CN105296914A

CN105296914A - Manufacturing method of steel in which an element of treatment gas is dissolved and diffused

Info

Publication number: CN105296914A
Application number: CN201510430901.9A
Authority: CN
Inventors: 平松真一; 稻垣功二; 金泽孝明
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 2014-07-23
Filing date: 2015-07-21
Publication date: 2016-02-03
Also published as: US20160024636A1; EP2977484A1; JP2016023344A; JP6168008B2

Abstract

A manufacturing method of steel (1a) in which an element of the treatment gas is dissolved and diffused includes heating the steel, making a treatment gas contact a surface of the steel such that an element of the treatment gas dissolves and diffuses from the surface of the steel into a surface layer thereof, and reducing a concentration of the treatment gas near a non-treatment surface that is a portion of the surface of the steel.

Description

Wherein dissolve and spread the manufacture method of steel of the element having process gas

Technical field

The present invention relates to and to dissolve aptly in the part on the surface of steel and to spread the manufacture method of the steel of the element having process gas.

Background technology

Carburizing, nitriding or carbonitriding etc. use process gas application in steel to improve the weather resistance etc. on the surface of steel.In these process, by making the surface contact of process gas and the steel through heating, the element of process gas dissolves from the treat surface of steel and is diffused in its upper layer.

Here, it is easy that the whole upper layer of steel carries out these process, but in an only part for the upper layer of steel, carries out these process and be not easy.Given this, such as, No. 11-217626th, Japanese Patent Application Publication (JP11-217626A) proposes a kind of gear wheel carburization method as an example.Here, the particle of anti-carburizer is injected on the curved surface of the tooth top in tooth-formation of gear portion, and described curved surface is non-process surface, makes anti-carburizer adhere to the curved surface of tooth top.In this state, use carburizing gas (process gas) to make the curved surface treat surface carburizing outside of eliminating tooth top, and then remove anti-carburizer from the curved surface of tooth top.As a result, the carbon amounts of dissolving in the curved surface of the tooth top in tooth-formation of gear portion can be reduced.

But adopt in JP11-217626A the technology described, because anti-treatment agent such as anti-carburizer uses together with carburizing, the dissolving of the element thus processing gas in the non-process surface of steel and diffusion can be prevented from or reduce.But make in this way, anti-treatment agent must be attached to the surface of steel and then remove, and this is pretty troublesome and spends a large amount of time just to terminate.Therefore, manufacturing cost increases.

Summary of the invention

This invention therefore provides a kind of manufacture method of steel, pass through the method, cheap and without the need to troublesome work, the element of the process gas of required amount can dissolve and be diffused in the upper layer of the treat surface of steel, suppresses the element of process gas dissolve and be diffused in the non-process surface of steel simultaneously.

A first aspect of the present invention relates to a kind ofly wherein dissolves and spreads the manufacture method of steel of the element having process gas, and described method comprises: heating steel; Process gas is made to contact the surface of described steel so that the element processing gas is diffused into its upper layer from the surface dissolution of described steel; And reducing the concentration of described process gas at non-process near surface, described non-process surface is the part on the surface of described steel.

According to this aspect of the invention, by pyrolysis processing gas, process gas is decreased to lower than the concentration of process gas near treat surface in the concentration of non-process near surface.Therefore, the amount being dissolved in the element of the process gas in non-process surface is less than the amount of the element of the process gas be dissolved in treat surface.As a result, cheap and without the need to troublesome work, the element of the process gas of required amount can dissolve and be diffused in the upper layer of the treat surface of steel, suppress the element of process gas dissolve and be diffused in the non-process surface of steel simultaneously.

Process gas reduces by pyrolysis processing gas in the concentration of non-process near surface.

The method of pyrolysis processing gas can be the method by metal catalyst pyrolysis processing gas, such as, uses heat to dissolve the element with DIFFUSION TREATMENT gas.In addition, can steel be arranged in process furnace, can steel be heated, and carry out by pyrolysis heater the pyrolysis processing gas.The manufacture method of steel also can comprise the non-process surface be arranged as by pyrolysis heater towards steel described in inside heating furnace.

According in this respect, pyrolysis heater is arranged in the position on non-process surface of the steel arranged in process furnace, makes the process gas of the non-process near surface of steel by pyrolysis heater pyrolysis.Therefore, it is possible to make to process the concentration of gas at the non-process near surface of steel lower than the concentration of process gas near treat surface.As a result, the element of aequum can dissolve and be diffused in the upper layer of the treat surface of steel, suppresses the element of process gas dissolve and be diffused in the non-process surface of steel simultaneously.

