JPH0459945A - Heat resistant and high toughness steel - Google Patents

Abstract

PURPOSE:To manufacture a steel improved in toughness in a high strength area by subjecting a steel having a specified compsn. in which each content of C, Cr, Mo and W is prescribed to hardening and tempering treatment under specified conditions. CONSTITUTION:An alloy material constituted of, by weight, 0.5 to 0.6% C, <=0.4% Si, 0.3 to 0.5% Mn, 3.5 to 4.5% Cr, 4.5 to 5.5% Mo, 5.0 to 7.0% W, 0.7 to 0.9% V and the balance Fe is treated at 1150+ or -50 deg.C hardening temp. and 530+ or -30 deg.C tempering treatment. In this way, the heat resistant and high toughness steel having higher toughness compared to that of a conventional tool steel in the case its hardness lies in the range of Hv 650 to 760 and maintaining temp. and toughness in a high temp. atmosphere can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to heat-resistant, high-toughness steel, and particularly to improved toughness in a high strength range.

"Conventional technology" Conventionally, gears that require high strength and toughness in high-temperature environments,
Carburizing and quenching is a method for making steel materials suitable for applications such as fuel injection valves and cutting tools, but although it is susceptible to shape limitations and increases hardness, it does not provide sufficient toughness in high-temperature atmospheres. There are some issues such as difficulty.

Therefore, it is common practice to use an oil pump or the like to send cooling oil to the parts exposed to the high-temperature environment to cool them.

On the other hand, some tool steels, such as SKI (-51M) compliant with JIS standards (Japanese Industrial Standards), have relatively high toughness in high-temperature environments and in the high strength (high hardness) range. It is said that

``Problem to be solved by the invention'' However, if the method uses cooling oil to cool the heat generating parts, an oil pump or cooling device is required to cool the parts that generate work heat such as frictional heat. If the heat resistance of the heat-generating steel material is low, it will be necessary to increase the size of the cooling device in order to supply and circulate a large amount of cooling oil, which will impair economic efficiency.

With the 5KH-51 steel, it is difficult to simultaneously satisfy desired hardness and toughness at high temperatures.

The present invention was made in view of the above circumstances, and aims to obtain relatively high toughness in a high temperature and high strength range.

"Means to solve problems" We propose two means to solve this problem.

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

C: 0.5-0.6 wt% Sl, 0.4 wt% or less Mn: 0.3-0.5 wt% Cr: 3
．． 5-L5 Weight % Mo: 4.5-5.5 Weight % W 5.
0 to 70 wt% ■ 07 to 0.9 wt% Fe Remainder The second means is that the heat treatment conditions are quenching temperature + 150 ± 5
0° C., and a tempering temperature of 530±30° C. is added to the first means to obtain a heat-resistant, high-toughness steel.

"Function" In the heat-resistant high-toughness steels according to the first and second means, there is a tendency for the toughness to be significantly improved when the viscosity hardness is within the range of Hv650 to 760. Further, when the quenching temperature is in the range of 1100 to 1200°C, a dense structure is maintained.

"Example" An alloy material having the composition shown in Table 1 was quenched and high-temperature tempered to produce the desired heat-resistant, high-toughness steel.

Table 1 (Alloy Composition) The heat treatment conditions in this case are that the quenching temperature is 1150±50
The tempering temperature was set within the range of 530±30°C, and the hardness was adjusted by a combination of these.

<Relationship between hardness and toughness> The relationship between hardness and toughness was determined for the obtained heat-resistant high-toughness steel (example sample). The results are shown in FIG.

For comparison, high-speed steel (
The characteristics of 5KH-51 material (comparative sample) are also listed.

As is clear from the comparison between curve A of the example sample and curve B of the comparative sample shown in FIG. curve r3
The superiority of the example sample is clear compared to the comparative sample.

<Relationship between quenching temperature and structure> In the example sample and the comparative sample, the quenching treatment conditions were set to 4 stages of temperature 1100°C, ll500C1
After heat treatment at 1200°C, 1250°C, 30 minutes, 411 cooling, and tempering conditions of 525°C, 120 minutes, air cooling, the micrograph of the structure when corroded with 5% Piracle solution is shown in the second figure. This is shown in Figures 5 to 5. In each of these figures, (A) is an example sample, and (B) is a comparative sample. However, in Fig. 2 (A) and (B), the quenching temperature is 1100°C, in Fig. 3 (A) and (B), the quenching temperature is 1150°C, and in Fig. 4 (Δ) and (B), the quenching temperature is 1100°C.
200℃, Fig. 5 (A XB) shows the quenching temperature 1250℃
It is ℃.

