JPH062034A - Heat treatment for fe-cr-ni-al ferritic alloy - Google Patents

Abstract

PURPOSE:To perform heat treatment for reducing the hardness of an Fe-Cr-Ni-Al ferritic alloy without causing embrittlement. CONSTITUTION:An Fe-Cr-Ni-Al ferritic alloy after plastic working is subjected, at 950-1200 deg.C, to soaking treatment satisfying the conditions in the following inequality X or Y [where T means treating temp. and (t) means treating time]: [950+250/(16t+1)] deg.C<=T<=[-1015+300/(t+1)] deg.C...X; [950+1100/(7 T+4)] deg.C<=T<=[-1015+300/(t+1)] deg.C...Y. Subsequently, slow cooling is done at <=10 deg.C/min cooling rate down to 650-800 deg.C, followed by rapid cooling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to Fe, which is suitable for the production of blades and abrasion-resistant parts having the hardness of ceramics and the strength of metals, as well as heater materials and exhaust gas parts for automobiles. The present invention relates to a heat treatment method for a -Cr-Ni-Al ferrite alloy.

[0002]

2. Description of the Related Art Ceramics or cemented carbide is generally used for cutting blades and wear resistant parts. However, the former ceramic has a very high hardness (Hv = 2000), but cracks and chips are likely to occur, while the latter cemented carbide is less likely to crack and chip, but the surface hardness is not sufficient compared to ceramics (Hv = 2000). = 700-150
0).

Therefore, the inventors have found that Fe--Cr--Ni--
Using an Al-based ferrite alloy, an alumina coating is deposited on the surface by heat treatment in an oxidizing atmosphere to obtain a wear resistant material that has both the surface hardness of ceramics and the strength of metal. Thought. The alumina coating also provides resistance to oxidation. However, there are the following problems. Usually, Fe-Cr-Ni-Al ferrite alloy is subjected to plastic working such as rolling, and then post-processing such as punching and bending is performed according to the shape of the part, and then alumina coating is formed. However, the hardness of the alloy is high due to NiAl finely dispersed and precipitated in the alloy, and the post-processing cannot be easily performed.

Fe-Cr-Ni-Al plastically worked
It is conceivable that the ferrite ferrite alloy is once heat-treated (annealed), the alloy hardness is lowered at the time of post-processing, and then the heat treatment is performed again to increase the hardness after the alumina coating formation process. However, even if the hardness of the alloy is lowered by the heat treatment for annealing, the alloy becomes embrittled, and as a result, another problem arises that processing defects such as cracks occur in the post processing. In the heat treatment for annealing, the heat treatment causes coarsening of ferrite crystal grains and embrittlement at 475 ° C. peculiar to high Cr steel.

[0005]

In view of the above circumstances, an object of the present invention is to provide a heat treatment method capable of reducing the hardness of a Fe-Cr-Ni-Al ferrite alloy without embrittlement.

[0006]

In order to solve the above problems, in the case of the alloy heat treatment method according to the present invention, 950 to 1200 is applied to the Fe-Cr-Ni-Al ferrite alloy which has been plastically worked. The following formula X at a temperature of ℃
Soaking condition (T: processing temperature, t: processing time) that satisfies the condition of [950 + 250 / (16t + 1)] ° C ≤ T ≤ [1015 + 300 /
(T + 1)] ℃ ・ ・ X After that, at a cooling rate of 10 ℃ / min or less, 650 ~ 800 ℃
After slowly cooling to the temperature of 1 to 1 at the temperature of 650-800 ℃
After soaking for less than an hour, it is cooled rapidly. Then, regarding the soaking treatment at a temperature of 950 to 1200 ° C. (T: processing temperature, t: processing time),
It is preferable to satisfy the condition of the following formula Y.

[950 + 1100 / (7t + 4)] ° C. ≦ T ≦ [10
15 + 300 / (t + 1)] ° C .... Y The present invention will be described in more detail below. In the case of the present invention, the Fe-Cr-Ni-Al-based ferrite alloy (hereinafter, simply referred to as "ferrite alloy") is first subjected to plastic working such as hot, warm or cold forging and extrusion rolling. Form thin plates suitable for processing. Then, the ferritic alloy that has been plastically worked is
Soaking is performed at a temperature of ~ 1200 ° C. The soaking treatment is a heat treatment performed in the state where the entire ferrite alloy to be treated (surface and inside) has the same temperature rising temperature.

