JPS582585B2 - Cold work tool steel and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cold work tool steel with improved mechanical anisotropy and excellent machinability.

More specifically, in steels that use S as an element that imparts free machinability, an appropriate amount of Te is also included in proportion to the amount of S to improve the shape of sulfide inclusions in the steel, thereby improving mechanical properties. The objective is to provide a cold work tool steel with improved anisotropy and excellent machinability.

The present invention also includes a method for producing cold work tool steel that improves the anisotropy of mechanical properties and has excellent machinability.

Cold work tool steel contains large amounts of alloying elements such as Cr, Mo, and V in order to ensure strength and toughness that can withstand severe usage conditions.

However, although strength and toughness are improved, if a large amount is contained, machinability inevitably deteriorates.

In recent years, there has been a strong demand for lower total costs, including reductions in mold processing costs, for cold work tool steels, and this trend is particularly strong for large cold work tools.

Conventionally, the most common method known to improve machinability is to include S and leave sulfide-based inclusions in the steel. Since sulfide-based inclusions extend in the forging direction, anisotropy occurs in mechanical properties, which causes deterioration of toughness, particularly in the direction perpendicular to the forging direction.

For this reason, it has been difficult to improve the machinability of cold work tool steel without degrading its original performance.

In view of the above circumstances, the inventors of the present application have determined what conditions need to be met in order to improve machinability without deteriorating the original characteristics of a cold work tool, and how to improve the cold work tool. As a result of various studies on what is a suitable method for producing steel, the following knowledge was obtained.

In other words, in order to provide free machinability without deteriorating the original properties of cold work tool steel, at least 80% of the contained sulfides should be relatively large with a major axis of 2μ or more.
However, such sulfide inclusions must have a Te/S weight ratio of 0.
This can be achieved by setting the value to 04 or higher.

Furthermore, this steel has T
It can be manufactured by adding and uniformly dispersing Te, and by introducing a non-oxidizing gas into the molten steel and forcibly stirring it before adding Te, the characteristics as a cold work tool steel and free machining can be improved. It has also been found that it is preferable to remove by flotation separation large-sized inclusions mainly consisting of oxide-based inclusions that are harmful to the properties of the steel.

The cold work tool steel of the present invention based on the above novel findings,
C: 0.40 to 2.60, Si: 2.0% or less, Mn:
3.0% or less, Cr: 0.1-20.0%, Mo: 0.
03 to 10.0%, S: 0.005 to 0.40%, and Te: 0.10% or less (however, the weight ratio of Te/S is 0.04 or more), and the remainder is substantially A relatively large sulfide inclusion having a composition consisting of Fe and having a major axis of 2 μ or more is characterized in that at least 80% of the inclusions have a major axis ratio of 10 or less. Furthermore, the above steel is optionally provided with improvements in hardenability, improvement in wear resistance by forming carbides, improvement in heat resistance, refinement of crystal grains, etc. depending on the use of the steel. If so, it contains at least one of the following groups of additive elements:

(i) Ni: 4.0% or less (ii) Co: 13.0% or less (iii) W: 2.0% or less, V: 5.0% or less, Nb
: 3.0% or less, Ti: 0.5% or less.

In addition, in order to further improve the free machinability of the above steel, Pb
: 0.20% or less, Se: 0.30% or less, Bi: 0.
Ca: 15% or less, Ca: 0.01% or less.

Next, the reasons for limiting the composition of the steel of the present invention will be described.

C: 0.40-2.60% If it is contained at 0.40% or more, the strength and hardenability will increase, and Cr,
Forms carbides with Mo, W, V, etc., increasing wear resistance.

However, if it is contained in a large amount, the toughness will deteriorate and the tool life will be shortened, so the upper limit was set at 2.60%.

Si: 2.0% or less It is an effective element as a deoxidizing agent during melting and refining, but if it is contained in a large amount, it deteriorates forgeability and toughness, so the upper limit is set at 2.0% or less.
It was set to 0%.

Mn: 3.0% or less It is an element necessary to improve hardenability, but if it is contained in a large amount, machinability deteriorates, the amount of retained austenite increases, and the hardening hardness decreases, so the upper limit is 3.
It was set to 0%.

