CN111375875A - Duplex stainless steel overlaying layer and preparation method thereof - Google Patents

Abstract

The invention discloses a preparation method of a duplex stainless steel surfacing layer, comprising the following steps: using intermediate alloy powder to mechanically mix alloy powder in proportion; using plasma arc welding to perform surface surfacing; The austenite is adjusted to 70~80%. The invention designs the Mn-N type duplex stainless steel, and practises a preparation method, which can effectively improve the cavitation corrosion resistance of the overflow parts, and can greatly reduce the protection cost of the overflow parts.

Description

A kind of duplex stainless steel surfacing layer and preparation method thereof

technical field

The invention relates to a stainless steel surfacing layer, in particular to a duplex stainless steel and a preparation method thereof.

Background technique

Cavitation corrosion is a common damage form in the use of hydraulic construction and hydraulic machinery, and it is a special form of wear and corrosion. It is caused by the uneven distribution of the internal pressure of the liquid under the condition of high-speed movement of multiphase flow, which leads to the formation of bubbles in the liquid and the collapse of the bubbles. The surface of the material will cause serious damage to the surface of the material.

Duplex stainless steel is an important part in the field of stainless steel. Its microstructure contains both austenite phase of face-centered cubic structure and ferrite phase of body-centered cubic structure, and the proportion of either phase at least occupies 30%. It is precisely because duplex stainless steel has the structural characteristics of two-phase structure at the same time, so its performance has the characteristics of both austenitic stainless steel and ferritic stainless steel. Compared with ferritic stainless steel, duplex stainless steel contains more alloying elements, so it has comprehensive and better corrosion resistance. In terms of mechanical properties, because duplex stainless steel contains about half of the austenite structure, it has better plasticity and toughness than ferritic stainless steel; compared with austenitic stainless steel, duplex stainless steel has higher strength, and its The resistance to intergranular corrosion, stress corrosion and corrosion fatigue has been significantly improved. In addition, duplex stainless steel also has good resistance to pitting corrosion, crevice corrosion, and stress corrosion, which is comparable to high-alloy austenitic stainless steel.

Surfacing is a process of cladding a layer of materials with specific properties on the surface of parts by welding. The purpose is not to connect the parts, but to cover the surface of the parts with a layer of cladding metal with better performance. It is an economical process. Effective surface modification method.

Plasma powder surfacing uses a plasma arc as a heat source, and the high temperature generated by the plasma arc is used to rapidly heat the alloy powder and the surface of the substrate to melt, mix, diffuse and solidify together. After the plasma beam leaves, it is self-excited and cooled to form a layer of high-performance alloy. layer, so as to realize the surfacing process of strengthening and hardening of the surface of the part.

To solve the cavitation corrosion of hydraulic overcurrent parts, we can start from the following two aspects: one is to develop new materials with better comprehensive anti-cavitation performance; the other is to use advanced surface engineering technology to provide protection for the surface of overcurrent parts. Because the research and development and manufacturing costs of new materials are very expensive, they are only suitable for large parts and main parts. In actual use, a layer of metal with stronger performance is clad on the surface of the material, which can not only save valuable materials, but also reduce the risk of voids. Targeted and efficient protection of the parts damaged by corrosion. The properties of duplex stainless steels vary greatly under different heat treatment states. There are few theoretical studies and practical applications of heat treatment to adjust the two-phase ratio of austenitic ferrite in cavitation service environments.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a duplex stainless steel surfacing layer with strong cavitation resistance, in order to achieve the above purpose, the technical scheme adopted in the present invention is:

A duplex stainless steel surfacing layer, comprising the following components by weight percentage

C 0.02~0.04%,

Cr 18.0~20.0%,

Ni≤0.8%,

Mo≤0.3%,

N≥0.15%,

Mn≥5.0%,

Si 0.5~1.0%.

Fe: 68.5~74.0%

Further, the PREN value of the duplex stainless steel is ≥20, wherein PREN=Cr%+3.3Mo%+30N%-Mn%, wherein Cr%, Mo%, N% and Mn% are Cr, Mo, N and Mn, respectively. The weight percentage of Mn.

Further, the deformation-induced martensite temperature of the duplex stainless steel Md≥50℃, wherein Md=580-520C%-2Si%-16Mn%-16Cr%-23Ni%-300N%-26Cu%-10Mo%, wherein C%, Si%, Mn%, Cr%, Ni%, N%, Cu%, and Mo% are the weight percentages of C, Si, Mn, Cr, Ni, Cu, and Mo, respectively.

The present invention also provides a preparation method using the duplex stainless steel surfacing layer, comprising the following steps

Alloy powder is configured and fully mechanically stirred and mixed;

The mixed alloy powder is added to the plasma surfacing welding machine for powder surfacing, and the thickness of the surfacing layer is 2~3mm;

The surfacing welded workpiece is subjected to solution heat treatment. After the solid solution heat treatment, the austenite content of the surfacing layer of the duplex stainless steel is 70-80%.

