JPS6274055A - Non-heattreated steel with high toughness for hot forging - Google Patents

Abstract

PURPOSE:To provide excellent toughness and superior machinability in the as-forged condition by specifying the content relationship between (Mn+Cr) and V in a non-heattreated steel having a specific composition. CONSTITUTION:The steel has a composition consisting of, by weight, 0.1-0.25% C, 0.05-1.0% Si, 0.6-2.5% Mn, <=2.0% Cr, 0.03-0.30% V, 0.015-0.060% Al, 0.003-0.020% N and the balance Fe with impurities and satisfying (Mn+Cr)/ V>=8.0, to which one or more elements among Ni, Mo, Nb and Ti or further one or more elements among S, Pb, Zr, Ca and Te are incorporated by proper quantities, if necessary. According to the non-heattreated steel having the above composition, excellent high strength as well as high toughness can be obtained only by letting stand to be cooled after hot forging.

Description

Detailed Description of the Invention [Industrial Application Field 1] The present invention relates to a high-toughness non-tempered steel for hot forging, and more specifically, it can be made into a quenched and tempered steel by simply allowing it to cool after hot forging. It relates to high toughness non-tempered steel for hot forging with equivalent strength and toughness (5).

[Prior art 1] Conventionally, mechanical structural parts used in automobiles and construction are often made using carbon steel or alloy steel for bottom structure, which is hot-forged, reheated, and quenched. By performing heat refining treatment such as tempering, the material is manufactured using E-1, which has strength characteristics depending on the purpose and use.

However, due to the cost of a large amount of thermal energy in heat treatment, an increase in processing steps, and an increase in work-in-progress as explained above, the production of mechanical parts (manufacturing parts for machining) has to be expensive. It was long.

In recent years, J
Carbon steel for mechanical structures specified in IS G4051 and J
The material is non-temperature steel for hot forging, which contains minute amounts of precipitation hardening alloy elements such as V, Nb, and Ti, in addition to manganese steel and manganese chromium steel for mechanical structures specified in ISG4106. Non-temperature forged steel products, which can obtain desired properties without heat treatment by heating and forging during hot forging and subsequent cooling, are attracting attention, and some products have already been put into practical use. .

Normally, non-thermal forged steel products are rated at 1100 to 413SO.
Start forging from a temperature of 'C, 1000-1300'
It is manufactured by completing forging at a temperature of C and then leaving it to cool in the atmosphere.

[Problem to be Solved by the Invention 1] As explained above, the present invention is directed to non-temperature forged steel products manufactured from non-temperature steel for hot forging that have already been put into practical use. The same strength can be obtained, but the toughness is low, for example, when the tensile strength is 8t) kgf/;off12 or more, the Charpy impact value of 2mmV/Tchi at room temperature is only about 4.5 kBf-m/c +++2, It cannot exceed 6k) (f-III/c+n) required for 855C quenched and tempered material with the same strength.The reason for this is that conventional non-thermal forged steel products are heated and worked in a high temperature range, and then released. Due to cooling, the structure is ferrite/pearlite transformed from coarse austenite grains, and its strength is mainly ensured by the precipitation of pearlite, nitrides such as Nb, and so on. The inventor adjusted the content of elements to give high strength and excellent toughness to conventional non-tempered steel, and as a result of various experimental studies, the tensile strength was 3 h' 60 kgf/mm.
-90k3f/Inll1: Even if the structure is coarse ferrite/pearlite when left to cool after hot forging, it does not require quenching and tempering after forging, and exhibits high strength and excellent toughness. Furthermore, they developed a high-toughness non-temperature steel for hot forging with good machinability.

