JPS582584B2 - Iron-based material casting mold pre-hardened mold steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a brihardon mold material used for casting of iron-based materials.

Conventionally, square casting molds have been used for molds used for casting ferrous materials. Due to rough skin, etc., the service life is shortened, and sufficient performance is not obtained, and the benefits of sand mold → mold casting are not fully obtained.

On the other hand, when using SCr-based hot work tool steel (such as JISSKD61), roughness due to oxidation is severe, and the standard hardness (HRC40-45) tends to develop into large cracks from heat cracks, which should be satisfied. The service life has not been achieved.

The present invention focuses on (1) occurrence and development of cracks due to severe thermal shock during casting of high-temperature iron-based materials; (2)
Analyze the basic properties to solve problems in usage performance such as oxidation effect due to temperature rise (3) molten metal corrosion (erosion loss), and consider materials and heat treatment hardness to impart these properties. In addition, we have invented a new pre-hardened mold material that provides an overall long life and has good machinability.

Table 1 shows the chemical composition and heat treatment conditions (target hardness HRC25) of the steel of the present invention.

*Hardness HRC20.5 Table 2 shows the oxidation resistance of the steel of the present invention.

It can be seen that the oxidation resistance is much higher than that of conventional materials, and the oxidation resistance is further increased by high Cr and high Si.

Ru.

Regarding the effects of elements such as Mo, W, and V that increase high-temperature strength, it can be seen that at the same Mo equivalent, W has a greater effect than Mo, and V has a greater effect.

*900℃×20Hr Table 3 compares the strength of the inventive steel at high temperatures (700℃) with conventional materials.Table 4 shows that the inventive steel clearly has higher high-temperature strength than the conventional material. The results of the heat crack resistance test of the steel of the present invention are shown in FIG.

This is the result of repeatedly heating a test piece to 750°C with a flame and then cooling it with water to 20°C 1000 times.

A' A steel of the present invention having component A and tempered to HRC45 A'' 〃 HRC34 A''' 〃 HRC10 The steel of the present invention has clearly greater heat crack resistance than conventional materials.

This is because the structure of the steel of the present invention is uniform and fine, and the combination of chemical composition and heat treatment conditions is appropriate, and it has both excellent toughness and appropriate high-temperature strength.

W, Mo, and V all increase high-temperature strength and heat crack resistance, but when the thermal shock is large as in this heat crack test, adding a large amount actually reduces the heat crack resistance.

In this case, the degree of decrease in heat crack resistance is relatively small in the case of Mo.

The steel of the present invention having component A is tempered at a lower temperature, and the hardness is reduced to H.
It can be seen that for steels with a high RC of 45 and 34 (comparative steels A' and A''), cracks develop more quickly and the maximum depth becomes larger especially in applications where thermal shock is particularly severe.

On the contrary, it can be seen that in the case of HRC10, which has a lower hardness, heat cracks are generated early due to insufficient high temperature strength, and the crack depth becomes larger overall.

The appropriate hardness standard for this mold application is HRC20-30.

In this way, it can be seen that there is an appropriate hardness value for heat crack resistance, and when thermal shock is large, the value is lower than the standard appropriate hardness (HRC around 45) for Al die-casting molds and the like.

Table 5 shows the number of seizure starts (ratio) in the repeated molten metal dripping test for the steel of the present invention.

It can be seen that the steel of the present invention has less seizure of molten metal than the conventional material.

In particular, E with high C and I with Co added are excellent.

The former is due to the effect of a relatively large amount of carbide, and the latter is due to the effect of a thin and dense oxide film.

Table 6 shows the thermal expansion coefficients (0 to 600°C average) of the steels of the present invention.

This coefficient is equivalent to the thermal expansion coefficient of general iron-based materials, and there is no particular problem.

Table 7 shows the machinability of the materials of the present invention.

The tool life in the drilling test using a drill is expressed as an index, with that of the material A of the present invention set as 100.

Materials E and F of the present invention have relatively low machinability compared to material A of the present invention.

For E, the cause is high Ni and high C and V, while for the material F of the present invention, W, Mo,
Even though V is low, the machinability is even lower than E.

This is due to the high Mn content.

The amounts of Mn and Ni added are limited by machinability.

Next, the reason for limiting the range of each component of the steel of the present invention will be described.

C is added as an austenite-forming element, and is necessary to obtain a uniform martensitic structure through quenching and increase strength at room and high temperatures. It is added to make the grains finer.

If the amount is too high, it will increase the segregation tendency, increase the amount of carbides, and reduce the heat crack resistance due to the formation of coarse carbides. It will also reduce the amount of Cr, which is effective for oxidation resistance, so it should be 0.45% or less. If it is too low, it will cause ferrite. The content is set to 0.15% or more since the above effects cannot be obtained due to the formation of carbon.

