JPS59193214A - Preparation of steel used in parts for constituting transmission apparatus - Google Patents

Abstract

PURPOSE:To inexpensively prepare steel used in the parts for constituting a transmission apparatus excellent in various characterisics, by a method wherein an alloyed steel composition containing C, Mn, Si, V, Al and S in a specific composition is subjected to hot forging or rolling while the forged or rolled steel composition is subjected to nitriding treatment after cooling. CONSTITUTION:An alloyed steel composition containing 0.35-0.65% C, 0.6-1.5% Mn, 0.15-0.35% Si, 0.1-0.3% V, 0.01-0.05% Al and 0.5% or less S as chemical components is subjected to hot forging of rolling while the forged or rolled steel composition is further subjected to nitriding treatment at about 500-600 deg.C for about 20hr in an NH3-gas atmosphere after cooled under a proper condition to obain steel used in parts for constituting a transmission apparatus constituted of light load gear parts such as an initial speed reducing gear having high strength and tenacity in the core part thereof and high dimensional accuracy. In this case, if necessary, surface hardness during nitriding can be obtained by further containing 1.0-1.5% Cr and, is impurities, Ni is pref. limited to 0.25% or less. Mo to 0.10% or less, Cu to 0.35% or less and P to 0.050% or less, respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing steel for transmission device components, typified by light load gear parts such as the initial reduction gear of an engine.

In general, light-load gear parts such as the initial reduction gear of an engine require a certain degree of surface and core strength and toughness from the viewpoint of durability, transmission efficiency, noise, etc., and also require high dimensional accuracy. Strict physical property conditions are imposed.

For example, for a certain initial reduction gear, the surface hardness HR/jr
Ng3 or more, HV'130, teno hardening depth 0.7-0.
/.

Seal and core hardness HRC, 20~? 5 is required.

In order to meet these demands, various methods have been tried in the past. Among these methods, the method of using carbon steel or alloy copper with a relatively high carbon content as a periphery has the advantage that it can be manufactured at low cost, but there is a high risk of quench cracking in gears with fine pitches, and it also has problems with hardness distribution and precision. It is difficult to expect co-stable quality.

In addition, the method of carburizing low carbon alloy steel (-) followed by quenching and tempering is widely used, but the treatment temperature is qoo°C.
Due to the above-mentioned height, there is a limit to the dimensional accuracy, which is one of the causes of machine noise.

On the other hand, in the method of manufacturing light-load gear parts by nitriding, these parts require a high degree of durability and strength, so a certain degree of core strength and a relatively deep nitrided layer are required. Therefore, the general manufacturing method for these is to heat a highly hardenable alloy steel containing Cr, MO% AI, etc., such as SCM-based or SACM-based low to medium carbon steel, to a specified level. After hardening, a method is adopted in which the material is machined and then heated in an ammonia gas atmosphere to about SθO to 600° C. to form a nitrided layer on the surface layer to obtain high surface hardness.

However, in the above method, heat refining is required as a pretreatment to obtain core strength, and at the same time, high hardenability is required depending on the mass of the part, which increases the material cost and nitriding. The problem is that it takes a long time to process.

In view of the above circumstances, this invention was made as a result of intensive research aimed at developing a method for producing steel for transmission device components that satisfies all of the above conditions. This type of steel is already being put into practical use because it allows the quenching and tempering process to be omitted.However, by selecting an appropriate chemical composition range for this non-tempered steel, it is possible to have excellent nitriding properties. Based on this knowledge, they completed a method for manufacturing steel for components of transmission devices. According to this invention, it is possible to manufacture light-load gear parts of the intended initial reduction gear in a short time with low material costs.

Specifically, this invention includes C: 0.3g-0.4g%,
Mn: 0, /, ~/, 5%, St: 0. /! 3:
~0.3. ! r%, V; 0. /~0.3%,
Al: o, ot~o, os%, s; After hot forging or rolling, an alloy steel composition containing all chemical components of o, ot to o, os%, s is cooled under appropriate conditions and further subjected to 9ization treatment. be.

Here, the addition ratio of C in the chemical components was set as an appropriate range for obtaining a predetermined strength.

In addition, Mn is added to act as a deoxidizing agent and to ensure strength by reinforcing ferrite, but if the S content is low, Mn exceeds 5%, and the stiffness decreases. Therefore, the upper limit was set to /, 5%.

Si is added as a deoxidizing agent and a ferrite-strengthening element, and its addition ratio was determined as a general range for the steelmaking process.

