JPH0219443A - Rolled wire rod steel having excellent machinability and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture the title bar steel by subjecting a steel material contg. specific trace amounts of S or Pb to hot rolling into the shape of a rod or a wire rod and thereafter coiling it at specific temp. or gradually cooling it in the range of specific temp. CONSTITUTION:A billet having the compsn. contg., by weight, 0.05 to 0.55% C, <0.40% Si and 0.30 to 2% Mn and furthermore contg. <0.040% S or at least one kind of 0.04 to 0.4% S and 0.05 to 0.4% Pb is subjected to hot rolling into the shape of a rod or a wire rod, which is thereafter coiled at 650 to 1,100 deg.C or gradually cooled in such a manner that the cooling speed till the passing time between the temp. of A3 transformation point to A1 transformation point is regulated to <=0.2 deg.C/sec in the cooling stage of the rolled material to grow large crystals of <=6.5 crystal size number, and by the presence of the elements to improve workability such as S and Pb, the rolled wire rod steel having excellent machinability can be manufactured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rolled wire rod with excellent machinability and a method for manufacturing the same.

Conventionally ■ Rolled wire rod steel for cutting, which is used as steel for polished polished bars, can be used to manufacture a wide variety of parts, including automobile parts, construction machinery parts, hydraulic equipment parts, decorative parts, electrical parts, and office equipment parts, after drawing. Widely used. In this field,
In particular, in recent years, with the aim of increasing precision and reducing manufacturing costs,
There is a demand for steel materials with excellent machinability.

Conventionally, steel materials with machinability include S, Pb, Ca, Bi,
Contains so-called free machinability imparting elements such as Te, for example,
SUM 24V steel contains 0.3% S and 0.20% Pb
545CL steel contains 0.2% PB. Also, for example, JP-A-59-118861
The publication describes a free-cutting steel having a ferrite-pearlite structure made by adding Pb, Bi, Te, etc.

However, when improving the machinability of steel by adding free-machining elements to it, the mechanical properties of the steel may deteriorate, limiting its uses. Alternatively, adding free-machining elements such as those mentioned above to steel requires special means, and depending on the free-machining elements added, they are expensive, which can significantly increase the manufacturing cost of steel materials. becomes.

In order to solve the various problems mentioned above in the production of conventional steel materials with excellent machinability used as steel for polished bars, the present inventors have developed a method for improving machinability in rolled steel materials. As a result of intensive research on the relationship between the heat treatment structure and grain size, we found that conventionally, the grain size number of steel for polishing is usually
8 to 12, for example, the above-mentioned Japanese Patent Application Laid-Open No. 59-118
In the free-cutting steel according to Publication No. 861, the grain size number is required to be 9 or more, but the present inventors have particularly improved the grain size by increasing the grain size number of the rolled steel material to a predetermined value or more. Rolled wire rod steel bars with excellent machinability can be obtained without adding free-machining elements such as those mentioned above to steel. In particular, steel for Kei bars has the advantage that the crystal grains of the rolled steel material are retained during cutting. Therefore, it has been found that the steel material according to the present invention can be suitably used as a polishing steel.

Furthermore, the present inventors also obtained a rolled wire rod steel bar with excellent machinability by increasing the grain size number of the rolled steel material to a predetermined value or more even for free-cutting steel containing free-machining elements. I found out that it is possible. The present invention has been made based on this knowledge.

Therefore, the present invention generally aims to provide a rolled wire rod with excellent machinability and a method for manufacturing the same, and in particular, a steel for polished bars with excellent machinability that is subjected to cold drawing. The purpose is to provide

The rolled wire rod steel bar with excellent machinability according to the present invention for cutting buds has a weight percentage of
A rolled wire rod steel bar consisting of C 0.04-0.55%, Si 0.40% or less, Mn 0.3 (1-2%, S 0.040% or less, the balance iron and unavoidable impurities), and the grain size is It is characterized by a number of 6.5 or less.

The rolled wire rod steel bar with excellent machinability according to the present invention contains, in addition to the above elements, at least one element selected from the group consisting of S 0.04 to 0.4% and Pb 0.05 to 0.4%. can contain.

