JPS6148557A - Machine structural steel - Google Patents

Abstract

PURPOSE:To obtain a machine structural steel having low anisotropy in bending fatigue strength by subjecting a steel contg. specified amounts of C, Si, Mn and S to induction hardening so as to regulate the ratio of bending fatigue strength after induction hardening to a specified value or above. CONSTITUTION:The composition of a steel is composed of, by weight, 0.3-0.8 % C, 0.01-0.39% Si, 0.4-2% Mn, <0.01% S and the balance Fe with inevitable impurities. One or more among <5% Ni, <2% Cr, <2% Mo and <0.01% B or one or more among <0.1% Al, <0.03% N, <0.5% Ti, <0.5% V and <0.5% Nb may be added to the composition. The steel is subjected to induction hardening so as to regulate the ratio of bending fatigue strength after induction hardening (6WT/6WL) to >=0.8.

Description

[Detailed description of the invention]

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[Industrial Application Field 1] The present invention relates to various types of mechanical structural steels to which repeated bending stress is applied in a direction (referred to as "downward direction") perpendicular to the working direction of rolling or forging (referred to as "rLh direction"). .
It is particularly useful for manufacturing gears and spline shafts. BACKGROUND OF THE INVENTION When manufacturing mechanical structural parts for applications where strong stress is applied to the surface, surface hardening treatment is often performed. Typical surface hardening treatment methods include carburizing and hardening and induction hardening. As is well known, carburizing and quenching can achieve a high degree of surface hardening, but it requires long heating times, consumes a lot of energy, and has the disadvantages of large deformation due to the treatment. On the other hand, induction hardening has the advantage that it can be carried out in a short time and is preferable from the viewpoint of energy saving, and that finishing processing is unnecessary or easy due to small deformation, but the degree of surface hardening is not as high as that of carburizing hardening. Also, the bending fatigue strength in the downward direction is lower than that of carburized and quenched materials. For this reason, in structural parts that are subjected to large stresses, carburizing is the usual means of surface hardening, and induction hardening is not often used. The applicant has made extensive research to take advantage of the above-mentioned advantages of induction hardening and to obtain high effects, and has achieved a higher S than conventional carbon steel.
We learned that mechanical structural parts with strong fatigue strength and high surface hardness can be obtained by induction hardening parts made of steel with a high content of i, and we would like to disclose this in Japanese Patent Application Laid-Open No. 58-171554. ).

[Problems to be solved by the invention]

An object of the present invention is to provide mechanical structural steel using induction hardening, which has a high bending fatigue strength in the downward direction, that is, in the direction perpendicular to the forging direction, and therefore -
C. An object of the present invention is to provide a steel for mechanical structures that has low anisotropy in bending fatigue strength. 11 to 11

[Means to solve the problem]