A more preferable range of C is 0.20 to 0.35%.

Si is a main element that improves oxidation resistance together with Cr, and is added depending on the purpose and use in order to raise the A1 transformation point.

If it is too high, the thermal conductivity will decrease, so it should be 1.50% or less, and if it is too low, the effect of the above addition cannot be obtained, so it is 0.10%.
% or more.

The generally preferred range of Si is 0.20 to 0.70%, but for applications where oxidation resistance is important, it is 0.50 to 1,50%.
% is considered high.

Mn is added in consideration of mold dimensions in order to improve hardenability, and is added as an austenite forming element for the purpose of suppressing ferrite formation.

If it is too large, the A1 transformation point will be lowered and the machinability will be reduced, so the upper limit is set at 1.50%, and if it is too low, the effect of the above addition cannot be obtained, so it is set at 0.10% or more.

A more preferable range of Mn is 0.20 to 1.00%.

Cr is an extremely important element for imparting oxidation resistance, and has the effect of increasing the A1 transformation point and combining with C to form carbide, thereby increasing wear resistance.

In the case of the steel of the present invention, setting the lower limit is extremely important, especially from the point of view of oxidation resistance, and the lower limit of 10 , 00%.

On the other hand, if it is too high, it is a ferrite-forming element, so it should be balanced with austenite-forming elements (C, Ni).
, Mn, N, etc.), and it is difficult to maintain the excellent thermal shock resistance, which is one of the characteristics of the steel of the present invention, due to a decrease in thermal conductivity and the formation of coarse carbides. Therefore, it is set to 17.00% or less.

A more preferable range of Cr is 11.00 to 14.00%.

However, for applications that require particularly high oxidation resistance, 12.50
~17.00%.

Ni is added to improve the crack growth resistance, which is extremely important in the steel of the present invention, and to improve the hardenability.

It is also added as an austenite-forming element for the purpose of suppressing ferrite formation.

If it is too large, the A1 transformation point will be lowered and the machinability will be reduced, so the upper limit is set at 150%, and if it is too low, the above-mentioned effect of addition cannot be obtained, so it is set at 0.10% or more.

W and Mo, together with V, have a high resistance to tempering softening.
It is added to prevent softening due to heat effects during use, increase high-temperature strength, refine crystal grains, raise the A1 transformation point, and suppress the occurrence and progression of heat cracks.

It is also added to form carbides to improve seizure resistance and erosion resistance against molten metal.

In the case of the steel of the present invention, it is inappropriate to add a large amount from the viewpoint of homogenizing and refining the structure (reducing segregation), and if it is too large, the above-mentioned segregation will increase, the amount of carbides will increase excessively, coarse carbides will be formed, and the thermal conductivity will decrease. To avoid this, it should be set at 2.50% or less at (1/2W + Mo), as this will cause a decrease in toughness and ferrite formation, and if it is too low, the effect of the above addition will not be obtained, so 0.50
% or more.

Note that W is more advantageous than Mo in terms of high-temperature strength, while Mo is more advantageous in terms of toughness, and may be added singly or in combination depending on the purpose and conditions of use.

By adding a small amount, ■ increases the tempering softening resistance like Mo and W, increases the high temperature strength, and refines the crystal grains.
Increases the transformation point and improves heat crack resistance.

It also forms carbide, which has the effect of preventing molten metal from seizing and melting damage caused by the molten metal.

(3) is added to obtain the above effect, but if it is too large, it will form coarse carbides, increase the segregation tendency, reduce toughness, and cause ferrite formation, so 0.80%
If it is too low, the effect of the above addition cannot be obtained, so 0
．． 10% or more.

In particular, when high temperature strength, seizure resistance, and erosion resistance are important, the content should be 0.30 to 0.80%.

N is added as an austenite-forming element to suppress ferrite formation, and even in the case of high Cr, W, Mo, ■, it has the effect of suppressing ferrite formation without increasing the amount of C, and has the effect of improving heat crack resistance. It has the following.

N is added in order to obtain the above effects, but in general manufacturing methods, the addition is at most 0.40%, so it is set to 0.40% or less.

As an austenite-forming element, Co has the effect of suppressing ferrite formation and the effect of increasing high-temperature strength.

Another important effect of Co is that it forms a dense and highly adhesive oxide film on the mold surface, which prevents melting and seizure caused by molten metal, and improves heat crack resistance due to its heat insulating effect.

Co is added in order to obtain the above effects, but if it is too large it will cause a decrease in toughness and will reduce the progress resistance of heat cracks, so it should be 3.50% or less, and if it is too low, the effects of the above addition cannot be obtained, so 0. 20% or more.

As described above, the steel of the present invention combines the component effects, takes into consideration the uniformity and refinement of the structure during manufacturing, and undergoes quenching and tempering (1000-1150℃ quenching, 680-750℃
Tempering is standard.

