JPH03153841A - Low alloy high speed tool steel having high hardness - Google Patents

Abstract

PURPOSE:To manufacture the low alloy high speed tool steel having high hardness and excellent in hardenability and grindability by incorporating specified ratios of C, Si, Mn, Cr, W, Mo and V into Fe. CONSTITUTION:A low alloy high speed tool steel contg., by weight, 0.95 to 1.20% C, <=1.5% Si, <=1.0% Mn, 4.6 to 7.5% Cr, <=7.0% W, <=6% Mo (where the total content of W+2Mo is regulated to 9 to 13%) and 0.5 to 1.0% V, furthermore contg., at need, <=0.25% Nb and the balance Fe with inevitable impurities is prepd. In this way, by validly operating the synergetic effect of C and Cr, the low alloy high speed tool steel having about >=65 HRC high hardness and excellent in hardenability and grindability can be obtd. and is useful for cold rolling rolls, tools for cold working or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a high-hardness, low-alloy, high-speed tool steel used primarily for cold rolling rolls, cold working tools, and the like. [Prior art] As a general type of low-alloy high-speed tool steel,
0.65% C1 disclosed in Publication No. 0-10808
0.3%Si, 0.4%Cr, 4.2%W, 4%Mo,
High-speed tool steel consisting of 1.5%
0.65% C, 1.4% Si disclosed in Publication No. 48,
High-speed tool steels made of 4% Cr, 2.8% Mo, and 1.8% ■ are known, but in these known examples,
Although the toughness is excellent, the hardness after heat treatment is HRC60~
I can only get about 62. Furthermore, as a low alloy high speed tool steel that can obtain high hardness,
．． 95%G, 4%Cr%1.7%W, 5%Mo, 1.
Based on high-speed tool steel of 2%■ and the above components as disclosed in Japanese Patent Publication No. 8503/1983, the C/V ratio is increased to 0.70-0.94, and the CO is further increased to 1.0. ~
High-speed tool steel is also known, which has an extremely hard martensitic base steel and improved ability to maintain hardness at high temperatures by adding 6.0% of C. Moreover, as a low alloy high speed tool steel that can obtain a high hardness of around FIRC66, one containing the following main alloying elements is known. This steel has 0.75%C10,3%Si,
4%Cr, 1%W, 5%MO10.9%V, 8%Go.The characteristics of this steel are that ΔC is about ±0 and G
The reason is that the hardness of the matrix is increased by increasing the O content to 8%. In addition, Japanese Patent Publication No. 1-5100 and Japanese Patent Application Publication No. 1-201442
Materials with reduced residual carbide content and improved toughness are shown in No. [Problem to be solved by the invention] In the field of cold rolling rolls and cold working tools,
When a high degree of wear resistance is required, a tool material that can obtain a heat treatment hardness of I (RC65 or higher) is required.In addition, the target tool is generally large in diameter, so it has good hardenability and is resistant to deformation. In order to prevent this, the material must be able to obtain hardness by heating at as low a temperature as possible.Furthermore, the material must have excellent grindability characteristics comparable to 5KDII.And above all, it must be a material that is inexpensive and highly economical. This is important when using it in place of the conventional 5KDII class cold work tool steel.
The general low-alloy high-speed tool steel disclosed in Publication No. 49148 and the like can only achieve a maximum hardness of 1 (around RC63), and cannot satisfy the purpose of obtaining a high hardness of HRC65 or higher. 4%C as known from the publication No.
r-1.7%W-5%Mo as the basic component and C/V ratio of 0.
Although steel with a hardness increased to 7-0.94 has high hardness, its toughness is significantly reduced and chipping and cracking are likely to occur. Furthermore, the grindability is not sufficient, and since it contains GO, it is also unsatisfactory from an economic standpoint. The main alloying elements are 0.75%C14%Cr, 1%W,
Steel consisting of 5% Mo, 0.9% V, 8% CO has HR
Although a hardness of around C66 can be obtained, since it contains a large amount of Co, it is not economical. In addition, in Japanese Patent Publication No. 1-51 (No. 10) and Japanese Patent Application Publication No. 1-201442, the hardness level of the material is HRC.
