CN100487140C - Method for heat-treating steel material - Google Patents

Abstract

Disclosed is an efficient heat treatment method which can be performed in a short time. Specifically disclosed is a method for heat-treating a steel material wherein a plastically deformed steel work is introduced into a heat treatment furnace when the work still retains the heat applied thereto during the plastic deformation, then the work is heated preferably at a heating rate of 15-50 DEG C/min and held at a temperature between Ac1 and Ac3 for 10 minutes or less, and then the work is slowly cooled at a cooling rate of 5-45 DEG C/min. This heat treatment method enables to easily produce a steel material having a uniform metal structure by simple facilities.

Description

The heat treating method of steel

Technical field

The present invention relates to a kind of heat-treating methods of steel, the heat-treating methods of these steel is aimed at the steel enforcement that produces viscous deformation because of viscous deformation processing.

Background technology

The outer coil component that constitutes the constant velocity cardan joint of motor-driven vehicle going mechanism generally is produced by following operation: to the carbon element steel workpiece of being made by right cylinder, carrying out forward extrusion shaping, upsetting shaping and reverse extrusion molding successively, is the shape of outer coil component by viscous deformation with this carbon steel workpiece.In addition, carry out above-mentioned forging first being processed, the carbon element steel workpiece will be heated to predetermined temperature sometimes.That is, outside making, under the situation of coil component, to carry out warm forging or forge hot sometimes.

Outer coil component cool to room temperature with the processing that is shaped like this obtains is transported in the Equipment for Heating Processing then.So,, perhaps, in this Equipment for Heating Processing, implement various thermal treatments such as low-temperature annealing, Spheroidizing Annealing or normalizing in order to realize the homogenizing of hardness for outer coil component is softening and raising deformability.

Then, remove the shot peening of the oxide skin that when above-mentioned thermal treatment, produces, also form on the outside surface of coil component outside by what zinc phosphate etc. constituted and lubricatedly generate mulch film with chemistry.Then, externally coil component carries out diameter reducing extrusion processing (finishing shaping), and this outer coil component has been finished the precision work to final size thus.In addition, this diameter reducing extrusion is processed normally cold forging.

Yet, through under the situation of these manufacturing processedes, just must be useful on the broad space that these thermal treatments outer coil component is before implemented in keeping, and be that purpose guarantees that the space is disadvantageous economically with the keeping.

In addition, thermal treatment for example is to carry out when the outer ring component transfer of mounting on travelling belt is in continuous furnace, and be admitted in the continuous furnace to the time of being sent from continuous furnace from outer coil component, in other words, the time of handling is long, therefore obviously has the low unfavorable condition of outer coil component production efficiency.In addition, even process furnace is changed to the time that batch processing formula process furnace also can't shorten processing.

Having, carry out the Equipment for Heating Processing that low-temperature annealing, Spheroidizing Annealing or normalizing are used, must be main equipment all, so facility investment be huge.

Yet, if avoid these unfavorable conditions and omit thermal treatment, outer coil component is softened can not make hardness even again, cause thus adding and crack man-hour, the unfavorable conditions such as dimensional precision reduction of this tooth portion when perhaps tooth portion being set on the axial region of coil component outside in diameter reducing extrusion.

From above viewpoint, people thirst for establishing the heat treating method that a kind of short period of time can finish and just can implement with simple equipment, for example carry out tempering and have saved the scheme of quenching with regard to having proposed a kind of in Japanese kokai publication hei 5-302117 communique.In addition, in Japanese kokai publication hei 5-255739 communique following scheme is disclosed: with steel workpiece at Ac ₁-Ac ₃Carrying out degree of finish under the temperature between the point is the viscous deformation processing of 45-65%, then, carries out air cooling (placing cooling naturally).

In the heat treating method that Japanese kokai publication hei 5-302117 communique is put down in writing, be that the molding that forges after processing is placed cooling.Thus, must guarantee to be used for the space of keeping molding.In other words, the heat treating method put down in writing of Japanese kokai publication hei 5-302117 communique can not reduce the keeping space.

In addition, the working method that Japanese kokai publication hei 5-255739 communique is put down in writing is warm forging, and existence can not be applicable to the problem of the situation of carrying out cold forging or forge hot.

