JPH04154909A - Production of cast material for tool excellent in crack resistance - Google Patents

Abstract

PURPOSE:To produce a cast material for tool excellent in wear resistance, seizure resistance, and crack resistance by subjecting a cast high alloy steel having a specific composition consisting of C, Si, Mn, Cr, Ni, S, P, O, and Fe to specific heat treatment. CONSTITUTION:A cast high alloy steel which has a composition consisting of, by weight, 0.7-2.5% C, <=3% Si, <=3% Mn, 20-40% Cr, 20-50% Ni, <=0.05% S, <=0.05% P, <=0.10% O, and the balance Fe with inevitable impurities and further containing, if necessary, either or both of 0.0001-0.050% Ca and 0.0001-0.50% REM and/or one or more kinds among 0.1-5.0% Mo, 0.1-5;0% W, 0.1-5.0% CO, 0.1-5.0% Ti, 0.1-5.0% V, and 0.1-5.0% Zr is heated and held at a temp. in the region between (solidus temp. -20 deg.C) and (solidus temp. +40 deg.C) for 1-20hr. By this method, a high temp. tool material free from the occurrence of cracks in many localities even if subjected to severe heating-cooling cycle or bearing and having long service life can be obtained.

Description

[Detailed Description of the Invention] <Industrial Application Fields> The present invention is applicable to high-temperature workpieces, such as guide shoes of inclined roll rolling mills for producing seamless pipes, dies for hot extrusion, etc. The present invention relates to a method for manufacturing a cast material for tools, which is suitable as a member that causes severe sliding friction.

<Prior art and its problems> When using high-temperature tool members such as guide shoes of inclined roll rolling mills for seamless pipe production and dies for hot extrusion,
It is subjected to extremely severe sliding friction between the workpiece and the heated workpiece. The tool life and product quality are dominated by wear and seizure caused by this sliding friction.

Therefore, hard P was conventionally used for such high-temperature tool parts.
e-1,2wtχC-25wtχCr-30wtXNi
-CCr-3OW high alloy cast steel is generally used as cast or after being subjected to carbide agglomeration and coarsening heat treatment as disclosed in JP-A-61-113713. Ta.

However, in recent years, there has been a growing trend toward high-quality steel pipes, and stainless steel #III class, which is difficult to process, is being used as the work material processed by rolling mills and hot extruders for seamless pipe manufacturing. As a result, the following problems have been pointed out. That is, for difficult-to-process materials such as stainless steel, the heating temperature during processing is 1100℃.
In addition to the higher temperature of ~1250'C, the friction conditions are very severe, such as high surface pressure during machining and complete sliding friction between the tool and the workpiece, so the conventional materials are used as tool materials. Even if a tool is used, not only will the life of the tool be reduced due to wear and defects on the surface of the workpiece due to seizure, but also cracks will easily form due to the repeated heat cycles applied to the tool surface. A phenomenon in which seizure was more likely to occur starting from the area occurred frequently.

These cracks on the tool surface, in the form of grain boundary cracks, reach a depth of approximately 511 mm from the tool surface, and as mentioned above, they tend to become a new starting point for tool surface seizure. This significantly deteriorates the unit consumption of the tool and the quality of the workpiece.

For this reason, the purpose of the present invention is to ensure that the surface does not crack frequently even when subjected to more severe heating/cooling cycles and surface pressure than ever before, and has a sufficient service life. The object of the present invention was to provide a low-cost material for high-temperature tools.

<Means for Solving the Problems> In order to achieve the above object, the present inventors conducted research while repeating numerous tests, and as a result, they were able to obtain the following knowledge.

(al. The above mentioned “
The occurrence of surface cracks observed in cast high-alloy steel high-temperature tool materials is largely related to grain boundary segregation of trace impurity elements such as S and P, and reduction of these trace elements improves the toughness of the material. It has a remarkable effect on suppressing surface cracks caused by heating and cooling cycles and surface pressure cycles.

(b) In addition to reducing the trace impurity elements mentioned above, when Ca or REM (rare earth element), which exerts the effect of controlling the trace element morphology, is added, the grain boundary segregation of the trace impurity elements becomes even more effective. The effect of suppressing surface cracks becomes even more pronounced.

