JP2915691B2 - High ductility austenitic-ferrite dual phase heat resistant steel and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-ductility austenitic-ferritic two-phase heat-resistant steel used as a welding wire that can be drawn and a method for producing the same.

[0002]

2. Description of the Related Art Heat-resistant steel H described in ASTM standards
As the welding material used for I, a wire having the same component as the base material is used. That is, the composition of this wire is as shown in Table 1 below, transcribed from the description given in the Stainless Steel Handbook, III, 6.2.1.

[0003]

[Table 1]

[0004] Since this heat-resistant steel HI has a high carbon content and a two-phase structure, it has a hot workability; for example, in both hot forging and hot rolling, the yield before welding becomes a wire rod for welding is lowered. Was remarkable. Further, fine cracks generated during hot working also remain in the wire drawing process, resulting in a decrease in quality and a decrease in yield. On the other hand, an attempt has been made to cast this heat-resistant cast steel HI into a rod having a relatively small diameter close to the wire, and then to perform cold working or wire drawing directly on the wire without performing hot working. Since the amount is high and the ductility is very poor, a desired wire diameter cannot be obtained unless a large number of steps are performed, and industrial production is particularly difficult in terms of cost.

[0005]

As described above,
Since the heat-resistant steel HI has a high C content and is extremely poor in ductility, conventionally, as-cast steel has been used. On the other hand, an attempt has been made to cast this heat-resistant steel HI into a wire rod, perform cold rolling and use it as a welding wire, but as described above, heat-resistant steel HI requires an extremely large number of steps. Without this, the desired wire diameter cannot be obtained, so that industrial production was difficult, particularly in terms of cost.

Accordingly, the present invention relates to a highly ductile heat-resistant steel and a method for producing the same, which can solve the above problems.
The purpose is to propose.

[0007]

Means for Solving the Problems The inventors have developed a heat resistant steel HI.
When the cause of poor ductility was investigated, firstly, the fracture of the drawn material in the wire drawing process occurred along the ferrite grain boundaries, and at this ferrite grain boundary, a large number of Cr carbides were precipitated. It has been found that suppressing the precipitation of carbides is effective for improving the ductility of heat-resistant steel HI,
The present invention has been completed.

[0008] That is, the present invention relates to the following: C: 0.10 to 0.50 wt
%, Si: 0.1 to 2.0 wt%, Mn: 0.1 to 2.0 wt%, Cr: 20
~ 35wt%, Ni: 10 ~ 20wt%, B: 0.0003 ~ 0.0100wt%,
P: 0.03 wt% or less, S: 0.01 wt% or less, N: 0.01 to 0.20
We propose a high-ductility austenitic-ferrite dual phase heat-resistant steel containing wt% and O: 0.0080 wt% or less, the balance being Fe and unavoidable impurities, and the ferrite content is 3 to 15%.

Further, the present invention relates to the above-mentioned components,
Mo: a component composition containing 0.01 to 0.5 wt%, or 0.01 to 0.5 wt% of Mo instead of or together with Mo.
High ductile austenite-Cu-containing component composition
A ferrite two-phase heat-resistant steel is proposed.

[0010] The heat-resistant steel of the present invention is obtained by casting a steel material having the above-mentioned composition and then heating the steel material to a temperature range of 1150 to 1400 ° C, and then to a temperature range of 800 ° C to 1150 ° C. After holding for more than one second, it can be advantageously produced by rapidly cooling from a temperature range of 800 ° C. or more.

[0011]

Next, the reasons for limiting each component of the present invention will be described. C: 0.10 to 0.50 wt% C must be contained in an amount of 0.10 wt% or more in order to secure the strength. However, if the content exceeds 0.50 wt%, the susceptibility to intergranular corrosion increases, so the upper limit is 0.50 wt%. And

Si: 0.1 to 2.0 wt% Si is a component that improves heat resistance and corrosion resistance in addition to weldability and castability, and must be contained in an amount of 0.1 wt% or more. On the other hand, when the content exceeds 2.0 wt%, precipitation of a brittle σ phase is caused, so that the content is set to 2.0 wt% or less.

Mn: 0.1 to 2.0 wt% Mn needs to be contained in an amount of 0.1 wt% or more in order to improve heat resistance. However, if it exceeds 2.0 wt%, the brittleness is deteriorated. wt% range.