And for example under the situation of carrying out forge hot, about the steel that the temperature when forging lowers, the metallographic that is present in the steel metal structure changes, and makes metal structure become inhomogeneous thus.If this thing happens, the various characteristics that will cause steel is according to the position and different unfavorable conditions, so people wish to have and make the metal structure heat treating method of homogenizing as far as possible.Yet, the up to the present this metal structure homogenizing and heat treating method is not known efficiently as far as possible that makes.

Summary of the invention

General objects of the present invention provides a kind of heat treating method that does not need the keeping spatial steel of steel.

Main purpose of the present invention provides a kind of heat treating method efficiently that can implement at short notice.

Another object of the present invention provides the heat treating method of the steel that the simple equipment of a kind of usefulness just can implement.

A further object of the present invention provides a kind of heat treating method of steel of metal structure homogenizing of easy realization the finished product.

According to an embodiment of the invention, a kind of heat treating method of steel is provided, the heat treating method of these steel comprises following operation: first operation, this first operation will have the steel of processing heat along with being subjected to viscous deformation processing, heat from the moment of residual process heat, make the temperature of above-mentioned steel remain on Ac ₁-Ac ₃The point between; With second operation, this second operation will have been carried out heating and the above-mentioned steel that keep are cooled to the pearlitic temperature of separating out end with 5-45 ℃/minute speed of cooling, and wherein, the hold-time in above-mentioned first operation is 10 minutes or shorter, but greater than 0 minute.

Carry out after the viscous deformation processing, in the steel that temperature has descended, metal structure can be inhomogeneous slightly.In the present invention, these steel are remained on Ac ₁-Ac ₃Temperature between the point in these steel, makes the metal structure of austenite and ferrite coexistence form roughly even thus.That is, by keeping this temperature, thus the metal structure that can make steel homogenizing roughly.

In addition,, make steel softening, and make the hardness of these steel all roughly the same and with the position with apart from the range-independence on surface by carrying out first operation and second operation.In other words, can in following process such as diameter reducing extrusion shaping, make all sites produce distortion with roughly the same degree.Therefore, molding is difficult to take place crackle, and the dimensional precision of this molding is good.

And, owing among the present invention,, therefore do not need the steel that the enforcement viscous deformation is processed are taken care of owing to the moment that in the moment of residual process heat, promptly has what is called to process self-heating heat-treats.Therefore, owing to do not need to prepare the space of keeping usefulness, thus just the space can be effective to other purposes.

In addition, owing to the time that keeps is in 10 minutes, so the scale of Equipment for Heating Processing just can be littler than Equipment for Heating Processing in the past such as Spheroidizing Annealing equipment.Thus, avoided huge facility investment.On this basis, owing to improved heat treated efficient, thereby reduced the required energy of thermal treatment, and improved production efficiency.Consequently, aspect cost, be favourable.

In addition, in the present invention, " viscous deformation processing " has comprised steel is exerted pressure and made it produce the processing of viscous deformation.Particularly, illustration has: forge processing, forging and pressing processing and rolling processing etc.

Here, the perlite of steel separate out end temp be according to the speed of cooling in second operation with steel type and different, big in 600-680 ℃ scope.Therefore, second operation is just enough as if proceeding to 600-680 ℃.

Preferably 5-10 ℃/minute of the speed of cooling of second operation.In this case, the further granular of tissue meeting consequently, has further suppressed the inhomogeneous of hardness.

Rise to Ac in temperature with steel ₁Point or higher temperature are carried out steel under the situation of viscous deformation processing, and the heating of these steel (intensification) preferably is in Ar in the temperature of these steel ₁The point or the moment lower and that be in 500 ℃ or the higher scope begin.

Ar ₁Point is defined as: when the cooling steel, begin the temperature of eutectoid transformation to ferrite and cementite from austenite.Therefore, drop to Ar ₁The metal structure of point or lower steel is to contain ferrite and pearlitic roughly uniform formation.Thus, through the further homogenizing of final metal structure of the steel of second operation, can obtain the steel of various characteristics approximate equality.

And, be lower than Ac in that steel are heated to ₁The temperature of point and steel being carried out under the situation of viscous deformation processing, the heating of these steel (intensification) are to begin in 500 ℃ or the higher moment in the temperature of steel preferably.

Here, under the situation of cold forging, if in the moment that keeps the processing self-heating, be that temperature is moment of implementing the temperature of viscous deformation first being processed or higher temperature to begin to heat up to get final product.

