JPS58130269A - Manufacture of soft-nitrided article having large hardening depth - Google Patents

Abstract

PURPOSE:To obtain a soft-nitrided article having a large hardening depth by hot working a steel blank contg. specified amounts of C, Si, Mn, Cr, V, N and Sol. Al at a temp. above the A3 point, cooling the hot worked blank at a specified surface cooling rate or below from 800 deg.C to 500 deg.C, and soft-nitriding it. CONSTITUTION:The composition of a blank to be worked is composed of, by weight, 0.15-0.35% C, <0.35% Si, 0.6-1.3% Mn, 0.7-1.5% Cr, 0.05-0.5% V, 0.006-0.02% N, 0.02-0.1% Sol.Al and the balance Fe with inevitable impurities. To the composition may be added one or two among 0.04-0.13% S, 0.03- 0.35% Pb and 0.001-0.01% Ca. The blank is suitably hot worked at a temp. above the A3 point, subjected to controlled cooling at <=2 deg.C/sec surface cooling rate from 800 deg.C to 500 deg.C, and soft-nitrided.

Description

[Detailed Description of the Invention] Akihiro Motoki, soft nitrided article, 41K, soft nitrided and has a large hardening depth at 9 and IIi, Oi from the surface to the main part! A method for manufacturing a nitrocarburized article that provides a medium-gradient hardening curve.

11 soft-nitriding companies, below the transformation point, generally 570℃l! For example, in a cyanide salt bath, RX gas (a
This is a surface hardening method in which the material to be treated is subjected to heat treatment (heat-generated denatured gas) or heat-generated denatured gas (heat-generated denatured gas) to infiltrate some carbon along with nitrogen into the steel to harden the surface layer. It is one type.

The ζO method differs from the carburizing-quenching method because it does not cause distortion in the worn footwear, and does not require a long time like the nitriding method, so it is suitable for use in mechanical parts, etc. However, the suitable steel type for nitrocarburizing is not yet fully developed, and the 011K process is still insufficient.

The desired properties can be obtained through nitriding treatment.

For example, JI8SCM43 is conventionally used as steel for soft nitriding.
5 (0,35C-0,75Ml1-1.1Cr-0,
2Me)4'aACM645 (0,45C-0,4
81-1,5Cr-0,2Mo) is often used, but in the case of SCM435 steel, the effective hardening depth after soft nitriding and hardening is small Vickers iI! The distance from am corresponding to H Mars 00) is at most 0.10 m at one time, and the surface hardness Ii top and bottom 25 fits and the minute Vickers hardness i5> does not exceed ＠50, so the fatigue strength SACM645 t) 1. A large amount of L and Cr were added to improve the nitriding properties by improving the defects such as ζO and ζO, which were not satisfactory in terms of wear resistance.
For 1 go, use nitrocarburizing treatment! I! Image hardness is Hv80
Although the hardness is very high at 0 to 1100, the effective hardening depth and expansion height are small at 0.15 x 8i degrees, so the hardness gradient from the surface to the core is too steep. Articles such as gears and bearings that are operated under high loads, such as rounding, hardening parts and cores
The phenomenon of peeling from near the boundary of the film was less likely to occur, and the pitting resistance or spalling resistance was poor.

According to the findings of the present inventors, under normal soft-nitriding treatment conditions, the am hardness is 50 or higher, and the effective hardening is t.
o, 2■ or more, the fatigue strength and abrasion resistance are improved, and at the same time, the hardness of the bare surface is improved by H muff 5.
By setting KII411ij to 0 or less and increasing the hardness of the base, the hardness gradient from the 11th surface part to the core part can be made gentler, and the resistance to scratching and cracking can be improved. J song has been improved considerably.

In view of this situation, the inventors of the present invention have conducted extensive research and have succeeded in obtaining copper for soft nitriding that has excellent fatigue strength and wear resistance, as well as pitting resistance and spalling resistance. Limited Express No. 56-167881, No. 56-1
67882 and Oka No. 56-167883), and after further research, he discovered that the optimal steel structure during soft nitriding treatment is a ferrite + pearlite structure near the surface. Complete your invention.

That is, Mizumoto@sha, KCr to obtain the desired surface hardness.
In order to adjust the amount of addition of M and M, and to soften the OH gradient from the surface, V, which is effective in increasing the hardening depth, is added to the tzu rattan, and at the same time, due to the coexistence effect with V, the core The essential feature is that the soft nitriding treatment is performed on nine copper products by combining a steel composition with a specified amount of N in the steel that is effective for improving the hardness of the steel, and a fe2ite + pearlite structure near the Il box. do.

