Study On The Compound Strengthening Technique Of CrWMn Steel Cold Extruding Die

The paper analyzes the working conditions of cold extruding die, investigation and analysis of failure performance,the corresponding performance requirements are put forward;four carbide spheroidization processes of CrWMn steel are researched,organization and performance of the two kinds of low temperature,short-hold time and fast heating quenching processes are analysised; at the same time the electro-spark surface strengthening process parameters are studied,carbide ball mechanism and the strengthening and toughening mechanism of steel are further analysised.According to analysis and discussion of test results, received the following conclusions:(1) The four effect of CrWMn steel carbide ball of conventional ball annealing, recycling ball annealing,troostite treatment(980℃oil cooling+conventional ball annealing) and 1000℃solution+700℃tempering for 2h(high-temperature solution +high temperature tempering) is researched,globular pearlite tissue can be got.The tissue signature of 1000℃solution+700℃tempering for 2h is the granular carbide on ferrite matrix basically reached small,round,equality,evenly diffuse distribution,large and cusp carbide is not exist.The others three types of carbide spheroidization process of the organization many large and cusp carbide is exist, even there are traces of net carbide.Therefore,the effect of carbide ball from good to poor:high-temperature solution+high-temperature tempering,troostite treatment, recycling the ball annealing and conventional ball annealing. (2) CrWMn steel is treated at 1000℃solution+700℃tempering for 2h,quenching heat temperature is 770℃,800℃,two temperature holding time is 1 min, 5min,10 min and 15 min,the metallographic structure after oil cooling is martensite+the carbide is small,round,equality,evenly diffuse distribution+less retained austenite.Among them,the largest number of lath martensite is exist at 770℃for 5 min oil cooling.The metallographic structure after 200℃tempering 2h isβ-martensite+small,round,equality,evenly diffuse distribution,and HRC is 62. This organization has a high hardness,strength and better strength and toughness.(3) The discharge capacity is 160μF,the hardening surface area of sample is 1.8cm~2,the best hardening period is 4min,forming a successive,well-distributed layer with a certain depth.If the hardening period is too short,the layer will be too thin and has less effect;on the other hand,if the hardening period is too long,the layer will break and come off,the hardening productiveness will decreases.(4) The optimum technology of electrical discharge surface hardening is that: to meet the requirement of a certain layer depth and improve the hardening productiveness,a lager electrical Parameter should be adopted first,and then a smaller electric parameter is selected to improve the layer's smoothing and compactness.(5) WC-Co cemented carbide electrode material is used,the discharge capacity is 160μF,the average hardness of white-bright layer,transition region and matrix are 1280HV,650HV and 734HV,respectively,transition region hardness slightly lower than the matrix due to martensite heat affected by tempering again. The strength ratio time is 2min/cm~2,when the capacity is 160μF,the surface of strengthening coating is glabrous and compact,thickness is 58.4μm.(6) Using the different capacity to make electro-spark strengthening,such as 20μF,40μF,80μF,160μF,220μF,all samples from 35～40μm surface hardness department increases first and then reduce when the capacity increase,the maximum value for the 1236 HV corresponding to 80μF capacity.(7) In the production of industry,the trial of CrWMn steel cold extruding die intensive processes are as follows:1000℃solution+700℃tempering+770℃for 5 min quenching+200℃tempering 2h+electrode materials for cemented carbide electro-spark strengthening.