JPS60208413A - Manufacture of carburizing steel - Google Patents

Abstract

PURPOSE:To prevent the coarsening of the grains during carburization by austenitizing a steel contg. specified percentages of C, Mn, Nb, N, O, etc. by heating to a prescribed temp. and by cooling and forging the steel under specified conditions. CONSTITUTION:A steel consisting of 0.1-0.5% C, <=0.4% Si, 0.1-1.5% Mn, <=0.025% P, <=0.025% S, <=0.0015% O, 0.02-0.08% Nb, 0.015-0.050% sol. Al, 0.12-0.020% N and the balance Fe or further contg. one or more among <=5% Ni, <=3% Cr, <=1% Mo and 0.03-0.20% Pb is uniformly austenitized by heating to >=900 deg.C. The steel is cooled from >=600 deg.C to the Ac1 point at >=100 deg.C/hr cooling rate and forged at room temp. - the Ac1 point. When the resulting steel is carburized at >=925 deg.C, the austenite grains are not coarsened, so a carburized steel of high quality is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION After forging at temperatures ranging from room temperature to AC, the present invention
iIf+7. when carburized at 25°C or higher. The present invention relates to a method for preventing total or partial coarsening of austenite crystal grains that occur. Forging between the room temperature and AC points mentioned above is called Wakupirema or warm forging.
There are differences depending on how many times the forging process is called cold 19a, so here we use A.
Forging in C, A and D is called "cold/warm forging." It has been a vexing problem for those skilled in the art that when carburizing is subsequently performed after performing this mild cold/warm forging, the austenite crystal grains become coarse in whole or in part. That is, deformation such as bending of the parts of the carburizing and quenching iron, low I of quality reliability fRvE, especially a decrease in working impact value and fatigue strength, and differences in local hardness occur.

Cold/warm! In the case of I9 structure (1), spheroidizing annealing is usually carried out as the best lj method to improve workability, but this heat treatment, as a pre-carburizing heat treatment, has the worst effect on grain size after carburizing. The ironic reality of bringing
It's the center.

The present invention uses a combination of pretreatment and chemical components to suppress the coarsening of austenite grains due to carburization.
This was done as a result of testing and tl of the method that can be used. l O, 025% or less 0: o, oo 1s% or less Nb: 0.02-0.0896 SoeAe: 0.015-0.050% N: 0.0
12~0020 type, and if necessary, N15% or less, Cr5q6 or more, Mo
: 196 or less, PLI: 0.03-0.20% After heating the first type of 25 to make uniform oakinite,
After cooling at a rate of 100°C/1+ru above 600°C to the AC point and completing the γ-・α transformation at that temperature, perform 19 threads from room temperature to the AC point of the steel. There is a method for producing steel for carburizing, which is characterized in that when carburized at a temperature of 925°C or higher, the austenite crystal grains do not coarsen completely or partially, and the cold/warm I9 buildability is improved. Good grain size can be obtained after carburizing without any hindrance.

Next, the reason for limiting the composition of the steel targeted in the present invention will be described.

(Carbon) For carburized parts, the core hardness is HRC to obtain the necessary strength.
It is necessary to adjust it to about 20-55.

For this purpose, 01 to 0.5% is sufficient in relation to the part size and other alloying elements described below.

Therefore, the upper limit of C is set to 0.05%, and the lower limit is set to 0.1%.

(Silicon) Si is generally used to adjust hardenability and strengthen ferrite.
9). However, in the present invention, when Si exceeds 0.4%, the ferrite becomes stronger, which actually increases the deformation resistance during cold forging.

Therefore, the upper limit of Si is set to 0496. On the other hand, even if Si is not added at all, the effects of the present invention are not impaired. Therefore 8
There is no lower limit of 1.

