JPS59143050A - Two-phase stainless cast steel with high corrosion resistance and toughness - Google Patents

Abstract

PURPOSE:To obtain a stainless cast steel having a two-phase structure provided with high corrosion resistance and toughness by specifying the amounts of C, Si, Mn, Cr, Ni and Mo, the relation between Cr and Ni equivs., and the areal percentage of ferrite. CONSTITUTION:A two-phase stainless cast steel is composed of, by weight, <=0.1% C, <=2.5% Si, <=1.5% Mn, 22.0-30.0% Cr, 7.0-35.0% Ni, 3.0-10.0% Mo and the balance essentially Fe. To the steel may be further added one or more among <=5.0% Cu, <=0.3% Ti and <=0.3% Nb. The ratio of the Cr equiv. of the steel to the Ni equiv. is regulated to 2-4, and the amount of ferrite in the two- phase structure is regulated to 30-90% by area. Thus, the steel is provided with high corrosion resistance and toughness. The steel is suitable for use as the material of a suction roll for a paper making machine, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a stainless steel cast steel that has excellent corrosion resistance, particularly acid corrosion resistance, and toughness, and is suitable for example as suction roll material for paper machines.

In a paper machine, the suction roll used to dehydrate the high-humidity paper produced in the press section must be able to withstand corrosion from the acidic solution contained in the high-humidity paper, and must also be able to withstand the load from the suppression roll that comes into contact with it. It must have sufficient toughness to withstand. In addition, corrosion resistance and toughness are also required for film manufacturing liquid processing equipment materials and seawater pump materials. Conventionally, such materials include 5US329. Duplex stainless steel such as JL is used, but depending on the conditions of use, the material deteriorates quickly and there are problems with durability.

The present invention has been made to solve the above problems. The stainless steel cast steel of the present invention contains 0.001% of these elements, as well as up to 50% of Cu added as desired.
3% or less of Ti, 0.3% or less of Nl), the total amount of one or two or more of them is 5.0% or less, the remainder substantially consists of Fe, and the ratio of Cr equivalent / Ni equivalent It is characterized in that it has a chemical composition with a ratio of 2 to 4, and that the amount of ferrite in its metal structure is 30 to 90%. Note that the Cr equivalent and Ni equivalent herein are calculated by the following formula [■] and CID, respectively. Each element symbol in the formula indicates the content (%) of that element.
means.

Cr per Pa (Cr cq) = Cr +Mo +1
．． 55i 10, 5 Nb...CI) Ni equivalent (Ni eq) -Ni+0.5Mn+30C
... [■] The reason for limiting the composition of the cast steel of the present invention is as follows.

All elemental contents (%) are by weight.

C: 0.1% or less C has a strength-imparting effect, but if it is included in a large amount, corrosion resistance and toughness will deteriorate due to the precipitation of Cr carbides (Cr23C6, etc.), so the content should be 0.1% or less.

Si: 2.5Lyo or less is added to deoxidize the molten alloy and ensure castability.
If the amount is too large, corrosion resistance will deteriorate, so the upper limit is set at 2.5%.

Mn2: 1.5% or less It has the effect of deoxidizing and desulfurizing the molten alloy and improving the castability, but if it is included in a large amount, the n-corrosion property will decrease, so it should be kept at 1.5% or less.

Ni Near, 0-35,0% Ni is a strong austenite-forming element, stabilizes the austenite phase in the two-phase structure, and increases toughness. Of course, the formation of the austenite-ferrite two-phase structure is due to the combination of Ni, ferrite-forming elements Cr, and Δ4o.
It depends on the presentational balance. In the present invention, in order to obtain a two-phase structure with a ferrite amount or area ratio of 30 to 90%, Cr
and M.

In relation to the content, the Ni content is defined as 7.0 to 350%.

Cr: 22.0-30.0% Cr is a basic element of stainless steel and is essential for ensuring n-corrosion resistance. In particular, in order to improve corrosion resistance against strong acids, the content must be at least 22.0%. As the content increases, the effect increases and the strength also improves, but if the content is too large, it causes deterioration of castability and a decrease in toughness, so the upper limit is set at 30.0%.

Mo: 8.0 to 10.0% Mo has a remarkable effect on improving corrosion resistance by stabilizing the passive state. For this reason, a small amount (at least 80%) is required, or a large amount is economically disadvantageous, and also promotes phase precipitation and deteriorates the material, so the upper limit is 100%, preferably 70%.
% or less.

The stainless steel cast steel of the present invention may contain one or more elements selected from the following (1), Ti, and Nb in addition to the above-mentioned elements for the purpose of improving the material quality, if desired. When two or more elements are contained in combination, the total content shall be 5.0% or less.

Cu: 5.0% or less, Cu is effective in solid solution strengthening of the austenite phase and improving corrosion resistance against non-oxidizing acids. However, since a large amount of content leads to a decrease in toughness, 50% is set as "-eye". Preferably it is 0.5 to 5.0%.

Ti: 0.3% or less T1 has a strong affinity with carbon, fixes C and improves n-erodibility, and also has a grain fine ripple effect and contributes to improving strength and toughness. However, if the amount is too large, not only will the effect become saturated, but the toughness will actually decrease.
The upper limit is 0.3%. Preferably 0005-03%
It is.

