JP5641992B2 - Machine structural steel with low heat treatment deformation - Google Patents

Description

  The present invention relates to a machine structural steel used as a power transmission component such as a gear and a shaft used in automobiles and industrial machines, for example, and more particularly to a machine structural steel having a small heat treatment deformation.

  Deformation of steel materials caused by heat treatment such as quenching (hereinafter referred to as “heat treatment deformation”) increases the number of manufacturing processes in order to correct the deformation, or the part defect rate increases if it cannot be corrected, Alternatively, when incorporated as a drive system component, there is an adverse effect of generating noise and vibration due to deformation. Therefore, it is a very important problem in practice to keep the heat treatment deformation as small as possible.

  Conventionally, this heat treatment deformation is considered to be affected by many factors besides the steel material, such as part shape, influence of pre-heat treatment processes, physical properties of refrigerants such as quenching oil, and non-uniform cooling. By doing so, the deformation of the heat treatment is reduced. For example, as a material countermeasure, a method has been proposed in which a soft ferrite phase is precipitated in the core of a hardened steel material to reduce heat treatment strain (see, for example, Patent Document 1).

  As an approach from the cooling method, a method using pressurized gas cooling instead of conventional oil quenching has been proposed (see, for example, Patent Document 2). In addition, a method for achieving uniform cooling of an object to be cooled using means for promoting or reducing the heat transfer coefficient has been proposed (for example, see Patent Document 3).

  In Patent Document 3, the means for promoting the heat transfer coefficient is due to the convection of the coating material that promotes cooling provided in the portion where cooling is delayed or the coolant formed around the portion where cooling is delayed, The means for reducing the heat transfer rate is said to be glass wool or a heat insulating coating material covering a portion where cooling is likely to proceed.

  However, in the conventional method proposed above, the technique of Patent Document 1 introduces a soft phase having a low strength inside the component, or the technique of Patent Document 2 does not change the heat treatment furnace itself. However, the technique disclosed in Patent Document 3 is not necessarily a general-purpose means because it requires processing of individual heat-treated parts.

  On the other hand, the inventors of the present application ensure sufficient steel strength without relying on a soft layer such as ferrite, and even when cooling of parts is not uniform under a general technique such as oil quenching. And earnestly researched on steel that can keep heat treatment deformation small. As a result, finally found that the heat treatment deformation can be suppressed small by appropriately controlling the chemical composition of the steel, the martensite transformation start temperature (Ms point), and the hardenability measured by the Jomini type one-end quenching method, The present invention has been reached.

JP 1997-111408 A JP 2008-121064 A JP 2010-174289 A

  The problem to be solved by the present invention is to provide a steel material with less heat treatment deformation made of mechanical structural steel used as power transmission parts such as gears and shafts used in automobiles and industrial machines.

The means of the present invention for solving the above problem is that in the means of claim 1, C: 0.16 to 0.35%, Si: 0.10 to 1.50%, Mn: 0 in mass%. .10 to 1.20%, P: 0.030% or less, S: 0.030% or less, Cr: 1.30 to 2.50%, Cu: 0.30% or less, Al: 0.008 to 0 .800%, O: 0.0030% or less, N: 0.0020 to 0.0300%, and a structural structural steel composed of the remaining Fe and inevitable impurities, and the martensitic transformation start temperature of the steel material composed of the steel The (Ms point) is 460 ° C. or less, and the steel material is measured by the Jominy-type one-end quenching method, the hardness J1.5 at a distance 1.5 mm from the quenching end of the steel material and the hardness J9 at a distance 9 mm. (J9 / J1.5) calculated by the following equation (1) using The value is in the range of 0.68 to 0.97, and further calculated by the following equation (2) using J1.5 of hardness at a distance of 1.5 mm and J11 of hardness at a distance of 11 mm (J11 / J1.5) is a steel for machine structural use with small heat treatment deformation, characterized in that it is in the range of 0.63 to 0.94.
However,
(J9 / J1.5) = (hardness at a distance of 9 mm from the quenching end measured by the Jomini type one-end quenching method) ÷ (distance from the quenching end measured by the Jominy type one-end quenching method. 5mm hardness) ... Formula (1)
(J11 / J1.5) = (hardness at a distance of 11 mm from the quenching end measured by the Jomini type one-end quenching method) ÷ (distance from the quenching end measured by the Jominy type one-end quenching method. (Hardness at 5 mm) (2)