Cr: 0.1-20.0% At least 0.03% as it is an effective element for improving hardenability and forming carbides to strengthen the matrix.
Although it is necessary to contain it, even if it is contained in a large amount, the above effects cannot be expected to improve much, so the upper limit was set at 20.0%.

Mo: 0.03-10.0% Like Cr, it improves hardenability, forms carbides, improves wear resistance, and further improves 2 during tempering.
Although it is an extremely effective element for subsequent hardening, even if it is contained in a large amount, the above effects cannot be improved much, so the upper limit has been set to 10
．． It was set to 0%.

S: 0.05-0.40% An essential element for the formation of MnS-based inclusions, which are the main inclusions that provide free machinability. S: 0.05% or more increases free machinability, but a large amount Since hot workability deteriorates if the content is made to be 0.40%, the upper limit was set at 0.40%.

Te: 0.10% or less Te is an important element in terms of adjusting the morphology of MnS-based inclusions that have a large effect on mechanical anisotropy and providing free machinability by itself.

If the content is too large, hot workability deteriorates, so the upper limit was set at 0.10%.

In addition, in order to improve the morphology of sulfide inclusions, Te/
It is necessary that the weight ratio of S is 0.04 or more.

Morphology and distribution of sulfide inclusions: The inventors have confirmed that free machinability and anisotropy of mechanical properties greatly depend on the morphology and distribution of sulfide inclusions in steel. The properties of steel with various shapes were investigated.

As a result, it was found that relatively large sulfide inclusions with a major axis of 2μ or more influence the anisotropy of mechanical properties, and that these inclusions have a ratio of major axis to minor axis of 10 or less and are extremely linearly elongated. based on the number of such inclusions in the total sulfide inclusions.
I learned that it is sufficient as long as the condition of accounting for a majority of 0% or more is satisfied.

This fact will be discussed later in Examples.

It has the above component composition and the form and distribution of sulfide inclusions.

Steel has excellent machinability and has sufficient performance as a cold tool with improved anisotropy of mechanical properties, but depending on the application, it is desirable to further include the following elements in the basic steel.

Ni: 4.0% or less Although it is an effective element for improving hardenability, the effect is not much different even if it is contained in a large amount, and the upper limit was set at 4.0% from the economic point of view.

Co: 13.0% or less Co has a remarkable effect in increasing high-temperature strength, but if contained in a large amount, free machinability deteriorates, so the upper limit was set at 13.0%.

W: 20.0% or less, V: 5. 0% or less, Nb: 3.0
% or less, Ti: 0.5% or less. Any element is effective for forming carbides, precipitation hardening, and improving strength.

However, when the above limits are exceeded, free machinability, hot workability, and toughness are reduced.

In addition, when it is desired to further improve the free machinability of the steel of the present invention, Pb: 0.20% or less, Se: 0.20% or less, Bi: 0.15% or less, Ca: 0.01%. 1 below
Containing one species or two or more species is effective.

The content limit was determined in consideration of the effect on the inherent properties of cold work tool steel.

Of course, these can also be used in combination with each of the above-mentioned contained elements.

The key to producing the cold work tool steel of the present invention described above, which has excellent free machinability and improved anisotropy of mechanical properties, is to properly adjust the components.

First, molten steel is prepared in which the content of alloy components other than free-cutting elements other than S is adjusted to a predetermined value in a furnace.

Next, Te may be added to this molten steel in a furnace, ladle or tundish so as to satisfy the condition of Te/S≧0.04 and uniformly dispersed.

Addition of Te can also be carried out in an injection tube.

When Pb, Se, Bi, or Ca is added, it may be added together with the addition of Te, or before or after the addition of Te.

When adding Te (and in some cases, other free-machinability imparting elements), it is desirable to remove as much as possible large non-metallic inclusions, which are mainly oxide-based inclusions.
For this purpose, it is effective to forcefully stir the molten steel by introducing a non-oxidizing gas such as argon into the molten steel in a furnace, ladle or tundish.

This operation can be performed before adding Te, or can be performed while adding Te.

According to the present invention, a cold work tool steel that is required to have good mechanical properties can be provided that has excellent free machinability without impairing these properties in any way.

In other words, in cold work tool steel, it has been possible to achieve both free machinability and anisotropy in mechanical properties, which was previously considered difficult.

Therefore, not only will it be significantly easier to use this cold work tool steel in various conventional applications, but it will also be possible to use this cold work tool steel in applications that have not yet been attempted due to limitations in cutting technology. It becomes possible.