Cr: 20 to 35 wt% Cr is a component that improves high-temperature strength and corrosion resistance.
A content of 20 wt% or more is required, but if it exceeds 35 wt%, embrittlement is caused, so the content is set in the range of 20 to 35 wt%.

Ni: 10 to 20 wt% Ni is an austenite-forming component, and it is necessary to contain 10 wt% or more in order to improve corrosion resistance and toughness. However, if it exceeds 20 wt%, the strength decreases. Since the intergranular corrosion tendency becomes strong, the content is set in the range of 10 to 20% by weight.

Mo: 0.01 to 0.5 wt% Mo is a component that improves the weldability and the pitting corrosion resistance. If the content is less than 0.01 wt%, such an effect cannot be obtained. In order to make the phase unstable, the range is 0.01 to 0.5 wt%.

Cu: 0.01-0.5 wt% Cu is a component for improving corrosion resistance, and its effect cannot be obtained when 0.01 wt% is added, whereas when it exceeds 0.5 wt%, it causes hot cracking. From the range of 0.01 to 0.5 wt%.

B: 0.0003 to 0.0100 wt% B must be contained in an amount of 0.0003 wt% or more in order to suppress grain boundary precipitation of carbides. On the other hand, when the content exceeds 0.0100 wt%, (Fe, Cr) ₂ B is formed and the toughness is deteriorated, so that welding cracks are easily generated.

P: not more than 0.03 wt% P becomes an impurity and embrittles the grain boundary, so that P is suppressed to not more than 0.03 wt%. S: 0.010 wt% or less S suppresses the content of S to 0.010 wt% or less because it embrittles grain boundaries. N: 0.01 to 0.20 wt% N is required to be 0.01 wt% or more in order to refine crystal grains and improve toughness. However, if N exceeds 0.20 wt%, ductility is deteriorated, so N is limited to 0.20 wt% or less. O: 0.0080 wt% or less O remains as non-metallic inclusions in steel during solidification and impairs cleanliness, and depending on its distribution, deteriorates deformability,
It causes red heat brittleness. In addition, since the corrosion resistance and the surface condition deteriorate, the content is controlled to 0.0080 wt% or less.

Ferrite content: 3 to 15% By limiting the ratio of the ferrite phase in the austenite-ferrite phase to 15% or less, the austenite region is increased so that C forms a solid solution and the precipitation of carbides is suppressed. The upper limit of the amount was 15%. On the other hand, the lower limit is set to 3% because it is necessary to suppress bead cracking during welding.

After casting, the steel having the composition described above is heated to a temperature range of 1150 to 1400 ° C., and then heated to 800 ° C. or more.
After holding for more than 5 seconds in a temperature range below 1150 ° C, 800 ° C
Rapid cooling from the above temperature range. That is, this temperature
When the temperature is lower than 1150 ° C., the absorbed carbide solids in the austenite matrix are insufficiently absorbed by the austenite matrix, and sufficient ductility cannot be obtained during wire drawing. On the other hand, when the material is heated to a temperature of 1400 ° C. or more, the strength and ductility of the material itself are rapidly reduced during the heat treatment, and there is a risk that the material may be broken.

Next, after the C is sufficiently dissolved in the austenite matrix by the solution heat treatment, the C
Must be kept in a temperature range of 800 ° C. or more and less than 1150 ° C. for 5 seconds or more in order to prevent the precipitation of carbides as carbides and to increase the austenite phase. By this treatment, C can be absorbed in the austenite phase. Note that the holding time is preferably 30 seconds or less in order to prevent carbide precipitation and reduce the ferrite phase and increase the austenite phase.

Further, if the above heat treatment is performed and then left to cool, precipitation of C easily occurs.
It is necessary to rapidly cool from the above temperature range. Here, the cooling rate is preferably 30 ° C./sec or more.

[0024]

EXAMPLE 500 kgf of molten steel having the composition shown in Table 2 was cast into a 10 mmφ wire rod using a horizontal continuous casting apparatus. Next, after performing each heat treatment shown in Table 3, the aperture value of each wire was measured. The results are shown in Table 3.

