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This standard is developed in accordance with the rules given in GB/T 1.1-2009.
This standard was proposed by the China Machinery Industry Federation.
This standard is under the jurisdiction of the National Technical Committee on Rolling Bearing of Standardization Administration of China (SAC/TC 98).
Rolling Bearings—
Parts Made from High-Carbon Chromium Bearing Steels—
Specifications for Heat Treatment
1 Scope
This standard specifies technical requirements and inspection methods for the G8Cr15, GCr15, GCr15SiMn, GCr15SiMo and GCr18Mo steel rolling bearing ferrules and rolling elements (hereinafter referred to as "bearing parts"), as specified in GB/T 18254 [1], after annealing, quenching and tempering.
This standard is applicable to interprocess inspection of the said steel bearing parts and heat treatment quality inspection of finished parts (commodities), as well as bearing parts made from other high-carbon chromium steels. For bearing parts subject to special requirements, corresponding product drawings shall apply.
2 Normative References
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 230.1-2009 Metallic Materials—Rockwell Hardness Test—Part 1: Test Method (Scales A, B, C, D, E, F, G, H, K, N, T)
GB/T 231.1 Metallic Materials—Brinell Hardness Test—Part 1: Test Method
GB/T 272-2017 Rolling Bearing—Identification Code
GB/T 1172 Conversion of Hardness and Strength for Ferrous Metal
GB/T4340.1 Metallic Materials—Vickers Hardness Test—Part 1: Test Method
GB/T 6394 Determination of Estimating the Average Grain Size of Metal
GB/T 17394 Metallic Materials—Leeb Hardness Test
GB/T 24606 Rolling Bearings—Non-destructive Testing—Magnetic Particle Testing
JB/T 7361 Rolling Bearings—Test Method for Hardness of Parts
JB/T 7362 Rolling Bearings—Determination of Decarburized Depth for Parts
3 Technical Requirements
3.1 Technical requirements of the bearing parts after spheroidizing annealing
The technical requirements of bearing parts after spheroidizing annealing are as given in Table 1.
3.2 Technical requirements of the bearing parts after martensite quenching and tempering
3.2.1 Hardness
The hardness of bearing part after martensite quenching and tempering, and the hardness difference of the same part respectively shall comply with Tables 2 and 3 respectively.
Table 1 Technical Requirements of the Bearing Parts after Spheroidizing Annealing
Inspection item Technical requirements
Hardness G8Cr15, GCr15 Other steel a
179HBW~207HBW (Impression diameter 4.5mm~4.2mm) or 88HRB~94HRB 179HBW~217HBW (Impression diameter 4.5mm~4.1mm) or 88HRB~97HRB
Microstructure In evenly distributed spheroidized fine structure; in line with Grade 2~Grade 4 of the first grading pattern; fine spotted spheroidized structures allowable; structures of Grade 1 and Grade 5 as shown in the first grading pattern unallowable
Carbide network In line with Grades 1~2.5 as shown in the fourth grading pattern
Decarburized layer depth ≤ 2/3 of the minimum finishing allowance of individual side
The annealed bearing part after special processing, e.g. cold forming or carbide refining, shall not be greater than 229HBW in hardness and not be less than 4.0mm in impression diameter.
a Other steels refer to GCr15SiMn, GCr15SiMo and GCr 18Mo; the same below.
Table 2 Hardness, in HRC, of the Bearing Part after Martensite Quenching and Tempering
Part Product size mm Hardness after quenching
min. Hardness after routine tempering Hardness after high-temperature tempering
> ≤ 200℃ 250℃ 300℃ 350℃
min. 400℃
min.
Effective wall thickness of ferrule a — 12 63 60~65 59~64 57~62 55~59 52 48
12 30 62 59~64 57~62 56~60 54~58
30 — 60 58~63 56~61 55~59 53~57
Nominal diameter of steel ball — 30 64 61~66 60~65b 58~63b 56~60
30 50 62 59~64 58~63b 57~61 55~59
50 — 61 58~64 57~62b 56~60 54~58
Effective diameter of roller b — 20 64 61~66 60~65b 58~63b 56~60
20 40 63 59~65 58~63b 57~61 55~59
40 — 61 58~64 57~62b 57~60 54~58
Note 1: The size division and corresponding hardness requirements may be determined according to the service conditions and performance requirements in accordance with the agreement between the manufacturer and user.
