JP2564531B2 - Hot forging steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a part manufactured by hot forging, for example,
The present invention relates to hot forging steel used as a material for knuckle arms, knuckle spindles, and the like.

(Prior Art) Conventionally, tempered steel such as carbon steel or alloy steel has been used as a material for automobile parts, particularly knuckle arms, knuckle spindles and the like, which are required to have high strength and high toughness. That is,
The above tempered steel is the one that has been subjected to heat treatment of quenching and tempering after hot forging, and this heat treatment is usually for heating for austenitizing, cooling from austenite, tempering after quenching, etc. This is done by going through a representative process.

However, such a refining treatment requires many steps, which causes an increase in manufacturing cost. In recent years, a non-tempered steel containing vanadium (V) has been developed and put into practical use for the purpose of reducing the number of steps. Has been converted.

Specifically, this V-containing non-heat treated steel is produced, for example, by adding about 0.1% by weight of V to a steel containing an alloy component such as carbon steel, and performing air cooling or wind blast cooling after hot forging. To be done.

(Problems to be solved by the invention) However, although this V-containing non-heat treated steel can omit the number of manufacturing steps, it has a low impact value, especially at low temperature, and a good balance between strength at room temperature and impact value at low temperature. There is a problem that it is not. Therefore, it has been difficult to use it as a material for undercarriage parts of automobiles, which are required to have high strength and high impact value at low temperature as described above.

The present invention has been made in view of the above conventional problems,
The strength at room temperature and the impact value at low temperature are both good without the need for tempering, and in particular hot forged steel useful as a material for undercarriage parts of automobiles such as knuckle arms and knuckle spindles. The purpose is to provide.

(Means and Actions for Solving Problems) In the steel composition, the present inventors have found that the contents of Mn and Cr individually, the sum of Cr and Mn (Cr + Mn), and the ratio of Cr and Mn contents (Cr / Mn). Mn) and the strength of the resulting hot forging steel, for example, tensile strength and impact value at low temperature, have been studied variously, and the optimum values have been found. That is, in order to achieve the above object, the steel for hot forging according to the first aspect of the present invention is wt%, C: 0.04 to 0.15%, Si: 1.0% or less, Mn: 0.3 to 3.
0%, Cr: 0.7 to 3.0%, Al: 0.01 to 0.06%, Mo: 0.02 to 0.50%, Nb: 0.01 to 0.20% and V: 0.03 to
At least one of 0.30% is included, Mn + Cr: 4% or less, Cr / Mn is 1.0 or more, and the balance is substantially Fe.
After hot forging, by rapidly cooling from a temperature of Ar ₃ transformation point or higher, high strength and high toughness at low temperature can be obtained.

Furthermore, according to the steel for hot forging according to the second aspect of the present invention, in% by weight, C: 0.04 to 0.15%, Si: 1.0% or less, Mn: 0.3 to 3.0.
%, Cr: 0.7 to 3.0%, Al: 0.01 to 0.06%, Mo: 0.02 to 0.50%, Nb: 0.01 to 0.20% and V: 0.03 to 0.
At least one of 30%, and S: 0.15% or less, P
b: 0.30% or less, Ca: 0.005% or less, Bi: 0.30% or less and Te:
Contains at least one of 0.30% or less, Mn + Cr: 4
% Or less, Cr / Mn is 1.0 or more, the balance is substantially Fe, and high strength and high toughness at low temperature can be obtained by quenching from a temperature of Ar ₃ transformation point or higher after hot forging. It was done.

Next, the reasons for limiting the contents of the respective constituent elements forming the main part of the chemical composition of the steel for hot forging according to the first present invention will be described.

C: 0.04 to 0.15 wt% C is a component element effective for improving the strength of the forged product, and at least 0.04 wt% is necessary for improving the strength. However, if it is too large, the toughness will decrease, so the upper limit is 0.15.
It was set to% by weight.

