Steel Grade Comparison Chart

 Common Steel Grades Used for Injection Molds

There are several steel grades commonly used for injection molds including:

P20 Mold Steel

P20 is a versatile, pre-hardened mold steel that can be heat treated to higher hardness levels. It has good machinability and polishability. P20 is often used for low to moderate production molds for parts made of thermoplastics.

H13 Mold Steel

H13 is a versatile chromium hot work steel that is pre-hardened. It has excellent thermal fatigue resistance and can withstand the stresses of repeated heating and cooling cycles. H13 is commonly used for molds with moderate to long production runs, especially for parts made of engineered plastics.

30% lower and 10 days less

S7 Mold Steel

S7 is an air hardening, high-carbon, high-chromium steel. It offers a good balance of wear resistance, toughness, and stable dimensions during heat treatment. S7 is used for larger molds and long production runs of over 500,000 cycles.

420 Stainless Steel

420 stainless steel offers good corrosion resistance for molds exposed to moisture. It is often used for food and medical industry molds where corrosion resistance is critical. 420 stainless has lower hardness than tool steels, limiting its use in high wear areas.

1018 Mild Steel

1018 mild steel is very machinable and affordable. It is often used for prototype molds before higher grade production molds are built. 1018 mold steel has low hardness and is only suited for very low volume production.

Factors to Consider When Choosing a Steel Grade

Several factors should be considered when selecting an injection mold steel grade including:

Part Requirements

Consider the material being molded and any special features needed in the final part like threads, inserts, texturing, etc. More complex parts often require higher grade mold steels.

Production Volume

Lower steel grades like P20 and 420 stainless can be used for production runs under 100,000 cycles. For higher volume production, H13, S7, or other tool steels are recommended.

Cost

Mild and stainless steels offer cost savings for very low production molds. Pre-hardened P20 and 420 stainless provide moderate cost savings. H13 and S7 are premium grades but best for high volume molds.

Comparing the Advantages and Disadvantages of Each Steel Grade

Here is a comparison of the key advantages and disadvantages of common injection mold steel grades:

Machinability

  • P20 has excellent machinability in the pre-hardened state.
  • H13 machines well but not quite as easily as P20.
  • 420 stainless has good machinability for a stainless steel.
  • S7 is more difficult to machine than other common mold steels.

Hardness

  • 1018 mild steel has very low hardness after machining.
  • P20 can be heat treated to the mid 40s Rockwell C.
  • 420 stainless achieves around 25-30 Rockwell C.
  • H13 reaches 50-52 Rc after heat treatment.
  • S7 has hardness levels up to 56 Rc.

Corrosion Resistance

  • 1018 and P20 have low corrosion resistance.
  • 420 stainless steel offers the best corrosion resistance.
  • H13 and S7 have moderate corrosion resistance.

Cost

  • 1018 is the most economical option.
  • P20 provides a good value for many applications.
  • 420 stainless is moderately priced.
  • H13 and S7 are more expensive premium grades.

Best Uses for Each Steel Grade

Based on properties, these are typical best uses for each grade:

SteelHardnessCyclesUses
P2028-32 HRCUp to 100kWide range of thermoplastics, cost-effective for low to moderate production
H1348-54 HRCUp to 250k+Engineering plastics, moderate to high production molds
S750-58 HRC500k+Complex, high production molds needing wear resistance
420 Stainless48-50 HRC after hardenVariesCorrosion resistance for food, medical applications
1018 Mild120 HB max<1kPrototype molds, not for production

Conclusion

Choosing the best steel grade for an injection mold requires balancing factors like part requirements, production volume, cost, machinability, and properties like hardness, corrosion resistance, and thermal fatigue strength. Mild steel works for prototypes. P20 offers versatile performance for low to moderate production. H13 is widely used for high volume molds. S7 and other premium alloys are best for the most demanding production runs. Consider both the advantages and disadvantages of each grade for your specific application.

FAQs

What steel is best for making injection molds?

For most production molds, P20 or H13 offer the best combination of machinability, properties, performance, and cost-effectiveness. P20 works well for lower volumes up to 100,000 cycles. H13 is excellent for higher volume molds above 100,000 cycles.

What steel is easiest to machine for injection molds?

1018 mild steel machines the quickest and easiest due to its low hardness. P20 steel also has very good machinability in its pre-hardened state. Avoid S7 if machining time and cost are critical.

Which steel grade offers the best hardness for injection molds?

S7 tool steel achieves the highest hardness and wear resistance after heat treatment, ranging from 52-56 Rc. H13 tool steel also provides good hardness around 50-52 Rc. For maximum mold tool life, S7 and H13 are best.

When should 420 stainless steel be used for injection molds?

420 stainless should be used when the mold or molded parts will be exposed to corrosion from moisture or chemicals. This is common in food processing and medical applications. The lower hardness limits 420 for high wear areas.

What steel is used for prototype injection molds?

For low volume prototypes, 1018 mild steel is commonly used. It machines extremely fast and cheaply but lacks hardness for more than a few test cycles. Once validated, prototypes should be remade from P20, H13 or other harder mold steel grades.

Here is a comparison chart of equivalent injection mold steel grades from different countries, including their applications, typical characters, hardness, and treatment:

ChinaUSAJapanGermanySwedenApplicationTypical CharactersHardnessTreatment
P20718S1361.23112311Low-run production molds, prototypes and other molding applicationsGood surface finish, high toughness28-32 HRCPrehardened, can be polished
718NAS136H1.27382312Production molds with high production ratesHigh-precision, high toughness, good polishability33-37 HRCPrehardened, can be polished
NAK80NASKD611.23448407High-quality molds with high precision and long lifeHigh strength, high toughness, good heat resistance37-43 HRCPrehardened, can be polished
S136HNASKD111.2083420Molds for high-volume productionHigh precision, good surface finish, high wear resistance38-45 HRCPrehardened, can be polished
H13NANA1.23438402High-volume production moldsHigh toughness, good wear resistance44-52 HRCHeat treated for increased hardness and toughness
420420SUS420J21.20834Cr13Molds for general useHigh hardness, good corrosion resistance48-52 HRCHeat treated for increased hardness and toughness
10451045S45CC451.1191Low-volume production molds and insertsHigh toughness, good machinability20-25 HRCHeat treated for increased hardness and toughness

Note: NA stands for “not applicable” or “not available.”

 
 
 

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