Next, the present invention will be explained in detail with reference to examples.

Examples Cold work tool steels having various compositions were melted using an electric arc furnace lined with basic refractories.

Adjustment of various components is carried out by adjusting the alloying elements other than elements that impart free machinability, including Te, to a predetermined amount in the above-mentioned furnace, and then adding Te to the ladle depending on the amount of S in the molten steel. In some cases, Pb, Se, Bi and/or Ca were also added and uniformly dispersed in the molten steel.

The molten steel whose composition had been adjusted was ingotted into a 1.3 t steel ingot by the bottom pouring ingot method, and then forged at a forging ratio of 10 or more.

The composition of each sample material is shown in Table 1.

In the same table, sample material numbers 1 to 4, 6, 7, 9, 10, 12 to
15, 17-19, 21-24, 27-30, 32-3
5, 37-39, 41-44, 46-48, 50-52
are examples according to the present invention, and 5, 8, 11, 16, 2
0, 25, 26, 31, 36, 40, 45, 49, 53
This is a comparative example.

A test piece was taken from the above sample material and tested as follows.

(1) Morphology and distribution of sulfide inclusions A microscope specimen was cut out from the specimen material in parallel to the forging direction.
It was polished and examined.

Measure the major axis (1) and minor axis (W) of sulfide inclusions that are visible within a certain field of view and have a major axis of 2 μ or more,
The number-based ratio R (%) occupied by those having a length ratio (1/W) of 10 or less was calculated.

The results are shown in Table 1.

(2) Anisotropy of toughness A test piece was cut from the test material in the forging direction (L) and a direction perpendicular to the forging direction (T), and after heat treatment, a 10R, C notch test piece was cut out. The impact value was determined by

The values are shown in Table 2 together with the heat treatment conditions.

When the anisotropy of toughness is evaluated by the ratio of the perpendicular direction (T)/forging direction (L), as is clear from the table, the comparative steel has a toughness of 0.3.
In contrast, the steel of the present invention is 0.33 to 0.69.
It can be seen that the anisotropy of the toughness has improved.

(3) Machinability In order to confirm machinability, the test materials were heat treated and a super tool turning life test was conducted under the turning conditions shown in Table 3.

In the same table, A for the depth of cut and cutting speed is for specimens ■1 to 31, and B is for specimens ■32 to 53.

The results are shown in Table 4 along with the heat treatment conditions.

As is clear from the same table, it can be seen that the steel of the present invention has superior rigidity compared to the comparative steel.

Claims (1)

