JPS6082618A - Production of steel bar wire rod having superior resistance to strain aging - Google Patents

Abstract

PURPOSE:To obtain steel bar wire rod generating only slight strain aging during processing even if a member having high forming rate is cold forged by hot- rolling C-Si-Mn steel material of a specified compsn. and then subjecting it to aging under specified conditions. CONSTITUTION:Steel bar rod wire consisting by wt% of <=0.45 C, <=0.35 Si, 0.20-2.00 Mn, <=0.040 P, <=0.025 S, 0.030-0.090 sol. Al and <=60ppm N, with >=15 sol. Al/N, and residual wt% Fe, is hot-rolled. Then, the steel bar rod wire is aged at 200-500 deg.C during cooling or after cooled. so as to obtain <=5 age hardening rate defined by the formula (wherein T.S' is tensile strength when it is aged after drawing, and T.S is tensile strength of the drawn wire as it is).

Description

[Detailed Description of the Invention] The present invention relates to steel for cold forging such as special bolts, nuts, machine screws, etc. that require a large degree of processing. It has improved toughness.

In recent years, in the field of cold forging, with the spread of bolt formers, parts formers, etc., parts of various shapes have come to be manufactured by cold forging.

Therefore, blanks subjected to cold forging have a
The temperature rises in the trench by ~200°C, and cold forging is performed in the temperature range of blue brittleness, so age hardening occurs during cold forging, significantly shortening tool life, and the product after cold forging also becomes brittle. It will become

The present inventor has developed a rod "i-wire" that reduces the occurrence of age hardening during processing even when parts with a high degree of processing such as bolt formers and parts formers are cold-rolled. As a result of various experiments and investigations, C0,45j6 or less, 5i035% or less, MU 0
120% - 2,00 light, Po, 040% or less, 30.0
25% or less, sOt, At, o, o 30% to 0.0
Contains 90 ppm or less of N60 ppm or less Al/N
15 or more, and the balance is PE and unavoidable impurities.
×100 is characterized by 5% reduction.O, o a OX'-0
,090% binding S○mu A4/N>'15
After fixing as AtN, C is cooled for 20 minutes during or after cooling.
By precipitating and fixing carbides through aging treatment at 0 to 500°C, age hardening due to CSN is suppressed.

As for the composition system of the steel of the present invention, the tensile strength of the wire rod, which can be universally cold-forged to rolling size, is 90'fi.
C, Si, Mn, Som At.

The composition ranges of N are determined as described above, and the reasons for these limitations are as follows.

C: In the steel of the present invention, if C exceeds 0.45%, processing cracks will occur at a compression ratio of 75%, so the upper limit is set to 0.45%.
And so. Regarding the lower limit, it is particularly difficult to specify since the lower the Cl content, the better the aging properties.

Si: Si does not affect aging properties, but is added for deoxidation or strength adjustment, so the upper limit should be set at 0.
It was set to 85X. If the content exceeds 0.35%, cold forging workability deteriorates, which is not preferable.

Mn: Mn is used to prevent cracking during hot ATJ rolling based on 5ftt and to adjust the strength of rod wI wire.
There is no need to exceed 2.00%, and the lower limit is still required to be at least 0.20% to prevent cracking due to S.

Som A2: 0.030% for Som AA
If it is below, it will not be enough to fix N, and if it exceeds 0090%, there will be a lot of inclusions, so o, o a o% ~ 0090
% range.

N: For N, sot,, A11i1r(1) Since the upper limit is 0.090%, S○mu A/! ,/N>
15, and set the upper limit of N to 60 ppm.

Aging treatment temperature 2 Aging treatment 3!1j As for the temperature, if the diffusion of C is below 200'C, precipitation will not occur sufficiently, and if it exceeds 500t, the solid solubility of C will be large and precipitation will not occur. Since the temperature was insufficient, the temperature range was set at 200 to 500°C. On the other hand, the temperature during cold forging is 100 to 200℃.
So, what about the “no” effect treatment of the steel bar? 1. I'm low on love, so
The effect of the aging treatment is not lost during cold forging, and in addition, no aging treatment has been performed on the rod 1;i (i wire rod) of the present invention.

