JPH0637669B2 - Method for manufacturing hot forged non-heat treated parts with small variation in mechanical properties - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a hot forged non-heat treated part having a small variation in mechanical properties.

[Prior Art] Most of the mechanical parts used in the fields of automobiles and industrial machinery are a process of quenching and tempering (tempering) cutting after machine structural steel is processed into a rough-shaped material by hot forging. Although it has been manufactured through the above process, a so-called non-heat treated steel for hot forging has recently been developed that can secure sufficient strength and mechanical properties such as toughness even if the heat treatment after hot forging is omitted. , Its practical application is spreading.

As a prior art related to the present invention, there is Japanese Patent Application No. 62-279058 (Japanese Patent Application Laid-Open No. 1-123031) filed by the present applicant (November 6, 1987), which is cold or hot. It is related to a heat-treated steel for which a tempering process is performed after forging in between, and foam is used as a cooling medium at the time of cooling in the quenching and tempering tempering process.

[Problems to be Solved by the Invention] By the way, such a non-heat treated component that is used while being cooled after hot forging has a complicated shape, uneven surface roughness, and
Due to the effect of non-uniformity of scale adhesion, the cooling rate was not uniform, resulting in large variations in mechanical properties between parts. Therefore, it has been a cause of impeding the practical application of non-heat treated steel.

[Means for Solving the Problems] The present inventors have completed various inventions in order to solve the above problems. That is, the present invention is as follows: (1) wt% C: 0.02 to 0.15%, Si: 0.10 to 1.00%, Mn: 0.60 to
3.00%, Cr: 0.50 to 3.00%, Ti0.010 to 0.050%,
B: 0.0005 to 0.0050%, Al: 0.01 to 0.05%, N: 0.01
Non-heat treated steel bar for hot forging, which contains 20% or less and the remaining is essentially unavoidable impurities and Fe, is heated to a temperature of 1300 ° C or less to perform hot forging, and then obtained by adding a foaming agent to water. Moisture content 0.
It is a method for producing a hot forged non-heat treated part having a bainite structure having a small variation in mechanical properties, which is characterized in that it is cooled in a foam of 01 to 60 g / 100 ml.

If the toughness and strength of the forged parts are required, 0.50% or less of M is added to the composition of the non-heat treated steel bar for hot forging described in (1) above.
It is effective to add o, 2.0% or less of Ni and 0.30% or less of V or Nb.

(2) C: 0.18 to 0.55%, Si: 0.10 to 2.00%, Mn: 0.60 to
2.00%, Cr: 1.00% or less, V: 0.03 to 0.20%, S: 0.
01 ~ 0.10%, N: 0.0030 ~ 0.020%, Al: 0.01 ~ 0.06
%, And the balance is substantially unavoidable impurities and non-heat treated bar steel for hot forging made of Fe is heated to a temperature of 1300 ° C or lower to perform hot forging, and then obtained by adding a foaming agent to water. Water content 0.
It is a method for producing a hot forged non-heat treated part having a ferrite-pearlite structure and a small variation in mechanical properties, which is characterized by cooling in a bubble of 01 to 50 g / 100 ml.

In addition, if the toughness and strength of the forged part are required, 0.03 to 0.2 is added to the component of the non-heat treated steel bar for hot forging described in (2) above.
It is effective to add one or two of 0% Nb and 0.005 to 0.07% Ti.

[Operation] The technical constitutional requirements of the present invention will be described below.

The chemical composition is an important factor that influences the mechanical properties of the obtained non-heat treated parts, and each element must be controlled within the range described below. First, the composition range of the non-heat treated bar steel for hot forging of claims (1) and (2) will be described.

C is necessary to adjust the strength and toughness of the obtained non-heat treated part, and if it is less than 0.02%, it is necessary to add an extremely large amount of alloying elements to obtain the required strength, which is not economically advantageous. Also, if added in excess of 0.15%, the toughness of the parts will be reduced and must be avoided.

Si is an element necessary for deoxidation and adjustment of strength, and is 0.10% for deoxidation.
The above is necessary. Also, if 1.00% is added as the content, the strength will be too high and must be avoided.

