JPH07179908A - Sulfur-containing powder metallurgy tool steel object - Google Patents

Abstract

PURPOSE: To provide an advantageous effect of improved machinability and grindability by hot working the particles of a tool steel alloy of specific sulfide size and sulfur content and forming a fully dense and consolidated mass. CONSTITUTION: The nitrogen-gas-atomized and prealloyed particles of a tool steel alloy having <=15 μm maximum sulfide size and 0.10 to 0.30 wt.% sulfur content are hot worked into a fully dense and consolidated mass, by which a machinable powder-metallurgy produced sulfur-containing tool steel article is formed. The tool steel alloy has a composition consisting of, by weight, 0.80-3% C, 0.20-2% Mn, 0.10-0.30% S, <=0.04% P, 0.20-1.50% Si, 3-12% Cr, 0.25-10% V, <=11% Ho, <=18% W, <=10% Co, <=0.10% N, <=0.025% O, and the balance iron with incidental impurities. By this method, the serious adverse effect of sulfur and occurring sulfide on mechanical properties can be prevented.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a tool steel body made of hot-worked powder metallurgy tool steel having a sulfur content higher than the general sulfur content and a method for producing the same.

[0002]

Tool steels are commonly used in the manufacture of tooling objects used in both cut and uncut tooling applications. This includes making rolls, punches, and molding components as well as broaches and hobs. In these tooling uses, the tool steel must have sufficient strength, toughness and wear resistance to withstand the conditions encountered in these typical uses. In addition, they must have suitable machinability and milling capabilities to facilitate the manufacture of the desired tooling ingredients.

The presence of sulfur in tool steel improves machinability and millability by making sulfides, cutting tools used to use tool components, and chips removed from the steel during operation. It is known to act as a lubricant between and. Sulfide also promotes chip breakage during the cutting operation associated with tool manufacturing, making it easier to operate.

The use of about 0.10% or more of sulfur is known to reduce the hot workability of conventional ingot-cast iron tool steels and adversely affect the mechanical properties, especially toughness. In conventional high-sulfur content tool steels, sulfides are typically large,
Stretched in the direction of hot working. Similarly, in conventional machined tool steels, the main carbides present in the steel are aligned during hot working, which creates carbide stringers. Carbide stringers adversely affect the mechanical properties of these steels and cause their negative effects, so that any adverse effects of sulfides are generally masked.

On the other hand, during the production of high-sulfur content tool steels by powder metallurgy in which the pre-alloyed particles of steel are compacted to give a completely dense body, the carbides are relatively small, compared to common tool steels. Well distributed. Due to the preferred size and distribution of carbides obtained in these tool steels, the adverse effects of the carbide stringers encountered in conventional machined steels are avoided. The properties of powder metallurgy tool steels are therefore more sensitive to changes in the sulfur content and the size and distribution of the sulphides introduced for the purpose of improving machinability or millability.

For this reason, sulfur is generally not used in powder metallurgy tool steels in amounts above about 0.07%. For example, due to the adverse effect of sulfide on mechanical properties, as shown by the decrease in flexural strength of steel.
If the adverse effects of sulfur on mechanical properties can be avoided,
Powder metallurgy tool steels with high sulfur content will be more widely used.

[0007]

Therefore, the first aspect of the present invention
The purpose of is to provide a tool steel object made from hot work powder metallurgy high sulfur tool steel, in which the presence of sulfur and the resulting sulfides have a significant detrimental effect on mechanical properties. In the end, it has the beneficial effect of improved machinability and millability.

A more particular object of the present invention is the hot working high sulfur content powder metallurgy tool steel in which the presence of sulfur and the resulting sulfide does not significantly degrade toughness, as indicated by flexural fracture strength. Is to provide a tool steel object made from.

[0009]

According to the present invention, a nitrogen gas micronized and prealloyed tool steel alloy having a sulfide size of up to about 15 microns and a sulfur content of 0.10 to 0.30% by weight. A machineable powder metallurgical sulfur-containing tool steel body is provided which comprises a hot-worked, fully densely consolidated mass of crushed particles.

