Carbon spring steel wire drawing Crack Cause Analysis
2019/7/26 view:
Wire surface cracks on subsequent cold heading steel wire or serving under alternating stress fatigue life greatly. Such as bearing steel surface cracks caused by rushing the ball when a large amount of waste, over the years has been China's steel industry has not been completely solved. By a spiral spring made of steel wire springs fatigue failure mode of primary fracture, the surface cracks and can easily become a source of fatigue crack initiation, thereby reducing the fatigue life of the spring. Thus, in order to prevent the ball bearing steel punch and cracking caused by upsetting of early spring break in service to avoid or reduce the crack surface of the wire is necessary.
1 surface crack morphology
In actual production, the surface of the wire may have two or more types of defects present in the same on a wire, the wire with a number of articles may also be present on the shades of cracks.
(A) the form of cracks and causes
Crack shape not rules, similar to the Turtle pattern, a larger gap, depth of not more than 1.0mm, steel and even cause serious regional fragmentation off. It does not pass bar generation, was discontinuous distribution, fissure length is generally not more than 200mm. Transverse crack region made of metallographic specimen sample, the steel cross-section of tissue observed in five regions obvious. Non-split plot are normal tissue. Cause cracking rod carbon component is partially because there is a serious segregation, enabling organizations to produce significant regional differences, eventually leading to the drawing rod deformation due to uncoordinated and cracks.
(2) transverse crack morphology and genesis
There are three forms of transverse cracking: The first one is a certain angle with the axial direction of the wire, plate gap was washboard cracks; second is the tongue crack; third axial direction perpendicular to the steel stripes.
Produce transverse cracking is due mainly to the following: ① compression rate when cold-drawn or drawn too big too fast; ② entrance taper die too, so that deformation zone is too short; ③ steel bad; ④ wire exists inappropriate drawn microstructure; ⑤ There pickling hydrogen embrittlement; ⑥ poor lubrication; ⑦ drawing dies broken. In actual industrial production, due to a more stable process parameters, generally does not appear the first two cases, and then four situations may exist. Thus, washboard tongue-shaped transverse cracking and transverse cracking caused by poor lubrication.
2 diastema morphology and genesis
Longitudinal surface of the wire, there are two forms: one is parallel to the wire axis linear crack; another wire axially along the curved surface of the distribution curve crack.
The wire is made at the lateral longitudinal metallographic sample, observed is actually curved longitudinal folds and macroscopic morphology of serrated folding at high phasor similar. Its main features are cracks in the surface of the wire bias, its edges are generally serious decarburization exist, often accompanied by seam oxide inclusions. A large number of test results show that the increase in depth of folded steel, heat number, place of origin, the different specifications vary widely, generally between 0.08-0.45mm, a few serious up to 1mm or more. There is only one rod folded, while others fold up to 7,8 bar, or even more. Generation due to uneven surface of the steel ingot or sharp edges, etc., and, in the stack attached to the steel during rolling, or on the ears when the composite made in subsequent rolling.
From the point of view causes longitudinal, straight longitudinal actually be subdivided into three: ① is actually folded; ② actually scratch; ③ true cracks. In these three cracks, mainly folding and scratches, cracks rarely true. Both folding and scratches large proportion who should be depending on the specific conditions, sometimes folded more, sometimes scratched more.
3 fold in the drawing process in the depth of the changes
Due to the wire surface quality is the biggest hazard folded, it examines the collapse of the depth in the drawing process changes. Due to rod or wire folded on different shades with position quite different. Folding depth and its percentage share of the wire diameter with wire diameter decreases. Was mainly due to a long rod spheroidizing annealing, pickling and semi repeated recrystallization annealing, pickling, the surface of the steel to remove a portion, such that the depth of the folded declined significantly. Combined heat till after the explosion collapsed in water (refer annealed wire rod or wire immersed in cold water immediately after being released, in order to remove or loosen the steel surface oxide scale) and the drawing process does not extend, and ultimately makes faded GCr15 steel surface defects by unqualified into qualified. In actual production, qualified rate was significantly greater than a passing rate is the reason.
4 Conclusion
(1) GCr15 bearing steel and spring steel wire (including 65Mn, 60Si2Mn, 70 gauge steel) surface cracks There are six basic forms.
(2) the main surface of the wire is folded substantially longitudinal and scratches, cracks rarely true.
