JP2017018999A - Ferritic stainless steel pipe excellent in bending workability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain plate thickness reduction on the bending outside in bending processing.SOLUTION: A ferritic stainless steel pipe being 2r+r≥4 in the relationship between an r value (r) in the pipe axis direction and an r value (r) in the direction of forming 45° with the pipe axis direction, is formed of a raw material of bending processing, and a crack on the bending outside or remarkable plate thickness reduction such as not satisfying a use purpose of a finished article is restrained. The ferritic stainless steel pipe made so that an r value (r) in the pipe axis direction of the ferritic stainless steel pipe is 1.5 or more and the pipe axis direction is orthogonal to the rolling direction of the ferritic stainless steel pipe being a pipe raw material, is desirable.SELECTED DRAWING: None

Description

The present invention relates to a ferritic stainless steel pipe excellent in bending workability.

Various metal pipes are used as pipes for automobiles, air conditioners, electrical equipment, various plants, and the like. These pipes are often used after being bent. In bending of a metal tube, with the bending neutral axis as a boundary, the arc length is longer than the neutral axis on the outer side of the bending, so that it is extended in the axial direction, and the plate thickness after processing becomes thinner than the plate thickness before processing. On the other hand, the inner side of the bend is compressed in the axial direction because the arc length is shorter than that of the neutral shaft, and the thickness after processing becomes thicker than the thickness before processing.
As a result, cracks are likely to occur on the outer side of the bend, or a reduction in plate thickness that does not satisfy the intended use of the processed product, and buckling tends to occur on the inner side of the bend. Furthermore, the cross section is likely to be elliptical after bending.

As a material for such various pipes, copper pipes and aluminum pipes, or austenitic stainless steel pipes are often used for applications that require corrosion resistance and heat resistance, but in terms of cost, ferritic stainless steel pipes are used. There are an increasing number of examples.
Ferritic stainless steel may be inferior in workability compared to austenitic stainless steel in terms of elongation or the like, but the demand for bending is only increasing. For example, even for severe machining where the bending radius at the neutral axis of the bending is 1.2 times the pipe diameter or less, thickness reduction and cracking on the outer side of the bend, buckling on the inner side of the bend, and ovalization of the cross section are suppressed. There is an increasing demand for bending technology and materials that can be used.

The present invention has been devised in order to suppress a decrease in the thickness of the outer side of the bending of the metal tube, particularly when the thickness of the metal tube is thin or the bending radius is small. An object of the present invention is to provide a ferritic stainless steel pipe that can suppress cracking and thickness reduction.

As a result of intensive studies on the influence of the material properties of the material on the decrease in the thickness of the outer side of the bending in the bending process of the ferritic stainless steel pipe, the present inventors have determined that the plastic anisotropy (r value) of the material, particularly the pipe, The larger the r value (r _i ) in the direction forming 45 ° with the axial r value (r _φ ) and the tube axis direction, the smaller the decrease in the plate thickness outside the bend, while the 90 ° direction with the tube axis direction. It was found that the r value (r _θ ) has a small effect on the decrease in thickness outside the bend.

The present invention has been developed on the basis of such knowledge, and the relationship between the r value (r _φ ) in the tube axis direction and the r value (r _i ) in the direction forming 45 ° with the tube axis direction is expressed as 2r. _{φ + r i} ≧ 4
By doing so, the present invention relates to a ferritic stainless steel pipe that can suppress a significant decrease in the plate thickness that does not satisfy the purpose of use of the processed product or a crack on the outside of the bending.

The r value is three types of JIS13B test cut out from a steel plate material along the direction parallel to the rolling direction, 45 ° to the rolling direction, and 90 ° to the rolling direction. A piece was prepared and evaluated with an amount of strain of 15% elongation to obtain an r value in three directions. And these the three directions of r values, the r value in the rolling direction parallel to the direction of the steel plate r _0, the direction of the r values forming the rolling direction and 45 ° in the direction forming r _45, the rolling direction and 90 ° r Let r ₉₀ be the value.
For example, in the case of pipe forming by roll forming, since the rolling direction of the steel sheet is parallel to the tube axis direction, r _φ = r ₀ and r _i = r ₄₅ .
In the case of pipe forming by sheet winding, r _φ = r ₀ and r _i = r ₄₅ as in the case of roll forming when the steel sheet is formed so that the rolling direction of the steel sheet is parallel to the tube axis direction. On the other hand, when the pipe is formed so that the rolling direction of the steel sheet is orthogonal to the pipe axis direction, r _φ = r ₉₀ and r _i = r ₄₅ .

ADVANTAGE OF THE INVENTION According to this invention, the ferritic stainless steel pipe which can suppress the crack of a bending outer side and plate | board thickness reduction | decrease can be provided in a bending process.

Examples of the present invention will be described below, but the present invention is not limited to the following examples.

