JPS63310940A - Steel material for cold forging - Google Patents

Abstract

PURPOSE:To improve the cold forgeability of a steel material without deteriorating the hardenability by specifying the amts. of C, Si, Mn, P, S, N, sol, Al, Cu and Ti. CONSTITUTION:This steel for cold forging contains, by weight, 0.005-0.6% C, 0.001-0.5% Si, 0.1-2% Mn, <=0.04% P, <=0.05% S, <=0.015% N and two or more among 0.005-0.1% sol. Al, 0.1-0.5% Cu and 0.005-0.07% Ti. The amts. of sol. Al, Cu and Ti are restricted so as to satisfy an inequality delta=sol. Al/27+Ti/48-N/14>=10<-3>(%).

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to steel materials for cold forging, and more particularly, to cold forging steel materials such as steel bars or wire rods that have improved cold forgeability without impairing their hardenability. Regarding steel materials for forging.

(Prior Art) For example, parts such as bolts, screws, screws, etc. are manufactured by cold forging steel materials for cold forging such as steel bars for cold forging or wire rods. As steel materials for cold forging,
Carbon steel containing 0.05 to 0.60% C by weight (J
IS G4051, Al5I C1005~1055)
, 0.90-1.20% Cr and 0.15-0.0% MO.
Chromium molybdenum steel containing 45% (JIS G410
5, Al5I C4130-4147), Ni 1
．． Nickel chromium steel (JIS G4102) containing 00 to 3.50% Cr and 0.20 to 1.00% Cr, 0.4 to 4.5% Ni, 0.4 to 3.5% Cr, and Mo Nickel chromium molybdenum containing 0.15 to 0.70% (JIS G4103, Al5I C8615 to 8
There are low alloy steels such as 640).

Steel bars or wire rods having these compositions for cold forging are manufactured through the following steps and then subjected to cold forging.

For example, to explain steel materials for cold forging of wire rods, first, the material steel is hot-rolled into wire rods, then pickled to remove oxide scale, and then soaked in a zinc phosphate or calcium phosphate aqueous solution. This phosphate film treatment acts as a base coating to retain lubricant during subsequent wire drawing and cold forging, and is usually 3 to 15 μm thick.
■A thick phosphate coating is applied.

After the phosphate coating treatment, the wire is drawn to adjust the wire diameter, and then subjected to a cold forging process. Or C is 0.30%
The above-mentioned high carbon steel and low alloy steel are subjected to an annealing treatment after the wire drawing treatment, and then subjected to a phosphate coating treatment and a wire drawing treatment again, and then subjected to a cold forging process.

In the cold forging process, the wire rod after wire drawing is cold forged into a predetermined part shape, then quenched and tempered, and depending on the item, surface treatment such as plating is applied to produce the final product.

Steel materials for cold forging are cold forged after going through each process as described above, but in the steel materials for cold forging with the conventional composition described above, the zinc phosphate is not densified by Cu. , and that C and N are not sufficiently fixed by Ti and Al, resulting in poor cold forgeability and short tool life.

One way to solve these problems is to lower the C content, but reducing the C content immediately leads to a decrease in hardenability, making it impossible to obtain the required product strength.

An object of the present invention is to provide a steel material for cold forging that has improved hardenability and has improved cold forgeability without any adverse effect on product strength.

(Means for Solving the Problems) The present inventors have conducted various studies on methods for improving cold forgeability without impairing the hardenability of steel materials for cold forging, and have obtained the following knowledge. Ta.

That is, SOI and Al% C are added to the cold forging steel material with the conventional composition.
Adding two or more of u and Ti, and sol,
If the content of Al and Ti is adjusted to a certain amount or more according to the amount of N, a phosphate film with excellent adhesion can be obtained, and as a result,
During cold forging, there is no peeling of the phosphate film, which further improves cold forgeability, and these elements can improve both cold forgeability and hardenability without increasing the strength of the steel material. The present invention has been completed.

