JP2018009214A - Ni-containing high-C martensitic heat-resistant steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Ni-containing high-C martensitic heat-resistant steel in consideration of the fact that the grain boundary coverage of carbides affects toughness in a high-C and Ni-containing high Cr-based heat-resistant steel used in a high-temperature environment. Offer. SOLUTION: In mass%, C: 0.40 to 0.85%, Si: 0.50 to 2.00%, Mn: 0.10 to 2.00%, P: ≤0.030%, Ni. : 0.10 to 2.00%, Cr: 16.0 to 23.50%, O: ≤0.0080%, N: ≤0.0600%, and Fe and unavoidable impurities, Charpy Toughness by impact value: 5.0 J / cm2 or more, grain boundary coverage index W value 16.3 [% C] + 15.4 x [% Ni] + 3.3 x [% Cr]: Ni content of ≤104 High C martensitic heat resistant steel. [Selection diagram] None

Description

  The invention of this application relates to a Ni-containing high C martensitic heat resistant steel used in a high temperature environment.

  Conventionally, martensitic heat-resisting steel is used at high temperatures, but since cold workability is poor, each member is usually manufactured by hot forging. For this reason, the material structure and hardness at the time of processing were not so important. However, manufacturing by hot forging has a problem that it is inferior to cold forging in terms of productivity and cost, and in recent years, development of cold forging of these martensitic heat resistant steels has been demanded. In this case, since the material is processed by using a cold forging machine or the like, the material hardness before processing is required to be as low as possible.

  On the other hand, Ni-containing high-C martensitic heat-resistant steel has been proposed as an invention relating to a method for producing a heat-resistant steel that is martensitic heat-resistant steel and has excellent cold forgeability (see, for example, Patent Document 1). . However, the proposed invention is a component system in which the range of C is not sufficient and the Cr content is low, and there is no description regarding the influence of the grain boundary coverage of carbides on toughness and oxidation resistance.

  Furthermore, an invention relating to a martensitic heat resistant steel that is unlikely to cause a characteristic change such as a reduction in hardness when used at a high temperature has been proposed (see, for example, Patent Document 2). The present invention includes C: 0.35 to 0.60%, Si: 1.0 to 2.5%, Mn: 0.1% or more and less than 1.5%, and Cr: 7.5 to 13.0% In addition, in claim 1, Mo + 0.5W: 1.5 to 3.0% is added, in claim 2, Nb + Ta is further added, and in claim 3, martensitic heat-resistant steel further added with V is there. However, the proposed invention has a different component system from the invention of the present application, and there is no description regarding the effect of carbide grain boundary coverage on toughness.

  As mentioned above, the conventional technology contains about 0.8% C and about 2% Ni, but there is no description about heat-resistant steels that are high Cr, and the toughness is low and the productivity is low. Is also a problem.

JP 2000-256735 A JP-A-11-323506

  The present invention is an invention related to a high Cr heat-resistant steel containing high C and containing Ni, and has been inspired by the discovery that the grain boundary coverage of carbides affects toughness, Furthermore, it is providing the Ni containing high C martensitic heat-resisting steel which considered the oxidation resistance in consideration of the use environment.

In the means for solving the above problems, the means of the developed steel 1 is mass%, C: 0.40 to 0.85%, Si: 0.50 to 2.00%, Mn: 0.10. 2.00%, P: ≦ 0.030%, Ni: 0.10 to 2.00%, Cr: 16.00 to 23.50%, O: ≦ 0.0080%, N: ≦ 0.0600% And toughness with Charpy impact value: 5.0 J / cm ² or less, grain boundary coverage index W value of 16.3 [% C] + 15.4 × [% Ni] + 3.3 × [% Cr]: Ni-containing high-C martensitic heat-resistant steel characterized by ≦ 104.

The means of the developed steel 2 is mass%, C: 0.40 to 0.85%, Si: 0.50 to 2.00%, Mn: 0.10 to 2.00%, P: ≦ 0.030. %, Ni: 0.10 to 2.00%, Cr: 16.00 to 23.50%, O: ≦ 0.0080%, N: ≦ 0.0600%, and Mo: ≦ 1. 00%, Ti: ≦ 0.20%, V: ≦ 0.30%, Nb ≦ 0.50%, W: ≦ 1.00%, B: ≦ 0.0200%, one or more And further containing Fe and inevitable impurities, toughness by Charpy impact value: 5.0 J / cm ² or less, grain boundary coverage index W value 16.3 [% C] + 15.4 × [% Ni] + 3.3 × [% Cr]: ≦ 104, A value [% Mo] + 1/2 × [% W]: ≦ 1.0, and B value 5 × [% Ti] + 2 × [% Nb] A Ni-containing high C martensitic heat resisting steel means developed steel 1, characterized in that ≦ 1.5.

