9SiCr tool steel

9SiCr Tool Steel is 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.