JPH02185920A - Manufacture of directly softened wire rod or rod stock - Google Patents

Abstract

PURPOSE:To manufacture a directly softened wire rod or rod stock capable of eliminating heat treatment before cold working by forming a steel having a specific composition containing REM into a steel wire rod or steel rod by means of hot rolling and subjecting the above to specific cooling after the conclusion of rolling. CONSTITUTION:A steel which has a composition consisting of, by weight, 0.30-0.60% C, 0.15-0.35% Si, 0.60-1.70% Mn, <=0.03% P, <=0.03% S, <=0.050% Al, <=0.0050% O, <=0.0050% N, 0.0005-0.05% REM, and the balance Fe with inevitable impurities and further containing, it necessary, 0.60-1.2% Cr and/or 0.15-0.35% Mo is hot-rolled into a steel wire rod or steel rod. At this time, after the conclusion of rolling, cooling is carried out down to 500 deg.C at <=0.1 deg.C/s cooling rate, by which ferrite fraction in the steel structure is remarkably increased and lamellar spacing in a pearlitic part is widened to carry out softening. By this method, the directly softened steel wire rod or steel rod capable of eliminating or simplifying heat treatment prior to secondary working can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing a directly softened cotton swab material used for cold forging.

<Prior Art> Wire rods or steel bars for cold forging are formed into various fasteners such as bolts and nuts, automobile parts, etc. by cold forging. However, in the as-rolled state, these wire rods or steel bars for cold forging lack deformability to withstand severe cold working, and at the same time have high deformation resistance.Therefore, in order to improve deformability and reduce deformation resistance, A softening annealing is performed.

<Problems to be Solved by the Invention> However, such softening annealing requires holding at high temperatures for a long period of time, and therefore requires expensive equipment such as a heat treatment furnace. There are also problems in terms of productivity, such as scale loss.

In order to avoid these processes, for example,
As disclosed in No. 1573 or Japanese Unexamined Patent Publication No. 143716/1984, the production of tgI wire rods in which softening annealing can be omitted by controlling the rolling temperature and the cooling rate after rolling within a specific range. A method is proposed.

These contents all attempt to soften the as-rolled microstructure by changing it to ferrite/pearlite.

However, although these methods can soften the material compared to conventional rolling methods, they have higher strength and lower ductility compared to off-line softened and annealed materials, and the material quality is lower than that of softened and annealed materials. There is a problem that it is inferior in quality.

The present invention has been made in order to solve the above-mentioned problems, and an object of the present invention is to provide a method for producing directly softened cotton rod steel that enables processing or simplification of heat treatment before secondary processing. .

<Means for Solving the Problems> As a result of intensive studies to solve the above-mentioned problems, the present inventors have come to the following findings.

The strength controlling factors of the ferrite-pearlite structure are the ferrite fraction and the lamella spacing of the pearlite portion. Here, if the soft ferrite increases, the strength decreases, and if the lamella spacing increases, the strength decreases. Therefore, in order to reduce the strength of as-rolled steel, it is effective to increase the ferrite fraction and at the same time widen the pearlite lamella spacing. When considering the rolling conditions and cooling conditions for obtaining such a microstructural form, first of all, in order to increase the ferrite area ratio, it is necessary to make the γ grain size before transformation fine. This is because the austenite grain boundaries are the sites where ferrite is generated during transformation, and the larger the grain boundary area, that is, the finer the austenite grain size, the greater the ferrite fraction. As the rolling conditions for this purpose, low-temperature finishing is preferable so that the γ grains become fine grains.

Furthermore, in order to widen the pearlite lamella spacing, it is important to lower the cooling rate as much as possible. This is because the slower the cooling rate, the higher the pearlite transformation temperature and the wider the pearlite lamella spacing. The conventional direct softening treatment method follows such a raw material ff1J, but as mentioned above, it has higher strength and lower ductility than offline annealed material. This is because in order to obtain a material that is comparable to that of an offline annealed material, a problem arises in that low-temperature finishing and slow cooling rates, which are industrially difficult, have to be applied.

The present inventors conducted intensive studies to solve the above problem, and found that the rare earth element I? IF) found that the addition of EH significantly increases the ferrite fraction under the same rolling conditions, which indicates that R[! M is an element that easily forms oxides, and RE? This is because monooxide becomes the starting point for ferrite generation, and the ferrite fraction increases dramatically compared to the conventional case of only austenite grain boundaries. Therefore, it is possible to obtain a steel wire or bar with extremely low strength and high ductility even under the same rolling and cooling conditions.

The present invention has been made based on the above findings, and includes:
The gist of it is: C: o, 3o~0°60w
L% Si: 0.15-0.35wt%, Mn
: 0.60-1.70wt%, P: 0.03
wt% or less, S: 0.03wt% or less, ^! :
0.050 wt% or less, O: 0.0050 mackerel L%
Below, Neo.

0050w L% or less, RUM: 0.0005
~0.05wt%, with the remainder being Fe and unavoidable impurities, when hot rolling the steel into a steel wire rod or steel bar.
This is a method for producing a directly softened cotton swab material, which is characterized by cooling at a temperature below C/s.

Further, as the chemical composition of the steel mentioned above, Cr: 0.6
0-1.2 wt%, Mo: 0.15-0.35
It may contain one or two wt%.

Effect〉 The reasons for this limitation are explained below.

C: C is a useful element for ensuring strength as mechanical parts, so it is actively used, but if it is less than 0.30, it is insufficient to ensure strength, and if it is less than 0.60%, it is insufficient to ensure strength. If the content exceeds 0.30 to 0, direct softening becomes difficult.
．． The range is 60 wt%.

