JPH07286248A - 5 percents-chromium type heat resistant steel - Google Patents

Abstract

PURPOSE:To produce a 5%Cr type heat resistant steel excellent in high temp. strength characteristic. CONSTITUTION:A 5%Cr type heat resistant steel, which has a comosition consisting of, by weight, 0.05-0.3% C, 0-0.3% Si, 0.1-1.5% Mn, 0.01-1% Ni, 4-6% Cr, 0.1-1.5% Mo, 0.5-3% Cu, and the balance Fe and containing, if necessary, 0.01-0.3% V, 0.01-0.1% N, and 0.01-0.2% Nb, is obtained, and also, a 5%Cr type heat resistant steel, which has a composition consisting of, by weight, 0.03-0.3% C, 0-0.3% Si, 0.1-1.5% Mn, 0.01-1% Ni, 4-6% Cr, 0.01-1.5% Mo, 0.3-3% W, 0.5-3% Cu, 0.01-0.3% V, and the balance Fe and containing, if necessary, 0.01-0.2% Nb and 0.01-0.1% N, is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to 5% Cr heat resistant steel, and is particularly useful as a material for nuts, bolts, shrouds, valve seats, valve rods and nozzle plates for steam turbines, members for gas turbines and members for boilers. The same heat-resistant steel.

[0002]

2. Description of the Related Art Conventionally, as a nut material for a high temperature bolt of a steam turbine, 5% Cr type steel having excellent seizure resistance and oxidation resistance has been used.

[0003]

However, the conventional 5% Cr steel cannot be said to have sufficient high-temperature strength, and it has been dealt with by designing measures such as dimensional changes. The present invention has been made in consideration of such circumstances, and an object thereof is to provide a 5% Cr heat-resisting steel having excellent high-temperature strength properties as compared with conventional ones.

[0004]

According to the present invention, C: 0.05 to 0.3% and Si: 0 to 0.
3%, Mn: 0.1 to 1.5%, Ni: 0.01 to 1
%, Cr: 4 to 6%, Mo: 0.1 to 1.5%, Cu:
A 5% Cr heat-resisting steel containing 0.5 to 3% and the balance Fe and incidental impurities (referred to as the first invention of the first group). The above-mentioned 5% Cr heat-resisting steel (referred to as the second invention of the first group), characterized by containing V: 0.01 to 0.3%. The above-mentioned 5% Cr heat-resisting steel (referred to as the third invention of the first group), characterized by containing N: 0.01 to 0.1%. The 5% Cr heat-resistant steel described above (referred to as the fourth invention of the first group), characterized in that the above components contain Nb: 0.01 to 0.2%.

C: 0.03 to 0.3% by weight, S
i: 0-0.3%, Mn: 0.1-1.5%, Ni:
0.01-1%, Cr: 4-6%, Mo: 0.01-
1.5%, W: 0.3 to 3%, Cu: 0.5 to 3%,
V: 0.01-0.3%, 5% Cr heat resistant steel characterized by the balance Fe and incidental impurities (referred to as the first invention of the second group). The 5% Cr heat-resistant steel as described above (referred to as the second invention of the second group), characterized in that Nb: 0.01 to 0.2% is contained in the above components. The above-mentioned 5% Cr heat-resisting steel (referred to as the third invention of the second group), characterized by containing N: 0.01 to 0.1%. Is.

[0006]

The 5% Cr heat-resisting steel according to the present invention is melted in an electric furnace or the like, or thereafter, a steel ingot is obtained by electronic melting or vacuum arc melting, and then this steel ingot is heated to 1000 ° C.
After heating to ˜1200 ° C. to perform hot working to form a body of each component, after heating to 900 ° C. to 1100 ° C., quenching in oil is performed, and subsequently, tempering heat treatment is performed at 550 ° C. to 700 ° C.