The machine structural steel of the present invention basically has a C: 0°30~
0.80%, Si: 0.01-0.39%, Mn
: 0.40 to 2.0% and S: 0.01% or less, with the balance consisting of Fe and unavoidable impurities, which is induction hardened and exhibits a certain low anisotropy after induction hardening. It is characterized by Bending fatigue strength ratio σWT/σWL of 0.8 or more It is also possible to add the following alloy components to the above basic composition. In order to improve the strength and toughness after induction hardening,
Further, one or more of Ni: 5% or less, Cr: 2% or less, Mo = 2% or less, and B: 0.01% or less. For the purpose of refining crystal grains and improving toughness and strength, A-bun2: 0.1% or less, N: 0.03% or less, ■+
:O0!596 or less, V: 0.5% or less and Nb:
Q, 5% or less of one or more types (Ti, V and Nb are also useful for improving surface pressure fatigue properties). Ca improves machinability: 0.01% or less, Te
: 0.5% or less and Pb : 0.5% type 1 or 2
(Note that Ca and Te have the function of spheroidizing MnS inclusions in the steel, improve downward bending fatigue resistance, and are also useful for improving toughness.) In addition, to prevent burning, Pro, preferably 0.020% or less, and in order to obtain high fatigue strength in the rolling direction, O:
It should be 0.0020% or less. 1 Effect] By lowering the S content of steel to 0.01% or less, the amount of MnS inclusions in steel is reduced. The present inventors found that the origin of fatigue failure due to downward bending stress in induction hardened materials was not the AJL203 inclusions, but M
It was found that these were nS inclusions. In the past, the presence of MnS was rather welcomed in order to improve machinability, but in order to improve the downward bending fatigue strength of induction hardened materials, it is necessary to reduce MnSm, that is, the S content in steel. It becomes clear what needs to be done. The roles of alloy components other than those mentioned above and the reasons for limiting the composition are as follows. C: 0.30 to 0.80% The lower limit is a value necessary to obtain the strength required for mechanical structural steel, and the upper limit is set to avoid burn cracks. Si: 0.01-0.39% 0.01% or more is required for deoxidation, and on the other hand, if the amount increases, the ease of plastic working will be lost, so 0.39%
Up to. Mn: Q, 40-2.0% It is added for the purpose of deoxidizing and ensuring strength, and the lower limit is the level necessary for this purpose. The upper limit was determined from the viewpoint of rigidity. [Embodiment 1] The effects of optionally added elements and the reasons for limiting the composition are explained in 9 below.
show. One or 2f of Ni: 5% or less, Ctl: 2% or less, Mo: 2% or less, and B: 0.01% or less! These are elements effective in improving the strength and toughness after induction hardening. However, since excessive addition impairs ductility, it should be within the above limits. A51: 0.1% or less, N: 0.03% or less, Ti:
0.5% or less, V: 0.596 or less #J[Nb: 0.
Either one type or two or more types having an amount of 5% or less has the effect of refining crystal grains. However, even if added in large amounts, the effect will be saturated, so each should be added within the limits listed. Note that when Ti, V, and Nb are added within the above composition range, they are also useful for improving surface pressure fatigue properties. Ca: 0.01% or less, Te: 0.5% or less, and P
b: Q, 5% or less of one or more types added when it is desired to improve machinability. Since excessive presence impairs hot workability and ductility, a limit was set as described above. [Example] Steel having the alloy composition shown in the table was melted in an electric furnace. After rolling into a round bar with a diameter of 100 mar, quenching and tempering, a smooth specimen with a parallel portion diameter of 8n+m was cut in the [direction and downward direction]. This test piece was induction hardened (effective hardened layer depth approximately 2 mm).
After the test was completed, a rotating bending fatigue test was conducted. The results are also shown in the table. σ L indicates the fatigue limit in the L direction, and σ indicates the fatigue limit in the downward direction. The ratio σ
It is interesting to note that the closer L/ is to 1, the lower the anisotropy. -Nkasa -Ω-" え -■--5= N Denkome Kaidan 1
0.55 0.25 150 0.
0052 0.45 0. IOO,750,0
02Mo: 0.43 0.65 0.35
1,45 0.0084 0.54 0
,24 0,65 0.0075 0.5
6 0.26 1.65 0.0046
0.55 0.25 0.85 0
．． 0057 0.54 0.22 1.4
8 Q, OQ7 Ni: 1.58 0
．． 56 0.24 145 0.005
Cr:L09 0.55 0.27
1.55 0.003 3:0.00310
0.57 0.22 153 0
．． 00811 0.53 0,25 1,
55 0.00512 0.5B O,
231,410,0%13 0.55 0.2
2 1.44 0.00514 0.5
4 0,25 1,56 0.00415
0.56 0,26 1,55
0.00216 0.55 0.22 1
,54 0.005 Mo+0.217
0.56 0.21 1.53 0.0
0618 0.57 0,25 1,55
0.008 Mo:0.2+9 0.
54 0.24 1.56 0.004
Mo: 0.2!
20 0.54 0.24 1. F.O.
0,0021ylo: 0.3 Comparative example 0.54
0,26 1,50 0.022 8 rika Gunri G small y Karasu 1 匡ヱdan -P--Ω-1 Intersection-Dan W
σWT/σW180 75 0.9f
181 76 G, 94V: 0.
2
83 77 0.93Ca
+ 0.002 80
74 0.930.012
81 76 0.940.0
008 85 80 0.941
12 75 0.9183 7
6 0.9282 76
0.93ΔQ: 0.03
82 73
0.89N:ll, 02
83 78
0.941i: Q, 1
82 75
0.92Nb: 0.2
83 74
0.89Te: 0.1
78 69 0.88Pb:
0.1 0.012 79
73 0.93V:O,+
84
77 0.92V: O,i
Ca: O, OQ3
85 79 0.93v: O
,i (J: 0.002
84 76
0.90v: 010. O12837F3 0
．． 91V: 0.1
0. (101286760,888052
0,65 and J'll The steel for induction hardening of the present invention has low anisotropy in bending strength, and the value of σWτ/σWL indicates that the structural steel for machine construction is isotropic. It exceeds 8, and is usually 0.9 or more.
Since many benefits can be enjoyed by induction firing, the present invention is suitable for manufacturing parts that are required to be produced at low cost even though high forces are applied, such as automotive transmission parts. Patent applicant suitable for Daido Steel Co., Ltd.

Claims (6)

[Claims] (1) C: 0.30-0.80%, Si: 0.01-0
．． 39%, Mn: 0.40-2.0% and S: 0.0
1% or less, with the balance consisting of Fe and unavoidable impurities, and is made by induction hardening, and has a low anisotropy with a bending fatigue strength ratio σWT/σWL of 0.8 or more after induction hardening. A mechanical structural steel characterized by the following: (2) The steel further includes Ni: 5% or less, Cr: 2% or less,
Any one of Mo: 2% or less and B: 0.01% or less
The machine structural steel according to claim 1, which contains one or more species. (3) Steel further includes Al: 0.1% or less and N: 0.03
% or less, Ti: 0.5% or less, V: 0.5% or less, and Nb: 0.5% or less. Mechanical structural steel as described. (4) The steel further contains Ca: 0.01% or less and Te: 0.
Claims 1 to 3 contain any one or more of 5% or less and Pb: 0.5% or less.
Machine structural steel as described in any of the above. (5) A steel for machine structural use according to any one of claims 1 to 4, which uses steel containing P: 0.020% or less. (6) The steel for machine structures according to any one of claims 1 to 5, which uses steel containing O: 0.0020% or less.