Further, the alloy powder includes ferromanganese, ferrochromium, ferronickel, chromium nitride, iron powder, and ferrosilicon.

Further, the solution heat treatment temperature is 1000-1150°C.

Further, the plasma surfacing process parameters in the powder surfacing process are:

Dimensional arc current main arc current Surfacing speed Powder feeding speed Swing speed Ionized gas protective gas 29A 110A 200mm/min 9L/min 500mm/min 3L/min 5L/min

Further, the powder surfacing welding adopts plasma powder surfacing welding.

Alloying elements in duplex stainless steel will affect its mechanical properties and corrosion resistance, and chromium in the present invention plays a decisive role in corrosion resistance. Chromium can form a stable and dense Cr2O3 protective film on the steel surface, which can reduce the current density of surface passivation, passivate stainless steel, and reduce the dissolution rate of steel in passivation state. At the same time, chromium can improve the oxidation resistance of steel, stabilize the ferrite phase, and reduce the area of the austenite phase.

Nickel can control the two-phase equilibrium of duplex stainless steels. Through synergistic action with chromium and molybdenum, the corrosion resistance of duplex stainless steel is improved.

The addition of manganese can improve the solubility of nitrogen in duplex stainless steel and play a significant role in nitrogen fixation in austenite.

Nitrogen is a strong austenite forming and stabilizing element. Nitrogen can effectively replace nickel in duplex stainless steel to save costs. Nitrogen also has solid solution strengthening and improved resistance to pitting and crevice corrosion of stainless steel. obvious effect.

Molybdenum is a ferrite-forming element. In duplex stainless steel, molybdenum and chromium can act synergistically to improve the pitting resistance of stainless steel. When the chromium content in stainless steel is at least 18%, molybdenum is three times more resistant to pitting and crevice corrosion than chromium in chlorine-containing environments. However, with the increase of molybdenum content, σ phase and χ phase in duplex stainless steel are also easy to precipitate.

The beneficial effects of the present invention include: the duplex stainless steel formula in the present invention is clad on a common metal plate by surfacing, and after heat treatment, the cavitation corrosion resistance is better than that of commercially available 2209 and 304 stainless steel surfacing layers .

Description of drawings

Fig. 1 is a metallographic structure diagram of the duplex stainless steel surfacing layer in the present invention.

Detailed ways

The present invention will be further explained in detail below with reference to the accompanying drawings and specific embodiments, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

The duplex stainless steel surfacing layer is prepared on the 304 stainless steel plate by the method of plasma powder surfacing, specifically the Mn-N type duplex stainless steel surfacing layer. The content of the main elements of chromium nitride, iron powder, ferrosilicon and alloy powder is shown in Table 1. In the table, the content of some elements uses "—" to indicate that the content of this element is too low and not detected. The particle size of the powder is 100 mesh. Use a high-precision balance to weigh out the alloy powder required for the formula and mix it mechanically. In order to mix the metal powder evenly, the time for each stirring is not less than 30min. Alloy powder, put into an oven before use, and dry at 70°C for one hour. Then add the alloy powder to the powder feeder, and tighten the powder feeder cover to avoid the failure of powder feeding due to air leakage.

Table 1 Chemical composition of alloy powder (mass fraction/%)

C Mn Ni Si S P N Fe Ferromanganese 0.615 80.13 - 0.69 0.021 0.16 - margin Ferrochrome 0.057 - - 0.83 0.028 0.025 - margin Ferronickel 0.37 - 36.12 0.53 0.12 - - margin Chromium Nitride 0.089 60.15 - 0.6 0.024 0.02 8.5 - iron powder 0.003 0.11 - 0.03 0.01 0.01 - 99.58 Ferrosilicon 0.01 0.40 - 77.00 0.022 0.15 - margin

In order to facilitate the development of subsequent inspection tests, it is necessary to obtain high-quality plasma arc surfacing layers, and it is necessary to reasonably pre-select process parameters. The main process parameters of plasma arc surfacing welding: surfacing current, surfacing speed, powder feeding speed, ion gas and powder feeding gas flow, welding torch swing amplitude and frequency, distance between nozzle and workpiece, etc. The process parameters of this plasma arc welding As shown in Table 2, surfacing was performed three times, and the total thickness of the surfacing layer after surfacing was 5 mm.

Table 2 Plasma surfacing process parameters

Dimensional arc current main arc current Surfacing speed Powder feeding speed Swing speed Ionized gas protective gas 29 110 200 9 500 3 5

After the welding is completed, solution heat treatment is carried out. The heating method of heat treatment adopts heating with the furnace. The heat treatment furnace uses the process route shown in Table 3. When cooling, the sample is taken out from the resistance furnace with pliers, and immediately after taking it out Shake the sample continuously during the process to avoid the accumulation of bubbles around the sample and reduce the cooling rate. The metallographic structure is shown in Figure 1. The bright white area is austenite structure, and the dark area is ferrite structure. After image pro According to the calculation of the software, the proportion of austenite structure reaches 72.2%.

