JPH0571658B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a tool steel used for tools such as veneer knives, shear blades, and saw blades. [Conventional technology] Conventionally, JIS.SK5, SK6,
SKS5, SKS51 or improved steels are used. [Problems to be Solved by the Invention] When the above-mentioned tools are used in low-temperature environments such as in cold regions, the incidence of chipping, bending, cracking, etc. increases, resulting in a problem of lowering work efficiency. For example, in the case of woodworking knives, the tool material itself becomes brittle due to low-temperature brittleness, and at the same time, the moisture contained in the wood freezes, making it hard and difficult to cut, leading to a synergistic increase in edge chipping. It is being The object of the present invention is to solve the above problems by providing a tool material with increased toughness at low temperatures. [Means for solving the problem] The present invention has a weight ratio of 0.65 to 0.85% C and 2% Si.
Below, Mn 2% or less, Ni 0.5-3.5%, Cr 0.45-
4.0%, Mo 0.2~1.8%, V0.05~1.2%, and if necessary, W1.5 or less, Nb, Ta, Ti, one or two types under specific selection conditions, total 0.5% or less,
This is a tool steel characterized by containing an appropriate amount of 5% or less Co, with the balance consisting of Fe and impurities. In the present invention, C is an essential element for obtaining the required hardness and strength and at the same time forming fine carbides to improve wear resistance. In order to obtain this effect, a C content of less than 0.65% is insufficient and the object of the present invention is not achieved. On the other hand, if it exceeds 0.85%, huge undissolved carbides appear and reduce toughness.
C was limited to 0.65-0.85%. Desired range is 0.7
~0.8%. Si has the effect of increasing the matrix hardness of tool steel and improving wear resistance, and also has the effect of reducing oxygen in molten steel and increasing toughness and fatigue strength. However, 2
%, the effect not only becomes saturated, but also
Since it has the disadvantage of deteriorating machinability, hot workability, etc., the content of Si is set to 2% or less. Desirable range is 0.9~
It is 1.5%. Like Ni, Mn has the effect of increasing hardenability and stabilizing retained austenite to improve low-temperature brittleness. Also, like Si, it is an important element as a deoxidizing agent, but if it exceeds 2%, its effect is saturated, and conversely, the amount of retained austenite increases and hardening becomes low, so Mn is limited to 2% or less. did.
The preferred range is 0.25-0.55%. Ni is one of the particularly important constituent elements in the present invention. The cause of embrittlement of tool steel at low temperatures is that austenite remaining during quenching becomes unstable in a low-temperature atmosphere and transforms into brittle martensite. Ni stabilizes this retained austenite,
It has the effect of suppressing the amount of martensitic transformation even at low temperatures. If Ni is less than 0.5%, this effect will be small, while if it exceeds 3.5%, the amount of retained austenite will increase extremely and the hardness will decrease, so the Ni content was limited to 0.5 to 3.5%. Desired range is 0.7~
It is 2.5%. Cr is also one of the important constituent elements. Cr improves hardenability and at the same time combines with C to form fine and stable carbides, improving wear resistance. Furthermore, the toughness of the matrix is improved by the uniform dispersion of stable fine carbides and the refinement of austenite crystal grains. If Cr is less than 0.45%, the above effects will be small;
Moreover, if it exceeds 4%, coarsening of carbides will occur, so Cr is limited to 0.45 to 4.0%. The preferred range is 0.55-1.5%. Mo has the same effect as Cr, but is an important constituent element that is more stable than Cr and forms fine carbides. Therefore, due to the synergistic effect with Cr contained at the same time, the toughness of the matrix is significantly increased. Further, in the case of tools used in a low-temperature atmosphere, it is preferable to perform the tempering treatment after quenching at as high a temperature as possible in order to stabilize retained austenite. Mo has tempering resistance (reduces the amount of softening caused by tempering)
Mo is an important element because it has a great effect of strengthening the If Mo is less than 0.2%, the above effects will be small, and if it exceeds 1.8%, the effect will not only be saturated, but also have negative effects such as coarsening of carbides and making the material expensive. Limited. The preferred range is 0.5-1.0%. V also has the same effect as Mo, but it is an important element that shows a strong effect even in small amounts, especially in refining austenite grains and resisting wear. If it is less than 0.05%, this effect will be small, while if it exceeds 1.2%, it will occur due to the crystallization of giant carbides, so V will be 0.05 to 1.2%.
limited to. The preferred range is 0.2-0.6%. Although the object of the present invention can be achieved with the above elemental structure, the effects will be enhanced if the following elements are further included. W has the effect of increasing the heat resistance strength of the substrate and forming stable fine carbides to improve wear resistance and toughness. However, even if it exceeds 1.5%, the material becomes expensive and is not economical, so it is limited to 1.5% or less. The desirable range is 0.3-1.0%. Co also increases the heat resistance strength of the substrate and has the effect of reducing tool wear, especially during high-speed cutting. However, 5
If it exceeds 5%, the toughness decreases and it is not economical, so it is limited to 5% or less. The inclusion of Nb, Ta, and Ti forms carbides that are more stable at high temperatures, and in some cases nitrides in some cases, which promotes refinement of austenite grains and further improves toughness. However, if it exceeds 0.5%, giant carbides tend to crystallize, so it was limited to 0.5% or less. Desirable elements and addition amounts are Nb 0.1~
It is 0.3%. In addition, the inclusion of small amounts of B, N, Al, rare earth elements, etc. is also permissible. [Example] Next, the present invention will be explained in more detail with reference to Examples. A total of nine types of test materials having the chemical compositions shown in Table 1 were prepared. Melting was performed in a 10Kg high-frequency induction furnace, and hot forging was performed to obtain a diameter of 20mm. After quenching and tempering, the 10R-C notched pea impact test was carried out at 10
It was carried out at each temperature from ℃ to -30℃, and the toughness value at each temperature was measured. Table 1 shows the above quenching of each sample.
Tempering conditions (margin), hardness at that time (HRC), amount of retained austenite after the above heat treatment (20°C), and amount of retained austenite when the sample is cooled to -30°C and then returned to room temperature (-30°C) are shown together. From this table, it can be seen that the steel of the present invention has a large amount of retained austenite both before and after cooling at a low temperature of -30°C. This is due to the stabilizing effect of retained austenite due to the addition of Ni mentioned above, which suppresses the transformation of retained austenite into brittle martensite. From this,
It is expected that it will show a high impact value both before and after low-temperature treatment. The impact value measurement results are shown in Figure 1. Inventive steel
Nos. 1 to 7 show higher impact values at all test temperatures than conventional steel SKS51 (No. 8) and comparison steel (No. 9), but especially at low temperatures below 0°C. It can be seen that the amount of decrease in impact value is small and the material satisfactorily achieves the object of the present invention. Furthermore, since the steel of the present invention has added Mo and V compared to conventional steel, it is presumed that it has high hardness and high wear resistance despite having a large amount of retained austenite. . Note that No. 4 in Table 1 is the fourth invention of the present application, which corresponds to the embodiment item of claim 6.