The tool steel alloy of the hot work article will have the composition of a worked high speed tool steel or a worked cold work tool steel. Therefore, sulfur is intentionally added in the range of 0.10 to 0.30% by weight. Broadly, the hot worked body tool steel is, by weight, 0.80 to 3.00% carbon, 0.20 to 2.00% manganese, 0.10 to 0.30% sulfur, 0.3%.
Phosphorus up to 04%, 0.20 to 1.50% silicon, 3.0
0 to 2.00% chromium, 0.25 to 10.00% vanadium, 11.00% molybdenum, 18.0% tungsten, 10.00% cobalt, 0.10
It will have up to% nitrogen, up to 0.025% oxygen and residual iron and incidental impurities. With a 2: 1 stoichiometry,
Tungsten will be replaced by molybdenum.

A machinable powder metallurgy sulfur-containing tool steel body will have a minimum transverse flexural fracture strength of 35,000 kg / cm ² (500 Ksi) when hot treated to a hardness of 64-66 HRC. The body consists of a hot-worked, fully compacted mass of nitrogen gas of a tool steel alloy, atomized and pre-alloyed particles, the tool steel alloy comprising:
% By weight, 1.25 to 1.50% carbon, 0.20 to 1.00%
Manganese, 0.10-0.26% Sulfur, 0.04% Phosphorus, 1.00% Silicon, 3.00-6.0% Chromium, 4.00-6.00% Molybdenum, 3.50-4.50%
Vanadium, 4.50-6.50% tungsten, 0.0
It consists of up to 25% oxygen, up to 0.10% nitrogen and residual iron and incidental impurities. The body has a maximum sulfide size of about 15 microns or less. Preferably, the sulfur content of the object according to the invention will be in the range 0.14 to 0.26%.

The invention relates to a hot-worked, complete, nitrogen-atomized, pre-alloyed particle of a tool steel alloy having a maximum sulfide size of about 15 microns and a sulfur content of 0.10 to 0.30% by weight. A method for making a closely compacted ingot powder metallurgy sulfur-containing tool steel object. By this method, prealloyed particles are produced by nitrogen gas atomization,
Temperature of 5 ° C (2165 ° F) and 1050 kg / cm ² (1
It is isostatically molded to full density at a pressure of 5 KSi. The obtained molded product has a temperature of 1121 ° C (2
Hot worked and annealed to the desired object mold at a temperature of 050 ° F.

The method of the invention is, by weight percent, 0.80 to 3.00.
% Carbon, 0.20-2.00% manganese, 0.10-0.3
0% Sulfur, 0.04% Phosphorus, 0.20-1.50% Silicon, 3.00-12.00% Chromium, 0.25-10.0
0% vanadium, up to 1.00% molybdenum, 18.
Pre-alloyed particles of tool steel alloy with a composition of up to 00% tungsten, up to 0.000 cobalt, up to 0.10% nitrogen, up to 0.025% oxygen, residual iron and incidental impurities. Will also be used.

Similarly, the method of the invention is 1.25% by weight.
~ 1.50% carbon, 0.20 ~ 1.00% manganese, 0.1
0-0.26% sulfur, 0.04% phosphorus, 1.00% silicon, 3.00-6.0% chromium, 4.00-6.0
0% molybdenum, 3.50-4.50% vanadium, 4.
Used in pre-alloyed particles of tool steel alloys with a composition of from 0 to 6.50% tungsten, up to 0.025% oxygen, up to 0.10% nitrogen, residual iron and incidental impurities. Ah Preferably, the sulfur content will be in the range 0.14 to 0.26% by weight.

According to the invention, the carbon present in the alloy combines with chromium, vanadium, molybdenum and tungsten, creating the desired dispersion of wear-resistant carbides and secondarily promoting hardness. Sufficient carbon is also present to provide strength to the steel matrix. The sulfur present in the steel first combines with manganese to form manganese sulphide or manganese-rich sulphides, which facilitates the machinability and crushability of the steel.

