JPS6167775A - Steel bar or wire for cold forging - Google Patents

Abstract

PURPOSE:To provide a steel bar or wire for cold forging having excellent strain aging resistance at a low cost with decreased stages by hot rolling a low-and middle-carbon aluminum killed steel consisting of a specific compsn. then subjecting the steel to an overaging treatment and descaling followed by an adequate lubricating treatment and drawing the treated steel. CONSTITUTION:The steel consisting of <=0.45% C, <=0.35% Si, 0.20-2.00% Mn, <=0.040% P, <=0.025% S, 0.030-0.090% SolAl, <=60ppm N and SolAl/N=15 and consisting of the balance Fe and unavoidable impurities is hot rolled and is subjected to the overaging treatment. The steel is subjected surface treatment for lubrication by calcium zinc phosphate soln, after descaling. The steel is subjected to the lubricating treatment using a stearic acid in succession thereto and is then drawn. The lubricating film consisting of >=5g/m<2> calcium zinc phosphate pickup, >=1g/m<2> reactive layer pickup and >=2g/m<2> hot water soluble soap pickup is formed on the surface of the wire after drawing. The need for the intermediate annealing and secondary lubricating treatment prior to preforming is thus eliminated and the steel bar or wire for cold forging is provided at the low cost.

Description

[Detailed Description of the Invention] Technical Field of the Invention The present invention relates to a steel bar wire rod for cold forging used when manufacturing screws and other various parts by cold forging, and particularly relates to a steel bar wire rod for cold forging, which is particularly suitable for strain aging resistance and cold forging. Lubricity (hereinafter referred to as "cold forging")
The present invention relates to a steel bar wire rod which has excellent properties (abbreviated as .

Prior Art and Its Problems Steel bar wire rods for cold forging are hot rolled, descaled, and lubricated, then cold wire drawn, and then processed into final products. Rimmed steel and low-medium carbon aluminum guild steel wire bars have been put into practical use as steel wire rods for cold forging that are processed in this manner.

However, in cold forging of general rimmed steel and general low-medium carbon steel, the temperature drops to about 100 to 200℃ during processing, and cold forging occurs in the blue brittle temperature range. Age hardens, significantly reducing tool life. Therefore, conventionally, after preforming, intermediate annealing is performed, and then descaling and secondary lubrication treatment are performed again to perform main molding.

Purpose of the Invention This invention was made in view of the above-mentioned conventional circumstances, and has excellent strain aging resistance and D/Do>2.0 (D
An object of the present invention is to provide a steel bar wire rod for cold forging, which makes it possible to omit intermediate annealing and secondary lubrication treatment after preforming in cold forging of a product having a diameter of 1.0: product diameter, Do: wire diameter).

Structure of the invention The steel bar wire rod for cold forging according to the present invention contains C0, 45% or less, SiO, 35% or less, Mn 0.20 to 2.00%.
,PQ.

040% or less, 30.025% or less, sot, N0. o
Using a material containing so~0゜090%, N60p\1m or less, Sol, kl/N = 15 or more and the balance consisting of Fe and inevitable impurities, during cooling after hot rolling or after cooling 200 ~ Overaged at 500℃,
The rolled material was descaled so that the age hardening rate calculated by the following formula was 5% or less, and then the lubricating base was treated with a zinc calcium phosphate solution (Ca/Zn = 0.1 to 1.0). Then, the wire is drawn after being lubricated with a lubricant mainly containing sodium stearate (reactive soap), and the surface of the drawn wire is coated with zinc calcium phosphate ≧5f.
/lrl, reaction layer (zinc stearate) adhesion amount ≧1f/
d. Amount of molten soap adhesion ≧211/rr? It is characterized by having a lubricating film of D/D0 > 2.0 (D: product diameter, Do: wire drawing material diameter), making it possible to omit intermediate annealing after preforming in cold forging of products. It's something.

However, T, S: Tensile strength of aging treated material after wire drawing (Kg)
/W) T, S: Tensile strength as drawn /-) Here, the reason for limiting the target steel of this invention will be explained.

As for the composition system of the target steel of this invention, the tensile strength of the wire rod, which can be practically cold-forged as rolled, is 90.
K9/Wd is required, and C, St.

The reason for determining the composition ranges of (1), Sol, fihl, and N as described above is as follows.

C Hato's invented steel has a compressibility of 7 when it is 0.45% or more.
Since processing cracks occur at 5%, the upper limit was set at 0.45%.

The lower limit is not particularly limited because the lower the C content, the better the aging properties.

