JPS6092454A - Heat resistant austenitic steel with superior hot workability and oxidation resistance - Google Patents

Abstract

PURPOSE:To provide superior hot workability to a heat resistant high-Si austenitic steel having a specified composition and to improve the oxidation resistance furthermore by adding a proper amount of N together with Ca, a rare earth element or Mg and by restricting the lower limit of the Ni equiv. CONSTITUTION:This hest resistant austenitic steel consists of, by weight, <=0.25% C, 1.5-3.5% Si, <=2.0% Mn, 0.8-35.0% Ni, 15.0-30.0% Cr, <=0.15% N, one or more among 0.0005-0.020% Ca, 0.005-0.100% rare earth element and 0.0005-0.030% Mg and the balance Fe or further contains one or more among 0.0005-0.0150% B, 0.05-1.0% Ti, 0.05-1.0% Nb, 0.05-1.0% Ta and 0.05-1.0% Zr and has >=-1.0 Ni equiv. To the steel may be added 0.05-6.0% Al. The steel has superior hot workability and oxidation resistance, and cracking can be prevented when the steel is cogged.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides heat treatment jigs, automobile exhaust gas treatment equipment, etc.
The present invention relates to an austenitic heat-resistant steel that has excellent hot workability and oxidation resistance and is used in steel materials that are easily oxidized at high temperatures.

Because heat treatment jigs are exposed to high-temperature combustion gas for long periods of time,
It is necessary to have excellent oxidation resistance, and conventionally, Al5I3Q2B (l13cr-9N Sea2,
5s;), A15I314 (25Cr-2ONi-2
Si) etc. are l! 'Used. These steels have good oxidation resistance, but because they have a height of 8st14, they have some problems in hot workability, such as tip cracking and corner cracking during hot rolling.

In addition, when the above-mentioned austenitic heat-resistant steel is repeatedly heated intermittently in an atmosphere surrounded by combustion gas at high temperatures, there is a problem that the τν scale peels off and the plate thickness decreases or progresses. In addition to this, it was also required that the product should have excellent anti-slip properties.

In recent years, in order to improve the thermal m1 workability and modification resistance of the above-mentioned 1TIS i austenitic heat-resistant steel, a trace amount of Cm has been added.
, B, 1vigyz, etc. have been attempted to have one side, and some have been offered. However, although Cm, B, and Mg have the effect of slightly improving hot workability and oxidation resistance, cracks still occur in some parts of block rolling, and they also stably improve hot workability. They are being asked to do something.

The present invention has been made in view of the drawbacks of conventional steels, and has found that this is due to the difference in deformation resistance between austenite and ferrite, which coexist during rolling.

Based on this knowledge, the present invention is based on Cs-rare earth element.

By containing one or more types of Mg, containing N at an appropriate temperature, and limiting the lower limit of -Ni, we aim to improve hot workability and oxidation resistance, and prevent cracking in single block rolling. This prevents the occurrence of

Description The present invention v14 will be detailed below.

% 1 mdAtRtt, H aspect ratio = L TECO, 25
* LJ lower, S il, 5-3-516. Mn
2.091L lower, Ni 8.0-35. OS, C
r15Jj-3L1.0#, N O, 15% LJ lower,
=, CmlJ, 00U5-0.020*, rarely similar to 0.0U5-OJ 0096. MgO,000
Contains trill or two or more of 5 to 0.030.

The remainder consists of Fe and impurity redundancy, and the Ni ratio is -1,
0 or more, and the 2nd @Meiko has BO,000 to the 1st invention steel.
5-0.0150%, Ti 0.05-1.0%, Nb
0.05-1. OL Tm O,005-1,0%,
The third invention steel contains IJll or two or more of zr o, o5-t, o*, and further improves the high temperature strength of the first invention steel, and the third invention steel contains AlO, 05-6 in the second invention steel. ．．
This steel further improves the oxidation resistance of the second invention steel.

The component-limited width increase of the steel of the present invention will be explained below.

It is a CIi mastenite type a element and is the main element that improves high-temperature strength by -1. but.

@Available or abundant] too much. ! Since the hot workability and oxidation resistance are lowered, the upper limit is set as L25-.

Si is an important element that improves oxidation resistance and descaling/descaling resistance at +t%m. In particular, even better oxidation resistance can be obtained by promoting the addition of -Cs and the rare earth element 1Mg. These effects can be obtained using IC + engineering 1. 'J%? )'l L
'> e force h""J J 7" h so, ftq
``'f('l E /41. However, -3.5%
If the content exceeds 3.5 inches, 3-Fight or 6-phase formation occurs, which deteriorates heat bending workability and mechanical properties at high temperatures, so the upper limit was set at 3.5 inches.

