weight, is particularly suitable for but is not restricted to part or the parts that those need high safe range of stress.

Another major advantage of the present invention is, can obtain by traditional process for stamping manufacturing steel part the spheroidal graphite cast iron parts of the shape that can not obtain, for example, part with a plurality of hollow shape, this hollow shape is located perpendicular to the junction surface, thereby carries out undercut with respect to forging (striking) or pressing direction.This shape is easy to obtain by model casting, and the casting blank of part has just had this shape, thereby it needs less viscous deformation rate just can make part obtain its net shape; The thermal calibration operation of carrying out in this little viscous deformation rate and container that core or instrument wherein are housed or the close die adapts, as of the present invention various

The same in the implementation method.

By non-limiting mode of giving an example, explanation hereinafter is about processing a connecting rod on the engine, the web of this connecting rod, promptly connecting the big end of this connecting rod and the middle body of small end, it has the profile of a H shape, wherein sunk part extends along interfacial direction, and the direction that promptly is suitable for punching press is extended.In order to make it have longer work-ing life, this profile should be perpendicular to the front profile of working as of component, and this profile can not be handled by traditional Sheet Metal Forming Technology on a steel part.Method of the present invention can be made an engine link that has the web of certain profile, the profile of its web is perpendicular to present profile, promptly, perpendicular to the junction surface, method of the present invention can make this part have longer work-ing life under work mechanism stress in the hollow shape of web part.

Further feature of the present invention and advantage will hereinafter become clearer about the explanation of a non-limiting example by reading.

To one 770 gram (g) heavy by traditional forged steel manufacturing but test by the automobile connecting bar that the inventive method is processed.In this part, longest dimension is 180 millimeters (mm), and the thickest size is 25 millimeters (mm).

According to the present invention, from being used to calibrate the required net shape of cast connecting rod, we determine this net shape by the blank shapes of setting cast connecting rod, this blank shapes is suitable for guaranteeing that the deformation rate scope of all parts in the calibration operation process of described blank is 1% to maximum 20%, and the blank volume equals the volume of required calibration cast connecting rod substantially, thereby can obtain one not with the calibration cast connecting rod of horizontal burr.In order to carry out The deformation calculation, the volume that the volume ratio of selection blank should be calibrated foundry goods is big by 2%.

By utilizing numerical software to come the emulation forging process that viscous deformation is studied, we can determine the geometrical shape and the size of connecting rod blank.According to this blank shapes, can determine the geomery of the truing tool of close die formula, can also determine the shape of the casting tool that constitutes by two metal half modules, the contraction that is produced when it is also conceivable that this connecting rod blank and the cooling of calibration cast connecting rod, and the expansion that casting tool and truing tool produced.

This truing tool comprises mould and element that can slide of two closures in one of mould, thereby can make the hole at big end; No matter where next step process operation occurs in, and the different positions place on this hole girth all is provided with the recess that holds excess metal, and a cavity is also arranged on small end, thereby also can carry out next step process operation on small end.

According to the present invention, the final component of cast iron is: 3.7%C; 2.62%Si; 0.19%Mn; 0.3%Ni; 0.4%Cu; 0.15%Mo; Remaining Mg content is in 0.028% to 0.042% scope; This cast iron is ready in an electric induction furnace, handles with iron-silicon-magnesium, is cast to a temperature in the time of then in temperature is 1380 ℃ to 1450 ℃ scopes and is adjusted to 270 ℃ being coated with in the protection releasing agent metal mold.

This metal mold has four cavitys that hold the connecting rod blank, thereby can cast out the connecting rod blank of four spheroidal graphite cast iron in each casting working cycle.According to the present invention, this cast connecting rod blank is deviate from from mould at a certain temperature, and this temperature remains in whole test process in 980 ℃ to the 950 ℃ scopes.

Just after from mould, deviating from, every group of foundry goods string of being made up of four connecting rod blanks is placed under the cutting tool that is installed on the punch press, thereby separates rising head and pouring gate.

