JPS5853710B2 - Steel for warm forging molds - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a steel for warm forging dies that has both wear resistance and toughness.

Warm forging involves heating the metal to a temperature of approximately 800 to 900 degrees Celsius, lower than that of hot forging, and applying pressure to shape it, but since the temperature is lower than that of hot forging, the forging dies used are harder. Because of this, forging dies are subjected to harsher conditions compared to hot forging.

Conventionally, high-speed steel has been used as a material for warm forging dies, but this material has high wear resistance but lacks toughness, so it is difficult to use it for warm forging dies. The drawback was that cracks and chips occurred in the mold, shortening its useful life.

The present invention has sufficient toughness to eliminate earthwork defects and prevent the occurrence of cracks and chips in warm forging molds, as well as wear resistance, impact resistance, low tempering softening properties, heat check resistance,
The object of the present invention is to provide a mold steel that also has various properties required as a warm forging mold steel, such as high-temperature strength and machinability.

The steel for warm forging molds of the present invention includes 0.3 to 0.6% by weight of carbon, 0.2 to 0.6% by weight of silicon, and 0.2 to 0% of manganese.
．． 6% by weight, 1.0 to 3.0% by weight of chromium, 1.0 to 3.5% by weight of serif def, 2.0 to 4.0% by weight of tungsten, preferably 2% or more, especially 2.1 to 4% by weight. 0.0% by weight Vanadium 0.5-1.0% by weight and the balance iron, the total of molybdenum and tungsten being 4-6% by weight
It is characterized by

The reason for limiting each additive element in the warm forging die steel of the present invention will be explained.

Carbon plays a major role in the properties of steel, and as the amount of carbon increases, hardness and wear resistance increase, but toughness also decreases.

In the present invention, carbon needs to be 0.3 to 0.6% by weight, and if it is less than 0.3% by weight, it will not be possible to obtain a hardness of HRC50 or higher required for warm forging molds, and 0.6% by weight. %, the formation of carbides increases, resulting in insufficient toughness and the occurrence of cracks, chips, etc. in the mold.

Silicon is mixed when deoxidizing steel, but in the present invention it needs to be 0.2 to 0.6% by weight, and 0.
．． If it is less than 2% by weight, castability will deteriorate, and if it exceeds 0.6% by weight, toughness and machinability will deteriorate.

Like silicon, manganese is an element that is mixed in when steel is deoxidized and affects hardenability, but in the present invention 0.2
It needs to be between 0.6% by weight and less than 0.2% by weight, which reduces hardenability, and more than 0.6% by weight, which deteriorates machinability.

Chromium is an element that increases hardenability and hardness, but in the present invention it needs to be 1.0 to 3.0% by weight, and if it is less than 1.0% by weight, the warm forging mold The hardness required for industrial steel cannot be obtained, causing sagging, and 3.0
If the weight percentage is exceeded, the toughness will decrease.

Molybdenum and tungsten form carbides and are secondary hardened by tempering, increasing wear resistance and also imparting high temperature strength.

In the present invention, the amount of molybdenum must be 1.0 to 3.5% by weight; even if it exceeds 3.5% by weight, no further effect can be expected and the toughness will decrease, and if it is less than 1.0% by weight, it will not be sufficient. Tempering hardness cannot be obtained and wear resistance is also insufficient.

Tungsten is 2.0-4.0% by weight, especially 2,1-4
．． It needs to be 0% by weight, and as in the case of molybdenum, even if it exceeds 4.0% by weight, no further effect can be expected and the toughness will decrease, and if it is less than 2.1% by weight, sufficient tempering hardness cannot be obtained and wear resistance is also insufficient.

Molybdenum and tungsten are elements that impart similar properties, and it is necessary for a warm forging mold to have a total amount of molybdenum and tungsten in the range of 4 to 6% by weight** with the amount of carbon within the above-mentioned allowable range. This is necessary to obtain steel with good properties.

