KR20180076081A - Heat-resistant steel having high mechanical property and workability - Google Patents

Abstract

Provided is a heat-resistant steel having excellent processability and high temperature characteristics. The heat-resistant steel of the present invention comprises: equal to or more than 0.05 wt% and equal to or less than 0.8 wt% of C; equal to or more than 0.05 wt% and equal to or less than 0.8 wt% of N; equal to or more than 9 wt% and equal to or less than 16 wt% of Mn; equal to or more than 10 wt% and equal to or less than 16 wt% of Cr; at least one of equal to or more than 0.1 wt% and equal to or less than 2 wt% of Nb, more than 0 wt% and equal to and less than 2 wt% of Mo, and equal to or more than 0.01 wt% and equal to or less than 2 wt% of V; and the remainder consisting of Fe and inevitable impurities.

Description

[0001] Heat-resistant steel having high mechanical property and workability [

The present invention relates to the production of heat resistant steels excellent in workability and high temperature characteristics, and more particularly to the production of heat resistant steels for use in high temperature atmospheres such as automobile engine parts and gas turbines, (Mn) content and chromium (Cr) content are controlled and Nb, Mo and V are added within 2% to improve the corrosion resistance and heat resistance. Resistant steel.

Generally, characteristics of heat resistant steel which are generally required include abrasion resistance, high temperature fatigue strength, thermal fatigue strength and high temperature strength, and it is required not only to satisfy various physical / mechanical characteristics, but also to have excellent processability and corrosion resistance and low cost.

The heat resistance means that it has high temperature strength and oxidation resistance at high temperature. The heat resisting steel is classified into a ferrite type, a martensite type, an austenite type and a precipitation hardening type depending on the microstructure to be constituted.

Since the temperature for the intake valve is about 350 ~ 550 ℃, STR 3 or STR 11, which is a martensitic heat resistant steel having a high silicon content, is used. STR 11 contains carbide forming elements such as chromium (Cr) and molybdenum (Mo), which facilitates the deposition of carbide. In the case of silicon (Si), it is limited to 1.5% (Ni), the addition amount of up to 1.88% was increased to retard cementite formation during tempering.

Since the use temperature for the exhaust valve is about 650 to 850 ° C, STR 35, which is a heat resistant steel of Cr-Mn-Ni-N type austenite having excellent heat resistance, is widely used. STR 35, which is used for the exhaust valve, has austenite structure at room temperature even if a large amount of austenite stabilizing element is added. In addition, manganese (Mn) is added in place of nickel (Ni), which is an expensive alloying element, in which chromium (Cr) based carbide is dispersed to improve heat resistance. However, Cr) is apt to form a sigma (sigma) phase which deteriorates the mechanical properties at high temperature and causes carbide coarsening phenomenon. Therefore, a large amount of nitrogen (N) is added to control this. Particularly, heat resistant steel widely used in a high temperature atmosphere is difficult to be processed at room temperature and chromium (Cr) type precipitates are formed at a temperature range of 700 to 950 ° C., and the workability is remarkably decreased. Therefore, The yield is very low, i.e., 40 to 60%, resulting in poor economical efficiency.

In general, carbon steel has a combination of excellent strength and ductility through phase transformation and heat treatment using various processing heat treatment processes. However, unlike carbon steel, heat resistant steel is not expected to be improved by heat treatment. Therefore, the improvement of various properties of steel is mainly dependent on the addition of alloying elements.

The heat-resisting steels which have been reported as research or invention in the prior art generally contain 7 to 21% chromium (Cr), 1 to 4% nickel, 1 to 10% manganese (Mn), 0.1 to 2% silicon (Si) The alloy is composed of 0 to 0.2% molybdenum (Mo) and 0.3 to 0.5% of carbon (C) and nitrogen (N) and has mechanical properties of tensile strength of 500 to 1,000 MPa and elongation of 20 to 40% . At this time, nickel (Ni) among the alloying elements is an austenite stabilizing element and has an advantage of contributing to enhancement of workability, and more than 60% of the total supply amount is used as an alloy element of heat resistant steel. However, the price of nickel (Ni) steadily rises and nickel (Ni) price is a key index for setting the cost of heat resistant steel. In addition to the economic aspect, it causes human allergy and discharges harmful gas when it is recycled. this

(N) as an alloy element and the austenite stabilization characteristics of nitrogen (N) as an alloying element as a new alloy developed to solve various problems of conventional heat resistant steel containing nickel (Ni) And high-nitrogen heat-resistant steel.

