Comparison Study of SKH51 Steel and 65Mn Steel Application in Al Alloy Die-casting Die Core
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The thermal fatigue and high temperature oxidation resistance of SKH51 steel and 65Mn steel were studied by circularly heating and cooling the samples in the aluminum die-casting die working temperature range(20～700 ℃).The results show that the microstructure of SKH51 has no significant change,an obvious oxidation layer is formed on the surface of 65Mn sample.SKH51 steel with high contents of chromium and tunstgen has better oxidation resistance at elevated temperature than that of 65Mn.The high temperature oxidation relative quality loss of 65Mn is hundreds times larger than that of SKH51.There are no thermal fatigue cracks on the surface of SKH51 and 65Mn samples with small diameter and simple configuration.SKH51 steel can be used for making the die-casting die core,but 65Mn steel can not be used.Keywords:
Die casting
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A new type of low carbon and no aluminum nitrided steel was investigated by multi-element alloying. The depth-hardness curve, matrix microstructure, microstructure and hardness of nitrided layer, as well as the effects of heat treatment on mechanical properties were studied. The results show that the steel has high hardenability. Also the tempering stability of the steel is good. After quenched at 920 ℃-930 ℃ for 30 min, subsequently oil cooling, and tempered at 600 ℃ for120 min, the steel has obtained tempered sorbite which makes the steel optimum core combination of strength and toughness and ductile external niritding layer. Furthermore, the stable and dispersed nitrides make the surface hardness of the new nitrided steel exceed 860HV5.
Hardenability
Tempering
High Speed Steel
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The composite die steel was prepared by vacuum diffusion welding with the cold work die steel Cr12MoV and the alloy steel 40Cr. The composition, microstructure and property changes of the welded joints were studied experimentally, and the relationship between the microstructure and the property after the final heat treatment was analyzed. Based on the experiment results, the suitable welding and heat treatment process were approached. The results show that the good metallurgical bonding is obtained via welding at 1100oC for 30 minutes with a pressure of 20 MP and not more than 0.01 Pa in vacuum. A number of voids are found in the tensile fracture surfaces when the welding temperature is below 1100oC. The grains of 40Cr steel grow obviously when the welding temperature is higher than 1100oC. After quenching at 1050oC and tempering at 200oC, the better mechanical properties are obtained in Cr12MoV because fine carbides distribute evenly. At the same time, the mechanical properties of 40Cr do not decrease dramatically because even though high temperature quenching brings coarse grain size, the amount of lamellar martensite, which is hard and brittle, decreases a lot and the amount of lath matensite increases. After quenching and tempering treatment, the bending strength of the composite die steel reaches 73% of that of Cr12MoV when treated by conventional processing. In the course of welding, carbon migrates from 40Cr to Cr12MoV, which results in a decrease in hardness at the interface of 40Cr.
Tempering
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The technological process of die steel H13 was inguired by low temperature salt-bath vanadium-nitrocarburizing,and microstructures,hardness,element distribution and phases of the infiltration of samples were investigated.The result shows that the microhardness is improved,and the phases of infiltration is benefit for improving the thermal fatigue properties and wear resistance.The life of dies which is made of steel H13 treated by the technics is improved obsviously.
Hot work
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The mechanical properties and corrosion resistance of nickle-saving nonmagnetic Cr18Ni6Mn3N stainless steel were studied after hot rolling and solution heat treatment.The microstructural evolution after solution heat treatment and aging treatment,the variation trend of deformation induced by martensite during cold working,and the magnetic property of the stainless steel were analyzed.The results indicate that single austenitic phase appears in the stainless steel at room temperature after solution heat treatment.Compared with SUS304 stainless steel,the mechanical properties and corrosion resistance of the stainless steel are better.Granular nitrides precipitate along grain boundaries after a 4h holding time at 800 ℃;however,when the holding time prolongs,lamellar precipitates begin to emboss along grain boundaries and then grow into grains.After a 20h holding time,the diameter of the embossed lamellar precipitates reaches to 20 μm.Deformation-induced martensite does not appear at a reduction rate of 18.3%,and with increasing deformation the amount of martensite gradually increases.Although the relative magnetic conductivity rises,it is less than that of SUS304 stainless steel under the same condition.After solution heat treatment the relative magnetic conductivity of the cold rolled plate drops to 1.002,and thus the stainless steel can be a low-cost candidate in the nonmagnetic stainless steel field.
