JPH0146582B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a high-performance, high-hardness steel for plastic molds, and in particular, a high-performance, high-hardness, high-mirror finish steel for plastic molds characterized by improved performance required for plastic mold steel, such as mirror finish. It's about steel. With the remarkable development of the plastics industry in recent years. Various resins have come to be used, but
Among them, many composite resins containing additives such as glass fiber are also used. On the other hand, some molded products require extremely high dimensional accuracy. Plastic molds for these applications are wear resistant,
High-hardness plastic mold steel with high pressure resistance is used. Conventionally, the steel for this high hardness plastic mold is
SKD11 is widely used, but problems during mold manufacturing include machinability during die carving, grindability during mold finishing, weld cracking during mold repair, etc.
The drawback was that pinholes remained on the finished surface after mirror polishing and were transferred to plastic products. For this reason, it was inconvenient to use SKD11 in molds for transparent products where mirror finish is particularly important.
In addition, when manufacturing molds with complex shapes, there is a strong demand for materials that are less susceptible to deformation during heat treatment. Furthermore, corrosion resistance against corrosion caused by plastics is required. As a result of various studies, the inventors of the present invention found that pinholes on the finished surface after mirror polishing are due to the large size of SKD11.
It was found that this was caused by M ₇ C ₃ carbide, and the problem with the finished surface was solved by reducing the amount of this carbide to an appropriate amount. At the same time, by controlling the balance of alloying elements in the base to an appropriate level, heat treatment deformation is extremely minimized, resulting in high-performance, high-hardness, high-mirror finish plastic molds with significantly improved machinability, grindability, weldability, and corrosion resistance. Obtained steel for use. That is, its chemical composition is C: 0.55 to 0.55% by weight.
1.2%, Si: 3% or less, Mn: 3% or less, Cr: 6.5
The basic composition is ~9.5%, Mo: 0.1~1.5%, V: 0.01~1.0%, and B: 0.0005~0.010 as necessary.
%, REM: one or more of 0.0005 to 0.300%, and S:
0.20% or less, Pb: 0.40% or less, Se: 0.30% or less,
Bi: 0.50% or less, Te: 0.30% or less, Ca: 0.0002~
One or more types of 0.010%, Ni: 1.2 or less, Cu: 2.0%
Below, W: 2% or less, Co: 2% or less, Nb: 2%
It contains one or more of the following, with the remainder consisting of Fe and unavoidable impurities. Next, the reason for limiting the composition (weight %) of the steel of the present invention will be described. C: 0.55 to 1.2% In the present invention, C increases the hardness of martensite and improves the finish of the polished surface after mirror polishing, but if C is less than 0.55%, compressive strength and wear resistance are insufficient. Moreover, if C exceeds 1.2%, the amount of giant carbides increases and machinability and grindability deteriorate, so it was set at 0.55 to 1.2%. Si: 3% or less Si is added to improve the tempering resistance of martensite. However, if it is too high, the forging properties deteriorate, so it was set at 3% or less. Mn: 3% or less Mn improves hardenability, but when added in large amounts, residual austenite remains and reduces hardness, so the maximum content is 3%. Cr: 6.5 to 9.5% Cr dissolves into the matrix during hardening and improves hardenability, forms chromium carbide, improves wear resistance, and further improves corrosion resistance and maintains the specularity of the finished surface for a long time. It maintains well over time, but if the amount added is too large, it will form giant carbides and reduce machinability.
In addition to reducing grindability and weld cracking resistance, it also deteriorates specularity, so it was set at 6.5 to 9.5%. Mo: 0.1 to 1.5% Mo is an element that dissolves in the matrix during quenching and forms carbides, improving hardenability and tempering resistance, but if it is added in too much, hot workability and toughness decrease. The content was set at 0.1 to 1.5%. V: 0.01 to 1.0% V is effective in preventing coarsening of austenite crystal grains in the matrix and improving wear resistance, but it reduces hot workability and grindability, so 0.01
~1.0%. B: 0.0005 to 0.010% B is an element that significantly improves hardenability and strength when added in a very small amount, and in order to effectively exhibit this effect, it must be contained in an amount of at least 0.0005% or more. However, if it is contained in a large amount, the forging properties will be significantly deteriorated due to the formation of large amounts of borides.
Limited to 0.010% or less. REM: 0.0005~0.300% Se, Y, La, Ce, Nd, Sm and others
REM (rare earth elements) has a great effect in suppressing the precipitation of pro-eutectoid carbides at austenite grain boundaries, pearlite transformation, and bainite transformation during the cooling process during quenching, and significantly improves hardenability, toughness, and grindability. . In order to effectively exhibit the above effects, it is necessary to contain at least 0.0005% or more of one or more types of REM in total. However, if added in large amounts, a large amount of MC-type huge carbides will be formed during solidification, significantly deteriorating forgeability, so the total amount of the above elements was limited to 0.300% or less. Machinability-improving elements (S, Pb, Te, Se, Bi, Ca) Addition of the above components is effective in improving machinability. However, if added in large amounts, hot workability
To reduce toughness, S: 0.20% or less, Pb:
Appropriate values are 0.40% or less, Se: 0.30% or less, Te: 0.30% or less, Bi: 0.50% or less, and Ca: 0.0002 to 0.010%. High wear-resistant elements (Ni, Cu, Co, W, Nb) To improve wear resistance, strengthen the base,
Addition of the above-mentioned components that form carbides is effective.
However, if added in large amounts, hot workability and toughness will decrease, so Ni: 1.2% or less, Cu: 2.0% or less,
Co: 2% or less, W: 2% or less, and Nb: 2% or less are suitable. Next, the performance of the steel of the present invention will be explained with reference to Examples. Example Table 1 shows the chemical components of the test materials used in this example.

