JPH0342194A - Marine propeller - Google Patents

Abstract

PURPOSE:To improve corrosion fatigue strength in seawater of the marine propeller and to improve erosion resistance thereof by performing cladding by welding of a Co-base alloy having specified composition on parts to sustain erosion damage of stainless steel marine propeller raw material. CONSTITUTION:The stainless steel marine propeller raw material having the chemical composition consisting of, by weight, <= 0.08% C, 0.1 - 1.5% Si, 0.1 - 5% Mn, 16 - 19% Cr, 5 - 7.5% Ni, 0.5 - 3% Mo and the balance Fe substantial ly is manufactured. Cladding by welding of the Co base-alloy 4 is then performed on the astern faces 3 liable to erosion of the propeller raw material. The chemi cal composition of the Co base-alloy 4 consists of, by weight, 20 - 32% Cr, 3 - 16% W, 0.7 - 3% C, <= 2% Si, <= 1.5% Mn, 0.5 - 1.5% Nb and the balance Co substantially. Accordingly, the propeller is remarkably excellent is corrosion fatigue strength in seawater and besides, erosion resistance thereof is remarkably improved.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention applies to marine propellers used in seawater.
L/ relates to an additive propeller that has corrosion fatigue strength and erosion resistance 4S higher than current copper alloy propellers.

[Conventional technology]

Traditionally, copper alloy materials have been used for marine propeller materials, and even nickel-aluminum bronze, which is the most commonly used material, has a fatigue strength of about 18 kgf/shin2 (repetition number 2 x 10 times) in seawater. be. Propeller blade thickness is determined based on seawater fatigue strength, and if materials with high seawater fatigue strength are developed, it will be possible to manufacture lightweight, highly efficient propellers.

In addition, for copper alloy propellers, avoid damage to the propeller blade tip trailing surface (the surface seen from the front of the propeller, i.e., from the bow side) due to erosion caused by the collapse of cavitation bubbles generated during propeller rotation. is impossible. Recently, as ships have become faster, even aluminum-bronze propellers, which are made of copper alloy and have good erosion resistance, are being made so that their blade tips undergo erosion in a short period of time and require repair.

Even if erosion occurs, the cost of docking the ship and the loss of the ship due to repairs are large, and as a countermeasure against damage, the damaged part is cut out and repaired using lotion, but if the damaged part of the erosion is removed, The propulsion efficiency of the propeller decreases.

[Problem to be solved by the invention]

Nickel-aluminum bronze, a copper alloy propeller material currently widely used, has excellent seawater corrosion resistance and workability, but its mechanical properties have the highest tensile strength of 70 kgf/m' and seawater fatigue strength of 20 kl. ? f/m” (number of repetitions 2
10? times) or less. (See Table 3, Nagi 11 below) Even if the erosion resistance is poor, the hardness is 150 to 160 on Purinel hardness, so erosion resistance cannot be expected in environments with severe cavitation.

In view of the above-mentioned technical level, the present invention has high corrosion fatigue strength that cannot be obtained with conventional copper alloy propeller materials, and
The objective is to provide a propeller material with excellent erosion resistance, and to provide a high-efficiency marine propeller that cannot be achieved with copper alloy propellers.

[Means to solve the problem]

In the present invention, C: a08% or less, Si: (Ll
~t5%, Mn:[lL1~3%, Cr:16~19%
, Ni: 5~7.5'! 6. Mo: (Contains 5 to 3% L and the remainder is substantially Fe, in the portion of the stainless steel marine probe material that suffers erosion damage.
In weight%, Cr: 20-32%, W: 3-16%, C:
117-5%, Si: 2% or less, Mn: 1.5% or less,
This is a marine propeller characterized by being formed by welding and overlaying a cobalt-based alloy consisting of Nb: cs to ts%, the remainder being substantially CO.

The reason why the alloy composition of the Probef material of the present invention is specified is as follows.

Since C forms nichrome carbide and precipitates at grain boundaries, providing corrosion resistance and lowering corrosion fatigue strength, its content is set to 0.08% or less.

St: As a deoxidizing agent during dissolution, it is necessary to add 11% or more. However, if the amount added exceeds 1.5%, it becomes brittle, so the upper limit is set at 1.5%.

Mn: Like Si, it is necessary to add 0.1% or more as a deoxidizing agent, but if it exceeds 3%, it will cause embrittlement, so the upper limit should be 3'! Make it A.

Cr: This is the most important element for ensuring corrosion resistance in this invention, and as the amount thereof increases, the corrosion resistance of the material improves. To maintain good corrosion resistance, 16% or more is necessary, so the content of chlorine is set at 16%, and if it exceeds 19%, the corrosion resistance increases but the tensile strength decreases, so the upper limit is set at 19%.

When the amount of Ni:Cr added is in the above range of 16-19%, a minimum of 5% N1 is required to obtain good impact values. If the amount of Ni exceeds 25%, the amount of retained austenite increases and the strength decreases, so the upper limit of the amount of Ni added is set at 7.5%.