Si: 1.0 wt% or less Si is an element that has a deoxidizing action during steel melting, but if it is too much, it decreases toughness, so the upper limit is 1.0 wt%.
And

Mn: 2.00 wt% or less Mn is an element that has a deoxidizing action and a desulfurizing action during steel melting, controls the morphology of inclusions, improves quenchability and enhances the strength of forged products. is there. However, if contained in a large amount, machinability and toughness will decrease, so
The upper limit was 2.00% by weight.

Cr: 0.7 to 3.0 wt% Cr is an element effective in improving the hardenability and the strength of the forged product, and at least 0.7 wt% is required to obtain such an effect. However, if a large amount is added, the strength transiently increases and the toughness decreases, so the upper limit is 3.0.
It was set to% by weight.

Al: 0.01 to 0.05% by weight Al is an element having a strong deoxidizing action during steel melting, and is effective in reducing oxide inclusions in steel and increasing strength. At least 0.01% by weight is necessary to obtain the effect. However, if the content is too large, the effect of adding solute N is reduced, so the upper limit is set to 0.
It was set to 05% by weight.

Mn + Cr: 4 wt% or less, Cr / Mn: 1.0 wt% or more To ensure sufficient toughness of forged products, especially to ensure toughness at low temperatures, the upper limit of Mn + Cr is set to 4% by weight and the lower limit of Cr / Mn is 1.0 wt% %.

The steel for hot forging according to the first aspect of the present invention further comprises, as toughness improving elements, 0.02 to 0.50 wt% Mo and 0.01 to 0.20 wt%.
At least 1 of Nb and 0.03 to 0.30% by weight of V
It contains seeds. Each of these elements requires at least the above lower limit values in order to obtain a sufficient addition effect. However, even if a large amount of these is added, not only the improvement of the addition effect cannot be expected, but also the price is unnecessarily increased, so the upper limit values are set for each.

Furthermore, the hot forging steel according to the second aspect of the present invention, in addition to the above-mentioned respective constituent elements of the hot forging steel according to the first aspect of the present invention,
As a machinability improving element, 0.15 wt% or less S, 0.30 wt%
Pb below, 0.005 wt% or less of Ca, 0.30 wt% or less of B
It contains at least one of i and 0.30 wt% or less of Te. However, if a large amount of these elements is added, the hot workability and toughness are deteriorated, so the respective upper limits are set.

The hot forging steels according to the first and second aspects of the present invention described above are capable of obtaining high strength and high toughness at low temperature by quenching from a temperature of Ar ₃ transformation point or higher after forging. is there. The Ar ₃ The transformation point or higher temperatures, for example, Ar ₃ transformation point temperature + 50 ℃ about temperature is preferred. Further, as the above-mentioned rapid cooling method, water cooling or oil cooling is preferable.

In the steel for hot forging of the present invention, tempering after quenching is not necessary, but tempering at about 200 ° C may be performed.

(Examples) Examples 1 to 8 and Comparative Examples 1 to 8 Hot forging steel ingots having an outer diameter of 60 mm and having the composition shown in Table 1 were forged at 1200 ° C to obtain a bar material having an outer diameter of 40 mm. It was The temperature at the end of forging was 950 ° C. Then, after being rapidly cooled by water cooling, each was processed to prepare a test piece. After that, the following evaluation tests were performed on the test pieces of each steel type.

Strength JIS Z 2201 standard No. 4 test piece (6 mmφ, gauge length 21.0 m
m) was used to measure the tensile strength (kgf / mm ² ) at room temperature, and the results are shown in Table 1.

Toughness Using a tensile test piece (2 mm U notch) specified by JIS Z2202,
The Charpy impact value (kgfm / cm ² ) at −50 ° C. was measured, and the results are shown in Table 1.

