JPS581062A - Corrosion- and abrasion-resistant cast steel - Google Patents

Abstract

PURPOSE:To provide two-phase stainless type cast steel of high corrosion and abrasion resistances by setting the volume ratio of the ferrite of steel of a specific compsn. at specific ratios, and subjecting said steel to a deposition hardening treatment at a specific temp. range after a solubilizing treatment. CONSTITUTION:The steel which consists of <=0.1%, 0.5-1.5% Si, 0.5-1.5% Mn, 22-28% Cr, 6-11% Ni, 1.5-3.5% Mo, 2.0-5.0% Cu, and the balance Fe and impurities, and in which the volume ratio of ferrite is 50-65% is subjected to solubilizing treatment. This is then subjected to a deposition hardening treatment at 450-550 deg.C. The ferrite-austenite type two-phase stainless cast steel having high corrosion and abrasion resistance in corrosive environment is obtained.

Description

[Detailed description of the invention] The present invention has excellent castability in corrosive environments.

The present invention relates to a ferrite-austenite type two-phase steel/less cast steel having excellent corrosion and wear resistance.

Due to recent demands for resource and energy conservation, technologies that apply low-grade oil and coal are increasing, such as in removal equipment and transport/stems for heavy oil and coal.

Equipment such as bogs that move corrosive slurry suffer from corrosion and wear. Conventionally, materials for such parts include: 5O814 (austenitic cast steel) and SO811 austenitic-ferritic duplex stainless steel cast steel, but these materials have few problems in terms of corrosion resistance, but have low hardness and have no wear resistance. Because of this lack of consideration, recent corrosion and abrasion environments have become more severe, leading to repair or scrapping due to wear after a short period of use. In addition, wear-resistant materials such as cast iron undergo thinning due to corrosion, and materials with both wear and corrosion resistance are required.Therefore, conventional methods for improving the wear resistance of corroding materials are needed. For austenitic-ferritic duplex stainless cast steels such as 80811.

Materials that harden the ferrite by heating it to 600 to 700°C to turn it into the Soge I phase have been considered, but the material is extremely brittle, which limits its application as equipment components. Since the wear progresses with the shedding, there is little improvement in wear resistance for hardness steels.

The present invention is a proposal for a corrosion-resistant and wear-resistant cast steel that is added with wear resistance in addition to the conventional corrosion-resistant materials as described above.
S, i 0.5-1.5%, Mn 0.5-15% lC
"22-28%, N16-11%, Mo1.5-35%
, Ou 2. O ~ 5.0%, the balance consists of Fa and impurities, and the volume fraction of ferrite is 50 ~ 65 cm, and after solution treatment at 900 ~ 1100 ° C., 450 ~ 55%
2 characterized by being subjected to precipitation hardening treatment at 0°C.
A material that has the same corrosion resistance and 2 to 3 times better wear resistance than conventional austenitic cast steel (SO8-14) or duplex stainless steel cast steel (SCS-11) due to the present invention. was gotten.

Next, the reasons for limitations in the present invention will be explained. It is desirable to have as little C as possible in order to maintain corrosion resistance.
If it exceeds 1%, the corrosion resistance deteriorates as with conventional materials. Si is an effective deoxidizing agent and is inevitably included in the normal steelmaking process, but if it is included in too much, it increases the tendency to form the Jig I phase and makes the material brittle. ~15%. Like Si, Mn is an element that maintains fluidity during deoxidation during the steel manufacturing process and during the casting process, and has a normal range of 05 to 15%.

Or is an important element for maintaining corrosion resistance, and in order to improve corrosion resistance, it is desirable to have a high content, but if it exceeds 28%, it may be as much as possible without causing any risk due to the cooling rate during solution treatment.

2 as the content that maintains the ferrite volume fraction of 50 to 65%, which is a feature of the present invention, in balance with the amount of Ni and Cu.
Limited to 2 to 28 inches. In order to maintain a ferrite volume fraction of 50 to 65 inches, which has excellent abrasion resistance, 6 to 11 inches of ferrite is required in consideration of the above-mentioned C content.M
O is an element that significantly improves local corrosion resistance when coexisting with C, and the present invention also contains 15 to 35% of the same as in the conventional alloy. Cu is an element that imparts precipitation hardenability to the alloy of the present invention, and is contained in large amounts in austenite, but its solid solubility in the ferrite phase is low.

A Cu-rich phase (e-phase) is precipitated and precipitation hardening occurs.

