Process Prototyping for Production Scale Sinter(Bainite)Hardening of PM Parts by Gas Quenching
The microstructure of sintered PM parts is generally ferrite and pearlite and the pearlite content is in proportion to the carbon content.This can be changed to martensite by the hardening process done by heating the parts & rapid cooling either in oil or under pressurized & recirculated gas.PM parts can also hardened by sinter hardening in a wire mesh belt sintering furnace within a module placed immediately after the furnace.The furnace atmosphere is re-circulated across heat exchangers & directed on parts as they emerge from the sintering furnace.Generally high alloy compositions(which harden easily)are required to obtain a predominantly martensitic structure as the cooling capability of recirculated gas is lower than oil or pressurized gas.Several machined or stamped(not PM)spring steel parts as well as cast ductile iron parts are hardened in a manner so a bainitic structure is formed instead of a martensitic structure(for improved fatigue properties).This is done by austenitising the parts & quenching them to 280℃ to 400℃ & holding them till complete transformation to bainite is achieved.This process is called Bainite Hardening or Austempering.Other researchers 1,2 have described methods of obtaining a bainitic microstructure in PM parts by suitable alloying & cooling rate control and have reported the resulting properties obtained.However,there are very few references on the results of conventional austempering performed by isothermal holding at the required temperature.It was decided to build an(open to public)process prototyping furnace to perform sintering followed by rapid cooling to the required lower temperature & iso-thermal holding between 250℃ to 500℃.The purpose was to study the response of different PM alloys and part geometries.As a first trial gears made in Astaloy CRM+0.5%C & Astaloy Mo+0.6%C were processed and the results are reported in this paper.
Bainite Hardening Gas quenching Sinter hardening PM Austempering
Gopinath N. Raghunathan V.
Fluidtherm Technology,India
国际会议
北京
英文
553-556
2018-09-16（万方平台首次上网日期，不代表论文的发表时间）