Therefore, in above-mentioned first operation, steel are up to reaching Ac ₁-Ac ₃Preferably 15-50 ℃/minute of heat-up rate till the temperature between the point.If be lower than 15 ℃/minute, heat treated efficient reduces.And if be higher than 50 ℃/minute, the steel metal structure produces defective sometimes.

And, preferred exemplary as steel contains at least: by quality %, and the Cr of Ni, the 0.1-1.2% of Cu, the 0.01-0.15% of the Mn of the C of 0.1-0.55%, the Si of 0.03-0.35%, 0.2-1.0%, P, the S smaller or equal to 0.03%, 0.03-0.15% and smaller or equal to 0.45% Mo smaller or equal to 0.03%.In addition, can also contain as required: for example B of the Al of the Ti of 0.03-0.05%, 0.02-0.04%, 0.001-0.002%, about 0.1% V, Nb, the Ca smaller or equal to 0.05%, Pb and smaller or equal to other elements such as Bi of 0.1% smaller or equal to 0.2% smaller or equal to 0.05%.

That is, carbon steel, boron steel, chromium steel, steel nickel chrome, nickelchrome molybdenum steel, manganese steel or chromium manganese steel can have been enumerated as the representational steel of the present invention.

Description of drawings

Fig. 1 is the schema of heat treating method of the steel of present embodiment.

Fig. 2 A-Fig. 2 E is that expression is the explanatory view of the operation of outer coil component from the workpiece to the viscous deformation.

Fig. 3 is explanation is transplanted on outer coil component the work-yard of heat treatment furnace from the forging processing station a synoptic diagram.

Fig. 4 is illustrated in to be lower than Ac ₁Forge the chart in the general temperature field that adds man-hour under the temperature of point.

Fig. 5 is illustrated in Ac ₁Forge the chart in the general temperature field that adds man-hour under point or the higher temperature.

Fig. 6 illustrates to heat up and remain on to be higher than Ac ₃Temperature the time the uneven chart of axial region hardness.

Fig. 7 is the horizontal sectional drawing apart from axial region leading section 50mm position at A-D position in the explanatory view 6.

Fig. 8 is the chart of expression through the hardness from the surface to inside of the outer coil component axial region after second operation.

Fig. 9 is that the speed of cooling that is illustrated in second operation is the chart of the hardness from the surface to inside of the outer coil component axial region under 5-10 ℃ of/minute situation.

Figure 10 is illustrated in the chart of not implementing the hardness from the surface to inside of heat treated outer coil component axial region after forging is processed.

Figure 11 is the chart of component proportions that the steel of test film are carried out in expression.

Figure 12 is the forging temperature of expression test film, the chart that heating keeps temperature, surface hardness, core rigidities and difference of hardness.

Figure 13 is the Ac of expression test film ₁Point, Ac ₃The chart of point and heat-up rate.

Embodiment

Below, be that example is enumerated preferred forms with following situation, and steel heat treatment process of the present invention be elaborated: will be heated to Ac by the workpiece that carbon steel is made with reference to accompanying drawing ₁Point or higher temperature perhaps are heated to and are lower than Ac ₁The proper temperature of point implement to forge processing then and viscous deformation is the outer coil component of constant velocity cardan joint.

Fig. 1 represents the schema of heat treating method of the steel of present embodiment.This heat treating method comprises: the outer coil component (carbon steel) that first operation, this first operation will be implemented viscous deformation processing remains on Ac ₁-Ac ₃Temperature between the point; And second operation, this second operation will heat and the outer coil component that keeps being through with cools off.

Earlier viscous deformation processing is described.At first, the workpiece 10 of the cylindrical shape that will be made by the carbon steel shown in Fig. 2 A is heated to predetermined temperature.The temperature of workpiece 10 for example can be 600-1250 ℃.Just, owing to, therefore preferably avoid this temperature province being higher than 720 ℃ and be lower than 800 ℃ region memory the transition point of carbon steel is being arranged.That is, the temperature of workpiece 10 is preferably 600-720 ℃ or 800-1250 ℃.

Then, this workpiece 10 being implemented forward extrusion is shaped.That is, under the state of an end face of supporting workpiece 10, push this workpiece 10 from the opposite side end face.Along with the distortion of this other end, consequently, shown in Fig. 2 B, obtained molding 18 for the first time, this, molding 18 was formed with reducing diameter part 14 and the axial region 16 that large-diameter portion 12, diameter are shrunk to taper first time.Then, carry out forward extrusion once more and be shaped, then shown in Fig. 2 C, formed molding 20 for the second time.

