GB2041783A - Surface-coated non-magnetic steel material - Google Patents

Abstract

A non-magnetic material comprising a non-magnetic manganese steel and a layer of non-magnetic protective material, e.g. a rust-resistant protective material, is of particular use for incorporating in concrete structures subject to external strong magnetic fields. The protective coating is preferably rust-resistant and/or electrically insulating. Examples of such protective material are non-magnetic metals, phosphates, oxalates, rubbers, synthetic resins, cotton or hemp cloth, jute and paper.

Description

SPECIFICATION Surface-coated non-magnetic steel material This invention relates to a non-magnetic material comprising a non-magnetic steel coated with a layer of protective material. Such non-magnetic material is particularly useful as a reinforcing material for concrete, and the invention also relates to concrete structures containing such non-magnetic material.

A non-magnetic steel material is a steel material which is not magnetized in an external magnetic field. A non-magnetic material, that is, a material having a low magnetic permeability, is often required as a construction material for steel frames or steel bars for use in concrete structures influenced by a strong external magnetic field, for example, experimental nuclear fusion equipment or a magneticaily fioating-type railway bed.

Known non-magnetic steels include austenite stainless steel, e.g. 1 8 Cr-8 Ni steel. Since this steel contains a relatively large amount of Ni it is relatively high in cost and has a low yield strength, and is therefore generally unsuitable as a material for use as a reinforcing material e.g. in the form of frames or bars for concrete.

A manganese non-magnetic steel is lower in cost than an 1 8-8 steel as it does not contain a large proportion of nickel. Such a steel is described for example in United States Patent No. 4,009,025.

Such a high manganese steel stable against a plastic work and heat, retains a low magnetic permeability and is therefore expected to be extensively utilized for the uses mentioned above. Such a steel as worked to a steel bar or the like by hot rolling satisfies the criteria of ,u (magnetic permeability) < 1.02, normally considered to be the specification standard of a nonmagnetic steel, and has sufficient performance for the use as a general nonmagnetic steel.

However, in structures where the slightest magnetic variation is to be avoided such as a geomagnetism observation testing equipment or in structures where a strong alternating magnetic field occurs such as an experimental nuclear fusion equipment, the steel material utilized in these structures should not only be of low magnetic permeability but also be stable in characteristics prior to installation as well as during use in a structure. The following problems prevent the above conditions from being met by conventional nonmagnetic steel materials; (1) Rust is produced on the surface of nonmagnetic steel which causes a rise in the magnetic permeability of the steel.

(2) Heat is generated by the induced current flowing through the steel material, particularly in steel bars incorporated in concrete.

The problem caused by rust is that the rust produced even on nonmagnetic steel material has iron oxide as a base. The apparent magnetic permeability y of a steel material having produced rust is represented by the following formula M = 1 + ( 1C)X1 + CX2 wherein x1 stands for a magnetization of the steel material, x2 stands for a magnetization of the rust and C stands for a production rate of the rust (a ratio of the weight of the produced rust to the weight of the steel material).

In a nonmagnetic steel, x, is very small ( < 0.01) but, as compared with it, x2 is so large as to be about 10. Therefore, even when the production of rust is slight and C is small, the apparent value of,u for the whole of steel material will be of a large value. Therefore, when these materials are used in a structure where a slight variation in magnetism is a problem as is mentioned above, an undesirable influence will be produced. However, the influence of rust in the nonmagnetic steel material has not yet been investigated and therefore no example of treating a nonmagnetic steel so as to be antirusting is known. Furthermore, the production of some rust may be naturally anticipated during the storage and transportation of the steel material or during the handling of the material in the work field.There is also a high possibility of rust being produced when the material has been embedded in concrete for an extended period of time. As mentioned above, that the slightest production of rust may cause significant problems in a special material such as a nonmagnetic steel.

The effect of induced current in the steel material shall be described in the following. Since nonmagnetic steel material is an electric conductor, if it forms an electric circuit and is placed in a magnetic field, an induced current will be generated. When nonmagnetic steel materials which are embedded in concrete are isolated from each other, that is, are not in direct contact with each other, there will be no problem. However, it is in fact difficult to utilize a number of steel bars or the like within a structure and have all in non-contact with each other. Thus, the formation of an electrically closed circuit cannot be avoided in a structure of steel bars or the like embedded in concrete.If such a structure is in a strong magnetic field produced by the use of large currents such as in an electrolytically refining equipment for aluminum or is in a strong magnetic field such as in nuclear fusion apparatus, the induced current generated in the steel bars will be so great that the structure will be likely destroyed due to the expansion of the steel material and the heated embrittlement of the concrete by the heat generation.

