JPS6358905B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention has particularly high wear resistance under severe friction conditions with the workpiece at high temperatures, and also has moderate strength, excellent toughness, and good thermal conductivity. Withstands repeated thermal shock from rapid cooling,
The present invention relates to a hot casting tool with a long service life. A piercer plug tool for manufacturing steel pipes in hot conditions causes severe abrasion with the high-temperature workpiece, and is subsequently subjected to a rapid cooling effect such as surface water cooling. Tool materials for these applications include conventional 1.5Ni3.5Cr steel and hot work tool steel SKD62.
However, it cannot withstand severe abrasion, causing seizures, peeling, etc., and heat cracks develop under severe thermal stress conditions of repeated rapid heating and cooling, resulting in rough skin. As a result, the load placed on the tool increases, leading to early wear and tear and not necessarily providing a satisfactory service life. On the other hand, even if a high-strength hot work tool steel made of a high alloy such as SUH310 (25Cr-20Ni) is applied, its thermal conductivity is relatively low and the tendency for scale formation is small, resulting in excessive temperature rise on the tool surface and premature This often led to heat cracks and shortened service life. The properties required for tool materials for severe applications such as those mentioned above are (1) moderate room temperature to high temperature strength that can withstand severe wear effects and working stress at high temperatures, and an appropriate amount of carbide and its distribution form. (2) Resistance to the occurrence and propagation of cracks under the action of thermal stress due to repeated rapid heating and cooling caused by rapid temperature rise due to severe frictional contact with high-temperature workpieces, lubrication, and cooling. (3) Protects the tool surface under severe abrasive conditions with high-temperature mating material, provides a lubricating effect,
Characteristics of forming an oxide film that suppresses frictional heat generation and provides heat insulation. (4) Good thermal conductivity to suppress the temperature rise on the tool surface as much as possible and prevent the formation of a sudden temperature gradient; characteristic (3) is particularly important for tools for this purpose. It is a factor. For the above required properties, 1.5Ni3.5Cr steel lacks strength at high temperatures, while current hot work tool steels such as SKD62 mentioned above have strength at high temperatures, but the most important factor is property (3). In addition, (2) and (4) were also insufficient, and there were cases where a sufficient lifespan could not be obtained due to premature seizure, fatigue, cracking, etc. The present invention eliminates the various drawbacks of conventional tools using steel as described above, and its greatest feature is improved seizure wear resistance by forming a strong protective oxide film based on the cast oxidized skin. We provide hot-cast tools with excellent strength, carbide, thermal conductivity, and toughness that significantly improve the service life under severe wear conditions at high temperatures and thermal shocks caused by rapid heating and cooling. It is something to do. That is, the present invention provides low to medium C-low Cr-low Mo
Tool material with (W)-Co-Cu as its basic component, excellent oxide film properties (easiness of formation, adhesion, peeling resistance in the film layer), moderate high temperature strength, carbide amount and distribution, and good heat resistance. In addition to imparting conductivity,
In addition, Nb, Zr, and
V is added to create an extremely strong cast oxidized skin, or by applying an appropriate oxide film treatment before use, or by using a combination of both to create an oxide film of 10 μm or more on the surface, it is possible to improve adhesion. Forms a good protective and heat insulating oxide film, has moderate strength and carbide distribution, and together withstands severe abrasion between the workpiece and the workpiece at high temperatures, has a strong cast structure, and has moderate high temperature strength and good properties. Combined with high thermal conductivity, it does not cause sagging (plastic flow) type wear.
In addition, large cracks do not occur even under the repeated stress of rapid heating and cooling in relation to lubrication and cooling during use.
This relates to a cast hot work tool that has significantly improved service life compared to tools made of conventional hot work tool steel such as SKD62. The tool of the present invention can be used after casting or after processing a cast product.
