1.2311 vs 1.2738 – Composition, Heat Treatment, Properties, and Applications
Share
Table Of Content
Table Of Content
Introduction
Engineers, procurement managers, and manufacturing planners routinely must select between close but distinct mold and tool-steel grades. The decision often balances machinability, polishability, and cost against hardenability, wear resistance, and fatigue life. Typical contexts include selecting steels for plastic-injection molds, general-purpose dies, or components where surface finish and dimensional stability are critical.
In practice, 1.2311 and 1.2738 are compared because both serve in mold and tooling roles, yet they are engineered for different priorities: one emphasizes ease of machining and surface finishing for plastic molds, while the other emphasizes higher carbon and alloy content for greater hardness, wear resistance, and load-bearing capability. Understanding the compositional philosophies, heat-treatment responses, mechanical behavior, and fabrication implications is key to choosing the right grade.
1. Standards and Designations
- EN/DIN: 1.2311 and 1.2738 are European DIN/EN numerical identifiers commonly used in procurement and material specifications.
- Other standards: Equivalents in ASTM/ASME, JIS, or GB may exist for specific alloys or proprietary versions; always confirm with supplier mill certificates.
- Classification:
- 1.2311 — Pre-hardened mold/tool steel (alloyed tool steel designed for plastic-mold applications; non-stainless).
- 1.2738 — Tool steel with higher carbon and alloying (used for molds and dies where higher hardness and wear resistance are required; non-stainless).
- Neither is a stainless grade nor a structural HSLA; both are in the tool/ mold steel family (alloy/tool steels).
2. Chemical Composition and Alloying Strategy
The following table presents qualitative composition emphasis rather than precise numeric ranges. Always confirm numeric limits from the specific supplier certificate or the applicable standard before design or welding.
| Element | 1.2311 (typical emphasis) | 1.2738 (typical emphasis) |
|---|---|---|
| C (Carbon) | Low–moderate (formable, better machinability/polishability) | Moderate–higher (improves hardness and wear resistance) |
| Mn (Manganese) | Moderate (deoxidation, strength) | Moderate (similar role; can assist hardenability) |
| Si (Silicon) | Low–moderate (deoxidation, strength) | Low–moderate |
| P (Phosphorus) | Low (kept low for toughness) | Low |
| S (Sulfur) | Low (for machining variants may be slightly higher in free-machining variants) | Low |
| Cr (Chromium) | Moderate (hardness, temper resistance, corrosion resistance) | Moderate–higher (greater hardenability and wear resistance) |
| Ni (Nickel) | Low–trace (sometimes present to improve toughness) | Low–trace |
| Mo (Molybdenum) | Low–moderate (improves hardenability/strength at temp) | Low–moderate (used to boost hardenability and strength) |
| V (Vanadium) | Low (carbide-former for fine-grain control) | Low–moderate (aids wear resistance via fine carbides) |
| Nb/Ti/B/N | Typically trace or absent (grain control not primary feature) | Trace possible (when designed for toughness/hardenability) |
How alloying strategy affects behavior: - Carbon and chromium are primary levers: increased carbon increases achievable hardness and wear resistance; chromium increases hardenability and temper resistance. - Alloying elements such as Mo and V increase hardenability and form carbides that improve wear resistance but reduce polishability. - 1.2311 is formulated to provide a balance favoring good machining and surface finish; 1.2738 shifts composition toward greater carbon and carbide-formers for wear and load resistance.
3. Microstructure and Heat Treatment Response
Typical microstructures and heat-treatment behavior:
1.2311 - As-supplied: often supplied pre-hardened and tempered (a “pre-hardened” mold steel) with a tempered martensitic matrix and relatively few coarse carbides. This results in a fine microstructure that machines and polishes well. - Heat-treatment response: can be re-hardened and tempered, but composition and alloy levels mean hardenability is moderate; careful control of austenitizing and quench rates is required to avoid quench cracks or excessive distortion. - Normalizing/refining: normalizing and tempering cycles reduce residual stresses and can slightly refine grain size, but the grade is optimized for minimal post-machining processing.