Therefore, in order to maintain wear resistance due to precipitation hardening, the amount of ferrite has a large influence.2 Appropriate precipitation hardenability and excellent wear resistance can be obtained at a ferrite volume ratio of 50 to 65% in the present invention. The range is 2 to 5 Cu, less than 2 Cu does not have sufficient precipitation hardening ability, and Cu is more than 5 Cu.
, the Ou+rich phase precipitates in lumps, significantly reducing toughness, causing pitting-like corrosion and wear, and reducing wear resistance.

The ferrite volume fraction determines the precipitation hardenability of the alloy of the present invention.1
．． This has a large effect on wear resistance; if the amount of ferrite is small, sufficient precipitation hardening ability cannot be obtained, resulting in insufficient wear resistance, and if there is a large amount of ferrite, precipitation hardening occurs and the ferrite becomes brittle. At the same time, the relationship between the matrix and the precipitation becomes weak, wear progresses in the form of pitting corrosion, and wear resistance decreases, so a ferrite amount of 40 to 70 inches is effective, but the optimum amount is limited to 50 to 65 inches.

Next, examples of the present invention will be presented along with comparative examples, and the characteristics of the alloy of the present invention will be described in detail. Table 1 is.

Table 2 shows the compositions, measurement results of ferrite volume fraction, and heat treatment conditions of the inventive alloy given as an example, the conventional alloy given as a comparative example, and the reference alloy. Table 2 shows the hardness and toughness of the alloys in Table 1. and PH3-4. O4-1500ppm
, F-500ppm.

The results of a slurry circulation rotary wear test in a sulfuric acid atmosphere using a 05-inch fly assembly and 40 wt% silica sand are shown. Reference alloys 1 to 5 in Table 1 are alloys close to the present invention, but the amount of ferrite is outside the limited range, as shown in Table 2 and FIG.

The greater the amount of ferrite, the greater the precipitation hardening ability.

Hardness increases almost linearly as the ferrite content increases, but wear resistance in a corrosive environment is not proportional to hardness, and the wear resistance is the best in the range of 50 to 65 inches of ferrite. ing.

In addition, in comparison with the alloys of the present invention, Reference Alloys 6 and 7 have the following differences depending on the O content, as shown in FIG.
Surface wear test conditions: Liquid composition, PH3-4, Ct-1500
ppm, F-500ppm fly ash 205 arc silica sand 4
0w1%, (30-50μ) Horse Ren: 5m/'sec Test time 4008r This shows the relationship between precipitation hardenability and wear resistance, and precipitation hardenability mostly increases as the amount of Cu increases, but Regarding wear resistance, if the hardness is too high, the toughness will decrease and wear will progress like pitting corrosion due to the blocky 0u-rich phase, so the amount of Cu within the range where the wear resistance is significantly improved is 2 to 5%.
It is.

In addition, Fig. 3 was conducted to determine the precipitation hardening conditions for the alloy of the present invention, and the precipitation hardening ability of the alloy of the present invention was 450~
It hardens most noticeably at 550°C, whereas conventional alloy 2
．． 3 (SC!811) is heated to 600 to 700°C, and the ferrite turns into I phase and hardens. But the second
As shown in the table, the wear resistance of conventional alloys is not improved due to the embrittlement caused by the formation of the N/G phase and the selective erosion of the /G phase.

As described above, the corrosion-resistant and wear-resistant cast steel of the present invention has a two-phase structure of austenite and ferrite, and by controlling the amount of ferrite to 50 to 65 inches and causing precipitation hardening by O, it has excellent wear resistance in an acidic corrosion environment. It is an excellent alloy and is widely used in pumps and other cast members that require the characteristics of the alloy of the present invention.

[Brief explanation of drawings]

Figure 1 is a diagram showing the characteristics of the present invention, which is a diagram showing the amount of ferrite, the amount of slurry wear in an acidic environment, and the precipitation hardening ability, and Figure 2 is a diagram showing the relationship between the physical conditions and hardness, which are the characteristic elements of the present invention. FIG.

Claims (1)

[Claims] 0, 0.1% or less, Si0.5-1.5%, M
n0.5-1, 5chi, 0r22-28%, Ni6-1
jchi, Mo1.5-3.596. Cu2. o~5
0%, the remainder Ft and impurities, and the volume fraction of ferrite is 50~6゛5 resistant and valuable wear cast steel.