Si: Si is not only a useful element for deoxidation, but also useful for ensuring the strength required for mechanical parts, so it is actively used, but if it is less than 0.15 wt%, its effect is small. If the content exceeds .30 wt%, the pickling properties will deteriorate, so the content should be in the range of 0.15 to 0.30 wt%.

Mn: Mn is a useful element in increasing the strength of mechanical parts, so it is actively added, but at 0.30 wt%.
If the content is less than 1.5 wt%, the effect will be small, and if the content exceeds 1.5 wt%, work hardening will be significant and cold working will become difficult.
The content should be in the range of 0.3 to 1.5 wt%.

P: P segregates at grain boundaries and reduces hot workability and causes quench cracking during tempering treatment, so it is desirable to reduce it, but 0.0
It is allowed up to 3 wt%.

While S improves machinability, it forms MnS and deteriorates cold workability. Therefore, 0°93 which satisfies both characteristics.
Addition should be less than wt%.

Al: AI! Since it is a useful element for deoxidation, it is actively used, but even if it is contained in an amount exceeding 0.05 wt%, its effect will be saturated and solid solution strengthening will occur, so it should not exceed 0.05 wt%. The addition of

0: 0 forms AlzOx-based oxides that are harmful to cold forgeability, so it is desirable to reduce it.
% is allowed.

N: N causes dynamic strain aging during cold working, so it is desirable to reduce it, but it is allowed up to 0.0050 wt%.

REM: In REM, Ce oxide serves as a nucleation site for ferrite during the γ-α transformation, and it is not only effective in significantly increasing the ferrite fraction in the rolled structure and lowering the strength, but also in cold JJI.
It is actively used because it is effective in improving cold workability by changing the elongated MnS, which is harmful to workability, into a spindle shape that is harmless to cold workability. The effect is small, and even if the content exceeds 0.05wt%, the effect is saturated, so o,ooos~0.05wt%
% addition.

In addition, the chemical components of the steel mentioned above include Cr: 0.60 to 1
．． 2-t%1Mo: 0.15 to 0.35wt% of 1
The reason for including one or two species is that both Cr and Mo are elements that significantly improve hardenability, and when the part is large, it is extremely useful for ensuring the hardening depth during tempering treatment, so it is actively used. However, in the case of Cr, if it is less than 0.60 wt%, the effect is small (if it is contained in excess of 1.2 wt%, the pearlite lamella spacing becomes smaller, increasing the strength of the as-rolled material. On the other hand, if Mo is less than 0.15 wt%, the effect on improving hardenability will be small, and if it is contained in excess of 0°35 W%, it will cause hard bainite in the as-rolled material. Since the M1 weave will develop, which is contrary to the purpose of the invention, the content should be 0.15 to 0.35 wt%.

Furthermore, the reason for cooling to 500°C at a rate of 0.1°C/s or less after rolling is to widen the pearlite lamella spacing and reduce the strength, but if the cooling rate exceeds 0.1°C/s, Since the effect is small, it is set to 0.1'C/s or less. The cooling end temperature is set to 500"C because the ferrite-pearlite transformation ends in the temperature range of 500℃ or higher, and the temperature range of less than 500℃ is set to 0゜l'c.
Even if the treatment is performed at a cooling rate of less than /s, the softening effect is poor and the treatment time becomes longer, so the cooling end temperature is set at 500°C.

<Example> Steel having the composition shown in Table 1 was melted in a converter furnace, and after being made into a 150mm billet by blooming rolling, it was made into a 14ff billet by wire rod rolling.
After rolling, the as-rolled material was cooled at the cooling rate shown in Table 1, and the mechanical properties of the as-rolled material were investigated. The results are also shown in Table 1.

No. 1-Nα6 is an example of the present invention. Also, Nα7~1
2 is a comparative material without RUM addition, Nα13 to 18 are N[11
- Using the same material as Nα6, only the cooling rate is outside the scope of the present invention. N (119~No, 24 is Nα7
Using the same material as those in 12 to 12, it was heated to 680° C. for 3 hours by a heat cycle not shown in FIG. 1, and then air cooled to undergo softening annealing.

As is clear from Table 1, it can be seen that only the inventive example of Hαl~6 has mechanical properties comparable to the offline annealed material.

<Effects of the Invention> As explained above, by using the present invention, it is possible to secure mechanical properties comparable to softened and annealed materials as rolled, and therefore It is possible to omit it. This can contribute to improving the productivity of mechanical parts through cold working.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram showing an elongation cycle during off-line softening annealing.

Claims (1)

[Claims] 1. C: 0.30-0.60wt%, Si: 0.15-0.15%
0.35wt%, Mn: 0.60-1.70wt%, P
: 0.03wt% or less, S: 0.03wt% or less, Al
: 0.050wt% or less, O: 0.0050wt% or less, N: 0.0050wt% or less, REM: 0.0005
~0.05 wt%, with the remainder being Fe and unavoidable impurities, when hot rolling the steel into a steel wire or bar, the temperature is 0.1°C/0.1°C/up to 500°C after rolling.
1. A method for producing a directly softened wire bar, characterized by cooling at a temperature of s or less. 2, C: 0.30~0.60wt%, Si: 0.15~
0.35wt%, Mn: 0.60-1.7wt%, P:
0.03wt% or less, S: 0.03wt% or less, Al:
0.010-0.050wt%, O: 0.0050wt
% or less, N: 0.0050wt% or less, REM: 0.0
005 to 0.05 wt%, furthermore, Cr: 0.60 to 1.
2 wt%, Mo: 0.15 to 0.35 wt%, and the remainder is Fe and unavoidable impurities. Method.