GCr15 Steel | 52100
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GCr15 steel is a widely used high-carbon chromium bearing steel and is also considered a low-alloy cold work mold steel. It is a representative grade among high-carbon chromium-bearing steels. This steel can be either water or oil quenched, depending on the application and desired properties.
1. Chemical Composition(GB / T 18254—2002)
| C | Si | Mn | Cr | P | S | V |
| 0.95 ~ 1.05 | 0.15 ~ 0.35 | 0.25 ~ 0.45 | 1.40 ~ 1.65 | ≤0.025 | ≤0.025 | — |
2. GCr15 Steel Critical Point Temperature
| Critical Point | Ac1 | Accm | Ar1 | Ms |
| Temperature (Approx. Value)/°C | 745 | 900 | 700 | 246 |
3. GCr15 Steel Forging Process Specification
| Item | Heating Temperature/°C | Initial Forging Temperature/°C | Final Forging Temperature/°C | Cooling |
| Steel Ingot | 1150 ~ 1200 | 1100 ~ 1150 | 800 ~ 880 | First air-cool to 700°C, then pit-cool |
| Steel Billet | 1080 ~ 1120 | 1050 ~ 1100 | 800 ~ 850 | First air-cool to 700°C, then pit-cool |
4. GCr15 Steel Heat Treatment Process Specification
4.1 Preheating
| Preliminary Heat Treatment Plan | Process Parameters |
| Isothermal Annealing after Forging | Slowly heat to 770 ~ 790°C, hold for 1 ~ 2h; furnace cool to 680 ~ 700°C, hold for 3 ~ 4h, then furnace cool to below 550°C and air cool. Hardness: 180 ~ 229HBW. |
| High-Temperature Tempering | Heating temperature: 600 ~ 700°C, hold for 2 ~ 3h; furnace cool or air cool. Hardness: 187 ~ 229HBW. Mainly used to eliminate machining stress before quenching. |
| Normalizing | Heating temperature: 930 ~ 950°C, air cool. Hardness: 302 ~ 388HBW. Used to refine the grains of overheated steel and eliminate network carbides. |
| Quenching and Tempering | Quenching temperature: 840 ~ 860°C, oil cool; tempering temperature: 660 ~ 680°C, furnace cool or air cool. Hardness: 197 ~ 217HBW. |
4.2 Quenching
| Quenching Process Plan | Process Parameters |
| Conventional Quenching Process | Heating temperature: 830 ~ 850°C, oil cool. Hardness: 62 ~ 65HRC. |
| Isothermal Quenching Process | Heating temperature: 830 ~ 850°C, isothermal quenching at 240 ~ 300°C. Tempering temperature: 180 ~ 200°C. Hardness: 58 ~ 62HRC. |
Note: To save energy and time, the residual heat from forging can be used for the isothermal quenching process to replace spheroidizing annealing.
Ultra-fine processing of carbides.
Carbide Super-refinement Process
| Heat Treatment Process | Process Parameters |
| Super-refinement Treatment | Solution temperature is 1050°C, followed by isothermal treatment in a salt bath at 300 ~ 350°C to obtain a lower bainite structure. The tempering temperature is around 720°C with a holding time of 2h, but the hardness is too high, leading to difficult machining. An alternative is a short-time spheroidizing process: heat to 720°C and hold for one hour, then raise the temperature to 780°C and hold for one hour, then cool back to 720°C and hold for another one hour. Finally, in furnace cooled to 500°C before removing. This process can obtain ultra-fine spheroidized carbides. |
4.3 Tempering
Tempering Process Specification
| Heating Temperature/°C | Cooling Method | Hardness HRC |
| 150 ~ 190 | Oil cool or air cool | 58 ~ 62 |
Tempering Temperature and Hardness
| Tempering Temperature/°C | Untempered | 200 | 300 | 400 | 500 | 550 | 600 | 650 |
| Hardness HRC | 62 | 61 | 56 | 49 | 40 | 36 | 31 | 28 |
Note: Oil quenched at 830°C, tempered for two hours.
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5. Mechanical Properties
GCr15 is a special steel for bearings. It has good hardenability, hardness, and wear resistance, high contact fatigue strength, and good dimensional stability during quenching and tempering. Tools and molds made with it have high toughness and wear resistance after low-temperature tempering, which can significantly extend their service life.
Relationship between Quenching Temperature, Microstructure, and Performance
| Quenching Temperature/°C | Mass Fraction of Carbon in Martensite (%) | Retained Austenite Content (volume fraction, %) | Hardness HRC | Bending Strength σbb/MPa | Impact Toughness αK /(J/cm²) |
| 820 | 0.41, Mainly lath martensite | — | 62.8 | 3234 | 6.67 |
| 835 | 0.49, Mainly lath martensite | 10.40 | 63.7 | 2724 | 5.19 |
| 845 | 0.52, Mixture of lath and acicular martensite | 14.70 | 64.1 | 3420 | 5.19 |
| 855 | 0.55, Mixture of lath and acicular martensite | — | 64.9 | 3263 | 3.53 |
| 865 | 0.59, Mixture of lath and acicular martensite | 16.90 | 65.1 | 2960 | 3.43 |
| 875 | 0.67, Mainly acicular martensite | 21.20 | 65.4 | 2739 | 2.55 |
| 885 | 0.67, Mainly acicular martensite | — | 65.3 | 2450 | 2.45 |
Note: Tempered at 160°C.
6. Applications
- Bearings: Its primary and most widespread application is in the manufacturing of various types of bearings, including races, steel balls, tapered rollers, cylindrical rollers, spherical rollers, and needles.
- Molds and Dies (Cold Work): It is frequently used for cold stamping dies, cold heading dies, drawing dies, extrusion dies, and cutting dies/blades. It’s also suitable for plastic molds, especially those requiring high wear resistance, strength, and ability to handle high loads, and for other molds like rolling dies and powder metallurgy dies.
- Precision Measuring Tools: GCr15 is a preferred material for precision measuring instruments such as gauge blocks, plug gauges, and thread ring gauges.
- Machine Parts: It’s utilized in various machine components, including guide pillars and guide bushings, diesel engine injectors, and precision lead screws.
- Other Applications: It’s also used for spring collets and as a material for general cutting tools.
7. Equivalent Material
- AISI/SAE: 52100
- DIN (German): 100Cr6 (or 1.3505)
- JIS (Japanese): SUJ2
- ISO: 100Cr6