The means of the developed steel 3 is% by mass, C: 0.40 to 0.85%, Si: 0.50 to 2.00%, Mn: 0.10 to 2.00%, P: ≦ 0.030. %, Ni: 0.10 to 2.00%, Cr: 16.00 to 23.50%, O: ≦ 0.0080%, N: ≦ 0.0600%, and Mo: ≦ 1. 00%, Ti: ≦ 0.20%, V: ≦ 0.30%, Nb ≦ 0.50%, W: ≦ 1.00%, B: ≦ 0.0200%, one or more Further, S is greater than 0 and 0.150% or less, further has Fe and inevitable impurities, toughness by Charpy impact value: 5.0 J / cm ² or less, grain boundary coverage index W value 16.3 [% C] + 15.4 × [% Ni] + 3.3 × [% Cr]: ≦ 104, A value [% Mo] + ½ × [% W]: ≦ 0.0 and a B value of 5 × [% Ti] + 2 × [% Nb]: ≦ 1.5, a Ni-containing high-C martensitic heat resistant steel as a means of the developed steel 1 or 2 .

  The present invention is a Ni-containing high-C martensitic heat-resisting steel having a wide C range of 0.40 to 0.85% and a high Cr content of 16.00 to 23.50%. Since the boundary coverage is as low as 50% or less, it has an effect of ensuring high toughness.

  Prior to the description of the mode for carrying out the invention, the reasons for limiting the chemical components of the steel of the present invention will be described.

C: 0.40 to 0.85%
C is an element necessary for ensuring strength and wear resistance. In order to obtain sufficient strength and wear resistance, it is necessary to add 0.40%. However, if the content is less than 0.40%, the quenching and tempering hardness of the steel is reduced. On the other hand, if the content is more than 0.85%, the annealing hardness of the steel is increased and the hot workability is deteriorated. Therefore, C is set to 0.40 to 0.85%. Preferably, the content is 0.55 to 0.80%.

Si: 0.50 to 2.00%
Si is an element necessary as a deoxidizer. However, if Si is less than 0.50%, the oxidation loss of the steel is increased. On the other hand, if it exceeds 2.00%, the toughness of the steel is deteriorated and cold forgeability cannot be obtained. Therefore, Si is 0.50 to 2.00%, preferably 1.00 to 2.00%.

Mn: 0.10 to 2.00%
Mn is an element necessary as a deoxidizing agent and a desulfurizing agent. However, if Mn is less than 0.10%, the toughness of the steel deteriorates. On the other hand, when Mn is more than 2.00%, the hot workability of steel is deteriorated. Therefore, Mn is 0.10 to 2.00%, preferably 0.30 to 1.00%.

P: ≦ 0.030%
P is an inevitable impurity element, but if it exceeds 0.030%, the hot workability of steel deteriorates. Therefore, P ≦ 0.030%, preferably 0.020% or less.

Ni: 0.10 to 2.00%
Ni is effective in improving hardenability and strength. However, if Ni is less than 0.10%, the oxidation loss of the steel is increased. On the other hand, if Ni is more than 2.00%, the annealing hardness of the steel is increased and the cost is increased. Therefore, Ni is 0.10 to 2.00%, preferably 0.50 to 1.70%.

Cr: 16.00 to 23.50%
Cr is effective in improving oxidation resistance. However, if the Cr content is less than 16.00%, the oxidation loss of the steel increases. On the other hand, if the Cr content exceeds 23.50%, the quenching and tempering hardness of the steel decreases and the toughness deteriorates. Therefore, Cr is set to 16.00 to 23.50%, preferably 18.00 to 21.50%.

O: ≦ 0.0080%
O is an unavoidable impurity element, but when it exceeds 0.0080%, it takes away Si and Cr effective for oxidation resistance, and therefore the oxidation loss increases. Therefore, O ≦ 0.0080%, preferably 0.0055% or less.

N: ≦ 0.0600%
N is an inevitable impurity element, but when it exceeds 0.0600%, the hot workability deteriorates and the toughness accompanying the increase in the W value of the grain boundary coverage index deteriorates. Therefore, N: ≦ 0.0600%, preferably 0.0500% or less.