Each connecting rod blank is put into a temperature then at once and is set in 950 ℃ the stove of nitrogen atmosphere, thereby guarantee temperature uniformity on the each several part of connecting rod blank before calibrating.

Each blank is maintained at and continues 15 minutes to 30 minutes time in the stove.

Subsequently, on the punch press with the front ready truing tool under 930 ℃ temperature, calibrate by viscous deformation.

After calibration operation, on three batches of different cast connecting rods of calibration, carry out three kinds of process of cooling:

For first connecting rod, the cast connecting rod of calibration in this batch cools off in free air;

For second batch of connecting rod, the cast connecting rod of calibration in this batch is after finishing calibration operation, put into a perforation tunnel furnace immediately, the speed of cooling of this stove is controlled in from 900 ℃ to 500 ℃ in the scope 20 ℃ of per minutes, can cool off in free air subsequently; And

For the 3rd batch of connecting rod, the cast connecting rod of calibration in this batch is after finishing calibration operation, put into the zircon sand fluidized-bed that a temperature is set at 360 ℃ immediately, enough greatly when guaranteeing to immerse a part therein, the temperature variation of fluidized-bed is less than 5 ℃ at every turn for the volume of this fluidized-bed.According to the present invention, each connecting rod all is subjected to 360 ℃ bainitic hardening, and keeps this temperature 110 minutes in fluidized-bed, takes out each connecting rod subsequently from fluidized-bed, makes it be cooled to envrionment temperature in air.

According to the present invention, the connecting rod of making is by the way carried out various measurements, with determine its output capacity, geometry and dimensional precision with and mechanical characteristics.Therefore, in order to determine size and geometric accuracy, size, roughness and weight distribution are measured.For mechanical characteristics, carry out following measurement: tensile strength (Rm: the breaking limit when this part is subjected to stretching); Elastic limit (Rp0.2), the safe range of stress (LF) of tension set (A%) and 3,000,000 Compression and Expansion.

About output capacity, i.e. the amount of metal of usefulness and by the ratio of the amount of metal (1000 kilograms (kg)) of institute manufactured parts representative altogether, measuring result is summarised in the following table 1, compares adopting other method to make the resulting numerical value of identical connecting rod.

Table 1

	The inventive method	The method of FR2837727	The tradition forging method
				Employed material	SG iron	SG iron	Steel
Metal consumption (kg)	??1520	????1800	????1650
				The amount of metal (kg) of institute's output part	??1000	????1000	????1000
Productive rate	??1.52	????1.8	????1.65

This expression the inventive method can reduce the metal consumption of finished parts.Compare with the method for patent FR2839727 formerly and traditional forged steel parts, this has improved output capacity.

Similarly,, connecting rod constructed in accordance is measured, and in following table 2, compared with the numerical value of making the identical parts gained with other method about how much and dimensional precision.

Table 2

Used method	The present invention	Patent FR2839727	The tradition forging method	The metal pattern casting
					Material therefor	SG iron	SG iron	Steel	SG iron
The weight in average of each part (g)	??770	??770	????835	????770
					Precision about pts wt	??±1.5％	??±2％	????±2％	????±3％
The dimensional precision (mm) of part longest dimension (180mm)	??±0.15	??±0.3	????±0.4	????±0.3
					Dimensional precision (mm) on the part thickness (25mm)	??±0.1	??±0.2	????±0.25	????±0.3
Roughness Ra (micron μ m)	5 to 6	6 to 7	7 to 8	7 to 9
					Tapering (degree)	0.5 ° to 2 °	??3°	????3°	????2°

This shows to show that actual geometry that obtains and dimensional precision are better than the resulting precision of subject methods of conventional cast method and forging method and French Patent FR2837727.