【table】

[Table] Figure 1 shows the tempering hardness curves of the steel of the present invention, SKD11, and SKD12. The steel of the present invention is tempered at around 500°C and has a hardness close to SKD11.
Note that the steel of the present invention (6) to which REM is added has good hardenability, and therefore has high hardenability. The above test piece is
After heating to 1025℃ x 20min (SKD12: 960℃ x 20min), it was embedded in a 100mm steel case and cooled in air. The measured values of heat treatment deformation and heat treatment dimensional change rate are as shown in FIG. 2, and the heat treatment deformation of the steel of the present invention is extremely small. This is probably due to the good balance of components of the steel of the present invention, such as C, Cr, Mo, and V.
A 60 mm C-type (navy) test piece was used to measure the amount of heat treatment deformation, and a 15 x 50 mm test piece was used to measure the heat treatment dimensional change rate, and both were oil-cooled during quenching. The measured compressive strength is as shown in Figure 3.
It can be seen that the steel of the present invention has a compressive strength equal to or higher than that of SKD11. Figure 4 shows the CCT curves of the invention steel and SKD11.
The austenitizing conditions during the test were 1025℃×
It is 15min. It can be seen that the steel of the present invention has pearlite and bainite transformation curves on the longer side than SKD11, and has excellent hardenability. Next, machinability tests and grindability tests were conducted on the steel of the present invention and SKD11 (each sample was quenched and tempered to a H _R C60±
Adjusted to hardness of 0.5. ) and are shown in Figures 5 and 6, respectively. Compared to SKD11, the steel of the present invention has
It was found that both machinability and grindability were excellent. It can be seen that the present invention steel (4) has improved machinability due to the addition of free-cutting elements, and the present invention steel (6) has improved grindability due to the addition of REM. The cutting conditions for the machinability test above are shown in Table 2.

[Table] Figure 7 shows the pit condition on the surface after final polishing (polished with 6μ and 1μ diamonds). As is clear from the figure, it can be seen that the number of point-like voids on the polished surface of the steel of the present invention is extremely small. Therefore, the polished surface of the steel of the present invention has an extremely excellent mirror finish. Figure 8 shows the results of a corrosion resistance test using 5% HCl (test temperature: 50°C). As is clear from the figure, the corrosion loss of the steel of the present invention is small, making it suitable for steel for plastic molds that require corrosion resistance. As explained above, the high-hardness steel for plastic molds of the present invention has a good mirror finish, a small amount of deformation due to heat treatment, and has excellent performance as a steel for plastic molds in terms of machinability, grindability, toughness, and weldability. It is a type of steel.

[Brief explanation of drawings]

Figures 1 to 8 show the test results comparing various properties of the inventive steel and comparative steel, respectively. Figure 1 is the tempering hardness curve, and Figure 2 is the amount of heat treatment deformation and heat treatment dimensional change rate. , Figure 3 shows compressive strength, Figure 4 shows CCT curve, Figure 5 shows machinability, Figure 6 shows machinability, and Figure 7 shows machinability.
The figure shows the number of pits after final polishing, and Figure 8 shows the corrosion resistance against HCl.

