A stabilizer formed by using a metal bar having a solid structure and configured to reduce a displacement between right and left wheels, including a torsion part extending in a vehicle width direction, being capable of a torsional deformation, and having a diameter of 10 to 32 mm, is provided. The stabilizer has a chemical composition containing at least C: 0.15% by mass or more to 0.39% by mass or less, Mn, B, and Fe, and also has a metal structure 90% or more of which is a martensite structure.

The invention provides a production method for stabilizers which produces with high productivity in a compact production line, without tempering. The production method for stabilizers of the invention includes: forming a steel bar material containing at least C: 0.15 wt % to 0.39 wt %, Mn, B and Fe into a product shape by bending; and quenching the bent steel bar material in a medium having a heat transfer coefficient higher than or close to that of water.

According to one embodiment, a stabilizer manufacturing device includes a first forming unit and a second forming unit. The first forming unit includes a first forming mandrel, a holding member and a first bending roller. The first forming mandrel includes a first forming portion having an arc shape when viewed from above, and a support portion which supports a workpiece. The first bending roller moves along the first forming portion. The second forming unit includes a second forming mandrel, a holding member and a second bending roller. The second forming mandrel includes a second forming portion having an arc shape when viewed from above, and a support portion which supports the workpiece. The second bending roller moves along the second forming portion.

The present invention provides a method for manufacturing a torsion beam, the method comprising: a planarization step, in which a protruding portion of an upper mold presses the opposite end portions in the width direction of the blank to be plastically deformed to be flat while the opposite end portions in the width direction of the blank are supported by a side cam to face each other; a welding and bonding step for bonding the planarized opposite end portions in the width direction of the blank via welding; and a quenching step for heating the welded and bonded blank within a range of 900 to 970° C. for a retaining time within a range of 1 to 20 minutes and for cooling down the blank in a treatment liquid including at least one of water and oil in a range of 20 to 90° C.

A method of manufacturing a forged product includes a heating step, a first and a second forging steps, wherein the forging temperature in the heating step is 450° C. or higher and 550° C. or lower, and surface temperatures of the upper molding part of the first upper die in the first forging step and the upper molding part of the second upper die in the second forging step are 150° C. or higher and 190° C. or lower, surface temperatures of the lower molding parts of the first and the second lower dies are 190° C. or higher and 230° C. or lower, and the surface temperatures of the lower molding parts of the first and the second lower dies are higher by 5° C. or more than the surface temperatures of the upper molding parts of the first and the second upper dies.

According to one embodiment, a stabilizer manufacturing device includes a first forming unit and a second forming unit. The first forming unit includes a first forming mandrel, a holding member and a first bending roller. The first forming mandrel includes a first forming portion having an arc shape when viewed from above, and a support portion which supports a workpiece. The first bending roller moves along the first forming portion. The second forming unit includes a second forming mandrel, a holding member and a second bending roller. The second forming mandrel includes a second forming portion having an arc shape when viewed from above, and a support portion which supports the workpiece. The second bending roller moves along the second forming portion.

A stabilizer formed by using a metal bar having a solid structure and configured to reduce a displacement between right and left wheels, including a torsion part extending in a vehicle width direction, being capable of a torsional deformation, and having a diameter of 10 to 32 mm, is provided. The stabilizer has a chemical composition containing at least C: 0.15% by mass or more to 0.39% by mass or less, Mn, B, and Fe, and also has a metal structure 90% or more of which is a martensite structure.

An electric resistance welded steel pipe for manufacturing a hollow stabilizer has a Rankford value in a pipe longitudinal direction of from 0.7 to less than 1.0. The electric resistance welded steel pipe is subjected to cold bending and then to a heat treatment including quenching and tempering to manufacture a stabilizer. The cold bending is cold rotary draw bending. When bent with a bend radius of from 1.0 times to 3.0 times an outer diameter of the pipe before cold bending, a flattening ratio is from 0% to 10%, a thickness reduction rate on a bending outside and a thickness increase rate on a bending inside are from 0% to 10%, and additionally, a circumferential length change of a bending center portion is from 0% to 10%. A Vickers hardness of the stabilizer after the heat treatment is adjusted to from 400 HV to less than 580 HV.

The invention provides a production method for stabilizers which produces with high productivity in a compact production line, without tempering. The production method for stabilizers of the invention includes: forming a steel bar material containing at least C: 0.15 wt % to 0.39 wt %, Mn, B and Fe into a product shape by bending; and quenching the bent steel bar material in a medium having a heat transfer coefficient higher than or close to that of water.

A hollow spring member and hollow spring member production method can be provided, which can save the time and energy necessary for carburization, thus requiring no dedicated carburizing furnace or the like for carburization, and further can make the interior space of a steel tube a rust-prevention atmosphere. A hollow stabilizer for a vehicle includes a steel tube sealed at one end and another end thereof and a carburizing gas sealed in the interior space of the steel tube.