Mo: ≦ 1.00%
Mo, in addition to increase the hardenability, increase the temper softening resistance, an element to increase the _point A, to form a carbide such as M ₇ C ₃ and M ₂ C during tempering, increasing the high-temperature strength Let When Mo is added in a large amount, the annealing hardness is increased and the toughness is deteriorated. On top of that, Mo is an expensive element. Therefore, Mo ≦ 1.00%, preferably 0.85% or less.

Ti: ≦ 0.20%
Ti is an element having an extremely strong affinity for N compared to B. BN by the formation of TiN
In order to suppress the precipitation of B and increase the effect of B which suppresses the coarsening of the carbide, it is preferable to add Ti in an amount of 0.005% or more. On the other hand, when Ti is added excessively, coarse TiC precipitates or crystallizes, and the toughness is lowered. Therefore, Ti is set to 0.20% or less, preferably 0.15% or less.

V: ≦ 0.30%
When V is added excessively, coarse VC is precipitated or crystallized to deteriorate toughness. Since V is an expensive element, V is set to 0.30% or less, preferably 0.20% or less. To do.

Nb: ≦ 0.50%
When Nb is added excessively, coarse NbC is precipitated or crystallized to deteriorate toughness and decrease the quenching hardness. Therefore, Nb is 0.50% or less, preferably 0.30% or less.

W: ≦ 1.00%
When W is added excessively, coarse carbides are precipitated to deteriorate toughness, quenching hardness is lowered, and W is an expensive element. Therefore, W is 1.00% or less, preferably 0.50% or less.

S: ≦ 0.150%
S is an unavoidable impurity element, but if it exceeds 0.150%, the hot workability of steel deteriorates. Therefore, S ≦ 0.150%, preferably 0.100% or less.

Charpy impact value as toughness: 5.0 J / cm ² or more When the Charpy impact value is less than 5.0 J / cm ² , the toughness is low and the productivity is lowered. Therefore, the Charpy impact value as toughness is set to 5.0 J / cm ² or more.

Grain boundary coverage index W value: 16.3 [% C] + 15.4 × [% Ni] + 3.3 × [% Cr] ≦ 104
When the grain boundary coverage index W value is larger than 104, the grain boundary coverage of the carbide increases and it becomes impossible to secure toughness. Therefore, the grain boundary coverage index W value of 16.3 [% C] + 15.4 × [% Ni] + 3.3 × [% Cr] is set to 104 or less.

A value: [% Mo] + 1/2 × [% W]
When the A value is greater than 1.0, the toughness of claim 2 of the present developed steel is deteriorated. Thus, [% Mo] + 1/2 × [% W] of the A value is 1.0 or less.

B value: 5 × [% Ti] + 2 × [% Nb]
If the B value is greater than 1.5, the toughness of claim 2 of the present developed steel is deteriorated. So B
The value 5 × [% Ti] + 2 × [% Nb] is 1.5 or less.

  Here, the form for implementing invention of this application is demonstrated. Each No. of each component of the developed steel of the present invention shown in Table 1 is shown. No. of each component of each steel and each comparative steel shown in Table 2. Each of these steels was melted at 100 kg VIM and cast into ingots.

  These ingots are forged into a forged material with a 65 mm diameter round bar in the first group, forged into 45 mmH × 95 mmW in the second group, and each of these groups is annealed at 850 to 950 ° C. did. The following tests were carried out from the materials adjusted to the respective sizes. Table 3 shows the value of the developed steel of the present invention in Table 3, and Table 4 shows the value of the comparison term. In addition, the hot workability was evaluated based on the occurrence of cracks during forging, and the case where cracks did not occur was evaluated as ○, and the case where cracks occurred was evaluated as ×.

  Evaluation of the first group was conducted after adjusting the forged material of a round bar with a diameter of 65 mm to a diameter of 60 mm, then measuring the annealing hardness, the quenching and tempering hardness, and measuring the grain boundary coverage of the carbide. Table 3 shows the values of the present invention steel, and Table 4 shows the values of the comparative steel.

  The annealing hardness (indicated as A hardness in Tables 3 and 4) was measured by measuring the hardness on the HRC scale in the middle circumference of the surface perpendicular to the longitudinal direction of the specimen. The invention steel in Table 3 and the comparative steel in Table 4 each showed an average value of 5 points.

  The quenching and tempering hardness (indicated as QT hardness in Tables 3 and 4) was quenched at 1000 to 1150 ° C., and then tempered at 550 to 650 ° C. Measurement was performed in the same manner as the annealing hardness, and the average value for each of the five points was shown.