  In the means of claim 2, in mass%, C: 0.16-0.35%, Si: 0.10-1.50%, Mn: 0.10-1.20%, P: 0.030% Hereinafter, S: 0.030% or less, Cr: 1.30 to 2.50%, Cu: 0.30% or less, Al: 0.008 to 0.800%, O: 0.0030% or less, N: 0.0020 to 0.0300%, Ni: 0.20 to 3.00%, Mo: 0.05 to 0.50% of one or two, containing the balance Fe and inevitable impurities Further, the steel material is made of mechanical structural steel, and the martensite transformation start temperature (Ms point) of the steel material is 460 ° C. or less, and the steel material is hardened as measured by the Jomini-type one-time quenching method. Hardness J1.5 at distance 1.5mm from end and at distance 9mm The value of (J9 / J1.5) calculated by the above equation (1) using J9 of the thickness is in the range of 0.68 to 0.97, and further, the hardness of J1.5 at the distance of 1.5 mm And J11 of hardness at a distance of 11 mm, the value of (J11 / J1.5) calculated by the above equation (2) is in the range of 0.63 to 0.94. It is a small steel for machine structural use.

  In the means of claim 3, in mass%, C: 0.16-0.35%, Si: 0.10-1.50%, Mn: 0.10-1.20%, P: 0.030% Hereinafter, S: 0.030% or less, Cr: 1.30 to 2.50%, Cu: 0.30% or less, Al: 0.008 to 0.800%, O: 0.0030% or less, N: It contains 0.0020 to 0.0300%, further contains at least one of Ti: 0.020 to 0.200% and Nb: 0.02 to 0.20%, and consists of the balance Fe and inevitable impurities. It is a steel material made of steel for machine structural use. Further, the martensitic transformation start temperature (Ms point) of this steel material is 460 ° C. or less, and the hardened end of the steel material measured by the Jomini type one-end quenching method for this steel material. J1.5 of hardness and distance 9 at a distance of 1.5 mm from The value of (J9 / J1.5) calculated by the above equation (1) using J9 of hardness at m is in the range of 0.68 to 0.97, and further the hardness at distance of 1.5 mm Using J1.5 and J11 of hardness at a distance of 11 mm, the value of (J11 / J1.5) calculated by the above equation (2) is in the range of 0.63 to 0.94. It is a steel for machine structural use with small heat treatment deformation.

  In the means of claim 4, by mass%, C: 0.16-0.35%, Si: 0.10-1.50%, Mn: 0.10-1.20%, P: 0.030% Hereinafter, S: 0.030% or less, Cr: 1.30 to 2.50%, Cu: 0.30% or less, Al: 0.008 to 0.800%, O: 0.0030% or less, N: 0.0020 to 0.0300%, further containing at least one of Ni: 0.20 to 3.00%, Mo: 0.05 to 0.50%, and further Ti: 0.020 ˜0.200%, Nb: 0.02 to 0.20% of one or two kinds of steel, a steel material made of steel for mechanical structure consisting of Fe and unavoidable impurities, and further martensite of this steel material The transformation start temperature (Ms point) is 460 ° C. or less, and Jominy type one-end firing of this steel material (J9 / J1.5) calculated by the above equation (1) using J1.5 of the hardness at a distance of 1.5 mm from the quenching end of the steel material measured by the method and J9 of the hardness at a distance of 9 mm. Is in the range of 0.68 to 0.97, and is calculated by the above equation (2) using J1.5 of hardness at a distance of 1.5 mm and J11 of hardness at a distance of 11 mm ( J11 / J1.5) is a steel for machine structural use with small heat treatment deformation, characterized in that the value is in the range of 0.63 to 0.94.

  The reasons for limiting the components in the means of the above claims will be described below. In addition,% of each component element shows the mass%.