[Means for solving the problem 1 The high toughness non-tuning 'j'1gA for hot forging according to the present invention is (
1) Co, 10-0.25 nwt%, Si0.05-1
．． 01%, Mn 0.6-2.5+wt%, Cr 2.
0wt% or less, ■0.03-0. : lo+wt%, A
l 0.015~0.060wt%, N 0.003~
0,020 wt%, the balance consists of Fe and impurities, and
A high toughness non-thermal steel for hot forging characterized in that the content of 0, Cr, and ■ satisfies the formula (Mn+Cr)/V ≧8.0 is defined as invention 11, (2) C0.10 ~0.25w%, S i 0.
05-1.0wt%, Mn 0.6-2.5wt%, C
r 2.0wt% or less, V 0.03-0.30wt%
, Al 0.015-0.060%, N 0.003
~0.020 wt%, and further contains Ni 1.0 wt% or less, Mo 0.50 wt% or less,
Nf) 0,005-0.05wt%, Ti 0.005
Contains one or more selected from ~0.050wt%, the balance consists of Fe and impurities, and M0
．． A second invention provides a high-toughness non-thermal steel for hot forging, characterized in that the content of Cr and \P satisfies the formula (Mn+Cr)/~1≧8.0, (3) C0. 10-0.25111t%, Si 0.0
5-1.0tuL%, Mn 0.6-2.6-2.5w
t%, Cr 2.0wt% or less, V 0.030,30
wt%, Al 0.015-0.060+IIL%,
Contains N 0.003 to 0.020 IJIt%, S 0.12 wt% or less, Pb 0.30 wt% or less,
Zr 0.20wt% or less, CaO6Oht% or less, T
e) containing one or more selected from 0.10 wt% or less, the balance consisting of Fe and impurities, and M0. A third invention provides a high-toughness non-thermal steel for hot forging, characterized in that the content of Cr and ■ satisfies the formula (Mn+Cr)/V ≧8.0, (4) C0.10- 0゜25w [%, Si 0.05~
1.0wt%, Mn 0.6-2.5wt%, Cr2
．． Owt% or less, ~' 0.03-0.30wt%, A
I 0.015-0.060wt%, N09003-
0.020+l+t%, and further contains Ni 1.0wt% or less, Mo 0.50wL% or less,
Nb 0.005-0.05wt%, Ti 0.00
Contains one or more selected from 5-0.050 wL%, S 0.12 wt% or less, Pb 0.30 wL% or less, Z
r 0020wt% or less, Ca 0. O'ht% or less,
Contains one or more selected from Te 0010wt% or less, the balance consists of Fe and impurities, and M0
．． The first invention is a high-toughness non-tempered steel for hot forging, characterized in that the content m of Cr and ■ satisfies the formula (Mn+Cr)/V ≧ 8.0. It is.

The high toughness non-temperature steel for hot forging according to the present invention will be explained in detail below.

First, the components and component ratios of the high toughness non-thermal steel for hot forging according to the present invention will be explained.

C is an essential element in order to increase the amount of pearlite and increase the strength of forged steel products, as well as form carbides with V and exert its precipitation strengthening effect1), and the content is 0.10u+I.
If it is less than 0.2%, such reinforcing effect is small;
If it exceeds 5 wt%, the impact value will be lower than that of the quenched and tempered material, resulting in insufficient toughness. Therefore, the content is 0.10 to 0
．． It is set to 25wt%.

Si is an effective element in strengthening the ferrite structure after cooling for forging in the deoxidizing pond, and if the content is less than 0.05 wt%, the effect is small, and 1.0 + 111
%, toughness and machinability deteriorate. Therefore, the Si content is set to 05 to 1.01%.

Mn is a deoxidizing and desulfurizing element that increases the strength of forged steel products,
It is an essential nuisance to improve toughness, and if the content is less than 0.6 wt%, this effect will be small, and if it exceeds 2.5 tmt%, toughness will decrease and machinability will decrease. have a harmful effect on Therefore, Mn content - clear is 0.6 to 2
．． It is set to 51nt%.

Like Mn, C is an element useful for increasing the strength and toughness of forged steel products, and if the content exceeds 2.0 wt%, bainite is generated and the toughness decreases. Therefore, the Cr content is set to 2.0 wt% or less.

■ is an element that forms carbonitrides with C and N during cooling after forging and imparts strength l), and the content is 0.03w
Below t%, this effect is small, and 0.30
If it exceeds wt%, the effect will be saturated. Therefore, the content is set to 0.03 to 0.30 wt%.

A1 is an effective element for deoxidizing effect and refining crystal grain size.
), such an effect is small when the content is less than 0.015 iuL%, and when the content exceeds 0.060 wt%, the effect is small compared to the increase in content, and
It also has a detrimental effect on machinability. Therefore, the A1 content is set to 0.015 to 0.060 wt%.

N is a useful element for combining with \・'' and A1 to form carbonitrides, refining crystal grains, and strengthening steel. If the content is less than 0.003+wt%, this effect is small;
Further, even if the content exceeds 0.020 wL%, no increase in the effect can be expected and the toughness will deteriorate. Therefore, the N content is set to 0.003 to 0.020 t%.

Both Ni and Mo are elements that increase the strength of steel forgings without impairing toughness, and if they are contained in large amounts, bainite is generated and the toughness is reduced. Therefore, it contains N1! ceremony]
, 0 IuL% or more F, and the helo content is determined to be 0.50 wt% or less.

Both Nb and T1 are elements that suppress the growth of austenite crystal grains during forging, and the toughness is further improved.If the content of both Nb and Ti is less than 0.005 + IIt%, this effect will not occur. less, also 0.050
If it exceeds wt%, no improvement in the effect of suppressing crystal grain growth can be expected. Therefore, the Nb content is 0.005 to 0.0
50 fields [%, Ti content is 03005~・0.05 axis L
%.

Si0. The content of Cr and N7 is (Mn+Cr)/V
≧S, O is an element that strengthens steel by forming carbonitrides during cooling after forging, and the content is (),
Up to 30 wt%, as the content increases, the strength improves, but the toughness decreases significantly, and M0. Cr is an element that makes the structure fine and improves the toughness.
In order to ensure the same balance of strength and toughness as quenched and tempered materials, M0. It is necessary to consider the balance of Cr and V contents, especially (Mn+Cr)/V
Excellent toughness is ensured by adjusting the Mn content, Cr content, and V content to satisfy ≧8.0.