) IO: This element is extremely effective in improving corrosion resistance and needs to be added in an amount of 5% or more. However, if it exceeds 5%, the strength decreases and becomes brittle, so the upper limit is set at 3%.

Since N is an effective element for stabilizing the Niostenite phase and strengthening the matrix, it may be contained in an amount of about 0.02% to [L2%]. However, N is not an essential condition.

C: 0.08% or less, Si: 0.1-1.5%, )l
]: Q, 1-3%, Cr: 16-19%, Ni: 5-7
．． 5%, Mo: (L) Containing 5 to 3%, the remainder being substantially Fe, the hardness of the stainless steel lag &! Button Probefu # is 220 to 254 on the Prinell hardness, which is the hardness of current copper alloys. 150 to 160, and the erosion resistance is extremely excellent.

However, when severe cavitation occurs, such as in a propeller for a high-speed boat, even the Probef material described above causes erosion damage to the trailing edge side of the trailing surface wing tip, reducing propulsion efficiency. An example of this will be explained with reference to FIG.

Figure 1 shows a marine propeller seen from the astern side, and 1 shows the propeller rotating to cut through the seawater (il; the leading edge, which is the nu edge of l,
2 is the wing on the opposite side, Nagato. Propeller cavitation occurs when a reduced E part is created around the trailing edge 2 of the propeller '7 due to the rotation of the propeller, causing air bubbles to form. When these air bubbles disperse, high pressure is generated and the propeller blade surface is damaged by shock waves. phenomenon, the result of which is erosion. In Fig. 1, 2a indicates the erosion part that has occurred on the rear edge 2 of the reversing surface, and it is usually damaged in a pear-shaped pattern, but in severe cases, it may penetrate the 61J reversing surface or curve toward the forward surface. be.

As countermeasures against these erosions, methods such as (1) cutting off the erosion-generating force end and changing the shape, and (2) polishing the surface of the erosion-generated area with a grinder and then repairing it using a closed bath are used. However, method (2) has the problem of reduced propulsion efficiency, and method (2) uses the same material as the propeller material as the overlay welding material, so there is a concern that erosion may occur again.

Therefore, the present invention has developed a propeller material made of stainless steel, which has high hardness and excellent erosion resistance.
) The base alloy is welded overlay during the propeller manufacturing process to areas that are susceptible to erosion damage, resulting in a marine propeller with high corrosion fatigue strength and excellent erosion resistance.

Figure 2 is a view of the propeller material of the present invention viewed from the reverse side.1 The blade tip side from the rear side where erosion is likely to occur (L6R (R is the propeller radius)) is welded with a cobalt-based alloy of high hardness. (Usually, when the propeller radius is R, erosion on the trailing surface occurs toward the tip of the wing from L6R.) In Figure 2, 1 is the leading edge, 2 is the trailing edge, and 3 is the leading edge.
4 shows the backward moving surface, and 4 shows the welded overlay cobalt-based alloy part.

The weld build-up situation of a cobalt-based alloy will be explained with reference to FIG.

As shown in FIG. 3(a)K, a propeller material is manufactured in which the reverse plane 3 side of the above-mentioned propeller material of the present invention is made thinner by a maximum of about 10 mm compared to the normal state.

Next, as shown in Fig. 3~), a cobalt base metal 4 is welded overlay on the thin-walled backward moving surface 3, and finally, as shown in Fig. 3(C), the excess thickness of the overlay part is Cut and polish to give a smooth finish. This treatment is applied to other propeller blades in the same way.

According to the present invention, the cobalt-based alloy is composed of C
r: 20-32%, W: 3-16%.

C: 0.7-3%, Si: 2% or less, Mn: 1
．． A Cobalt/1/)-based alloy containing 5% or less Nb: Q, 5 to 1.5%, and the remainder substantially Co is used. The composition ratio of this cobalt-based alloy was determined based on the ring conditions described below. That is, the hardness of a cobalt-based alloy containing Cr is influenced by the primary carbide Cr, C, or the eutectic of cr7C3 and Co-Cr-W. therefore,
In particular, the amounts of Cr, W, and C were determined based on these microstructure ratios, that is, the hardness and weldability of the cobalt-based alloy.

Cr: Addition of Cr increases the amount of Crt c' precipitated, increasing the hardness of the weld and increasing the corrosion resistance of the weld. Therefore, in order to ensure the corrosion resistance of the built-up part in seawater, it is necessary to contain 20% or more of Cr. On the other hand, Cr i
If it exceeds 32%, cracks are likely to occur in the welded part, so the upper limit was set at 32%.

77: W increases with increasing amount of Cr7 C3 and C
The eutectic structure of o-Cr-W increases and the hardness of the alloy increases. However, if the amount exceeds 16%, the impact resistance will be poor, so the upper limit was set at 16%. On the other hand, if it is less than 3%, no improvement in hardness can be expected, so the lower limit was set at 3%.

