KR101850805B1 - Steel material for machine structural use reduced in thermal deformation - Google Patents

Abstract

There is provided a steel material which is made of steel for machine structural use and which is used as power transmission parts for gears, shafts, etc. used in automobiles, industrial machines, etc., and which has a small heat treatment strain. This steel material contains 0.16 to 0.35% of C, 0.10 to 1.50% of Si, 0.10 to 1.20% of Mn, 0 to 0.030% of P, 0 to 0.030% of S, Ni: 0.00 to 0.0300%, Ni: 0 to 3.00%, Mo: 0 to 0.50%, Ti: 0 to 0.20%, Nb : 0 to 0.20%, and the balance Fe and inevitable impurities. The steel has a Martensenite transformation starting temperature (Ms point) of 460 DEG C or less and is measured at a distance of 1.5 mm from the quenched end of the steel material when measured by a Jominy single stage quenching method (J9 / J1.5) of the hardness J9 at a distance of 9 mm from the quenched end of the steel to the hardness J1.5 of the steel is in the range of 0.68 to 0.97, And the ratio (J11 / J1.5) of hardness J11 at a distance of 11 mm from the quenching end is in the range of 0.63 to 0.94.

Description

[0001] STEEL MATERIAL FOR MACHINE STRUCTURAL USED REDUCED IN THERMAL DEFORMATION [0002]

The present application claims priority to Japanese Patent Application No. 2011-61209 filed on March 18, 2011, the entire disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel for machine structural use, which is used, for example, as a power transmission component for gears and shafts used in automobiles and industrial machines, and particularly relates to steel for machine structural use with small heat treatment deformation.

Deformation of a steel material (hereinafter referred to as " heat treatment deformation ") caused by heat treatment such as quenching increases the number of manufacturing steps to correct the deformation, increases the component defective ratio when the number of manufacturing steps can not be completely corrected, Or when it is incorporated as a driveline component, there is an adverse effect of generating noise or vibration due to deformation. Therefore, it is a very important problem in practice to suppress heat treatment deformation as small as possible.

Conventionally, the aforementioned heat treatment deformation is considered to be influenced by many factors other than the steel material, such as the shape of the component, the influence of the pre-heat treatment process, the property value of the coolant such as quenching oil and the unevenness of cooling. . For example, Japanese Patent Application Laid-Open (JP-A) No. 2001-348868 proposes a method for reducing non-uniform heat treatment by precipitating a soft ferrite phase on a core portion of a quenched steel material as a countermeasure against a material (for example, refer to Patent Document 1) .

In addition, a method of using pressurized gas cooling instead of conventional oil quenching as an approach from the cooling method has been proposed (see, for example, Patent Document 2). Further, there is proposed a method of uniformly cooling the object to be cooled by using a means for promoting or reducing the heat transfer rate (see, for example, Patent Document 3).

In Patent Document 3, the means for promoting the heat transfer rate is due to the convection of a coating material promoting cooling provided at a portion where cooling is delayed or a coolant formed around a portion where cooling is delayed, And is made of glass fiber or heat insulating coating material covering a portion where cooling is likely to proceed.

Japanese Patent Application Laid-Open No. 1997-111408 Japanese Patent Application Laid-Open No. 2008-121064 Japanese Patent Application Laid-Open No. 2010-174289

However, in the conventional method proposed in the above, in the technique of Patent Document 1, a soft phase having a low strength is introduced into the component, and in the technique of Patent Document 2, the heat treatment furnace itself must be changed, 3 is not always a general-purpose means because of the necessity of processing for each heat-treated part.

On the other hand, the inventors of the present invention have found that, even after sufficient steel strength is secured without relying on a soft layer such as ferrite, even if the cooling of the parts becomes uneven under a general method such as oil quenching and the like, Respectively. As a result, the present inventors have found that the heat treatment strain is suppressed to be small by properly controlling the chemical composition of the steel, the transformation temperature of the marutensite transformation initiation temperature (Ms point), and the hardenability measured by the Jominy single stage quenching method .

