JPH04354851A - Non-magnetic reinforcing bar - Google Patents

Abstract

PURPOSE:To offer a non-magnetic reinforcing bar suitable for reinforcing bar concrete structures requiring non-magnetic properties such as buildings for setting nuclear magnetic resonance diagnostic devices, buildings for fusion reactors and guide ways for magnetic levitation type railroads, low in magnetic permeability, showing stable non-magnetic properties and, furthermore, excellent in strength, workability, weldability and rusting resistance. CONSTITUTION:The compsn. contg., by weight, 0.25 to <0.4% C, 0.1 to 1.0% Si, 20 to 24% Mn, 7 to <10% Cr, 0.08 to 0.18% N and the balance Fe with inevitable impurities and satisfying 0.4%<C+1.5N is regulated to obtain a reinforcing bar.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is suitable for reinforced concrete structures that are required to be non-magnetic, such as buildings for installing nuclear magnetic resonance diagnostic equipment, buildings for nuclear fusion reactors, and guideways for magnetic levitation railways. Regarding magnetic reinforcing bars, in detail, they have low magnetic permeability, stable non-magnetic properties, and even strength and strength.
This relates to non-magnetic reinforcing bars that are excellent in workability, weldability, and rust resistance.

0002

[Prior art] The characteristics required for non-magnetic reinforcing bars are as follows:
It must have low magnetic permeability, stable non-magnetism, and excellent mechanical properties, such as magnetic permeability of 1.1 or less and yield strength of 35 kgf/mm2 or more, as well as cutting workability. , excellent workability such as bending workability and weldability, and rust resistance.

Commercially available stainless steel SUS304 is commonly used as the non-magnetic reinforcing bar. However, this stainless steel has the problem that it may become magnetic when subjected to bending, etc., and its non-magnetism is unstable, and its yield stress is low and its mechanical properties are insufficient.

[0004] Also, JP-A-52-150721 and JP-A-53-53513 propose high-Mn nonmagnetic steel containing a relatively large amount of Mn. However, when this high Mn non-magnetic steel is hot rolled, decarbonization and demanganization occur on the steel surface, and the Ni equivalent in the so-called Schaeffler phase diagram decreases, resulting in a decrease in the stability of the austenitic structure of the steel. It loses its non-magnetic properties. Furthermore, the surface of high-Mn non-magnetic steel after hot rolling has the problem that Mn, etc. in the steel is oxidized and forms scale, which makes it magnetic, and the mechanical strength is also insufficient. .

Furthermore, non-magnetic reinforcing bars used in advanced technology fields such as buildings for nuclear fusion reactors have a magnetic permeability of 1.0.
A high level of non-magnetic properties of 1 or less is desired.

[0006]

[Problems to be Solved by the Invention] The present invention has been made in view of the above circumstances, and has low magnetic permeability as well as
The aim is to provide non-magnetic reinforcing bars whose non-magnetic properties are stable even when processed, and in terms of mechanical properties, the yield strength is 35.
kgf/mm2 or more, tensile strength of 70 kgf/mm2 or more, elongation of 20% or more, and has excellent rust resistance and good hot workability, and is easy to cut and bend during construction, making it an excellent welding material. The purpose of the present invention is to provide a non-magnetic reinforcing bar with magnetic properties.

[0007]

[Means for Solving the Problems] The present invention that achieves the above objects is: C: 0.25% or more and less than 0.4% Si: 0.1
% to 1.0% Mn: 20% to 24% Cr: 7% to less than 10% N: 0.08% to 0.18%, the balance consists of Fe and inevitable impurities, and C+1.5N >0.4%.

[0008]

[Operation] In order to obtain steel with stable non-magnetic properties, it is necessary to stabilize the austenitic structure. Conventional high M
n steel attempts to stabilize the austenite structure by containing only a large amount of C and Mn,
As mentioned above, C and Mn removal may occur during hot rolling, and stabilization of non-magnetic properties cannot be achieved with C and Mn alone. Furthermore, increasing the C content impairs workability such as cutting/bending workability and weldability.

[0009] As a result of various studies from the above-mentioned viewpoints, the inventors of the present invention have determined that the amount of C should be suppressed as much as possible without causing a decrease in strength, and that the austenite structure should be stabilized and rust resistance should be improved. The present inventors have discovered that by adjusting the amount of Mn in accordance with the balance between N and Cr, a non-magnetic reinforcing bar exhibiting excellent properties in all aspects of workability, weldability, and rust resistance can be obtained, and the present invention has been completed. The reason for limiting the component range of the non-magnetic reinforcing steel according to the present invention will be explained below.

C: 0.25% or more and less than 0.4% C is effective in stabilizing the austenite structure and improving strength, and it is necessary to add at least 0.25% or more. However, if the amount is too large, the coefficient of thermal expansion increases and cutting/bending workability and weldability deteriorate, so the upper limit was set at 0.4%.

FIG. 2 shows the effect of C on the gas pressure weldability of high Mn steel.
This is a graph that examines the influence of That is, high M
Ten test pieces were prepared by changing the amount of C in stages from n-series steel (inventive steel No. 2 shown in Table 1), and the same composition was prepared using a commonly used semi-automatic gas pressure welding device. The third high Mn steel is
Pressure welding was performed under the conditions shown in the figure, and a bending test (R = 4D
, 90°).