An object of the present invention is to therefore provide a nonmagnetic steel material in which such problems inherent to a nonmagnetic steel material as are mentioned above are minimized or even eliminated.

The present inventors have discovered that, in order to solve the above mentioned problem (1), a protective coating is applied to the nonmagnetic steel which will not raise the apparent magnetic permeability of the nonmagnetic steel and which can effectively prevent the production of rust on the surface of the steel and that, in order to solve problem (2), an electrically insulating coating is applied to the nonmagnetic steel. Preferably, it is very desirable to appiy a nonmagnetic coating having both antirusting and electrically insulating properties.

In the drawing, Fig. 1 is a plan view showing a portion of a nonmagnetic steel bar lattice using surface-coated nonmagnetic steel materials embodying the present invention, and Fig. 2 is an explanatory view for measuring the electric resistance of a concrete slab having the steel bar lattice of Fig. 1.

In the present invention, suitable coatings to prevent rusting include metal coatings such as Zn, Al or Sn, a coating having as a base an inorganic compound e.g. a phosphate; or an organic coating e.g. an oxalate; a synthetic resin; or an oil or fat or a byproduct of petroleum refining. Needless to say, the metal coating, if a metal coating is utilized for the steel material, must be of a nonmagnetic metal Methods of coating include a method wherein nonmagnetic steel material is dipped in a molten metal, an electroplating method, or an Al or metal melt-spraying or calorizing method. Such coating methods can be used in the same step as that for general steel materials. However, prior to coating the nonmagnetic steel, it is essential that the steel be well descaled.

A coating for electrical insulation shall be described in the following. As set forth above, the electrically insulating coating is to maintain steel bars or the like which are embedded in a concrete structure electrically insulated even if they contact each other. Therefore, this coating may be applied only to those portions which are anticipated to contact each other. However, in the situation where the coated steel material is produced in advance of installation in a factory production, it will be more practical to coat the entire surface of the steel.

Needless to say, the coating material must have a high electrically insulating property. The metal antirusting coatings mentioned above such as Al or Zn cannot be adopted for use as the insultating coating. However, in contrast to the antirusting coating, close contact with the nonmagnetic steel material is not such a problem and therefore, a method for coating may be utilized wherein, for example, a tubular rubber or synthetic resin is fitted on the outside of the steel material.

Forthe insulating coating, materials such as rubber, cotton cloth, hemp cloth, jute, or paper as is or as impregnated with grease, tar or any synthetic resin can be used. Such insulating coatings may be applied to the entire surface of the steel material by an ordinary coating method or can be applied only to a portion of the steel so as to prevent contact of the steel materials wich each other as a so-called spacer during use.

The antirusting or insulating coating has been described above. However, some coating materials provide the function of both of these coatings. For example, a synthetic resin coating has excellent properties as both an antirusting and insulating material, is comparatively simple to apply and is high in the strength of the coating layer and in the case of handling the coated steel material.

Suitable synthetic resins for the coating material include vinyl chloride resin, epoxy resin or a polyolefin series resin such as, for example, polyethylene or polypropylene. Suitable coating methods for these materials include a powder spray thermosetting method, a liquid resin painting method or a melting-extruding coating method.

The composition of the nonmagnetic steel to be coated need not be particularly limited. Since just the nonmagnetic steel material having the coating layer of the present invention is directed to such uses as are mentioned above, a high Mn series nonmagnetic steel low in cost and having the most practical mechanical and other properties may be selected.

Sumitomo Metal Industries, Ltd. owns a Japanese Patent Laid-open Print No. 150721/77 which was published for public inspection on December 14, 1 977. The steel described therein, that is, a steel containing 0.2 to 1.5% C, 5 to 30% Mn and 0.1 to 1.5% Si and satisfying 100 [C] [c] + 2[Mn] > 25 9 or the steel further containing less than 1 5% Cr, less than 5% Niu, less than 1% Cu, less than 5% Mo and small amounts of Ti, Nb, V, W and Zr are especially desirable as a high Mn series nonmagnetic steel.

This is because, as mentioned in the specification of the above-mentioned print, such a steel has many excellent characteristics, particularly for use as nonmagnetic steel bars in concrete structures.

The shape of the nonmagnetic steel material also need not be particularly limited. The forms to be used in. concrete structures include straight steel bars, different shaped steel bars, steel forms for steel bars, steel frame materials and other forms of various products such as wires and fibers. In each of these forms, by forming a coating layer on the surface, the beneficial effect of the present invention can be realized.

