Pearlitic Malleable Cast Iron Heat Treatment Process

This paper is on study of heat treatment of pearlitic malleable iron required by Yunnan Foundry Steel. The aim of this paper is to make pearlitic malleable iron to meet Clause M7002 of USA Malleable Iron Standard A602 for Automobile, namely, strength is no less than 621Mpa, tensile ductility is no less than 2% and hardness is between HB229 ~ 269.The final heat treatment is liquid quenching and tempering.This paper is mainly to study this material on the following aspects.1. Heat treatment test of Manganese pearlitic malleable iron.The ferrite malleable iron with suitable Mn is melted .Heat treatment of this material is annealing and oil quenching and high temperature tempering. By this way, it is acquired that pearlite and group graphite/Mechanic of this material can meet requirement of M7002.2. Test of quenching mediumCooling curve method used and according to requirement of JB/T7951-2004,cooling property of this material is tested with virtual instruments by pure water,N32 engine oil,saturated calcium chloride solution, trinitro-water solution, polyvinyl alcohol solution and water glass solution. Through judgment and appraisal of cooling curve, theory basis is provided for diverse choice of quenching medium of pearlitic malleable iron.3. Process test of heat treatment for normal ferrite malleable iron to produce pearlitic ironWithout any alloy, ferrite malleable iron can acquire pearlitic structure and well mechanic properties by quenching and faster quenching medium.Based on relationship among chemical composition, heat treatment, structure and mechanical properties, This paper is mainly to discuss the effect of quenching temperature, tempering temperature and tempering time, Mn percentage and cooling rate of quenching medium on structure and mechanic properties, which sets up the best process of quenching and tempering in the second heat treatment, draws up the conclusion that Mn can increase strength of malleable iron and saturated calcium chloride solution and 50%~65% silicate solution can be applied to pearliticmalleable iron and gets recursive equation of concentration- max cooling rate, concentration-cooing rate at 300℃ for the saturated calcium chloride solution and silicate solution and hardness-strength and hardness-ductility for N32 engine oil saturated calcium chloride solution,50% silicate solution. The line recursive relationship is close and the result is quite ideal.Yunnan Foundry Steel used the heat treatment technology in this paper to prototype axle of automobile and its structure and mechanical properties can meet the requirement of M7002. Now samples of this product is sent to USA for customer's confirmation.