As a general rule, oxidation treatment is performed in various atmospheres such as air, air, and steam atmosphere depending on the purpose and application. It is also possible to utilize the oxide film itself and use it without prior oxide film treatment. Chemical composition weight % of the steel applied to the present invention tool (hereinafter referred to as "the present invention applicable steel") and conventional steel (1.5Ni, 3.5Cr series and SKD62), baking critical load ratio and adhesion film thickness in high temperature baking wear test The values are shown in Table 1. In Table 1, samples A to O are steels to which the present invention is applied (cast), and samples P and Q are conventional steels. The test piece used in the high-temperature baking wear test is a cylindrical test piece (the test end surface is a cast skin), which has been subjected to a surface oxide coating treatment at 950℃ in advance, and then rotated at high speed against a mating material heated to a high temperature (950℃). The maximum load (critical load) at which seizure does not occur when the end face is pressed and a frictional effect is applied is determined, and the critical load for seizure of conventional materials is determined.
The seizure critical load ratio is expressed as an index with 100 as the index. The adhesion coating thickness is the average value of the thickness (μm) of the difficult-to-peel coating after removing the easily-peelable oxide coating. It can be seen that the steel to which the present invention is applied has a clearly higher seizure critical load than the conventional steel. This is because the oxide film formed on the surface of the steel to which the present invention is applied is extremely strong, has lubricating and protective effects, and even if the oxide film partially peels off during use, it immediately forms a strong oxide film.

[Table] The effect of regenerating the film is large, and the wear life is also extended by the strong cast structure that can withstand plastic flow on the surface, the appropriate room temperature to high temperature strength, and the improvement of high temperature seizure wear resistance due to the appropriate distribution of carbides. It is something to improve. The superiority of the cast sample of the steel to which the present invention is applied is that the strong oxide film that is formed has extremely good adhesion compared to conventional steel, and an excellent protective oxide film with an appropriate thickness is formed. This is one of the major features of the steel of the present invention. Table 2 shows the heat crack resistance of steel samples A, I, and N to which the present invention was applied and conventional steel sample P after coating treatment.

[Table] Table 2 shows the results of 1000 repetitions of immersing a 18 mmφ x 25 mm test piece in a heating bath at 900°C, rapidly heating it, and cooling it with water to 200°C. It can be seen that the steel to which the present invention is applied has better heat crack resistance than conventional steel. This is because the protective effect of the oxide film and the toughness and ductility have a great effect on heat crack resistance under severe thermal shock conditions of rapid heating and cooling. Next, the reason for limiting the composition range of the steel to which the present invention is applied will be described. C prevents ferrite formation, Cr, Mo (W),
It is added to form carbides by combining with carbide-forming elements such as V and Ti, to improve seizure resistance against severe abrasion at high temperatures, and to impart appropriate strength at room to high temperatures. If it is too high, the amount of carbide becomes too large, and coarse carbides are likely to form, reducing toughness, so it should be 0.60% or less, and if it is too low, the effect of the above content cannot be obtained, so it is 0.15%.
The above shall apply. Si has the effect of increasing oxidation resistance, and is added depending on the purpose and use in order to adjust the oxidation resistance of the steel of the present invention. If it is too large, the formation and growth of an oxide film will be excessively small, reducing seizure resistance at high temperatures and reducing thermal conductivity, so it should be 1.50% or less. Mn has the effect of promoting the formation and growth of an oxide film, and is added to adjust oxidation resistance depending on the intended use. If it is too large, it lowers the _A1 transformation point, increases annealing hardness, and reduces machinability, so it should be 1.50% or less. Ni is added to improve the adhesion of the oxide film and increase the seizure resistance at high temperatures.
If it is too large, it will lower the _A1 transformation point, increase the annealing hardness, and reduce machinability, so 2.00
% or less. Cr is added to provide appropriate oxidation properties, and also combines with C to form carbides to improve seizure wear resistance, provide appropriate hardenability, and improve the _A1 transformation point. . If the content is too high, the formation and growth of the oxide film will be excessively small, reducing seizure resistance at high temperatures, as well as reducing thermal conductivity and thermal shock resistance. is not obtained, so it should be set at 0.30% or more. Mo and W combine with C to form carbides,
Improves seizure resistance at high temperatures, provides appropriate strength at room and high temperatures, refines grain size, and
_A1 It is added singly or in combination for the purpose of increasing the transformation point. In this case, the strength improving effect of W is relatively greater than that of Mo, and the amounts of W and Mo added are adjusted in consideration of the purpose and usage conditions. If it is too much, it will lower the thermal conductivity and also cause a decrease in toughness, so (1/3W + Mo) is 2.50%.
