The Influence of Tempering Stability of H13 Mold Steel on Long Cycle Mass Production | Selection of Base Materials for Low Pressure Casting Fixtures and Molds
Insufficient tempering of H13 steel and unstable secondary hardening of the substrate are the root causes of early thermal fatigue cracking in 48% of casting molds.
The tempering and insulation time is less than 2.2 hours, the residual austenite in the matrix is not completely decomposed, and the microstructure changes and mold size changes under continuous thermal cycling.
The single tempering temperature is below 560 ℃, with a high hardness of HRC48-50 and insufficient toughness. The crack initiation rate under cold and hot shock is increased by 57%.
When the tempering temperature is higher than 620 ℃, the hardness of the substrate drops below HRC40, and the mold cavity is prone to collapse and deformation, resulting in a significant decrease in wear resistance.
Only one tempering without a second tempering will result in insufficient release of residual stress, and the probability of deformation after nitriding will increase by 33%.
If the original inclusion grade of steel is greater than grade 3, even if the tempering process is qualified, thermal cracks will preferentially occur at the inclusion location under repeated thermal shock.
H13 is the most mainstream substrate for low-pressure die-casting molds (LPDC), reverse pressure casting molds (CPC), gravity casting molds, differential pressure casting molds for wheel hubs, low-pressure casting molds for wheel hubs, motorcycle wheel hub casting molds, structural casting molds, aluminum alloy wheel hub molds, and aluminum casting molding molds. The vast majority of export orders specify H13. Zhejiang Xinfeng Machinery compares different steel plant materials, and the difference in service life between the same grade H13, electric slag remelted material, and ordinary refined material can reach 1.8 times; Priority should be given to using H13 electric slag for export molds. Many outsourced heat treatment plants simplify the tempering process in order to meet delivery deadlines. They ship quickly after one tempering process, and there are no problems detected during the initial mold testing. As a result, cracks appear in 1500-3000 molds after production. After tempering, the air cooling rate should not be too fast. Rapid cooling will reintroduce residual stress, and the furnace should be slowly cooled to below 200 ℃ before being discharged. Nitriding must be carried out after complete tempering. If the tempering is not sufficient, direct nitriding can easily cause deformation and scrap of the mold cavity due to stress accumulation. Middle East Class 3 continuously produces molds with high frequency of thermal shock. It is recommended to temper H13 to HRC44-46, with priority given to toughness, balancing hardness and resistance to thermal fatigue. Many overseas purchases only indicate the material H13, without specifying the smelting method, tempering frequency, and hardness range. It is difficult to protect the rights after the quality of the incoming materials is out of control, and the technical agreement must be supplemented with indicators.
FAQ
1. Question: What is the minimum duration of single tempering insulation for H13?
Answer: The tempering and insulation time shall not be less than 2.2 hours, and the structural transformation shall be sufficient.
2. Question: What is the recommended temperature range for tempering?
Answer: 560-620 ℃, match the target hardness as needed.
3. Question: What is the recommended hardness range for export mold H13?
Answer: HRC44-46 is preferred for long-term continuous mass production.
4. Question: How many tempering processes are suitable for casting mold substrates?
Answer: At least two rounds of tempering to fully release residual stress.
5. Question: What are the requirements for H13 inclusion grade control?
Answer: The inclusion level is better than level 3, which reduces the starting point of cracks.
6. Question: What are the advantages of electric slag remelting H13 compared to ordinary materials?
Answer: The purity of the organization is high, and the lifespan under the same working conditions is increased by nearly 80%.