In addition, in above-mentioned, can steel be arranged in process furnace, can steel be heated, and carry out by pyrolysis heater the pyrolysis processing gas.The manufacture method of steel also can comprise, by pyrolysis heater, the space of the inside of process furnace is divided into process space and non-process space, the non-process surface of steel is arranged in described non-process space, process gas is flowed in described process space, and by process gas that pyrolysis heater pyrolysis is advanced from described process space towards described non-process space.

According in this respect, when processing gas from described process spatial flow to described non-process space, this process gas, by pyrolysis heater pyrolysis, thus processes the concentration of gas in described non-process space and can remain lower than the concentration of process gas in described process space.As a result, the element of required amount can dissolve and be diffused in the upper layer of the treat surface of steel, suppresses the element of process gas dissolve and be diffused in the non-process surface of steel simultaneously.

Can repeat process gas to be fed to process in process furnace and interrupt handling gas to the supply in process furnace and discharge the process of described process gas from process furnace.

According in this respect, be supplied in the process in process furnace by process gas, the element of process gas dissolves from the treat surface of steel.Discharge the process of described process gas at interrupt handling gas to the supply in process furnace and from process furnace, the dissolving of process gas is limited and steel is in heated condition, thus once the diffusion energy of the element dissolved accesses promotion.

As a result, dissolving and the diffusion of the element of process gas are able to repetition, and the element thus processing gas can dissolve from treat surface and be diffused into its upper layer.On the other hand, the element of process gas is from non-process surface to its internal divergence, and it dissolves slightly each time, and thus the constituent content of the upper layer on non-process surface can reduce.

At interrupt handling gas to the supply in process furnace and from the process of process furnace discharge process gas, the heating of interruptible price pyrolysis heater.According in this respect, the non-process surface of steel is not heated continuously by pyrolysis heater, and the heat effect thus in the part on non-process surface comprising steel can reduce.

According to this aspect of the invention, cheap and without the need to troublesome work, the element of the process gas of required amount can dissolve and be diffused in the upper layer of the treat surface of steel, suppress the element of process gas dissolve and be diffused in the non-process surface of steel simultaneously.

Accompanying drawing explanation

The feature of exemplary of the present invention, advantage and technology and industrial significance will hereafter describe by reference to the accompanying drawings, and in the accompanying drawings, identical Reference numeral represents identical key element, and wherein:

Fig. 1 illustrates to be suitable for implementing the concept map according to the frame form of the cementing plant of the steel making method of the first example embodiment of the present invention;

Fig. 2 is the temperature distribution of steel and the view for the treatment of condition, to illustrate according to the steel making method of the first example embodiment of the present invention;

Fig. 3 A is the skeleton view of steel before carburizing, with the steel making method shown in schematic diagram 1;

The skeleton view of steel when Fig. 3 B is carburizing and the position relationship between pyrolysis heater, with the steel making method shown in schematic diagram 1;

Fig. 3 C is the view of signal carburizing gas to the pyrolysis of the carburizing in the treat surface of steel and carburizing gas, with the steel making method shown in schematic diagram 1;

Fig. 3 D is the skeleton view of steel after carburizing, with the steel making method shown in schematic diagram 1;

Steel when Fig. 4 A is signal carburizing and the view of position relationship between pyrolysis heater, to illustrate according to the steel making method of a variation of the first example embodiment of the present invention;

Fig. 4 B is the skeleton view of steel after carburizing, to illustrate according to the steel making method of the described variation of the first example embodiment of the present invention;

Fig. 5 A illustrates to be suitable for implementing the concept map according to the frame form of the cementing plant of the steel making method of the second example embodiment of the present invention;

The view of steel when Fig. 5 B is signal carburizing and the position relationship between pyrolysis heater;

Fig. 6 A is the view of signal to the pyrolysis of carburizing in the treat surface of steel and carburizing gas, to illustrate according to the steel making method of the second example embodiment of the present invention;

Fig. 6 B is the side-view of steel after carburizing, to illustrate according to the steel making method of the second example embodiment of the present invention;

Fig. 6 C is the sectional view of Application way of signal steel, to illustrate according to the steel making method of the second example embodiment of the present invention;

Fig. 7 is the temperature distribution of steel and the view for the treatment of condition, to illustrate according to the steel making method of the 3rd example embodiment of the present invention;

Fig. 8 is the view according to relation between the concentration of the carburizing gas of validation test 1 and process gas temperature;

Fig. 9 is the view according to relation between the carburizing amount in the steel of validation test 2 and the concentration of carburizing gas;

Figure 10 A is the view of the relation between steel and pyrolysis heater;

Figure 10 B is the cross sectional photograph of converted steel;

Figure 10 C is the enlarged photograph of part c in Figure 10 B; With

Figure 10 D is the enlarged photograph of part d in Figure 10 B.

