SM45 Carbon Steel for Plastic Molds

SM45 Plastic Mold Steel is a high-quality carbon steel commonly used in the manufacture of plastic molds. Its main advantage over standard 45 carbon structural steel is its higher purity, specifically lower levels of sulfur (S) and phosphorus (P). This improved cleanliness provides a more consistent and reliable material for your production needs.

1. SM45 Steel Chemical Composition (YB/T 107-1997)

The performance of SM45 Plastic Mold Steel relies on its controlled chemical composition. According to the YB/T 107-1997 standard, the typical composition (weight%) is:

• Carbon (C): 0.42 – 0.48%
• Silicon (Si): 0.17 – 0.37%
• Manganese (Mn): 0.50 – 0.80%
• Phosphorus (P): ≤ 0.030%
• Sulfur (S): ≤ 0.030%

2. SM45 Steel Heat Treatment Guidelines

Correct heat treatment is vital to achieve the desired properties of SM45 Steel.

2.1 Critical Temperatures (Approximate)

• Ac1: 724°C
• Ac3: 780°C
• Ar3: 751°C
• Ar1: 682°C

These points guide the setup of effective heat treatment cycles.

2.2 Pre-Heat Treatment Options

To improve machinability and refine the structure before hardening, consider:

• Annealing: 820-830°C, furnace cool.
• High-Temperature Tempering: 680-720°C, air cool.
• Normalizing: 830-880°C, air cool.

2.3 Quenching

• Temperature: The recommended range is 820-860°C.
• Medium: SM45 Steel has limited hardenability and can be prone to cracking, especially with complex shapes. Use water quenching with caution. Oil quenching or polymer water solutions are generally preferred to minimize the risk of cracking. For some smaller molds, boiling water quenching is used.

2.4 Tempering

• Purpose: To balance hardness and toughness after quenching.
• Temperature: Generally 500-560°C, followed by air cooling.
• Resulting Hardness: Typically 25-33 HRC after quenching and tempering in this range. Lower tempering temperatures (e.g., 200-230°C) can achieve higher hardness (up to 50-55 HRC) but with reduced toughness, suitable for specific applications like punching dies.

3. Mechanical Properties and Hardenability

The final mechanical properties of SM45 Steel5 depend heavily on the tempering temperature used after quenching.

• Example (Quenched 840°C water):
  
  • Tempered at 200°C: ~55 HRC, ~1520 MPa tensile strength (Rm), ~1450 MPa yield strength (ReL).
  • Tempered at 500°C: ~33 HRC, ~870 MPa tensile strength (Rm), ~780 MPa yield strength (ReL).

Keep in mind that SM45 Steel has relatively shallow hardenability. For components with larger cross-sections, the hardness in the core will be lower than at the surface.

4. SM45 Steel Supply Forms and Common Applications

4.1 Supply Conditions

We typically supply SM45 steel in several forms to meet different manufacturing requirements:

• Hot-rolled flat steel
• Hot-forged flat steel
• Normalized thick plates
• Pre-machined blocks (modules)

4.2 Typical Uses

SM45 Steel is a practical choice for:

• Medium to small-sized plastic molds with standard precision requirements. Its cost-effectiveness and good machinability are key benefits here.
• Larger plastic molds where high hardness is not the primary factor (often used in the as-rolled, forged, or normalized state).
• Simpler, smaller mold designs.
• Mold bases.
• Die pads and fixing plates in tooling applications.

5. SM45 Steel Equivalent Grades

SM45 Steel corresponds to several international standards, which can be useful when comparing specifications:

• Japan (JIS): S45C / S48C
• Germany (DIN): C45 (W.Nr. 1.0503)
• USA (AISI/SAE): 1045
• International (ISO): C45E4
• UK (BS): IC45 / 080A47
• France (AFNOR/NF): CC45 / C45
• Italy (UNI): C45
• Spain (UNE): F.114
• Sweden (SS): 1650
• Belgium (NBN): C45-1

6. SM Designation in Mold Steel

In China, the “SM” prefix designates carbon steels, such as SM45, as having enhanced quality, specifically for plastic mold applications, with stricter controls on impurities.

Aobo Steel Expertise

Aobo Steel has over 20 years of experience forging and supplying tool steel and alloy steel, including SM45 Steel. We have the expertise to help you select the right material and understand its processing requirements.