JPS63111160A - High toughness non-heattreated steel for hot forging - Google Patents

Abstract

PURPOSE:To improve the toughness of a steel as non-heattreated after hot forging by specifying the amts. of C, Si, Mn, Cr, Ti, B, Al and N. CONSTITUTION:This high toughness non-heattreated steel for hot forging consists of, by weight, 0.02-0.05% C, 0.1-1% Si, 0.6-3% Mn, 1.4-4.5% Cr+Mn, 0.005-0.03% Ti, 0.0003-0.003% B, 0.01-0.05% Al, <=0.006% N and the balance Fe. When the steel is hot forged and air-cooled or allowed to cool, high toughness is obtd. without requiring any heat treatment.

Description

[Detailed Description of the Invention] "Objective of the Invention" (Industrial Application Field) The present invention relates to the composition of high-toughness non-tempered steel that is used as automobile parts and other mechanical parts without being tempered after hot forging. It is something.

(Prior Art) Automotive parts and many other mechanical parts are generally formed from steel bars by hot forging, then quenched and tempered (refined), and then cut.

However, even in this manufacturing process, heat treatment is omitted for the purpose of saving energy or reducing manufacturing costs, and ferrite+ is produced using trace additive elements such as V and Ti.
Pearlitic non-thermal steel and Cr.

Bainitic non-temperature steels utilizing Mn or B have been developed and proposed. An example of the former is JP-A-59
-100256, which uses VN (7) to increase strength and uses TiN to achieve high toughness, but the C content is high at 0.20 to 0.40% by weight (hereinafter simply referred to as %). Therefore, there was a limit to increasing the toughness. Examples of the latter include JP-A-61-19761 and JP-A-61-10316.
1, 1986-139646, and “Iron Manufacturing Research” No. 3
No. 20 (1986), there are papers such as ``Non-tempered tough steel bars for hot forging,'' and although high strength is certainly obtained, in terms of toughness, ferrite + using TiN
The level was equal to or lower than that of pearlite type. or,
Although the above-mentioned Japanese Patent Application Laid-Open No. 61-139646 is based on bainite, it is cooled with hot water after hot forging, so heat treatment is not completely omitted, and the technology has problems in terms of manufacturing process or manufacturing cost. That is undeniable. In this way, although conventional non-tempered steel has a slight improvement in toughness, it cannot be said that the toughness required for the material can be obtained at a low cost, and these materials are used in all mechanical parts that require high toughness. It has not yet been applied.

(Problems to be Solved by the Invention) The present invention has been devised in view of the current state of the prior art as described above, and is an inexpensive and more efficient method that does not require any heat treatment by air cooling or standing to cool after hot forging. The purpose is to provide a composition of non-tempered steel that provides high toughness.

(Means for Solving the Problems) The present invention for achieving the above objects has the following features: (1) C: 0.02 to 0.05% by weight St: 0.10
~1.00%Mn: 0.60~3.00%C
r+Mn: 1.40-4.50%Ti: 0.0
05~0.030% B: 0.0003~0.0
030%Al: 0.01~0.05%N
: A high-toughness non-thermal steel for hot forging, containing 0.0060% or less, with the remainder consisting of Fe and unavoidable impurities.

(2) C in weight%: 0.02-0.05% Si: 0.10
~1.00%Mn: 0.60~3.00%C
r+Mn: 1.40-4.50%Ti: 0.0
05-0.030% B: 0.0003-0.
0030%Al: 0.01-0.05%
N: 0.0060% or less, Ni: 1.0% or less, Cu: 1.0% or less. 0% or less M
o: 0.50% or less V: 0.10% or less Nb: 0.05% or less Contains one or more types, the balance being Fe and unavoidable impurities High toughness non-temperature for hot forging The invention relates to nets, and provides a non-heat treated steel for hot forging that is cheaper and has higher toughness than conventional non-heat treated steels used for the same purpose.