Embodiment

Hereinafter, the some example embodiment according to steel making method of the present invention will be described by reference to the accompanying drawings.Term " treat surface " in this specification sheets can be the part on the surface of steel, its will with process gas contact and dissolve in it and spread have process gas element (namely, the element of process gas dissolves and is diffused in the upper layer of steel), to obtain required character.On the other hand, term in this specification sheets " non-process surface " can be the part on the surface of steel, its be adjacent to treat surface and the amount of the element of the process gas wherein dissolved lower than the amount in treat surface.Therefore, non-process surface is not limited to the surface of the element of not dissolution process gas wherein.In addition, term " steel making method " in this specification sheets at least can comprise and to dissolve in its upper layer from the surface of steel and the element of DIFFUSION TREATMENT gas, and this front process also can comprise machining process if the thermoforming of steel or machining or forming process are as the press forming etc. of steel.

[the first example embodiment]

1. steel

Be the method for carburizing making steel carburizing according to the steel making method of this example embodiment.Be the steel comprising such as ferrite structure and pearlitic texture according to the steel of this example embodiment carburizing.In this example embodiment, use bloom (see Fig. 3 A, hereafter will describe).

The example of steel comprises chromemolybdenum steel (JIS standard: SCr415 to 435) and chromemolybdenum steel (JIS standard: SCM415 to 435) etc.But material is not confined to this especially, as long as carbon can be diffused in its upper layer from the surface dissolution of steel by carburizing.

2. cementing plant

In this example embodiment, prepare above-mentioned steel, then use the cementing plant 10A shown in Fig. 1 to this steel carburizing.This cementing plant 10A will hereafter briefly describe.Fig. 1 illustrates to be suitable for implementing the concept map according to the frame form of the cementing plant of the steel making method of the first example embodiment of the present invention.

As shown in fig. 1, be by steel 1a to be arranged in process furnace 11 and to make carburizing gas (process gas) G contact with the treat surface of steel 1a thus dissolve in its upper layer from the treat surface of steel 1a and spread the device of the carbon (a kind of element) of carburizing gas G according to the cementing plant 10A of this example embodiment.

More specifically, cementing plant 10A comprises process furnace 11.Carburizing well heater 13 is arranged in the inside of process furnace 11.Lagging material 12 is arranged in around carburizing well heater 13 so that the heat from carburizing well heater 13 does not escape into outside.Carburizing well heater 13 is surface for heating steel 1a and makes the carbon dissolution of carburizing gas and be diffused into the well heater in the upper layer of steel 1a.

Supply line 23 is connected to process furnace 11 so that the carburizing gas G from carburizing gas supply source 21 flows in process furnace 11 via flow regulation device 22.Some examples of carburizing gas be gas as acetylene gas, butane gas, propane gas and ethane gas, but use acetylene gas in this example embodiment.Acetylene gas will be described below, and it is the gas of pyrolysis easier than other gas, and is therefore the suitable gas in this example embodiment.

Meanwhile, vent line 31 is connected to process furnace 11 so that the carburizing gas G be supplied in process furnace 11 can discharge from process furnace 11.Drawdown pump 32 and pressure regulating device 33 are connected to the downstream side of vent line 31 in order.Drawdown pump 32 attracts carburizing gas G from the inside of process furnace 11, and pressure regulating device 33 regulates the pressure of process furnace 11 inside to predetermined pressure by regulating the amount of the carburizing gas of discharging.

Fixedly treat the fixture 14 of the steel 1a of carburizing and make the pyrolysis heater 15A of carburizing gas G pyrolysis be arranged in the inside of process furnace 11.Pyrolysis heater 15A will be described in more detail below.

3. steel method for carburizing (steel making method)

The cementing plant 10A shown in Fig. 1 is used to come steel 1a carburizing.Fig. 2 is the temperature distribution of steel 1a and the view for the treatment of condition, to illustrate according to the manufacture method of the steel 1a of the first example embodiment.Fig. 3 A to 3D is the view of the steel making method shown in schematic diagram 1.More specifically, Fig. 3 A is the skeleton view of steel 1a before carburizing.The skeleton view of position relationship when Fig. 3 B is carburizing between steel 1a and pyrolysis heater 15A.Fig. 3 C is signal carburizing gas G to the view of the pyrolysis of the carburizing in the treat surface 2a of steel 1a and carburizing gas G.Fig. 3 D is the skeleton view of steel 1A after carburizing.