Austenitic stainless steel
Martensitic stainless steel
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In order to improve the properties of the wet rod and ball mill liners suffering the abrasive wear from the impacting mill materials in ferrous and nonferrous metal mines,and its service life under the condition of acid and alkaline corrosion from wet limestone raw material millstones in cement factory,a new wear-resistant alloy steel ZG25Cr7 with low carbon medium chromium has been studied.The microstructure of the wear-resistant material consists of both fine tempered lath martensite and a little retained austenite,and its impact toughness and hardness is 173.6 J/cm2 and HRC 53.5,respectively,after oil-quenched by 960 ℃ and tempered at 240 ℃.The static corrosion test shows that in the weak acid of pH 4.5,high manganese steel ZGMn13Cr2 has average corrosion rate of 15.61 times higher than that of this new alloy steel ZG25Cr7,while Si-Mn steel has average corrosion rate of 2.24 times higher than that of this new alloy steel ZG25Cr7.The results demonstrated that the alloy steel has excellent weak acid-resistant property.Besides;in the strong alkaline of pH 10.5,the test result shows that above three kinds of steels have less corrosion rates;the average corrosion rate of Si-Mn steel is 1.96 times higher than that of this steel,and high manganese steel is 1.19 times higher than that of this steel.So this steel is a good corrosion-resistant,abrasion-resistant and impact-resistant material.
Alloy steel
Carbon steel
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A kind of high strength and wear-resistant high B steel castings has been obtained by increasing the B concentration in the carbon steel.The effect of quenching temperature on the microstructure and hardness of high B steel casting liner has been investigated,resulting in that the hardness of high B cast steel increased with the quenching temperature increase. When the quenching temperature reached 1000℃,the matrix of high B cast steel all transformed into lath martensite which has high strength and toughness. After quenching at 1000℃ and tempered at 230～240℃,high B cast steel liner has excellent strength,toughness and wear resistance. High B cast steel liner did not break in use with service life 180%～200% longer than that of high Mn steel liner. Moreover, no valuable alloy elements in high B cast steel liner needed hence low production cost and brief technology.
Lath
High carbon
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The influence of the heat treatment on microstructure and properties of the high carbon low alloy steel commonly used at home and abroad was studied,and the mechanism was discussed.The experiment results show that this steel has good hardenability.After air-blast quenching at 870 ℃ for 2 h and tempering at 550 ℃ for 2 h,the microstructure of the steel is consisted of tempered martensite,troostite and carbides,and the hardness of steel was HB 477,the impact toughness was 73 J/cm2.This steel is especially suitable for work conditions subjected to heavy impact abrasion because of its good comprehensive mechanical properties.
Hardenability
Tempering
Abrasion (mechanical)
Alloy steel
Carbon steel
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Thermal-stability of 4Cr3SiWMoVNb steel and 4Cr5SiWMoVNb steel with different content of Cr was investigated by means of OM,SEM,TEM and calculation using ThermoCalc software and TCFE3 database.The results show that the optimum quenching temperature of 4Cr3SiWMoVNb steel and 4Cr5SiWMoVNb steel is 1000 ℃ and 1030 ℃.When the tempering temperature is higher than 600 ℃,4Cr3SiWMoVNb steel shows better tempering resistance.The hardness of 4Cr3SiWMoVNb steel and 4Cr5SiWMoVNb steel both decreases during long time aging at the tempering temperature.But there is more Cr 23 C 6 carbides in the 4Cr5SiWMoVNb steel,which tend to grow and coarsen during tempering,and the recrystallization of the steel occurs more quickly.That is the reason that the hardness of 4Cr5SiWMoVNb steel decreases more quickly than that of 4Cr3SiWMoVNb steel during tempering.And the 4Cr3SiWMoVNb steel has better thermal-stability.
Tempering
Recrystallization (geology)
Thermal Stability
Hot work
High Speed Steel
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In order to explore the methods of improving the toughness of high silicon cast steel,with the help of corresponding equipment,the microstructure and mechanical properties of high silicon cast steel under different austempering temperatures and times were studied.The result shows that high silicon cast steel,isothermal quenched in the range of 280 ～ 360 ℃,can get good comprehensive in strength,toughness and hardness with excellent dual phase structure.With the ADI temperature increasing,carbon content of retained austenite and the quantity of retained austenite firstly were increasing and then decreased,as quenched at 360 ℃ the both maximum value appeared.When Austenitizing was 900 ℃×120 min and the isothermal quench was 320 ℃×120 min,the better mechanical properties could be obtained.It provided the theoretical reference for high silicon cast steel as an alternative to the materials such as wear-resistant low alloy steel and high Mn steel and high chrome cast iron.
Austempering
Isothermal process
Alloy steel
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The heat treatment process of a new type of copper alloy die casting die steel was discussed.The effects of quenching temperature,tempering temperature and time on microstructure and mechanical properties of steel were studied.The results show that with quenching temperature increasing,the size of grain growes up,when quenching temperature is higher than 1100 ℃,the grain becomes bulky.At the quenching temperature of 1100 ℃,the hardness of steel is 63 HRC,and the room temperature tensile strength of steel is 1897 MPa.At 600 ℃,high temperature tensile strength is 1117 MPa.The best heat treatment process is:quenching at 1100 ℃ and then tempering at 500 ℃ for 5 h.
Tempering
Heat treating
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