Weldability of sulphur free machining steel in friction welding was investigated. Base metal has a diameter of 12 mm.
Results are summarized as follows:
(1) A suitable welding condition for sound welds in tensile test is;
Rotational speed N: 3620 rpm
Heating pressure Ph: 3.0 kg/mm
2Upsetting pressure Pu: 8.0-12.0 kg/mm
2Heating time Th: 0.5 s.
(2) In any case, increase of heating time lowers tensile strength of weld.
(3) Even the welded joint, which is made under suitable condition, has poor bending ductility. Normalizing can improve ductility of weld. However, it makes the joint break at the weld in tensile test.
(4) The weld made under suitable condition has impact value of 1.3 kg-m/cm
2in Charpy test by using specimen with V notch. On the whole, impact value of the weld of free machining steel is much lower than that of base metal, 3.2 kg-m/cm
2.
(5) Fatigue strength of the weld is 29.0 kg/mm
2, which is lower than that of base metal by 10 %.
(6) When heating time is prolonged, softened area in the weld becomes wider, and it deteriorates mechanical properties of weld.
(7) Mechanical properties of weld is affected by shape, size and orientation of sulphide at the heat-affected zone.
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