JPH01152242A - High-toughness and high-speed steel by powder metallurgy - Google Patents

Abstract

PURPOSE:To improve the toughness of the subject steel by prepg. the high-speed steel contg. specific ratios of C, Si, Mn, Cr, V, Mo and W and having the specific grain size of its carbide by powder metallurgy. CONSTITUTION:The steel material is formed by using the steel powder contg., as essential components, by weight, 0.7-2.5% C, <=2.0% Si, <=1.5% Mn, 3.0-6.0% Cr and 0.8-25.0% V, contg., as selectional components, either or both between 3.0-10.0% Mo and 1.0-20.0% W and consisting of the balance Fe with inevitable impurities by powder metallurgy to prepare the high-speed steel contg. the carbide having, by the equivalent diameter to a circle, <=1.0mu grain size. By this method, the high-speed steel having excellent hardness and wear resistance and having much more improved toughness is obtd.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to high-speed tool steel produced by powder metallurgy.
In particular, it relates to improving its toughness.

<Prior Art> Hitherto, high-speed steels have been known in which, for example, the components (wt%) shown in Table 1 are added to iron.

Table 1 (Conventional high-speed steels) The high-speed steels mentioned above are generally used as ingot materials, but in recent years, as tool usage conditions have become more severe, powder metallurgy materials have been developed to improve toughness. is used. Most powder metallurgy materials are manufactured by solidifying the powder using hot pressing, then forging and rolling. ,
Because the crystal grains are fine, it has excellent properties in many aspects, especially toughness.In the case of the above steel A, the hardness is HRC66.
Transverse rupture strength at level is approximately 300Kgf/mm for melted lumber
2, whereas for powder metallurgy materials it is about 480Kgf/a.
m2, indicating a value of 1.5 times or more.

<Problems to be Solved by the Invention> However, as the conditions for use of tools become more severe, even the powder metallurgy materials described above do not have sufficient toughness, and further improvements in properties have been desired.

This invention aims to realize a tool steel that has hardness and wear resistance equal to or greater than conventional powder metallurgy materials of high-speed steel, and has higher toughness.

<Means for Solving the Problems> In order to achieve the above-mentioned object, the inventor focused particularly on the particle size and distribution state of carbides, and as a result of research on this, found that:
In order to increase the toughness of powder metallurgy materials for high-speed steel, conventional
It has been found that it is extremely effective to suppress the carbide particle size to 1.0 micron or less, which was previously 4 microns.

That is, the steel material of the first invention of this application has C as a raw material in weight% of 0.7 to 2.5, Si of 2.0 or less, and M as a raw material.
n is 1.5 or less, Cr is 3.0 to 5.0, V is 0.
Steel consisting of an essential component of 8 to 25.0, a selected component of Mo or 3.0 to 10.0 and one or both of W or 1.0 to 20.0, and the remaining Fe and unavoidable impurities. The steel material is made by powder metallurgy using the powder, and the carbide contained therein is characterized in that the grain size or equivalent circle diameter is 1.0 microns or less.

Further, the steel material of the second invention of this application contains G in addition to the essential components and optional components in the first invention.

is 4.0 to 12.0, and contains a second selected component of Nb, 0.1 to 5.0 Noy, or both.

Next, the reason for limiting the components in this invention will be described.

C is essential for the formation of carbides of Cr, V, Mo, W, and Nb, and is also a necessary component to form a solid solution in the matrix during quenching and provide high tempering hardness. In order to obtain a hardness of HRC62 or higher by quenching and tempering, it is necessary to add at least 0.7% by weight, but 2.
．． If it exceeds 5% by weight, it will not be possible to obtain the carbide particle size of 1.0 microns or less required in the present invention.

Si is mainly added as a deoxidizing agent and improves hardenability, but if it exceeds 2.0% by weight, it causes deterioration of toughness.

Like Si, Mn is added as a deoxidizing agent and improves hardenability, but if it exceeds 1.5% by weight, toughness and softening resistance during tempering decrease.

A minimum amount of 3.0% by weight of Cr is required to ensure hardenability, but it is not preferable to exceed 6% by weight since Cr carbides tend to aggregate and coarsen.