The grain boundary coverage is a value obtained by dividing the sum of the precipitate lengths on the large angle (degree) grain boundary by the sum of the large angle (degree) grain boundary lengths, and is 100% when completely covered. This is a parameter for determining 0% when there is no coating.
The grain boundary coverage of the carbide was measured by observing the structure in the longitudinal direction of the test material in the annealed state. Grain boundary coverage is first measured by electron microscope observation at a magnification of 10,000, and the particles deposited on the large-angle (degree) grain boundary are analyzed by energy dispersive X-ray spectroscopy (EDX) or a 10,000 times thin film transmission electron microscope. Precipitates that can be determined as M ₂₃ C ₆ type carbide or M ₇ C ₃ type carbide are identified by transmission electron diffraction pattern analysis in the analysis. The length of the grain covering the large-angle (degree) grain boundary is measured, and the measurement is performed by collecting at least 5 visual fields per sample and 5 or more test pieces per alloy. It can be determined by observation or analysis with an electron microscope.

  The evaluation of the second group is the continuous oxidation test of the 45 mmH × 95 mmW material produced above, the Charpy impact test in the quenched and tempered state, Table 3 shows the results of the present invention steel, and Table 4 shows the comparative steel. The result was shown.

  That is, in the continuous oxidation test, the 45 mm high × 95 mm wide material prepared above was adjusted to a diameter of 12 mm and a length of 21 mm, and then a continuous oxidation experiment was performed at 1100 ° C. for 100 hours. Furthermore, descaling was performed by shot blasting, and the value of oxidation loss was measured.

  In the Charpy impact test, the specimen was quenched at 1000 to 1150 ° C., then tempered at 550 to 650 ° C., adjusted to a standard test piece of 10 × 55 mm square, and 2 mm U notch in accordance with JIS Z 2242. The Charpy impact test was carried out, and the average value of the three times was shown in Table 3, the toughness of the developed steel in the Charpy impact value, and in Table 4, the toughness of the comparative steel was shown in the Charpy impact value.

Claims (3)

In mass%, C: 0.40 to 0.85%, Si: 0.50 to 2.00%, Mn: 0.10 to 2.00%, P: ≦ 0.030%, Ni: 0.10 ~ 2.00%, Cr: 16.00-23.50%, O: ≤0.0080%, N: ≤0.0600%, and Fe and inevitable impurities, toughness by Charpy impact value : 5.0 J / cm ² or less, grain boundary coverage index W value 16.3 [% C] + 15.4 × [% Ni] + 3.3 × [% Cr]: ≦ 104 Ni-containing high-C martensitic heat-resistant steel. In mass%, C: 0.40 to 0.85%, Si: 0.50 to 2.00%, Mn: 0.10 to 2.00%, P: ≦ 0.030%, Ni: 0.10 -2.00%, Cr: 16.00-23.50%, O: ≤0.0080%, N: ≤0.0600%, Mo: ≤1.00%, Ti: ≤0 20%, V: ≦ 0.30%, Nb ≦ 0.50%, W: ≦ 1.00%, B: ≦ 0.0200%, containing one or more, and Fe and Toughness due to Charpy impact value: 5.0 J / cm ² or less, grain boundary coverage index W value of 16.3 [% C] + 15.4 × [% Ni] + 3.3 × [% Cr ]: ≦ 104, A value [% Mo] + 1/2 × [% W]: ≦ 1.0, and B value 5 × [% Ti] + 2 × [% Nb]: ≦ 1.5. Ni-containing high C martensitic heat resisting steel according to claim 1, wherein the door. In mass%, C: 0.40 to 0.85%, Si: 0.50 to 2.00%, Mn: 0.10 to 2.00%, P: ≦ 0.030%, Ni: 0.10 -2.00%, Cr: 16.00-23.50%, O: ≤0.0080%, N: ≤0.0600%, Mo: ≤1.00%, Ti: ≤0 20%, V: ≦ 0.30%, Nb ≦ 0.50%, W: ≦ 1.00%, B: ≦ 0.0200%, or one or more of them, and S : Greater than 0 and 0.150% or less, further Fe and inevitable impurities, toughness by Charpy impact value: 5.0 J / cm ² or less, grain boundary coverage index W value 16.3 [% C] + 15.4 × [% Ni] + 3.3 × [% Cr]: ≦ 104, A value [% Mo] + ½ × [% W]: ≦ 1.0, and B value 5 × [% Ti] + 2 × [% Nb]: Ni-containing high C martensitic heat resisting steel according to claim 1 or 2, characterized in that a ≦ 1.5.