S is generally treated as a harmful impurity, but its upper limit f O
，! It was set as i%.

Next, V is added to give strength to the product during the cooling process after hot rolling or hot forging and to improve nitriding properties.For that purpose, the addition ratio is reduced to 0. ．． /~0.3% range.

The reason for setting the addition ratio fO,/% or higher is to obtain a predetermined nitriding depth and surface hardness.

That is, in order to increase the nitriding depth,
■, MO, etc. are said to be effective, but the effect of the addition ratio of V on V-based non-thermal treated steel has been investigated using Cr-MO-based SCMIIIO, which is conventionally used as a standard steel for light-load gear parts.
(+/) ) and SACM 411 & (+5) (Table 1 and Figures 1 to 3 below).

Table 1 shows the chemical component ratio of samples +1 to +6 and 30φ
After forging and stretching into a bar material //! This shows the mechanical properties when the car body is allowed to cool after being reheated to 0℃ and held for 1 hour, and the surface hardness and core hardness when nitriding is performed at 525℃ for 2 hours and 1Ig hours. , +1 to +4 are non-tempered steels, and 4
-4 indicates that the V amount is too low, and +1 indicates that the V amount is somewhat high.

1st, - figure is 2jt "C" to the left of +1 to +6 in Table 1.
Figure 3 shows the relationship between nitriding depth and hardness when nitriding is carried out for /hour, pg hours. ;, 2s
The nitriding treatment at 0.degree. C. is shown in terms of the relationship between the nitriding treatment time and the nitriding depth.

According to the above results, when V; θ and OA are approximately 4% (≠4), the nitriding depth is deeper in SCM++θ. At about 0.70% (+5) of V2, an effect exceeding that of SCM '1170 was obtained, and from this point, V2 of 0.10% or more is required.

tev;0. ．． Comparing 20% (+2) and v; o, 33%, the more V there is, the deeper the layer is obtained, but generally the depth required for nitrided parts is 0.7 to 0. V: 0.2 to 0.3% is sufficient to obtain this value. When the entire nitriding treatment is performed for a long time, ■;0. There is no difference in nitriding depth by 0.3% for flatheads (Figures 1! and 2).

In addition, for hard core type, in most cases HRC No. 0 to 30
However, in some cases, the HRCB is about 35 and the hardness is slightly higher than 8C.

According to Table 1, if HRC is about 20 to 30, V;
θ, 01-% (+4) is also possible, but HRC,
Cannot meet the demands of 2J to 3.5 8 However, if it is necessary for o, lo or above, HRC, 2J to 3
It can also meet the demands of about 5.

The addition rate of 10,000 ■ is θ. The first ball launch was 3% or less.
In order to obtain the required nitriding depth of 0, / to o, s as described above, V: 0.30% is sufficient, and from the viewpoint of economy, the upper limit is set at 0.30%. .

In addition, the second reason 1d is that the lower limit of elongation required for conventional fermentation-loaded gear parts steel is 1f or 10 for 70 yen.
Regarding the V:0. , for j:lch (≠1), the lower limit is 5
Therefore, in order to set the lower limit of elongation to around 70%, the upper limit of (2) is set to 0.30 inches.

On the other hand, the darkness of AI does affect the hardness of the inner surface when it is turned into - (see Figure 3), but the effect is not much different below θ. On the contrary, when the amount of A] increases, the precipitation hardening ability of V is impaired due to the formation of AIN, and embrittlement progresses due to the increase in the oxidized compound layer, so the amount of Al added is required as a deoxidizing agent. The content is 0, O/~O, OS%
And so.

Note that Cr is related to the surface hardness during nitriding, so if it is particularly required, it may be added in the range of 0 to 7.5.

Further, pSNi, MO, and cu are not intentionally added, but considering that they are included as impurities in the manufacturing process, the upper limits are set as follows: P: 0.05%, Ni: 0.05%. Section 5, Mo:
O,/%, Cu; 0. Jj%.

After hot forging or rolling, the alloy steel composition as described above is cooled under appropriate conditions.

For example, the temperature range of 700 to 1.00℃ is S to 700℃/
Cool by air cooling, etc. at a cooling rate of 100 min.