Machinability Tool: SKH9 (φ5) drill Feed: 0.1mm / rev Cutting speed: 21m / min Hole depth: 20mm (blind hole) Cutting fluid: None (dry type) Life judgment: Cutting distance until tool melting (mm) ) Examples 6 to 7 and Comparative Example 9 Regarding the steel types used in Example 4 above, after changing the cooling method after forging variously to prepare test pieces, the strength and toughness were measured in the same manner as above, The results are shown in Table 2.

As is clear from Tables 1 and 2, the hot forging steel of the present invention has strength at room temperature and low temperature (-50
(° C), the toughness is well balanced (Table 1), and the high strength and high toughness are exhibited only when rapid cooling such as oil cooling or water cooling is performed after hot forging (No. 1). Table 2) was confirmed.

(Effects of the invention) As described above, according to the hot forging steel according to the first aspect of the present invention, in% by weight, C: 0.04 to 0.15%, Si: 1.0% or less,
Mn: 0.3 to 3.0%, Cr: 0.7 to 3.0%, Al: 0.01 to 0.06%, Mo: 0.02 to 0.50%, Nb: 0.01 to 0.20% and V: 0.03 to 0.30% at least one kind Containing Mn +
Cr: 4% or less, Cr / Mn is 1.0 or more, the balance is essentially Fe, and high strength and high toughness at low temperature are obtained by quenching from the temperature of Ar ₃ transformation point or higher after hot forging. Therefore, high strength and high toughness at low temperature are achieved in a well-balanced manner.

According to the hot forging steel according to the second aspect of the present invention, the weight% is
, C: 0.04 to 0.15%, Si: 1.0% or less, Mn: 0.3 to 3.0%, C
r: 0.7 to 3.0%, Al: 0.01 to 0.06%, and M
o: 0.02-0.50%, Nb: 0.01-0.20% and V: 0.3-0.30%, at least one, and S: 0.15% or less, Pb: 0.30
% Or less, Ca: 0.005% or less, Bi: 0.30% or less and Te: 0.30%
At least one of the following is contained, Mn + Cr: 4% or less, Cr / Mn is 1.0 or more, and the balance is substantially Fe.
It was decided that high strength and high toughness at constant temperature could be obtained by quenching from a temperature above the Ar ₃ transformation point after hot forging, so not only high strength and high toughness but also machinability was greatly improved. To do.

Thus, the steel for hot forging of the present invention is confirmed to be extremely useful as a material for undercarriage parts of automobiles that require high strength such as knuckle arms and knuckle spindles and high toughness at low temperatures. It was

Claims (2)

(57) [Claims] 1. By weight%, C: 0.04 to 0.15%, Si: 1.0% or less, Mu: 0.3 to 3.0%, Cr: 0.7 to 3.0%, Al: 0.01 to 0.06%
In addition to containing Mo: 0.02 to 0.50%, Nb: 0.01 to 0.20
% And V: 0.03 to 0.30% of at least one kind,
Mn + Cr: 4% or less, Cr / Mn is 1.0 or more, the balance is substantially
A steel for hot forging, which is made of Fe and is capable of obtaining high strength and high toughness at low temperature by quenching from a temperature of Ar ₃ transformation point or higher after hot forging. 2. By weight%, C: 0.04 to 0.15%, Si: 1.0% or less, Mn: 0.3 to 3.0%, Cr: 0.7 to 3.0%, Al: 0.01 to 0.06%
In addition to containing Mo: 0.02 to 0.50%, Nb: 0.01 to 0.20
% And V: at least one of 0.03 to 0.30%, and
S: 0.15% or less, Pb: 0.30% or less, Ca: 0.005% or less, Bi: 0.
It contains at least one of 30% or less and Te: 0.30% or less, Mn + Cr: 4% or less, Cr / Mn is 1.0 or more, the balance is substantially Fe, and the Ar ₃ transformation point after hot forging A steel for hot forging, which has high strength and high toughness at a constant temperature when rapidly cooled from the above temperature.