Comparison of the microstructures and abrasive wear properties of stellite hardfacing alloys deposited by arc welding an

  • PDF / 7,001,957 Bytes
  • 18 Pages / 590.28 x 785 pts Page_size
  • 81 Downloads / 183 Views

DOWNLOAD

REPORT


L

INTRODUCTION

C O B A L T - b a s e d hardfacing alloys are u s e d in appliea, tions requiring g o o d wear; oxidation~ and corrosion properties during s e r v i c e at elevated temperat~es.t~'el In their commercially available f0rms~ they most commordy derive their:hardness from the presence of a high volume t?action ( = 0 , 2 to 073) of carbides and are referred to as Stetlites. The cobalt-based hardfacing alloys are t h e most popular within the Stellite range; typically, they h a v e t h e composition C0-28Cr~r IC w t p e t a n d can b e deposited by processes such as arc welding; laser cladding, etc. The first phase to form during cooting from the liqu i d stare'consists o f unfaceted cobalt-rich dendrites' w i t h a face.centered cubic (fcc) cwstal structure. T h e remaining liquid eventually soIidifies b y a eutectic react i o n i n t o ~ irrterdendritic; intimate l a m e l l ~ mixture o f the fcc phase and (Cr;Co;W)TC3 eute~ic~ carbides:~ T h e carbide i s cfiromium,rich with a typical composition (Cr0.85Co&~14~/0:0a)TC3~ depending o n alloy composition and? cooling conditions; henceforth, i t i s referred to. as: M7C3 carbide. Thepresent!work:is p a r t o f a p ~ g r a m o f research :into the: relationship between alloy chemistry, microstrue. ~ ture; a n d abrasive: wear properties:: o f hardfacing materials,[3'4} T h e s~cific p u r p o ~ o f ~ s work was to examine S . ATP/MERT, Research Student; a ~ H i K ; O . H BHADESHIA~ University Lect,a~er; are with the Department of M'ateriats Science a n d Metallurgy, University of;Cambridge; Pembroke Street, Cambridge: CB2 3QZ, United. Kingdom. Manuscript submitted;May 25; I988i METALLURGICALTRANSACTIONS A

any differences i n microstructure a n d abrasive wear properties between cobalt-based hardfacing alloys deposited b y three different techniques: manual metal arc welding; tungsten inertgas welding; and laser ctad~ng. T h e relationship, between m ~ o s t r u c t u r e a n d w e a r properties c a n b e confusing and is not well-estabiish~; indeed~ w e a r n o t j u s t a property o f t h e hardfacing alloy b u t also o f the type o f abrasive involved a n d o f the specific w e a r process: (impact, corrosion-erosion, etc.)t,s-s~ T~herefore; ,it is emphasized at the outset that the microstructure is just a p a r t o f the w e a r problem. On t h e other band, i t i s well;establishedithat microstructure isan:important c o m p o n e n t in determining the properties o f hardfacing alloys, a n d since at:least: a working hypothe. s i s i s necessary in any alloy design proceduxe, we b e g i n w i t h a brief assessment o f the:problem for cobalt~based alloys:

The Microstructure/Wear Relationship f o r Stellites In a microstructureconsisting o f a mixture o f a b i d e s in a s o f t matrix, it i s approximately the ease that the.hard~ carbide: particles p r o v i d e the: resistance t o abrasion, whereas t h e t o u g h matrix, serves t h e role o f binding the relatively brittle carbides~ B o t h the matrix a n d carbide phases have t o contain sufficie