In addition, in following table 3, provided observed value in the resulting basic calibration connecting rod mechanical characteristics for bainite structure of 360 ℃ of marquenching 110 minutes, and with make the resulting numerical value of identical connecting rod with other method and compare.

Table 3

Used method	The present invention	Patent FR2839727	The tradition forging method	The metal pattern casting
					Material therefor	SG iron	SG iron	Steel	SG iron
Average Rm (MPa)	??1070	????1020	????915	????980
					Average Rp0.2 (MPa)	??735	????700	????570	????665
Average A %	??6.8	????5.6	????10.4	????6.8
					Average LF (MPa)	??380	????345	????315	????345

These results show, compare with the method for forging method and patent FR2839727 with conventional cast, have improved mechanical characteristics.Especially, in this case,, compare with patent FR2839727 formerly and to have obtained significant raising by 300 ten thousand Compression and Expansion determined safe range of stress that circulates.

In following table 4, summarized two batches of measurements that connecting rod carried out to basic perlite or basic ferrite structure, and with same use spheroidal graphite cast iron and identical cooling conditions, but only cast and the numerical value of the connecting rod do not calibrated by viscous deformation compares at a metal mold.

Table 4

Type of cast	The perlite SG cast iron part of same structure		The perlite SG cast iron part of same structure
					The method that adopts	The present invention	The metal die casting	The present invention	The metal die casting
Average hardness HB	????280	????260	????200	????185
					Average Rm (MPa)	????820	????775	????505	????475
Average Rp0.2 (MPa)	????515	????470	????350	????310
					Average A %	????4	????3.8	????10	????9.2
Average LF (MPa)	????320	????295	????310	????290

Here the part that compares be the inventive method resulting with those parts with identical metallographic structure by the manufacturing of metal die casting process, promptly major part is pearlitic or ferritic part, because they all are to carry out refrigerative under identical control speed.

Last table shows, when using identical metallographic structure, when the perlite of same amount and/or ferrite were promptly arranged in cast iron, the inventive method can obtain really than the better mechanical characteristics of conventional cast method.

Claims (16)

1. one kind is manufactured on the method that has high precision on geometrical shape and the size and possess the spheroidal graphite cast iron part of improved mechanical properties, and this method comprises the following steps:

A) mixture of a kind of liquid state of preparation, it has the following component of calculating by weight: 3% to 4% C; 1.7% to 3% Si; 0.1% to 0.7% Mn; 0 to 4% Ni; 0 to 1.5% Cu; 0 to 0.5% Mo; Have this residual content of Mg that residual content and part thickness adapt in 0.025% to 0.080% scope; Remaining in iron and the preparation process with impurity; Described impurity can be content less than 0.015% S and content less than 0.10% P especially;

B) be cast to when the mixture of these liquid states is in temperature is 1350 ℃ to 1550 ℃ scopes in the mould to obtain a required part blank, the shape of this blank approaches the shape of part;

C) when temperature is Ts described blank is deviate from from mould, this temperature T s is between solidus and AR3, and wherein solidus and AR3 represent the ultimate temperature of the austenitic range of described composition;

D) when being Tf, temperature carries out moulding by viscous deformation, this temperature T f at 1050 ℃ between the AR3, described shaping directly keeps carrying out after Tm=Tf+20 ℃ to 50 ℃ one 10 minutes to 60 minutes long period in the heat of casting or with temperature, thus the part that can obtain to have its net shape and size;

E) described part is directly quenched in the formed heat under temperature T b, this temperature is between 260 ℃ to 420 ℃ and be in the bainite scope, and this part is kept Tb temperature for some time tb, and time tb is in 60 minutes to 180 minutes scope; And

F) the described part of cooling is to envrionment temperature;

The method is characterized in that, substantially equal the volume of part by the volume of the molded blank that obtains, and the operation of carrying out moulding by thermoplastic distortion is a calibration operation that carries out in unopened container or mould, this operation can so that to calibrated mo(u)lded piece do not have horizontal burr.

