JPH073384A - Non-refining steel for induction hardening - Google Patents

Abstract

PURPOSE:To provide non-refining steel good in hardenability, in which the core part has high strength and high toughness and suitable for induction hardening. CONSTITUTION:The chemical components of non-refining steel for induction hardening are constituted of (1) ones contg., by weight, 0.25 to 0.40% C, 0.05 to 0.60% Si, 1.00 to 2.50% Mn, 0.05 to 0.5% V, 0.2 to 1.5% Cr, 0.01 to 0.10% S, 0.015 to 0.050% Al and 0.01 to 0.1% N, and the balance Fe with inevitable impurities, (2) ones furthermore contg. 0.005 to 0.1% Ti in addition to the same chemical components, (3) ones moreover contg. one or >= two kinds among 0.02 to 0.3% Pb, Bi, Se and Te and 0.001 to 0.01% Ca in addition to the chemical components in the (1) or (4) ones furthermore contg. 0.005 to 0.1% Ti in addition to the chemical components in the (3).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-heat treated steel which has sufficient strength and toughness without being subjected to heat treatment such as quenching and tempering after hot forging and is suitable for induction hardening.

[0002]

2. Description of the Related Art Conventionally, pins for which abrasion resistance, galling resistance or fatigue strength are required for industrial vehicles and construction machines,
JIS S45C which is steel for machine structure and SCM435 which is alloy steel for machine structure are used for shafts and rods.
Cr-Mo steels such as are commonly used. These steel types are so-called heat-treated steels.The above parts are formed by quenching and tempering a rolled material or rough-worked product to give it predetermined strength and toughness, and then induction hardening at a required site to form a surface hardened layer. As a result, wear resistance, galling resistance or fatigue strength was improved.

However, since such heat-treated steel is subjected to heat treatment after hot working, the cost for this heat treatment is high, and for carbon steel such as S45C, induction hardening is applied to large diameter parts. It was difficult to achieve a satisfactory hardening depth due to insufficient penetrability, and it was necessary to use expensive alloy steel such as SCM435.

For this reason, non-heat treated steel that does not require heat treatment such as quenching and tempering after hot rolling or forging is adopted to reduce the cost. However, induction hardening is applied to such non-heat treated steel. Even if it was applied, quenching strain and coarsening of crystal grains occurred, and a satisfactory hardened layer depth was not sufficiently obtained. As a means for solving such a problem, JP-A-63-10015 has been proposed.
There are inventions of non-heat treated steels for induction hardening in Japanese Patent Laid-Open No. 7 and Japanese Patent Application Laid-Open No. 2-179841, but these are added with Mo or Nb so as to produce a bainite structure, or B is contained to obtain SCM435-like. There are some that try to obtain the hardenability of.

When induction hardening is performed on conventional non-heat treated steel for hot forging, the core has high strength (σ _B = 882 MP).
a), there is no example of induction hardening of a material satisfying high toughness ( _2U E ₂₀ ° C = 49 J / cm ² ).

[0006]

DISCLOSURE OF THE INVENTION The present invention has sufficiently good hardenability without the addition of Mo, Nb or B as described above, and the core has high strength and high toughness. And it is to provide a non-heat treated steel suitable for induction hardening.

[0007]

In order to solve the above problems, the present invention provides a chemical composition of non-heat treated steel for induction hardening in a weight ratio of 1) C: 0.25 to 0.40%, Si: 0.05
.About.0.60%, Mn: 1.00 to 2.50%, V: 0.
05-0.5%, Cr: 0.2-1.5%, S: 0.0
1 to 0.10%, Al: 0.015 to 0.050%,
N: 0.01 to 0.1%, balance Fe and inevitable impurities, 2) Ti: 0.005 to 0.1% in addition to the above chemical components, 3) above In addition to the chemical components of 1), Pb, Bi, Se or T
e: 0.02-0.3% or Ca: 0.001-
0.01% of any one kind or two kinds or more, 4) the chemical component of 3) above, and T
i: 0.005-0.1% shall be contained.

[0008]

The steel of the present invention has a high tensile strength σ _B of 882 MPa or more (σ _B ≧ 882 MPa) and an impact value of JIS J Charpy impact test piece of 49 J / cm ² or more ( _2U E ₂₀ ° C ≧
It has a high toughness of 49 J / cm ² ) and an ideal critical diameter: DI of 1.5 (inch) or more, which is a measure of easiness of quenching, that is, easiness of hardening in order to secure induction hardenability. There is.

The reasons for limiting the components of the steel of the present invention will be described below. C requires 0.25% or more in order to secure induction hardening hardness and strength as steel for machine structural use. However, if the amount is too large, the toughness decreases, so the upper limit is 0.40%.
And

Si is a deoxidizer during melting and is added to secure the strength. If it is less than 0.05%, its action is insufficient, and if it is too much, the toughness decreases, so the upper limit is 0.60. %.

Like Mn, Mn is a deoxidizing agent during melting and secures strength, and it is necessary to add 1.00% or more in order to further improve toughness.
However, the machinability deteriorates, so the upper limit is made 2.50%.

V is an element necessary for precipitating fine carbides and ensuring the necessary strength and toughness, and in order to obtain the effect, V must be added in an amount of 0.05% or more. However, even if added in a large amount, the effects of strength and toughness are saturated, so the upper limit is made 0.5% from the viewpoint of cost.