(Mankan) In the present invention, Mu is used to adjust the hardenability in order to obtain appropriate hardness. For this purpose, Mn of 01 to 15% in relation to the alloy elements of the song is enough to reach the target. Therefore, the lower limit of Mu is set to 0.1% and the upper limit is set to 15%.

If the amount increases, each has the property of promoting cracking during cold and warm forging. The steel of the present invention has PO, 025%, S:
0.025q6, O: If each exceeds 0.0015%, the adverse effects become significant, so the upper limit values were set for each. In the present invention, Nb is treated as fine Nb (C, N) in steel It is dispersed and together with Ae and N, which will be described later, comprehensively prevents crystal grains from becoming coarser.

In this case, the more Nb there is, the stronger the IL effect of inhibiting crystal grain growth becomes, but the more Nb (C, N) there is, the more the machinability deteriorates and, as will be described later, the rolling life is reduced. In addition to N and Al described in Nb1jl of the present invention, Il
0.02-008 in comprehensive combination with l heat treatment
The goal can be achieved in %.

Therefore, the upper limit of Nb is set to 008% and the lower limit is set to 002%.

: Acid-soluble aluminum) In steel, Sol and Al form AeN together with N, which will be described later, and are finely dispersed to inhibit the growth of crystal grains.

In the steel of the present invention, SOe and Ae are 0.015 to 0050 depending on the relationship between Nb described in n11, N and +iil P treatment described below.
The objective can be achieved in %.

Yo Te, Sue, Al (1) The upper limit is o, oso=7, and the lower limit is 0015%.

(Nitrogen) In the present invention, N is 1] Combined with Nl+ and Ae mentioned in 11. 14 For steels with compositions regulated by undeveloped steel, it is better to increase N or to increase N in Ni1 (C, N). Therefore, together with Al'N, it has an excellent grain growth inhibiting effect, or in this way, the relationship between N13 and Al described in Ai+ requires a minimum of 0012%. Therefore, the lower limit of N is 1o, ox2
Let it be Φ. On the other hand, the higher the value of N, the better, but if 0020Φ is exceeded, there is a possibility that cavities will be formed in the steel ingot, so the upper limit is set to 0.020a6.

(nickel, chromium, molybdenum)
Add Cr and MO.

In this case, N1 is 5% or more, Cr is 3% or more, Mu
can achieve its purpose by adding less than 1% in 1 minute. Therefore, the upper limit for Ni is 5%, and that for Cr is 3%.
%, and that of MO is 1%.

(Lead) If cutting 11 is particularly required in steel having the composition regulated in the present invention, PB is added. The machinability improving effect of Pb is sufficient for 003 to 020@.

Therefore, the upper limit of pb is set as 020%, and the toe limit is set as 003%.
shall be.

(Interrelationship between heat treatment and chemical components l-f+) The limitations on the interrelationship between heat treatment and chemical components listed in the claims of the present invention are shown in the Examples and Comparative Examples in Table 2, respectively. It is based on That is, heating of the 900 ml is necessary to bring about the decomposition of the AeN. Further, the reason why the temperature between 600° C. and AO1 is cooled at 100° C./11r or more is because if the cooling is too slow, the crystal grain size becomes poor. This is probably due to the fact that AeN becomes larger than Fil. Furthermore, the temperature is set above 600°C because below this temperature, the grains become mixed, and this is thought to be due to the formation of a structure containing bainite. It will be done.

Also, the reason why we use AC and J 'l' is because if we go beyond this, the γ/α change will be 1 mind or the end will not end.
It is already common knowledge among those skilled in the art that good crystal grain characteristics cannot be obtained when direct air cooling is performed from an austenitic sheet.

Next, examples of the present invention will be described. Table 1 shows the chemical composition of the sample materials. These are all ItlO'91: et al.
One skin vacuum! ', la'i and took a bath.