[Claims] 1 C: 0.40 to 2.60%, Si: 2.0% or less,
Mn: 3.0% or less, Cr: 0.1 to 2.0%, Mo:
0.03 to 10.0%, S: 0.005 to 0.40%, and Te: 0.1% or less (however, the weight ratio of Te/S is 0.04 or more), and the remainder is substantially A sulfide inclusion having a composition consisting of Fe and existing therein,
For relatively large ones with a major axis of 2 μ or more, at least 8
A cold work tool steel characterized in that 0% has a long/short axis ratio of 10 or less. 2 C: 0.40 to 2.60%, Si: 2.0% or less,
Mn: 3.0% or less, Cr: 0.1 to 2
0%, Mo: 0.03-10.0%, S: 0.005-
0.40% and Te: 0.10% or less (however, the weight ratio of Te/S is 0.04 or more), and Ni: 4.0%.
% or less, Co: 13.0% or less, W: 20.0% or less,
V: 5.0% or less, Nb: 3.0% or less, Ti: 0.5
Relatively large sulfide inclusions with a major axis of 2 μ or more that have a composition of 0% or less of one or more types, the remainder being substantially Fe, are classified as A cold work tool steel characterized in that at least 80% of the steel has a length-to-width ratio of 10 or less. 3C: 0.40-2.60%, Si: 2. 0% or less,
Mn: 3.0% or less, Cr: 0.1 to 20%, Mo: 0
．． 03 to 10.0%, S: 0.005 to 0.40%, and Te: 0.10% or less (however, the weight ratio of Te/S is 0.04 or more), and Pb: 0.20%. Below, Se
: 0.20% or less, Bi: 0.15% or less, Ca: 0.
01% or less of one or more types, the remainder being substantially Fe
Among the relatively large sulfide inclusions with a major axis of 2μ or more, at least 80% of them have a major axis ratio of 10 or less. Cold work tool steel. 4 C: 0.40 to 2.60%, Si: 2.0% or less,
Mn: 3.0% or less, Cr: 0.1 to 20%, Mo: 0
, 03 to 10.0%, S: 0.005 to 0.40%, and Te: 0.10% or less (however, the weight ratio of Te/S is 0.04 or more), and Ni: 4.0%. % or less, Co:
13.0% or less, W: 20.0% or less, ■: 5.0% or less, Nb: 3.0% or less, Ti: 0.50% or less, and further Pb: 0.20% or less, S
e: 0.2% or less, Bi: 0.15% or less, Ca: 0.
01% or less of one or more types, the remainder being substantially Fe
Among the relatively large sulfide inclusions with a major axis of 2μ or more, at least 80% of them have a major axis ratio of 10 or less. Cold work tool steel. 5 C: 0.40 to 2.60%, Si: 2.0% or less,
Mn: 3.0% or less, Cr: 0.1 to 20%, Mo: 0
．． 03 to 10.0%, S: 0.005 to 0.40%, and the remainder is prepared in a furnace and added to the molten steel in the furnace, ladle or tundish. , Te: such that the weight ratio of Te/S is 0.04 or more.
When adding 0.10% or less, non-oxidizing gas is introduced and forced stirring is carried out to float and separate large non-metallic inclusions while uniformly dispersing sulfide-based inclusions before casting. Method of manufacturing cold work tool steel. 6 C: 0.40 to 2.60%, Si: 2.0% or less,
Mn: 3.0% or less, Cr: 0.1 to 20%, Mo: 0
．． 03 to 10.0%, S: 0.005 to 0.40%, and Te: 0.10% or less (however, the weight ratio of Te/S is 0.04 or more), and Ni: 4. 0% or less, Co: 13.0% or less, W: 20.0% or less, V: 5.0% or less, Nb: 3.0% or less, Ti: 0.
A molten steel having a composition containing 50% or less of one kind or two or more kinds with the remainder substantially consisting of Fe is prepared in a furnace, and a weight ratio of Te/S is added to the molten steel in the furnace, ladle or tundish. When adding Te: 0.10% or less so that A method for producing cold work tool steel, which consists of uniformly dispersing and casting. 7 C: 0.40 to 2.60%, Si: 2.0% or less,
Mn: 3.0% or less, Cr: 0.1-20.0%, M
o: 0.03-10.0%, S: 0.005-0.40
% and Te: 0.10% or less (however, Te/
The weight ratio of S is 0.04 or more), Pb: 0.20% or less, Se: 0.2% or less, Bi: 0.15% or less, Ca:
A molten steel having a composition containing 0.01% or less of one kind or two or more kinds with the remainder substantially consisting of Fe is prepared in a furnace, and the molten steel in the furnace, ladle or tundish is added with Te/S. When adding Te: 0.10% or less so that the maximum gravity ratio is 0.04 or more, by introducing a non-oxidizing gas and forcibly stirring, large non-metallic inclusions are floated and separated while sulfide-based A method for producing cold work tool steel, which consists of casting with uniformly dispersed inclusions. 8 C: 0.40 to 2,60%, Si: 2.0% or less,
Mn: 3.0% or less, Cr: 0.1 to 20%, Mo: 0
．． 03 to 10.0%, S: 0.05 to 0.40%, and Te: 0.10% or less (however, the weight ratio of Te/S is 0.04 or more), and Ni: 4.0%. Below, Co:1
3.0% or less, W: 20.0% or less, V: 5.0% or less, Nb: 3.0% or less, Ti: 0.50% or less, and further Pb: 0.20% or less, Se
: 0.2% or less, Bi: 0.15% or less, Ca: 0.0
Prepare molten steel in a furnace and have a composition containing 1% or less of one or more of Fe with the remainder substantially consisting of Fe,
When adding Te: 0.10% or less to the molten steel in a ladle or tundish so that the Te/S weight ratio becomes 0.04 or more, a non-oxidizing gas is introduced and forced stirring is performed. A method for producing cold work tool steel, which consists of casting with sulfide inclusions uniformly dispersed while nonmetallic inclusions are floated and separated.