WO1999035298A1 - Pipe joint made of shape memory stainless steel - Google Patents

Abstract

A pipe joint made of shape memory stainless steel, makes of shape memory stainless steel containing iron, manganese, silicon and so on, which chemical composition (by wt. %) comprises following range: Cr:12-20, Si:3-8, Ni:0.1-8, Mn:0.1-14.8, Co:0.1-20, N:0.05-0.4, C:≤0.03, one or more of lanthanum system rare earths: 0.01-0.15 in total, one or more of Nb, Ti, V, Zr, Ta, Hf, W, Mo, A1, Cu:0.05-2 in total, and the balance of iron and inevitable impurities. This alloy material has better index in three aspects of the shape memory properties, corrosion resistance properties and mechanical properties. This pipe joint structure has good sealability and simple structure, properly uses, and can appropriately solve engineering practical problem, which exists now.

Description

Shape memory stainless steel pipe joint Technical field

The invention relates to a shape-memory stainless steel pipe joint, which belongs to the technical field of alloys.

Background technique

The stress of shape memory alloy can induce the transformation of parent phase to martensitic phase, and at the same time, the parts made of the alloy undergo certain deformation on the macroscopic scale. If the above-mentioned parts are heated above the reverse transformation temperature, the martensite phase reverses into the parent phase, and the corresponding parts return to their original shape. This kind of alloy with shape memory function is called shape memory alloy. In iron-based shape memory alloys, except that the martensite of iron-palladium alloy has fct structure, and the martensite of iron-platinum and nickel-cobalt-titanium alloy has bet structure, the martensite of general iron-based shape memory alloy is mostly hep type 2 H structure, commonly referred to as ε martensite. Recently we discovered the 4 Η, 6 Η, 8 Η structure of this martensite. The parent phase γ is a fee type 3 R structure, which can also be called alloy austenite. The essence of the martensitic transformation of γ→ε is the change of atomic stacking order. Martensite has different types of combined stacking faults relative to the parent phase.

The low-temperature proliferation of stacking faults and the high-temperature degradation of stacking faults constitute the basic process of martensitic transformation and reversal. Although non-ferrous based shape memory alloys such as nickel-titanium alloys have been used for a long time, they are expensive. Iron-based shape memory alloys have low cost and moderate operating temperature, so they have broad development prospects.

The patents and their features related thereto prior to the present invention are listed as follows:

CN1064319A composition (wt%) is characterized by n: 15-35%, Si: 0. 2-6. δ%, A1: 0. 2-8%, Cu: 0- 0. 5%, Pr, Pm, Eu, One or more of Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, La, Ce, Nd, Sm, the amount is 0.008-0.12%, and the rest is iron and unavoidable impurity elements.

One of JP170457 composition characteristics is Mn: 15-40%, one or two kinds of Cr and Co, the amount is 1-20%, Si, Al, Ge, Ga, b, V, Ti, Cu, Ni, Mo one kind Or two or more, the addition amount is 15%, La, Ce, Nb, Sm, Y - one or more, the addition amount is 2%.

JP2270938A 0JSP5032195) composition feature is Mn: 15-20%, Si 3%, Cr > 10%, and the rest are iron and unavoidable impurity elements.

The composition of JP216946 is characterized by Mn: 15-30°/. , one or two kinds of Cr and Ni, the addition amount is 15%, and one or two kinds of Si and Co are added, the addition amount is 6%.

The composition of JP201761 (USP4780154) is characterized by Mn: 20- 0%, Si: 3.5-8%, and the following elements include at least -: Cr 10%, Ni ^ 10%, Co 10%, Mo 2%, C 1%, Al 1%, Ci 1%, and the rest are iron and unavoidable impurity elements. In the above-mentioned patented technologies, the Mn content is above 15%. Due to the high n content, the overheating sensitivity of the alloy is relatively large, and it is difficult to control the thermal processing process. In addition, it is not easy to prevent rust, and even if Cr is added, it is difficult to significantly improve its corrosion resistance. The following are patents and published literature with Mn below 15% -

The composition of JP2301514 is characterized by Cr:10-17%, Si:3.0-6.0%, at least one of the following elements: Mn:10-25%, Ni 7.0%, Co:2.0-10.0%, Ti, Zr, V, Xb, Mo , Cu and a small amount, and the rest are iron and unavoidable impurity elements.