The results shown in FIG. 2 show the significance of setting the C content to less than 0.4% for high Mn steel.

[0013] Si: 0.1% to 1.0% Si is an element added for the purpose of deoxidizing during steel melting, and has the effect of improving strength and fluidity by solidly dissolving in the austenitic base. , and it stabilizes the austenitic structure of high Mn steel, so it is necessary to add at least 0.1% or more. However, if it is too large, it deteriorates high-temperature ductility and makes blooming difficult, and also destabilizes the austenite structure and increases magnetic permeability, so it is limited to 1.0% or less.

Mn: 20% to 24% Mn is the most important element in stabilizing the austenite structure and keeping magnetic permeability low, and is also effective in lowering the coefficient of thermal expansion, so 20% It is necessary to contain the above amount. On the other hand, if it is too large, problems will arise in dissolution and workability as reinforcing bars, so 24% is set as the upper limit.

Cr: 7% or more and less than 10% Cr is an effective element for stabilizing the austenitic structure of high-Mn steel, increasing its strength, and increasing the amount of N solid solution. Furthermore, it is necessary to improve the rust resistance of concrete, and it should be contained in an amount of 7% or more. However, if it is too large, the coefficient of thermal expansion increases and it is not economical, so 10
The upper limit was %.

N: 0.08% to 0.18% N is an element that, like C, stabilizes the austenite structure and improves strength and rust resistance, and must be added in an amount of 0.08% or more. However, if the content is too large, hot workability will deteriorate, so the upper limit was set at 0.18%.

C+1.5 N: 0.4% or more Figure 1 shows the C+1.5 N content and 0.2% yield strength and elongation (
Gl=4D), which is a graph showing the relationship between cutting and bending workability. The cutting workability was evaluated by the number of pieces that could be cut with a band saw cutter, and the bending workability was evaluated by the presence or absence of cracks in a bending test (R=D90°). Looking at Figure 1, it is 0.2%.
There is a positive correlation between yield strength and C+1.5N, and 0
．． 2 To make the proof stress 35kgf/mm2 or more, C+
It can be seen that 0.4% or more of 1.5N is required.

[0018] However, if the content is too large, the elongation and cutting/bending workability will deteriorate, so the content is preferably 0.675% or less, more preferably 0.4% or more and 0.6% or less.

[0019]

[Example] Using the present invention steel and comparative steel whose components are shown in Table 1, they were melted in a conventional electric furnace and hot rolled. Comparison steel No. 17 is commercially available steel SUS304. A test piece was taken from the obtained steel material, and 0.2% proof stress, magnetic permeability,
The coefficient of thermal expansion and the incidence of red rust were measured using a salt spray test. The results are shown in Table 2. Further, a cutting test and a bending test were conducted to examine the cuttability with a cold band saw, the difficulty of bending, and the bending workability of the welded part according to the following evaluation method.

[0020] Cutability with cold bandsaw ○: Number of reinforcing bars (D25 size) cut: 10 or more ×
: Number of cut reinforcing bars (D25 size) Less than 10 bending difficulty ○: No cracks in the bent part ×: Cracks in the bent part Bending workability of welded parts ○: No cracks in the bent part ×: Cracks in the bent part The bending process was performed at 1.5 times the nominal diameter (25.4 mm, A25) and at a bending angle of 180°. The results are in Table 2
Also listed in

[0021]

[Table 1]

[0022]

[Table 2]

[0023]No. Examples 1 to 5 are examples according to the present invention, which have a high 0.2% yield strength of 35 kgf/mm2 or more, low magnetic permeability, stable non-magnetism even after bending, and rust resistance. It has excellent cutting, bending, and welding properties.

On the other hand, No. Examples 6 to 17 are comparative examples in which one or more of the conditions according to the present invention are not satisfied, and one of the characteristics is insufficient.

[0025]No. No. 17 is SUS304, which has high mechanical properties and high magnetic permeability after bending, and is unstable in non-magnetism.

[0026]

[Effects of the Invention] Since the present invention is constructed as described above, it is a non-magnetic reinforcing bar that has low magnetic permeability and stable non-magnetism even after processing, and has good mechanical properties and rust resistance. It has now become possible to provide a non-magnetic reinforcing bar that has excellent hot workability, is easy to cut and bend during construction, and has excellent weldability.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the C+1.5 N content and mechanical properties of high Mn steel.

FIG. 2 is a graph showing the relationship between C content of high Mn steel and bending workability after pressure welding.

3 is a graph showing the pressure welding conditions performed in the test of FIG. 2. FIG.

Claims (1)

[Claims] [Claim 1] C: 0.25% (meaning of weight %, the same applies hereinafter) or more 0
．． Contains less than 4% Si: 0.1% to 1.0% Mn: 20% to 24% Cr: 7% to less than 10% N: 0.08% to 0.18%, the remainder being Fe and unavoidable impurities A non-magnetic reinforcing bar comprising: and adjusted to satisfy C+1.5 N>0.4%.