C: 0.16-0.35%
C is an element necessary for ensuring the strength after quenching and tempering of steel or the strength of the core after carburizing, quenching and tempering as machine structural parts, and is adjusted to a predetermined range in order to reduce heat treatment deformation. There is a need to. If the range is less than 0.16%, the strength cannot be secured, and if it exceeds 0.35%, deformation due to heat treatment becomes too large. Therefore, C is 0.16 to 0.35%, preferably 0.20 to 0.30%, more preferably 0.22 to 0.27%.

Si: 0.10 to 1.50%
Si is an element necessary for deoxidation and is an effective element for imparting necessary strength and hardenability to steel. However, if Si is less than 0.10%, the effect cannot be obtained, and if it exceeds 1.50%, the machinability is lowered. Therefore, Si is 0.10 to 1.50%, preferably 0.20 to 1.00%.

Mn: 0.10 to 1.20%
Mn is an element necessary for ensuring hardenability. However, if Mn is less than 0.10%, a sufficient effect on hardenability cannot be obtained, and if it exceeds 1.20%, the machinability is lowered. Therefore, Mn is 0.10 to 1.20%, preferably 0.20 to 0.80%, and more preferably 0.20 to 0.55%.

P: 0.030% or less P is an unavoidable element contained in scrap, but segregates at the grain boundary and lowers properties such as impact strength and bending strength. Therefore, P is set to 0.030% or less.

S: 0.030% or less S is an element that improves machinability, but produces MnS that is a non-metallic inclusion and lowers the toughness and fatigue strength in the transverse direction. Therefore, S is set to 0.030% or less.

Ni: 0.20 to 3.00%
Ni is an element that improves hardenability and toughness, and in order to obtain the effect, addition of 0.20% or more is necessary. However, if Ni is contained over 3.00%, the workability is remarkably lowered and the cost is increased. Therefore, Ni is set to 3.00% or less.

Cr: 1.30 to 2.50%
Cr is an element necessary for ensuring hardenability. However, if Cr is less than 1.30%, a sufficient effect on hardenability cannot be obtained. Therefore, Cr is 1.30 to 2.50%, preferably 1.50 to 2.25%.

Mo: 0.05 to 0.50%
Mo is an element that improves hardenability and toughness, and 0.05% or more of addition is necessary to obtain the effect. However, if Mo exceeds 0.50%, workability is reduced. Therefore, Mo is set to 0.05 to 0.50%.

Cu: 0.30% or less Cu is an inevitable element contained from scrap, but has aging properties and an effect of increasing strength. However, when Cu exceeds 0.30%, the hot workability decreases. Therefore, Cu is made 0.30% or less.

Al: 0.010-0.800%
Al is an element used as a deoxidizing material, and also binds to N and precipitates as AlN as will be described later, thereby bringing about an effect of suppressing grain coarsening. In order to obtain this effect, Al needs to be added in an amount of 0.010% or more. On the other hand, when Al is added in excess of 0.800%, large alumina inclusions are formed, and fatigue characteristics and workability are deteriorated. Therefore, Al is made 0.010 to 0.800%, preferably 0.014 to 0.600%.

O: 0.0030% or less O is an element inevitably contained in steel. However, if O exceeds 0.0030%, workability and fatigue strength are reduced due to an increase in oxide. Therefore, O is set to 0.0030% or less, preferably 0.0020% or less.

N: 0.0020 to 0.0300%
N precipitates finely as AlN or Nb nitride in the steel and brings about an effect of preventing coarsening of crystal grains, and 0.0020% or more needs to be added to obtain the effect. However, if it exceeds 0.0300%, nitrides increase, and fatigue strength and workability decrease. Therefore, N is 0.0020 to 0.0300%, preferably 0.0020 to 0.0200%. However, especially in steel containing 0.020% or more of Ti, N is made 0.0020 to 0.0100% in order to avoid a decrease in fatigue strength due to excessive TiN formation.

Ti: 0.020 to 0.200%
Ti combines with C in steel to form carbides finely and brings about the effect of preventing crystal grain coarsening. To obtain this effect, it is necessary to add 0.020% or more of Ti. . On the other hand, since addition exceeding 0.200% impairs machinability, the upper limit is made 0.200%.

