JPH0225543A - High strength hot working tool steel - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Industrial application field] In the present invention, very severe stress is applied during processing.

In particular, the present invention relates to a new material suitable for use in hot extrusion tools and the like.

[Prior art] Among hot extrusion tools such as bearing steel, alloy steel, stainless steel, and high alloy steel, dies and mandrels are particularly required to have high hot strength (hardness) and toughness. Examples include excellent hardness, wear resistance, heat check resistance, and hardenability. .

Various materials have been studied for use in these extrusion materials, but at present, 5KD6], 62 class, which has a good balance between lifespan and economic efficiency, is mainly used.

Also, JP-A-55-24931 and JP-A-61-13
0260, an SKD-based improved invention steel has been proposed for almost the same purpose as the present invention. However, the steel of the present invention has been completed by further studying these known steels and taking into consideration characteristics such as toughness and heat check resistance, as well as economic efficiency.

[Problems to be Solved by the Invention] In hot extrusion processing of steel, the life form of the mandrel is roughly classified by the size of the mandrel diameter.

If the diameter is relatively small, tearing of the mandrel core7) Overall deformation due to softening, especially local constriction at the tip, often determines the service life, and as the diameter becomes larger, plastic deformation due to softening of the surface layer will occur. The resulting pockmark is often the cause.

In particular, in the case of small-diameter mandrels for stainless steel/high-alloy steel pipes with high extrusion ratios, 5KD81 has significant elongation and constriction at the tip, so a 3Cr-3Mo material with higher softening resistance is used for the mandrel material. has been done.

However, when this 3Cr-3Mo steel is used for large-diameter mandrels for the purpose of improving lifespan, it has poor hardenability and causes vertical cracking due to lack of toughness, so currently the mandrel material is used differently depending on the diameter. .

On the other hand, the lifespan of dies is mostly due to changes in the size of the die hole due to scratches or wear (flow). If 3Cr-3Mall is used for the die, most of the dies will break and the life will end, so 5KD61 class is used for all dies.

As described above, the lifespan of steel hot extrusion dies and mandrels is largely due to dimensional changes resulting from plastic deformation such as wear, flaws, and set-off due to softening of the material during machining. It has been confirmed that this softening has already occurred in just a few bushes, and it is desired that the material has high softening resistance, little strength deterioration during use, and excellent wear resistance.

[Means for Solving the Problems] In order to solve these problems, the present inventor has proposed the conventional method (7).
) As a result of many improvement studies on the components of SKD61 class and 3Cr-3Mo class, we have improved the C content of 5KD81 (JIS standard: 0.32 to 0.4) for the purpose of improving strength.
2X) in a component system with a slightly increased value.

By appropriately controlling Cr and Mo, which affect hardenability and softening resistance, which affect toughness, and adding small amounts of V and Nb, high toughness and excellent softening resistance can be achieved in high-strength steel. I found out what I can get.

In addition, W is generally M for wear resistance, softening resistance, etc.
It has the same effect as o and is often added to Koshinko. but,
W, like Mo, is an expensive element, and its effect is half that of MO, so in order to obtain the same effect, it is necessary to
It is not economical because it needs to be added twice as much as Mo, and in terms of properties, it is an element that actually has a negative effect on toughness.
As described in No. 550, W is an element unfavorable for heat check resistance, so it was decided not to add it to the steel of the present invention.

That is, in the present invention, C: 0.4-0.5% Si: 0.1-1.0% Mn: 0.1-L, 0% Cr: 3.5-4. Contains 5% Mo: 2.0-4.0% V: 0.2-0.6% Nb: 0.01-0.20%, and the balance is free from Fe and inevitable impurities [rP
] First, the experimental results that led to the present invention will be explained.

The 12 heats of A-L shown in Table 1 were tapped in a 100 kg vacuum induction melting furnace and cast into ingots with an average diameter of 190 mm.
It was forged and elongated to mm and used as a test material.

The quenching conditions for the test materials for each property test were all at 1030°C.
Air-cooled quenching was performed, and the subsequent tempering conditions were as follows: for test materials for tempering hardness, 0.2% yield strength, and Charpy impact value measurements, the specimens were held at 600° C. for 1 hour and then air-cooled twice. For the softening resistance test, tempering was performed at about 550 to 650°C so that the initial hardness was HRC52±1.

First, the strength characteristics are evaluated based on the hardness after tempering at 600℃ and the hardness after tempering at 600℃.
The test was carried out by measuring the 0 and 2% yield strength in a 0°C high temperature tensile test. A JIS No. 4 test piece was used as the tensile test piece.

The toughness was evaluated using a JIS No. 3 2mrqU notch test piece, which is a high-strength hot JO working tool steel that is tough at room temperature.

A bee impact test was conducted. Softening resistance is 1 at 600℃
The hardness of the base material after being held for 0 hours was measured and evaluated. Furthermore, the hardness of the core of a large test piece with a diameter of 120 mm and a length of 120 mm in the hardened state was measured to evaluate the hardenability of the 6-stain test piece.

At that time, the evaluation criteria as a guideline for the properties that should be satisfied in the present invention are that the high temperature strength and softening resistance are respectively equivalent to 3 Cr - 3 Mo system.
The target yield strength was set at 85 kg f/m, m'' or higher. Also, the toughness and hardenability were set at 5KD81.
The target impact value is approximately 5kgfm/
am” or more.

