CORROSION BEHAVIOUR OF TEMPERED 42CrMo4 STEEL

Low-alloy 42CrMo4 steel (AISI 4140) is a medium carbon steel, commonly used as a quenched and tempered steel. Because of its good mechanical properties, high tensile strength and toughness, 42CrMo4 is one of the widely used and investigated steels. In order to increase ductility even more, in addition to standard quenching and tempering, steel is often hardened by double quenching and tempering and austempering. The aim of this paper was to investigate the corrosion behaviour of 42CrMo4 steel after quenching and tempering, double quenching and tempering and austempering. For this purpose, microstructural characterization and electrochemical investigation after different hardening processes were performed. Microstructure of specimens was observed using optical microscopy and scanning electron microscopy. Open circuit potential and potentiodynamic polarization measurements of tempered specimens were carried out using computer-controlled potentiostat with three electrode set-up in 0.6 M NaCl naturally aerated solution. It was concluded that applied heat treatment processes increase the corrosion resistance of 42CrMo4 steel in comparison to normalized steel. In comparison to quenched and tempered steel, double quenching and tempering, as well as austempering, do not significantly change corrosion resistance of steel.

Study on methods to improve the impact toughness of steel 40XA

In this paper, methods of improving the toughness, eliminating the tempering embrittlement of steel 40XA (GOST 4543 -71) were used. The mechanical properties of this steel after conventional oil quenching followed by high temperature tempering with air cooling and with oil cooling after high temperature tempering were investigat- ed. Besides, a double quenching process consisting of a preliminary quenching from high temperature and a sec- ondary quenching with intermediate holding at sub-critical temperature was conducted. After this double quench- ing and high temperature tempering, the steel acquired mechanical properties (tensile strength, elongation and impact toughness) notably higher than the respective properties obtained by conventional heat treating. These research results can be applied to improve the mechanical properties of important details from this steel.

PENGARUH VARIASI PENDINGINAN SETELAH PROSES CARBURIZING TERHADAP KEKERASAN BAJA

Komponen mesin yang saling bersinggungan dalam pengoperasiannya secara terus menerus akan menyebabkan keausan. Komponen mesin seperti poros, crankshaft dan roda gigi selain memerlukan kekuatan dan keuletan yang tinggi juga memerlukan kekerasan yang tinggi. Untuk memperlambat keausan yang timbul di permukaan, dibutuhkan kekerasan permukaan yang tinggi. Proses karburasi (carburizing) adalah salah satu metode untuk meningkatkan kekerasan permukaan. Dalam penelitian ini baja dikarburasi, yaitu baja dipanaskan diatas suhu austenisasi dalam lingkungan karbon. Karburasi menggunakan arang tempurung kelapa dan Na2CO3 sebagai katalisnya dengan waktu penahanan 5 jam pada temperatur 950°C dan dilanjutkan dengan proses pendinginan. Pendinginan dilakukan dengan tiga variasi cara pendinginan, yaitu , direct quenching, single quenching, dan double quenching. Pengujian yang dilakukan adalah pengujian kekerasan mikro Vickers dan pengamatan struktur mikro. Hasil pengujian menunjukkan kekerasan pada raw material sebesar 374,1 HV. Pendinginan dengan metode single quenching setelah carburizing menunjukkan nilai kekerasan yang paling tinggi yaitu 860,7 HV, naik sebesar 130% dari raw material, kekerasan dengan metode single quenching 704,9 HVdan double quenching 514,4 HV. Walaupun nilai kenaikan kekerasan double quenching paling rendah dibanding direct dan single quenching, namun butiran-butiran yang dihasilkan oleh metode ini lebih halus karena proses berganda yang memungkinkan perbaikan struktur. Penggunaan jenis metode pendinginan dalam carburizing ini kita sesuaikan dengan sifat akhir material yang kita inginkan. Kata kunci : carburizing, direct quenching, single quenching, double quenching, kekerasan

A novel amplified double-quenching aptasensor for cocaine detection based on split aptamer and silica nanoparticles

Herein, a sensitive and rapid fluorescent aptasensor was developed for the detection of cocaine as an illicit drug, based on an amplification strategy involving the use of silica nanoparticles coated with streptavidin (SNPs), double quenching of FAM fluorophore and cocaine split aptamer.