Nb: 0.02 to 0.20%
Nb forms carbides or nitrides, and has an effect of preventing crystal grain coarsening. In particular, nano-order sized NbC or Nb (C, N) finely dispersed in steel suppresses the growth of crystal grains. If Nb is less than 0.02%, the effect cannot be obtained, and if it exceeds 0.20%, the amount of precipitates becomes excessive and the workability deteriorates. Therefore, Nb is 0.02 to 0.20%, preferably 0.02 to 0.12%.

Ms point: 460 ° C. or lower In order to reduce the heat treatment deformation of the steel material in the means of the present invention, it is necessary to regulate the martensitic transformation start temperature (Ms point) to 460 ° C. or lower. The reason why heat treatment deformation can be reduced by restricting the Ms point to 460 ° C. or lower is that martensite transformation occurs in a temperature range where the cooling performance of the refrigerant is high even if the parts are not evenly cooled when quenched. This is because it is possible to avoid this, and as a result, it is possible to prevent the time of martensitic transformation from being greatly shifted depending on the parts. Therefore, the Ms point is restricted to 460 ° C. or lower, but preferably the Ms point is restricted to 450 ° C. or lower. In this case, the heat treatment deformation refers to bending of a shaft-like component or falling or twisting of gear teeth.

(J9 / J1.5) value: 0.68 to 0.97, (J11 / J1.5) value: 0.63 to 0.94
From the J1.5 hardness at a distance of 1.5 mm from the quenching end of the steel material measured by the Jominy-type one-end quenching method of the steel material, the J9 hardness at a distance of 9 mm, and the J11 hardness at a distance of 11 mm The reason why the calculated value of (J9 / J1.5) is regulated to 0.68 to 0.97 and the value of (J11 / J1.5) is regulated to 0.63 to 0.94 is This is because the heat treatment deformation of the steel material can be suppressed small. The heat treatment deformation referred to here is a change in dimensions (length, diameter, thickness) before and after quenching of the part. The mechanism by which heat treatment deformation is suppressed by appropriate control of Jominy hardenability has not yet been elucidated, but even if the hardenability of steel is too low or too high, heat treatment deformation is large. It has become experimentally clear by the inventors.

  Quenching and carburizing and quenching to harden the parts after processing the steel into parts by limiting the steel component and Ms point of the means of the present invention and by limiting the hardenability as measured by the Jomini-type one-end quenching method As a result, the present invention can improve the yield of parts, simplify or eliminate the correction process of parts, or gear tooth surfaces for noise and vibration countermeasures. There is a beneficial effect that grinding can be omitted.

EMBODIMENT OF THE INVENTION The form for implementing this invention is demonstrated with reference to a table | surface below.
As steel for machine structure used as power transmission parts such as gears and shafts used in automobiles and industrial machines, No. 1 of the present invention shown in Table 1 is shown. Machine structural steel consisting of 1 to 23 component compositions, the balance Fe and inevitable impurities was melted in a vacuum induction melting furnace to obtain a 100 kg steel ingot.

  As in the above-described examples of the present invention, as a steel for machine structural use used as a power transmission component such as a gear or a shaft used in automobiles, industrial machines, etc., the comparative example No. Steel consisting of 1 to 16 component compositions, the balance Fe and inevitable impurities was melted in a vacuum induction melting furnace to obtain 100 kg of steel ingot.

  First, the steel ingots of these inventive examples and comparative examples were heated at 1250 ° C. for 5 hours, and then forged into a steel bar having a diameter of 32 mm. Next, normalizing was performed by heating and holding at 900 ° C. for 1.5 hours and then air cooling. Subsequently, a test piece having a diameter of 20 mm and a length of 200 mm was produced from a steel 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 applied to the side surface of the test piece. When quenching was performed by this groove processing, the cooling rate was varied greatly depending on the portion in the test piece. Moreover, the length of the test piece after groove processing was measured. Then, after heating these test pieces at 930 ° C. for 1 hour, the temperature was lowered to 850 ° C. in the furnace, and further kept for 1 hour, and then quenched into quenching oil at 60 ° C. About the test piece fully cooled after hardening, the bending and length of the test piece were measured.

  For bending after heat treatment, hold both ends of the test piece with V block, and measure the maximum and minimum displacement on the circumference of the center of the test piece with a dial gauge when the test piece is rotated once. The difference between the maximum displacement and the minimum displacement was obtained by dividing by 2. In this measurement, the displacement of the bottom portion of the groove existing on the circumference of the test piece was ignored. Further, as an index of dimensional change, a difference in length of the test piece before and after the heat treatment was obtained, and the absolute value was evaluated.