B. E. Wilde, Corrosion-Nace (1986), Vol.42, P.678. Published compositions are Cr: 17- 19%, Si: 0.3δ-4.79%, Ni: 8.83-9.08%, Mn: 1.30- 1 · 53, Cu: 0.009-0.20%, N: 0.011-0.040%, O: 0.019-0.21%.

EP 336157A (JP2030734A, ISP4929289A) Composition features Cr:0.1-5.0%, Si:2.0-8.0%, Mn: 0.1-14.8%, Co:0.1-30%, Ni:0.1-2.0%, Cu:0.1-3 %, N:0.01-0.4%, the rest is Fe and unavoidable impurity elements.

USP 4933027 (EP336175A), its composition range is Cr: 5-20%, Si: 2.0-8.0%, at least one of the following elements Mη: 0.1-14.8%, Ni: 0.1-2.0%, Co: 0.1-30.0 %, Cu:0.1-3.0%, N:0.001-0.4%, the rest are iron and unavoidable impurity elements.

EP 0506488A1, its composition range is Cr: 16-21%, Si: 3.0-7.0%, Ni: 11-21%, one or more of the following elements: Μη: 0.Ι-δ.0%, Cu: 0.1-1.0%, N:0.001-0.100%, Mo:0.1-3.0%, W:0.1-3.0%, Ti:0.01-1.0%, Zr:0.011-2.0%, Hf:0.01-2.0%, V:0.01 -1.0%, Nb: 0.01-2.0%, Ta: 0.01-2.0%.

As a shape memory material for practical engineering applications, it is often required that the yield strength is higher than 300Mpa, the memory recovery temperature is moderate (As: 60-120'C), corrosion-resistant and easy to process into materials. But the alloys listed in the above-mentioned patents and documents are difficult to meet the requirements of these three aspects simultaneously.

Contents of the invention

The object of the present invention is to provide a shape memory stainless steel that can meet the technical requirements of the above three aspects at the same time, and to use this material to make pipe connectors.

To achieve the above object, the present invention provides a shape memory stainless steel made of iron, manganese, silicon, chromium, nickel, etc., characterized in that the weight % range of the chemical composition is as follows:

Cr: 12-20, Si: 3-8, Ni: 0.1-8, Mn: 0.1-14.8, Co: 0.1-20, N: 0.05-0.4, C: 0.03,

Lanthanide rare earth elements La, Ce, Sm, Nd, Pm, Eu, Tb, Dy, Pr, Gd, Ho,

One or more of Er, Tm, Yb, Lu, the total content is 0.01-0.15, , Ti, V, Zi", Ta, Hf, W, Mo, A!, Cu elements one or more, with a total content of 0.05-2, and the rest are Fe and unavoidable impurity elements.

In the above-mentioned shape-memory stainless steel provided by the present invention, the preferred Cr, Si, Ni, Mn, Co and N content ranges by weight are: Cr.lZO-lS.O'SiJ.Z^.l'NiAO -S.OAtnUlO'Co O-ZO.O'N^.OS-O.

The difference between the present invention and patents CN1064319A, JP170457, JP2270938A, JP216946, JP201761 is that it contains 14.8% n, which can ensure the alloy has excellent corrosion resistance. One of the differences between the present invention and JP2301514, Wilde, EP336157A, LSP4933027, EP0506488A1 and other patents and documents is the addition of RE, the main purpose of which is to reduce the dendrite deflection of elements and improve the uniformity of component distribution, which can significantly increase memory effect. The difference between the present invention and the alloys listed in JP2301514 and Wilde documents is that 0.05-0.4%N is added, the purpose is to reduce the stacking fault energy, adjust the phase transition point, and at the same time improve the strength of the material. The other difference between the present invention and EP336157A, USP4933027 is Containing carbonitride forming elements \b, Ti, V, Zr, Ta, Hf, W, Mo, can effectively reduce the overheating sensitivity of the material and improve the strength of the material.

The function of the alloy elements involved in the present invention will be briefly explained below.

Cr: Ferrite forming element, the main function is to improve the corrosion resistance of the alloy. The corrosion resistance effect is not significant if it is less than 5%, and generally Cr>12.0% can be used as stainless steel. Its influence on the stacking fault energy and phase transition point presents a relatively complex law. When it is less than 9%, the stacking fault energy is reduced, and if it is greater than 9%, Cr obviously increases the stacking fault energy and reduces the phase transition point, and at the same time promotes the formation of brittle 0 phase. In the present invention, Cr is 12-20%, preferably 12.0-18.0%.