In order to obtain the properties required for the powder metallurgy tool steel object of the present invention, the high-sulfur powder metallurgy tool steel used for the structure has the high mechanical strength required for the tooling component. It is indispensable to perform hot working after consolidation. It is also possible that the manufacturing and processing conditions for the powder metallurgy tool steel used in the body of the invention are controlled, so that the sulphide size and distribution induced by sulfur addition does not significantly deteriorate the mechanical properties. Required. In the powder metallurgy tool steels used in the tool steel objects of this invention, this is achieved by retaining a maximum sulfide size of about 15 microns or less in the longest dimension.

[0017]

EXAMPLES To demonstrate the invention, a system of experimental tool steels was made with varying sulfur contents and subjected to various mechanical properties and machinability tests. Several commercial powder metallurgical high speed tool steel samples were also tested for comparison. Except for the sulfur content, commercial powder metallurgy tool steels generally have the same nominal composition as experimental tool steels. The actual chemical compositions of the experimental tool steels and commercial tool steels are shown in Tables 1 and 2.

[0018]

[Table 1]

[0019]

[Table 2]

The production of experimental tool steel was designed to minimize the size of sulfides in a microstructure. They are 136.
Made from a 2 kg / (300-pound) induction melt sample, made from nitrogen gas atomized, pre-alloyed powder.
Approximately 90.8 kg (200 lbs) from each sample was screened to -16 mesh (American Standard), 8-inch diameter, and hot degassed at 204 ° C (400 ° F) low. It was filled in a carbon steel container and sealed by welding. The container was then heated to 2165 ° F. (1185 ° C.), molded at this temperature at a pressure of 1050 kg / cm ² (15 KSi) for 4 hours, and allowed to cool slowly to ambient temperature. The resulting compact was heated to a temperature of 1121 ° C (2050 ° F) and hot worked into a 7.6 cm (3-inch) diameter bar,
Finally, it was annealed using a conventional high speed tool steel annealing cycle.

Commercial powder metallurgical tool steels represent materials made from -16 mesh nitrogen atomized powders that have undergone different amounts of hot reduction after consolidation by hot equilibrium pressing.
No particular scale was used in the manufacture of these steels to control sulfide size.

Several tests were carried out in order to compare the properties of the inventive tool steel objects to those of objects made from different production methods of high sulfur content powder metallurgy tool steels. Tests were conducted to demonstrate the effect of composition and manufacturing method on sulfide size, flexural strength, impact strength, and machinability. Machinability tests were performed on the specimens in fully annealed conditions, flexural fracture and impact tests were performed in hardened and tempered conditions. The heat treatment of the latter specimen is 120
Austenitize in molten salt for 4 minutes at 4 ° C (2200 ° F), oil cool to room temperature, and 552 ° C (10
Included was triple tempering in molten salt at 25 ° F for 2 hours plus 2 hours plus 2 hours. After this heat treatment,
The hardness of the specimen was between 64-66 Rockwell C.

Sulfide sizes and distributions in experimental and commercial tool steels are shown in FIGS. 1 and 2, respectively. As expected, the sulphide number in the experimental tool steel increased with sulfur content, which is that of steels 92-17, 92- in FIG.
It can be seen by comparing the microstructures of 18, 92-19 and 92-20. It is also clear that all the sulphides in the experimental tool steel according to the invention are less than about 15 microns in their longest dimension, regardless of the sulfur content. Furthermore, it is clear that the sulphide size in the experimental tool steel is considerably smaller in its longest dimension than the sulphide in commercial tool steels of similar composition. As shown in FIG. 2, the size of the sulfides in these latter steels range from about 20 to 30 μm in length, depending on the amount of hot reduction produced.

The Charpy C-notch impact property and flexural fracture strength of experimental and commercial tool steels are given in Tables 3 and 4, respectively. A comparison of the experimental tool steel results shows that keeping the maximum sulfide size below 15 μm can increase the sulfur content for the purpose of improving machinability without compromising toughness. This is demonstrated by the fact that the impact and flexural fracture strengths of the experimental steels, both in the machine and transverse directions, are essentially equivalent to the sulfur content in the range between 0.005 and 0.26%.