The nitrogen is a strong austenite stabilizing element and has many advantages such as a large solubility strengthening effect, a decrease in ductility accompanied by an increase in strength, and an improvement in corrosion resistance. Conventionally, the development of high-nitrogen steels has not been actively pursued due to the difficulty in manufacturing steels for stably incorporating nitrogen in steel materials. Recently, the development of various manufacturing process technologies such as pressure induction melting, powder metallurgy and solid- And many research and development are proceeding. However, the biggest obstacle to commercialization of high nitrogen steel is that it requires expensive facilities and special manufacturing processes that require complicated manufacturing processes. Therefore, various problems have been raised in commercialization because it is necessary to remodel the manufacturing process equipment used for manufacturing heat resistant steel or to introduce new equipment.

Recently, in order to solve such a problem, the H. Berns group has found that the minimum content of nickel (Ni) is used in the international patent PCT / EP / 008960, the content of chromium (Cr) is 16 to 21 wt%, the content of manganese (Mn) in an amount of 0.5 to 2.0 wt%, molybdenum (Mo) of 0.5 to 2.0 wt%, carbon (C) and nitrogen (N) of at least 0.8 wt% There is a problem that the corrosion resistance is low.

Accordingly, it is an object of the present invention to overcome the above-mentioned limitations of the prior art, and it is an object of the present invention to provide a method of manufacturing a metal alloy which can minimize the addition of expensive alloying elements or replace other alloying elements, The present invention has an object to provide a heat-resistant steel having both high workability and high temperature characteristics and having high corrosion resistance.

Further, the technical problems to be solved by the present invention are not limited to the technical problems mentioned above, and other technical problems which are not mentioned can be understood from the following description in order to clearly understand those skilled in the art to which the present invention belongs .

According to an aspect of the present invention,

Mn: not less than 9% and not more than 16%, Cr: not less than 10% and not more than 16%, Nb: not less than 0.1% and not more than 2%, C: not less than 0.05% Mo: more than 0% and not more than 2%, and V: not less than 0.01% and not more than 2%, and the balance Fe and unavoidable impurities.

In the present invention, it is preferable to further include not less than 0.01% and not more than 0.15% of W, and more preferably not more than 0.01% and not more than 0.15% of Mo.

The heat resistant steel may have a tensile strength of 360 MPa or higher at 800 DEG C, an elongation of 20% or more, and a hot workability of 30.1% or more.

The present invention having the above-described structure makes it possible to manufacture a low-cost horizontal alloy, thereby improving the price competitiveness of the developed steel.

The heat resistant steel produced according to the present invention has a tensile strength of 360 MPa or more and a elongation of 20% or more at 800 ° C. through control of the content of the intercalating element (C + N, C / N) and the substitutional element (Mn + And 30.1% in hot workability. Thus, the processability can be improved and the process yield can be improved by 30% or more as compared with the currently used STR 35 material.

In addition, since the processability and the high-temperature characteristics are improved by securing the workability at a temperature of less than 1000 ° C., the excellent biocompatibility is improved by excluding nickel (Ni), which is an alloy element harmful to human body, And can be usefully applied to the manufacture of functional parts.

Hereinafter, the present invention will be described in detail.

The present invention is characterized in that nickel (Ni), which is an alloy element harmful to the environment and human body, is not added or added in a small amount and the content of manganese (Mn) and chromium (Cr) To provide heat-resistant steel having excellent workability and high-temperature characteristics as well as excellent corrosion resistance and a yield of 30% or more. That is, the present invention provides a method of producing a steel sheet having a tensile strength of at least 370 MPa, an elongation of not less than 20% at 800 ° C and a hot workability (tensile strength of at least 200 MPa) by controlling the content of intercalating elements (C + N, C / N) Resistant steel having excellent workability and high temperature characteristics that can improve the workability by 50% or more and obtain a processing yield of 30% or more, compared with the STR 35 material which has a widespread use rate of 30.1% or more.

The heat-resisting steel excellent in workability and high-temperature characteristics according to the present invention contains C: 0.05 to 0.8%, N: 0.05 to 0.8%, Mn: 9 to 16%, Cr: 10% , At least one of Nb: at least 0.1% and not more than 2%, Mo: more than 0% and not more than 2%, and V: not less than 0.01% and not more than 2%, the balance being Fe and unavoidable impurities.

Hereinafter, the steel composition component of the heat resistant steel of the present invention and the reason for limiting the content thereof will be described.

