Mine car after large forgings forging heat treatment
Harmfulness White Point White Point 1.1 is an internal cracks caused by hydrogen in steel, solid state high hydrogen content in the steel, the steel becomes brittle significantly, in essence, the white spots are also brittle failure. The presence of white spots so that the mechanical properties of the steel, particularly the drastically reduced transverse ductility and toughness, has become the most dangerous source of fracture, seriously affecting the performance and life of parts. Therefore, the forging Once the white point, the forging must be scrapped.
1.2 Morphology white dots in the longitudinal direction of the fracture surface of the forging appear as sharp edges rounded or oval silver-white spots; low magnification in the transverse specimens as small hairline crack, the length of a few millimeters, the largest tens of millimeters .
1.3 Conditions and white spots produced by forming temperature after forging, steel and hydrogen stress (deformation stress, thermal stress, organizational stress, especially in the stress) under the combined effect produced. White spots formation temperature is cooled to a blank forging a relatively low temperature of about 250 ℃ to room temperature this range.
1.4 stresses the relationship between the hydrogen and the formation of white spots in the literature [2 authors pointed out: "the steel contains a sufficient amount of hydrogen is a necessary condition for the formation of white spots, the presence of internal stress can promote the formation of white spots effect, so supersaturated hydrogen content is to produce white dots 'culprit', while the internal stress is 'accomplice'. "very thorough to say the relationship between the two white spots.