Mn is an element that controls the deoxidation and hardenability of steel and affects the strength and toughness of the obtained parts. If it is less than 0.60%, its effect is not sufficient, while if it exceeds 3.00%, it is difficult to manufacture. As the machinability increases, the strength becomes too high and the machinability also deteriorates, so this must be avoided.

Cr, like Mn, is an element that controls the hardenability and affects the strength and toughness of the obtained parts. If it is less than 0.5%, its effect is not sufficient, and even if it exceeds 3.00%, the strength is high. It's just too much, so you have to avoid it.

Ti is necessary to fix N in steel and effectively work B,
If less than 0.010%, the effect is not sufficient, and 0.05%
If it is added over the range, not only will it not be possible to obtain further effects, but the toughness will decrease, so this must be avoided.

B is an element for improving the hardenability of steel and saving expensive alloying elements. If it is less than 0.0005%, the effect cannot be sufficiently obtained.
If it exceeds 0.005%, it is uneconomical and impairs toughness, so it must be avoided.

Al is an element necessary for deoxidizing steel and preventing coarsening of crystal grains.
If it is less than 0.01%, the effect of deoxidation is not sufficient, and if it is added in excess of 0.05%, no further effect can be obtained, so it was excluded from the scope of the claims.

N combines with B in the steel and impairs the effect of improving the quenching of B, so it must be kept low. The limit is 0.0120%, and if this amount is exceeded, the toughness will decrease and must be avoided.

Like Mo, Mo is added to adjust the strength and toughness, so 0.50% or less is added.

Ni is mainly added to improve the toughness, and the amount required for this is 2.0% or less.

V and Nb are elements for suppressing the coarsening of crystal grains, contributing to precipitation hardening and controlling the strength and toughness of the material, and are added in an amount of 0.3% or less.

Next, the reasons for limiting the composition range of the non-heat treated bar steel for hot forging of claims (3) and (4) can be extended.

C is an element that controls the strength and toughness of non-heat treated parts. If it is less than 0.18%, the required strength cannot be obtained, and if it exceeds 0.55%, the strength becomes excessively high and the toughness also decreases, so it must be avoided. I have to.

Si is an element necessary for deoxidizing steel and adjusting strength, and is 0.10%.
If the amount is less than the above, a sufficient deoxidizing effect cannot be obtained, and if it exceeds 2.00%, the strength becomes too high and decarburization on the surface becomes remarkable, so that it must be avoided.

Mn is an element that controls the deoxidation and hardenability of steel and affects the strength and toughness of the obtained parts. If it is less than 0.06%, its effect is not sufficient, while if it exceeds 2.00%, it causes However, it is necessary to avoid it because the strength of the steel becomes too high and the machinability deteriorates.

Cr, like Mn, is an element that controls the hardenability and affects the strength and toughness of the obtained parts. If added in excess of 1.00%, the strength will be too high and must be avoided.

S is an element that imparts machinability. If it is less than 0.01%, its effect is not sufficient, and if it is added over 0.10%, toughness decreases and anisotropy of material properties increases, so S must be avoided.

N is an element that exists as VN or AIN, suppresses the coarsening of crystal grains during hot forging, or precipitates during forging cooling, and affects the strength and toughness of parts. If less than 0.0030%, the effect cannot be expected, and even if 0.020% or more is added,
Since no further effect can be obtained and manufacturing difficulty is increased, it is excluded from the scope of the claims.

Al is an element necessary for deoxidizing steel and preventing coarsening of crystal grains.
If it is less than 0.01%, the deoxidizing effect is not sufficient, and if it is added in excess of 0.06%, no further effect can be obtained.

V is an element necessary for increasing the hardness and ensuring the strength of parts by cooling during the cooling process after hot forging. If it is less than 0.03%, the effect is not sufficient. Must be avoided because it rises too much and the toughness deteriorates.

Nb is an element for suppressing the coarsening of crystal grains, contributing to precipitation hardening and controlling the strength and toughness of the material.If added in an amount of less than 0.03%, its effect is not observed, while even if added in excess of 0.20%,
It must be avoided as it will become too hard and will only impair toughness.