  Further, a test piece having a diameter of 3 mm and a length of 10 mm was determined from the above-mentioned normalized steel bar having a diameter of 32 mm, and the Ms point, which is the martensitic transformation start temperature of the steel material, was measured using a fully automatic transformation recording measuring device. . The Ms point mentioned here is measured under the condition that the cooling process of the part is assumed. In the present embodiment, oil quenching in the case of the above-described grooved test piece with a diameter of 20 mm at an oil temperature of 60 ° C. Assuming that the cooling rate during quenching is 30 ° C./s. For the measurement of the hardenability of the steel material by the Jominy type one-end quenching method, a test piece is prepared from the above-described forged steel bar having a diameter of 32 mm, and the “steel hardenability test method (one end) is defined in JIS G 0561. The test was conducted under the conditions according to the quenching method) and evaluated.

Table 3 shows the measured Ms point of the example of the present invention, J1.5 of hardness at a distance of 1.5 mm, J9 of hardness at a distance of 9 mm, and a distance of 11 mm from the quenching end measured by the Jomini type one-end quenching method. The respective values of the hardness J11, and the obtained values (J9 / J1.5) and (J11 / J1.5) are shown. Furthermore, the bending (mm) evaluated after quenching the test piece and the absolute value (mm) of the difference in length of the test piece before and after the heat treatment are shown. Invention Example No. In the steel material consisting of 1 to 23, as shown in Table 3, the martensite transformation start temperature, that is, the Ms point is in the range of 372 to 442 ° C., and (J9 / J1.5) of this steel material is represented by the following formula (1 ) Is in the range of 0.70 to 0.95, the value of the formula (2) shown below in (J11 / J1.5) is in the range of 0.65 to 0.90, and the bend after heat treatment Was 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 was 0.01 to 0.20 mm.
However,
(J9 / J1.5) = (hardness at a distance of 9 mm from the quenching end measured by the Jomini type one-end quenching method) ÷ (1.5 mm from the quenching end measured by the Jominy type one-end quenching method) (Hardness) …… (1)
(J11 / J1.5) = (hardness at a distance of 11 mm from the quenching end measured by the Jomini type one-end quenching method) ÷ (a distance of 1.5 mm from the quenching end measured by the Jominy type one-end quenching method) (Hardness) …… (2)

  Similarly, Table 4 shows the measured Ms point of the steel of the comparative example, J1.5 of the hardness at a distance of 1.5 mm from the quenching end measured by the Jomini type one-end quenching method, and J9 of the hardness at a distance of 9 mm. And Jominy hardenability which is J11 of hardness at a distance of 11 mm, and the obtained values of (J9 / J1.5) and (J11 / J1.5) are shown. Furthermore, the bending (mm) after quenching of the test piece and the absolute value (mm) of the difference in length of the test piece before and after the heat treatment are shown.

  No. of the above invention example. 1 to 23, the composition range excluding unavoidable impurities excluding Fe, Ni, and Mo of steel materials is shown in Table 1, and the Ms point is set to 372 to 442 ° C. of 460 ° C. or less, and measured by the Jomini type one-end quenching method By appropriately controlling the hardenability to be performed, the value of (J9 / J1.5) calculated from the equation (1) is calculated from the range of 0.70 to 0.95 and from the equation (2) (J11 /J1.5) in the range of 0.65 to 0.90, the bending of the specimen after the heat treatment is reduced to a small range of 0.10 to 0.36 mm, and the length of the specimen before and after the heat treatment is further increased. The absolute value of the difference in thickness could be suppressed to a small range of 0.01 to 0.20 mm.