The reasons for limiting the alloy composition of the first group in the present invention will be described below. (1) C (Carbon) C is an element that forms an alloy carbide and significantly changes the material strength and the toughness at room temperature, and is an element necessary to secure the tensile strength and the creep rupture strength. If C is less than 0.05%, the hardenability is insufficient and it is difficult to obtain the required properties. On the other hand, if C is added in an amount of more than 0.3%, the toughness at room temperature will be reduced, and further, the coarsening of carbide will be remarkable and the creep rupture strength will be reduced for a long time. Of this range, the preferable range of C is 0.1 to 0.25%. (2) Si (Si) Si is an element effective as a deoxidizing agent, but addition of a large amount reduces toughness. The lowering of Si reduces the deterioration of toughness after long-term use, and also improves the high temperature characteristics.
Was 0 to 0.3%. However, it is difficult to reduce Si to 0% at the actual product level, but Si is 0.1%.
Even in the following, a remarkable effect can be obtained. (3) Mn (manganese) Mn is added as a deoxidizing agent, but if it is less than 0.1%, it is insufficient and the effect is small. If added in excess of 1.5%, it hardens the steel, impairs workability, and lowers the creep rupture strength. Of this range, the preferable range of Mn is 0.3 to 1%. (4) Ni (Nickel) Ni is an element that improves hardenability and toughness at room temperature, but deteriorates high temperature characteristics such as creep rupture strength, and Ni is 0.01 to 1%. Especially 0.1 to 0.
4% is a preferable range. (5) Cr (Chromium) Cr is necessary to improve mechanical properties, oxidation resistance and corrosion resistance, and creep rupture strength, and is 4 to 6% in order to secure stable seizure resistance. Of this range
The preferable range of Cr is 4.5 to 5.5%. (6) Mo (Molybdenum) Mo is effective as a solid solution strengthening and fine carbide precipitation strengthening element for improving the creep rupture strength, but if it is less than 0.1%, the effect is not sufficiently obtained, and if it exceeds 1.5%. Toughness and workability are reduced. Of this range, the preferable range of Mo is 0.3 to 1.5%. (7) Cu (Copper) Cu is effective in improving the room temperature strength and the creep strength, and is positively added to improve the oxidation resistance.
If it is less than 0.5%, the effect is small, and if it is added in a large amount, the workability is deteriorated. Therefore, 0.5 to 3% is effective. In this range, the preferable range of Cu is 0.5 to 2%. (8) V (Vanadium) V forms fine precipitates of VC and improves creep rupture strength, but if it is less than 0.01%, a sufficient effect cannot be obtained, and if it exceeds 0.3%, strength and toughness are rather increased. Spoil. Of this range, the preferable range of V is 0.1 to 0.2%. (9) N (Nitrogen) N is an element effective for improving the creep rupture strength, but if it is less than 0.01%, a sufficient effect cannot be obtained, and N.
If N is added in excess of 1%, not only the toughness at room temperature decreases, but also the nitride aggregates and coarsens to reduce creep rupture strength. Therefore, N was made 0.01 to 0.1%. . (10) Nb (niobium) Nb forms carbides and NbC similarly to V, significantly improves creep rupture strength, and is also effective for refining crystal grains. Can't get On the other hand, if it exceeds 0.2%, N that is not solid-solubilized by the quenching treatment.
bC increases and coarse NbC is also generated, which reduces ductility and toughness, and further reduces long-term creep rupture strength. Of this range, the preferable range of Nb is 0.03 to
It is 0.1%.

Next, the reasons for limiting the alloy composition of the second group in the present invention will be described. (1) C (Carbon) C is an element that forms an alloy carbide and significantly changes the material strength and the toughness at room temperature, and is an element necessary to secure the tensile strength and the creep rupture strength. If C is less than 0.03%, the hardenability is insufficient and it is difficult to obtain the required characteristics. On the other hand, if C is added in an amount of more than 0.3%, the toughness at room temperature will be reduced, and further, the coarsening of carbide will be remarkable and the creep rupture strength will be reduced for a long time. A preferable range for securing these material properties is 0.1 to 0.25%. (2) The reason for limiting the contents of Si (silicon), Mn (manganese), Ni (nickel), Cr (chrome), Cu (copper), V (vanadium), Nb (niobium) and N (nitrogen) is as described above. It is the same as described for the alloy composition of the first group. (3) Mo (molybdenum) Mo is a solid solution strengthening and fine carbide precipitation strengthening element,
Although it is effective in improving the creep rupture strength, even if it is added in combination with W, if it is less than 0.01%, a sufficient effect cannot be obtained, and if it exceeds 1.5%, toughness and workability deteriorate. (4) W (Tungsten) W is effective as a solid solution strengthening and fine carbide precipitation strengthening element in the same manner as Mo, and is effective in improving creep rupture strength. W is M
It is more effective in improving the high temperature strength than o, but the effect of improving the creep rupture strength is large by the combined addition with Mo, and the effect becomes remarkable with the addition of 0.3% or more.
If it exceeds%, toughness and workability are impaired. Of this range
The preferable range of W is 0.5 to 2.5%. It should be noted that the effect becomes greater when W is added in a larger amount than Mo.