Note 2: The high temperature tempering temperatures of 200℃, 250℃, 300℃, 350℃ and 400℃ respectively correspond to the common tempering temperatures required by the operating temperature codes of S0, S1, S2, S3 and S4 as specified in GB/T 272-2017.
Note 3: The temperature for high temperature tempering may be within ± 20℃, e.g. 200℃±20℃.
a The effective wall thickness of ferrule and effective diameter of roller are as specified in Annex A; the same below.
b For the hardness value of commodity rolling element, the hardness after routine tempering applies; high temperature tempering, if required, is determined according to the agreement between the user and the manufacturer.
Table 3 Hardness Difference of the Same Bearing Part after Martensite Quenching and Tempering
Part Ferrule (outside diameter)
mm Rolling element (effective diameter)
mm Miniature bearing part
Product size
mm > — 100 400 — 22 —
≤ 100 400 — 22 —
Hardness difference
HRC max. 1 2 3 1 2 Omitted
Note: The hardness difference of the same part refers to the hardness difference of the same surface of the same part.
3.2.2 Microstructure
The microstructure of bearing part after martensite quenching and tempering shall be composed of cryptocrystals, fine crystalized or acicular martensites, evenly distributed fine carbide residuals and few residual austenites; except for miniature bearings, a small amount of acicular or lumpy troostites is allowed. The microstructure after quenching and tempering shall be as specified in Table4.
Table 4 Microstructure of Bearing Part after Quenching and Tempering
Tolerance grade Part material Product dimension/mm Microstructure
Effective wall thickness of ferrule Nominal diameter of steel ball Effective diameter of roller Martensite (the second grading pattern) Troostite b (the third grading pattern)
≤
> ≤ > ≤ > ≤ Within 3 mm from the working face Beyond 3 mm from the working face
PN, P6,
P6X, P5 G8Cr15
GCr15 — 12 — 25.4 — 12 Grade 1~Grade 4 Grade 1
12 15 25.4 50 12 26 Grade 1 Grade 2
15 — 50 — 26 — Grade 2
Other steel — 30 — 50 — 26 Grade 1 Grade 2
30 — 50 — 26 — Grade 2
P4, P2 All steel type a — 12 — 25.4 — 12 Grade 1~Grade 3 Grade 1
12 — 25.4 — 12 — Grade 1~Grade 4 Grade 1 Grade 2
Total tolerance grade GCr15 Miniature bearing part Grade 1 ~ Grade 3 Unallowable
Note: The microstructure requirements may be determined according to the service conditions and performance requirements of bearing by the agreement between the manufacturer and user.
a It refers to G8Cr15, GCr15, GCr15SiMn, GCr15SiMo and GCr18Mo.
b Troostites include acicular troostites and lumpy troostites, the same below.
3.3 Technical requirements of the bearing parts after Bainite isothermal quenching
The structure of bearing part after isothermal quenching shall be composed of lower Bainites and carbide residuals; small amounts of acicular or lumpy troostites and residual austenites are allowed. The hardness and microstructure of bearing part after isothermal quenching are as specified in Table 5.
Table 5 Hardness and Microstructure of Bearing Part after Isothermal Quenching
Steel Effective wall thickness of ferrule Hardness Microstructure Average grain size
mm Bainite (the fifth grading pattern)
≤ Troostite (the third grading pattern)
≤
> ≤ HRC
Within 3mm from the working face Beyond 3 mm from the working face
GCr15 — 25 58~62 Grade 1 Grade 1 Grade 2 Grade 8 or finer
GCr18Mo
GCr15SiMo — 45 58~62
Note: The requirements of the hardness difference of the same bearing part after Bainite isothermal quenching are as specified in Table 3.
3.4 Other technical requirements
Other technical requirements for heat treatment of bearing part are as specified in Table 6.
Table 6 Other Technical Requirements for Heat Treatment of Bearing Part
Inspection item Technical requirement
Cracking No cracking is allowed on the bearing parts after quenching and tempering.
Steel ball crushing load The crushing load value of steel ball after quenching and tempering shall not be less than those specified in Table B.1 of Annex B.
Temper resistance The hardness difference on the corresponding point of the specimen or bearing part after temper resistance testing shall not be greater than 1HRC.
Decarburized layer depth and surface soft spot For interprocess decarburized layer depth, refer to Annex C or subject to the agreement between the manufacturer and user. No decarbonization or surface soft spot is allowed on the working face of product part.
Ferrule deformation For the allowable deformation after quenching and tempering, refer to Annex D or subject to the agreement between the manufacturer and user.
