JPS6215628B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a tool steel for hot working that has improved hot wear resistance, heat crack resistance, and corrosion resistance against molten metal. Conventional tool steel for hot working is 5% Cr.
SKD61, SKD62, 3% Cr-based AISIH10, and the highest grade material AISIH19, SKD4, and SKD5 are used depending on the application. However, the practical performance (life) is not necessarily satisfactory. The present invention has C0.10~0.60%, Si0.10~1.50%,
Mn0.10~2.00%, Cr8.00% or less, V2.50% or less, and W, Mo alone or in combination (1/2W+Mo)
0.30 to 9.00%, and Mg 0.30% or less, the balance is Fe and normal impurities.The base steel is a tool steel for hot working, and depending on the usage conditions, the above components are further added to Ni5.00% or less, or Co8.00% or less. Ni5.00% or less
By using tool steel for hot working with co-added Co 8.00% or less, a dense and adhesive protective oxide film is formed on the mold surface as the mold surface heats up during use, resulting in high temperature baking wear resistance. The purpose of this is to significantly improve heat crack resistance and corrosion resistance against molten metal, etc., and to extend service life.

【table】

[Table] Table 1 shows the chemical composition of the inventive steel and conventional steel, and Table 2 shows the heat treatment conditions (target hardness H _R
C45) and the seizure critical load in the high temperature seizure wear test.

【table】

[Table] The sample is a cylindrical sample that has been oxidized at 620℃ in advance, and the maximum load without causing seizure ( The critical load for seizure of each component system A', C', E', F' of conventional steel was determined as 100, and the improvement effect of the critical seizure load of the invention steel for each component system was expressed as an index. It is something. From Tables 1 and 2, each component system (SKD61 system, AISIH10 system, AISIH19 system, 3Ni-3Mo
As is clear from the effect of Mg content in the steel system), the steel of the present invention clearly has a higher seizure critical load than the conventional steel. This is due to the protective and lubricating effects of the dense and hard-to-peel oxide film formed on the surface of the steel sample of the present invention by the above-mentioned oxidation treatment. Table 3 shows the heat crack resistance of the steel of the present invention, and it can be seen that the steel has better heat crack resistance than conventional steel. The heat treatment conditions and hardness are the same as those in Table 2.

[Table] (Test piece 14φ x 15, heated in lead at 700℃ x 15 seconds →
(Immersion in a water bath at 20°C, repeated 1500 times) This is due to the surface protection and heat insulation effect of the dense oxide film formed on the surface of the steel sample of the present invention, which is difficult to peel off. The reasons for limiting the chemical composition of the steel of the present invention will be described. C is the hardenability of the steel of the present invention, the quenching and tempering method;
Added to maintain high-temperature hardness and to form carbides by combining with carbide-forming elements such as W, Mo, V, and Cr to provide fine grain size, wear resistance, temper softening resistance, and high-temperature strength. If the amount is too high, the toughness will decrease, so the content should be set to 0.60% or less, and if it is too low, the effect of the above addition cannot be obtained, so the content should be set to 0.10% or more. Si is added to strengthen the matrix of the steel of the present invention and maintain appropriate oxidation resistance. If it is too large, it will excessively increase oxidation resistance, hinder the formation of a protective oxide film, reduce thermal conductivity, and lead to a decrease in toughness, so it should be 1.50% or less, and the lower limit is possible in general steelmaking work. The value shall be 0.10% or more. Mn is added to maintain the hardenability of the steel of the present invention, and if it is too large, it will lower the _A1 transformation point.
Since it increases annealing hardness and reduces machinability, the upper limit is set at 2.00%, and the lower limit is set at 0.10% or more as a value that is possible in general steelmaking operations. Ni is added to increase the toughness and hardenability of the steel of the present invention. If it is too large, it will lower the _A1 transformation point, excessively increase the annealing hardness, and reduce machinability.
5.00% or less. The setting of the Cr content is to improve tempering softening resistance, high temperature strength, and provide appropriate oxide film properties.
Wear resistance improvement effect by forming carbide,
_A1 This is more important than the effect of improving the transformation point and the effect of improving hardenability. If it is too high, it will suppress the early formation of the oxide film, making it difficult to form the oxide film that provides the lubricating and heat-insulating properties of the steel of the present invention, and reducing the tempering softening resistance and high-temperature strength, so it should be 8.00% or less. . Mo and W are added to form carbides to provide wear resistance, and to precipitate fine carbides during tempering to increase temper softening resistance and high-temperature strength. Mo and W are added for the above reasons. If too much, they will form coarse carbides and reduce toughness, so the upper limit is set at (1/2W + Mo) 9.00%, and if too little, the effect of addition will not be obtained. Must be 0.30% or more. V precipitates fine carbides during tempering, increases tempering softening resistance, and improves high-temperature strength.
It also forms highly hard carbides, providing wear resistance and seizure resistance at high temperatures, and improves toughness by making crystal grains finer and raises the _A1 transformation point.
It is added to improve heat crack resistance. If it is too large, coarse carbides will be formed, leading to a decrease in toughness and processability, so the content should be 2.50% or less. Like Mg, the addition of Co generates a dense protective oxide film as the temperature rises during use, which has the effect of improving seizure and wear resistance at high temperatures. Furthermore, an increase in the content brings about the effect of increasing high temperature strength. Co is added to obtain the above effects, but if it is too large, it will lead to a decrease in toughness and is not practical, so it should be kept at 8.00% or less. Mg is an essential and important additive element for forming the characteristics of the steel of the present invention. In other words, Mg addition forms a dense protective, lubricating, and insulating oxide film on the surface as the temperature rises during use, improving seizure resistance at high temperatures, as well as improving heat cracking resistance and corrosion resistance against molten metal. It is something. 0.30% as too much will reduce the cleanliness of the steel
The following shall apply. As described above, the addition of Mg allows the steel of the present invention to form a protective, heat insulating, and oxide film that is dense and difficult to peel off during use, and significantly improves seizure and wear resistance at high temperatures, as well as heat crack resistance and Improves corrosion resistance against molten metal,
It has effects such as providing excellent usability.

Claims (1)

[Claims] 1 C0.10~0.60%, Si0.10~1.50%, Mn0.10~
2.00%, Cr8.00% or less, V2.50% or less and W,
Mo alone or in combination (1/2W + Mo) 0.30-9.00%
In addition, hot working tool steel consisting of 0.30% Mg or less with the balance Fe and normal impurities. 2 C0.10~0.60%, Si0.10~1.50%, Mn0.10~
2.00%, Ni5.00% or less, Cr8.00% or less, V2.50%
The following and W, Mo alone or in combination (1/2W +
Hot working tool steel consisting of Mo) 0.30~9.00% and Mg0.30% or less balance Fe and normal impurities. 3 C0.10~0.60%, Si0.10~1.50%, Mn0.10~
2.00%, Cr8.00% or less, V2.50% or less, Co8.00%
The following and W, Mo alone or in combination (1/2W +
Hot working tool steel consisting of Mo) 0.30~9.00% and Mg0.30% or less balance Fe and normal impurities. 4 C0.10~0.60%, Si0.10~1.50%, Mn0.10~
2.00%, Ni5.00% or less, Cr8.00% or less, V2.50%
The following is a tool steel for hot working tools consisting of Co8.00 or less, W, Mo alone or in combination (1/2W + Mo) 0.30 to 9.00%, and Mg 0.30% or less the balance Fe and normal impurities.