  On the other hand, No. of the above comparative example. In Table 2, the composition range excluding inevitable impurities excluding Fe, Ni, and Mo of steel materials 1 to 16 is shown in Table 2. 2, no. The remaining 14 cases, excluding 16 2 cases, were out of the composition range of the present invention. These No. Among the steels of Comparative Examples 1 to 16, 10 cases where the measured Ms point exceeds 460 ° C. are 0.49 to 0.76 mm in bending of the test piece after the heat treatment, which is larger than the steels of the inventive examples. . In addition, these No. Among the comparative steels 1 to 16, the range (J9 / J1.5) determined by the formula (1) and the formula (2) is 0.68 to 0.97 from the hardness measured by the Jomini type one-end quenching method. 15 examples in which the value of (J11 / J1.5) is outside the range of 0.63 to 0.94, the absolute value of the difference in length of the test piece before and after the heat treatment is 0.27 to 0 .45 mm, which is larger than the steel of the invention example. Therefore, among the comparative examples, there was no example in which the absolute value of the difference between the bending of the test piece after the heat treatment and the length of the test piece before and after the heat treatment was equivalent to that of the steel of the present invention.

  No. of the comparative example in which the measured Ms point is outside the scope of the claims. 1 to 3, 5 to 7, 9, 10, 14, and 15 in which the Ms point satisfies the claims. In Nos. 1 to 23, 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) are out of the scope of claims. Compared with 1 and 3 to 16, the values of (J9 / J1.5) and (J11 / J1.5) satisfy the scope of claims. In Nos. 1 to 23, the absolute value of the difference in length of the test pieces before and after the heat treatment is small, and the heat treatment deformation is suppressed. In this embodiment, heat treatment deformation is evaluated not by carburizing and quenching but by quenching. However, even when carburized and quenched, it is confirmed that the heat treatment deformation of the steel material satisfying the present claim is small. The steel material of the present invention is used after tempering after quenching.

  From the above, according to the present invention, the steel material is processed into a part by the limitation of the steel component, the Ms point which is the martensitic transformation start temperature, and the limitation of the hardenability measured by the Jominy one-side quenching method. Heat treatment deformation when hardening for hardening or carburizing and quenching can be reduced. Such a steel material according to the present invention is a steel material applicable to power transmission parts such as gears and shafts used in automobiles and industrial machines.

Claims (4)

