Q345 is a low-alloy high-strength structural steel, not a traditional special injection molding die steel. Its name originates from "yield strength 345MPa" (Q represents yield strength, and 345 is the numerical value). This steel is widely used in construction, bridges, mechanical manufacturing, etc., but it is a non-typical choice for injection molds and requires cautious use.
| Element | Content (%) |
|---|
| C (Carbon) | ≤0.20 |
| Si (Silicon) | ≤0.55 |
| Mn (Manganese) | 1.00-1.60 |
| P (Phosphorus) | ≤0.035 |
| S (Sulfur) | ≤0.035 |
| V (Vanadium) | 0.02-0.15 |
| Nb (Niobium) | 0.015-0.060 |
| Ti (Titanium) | 0.02-0.20 |
Yield Strength: ≥345MPa (when thickness ≤16mm)
Tensile Strength: 510-640MPa
Elongation: ≥21%
Impact Energy (20℃): ≥34J (V-notch)
Hardness: Annealed state ≤187HBW
Low-cost Simple Molds: Suitable for producing injection parts with extremely small batch sizes and very low requirements for precision and service life (e.g., temporary sample molds).
Non-corrosive Plastics: Only applicable to molding non-corrosive plastics such as PE and PP, and should not contact materials with corrosive components like PVC or nylon.
Insufficient Wear Resistance: Low hardness makes it prone to wear during long-term use, leading to a decline in mold dimensional accuracy.
Poor Corrosion Resistance: No rust-proof performance; it is easy to rust when exposed to humid air or corrosive plastics, affecting the surface quality of plastic parts.
Limited Heat Treatment Characteristics: Quenching hardness improvement is limited (usually ≤30HRC), and hardenability is poor, making it unsuitable for complex mold structures.
Average Machinability: Better machinability than high-alloy die steels, but poor polishing performance, making it difficult to achieve a mirror effect.
| Performance Index | Q345 | Common Injection Molding Die Steels (e.g., P20, 718H) |
|---|
| Hardness | Annealed state ≤187HBW | Pre-hardened 28-35HRC (P20), 35-40HRC (718H) |
| Wear Resistance | Low | High (containing alloy elements such as Cr and Ni) |
| Corrosion Resistance | Poor | Some models (e.g., S136) have corrosion resistance |
| Polishing Performance | Poor | Can be polished to a mirror (roughness Ra≤0.01μm) |
| Suitable Production Batch | Small batch (≤10,000 pieces) | Mass production (over 100,000 pieces) |
| Typical Applications | Temporary molds, low-requirement parts | Precision molds for auto parts, home appliance casings, etc. |
If similar materials are considered due to cost or other factors, it is recommended to prioritize the following special die steels:
P20 Series: Pre-hardened die steel with a hardness of 28-35HRC, balanced comprehensive performance, suitable for medium batch production.
718H: An improved P20 type with Ni element, better polishing and toughness, suitable for precision molds.
S136: High Cr stainless steel, hardness up to over 50HRC, excellent corrosion resistance, suitable for molds in contact with corrosive plastics or requiring high mirror effects.
As a low-alloy structural steel, Q345 is not recommended as a conventional injection molding die material due to limitations in mechanical properties and surface performance. Forced use may lead to problems such as short mold life and poor part precision. In injection mold design, special die steels should be selected based on production batch size, plastic characteristics, and precision requirements to ensure mold performance and production efficiency. To reduce costs, pre-hardened die steels (such as P20) can be considered instead of Q345 structural steel.
