JPS5845362A - Heat resistant cast steel with superior thermal impact resistance and superior oxidation resistance at high temperature - Google Patents

Abstract

PURPOSE:To obtain a heat resistant cast steel with superior thermal impact resistance and superior oxidation resistance at high temp. by adding specified wt% of C, Si, Mn, Cr, Ni, Co, W and Ca to a cast steel. CONSTITUTION:The composition of a heat resistant cast steel is composed of, by weight, 0.2-0.7% C, 0.5-2% Si, 0.5-2% Mn, 25-30% Cr, 32-37% Ni, 2- 7% Co, 0.2-2% W, 0.001-0.05% Ca and the balance Fe with inevitable impurities. Thus, by restricting the compositional ranges of the constituent components of a conventional heat resistant Ni-Cr-Co-W cast steel, especially reducing the Co and W contents, and adding Ca, the thermal impact resistance and the oxidation resistance at high temp. are remarkably enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of Nj-Cr-Co heat-resistant cast steel used in a 71n heat furnace or the like at a temperature of 1000 to 1300°C.

For example, the so-called heat-resistant materials used for the skids and sliders of calothermal furnaces are said to have excellent thermal shock resistance and to have excellent high-temperature strength.
■ Three characteristics of excellent fresh temperature oxidation resistance
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Due to its strong resistance to thermal shock, it expands, contracts and warps when subjected to thermal shock such as repeated high temperature heating and rapid cooling during use. ⑤Maintain high-temperature hardening so that it does not deform due to mechanical stress when exposed to high temperatures for long periods of time. (2) The weight loss due to oxidation is small even when exposed to an oxidizing atmosphere at high temperatures for a long period of time.

Heat-resistant materials may also be required to have high-temperature gauze resistance, high-temperature toughness, and carburization resistance, but thermal shock resistance is the most important for heat-resistant materials used in heat treatment furnaces! 'is.

In other words, due to the thermal shock received during use, the first
As shown in the figure, cracks occur in many cases and the material is discarded, which has the greatest impact on the service life of the material.

Next, a grain with little oxidation loss at high temperatures is important for extending the service life.

So'5co-281 is a heat-resistant material for conventional heating furnaces.
There is a 1Cr-remaining Fe cobalt-based alloy (UMCO50), which is suitable for the composition range shown below.

CSt Mn P-8Cr Co
However, as shown in the data of comparative test A7 described later, such Co-based alloys have excellent high-temperature hardness, but are inferior in thermal shock resistance and high-temperature oxidation resistance.
In addition, the cost is extremely high due to the addition of about 50 liters of cobalt, an expensive raw material.In particular, when extracting steel materials during use of a heating furnace, the steel material must be repeatedly cooled as air flows into the furnace and heated by the steel material. It does not stand up to long-term use because it is exposed to heat.

In addition, the following acid content is used as an N1-Cr-Co-W heat-resistant alloy similar to the present invention! There are 11 scales.

CSi Mn Cr Ni Co W
O, 30, 9082026 & 50.3 -09 逼 Supplement D ~ 30 Pack 〇 - 4D This is because, as shown in the comparative test data (Ban 10) described later, it has a small oxidation loss, particularly excellent high temperature strength, and very high thermal shock resistance. It is obvious that many cracks occur during use in a heating furnace, and it cannot withstand long-term use.

Also, as a M i -Cr-Co-W heat-resistant alloy, CO is added to 171%W'f! -4(7) containing 5 to 6g6, but as shown in comparative test data A8 mentioned below, it has extremely high temperature strength, but stool 1, hot acid resistance and thermal shock resistance are both poor. Because of this, it cannot be used in applications where it is rapidly heated and cooled in an oxidizing atmosphere, such as in a heating furnace.