Also, S 0.12% or less, Pb 0.30+wt
% or less, Zr 0.20wt% or less, Ca 0.01w
t% or less, Te 0010/111% or less is contained to improve machinability, and it is contained when machining the product after forging, and if it is contained in too large a quantity, the toughness decreases. No significant effect was observed on machinability ty. Therefore, these elements are contained within the above ranges.

[Example 1] Next, an example of the high toughness non-tempered steel for hot forging according to the present invention will be described.

Example Steel having the content and V component ratios shown in Table 1 was melted in a high frequency furnace, and after casting, it was rolled to 50nunφ to a length of 2.
Cut into 50++ml.

Furthermore, it was heated to a temperature of 1250'C and forged into a round bar with a diameter of 35 nm+m using a hammer. The finishing temperature during final molding was 1150'C, and then it was left to cool in the atmosphere.

The sample steel No. 15 was 55SC and was hot forged and then reheated and subjected to quenching and tempering.

From the center of these round bars in the longitudinal direction (JIS 4
A No. 1 tensile test piece and a JIS No. 3 impact test piece were taken, and the tensile strength and Charpy impact value were determined.

In Table 1, No. 1 to No. 11 is the heat 11) high toughness non-tempered steel for forging according to the present invention. 12~No
, 15 is comparative steel.

From this Table 1, it can be seen that the high toughness non-tempered steel for hot forging according to the present invention has a strength equivalent to or higher than comparative steel No. 15,
It has toughness and is the No. 1 comparison steel.

No. 12 has a low value of (Mn+Cr)/V, and the comparison steel No.
.

No. 14 has a high C content, and Comparative iNo. 13 has a low value of (N41 juice Cr)/\7, indicating that both have a high C content and lack toughness.

[Effects of the Invention 1] As explained in 2 below, since the high toughness non-temperature steel for hot forging according to the present invention has the above structure, conventionally, after hot forging,
We manufacture parts that require high toughness by reheating, quenching, and tempering.However, we can obtain toughness and strength equal to or higher than conventional products by simply allowing the parts to cool after hot forging.・It has excellent effects.

Claims (4)

[Claims] (1) C 0.10-0.25wt%, Si 0.05
~1.0wt%, Mn 0.6~2.5wt%, Cr
2.0wt% or less, V 0.03-0.30wt%, A
l 0.015~0.060wt%, N 0.003~
0.020wt%, the remainder consists of Fe and impurities, and the content of Mn, Cr, and V satisfies the formula (Mn+Cr)/V≧8.0. Toughness non-thermal steel. (2) C 0.10-0.25wt%, Si 0.05
~1.0wt%, Mn 0.6~2.5wt%, Cr
2.0wt% or less, V 0.03-0.30wt%, A
l 0.015~0.060wt%, N 0.003~
Contains 0.020 wt%, and further contains Ni 1.0 wt% or less, Mo 0.50 wt% or less,
Nb 0.005-0.05wt%, Ti 0.005
Contains one or more selected from ~0.050wt%, the balance consists of Fe and impurities, and M
A high-toughness non-thermal steel for hot forging, characterized in that the contents of n, Cr, and V satisfy the formula (Mn+Cr)/V≧8.0. (3) C 0.10-0.25wt%, Si 0.05
~1.0wt%, Mn 0.6~2.5wt%, Cr
2.0wt% or less, V 0.03-0.30wt%, A
l 0.015~0.060wt%, N 0.003~
Contains 0.020 wt%, and S 0.12 wt% or less, Pb 0.30 wt% or less,
Contains one or more selected from Zr 0.20wt% or less, Ca 0.01wt% or less, Te 0.10wt% or less, and the balance consists of Fe and impurities,
A high-toughness non-thermal steel for hot forging, characterized in that the contents of Mn, Cr, and V satisfy the formula (Mn+Cr)/V≧8.0. (4) C 0.10-0.25wt%, Si 0.05
~1.0wt%, Mn 0.6~2.5wt%, Cr
2.0wt% or less, V 0.03-0.30wt%, A
l 0.015~0.060wt%, N 0.003~
Contains 0.020 wt%, and further contains Ni 1.0 wt% or less, Mo 0.50 wt% or less,
Nb 0.005-0.05wt%, Ti 0.005
Contains one or more selected from ~0.050 wt%, and S 0.12 wt% or less, Pb 0.30 wt% or less,
Contains one or more selected from Zr 0.20wt% or less, Ca 0.01wt% or less, Te 0.10wt% or less, and the balance consists of Fe and impurities,
A high-toughness non-thermal steel for hot forging, characterized in that the contents of Mn, Cr, and V satisfy the formula (Mn+Cr)/V≧8.0.