[Table] When a steel material with a chemical composition corresponding to No. 4 in Table 1 was manufactured on an industrial scale and delivered to a knife manufacturer for use in plywood knives for cold regions, conventional materials caused problems such as chipping of the blade during the harsh winter months. However, the steel mill has been used continuously without any problems. [Effects of the Invention] According to the present invention, it is possible to prevent the occurrence of chipping, bending, cracking, etc., which have conventionally caused problems when used in low-temperature environments such as cold regions.

[Brief explanation of drawings]

FIG. 1 is a diagram showing Charpy impact values at various temperatures from 10°C to -30°C.

Claims (1)

[Claims] 1. C 0.65 to 0.85%, Si 2% or less by weight,
Mn 2% or less, Ni 0.5-3.5%, Cr 0.45-4.0%,
A tool steel with improved low temperature brittleness characterized by comprising 0.2-1.8% Mo, 0.05-1.2% V, and the balance F and impurities. 2 C 0.65-0.85%, Si 2% or less by weight ratio,
Mn 2% or less, Ni 0.5-3.5%, Cr 0.45-4.0%,
W 1.5% or less, Mo 0.2-1.8%, V 0.05-1.2
%, the balance being Fe and impurities.A tool steel with improved low-temperature brittleness. 3 C 0.65 to 0.85%, Si 2% or less by weight,
Mn 2% or less, Ni 0.5-3.5%, Cr 0.45-4.0%,
Mo 0.2-1.8%, V 0.05-1.2%, Nb alone or Nb and Ti in total 0.5% or less, balance
A tool steel with improved low temperature brittleness characterized by comprising Fe and impurities. 4 C 0.65 to 0.85% by weight, Si 2% or less,
Mn 2% or less, Ni 0.5-3.5%, Cr 0.45-4.0%,
W 1.5% or less, Mo 0.2-1.8%, V 0.05-1.2
%, and one of Nb and Ta at 0.5% or less, with the balance being Fe and impurities.A tool steel with improved low temperature brittleness. 5 C 0.7-0.8%, Si 0.9-1.5% by weight,
Mn 0.25~0.55%, Ni 0.7~2.5%, Cr 0.55~1.5
%, W 0.3~1.0%, Mo 0.5~1.0%, V 0.2~
0.6% Nb, 0.1 to 0.3% Nb, and the balance Fe and impurities. 6 C 0.65 to 0.85% by weight, Si 2% or less,
Mn 2% or less, Ni 0.5-3.5%, Cr 0.45-4.0%,
W 1.5% or less, Mn 0.2-1.8%, V 0.05-1.2
%, Co 5% or less, and a total of 0.5% or less of Zr and Hf, with the balance being Fe and impurities.A tool steel with improved low temperature brittleness.