[0009]

[Examples] The effects of the present invention will be clarified by giving specific examples of the 5% Cr heat-resistant steel of the present invention. (Example 1) Table 1 shows the chemical composition of the first group of 5% Cr heat resistant steels of the present invention and comparative steels. Test Steel N
o. 1-No. No. 6 is the first group of 5% Cr heat-resisting steel of the present invention. Reference numerals 7 and 8 are comparative steels, which are 5% Cr-based steels that are currently used as high temperature nut materials. Although the comparative steel is a practical material, the sample steel No. 1-No.
No. 6 was melted in a high-frequency induction furnace, forged a steel ingot, heated to 900 ° C to 1100 ° C, and then quenched in oil to perform a quenching treatment, and then the tensile strength was 85 kgf / mm.
^{2 ~95kgf} / mm ² to become as 640 ° C. to 700
A tempering treatment was performed in the range of ° C.

Table 2 shows the results of the room temperature tensile test. Creep rupture test was performed at 600 ° C. under a stress of 20 kgf / mm ² , 65
It was carried out under the conditions of a stress of 15 kgf / mm ² at 0 ° C. Table 3
The creep rupture test results are shown in. The creep rupture life of the 5% Cr heat resistant steel of the first group of the present invention was remarkably improved as compared with the comparative steel.

[0011]

[Table 1]

[0012]

[Table 2]

[0013]

[Table 3]

(Example 2) Table 4 shows the chemical composition of the second group of 5% Cr heat resistant steels of the present invention and the comparative steel. Specimen No. 1-No. No. 6 is the second group of 5% Cr heat-resisting steel of the present invention. 7 and 8 are comparative steels, and 5% C is used as the current high temperature nut material.
r-based steel. Similar to Example 1, the comparative steel is an actual material, but the sample material No. 1-No. No. 6 was melted in a high frequency induction furnace, and after forging a steel ingot,
A quenching treatment is performed in which the material is heated to 00 ° C. and then rapidly cooled in oil, and then the tensile strength is 85 kgf / mm ^{2 to} 95 kgf / m.
The tempering process was performed in the range of 640 ° C. to 700 ° C. so as to be m ² .

Table 5 shows the results of the room temperature tensile test. Creep rupture test was performed at 600 ° C. under a stress of 20 kgf / mm ² , 65
It was carried out under the conditions of a stress of 15 kgf / mm ² at 0 ° C. Table 6
The creep rupture test results are shown in. The creep rupture life of the 5% Cr heat resistant steel of the second group of the present invention was remarkably improved as compared with the comparative steel.

[0016]

[Table 4]

[0017]

[Table 5]

[0018]

[Table 6]

[0019]

EFFECTS OF THE INVENTION The 5% Cr heat resistant steel of the present invention is excellent in high temperature strength, and can be used for applications requiring such characteristics and can obtain life and reliability superior to those of conventional steels.

Continuation of front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display area F02C 7/00 C

Claims (7)

[Claims] 1. C: 0.05 to 0.3% by weight, S
i: 0-0.3%, Mn: 0.1-1.5%, Ni:
0.01-1%, Cr: 4-6%, Mo: 0.1-1.
5%, Cu: 0.5 to 3%, 5% Cr heat resistant steel characterized by the balance Fe and incidental impurities. 2. The 5% C according to claim 1, wherein V: 0.01 to 0.3% is contained in the above component.
r series heat resistant steel. 3. The 5% C according to claim 2, wherein the above component contains N: 0.01 to 0.1%.
r series heat resistant steel. 4. Nb: 0.01 to 0.2% in the above component
5% according to claim 3, characterized in that
Cr heat resistant steel. 5. C: 0.03 to 0.3% by weight, S
i: 0-0.3%, Mn: 0.1-1.5%, Ni:
0.01-1%, Cr: 4-6%, Mo: 0.01-
1.5%, W: 0.3 to 3%, Cu: 0.5 to 3%,
V: 5% Cr heat-resisting steel containing 0.01 to 0.3%, the balance being Fe and incidental impurities. 6. Nb: 0.01 to 0.2% in the above component
5% according to claim 5, characterized in that
Cr heat resistant steel. 7. The 5% C according to claim 6, wherein said component contains N: 0.01 to 0.1%.
r series heat resistant steel.