This soaking treatment causes defects caused by plastic working, namely, relaxation of work strain of ferrite crystal grains, anisotropy relaxation of fine ferrite crystal grains, and anisotropy relaxation / grain shaping (shape and shape of NiAl grains). This is done to adjust the size), and to relax the strain at the interface between ferrite crystal grains and NiAl grains. When the temperature is 950 ° C. or higher, the NiAl grains stretched by plastic working and deformed into a linear or flat plate become coarse due to solid solution / reprecipitation and change into a round bar or a sphere, which causes anisotropy of the NiAl grains. Will be alleviated. Besides, ferrite crystal grains and NiA
As the atomic diffusion occurs between the l grains, the strain at the interface between the two grains is also relaxed. At the same time as the anisotropy of the NiAl grains is relaxed, the strain and anisotropy of the ferrite crystal grains themselves are also relaxed. The defects of the worked structure caused in the structure by the plastic working are eliminated. However, when the soaking temperature exceeds 1200 ° C, the NiAl grains, which improve hardness, rapidly disappear as a solid solution in the base material, and coarsening of ferrite crystal grains cannot be suppressed, and the temperature is lowered to 1200 ° C or less. NiA along with
Although l is re-precipitated, NiAl is also precipitated at the ferrite grain boundaries at this time, resulting in embrittlement of the alloy.

In the case of soaking at a temperature of 950 to 1200 ° C., the temperature is not higher than the complete solution temperature but it is thermally activated due to the high temperature, and NiAl violates solid solution / reprecipitation in the ferrite matrix phase. Is repeating. Although the solid solution rate / reprecipitation rate of NiAl is a function of temperature, the precipitation rate is larger, and NiAl grains having a certain size from the beginning become coarse (average particle size of several μm). On the other hand, although nucleation of new NiAl grains is occurring in the ferrite matrix phase, the NiAl nuclei having a small grain size are unstable at a high temperature and cannot grow large. While suppressing the increase in hardness,
Therefore, it becomes possible to eliminate defects in the processing structure.

In the soaking treatment at 950 to 1200 ° C., the processing temperature T (° C.) and the processing time t (hr) must satisfy the following formula X. [950 + 250 / (16t + 1)] ° C ≦ T ≦ [1015 + 300 /
(T + 1)] ° C..X It is better to lengthen the soaking time at low temperature and shorten the soaking time at high temperature. If the soaking time is low at a low temperature, defects in the work structure cannot be resolved, and the alloy hardness will not decrease. If the soaking time at a high temperature is too long, the NiAl grains and ferrite crystal grains become excessively large, and alloy embrittlement occurs, which easily causes cracking during processing.

In the soaking treatment at 950 to 1200 ° C., the processing temperature T (° C.) and the processing time t (hr) are preferably in the range of the following formula Y. [950 + 1100 / (7t + 4)] ° C ≤ T ≤ [1015 + 300 /
(T + 1)] ° C ··· In the case of soaking treatment that satisfies the Y X formula, the post-processing is rolling punching or bending in the direction parallel to the rolling direction (same direction) of straight bending (bending in the same direction) ) Does not cause cracking, but cracking occurs in bending in the direction perpendicular to the rolling direction (bending in the direction perpendicular to rolling) or embossing. Only sufficient improvements can be made for specific post-processing. In the case of soaking that also satisfies the Y formula, cracks do not occur even in the direction perpendicular to the rolling or embossing. Not only the suitability for cold shearing and compression shearing such as press punching, but also the suitability for cold rolling right-angle direction bending, embossing, and other processing involving bending and tensile deformation will be improved.

After soaking at 950 to 1200 ° C., the temperature is lowered, but it is not cooled as it is, but it is gradually cooled to a temperature of 650 to 800 ° C., usually 650
Soaking is performed at a temperature of 800 ° C. At this time, 9
Gradually cool from a temperature of 50 to 1200 ° C. to a temperature of 650 to 800 ° C. at a cooling rate of 10 ° C./minute or less. The soaking treatment after gradual cooling is not essential, and the gradual cooling may be followed by rapid cooling without soaking treatment. This is because the hardness of the alloy does not become sufficiently low when the temperature is lowered at a cooling rate higher than this. That is, when the temperature is lowered from 950 to 1200 ° C. to 650 to 800 ° C. at a cooling rate of 10 ° C./minute or less,
Compared with the case of quenching at a cooling rate of over 0 ° C./minute, the former produces less NiAl grains of 1 μm or less, and as a result, the required hardness can be reduced. This is NiAl with a grain size of 1 μm or less during slow cooling.
It is speculated that this is because the grains grow larger and the generation of fine NiAl grains is hindered accordingly. Usually 5
A cooling rate of about 8 ° C./minute is preferable. The lower the cooling rate, the greater the decrease in hardness, but at about 1 ° C./minute, the effect of hardness decrease becomes saturated and energy is wasted. .