Then, to this second time molding 20 carry out upsetting and be shaped.Particularly, shown in Fig. 2 D, by to the second time molding 20 large-diameter portion 12 compress, thereby make the enlarged-diameter of this large-diameter portion 12, become the 3rd molding 24 with glass portion 22.

Then, the 3rd molding 24 carried out reverse extrusion molding, make 22 elongations of glass portion, and in this glass portion 22, form 6 ball groove 26a-26f.That is, allow drift butt, next, push the leading section of axial region 16, the 3rd molding 24 is shifted towards the direction of this drift indication to an end face central part of cup portion 22 with the protuberance that is used to form ball groove 26a-26f.Thus, obtained the outer coil component 28 shown in Fig. 2 E.

And, each forge processing by respectively independently the forging and molding device carry out, workpiece 10, for the first time molding 18, molding 20, the 3rd molding 24 are transferred by e Foerderanlages such as forwarders between each forging and molding device for the second time.

As shown in Figure 3, be implemented the outer coil component 28 of above-mentioned forging processing, during forge processing station 30 and be transplanted on heat treatment furnace 32, by the operation of mechanical manipulator 34, thus outer coil component 28 on the forwarder 36 with axial region 16 towards above mode form a line.

As mentioned above, outer coil component 28 is heated to preset temperature in advance forging first being processed.In addition, outer coil component 28 becomes the condition of high temperature that has processing heat along with being implemented the viscous deformation of forging processing and causing.

In the present embodiment, outer coil component 28 is keeping this pyritous to be directed to constantly in the heat treatment furnace 32.

Fig. 4 and Fig. 5 represent to forge processing respectively and are being lower than Ac ₁Put or be higher than and equal Ac ₁Forge the general temperature field that adds man-hour under the temperature of point.Fig. 4 wherein is illustrated in and is lower than Ac ₁Forge the situation of processing under the higher temperature of point.In this case, because the temperature of workpiece 10 compares Ac ₁Point is low, in the outer coil component 28 after oppositely extrusion molding is finished, presents the shape of ferrite and perlite elongation in the crystal grain.

Implementing to forge with temperature field shown in Figure 4 under the situation of processing, the temperature of forging the workpiece 10 that adds man-hour for example is preferably set to from Ac ₁The numerical value of point deducts 180 ℃ value, and further is preferably set to from Ac ₁The numerical value of point deducts 150 ℃ value (about 580 ℃).

On the other hand, Fig. 5 is illustrated in above Ac ₁Forge processing under the high temperature of point, the temperature of outer coil component 28 drops to and compares Ac ₁Be imported into the situation in the heat treatment furnace 32 after point is low.And as shown in Figure 5, the temperature that adds the workpiece 10 in man-hour in forging is to surpass Ac ₁Under the pyritous situation of point, be preferably set to Ac ₃Point or higher.In this case, because the temperature of workpiece 10 has surpassed the Ac that ferrite is finished towards austenitic conversion ₃Point, austenite has accounted for most in the metal structure of the outer coil component 28 after therefore oppositely extrusion molding has just finished.And, in above-mentioned metal structure, produced recrystallize, thereby significantly reduced inconsistent phenomenon (transition).That is, the temperature of the workpiece 10 by forging being added man-hour is set in Ac ₃Point or higher, thus can realize the further homogenizing of metal structure.

To be implemented the outer coil component 28 that forges processing and promptly to be directed in the heat treatment furnace 32 in order to make, and will get to the distance setting of heat treatment furnace 32 and lack (with reference to Fig. 3) as far as possible from forging processing station 30.And the transfer rate of forwarder 36 is set at consistent with the production number of unit time Internal and external cycle parts 28.

Like this, according to present embodiment, the outer coil component 28 that has heat after viscous deformation is just imported in the heat treatment furnace 32 as quickly as possible.Therefore do not need the space of the outer coil component 28 of keeping, so the space can be used for effectively other purposes.

Outer coil component 28 from the metal die that carries out reverse extrusion molding, be fetched into send into heat treatment furnace 32 during in be exposed in the atmosphere, thereby the temperature of being somebody's turn to do outer coil component 28 can descend slightly, but such as mentioned above, outer coil component 28 is imported in the heat treatment furnace 32 under keeping the pyritous state.