Therefore, an object of the present invention is to provide a steel material having mechanical strength for machine structural use, which is used for power transmission parts such as gears and shafts used in automobiles, industrial machines, etc., and which has a small heat treatment deformation.

According to one aspect of the present invention, there is provided a mechanical structure steel material having a small thermal deformation, wherein the steel material comprises, by mass%

C: 0.16 to 0.35%

Si: 0.10 to 1.50%

Mn: 0.10 to 1.20%

P: 0 to 0.030%,

S: 0 to 0.030%,

Cr: 1.30 to 2.50%

Cu: 0 to 0.30%

Al: 0.008 to 0.800%

O: 0 to 0.0030%,

N: 0.0020 to 0.0300%

Ni: 0 to 3.00%

Mo: 0 to 0.50%

Ti: 0 to 0.200%,

Nb: 0 to 0.20%

And the balance Fe and inevitable impurities, wherein the steel has a maltitanium transformation start temperature (Ms point) of 460 DEG C or lower,

The hardness of the steel material at a distance of 9 mm at a distance of 9 mm from the hardened end of the steel material to the hardness J1.5 at a distance of 1.5 mm from the hardened end of the steel material, (J9 / J1.5) is in the range of 0.68 to 0.97 and the distance from the quenching end of the steel to the hardness J1.5 at a distance of 1.5 mm from the quenching end of the steel is 11 mm (J11 / J1.5) of the hardness J11 of the steel is in the range of 0.63 to 0.94.

According to a preferred embodiment of the present invention, the steel material contains Ni, Mo, Ti and Nb at a level substantially free of or unavoidable impurities.

According to another preferred embodiment of the present invention, the steel material contains one or two kinds of, by mass%, 0.20 to 3.0% of Ni and 0.05 to 0.50% of Mo.

According to another preferred embodiment of the present invention, the steel material includes one or two of Ti: 0.020 to 0.200% and Nb: 0.02 to 0.20% in mass%.

According to another preferred embodiment of the present invention, the steel material comprises, in mass%, one or two of Ni: 0.20 to 3.00% and Mo: 0.05 to 0.50%, Ti: 0.020 to 0.200% and Nb: 0.20%. ≪ / RTI >

Hereinafter, the present invention will be described in detail. In the present specification, "% " means mass%, unless otherwise specified.

The steel material for mechanical structural use according to the present invention is characterized by containing 0.16 to 0.35% of C, 0.10 to 1.50% of Si, 0.10 to 1.20% of Mn, 0 to 0.030% of P, 0 to 0.030% of S, Al: 0.008 to 0.800%, O: 0 to 0.0030%, N: 0.0020 to 0.0300%, Ni: 0 to 3.00%, Mo: 0 to 0.50%, Cr: 1.30 to 2.50% , Ti: 0 to 0.200%, Nb: 0 to 0.20%, the balance being Fe and inevitable impurities, and preferably consisting essentially of these elements and inevitable impurities, More preferably consisting essentially of these elements and inevitable impurities.

The steel according to the present invention contains C in an amount of 0.16 to 0.35%, preferably 0.20 to 0.30%, more preferably 0.22 to 0.27%. C is an element necessary for securing strength after quenching and tempering of steel or core strength after tempering (carburizing) quenching and tempering, and it is necessary to adjust to a predetermined range in order to reduce heat treatment deformation. If the content of C is less than 0.16%, the strength can not be secured. If the content of C is more than 0.35%, the deformation due to the heat treatment becomes too large.

The steel according to the present invention contains 0.10 to 1.50%, preferably 0.20 to 1.00% of Si. Si is an element necessary for deoxidation and is an effective element for imparting strength and hardenability required for steel. However, if the content of Si is less than 0.10%, the effect can not be obtained. If the content exceeds 1.50%, the machinability is deteriorated.

The steel according to the present invention contains Mn in an amount of 0.10 to 1.20%, preferably 0.20 to 0.80%, more preferably 0.20 to 0.55%. Mn is an element necessary for securing hardenability. However, when the Mn content is less than 0.10%, the effect on the hardenability can not be sufficiently obtained, and when it exceeds 1.20%, the machinability is deteriorated.