The embodiments and effects of the coating shall be further explained with reference to the following examples.

By using the nonmagnetic steels of the compositions shown in Table 1, various coatings and their anti rusting effects and insulating effects were tested.

Table 1: Sample Material Compositions (%)

7 C Si Mn Or Ni Mo V Total Sol N A1 A 0.87 0.32 14.26 - - - - 0.0103 0.022 1.006 B 0.54 0.30 16.90 - - - - 0.2600 0.006 1.007 C 0.56 0.58 16.87 5140 - - - 0.2130 0.002 1.007 D 0.43 0.44 15.00 6.10 2.04 - - P.0110 0.035 1.010 E 0.46 0.59 17.05 4.00 - - - 0.0117 0.028 1.009 F 0.32 0.30 18.00 - - - 0.20 0.2041 0.007 1.007 G 0.47 0.31 16.05 3.88 - 0.31 - 0.0111 0.020 1.011 * Magnetic permeability at a magnetic field intensity of 100 Oe after solution treatment of 1 0500C heating and rapidly cooling.

(a) Antirusting Test.

The steels A to F in Table 1 were hot-rolled into straight bars of a diameter of 10 mm and were left to cool. The surface coatings shown in Table 2 were then applied to each and they were then tested in the ambient atmosphere and in artificial sea water.

The coating methods were as follows: No treatment As pickled to be descaled.

Zn-plating Pickled to be descaled and then dipped in molten Zn.

Antirusting oil Pickled to be descaled and then painted with a water-soluble antirusting oil.

Epoxy resin coating Shot-blasted to be descaled and then painted with electrostatic powder of acid anhydride setting type bisphenol epoxy resin and baked at 2400C. for 30 minutes to form a film having a thickness of about 170-200 micron meters.

Vinyl chloride resin coating Pickled to be descaled, then pre-heated to 1 000C., painted with electrostatic powder of vinyl chloride resin and baked at 22000. for 30 minutes to form a film having a thickness of about 170 microns meters.

The test results are shown in Table 2.

Teble 2: Antirusting Test Results

Sample Kind of Base material 1 month in 6 months in 12 months in 1 month in 6 months in 12 months in steel coating the atmos- the atmos- the atmpos- artificiat artificiat artificiat sign phere phere phere sea water sea water sea water Amount Amount Amount Amount Amount Amount Amount of pro- of pro- of pro- of pro- of pro- of pro- of produced duced duced duced duced duced duced rust rust rust rust rust rust rust A No 0mm 1.006 0.033mm 1.022 0.288mm 1.153 0.511mm 1.254 0.164mm 1.107 0.835mm 1.418 1.705mm 2.004 treatment " Zn- 0 1.006 0.004 1.006 0.008 1.006 0.012 1.007 0.015 1.006 0.025 1.006 0.030 1.007 plating " Antirust- 0 1.005 0 1.006 0.025 1.018 0.224 1.118 0.153 1.100 0.645 1.342 1.662 1.763 ing oil " Epoxy 0 1.006 0 1.006 0 1.005 0 1.006 0 1.006 0 1.006 0 1.005 resin vinyl 0 1.005 0 1.005 0 1.005 0 1.005 0 1.005 0 1.006 0 1.005 " chloride resin B No 0 1.007 0.031 1.020 0.228 1.137 0.474 1.238 0.135 1.100 0.844 1.365 1.640 1.812 treatment " Zn- 0 1.006 0.002 1.007 0.006 1.007 0.003 1.007 0.011 1.006 0.032 1.009 0.058 1.017 plating " Antirust- 0 1.006 0 1.007 0.17 1.011 0.206 1.109 0.104 1.097 0.592 1.318 1.603 1.672 " Epoxy 0 1.007 0 1.007 0 1.006 0 1.006 0 1.007 0 1.006 0 1.007 resin Vinyl 0 1.007 0 1.006 0 1.006 0 1.007 0 1.006 0 1.007 0 1.006 " chloride resin Table 2 (Continued)