Herein, one aspect of the present invention is that C: 0.15 to 0.35%, Sl
: 0.35% or less, Mn: 0.60 to 1-30
%, Cr: more than 0.70-1.50511, V: 0.05-0.50-. 5o144: o, o
2~0.101! , N: 0.006-0.020
Chi, moreover, IKI, 8:0.04-0.131G.

Pb: 0.03~0.35 s>! HiCa: 0.
0010 to 0.50 - Types 01 and 9 of the steamed buns contain two or more types, and the processed material has a composition consisting of residual sF and Fukamiyu impurities.The processed material is appropriately heated on the fish body and then cooled. L when you do? 800℃, 5oot and 0 temperature am cooling rate f2℃
A soft-nitrided article OVa with a large hardening S0, characterized by controlled cooling at a speed of less than /second and then soft-nitrided treatment.
In addition, when processing the processed material having the same steel composition as above and heating it on the fish body to smooth the hook, cool the temperature between 800C and 500°C at a moderate rate of 2°C/sec. This is a method for producing a soft nitrided article that is hardened and is characterized by the following: controlled cooling, followed by soft nitriding.

In the present invention, as mentioned above, the structure in the vicinity of am, for example within about 1 inch below the surface, is treated with ferrite+ having good soft-nitriding properties.
According to the present invention, hot rolling is carried out after hot working such as Kusha forging, or by heating on a point plate. The article surface cooling rate after normalizing is limited to 2°C/sec or less between 800°C and 500°C. Due to the round steel weave thus obtained, coupled with its fixed steel composition, the article nitrocarburized by the method according to the invention exhibits excellent nitrocarburizing properties.

The original f! As can be easily understood from the purpose of Ao, the above-mentioned "processed material" includes not only general plate steel or steel bar, but also all materials that are processed into the shape of IIky#. "Soft-nitrided products" includes general steel products that are not only subjected to nitrocarburizing, but are ultimately used after being nitrocarburized.Next, the steel used in the method according to the present invention is S itself whose composition is limited within the above-mentioned range will be described.

C: C is the basic component of rounding to ensure strength, and a minimum of 0.15 inches is required for rounding to ensure core strength.

However, if it exceeds 0.35 inch, the core O ductility and toughness will decrease, and the cutting PIIJ property, cold workability, and S weldability will decrease, as well as the soft nitriding*0* hardness and hardening resistance. It becomes comfortable to wear. Therefore, the lower limit of C1k in the present invention is 0.15
11. The upper limit was set to 0.35 S.

81: 81 is usually added as a deoxidizing agent, or is an element that inhibits carburization. Even in soft-nitriding, where carburization and nitriding proceed simultaneously, the less 81 is, the better the hardening properties are, and the greater the hardening depth. is obtained.

In particular, when Si becomes 0.35 S or less, the effect increases, so in this wA, the upper limit of S and St is set to 0.
351 Toshi9, 19, Sl is an element that is harmful to Il collapsibility, Il vibration heat affected zone toughness, and cold workability.%
If the value exceeds KO, 10-, these characteristics will rapidly deteriorate and become thinner. In the 709th year, the upper limit of S1 lid is 0.1'・Oman.

11ix: Mlk is indispensable as a deoxidizing agent during copper manufacturing, and is also effective on % core 0**@toughness O meat, and is rumored to have a minimum of 0.60 to ensure the performance of soft-nitrided products. is necessary. However, if it exceeds 1.30%, the machinability begins to deteriorate significantly, so the lower value is set to 0.6011, and the upper limit is set to 1.30%.
30- Closed.

Cr: Cr is an extremely effective element that increases the surface hardness and increases the hardening depth by combining with the N intruded by nitrocarburizing. For K to fully exhibit its effect, an amount of OCr exceeding 0.70 is required, but 1. If it exceeds l$O-, the O soft-nitrided product under normal soft-nitriding sensitive layer conditions: 11-face hardness becomes H Muff 50 or higher, and the upper limit is set to 1.50-9.

■: V combines with intruded N and C by soft nitriding to precipitate moldy vanadium carbonitrides, K! lI
Improves surface hardness and am depth.

In particular, compared to V acr K, the contribution to the increase in hardness is relatively small, but the contribution to the increase in hardening stress is large. In addition, since ■ increases the hardness of the core by precipitation hardening, the hardening effect is deep, and the i! It is a very effective element for obtaining a hardening curve with a gentle gradient.

At least 0.05 in order to fully realize the effect of KM.
-Although it is necessary, if it exceeds 0.50%, the effect of the child will be saturated or even begin to decrease, so the upper limit of 0.05 was set to 0.501 A.

l・1. AL: ) d also combines with intruding N like Cr to increase the surface hardness, but it is not very effective in improving the hardening depth.When combined with 41KV, 0.10% or more of On is added. When added, the hardening effect is rather reduced.

