JPS60208414A - Manufacture of directly-hardened hot-forged article - Google Patents

Abstract

PURPOSE:To improve and uniformize the hardenability of a steel material contg. specified weight percentages of C, Si, Mn, Cr, Al and N by heating the steel material to a prescribed temp., forging, it, and carrying out hardening at a specified temp. CONSTITUTION:A steel material having a composition contg. 0.26-0.50% C, <=0.50% Si, 0.30-1.8% Mn, <=0.020% P, 0.01-0.2% S, <=0.006% Al and <=0.005% N or further contg. <=1.2% Cr and/or <=0.3% Mo is heated at 990-1,200 deg.C and forged, and direct hardening is carried out at >=850 deg.C. Since the steel material having said regulated Al and N contents is heated at 990-1,200 deg.C and forged, the formation of soft spots during the hardening is prevented owing to mixed austenite grains and the hardenability is improved and uniformized.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing direct hardened PP+ 17JL forgings.

Conventionally, mechanical structural parts used in automobiles and construction machinery that require high strength have been produced by hot-forming steel materials, then reheating and subjecting them to heat treatment such as quenching and tempering to suit the purpose and use. ζ
There is. In this method, in which heat treatment is performed after forging, alloying elements such as Cr and MO are added to the steel material to ensure hardenability, and austenite crystal grains are added to the steel material to ensure hardenability. In order to make the steel finer and ensure toughness after quenching and tempering, Ap, Nb, Ti, and JLR alloying elements of V-gei are added.

However, the above heat treatment after hot forging necessarily involves
Along with an increase in the number of 1" culms and an increase in work-in-progress, four -
[The steel used (AC is 1.
Since it is necessary to add various alloying elements as described above, the manufacturing cost is inevitably high.

For this purpose, in recent years, in order to reduce production costs and simplify the culm, a method has been developed in which steel A) is directly quenched after hot forging to obtain a forged product, in which the amount of expensive alloying elements added is reduced as much as possible. °C has come to be desired.

However, when a steel material as described in 1- is directly quenched after hot forging, the hardness of the forged product after quenching varies depending on the heating temperature and forging conditions before forging. That is, for example, 125
When forged by heating to a high temperature such as 0°C, the Osti J°41- grains of the preparation become lil-sized due to the high temperature heating.
Then, although the grains become finer through hot forging, they immediately grow and become larger again.The hardenability is good even if the grains are hardened directly after forging. However, when the forging temperature drops below 1050℃ or when forging is repeated, austenite grains do not grow into uniform coarse grains, but instead become mixed grains with fine grains mixed in. Direct quenching causes non-uniform hardenability in the forged product, resulting in areas where the hardness is not sufficiently high, resulting in uneven hardness.

In order to avoid the occurrence of such uneven hardness, conventionally, steel materials are forged by applying a high temperature of 1200'C or more to
At the same time, quenching after forging is also started at a temperature as high as possible. However, high-temperature forging shortens the life of the die, and there is also the problem that an oxide layer is formed before quenching, resulting in uneven quenching on the surface.

As a result of intensive research in order to solve the above-mentioned problems, the present inventors have found that the chemical composition of steel materials, especially AA'
It is possible to obtain uniform forged products with good hardenability by directly quenching after hot forging, by regulating the This discovery led to the present invention.

The method for producing a direct quenched forged product according to the present invention has a
contains CO, 26-0.50%, Si 0.50% or less and Mn 0.30-1.8%, P 0.020
% or less, SO, 01-0.2%, △E 0.00696 or less, and NO, 005% or less, the copper phase is regulated to 900-120%.
Heated to a temperature of 0℃, then forged, then ζ, 850℃
It is characterized by being quenched at a temperature above or above.

First, silver grain 4 used as material steel in the method of the present invention
The reason for limiting the composition of is explained.

C is added as an essential element to ensure the strength of the zeta sacrificial crystal through direct quenching and tempering treatment after hot forging, but its content is less than 0.26% (such strengthening effect On the other hand, if it exceeds 0.50%, the quenching film during direct quenching after forging should be
．． Sill. Therefore, the addition range of C is 0.26 to 0.50
%.

Si is added for deoxidation, but when added in excess, it deteriorates ductility. ], the Si addition amount range is 0
．． 5% or less.

Mn is at least 0.00 to prevent surface cracking during pseudo-solidification.
It is necessary to add 3% of Ni, which is effective in improving hardenability and increasing strength. However, 1
．． If the content exceeds 8% °C, it may cause cracking, so the upper limit is set at 1.8%.

Since P deteriorates the ductility of the steel material, promotes quench cracking, and deteriorates the toughness during tempering, the content of f1m is 0°020%.
The following shall apply.

S is effective for improving the machinability of forged products, but on the other hand, it reduces ductility. When ductility is important, the upper limit is preferably 0.03%, and when machinability is important, the upper limit is 0.20%.

AI is added as a strong deoxidizer, but at 0.006%
If it is added in excess of 0.006, the -L limit may be set to 0.006 as above, as it may result in mixed grains of A-stenite grains in quenching 1 after forging, resulting in uneven quenching. %.

Since N has a strong bonding force with Ae, if a large amount of F1 is contained in steel, it will combine with Ae as a deoxidizing agent, and as a result, it will slough off austenite mixed grains during quenching after forging, resulting in uneven quenching. It causes -Uru. For your convenience, in the present invention, the odor is N.
fil is 0.006% or less.

Historically, the grained steel used in the present invention has been treated as necessary for various improvements in mechanical quality, such as increasing the hardenability when surface hardening of forged products. C “and M
It is possible to add at least one selected from o to 9. Fill in the amounts of these elements added! I, (゛[and Mo respectively 1.2% and Il, 3%5
shall be. This is because if the amount of each of these additives exceeds L=1;k, quench cracking will occur.