(Function) First, the inventors of the present invention used C: 0.02 to 0 as a sample material for a preliminary test in order to develop a material with higher toughness compared to conventional non-tempered steel for hot forging. .22%, Si: 0.10
~1.00%, Mn: 0.60~3.50%, Cr
+Mn: 1.40~5.50%, Ti: O~0
．． 030%, B: 0 to 0.0030%, AA: 0.01
~0.05%, N: 0.0060% or less, Ni: O~1
．． 0%, Cu: O ~ 1.0%, Mo: O ~ 0.5%, V
: Q ~ 0.20%, Nb: 0 ~ 0.05%,
A steel bar with a diameter of 60 mm was made using steel with the remainder consisting of Fe. This steel bar was heated to 1250°C, hot forged to a diameter of 301 m, allowed to cool, and test pieces were taken to investigate various mechanical properties. .

FIG. 1 is a diagram showing the influence of the amount of C on the strength and toughness of the sample material, and the vertical axis shows the Charpy impact value (uE
,. ) is the tensile strength (TS) plotted on the horizontal axis.

As can be understood from the figure, the influence of the amount of C on the balance between strength and toughness is extremely large, and the amount of C has a large effect on the balance between strength and toughness.
In the range of 0.05%, a low carbon bainite structure appeared, and a good balance between strength and toughness was observed. Based on the above knowledge, we further researched and developed the steel of the present invention, and by using the steel of the present invention, the tensile strength (TS) was 70 kg-f/ Charpy impact value (uE,.) 18k at 20°C with alcohol level 2 or higher
It was confirmed that gf -rn/a1 or higher was obtained.

Next, the reason for limiting the numerical values of additive elements in the present invention will be explained.

C: An element that greatly affects strength and toughness.

However, if it is less than 0.02%, sufficient strength cannot be obtained;
．． It is necessary to add 0.02% or more, and if it exceeds 0.05%, high toughness cannot be obtained, so this was set as the upper limit.

Si: An element necessary for deoxidation and at the same time a strengthening element. If it is less than 0.10%, a sufficient deoxidizing effect cannot be obtained, while if it exceeds 1.00%, toughness is impaired, so this was set as the upper limit.

Mn: Like C and Cr, Mn is an element that greatly affects strength and toughness. If it is less than 0.60%, sufficient strength and toughness cannot be obtained, and if it exceeds 3.00%, toughness may be impaired, so this was set as the upper limit.

Cr: Like C and Mn, this element has a large effect on ensuring strength and toughness. However, when the amount of Cr + Mn is 1.
If the total amount is less than 40%, the strength will be insufficient, so this is set as the lower limit.If the total amount exceeds 4.50%, the effect will not be improved and there will be a disadvantage in terms of cost, so this is set as the upper limit.

Ti s An element that fixes N in steel and is effective in improving the hardenability of B. If it is less than 0.05%, the effect of fixing N is not sufficient, and if it is added in excess of 0.030%, the effect will be saturated, and the toughness may be impaired due to the production of excessive TiN. Therefore, the upper limit was set to 0.030%.

B: An element that has the effect of improving hardenability. 0
．． If it is less than 0003%, the effect is small, and O, OO
Even if it is added in excess of 30%, the effect will be saturated, so this was set as the upper limit.

2: It is an element with a strong deoxidizing effect. But 0.0
If it is less than 1%, no effect will be observed, and if it is added in excess of 0.05%, the effect will be saturated, so this was set as the upper limit.

When N: exceeds 0.0060%, it is necessary to increase the amount of Ti necessary to fix N, and a large amount of Ti is generated.
Since N reduces the toughness of steel, this is set as the upper limit.

Since the object of the present invention can be achieved with each component composition for which the reasons for the numerical limitations are listed above, this is defined as the first claim.

The following elements can be added to contribute to further improving strength and toughness.

Ni: An element effective in improving high strength and toughness. However, from an economical point of view, the upper limit was set at 1.0%.

Cu: Addition has the same effect as Ni, but the upper limit was set at 1.0% from an economical point of view.

