Microstructure of Hot Rolled 1.0C-1.5Cr Bearing Steel and Subsequent Spheroidization Annealing

Abstract

The effect of final rolling temperature and cooling process on the microstructure of 1.0C-1.5Cr bearing steel was studied, and the relationship between the microstructure parameters and subsequent spheroidization annealing was analyzed. The results indicate that the increase of water-cooling rate after hot rolling and the decrease of final cooling temperature are beneficial to reducing both the pearlite interlamellar spacing and pearlite colony size. Prior austenite grain size can be reduced by decreasing the final rolling temperature and increasing the water-cooling rate. When the final rolling temperature was controlled around 1103 K (830°C), the subsequent cooling rate was set to 10 K/s and final cooling temperature was 953 K (680°C), the precipitation of grain boundary cementite was suppressed effectively and lots of rod-like cementite particles were observed in the microstructure. Interrupted quenching was employed to study the dissolution behavior of cementite during the austenitizing at 1073 K (800°C). The decrease of both pearlite interlamellar spacing and pearlite colony size could facilitate the initial dissolution and fragmentation of cementite lamellae, which could shorten the spheroidization time. The fragmentation of grain boundary cementite tends to form large-size undissolved cementite particles. With the increase of austenitizing time from 20 to 300 minutes, mean diameter of undissolved cementite particles increases, indicating the cementite particle coarsening and cementite dissolution occuring simultaneously. Mean diameter of cementite particles in the final spheroidized microstructure is proportional to the mean diameter of undissolved cementite particles formed during partial austenitizing.

Microstructure and Properties of 1.0C–1.5Cr Bearing Steel in Processes of Hot Rolling, Spheroidization, Quenching, and Tempering

“…Because the volume fraction of cementite in hot rolled microstructure is almost constant. When the thickness of cementite lamellae is smaller, the number of cementite lamellae per unit volume will be larger, which is beneficial to obtaining more undissolved cementite particles after austenitization . In other words, the undissolved cementite will be distributed more dispersedly, and its number density will also be larger.…”

Influence of Cooling Parameters on the Microstructure and Primary Carbide Precipitation in GCr15 Steel

“…With the high‐temperature confocal laser scanning microscope (HT‐CLSM) applied, Zang et al [ 12 ] indicated that the primary carbide is obviously reduced and the microstructure is refined with a higher cooling rate. As the primary carbide cannot be eliminated in the solidification process, Li et al [ 13 ] investigated the carbide resolution in the heat treatment and found the diameter of undissolved carbides increase with the austenitizing time, which indicates the carbide dissolution and coarsening occur simultaneously. Ota et al [ 14 ] pointed out that the Cr diffusion rate in the solid phase of bearing steel was extremely low, which severely limited the dissolution rate of carbides in the heat treatment process.…”

Tailoring Strength and Ductility of a Cr-Containing High Carbon Steel by Cold-Working and Annealing

“…The spheroidization of cementite lamellae is beneficial to the cold formability of steels; hence, the pearlite steel is usually to be subjected to spheroidization annealing [4,6]. During annealing, the cementite lamellae gradually change their shapes into spherical particles to produce a mixed microstructure, in which globular cementite particles are uniformly distributed throughout the ferrite matrix [7][8][9]. In 1.0C-1.5Cr steel, each element has its irreplaceable role.…”

“…In 1.0C-1.5Cr steel, each element has its irreplaceable role. Cr promotes the solid solution strengthening and reduces the spacing of pearlite lamellae, leading to work hardening [9]. Si induces the solid solution strengthening and suppresses the precipitation of proeutectoid network carbides, which are harmful to the strength and toughness of steel [10].…”

“…Many factors, such as the history of heat treatment [13][14][15], prior microstructure [16,17], chemical compositions [1,11,18], can influence the effect of spheroidization annealing. It was reported that the mean diameter of cementite particles could be reduced by suppressing the precipitation of grain boundary cementite and decreasing the pearlite interlamellar spacing of hot rolled steels [9]. Initial fine pearlite microstructure induces faster spheroidization, and the difference between coarse and fine pearlite microstructures arises from the higher defect density present in the latest [14].…”