11, T, 12 In order to improve the machinability of the manufactured product, Pb is added in an amount of 0.05 to 0.30 with or in place of S.
It may be added within a range of %.

According to the present invention, especially in steel,
By suppressing the heating temperature to 900 to 1200℃, we were able to prevent mixed austenite grains from forming and causing uneven heating during quenching after hot forging. If the forged product is then quenched at a temperature of 850°C or higher and then tempered at about 450 to 650°C according to a conventional method, a forged product with good and uniform hardenability and uneven toughness can be obtained. can. Quenching temperature is 850
When the temperature is lower than ℃, the hardenability decreases and uneven hardening may occur, which is not preferable.

When using conventional steel materials, if forged at a temperature range of 1100 to 1000°C and directly quenched, the austenite grains become mixed, the quenching becomes uneven, and the quenching is not uniform. If directly quenched after forging at a low temperature below °C, the austenite grains will become finer and the hardenability will deteriorate; however, according to the present invention, 1100
It is possible to forge at a low temperature such as (~900°C CO), and to obtain a forged product with good and uniform hardenability. Furthermore, according to the method of the invention, use is made. 'r2 (A I4 Ni is high 1111114C goryo 几J) addition f・l! 1' or '11 with hardenability of 1
1j, add a very small amount of alloy base to
Since it is v ril, the elementary 4A costs should also be reduced.

1.Examples are shown below.

Example 1 First step, 301 diameter t having the chemical composition shown in Δ~1・゛
Ki:, il to 9001:, 1000°C, 1100°C or 12 tl tl'L:, after 20am
Die forged to diameter, then 1, ) C5 each 8 [i 0 '
After cooling with water from temperatures of 950° C. and 1030° C., the hardness distribution of the obtained forged product was measured in the cross section at 1°ζ. The results are shown in Figure 1. According to the steel of the present invention, since the austenite crystal grains coarsen immediately after forging, even if the tempering temperature before forging is low, the hardenability after forging is good. There is.

Once upon a time, fiC in which the amount of An was larger than the amount specified in the present invention
According to Kikou, the heating temperature before forging is 900℃ and 900℃, respectively.
When the temperature is I 000'c and 1100°C, the austenite grains become fine during quenching, and when the temperature is 1200°C, the austenite grains become mixed grains. When heated to 900°, it becomes a single grain, and when heated to a higher temperature, it becomes a mixed grain, so in these cases, the hardenability after forging is significantly uneven. .

Next, a 40-diameter steel bar having the chemical composition shown in Table 1 A-D was heated to 1000°C, die-forged to a diameter of 251+1, and then water-cooled from a temperature of 900°C to determine the tensile strength. The steel of the present invention was tempered at 500° C., and the conventional steel and comparative steel were tempered at 420° C. for 2 hours so that the values were the same.

From each of the forged products thus obtained, a tensile jA' test piece and a glossy ruby test piece were taken from the center of the round bar and tested.

The results are shown in Table 2. When the strength is the same, the steel of the present invention has inferior toughness.

Example 2 A 75 square piece having a chemical composition not shown in Table 1 E and F was heated to 1050°C, hot forged into a 50mm negative diameter bar, and then oil quenched at a temperature of 950°C. Afterwards, the hardness distribution in the cross section was measured. The results are shown in Figure 2.

According to the method of the present invention, a steel kumquat whose hardenability is improved by adding Cr and MO is hardened during forging hardening.
has been changed into history.

Example 3 3011j TJ material, which has improved free machinability due to the γ composition shown in Table 1 ('J and 11), was heated to 1000°C and 20I
After processing and false forging into IIIi-1 steel, the hardness distribution of the groove cross section was determined to be 41 after cooling with water from a temperature of 900°.

The results are shown in Figure 3゛4゜

[Brief explanation of the drawing]

・f) 1 Figure (f) l; 1 Graph showing the hardness of the directly quenched 513 i product obtained by the present invention, (sil)
はjJtからI、法に、１-りあおら! 2. Same as 1. for straight forged products. The horizontal axis shows the last month from the center of the forged product. Figure 2 shows the distribution of steel containing 105 (] C'('jlD, forged JΔ product that has been subjected to contact hardening and quenching). l) steel containing 1.000 't: '<'
7! ! After 1til jf casting, ll'I contact hardening,
The hardness distribution of the forged product is as follows. 1'4"rL+kQnA nA*u2*r4ffjD)
Mr. E's attorney (Patent attorney 1) Makino Ittsu (Bujo) 871

Claims (1)

[Claims] Ill +li %ζ (: fl, 26~o, tl (196, S i
(includes 1,5096 and above and !vln o, 3o to 1.89z, rfb, 1'
(1,020% or less, 2) 0. (11~(1,256, △i1' 0.006% or more) and NO, 00596 or more [・900~I
Forging after heating to a temperature of 20 (1't'), then quenching at a temperature of c', 115 (1't・l;21'E-IY tik and 4H (+ contact hardening p4H) Method for manufacturing forged products. i2+ (:0.2 (i~F1.50%, 5it),
50 M O, : l fl ~ 1.896, t: selected from +12% or more 1. and M D O, 3% or less a) small... 1
Steel materials containing at least one type (r) regulated to P O, 020% or less, SO, 01 to 0.2%, Ai O, 006% or less, and NO, 005% or less to 900 to 120
After heating to a temperature of 0℃, forging 6, then 850
A method for producing a directly quenched hot forged product, characterized by quenching at a temperature of C to L.