7CrSiMnMoV Tool Steel: A Comprehensive Guide

7CrSiMnMoV tool steel, often referred to as CH-1 steel, is a standout low-alloy cold work die steel that’s earned its reputation in the industry for its exceptional qualities. What makes it special? It’s particularly well-suited for flame hardening, offering excellent hardenability, a broad quenching temperature range, and a low tendency to overheat. This means it remains stable during heat treatment with minimal deformation—a significant advantage for manufacturers seeking reliability and precision.

1. 7CrSiMnMoV tool steel Chemical Composition

• Carbon (C): 0.65 – 0.75%
• Silicon (Si): 0.85 – 1.15%
• Manganese (Mn): 0.65 – 1.05%
• Phosphorus (P): ≤ 0.030%
• Sulfur (S): ≤ 0.030%
• Chromium (Cr): 0.90 – 1.20%
• Molybdenum (Mo): 0.20 – 0.50%
• Vanadium (V): 0.15 – 0.30%

This mix is what gives the steel its strength, toughness, and wear resistance, making it perfect for heavy-duty applications.

2. 7CrSiMnMoV tool steel Applications

This steel is a real workhorse, finding its way into a wide range of tools and dies. Here’s where it shines:

• Large insert dies and blanking dies
• Punches and forming dies
• Deep drawing dies and cold stamping dies
• Specialized molds like bakelite and clay molds
• Cutting tools such as shear blades and paper cutting knives
• Industrial components, including rollers and machine tool guide strips

It’s also a go-to for large dies, like those used for automotive outer panels and cold-bending dies. In fact, it outperforms other steels, such as GCr15 and Cr12MoV, in terms of tool lifespan for piercing and blanking tasks. Plus, it’s handy as inserts in big stamping dies, where localized hardening simplifies production.

3. 7CrSiMnMoV tool steel Heat Treatment Processes

To achieve the best results with 7CrSiMnMoV steel, heat treatment is crucial. Here’s how it’s done:

3.1 Forging

Start by heating the steel billets to 1100-1200°C, then finish at 800-850°C, and let them cool slowly. A preheat to 800-900°C ensures everything heats evenly, setting the stage for a solid result.

3.2 Pre-heat Treatment

• Normalizing: Heat it to 840-860°C to refine the grain structure, clear out network carbides, and make it easier to machine.
• Isothermal Annealing: Heat to 820-840°C, hold for several hours, then cool slowly to approximately 680-700°C before finishing with air cooling. Both methods hit a hardness of 217-241 HBW.

3.3 Quenching

This is where the steel gets tough. Heat it to 860-920°C and cool it fast—oil or air works. Oil quenching at 860°C can achieve a hardness of 62 HRC, while air cooling reaches 59 HRC. Even in an 80mm sample, you’ll still achieve 60 HRC at 30mm depth, showcasing its impressive hardenability.

3.4 Tempering

After quenching, temper at 160-200°C to fine-tune the balance between hardness and toughness, achieving a hardness of 58-62 HRC. For smaller parts, self-tempering may be the solution.

3.5 Surface Hardening Treatments

Flame hardening is a game-changer here—preheat the mold to 180-200°C, then heat it to 900-1000°C and air cool. It’s perfect for boosting die lifespan, especially in automotive uses. Another option? Vanadium diffusion treatment in a borax bath, creating a 10-15 μm layer with a hardness of 2820-3010 HV for top-notch wear resistance.

4. Physical Properties

Here’s a quick look at what makes this steel tick:

• Critical Temperatures: Ac1: ~776°C, Ac3: ~834°C, Ar1: ~694°C, Ar3: ~732°C, Ms: ~211°C
• Linear Expansion Coefficient: Ranges from 12.7 × 10^ (- 6)/°C (11-100°C) to 14.3 × 10^ (- 6)/°C (11-500°C), varying with temperature.

These stats help predict how it’ll handle heat and stress on the job.

5. Conclusion

When it comes to cold work dies and tools, 7CrSiMnMoV steel is a standout choice. Its blend of high hardness, great wear resistance, and solid toughness—plus that flame-hardening edge—makes it a favorite for everything from automotive dies to precision cutting tools. With the right heat treatment, this steel delivers performance and durability that manufacturers can count on.