The Process Study On Heating Treatment Of 17CrNiMo6 Valve Block

The valve block is one of the important components in the marine diesel engine.For those problems in the manufacture procedures of valve blocks in some machinery manufacturing enterprise,such as the existence of carbide level out-of-tolerance,fluctuation of effective case depth and not enough high surface hardness,a serises of improved heating treatment processes of valve blocks were designed by adjusting relevant process prameters on the basis of the existing heating treatment processes.These new processes were implemented on these quipments like sealed box allcase furnace,low-pressure vacuum carburizing furnace and vacuum continuous production line,respectively.The metallographic structure and mechanical properties were analyzed and the better heating treatment processes were optimized to produce valve blocks of which using effect of batches was good.Their technicality and economics was analyzed.By analyzing and studying the experiment results,the conclusions were as follows:(1)In the sealed box allcase furnace,the main technological parameters of the better heating treatment process of 17 Cr Ni Mo6 heavy load valve blocks were: 920oC carburzing temperature,1.1% intensive carburization potential,0.95% diffusion potential,790 min carburzing time,quenching at 830oC and soaking 120 min and tempering at 170oC and soaking 300 min.In the sealed box allcase furnace,the main technological parameters of the better heating treatment process of 17 Cr Ni Mo6 light load valve blocks were: 920oC carburzing temperature,1.0% intensive carburization potential,0.9% diffusion potential,360 min carburzing time,quenching at 830oC and soaking 180 min and tempering at 170oC and soaking 300 min.The metallographic structure and its level,surface hardness,hardness gradient and effective case depth of heavy and light load valve blocks treated by these processes both meeted the complex technicial requirements.(2)The main parameters of the better heating treatment process of light load treated in the low-pressure vacuum carburizing furnace were: 920oC carburzing temperature,7pulses,400~430L/h C2H2 flow rate,840oC quenching temperature after precooling and soaking 33 min,-80 oC and 120 min deep-cooling and tempering at 180oC and soaking180 min.The metallographic structure and its level,surface hardness(62~63HRC),core hardness(421HV),hardness gradient and effective case depth of light load valve blocks treated by this process meeted the complex technicial requirements.(3)The main parameters of the better heating treatment process of light load treated by the vacuum continuous production line were: 920oC carburzing temperature,8 pulses,2200/h C2H2 flow rate,845oC quenching temperature after precooling and soaking 120 min,-140 oC and 120 min deep-cooling and tempering at 170oC and soaking 300 min.The metallographic structure and its level,surface hardness(60.5~63HRC),core hardness(431HV),hardness gradient and effective case depth of light load valve blocks treated by this process meeted the complex technicial requirements.(4)The technicality and economics of 17 Cr Ni Mo6 heavy and light load valve blocks,which were treated repectively by sealed box allcase furnace and low-pressure vacuum carburizing furnace with better heating treatment processes,was analyzed.This showed that the two were better among those heating treatment processes of heavy and light load valve blocks.After the two processes being put into production,the qualified rate of these valve blocks increased by 3% and their durability increased by 5%.By calculating,heavy and light load valve blocks treated by the two processes could comprehensively save cost about 0.36 million and 0.26 million,respectively.The volume production and consumers' application examination showed that the valve blocks run overall in good condition with stable properties.