9SiCr Steel Technical Overview

9SiCr Steel Technical Overview: It’s a low-alloy tool steel, and its key characteristics come from silicon (Si) and chromium (Cr) being the main alloying elements. The typical chemical composition, by weight percentage (wt%), generally falls within these ranges, although you’ll see slight variations between different standards.

1. 9SiCr Tool Steel Chemical Composition

• Carbon (C):85% to 0.95%.
• Silicon (Si): Usually 1.20% to 1.60%, though some standards like the German DIN 90CrSi5 specify 1.05% to 1.25%.
• Manganese (Mn): Typically 0.30% to 0.60%. Again, the German standard might show a slightly higher range (0.60% to 0.80%).
• Chromium (Cr): Generally 0.95% to 1.25%, with the German standard at 1.05% to 1.30%.
• Phosphorus (P) & Sulfur (S): These are impurities, usually kept low, with maximum limits often set at ≤0.030% for both.

It’s good to know the equivalents across different international standards: 9SiCr matches AISI L3 (USA), DIN 90CrSi5 / 1.2067 (Germany), BS BL3 (UK), ГОСТ 9ХС (Russia), and UNE 100Cr6 (Spain). In the Chinese system (ISC), it’s T30100.

2. 9SiCr Steel Physical Properties

Regarding physical properties:

2.1 Density: Around 7.80 g/cm³.

2.2 Critical Temperatures: These are vital for planning heat treatment:

• Ac1 (start of austenite formation on heating): ~770°C
• Accm (cementite fully dissolves): ~870°C
• Ar1 (start of pearlite formation on cooling): ~730°C
• Ms (martensite start): ~160°C
• Mf (martensite finish): ~ -30°C

2.3 Magnetic Properties: Coercive force is about 795.8 A/m, and saturation magnetic induction is 1.78 to 1.82 T.

2.4 Linear Expansion Coefficient: While specific values weren’t in the provided source material, this is a critical factor for precision parts, especially considering temperature changes during heat treatment and use.

3. Heat Treatment

Heat treatment is crucial to obtaining the right mechanical properties from 9SiCr. The standard process involves hardening (quenching) and tempering.

3.1 Pre-heat Treatment Options

• Annealing after forging: Heat to 790-810°C, hold 1-2 hours, let the furnace cool below 550°C, and then air cool. This results in 197-241 HBW hardness. Isothermal annealing (similar heating, hold at 700-720°C) achieves the same hardness range and typically yields a spheroidal pearlite structure.
• High-temperature tempering: Heat to 600-700°C for 2-4 hours, then furnace or air cool. Used to relieve stress from cold working.
• Normalizing: Heat to 900-920°C, then air cool. Refines grains in overheated steel and removes network carbides, resulting in 321-415 HBW hardness.
• Quench and Temper (alternative pre-treatment): Heat to 880-900°C, oil quench, then temper at 680-700°C (2-4 hours) for 197-241 HBW hardness. Forged parts can sometimes be directly quenched from forging heat followed by high-temp tempering.

3.2 Hardening (Quenching)

The recommended temperature is 860-880°C.

• Oil Quenching: Cool in oil (various temps possible), then air cool. Hardness: 62-65 HRC.
• Salt/Alkaline Bath Quenching: Use a molten bath (150-200°C) for specific times, then air cool. Hardness: 59-63 HRC. These methods help minimize deformation in complex parts. The structure after quenching is mainly lath martensite, fine carbides, and some retained austenite.

3.3 Cold Treatment

For high-precision, dimensionally stable tools, a cold treatment (-70°C) shortly after quenching can slightly increase hardness (0-1 HRC). Best done within an hour of quenching.

3.4 Tempering

This step relieves stress and fine-tunes hardness and toughness. Typical results:

• 140-160°C Temper: 62-65 HRC
• 160-180°C Temper: 61-63 HRC
• 180-200°C Temper: 60-62 HRC
• 200-220°C Temper: 58-62 HRC

Higher tempering temps reduce hardness further. Double tempering (e.g., 180°C then a higher temp like 240°C) can significantly improve toughness and tool life.

4. 9SiCr Steel Mechanical Properties

The mechanical properties of 9SiCr depend heavily on the heat treatment. After quenching and low-temperature tempering, it offers high hardness (can stay around 60 HRC even after 300-400°C tempering), good hardenability, and good wear resistance. Bending strength after an 850°C quench is about 2250 MPa. However, for some very demanding jobs, its compressive strength and wear resistance might not be enough.

5. 9SiCr Tool Steel Applications

Regarding applications, 9SiCr is a versatile choice for cold work dies and tools needing high wear resistance with minimal deformation during heat treatment. Common uses include:

• Low-speed cutting tools (where wear resistance is key).
• Complex cold work dies: manual reamers, shear blades, threading dies, cold rolling/straightening rolls, thread rolling dies, deep drawing dies, stamping dies, cold heading dies.
• Precision measuring tools and gauges.
• Small/medium stamping, cold punching, and blanking dies.
• Plastic mold parts (when carbon steels aren’t sufficient).
• Cold extrusion and pressing dies.
• Cam dies, punches, trimming dies.
• Drawing dies, forming dies, extrusion dies, rolls.
• Ejector pins.
• Large, complex, high-precision plastic molds.
• Shear blades (e.g., large blades achieving 57-60 HRC with controlled deformation via isothermal quenching/tempering).

6. 9SiCr Steel Comparisons and Considerations

Compared to basic carbon tool steels, 9SiCr provides better hardenability, toughness, and wear resistance. Its drawbacks include sensitivity to decarburization during heating and relatively high annealed hardness.

• A grade like Cr8MoWV3Si (with more carbon and carbide formers) might be considered if you need even higher wear resistance and toughness.
• For large dies where simpler heat treatment is preferred, an air-hardening steel like 7CrSiMnMoV could be an alternative.
• Surface treatments (like nitriding combined with quenching) can extend the life of 9SiCr dies in applications like cold heading.
• Thermomechanical treatment can improve strength and plasticity if high bending strength is critical.

Ultimately, determining if 9SiCr is the right choice depends entirely on the specific requirements of the application—the type of operation, material being worked, expected tool life, and part complexity are all important factors. We can discuss your specific needs further to ensure you’re using the best steel grade and heat treatment for your situation.