First the block of steel 1a is prepared.In this example embodiment, as shown in fig. 3, the surface of steel 1a is provided as the treat surface 2a of the part on the surface of steel 1a, and in its upper layer, dissolves the carbon of predetermined amount from treat surface 2a by the process that will be described below.More specifically, in this example embodiment, the treat surface 2a being adjacent to steel 1a provides the non-process surface 3a of rectangular shape, and in its upper layer, dissolves the carbon of predetermined amount by the surface of process outside the 3a of this non-process surface of eliminating that will be described below.

Next, obtained steel is fixed to the fixture 14 of process furnace 11 inside.Here, above-mentioned pyrolysis heater 15A is the well heater of tabular, and it is corresponding with the shape of the non-process surface 3a of steel 1a, as shown in Figure 3A and 3B.When steel 1a is fixed to fixture 14, this pyrolysis heater 15A is arranged as towards non-process surface 3a.Pyrolysis heater 15A is designed to decompose carburizing gas G near the 3a of non-process surface, but is not designed to the dissolving being promoted carbon in carburizing gas G by the temperature that the non-process surface 3a of heating steel 1a is extremely high than other surface.

Next, (in heat-processed) heats the steel 1a be fixed as shown in Figure 2.More specifically, steel 1A is heated to the A being equal to or higher than steel by carburizing well heater 13 ₁transition point, be more preferably equal to or higher than A ₃the temperature of transition point (carburizing temperature), so that the ferrite structure of steel 1a and pearlitic texture are converted into austenitic structure.In this heat-processed, in process furnace 11, do not introduce carburizing gas G, and do not start pyrolysis heater 15A.In this example embodiment, heat steel 1a by carburizing well heater 13, but the steel 1a heated by another process furnace in advance also can be put in process furnace 11.

Next, as shown in Figure 2, (in cementation process) is to the steel 1a carburizing through heating.More specifically, make steel 1a remain on heated condition by carburizing well heater 13, and in process furnace 11, supply carburizing gas G from carburizing gas supply source 21 via flow regulation device 22.On the other hand, discharge some carburizing gas G via vent line 31 from process furnace 11 by drawdown pump 32 and keep constant with the concentration making carburizing gas G in process furnace 11 inside.

Pyrolysis heater 15A is started while furnace interior keeps this state.Now, by the heating temperatures on the surface of pyrolysis heater 15A to the temperature of carburizing gas G pyrolysis, or more preferably to the temperature of the temperature on the surface higher than the steel 1a through heating.As a result, the carburizing gas G around pyrolysis heater 15A can pyrolysis before it arrives the surface of steel 1a.

In this way, by the treat surface 2a making the carburizing gas G as process gas contact steel 1a, the carbon in carburizing gas G is dissolved in its upper layer from the treat surface 2a of steel 1a, as shown in FIG. 3 C.As a result, cementation zone 2A is formed in the inside of treat surface 2a.

Meanwhile, the carburizing gas G near the non-process surface 3a of steel 1A and towards the non-process surface carburizing gas G that advances of 3a by pyrolysis heater 15A pyrolysis.More specifically, in this example embodiment, use acetylene gas as carburizing gas G, thus acetylene gas resolves into carbon and hydrogen.As a result, the concentration of carburizing gas G around pyrolysis heater 15A becomes the concentration lower than around carburizing gas G, and the concentration of carburizing gas G near the 3a of non-process surface becomes lower than the concentration of carburizing gas G near the treat surface 2a of steel 1A.

In this way, the carbon in carburizing gas G can dissolve from treat surface 2a, suppresses the carbon in carburizing gas G to dissolve from non-process surface 3a simultaneously.As a result, the carbon of predetermined amount can be dissolved in the upper layer of the treat surface 2a of steel 1a, and the carbon dissolution in carburizing gas G can be suppressed in the non-process surface 3a of steel 1a simultaneously.

Although some are from the carbon diffusion that treat surface 2a dissolves, more carbon dissolves along treat surface 2a from inner.Therefore, the carbon dissolved in steel 1a spreads wherein, as shown in Figure 2 (in diffusion process).