The temperature range of 650 to 800 ° C. is
This is because if the temperature is lower than 650 ° C, the alloy becomes brittle.
This is because if the temperature exceeds 00 ° C, the effect of decreasing the hardness does not sufficiently appear. In terms of ensuring sufficient reduction of alloy hardness, 6
It is preferably in the range of 50 to 750 ° C. The treatment time for soaking is within 1 hour. This soaking treatment reduces the amount of fine NiAl grains and makes it possible to achieve a sufficient hardness reduction. The effect of soaking is 1 treatment time
Even if saturation is reached in time and further processing is not expected, the effect cannot be expected to increase, and the amount of energy consumed only increases, so the processing time is set to 1 hour or less.

Then, rapid cooling is performed. Fe-
It rapidly passes through the embrittlement temperature range (about 400 to 550 ° C.) of a Cr-Ni-Al ferrite alloy, causing σ embrittlement and 475
Do not allow embrittlement at ° C. As the rapid cooling method, normal air cooling that is left in a room temperature atmosphere, forced air cooling using a fan or a blower, or the like is used. Water cooling is not recommended because it may cause thermal stress cracking.

In this way, the heat-treated alloy is post-processed to prepare it into a predetermined shape, and then it is usually heat-treated at about 1100 to 1350 ° C. in an oxidizing atmosphere to obtain α
Forming an alumina coating. After forming the alumina coating, the alloy hardness is increased by rapid cooling or the like. Next, the reasons for limiting the content of the elements contained in the Fe-Cr-Ni-Al ferrite alloy that is the raw material will be described.

The alloy of the present invention is a Fe-based alloy containing a large amount of ferrite-forming elements Cr and Al and austenite-forming element Ni, and the reason why the alloy is mainly in the ferrite phase is as follows. is there. Ferrite phase alloys tend to form a dense alumina (Al ₂ O ₃ ) film that is dense and has good adhesion to the substrate by oxidation heat treatment, but austenite phase alloys do not form an alumina film uniformly and peel off. Because.

[Cr: 20-40 wt%] Cr is necessary for forming a dense and uniform alumina film on the alloy surface, but since the alloy of the present invention contains Ni,
In order to make the alloy into a ferrite phase, Ni is the lower limit value of A
Even when 1 is the upper limit value, 25 wt% or more of Cr is required. Ni content is lower limit, Al content is near upper limit, Cr content is 2
If the alloy content is less than 5% by weight, the formation of alumina film is incomplete. Therefore, the lower limit of Cr is 25 wt%. Further, since the tendency of embrittlement increases as the Cr content in the alloy increases, the upper limit of Cr is 35 wt%.

[Ni: 10 to 25 wt%] Ni is presumed to precipitate fine NiAl in the alloy to improve the mechanical properties (eg, hardness) of the base material, but in the coexistence with Al. Is an essential element for precipitating NiAl. 15 to be effective enough to improve mechanical properties
Requires more than wt% Ni. If the amount of Ni increases, N
Although it is convenient for the precipitation of iAl, if the content of Ni which is an austenite forming element is increased, C
It is necessary to increase the content of r and Al. However, if the Ni content exceeds 25 wt%, the Cr content must be increased, and if this is the case, embrittlement easily occurs, so the upper limit of Ni is 25 wt%.

[Al: 4-8 wt%] Al is a fine N
It is an essential element for precipitating iAl in the alloy and for forming an alumina film on the alloy surface by high temperature oxidation treatment. In order to form a dense and uniform film,
It is necessary to contain 4 wt% or more of Al. An increase in the Al content is advantageous for the precipitation of NiAl and the formation of an alumina film, but if it exceeds 8 wt%, the workability of the alloy decreases, so the upper limit of Al is 8 wt%.

[Any one or more of Zr, Y, Hf, Ce, La, Nd and Gd: 0.05
Each of these elements is added as necessary, and is mixed in the aluminum film to improve the brittleness of the film and to be dispersed as internal oxide particles in the alloy immediately below the film. And significantly improves the adhesion of the film. In order to exert these effects, it is preferable to contain 0.05 wt% or more. On the other hand, if the content exceeds 1 wt%, the workability of the alloy will drop sharply, so the upper limit is 1 wt%.
Is.