The gist of the present invention is that in weight %, C: 0.00
5-0.60%, Si: 0.001-0.50%, M
Contains n: 0.10-2.00%, P: 0.040% or less, S: Q, 050% or less, N: 0.015% or less, and further sol, Al: 0.005-0.1
00%, Cu: 0.10-0.50% and Ti: Q, O
Q5~0.070! /6, sol, Al, Ti, and N are within the above-mentioned content ranges and satisfy the following formula, and the remainder is Fe and inevitable impurities.

δ=sol, Al/27+Ti/48-N/14
≧10-'("4) In the steel material for cold forging of the present invention described above, Ni, Cr, and Mo are incidental impurities, and their content is usually allowed up to the permissible value specified in standards such as JIS. The permissible values are Ni: less than 0.20%, Cr:
less than 0.20% and Mo: less than 0.15%.

In addition, the element symbol in the above formula indicates the content (weight%) of that element.
shows.

From another aspect, the cold forging steel material of the present invention includes Ni, Cr.
and 0.20 to 0.70% for Ni and 0.20-1 for Cr, exceeding the content of Mo as an impurity.
The steel material for cold forging contains one or more types of Mo in the range of 0.15 to 0.50%.

By containing one or more of these Ni, Cr, and A0, it is possible to increase the quenched size and improve the tempering resistance.

(Function) Hereinafter, the reason why the composition of the cold forging steel material of the present invention is limited as described above will be explained. In the present invention, "%" for each element means "% by weight" unless otherwise specified.

C: The amount of C of o, oos% is the lower limit that can be produced as a steel material for cold forging, and if it is less than o, oos%, the refractory will be significantly eroded and damaged, and it is not practical. On the other hand, 0.60% The C content is not common in the composition of general strong cold forged parts, except for special cold forged parts such as bearing steel.
Furthermore, if C is contained in excess of 0.60%, the strength of the steel material increases and cold forgeability deteriorates. Furthermore, the amount of TiC precipitated increases, which deteriorates the functionality of products, such as high-strength parts (HRc≧40).

If the content exceeds %, the strength of the material increases, deformability decreases, and cold forgeability and workability significantly deteriorate.

Mn: If Mn is small, weldability will be significantly deteriorated, so it should be 0.10% or more. On the other hand, if the content exceeds 2.00%, the strength of the steel material increases, and the steel wire manufacturing process requires several annealing and then cold forging, resulting in high costs.

P and S: The lower the content of these elements, the more preferable they are. If the P content exceeds 0.040% and the S content exceeds o, oso%, the material steel will become weak and cracks may occur during cold forging or embrittlement may occur. It will be promoted.

N: N is an element that causes blue brittleness, and it is desirable to have as little as possible.Increase in N content is 3o1.N, which is necessary to fix N as nitride. It is set at 0.015% or less because it not only increases the amount of Al and Ti added, but also increases the strength of the steel material and reduces cold forgeability.

Cu, Ti, sol, and Al: In the present invention, two or more of these elements are added. These elements have the effect of improving cold forgeability and hardenability without increasing the strength of steel.

Cu makes the crystals of zinc phosphate fine and makes Ti and sol
, Al1 fixes N to make the lubricity or lubricant film uniform and improve cold forgeability. The content of these elements is Cu
: less than 0.10%, Ti: less than 0.005% and sol
, Al: If the content is less than 0.005%, the desired effect of improving the above action cannot be obtained.

The reason why two or more of these elements are used is that 5U is preferably contained in an appropriate amount in order to make the phosphoric acid film dense. sol
, Al, and Ti have the effect of fixing N and making the lubricating film uniform. It is preferable to add two or more of these in combination.