Mn is an austenite-forming element or has oxidation resistance t-
It is also a harmful element, and it is not preferable to contain it in large amounts, so the upper limit was set at 2.0%.

Ni is one of the basic elements of austenitic heat-resistant steel, and is also an element that suppresses the formation of S ferrite due to the inclusion of 8i, and therefore needs to be included in a and osIi. However, even if the content exceeds 350, the effect is only slightly improved.
Since it is non-Mffi, the upper limit is set to 350chi.

Since Or is a major source of improving oxidation resistance at high temperatures, it produces 3 ferrites and deteriorates hot workability and mechanical properties at high temperatures, so the upper limit was set at 30.0.

N is an austenite-forming element and a main element that increases high-temperature strength. However, if the content exceeds 0.15 h, the hot workability deteriorates, so the upper limit was set at O, +5*.

C@ is an element that improves hot workability and oxidation resistance, and to obtain the above effects, it must be contained in an amount of 0.0005 or more. However, if the content exceeds 0.021, it will actually impair gauge workability, so the upper limit should be set at 0.0.
It was set at 20%.

Rare earth elements such as Co, Lm, and Y are elements that, like Cm, improve hot workability and oxidation resistance.

In addition, rare earth elements are 0. Strong affinity with S etc.

It is also an element that has a deoxidizing and desulfurizing effect and purifies grain boundaries, etc., and in order to obtain these effects, the content must be 0.0051 or more. However, 0. If the content exceeds +00, it will actually impair hot workability, and in addition, @1ko, +o
I made uchi.

Like Cm and rare earth elements, Mg improves hot workability and oxidation resistance, and also has a deoxidizing and desulfurizing effect.

S is an element that suppresses impurity elements from forming at grain boundaries, and must be contained in an amount of 0.0005% or more to obtain these effects. However, if the content exceeds 0.030 seconds, a low melting point compound will be generated and hot workability will be impaired, so the upper limit was set at 0.030 seconds.

B is an element that improves hot workability and high temperature strength. That is, B retards grain boundary diffusion and 0. It suppresses the grain boundary concentration and grain boundary precipitation of impurity elements such as S, increases the ductility of the grain boundary region, and improves hot workability. It is necessary to contain but.

If the content exceeds 0.0150%, hot workability at temperatures above 1200°C will be impaired, so the upper limit was set at 0.0+50*. Ti, Nb, T@, and Zr are all elements that form stable carbide nitrides and improve high m strength, and each requires 0.05 to obtain these effects! # It is necessary to have at least the following. - - ~ -- Ne4A11444; The upper limit was set to 1.0%.

AI is an element that improves oxidation resistance and scaling resistance, and in order to obtain these effects, it is necessary to contain it in an amount of 0.05-1 or more. However, At is also a strong fephite-forming element, and if it is contained in an amount exceeding 6.0%, it tends to generate δ ferrite (which impairs hot workability, so the upper limit is set at 6.0%).
．． It was set to 01.

Ni equivalent shows the balance between the ability to form γ phase and the ability to form three phases in the solidified structure, and Ni equivalent t=Ni-1-30C+1
5N+14.5'-1,3Cr-28i-3(A1
+Ti)-2 (Nb+Ta+Zr), and if the Ni equivalent is low, too much 8-feuite formation occurs, making cracks more likely to occur during one-blob rolling, so at least -1,
It is necessary to make it 0 or more, and the lower limit is set to -1.0.

Next, the characteristics of the steel of the present invention will be clarified by comparing it with conventional steel and Hikari steel using a dormitory example.

Table 1 shows the chemical compositions of conventional steel, Hibana steel, and steel of the present invention.

Looking at Table 1, A and Bm are conventional steels, and A steel is Al8I.
302B, Bm)! Al51314, C-Fm)i comparative steel, and G-1ζ steel is the invention steel.

Table 2 shows the hot workability of the sample mA-R steel shown in Table 1. For the hot workability investigation, 10φ x 30 parallel specimens were prepared.

The test conditions were heating temperatures of 1000°C and 1100°C.

1 rotation Pi 25 r, p at 1200℃ and 1250℃
, m The number of T-rupture twists was measured.

As is clear from Table 2, A is a conventional steel.