Although St does not affect aging properties, it is only added for deoxidation or strength adjustment, so the upper limit is set at 0.35%.

If the content exceeds 0.35%, the cold forging workability deteriorates, so it is preferable. 2. Seeds are those used for preventing cracking during hot rolling and adjusting the strength of steel wire rods based on S-i. There is no need for it to exceed 0%, and the lower limit of the trench depth should be at least 0.2% to prevent cracking due to S.

If SataAJ is less than 0.03%, it is insufficient to fix N, and if it exceeds 0.09%, inclusions will increase.
．． It was set in the range of 0.03% to 0.09%.

Since the upper limit of the value of 806M is 0.09%, N is Sat.
.

Al/N 〉1'5 deka-)N(1) upper limit to 60pp
m and toshida.

The age hardening rate (5% or less) can be obtained by hot-rolling a material made of the above-mentioned components and subjecting it to a separate over-aging treatment at ~500° C. during or after cooling. That is, with respect to the aging treatment temperature, if the aging treatment temperature is 200° C. or lower, the diffusion of C is poor, so precipitation is not sufficient, and if it exceeds 500° C., the solid solubility of C is large, so precipitation is also insufficient. Therefore, the aging treatment temperature is preferably in the range of 200 to 500°C.

On the other hand, the temperature during cold forging is 100 to 200°C, which is lower than the aging treatment temperature of the steel bar wire rod, so the effect of the aging treatment is not lost during cold forging.

That is, in the invention of Sat, A/content is 0.0
3 to 0.09%, and Sat and N/N to 15, and after fixing N as AtN, C is precipitated and fixed as a carbide by aging treatment at 200 to 500 ° C. during or after cooling. Age hardening caused by C and N is suppressed. This is clear from the relationship between the SO ratio Aj' /N and the age hardening rate shown in FIG. 1 and the relationship between the overaging temperature of the wire and the age hardening rate shown in FIG.

In addition, the aging conditions in Fig. 1 are 80°C x 1 hr, and A
Overaging treatment (300° C. X l hr); B indicates the age hardening rate without overaging treatment. In addition, the second figure A shows C0.06%, SiO,05%, Mn0
．． 30%, Sol, fi-1/N = 12.8, mouth C0,06%, SIo.

05%, Mn Q, 3 Q%, SOI, Al/N =
31.4, Ha is C0, 23%, SiQ, 25%, Mn
1.5%, Sol, fiJ/N = 20.3 wire rod age hardening rate, both aging conditions 80 ° C × l h
This is the result for r.

In addition, in this invention, a lubricating film is formed on the surface after wire drawing with an amount of zinc phosphate adhesion ≧59/rl, a reaction layer adhesion amount ≧1f/m and a molten soap adhesion amount ≧2(1/rr?). It is characterized by the following reasons.

First, the zinc-calcium phosphate coating has excellent heat resistance and is characterized by not cracking during wire drawing. The adhesion amount of zinc calcium phosphate ≥ 517 rl, reaction layer (zinc stearate) adhesion amount ≥ 1 firl, and molten soap adhesion amount ≥ 2 firl are all taken into consideration the lubrication performance during cold forging. , zinc phosphate calcium adhesion amount ≧59/d is the conventional zinc phosphate adhesion amount ≧79
/d (which is introduced as 7f or higher in literature), but this is because the zinc calcium phosphate film has excellent heat resistance and good adhesion.

Also, is the zinc phosphate calcium adhesion amount ≧59/rr? , reaction layer adhesion amount≧1f/rrl, hot water molten soap adhesion amount≧2f
ize is the lowest adhesion amount when lubricating ability is taken into account; below this amount, seizure occurs during cold forging.

The above-described steel bar wire rod for cold forging according to the present invention will be explained.

First, after hot rolling the steel made of the above ingredients into a steel bar wire rod,
During cooling, the rolled material is subjected to over-aging treatment at 200 to 500°C after cooling so that the age hardening rate is 5% or less, and after descaling (pickling), zinc calcium phosphate solution (C
a/Zn = 0.1 to 1.0), the wire is subjected to a lubricating base treatment, and then subjected to a reactive surface treatment, followed by wire drawing.

Here, the reason why the Ca/Zn ratio of the zinc calcium phosphate solution was set to 0.1 to 1.0 was based on the relationship between the Ca/Zn ratio and the amount of phosphate film deposited as shown in Figure 3. When the ratio is less than 0.1, the Ca ratio is small, so the effect of Ca addition is small and the heat resistance is insufficient, and when the Ca/Zn ratio is more than 1.0, chemical conversion treatment properties and reactive surface oxidation are poor. According to the relationship between the Ca/Zn ratio and the amount of reaction layer adhesion shown in Figure 4, the predetermined amount of adhesion of calcium zinc phosphate (
This is because it is difficult to obtain a reaction layer adhesion amount (≧1f/y/).