In mass%, C: 0.16-0.35%, Si: 0.10-1.50%, Mn: 0.10-1.20%, P: 0.030% or less, S: 0.030 %: Cr: 1.30-2.50%, Cu: 0.30% or less, Al: 0.008-0.800%, O: 0.0030% or less, N: 0.0020-0.0300 %, The balance is Fe and inevitable impurities, and the steel material is martensitic transformation start temperature (Ms point) of 460 ° C. or less. Using the following formula (1), J1.5 of the hardness at a distance of 1.5 mm from the quenching end of the steel material measured by the method and J9 of the hardness at a distance of 9 mm was calculated (J9 / J1.5 ) In the range of 0.68 to 0.97, and the distance 1. The value of (J11 / J1.5) calculated by the following equation (2) using J1.5 of hardness at mm and J11 of hardness at distance 11 mm is in the range of 0.63 to 0.94. A machine structural steel material having a small heat treatment deformation.
However,
(J9 / J1.5) = (hardness at a distance of 9 mm from the quenching end measured by the Jomini type one-end quenching method) ÷ (distance from the quenching end measured by the Jominy type one-end quenching method. (Hardness of 5mm) …… Formula (1)
(J11 / J1.5) = (hardness of a distance of 11 mm from the quenching end measured by the Jomini-type one-end quenching method) ÷ (distance from the quenching end measured by the Jomini-type one-end quenching method. (Hardness of 5mm) …… Formula (2) In mass%, C: 0.16-0.35%, Si: 0.10-1.50%, Mn: 0.10-1.20%, P: 0.030% or less, S: 0.030 %: Cr: 1.30-2.50%, Cu: 0.30% or less, Al: 0.008-0.800%, O: 0.0030% or less, N: 0.0020-0.0300 Is a steel for machine structural use that further contains one or two of Ni: 0.20 to 3.00% and Mo: 0.05 to 0.50%, the balance being Fe and inevitable impurities. The steel material made of the steel has a martensite transformation start temperature (Ms point) of 460 ° C. or less, and the steel material has a hardness at a distance of 1.5 mm from the quenching end of the steel material measured by the Jominy one-end quenching method. The following formula (1) using J1.5 of the thickness and J9 of the hardness at a distance of 9 mm Therefore, the calculated value (J9 / J1.5) is in the range of 0.68 to 0.97, and further using the hardness J1.5 at the distance 1.5 mm and the hardness J11 at the distance 11 mm, (J11 / J1.5) calculated by the equation (2) in the range of 0.63 to 0.94, a steel material for mechanical structure having a small heat treatment deformation.
However,
(J9 / J1.5) = (hardness at a distance of 9 mm from the quenching end measured by the Jomini type one-end quenching method) ÷ (distance from the quenching end measured by the Jominy type one-end quenching method. (Hardness of 5mm) …… (1)
(J11 / J1.5) = (hardness of a distance of 11 mm from the quenching end measured by the Jomini-type one-end quenching method) ÷ (distance from the quenching end measured by the Jomini-type one-end quenching method. (Hardness of 5mm) …… (2) In mass%, C: 0.16-0.35%, Si: 0.10-1.50%, Mn: 0.10-1.20%, P: 0.030% or less, S: 0.030 %: Cr: 1.30-2.50%, Cu: 0.30% or less, Al: 0.008-0.800%, O: 0.0030% or less, N: 0.0020-0.0300 Is a steel for machine structural use that contains 1 or 2 types of Ti: 0.020-0.200%, Nb: 0.02-0.20%, and the balance Fe and inevitable impurities. , The martensitic transformation start temperature (Ms point) of the steel material made of the steel is 460 ° C. or less, and the steel material has a hardness at a distance of 1.5 mm from the quenching end of the steel material measured by the Jomini type one-end quenching method. J1.5 and hardness of 9 at a distance of 9 mm, the following formula (1 The value of (J9 / J1.5) calculated by the above is in the range of 0.68 to 0.97, and further using the hardness J1.5 at a distance of 1.5 mm and the hardness J11 at a distance of 11 mm, (J11 / J1.5) calculated by the equation (2) in the range of 0.63 to 0.94, a steel material for mechanical structure having a small heat treatment deformation.
However,
(J9 / J1.5) = (hardness at a distance of 9 mm from the quenching end measured by the Jomini type one-end quenching method) ÷ (1.5 mm from the quenching end measured by the Jominy type one-end quenching method) (Hardness) …… (1)
(J11 / J1.5) = (hardness at a distance of 11 mm from the quenching end measured by the Jomini type one-end quenching method) ÷ (a distance of 1.5 mm from the quenching end measured by the Jominy type one-end quenching method) (Hardness) …… (2) In mass%, C: 0.16-0.35%, Si: 0.10-1.50%, Mn: 0.10-1.20%, P: 0.030% or less, S: 0.030 %: Cr: 1.30-2.50%, Cu: 0.30% or less, Al: 0.008-0.800%, O: 0.0030% or less, N: 0.0020-0.0300 %
In addition, Ni: 0.20 to 3.00%, Mo: 0.05 to 0.50%, or one or two of Ti: 0.020 to 0.200%, Nb: It is a steel for machine structural use containing 0.02 to 0.20% of 1 type or 2 types and the balance being Fe and inevitable impurities, and the martensitic transformation start temperature (Ms point) of the steel material made of the steel is 460 ° C. The following formula is used, using J1.5 of the hardness at a distance of 1.5 mm and J9 of the hardness at a distance of 9 mm from the quenching end of the steel material measured by the Jominy one-side quenching method for the steel material. The value of (J9 / J1.5) calculated by (1) is in the range of 0.68 to 0.97, and further, J1.5 of hardness at a distance of 1.5 mm and J11 of hardness at a distance of 11 mm are used. Calculated by the following formula (2) Small mechanical structural steel of heat treatment deformation, characterized in that the value of the (J11 / J1.5) is in the range of 0.63 to 0.94.
However,
(J9 / J1.5) = (hardness at a distance of 9 mm from the quenching end measured by the Jomini type one-end quenching method) ÷ (1.5 mm from the quenching end measured by the Jominy type one-end quenching method) (Hardness) …… (1)
(J11 / J1.5) = (hardness at a distance of 11 mm from the quenching end measured by the Jomini type one-end quenching method) ÷ (a distance of 1.5 mm from the quenching end measured by the Jominy type one-end quenching method) (Hardness) …… (2)