More specifically, make steel 1a keep heating by carburizing well heater 13, interrupt carburizing gas G to the supply in process furnace 11, and discharged the carburizing gas G of process furnace 11 inside by drawdown pump via vent line 31.Now, rare gas element can be supplied as nitrogen, helium or argon gas in process furnace 11.Interrupt by the heating of pyrolysis heater 15A create this state in stove while.

As a result, the carbon be dissolved in the treat surface 2a of steel 1a can be diffused in its upper layer.In addition, carbon is less than the meltage of carbon from treat surface 2a from the meltage of non-process surface 3a, because the carbon that slightly dissolves near the surperficial 3a of non-process very fast diffusion is to wherein.

Then, (in process of cooling) by water-cooled or oil cooling by the steel cooling after diffusion so that the structure of the carbon wherein at least dissolved in steel 1a becomes martensitic structure from austenitic structure, as shown in Figure 2.Then can to the steel tempering of gained.

In this way, as shown in fig.3d, obtain the steel 1A that not only there is antiseepage carbon-coating 3A but also there is cementation zone 2A, element in described antiseepage carbon-coating 3A in carburizing gas G is inhibited to the dissolving in the 3a of non-process surface and diffusion, described cementation zone 2A by the dissolving of predetermined amount and the carbon be diffused in the upper layer of treat surface 2a formed.

4. the variation of the first example embodiment

Fig. 4 is the view of signal according to the steel making method of the variation of the first example embodiment.More specifically, Fig. 4 A is the view of steel when carburizing is shown and the position relationship between pyrolysis heater.Fig. 4 B is the skeleton view of steel after carburizing.

As shown in Figure 4A and 4B, in this variation, the steel through carburizing is vehicle input shaft 1b.As shown in Figure 4 A, input shaft 1b has step shaft portion 5.Gear part 5a is formed on the side in this axle portion 5, and flange portion 4 is formed on end on another side.

In this variation, the peripheral edge surface of flange portion 4 and upper edge thereof are divided into non-process surface 3a, and other surface is treat surface 2a.Make carburizing gas contact pairs surface 2a, and the carbon of predetermined amount is dissolved in its upper layer from treat surface 2a.

More specifically, as shown in Figure 4 A, by the non-process surface 3a with flange portion 4 (namely, its peripheral edge surface and upper rim) the corresponding ring-type pyrolysis heater 15B of surface shape be arranged in process furnace 11 inside to cover the non-process surface 3a of flange portion 4, and the carburizing gas near the 3a of pyrolysis non-process surface.

Input shaft 1B can be obtained, wherein cementation zone 2A inner to be formed to it from the surface as axle portion 5 grade of treat surface 2a, and antiseepage carbon-coating 3A (part near base material) is formed in as in the peripheral edge surface of the flange portion 4 of non-process surface 3a and upper rim thereof.The carbon amounts that the peripheral edge surface of flange portion 4 and upper rim thereof dissolve is less than other parts place, and the cracking thus caused because of the thermal strain of welding can be prevented at this portion.

5. another variation

In the first example embodiment, describe carburizing, but also can use such as nitrogenize or nitriding.More specifically, these process use ammonia as process gas.During nitrogenize, at 590 DEG C, heat steel at 480 DEG C, and during nitriding, steel is heated to 590 DEG C to 850 DEG C.

Then, the pyrolysis heater 15A shown in the first example embodiment (see Fig. 3 A and 3B) is used to make ammonia pyrolysis be nitrogen and hydrogen.As a result, by making ammonia contact with treat surface 2a, illustrating as carburizing, the nitrogen in ammonia dissolves from the treat surface 2a of carburizing gas G and is diffused in its upper layer.Meanwhile, by pyrolysis heater, the concentration of ammonia near the 3a of non-process surface is become lower than the concentration of ammonia near treat surface 2a.

In this way, cheap and without the need to troublesome work, the nitrogen solubilized of aequum is also diffused in the upper layer of the treat surface 2a of steel, suppresses the nitrogen in ammonia to the dissolving in the non-process surface 3a of steel 1a and diffusion simultaneously.In addition, combine in the carbonitriding of carburizing and nitrogenize wherein, two kinds of process gases are by identical method pyrolysis.

In addition, in the first example embodiment illustrated in FIG, pyrolysis heater 15A pyrolysis carburizing gas is used.Or, such as, the pyrolysis component formed by metal catalyst with pyrolysis heater 15A same shape can be prepared, and carburizing gas can be decomposed by this metal catalyst.In addition, metal catalyst also can be included in the surface of pyrolysis heater 15A.