Comparing (A) and (B) in Figures 2 to 5, the example sample has a quenching temperature of 1100 to 12
While the comparative sample maintained a dense structure in the range of 00°C, the structure tended to become coarser in the range of 1150 to 1200°C. When the quenching temperature was 1250° C., the comparison samples tended to have carbides precipitated at grain boundaries and became brittle, and the example samples tended to have intergranular cracks.

Therefore, in the example sample, it is concluded that when the Vickers hardness is within the range of Hv650 to 760, the T-T requirement is high and the quenching temperature is 1100 to 1200°C or less, a dense structure is maintained. is obtained.

<Relationship between ambient temperature and hardness> Figure 6 shows the temperature-hardness reduction characteristics of the example sample and the comparative sample, using a micro Vickers hardness tester at an ambient temperature of 20°C to 4°C.
This is a measurement of the decrease in teno hardness (Ml(V2O3)) at 00°C.As shown in Figure 6, when the hardness at room temperature of 20°C is taken as the standard (0), the hardness decreases as the temperature increases. It was confirmed that the example sample (A) shows a tendency to decrease in hardness, or maintains a practically sufficient hardness up to around the tempering temperature.In addition, the comparative sample (B) shows that the hardness There is a tendency for the decrease to become relatively large.

"Effects of the Invention" As explained above, the heat-resistant high-toughness steel of the present invention has
By using a medium carbon - 4% chromium - 5% molybdenum 6% tungsten - 08% composition and by performing appropriate quenching and tempering treatments, the toughness is higher than that of the conventional example when the hardness is within the range of Hv650 to 760. It is higher than tool steel, and can maintain temperature and toughness in high-temperature atmospheres.

The above makes it suitable for equipment that has friction and sliding surfaces that easily heat up, and combined with its excellent high-temperature properties, it increases its applicability to parts for which carburizing surface hardening treatment is unsuitable, and it cools compared to conventional examples. This has excellent effects such as simplifying the device.

Envy Utyt -11 → Teno1rr i (-19rη Figure 6 Procedure kan) Official document (method) 1. Indication of the case 1990 Patent Application No. 169216 2. Name of the invention Heat-resistant high-toughness steel 3 Amendment Patent applicant (009) Ishikawajima Harima Heavy Industries Co., Ltd. 4 Agent 2-1-5 Yaesu, Chuo-ku, Tokyo Tokyo Station Building 6th floor Temperature (0C) 7. Contents of amendment (1) No. 9 Correct the sentence from line 5 to line 9 of the page to the following sentence.

r FIG. 2(A) shows a microscopic photograph of the metallographic structure of the steel material of the example sample treated at a quenching temperature of 1100°C.

FIG. 2(B) shows a microscopic photograph of the metallographic structure of a comparative sample of steel treated at a quenching temperature of 1100° C. and corroded.

FIG. 3(A) shows a microscopic photograph of the metallographic structure of a steel material of an example sample treated at a quenching temperature of 1.50° C. and corroded.

FIG. 3(B) shows a micrograph of the metallographic structure of a steel material of a comparison sample treated at a quenching temperature of 1150° C. and corroded.

FIG. 4(A) shows a microscopic photograph of the metallographic structure of a steel material of an example sample treated at a quenching temperature of 1200° C. and corroded.

FIG. 4(B) shows a microscopic photograph of the metal structure of a steel material of a comparison sample treated at a quenching temperature of 1200° C. and corroded.

FIG. 5 (Δ) shows a microscopic photograph of the metallographic structure of the steel material of the example sample which was quenched at 1250° C. and subjected to corrosion.

FIG. 5(B) shows a microscopic photograph of the metal structure of a comparative sample of steel treated at a quenching temperature of 1250° C. and corroded. ” ”−

Claims (1)

[Scope of Claims] i. A heat-resistant, high-toughness steel characterized by being made by quenching and high-temperature tempering an alloy material having the following composition. C: 0.5-0.6% by weight Si: 0.4% by weight or less Mn: 0.3-0.5% by weight Cr: 3.5-4.5% by weight Mo: 4.5-5.5 Weight % W: 5.0 to 7.0 weight % V: 0.7 to 0.9 weight % Fe: remainder ii, heat treatment conditions are quenching temperature 1150 ± 50 ° C, tempering temperature 530 ± 30 ° C The heat-resistant, high-toughness steel according to claim i.