The steel according to the present invention comprises 0 to 0.030% P, typically from greater than 0 to 0.030%. P is an inevitable element contained in scrap. When the content exceeds 0.030%, segregation occurs at the grain boundaries to deteriorate characteristics such as impact strength and bending strength.

The steel according to the present invention comprises 0 to 0.030%, typically 0 to 0.030%, of S by weight. S is an element that improves machinability. When the content exceeds 0.030%, MnS, which is a nonmetallic inclusion, is generated to lower the toughness and fatigue strength in the transverse direction.

The steel according to the present invention contains 0 to 3.00%, preferably 0.20 to 3.00% Ni. Ni is an optional element for improving the hardenability and toughness, and in order to obtain the effect, it is preferable to add Ni in an amount of 0.20% or more. However, when Ni is contained in an amount exceeding 3.00%, the workability is remarkably lowered and the cost is increased.

The steel according to the present invention contains Cr at 1.30 to 2.50%, preferably 1.50 to 2.25%. Cr is an element necessary for securing hardenability. If the content of Cr is less than 1.30%, the effect on the hardenability can not be sufficiently obtained. If the content of Cr is more than 2.50%, the carburization is inhibited and the machinability also deteriorates.

The steel according to the present invention contains 0 to 0.50%, preferably 0.05 to 0.50% Mo.

Mo is an element which improves the hardenability and toughness, and the addition of 0.05% or more is necessary to obtain the effect.

However, when Mo is contained in an amount exceeding 0.50%, workability is deteriorated.

The steel according to the present invention contains 0 to 0.30%, typically 0 to 0.30%, of Cu.

Although Cu is an inevitable element contained in scrap, it has a viability and has an effect of increasing the strength.

However, if the content of Cu exceeds 0.30%, the hot workability deteriorates.

The steel according to the present invention contains 0.010 to 0.800% of Al, and preferably 0.014 to 0.600% of Al.

Al is an element used as a deacidification material, and as described later, it binds with N and precipitates as AlN to give a crystal particle coarsening inhibiting effect.

In order to obtain this effect, it was necessary to add 0.010% or more of Al.

On the other hand, when Al is added in an amount exceeding 0.800%, large alumina inclusions are formed, and fatigue characteristics and workability are deteriorated.

The steel according to the present invention contains 0 to 0.0030% O, typically greater than 0% to less than 0.0030%, preferably less than 0.0020%. O is an element inevitably contained in steel. However, when O is contained in an amount exceeding 0.0030%, the workability and fatigue strength are lowered due to the increase of the oxide.

The steel material according to the present invention contains N in an amount of 0.0020 to 0.0300%, preferably 0.0020 to 0.0200%. N is fine precipitated as AlN or Nb nitride in the steel to prevent crystal grain coarsening, and it is necessary to add 0.0020% or more to obtain the effect. However, if it exceeds 0.0300%, the nitride increases and the fatigue strength and workability deteriorate. However, in a steel containing 0.020% or more of Ti in particular, it is preferable that N is 0.0020 to 0.0100% in order to avoid a decrease in fatigue strength due to the excessive production of TiN.

The steel according to the present invention contains 0 to 0.200% of Ti, preferably 0.020 to 0.200%. Ti is an arbitrary element that combines with C in the steel to finely form a carbide and prevent coarsening of the crystal grains. However, when it is desired to obtain the effect, Ti is preferably added in an amount of 0.020% or more Do. On the other hand, addition of more than 0.200% deteriorates the mechanical workability.

The steel according to the present invention contains 0 to 0.20% Nb, preferably 0.02 to 0.20%, more preferably 0.02 to 0.12% Nb. Nb forms a carbide or nitride, and has an effect of preventing coarsening of crystal grains. In particular, NbC or Nb (C, N) of nano-order size finely dispersed in the steel suppresses the growth of crystal grains. When Nb is less than 0.02%, the effect can not be obtained, and when Nb is more than 0.20%, the amount of precipitate becomes excessive and workability is deteriorated.