Ni: It can strongly promote the formation of austenite and reduce the yield strength. Therefore, in the invention, the nickel content is controlled within the range of 0.1-8%, and is ideally 4.0-8.0%. Because nickel increases the stacking fault energy, a certain amount of elements such as Si and Mn should be added to reduce the stacking fault energy.

Si: It can significantly reduce the stacking fault energy, so the Si content should generally be increased. The effect of reducing stacking fault energy is weak when Si is less than 3%, and the processing performance is deteriorated if the Si content exceeds 7%. Therefore, the Si content in the present invention is 3-8%, and the ideal Si content is 3.2-6.1%.

N: is an austenite forming element, which can significantly reduce the stacking fault energy and has the effect of stabilizing Ms points. Adding N can partially form carbonitrides, which has a good effect of suppressing thermal sensitivity. At the same time, N can improve the yield limit and pitting resistance of the alloy. But more than 0.4% is easy to form a large amount of nitrides, which will make the material brittle, so the N content is controlled at 0.050-0.40%, and the ideal is 0.05-0.2%.

Nb: Including Ti, Ta, V, Zr, Hf, W and other carbon-nitride forming elements, which can fix carbon elements, prevent the precipitation of chromium carbides, and avoid the depletion of chromium and grain boundary corrosion. Simultaneous formation of fine carbides can prevent The grain grows to prevent the alloy from overheating at high temperature. 05 - 2%。 Adding too much will cause intergranular brittleness, so its content is selected at 0. 05 - 2%.

Mo: The purpose of adding molybdenum is to improve the ability to resist intergranular corrosion and stress corrosion. Mo is less than 0.05% and has no effect, and exceeding 2% will lead to deterioration of memory performance, so the amount of Mo added is controlled at 0.05-2% .

Cu: is an austenite forming element, which can improve the corrosion resistance of the alloy, but at the same time increase the austenite stacking fault energy, too much will inhibit the formation of ε martensite and deteriorate the memory performance. Generally, the addition of copper is controlled within 2%.

A1: Refine the grains to reduce the stacking fault energy and improve the memory performance of the alloy, but if the A1 content exceeds 2%, the processing performance will deteriorate, so the A1 content should be controlled within 2%. At the same time, one or more of the above Nb, Ti, V, Zr, Ta, Hf, W, Mo, Al or Cu elements can be selected, and the total content is 0.05-2%.

The role and composition range of each element are described qualitatively above. The specific composition and collocation need to comply with the following three criteria:

1. It must be ensured that the parent phase of the alloy is a single austenite phase. For this purpose, the alloy composition (wt%) should satisfy the following relationship:

(Ni+0.δ.Μη+0. 4Co+0. 06Cu+0. 002N+3) > [0. 67 (Cr+ o) +0. 804 (Si+Ti+Zr+Hf+V+Nb+

Ta) ]

2. In order to ensure that the alloy has the ability to resist stress corrosion and pitting corrosion. For this purpose, the alloy composition (wt%) should satisfy the relationship:

Cr+Si〉18 ; Cr+3. 3Mo+30N>18

3. It must be ensured that the positive alloy has good memory performance and moderate phase transition temperature. Therefore, a sufficient amount of alloying elements that can reduce the stacking fault energy should be added, and the following formula should be satisfied:

7Si+Mn+3Co+100N>50

The performance indicators that the invented memory stainless steel with the above chemical composition can achieve are as follows:

1. Relatively high shape memory performance. 3% tensile deformation, the memory recovery rate can reach 80%. With proper thermomechanical training, the linear recovery can reach more than 4%.

2. It is resistant to stress corrosion and pitting corrosion, and can be matched with 304 stainless steel.

3. Yield strength 0. ₂ ^ 300Mpa, o _b ^ 650Mpa, this performance index exceeds the level of standard 304 stainless steel. (304 stainless steel composition (wt%): C 0. 08, Cr : 18-20, Ni : 8-12, n : 1-2, N 0. 03 mechanical properties: o ₀₂ =247Mpa, o _b =541Mpa, δ =50%) 4. The alloy has good cold and hot pressure processing performance.

5 alloy has a moderate phase transition point, -40 20 .