[Any One or Two or More of Ti, Nb and Mo: 2% by Weight or Less] Each of these elements is also added as necessary, and is mixed in the aluminum film to form a film. It has the effects of improving the brittleness of the alloy and dispersing it as internal oxide particles in the alloy immediately below the coating to remarkably improve the adhesiveness of the coating. However, if the content exceeds 2% by weight, the alloy characteristics are deteriorated, so the upper limit is limited to 2% by weight.

[Fe: Remainder] In addition to the above components, Fe occupies. However, it is not limited to the case where the balance is completely Fe, and there may be inevitable impurities (such as Si) present in Fe. The use of the Fe-Cr-Ni-Al ferrite alloy with an alumina coating obtained by the method of the present invention is to fix the inner blade, outer blade, and clipper blade of an electric razor that requires abrasion resistance and corrosion resistance. It can be applied to blades such as blades and movable blades, shafts such as electric tools, mechanical parts such as chucks and gears, valves for internal combustion engines or corrosive atmospheres. However, the application is not limited to these.

[0023]

According to the heat treatment method for a ferrite alloy according to the present invention, since the heat treatment conditions are appropriate, it is possible to eliminate fine Ni particles from the grains in the alloy and strains between the grains caused by plastic working.
The precipitation of Al grains is suppressed and relaxed, and as a result, the hardness of the alloy can be reduced without embrittlement of the alloy.

The method of the present invention is easy to carry out without any difficulty because it only requires an operation of appropriately setting the heat treatment temperature and the treatment time.

[0025]

Embodiments of the present invention will be described below. It goes without saying that the present invention is not limited to the following embodiments.
In the examples, columnar ingot alloys 1 and 2 having the following compositions were used. [Alloy 1] Cr: 26.0 wt% Ni: 15.0 wt% Al: 4.5 wt% Zr: 0.2 wt% Y: 0.6 wt% Ti: 0.5 wt% Balance: Fe [ Alloy 2] Cr: 35.0 wt% Ni: 21.0 wt% Al: 7.0 wt% Zr: 0.3 wt% Balance: Fe-Examples 1 to 13-Alloy 1 is vacuum melted and hot Two types of thin plates having a thickness of 0.3 mm and a thickness of 3 mm were obtained by extrusion, hot rolling, and hot rolling. In other words, a ferrite alloy thin plate that has undergone plastic working was obtained. The base metal hardness of this thin plate is about Hv =
It was 450.

The alloy thin plates were heat-treated under the temperature change shown in FIG. 1 under the specific conditions shown in Table 1. The temperatures T1, T2, t1, in FIG. 1 and Table 1 are
t2 is as follows. T1: soaking temperature at 950 to 1200 ° C t1: soaking time at 950 to 1200 ° C α: cooling rate from 950 to 1200 ° C to 650 to 800 ° C T2: soaking temperature at 650 to 800 ° C t2: Soaking time at 650 to 800 ° C. The base metal hardness of the thin plate after the heat treatment was sufficiently reduced to about Hv = 290 in all cases.

After the heat treatment, the 3 mm thin plate was post-processed by cold rolling to a rolling reduction of 60%.
Also, for a 0.3 mm thin plate, the reduction amount is 70
%, And the punching was performed using a press die for bending at right angles to the rolling under conditions of a bending radius of 0.4 R and a bending angle of 80 °, bending in the same direction of rolling, and embossing. The presence of cracks after cold rolling, bending, embossing and punching was examined. The results are shown in Table 2.

[0028]

[Table 1]

[0029]

[Table 2]

-Comparative Examples 1 to 12-Heat treatment was carried out under the conditions shown in Table 3 which deviate from the conditions of the present invention, and post-processing and crack investigation similar to those in Examples 1 to 13 were performed. Table 4 shows the results of the examination for cracks.

[0031]

[Table 3]

[0032]

[Table 4]

-Examples 14 to 26-Alloy 2 was vacuum melted, hot extruded, hot rolled, and hot rolled into two kinds of thin plates having a thickness of 0.25 mm and a thickness of 3 mm. In other words, a ferrite alloy thin plate that has undergone plastic working was obtained. The base metal hardness of this thin plate is about Hv
= 550.

The alloy thin plates were heat-treated under the temperature change shown in FIG. 1 under the specific conditions shown in Table 5. The temperatures T1, T2, t1 in FIG. 1 and Table 5 are
t2 is the same as above. The base metal hardness of each thin plate after the heat treatment was sufficiently reduced to about Hv = 340.