However, even a small amount of addition is effective against ****.
Since at least 0.02- is required to ensure a minimum SSO or higher, it is best to set the lower limit to 0.02% and the upper limit to 0.10-.

N: Nd fine grain size refinement, which improves the toughness of the core, and when coexisting with T- produces V and O-containing food, K causes precipitation hardening, which increases the core hardness. The improvement also increases by 4 hours. At least o and oos- are necessary to cause such precipitation hardening. but,
If it exceeds 0.02011+, an excessive amount of Ca1l oxide is generated, resulting in rapid deterioration of cold workability and core SO toughness.
, h was set to 0.02011i.

S + Pb + Ca: These components are effective in improving machinability when cutting is performed before soft-nitriding treatment. When deep hole drilling, heavy cutting, high-speed cutting, etc. are performed before soft-nitriding treatment, one type of these elements or 211 or more of these elements can be contained depending on the degree of machinability required. These ingredients have no effect on the curing properties.

The minimum amount added to improve the machinability of structural steel is:
S: 0.041, Pb: 0.03'jl,
Ca: 0.0010-theal. ttas is 0.131g,
If Pb #i exceeds 0.351, it is inevitable that the strength and toughness will decrease. On the other hand, it is difficult to add Ca for more than 0.0100 s due to melting, so the lower limit for S is set to 0.04%.
, the upper limit is o, 13 points, the lower limit is 0.03 o, the upper limit is o for pb, the lower limit is 0.001 for 35-1Ca.
0%, and the upper limit is set to 0.0100-.

According to the present invention, a processed material having such a steel composition is A
After heating to the s point or above, perform appropriate hot processing such as hot forging 1 bending, or after appropriate processing, heat from 800°C to 5°C.
Controlled cooling is performed by cooling between 00°C and a surface cooling rate of 2°C/second or less. In the present invention, when the steel composition is specified as described above, a ferrite+perdite structure suitable for nitrocarburizing is formed near the surface by the controlled cooling.

When the above surface cooling rate exceeds 2°C/sec and is rapidly cooled,! A rutinsite structure or a bainite structure is generated, and the hardening depth obtained by nitrocarburizing is insufficient, making it impossible to obtain satisfactory fatigue strength and pitting resistance. Therefore, in the present invention, the above-mentioned Limit surface cooling rate to 2°C/sec or less.

＼ When cooling, the cooling rate is fastest near the surface. Rutincytic bile tissue develops in the middle pancreas. In addition, in order to secure the shape and accelerate cooling, bainite may be formed on some surfaces due to hot processing or hot lI & salt water injection. Therefore, in order to prevent the formation of such bainite or martensite, the cooling after hot rolling is controlled at the cooling rate of the product in this IA process.

Note that if the vicinity of Table (3) is a ferrite + pearlite structure, the interior is also a ferrite + pearlite structure, but in the present invention, L, as already mentioned, and N addition The required core rigidity is maintained by the alloy composition 1llII11, which includes optimization of the amount.

Thus, according to the present invention, a product (article) to be soft-nitrided, such as a car, in which a ferrite structure having excellent soft-nitriding properties evenly leaks out near the surface can be obtained. Such products are then subjected to further cold working (e.g., forging, drawing, cutting F!N) to obtain the final shape, and then nitrocarburized, but the previous structure is the same as described above. It is determined by the cooling rate during piece cooling after hot working or normalizing. Therefore, according to the present invention, by suitably processing the processed material having the above-mentioned composition to the final shape and then nitrocarburizing it, a nitrocarburizing product exhibiting excellent nitrocarburizing properties as described above can be obtained.

Note that the soft nitriding treatment employed in the present invention is not particularly limited and may be any commonly practiced treatment, but preferably, for example, ammonia gas and RX gas (volume ratio 1:
This method uses the mixed gas of 1) and processes at 550 to 600°C for 1 to 6 hours.

Next, the present invention will be further explained by examples.

EXAMPLE 1 100 kgf steel of each steel type having the steel composition shown in Table 1 was heated to 1250° C. and hot rolled to obtain a 100 square billet. Using this as a processed material, the following two types of processing and controlled cooling were performed.

(1) This example shows an example of the as-hot forged material, in which the processed material was heated to 1250°C and the heat-forged material was heated to TI.
A round bar with an IL diameter of 25 mm was forged at 1000°C. Upon cooling from this finishing temperature! ! The temperature range of 800°C to 500°C was adjusted to 1.5°C by adjusting the cooling rate and achieving cooling within the heat insulation cover, air cooling, air cooling, and spray cooling. Cooling was performed at a surface cooling rate of θ~5.0°C/sec.

