Effect of Quenching Conditions on the Microstructure and Mechanical Properties of 51CrV4 Spring Steel

Abstract

51CrV4 steel is extensively used in large-size damping springs for trains and vehicles. Quenching conditions play an important role in performance enhancement. The present work investigated the effects of various oil-bath temperatures and out-of-oil temperatures on the microstructure and the mechanical properties of this steel. The morphological examination focused on both the quenched martensite and the tempered troostite. Tensile and hardness tests were carried out to evaluate the mechanical properties. The results showed that a coarsening of the martensite occurred at a high oil-bath temperature. In addition, the size and fraction of bainite islands also increased with the increase of oil-bath temperature. In contrast, the carbide size and the intercarbide spacing both increased with the increase of oil-bath temperature. Thus, the tensile strength and the hardness both decreased with increasing oil-bath temperature in accordance with the Hall-Petch relationship. Correspondingly, the ductility increased as the oil-bath temperature increased. At a relatively high out-of-oil temperature, the martensite underwent an auto-tempering process, which led to the precipitation of many tiny carbide particles in the as-quenched martensite laths. This auto-tempering effect enhanced the width of large-sized carbides and reduced their length in the final microstructure. The intercarbide spacings increased with increasing out-of-oil temperature. As the oil-bath temperature increased, the tensile strength and hardness decreased, and the ductility increased. The fracture morphology was examined to explain the results of mechanical properties.

FARKLI MENEVİŞLEME SICAKLIKLARININ 51CrV4 ÇELİĞİNİN MEKANİK ÖZELLİKLERİNE ETKİLERİNİN İNCELENMESİ

“…Yapılan çalışmada, 51CrV4 çeliklerine yağda soğutma işleminden sonra farklı sıcaklıklarda temperleme işlemleri uygulanmış ve bu işlemlerin morfolojiye, mekanik özelliklere ve aşınma dayanımlarına etkisi incelenmiştir. [16], çalışmalarında da farklı sıcaklıklarda temperlenmiş 51CrV4 çeliklerinde benzer piklere rastlanmıştır. Yine aynı çalışmada, 90℃ sıcaklıkta temperleme işlemi gerçekleştirilen numunelerde bu fazlara yani 50° 2Θ değerindeki pike rastlanabilir.…”

“…Yine aynı çalışmada, 90℃ sıcaklıkta temperleme işlemi gerçekleştirilen numunelerde bu fazlara yani 50° 2Θ değerindeki pike rastlanabilir. XRD analizinden temperlenen 51CrV4 malzemelerinde 2h = 44.803'teki tepe martenzit fazına ve 2h = 65.023 tepe noktasında ferrit fazına atanmıştır [16]. Oluşan karbürlü fazlar, karbon pik şiddetinin demire göre çok düşük olması nedeni ile gözlemlenememiştir.…”

Description of Hot Compressive Stress-Strain Curves Using Transfer Functions

“…Investigated specimens are made of laboratory scale produced 51CrV4 spring steel grade, hot rolled in the temperature range from 1200 • C to 1000 • C into flat bars 22 mm thick with chemical composition given in Table 1. Investigated steel grade is in this temperature range in the austenitic phase [16]. Specimens for dilatometer experiments are machined into cylinders with height and diameter of 10 mm and 5 mm, respectively.…”

Prediction of Microstructure Constituents’ Hardness after the Isothermal Decomposition of Austenite

“…The process of steel quenching is one of the physically most complicated engineering processes which involves many physical processes, such as microstructure transformations, heat exchange, heat transfer and heat conduction, generation of distortion and residual stresses and crack formation [1][2][3][4][5][6][7][8][9][10].…”