The following shall apply. Co is an essential and important additive element that increases the adhesion of the oxide film, provides lubrication and heat insulation effects by forming a strong oxide film, and provides excellent seizure and wear resistance at high temperatures. Too much content causes a decrease in toughness, so the content should be 6.00% or less, and if too low, the effect of inclusion cannot be obtained, so the content should be 2.00% or more. Cu increases the fracture resistance and peeling resistance of the formed oxide film layer, and in addition to the adhesion improvement effect of Co, it has an important effect of improving the seizure wear resistance at high temperatures based on the formation of a strong oxide film on the steel of the present invention. It is an additive element. If it is too large, hot plastic workability is reduced and cracks are more likely to occur, so the content should be 5.00% or less. Nb, Zr, and V form carbides with C, increasing wear resistance, refining crystal grains, and improving the _A1 transformation point.
It is added to impart appropriate strength at room temperature to high temperature.
If it is too large, it will form coarse carbides, reduce toughness, and reduce thermal conductivity, so reduce the total amount to 1.00%.
The following shall apply. Rare earth elements such as Ce, Y, La, and Re improve the adhesion, fracture resistance, and peeling properties of the oxide film of the steel of the present invention, and have the effect of greatly improving the seizing wear resistance at high temperatures. It also has the effect of making the casting structure finer and stronger and improving crack resistance. Rare earth elements are added to obtain the above effects, but they do not need to be added in large amounts; too much will lead to an increase in inclusions and reduce toughness, so the amount should be 0.50% or less. The reason for forming an oxide film of 10μ or more is because if the oxide film is less than 10μ, the heat insulation effect is insufficient and the temperature of the tool base material rises, which tends to cause wear and fatigue. As described above, the present invention is a hot cast tool having a strong cast oxidized surface and excellent wear resistance. In other words, an extremely dense and highly adhesive oxide film is formed on the tool surface, with an appropriate balance of carbide distribution, room temperature to high temperature strength, good thermal conductivity, and excellent toughness, resulting in severe wear at high temperatures and rapid heating. It has many effects such as being able to withstand the thermal shock of rapid cooling and providing long life.

Claims (1)

[Claims] 1 C0.15-0.60%, Si1.50% or less, Mn1.50% or less, Ni2.00% or less, Cr0.30-3.50% or less, (1/3W
+Mo) 2.50% or less, Co2.00-6.00%, Cu5.00%
1. A hot-cast tool with excellent wear resistance, characterized in that an oxide film of 10 μm or more is formed on the surface of the tool having an alloy composition consisting of the balance Fe and normal impurities by casting, heat treatment, or a combination of both. 2 C0.15~0.60%, Si1.50% or less, Mn1.50% or less, Ni2.00% or less, Cr0.30~3.50%, (1/3W+
Contains Mo) 2.50% or less, Co2.00 to 6.00%, Cu 5.00% or less, and further contains one or more of Nb, Zr, and V in a total of 1.00% or less, and the balance is Fe and normal impurities. By casting or heat treatment or a combination of both, the tool surface has an alloy composition of
A hot-cast tool with excellent wear resistance, characterized by the formation of an oxide film of 10 μm or more. 3 C0.15~0.60%, Si1.50% or less, Mn1.50% or less, Ni2.00% or less, Cr0.30~3.50%, (1/3W+
Casting or heat treatment, or a combination of both, is applied to the tool surface with an alloy composition containing Mo) 2.50% or less, Co2.00 to 6.00%, Cu 5.00% or less, and rare earth elements 0.50% or less, with the balance consisting of Fe and normal impurities. by
A hot-cast tool with excellent wear resistance, characterized by the formation of an oxide film of 10 μm or more. 4 C0.15~0.60%, Si1.50% or less, Mn1.50% or less, Ni2.00% or less, Cr0.30~3.50%, (1/3W+
Mo) 2.50% or less, Co2.00 to 6.00%, Cu 5.00% or less, and one or more of Nb, Zr, and V in a total of 1.00% or less, and rare earth elements.
A tool with excellent wear resistance characterized by having an oxide film of 10 μm or more formed on the tool surface by casting, heat treatment, or a combination of both, with an alloy composition containing 0.50% or less and the balance consisting of Fe and normal impurities. Hot casting tools.