After the heat treatment, the 3 mm thin plate was post-processed by cold rolling to a rolling reduction of 60%.
In addition, for a thin plate of 0.25 mm, the cold reduction amount is 7
Rolling was performed to 0%, and bending was performed in a direction perpendicular to rolling under the conditions of a bending radius of 0.4 R and a bending angle of 80 °, bending in the same direction of rolling, and embossing were punched using a press die. The presence of cracks after cold rolling, bending, embossing and punching was examined. The results are shown in Table 6.

[0036]

[Table 5]

[0037]

[Table 6]

-Comparative Examples 13 to 24-Heat treatment was carried out under the conditions shown in Table 7 which deviate from the conditions of the present invention, and the same post-processing and crack investigation as in Examples 14 to 26 were carried out. Table 8 shows the results of the examination for cracks.

[0039]

[Table 7]

[0040]

[Table 8]

From the results of investigations on the presence or absence of cracks in Examples and Comparative Examples, it is well understood that the heat treatment according to the present invention sufficiently enhances the workability in the post-processing. In addition, in FIG. 2, Examples 1-26 and Comparative Examples 9-13 and 22 are shown.
The temperature and time of soaking at temperatures of 950 to 1200 ° C. of ˜26, the treatment time on the horizontal axis and the treatment temperature on the vertical axis, 950 + 250 / (16t + 1), 1015 + 300 / (t +
1), 950 + 1100 / (7t + 4) and three curves were plotted. Examples 1 to 8 and 14 to 21 satisfy both of the above X and Y expressions, whereas Examples 9 to 13 and 22 to 2 satisfy
6 Only the above formula X is satisfied, and it is well understood that the results of crack inspection are met.

The correspondence between the plotted points in FIG. 2 and the numbers of the examples and comparative examples is as follows. A .. Examples 1 and 14 B .. Examples 2 and 15 C .. Examples 3 and 16 D .. Examples 4 and 17 E .. Examples 5 and 18 F .. Examples 6 and 19 G. -Examples 7 and 20 H-Examples 8 and 21 I-Examples 9 and 22 J-Examples 10 and 23 K-Examples 11 and 24 L-Examples 12 and 25 M- Example 13, 26 a .. Comparative example 9, 22 b .. Comparative example 10, 23 c .. Comparative example 11, 24 d .. Comparative example 12, 25 e .. Comparative example 13, 26

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the treatment time and the treatment temperature in the heat treatment of the present invention.

FIG. 2 is a graph showing the temperature and time of soaking in Examples and Comparative Examples as expressed by X.
-It is a graph that is plotted together with the curve in Y.

[Explanation of Codes] T1 soaking temperature at 950 to 1200 ° C t1 soaking time at 950 to 1200 ° C α cooling rate from 950 to 1200 ° C to 650 to 800 ° C T2 soaking temperature at 650 to 800 ° C t2 Soaking time at 650-800 ℃

Claims (4)

[Claims] 1. A Fe—Cr—Ni— which has been plastically worked.
In the method of heat treating an Al-based ferrite alloy,
Soaking (T: processing temperature, t: processing time) satisfying the condition of the following formula X is performed at a temperature of 0 to 1200 ° C., and [950 + 250 / (16t + 1)] ° C. ≦ T ≦ [1015 + 300 /
(T + 1)] ℃ ・ ・ X After that, at a cooling rate of 10 ℃ / min or less, 650 ~ 800 ℃
After slowly cooling to the temperature of 1 to 1 at the temperature of 650-800 ℃
A heat treatment method for a Fe-Cr-Ni-Al ferrite alloy, which comprises soaking for less than or equal to time and then quenching. 2. A soaking treatment (T: treatment temperature, t: treatment time) at a temperature of 950 to 1200 ° C. satisfies the condition of the following formula Y: [950 + 1100 / (7t + 4)] ° C. ≦ T ≦ [1015 + 300 /
(T + 1)] ° C .... Y The heat treatment method for the Fe—Cr—Ni—Al ferrite alloy according to claim 1. 3. The Fe- according to claim 1 or 2, wherein after being gradually cooled to a temperature of 650 to 800 ° C., soaking is carried out at a temperature of 650 to 800 ° C. for 1 hour or less and then rapid cooling. A heat treatment method for a Cr-Ni-Al ferrite alloy. 4. An Fe-Cr-Ni-Al ferrite alloy comprising Cr: 20 to 40% by weight, Ni: 10 to 25% by weight, Al: 4 to 8% by weight, Zr, Y, Hf, Ce, L.
Any one or more of a, Nd and Gd: 0 to 1.0% by weight, any one or more of Ti, Nb and Mo: 0 to 2% by weight, and the balance: F
The heat treatment method for an Fe-Cr-Ni-Al ferrite alloy according to any one of claims 1 to 3, which has a composition of e.