Among ferritic stainless steel sheets having a 14Cr—Si—Mn—Nb chemical component, the r value (r _i ) in the direction of twice the r value (r _φ ) in the tube axis direction and 45 ° with the tube axis direction. ) the sum of the (2r φ _{+ r i)} is such that four or more, outer diameter D40mm, a ferritic stainless steel having a thickness of T1.2mm to pipe-making by roll forming. Using these as materials for bending, bending by the rotational pulling method was performed so that the radius of curvature (bending radius) R of the neutral axis of bending was 48 mm (bending radius R = 1.2D). In bending using the rotary pulling method, side boosters and back boosters are provided to supply materials to the bent parts and suppress cracks and reductions in plate thickness, and cores to suppress buckling and cross-sectional ovalization. used. The thickness reduction rate at the maximum thickness reduction position outside the bend was evaluated. The results are shown in Table 1.

By bending as a processing material ferritic stainless steel, the sum of twice the axial direction of the tube and r value in a direction which forms a 45 ° of r value of the tube axis direction (2r φ ₊ r _i) 4 or more The maximum thickness reduction rate outside the bend is a good value of about 25% or less. Preferably, twice the axial direction of the tube and the sum of the r values in the direction forming an 45 ° a (2r φ ₊ r _i) by 5 or more, the bending maximum thickness reduction rate of the outer r value in the tube axis direction Is better at about 20% or less. Further, the sum of twice the axial direction of the tube and r value in a direction which forms a 45 ° of r values in the tube axis direction (2r φ + r _i) is at least 4, and the tube axis direction of the r value (r _phi) Is preferably 1.5 or more.

A steel plate whose r values in three directions are (r ₀ , r ₄₅ , r ₉₀ ) = (1.2, 1.0, 1.7) and (1.5, 0.9, 1.8) As described above, a ferritic stainless steel pipe having an outer diameter of D40 mm and a thickness of T1.2 mm was formed by sheet winding so that the rolling direction of the steel sheet was parallel and orthogonal to the pipe axis direction. Using these as materials for bending, bending by the rotational pulling method was performed so that the radius of curvature (bending radius) R of the neutral axis of bending was 48 mm (bending radius R = 1.2D). The conditions for bending by the rotational pulling method were the same as in Example 1. The thickness reduction rate at the maximum thickness reduction position outside the bend was evaluated. The results are shown in Table 2.

By changing the material taking direction in the plate-rolled pipe, the sum of the r value in the direction of 45 ° to the pipe axis direction and twice the r value in the pipe axis direction of the ferritic stainless steel pipe that is the material of the bending process with (2r φ ₊ r _i) four or more, even for a radius of severe working such that following 1.2 times the tube diameter bend in the neutral axis of bending, the maximum thickness reduction rate of the bending outer Good value of about 25% or less.

A steel plate whose r values in three directions are (r ₀ , r ₄₅ , r ₉₀ ) = (1.2, 1.0, 1.7) and (1.5, 0.9, 1.8) As described above, a ferritic stainless steel pipe having an outer diameter of D40 mm and a thickness of T1.2 mm was formed by sheet winding so that the rolling direction of the steel sheet was parallel and orthogonal to the pipe axis direction. Using these as materials for bending, bending by the rotary pulling method was performed so that the radius of curvature (bending radius) R of the neutral axis of bending was 60 mm (bending radius R = 1.5D). The conditions for bending by the rotational pulling method were the same as in Example 1. The thickness reduction rate at the maximum thickness reduction position outside the bend was evaluated. The results are shown in Table 3.

When the radius of curvature (bending radius) R of the neutral axis of bending is 60 mm (bending radius R = 1.5D), there are twice the r value in the tube axis direction and the r value in the direction of 45 ° with the tube axis direction. sum (2r φ ₊ r _i) is the maximum thickness reduction rate of the outer bend be less than 4 becomes a good value at about 25%. However, the sum (2r φ ₊ r _i) is the maximum thickness it is bent outside of the 4 or more of the r values in the direction forming twice the axial direction of the tube and 45 ° of r values in the tube axis direction is the invention It can be seen that the reduction rate is small and it is difficult to reduce the thickness. Therefore, the present invention is effective in suppressing the decrease in the thickness of the outer side of the bend, and the utility of the present invention is particularly useful in severe processing where the bend radius at the neutral axis of the bend is 1.2 times or less the tube diameter. Becomes prominent.

Claims (3)

The relationship between the r value (r _φ ) in the tube axis direction and the r value (r _i ) in the direction forming 45 ° with the tube axis direction is 2r _φ + r _i ≧ 4
It is characterized by
Ferritic stainless steel pipe with excellent bending workability. The r value ( _rφ ) in the tube axis direction is 1.5 or more,
The ferritic stainless steel pipe | tube excellent in the bending workability of Claim 1. It is characterized in that the rolling direction of the ferritic stainless steel sheet, which is a pipe material, is piped so that it is perpendicular to the pipe axis direction.
The ferritic stainless steel pipe excellent in bending workability according to claim 1 or 2.