Next, test results of the present invention will be explained.

006%C-0,05%5i that yields to the composition system of uninvented steel
-0.30% Mn-based steel material was rolled for 18IljIf nights (I7.6m). $
100'Cx for wire drawing and age hardening test
FIG. 1 shows the results of investigating the relationship between Sot, A4/N, and age hardening rate for test pieces held for 1 hour.

Figure 1 shows S○mu A1 on the horizontal axis. (%) / N etJ, the vertical axis shows the age hardening rate, curve (3) shows the one subjected to aging treatment, curve (■) shows the one without aging treatment,
Aging hardness T, S: Tensile strength when subjected to aging treatment after wire drawing.

T, S: Tensile strength as drawn.

As shown in Figure 1 (SomAtC'A/N(to) is 1
5 or more and subjected to aging treatment, it is understood that the auxiliary hardening value is 5 light or less (the range of the present invention indicated by diagonal lines).

Furthermore, Fig. 2 shows that three types of test materials, which are steels belonging to the compositional system of uninvented steels and have a high Som A4/N value, were rolled between 18IIIf and then aged for 1Hr at different aging temperatures. The relationship between the aging treatment temperature and the age hardening rate is shown for the test results of the test piece which was then wire drawn to L7.611Mj and held at 1001S x IHr for the age hardening test. Curves (a) and (b) in the figure are 0.06%C-
〇, 05%Si -0,80%j Ding-based copper steel wire (c) is 0.23%C-0,25%Si, -1,50%Mn-based steel, and the curve (a) is soz, A4/N = 12.8, curve (b) is SOmu A4/N = 31.4, curve (c)
is SOt, At/N = 20.8, the horizontal axis shows the aging temperature of the wire, the vertical axis shows the age hardening rate, and the range of the two-dot chain line shows the aging temperature range of the present invention. Note that the formula for the age hardening rate is the same as in the case of FIG.

As understood from the results in Figure 2, SOt, A4//N
When is 15 or more, an excellent age hardening rate is obtained by aging treatment at 200 to 500 tons.

Table 1 shows a comparison between the uninvented steel manufactured based on the test results shown in FIGS. 1 and 2 above and the conventional steel shown as comparative steel.

The ○ mark in the “Judgment” column of Table 1 indicates I+, which is the objective of the present invention.
1j indicates that the effective hardening rate is 5% or less, and the mark X indicates that it exceeds 5%.

As is clear from the examples in Table 1, the rod 1 according to the present invention
Although the desired age hardening rate was obtained for each of the 1 wire rods,
The age hardening rate desired by the present invention cannot be obtained in the comparative steel, and therefore, the comparative steel cannot be expected to have the effect of suppressing strain aging that occurs during cold forging of products as contemplated by the present invention.

As explained in detail above, this book is a 1i for cold forged parts such as special bolts, nuts, machine screws, etc. that require a large degree of machining.
71U, it has made it possible to manufacture a steel bar wire rod that has the great effect of reducing deformation resistance, extending tool life, and significantly improving the toughness of υψ products.

[Brief explanation of the drawing]

Figure 1 is a curve diagram showing the relationship between SOI, Al/N and age hardening rate, and Figure 2 is a curve diagram showing the relationship between aging treatment temperature of wire and age hardening rate. °2°Ae (%yN (%) Figure 2 Line Feather/) Leg effect treatment warm skin (°C)

Claims (1)

[Claims] (1) CO, 45XDIT, Si O, 85XJ”J
Bottom, Mn 0.20%-2,00%, PO, 040%
Below, 30.025% or less, Sol, Al O, 030
%-0,090%, N 60 I) 9m or less, 5oi-A4/N15 or more, the balance Fe and a lot of inevitable impurities, after hot rolling, during cooling or after cooling 200 ~ A 1ω1 strained material characterized by being subjected to 11.5-effect treatment at 500°C and having an 11-total infant hardening rate of 5% or less according to the following formula. strength. T, S: Tensile strength of wire drawing.