Thereafter, it was cold machine cut to a diameter of 24.5 m.

(2) This example shows an example in which normalizing is performed after the heat treatment.The above processed material is heated to 1250℃ and hot forged into a round bar with a diameter of 25cm.The finished material is forged at a temperature of 1000℃. did. Air cooled in the air from this finishing temperature to the highest temperature. Next, it was heated to 900°C for normalizing. At 1 o'clock in this normalizing process, the surface cooling rate was adjusted during cooling from the above normalizing temperature, and cooling within a heat insulating cover, air cooling, air cooling, and spray cooling were carried out, and the temperature reached 800°C. ~50
Temperature range t-1 of 0°C, cooling is possible at a surface cooling rate of 0 to 5.0°C/sec. Thereafter, it was cold machine cut to a diameter of 24.5 mm.

Furthermore, among the steel machines shown in Table 1, fI type 4 Arashi 1 to 13 have steel compositions within the scope of the present invention, while steel types UG14 to 2 have steel compositions within the scope of the present invention.
0Fi, has a steel composition outside the range H of the present invention, and also has a steel &N1
21 and 22 are copper corresponding to JIS-8CM435 and JIS-8ACM645, respectively.

Next, the steel bar with a diameter of 24.5-0 obtained in this way was
When corroding with a nital corrosive solution for 1 s and examining the metallographic structure of the steel bar surface, the temperature was 570°C for 4 hr.

NHa:RX-1: Endothermic modified gas (
RX gas), the surface hardness & micro Vickers hardness at a depth of 25 am from the surface) and the effective hardening depth and micro Vickers hardness of 1 (distance 1 m from the I! surface corresponding to v500) were applied. ) was scooped up. (These results are summarized in Tables 2 and 3.

As such, any product that has a steel composition within the range of the present invention and that is cooled at a predetermined surface cooling rate after hot working or normalizing has a ferrite and pearlite structure, Effective hardening depth after soft nitriding treatment is α2
111 or more, and the surface hardness is stable at 50 to 75G, showing a value of 9.

The Vickers hardness (H) at a depth of 1s11 from the hard core surface was 180 to 30G, which caused no practical problems.

On the other hand, even if the steel has a composition within the scope of the present invention, the K after hot working or during conditioning cooling after normalizing.

KFi when cooled at a surface cooling rate exceeding 20°C/sec
, martensite structure is mixed in bainite,
The effective hardening depth after soft nitriding decreases rapidly and is all α2
■It turns out that the following is true.

In addition, regarding steel types N114 to 22 as comparative examples,
Even if the structure is a ferrite + amount-light structure, the effective hardening depth due to soft electrification treatment 1 is less than α2- or the surface hardness is Hv65.
9, which was outside the appropriate range of 0-750.

Thus, the present invention makes it possible to obtain, for the first time, a soft nitrided product exhibiting excellent soft nitriding properties, such as an effective hardening depth after soft nitriding of α2- or more and a surface hardness H of 50 to 750.

Claims (1)

[Claims] (1) C: 0.15-0.35 capsules, 81:0
．． 35- or less. Mn: o, a O~1.30-, Cr: 0.70
More than m and less than 1.50. V: 0.05-0.501G, N: 0.0
06-0.020-. sol,, U: 0.02~0.10% - further as required, S: 0.04~0.13%, Pb-0,03~
0.35 and Ca: 0.0010-0.010
0'j! A processing material containing one or more of the above, and having a composition consisting of residual sF and unavoidable impurities, is appropriately processed at one or more hot points and then cooled at 800°C and 500'C. A method for manufacturing a soft nitrided l& footwear article with a large hardening depth, in which the surface cooling rate is controlled to be 2° C./second or less, and then soft nitrided II & hardening is performed. (1) C: 0.15-0.351s, St: 0.35%
below. Ml: 0.60-1.30%, Cr: 0.70
More than % and less than 1.8011. V: 0.03~0.50'3G, N: 0
．． 006-0.020-. 5elj4: 0.02-0.101G. More must! According to 8: 0.04-0.1311, Pb: 0.
03-0.351 and Ca: 0.001G=0.
01001GO 1lltt contains 2 or more types. When a processed material having a composition consisting of the remainder F and unavoidable impurities is suitably processed and then heated onto the fish body for normalizing, the cooling rate of IIw is 2°C/sec between 800°C and 500°C. A soft nitriding crystal OS method with a large hardening depth, which is characterized by adjusting cooling and then performing a soft nitriding treatment.