1.What are the effects of materials metallurgy and microstructure factors?
Hard and brittle second-phase particles: Inclusions or precipitates in steel, such as oxides (e.g., Al₂O₃, SiO₂), sulfides (MnS), and carbonitrides (TiN, NbC), are hard and brittle. When they accumulate on the surface or subsurface, they become stress concentration points and crack initiation sites, detaching from the matrix during deformation to form flaky particles.
Grain boundary embrittlement: Improper annealing processes can cause cementite or other precipitates to be continuously distributed along grain boundaries, severely weakening grain boundary strength and causing intergranular spalling.
Surface decarburization or carburization:
Decarburization: Reduced surface carbon content leads to insufficient surface layer strength and hardness, making it easily "crushed" during deformation.
Carburization: Accidental carburization can cause abnormal surface hardening and brittleness.
Inappropriate hardness/strength: Materials that are too hard (e.g., fully hardened) or have excessively high strength have insufficient plastic deformation capacity and are prone to brittle fracture.
2.What are the effects of surface quality and adhesion layer factors?
Oxide Layer Issues:
Excessively Thick Passivation/Oxide Film: Especially when the chromate passivation film or natural oxide film is too thick, it is brittle and has poor adhesion to the substrate, making it the first to crack and detach during deformation.
Residual Iron Oxide Scale: Incomplete pickling leads to residual iron oxide scale (FeO, Fe₃O₄), which is extremely easy to peel off.
Contamination Layer Issues:
Foreign Hard Particles: Calcium silicate aluminates (from emulsions or cleaning agents), dust, sand, etc., embedded in the surface during rolling or handling.
Residues: Residual oil and residual iron powder resulting from incomplete cleaning carbonize during stamping, forming hard particles.
3.What are the effects of stamping process and die factors?
Poor Die Condition:
Inappropriate Die Clearance: Insufficient clearance generates excessive shearing and squeezing effects, causing material to be "bitten" off.
Weared or Rough Die Surface: Rough or worn cutting edges/surfaces scrape the material surface like a file.
Insufficient Die Hardness: Wear produces iron filings that mix with material chips.
Inappropriate Process Parameters:
Excessive Blank Holder Force: Causes difficulty in material flow, leading to a sharp increase in localized friction and stress.
Excessive Stamping Speed: Causes excessively high material strain rates, tending towards brittle fracture.
4.What are the effects of lubrication factors?
Insufficient or failed lubrication: The lubricant film strength is insufficient, failing to effectively isolate the mold from the material under high pressure, leading to dry friction or boundary friction, resulting in high temperatures and material transfer.
Incorrect lubricant selection: Insufficient extreme pressure and anti-wear properties, unable to withstand high-load stamping.
Uneven lubrication: Localized areas lack oil film protection.
5.How to thoroughly investigate issues related to materials and incoming supplies?
Metallographic and microscopic analysis (the most crucial step):
Sampling: Samples are taken from the unpressed raw material and the chipped area.
Surface condition inspection:
Cleanliness inspection: Use solvent wiping or gravimetric methods to determine the total amount of residue. Ensure the cleaning process is effective.