Claims (1)

[Claims] 1% by weight, C: 0.55 to 1.2%, Si: 3% or less,
Mn: 3% or less, Cr: 6.5-9.5%, Mo: 0.1-1.5
%, V: 0.01 to 1.0%, the balance being Fe and unavoidable impurities. High hardness and high mirror finish plastic mold steel. 2% by weight, C: 0.55 to 1.2%, Si: 3% or less,
Mn: 3% or less, Cr: 6.5-9.5%, Mo: 0.1-1.5
%, V: 0.01 to 1.0% as the basic composition, containing one or more of B: 0.0005 to 0.010%, REM: 0.0005 to 0.300%, and the balance consisting of Fe and inevitable impurities. High hardness and high mirror finish. Steel for plastic molds. 3 In weight%, C: 0.55 to 1.2%, Si: 3% or less,
Mn: 3% or less, Cr: 6.5-9.5%, Mo: 0.1-1.5
%, V: 0.01-1.0% as the basic composition, S: 0.20% or less, Pb: 0.40% or less, Se: 0.30% or less, Bi: 0.50% or less, Te: 0.30% or less, Ca:
A steel for plastic molds with high hardness and a high mirror finish, containing 0.0002 to 0.010% of one or more elements, with the balance being Fe and unavoidable impurities. 4 In weight%, C: 0.55 to 1.2%, Si: 3% or less,
Mn: 3% or less, Cr: 6.5-9.5%, Mo: 0.1-1.5
%, V: 0.01~1.0% is the basic composition, and this
Ni: 1.2% or less, Cu: 2.0% or less, W: 2% or less,
A steel for plastic molds with high hardness and a high mirror finish, containing one or more of Co: 2% or less, Nb: 2% or less, and the balance being Fe and unavoidable impurities. 5% by weight, C: 0.55 to 1.2%, Si: 3% or less,
Mn: 3% or less, Cr: 6.5-9.5%, Mo: 0.1-1.5
%, V: 0.01 to 1.0% as the basic composition, and one or more of B: 0.0005 to 0.010%, REM: 0.0005 to 0.300%, S: 0.20% or less, Pb: 0.40 or less,
Contains one or more of Se: 0.30% or less, Bi: 0.50% or less, Te: 0.30% or less, Ca: 0.0002 to 0.010%,
Steel for plastic molds with high hardness and mirror finish, consisting of the balance Fe and unavoidable impurities. 6 Weight%: C: 0.55 to 1.2%, Si: 3% or less,
Mn: 3% or less, Cr: 6.5-9.5%, Mo: 0.1-1.5
%, V: 0.01-1.0% as the basic composition, and one or more of B: 0.0005-0.010%, REM: 0.0005-0.300%, Ni: 1.2% or less, Cu: 2.0% or less,
A high-hardness, high-mirror finish plastic mold steel containing one or more of W: 2% or less, Co: 2% or less, and Nb: 2% or less, with the balance being Fe and unavoidable impurities. 7 In weight%, C: 0.55 to 1.2%, Si: 3% or less,
Mn: 3% or less, Cr: 6.5-9.5%, Mo: 0.1-1.5
%, V: 0.01-1.0% as the basic composition, S: 0.20% or less, Pb: 0.40% or less, Se: 0.30% or less, Bi: 0.50% or less, Te: 0.30% or less, Ca:
One or more types of 0.0002 to 0.010%, Ni: 1.2% or less,
Cu: 2.0% or less, W: 2% or less, Co: 2% or less,
A steel for plastic molds with high hardness and a high mirror finish, containing one or more types of Nb: 2% or less, with the balance consisting of Fe and unavoidable impurities. 8% by weight, C: 0.55 to 1.2%, Si: 3% or less,
Mn: 3% or less, Cr: 6.5-9.5%, Mo: 0.1-1.5
%, V: 0.01-1.0% as the basic composition, and one or more of B: 0.0005-0.010%, REM: 0.0005-0.300%, S: 0.20% or less, Pb: 0.40% or less,
One or more of Se: 0.30% or less, Bi: 0.50% or less, Te: 0.30% or less, Ca: 0.0002 to 0.010%, and
Ni: 1.2% or less, Cu: 2.0% or less, W: 2% or less,
A steel for plastic molds with high hardness and a high mirror finish, containing one or more of Co: 2% or less, Nb: 2% or less, and the balance being Fe and unavoidable impurities.