Similarly, when using ammonia in nitrogenize or nitriding, Pt, Pd, Ir or Rh etc. can be used as metal catalyst.These metals can decompose ammonia at 550 DEG C at 1100 DEG C.As a result, the ammonia of non-process near surface can be decomposed, and carries out nitrogenize or nitriding to treat surface simultaneously.

[the second example embodiment]

Fig. 5 A illustrates to be suitable for implementing according to the concept map of the frame form of the cementing plant of the steel making method of the second example embodiment of the present invention, and the view of steel when Fig. 5 B is signal carburizing and the position relationship between pyrolysis heater.

Fig. 6 is the view of signal according to the steel making method of the second example embodiment.More specifically, Fig. 6 A is the view of signal to the pyrolysis of carburizing in the treat surface of steel and carburizing gas.Fig. 6 B is the side-view of steel after carburizing.Fig. 6 C is the sectional view of the Application way of signal steel.

Second example embodiment is from the different of the first example embodiment, and pending steel is weld bolt 1c, and the shape of pyrolysis heater 15C is different.Therefore, other structure with identical function is represented by identical Reference numeral, and will give part omission to the detailed description of these structures.

As shown in Figure 5 A, use the cementing plant 10B according to this example embodiment, carbon dissolution is also diffused in multiple weld bolt 1c of process furnace 11 inside, and carburizing gas G is by pyrolysis heater 15C pyrolysis.Here, as shown in Figure 5 B, pyrolysis heater 15C is the well heater of tabular.Multiple through hole 15a that the threaded portion being formed with weld bolt 1c in pyrolysis heater 15C is inserted through.Each through hole 15a enough large in case when weld bolt 1c is fixed by fixture 14 its not contact bonding bolt 1c (that is, there is gap between the edge of through hole 15a and weld bolt 1c).

This pyrolysis heater 15C is arranged in process furnace 11 the space 17 of process furnace 11 inside to be divided into process space 17a and non-process space 17b.Make each weld bolt 1c in the state of being fixed by fixture 14, the treat surface 2a of the threaded portion 6 of weld bolt 1c is arranged in process space 17a, and the non-process of the head 7 of weld bolt 1c surface 3a is arranged in the 17b of non-process space, as shown in FIG.Now, weld bolt 1c does not contact pyrolysis heater 15C.

Under this arrangement states, by carrying out from being heated to cooling a series of processes with same procedure illustrated in Figure 2.Here, in this example embodiment, in cementation process, as shown in FIG, by making carburizing gas G flow in process space 17a threaded portion 6 carburizing processing weld bolt 1c in the 17a of space.Meanwhile, the carburizing gas G advanced from process space 17a towards non-process space 17b is by pyrolysis heater 15C pyrolysis.

In this way, when carburizing gas G flows into the 17b of non-process space from process space 17a, carburizing gas G is decomposed by pyrolysis heater 15C, and thus the concentration of carburizing gas G in the 17b of non-process space can keep below the concentration of carburizing gas G in process space 17a.As a result, the carbon of aequum can dissolve and be diffused in the upper layer of the treat surface 2a of the threaded portion 6 of weld bolt 1c, suppresses carbon from the dissolving of the non-process of the head 7 of weld bolt 1c surface 3a and diffusion simultaneously.

When carburizing, even if there is weld bolt 1c in the multiple through hole 15a in pyrolysis heater 15C not by the through hole 15a of its insertion, when carburizing gas G passes through to non-process space 17b from process space 17a via this through hole 15a, some in this gas are also by pyrolysis.As a result, the concentration of carburizing gas G in the 17b of non-process space can keep below the concentration of carburizing gas G in process space 17a.

For the weld bolt 1C obtained in this way, also on the welding projection 7a of head 7, form antiseepage carbon-coating 3A, described antiseepage carbon-coating 3A suppresses the element of carburizing gas G to dissolve and is diffused in the 3a of non-process surface, as depicted in figure 6b.

Result, even if the welding projection 7a of the head 7 of weld bolt 1C melts and weld bolt 1C is soldered to steel plate 9, as shown in figure 6c, in this weld part 7b, the amount of carbon can not have a great difference with the amount of carbon in base material, and the cracking thus caused because of the thermal strain of welding 7b can be reduced.On the other hand, by dissolving and the diffusion of the carbon of required amount, will form cementation zone 2A on threaded portion 6, thus weld bolt 1C can be guaranteed in the intensity at threaded portion 6 place.

In this external second example embodiment, process gas can by metal catalyst pyrolysis, and can adopt nitrogenize or nitriding instead of carburizing, as above described in part " 5. another variation ".In addition, the carbonitriding of the combination as carburizing and nitrogenize can be adopted.