Nb: 0.3% or less Nb forms carbides and nitrides, increases corrosion resistance and strength,
It also has a crystal grain refining effect, but the effect is saturated even if added in large amounts, so it is set at 0.3% or less. Preferably 0.0
05-0.3%.

Of course, it is preferable that the amount of P, S, and other impurities mixed in is as low as possible, but the unavoidable contamination that accompanies ordinary atmospheric furnace melting is allowed. For example, there is no problem with P being mixed in at 0.06% or less, or less than 606% in 5O. Note that the above-mentioned C, Si, and Mn contents do not require any special refining technology, and are at levels that can be easily met by ordinary atmospheric dissolution.

Furthermore, in order to control the amount of ferrite in the two-phase structure, in addition to the above-mentioned content regulations for each element, the present invention also provides the
The ratio to i equivalent (Cr equivalent/Ni equivalent) is required to be 2 to 4. This is because if this ratio is less than 2, the amount of ferrite will be insufficient, whereas if it exceeds 4, the amount of ferrite will be excessive. In this way, the area ratio exceeds 30% and 90%
By creating a two-phase structure containing less than % ferrite,
In addition to high corrosion resistance, it has excellent toughness, and as shown in the examples below, it has excellent mechanical properties such as tensile strength, elongation O1 reduction, corrosion resistance, and general corrosion resistance. Side 4
In terms of edibility, it exhibits material properties that surpass those of conventional materials such as SUS 329J.

Note that the material and structure of the cast stainless steel of the present invention are finally adjusted by heat treatment. The heat treatment is preferably achieved by heating and maintaining the temperature at 1250°C or less (usually 1050 to 1250°C) and then cooling with water.

The mechanical properties and nitrification corrosion resistance of the stainless steel cast steel of the present invention are shown in Table 1 in comparison with the conventional material 5US329J1.

However, the composition of each sample material, the proportion of ferrite teeth in the two-phase structure, and the pitting corrosion test conditions are as follows.

Fit Test material Invention casting go: CO, 055%, Si2.46%
, 81n0.38%, Ni10.0%, Cr24-. 0
%, Mo6.0%, Cr equivalent/Ni equivalent = 285° ferrite nobleness = 70% (according to Schiefler phase diagram).

5US329J 1: C0.08%, SiO, 8%,
8fn1.2%, Ni 5.0%,
Cr25.0%, Mo1.5%. C
r Equivalent/Ni equivalent = 342° Ferrite amount 82%.

(11) Pitting Corrosion Resistance Test The critical pitting corrosion potential regarding the pitting corrosion sweep in 10% FeCjl'3+0.05N HC, g j corrosion melt (liquid temperature 40°C) was determined. The higher the potential, the better the pitting corrosion resistance.

Table 1 Compared to the conventional material 5US329JI, the cast steel of the present invention has
It can be seen that both toughness and corrosion resistance are 0.

Other examples regarding corrosion resistance are shown in Table 2. In the table, [1
14 servings less ft (!91J is 10% FeC, J3
+ 0.05N HCI Wli Food test melt f'ai
(i'f temperature 400C) This is the weight loss of the specimen due to pitting corrosion when soaked for 48 hours. Incense (1) ~ (1
3) is an example of the present invention, (10(,1) to (102) are comparative examples. Among the comparative examples, (100) is Cr, Mo content, Cr equivalent/Ni equivalent, and Ferrite in a two-phase structure) 41 deviates from the regulations of the present invention, (101) has a Cr equivalent/Ni equivalent, ferrite teeth etc. meet the regulations of the present invention, but the Mo content is insufficient, and (10
2) lacks N1 and Mo content, and Cr equivalent/N
This is an example in which the value of i equivalent is large.

As shown in the table, the corrosion loss of the cast steel of the present invention is
The amount is extremely small, less than 1/3 of the bites, and shows excellent resistance to acid.

As described above, the stainless steel cast steel of the present invention has excellent corrosion resistance and mechanical properties, so it can be used as suction roll rolls for paper machines, seawater pump materials, film manufacturing liquid processing equipment materials, liner materials for stern tube seals, etc. It is suitable for applications that require corrosion resistance and toughness, and guarantees durability that exceeds conventional materials such as 5US329J1.

Agent: Patent Attorney Shinhachibe Miyazaki

Claims (2)

[Claims] (1) C0.1% or less, Si2.5% or less, M n
l, 5% or less, Cr 22.0-30.0%, Ni7.
0 to 350%, Mo 8.0 to 10.0%, the balance substantially consists of Fe, and the Cr ratio fi/Ni ratio is 2 to 4, and the amount of ferrite in the two-phase structure is 30% in terms of area ratio.
High corrosion resistance toughness duplex stainless cast steel characterized by exceeding 90% or less. (2) C0.1% or less, Si2.5% or less, Mn1.5
% or less, Cr22.0-30.0%, Ni 7.0-3
5. od. Mo 3.0 to 10.0%, and any one or more of Cu 5.0% or less, TiO 23% or less, NbO, 3% or less, total 5.0% or less, the balance being substantially Fe
A highly corrosion-resistant and tough duplex stainless steel cast steel, characterized in that the Cr equivalent/Ni equivalent is 2 to 4, and the amount of ferrite in the duplex structure is more than 30% and less than 90% in terms of area ratio. .