1.2738 - As-supplied: typically supplied in a soft-annealed condition for machining, or as-hardened blanks; microstructure in annealed state is ferrite + pearlite with alloy carbides dispersed. - Heat-treatment response: higher carbon and alloy content yield higher hardenability—responds well to quenching and tempering to achieve higher hardness levels and a tempered martensitic microstructure with dispersed alloy carbides for wear resistance. - Thermo-mechanical treatments: more responsive to deeper hardening treatments, and will achieve higher through-hardness for thicker sections compared with 1.2311.
Practical implication: 1.2311 favors minimal post-machining heat treatment and predictable surface finish; 1.2738 allows higher final hardness and wear resistance at the expense of more aggressive heat treatment and greater distortion risk.
4. Mechanical Properties
The following table gives comparative qualitative mechanical-property tendencies. Exact values depend on heat treatment and specification; consult supplier data sheets for certifiable numbers.
| Property | 1.2311 (typical as-supplied / tempered) | 1.2738 (typical annealed / quenched & tempered) |
|---|---|---|
| Tensile Strength | Moderate | Higher (after quench & temper) |
| Yield Strength | Moderate | Higher |
| Elongation | Higher (more ductile) | Lower (higher hardness reduces elongation) |
| Impact Toughness | Good (balanced for mold applications) | Variable — can be good if tempered properly, but generally lower at high hardness |
| Hardness (as-supplied) | Moderate (easy to machine/polish) | Lower when annealed; can be hardened to higher HRC after heat treatment |
Which is stronger/tougher/ductile and why: - Strength and hardenability: 1.2738 generally achieves higher strength and hardness after appropriate quench & temper cycles because of its higher carbon and alloy content. - Toughness and ductility: 1.2311 generally retains greater ductility and easier polishability in the pre-hardened condition, making it preferable for injection-mold cavities where surface finish and resistance to cracking during machining are priorities.
5. Weldability
Weldability is influenced by carbon equivalent and alloying. Two common indices used for qualitative interpretation:
-
Carbon equivalent (IIW):
$$CE_{IIW} = C + \frac{Mn}{6} + \frac{Cr+Mo+V}{5} + \frac{Ni+Cu}{15}$$ -
Pcm (Welding criticality):
$$P_{cm} = C + \frac{Si}{30} + \frac{Mn+Cu}{20} + \frac{Cr+Mo+V}{10} + \frac{Ni}{40} + \frac{Nb}{50} + \frac{Ti}{30} + \frac{B}{1000}$$
Qualitative interpretation: - 1.2311: lower carbon and fewer alloying elements generally yield a lower $CE_{IIW}$ and $P_{cm}$ than 1.2738, making it comparatively easier to weld with lower preheat and interpass temperature requirements. Still, as a tool/mold steel, welding requires attention to avoid hot cracking and to match metallurgy for post-weld heat treatment. - 1.2738: higher C and alloying raise the carbon equivalent, increasing the risk of hard, brittle heat-affected zones and cold cracking. Preheat, controlled interpass temperature, and post-weld heat treatment are more often required.
Practical note: For both grades, welding is usually limited to repair or fabrication of non-critical features. For critical tooling, mechanical fastening or producing from a single block is preferred; welding repair should follow supplier and welding metal recommendations.
6. Corrosion and Surface Protection
- Neither 1.2311 nor 1.2738 is a stainless steel; therefore atmospheric and chemical corrosion protection is necessary where environment demands it.
- Common protection strategies: clear or pigmented coatings, paint, phosphating, oil preservation, or zinc plating where appropriate. For high-precision mold cavities, coatings (e.g., PVD, nitriding) are sometimes applied to improve wear and corrosion resistance while preserving surface finish.
- PREN (Pitting Resistance Equivalent Number) is not applicable because these grades are non-stainless. For stainless grades the index is: $$\text{PREN} = \text{Cr} + 3.3 \times \text{Mo} + 16 \times \text{N}$$
- When corrosion resistance is a priority, select stainless tool steels or apply surface engineering (hard coatings, nitriding, corrosion-resistant platings) rather than relying on base-alloy corrosion resistance.