The shape memory alloy of the present invention has high strength, good processability, moderate phase transition point and good corrosion resistance. Therefore, the shape-memory sleeve that utilizes the shape-memory stainless steel of the present invention to be made connects pipes. Current similar products are for example: JP04069481A proposes to apply epoxy resin on the inner wall of the pipe sleeve for sealing when using Fe Mn Si alloy pipe sleeve to connect pipes. JP05215277CN proposed that in addition to coating the sealant on the inner wall, the inner wall should also be engraved to enhance the effect of fastening connection. In addition, CX21 16140 proposed a closed coating pipe connection structure for high reliability connection. But above-mentioned patent all relates to and will sealant be coated on the pipe sleeve inner wall when installing. Such construction is complicated. The present invention proposes a new, simple and practical pipe joint connection structure, as shown in FIG. 1 . The structure of the invention is characterized by a memory stainless steel or alloy collar 1, an intermediate sealing ring 2, a ring end sealant 3 and a connected pipe 4. The intermediate sealing ring is a solid high plastic alloy ring or a rubber ring or other high plastic material rings fixed on the inner middle part of the memory alloy collar. The cross-section of the sealing ring can be circular, oval, rectangular, trapezoidal or other shaped. Sealant is then coated on the resin, water glass or plastic inorganic paste or solid on the near end of the inner wall part of the memory alloy collar. The intermediate sealing ring of the above structure and the sealant at the ring end can be used simultaneously or separately. The middle sealing ring can play the role of axial front and rear positioning when installing the pipe, and is pressed and sealed by the pipes on both sides in the middle during assembly. The sealant is only applied to the inner wall portion near the end of the shape memory alloy ring. In this way, while the sealing is ensured, it will not overflow into the inside of the pipe during the assembly process. The memory alloy collar shrinks when heated, and tightens the pipe to achieve the purpose of connection. This kind of pipe joint is simple in structure, practical and economical, easy to install and reliable in use.

BEST MODE FOR CARRYING OUT THE INVENTION

The technology of the present invention is described in further detail below by way of examples.

Example 1

The alloy steel with different chemical composition (wt%) of the present invention is produced according to the conventional method of manufacturing shape memory stainless steel, and its performance is tested according to the conventional test method, and its memory performance, corrosion resistance, mechanical performance and processing performance are evaluated. If the test results meet the above performance indicators, the evaluation is "0", and if the test results do not meet the above performance indicators, the evaluation is "X". The composition and performance evaluation results of the 15 alloys tested are listed in Table 1.

comparative example

Alloy steels 16-23 as comparative examples with different chemical compositions were produced in the same manner as in Example 1, and their properties were tested under the same conditions as in Example 1. The results of their chemical compositions and performance evaluations are listed in Table 1.

It can be seen from the results in Table 1. The samples with alloy numbers 1-15 within the chemical composition range of the present invention exhibit good memory performance, corrosion resistance, mechanical properties and processing properties. And as the alloy number of the comparative example The samples of 16-23 are not as good as the alloy steel of the present invention. Specifically, the sample of alloy No. 16 has poor memory performance and corrosion resistance because it does not contain rare earth elements. The sample of alloy No. Π has poor performance in other properties except for better corrosion resistance due to its high Si content. The sample of alloy No. 18 has poor corrosion resistance due to too low Si content, and its memory performance and mechanical properties are also not good. Since the sample of alloy No. 19 does not contain X, it has poor properties except for easy processing. The alloy No. 20 sample has poor corrosion resistance due to its low Cr content. Alloy No. 21 has poor memory performance and corrosion resistance due to its low N content. The samples of alloy Nos. 22 and 23 had n contents of 15% and 18%, respectively, which were higher than the Mn content of the present invention, so the corrosion resistance and processing performance deteriorated.