C No 0 1.007 0.026 1.031 0.255 1.184 0.423 1.286 0.159 1.104 0.801 1.403 1.611 1.996 treatment " Zn- 0 1.007 0.001 1.006 0.004 1.008 0.006 1.007 0.010 1.007 0.028 1.007 0.040 1.007 plating Antirust 0 1.006 0 1.007 0.022 1.010 0.194 1.104 0.118 1.101 0.795 1.402 1.647 2.000 ing oil " Epoxy 0 1.008 0 1.007 0 1.007 0 1.007 0 1.007 0 1.008 0 1.007 " resin @ Vinyl 0 1.006 0 1.007 0 1.008 0 1.007 0 1.008 0 1.007 0 1.007 chloride " resin D No 0 1.010 0.022 1.028 0.189 1.112 0.387 1.227 0.160 1.105 0.877 1.412 1.673 2.001 treatment " Zn- 0 1.008 0.001 1.009 0.005 1.009 0.009 1.009 0.012 0.010 0.030 1.009 0.044 1.010 " plating Antirust- 0 1.009 0 1.010 0.019 1.017 0.115 1.101 0.106 1.089 0.658 1.333 1.537 1.604 " ing oil Epoxy 0 1.009 0 1.009 0 1.009 0 1.010 0 1.010 0 1.009 0 1.009 resin " Vinyl 0 1.009 0 1.010 0 1.009 0 1.009 0 1.009 0 1.009 0 1.009 chloride resin E No 0 1.009 0.035 1.021 0.213 1.165 0.403 1.262 0.148 1.099 0.882 1.423 1.614 1.761 treatment " Zn- 0 1.009 0.001 1.009 0.005 1.009 0.008 1.009 0.009 1.009 0.019 1.010 0.033 1.010 plating " Antirust- 0 1.008 0 1.009 0.016 1.012 0.220 1.116 0.114 1.103 0.679 1.333 1.405 1.600 ing oil " Epoxy 0 1.009 0 1.009 0 1.009 0 1.010 0 1.009 0 1.008 0 1.009 resin " Vinyl 0 1.009 0 1.008 0 1.009 0 1.008 0 1.009 0 1.008 0 1.008 chloride resin Table 2 (Continued)

F No 0 1.007 0.036 1.023 0.301 1.158 0.572 1.266 0.154 1.102 0.843 1.422 1.713 1.915 treatment " Zn- 0 1.007 0.002 1.007 0.004 1.007 0.011 1.008 0.017 1.007 0.023 1.006 0.038 1.007 plating " Antlrust 0 1.007 0 1.006 0.010 1.007 0.136 1.100 0.138 1.103 0.685 1.344 1.620 1.670 ing oil " Epoxy 0 1.007 0 1.007 0 1.007 0 1.007 0 1.007 0 1.006 0 1.007 resin Vinyl 0 1.007 0 1.007 0 1.007 0 1.007 0 1.006 0 1.006 0 1.007 " cholride resin G No 0 1.011 0.002 1.029 1.202 1.160 0.409 1.264 0.162 1.107 0.857 1.433 1.630 1.785 treatment " Zn- 0 1.011 0.002 1.010 0.006 1.010 0.008 1.011 0.011 1.010 0.019 1.011 0.030 1.010 plating " Antirust- 0 1.010 0 1.010 0.012 1.017 0.128 1.099 0.121 1.098 0.734 1.401 1.494 1.615 ing oil " Epoxy 0 1.010 0 1.010 0 1.010 0 1.010 0 1.010 0 1.010 0 1.011 resin " Vlinyl cholride 0 1.011 0 1.010 0 1.010 0 1.011 0 1.011 0 1.011 0 1.010 resin To determine the amount of rust produced, the weight of the sample (of a diameter of 10 mm) before the test was measured and then, after the test, the rust was removed with an aqueous solution of ammonium citrate, the weight of the sample was measured, and the weight difference was converted to the average diameter reduction (mm) of the sample.

The magnetic permeability was measured with a magnetic balance on the sample of a diameter of 10 mm and a length of 30 mm.

From the results set forth in Table 2, it is found that when the non-coated sample was left standing in the atmosphere for one month, the increase in y due to the production of rust already exceeded 1.02. The sample painted with the antirusting oil showed a considerable beneficial effect in the atmosphere but had substantially no beneficial effect in the artificial sea water. On the other hand, the Zn-plating, epoxy resin and vinyl chloride resin coating materials showed favorable results in both atmosphere and artificial sea water. Particularly, the two resins produced no rust at all in either test.

Therefore, it is found that any rise of the magnetic permeability of the material was effectively prevented by these materials.

(b) Insulation Test.

Deformed steel bars D22 (22 mm in nominal diameter) were produced by hot-rolling the steels A, C and D in Table 1 and were surface coated with the materials shown in Table 3. Then the electrical resistances of each were measured by the testing method shown in Figs. 1 and 2. Specifically, test pieces 1 of a length of 700 mm and test pieces 1' of a lenght of 900 mm were assembled in a square, the intersections 2, 3 and 4 were bound with low carbon steel wires or nylon strings and the intersection 5 was insulated with rubber hoses. This assembly was embedded in a concrete slab 6 (800 x 800 x 50 mm) shown in Fig. 2 and the electric resistance between the ends A and B was measured with a resistance meter 7. Five concrete slabs made of each type were tested.