7. Fabrication, Machinability, and Formability
- Machinability:
- 1.2311: typically engineered for good machinability and very good polishability in pre-hardened condition. Less tool wear during roughing and finishing; good for tight-tolerance machining.
- 1.2738: in annealed state is machinable, but when hardened to working hardness it is more abrasive and causes greater tool wear. Carbide tooling and grinding are often necessary.
- Formability and bending:
- Both are steels with limited formability compared with low-carbon structural steels; 1.2311’s lower hardness in pre-hardened condition gives more latitude for minor forming. Major forming operations are uncommon for mold steels.
- Finishing:
- 1.2311 allows superior surface finish and polish — important for glossy plastic parts.
- 1.2738 is more challenging to achieve mirror finishes due to higher carbide content; additional polishing steps or coating may be required.
- Heat treatment distortion:
- 1.2738 is more prone to distortion during aggressive hardening cycles because of higher hardenability and higher transformations; careful fixturing and machining allowance planning needed.
8. Typical Applications
| 1.2311 — Typical Uses | 1.2738 — Typical Uses |
|---|---|
| Injection-molding plates and cavity inserts where good polish and dimensional stability are priorities | Dies and tooling subjected to higher wear, such as cutting dies, blanking dies, and heavy-load mold components |
| General-purpose pre-hardened mold bases and plates | Mold cores and inserts where high contact stresses and abrasive wear are expected (after hardening) |
| Prototype molds and low-volume production where fast machining and polishing are required | High-volume production tooling requiring longer life and higher hardness |
Selection rationale: - Choose 1.2311 for components where surface finish, polishability, and reduced machining time are dominant selection criteria (e.g., optical or high-gloss plastic parts). - Choose 1.2738 when the primary requirement is higher wear resistance, higher operating hardness, or when the tooling will operate under heavier loads or abrasive conditions.
9. Cost and Availability
- Relative cost: 1.2311 is often more economical for pre-hardened mold plates and is widely stocked in plate and block forms for mold-makers. 1.2738, depending on its exact composition and heat-treatment condition, may be slightly higher in cost, especially if supplied in hardenable blank form or with specific annealing cycles.
- Availability by product form:
- 1.2311: commonly available as plate, blocks, and ground plate in pre-hardened conditions; popular in tooling distribution channels.
- 1.2738: available in bar, plate, and custom blanks; may require ordering to specification for hardened conditions.
- Lead times: stock availability for both grades is generally good in mature tooling markets, but specialized sizes or heat-treat conditions can add lead time. Coated or pre-hardened variants may be more readily available for 1.2311.
10. Summary and Recommendation
Summary table — qualitative rating (Higher / Moderate / Lower):
| Attribute | 1.2311 | 1.2738 |
|---|---|---|
| Weldability (practical) | Higher (easier) | Lower (more preheat/tempering needed) |
| Strength–Toughness balance | Moderate (good balance, more ductile) | Higher strength (at cost of ductility when hardened) |
| Cost (typical in mold market) | Lower–Moderate | Moderate–Higher |
Final recommendations: - Choose 1.2311 if: - You need a pre-hardened mold steel with excellent machinability and polishability for plastic injection molds. - Surface finish and dimensional stability with minimal post-processing are critical. - Welding repairs will be occasional and ease of welding is desired. - Shorter lead times and cost containment are priorities.
- Choose 1.2738 if:
- The application requires higher achievable hardness and wear resistance after quench & temper.
- Tooling will face higher mechanical loads, abrasive wear, or longer productive life is required.
- You accept more involved heat treatment, potential for greater distortion, and the need for carbide-resistant tooling in machining/grinding.
Closing note: Both grades are valuable in tooling and mold-making. The correct choice depends on the prioritized performance envelope: surface finish and ease of machining versus maximum hardenability and wear resistance. For any critical procurement or design, confirm specific chemical and mechanical limits from the mill certificate and consult with your heat-treat vendor to align material selection with intended processing and service conditions.