The former Soviet Union from the mid-1960s began to research and development of limited hardenability bearing steel, and the use of integral induction through heating, strong water cooling process, so that the surface of Xix4 steel has a certain depth of hardened layer, the heart of the non-martensitic structure, with high surface hardness, low hardness of the heart, high impact toughness advantages, and the surface is compressive stress state. This material has been applied to railway passenger car bearings, railway freight car bearings and some rolling mill bearings and obtained good results.

China's research on ⅲx4 steel (GCr4) started late, and was included in the Ministry of Machinery Industry technology development fund project in 1993. Led by Luoyang Bearing Research Institute from 1994 to 1997, GCr4 steel has been systematically studied, in which the contact fatigue life of GCr4 steel and GCr15 steel has been compared. The results show that the rated life of GCr4 steel is increased by 26% and the median life by 19%. However, the comparison test of contact fatigue life between GCr4 steel and G20CrNi2Mo steel and G20Cr2Ni4 steel is lacking. Therefore, the comparison test of contact fatigue life between GCr4 steel and G20CrNi2Mo steel and G20Cr2Ni4 steel is carried out in order to provide theoretical basis for future application.

1 Processing and heat treatment of samples

1.1 Test materials

For GCr4 steel, use vacuum deaerated ∅100mm bar stock to forge and pull it to ∅70mm. G20CrNi2Mo uses Fushun Steel ∅80mm vacuum degassed steel. G20Cr2Ni4 uses Fushun Steel ∅65mm electroslag remelting steel.

1.2 Final Heat Treatment

G20Cr2Ni4 is carburized at 940℃, quenched at 880℃, tempered at 650℃, quenched at 810℃ and tempered at 160℃ in RJJ-180 furnace together with large ferrules.

G20CrN2iMo was carburized on the carburizing line together with the 197726 ring, the carburizing temperature was 935 ℃, the furnace was cooled to 870℃ for a quenching, and then cleaned and tempered at 200℃. The secondary quenching is carried out in the RJGD-200 furnace, the quenching temperature is 800℃, and then the tempering is 160℃.

GCr4 steel is heated in a medium temperature salt furnace to 850℃ quenching water, and then tempered at 200℃.

1.3 Sample finishing

The sample is made directly from annealing rod material, and after final heat treatment, it is finished.

1.4 Quality detection of samples

Surface roughness Ra, parallel difference, surface hardness, depth of hardened layer of channel surface (bounded by 50HRC) and core hardness of the sample are listed in Table 1.

GCr4 quenching structure according to JB1255-91 standard can be rated 3, but the individual carbides are coarse. G20CrNi2Mo quenched structure can be rated 3 grades according to JB/T8881-1999. G20Cr2Ni4 quenching structure according to JB/T8882-1999 grade 1 ~ 2.

2 Contact fatigue test

The contact fatigue test is carried out on three TLP contact fatigue test machines of the tile shaft.

2.1 Test conditions

(1) Test revolution 2016r/min.

(2) The number of steel balls is 20.

(3) Test load 8879kN.

(4) Contact stress 4116MPa.

(5) Stress cycle times 20,160 times/min.

(6) Sample size ∅60mm x ∅20mm x 20mm.

2.2 Test results

The test results are shown in Table 2, and the data in Table 2 are processed by the best linear invariant estimation method, and the results are listed in Table 3. The Weibull distribution curve (FIG. 1) is derived from the data processing results.

It can be seen from Table 3 and Weibull distribution curve. Under the experimental conditions described in this paper, the L10t life of the three materials is comparable.

The characteristic life of GCr4 is slightly lower than that of the two kinds of carburizing steel, GCr4 has the largest slope, and the slope of the two kinds of carburizing steel is slightly smaller, but the difference between them is very small, and their slopes can be considered to be basically similar. In addition, it can be seen from the Weibull distribution curve that there is no significant difference in their median life expectancy of L50.

In summary, the contact fatigue life of these three materials is basically the same. From the test results of contact fatigue life alone, GCr4 steel can replace G20CrNi2Mo and G20Cr2Ni4 steel to produce some rolling mill bearings and other bearings resistant to impact loads. Whether it can be widely used remains to be proved by practice.