(2) forms stable Md-type carbides that are difficult to form solid solutions, makes crystal grains finer, helps improve toughness, and significantly improves wear resistance. If it is less than 0.8% by weight, the effect of improving wear resistance is small, and if it exceeds 25% by weight, giant eutectic carbides are produced.

Both Mo and W form M6C type carbides and improve #wear properties, but this effect is greater for MO, about 2
have twice as much influence. Mo increases hardenability as well as wear resistance, and in order to obtain these effects, the content is at least 3.0% by weight.
is necessary, but if it exceeds 10.0% by weight, the carbide will become coarse. In addition, at least 1.0% by weight of W is required to improve wear resistance, but since it is less likely to form coarse carbides than MO, the upper limit was set to twice that of Mo.

Co and Nb are added depending on the purpose to improve heat resistance and toughness, respectively. Go forms a solid solution in the matrix, suppresses the agglomeration and coarsening of carbides, and increases the softening resistance during tempering. To get this effect, at least 4
．． Although 0% by weight is required.

Even if it is added in excess of 12.0, the effect will not increase.

Nb forms stable carbides and prevents coarsening of crystal grains. If it is less than 0.1% by weight, the effect will not appear;
Exceeding this percentage by weight results in a decrease in softening resistance during tempering and a decrease in toughness. - <Effect> Typical high-speed steels A, B, and C shown in Table 1 were made into steel materials by powder metallurgy, and the relationship between carbide grain size and toughness was determined.

Each sample was made by filling gas atomized powder of 35 meshes or less of each test steel A, B, and C into a mild steel capsule with a diameter of 160 a + m, degassing and sealing, and hot extruding it into a bar with a diameter of 50 II and 11. I got it and started cutting it out.

The particle size of the carbide in each sample was adjusted by adjusting the heating temperature and holding time at the same temperature during induction heating for hot extrusion.

(B) 1ooo℃ x 5 minutes (B) 105
0℃XIO minutes (c) 1100℃× 10 minutes
(d) Four tests were conducted at 1100°C for 20 minutes.

The cut samples were subjected to the following heat treatment.

Quenching 1190°C x 3 minutes → Oil cooling tempering 57
06CX 1 hour → air cooling (3 times) The carbide particle size was measured on the sample after heat treatment and the equivalent circle diameter was adopted, but the sample under the above induction heating conditions (a) and (b) had a carbide particle size of 1.
It became less than 0 micron.

The results of measuring the transverse rupture strength and Charpy impact value of each of the above samples are shown in Figures 1 and 2, respectively. The toughness of high-speed tool steel could be improved.

The transverse rupture strength test was conducted on a test piece with a diameter of 81 mm and a length of 80 mm with a span of 50 + sm, and the Charpy impact test was conducted with a radius of curvature at the center of one side of a 10 mm square and 55 mm long square piece. 10mm notch 211I11
The test was carried out using a test piece placed at a depth of .

<Example> Twelve types of high-speed steel samples \1 to 12 shown in Table 2 were manufactured by a combination of powder metallurgy and hot extrusion. Each steel is made of gas atomized powder of 35 mesh or less with a diameter of 16 hm.
The mixture was filled into a mild steel capsule, degassed and sealed, and then subjected to induction heating to produce a steel bar with a diameter of 50 a+m by hot extrusion, from which a sample was cut and heat treated under the following conditions.

Quenching 1190°C x 3 minutes → Oil cooling Tempering 570°C x 1 hour → Air cooling (3 times) Here, the sample number with a is attached to the example of this invention, and the above induction heating was performed at 1030°. This test was carried out under the same conditions as CXT. Moreover, the test number with b appended to it is a comparative example, in which the above-mentioned induction heating was carried out at 1100° C. for 14 minutes.

These samples were subjected to a transverse rupture strength test and a Charpy impact test to determine their toughness, and the conditions for these tests were the same as in the cases of FIGS. 1 and 2, respectively.

