Microstructure, hardness and contact fatigue properties of X30N high nitrogen stainless bearing steel

Microstructure, hardness and fatigue properties of X30N high nitrogen stainless bearing steel were investigated. It was found that nitrogen addition could effectively reduce the amount and size of coarse carbides. The original austenite grain size was obviously refined. Additionally, more retained austenite was found in X30N steel after quenching at 1050 ℃, which could be reduced from about 30% to about 6% by cold treatment at - 73 ℃ and subsequent tempering, and thus, the ultimate hardness was increased up to about 61 HRC with reduction of austenite and precipitation of carbonitrides. Furthermore, the rolling contact fatigue lives of X30N steel ate superior to those of 440C steel, which was attributed to the enhanced hardness and a certain retained austenite in the high nitrogen steel.

Enhanced strength and toughness of high nitrogen stainless bearing steel by controlling interstitial partitioning via V-microalloying

High-nitrogen stainless bearing steel(HNSBS)with ultra-high tensile strength(∼2403 MPa)and good toughness(∼80.0 J)was obtained by V-microalloying,overcoming the strength-toughness trade-off of conventional V-free HNSBS.In this work,since V-microalloying facilitated the enrichment of interstitial atoms(C and N)in precipitates,the content of interstitial atoms in the matrix was reduced accordingly(i.e.,interstitial partitioning).On the one hand,V-microalloying reduced the substantial intergranular precipitates and transformed the precipitates from M_(23)C_(6)+M_(2)N into V-containing M_(23)C_(6)+M_(2)N+MN with multi-scale particle sizes,causing a coupling strengthening effect,which contributed to the toughness and additional strength increase.On the other hand,V-microalloying controlled interstitial partitioning,effectively refined coarse retained austenite(RA),increased the fraction of dislocation martensite,and reduced the fraction of twin martensite.The more film-like RA and dislocation martensite with high dislocation density coordinated plastic deformation and prevented crack propagation,thus obviously enhancing the strength and toughness of 0.2 V steel.This study provides a new route to develop high-performance HNSBS for aerospace applications.

Infuence of Mg on Thermoplasticity of High-Temperature Stainless Bearing Steel Cr_(14)Mo_4

Through the addition of appropriate amount of Mg （0.01-0.01 5 wt%） to the stainless bearing steel Cr14Mo4, the high-temperature thermoplasticity of steel was improved. The mechanism has been uncovered that the added Mg plays an important role in refining and uniforming the carbide precipitations in the steel. It has been found that the segregation of trace Mg is the key to improve the dispersed carbide. Moreover, considerable segregation of Mg in steel during annealing was evidenced by the theoretic analysis.