GCr15 steel

GCr15 steel
GCr15 steel is a representative steel of high-carbon chromium bearing steel with good overall performance. After quenching and tempering, the hardness is high and uniform, and the wear resistance and contact fatigue resistance are high. Good thermal workability. After spheroidizing annealing, it has good workability, but it is sensitive to the formation of white spots. It is mainly used to manufacture steel balls, rollers and bushings on drive shafts of internal combustion engines, electric locomotives, machine tools, tractors, steel rolling equipment, drilling machines, railway vehicles and mining machinery.
 
Material: GCr15 steel
Standard: GB/T 18254-2016
Attributes: high carbon chromium bearing steel


Chemical composition

Grade	C	Si	Mn	Cr	Mo	P	S	Ni	Cu	Ni+Cu
GCr15	0.95 ~ 1.05	0.15 ~ 0.35	0.25 ~ 0.45	1.40 ~ 1.65	≤ 0.10	≤ 0.025	≤ 0.025	≤ 0.30	≤ 0.25	≤ 0.50

 

Heat treatment process
1. Incomplete annealing: heating at 770~790℃, and then cooling with the furnace to below 550℃, air cooling, hardness requirement 187~229HBS, process characteristics Ac1=745℃, Accm=900℃, heating temperature should be between Ac1~Accm between.
2. Isothermal spheroidizing annealing: heating 770~790℃, 680~700℃ isothermal and then cooling to below 550℃ with the furnace, air cooling, hardness requirement 187~229HBS, process characteristics, heating temperature should be between Ac1~Accm, isothermal temperature should 20°C lower than Ar1=700°C line to obtain granular pearlite structure.
3. Stress relief annealing: heating 600~700℃, heat preservation, furnace cooling, mold steel hardness requirement 187~229HBS, process characteristics eliminate residual stress and eliminate work hardening.
4. Normalizing: heating 930~950℃, heat preservation, air, hardness requirement of 302~388HBS, heating temperature higher than Accm, eliminating segregation, band structure, network structure, and fine grain.
5. Lower bainite austempering: heat 855~875℃, keep for 50-70min, 220-240℃ nitrate bath isothermal for 3-4 hours, then wash with 70-80℃ hot water, hardness requirement 58~62HRC. For large bearing parts, tempering at 260°C and heat preservation for 2.5 hours are required. The austempered structure is lower bainite + carbides + a small amount of martensite + a small amount of retained austenite, with small quenching deformation, high strength and good toughness.
6. Lower bainite austempering: heating 830~850℃, 240~300℃ nitrate salt bath isothermal, then air cooling, hardness requirement 58~62HRC, Ms=202℃, austempering structure is lower bainite + carbonization Substance + a small amount of martensite + a small amount of retained austenite, the quenching deformation is small, the strength is high, and the toughness is good.
7. Tempering: heating at 150~190℃, holding time for 2h, furnace cooling, hardness 58~62HRC, the process characteristic is to emphasize the hardness to take the lower limit, and the toughness to take the upper limit.
8. Quenching and tempering: quenching heating 840~860℃, oil cooling, tempering heating 660~680℃, furnace cooling or air cooling after heat preservation, hardness requirement is 197~217HBS, the characteristic is that high temperature quenching can eliminate defects in carbide structure, high temperature The fine tempered sorbite structure obtained by tempering is prepared for re-quenching. While improving the toughness, it also increases the strength and re-quenching. The heating temperature is 820~840°C and oil cooling.
9. Solid boronizing: heating at 920°C for boronizing, heat preservation for 5 hours, oil cooling. Penetrating agent 3%B4C+5%KBF4+5%(NH2)2CO+87%SiC hardness requires 1500~1700HV, high hardness boride layer is obtained on the surface, the core is quenched structure, and the thickness of the layer is 0.145mm.
10. Liquid chromizing: heating at 950°C, heat preservation for 4h, oil cooling. Penetrating agent 15%Cr2O3+12.5% ​​rare earth silicon-magnesium+72.5% borax, hardness requirement 1665HV, infiltration layer thickness 0.01056mm. Improve surface hardness, wear resistance and corrosion resistance.
11. Liquid vanadium infiltration: heating at 950℃, holding for 4h, cooling at 860℃, holding for 2h; heating at 950℃, holding for 4h, oil cooling. Penetrating agent 90%BaCl2+7%V2O5+3%Na2B4O7+Al powder, the hardness requirement is 2500HV0.1, the process feature is the thickness of the infiltration layer 0.020mm, which improves the surface hardness and wear resistance.
 

Physical properties
The mechanical properties of annealed GCr15 bearing steel (typical for steel) are outlined in the table below:

Grade	Tensile	Yield	Bulk modulus	Shear modulus	Poisson’s ratio	Thermal conductivity
GCr15	MPa	Mpa	Gpa	Gpa	%	W/mK
	520	415 Min	140	80	0.27-0.30	46.6

1. The influence of quenching temperature. The normal quenching heating temperature of GCr15 steel is 830-860℃, and oil cooling is mostly used. The best quenching heating temperature is 840℃, and the hardness after quenching reaches 63-65HRC. Under actual production conditions, the quenching temperature used can be slightly different depending on the effective cross-sectional size of the mold and the quenching medium. Such as larger size or nitrate grade quenching mold, it is advisable to choose a higher quenching temperature (840-860℃) in order to improve the hardenability, obtain sufficient hardened layer depth and higher hardness; Oil-cooled molds generally choose a lower quenching temperature (830-850°C). Molds of the same specifications should be heated in a box furnace at a slightly higher temperature than that in a salt bath furnace.
2. The influence of tempering temperature. As the tempering temperature increases, the hardness after tempering decreases. After the tempering temperature exceeds 200℃, it will enter the first type of temper brittleness zone. Therefore, the tempering temperature of GCr15 steel is generally 160-180℃. [3]

Main features and applications
After quenching and tempering, the hardness is high and uniform, and the wear resistance and fatigue resistance are high. Good thermal workability. After spheroidizing annealing, it has good workability, but it is sensitive to the formation of white spots. It can be used to manufacture various bearing rings with wall thickness ≤12mm and outer diameter ≤250mm; also for rolling elements with a wide range of sizes, such as steel balls, tapered rollers, cylindrical rollers, spherical rollers, needle rollers, etc.; It is also used to manufacture molds, precision measuring tools and other mechanical parts that require high wear resistance, high elastic limit and high contact fatigue strength. It is mainly used to manufacture steel balls, rollers and bushings on drive shafts of internal combustion engines, electric locomotives, machine tools, tractors, rolling equipment, drilling machines, railway vehicles, and mining machinery [1].