On the other hand, if Cu is contained in excess of 0.50%, ductility decreases and workability is impaired. When Ti is contained in excess of 0.070%, the amount of Tic precipitated increases, increasing the strength of the steel material. Moreover, if sol or Al is contained in excess of 0.100%, AlzOs-based inclusions will increase and cracks will easily occur due to insufficient deformability when cold forging the material steel.

Furthermore, as mentioned above, Ti, sol, and Al are added to fix N, but their optimal contents are within the above range and are simultaneously expressed by the following formula: δ-5o1. Al/27 +Ti/48-N/14≧1
The content satisfies 0-"fi. This is because the larger the δ value, the more sufficient N is fixed, resulting in superior lubricity and improved cold forgeability. If the δ value is small, the s
The fixation of N by the addition of ol, Al, and Ti is insufficient, the ductility of the surface deteriorates, and cranks tend to occur in the phosphate coating, making it impossible to expect an improvement in lubricity.

FIG. 1 shows the relationship between cold forgeability and δ value as determined by Bauden number.

This investigation was conducted as follows. That is, after hot-rolling steel with the composition shown in Table 1 to make a wire rod of 15mmφ, steel type N
u The wire rods of A-1 and B-2 are hot-rolled and the steel type is C.
The wire rods of -1-E-2 were annealed by heating at 750 to 780° C. for 10 to 16 hours.The wire rods were then pickled and coated with a zinc phosphate coating having a thickness of 10 μm. Thereafter, test pieces were taken from these wire rods and subjected to a Bauden test, and the adhesion of the lubricating film was evaluated by the number of Bauden tests.

In the diagram, the mark ・ is the steel type NI A-1, and the mark O is the steel type & A-2.
, Mu mark indicates steel type 11h B-1, Δ mark indicates steel type 11h B-
2. The mark is steel type 11hC-t, and the seal is steel type NI C-2.
, Mark is steel grade D-1, mark is steel grade 11h El-2, ★
The mark indicates the steel type NII E-1, and the ☆ mark indicates the steel type NI E-2.

Also, the same shape means the same steel type.

As is clear from FIG. 1, among wire rods of the same steel type, the steel of the present invention with a larger δ value has better cold forgeability than the Bauden number.

On the other hand, conventional steel has a small δ value and poor cold forgeability.

Furthermore, the aforementioned Cu, Ti, sol, and Al have the effect of improving not only cold forgeability but also hardenability.

Figure 2 shows steel types Nll C-1, C-2, and
[1-1 and D-2 steel bars with a diameter of 25 mm were heated to a temperature of 900°C for 60 minutes to harden them, and then the hardness distribution from the surface to the center was measured using HRc hardness to examine the hardenability. It is something that

In the figure, the ■ mark is steel grade C-1, and the mouth mark is i'! Seed NQC-2
, the mark means a steel bar having a composition of steel type Nu D-1, and the mark means a steel bar having a composition of steel type 11h D-2.

As is clear from Fig. 1, steel types ThC-1 and D-1
The steels of the present invention of steel types NIC-2 and D-2 have excellent hardenability compared to conventional steels. In particular, the hardenability of the steel of the present invention, which is a steel grade D-2 containing Cr and Mo, is greatly improved compared to the conventional steel, steel grade 1m D-1.

The first cold forging steel material of the present invention consists of the above alloying elements and the remainder being unavoidable impurities. As an impurity, Ni: 0.
Less than 20%, Cr: less than 0.20% and Mo: 0.15
Less than %.

Another steel material for cold forging of the present invention is the Ni, Cu
, and Mo exceeding the amount of impurities and Ni: 0.20 to 0.
70%, Cr: 0.20-1.50% and Mo0.15
It contains one or more kinds in the range of 0.50%.

These elements are effective in improving hardenability and tempering resistance, and if Ni: less than 0.20%, Cr: less than 0.20% and Mo: less than 0.15%, the desired effect is not achieved. On the other hand, Ni: over 0.70%, Cr: 1.
If the content exceeds 50% and Mo: exceeds 0.50%, the composition will be thicker (deviating from the composition system of ordinary structural alloy steel), and it is not common as a steel material for cold forging.