Table 3 Heat treatment process parameters

Heating rate holding time holding temperature cooling method 10℃/min 60min 1100℃ water cooling

The difference between Examples 2-5 and Example 1 is only that the weight of each alloy powder added is different, so that the chemical composition of the final configuration of the surfacing layer is shown in Table 4, and the amount of each alloy powder used is based on the required surfacing welding. Layer composition percentage configuration.

The samples in the control group are 2209 duplex stainless steel and 304 austenitic stainless steel surfacing layers, which are prepared by TIG surfacing with commercially available welding wires. The chemical composition of the surfacing layer is shown in Table 4, and the comparative test results are shown in Table 4. The content of austenite in Examples 1-5 is all 65-75%.

Table 4 Chemical composition of surfacing layer (mass fraction/%)

C Cr Ni Mo N Mn Si Fe Example 1 0.03 19.53 0.61 0.11 0.19 5.61 0.71 73.21 Example 2 0.02 20.01 0.82 0.23 0.15 6.31 0.71 71.75 Example 3 0.03 18.94 0.53 0.15 0.20 6.10 0.69 73.36 Example 4 0.03 18.06 0.62 0.19 0.18 5.93 0.69 74.3 Example 5 0.02 19.01 0.71 0.31 0.15 6.51 0.91 72.38 Contrast 1 0.02 22.81 8.87 3.01 0.09 1.01 0.38 63.81 Contrast 2 0.051 18.68 8.64 — — 1.11 0.028 71.491

table 5

Pitting rate Cavitation rate (5h) Example 1 11.5g/m²·h^-1 0.22mg/h Example 2 10.9g/m²·h^-1 0.24mg/h Example 3 11.9g/m²·h^-1 0.20mg/h Example 4 12.6g/m²·h^-1 0.21mg/h Example 5 11.2g/m²·h^-1 0.19mg/h Contrast 1 2.5g/m²·h^-1 0.34mg/h Contrast 2 23.1g/m²·h^-1 1.5mg/h

After pitting immersion and cavitation corrosion experiments, the cavitation resistance performance in the present invention is "Example" > "Comparison 1" > "Comparison 2", and pitting corrosion resistance "Comparison 1" > "Example" > "Comparison 2". This kind of surfacing layer has excellent comprehensive performance in seawater, good performance, better cavitation corrosion resistance than typical commercially available materials, and saves the use of nickel, molybdenum and chromium, and has good economic benefits.

The above are only the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the technical principle of the present invention, several improvements and modifications can also be made. These improvements and modifications It should also be regarded as the protection scope of the present invention.

Claims (7)

1. A duplex stainless steel weld overlay, characterized in that: comprises the following components in percentage by weight

C 0.02~0.04%,

Cr 18.0~20.0%,

Ni≤0.8%,

Mo≤0.3%,

N≥0.15%,

Mn≥5.0%,

Si 0.5~1.0%。

2.Fe:68.5~74.0%

The duplex stainless steel weld overlay of claim 1, wherein: the PREN value of the duplex stainless steel is more than or equal to 20, wherein PREN = Cr% +3.3Mo% +30N% -Mn%, and Cr%, Mo%, N% and Mn% are the weight percentage of Cr, Mo, N and Mn respectively.

3. The duplex stainless steel weld overlay of claim 1, wherein: the deformation-induced martensite temperature Md of the duplex stainless steel is more than or equal to 50 ℃, wherein Md = 580-Si 520-2 Si-16 Mn-16 Cr-23 Ni-300N-26 Cu-10 Mo%, and the contents of C%, Si%, Mn%, Cr%, Ni%, N%, Cu% and Mo are the weight percentages of C, Si, Mn, Cr, Ni, Cu and Mo respectively.

4. A method of preparing a duplex stainless steel weld overlay as defined in claim 1, wherein: comprises the following steps

Preparing alloy powder and fully and mechanically stirring and mixing the alloy powder;

adding the mixed alloy powder into a plasma surfacing welding machine, and performing powder surfacing, wherein the thickness of a surfacing layer is 2-3 mm;

and carrying out solution heat treatment on the surfacing workpiece, wherein after the solution heat treatment is finished, the austenite content of the duplex stainless steel surfacing layer is 70-80%.

5. The method of claim 4, wherein: the alloy powder comprises ferromanganese, ferrochrome, ferronickel, chromium nitride, iron powder and ferrosilicon.

6. The method of claim 4, wherein: the temperature of the solution heat treatment is 1000-1150 ℃.

7. The method of claim 4, wherein: the plasma surfacing process parameters in the powder surfacing process are

Pilot arc current Main arc current Speed of build-up welding Powder feeding speed Speed of oscillation Ion gas Protective gas 29A 110A 200mm/min 9L/min 500mm/min 3L/min 5L/min

The method of claim 4, wherein: and the powder overlaying adopts plasma powder overlaying.

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