Thereafter, nitriding treatment is performed using a normal method. For example, the nitriding treatment is performed by reheating to SOO to 1.00° C. in an ammonia gas atmosphere. Then, during the nitriding process, the conventional SCM μda 0 (+6), SACM4113 (+5
) required nearly 50 hours of nitriding time to obtain a product with a predetermined nitriding depth, but with this invention, a product with a predetermined nitriding depth can be obtained with a nitriding process of approximately I hours ( (See Figure 3), but according to the present invention, there is no need for alloy components for hardenability, it is possible to use cheaper materials, and at the same time, the quenching and tempering steps can be reduced. Since it can be omitted and the nitriding time is shortened due to improved nitriding properties, the manufacturing process of steel for transmission device components such as light-load gear parts can be simplified.

Examples of this invention will be shown below.

Example 1 (1) Sample components, heat treatment history, and hardness The sample components, heat treatment history, and hardness used in this example are shown in Table IIIU below.

Table 2 (2) Hardness gradient of nitrided layer
This figure shows the hardness gradient from the surface of the nitrided layer when gas nitrided for 5 hours.
When the depth of is taken as the nitriding depth, (cL) is 0.3! ;r
trm, (b) is 0.23tttyn, (b)) is (
The nitriding depth was approximately HaS times that of b).

FIG.
) is nitrided at 525° C. for 175 hours, and shows the hardness gradient from the surface of the nitrided layer. According to this, although (C) has a high surface hardness, the nitriding depth does not increase unexpectedly, and the invention steel (α)
inferior to. Therefore, as in the present invention, the surface hardness HR/! ;Ng! It is clear that the present invention is the most suitable method for parts requiring a hardness of about r or more, as it can achieve the desired nitriding depth in the shortest time.

In addition, the thickness of the compound layer on the surface of both samples during the above-mentioned is waiting time lIgq was less than .mu.m, and did not pose any problem.

(3) Nitriding time Figure 6 shows the nitriding depth and nitriding time at HV'130i at 525°C for the test pieces of the invention steel (cL), S CM 1tllO steel (b), and SACMAqS steel (C). Although this shows the relationship, it is clear that in (α) using the method of the present invention, a deep nitrided layer can be obtained in the same time compared to (b) and (c).

EXAMPLE 1 The surface hardness, core hardness, hardness gradient, etc. of gear scavenge pump driven gears having the following alloy steel compositions are shown when nitriding is performed.

(1) Alloy steel composition (2) Nitriding material (c) Heating temperature:! ; 2J°C, heating time; 2/hour (b) Heating temperature: 5.25°C, heating time; 72 hours (
3) Results The results of the nitriding treatment are shown in Table 3 below. According to this, the steel of the present invention was able to obtain superior results compared to the conventional SCM 't'lO steel in terms of surface hardness, hardness gradient, and hardness depth. , Table 3

[Brief explanation of the drawing]

The first figure shows samples +1 to + shown in Table 1 in the specification.
Figure 3 shows the relationship curve between nitriding depth and hardness when -6 is nitrided for -1 hour and l1g time under the temperature condition of 5.25℃, respectively.
Figure 4 shows the relationship curve between nitriding time and nitriding depth when nitriding is performed under a temperature condition of 25°C. , S is a diagram showing the hardness gradient from the surface of the nitrided layer when gas nitriding is performed at 11-℃ for 1 hour.
Invention steel (α), SCMvao steel (b) 1 by the same method as above.
．． Figure 4 shows the hardness gradient from the surface of the nitrided layer when a test piece of SACM14 steel (c) was gas nitrided at SSS°C for ttg hours.
FIG. 3 is a diagram showing the relationship between the nitriding depth up to KV II3θ and the nitriding time at 515-°C for test pieces of tθ steel (b) and SACMAjS steel (C). 7 Figure 4-73- Figure 6'J 10 20 3 (J 4
(Between J and LJ1 and O and σγ (between e1)

Claims (1)

[Claims] fil C; 0.3! t~0. A! r%, Mn
”, 0.A ~/, sq6, SiO, / & ~0.3
5%, V:0. / ~0.3%, Al; o, o/~0
．． 05%, S:0. 1. A method for producing steel for transmission device components, which comprises hot forging or rolling an alloy steel composition containing chemical components of jt% or less, cooling it under appropriate conditions, and further subjecting it to nitriding treatment. (2) The manufacturing method according to claim (1), wherein the transmission device is comprised of light-load gear components such as an initial reduction gear. (3) The manufacturing method according to claim (1) or (2), wherein the alloy steel composition contains Cr;/, θ~/, S%. (4) Alloy steel composition is Ni; 0.25% or less, Mo'', 0
．． /θ chi or less, cu; o, 3s% or less, P; 0.050
% or less, the manufacturing method according to claim '(1) or (2).