Here, soon be imported into the temperature of heat treatment furnace 32 outer coil component 28 before, the temperature that adds the workpiece in man-hour with forging is to be higher than to equal Ac ₁Point still is lower than Ac ₁Point is irrelevant, but preferably 500 ℃ or higher.If being dropped to the outer coil component 28 that is lower than 500 ℃, temperature imports in the heat treatment furnace 32, owing to must workpiece be warmed up to Ac with the short period of time ₁-Ac ₃Therefore point needs to set big heat-up rate, and in this case, will produce defective owing to the metal structure that coarsening causes, sometimes the undercapacity of feasible outer coil component 28.

In addition, for fear of this situation, temperature need be dropped to the outer coil component 28 that is lower than 500 ℃ and heat up with heat-up rate slowly, this just need be arranged to large-scale equipment with heat treatment furnace 32, thereby causes the huge of facility investment.

With Ac ₁Point or higher temperature and forging under the situation of processing, the temperature that soon imports heat treatment furnace 32 outer coil component 28 before is generally about 600-720 ℃, and as shown in Figure 5, two kinds of moment import to outer coil component 28 in the heat treatment furnace 32 below: a kind of be temperature reach be lower than when cooling carry out the Ar of the beginning temperature of eutectoid transformation to ferrite from austenite ₁The point temperature for example reaches from Ar ₁The numerical value of point deducts the moment of the temperature about 50 ℃; Another kind is further to drop to 500 ℃ the moment.In this case, because austenite disappears from the metal structure of outer coil component 28, therefore also obtaining so outer coil component 28 easily, promptly being somebody's turn to do outer coil component be that the roughly even metal tissue that ferrite and perlite coexist forms.

Ar ₁The numerical value of point changes Ar according to the difference of temperature lowering speed ₁The numerical value of point is not certain, is under 20-40 ℃/minute the situation in the temperature lowering speed, Ar ₁The point numerical value the chances are 710-720 ℃.

In this case, heat treatment furnace 32 has heating furnace 38, soaking pit 40,42 3 stoves of cool furnace.Wherein, heating furnace 38 remains on identical temperature with soaking pit 40.In addition, also can import nitrogen, heat, keep and cool off being full of under the state of nitrogen in the inside of three stoves.

Outer coil component 28 at first is imported in the heating furnace 38 under the state that is positioned on the forwarder 36, begins the first operation S1 shown in Figure 1.

The outer coil component 28 that imports in the heating furnace 38 is heated to Ac ₁-Ac ₃Temperature between the point.

Here, too much as if heat-up rate is set as mentioned above, will in metal structure, produce defective owing to coarsening.For fear of this situation, the temperature of heating furnace 38 preferably sets into 50 ℃/minute or lower heat-up rate.And if heat-up rate is lower than 15 ℃/minute, the heat treatment efficiency of then outer coil component 28 will reduce.Even and, heat treatment furnace 32 is maximized, thereby facility investment is huge for heat treatment efficiency still not being descended being lower than under 15 ℃/minute the heat-up rate.Conclusion is that heat-up rate is preferably 15-50 ℃/minute, more preferably 17-46 ℃/minute.

In the present embodiment, in order to obtain this heat-up rate, the temperature of heating furnace 38 is set to 800-850 ℃.The outer coil component 28 that imports temperature before the heating furnace 38 and be 500-720 ℃ is by before the heating furnace 38, and temperature reaches 720-780 ℃.

So, next be imported in the soaking pit 40 by the outer coil component 28 after the heating furnace 38.In this soaking pit 40, the outer coil component 28 that has been warmed up in heating furnace 38 about 720-780 ℃ remains on this temperature.

Above-mentioned intensification and keeping altogether at 10 minutes with interior just enough.Under thermal treatment is carried out situation more than 10 minutes, heat treatment furnace 32 and forwarder 36 will extend, and make the Equipment for Heating Processing maximization that becomes.That is, facility investment is huge.In addition, even surpass 10 minutes heating and maintenance, the degree of softening or hardness homogenizing and 10 minutes are also basic identical with interior situation, thereby are disadvantageous with regard to cost.The time of heating up and keeping altogether 5 minutes with interior also enough, for example can be 3 minutes.

Be maintained at Ac ₁-Ac ₃ Outer coil component 28 on the temperature between the point becomes the metal structure of austenite and ferrite coexistence.