The test results are also shown in Table 3.

Table 3: Insulation Test Results

Sample steel Electric reslstance between A-B sign kind of coating Intersection binding manner # # # # # Bound with soft steel wires < 1# < 1# < 1# < 1# < 1# steel bar D22 as rolled Bound with hylon strings < 1# 2.5# < 1# 3.8# < # Steel bar D22 painted with Bound with soft steel wires # # # 40# # tar (50 mlcrons thick) Bound with mylon strings # # # # # A Steel bar D22 coated with Bound with soft steel wires # # # # # epoxy resin Bound with nylon strings # # # # # Steel bar D22 coated with Bound with soft steel wires # # # # # vinyl chloride resin Bound with nylon strings # # # # # Steel bar D22 as rolled Bound with soft steel wires < 1# < 13 < 1# < 1# < 1# Steel bar D22 painted with " " " # 20# # # # tar (50 microns thick) Steel bar D22 coated with " " " # # # # # C epoxy resin Steel bar D22 coated with " " " # # # # # vinyl ohlorlde resin Steel bar D22 as rolled Bound with soft steel wires < 1# < 1# < 1# < 1# < 1# Stee; bar D22 painted with " " " # # # # # tar (50 microns thlck) D Steel bar D22 coated with " " " # # # # # epoxy resin Steel bar D22 coated with " " " # # # # # vinyl chloride resin With the steel bar as rolled, it was found that the electric resistance at the intersection was small and the possibility of an electric closed circuit being formed by the contact of the steel bars with each other was very large. In one instance, the coating layer made by painting with tar was broken by binding with low carbon steel wire and the insulation therefore failed.It is not proper as an insulating coating in consideration of the actual working method.

On the other hand, the electrical resistance of all the coatings with the synthetic resins was infinite, that is, the coatings were perfect insulators and their excellent performance was therefore confirmed.

Together with the results of the preceding antirusting tests, it is evident that the synthetic resin coatings are excellent for the purposes of both antirusting and insulation. In the above mentioned example, the epoxy resin and vinyl chloride resin were exemplified as being typical. However, such effects are confirmed to be attained even with the previously mentioned various kinds of synthetic resin coatings. Such synthetic resin coatings have excellent mechanical characteristics against bending or impact and are therefore excellent materials for coatings for nonmagnetic steel materials.

Claims (14)

1. A non-magnetic material comprising a non-magnetic manganese steel and a layer of nonmagnetic protective material coated on the surface of the steel.

2. A material according to Claim 1, wherein the said protective material is a rust-resistant material.

3. A material according to Claim 2, which is formed by dipping the said non-magnetic steel in a molten non-magnetic metal to provide the said protective coating.

4. A material according to Claim 2, which is formed by electroplating the said non-magnetic steel with a metal to provide the said protective coating.

5. A material according to Claim 2, which is formed by melt-spraying the steel to provide the said protective coating.

6. A material according to Claim 2, which is formed by calorizing the steel to provide the said protective coating.

7. A material according to any of Claims 2 to 6, wherein the said rust-resistant material is Zn, Al or Sn.

8. A material according to Claim 2, wherein the said rust-resistant material is a phosphate.

9. A material according to Claim 2, wherein the said rust-resistant material incorporates an antirust agent.

10. A material according to Claim 1 or Claim 2, wherein the said protective material is an electrically insulating material.

1 A material according to Claim 10, wherein the said electrically insulating material is a rubber, cotton cloth, hemp cloth, jute or paper.

12. A material according to Claim 10, wherein the said electrically insulating material includes an outer cover of a rubber.

13. A material according to Claim 10, wherein the said electrically insulating material is cotton cloth, hemp cloth, jute or paper,lmpregnated with a grease or.a tar.

14. A material according to any of Claims 1 to 13, wherein the surface of the said non-magnetic steel is descaled before being provided with the protective layer.

1 5. A material according to Claim 2, wherein the said protective material is both rust-resistant and electrically insulating.

1 6. A material according to Claim 16, wherein the said protective material is a synthetic resin.

1 7. A material according to Claim 16, wherein the said synthetic resin is a vinyl chloride resin, epoxy resin or polyolefin resin.

1 8. A non-magnetic material according to Claim 1, substantially as hereinbefore described, with particular reference to the Examples.

1 9. A concrete structure containing a non-magnetic material according to any of Claims 1 to 1 8.