(C1 In addition, a specific heat treatment is applied to cast high-alloy steel for high-temperature tools to reduce trace impurity elements or to add Ca, Mg, and REM, to create a structure in which carbides have aggregated and coarsened. Once developed, its wear resistance and seizure resistance will be significantly improved, making it possible to create a material for high-temperature tools that has a sufficiently satisfactory service life even under the harsh conditions of machining high-alloy materials. .

The present invention was made based on the above-mentioned findings, etc. rc:o, 7 to 2.5% (hereinafter, the component ratio is not expressed and % is expressed as weight %).

Si: 3% or less, Mn: 3% or less.

Cr: 20-40%, Ni: 20-5
0%.

s: o, os% or less; P: 0.05% or less.

○: 0.10% or less including, Ca: 0.0001-0.050%.

REM: 0.0001-0.50%Mo: 0.
1-5.0%, W: 0.1-5.0%.

Co: 0.1-5.0%, Ti: 0.1
~5.0%.

V: 0.1-5.0%, Zr: 0.1-5.
0%, and the remainder is substantially Fe.
Cast high alloy steel consisting of (Fe and unavoidable impurities),
[Temperature 20℃ lower than the solidus line] ~ [40℃ lower than the solidus line]
By heating and holding the material at a high temperature for 1 to 20 hours, a cast material for tools with a structure containing agglomerated and coarsened carbides, which has excellent crack resistance and a long service life, is produced. It has a major feature in that it has been realized.

Hereinafter, in the present invention, the reason why the chemical composition and heat treatment conditions of the steel to be applied are limited as described above will be explained in detail together with the effects thereof.

^) Chemical composition of steel: C combines with Cr, Fe, etc. in steel to form M23Cb type, M7C, and l type carbides, which improves the wear resistance of the material.
It exerts the effect of improving seizure resistance, but in order to ensure the desired effect of this effect, it is necessary to agglomerate and coarsen these carbides through a prescribed heat treatment. It is necessary to secure the desired amount of carbide. If the C content is less than 0.7%, the desired amount of carbide cannot be secured, so even if heat treatment is performed, the effect of improving wear resistance and seizure resistance will be insufficient. If C content exceeds 5%, the amount of carbides becomes too large, leading to a decrease in toughness and making cracks more likely to occur, so the C content was set at 0.7 to 2.5%.

Although Si is an effective component for adjusting deoxidation and improving castability, if it is included in excess of more than 3%, it will impair the toughness of the material, so the upper limit of the St content is set at 3%. Established.

In addition to having a deoxidizing effect, Mn has the effect of increasing high-temperature strength and improving wear resistance.
The upper limit of the n content was set at 3%.

Cr has the effect of increasing high-temperature strength by forming a solid solution in the matrix of steel materials, and as mentioned above, it combines with C to form carbides and improves the wear resistance and seizure resistance of the material. If the Cr content is less than 20%, the desired effect due to the above action cannot be obtained. On the other hand, if the Cr content exceeds 40%, the σ phase will precipitate and the material will become brittle.
It was set at ~40%.

Ni has the effect of increasing the toughness and thermal shock resistance of the material, but if its content is less than 20%, the desired effect of the above effect cannot be obtained; on the other hand, even if it contains more than 50%, Since no further effect was observed, the Ni content was determined to be 20 to 50% in consideration of economic efficiency.

S is an impurity element that segregates as a compound at grain boundaries and deteriorates the cracking resistance of the material and adversely affects tool life, and its content is preferably as low as possible. However, the S content was determined to be 0.05% or less because the desired cracking resistance can be ensured by simultaneously reducing the P content and suppressing the S content to a range of 0.05% or less.

Like S, P is an impurity element that deteriorates cracking resistance, so it is preferable that its content be as low as possible. However, S
The P content was determined to be 0.05% or less because the desired cracking resistance can be ensured by reducing the amount and suppressing the P content to a range of 0.05% or less.

O is also an impurity element that inevitably mixes into steel, but 0
．． If more than 10% of O is present in steel, it becomes an oxide and is involved in underground formation, so the O content was set at 0.10% or less.