The cold forging steel material of the present invention has the above composition. Cold forging steel materials with such a composition are
After being formed into a wire rod or steel bar by hot rolling, it undergoes the following steps and is then subjected to cold forging.

For example, in the case of wire rods, steel with the above composition is hot-rolled into wire rods, and the wire rods are either hot-rolled or annealed at 750 to 780°C depending on the product, and then decomposed by pickling or the like. Apply scale treatment and phosphate coating. The phosphate coating treatment is carried out using zinc phosphate, calcium phosphate, or a mixture of both, and the coating thickness is preferably about 10 μm. After the phosphate coating treatment, the wire is drawn and further annealed if necessary, and then subjected to the phosphate coating treatment again and subjected to cold forging.

Next, the present invention will be further explained with reference to Examples.

(Example) Steel having the composition shown in Table 2 was hot-rolled into a wire rod of 20 mφ, and the hot-rolled wire rod or a part of the wire rod was annealed under the annealing conditions shown in Table 3. After pickling, a phosphate coating was applied under the phosphate coating treatment conditions shown in the same table.

Tensile test pieces and Bowden test pieces were taken from the wire rods obtained in this manner, and cold forgeability was examined using mechanical properties and Bowden cycles. These test results are summarized and also listed in Table 3.

The equivalent Al5I standard shown in the notes column of Tables 2 and 3 indicates to which class of the 4151 standard the steel having the composition shown in Table 2 corresponds.

As is clear from Table 3 (with the same equivalent AlSr standard, comparative steels in which two or more of Cr, sol, M, and Ti are outside the range specified by the present invention have mechanical properties that are not the same as the present invention steel. Although there is no difference, the Bauden number is low and the cold forgeability is poor.In contrast, the steel of the present invention has excellent cold forgeability as well as mechanical properties.

(Effects) As explained above, the cold forging steel of the present invention has excellent cold forgeability and hardenability.

For this reason, the tool life of cold forging is extended, and the resulting forged parts are of excellent quality with no difference in hardness.

[Brief explanation of the drawing]

Figure 1 shows the relational expression δ= sol, Al, Ti, and N.
sol. 8 Q/21 + Ti/48- N/14) x 104
Figure 2 is a graph showing the relationship between Bauden number and C-I C- in the steel type test shown in Table 1.
2 is a graph showing the hardenability of steel bars No. 2, D-1, and D-2. Zhuli! 】Yu 2 concave noodles (duck)

Claims (1)

[Claims] (1) In weight%, C: 0.005-0.60%, Si: 0.001-0.
50%, Mn: 0.10-2.00%, P: 0.040
% or less, S: 0.050% or less, N: 0.015% or less, and sol, Al: 0.005 to 0.100
%, Cu: 0.10-0.50% and Ti: 0.005
Contains ~0.070% of two or more types and sol, A
A cold forging steel material in which L, Ti, and N are within the above content range and satisfy the following formula, and the remainder is Fe and inevitable impurities. δ=sol, Al/27+Ti/48-N/14≧10
^-^3 (%) (2) In weight%, C: 0.005 to 0.60%, Si: 0.001 to 0.
50%, Mn: 0.10-2.00%, P: 0.040
% or less, S: 0.050% or less, N: 0.015% or less, further Ni: 0.20 to 0.70%, Cr: 0
．． 20 to 1.50% and one or more of Mo: 0.15 to 0.50% and sol, Al: 0.005 to 0.100%,
Cu: 0.10-0.50% and Ti: 0.005-0
．． Contains two or more of 070% and sol, Al,
A cold forging steel material in which Ti and N are within the above content range and satisfy the following formula, and the remainder is Fe and unavoidable impurities. δ=sol, Al/27+Ti/48-N/14≧10
^-^3 (%)