Ti is also an element for controlling the coarsening of crystal grains, contributing to precipitation hardening and controlling the strength and toughness of the material, and if it is added in an amount less than 0.005%, its effect is not recognized, while if it is added in excess of 0.07%, It must be avoided as it will become too hard and will only impair toughness.

The heating temperature during forging of parts in claims (1) to (4) is 1300.
If the temperature exceeds ℃, it is necessary to avoid it because it causes remarkable coarsening of crystal grains, deteriorates toughness, increases hardenability, and causes variations in hardness.

Cooling after forging water content 0.01 to 60 g / 100 ml (claim 1,
The inventors have found that the reason why variations in mechanical properties are reduced by carrying out in 2) and 0.01 to 50 g / 100 ml (claims 3 and 4) is as follows.

First, even if the foam, which is a cooling medium, has an appropriate fluidity and the cross-sectional shape of the material to be heat treated is different, the portion with a large heat capacity and a large amount of heat radiation consumes a large amount of foam, and Since more foam is supplied as compared with the part, the cooling rate is less likely to be affected by the change in the external shape of the material to be heat treated as in the conventional heat treatment method.

Secondly, since bubble cooling is a boiling heat transfer, when the material to be heat treated is at a high temperature, vapor is generated between the material to be heat treated and the cooling medium as in the conventional cooling method using cold water or hot water. Although there is no change in the presence of a film, foam cooling means that cooling can be uniformly obtained by significantly increasing the thickness of the vapor film (boundary film).

Accordingly, the inventors have found that the foam cooling can be uniformly cooled without being affected by the surface properties of the material to be heat-treated, particularly the thickness of the scale, the adhered state or the surface roughness such as unevenness, and achieved the invention.

Therefore, the water content of foam, which is the cooling medium in claims (1) and (2), is
It is necessary to use it in the range of 0.01 to 60 g / 100 ml. This water content range is a condition for obtaining the cooling rate obtained when naturally cooling in a round bar of 20 to 70 mmφ in air to cooling in hot water or cold water.

To obtain the cooling rate obtained when cooled in hot water or cold water, it can be achieved by stirring the foam or by directly injecting the foam onto the object to be cooled to increase the supply amount of the foam.

If the water content is less than 0.01 g / 100 ml, the cooling rate is too slow to obtain the required strength, while if it exceeds 60 g / 100 ml, the cooling rate is too high, the strength becomes too high, and the toughness deteriorates. Must be avoided.

Further, the water content of the foam, which is the cooling medium in claims (3) and (4), is 0.
It must be used in the range of 01-50g / 100ml. This water content range is a condition for obtaining a cooling rate obtained when a 20-70 mmφ round bar is naturally cooled in air or slightly forcedly cooled in air.

If the water content is less than 0.01 g / 100 ml, the cooling rate is too slow to obtain the required strength, while if it exceeds 50 g / 100 ml, the cooling rate is too high, the strength becomes too high, and the toughness deteriorates. Must be avoided.

It is necessary to use a surfactant or a water-soluble polymer as a foaming agent for performing foam cooling. This is because when a surfactant is used as a foaming agent, the surfactant is adsorbed on the gas-liquid surface to reduce the surface tension and increase the surface viscosity,
Improves foamability, foam size or uniformity, stability, etc. during foam formation, and when a water-soluble polymer is used, these mainly improve the surface viscosity or surface elasticity of the gas-liquid surface and stabilize the foam. It is by generating.

As the surfactant, a water-soluble organic compound such as a fatty acid salt or a higher alcohol sulfate ester which is adsorbed on the gas-liquid surface to reduce the surface activity can be used.

As the water-soluble polymer, a natural or synthetic water-soluble polymer such as starch or polyvinyl alcohol can be used.

[Examples] The present invention is further described below with reference to Examples of the present invention. Note that (1) to (3) of the embodiments correspond to claims (1) and (2), and the embodiments (4) to (6) correspond to claims (3) and (4).

Example 1 A steel having the chemical composition shown in Table 1 was prepared to have a diameter of 70
mm rolled steel bar. This steel bar was forged into an automobile shaft component under the conditions shown in Table 2. The hardness of the obtained parts was measured and the results are shown in Table 2. As can be seen from the table, the variation in hardness of the non-heat treated forged parts obtained by the method of the present invention is extremely small.