In the steel material according to the present invention, the marutensite transformation starting temperature (Ms point) is regulated to 460 DEG C or lower, preferably 450 DEG C or lower, in order to reduce heat treatment deformation of the steel material. The reason why the heat treatment strain can be reduced by regulating the Ms point to 460 占 폚 or less is that it is possible to avoid the occurrence of the maltotensitic transformation in the temperature region where the cooling performance of the refrigerant is high even if the components are unevenly cooled As a result, it is possible to suppress a large deviation of the marutin site transformation timing depending on the part of the component. In this case, the heat treatment deformation means that the axial part is bent or the teeth of the gears snap or twist.

In the case of the steel according to the present invention, when measured by the quenching method of the mini-mill method, the distance from the quenching end of the steel material to the hardness J1.5 at a distance of 1.5 mm from the quenching end of the steel material The ratio (J9 / J1.5) of the hardness J9 at 9 mm is in the range of 0.68 to 0.97 and the hardening of the steel with respect to the hardness J1.5 at the distance of 1.5 mm from the hardened end of the steel And the ratio J11 / J1.5 of the hardness J11 at a distance of 11 mm from the edge is in the range of 0.63 to 0.94. Within this range, heat treatment deformation of the steel can be suppressed to a small extent. The heat treatment deformation referred to here is a change in dimensions (length, diameter, thickness) before and after quenching of the component. The mechanism by which the annealing deformation is suppressed by appropriate control of the joining mini-quenchability is not yet clarified. However, the inventors of the present invention have found that the quenchability of the steel is too low and the heat treatment deformation becomes large even if it is excessively high It is experimentally revealed.

The quenching and carburizing quenching to harden the components after the steel is processed into parts by the limitation of the steel component as described above, the limitation of the Ms point, and the quenching property measured by the quenching- It is possible to reduce the heat treatment deformation in the case of performing the heat treatment. As a result, according to the present invention, it is possible to obtain a beneficial effect that it is possible to improve the yield of parts, to simplify and dismantle the process of calibrating parts, and to omit tooth surface grinding of gears for noise and vibration countermeasures.

[Example]

The steel material according to the present invention will be described in detail with reference to the following examples.

Mechanical steels for machine structural use, which are used as components for power transmission such as gears and shafts used in automobiles and industrial machines, are composed of the composition of Nos. 1 to 23 of the present invention shown in Table 1 and the balance Fe and unavoidable impurities (Melting) by a vacuum induction melting furnace to obtain 100 kg of steel ingots.

[Table 1]

As the mechanical steels for use in power transmission parts such as gears and shafts used for automobiles and industrial machines, the compositions of Nos. 1-16 of comparative examples shown in Table 2 and the balance Fe and inevitable Steel made of an impurity was dissolved by a vacuum induction melting furnace to obtain a ingot of 100 kg.

[Table 2]

First, the ingot of these inventive and comparative examples was heated at 1250 占 폚 for 5 hours, and then forged (forged) and stretched to obtain a bar steel having a diameter of 32 mm. Next, heating and holding at 900 占 폚 for 1.5 hours were followed by normalizing by air cooling. Then, a test piece having a diameter of 20 mm and a length of 200 mm was prepared from a bar having a diameter of 32 mm, and a groove having a depth of 5 mm, a width of 8 mm and a length of 200 mm was formed on the side surface of the test piece. When the quenching is performed by this groove machining, the cooling rate is greatly different depending on the portion in the test piece. Further, the length of the test piece after the groove processing was measured. Subsequently, these test pieces were heated at 930 ° C for 1 hour, then cooled down to 850 ° C in a furnace, held for 1 hour, and then quenched in a quenching oil at 60 ° C. After quenching, the sufficiently cooled specimens were measured for flexure and length.

With respect to the bending after the heat treatment, the maximum displacement and the minimum displacement on the circumference of the central portion of the test piece when the test piece was rotated for one week while holding both ends of the test piece with the V block were measured with a dial gauge, and the maximum displacement and the minimum displacement The difference was obtained by dividing by 2. In this measurement, the displacement of the bottom part of the groove present on the circumference of the test piece was ignored. In addition, as the index of dimensional change, the difference in length of the test piece before and after the heat treatment was obtained, and the absolute value thereof was evaluated.