As is clear from Table 2, the grain sizes of the carbides are all 1 micron or less in the Examples of the present invention, whereas they are much larger in the Comparative Examples. FIGS. 3 and 4 show micrographs (1000 times magnification) of Example 10a and Comparative Example 10b, respectively. In each example, the Charpy impact value and transverse rupture strength were clearly improved compared to the corresponding comparative example.

<Effects of the Invention> As is clear from the above examples, according to the present invention, the toughness of high-speed steel produced by powder metallurgy can be further improved by controlling the grain size of precipitated carbides to be 1 micron or less. I've been able to improve it.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between carbide particle size and transverse rupture strength;
The figure is a diagram showing the relationship between carbide particle size and Charpy impact value, Figure 3 is an 11li microphotograph of an example of the present invention, and Figure 4 is a micrograph of a comparative example corresponding to the above example. . ' : f Oral letter (spontaneous) February 7, 1999 1 Display of 21G Patent Application No. 1983-313494 2 Name of the invention High toughness high speed steel made by powder metallurgy 3 Person making the amendment Postal code 651 Address Kobe City 7-1-1-5 Kumoidori, Chuo-ku "Detailed Description of the Invention" column of the specification to be amended. 6. Contents of the amendment (1) The following shall be inserted after the 6th line of the 3rd page of the specification. Note that in order to give these high-speed steel materials the necessary hardness and toughness, quenching at a high temperature close to 1200°C and tempering at a temperature close to 600°C are usually performed. (2) Insert the following after line 14 of the circular page of the same book. In addition, in view of the fact that conventional high-speed steel powder metallurgy materials require quenching from high temperatures, which increases the cost required for quenching, we have reduced the cost required for heat treatment by lowering the quenching and tempering temperatures. The aim is to reduce the (3) Insert the following after page 6, line 18 of the same book. As heat recording treatment conditions, quenching from around 1200°C and tempering from around 600°C, similar to those for conventional powder metallurgy materials of high-speed steel, can be carried out, or lower temperatures of 1000 to 1050°C can be carried out. Quenching from around ℃ and 500~
Even when tempering is performed from around 550℃, IIRc
It is possible to obtain a high degree of hardness of approximately 65 or higher. (4) Insert the following after page 8, line 1, O of the same book. Under the above heat treatment conditions, all samples showed hardness of HRC65 or higher, but the heat treatment conditions were quenched at the same level as die steel, 1050°C x 30 minutes → oil-cooled tempering 530
When CX was used for 1 hour → air cooling (3 times), the hardness of samples (c) and (d) was only at the HRC62-64 level. However, samples (a) and (b) were able to exhibit hardness of 11Rc65 or more even under these heat treatment conditions. This is because in the case of samples (a) and (b), the carbide is extremely fine and easily becomes a solid solution even at a relatively low quenching temperature. (5) Insert the following after line 8 on page 11 of the same book. In addition, the above-mentioned Examples 18 to 12a and Comparative Examples 1b to 12
Regarding b, the hardness after heat treatment under different conditions was as shown in Table 3. Table 3 (Comparison of heat treatment effects) I was able to make it manifest,” he corrected. that's all

Claims (2)

[Claims] (1) In weight%, C is 0.7 to 2.5, Si is 2.0 or less, Mn is 1.5 or less, Cr is 3.0 to 6.0, V is 0
．． Essential components of 8 to 25.0 and Mo of 3.0 to 10.0
, and W is 1.0 to 20.0, or both selected components, and the remaining Fe and unavoidable impurities, and the carbide grain size is 1.0 micron or less in equivalent circle diameter. High-toughness high-speed steel manufactured by powder metallurgy. (2) In weight%, C is 0.7 to 2.5, Si is 2.0 or less, Mn is 1.5 or less, Cr is 3.0 to 6.0, V is 0
．． Essential components of 8 to 25.0 and Mo of 3.0 to 10.0
, and one or both of the first selected components having W of 1.0 to 20.0, Co of 4.0 to 12.0, and Nb
0.1 to 5.0, and the remaining Fe and unavoidable impurities, and the carbide grain size is 1.0 micron or less in equivalent circle diameter. High-toughness high-speed steel made by powder metallurgy.