In addition, outside the outlet temperature of coil component 28 for being lower than Ac ₁Under the situation of point, be difficult to the homogenizing of the softening and hardness of this outer coil component 28 of realization.In addition, be higher than Ac heating up and be retained to ₃Under the situation of the temperature of point, can cause austenitic thickization (grain growing is unusual).Therefore, as shown in Figure 6, according between the different positions or apart from surperficial distance, hardness can be inhomogeneous as can be seen.And the A-D among Fig. 6 shows the observed value on the position A-D of leading section 50mm position apart from axial region 16 shown in Figure 7, and each observed value is measured from the surface to horizontal section inside, down with.

Next the outer coil component 28 that is heated like this and keep is imported in the cool furnace 42, begins the second operation S2 thus.

In cool furnace 42, the speed of cooling of outer coil component 28 is set in the predetermined scope, particularly, is set at 5-45 ℃/minute.By speed of cooling is set in such scope, thereby can obtain from the surface to inside roughly uniform tissue, as shown in Figure 8, almost not observe the inhomogeneous of hardness.

It is 5-10 ℃/minute that speed of cooling is more preferably.In this case, can form the spheroidization tissue, as shown in Figure 9, the further homogenizing of the hardness from the surface to inside, and the stretching of outer coil component 28 and punching performance are improved.

Here, Figure 10 is illustrated in the hardness that is not subjected to after forging is processed in the heat treated outer coil component 28.If above-mentioned Fig. 8, Fig. 9 and Figure 10 are compared, then by implementing the thermal treatment of present embodiment, can make outer coil component 28 soften significantly, and can suppress hardness inhomogeneous of this outer coil component 28.

Cooling can be performed until the pearlitic temperature of separating out end.This separates out end temp according to the kind of cooling rate and steel and different, probably between 680-600 ℃.Thereby the cooling last till that preferably temperature is between 680-600 ℃, for example can proceed to be lower than 650 ℃.Along with this decrease of temperature, formed the metal structure of ferrite and perlite coexistence outside on the coil component 28.

Like this, in the present embodiment, outer coil component 28 passes through heating furnace 38, soaking pit 40 and cool furnace 42 in very short time.Therefore, can make from heating furnace 38 to cool furnace 42 Equipment for Heating Processing is simple structure.

The outer coil component 28 that the second operation S2 is through with is sent from cool furnace 42 by forwarder 36, is cooled to room temperature, carries out shot peening then and forms the lubricated processing of using chemistry to generate mulch film, is transported to the forging processing station that carries out diameter reducing extrusion.

In this diameter reducing extrusion forming process, owing to improved the stretching and the punching performance of outer coil component 28, this outer coil component 28 is easy to distortion.In addition, the hardness of outer coil component 28 and position have nothing to do and roughly are equal to, and, roughly certain from the surface to inside.Therefore the deformability on all sites roughly is equal to, and Bian Xing degree is also roughly the same like this.Thereby can produce up to all excellent outer coil component 28 of the dimensional precision at the less position of shapes such as tooth portion.

And the workpiece that above-mentioned embodiment is an illustration is made by carbon steel is at Ac ₁Point or higher temperature or be lower than Ac ₁Forge processing under the temperature of point, and viscous deformation is that the situation of coil component 28 describes outside the constant velocity cardan joint, but the present invention is not particularly limited in this certainly.For example workpiece can be the steel outside the decarburize steel, as boron steel, chromium steel, steel nickel chrome, nickelchrome molybdenum steel, manganese steel or chromium manganese steel, also can be to have added the high-speed cutting steel that plumbous high speeds such as (Pb) cuts into branch.In addition, the parts beyond the outer coil component 28 can also be made as the finished product.

In addition, can also implement cold forging to steel workpiece.In this case, steel workpiece has processing heat along with viscous deformation.Can also in other words, than the high moment before implementing viscous deformation processing, carry out above-mentioned thermal treatment in the moment that keeps this processing heat to steel workpiece in temperature.

Have, viscous deformation processing is not particularly limited in forging processing again, so long as workpiece exerted pressure the processing of this workpiece deformation is got final product.For example, comprise rolling processing.

Embodiment 1

Produce respectively the test film of the cylindrical shape of the diameter 23.8mm * length 48mm that makes by steel 1-10 with composition shown in Figure 11 (numeral is quality %).This test film is warmed up to predetermined temperature by thermatron, after the temperature of carrying out 1 minute keeps, temperature is reduced by 50 ℃ by air cooling.Then, imposing its surface compressed rate is that 65% forward extrusion is shaped.In addition, additional before the element term " s-" is meant that this element is present in the steel with the state of solid solution in Figure 11.

