JP2817364B2 - Heat resistant high toughness steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial application field" The present invention relates to a heat-resistant and high-toughness steel, and more particularly, to an improvement in toughness in a high-strength region.

"Conventional technology" Conventionally, there is a carburizing and quenching method as a method of adapting steel to applications such as gears, fuel injection valves, and cutting tools that require high strength and high toughness in a high-temperature environment. Although it is easy to receive and has high hardness, there are problems such as that it is difficult to obtain sufficient toughness in a high-temperature atmosphere.

Therefore, cooling is generally performed by sending cooling oil to a portion exposed to a high-temperature environment by an oil feed pump or the like.

On the other hand, some tool steels, such as SKH-51 steel conforming to JIS (Japanese Industrial Standards), are said to have relatively high toughness even in high temperature environments and high strength (high hardness) regions. ing.

[Problems to be Solved by the Invention] However, in the method of cooling a heat-generating portion with cooling oil, an oil feed pump or a cooling device for cooling a portion that generates work heat such as frictional heat is required. On the other hand, when the heat resistance of the heat-generating steel material is low, a large amount of cooling oil is supplied and circulated, so that it is necessary to increase the size of the cooling device, which impairs economic efficiency.

When the SKH-51 steel is used, it is difficult to simultaneously satisfy desired hardness and toughness in a high temperature state.

The present invention has been made in view of the above circumstances, and has as its object to provide relatively high toughness in a high temperature and high strength region.

"Means for Solving the Problem" There are proposed two means for solving the problem.

The first means is a heat-resistant high-toughness steel obtained by quenching and high-temperature tempering an alloy material having the following composition.

C: 0.5 to 0.6% by weight Si: 0.4% by weight or less Mn: 0.3 to 0.5% by weight Cr: 3.5 to 4.5% by weight Mo: 4.5 to 5.5% by weight W: 5.0 to 7.0% by weight V: 0.7 to 0.9% by weight Fe: The second means is that the heat treatment condition is a quenching temperature of 1150 ± 50.
° C and a tempering temperature of 530 ± 30 ° C are added to the first means to form a heat-resistant and high-toughness steel.

"Action" In the heat-resistant and high-toughness steel according to the first and second means,
When the Vickers hardness is in the range of Hv 650 to 760, a tendency to significantly improve toughness appears. Also, the quenching temperature is 1100 ~
When the temperature is in the range of 1200 ° C., a dense tissue is maintained.

Example An alloy material having the composition shown in Table 1 was subjected to quenching and high-temperature tempering to produce a target heat-resistant and high-toughness steel.

The heat treatment conditions in this case were set such that the quenching temperature was in the range of 1150 ± 50 ° C. and the tempering temperature was in the range of 530 ± 30 ° C., and the hardness was adjusted by a combination of these.

<Relationship between hardness and toughness> Regarding the obtained heat-resistant and high-toughness steel (example sample),
The relationship between hardness and toughness was determined. The result is shown in FIG. For comparison, the characteristics of a high-speed steel (SKH-51 material, comparative sample) based on JIS standard tool steel are also shown.

As is clear from the comparison between the curve A of the example sample in FIG. 1 and the curve B of the comparative sample, the curve A shows a tendency that the toughness is significantly improved when the Vickers hardness is in the range of Hv650 to 760. As compared with the comparative sample of the curve B, the superiority of the example sample is apparent.

<Relationship between quenching temperature and structure> In the example sample and the comparative sample, the quenching treatment conditions were set to four stages of temperatures of 1100 ° C, 1150 ° C, 1200 ° C,
1250 degrees, 30 minutes, oil-cooled, tempering treatment conditions 525 ℃, 120
FIG. 2 to FIG. 5 show micrographs of the structure in the case where the microstructure was corroded by 5% Pilacle solution after the heat treatment for air cooling. In each of these figures, (A) is an example sample and (B) is a comparative sample. However, FIGS. 2 (A) and (B) show a quenching temperature of 1100 ° C., FIGS. 3 (A) and (B) show a quenching temperature of 1150 ° C., FIGS. 4 (A) and (B) show a quenching temperature of 1200 ° C. (A) and (B) show a quenching temperature of 1250 ° C.