Ca, and REM (±7-1) These components combine with S in steel and have the effect of suppressing the segregation of S at grain boundaries, so they can be included alone or in combination as necessary. However, each content is 0
．． If it is less than 0.0001%, the desired effect cannot be obtained by the above action, while in the case of Ca, 0.050% and R
In the case of EV, if the content exceeds 0.50%, it will cause underground formation, so the Ca content is 0.0001 to 0.050% and the REM content is 0.
．． 0001 to 0.50%, respectively.

Mo, W, Co, Ti, L and Zr These components all form a solid solution in the base of the steel material to increase its strength, and combine with C to form carbides to improve wear resistance,
Since it has the effect of improving seizure resistance, one or more types may be added if necessary, but in any case, the content is 0.
．． If it is less than 1%, the desired effect cannot be obtained by the above-mentioned action, and on the other hand, the effect increases as the content of each component increases, but considering economic efficiency, the content of each component is 0.1 to 0. 5.0
%.

B) Heat treatment conditions The heat treatment according to the present invention aggregates and coarsens the primary carbides crystallized from the liquid phase, thereby realizing a structure with large carbides that cannot be obtained with normal heat treatment, resulting in excellent wear resistance, Since the purpose is to ensure seizure resistance, unlike normal heat treatment, it is essential to heat and hold at a very high temperature.

In this case, the heating temperature is [20°C lower than the solidus line]
If the temperature is less than
If the material is heated to a temperature higher than 0℃ above the solidus line, the material will begin to partially melt and will no longer maintain its original shape, so the heating temperature should be between 20℃ below the solidus line and 20℃ below the solidus line. 40°C higher temperature]. -19= Here, the above-mentioned "solidus line" means the solidification end temperature obtained from the thermal analysis curve, and the solidus line temperature differs depending on the component system, but it is In this case, the solidus temperature is about 1250 to 1350°C, so the range of the heat treatment temperature actually applied is 1230 to 1390°C.

In addition, the heating holding time during heat treatment must be determined in consideration of the heating temperature, but in order to coagulate and coarsen the carbide at a temperature where the material to be heat treated does not begin to melt, it is necessary to determine the length for at least 1 hour. In the case of heat treatment at a relatively low temperature (temperature close to the lower limit), it is necessary to maintain the temperature for a longer time. However, in practice, treatment for more than 20 hours is extremely disadvantageous in terms of cost, so the upper limit of the holding time was set at 20 hours in consideration of economic efficiency.

Note that the cooling rate after heat treatment does not have a direct effect on the agglomeration and coarsening of carbides, so there is no need to specifically limit it.
Since a larger amount of carbide is more advantageous for wear resistance and seizure resistance, it is preferable to perform slow cooling in order to precipitate as much of the carbon solid-solved in the matrix as possible at high temperatures as carbide.

Therefore, in consideration of actual workability and economic efficiency, the heat treatment of alloy steel with the above chemical composition should be performed by heating at [solidus temperature] to [40°C higher than solidus temperature] for 1 to 5 hours. - It can be said that it is preferable to carry out the process under the conditions of holding and then furnace cooling to 600°C or less. The heat treatment atmosphere does not have a particular effect on the agglomeration and coarsening of carbides, so there is no need to limit it in particular, and the atmosphere may normally be used.

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

<Example> First, high-alloy steel having the chemical composition shown in Table 1 was melted using a high-frequency furnace, and then this was melted to a diameter of 280 mm and a length of 4.
It was cast into a 0Qmm round bar and cooled to room temperature.

In addition, when melting the above-mentioned high alloy steel, the main components are 16
After dissolving at 50°C, Ca, REM (here Ce +
For steel types containing La), these additive elements are added by the ladle bottom method, and Mo, w, Go+ 7++
For steel types containing V and Zr, these additional elements were added by applying the in-furnace addition method after deoxidation.

Then, the solidus temperature was confirmed by a thermal analysis test. That is, a sample with dimensions of 18φ x 401mm was heated in a Tammann furnace for 14 minutes.
After heating to 50 to 1500°C to melt, this was slowly cooled and the solidification completion temperature was measured, and the measured solidification completion temperature was taken as the solidus line.

Next, after subjecting the obtained round bars to spheroidizing annealing at 1300°C for 5 hours, test pieces were taken from these and their "tensile properties", "Charpy impact absorption energy" and "fracture toughness" were investigated. , a quench cracking test was conducted.