The present invention provides particularly high thermal shock resistance and ? i1. The purpose is to provide a heat-resistant cast copper suitable for applications such as warm acid resistance, oxidation resistance, and heating furnace skids, and its gist is that the composition range is heavy BS, Cα2 ~
α7, SiO, 5-2.0, Mn0.5-2.0
, Cr 25-30, Ni32-37, C02-7
, wo, 2 to 2.0, CaO, 001 to 0.05, and the balance is composed of minerals and unavoidable impurities.It is a heat-resistant cast pot with excellent thermal shock resistance and high-temperature oxidation resistance.

Below is the first explanation of the reason for the addition of each of the above ingredients and their composition range! ! ``Composition of Invention Steel and Comparative Steel''.

Based on Table 2 "Test Results of Invention Steel and Comparative Steel", the difference between shells is - = 32C First, CFi is generally 0.1 to 0.911 to impart high temperature strength to Ni-Cr heat-resistant cast copper. Although it contains
As shown in Comparative Steel Layer 17 in Tables 1 and 2, when Fi is less than 0.2%, the high-temperature hardness rapidly decreases even if other components are within the composition range of the present invention. Ma+C content is 0.7'
If the value exceeds 1, it combines with Cr and crystallizes a large amount of carbide, lowering the Cr IIIWt of the matrix.
As shown in No. 5 and No. 16, it was found that the oxidation resistance at sieving temperature was poor, and the hardness at high temperatures, particularly 1200° C., rapidly decreased. Therefore, the lower limit of the C content IIA-Q is required to be 211, and the upper limit is set to G, 7s.

Next, regarding 81, it increases the fluidity of the molten metal and contributes to the desired high-temperature oxidation resistance, so the lower limit is 0.5.
However, even if two or more are added, the effect of increasing the amount is small, and on the contrary, there is a tendency to deteriorate the thermal shock resistance, so the upper limit was set at 2.0.

Adding a small amount of MnK is effective in improving high-temperature strength, but adding a small amount of less than 0.5 capsules does not contribute much, so we set the lower limit #'iQ, 5s, and 0.5-2.0ts was struck.

Regarding Cr% N1-Cr- (in o-based heat-resistant materials, it is usually added in order to provide high-temperature oxidation resistance, but if the addition amount is less than 25%, high-temperature oxidation resistance such as Comparative Steel 48 and 49) There is an axis direction where the property decreases, ``1st order 309
Even if 6 or more were added, it would not be effective in improving Hatate's oxidation resistance, so the lower limit was set at 25 and the lower limit was set at 30 tatami.

Next, Ni is %2 in Fe-Ni-Cr heat-resistant alloys.
8. Cr-35S Ni area has good high temperature oxidation resistance and high high temperature strength, so it is JIS heat resistant steel cast steel product 5CH24.
It is also used as a material, and its Ni content is 33 to 37%.
It is. Therefore, in the present invention, the lower limit is set to 52% and the upper limit is set to 37 whispers.

CO/d 8 to 1 in Fe-Ni-Cr heat-resistant alloys
Addition of 7% improves high temperature strength and also provides good thermal shock resistance at the same time. Comparative steel has a strength of around 10 to 15 degrees. 18.19 However, following the recent sharp rise in the price of cobalt, we considered lowering this content, and found that if we reduced the amount of W added to 1/2 and added Ca in bulk, it would be possible to reduce the cobalt content. It is clear that even if the content of 711 or less, the high temperature strength decreases to some extent, but the thermal shock resistance does not decrease [7Th]. Therefore, the object of the present invention can be fully achieved with a CO content of 2 to 7 degrees.

When the addition of W exceeds 3%, the high temperature oxidation resistance deteriorates even in the presence of Ca. -41
1. As is clear from AI 2, as a result of experiments on the steel of the present invention, in the presence of Ca, the high-temperature oxidation resistance (oxidation sound reduction) is 12.0 to 1.8 when the hardness is 0.5 to 1.8. 13.911If/1
0R proverb was the best result. In addition, when W is not used in the swimming direction, the high temperature strength deteriorates as shown in comparative steel A14, so the lower limit was set to 0.2 and the upper limit was set to 2.0. A comparison between OtaW and ('a) shows that, even if other components satisfy this invention steel, the thermal shock resistance decreases at the rod end.
11413, it was proved by.