2 to 5, comparing (A) and (B), the sample of the example maintains a dense structure at a quenching temperature of 1100 to 1200 ° C., whereas the sample of the comparative example has a quenching temperature of 1150 to 1200 ° C. At 1200 ° C, the structure tended to become coarse. When the quenching temperature was 1250 ° C., carbides tended to precipitate at the grain boundaries in the comparative sample, and became brittle, and in the example samples, grain boundary cracks appeared.

Therefore, in the example sample, the usefulness is high when the Vickers hardness is in the range of Hv650 to 760, and when the quenching temperature is 1100 to 1200 ° C or less, it can be concluded that the dense structure is maintained. .

<Relationship Between Ambient Temperature and Hardness> FIG. 6 shows the temperature-hardness reduction characteristics of the example sample and the comparative sample.
It is a measure of the decrease in hardness (MHV500) at ° C. As shown in FIG. 6, the hardness at room temperature of 20 ° C. is standard (0).
In this case, the hardness tends to decrease as the temperature increases, but it was confirmed that practically sufficient hardness was maintained in the example sample (A) up to near the tempering temperature. Moreover, in the comparative sample (B), a tendency that the decrease in hardness is relatively large is recognized.

[Effects of the Invention] As described above, the heat-resistant and high-toughness steel according to the present invention has a composition of medium carbon-4% chromium-5% molybdenum-6% tungsten-0.8%, and performs appropriate quenching and tempering. Thereby, when the hardness is in the range of Hv650 to 760, the toughness is higher than that of the conventional tool steel, and the temperature and toughness in a high-temperature atmosphere can be maintained.

As described above, it is suitable for equipment that has a friction and sliding surface and is easily heated to high temperature. This provides excellent effects such as simplification of the device.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between hardness and toughness, together with characteristics of a heat-resistant high-toughness steel according to the present invention and a high-speed steel for comparison. FIG. 2 (A) is a photomicrograph of the metallographic structure when the steel material of the example sample treated at a quenching temperature of 1100 ° C. is corroded. FIG. 2 (B) shows a micrograph of the metal structure of a comparative sample treated at a quenching temperature of 1100 ° C. when the steel material is corroded. FIG. 3 (A) is a photomicrograph of the metallographic structure when the steel material of the example sample treated at a quenching temperature of 1150 ° C. is corroded. FIG. 3 (B) is a photomicrograph of the metal structure of a comparative sample treated at a quenching temperature of 1150 ° C. when the steel is corroded. FIG. 4 (A) is a photomicrograph of the metallographic structure when the steel material of the example sample treated at a quenching temperature of 1200 ° C. was corroded. FIG. 4 (B) shows a micrograph of the metal structure of a comparative sample treated at a quenching temperature of 1200 ° C. when the steel material is corroded. FIG. 5 (A) is a photomicrograph of the metallographic structure when the steel material of the example sample treated at a quenching temperature of 1250 ° C. was corroded. FIG. 5 (B) is a photomicrograph of the metal structure of a comparative sample treated at a quenching temperature of 1250 ° C. when the steel is corroded. FIG. 6 is a characteristic diagram showing the relationship between the temperature and the decrease in hardness in the example sample and the comparative sample.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C22C 38/00-38/60 C21D 6/00 101

Claims (2)

(57) [Claims] 1. A heat-resistant and high-toughness steel obtained by quenching and high-temperature tempering an alloy material having the following composition. C: 0.5 to 0.6% by weight Si: 0.4% by weight or less Mn: 0.3 to 0.5% by weight Cr: 3.5 to 4.5% by weight Mo: 4.5 to 5.5% by weight W: 5.0 to 7.0% by weight V: 0.7 to 0.9% by weight Fe: Rest 2. The heat-resistant and high-toughness steel according to claim 1, wherein the heat treatment conditions are a quenching temperature of 1150 ± 50 ° C. and a tempering temperature of 530 ± 30 ° C.