Nitrogen (N): 0.05 wt% or more and 0.8 wt% or less

Nitrogen (N) is added together with carbon (C) and manganese (Mn) for the purpose of replacing nickel (Ni) having the abovementioned problems as austenite stabilizing element, and also increases strength without significant deterioration of ductility, To increase the corrosion resistance. For this effect, 0.05 wt% or less (hereinafter simply referred to as%) of nitrogen should be used in the present invention. However, when nitrogen (N) is added excessively, there is a problem of causing brittleness as well as reducing ductility due to formation of segregation and nitride. Therefore, it is preferable to limit the content of nitrogen to not less than 0.05% and not more than 0.8%.

Carbon (C): not less than 0.05% and not more than 0.8%

Carbon (C) is added for the purpose of stabilizing austenite like nitrogen (N), and enhances strength of heat resistant steel through solid solution strengthening effect. For this effect, more than 0.05% of carbon should be used. However, when carbon (C) is added excessively, the mechanical properties (typically toughness) are lowered, and carbides such as M ₂₃ C ₆ and M ₆ C are generated in the grain boundary to promote sensitization of the heat resistant steel, . Therefore, the content of carbon (C) in the heat resistant steel of the present invention is limited within the range of 0.05% to 0.8%.

chrome( Cr ): 10% or more and less than 16%

Chromium (Cr) is an alloy element added to improve the corrosion resistance of steel, and the critical content of chromium is 10%. However, when Cr (Cr) is added in excess, excessive delta ferrite remains after coagulation or promotes the formation of various kinds of second precipitation phases during heat treatment, thereby reducing the corrosion resistance and workability of the heat resistant steel. It is preferable to control it in the range of 10 to 15%.

manganese( Mn ): 9% or more and less than 16%

Manganese (Mn) is an austenite stabilizing element that can replace expensive nickel (Ni) and is added to heat resistant steel to increase the nitrogen solubility and increase the strength of the material. On the other hand, when manganese (Mn) is added in excess, it is combined with sulfur (S) or oxygen (O) which is an impurity element to form manganese sulfide (MnS ) Or manganese oxide (MnO). Since the generated nonmetallic inclusions serve as a main source of formaldehyde, the resistance to heat of the heat resistant steel is lowered. Therefore, in the present invention, the manganese (Mn) content is preferably limited to a range of 9% or more to less than 16%.

The heat-resisting steel of the present invention further includes at least one element selected from the group consisting of Nb, Mo and V, and the reason for addition and the reason for limiting the content of the steel are as follows.

Nb : 0.1% or more and 2% or less

Niobium (Nb) forms a carbide and finely disperses in the matrix to improve creep strength. For this purpose, it must be contained at least 0.1% or more, and the addition of a large amount of niobium (Nb) deteriorates the weldability. Therefore, in the present invention, the content of niobium (Nb) is limited to 2% or less, more preferably 0.1% to 1%.

Mo : More than 0% and less than 2%

Molybdenum (Mo) is an alloy element that improves the corrosion resistance of austenitic heat resistant steel together with chromium (Cr). However, if it is added in excess, it will decrease the austenite fraction, which causes a decrease in workability. Like the chrome (Cr), it forms a harmful second phase such as carbide and intermetallic compound, Or less.

V: not less than 0.01% and not more than 2%

Vanadium (V), like niobium (Nb), produces carbides to improve creep strength. However, when the content is less than 0.01%, the above effect can not be obtained. When the content is more than 2%, an unstable phase is formed and the austenite fraction is decreased to lower the high-temperature processability. Therefore, in the present invention, it is preferable to limit the content of vanadium (V) to 0.01 to 2%.

The heat resistant steel of the present invention may further contain not less than 0.01% and not more than 0.15% of tungsten (W) in addition to the above-mentioned composition components. The tungsten (W) together with chromium (Cr) and molybdenum (Mo) is an alloy element that improves the corrosion resistance of the heat resistant steel, thereby increasing the high temperature strength and improving the creep resistance. Since tungsten (W) is also a ferrite stabilizing element, it increases the ferrite fraction when added excessively, and forms a harmful second phase such as chromium (Cr) and molybdenum (Mo) do. Accordingly, in the present invention, the content of tungsten (W) is preferably limited to 0.01% or more and 0.15% or less.

On the other hand, when tungsten is added as described above, it is more preferable to limit the addition amount of Mo to not less than 0.01% and not more than 0.15%.

     (C + N, C / N) and a substitutional element (Mn + Cr, Mn / Cr) by adding a composite of carbon (C) and nitrogen (N) according to the present invention, It is possible to provide heat resistant steel having excellent mechanical properties such as a tensile strength of at least 370 MPa, an elongation of at least 20% and a hot workability of at least 30.1% at 800 ° C.