It is around 131 to 63, which is not sufficient for fields where higher hardness and wear resistance are required. In view of the above-mentioned problems, the object of the present invention is to optimize the component balance and the amount of carbide, thereby improving f(RC) after heat treatment.
The object of the present invention is to provide a high-hardness, low-alloy, high-speed tool steel that has a high hardness of 65 or higher, has excellent hardenability and grindability, and is highly economical. [Means for Solving the Problems] The present invention contains, in weight%, C; 0.95 to 1.20%, Si
; 1.5% or less, Mn; 1.0% or less, Cr; 4.
6-7.5%, W: 7.0% or less, MO: 6% or less (however, W+2MO; 9-13%), V, 0.5-1.0%
, and further Nb as required; 0.26% or less, balance F
It is a high-hardness, low-alloy, high-speed tool steel consisting of E and unavoidable impurities. In the present invention, the contents of W, Mo, and V, which are highly economical or expensive alloying elements, are kept to the necessary minimum, and Go and NL are basically not added to achieve high hardness of HRC65 or higher. In order to obtain this, the synergistic effect of C and Cr was effectively used. The synergistic effect of C and Or also has the effect of lowering the quenching heating temperature and increasing the hardenability. In order to maintain grindability comparable to 5KDII, this was achieved by suppressing the content of ■ as much as possible. However, if the content of ■ is simply reduced, the crystal grains become abnormally coarse and the toughness deteriorates. In the present invention, this phenomenon could be avoided by lowering the quenching heating temperature due to the synergistic effect of C and Cr. [Operation] The reason for the numerical limitation of the present invention will be described in detail below. C is 0.95-1.20%. C is one of the most important elements in the present invention. C is Cr
, W, Mo, and V in amounts of carbide-forming elements,
A carbide is formed, and the remainder is dissolved in the matrix to produce hard martensite. In the present invention, the C content is made higher than that of conventional low alloy high speed tool steel, and the Cr content described later is
By increasing the content, a large amount of M, C, type carbide is formed. As a result, a sufficient amount of C and alloying elements can be solid-dissolved in the matrix even by austenitization at a relatively low temperature, and the desired high hardness of HRC 65 or higher can be achieved. 0
．． If it is 95% unstructured, this effect is small, and if it exceeds 1.2%, a large amount of retained austenite will remain, making it difficult to obtain high hardness. Therefore, the C content is 0.
It was limited to 95-1.20%. Si is contained in steel as a deoxidizing agent, but it also forms a solid solution in the matrix and has the effect of increasing the hardness of the matrix. However, if added in excess of 1.5%, it will increase central segregation of the steel and reduce toughness, so the upper limit should be set at 1.5%.
And so. Like Mn+J5i, it is added as a deoxidizing agent, but 1.0
If added in excess of 1.0%, the toughness deteriorates, so the content was set at 1.0% or less. Cr combines with C to form M, , C1 type carbide. The advantage of the low-alloy high-speed steel of the present invention is that it is highly economical and can have high hardness due to its high C-high Cr content. It also has the effect of increasing hardenability, and
．． If the Cr content is less than 6%, the effect is insufficient, and if it exceeds 7.5%, segregation becomes significant and toughness decreases.
It was set at 6 to 7.5%. W is 7.0% or less, MO is 6.0% or less, and W+2M
. 9 to 13%. W and MO combine with C to form a hard carbide and provide wear resistance. If the amount of W+2Mo is less than 9%, sufficient heat treatment hardness and wear resistance cannot be obtained, and if it exceeds 13%, problems will arise in terms of raw material cost and toughness, so it is set to 9 to 13%. V combines with C to form extremely hard carbides, which improves wear resistance and is effective in refining crystal grains, and in order to exhibit these effects, at least 0.5% or more is required. However, if the amount is too high, the grindability will deteriorate. In the present invention, in order to provide good grindability equivalent to 5KDII, the content (2) is limited to 0.5 to 1.0%. A small amount of Nb has the same effect on grain refinement as V and improves toughness, so it is desirable to contain it in an amount of 0.26% or less. [Example] Next, the present invention will be described in more detail based on an example. Table 1 10 kg of high-speed tool steel with the composition shown in Table 1 was melted in a high-frequency melting furnace, hot-worked into a 18 mm square material, annealed, and further parallel to the forging direction. 5Mφx75
A bending test piece of mmQ was manufactured. Note that No. 6 in the table is 5KDII, which is a conventional steel. FIG. 1 is a diagram showing the relationship between quenching heating temperature and austenite crystal grain size. In addition, the crystal grain size was determined by the intercept method for 6 invention steels No., 1, No. 2°, No. 3 and 1.