As a result, as shown in Table 2, the steel of the present invention was found to be superior in strength, toughness, softening resistance, and hardenability compared to comparative steel and conventional steel.

That is, as shown in Figure 1, the amount of C is 0.4 to 0.5%.
In steel limited to
．． It has been found that it is necessary to set the content to 0 to 4.0%.

Next, the reasons for limiting the chemical components of the present invention will be described.

C is an essential element for obtaining sufficient matrix hardness through quenching and tempering to increase high-temperature strength.
In order to obtain a hardness of about 50 or more, at least 0.4
0% required. On the other hand, since adding a large amount causes a decrease in toughness, the upper limit was set at 0.5%.

3i is mainly added as a deoxidizing agent and is effective for improving oxidation resistance and hardenability. If it is less than 0.1%, no deoxidizing effect can be obtained in steel manufacturing, and if it is added in excess of 1.0%, the tool life will be shortened due to a decrease in thermal conductivity and deterioration of toughness, so the upper limit is set at 1. It was set to 0%.

Like Si, Mn is an element added as a deoxidizer to increase the cleanliness of steel and improve the hardenability, and must be added in an amount of at least 0.1%. However, if the weight exceeds 1.0%, the toughness decreases, and at the same time, the peak of the secondary effect shifts to the low-temperature tempering side, reducing the softening resistance, so the upper limit was set at 1.0%.

Cr is an element that combines with C to form hard carbides and improves wear resistance and hardenability, but when added in large amounts, it deteriorates the softening resistance.
In order to achieve both the targeted hardenability and softening resistance within the range of the amount, the amount of Cr was set to 3.5 to 4.5%.

Like Cr, Mo improves wear resistance and hardenability, as well as increases softening resistance and high-temperature strength9 In order to satisfy these target characteristic values in the invention steel, Mo must be at least 2.0%. The above is necessary. However, if added in excess of 4.0%, the toughness deteriorates, so the upper limit was set at 4.0%.

(2) is an element that forms fine carbides in solid solution to improve wear resistance and softening resistance, as well as refine crystal grains and improve toughness, and is required in the steel of the present invention in an amount of at least 0.2%. However, if it is added in excess of 0.6%, distortion is likely to occur during heat treatment, so the upper limit is set at 0.6%.
And so.

Nb forms stable carbides that are less likely to form solid solutions than carbides, and has a large grain refining effect, improving toughness and improving wear resistance.In order to obtain this effect in the steel of the present invention, Nb must be at least 0. .01% is required and 0.01% is required.
Since the crystal grain refining effect is saturated even if it is added in excess of 20%, the upper limit was set at 0°20%.

For the reasons mentioned above, W is preferably not added to the steel of the present invention from the viewpoint of economy and properties, and even as an impurity, it is desirable to limit it to 0.2% or less.

[Example] The present invention will be described below with reference to examples.

<Example 1> 5U of mandrels made of the invention steels A and C shown in Table 1
When used in hot extrusion processing of S304, the lifespan was approximately doubled compared to that of conventional #llK, as shown in the third barley. The processing conditions are shown below.

Press equipment: 2000T press Material to be processed: 5US304 Processing temperature: +1200 to 1230°C Mandrel diameter near 1.7 to 61.5 mm <Example 2> A die made of the steel of the present invention shown in Table 1 was used for extrusion of AQ. . Party A extrusion dies have sharp corners and are subjected to high impact loads during extrusion, resulting in breakage and deformation of the center of the die due to the notch effect from the sharp corners, resulting in the end of its life. Furthermore, since An extrusion dies are generally used by repeatedly undergoing nitriding treatment at about 570°C, softening of the base layer due to this becomes a problem, resulting in high strength, high toughness, and excellent Softening resistance is desired.

As a result of the test, as shown in Table 3, the life of the die made of the present invention was approximately three times longer than that of the die made of conventional steel.

Press device: 1800T press Material to be processed: A2 Processing temperature: 450-460℃ <Example 3> Furthermore, in addition to the above-mentioned applications, the horse of the present invention can also be used as a tool for severe high stress at 1 temperature and hot working. It may also be suitable for Therefore, knockout punches (punches for receiving) made of the invention steels B and E of Daiichi Mugi were used for warm forging of 5UJ2. The result is conventional steel J. The lifespan is approximately twice as long compared to the knockout punch.

Press equipment: 1OOOT press 2nd process workpiece: 5
UJ2 Forging temperature: 670-710℃ Punch diameter: 49mm Effect] As stated above, the steel of the present invention has not only the excellent hardenability and toughness of the conventional 5KD61 class, but also the high strength and excellent strength of the 3Cr-3Mo class. fII has excellent softening resistance, and can be used in steel hot extrusion tools, Affi extrusion tools, and hot/hot mold applications where extremely high stress is applied during machining. It showed a service life of about 2 to 3 @ compared to that of conventional products.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the amounts of Cr and Mo and the gJ ratio of each characteristic. O (wt%)

Claims (1)

[Claims] C: 0.4-0.5% Si: 0.1-1.0% Mn: 0.1-1.0% Cr: 3.5-4.5% Mo : 2.0-4.0% V: 0.2-0.6% Nb: 0.01-0.20% A high-strength hot working tool steel containing Fe and unavoidable impurities.