Cr is an element necessary for ensuring strength and toughness, and it is necessary to add it in an amount of 0.2% or more in order to obtain its effect. However, if added in a large amount, the toughness is significantly reduced, so the upper limit is made 1.5%.

S is an element necessary for improving the machinability, and in order to obtain the effect, it is necessary to add 0.01% or more. However, if it is contained in a large amount, the hot workability is deteriorated, the toughness is further deteriorated, and a problem occurs in manufacturing, so the upper limit is made 0.10%.

Al, like Si, is a deoxidizing agent at the time of melting, and is an element necessary to combine with N to generate AlN and to refine the crystal grains. In order to obtain the above effect, it is necessary to contain 0.015% or more. However, if the content exceeds 0.030%, the toughness decreases, so the upper limit is made 0.030%.

N is AlN by combining with Al as described above.
Is necessary to prevent the crystal grain coarsening, and to obtain the effect, it is necessary to contain 0.01% or more. However, if the content exceeds 0.03%, the toughness decreases, so the upper limit is made 0.03%.

[0017] Ti is an element effective in combining with N to form TiN to refine the crystal grains and increase the strength, and in order to obtain the effect, 0.005% or more is contained. is necessary. However, even if the content exceeds 0.1%, the effect is saturated, so the upper limit is made 0.1%.

Pb, Bi, Se, Te and Ca are all elements effective for improving machinability, and Pb, B
i, Se, Te: 0.02-0.3% and Ca: 0.00
Within the range of 1 to 0.01%, each element is substitutable in terms of its effect. 0.02% for Pb, Bi, Se, Te
And Ca less than 0.001% have no effect. However, Pb, Bi, Se and Te exceed 0.3%, and C
When a is contained in excess of 0.01%, the hot workability is deteriorated, so the upper limit of each element of Pb, Bi, Se and Te is set to 0.
3%, the upper limit of Ca is 0.01%.

[0019]

EXAMPLES Next, the features of the present invention will be shown by examples in comparison with comparative steels. Table 1 shows chemical compositions of these test steels other than Fe and inevitable impurities. Test Steel 1 of the invention steels
6 to 6 are the invention steels of claim 1, and the test steels 7 to 10 are claim 2
Of the invention steels, the test steels 11 to 15 are the invention steels of claim 3,
The steel under test 16 relates to claim 4. Among the comparative steels, the sample steel 17 has less C content than the present invention, the sample steel 18 has less Mn content than the present invention, and the test steel 19 has less C content than the present invention. There are many.

[0020]

[Table 1]

Specimen steel 100 having the chemical composition shown in Table 1
kg is melted using a vacuum melting furnace, this 100 kg steel ingot is hot forged at 1200 ° C., forged into a steel bar with a diameter of 30 mm, and using this, JIS No. 3 Charpy impact test piece and JIS No. 4 tensile A test piece was prepared. Tensile strength: σ _B (MPa), impact value: _2U E ₂₀ ° C ( ₂ mm _U notch, J / cm ² ) were measured for each test piece of the obtained test steel,
The ideal critical diameter: DI (inch) (easiness of quenching, that is, ease of hardening) was calculated, and the results are shown in Table 2.

[0022]

[Table 2]

From Table 2, each of the invention steels has a high tensile strength σ _B of 882 MPa or more (σ _B ≧ 882 MPa) and an impact value of 49 J / cm ² or more at ² mm _U notch ( _2U E
It has a high toughness of ₂₀ ° C. ≧ 49 J / cm ² ) and has an ideal critical diameter DI of 1.5 (inch) or more, which is a measure of the ease of quenching in induction hardening, that is, the ease of hardening. On the other hand, the comparative steels 17 and 18 had a DI of not more than 1.5, and the comparative steel 19 had a _2U E ₂₀ ° C. of less than 49 J / cm ² and had insufficient toughness.

[0024]

The steel of the present invention has a tensile strength σ _B of 882 M.
High strength of Pa or more, impact value is 49 J / cm with 2mm U notch
It has a high toughness of ² or more and in order to ensure induction hardenability,
Ideal critical diameter, which is a measure of easiness of quenching, that is, easiness of hardening, has a DI of 1.5 (inch) or more, has good hardenability, and has a core having high strength and high toughness. In addition, it is a non-heat treated steel suitable for induction hardening.

Claims (4)

[Claims] 1. A weight ratio of C: 0.25 to 0.40%, S
i: 0.05 to 0.60%, Mn: 1.00 to 2.50
%, V: 0.05 to 0.5%, Cr: 0.2 to 1.5
%, S: 0.01 to 0.10%, Al: 0.015
A non-heat treated steel for induction hardening characterized by containing 0.030% and N: 0.01 to 0.03%, and the balance being Fe and unavoidable impurities. 2. The steel according to claim 1, further comprising Ti:
A non-heat treated steel for induction hardening characterized by containing 0.005 to 0.1%. 3. The steel according to claim 1, further comprising Pb,
Bi, Se or Te: 0.02-0.3% or C
a: any one of 0.001 to 0.01% or 2
A non-heat treated steel for induction hardening characterized by containing at least one kind. 4. The steel according to claim 3, further comprising Ti:
A non-heat treated steel for induction hardening characterized by containing 0.005 to 0.1%.