[0025]

[Table 2]

[0026]

[Table 3]

[0027]

According to the present invention, the ductility of heat-resisting steel, which conventionally had an aperture value of less than 40%, can be remarkably improved, and in particular, the aperture value required for realizing ordinary wire drawing. ： 50
% Or more, it is possible to obtain a welding wire having excellent characteristics at low cost.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C22C 38/00 382 C22C 33/04 C22C 38/54

Claims (6)

(57) [Claims] 1. C: 0.10 to 0.50 wt%, Si: 0.1 to 2.0
wt%, Mn: 0.1-2.0 wt%, Cr: 20-35 wt%, Ni: 10-20 wt%, Mo: 0.01-0.5 wt%, B: 0.0003-0.0100 wt%, P: 0.03 wt% or less, S: 0.01 wt% or less, N: 0.01 to 0.20 wt% and O: 0.
High ductility austenitic-ferritic dual phase heat resistant steel containing 0080 wt% or less, the balance being Fe and unavoidable impurities, and having a ferrite content of 3 to 15%. 2. C: 0.10 to 0.50 wt%, Si: 0.1 to 2.0
wt%, Mn: 0.1-2.0 wt%, Cr: 20-35 wt%, Ni: 10-20 wt%, B: 0.0003-0.0100 wt%, Cu: 0.01-0.5 wt%, P: 0.03 wt% or less, S: 0.01 wt% or less, N: 0.01 to 0.20 wt% and O: 0.
High ductility austenitic-ferritic dual phase heat resistant steel containing 0080 wt% or less, the balance being Fe and unavoidable impurities, and having a ferrite content of 3 to 15%. 3. C: 0.10 to 0.50 wt%, Si: 0.1 to 2.0
wt%, Mn: 0.1-2.0 wt%, Cr: 20-35 wt%, Ni: 10-20 wt%, Mo: 0.01-0.5 wt%, B: 0.0003-0.0100 wt%, Cu: 0.01-0.5 wt%, P : 0.03% by weight or less, S: 0.01% by weight or less, N: 0.01 to 0.20% by weight and O: 0.0080% by weight or less, the balance being Fe and inevitable impurities, and the amount of ferrite is 3 to 15%. High ductility austenitic-ferrite dual phase heat resistant steel. 4. C: 0.10 to 0.50 wt%, Si: 0.1 to 2.0
wt%, Mn: 0.1-2.0 wt%, Cr: 20-35 wt%, Ni: 10-20 wt%, Mo: 0.01-0.5 wt%, B: 0.0003-0.0100 wt%, P: 0.03 wt% or less, S: 0.01 wt% or less, N: 0.01 to 0.20 wt% and O: 0.
After casting a steel material containing 0080 wt% or less and the balance of Fe and unavoidable impurities, it was heated to a temperature range of 1150 to 1400 ° C and then kept at a temperature range of 800 ° C or more and less than 1150 ° C for 5 seconds or more. A method for producing a high-ductility austenitic-ferrite dual phase heat-resistant steel, characterized by rapidly cooling from a temperature range of 800 ° C or higher. 5. C: 0.10 to 0.50 wt%, Si: 0.1 to 2.0
wt%, Mn: 0.1-2.0 wt%, Cr: 20-35 wt%, Ni: 10-20 wt%, B: 0.0003-0.0100 wt%, Cu: 0.01-0.5 wt%, P: 0.03 wt% or less, S: 0.01 wt% or less, N: 0.01 to 0.20 wt% and O: 0.
After casting a steel material containing 0080 wt% or less and the balance of Fe and unavoidable impurities, it was heated to a temperature range of 1150 to 1400 ° C and then kept at a temperature range of 800 ° C or more and less than 1150 ° C for 5 seconds or more. A method for producing a high-ductility austenitic-ferrite dual phase heat-resistant steel, characterized by rapidly cooling from a temperature range of 800 ° C or higher. 6. C: 0.10 to 0.50 wt%, Si: 0.1 to 2.0
wt%, Mn: 0.1-2.0 wt%, Cr: 20-35 wt%, Ni: 10-20 wt%, Mo: 0.01-0.5 wt%, B: 0.0003-0.0100 wt%, Cu: 0.01-0.5 wt%, P : A steel material containing 0.03% by weight or less, S: 0.01% by weight or less, N: 0.01 to 0.20% by weight and O: 0.0080% by weight or less, with the balance being Fe and unavoidable impurities, and then cast at 1150 to 1400 ° C To a temperature range of 800
After holding for 5 seconds or more in the temperature range between 1 ° C and 1150 ° C,
A method for producing a high-ductility austenitic-ferritic duplex heat-resistant steel, characterized by rapidly cooling from a temperature range of 800 ° C or higher.