[the 3rd example embodiment]

Fig. 7 is the temperature distribution of steel and the view for the treatment of condition, to illustrate according to the steel making method of the 3rd example embodiment of the present invention.3rd example embodiment is different from the first example embodiment in the method for carburizing.Therefore, the description of common ground in addition will give part and omit.

As shown in Figure 7, in this example embodiment, carbon dissolution is also diffused in the steel 1a of process furnace 11 inside, alternately repeatedly performs cementation process and diffusion process simultaneously.More specifically, in cementation process, carburizing gas G is fed in process furnace 11, and in diffusion process, carburizing gas G is interrupted to the supply in process furnace 11, and discharges carburizing gas G from process furnace 11.In both cementation process and diffusion process, steel 1a is heated by carburizing well heater 13.In cementation process, pyrolysis heater 15A is activated and carburizing gas G is heated and pyrolysis, but in diffusion process, is interrupted by the heating of pyrolysis heater 15A.

In this way, in cementation process, the carbon in carburizing gas G dissolves from the treat surface 2a of steel 1a.On the other hand, in diffusion process, the dissolving of carburizing gas G is limited and vehicle 1 is in heated condition, thus once the carbon dissolved in cementation process can be diffused in the upper layer of steel 1a further.

As a result, carbon dissolves repeatedly and spreads, and thus the element of carburizing gas G can dissolve from treat surface 2a and be diffused in its upper layer.On the other hand, the carbon each time in carburizing gas G dissolves slightly from non-process surface 3a, and this carbon will from non-process surface 3a to its internal divergence, and thus the content of this element in the upper layer of non-process surface 3a can be reduced.

In addition, in diffusion process, the non-process surface 3a of steel 1a is not heated continuously by pyrolysis heater 15A, thus can reduce the heat effect of the part of the surperficial 3a of the non-process comprising steel 1a.This method is also applicable to nitrogenize or nitriding.

< validation test 1>

In validation test 1, prepare acetylene gas as carburizing gas, and verify the pyrolysis phenomenon of acetylene gas.More specifically, in stove, the acetylene gas that dividing potential drop is 100% is supplied under the flow of 20m/ minute, the temperature of inside heating furnace is set to 900 DEG C, 950 DEG C, 1000 DEG C, 1100 DEG C, 1200 DEG C and 1300 DEG C, and measure the concentration of now acetylene gas (carburizing gas), that is, the dividing potential drop of carburizing gas.Result is shown in Figure 8.Fig. 8 is the view according to relation between the carburizing gas concentration of validation test 1 and process gas temperature.In fig. 8, show carburizing gas dividing potential drop at different temperatures, the dividing potential drop of this carburizing gas at 900 DEG C is 100%.

From these results clearly, carburizing gas heating also pyrolysis, and the concentration of furnace interior carburizing gas raises along with furnace interior temperature and reduces.Passable from this result, carburizing gas G (acetylene gas) can use pyrolysis heater 15A by pyrolysis, and carburizing gas G can reduce in the concentration of the non-process near surface of steel 1a, as shown in fig. 1.

< validation test 2>

In validation test 2, prepare acetylene gas as carburizing gas, and verify carburizing gas (acetylene gas) concentration (dividing potential drop) and now in steel carbon dissolving between relation.More specifically, the chromium steel (JIS:SCr20) of long 50mm, diameter 18mm is prepared.Next, under the flow of 20m/ minute, supply the mixed gas that wherein nitrogen mixes with acetylene gas, make the dividing potential drop of acetylene gas be 30%, 50%, 70% and 100%, steel is heated to 950 DEG C, and measure carbon to the carburizing amount in steel.Result is shown in Figure 9.Fig. 9 is the view according to relation between the carburizing amount in the steel of validation test 2 and the concentration of carburizing gas.

As shown in Figure 9, be apparent that, carbon increases to the carburizing amount (meltage) in steel along with the increase of the concentration of the acetylene gas as carburizing gas.It can be said that, if use pyrolysis heater 15A pyrolysis carburizing gas G (acetylene gas) and carburizing gas G reduce in the concentration of the non-process near surface of steel 1a, then can reduce from the amount of the carbon of non-process surface dissolution.

Hereafter by an example, the present invention will be described.First, prepare a block length 50mm, diameter 18mm cylindrical steel (material: chromemolybdenum steel (JIS standard: SMC420)) as described steel.Next, the cementing plant 10A shown in Fig. 1 is used by the method shown in Fig. 7 to this steel carburizing.