A test piece having a diameter of 3 mm and a length of 10 mm was extracted from the bar having a diameter of 32 mm after the normalization, and the Ms point of the marutensite transformation start temperature of the steel was measured using a fully automatic transformation recording apparatus. Here, the Ms point is measured under the condition assuming the cooling process of the component. In the present embodiment, assuming oil quenching at the oil temperature of 60 DEG C of the above-mentioned test piece having grooves with a diameter of 20 mm, The cooling rate was measured at 30 캜 / s. For the measurement of the quenchability according to the quenching method according to the first-stage quenching method of steels, test pieces were prepared from the forged and elongated bar having a diameter of 32 mm and the quenchability test method of steel specified in JIS G 0561 Method) " under the following conditions.

Table 3 shows J1.5 of the hardness at the distance of 1.5 mm, J9 of the hardness at the distance of 9 mm, and the distance from the quenched edge measured by the coarsened mini- mm and the values of J11 / J1.5 and J11 / J1.5, respectively. In addition, the curve (mm) evaluated after quenching of the test piece and the absolute value (mm) of the difference between the lengths of the test pieces before and after the heat treatment are shown. In the steels of Nos. 1 to 23 of the Inventive Examples, as shown in Table 3, the marutensite transformation start temperature, that is, the Ms point is in the range of 372 to 442 DEG C, and therefore the (J9 / J1.5) The value of the formula (1) is in the range of 0.70 to 0.95, the value of the formula (2) shown below in the formula (J11 / J1.5) is in the range of 0.65 to 0.90 and the bending after the heat treatment is 0.10 to 0.36 mm , And the absolute value of the difference in length between the test pieces before and after the heat treatment was 0.01 to 0.20 mm.

only,

(J9 / J1.5) = (hardness at a distance of 9 mm from the quenched end measured by the quenching method of the Mini-type formula 1) ÷ (distance from the quenching end measured by the quenching method of the Mini-Type 1step 1.5 mm Hardness of the ...) ... (One)

(J11 / J1.5) = (hardness at a distance of 11 mm from the quenched end measured by the quenching method of the Mini-Type 1 st step) ÷ (distance from the quenched end measured by the quenching method of the mini-formula 1 Hardness of the ...) ... (2)

[Table 3]

Similarly, in Table 4, the measured Ms point of the steel of the comparative example, the J1.5 of the hardness at the distance of 1.5 mm from the quenched end measured by the quenching method of the JSMIN method and the hardness of J9 at the distance of 9 mm (J11 / J1.5) and (J11 / J1.5), respectively, which are the J1 / J1.5 hardness at a distance of 11 mm and the J1 mini- In addition, the curve (mm) after quenching of the test piece and the absolute value (mm) of the difference between the lengths of the test pieces before and after the heat treatment are shown.

[Table 4]

In the Nos. 1 to 23 of the inventive examples, the composition ranges excluding Fe, Ni, and Mo inevitable impurities of the steel are shown in Table 1, the Ms point is set to 372 to 442 캜 at 460 캜 or lower, However, the hardenability measured by the quenching method is appropriately controlled so that the value of (J9 / J1.5) calculated from the equation (1) falls within the range of 0.70 to 0.95, and the value calculated from the equation (2) 5) is set in the range of 0.65 to 0.90, the bending of the test piece after the heat treatment is controlled within a small range of 0.10 to 0.36 mm and the absolute value of the difference in length of the test piece before and after the heat treatment is controlled within a small range of 0.01 to 0.20 mm can do.