As for the total acidity (processing concentration), temperature, and time, you can change it appropriately as in the conventional zinc phosphate treatment depending on the difficulty of the target product (usually, the total acidity is 30 to 40 points and the temperature is 70 points). ~80°C, time 5-20 minutes).

Further, the reactive surface cleaning treatment after the zinc calcium phosphate treatment may be the same as the conventional zinc phosphate treatment.

In either case, the amount of lubrication deposited during zinc calcium phosphate treatment, reactive surface cleaning treatment, and wire drawing, i.e., zinc phosphate l
A sample material having the amount of calcium deposited, the amount of reaction layer deposited, and the components shown in Example Table 1 was used, and as a lubrication treatment, zinc phosphate calcium treatment (Ca/Zn =
0.3) - Using the wire obtained by carrying out the reaction type surface treatment and drawing, a product with a total compression rate of about 80% was cold forged.

For comparison, conventional steel (rimmed steel - zinc phosphate treatment)
The same procedure was carried out for (reactive surface treatment).

The results of this example are shown in Table 2. Table 3 shows the amount of lubricant applied to the wire drawn material in test sales 4.5.

From the results in Table 2, the wire obtained by subjecting the non-time-hardened wire rod of the present invention to zinc calcium phosphate treatment (+reactive surface treatment) and drawing it can omit intermediate annealing, and It can be seen that there is almost no difference in cold forging load compared to the intermediate annealed product.

Even with the non-aging wire rod of the present invention, cold forging was impossible due to poor heat resistance of the lubricating film when treated with zinc phosphate.

In addition, as is clear from the amount of lubricant applied to the drawn wire material shown in Table 3, cold forging properties vary greatly depending on the amount of lubricant applied to the drawn wire material.
9/rt? , reaction layer adhesion amount≧If/rr? .

Requires zinc phosphate calcium adhesion amount ≧591r&. It should be noted that each N:N value differs depending on the ratio of calcium and zinc in the zinc phosphate treatment even under the same treatment conditions. Therefore, it is necessary to consider the processing conditions (concentration, time, temperature) depending on the Ca/Zn ratio.

Table 1 Sample material composition (96) Table 2 Cold forging test results However, primary lubrication: Type of phosphate treatment before wire drawing Preforming: Umbrella shape Secondary lubrication: Before main forming (after preforming) ) types of phosphate treatment Table 3 Amount of lubricant deposited on wire drawing material Cf1rl) □ Effects of the invention As described above, this invention
0.09%, over-aged at 500°C), and has a highly heat-resistant zinc calcium phosphate coating on the surface after wire drawing, a reaction layer and a molten soap coating, and It has non-aging properties with an age hardening rate of 5% or less, so it does not age harden during cold forging, and intermediate annealing and secondary lubrication treatment before preforming can be omitted, resulting in the elimination of processes and product oil refinement. It is possible to significantly reduce costs.

[Brief explanation of the drawing]

Figure 1 is a chart showing the relationship between sot, At/N and age hardening rate in this invention, Figure 2 is a chart showing the relationship between overaging treatment temperature and age hardening rate, and Figure 3 is the same (Ca/Z
FIG. 4 is a chart showing the relationship between the n ratio and the amount of phosphate film deposited, and FIG. 4 is a chart showing the relationship between Ca/Zn and the amount of reaction layer deposited. (r/i) ) η Gorge I Nanjyu Station 10 (-4) Hikime 嫂 dent η (%) *Ha1e佼到(%) *Hayurikyou Light

Claims (1)

[Claims] C0.45% or less, Si0.35% or less, Mn0.20
~2.00%, P0.040% or less, S0.025% or less, Sol. Al0.030-0.090%, N60p
pm or less, and Sol. A steel with Al/N = 15 or more and the balance consisting of Fe and unavoidable impurities is hot-rolled and then over-aged, and after descaling, the rolled material is lubricated with a zinc calcium phosphate solution, and then treated with stearic acid. The wire is drawn after being lubricated with a sodium-based lubricant, and the amount of zinc calcium phosphate deposited on the surface after drawing is ≧5.
A steel bar wire rod for cold forging, characterized by having a lubricating film with a reaction layer coating amount of 1 g/m^2, a molten soap coating amount of 2 g/m^2, and strain aging resistance.