JOURNAL OF SCIENCE & TECHNOLOGY * No 94 - 2013 THE FORMATION AND INFLUENCE OF INTERMEDIATE LAYER ON MICROSTRUCTURE AND MICROHARDNESS OF NITRIDING LAYERS ON S K D l l MOULD STEEL A N H HUdNG C U A V I E C T A O L P T R U N G G I A N D E N T O C H U C V A T I N H C H A T CUA L6V T H A M N I T O T R E N T H E P S K D I Phung Thi To Hang', Nguyen Van Due', Le Minh Ngoc', Le Thanh Binh^ 'Hanoi University of Science and Technology Institute of Energy and Mining Mechanical Engineering Received March 01, 2013; accepted April 24, 2013 ABSTRACT Nitriding is a process that brings to the sudace of the steel pads, especially tool steel ones, valuable properties such as: high hardness (up to 70HRC), excellent resistance to wear, corrosi fatigue, thereby improving their service life The nitnding process is earned out nomally at the temperature range, therefore to achieve nitriding layers with the thickness of hundreds of micron nitriding time needs to be very long resulting in high cost Accelerating of the nitriding process is aim of many research worif to shorien the process while still maintains the quality of the nitriding on the tool steel This paper studies the influence of the presence of intermediate layer on the micmstructure and properties of the nitriding layer Then, appropriate pre-treatment method for S tool steel will be investigated Keyword: Nitriding, phosphate, intermediate layer, nitriding layer TOM TAT Thim nl ta la cdng nghe mang din cho bi mat ciJa cic chi tiit thip dac biit li thip dpng cu nhirng tinh chit qui gii: dd cCrng cao (t&i 70HRC), kha ning chong mai mdn, chdng an mdn va c mdi cao ding ki, nha dd ning cao tudi thp cua cic chi tiit Tuy nhien, cdng nghe thwc hiin & v nhiit dd thip, mudn d^t dwac chiiu day l&p thim din hing tram micron, th&i gian thim rit dai, gi thinh cua sin phim vi viy si cao V&i muc ttiu tang tdc qui trinh thim nhwng vin giw dwpc chit lupng l&p thim nita tren thip dung cp SKD11, viec tao lap trung gian dupc nghien ci^u Bii bio cap din nghien cwu inh hw&ng cua cic l&p trung gian niy din td chijc ti vi vi tinh chit ctia l&p th ni ta TO- dd Iwa chpn phwang phap tiin xw /j^ thich hap cho thep dung cu SKD11 INTRODUCTION , , , ^ Nitndtng ,s the surface process perfomted on the surface of steel parts to mcrease the.r servtee hfe due to h'gh hardness of the nitridmg ayer (up to 65-75 HRC), , n ^ , • • J therefore increase their wear, corrosion and i J ,, ratigue resistance A harden-able steels must , , , c I • be hardened and tempering before being ^., , _ • , nitrided The tempering temperature must be , , , , , , •,._ nigh enough istousually keep structural the temperature at least 30stability C higheratthan •f ^ ^ , mtriding temperature, thetemperature minimum tempering the maximum nitriding which is „ , c TAO^ 11^ , ^,A^^ ^rr.^^\ II , u-1 I.n ,.1 * norma tpmnpratiirp y bwro(480-650 iiciiallv atC)(inct for ^(1 all f steels nioner Due than to ^, , ã' *ã L j-ô- ã f ã the low temperafture, the diffusion of atomic _ ,^ , , L r ^ f find mfroeen n the steel IS sow, therefore to form a "° , , , v: ' ,„ nitriding thick ayer (about 150 microns) the nitriding time required is very long Ammonia (NHi) is usually used in gas nitriding At a ^^.,^|^|^ temperature, the ammonia is decomposed according the following reaction to ^ ^ ^ ^,^_^.^ ^ ^^^ ^^^^ ^ j + _,, ,, ' ^ f ^ „ „,, 3H2, A small amount of the formed nitrogenous • j L J *I, ^„„„ „f ,„oi „r,^ atoms IS adsorbed on the surtace or steel and , • j- _ „;^,.;^:„„ I.„,„P then diffuses mto steel to form nitriding layers »,