Residual austenite content For the residual austenite content after quenching and tempering, refer to Annex E or subject to the agreement between the manufacturer and user.
Appearance quality After quenching and tempering, no bump-related damage, corrosion, spots or staining shall occur and the overall appearance shall be even in color (silver grey, blue and black).
4 Inspection Methods
The inspection methods are as specified in Table7.
Table 7 Inspection Methods
Inspection item Inspection method
Hardness a) Rockwell hardness tester, Brinell hardness tester, Vickers hardness tester or Leeb hardness tester shall be selected depending on the hardness value and size of the part to be tested; for the testing method, GB/T 230.1, GB/T 231.1, GB/T 4340.1, GB/T 17394 and JB/T 7361 shall apply. Hardness value is converted as specified in GB/T 1172;
b) For steel ball ≤ 15.875mm in nominal diameter and roller ≤ 15mm in nominal diameter, the hardness of the measured curved surface shall be corrected by applying the correction factor as specified in Tables F.1 and F.2 of Annex F. The hardness measurement of spherical roller is made on end surface.
Microstructure The inspection is performed with metalloscope by amplification of 500 or 1000.
a) Structure treated by spheroidizing annealing is subjected to etching with 2% nitric acid alcohol solution and is tested by carbide particle size, quantity and shape according to the first grading pattern;
b) Microstructure after quenching and tempering is tested on longitudinal section; steel ball may be tested on any section or vertical section if in dispute; 2%~4% nitric acid alcohol solution is used for etching;
c) Martensitic structure treated by quenching and tempering is tested by martensite size, residual carbide particle size and quantity according to the second grading pattern;
Microstructure may be inspected as quenched; in case of disagreement, it shall be inspected as tempered;
d) Troostitic structure treated by quenching and tempering is tested by troostite shape, size and quantity according to the third grading pattern. Acicular or lumpy troostite is inspected according to respective troostite grading pattern; acicular and lumpy troostite mixture is inspected according to the troostite morphotype dominant in the field of view.
e) Bainite structure is tested by bainite size, residual carbide particle size and quantity according to the fifth grading pattern.
Carbide network Test with metalloscope by amplification of 500. Annealed specimen is tested on the cross section after normal quenching and tempering, which is subjected to deep etching with 4% nitric acid alcohol solution, by carbide network size and closed extent according to the forth grading pattern;
Decarburized layer depth and surface soft spot a) Surface decarburization and soft spot may be subjected to cold pickling, the specifications of which are as specified in Annex G;
b) The determination of decarburized layer depth is as specified in JB/T 7362. If tested by metallographic method, it as annealed shall be subjected to etching with 2% nitric acid alcohol solution; for hot upset steel ball, the grinding surface of the specimen shall be perpendicular to the annuli. If as quenched and tempered, it shall be subjected to etching with 4% nitric acid alcohol solution;
c) The decarburized layer depth is determined at the deepest position of decarbonization.
Cracking This test shall be performed according to GB/T 24606 (except for steel ball) and may adopt cold and hot pickling (see Annex G) and other apparatus and method. In case of disagreement, hot pickling inspection is adopted.
Steel ball crushing load Annex B shall apply.
Ferrule deformation For small ferrules, test with dial indicator, passimeter, passatest and planeness gauge; for large ferrules, test with dialgauge, caliper, bridge gauge and feeler gauge.
Temper resistance The specimen or part under test has the hardness difference of corresponding point before and after tempering tested after re-tempering according to the original tempering process.
Average grain size GB/T 6394 shall apply.
Residual austenite content X-ray diffraction (XRD) or magnetic measurement is adopted; in case of disagreement, X-ray diffraction (XRD) applied
Appearance quality Visual inspection
Foreword i
1 Scope
2 Normative References
3 Technical Requirements
4 Inspection Methods
Annex A (Informative) Effective Wall Thickness of Ferrule and Effective Diameter of Roller
Annex B (Normative) Steel Ball Crushing Load Test Specifications and Crushing Load Value after Heat Treatment
Annex C (Normative) Decarburized Layer Depth of Bearing Part after Quenching and Tempering
Annex D (Informative) Allowable Deformation of Bearing Ferrule after Quenching and Tempering
Annex E (Informative) Residual Austenite Content of Bearing Part after Quenching and Tempering
Annex F (Normative) Hardness Correction of Curved Surface
Annex G (Normative) Pickling Inspection Specifications
Bibliography