Vanadium is also an element that easily forms carbides with carbon, making crystal grains finer and increasing high-temperature strength and wear resistance.
In the present invention, it needs to be 0.5 to 1.0% by weight, and 0.
．． If it is less than 5% by weight, no effect can be expected from adding vanadium, and if it is more than 1.0% by weight, machinability and impact resistance will decrease. It may contain trace amounts of impurities.

A special method is required to manufacture the steel of the present invention.
It can be carried out in a conventional arc-type electric furnace, a high-frequency electric furnace, or other methods.

Next, the present invention will be further explained with reference to Examples, but the present invention should not be limited to these Examples.

Examples Steels of the present invention 1 to 5 having the components shown in the table below, conventional high-speed steel (JIS 5KH-9), and samples A and B were tested for properties required as steels for warm forging dies.

The mechanical properties of the steels shown in Table 1 are shown in Table 2 below.

Conventional high-speed steels (JIS 5KH-9) 1 and 2 have high hardness and therefore have excellent wear resistance, but their impact values are small and their toughness is insufficient, so they cannot be used for molds with complex special shapes. Cracks and chips occurred in the mold after ~6 warm forging cycles.

Also, the service life of common shapes is 3,000 years.
~5,000 times, and the maximum was about 6,000 times.

Sample A was intended to lower the carbon content of the high-speed steel to suppress the formation of carbides and provide toughness, but the heat check was too thick (cracking occurred after 5 to 6 warm forgings).

Sample B further lowered the carbon content and significantly reduced the amounts of molybdenum, tungsten, and vanadium, which are carbide-forming elements, to have a composition close to 5KD-62, but this had a large sag in the mold corner and was tough. However, it lacked wear resistance.

Inventive steels 1, 2, 3, 4 and 5 all have little heat check even after being struck 10,000 times, no cracking or chipping due to insufficient toughness, and no wear due to insufficient wear resistance. There wasn't.

As is clear from Table 2, this result shows that the invention steel L2,
Steels 3, 4, and 5 have significantly improved impact resistance compared to conventional steels, so they have excellent toughness, and they also have enough wear resistance to meet the requirements for warm forging dies. Depends on being there.

In addition, when the present invention steels 1 to 5 are made into a mold with a complicated special shape, the number of times is 4,000 to 6,000 times, and when it is made into a mold with a general shape, the number of times is 8,000 to 10,000 times, and the maximum number of times is 1,500 times.
Withstood 0 warm forgings.

The steel of the present invention has excellent properties such as wear resistance, impact resistance, heat checkability, and toughness, and also has good castability and machinability, so it can only be used with warm forging dies. It can also be used for hot forging molds using precision casting.

Fig. 1 shows the microscopic structure of the conventional steel with the composition shown in the above table, and Fig. 2 shows the microscopic structure of the inventive steel 1. Compared to the conventional steel, the inventive steel has the above-mentioned superior properties. This fact has not been sufficiently elucidated both academically and from this organizational chart.

As mentioned above, when the steel of the present invention is used as a warm forging die, it is extremely unlikely to suffer from warping or chipping of the die due to lack of toughness, unlike conventional high-speed steel, so the service life of the forging die will be limited. This is an excellent steel for warm forging dies that can significantly improve the properties of steel for warm forging dies and also satisfy other properties required for warm forging dies.

[Brief explanation of drawings]

Figure 1 is a photograph showing the microscopic structure of conventional high-speed steel;
The figure is a photograph showing the microscopic structure of the steel of the present invention.

Claims (1)

[Claims] 1 Carbon 0.3-0.6% by weight, silicon 0.2-0.6
Weight%, manganese 0.2-0.6 weight i%, chromium 1.
0 to 3.0% by weight, molybdenum 1.0 to 3.5% by weight,
Tungsten 2.1-4.0% by weight, vanadium 0.5
1.0% by weight, the balance being iron, and the total amount of molybdenum and tungsten is 4 to 6% by weight.