The addition of Ca is the most characteristic feature of this invention.

A final content of 0.001 to 0.05* in the alloy significantly improves the thermal shock resistance and high temperature oxidation resistance of cast copper. Approximately 0.2516 Ca equivalent is added as Ni-Ca alloy in the Ca casting process, but most of it is transferred to the 71 mouth and only 1 1 Ca remains in the product cast steel, but during the casting process NK. Among the 14 varieties of 'It's test cheaters with unclear behavior and tissue status in Tables 1 and 2, 4 were found to have Ca added.
15. Except for the flat plate 16, all of them have the highest thermal shock resistance. This is because the amount of A15 and A16FiC is excessive after 0.8 liters of addition.

On the other hand, 5 types of steel without Catf# (A6.7゜8.1
0.13) are at the lowest level of heat resistance.

II! Specifically, comparative steel AI obtained by removing Ca from this invention steel
Just as the thermal shock resistance of O is poor, the effect of improving the thermal shock resistance by adding Cat's is clear.

Regarding high-temperature oxidation resistance, steel grades with Ca added,
M9 and A11, which have a large reduction in recognition due to the addition of W polyphonic sounds. A
Except for AI5.416, which is due to excessive addition of C.12 and C, all of them are most superior in high temperature oxidation resistance. On the other hand, those that do not contain Ca have poor high-temperature oxidation resistance.

Next, although it cannot be said that the high-temperature strength of the steel of the present invention is particularly excellent, tests have shown that it can withstand long-term use as a heating furnace.

Note that thermal shock resistance, high temperature oxidation resistance, and high temperature strength were measured by the following methods.

Thermal shock resistance: A test piece as shown in Figure 2 was prepared from each test piece in Table 1, and one cycle consisted of holding this test piece in a furnace at 1200°C for 15 minutes and then rapidly cooling it with water. After 72 cycles, the specimen is cut longitudinally along an arbitrary center line.

The number of cracks that can be identified with a metal mold mirror is indicated as the "number of cracks," and the total length of the cracks on the cut surface is indicated as the "total crack depth." The longer one is indicated by a minus sign as the "maximum crack depth."

High-temperature oxidation resistance: A test piece with a diameter of 20 cm and a thickness of 10 cm was prepared from each specimen, and after keeping it in an oxidizing atmosphere furnace at 1300 °C for 100 hours, one of the shoulder test pieces before heating was measure quantity. R
The loss on heating is expressed as "oxidation loss" in q/cm.

High temperature strength: A test piece with a diameter of 10 cm and a thickness of 5 m was prepared from each specimen.
Heated in argon gas to 1000°C, 1100°C,
The hot hardness at 1200℃ was measured using a high temperature hardness tester.
"High temperature hardness" and is expressed in units of HV.

As detailed above, the present invention is based on the conventional N1-Cr-C
By limiting the composition range of each component of the o-W heat-resistant cast steel, particularly reducing CO and W and adding Cat-saturation, it has particularly excellent thermal shock resistance and high-temperature oxidation resistance, and can be manufactured economically. It provides heat-resistant cast steel, and has been recognized to withstand long-term use in applications where the skid rails of slab heating furnaces and sliders are exposed to repeated thermal shocks and mechanical shocks due to rapid heating and cooling in an oxidizing atmosphere.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a state in which a t# heat material has cracked due to thermal shock, and FIG. 2 is a plan view showing the shape and method of a test piece subjected to 1 heat O# shock. Agent: Patent Attorney Masaru Sato, 2013 Figure 1

Claims (1)

[Claims] Acid composition range is C002 to 0.7, Sjα5
~2.0, Mn0.5~2.0, Cr25~30,
Ni32-37, CO2-7, W 0.2-2. O
Hot cast copper with excellent thermal shock resistance and high temperature oxidation resistance, consisting of 1Ca 0.001 to 0.05, the balance being Fe and unavoidable impurities.