Here, the Charpy impact test was carried out at 26 to 180°C on a 2-notch test piece. In addition, the WOL test (^STM E399 method) was applied to measure the fracture toughness.
The test was carried out under the conditions of ton x 0.5 sec. For the quench cracking test (thermal shock test), the thickness 5w1 shown in Figure 1 was used.
A test piece was heated and held at 600 to 1150°C for 10 minutes, and then water quenched, and the presence or absence of cracking during this process was examined.

These results are shown in Table 2.

As is clear from the results shown in Table 2, the cast material manufactured according to the conditions specified in the present invention has excellent strength, Charpy impact value, and fracture toughness (K+c).

It can be seen that, while both have excellent resistance to quenching, those obtained by the comparative method are inferior in any of the above properties.

In particular, materials containing a large amount of s, p, and o, such as the material obtained in test number 1.3.5, have extremely poor resistance to quench cracking.

In addition, as in test number No. 3, 5.7, impurity element s,
When p and o are reduced, the resistance to quenching is improved.

In addition, like the material obtained in No. 7.9, Ca + RE
Adding M improves the fracture toughness value (KIC), but C
a. When REM is excessive, oxide-based inclusions increase as seen in test number 8.10, and the quench cracking resistance deteriorates.

<Summary of Effects> As explained above, according to the present invention, it is possible to industrially stably provide a cast material for tools that not only has excellent wear resistance and seizure resistance, but also has excellent cracking resistance. It can be applied to the guide shoes and hot extrusion dies of inclined roll rolling mills to greatly improve their service life, bringing about extremely useful effects industrially.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a test piece for quench cracking test (thermal shock test) used in Examples.

Claims (4)

[Claims] (1) In weight percentage: C: 0.7-2.5%, Si: 3% or less, Mn: 3% or less, Cr: 20-40%, Ni: 20-50%, S: 0.05 % or less, P: 0.0
5% or less, O: 0.10% or less, and the balance substantially consists of Fe at a temperature of [20°C lower than the solidus line] to [4°C lower than the solidus line].
A method for producing a cast material for tools having excellent crack resistance, the method comprising heating and holding at a temperature of 0° C. higher for 1 to 20 hours. (2) In weight percentage: C: 0.7-2.5%, Si: 3% or less, Mn: 3% or less, Cr: 20-40%, Ni: 20-50%, S: 0.05 % or less, P: 0.0
5% or less, O: 0.10% or less, and also contains one or more of Ca: 0.0001-0.050%, REM: 0.0001-0.50%, and the remainder is substantially Cast high-alloy steel made of iron is heated to a temperature 20°C lower than the solidus line.
1 in the temperature range of ~[40℃ higher than the solidus line]
A method for producing a cast material for tools with excellent crack resistance, characterized by heating and holding for 20 hours. (3) In weight percentage: C: 0.7-2.5%, Si: 3% or less, Mn: 3% or less, Cr: 20-40%, Ni: 20-50%, S: 0.05 % or less, P: 0.0
5% or less, O: 0.10% or less, Mo: 0.1 to 5.0%, W: 0.1 to 5.0%, Co
:0.1~5.0%, Ti:0.1~5.0%, V:0
．． 1 to 5.0%, Zr: 0.1 to 5.0%, and the balance is Fe and unavoidable impurities. ℃lower temperature〕〜
1 to 2 in the temperature range [40℃ higher than the solidus line]
A method for producing a cast material for tools with excellent crack resistance, characterized by heating and holding for 0 hours. (4) In weight percentage: C: 0.7-2.5%, Si: 3% or less, Mn: 3% or less, Cr: 20-40%, Ni: 20-50%, S: 0.05 % or less, P: 0.0
5% or less, O: 0.10% or less, and one or more of Ca: 0.0001-0.050%, REM: 0.0001-0.50%, and Mo: 0.1-0. 5.0%, W: 0.1-5.0%, Co
:0.1~5.0%, Ti:0.1~5.0%, V:0
．． 1 to 5.0%, Zr: 0.1 to 5.0%, and the balance is Fe and unavoidable impurities. ℃lower temperature〕〜
1 to 2 in the temperature range [40℃ higher than the solidus line]
A method for producing a cast material for tools with excellent crack resistance, characterized by heating and holding for 0 hours.