Research And Application Of One New Style Hot Work Die Steel For Precision Forging Die To Valve

Nowadays, mould technology has been an important symbol that can measures the manufacturing of one country ability.In this paper, we studied one new style of hot work die steel (RJD steel) for precision forging to valve. The application of this new style of hot work die steel can increase the life of precision forging die to vale obviously. The performance indicators just as impact toughness, hardness and microstructure have been researched through SEM, EDS, TEM, etc.In the present study, the effects of the chemical composition and heat treatment on the mechanical properties of RJD steel were investigated. Optimized chemical composition, temper temperature and parameters were carried out to be ready for practice products. Optimized chemical compositions are as follows (wt. %): C: 0.35～0.45, Cr: 2.5～3.5, Mo: 1.9～2.2, Si: 0.1～0.3, V: 0.8～1.0, W: 3.5～4.5, Mn: 0.4～0.6, Nb: 0.1～0.2. Optimized heat treatment parameters are as follows: austenizing heating to 1120℃for 1 hour and oil quenching; tempering for 3 hour at 620℃and air cooling(2～3 times). The tempering microstructures of the new type hot work die steel are mainly the lath Martensite, followed the Bainite with a trace of remained Austenites. The impact toughness is 9～24 J/cm~2, and the hardness is 50～53(HRC).The experimental results indicate that the thermal stability of RJD steel is better than those of the steel of H13 steel and ASSAB8407 steel. Under the 620℃for 21 hours, the hardness of RJD steel is still larger than HRC40 (46), while the hardness of the steels of H13 and ASSAB8407 decreased to HRC32～35. The oxidation resistance of RJD steel is much better than those of H13 and ASSAB8407 steels. With the tempering at 620℃for 50 hours, the oxidation adding weight of the H13 and ASSAB8407 steels are much larger than RJD die steel, respectively. All the three steels were investigated under the same experimental condition.The new type hot work die steel (RJD steel), which has many superior aspect such as high life expectancy, can be applied to many kinds of die forging at hightemperature.