More specifically, as shown in FIG. 10A, one piece of cylindrical steel 1d is arranged so that cylindrical pyrolysis heater (radiant tube heater) 15D is positioned at away from the side surface 3 millimeters of steel 1d.This pyrolysis heater is of a size of as follows: external diameter=400mm, internal diameter=300mm, height=200mm.

Next, in 5 minutes 15 seconds, steel is heated to 980 DEG C by pyrolysis heater, and repeats cementation process and diffusion process in order under those conditions such as shown in following table 1.Here, in cementation process, to supply acetylene gas in 100ml/ point of clockwise stove, and in diffusion process, interrupt the supply of acetylene gas, from stove, discharge acetylene gas and supply the nitrogen of same traffic.In addition, in cementation process and diffusion process, at 1200 DEG C, pyrolysis heater is heated continuously.Then, by 5 minutes used times, steel oil cooling to room temperature is come steel tempering.

[table 1]

Process	Temperature (DEG C)	Time (second)	Gas
				Carburizing	980	51	Acetylene gas
Diffusion	980	269	Nitrogen
				Carburizing	980	10	Acetylene gas
Diffusion	980	80	Nitrogen
				Carburizing	980	10	Acetylene gas
Diffusion	980	550	Nitrogen

Then the cross section of the cylindrical steel of gained is observed in microscope mode.Result is shown in Figure 10 B to 10D.Figure 10 B is the cross sectional photograph of converted steel.Figure 10 C is the enlarged photograph of part c in Figure 10 B, and Figure 10 D is the enlarged photograph of part d in Figure 10 B.

As shown in Figure 10 B and 10D, near pyrolysis heater steel upper layer in do not form cementation zone, but in the upper layer of other region place steel, really define cementation zone, as shown in Figure 10 B and 10C.It is believed that this is because near pyrolysis heater, the concentration of carburizing gas is reduced by pyrolysis because of carburizing gas.Also possibly, even if carbon dissolves in the region slightly, the carbon of this dissolving also can spread, result because carrying out diffusion process repeatedly between the circulation of cementation process, does not form cementation zone.

The aspect of the invention described above provides a kind of manufacture method of steel, pass through the method, cheap and without the need to troublesome work, the element of the process gas of aequum can dissolve and be diffused in the upper layer of the treat surface of steel, suppresses the element of process gas dissolve and be diffused in the non-process surface of steel simultaneously.

Although described example embodiment of the present invention in detail, the present invention has never been limited to these example embodiment.On the contrary, any one in all design change can be implemented in spirit of the present invention as disclosed in the claims.

Claims

1. wherein dissolve and spread the manufacture method of steel of the element having process gas, it is characterized in that described method comprises:

Heating steel (1a);

Described process gas is made to contact the surface of described steel so that the described element of described process gas is diffused into its upper layer from the described surface dissolution of described steel; And

Reduce the concentration of described process gas at non-process near surface, described non-process surface is the part on the described surface of described steel.

2. manufacture method according to claim 1, is characterized in that

The concentration of described process gas at described non-process near surface is reduced by processing gas described in pyrolysis.

3. manufacture method according to claim 2, is characterized in that

Described steel is arranged in process furnace (11) inner, heats described steel, and carry out the described pyrolysis of described process gas by pyrolysis heater (15A),

Described manufacture method also comprises:

Described pyrolysis heater is arranged as the described non-process surface of the described steel towards described inside heating furnace.

4. manufacture method according to claim 2, is characterized in that

Described steel is arranged in inside heating furnace, heats described steel, and carry out the pyrolysis of described process gas by pyrolysis heater (15C),

Described manufacture method also comprises:

By described pyrolysis heater, the space of the inside of described process furnace is divided into process space (17a) and non-process space (17b);

The described non-process surface of described steel is arranged in described non-process space;

Described process gas is made to flow in described process space; And

By the process gas that described pyrolysis heater pyrolysis is advanced from described process space towards described non-process space.

5. the manufacture method according to claim 3 or 4, is characterized in that described method comprises:

Described process gas is fed to the process in described process furnace; With

Interrupting described process gas to the supply in described process furnace discharges the process of described process gas from described process furnace, it is characterized in that

Repeat described process gas to be fed to the process in described process furnace and interrupt described process gas to the supply in described process furnace and discharge the process of described process gas from described process furnace.

6. manufacture method according to claim 5, is characterized in that

To discharge from described process furnace the process of described process gas to the supply in described process furnace at the described process gas of interruption, interrupt the heating of described pyrolysis heater.