On the other hand, the composition ranges of the compositions Nos. 1 to 16 of the comparative examples, except Fe and the inevitable impurities except for Ni and Mo, are shown in Table 2, except for the two cases of No. 2 and No. 16, The remaining 14 cases were deviated from the composition range of the present invention. Of the steels of the comparative examples Nos. 1 to 16, the ten specimens having Ms points exceeding 460 占 폚 have a flexural strength of 0.49 to 0.76 mm after heat treatment, which is larger than that of the inventive steel. Of the comparative steels of Nos. 1 to 16, (J9 / J1.5) obtained by the equations (1) and (2) from the hardness measured by the quench- And the values of (J11 / J1.5) out of the range of 0.63 to 0.94 are in the range of 0.27 to 0.45 mm, the absolute value of the length difference between the specimens before and after the heat treatment is 0.27 to 0.45 mm, Respectively. Therefore, in the comparative examples, none of the absolute values of the difference in the lengths of the specimens before and after the heat treatment and the bending of the test pieces after the heat treatment were equal to those of the inventive example.

Nos. 1 to 23 of the present invention, in which the Ms point satisfies the claimed range, as compared with the Nos. 1 to 3, 5 to 7, 9, 10, 14 and 15 of the comparative examples in which the measured Ms point is outside the claimed range, The bending of the test piece after the heat treatment is small and the heat treatment deformation is suppressed. In addition, the values of (J9 / J1.5) and (J11 / J1.5) and (J9 / J1.5) J11 / J1.5) satisfies the claims, the absolute value of the difference in the lengths of the test pieces before and after the heat treatment is small and the heat treatment deformation is suppressed. In the present embodiment, heat treatment deformation is evaluated by quenching instead of carburizing quenching, but it is confirmed that the heat treatment deformation of the steel material satisfying the present invention is small even in the case of carburizing quenching. The steel material of the present invention is used after quenching and tempering.

As described above, by limiting the steel component in the present invention, limiting the Ms point, which is the start temperature of the marutensite transformation, and quenching property measured by the quenching method of the mini-mill method, It is possible to reduce the deformation of the heat treatment in the case of performing quenching or carburizing quenching for curing. The steel material according to the present invention is a steel material applicable to power transmission parts such as gears and shafts used for automobiles and industrial machines.

Claims (10)

As a steel material for mechanical structure having small heat treatment strain,
The steel material according to claim 1,
C: 0.16% to 0.35%,
Si: 0.10% to 1.50%,
Mn: 0.10% to 0.48%,
P: 0% to 0.030%,
S: 0% to 0.030%,
Cr: 1.30% to 2.50%
Cu: 0% to 0.30%,
Al: 0.008% to 0.800%,
O: 0% to 0.0030%,
N: 0.0020% to 0.0300%,
Ni: 0% to 3.00%,
Mo: 0% to 0.50%,
Ti: 0% to 0.200%,
Nb: 0% to 0.20%
And the balance Fe and unavoidable impurities,
Wherein the steel has a marutensite transformation start temperature (Ms point) of 460 DEG C or lower,
A distance from the quenched end of the steel material to a hardness J1.5 at a distance of 1.5 mm from the quenched end of the steel material when measured by a Jominy single step quenching method is 9 mm (J9 / J1.5) of the hardness J9 in the range of 0.68 to 0.97 and the hardness J1.5 at a distance of 1.5 mm from the quenched end of the steel (J11 / J1.5) of the hardness J11 at a distance of 11 mm from the center to the center is in the range of 0.63 to 0.94,
Steel for machine structural use. The method according to claim 1,
Wherein the steel material is substantially free of Ni, Mo, Ti, and Nb. The method according to claim 1,
The steel material according to claim 1, wherein the steel material contains one or two of Ni: 0.20% to 3.00% and Mo: 0.05% to 0.50% in mass%. The method according to claim 1,
Wherein the steel material comprises one or two of Ti: 0.020% to 0.0200% and Nb: 0.02% to 0.20% in mass%. The method according to claim 1,
Wherein the steel material comprises one or two of Ni: 0.20% to 3.00% and Mo: 0.05% to 0.50%, Ti: 0.020% to 0.200% and Nb: 0.02% to 0.20% Steel for machine structural use, including two kinds. The method according to claim 1,
And the content of Mn is 0.10 to 0.45 mass%. The method according to claim 1,
And the content of Mn is 0.10 to 0.43 mass%. delete delete delete