Next, the test film that temperature is reduced to 600 ℃ imports in the heat treatment furnace, heat and be retained to predetermined temperature, and then, on one side controlled chilling speed be cooled to 680 ℃ on one side.So, test film is derived from heat treatment furnace, place cooling until becoming room temperature.

Then, the position of the dark 0.5mm in surface of measuring distance press section and the Vickers' hardness and the calculating mean value of central part on three points.Then, calculate the difference of hardness of surface hardness and core rigidities.

Figure 12 has represented that in the lump above-mentioned forging temperature, heating keep temperature, speed of cooling, surface hardness, core rigidities and difference of hardness.Surface hardness is low more and difference of hardness is more little, difficult breaking more just in diameter-reducing formation, and this just means that the dimensional precision after the shaping is good.

In addition, in order to compare, the test film of same size have been applied heating kept temperature to be lower than Ac ₁Point or be higher than Ac ₃The thermal treatment of point.Figure 12 has represented that in the lump heating in this case keeps temperature, speed of cooling, surface hardness, core rigidities and difference of hardness.From Figure 12, can very clearly draw the big conclusion of test film difference of hardness of comparative example.

Embodiment 2

Produce the test film of same size with the steel 1-steel 4 among Figure 11, steel 8-steel 11, after separately each test film being heated, in air, be cooled to and be reduced to predetermined temperature.And then, be heated to each Ac shown in Figure 13 with predetermined heat-up rate ₁-Ac ₃Temperature between the point.Decline temperature and heat-up rate have been represented among Figure 13 in the lump.

So, test film is remained on Ac ₁-Ac ₃After the temperature between the point, on one side controlled chilling speed be cooled to 650 ℃ on one side, then test film is derived from heat treatment furnace, place and be cooled to room temperature.With the metal structure of each test film of scanning electron-microscopic observation, can confirm this metal structure and be roughly uniform tissue of ferrite and perlite, there is not defective basically.

Claims (8)

1. the heat treating method of steel is characterized in that, the heat treating method of these steel comprises following operation:

First operation, this first operation will have the steel of processing heat along with being subjected to viscous deformation processing, heat from the moment of residual process heat, make the temperature of above-mentioned steel remain on Ac ₁-Ac ₃The point between; With

Second operation, this second operation will have been carried out heating and the above-mentioned steel that keep are cooled to the pearlitic temperature of separating out end with 5-45 ℃/minute speed of cooling,

Wherein, the hold-time in above-mentioned first operation is 10 minutes or shorter, but greater than 0 minute.

2. heat treating method as claimed in claim 1 is characterized in that, it is 600-680 ℃ that above-mentioned second operation proceeds to steel.

3. heat treating method as claimed in claim 1 is characterized in that, the speed of cooling of above-mentioned second operation is 5-10 ℃/minute.

4. heat treating method as claimed in claim 1 is characterized in that, above-mentioned steel are being heated to Ac ₁Under point or the higher temperature, these steel are carried out above-mentioned viscous deformation processing, and in above-mentioned first operation, be in Ar in the temperature of above-mentioned steel ₁The point or the moment lower and that be in 500 ℃ or the higher scope begin to heat these steel.

5. heat treating method as claimed in claim 1 is characterized in that, is lower than Ac in that above-mentioned steel are heated to ₁Under the temperature of point, these steel being carried out above-mentioned viscous deformation processing, and in above-mentioned first operation, is 500 ℃ or the higher moment to begin to heat these steel in the temperature of above-mentioned steel.

6. heat treating method as claimed in claim 1 is characterized in that, in above-mentioned first operation, up to reaching Ac ₁-Ac ₃Heat-up rate till the temperature between the point is 15-50 ℃/minute.

7. heat treating method as claimed in claim 1, it is characterized in that, above-mentioned steel contain at least: by quality %, and the Cr of Ni, the 0.1-1.2% of Cu, the 0.01-0.15% of the Mn of the C of 0.1-0.55%, the Si of 0.03-0.35%, 0.2-1.0%, P, the S smaller or equal to 0.03%, 0.03-0.15% and smaller or equal to 0.45% Mo smaller or equal to 0.03%.

8. heat treating method as claimed in claim 7 is characterized in that, above-mentioned steel are carbon steel, boron steel, chromium steel, steel nickel chrome, nickelchrome molybdenum steel, manganese steel or chromium manganese steel.

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