(3) process management should be strengthened, as far as possible from the process factors arising from scratches and transverse cracking.
(4) should be strengthened incoming inspection of raw materials, try to choose a less folded or scratches and shallow feeding hot rod.
(5) For some requiring high quality steel, such as car suspension springs and valve spring wire with a wire that can be used peeler to remove surface scratches rod and folding.
1 surface crack morphology
In actual production, the surface of the wire may have two or more types of defects present in the same on a wire, the wire with a number of articles may also be present on the shades of cracks.
(A) the form of cracks and causes
Crack shape not rules, similar to the Turtle pattern, a larger gap, depth of not more than 1.0mm, steel and even cause serious regional fragmentation off. It does not pass bar generation, was discontinuous distribution, fissure length is generally not more than 200mm. Transverse crack region made of metallographic specimen sample, the steel cross-section of tissue observed in five regions obvious. Non-split plot are normal tissue. Cause cracking rod carbon component is partially because there is a serious segregation, enabling organizations to produce significant regional differences, eventually leading to the drawing rod deformation due to uncoordinated and cracks.
(2) transverse crack morphology and genesis
There are three forms of transverse cracking: The first one is a certain angle with the axial direction of the wire, plate gap was washboard cracks; second is the tongue crack; third axial direction perpendicular to the steel stripes.
Produce transverse cracking is due mainly to the following: ① compression rate when cold-drawn or drawn too big too fast; ② entrance taper die too, so that deformation zone is too short; ③ steel bad; ④ wire exists inappropriate drawn microstructure; ⑤ There pickling hydrogen embrittlement; ⑥ poor lubrication; ⑦ drawing dies broken. In actual industrial production, due to a more stable process parameters, generally does not appear the first two cases, and then four situations may exist. Thus, washboard tongue-shaped transverse cracking and transverse cracking caused by poor lubrication.
2 diastema morphology and genesis
Longitudinal surface of the wire, there are two forms: one is parallel to the wire axis linear crack; another wire axially along the curved surface of the distribution curve crack.
The wire is made at the lateral longitudinal metallographic sample, observed is actually curved longitudinal folds and macroscopic morphology of serrated folding at high phasor similar. Its main features are cracks in the surface of the wire bias, its edges are generally serious decarburization exist, often accompanied by seam oxide inclusions. A large number of test results show that the increase in depth of folded steel, heat number, place of origin, the different specifications vary widely, generally between 0.08-0.45mm, a few serious up to 1mm or more. There is only one rod folded, while others fold up to 7,8 bar, or even more. Generation due to uneven surface of the steel ingot or sharp edges, etc., and, in the stack attached to the steel during rolling, or on the ears when the composite made in subsequent rolling.
From the point of view causes longitudinal, straight longitudinal actually be subdivided into three: ① is actually folded; ② actually scratch; ③ true cracks. In these three cracks, mainly folding and scratches, cracks rarely true. Both folding and scratches large proportion who should be depending on the specific conditions, sometimes folded more, sometimes scratched more.
3 fold in the drawing process in the depth of the changes
Due to the wire surface quality is the biggest hazard folded, it examines the collapse of the depth in the drawing process changes. Due to rod or wire folded on different shades with position quite different. Folding depth and its percentage share of the wire diameter with wire diameter decreases. Was mainly due to a long rod spheroidizing annealing, pickling and semi repeated recrystallization annealing, pickling, the surface of the steel to remove a portion, such that the depth of the folded declined significantly. Combined heat till after the explosion collapsed in water (refer annealed wire rod or wire immersed in cold water immediately after being released, in order to remove or loosen the steel surface oxide scale) and the drawing process does not extend, and ultimately makes faded GCr15 steel surface defects by unqualified into qualified. In actual production, qualified rate was significantly greater than a passing rate is the reason.
4 Conclusion
(1) GCr15 bearing steel and spring steel wire (including 65Mn, 60Si2Mn, 70 gauge steel) surface cracks There are six basic forms.
(2) the main surface of the wire is folded substantially longitudinal and scratches, cracks rarely true.
(3) process management should be strengthened, as far as possible from the process factors arising from scratches and transverse cracking.
(4) should be strengthened incoming inspection of raw materials, try to choose a less folded or scratches and shallow feeding hot rod.
(5) For some requiring high quality steel, such as car suspension springs and valve spring wire with a wire that can be used peeler to remove surface scratches rod and folding.
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