C: Less than +17%, carbide precipitation is insufficient, 3%
If it exceeds 3%, the influence of primary crystals of Cr and C will increase and the weld will easily crack, so the upper limit was set at 3%.

Si: Si is necessary as a deoxidizing agent, but too much Si tends to cause weld cracking, so it was set to 2% or less.

Mn: Mn is an element necessary as a deoxidizing agent, and the amount added is 1.5
Do not kneel if it exceeds t5, as cracks are more likely to occur.
% or less.

Nb: Nb is an attempt to increase hardness by precipitating Nb carbide, and if it is less than 0.5%, no improvement in hardness can be expected;
．． If it exceeds 5%, weld cracking is likely to occur, so the upper limit should be set at 1.
It was set at 5%.

〔Example〕

Next, an example of the manufacturability of the propeller material of the present invention will be shown, and the present invention will be explained in detail.

Table 1 shows the chemical components of the propeller materials of the present invention. Samples 1 to Nagi 4 are materials of the present invention, samples m5 to Nagi 10 are comparative materials, and l and kll are current Probef materials. It is shown in Table 2. Table 3 shows these mechanical properties and J noodle skins that suffer from corrosion.

Table 1 No. table No. table From the above table, the following is clear.

If the chemical components are outside the scope of the present invention, the test items will be included in the sample. As seen in A10, the corrosion fatigue strength in seawater is 21 kgf/
-” 29-30 k for floors 1 to 4 accompanying this invention!
9f/m", which is significantly lower than that of 9f/m".
~) C4 is the current copper alloy material of Company 11's 18-f/ts
This is more than 1.6 times higher than that of ``29-30 kg f/arm'', making it possible to manufacture lightweight and highly efficient propellers.

For the corrosion fatigue test, a Weller rotary bending fatigue tester (rotation speed s, 4s o rprn) was used as the testing machine, the test piece straight line was &Oz, the number of test runs was 2 x j O', and the test liquid was natural seawater. However, the test temperature was room temperature.

Next, Table 4 shows the chemical composition, hardness, and erosion loss of the cobalt-based alloy to be hot-plated onto the Probera material of the present invention.

Additionally, Table 5 shows the chemical composition and erosion of the Provera material of the present invention without overlay (Table 1 m1), and Table 6 shows the current Provera material without overlay, aluminum bronze (Table 2 m11). Indicates weight loss.

Table 5 Table 6 As can be seen from Tables 4, 5, and 6 above, the overlay cobalt-based alloy of the present invention
It has more than twice the erosion resistance. These erosion tests were carried out using a jet erosion tester.
These are the results of the time (h) test.

In the erosion test, tap water was used as the test liquid, and the circumferential velocity at the center of the test piece was qhsrn/ss, the flow rate of the jet water was 1! L 2
m / s Relative velocity for the s test piece 9'14 m /
The experiments were carried out at a temperature of 15 to 25°C.

As is clear from this result, the cobalt-based alloy of the present invention containing Cr, W> and Nb has significantly higher hardness than the material of the present invention and the copper alloy), and is welded to the propeller material of the present invention. When mounted, it shows superior erosion resistance (compared to current nickel-aluminum propellers).

Therefore, the cobalt-based alloy for weld overlay of the present invention is applied to the blade tips of 0 and 8R (R is radius) where erosion is likely to occur in the propeller material of the present invention by the method described above with reference to FIG. By overlaying, the marine prover of the present invention was made.

As described in detail above, the propeller of the present invention has high hardness and Cr in the portion of the propeller material of the present invention which has excellent corrosion fatigue strength and is damaged by erosion.

By welding and overlaying a cobalt-based alloy containing W and Nb, an erosion-resistant propeller is provided that will not be corroded even if the propeller blades receive shock waves caused by propeller cavitation.

〔Effect of the invention〕

The propeller of the present invention has significantly superior corrosion fatigue strength in seawater compared to current copper alloy propellers, and has dramatically improved erosion resistance compared to copper alloy button and stainless steel propellers, and its industrial effects are remarkable. It is.

[Brief explanation of drawings]

Figure 1 is a front view of a general marine propeller seen from the astern side.
Fig. 2 is a front view of a marine propeller according to an embodiment of the present invention as seen from the reverse side, and Fig. 5 is an explanatory view showing the manufacturing process of the marine propeller of the present invention. The process of plating is shown. Inside the human race

Claims (1)

[Claims] In weight%, C: 0.08% or less, Si: 0.1 to 1.
5%, Mn: 0.1-3%, Cr: 16-19%, Ni
Cr: 5 to 7.5%, Mo: 0.5 to 3%, and the remainder substantially consists of Fe, on the part of the stainless steel marine propeller material that is subject to erosion damage, in weight%.
20-32%, W: 3-16%, C: 17-3%, Si
: 2% or less, Mn: 1.5% or less, Nb: 0.5-1.
A marine propeller, characterized in that it is made by welding overlay of a cobalt-based alloy consisting of 5% Co and the remainder substantially Co.