Example 2

The connected ones are Φ15.9×1min 304 austenitic stainless steel pipes, and the connected collar is the shape memory stainless steel of the present invention. The specific chemical composition (wt%) is as follows: C: 0.02, Cr: 12.8, Si: 5.03, o: 1.02, Ni: 5.10, Mn: 14.13, Co: 3.0, N: 0.10, Ti : 0.20, Ce: 0.02, La: 0.03, and the rest are Fe and other unavoidable impurity elements. The trained shape memory stainless steel collar has a length of 25 mm, a wall thickness of 1 mm, and an inner diameter of φ16 ± 0.05 mm. Memory stainless steel is smelted in a _25kg vacuum induction furnace and poured into round ingots. Memory stainless steel ingot heats up to 1100. C heat preservation for 6h, forging into a billet with a rectangular section of 50 X 20mm, and then hot rolling into a steel strip with a thickness of 3mm. After pickling, it is cold-rolled to 1mm thin plate, and bright annealed in the middle. After trimming, high-frequency welding is used to make memory stainless steel welded pipes. The pipe jacking test with a circular convex cone at a 90° angle proves that the plasticity of the weld is good. The training loading of the welded pipe adopts the rolling method of the mandrel and two outer plates, and the memory recovery of the empty casing reaches 2%. Only use resin sealant at both ends of the memory stainless steel collar during installation and connection. Then it is slowly heated by a gas blowtorch for one minute, and the memory collar shrinks and tightens the connected 304 stainless steel pipe. Carry out hydraulic pressure test on the connection structure, the pressure rises to 50kg/ _C m ² and maintains for 30 minutes, no abnormality is found, and there is no leakage.

Description of drawings

Figure 1: Schematic of the structural method for connecting tubes utilizing shape-memory stainless steel.

Among them: 1-memory stainless steel or alloy collar, 2-intermediate sealing ring, 3-ring end sealant, 4-connected pipe.

Industrial applicability

With the development of science and technology and the improvement of people's living standards, the original galvanized low-carbon steel pipes used as domestic water supply pipes no longer meet the requirements. This is because the corrosion resistance of the galvanized pipe is poor, and the inside of the pipe is prone to rust, which greatly reduces the service life of the pipe and affects the quality of water supply. There is a tendency to use stainless steel pipes and copper pipes as water supply pipes. In order to reduce costs, it is more appropriate to use thin-walled stainless steel pipes, but this kind of thin-walled pipes should not be connected by threading. If the shape-memory stainless steel pipe joint of the present invention is adopted, this difficulty will be easily solved. this new type The pipe joint can also be used for the connection of hot water pipes (mainly copper pipes), which is convenient and firm and can avoid the original brazing process. In addition, the stainless steel pipe used to protect the cable is difficult to construct with threaded connection, and the welding method is not allowed, so as not to damage the cable conductor. At this time, a low-temperature connection method is required, and the shape-memory stainless steel pipe joint of the present invention is ideal for connecting stainless steel pipes of communication cables.

Table I

★ The rest of the chemical composition is divided into 1¾ and unavoidable ft« elements

*K also contains «elements Pr, (¾, Ho, Er, Tm, Yb, Lu¾P'1 when adding I: the real «W Γ«0. 03

Claims

Rights request 1. A shape-memory stainless steel composed of iron, manganese, silicon, etc., characterized in that the weight % range of the chemical composition is as follows: Cr: 12-20, Si: 3-8, Ni: 0. l-8, Mn: 0, l-14.8, Co: 0.1-20, N: 0.05-0.4, C: 0.03, Lanthanide rare earth elements La, Ce, Sm, Nd, Pm, Eu, Tb, Dy, Pr, Gd, Ho, One or more of Er, Tm, Yb, Lu, the total content is 0.01-0.15, One or more of N, Ti, V, Zr, Ta, Hf, W, Mo, Al, Cu elements, the total content is 0.05-2, and the rest are Fe and unavoidable impurity elements. 2. According to the shape memory stainless steel described in patent claim 1, it is characterized in that Cr, Si, Ni, Mn, Co and N are contained in the range of weight %: C U.O-l SASiJ.Z^ l'NiAO-SAM^ l .^K^Co O-ZO.O'N^.OS-OJ. 3. A pipe connection structure mainly composed of memory stainless steel according to claim 1 or 2, characterized in that the inner side of the memory stainless steel or alloy collar [1] and the two pipe ends of the connected pipe [4] There is an intermediate sealing ring [2], and there is a ring end sealant [3] between the inner side of both ends of the collar [1] and the outer side of the connected pipe [4]. 4. The pipe connection structure according to claim 3, characterized in that the intermediate sealing ring [2] is a solid high-plastic alloy ring, a rubber ring or a high-plastic material ring, and its cross-section is circular, oval, rectangular, Trapezoidal or other shaped. 5. The pipe connection structure according to claim 3, characterized in that said ring end sealant [3] is resin, water glass, plastic inorganic paste or solid. 6. The pipe connection structure according to claim 3, characterized in that the intermediate sealing ring [2] and the ring end sealant [3] are used at the same time, or used separately.