In addition, the heat-resisting steel has improved processability and high-temperature characteristics and exhibits excellent corrosion resistance. Since the biocompatibility is improved by restricting the amount of nickel (Ni), which is an alloy element harmful to the human body, manufacture of various functional parts such as medical biomaterials, . ≪ / RTI >

Hereinafter, the present invention will be described in detail by way of examples.

(Example)

division C N Mn Cr Ni Si P S W Nb V Mo Comparative Example 1 0.55 0.42 9.45 21.5 3.30 0.16 0.022 0.0015 0.17 Comparative Example 2 0.66 0.54 21.3 24.2 0.2 0.024 0.0005 0.6 Comparative Example 3 0.48 0.58 17.8 18.5 0.45 0.022 0.0011 0.51 Comparative Example 4 0.43 0.53 17.8 17.9 0.36 0.025 0.0010 1.5 0.52 Inventory 1 0.52 0.51 10.3 10.2 0.019 0.0060 0.15 Inventory 2 0.51 0.49 10.2 15.1 0.027 0.0027 0.15 Inventory 3 0.51 0.52 15.1 15.2 0.020 0.0032 0.15 Honorable 4 0.52 0.51 14.9 15.3 0.023 0.0011 0.15 0.15

* In Table 1, the composition is expressed in weight%, and the remaining components are Fe and unavoidable impurities.

Fe-Cr-Mn heat-resistant steel having a basic composition of Fe-15% Mn-15% Cr-0.5% C-0.5% N was prepared. Specifically, the contents of manganese (Mn), chromium (Cr), tungsten (W), niobium (Nb), vanadium (V) and molybdenum (Mo) And the comparative examples which are not so different are presented.

Then, each of the above-mentioned composition components was melt-cast from each of the heat-resisting steels, followed by hot rolling, cold rolling, and annealing and pickling to obtain a 1 mm-thick plate. Tensile test and hot workability were evaluated for the thus prepared plates, and the results are shown in Table 2 below.

division
Tensile Strength (MPa) Yield strength (MPa) Elongation (%) Hot workability (RA:%) Room temperature 800 ° C Room temperature 800 ° C Room temperature 800 ° C Room temperature 800 ° C Comparative Example 1 700 360 412 285 9.1 15 6.4 29.2 Comparative Example 2 960 495 537 425 5.0 13 3.4 18.3 Comparative Example 3 903 475 493 412 6.3 14 3.5 17.5 Comparative Example 4 868 415 476 406 9.8 16 4.1 19.8 Inventory 1 720 370 421 296 12.1 20 6.9 36.2 Inventory 2 836 390 445 300 11.4 23 5.8 34.5 Inventory 3 897 480 489 410 8.8 25 4.7 32.4 Honorable 4 920 490 514 415 7.1 22 4.4 30.1

As shown in Table 1-2, tensile strength (TS), yield strength (YS) and elongation (El) indicating moldability were measured in Inventive Examples 1-4 in which the compositional components of the heat resistant steel satisfied the range of the present invention. ) And excellent hot workability. Specifically, in Examples 1-4, tensile strength is 370 to 490 MPa, elongation is 20 to 25%, and hot workability is 30.1 to 36.2% at 800 ° C, which indicates excellent quality properties such as high temperature processability and high temperature characteristics.

On the contrary, in the case of Comparative Examples 1-4 in which the content of manganese (Mn) and / or chromium (Cr) is higher than those of the present invention, manganese or chromium carbide and nitride are easily formed at high temperature and high temperature mechanical properties such as hot workability . ≪ / RTI >

While the present invention has been particularly shown and described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, Of course, this is possible. Therefore, the scope of the present invention should not be limited to the above-described embodiments but should be defined by the following claims as well as equivalents thereof.

Claims (3)

Mn: not less than 9% and not more than 16%, Cr: not less than 10% and not more than 16%, Nb: not less than 0.1% and not more than 2%, C: not less than 0.05% Mo: more than 0% and not more than 2%, and V: not less than 0.01% and not more than 2%, and the balance Fe and unavoidable impurities.
The heat-resistant steel according to claim 1, further comprising W: not less than 0.01% and not more than 0.15%, wherein Mo: not less than 0.01% and not more than 0.15%.
The heat-resistant steel according to claim 1, wherein the heat-resistant steel has a tensile strength of 360 MPa or more at 800 ° C, an elongation of 20% or more, and a hot workability of 30.1% or more.