) provides pre-hardened mold steel for casting and molding iron-based paulownia materials with a standard hardness of HRC20-30.It can be used as is after die carving, and is resistant to thermal shock, melting damage, and seizure caused by pouring high-temperature molten metal. It is a new mold material that provides durability and long life.

Claims (1)

[Claims] 1. C0.15-0.45%, Si 0.10-0.10% by weight
1.50%, Mn0.10-1.50%, Ni0.10
~1.50%, Cr10.00~17.00%, 1/2
W+Mo0.50~2.50%, V0.10~0.80
%, balance Fe and normal impurities, Cr equivalent = Cr-40C-2Mn-4Ni+5Si+4Mo+2
Cr equivalent value indicated by W+8V+2Co-40N is +1
2.50 or less, a pre-hardened iron-based material casting molding steel (standard HRC 20-30) for molds. 2 C0.20-0.35%, Si0.20-0.20% by weight
0.70%, Mn0.20-1.00%, Ni0.20
~1.00%, Cr11.00~14.00, 1/2W
+Mo0.80~2.00%, V0.15~0.50%
A ferrous material casting pre-hardened (standard HRC 20-30) mold steel according to claim 1, comprising: 3 C0.15~0.45%, Si0.50~ by weight ratio
1.50%, Mn0.10-1.50%, Ni0.1
0-1.50%, Cr10.00-17.00%, 1/
2W+Mo0.50~2.50%, V0.10~0.8
The iron-based material casting pre-hardened mold steel (standard HRC 20-30) according to claim 1, comprising 0%. 4 C0.15~0.45%, Si0.10~ by weight ratio
1.50%, Mn0.10-1.50%, Ni0.10
~1.50%, Cr10.00~17.00%, W0.
10-0.90%, Mo0.50-1.80%, ■0.
The iron-based material casting pre-hardened mold steel (standard HRC 20-30) according to claim 1, comprising 10-0.80%. 5 C0.15~0.45%, Si0.10~ by weight ratio
1.50%, Mn0.10-1.50%, Ni0.10
~1.50%, Cr10.00~17.00%, Mo0
．． 70 to 2.00%, V 0.10 to 0.80%, and pre-hardened iron-based material casting molding steel (standard HRC 20 to 30) according to claim 1. 6 Weight ratio: C0.15~0.45%, Si0.10~
1.50%, Mn0.10-1.50%, Ni0.10
~1.50%, Cr12.50~17.00%, 1/2
W+Mo0.50~2.50%, V0.10~0.80
% of iron-based material casting molding pre-hardened HRC20-30 as defined in claim 1). 7 C0.15~0.45%, Si0.10~ by weight ratio
1.50%, Mn0.10-1.50%, Ni0.10
~1.50%, Cr10.00~17.00%, 1/2
+Mo0.50~2.50%, V0.30~0.80%
Steel for molds made of ferrous material casting molding brihardon (standard HRC 20-30) as set forth in claim 1. 8 C0.15~0.45%, Si0.10~ by weight ratio
1.50%, Mn0.10-1.50%, Ni0.10
~1.50%, Cr10.00~17.00%, 1/2
W+Mo0.50~2.50%, V0.10~0.80
%, Co0.20-3.50%, balance Fe and normal impurities, and the following formula Cr equivalent = Cr-40C-2Mn-4Ni+5Si+4
Steel for molds made of iron-based material casting molding brihardon (standard HRC 20-30), characterized in that the Cr equivalent value expressed by Mo+2W+8V+2Co-40N is +12.50 or less. 9 C0.15~0.45%, Si0.10~ by weight ratio
1.50%, Mn0.10-1.50%, Ni0.10
~1.50%, Cr10.00~17.00%, 1/2
W+Mo0.50~2.50%, V0.10~0.80
%, N0.40% or less, balance Fe and normal impurities, Cr equivalent = Cr-40C-2Mn-4Ni+5Si+4
Steel for molds made of iron-based material casting pre-hardened steel (HRC 20-30 is standard), characterized in that the Cr equivalent value expressed by Mo+2W+8V+2Co-40N is +12.50 or less. 10 Weight ratio: C0.15-0.45%, Si0.10
~1.50%, Mn0.10~1.50%, Ni0.1
0-1.50%, Cr10.00-17.00%, 1/
2W+Mo0.50~2.50%, V0.10~0.8
0%, N0.40% or less, Co0.20-3.50%,
The balance consists of Fe and normal impurities, and the amount of Cr is as follows: Cr-40C-2Mn-4Ni+5Si+4
Steel for molds of iron-based material casting pre-hardened (standard HRC 20-30) characterized in that the Cr equivalent value shown by Mo+2W+8V+2Co-40N is +12.50 or less.