Bielt! l0LIO℃, 1100℃, 120 times℃,
The number of twists at fracture was low at each temperature of 1250°C, indicating poor hot workability, and the comparison steel C, l)
, E, and F steels contain Ca, KklVl, and Mg, but the Ni equivalent is low at less than -1.0, so #
: Compared to the new steels A and BgI4, the number of fractures and twists is lower.

On the other hand, G-Rw4, which is the steel of the present invention, is CmREM.
, contains one or more types of Mg and has a Ni equivalent of -1,
By setting the value to 0 or more, the number of twists at rupture is 5 at 1000°C.
more than 8.6 times at 1100°C.

It shows a high value of 10.2 times or more at 1200°C, and it is clear that the steel of the present invention has superior hot workability compared to the conventional steel and vfIaIc.

Table 3 shows the results of examining the oxidation resistance, particularly the scale flaking resistance, of the sample steel A-R shown in Table 1.

For the oxidation resistance test f, the sample was heated at 1100° C. for 25 minutes in 1 meter of air using a repeated oxidation tester.

The operation of air cooling for 5 minutes was repeated and the weight change was measured.

Table 3 (repeated oxidation test results) As is clear from Table 3, A is a conventional steel.

Because By4 does not contain Cm or 1Mg of rare earth elements, it suffers from monoxide thinning and has poor oxidation resistance.In contrast, the G-R steel, which is the steel of the present invention, has poor oxidation resistance. !Because the wax contains 1 Mg of Ca and 1 Mg of Futochingen, the weight loss due to oxidation after 100 repetitions of IsufL is 0.
2mg/d or less, 200 times - 2mg/d
It is clear that the steel of the present invention has excellent not only hot workability but also oxidation resistance. It is.

As mentioned above, in order to improve the hot workability, which is a drawback of high-Si austenitic heat-resistant steel, the steel of the present invention appropriately contains C@, rare earth elements, Mg, B, etc., and the lower limit of Ni ? 1. The steel of the present invention can prevent cracking during blooming. 1. Heat treatment jigs, automobiles. Exhaust gas treatment equipment TR - Made of optimal steel and has practicality.

patent applicant Procedure correction store, (method) %formula% 2. Name of the invention Hot workability, oxidation resistance Superior austenitic heat-resistant steel 3. Person who makes corrections Relationship to the incident: Patent applicant Aichi Tokai Alao 1 Wanowari, Arao-cho, Tokai City, Aichi Prefecture January 110, 1981 (Shipping port: January 31, 1982) 5. Subject of correction Specification --゛ 6. Contents of amendment as attached Engraving of the detailed statement (with changes to the Song Dynasty)

Claims (1)

[Claims] 1. Weight ratio C0.25 or less, Si l, 5
~3.5%, Mn 2.0% or less, Ni 8.0-
35.0%, Cr 15.0~30.0chi, NO, +5
Cs o, 0'o5~0.020%, rare earth mycRO,005-0,100%, Mg 0.000
Contains one or more lumps of 5-0.030%,
The remainder consists of Fs and other impurity elements - Ni 5 information -
An austenitic heat-resistant steel with excellent hot workability and oxidation resistance, characterized by a hardness of 1.0 or more. 2.311 ratio, Cα25 or less, 8i i, 5~
3.5Wt±114y'c* (LOO5-U, 100
%, MgO,0005-0,030- contains one or more yuzu chunks, and BO,0OL15-0. U
150%, T i αl-1, US, “Nb ro,
05-1.0%, Ta (LO5-1,0IJ1.Z
r Contains 1 lump of O,05-1,0% or more than 211O1, and the remainder consists of F and impurity elements -N
1l is characterized by being greater than or equal to 1t-1,0 for i
Austenitic heat-resistant steel with excellent processability and oxidation resistance. 3. under tl ratio i site c a25LLJ, Si 1.
5-3.5chi, Mnz, os or less, Ni 8.0-3
! aO-, Cr t5.0-30.0chi, NO, 15%
The following, Cfi O, O'05~0.020chi, rare earth element Q, 005~Q, 100chi Mg 0.000
Contains one to 211 or more of 5 to 0.030%, and further contains Bo, 0005 to [LO150chi, Tiα05
~1.0chi, NbO,05-1,0%-TlO,05
-1,0%, 1fIf of Zr O,05-1,01
Hot workability characterized by containing I to 21 #i or more and A 0.05 to 6.0 #i, the balance consisting of Fe and t impurity elements and having a Ni equivalent of -1.0 or more , an austenitic heat-resistant steel with excellent oxidation resistance.