Mo: The effect of addition is the same as that of Ni and Cu, but from an economical point of view, the upper limit was set at 0.5%.

72 is a powerful strengthening element. However, if it exceeds 0.10%, toughness will be impaired, so this was set as the upper limit.

Nb: Like V, it is a powerful reinforcing element. But 0.05%
If it exceeds 0.05%, the toughness will be impaired, so the upper limit was set at 0.05%.

Since each of these elements has a unique effect, one or more of these elements can be added depending on the purpose of the steel material, and this is included in the second item of claim 4.

In addition, the high toughness non-thermal steel for hot forging of the present invention has a content of 0607%
It is also possible to improve the other machinability by adding up to 0.3% S or up to 0.3% PB.

Regarding the conditions for hot forging the steel of the present invention, there are no special conditions to be controlled, and sufficient properties can be obtained by heating and forging under normal heating conditions.

Regarding the cooling conditions, the transformation period from 800 to 400℃ was
0 to b The expected high toughness non-thermal steel having a low carbon bainite structure is obtained.

(Example) The test steel was melted in a vacuum melting furnace in 150 kg each, made into a steel ingot, forged into a 90 m1 steel bar, which was then hot forged into a front axle beam of an automobile, and air-cooled (800 kg).
Average cooling rate of ~400°C 30°C/m1n). A tensile test piece and an impact test piece were cut out from this front axle beam and subjected to mechanical properties at °C. Table 1 shows the chemical composition of the test steels, in which columns 1 to 15 are the steels of the present invention, and columns 16 to 19 are conventional non-tempered steels used to compare the effects. Table 2 shows the mechanical properties of each test steel in the previous table, and all of the steels of the present invention in columns 1 to 15 have a TS≧70 kgf/l112+ uE'go
It shows good strength and toughness of ≧18 kgf-m/cal, which is in good agreement with the preliminary test data shown in FIG. In FIG. 1, the marks indicate the invention steels in Table 2, and the marks with mu indicate the comparative steels in the same table. Compared to the steel of the present invention, the comparative steel N116 does not contain Ti + B, so its strength is lower than 70 kgf/m2 in TS,
Comparative steel No. 17 contains a large amount of Mn and Cr, and although it satisfies high strength and toughness, it is economically disadvantageous. Comparison steel! IkL18. It can be seen that both N[Li2 have a high C content and the absorbed energy in the impact test is lower than that of the steel of the present invention.

1 vinegar tensile test piece of the second front leg: JIS No. 4, impact test piece: JIS No. 3 (Effects of the invention) As detailed above, in the case of the present invention, no heat treatment after hot forging is required and air cooling Or just leave it to cool, TS4i has high strength of 70 kgf/m2 or more and LIF,
18 kgf-m/co at 2° value! Since it is possible to produce non-tempered steel with higher toughness and toughness values superior to the conventional non-heat-treated steels mentioned above at a relatively low cost, 1. Can be widely applied to other mechanical parts.

[Brief explanation of the drawing]

FIG. 1 is a drawing showing the influence of the amount of C on the strength and toughness of non-tempered steel.

Claims (2)

[Claims] (1) C: 0.02-0.05% Si: 0.10-1.00% by weight
Mn: 0.60-3.00% Cr+Mn: 1.40-4
．． 50%Ti: 0.005-0.030%B: 0.00
03-0.0030% Al: 0.01-0.05% N:
High toughness non-temperature steel for hot forging, containing 0.0060% or less, with the remainder consisting of Fe and unavoidable impurities. (2) C: 0.02-0.05% Si: 0.10-1.00% by weight
Mn: 0.60-3.00% Cr+Mn: 1.40-4
．． 50%Ti: 0.005-0.030%B: 0.00
03-0.0030% Al: 0.01-0.05% N:
Ni: 1.0% or less Cu: 1.0% or less Mo: 0.50% or less V: 0.10% or less Nb: 0.05% or less A high-toughness non-heat-refined steel for hot forging, containing at least 100% of the total amount of iron, and the remainder consisting of Fe and unavoidable impurities.