How to match the thickness and hardness of the nitride layer with the working conditions in the LPDC mold nitriding process?
Nitriding is the most mainstream surface strengthening method for H13 low-pressure casting molds, which enhances the wear resistance, aluminum adhesion resistance, and thermal fatigue resistance of the mold cavity; Mismatching nitriding parameters can easily lead to brittle cracking, peeling, and aluminum adhesion in the nitriding layer without improvement.
1、 Quantitative matching standard for nitride layer parameters
Conventional LPDC mold gas nitriding, with a total depth of 0.25-0.4mm for the nitriding layer and an effective hardening layer (white layer+diffusion layer) of 0.12-0.22mm; the white layer is controlled at 0.008-0.015mm. The white layer is too thick and brittle, and is prone to peeling and peeling under cold and hot impacts.
Surface hardness after nitriding HV950-1150; Below HV900, there is insufficient wear resistance, aluminum adhesion, and rapid pulling; Exceeding HV1200, the brittleness of the nitride layer is too high, and network cracks occur under thermal shock.
For automotive parts and thin-walled shell molds, the middle and lower limits should be taken, with a nitride layer of 0.25-0.32mm; for thick walled engineering machinery and high cycle mass production molds, 0.32-0.4mm can be taken.
The nitriding temperature should be controlled between 500-530 ℃. If the temperature is higher than 550 ℃, it will cause the H13 substrate to soften during tempering, resulting in a decrease in substrate hardness. Even if the surface layer is very hard, the overall thermal fatigue resistance will deteriorate.
Xinfeng Machinery provides a nitriding process parameter sheet based on the customer's casting type and cycle time, distinguishing between ordinary nitriding and soft nitriding solutions.
2、 Pre treatment before nitriding and taboos after nitriding
Before nitriding, stress relief tempering and polishing must be completed, and the surface Ra of the mold cavity must be ≤ 0.8 μ m; The surface has oil stains, residual release agent, areas of untempered welding repair, uneven nitride layer, and localized peeling.
The sealing tape of the parting surface, the mating surface of the guide column, and the wear-resistant surface of the slider are synchronously nitrided, but the threaded holes and cooling water holes need to be protected and shielded to prevent the shrinkage of the aperture and screw biting after nitriding.
After nitriding, it is not allowed to polish or polish extensively, as polishing will directly remove the effective hardening layer; A small amount of polishing can only do slight mirror finishing.
The nitride layer is not resistant to arc welding, and the nitride layer in the welding repair area is completely destroyed. After welding repair, re nitriding is required.
3、 Differences in Nitriding Standards for Overseas Customers
Most Southeast Asian customers use low-cost soft nitriding, with a thin nitride layer and a focus on short-term anti sticking aluminum. The lifespan is generally 3000-6000 molds, making it suitable for low-cost trial production of molds.
For the North American automotive project, the thickness of the nitride layer, white layer, and surface hardness are all included in the inspection report, and metallographic samples are attached to each mold for PPAP review.
European customers prefer controllable gas nitriding, strictly limiting the thickness of the white layer, prioritizing the reduction of brittleness, minimizing thermal shock peeling, and pursuing long life and stable mass production.
Large thick walled molds in the Middle East require a thick nitride layer due to severe thermal shock, while strictly controlling the nitriding temperature to protect the substrate hardness and reduce thermal fatigue cracks.
4、 Poor Failure Performance of Nitriding
The white layer is too thick → under cold and hot cycling, the nitride layer peels off in flakes, and the peeling points continue to adhere to aluminum;
Excessive nitriding temperature → softening of the substrate, easy collapse and deformation of the mold cavity;
Stress not released before nitriding → deformation of the mold cavity during nitriding heating process, misalignment and flash of the parting surface;
Inadequate surface cleaning → uneven and mottled nitride layer, with localized premature pulling and sticking of aluminum.
5、 Long tail traffic layout ideas
Mold nitriding, gas nitriding, and white layer belong to surface heat treatment topics, which are targeted at heat treatment and mold engineers.
keywords LPDC mold nitriding treatment、H13 die nitriding layer thickness for low pressure casting；
Problem class: Nitriding white layer control for aluminum casting die;
Comparison class: Gas Nitriding vs Soft Nitriding for LPDC Mold.
Suitable for mold heat treatment matching pages, accepting inquiries for nitriding outsourcing and mold life upgrade.
6、 Common misconceptions in the industry
Misconception 1: The thicker the nitride layer, the better. If the nitride layer is too thick, the brittleness will increase, and thermal shock will peel off, which will accelerate the damage of the mold cavity.
Misconception 2: After nitriding, casually polish and remove the hardened layer, making nitriding meaningless.
Misconception 3: Nitriding can repair cracks, but it only strengthens the surface and cannot heal internal cracks.
FAQ
Q: Recommended Depth of Nitriding Layer for LPDC Mold?
A：0.25–0.4mm， White layer control 0.008-0.015mm.
Q: What is the range of surface hardness after nitriding?
A：HV950–1150。
Q: What is the upper limit of nitriding temperature?
A: ≤ 530 ℃, to prevent the matrix from tempering and softening.
Q: Why is it necessary to relieve stress before nitriding?
A: Prevent deformation of the nitriding heating cavity and dimensional deviation.
Q: What should be done before nitriding threaded holes?
A: Shielding protection to prevent the aperture from shrinking and biting the screw.
Q: What scenarios are suitable for soft nitriding?
A: Low cost, short cycle trial production of molds.
Q: What are the main causes of nitrogen layer peeling?
A: The white layer is too thick, and the nitride layer is brittle.
Q: What will happen to the nitride layer in the welding repair area?
A: Arc damage to the nitride layer requires re nitriding after repair.