[0025]

[Table 3]

[0026]

[Table 4]

A comparison of the mechanical properties of the commercial tool steels given in Table 4 shows that their impact and flexural fracture strengths are general by increasing the amount of hot shrinkage, even if it causes some elongation of the sulfide. It is shown to be improved. However, due to the large size of the sulfides in these steels, their mechanical properties are significantly lower than those of experimental tool steels with essentially the same composition and amount of hot reduction. For example, maximum sulfide size of about 15 μm and 53970 kg / cm ² (771 KSi)
The mechanical properties of steel 92-20 (0.26% S), which has a vertical bending fracture strength of 39270 kg / cm ² (561 KSi) and a maximum sulfide size of about 30 μm. Steel 92-7 having a breaking strength of 45570 kg / cm ² (651 KSi) and a lateral bending breaking strength of 26810 kg / cm ² (383 KSi).
It is clear when compared with that of 8 (0.24% S).

The results of the drill machinability tests conducted on experimental tool steels with annealing conditions are given in Table 5. The drill machinability index in this table compares the time taken to drill holes of the same size and depth in these steels to give a ratio of the time for each steel of 0.005% sulfur to the experimental steel of 100. It is obtained by doubling. An index of greater than 100 indicates that the drill machinability of the steel being tested is greater than that of the experimental tool steel body containing 0.005% sulfur (Steel 91-60). The results show that increasing the sulfur from 0.005 to 0.26% improves the machinability of the experimental tool steel and a greater improvement can be achieved with a sulfur content of about 0.14% or higher. ing.

[0029]

[Table 5]

From the above, it can be seen that by reducing the size of the sulphide in an object made of hot-worked powder metallurgy tool steel, the negative effect of high sulfur content can be substantially canceled in its properties. You will understand. Therefore, in particular,
In order to obtain improved machinability without significant degradation of mechanical properties, as indicated by the bending fracture strength of steel,
It is possible with the present invention to obtain powder metallurgy tool steel objects with higher sulfur contents that are generally accepted. The term "sulfur-containing tool steel object" is limited to cold work tool steels and high speed tool steels.

[0031]

According to the present invention, which is made from hot work powder metallurgical high sulfur tool steel, sulfur and the resulting sulfides do not have a significant detrimental effect on mechanical properties, and improved machinability and A tool steel object having a grinding ability is obtained.

[Brief description of drawings]

FIG. 1 is a micrograph showing the crystal structure of sulfide size and distribution in a powder metallurgy tool steel used in an experiment in the present invention.

FIG. 2 is a micrograph showing the crystal structure of sulfide size and distribution in a commercial high sulfur powder metallurgy tool steel.

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[Procedure amendment]

[Submission date] October 20, 1994

[Procedure 3]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Figure 1]

[Fig. 2]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenneth E. Pinnau United States Pennsylvania 15237 Pittsburgh Draud Lane 131

Claims (8)