The method of manufacturing a rolled wire rod steel bar with excellent machinability according to the present invention involves (a) winding a steel billet having the above-mentioned chemical composition at a temperature in the range of 650 to 1100°C after rolling; ) A rolled wire rod steel bar having a grain size number of 6.5 or less is obtained by setting the average cooling rate from the transformation point A to passing the transformation point A to 0.2° C./sec or less.

First, the reason for limiting the chemical components in the rolled wire rod according to the present invention will be explained.

C is an element for imparting mechanical strength to the steel of the present invention, and for this purpose, it is necessary to add at least 0.04%. However, when adding too much, the hardness of the steel increases beyond the appropriate range, which not only deteriorates the machinability but also the toughness. Even if the amount is increased, machinability cannot be significantly improved, so the upper limit of the amount added is set at 0.55%.

When added in excess, Si increases the hardness beyond the appropriate range, deteriorating machinability and toughness, and as mentioned above, even if the crystal grains of the steel material are enlarged, the hardness increases beyond the appropriate range. Since it is not possible to significantly improve machinability, the upper limit of the amount added is set to 0.
．． It shall be 40%.

Mn has a deoxidizing effect, forms MnS, suppresses the formation of FeS, improves hot workability of steel, and further improves hardenability to improve strength and toughness of steel. added. However, when Mn is added in excess, it not only unnecessarily increases the hardness of the steel and deteriorates machinability, but also deteriorates toughness. Therefore, the upper limit of the amount added is set at 2%.

S is an element that improves machinability, but when it is added in excess of 0.4%, the mechanical strength deteriorates significantly and it cannot be used to manufacture the above-mentioned parts. In the present invention, when making a rolled wire rod steel that has good machinability without adding free-machining elements, the amount of S is 0.0
When S is added as a free-machining element, the amount added is 0.4% or less for the above reasons.

In order to further improve the machinability of the wire rolled steel bar according to the present invention, as described above, Pb may be added in the range of 0.05 to 0.4% together with S or alone. can.

The steel according to the present invention needs to have the above-mentioned chemical composition and a grain size number of 6.5 or less. According to the present invention, satisfactory machinability can be obtained by setting the grain size number to 6.5 or less.

Next, the steel material with excellent machinability according to the present invention can be obtained by (a) rolling a steel billet having the above-mentioned chemical composition at a temperature in the range of 650 to 1100°C after rolling, or (b) using As. This can be obtained by setting the average cooling rate from the transformation point to passing through the A1 transformation point to 0.2° C./second or less, and by setting the grain size number to 6.5 or less. When the coiling temperature is lower than 650° C., a suitable cooling structure is generated, which deteriorates machinability and also tends to cause flaws during rolling. On the other hand, when the winding temperature exceeds 1100°C, the scale becomes thick and the surface texture of the product after pickling becomes poor.

According to the present invention, a combination of the two methods described above can also be employed. If at least one of the above methods is not used, crystal grains cannot be grown large,
In the obtained steel material, the grain size number exceeds 6.5 and the crystal grains become fine, so that the desired excellent machinability cannot be imparted to the steel material.

As described above, the rolled wire rod steel bar according to the present invention has high machinability without substantially containing free machinability imparting elements, and therefore is suitable for manufacturing the above-mentioned parts. The rolled wire rod steel bar according to the present invention can be suitably used as a steel for polished bars in which the crystal grains of the rolled material are retained during cutting. can.

Furthermore, according to the present invention, by adding S and/or Pb as a free-machining element and setting the grain size number of the rolled steel material to a predetermined value or more, a rolled wire rod steel bar with excellent laminar fluid machinability can be obtained. Obtainable.

EXAMPLES The present invention will be described below with reference to Examples, but the present invention is not limited to these Examples in any way.

Example 1 A SIIM 22 steel piece consisting of co, os%, trace amount of Si, 1.04% Mn, 0.075% P, 0.330% S, the balance iron and unavoidable impurities was heated to the temperature shown in Table 1. A 25III11 diameter rolled steel bar having the grain size number shown in Table 1 was obtained.

After cold drawing these rolled steel bars to a diameter of 22 mm, cutting was performed using an automatic lathe under the cutting conditions shown in Table 2.
The machinability of the obtained machined parts was evaluated based on the finished surface roughness and the amount of tool wear.