2. a manufacturing has the method that has high precision and possess the spheroidal graphite cast iron part of improved mechanical properties on geometrical shape and size, the method is characterized in that it comprises the following steps:

A) mixture of a kind of liquid state of preparation, it has the following component of calculating by weight: 3% to 4% C; 1.7% to 3% Si; 0.1% to 0.7% Mn; 0 to 4% Ni; 0 to 1.5% Cu; 0 to 0.5% Mo; Have the Mg that residual content and part thickness adapt, this residual content is in 0.025% to 0.080% scope; Remaining in iron and the preparation process with impurity; Described impurity can be content less than 0.015% S and content less than 0.10% P especially;

B) be cast to when the mixture of these liquid states is in temperature is 1350 ℃ to 1550 ℃ scopes in the mould to obtain a required part blank, the shape of this blank is near the shape of part, and the volume utmost point originally equals the volume of this part;

C) when temperature is Ts described blank is deviate from from mould, this temperature T s is between solidus and AR3, and wherein solidus and AR3 represent the ultimate temperature of the austenitic range of described composition;

D) when being Tf, temperature in container or mould, calibrates described part blank by pyroplastic deformation, this temperature T f at 1050 ℃ between the AR3, described pyroplastic deformation directly keeps carrying out after Tm=Tf+20 ℃ to 50 ℃ one 10 minutes to 60 minutes long period in the heat of casting or with temperature, thus the part that can obtain to have net shape and size; And

E) cool off described calibrated foundry goods to envrionment temperature with free way, control mode or by quenching, thereby such as making this part have required mechanical characteristics.

3. one kind is manufactured on the method that has high precision on geometrical shape and the size and possess the spheroidal graphite cast iron part of improved mechanical properties, the method is characterized in that it comprises the following steps:

A) mixture of a kind of liquid state of preparation, it has the following component of calculating by weight: 3% to 4% C; 1.7% to 3% Si; 0.1% to 0.7% Mn; 0 to 4% Ni; 0 to 1.5% Cu; 0 to 0.5% Mo; Have the Mg that residual content and part thickness adapt, this residual content is in 0.025% to 0.080% scope; Remaining in iron and the preparation process with impurity; Described impurity can be content less than 0.015% S and content less than 0.10% P especially;

B) be cast to when the mixture of these liquid states is in temperature is 1350 ℃ to 1550 ℃ scopes in the mould to obtain a required part blank, the shape of this blank is near the shape of part, and the volume utmost point originally equals the volume of this part;

C) after temperature is cooled to be lower than AR3, described part blank is deviate from from mould, finally be cooled to envrionment temperature;

D) heating and the temperature of this part blank remained in AC3 to the 1050 ℃ of scope, and continue one 10 minutes to 90 minutes period, to guarantee in blank, having height uniform temperature and chemical composition;

E) by pyroplastic deformation in unopened container or mould calibrate described part blank at 1050 ℃ between AR3 the time in temperature, to obtain one not with the foundry goods of calibration of horizontal burr; And

F) cool off described calibrated foundry goods to envrionment temperature with free way or with certain control mode or by quenching, adopt which kind of mode to depend on the required mechanical characteristics that possesses of part.

4. according to any one described method of claim 1 to 3, it is characterized in that, the specified shape of the casting blank of this part is to be determined by the net shape of part, with the deformation rate scope of all parts in the calibration operation process that guarantees this blank is 1% to maximum 20%, and can guide wire in this operating process, flow along the direction that helps the fatigue stress characteristic in mechanical characteristics, especially the part time job process.

5. according to any one described method of claim 1 to 3, it is characterized in that, calibration operation in unopened container or mould, be by at least two tool room punching presses or forge this blank or implement at the moving part and/or the drift of mould or cutter inner slide, particularly can obtain the multiaxis viscous deformation of this blank by utilizing.

6. method according to claim 1 and 2, it is characterized in that, with blank stripping operation c) and pyroplastic deformation operation d) between, perhaps at blank demoulding c) and the additional operation that blank is remained on the temperature T m between, add one by cutting or some other methods the intermediate steps of separating casting head (rising head, skewed slot) from the blank, to obtain the independent blank of foundry goods volume after the calibration that a volume equals to obtain substantially.

7. according to any one described method of claim 1 to 3, it is characterized in that the volume of casting blank equals to calibrate the volume of back foundry goods, maximum allowance is in 0 to+6% scope.

8. according to any one described method of claim 1 to 3, it is characterized in that, can guide on the blank corresponding to the unnecessary volume in the tolerance range, in calibration operation, enter in the recess of excess metal, this recess or be positioned at one or more blind holes or the through hole of arranging on the part that will process, or be positioned at the one or more cavitys that are used for this purpose, this cavity is positioned at the zone of the geometric accuracy that can not influence calibration back foundry goods.

9. according to any one described method of claim 1 to 3, it is characterized in that, the mould of blank of being used to cast is preferably a permanent mold, this permanent mold is made of at least two metals that are coated with releasing agent half part, but also can be mould volatile, that made by sand or other material.

10. method according to claim 3, it is characterized in that, the last finishing operations that after the blank demoulding, carries out, if necessary, can comprise a milling or machining, obtaining a blank volume that equals the part volume substantially, and/or one is designed to make the more accurate blank volume of described blank shapes.

11. according to claim 2 or 3 described methods, it is characterized in that, come to cool off calibrating the back foundry goods with free way, controllable manner or quenching mode, this cooling is in free air, flowing air or airtight medium or carries out in the atmosphere.

12., it is characterized in that this method also is included in the annealing heat treatment step after the foundry goods step of cooling calibration back according to claim 2 or described method, in order to adjust described calibration back THE STRUCTURE OF CASTINGS and/or mechanical characteristics.

13. a spheroidal graphite cast iron, it has the following component of calculating by weight: 3% to 4% C; 1.7% to 3% Si; 0.1% to 0.7% Mn; 0 to 4% Ni; 0 to 1.5% Cu; 0 to 0.5% Mo; Have the Mg that residual content and part thickness adapt, this residual content is in 0.025% to 0.080% scope; Remaining in iron and the preparation process with impurity; Described impurity can be content less than 0.015% S and content less than 0.10% P especially, its method according to claim 1 is prepared and moulding, it is characterized in that, it has one and is the structure of bainite substantially, and during calibration operation, be subjected to the viscous deformation of a restricted and inclusive ratio, thereby the planarization of restriction graphite pebbles.

14. a spheroidal graphite cast iron, it has the following component of calculating by weight: 3% to 4% C; 1.7% to 3% Si; 0.1% to 0.7% Mn; 0 to 4% Ni; 0 to 1.5% Cu; 0 to 0.5% Mo; Have the Mg that residual content and part thickness adapt, this residual content is in 0.025% to 0.080% scope; Remaining in iron and the preparation process with impurity; Described impurity can be content less than 0.015% S and content less than 0.10% P especially, it is prepared and moulding according to claim 2,3,11,12 method, it is characterized in that, its structure or for ferritic substantially or for pearlitic substantially or be ferrite-pearlite, with and during calibration operation, be subjected to the viscous deformation of the ratio of a restricted and inclusive, thereby the planarization of restriction graphite pebbles.

15. cast iron according to claim 13 or 14, it is characterized in that, the deformation rate of this blank all parts in the calibration operation process arrives in the scope of maximum 20% 1%, thereby make in the calibration operation process, metal flow can be directed to one and help the particularly direction of the work fatigue stress of this part of its mechanical characteristics, limits the distortion of graphite pebbles in this way.

16. a cast iron part is characterized in that, it is by constituting according to claim 13,14 or 15 spheroidal graphite cast iron.