[Claims] 1. A maximum sulfide size of 15 μm or less, and
A machinable powder metallurgy consisting of a hot-worked, fully compacted mass of nitrogen gas atomized and pre-alloyed particles of a tool steel alloy with a sulfur content of between 10 and 0.30% by weight. Sulfur-containing tool steel object. 2. The tool steel alloy, in% by weight, is 0.80-3.
00% carbon, 0.20-2.00% manganese, 0.10
0.30% sulfur, up to 0.04% phosphorus, 0.20 to 1.50
% Silicon, 3.00-12.00% Chromium, 0.25-1
0.00% vanadium, up to 1.00% molybdenum,
The machinable powder metallurgy of claim 1 comprising up to 18.0% tungsten, up to 0.000 cobalt, up to 0.10 nitrogen, up to 0.025% oxygen, residual iron and incidental impurities. Sulfur-containing tool steel objects. 3. A machinable powder metallurgical sulfur-containing tool steel body having a minimum transverse bending fracture strength of 35,000 kg / cm ² (500 KSi) when heat treated to a hardness of 64-66 RHC, said body comprising: , Essentially 1.25% by weight,
1.50% carbon, 0.20-1.00% manganese, 0.10
~ 0.26% Sulfur, 0.04% Phosphorus, 1.00% Silicon, 3.00-6.0% Chromium, 4.00-6.00
% Molybdenum, 3.50 to 4.50% vanadium, 4.0
0 to 6.50% tungsten, up to 0.025% oxygen,
Nitrogen gas of a tool steel alloy consisting of up to 0.10% nitrogen, residual iron and incidental impurities, consisting of hot-worked, fully-consolidated agglomerates of atomized and pre-alloyed particles and not more than 15 μm Tool steel object characterized by having a maximum sulfide size of 4. The sulfur content, by weight, is 0.14 to 0.26%.
4. A powder metallurgical sulfur-containing bearing tool steel object according to any one of claims 1 to 3 inclusive. 5. With a maximum sulfide size of 15 μm, 0.10
Manufacture of powder metallurgical sulfur-containing tool steel bodies consisting of hot-worked, fully compacted agglomerates of nitrogen atomized and pre-alloyed particles of tool steel alloys with a sulfur content of ~ 0.30% by weight A method for producing pre-alloyed particles by nitrogen gas atomization, 1185 ° C (2165).
Hot forming an equilibrium of prealloyed particles to a perfect density at a temperature of ° F) and a pressure of 1050 kg / cm ² (15 KSi) at a temperature of 1201 ° C (1201 ° C).
A method of manufacturing, comprising hot working the obtained molded body into a desired shape of an object and baking the object. 6. Wt%, 0.80 to 3.00% carbon, 0.0.
20-2.00% manganese, 0.10-0.30% sulfur,
Phosphorus up to 0.04%, 0.20 to 1.50% silicon, 3.0
0-12.00% chromium, 0.25-10.00% vanadium, 11.00% molybdenum, 18.0% tungsten, 10.00% cobalt, 0.10% Nitrogen gas of a tool steel alloy with a maximum sulphide size of 15 μm, consisting of nitrogen, up to 0.025% oxygen, residual iron and incidental impurities, of nitrogen gas atomized and prealloyed particles, hot worked and completely dense. A method for producing a powder metallurgical sulfur-containing tool steel object comprising a compacted mass, the method comprising producing the pre-alloyed particles by nitrogen gas atomization, the pre-alloyed particles being 1185 ° C. Hot equilibrium molding to a perfect density at a temperature of (2165 ° F) and a pressure of 1050 kg / cm ² (15 KSi).
A method of manufacturing comprising hot working an object of the desired shape at a temperature of (2050 ° F.) and annealing the object. 7. A method of making a powder metallurgy sulfur-containing tool steel object having a minimum lateral bending fracture strength of 35,000 kg / cm ² (500 KSi) when heat treated to a hardness of 64-66 RHC, said object comprising: In essence, 1.25 to 1.50% by weight.
% Carbon, 0.20 to 1.00% manganese, 0.10 to 0.2
6% sulfur, up to 0.04% phosphorus, up to 1.00% silicon, 3.00 to 6.00% chromium, 4.00 to 6.00% molybdenum, 3.50 to 4.50. % Vanadium, 4.0-6.
50% tungsten, 0.025% oxygen, 0.10
% Nitrogen, balance iron and incidental impurities, 15
a hot worked and fully compacted mass of nitrogen atomized and pre-alloyed particles of a tool steel alloy having a maximum sulfide size of μm, the method comprising pre-alloying by nitrogen gas atomization To produce crushed particles, 1185 ° C (216
Compacting the pre-alloyed particles to full density at a temperature of 5 ° F. and a pressure of 1050 kg / cm ² (15 KSi),
A method of manufacturing comprising hot working a compact at 11250C (2050F) to the desired shape of the article and annealing the article. 8. A process according to claim 5, 6 or 7 wherein the sulfur content is in the range 0.14 to 0.26% by weight.