Sufficiently fine crystal grains can be obtained at a quenching temperature of 140°C or lower. When quenched at 1160°C, the grain size number is 9 to 10,
Even under these conditions, crystal grains with no practical problems were obtained. In the present invention @ No. 4 and No. 5, Nb was added, and compared to No. 1 to No. 3 to which Nb was not added, the crystal grains were significantly finer, and the effect of Nb addition was recognized. FIG. 2 is a diagram showing quenching-tempering hardness. Present invention #1 No. 1. No, 2. No, 3. No
,4. Both No. 5 and No. 5 obtained a maximum tempering hardness of HRC 65 or higher at a quenching temperature of 1120° C. or higher, thus satisfying the purpose of the invention. However, no. No. 4 has a characteristic that the quenching hardness and the tempering hardness at 500 to 560° C. are significantly lower than the others. This is due to the presence of a large amount of retained austenite, and the carbon content is
No. 4 composition is close to the upper limit. Note that the conventional steel No. 6, which is 5KDII, cannot satisfy the hardness of HRC65 or higher. FIG. 3 is a diagram showing hardenability. The horizontal axis of the figure represents the time (H, T, T,) required for cooling to half the quenching temperature (570°C in this case), and the vertical axis represents the quenching and tempering hardness (1
140°C-560°C). In the case of large tools to which the present invention is applied, it has been found from experience that the half-cooling time is within 10 m1n. For example, in the case of a roll of 70φ×1200Q, the half-cooling time is 4 to 5 m1n. From this figure, the material of the present invention achieves the target of HRC 65 or higher even under relatively slow cooling conditions of 5 to lomin. Although the hardness change of 5KDII, which is a conventional steel, is illustrated, the hardness of the steel of the present invention is much higher than that of 5KDII under any cooling conditions. [Effects of the Invention] The steel of the present invention has higher hardness than conventional cold work tool steels, has excellent hardenability and grindability, and is highly effective industrially.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between quenching heating temperature and austenite grain size, Figure 2 is a diagram showing quenching-tempering hardness, and Figure 3 is a diagram showing the relationship between quenching heating temperature and austenite grain size.
The figure shows hardenability. Preparation of drawings Figure 2-a--1120 + 1140 h1160 -<To-1180 Thmperature (-c) Temperature (''c) Tempera
ture ("C) Drawing 1) Figure 2 + D, l' Figure 3 5 10 15 H, T, T, (min) 0 Procedure amendment procedure (method) 1. Indication of incident 1999 patent application No. 292890 2, Title of invention: High hardness, low alloy, high speed tool steel 3, Patent related to the amended person case

Claims (1)

[Claims] 1% by weight, C; 0.95-1.20%, Si; 1.
5% or less, Mn; 1.0% or less, Cr; 4.6 to 7.5
%, W; 7.0% or less, Mo; 6% or less (however, W+2
Mo; 9-13%), V; 0.5-1.0%, balance Fe
and high-hardness, low-alloy, high-speed tool steel consisting of unavoidable impurities. 2% by weight, C; 0.95-1.20%, Si; 1.
5% or less, Mn; 1.0% or less, Cr; 4.6 to 7.5
%, W; 7.0% or less, Mo; 6% or less (however, W+2
Mo; 9-13%), V; 0.5-1.0%, Nb; 0
．． A high hardness, low alloy, high speed tool steel consisting of 26% or less, the balance being Fe and unavoidable impurities.