Laser processing of high chromium white iron

Mechanical properties, such as wear-resistance and hardness, of laser welded and cladded high chromium white iron were investigated. The study involves the laser welding, cladding, and laser surface melt treatment by 3-kW Nd:YAG continuous wave high power laser. The laser welding of 2-mm thick high chromium white iron samples was laser welded in two combinations: iron-to-iron and iron-to-steel. Strong metallurgical bonding was witnessed between not only the iron samples but also iron and steel samples by laser welding. Three types of powder materials were used to laser clad the samples: metal-ceramic (compositionally close to INCO-702), stellite-21, and stellite-1 in order to estimate mechanical property changes and process ability of high chromium white iron. Even though the microstructure of metal-ceramic coating shows worse than stellite powder coatings it has more hardness and wear resistant property which were comparable to base iron. Hardness of metal-ceramic coating was slightly lower than base iron, yet the wear resistance was increased twofold.

Effects of Primarily Solidified Dendrite and Thermal Treatments on the M23C6 Precipitation Behavior of High-Chromium White Iron

The precipitation behavior of M23C6 carbide during thermal treatment of high-Cr white iron with various fractions of primarily solidified dendrite was studied and reviewed. M23C6 precipitation in the primarily solidified dendrite occurred preferentially during conventional heat treatment, whereas it occurred scarcely in the eutectic austenite. The reaction between M7C3 and austenite caused the dissolution of M7C3 into austenite, followed by precipitation of M23C6 along the periphery of eutectic M7C3. Relatively low-temperature thermal treatment (modified heat treatment) led to precipitation of M23C6 particles in the eutectic austenite, which is presumed to be caused by solubility difference depending on temperature.

Evaluation of Hardness, Sliding Wear and Strength of a Hypoeutectic White Iron with 25%Cr after Heat Treatments

Hypoeutectic white cast irons with a high chrome content are commonly used in the industrial mining sector where there is a demand for both high resistance to adhesive wear and an acceptable toughness for the absorption of impacts and falls of diverse materials. Through the application of a design of experiment (DoE) technique, factors related to thermal treatment are analyzed with respect to resistance to sliding wear, maximum rupture stress and toughness. The results show that, in order to increase resistance to adhesive wear, it is convenient to use destabilization temperatures of 1050 °C and tempering of two hours at 400 °C. This foments a very hard martensite and a high proportion of highly alloyed retained austenite, which, with low tempering, achieves a precipitation of carbides from this austenite with hardly any loss of hardness of the martensite. In order to increase the energy which this material is capable of absorbing until breakage, furnace cooling set at 150 °C followed by tempering at 550 °C would be favorable. Slower cooling implies a greater quantity of conditioned retained austenite, so that, following this, it may be transformed into lower bainite with a high density of finely dispersed precipitated carbides. Furthermore, this tempering also allows the transformation of martensite into ferrite with finely dispersed carbides.

ANALISIS MATEMATIS PENGELASAN GREY CAST IRON MENGGUNAKAN PROSES GTAW DENGAN DAN TANPA PREHEAT

Pemberian pemanasan awal pada proses pengelasan memberikan efek pengurangan tegangan, distorsi, retakan dan kekerasan pada daerah Heat Affected Zone (HAZ) dengan memperlambat laju pendinginan. Distribusi temperatur saat pengelasan didekati dengan menggunakan persamaan analitik Rosenthal pada logam grey cast iron. Grey cast iron termasuk sulit untuk dilas dan memerlukan perlakuan khusus. Pada penelitian ini, perhitungan distribusi temperatur dan laju pendinginan dibandingkan dengan struktur mikro dan kekerasan untuk grey cast iron yang dilas dengan menggunakan Gas Tungsten Arc Welding (GTAW). Persamaan Rosenthal dengan solusi Bessel hanya cocok untuk distribusi temperatur pada daerah lelehan, sedangkan solusi quasi steady state dapat digunakan untuk prediksi distribusi temperatur arah lateral dan transversal pada logam lasan. Preheating pada suhu 315 berpengaruh pada lebar HAZ yang dihasilkan menurut persamaan eksponensial terhadap travel speed, memperlambat laju pendinginan dan menurunkan kekerasan karena berkurangnya carbon equivalent (CE). Struktur mikro HAZ pada grey cast iron yang diberi preheating menunjukkan dominasi martensit nikel dan eutektik ledeburit, sedangkan tanpa preheating menghasilkan struktur mikro didominasi oleh eutektik ledeburit dan besi karbida dalam white iron.