After hot forging a steel ingot with the ingredients in Table 1 to 30y8, 4i1 as shown in 1. (A) ~ 0 → 4i1: After applying cram school treatment, 70 for those left at room temperature and preheated to 600℃ After performing % upsetting and cooling to the seat temperature, the austenite grain size was investigated after heating at 950° C. x 6 br assuming carburization in Asahikawa, without water quenching. The results are shown in Table 2.

(011 heat treatment) (a) Air cooling after heating at 900℃X11+r ■PI 850
℃X2hr aI? ? & 10℃/11r furnace cooling (
C) 760℃×2br After heating 10'(:/l+r
Qi cooling (SA)) 700°C x 3 II r Air cooling after heating 6) Inside 930°C x l l+ r After heating,
67o (salt lotus color cooled 21+r i t,
i, empty/= (IA) The reason why the grain size at the time of heating at 950° C.

Table 2 Austenite grain size (950'CX61
+r heating) ○ 1llI! :%L7. A: Light 1ρ mixed rU, X: 'lishi mixed grain or OII grain 4-
Nawa')]iil? In the case of treatment or IA, the chemical composition within the scope of the present invention has a good grain size in Xt.

So next, let's talk about the conditions for IA. Therefore, copper metal 5 was used as the test material. As conditions, the austenitizing temperature '%T, %, the inversion temperature %T, 'J:, the cooling rate ')V% and T9, and the actual holding times e1, e were investigated.

The various conditions and test results are summarized in Table 3.

In Table 3, the holding time of T is 111r, and V ℃
After cooling at /hr, holding times T and T were respectively 111r to completely complete the deformation, and then cooling to room temperature, followed by heat treatment at 950°C x 5hr, and the maestenite grain size was measured.

From this result, it can be seen that the appropriate temperature for T1 is 900°C, and that T is about 600°C to AC. Also, suppose the cooling rate is between T, -T, and -(
It is also preferable to keep the temperature at about 100℃/11r or higher.
It was clear. Based on this, the heat treatment conditions within the scope of the claims were determined.

Next, we will discuss the results of a thrust type rolling fatigue test to see the effect of Nb on rolling life. The test conditions are as follows.

Pmnx: 500 kt f/ij, lubricant mist 6
0 spindle oil ill, 1 wipe () as steel noti 5.
After soaking and softening using No. 7 and No. 10, the hardness of the Snost test piece was adjusted to HRC 61 to 62, and the test was conducted. The results are shown in No. 4k.

Table 4 Rolling life test Based on the results, Q'I indicates the negative effect on rolling life.
! Then, the upper limit of Nl+ is considered to be about 0.008%.

In addition, the steel whose composition is regulated in the present invention is produced by JL (cold working without any problem in IN) of Steel Manufacturing, 11
In,! 1□1 period! of lubricant at IQ m ('I i
I'7 is not a problem at all, and the production process is the same as that of the regular 114.

Hereinafter, j14 of the ingredients regulated by the present invention
When the treatment specified in the present invention is applied, partial or total grain coarsening occurs in the subsequent high-temperature carburizing process. Alternatively, quenching deformation can be avoided.

Special applicant: Sanyo Special Steel Co., Ltd.” Representative Shun Ouchi “jj

Claims (1)

[Claims] Mountain C゛ 01-05% Si: 0.4% or less Mu: 0.1-1 P: 0.025% or less SiO, 025% or less 0: 0.0015% or less Nb : 0.02-008% 5neAe: 0.015-o, oso4. sN:
0.012~0020% 4. N1: 5% or less, Cr: 3% or more 1', as required
Mu: 1% or less, Pb: 0.03-0.20%≠Steel that contains more than 1 tumor and the remainder is substantially Fe91)
After heating to below 0℃ to make uniform austenite, 6
AC of the steel from room temperature after cooling at a temperature of 100°C/br or more to complete the γ-α transformation at that temperature. A carburizing steel characterized in that A-stenite crystal grains do not become larger than 11 in whole or in part when carburized at a Z grade of 925°C or higher by forging up to a point. manufacturing method.