Example 2 A steel having the chemical composition shown in Table 3 was used to form
65 mm rolled square steel was used. This square steel was forged into undercarriage parts for automobiles under the conditions shown in Table 4. The hardness of the obtained parts was measured and the results are shown in Table 4. As can be seen from the table, the variation in mechanical properties of the non-heat treated forged parts obtained by the method of the present invention is extremely small.

Example 3 A steel having the chemical composition shown in Table 5 has a diameter of 80
mm rolled steel bar. This steel bar was forged into undercarriage parts for automobiles under the conditions shown in Table 6. The hardness of the obtained parts was measured and the results are shown in Table 6. As can be seen from the table, the variation in mechanical properties of the non-heat treated forged parts obtained by the method of the present invention is extremely small.

Example 4 A steel having the chemical composition shown in Table 7 was prepared by a conventional method to obtain a diameter of 70
mm rolled steel bar. This steel bar was forged into automobile shaft parts under the conditions shown in Table 8. The hardness of the obtained parts was measured and the results are shown in Table 8. As can be seen from the table, the variation in hardness of the non-heat treated forged parts obtained by the method of the present invention is extremely small.

Example 5 A steel having the chemical composition shown in Table 9 has a diameter of 50
mm rolled steel bar. This steel bar was forged into parts for automobile propulsion shafts under the conditions shown in Table 10. The hardness of the obtained parts was measured and the results are shown in Table 10. As can be seen from the table, the variation in mechanical properties of the non-heat treated forged parts obtained by the method of the present invention is extremely small.

Example 6 A steel having the chemical composition shown in Table 11 has a diameter of 80 by a conventional method.
mm rolled steel bar. This steel bar first The underbody parts of automobiles were forged under the conditions shown in Table 2. The hardness of the obtained parts was measured and the results are shown in Table 12. As can be seen from the table, the variation in mechanical properties of the non-heat treated forged parts obtained by the method of the present invention is extremely small.

[Effects of the Invention] As described in detail above, according to the method of the present invention, it is possible to extremely reduce the variation in the mechanical properties of the hot forged non-heat treated parts that are used after cooling after hot forging, so that non-heat treated steel is obtained. Can be promoted.

Claims (4)

[Claims] 1. C: 0.02-0.15%, Si: 0.10-1.00%, Mn: 0.60-
3.00%, Cr: 0.50 to 3.00%, Ti0.010 to 0.050%,
B: 0.0005 to 0.0050%, Al: 0.01 to 0.05%, N: 0.01
Non-heat treated bar steel for hot forging, which contains 20% or less and the remainder is essentially unavoidable impurities and Fe, is heated to a temperature of 1300 ° C or less and processed into the shape of machine parts by hot forging, and then water A method for producing a hot forged non-heat treated part having a bainite structure and having small variations in mechanical properties, characterized by cooling in a foam having a water content of 0.01 to 60 g / 100 ml obtained by adding a foaming agent. . 2. The non-heat treated bar steel for hot forging further contains 0.50% or less of Mo, 2.0% or less of Ni, and 0.30% or less of V or Nb. Manufacturing method for hot forged non-heat treated parts with small size. 3. In% by weight, C: 0.18 to 0.55%, Si: 0.10 to 2.00%, Mn: 0.60 to
2.00%, Cr: 1.00% or less, V: 0.03 to 0.20%, S: 0.
01 ~ 0.10%, N: 0.0030 ~ 0.020%, Al: 0.01 ~ 0.06
%, And the balance is substantially unavoidable impurities and non-heat treated bar steel for hot forging made of Fe is heated to a temperature of 1300 ° C or lower to perform hot forging, and then obtained by adding a foaming agent to water. Water content 0.
A method for producing a hot forged non-heat treated part having a ferrite / pearlite structure and having a small variation in mechanical properties, which is characterized by cooling in a foam of 01 to 50 g / 100 ml. 4. A non-heat treated steel bar for hot forging further comprises 0.03 to 0.
The method for producing a hot-forged non-heat treated component having a small variation in mechanical properties according to claim (3), which contains one or two of 20% Nb and 0.005-0.07% Ti.