As the results are shown in Figures 1 and 2, the winding temperature was set to 95
All of the steels of the present invention having a grain size number of 6.5 or less at a temperature of 0° C. or higher have excellent machinability.

Example 2 A piece of 515C steel consisting of 0.15% C, 0.27% Si, 0.45% Mn, 0.020% P, 0.025% S, and the balance iron and unavoidable impurities was first
As shown in the table, the average cooling rate from the A transformation point to when passing through the A1 transformation point was varied to obtain 25 mm diameter rolled steel bars having the grain size numbers shown in Table 1.

These rolled steel bars were cold drawn to a diameter of 22 mm in the same manner as in Example 1, and then cut under the cutting conditions shown in Table 2 to evaluate machinability. The results are shown in Figures 1 and 2. All of the steels of the present invention in which the average cooling rate from the A3 transformation point to the A1 transformation point is 0.20° C./second or less and the grain size number is 6.5 or less have excellent machinability.

Example 3 A SUM 24L steel billet consisting of co, os%, trace amount of Si, 1.05% Mn, 0.080% P, 0.320% S, 0.26% Pb, and the balance iron and unavoidable impurities was first prepared. It was coiled at the coiling temperature shown in the table to obtain a 25 mm diameter rolled steel bar having the grain size numbers shown in Table 1 and shown in Figures 1 and 2.

These rolled steel bars were cold drawn to a diameter of 22a+ in the same manner as in Example 1, and then cut under the cutting conditions shown in Table 2 to evaluate machinability. The results are shown in FIGS. 3 and 4. The steel of the present invention has less tool wear compared to conventional steel.
The finished surface has good roughness.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the number of cut pieces and finished surface roughness for the invention steel and comparative steel, and Figure 2 is a graph showing the relationship between the number of cut pieces and tool wear for the invention steel and comparative steel. , 3rd
The figure is a graph showing the relationship between the number of cut pieces and the finished surface roughness of the inventive steel and the comparative steel. Figure 4 is the graph showing the relationship between the number of cut pieces and the amount of tool wear of the inventive steel and the comparative steel. . Figure 3 Figure 4 Gong h11 table (pieces)

Claims (4)

[Claims] (1) A rolled wire rod steel bar consisting of 0.04 to 0.55% C, 0.40% or less Si, 0.30 to 2% Mn, and 0.040% or less S, the balance being iron and unavoidable impurities in weight percent, A rolled wire rod steel bar with excellent machinability, characterized by a grain size number of 6.5 or less. (2) Contains (a) 0.04 to 0.55% of C, 0.40% or less of Si, and 0.30 to 2% of Mn in weight%, and further contains (b) 0.04 to 0.4% of S, and A rolled wire rod steel bar containing at least one element selected from the group consisting of 0.05 to 0.4% Pb, with the remainder being iron and unavoidable impurities, and having a grain size number of 6.5 or less. A rolled wire rod with excellent machinability. (3) Rolling a steel billet consisting of 0.04 to 0.55% C, 0.40% or less Si, 0.30 to 2% Mn, and 0.040% or less S, the balance being iron and unavoidable impurities in weight percent. After finishing, coil it at a temperature in the range of 650 to 1100°C, or (b) set the average cooling rate from the A_3 transformation point to the time of passing through the A_1 transformation point to 0.2°C/second or less, so that the grain size number is A method for producing a rolled wire rod and steel bar having excellent machinability, the method comprising obtaining a rolled wire rod and steel bar having a hardness of 6.5 or less. (4) Contains (a) 0.04 to 0.55% of C, 0.40% or less of Si, and 0.30 to 2% of Mn in weight%, furthermore, (b) 0.04 to 0.4% of S, and A steel billet containing at least one element selected from the group consisting of 0.05 to 0.4% Pb and the balance consisting of iron and unavoidable impurities is (a) heated at a temperature in the range of 650 to 1100°C after rolling. (b) Obtain a rolled wire rod steel bar with a grain size number of 6.5 or less by winding it or (b) setting the average cooling rate from the A_3 transformation point to the time of passing through the A_1 transformation point to 0.2°C/second or less. A method for manufacturing a rolled wire rod with excellent machinability, characterized by: