DJM Technical Introduction

    A study of ZG40Cr3NiMo high strength martensitic steel

    A study of ZG40Cr3NiMo high strength martensitic steel
    At the same time to undertake the first American CSP company of mine pulverizer hammer, the material chemical composition. The requirements of mechanical properties. Above, microstructure of tempered martensite. The author study reference counterparts, under production conditions with high strength casting martensite steel castings the user design requirements. In the 5506 factory, vigorously assist the Shenyang Research Institute of Foundry electron probe chamber and the relevant departments of experts, from prototype to mass production in the whole process, and constantly improve the process, strictly control the process quality, smoothly through the chemical composition, mechanical properties, penetrant testing, anatomy (with due to magnetic particle and X-ray flaw detector, the user agrees to regularly check the anatomy of casting factory testing), metallographic microstructure analysis since he order pattern documentation requirements of chemical products inspection, quality of CSP company in the United States after receiving re recognition. The production of Z G40Cr3NiMo casting process quality control production - introduction.
    1 process quality control
    1.1 smelting process in order to effectively in the steel dephosphorization and desulfurization determined in 250kg alkaline medium frequency induction furnace for melting, the oxidizing smelting. Due to the absence of oxidation period, easy to remove the gas in the liquid steel and slag inclusion, especially intermediate frequency electric furnace dephosphorization is difficult, and therefore must be in order to restore seriously deoxidation, dephosphorization, desulphurization. Specific approach is: early slagging, low temperature dephosphorization slagging many, thorough cleaning slag. In operation process on the master slagging time, the relationship between temperature and the amount of slag. The melting process are as follows:
    A. the good selection of steel scrap, scrap and ferromolybdenum and smelting furnace, medium added nickel chromium 1Cr18Ni9 Stainless steel scrap and scrap replacement, addition of small pieces, add chunks.
    B. in the smelting of the edge of the feeding side of the material to prevent bypass, in order to facilitate the rapid melting.
    C. until melted charge 80% added slag covering of liquid steel, slag amount to 0.8% of the burden, actual slag ratio for lime pieces: Fluorite particles = 1:1 (i.e. until the burden of clear, stripped off all slag.
    D. sampling and testing of liquid steel composition.
    E. added 0.3% of the burden of ferromanganese. Precipitation deoxidation and subsequently joined the second residue (ratio ibid.), and reduced 50% power continued 5~7min. then charge just cleaning, slag and molten steel temperature is low, into the furnace and ferromanganese phosphorus under low temperature easily dephosphorization reaction. Observe the slag surface boiling, continuous foaming, with a rod of iron stained with liquid slag slag thickness in mm, color is light white that about 4CaP2O5 dephosphorization reaction of calcium phosphate content was low, slag basicity is higher, be helpful for dephosphorization and dephosphorization reaction continued 15min, and then stripped off all slag.
    According to the analysis results of F. adjustment of liquid steel composition, wherein the silicon content adjustment before tapping within 5~7min.
    G. temperature measurement and make a round cup of samples, observation of the oxygen, such as the sample shrinkage is good, explain the basic improvement of oxygen.
    H. joined third slag (ratio ibid.), adding 0.2% silicocalcium or ferrosilicon further deoxidation, and adding 0.05% of rare earth alloy to strengthen deoxidization, to slag, purifying molten steel and slag.
    I. added 0.1% aluminum scraps final deoxidation and prepare tapping. Complete deslagging and each slag after in liquid steel and slag liquid sprinkle - layer slag collecting agent, Eli in slag and cover the liquid steel to prevent oxidation inspiratory.
    1.2 the selection of chemical composition of this kind of steels is carbon and chromium content are also high in alloy steel, the chromium content is not in accordance with the distribution ratio of 2: 1 Ni Cr Ni Cr but the relationship between the ratio of 1 to 3, the chromium content of up to 3%, which brings new problems to the casting process. The chromium content increased too large, will make the steel eutectoid point left, critical quenching temperature of steel decreases in the mould cooling when self quenching, the formation of coarse martensite and carbides. The coarse grains, the casting stress increases, increase the cracking tendency of casting. Chromium is strong carbide forming elements the chromium content, improve, can strengthen the ferrite, reduce the critical cooling rate, improve the stability of supercooled austenite, martensite to steel, improve the steel hardness, strength and wear resistance. The chromium content should be suitable for many times between 2.6%~3.1%. In alloy steels 0.4-0.6%. steel in 0.8%~1.0%. martensite formation with low hardness higher than 0.43% less than 0.37% of 0.37%~0.43% hardness with carbon content increased and improved. Considering the steel the comprehensive mechanics performance and the production practice verification, including the amount of carbon in range is more appropriate. Carbon hardness to meet the requirements, the carbon does not improve much plasticity and toughness decrease. Nickel expanded austenite range and improve steel hardenability, increase the strength and hardness, prompting generated in the steel, nickel content can be selected in the addition of molybdenum elements, significantly improve hardenability, reducing the tempering brittleness, grain refinement, reduce stress, prevent crack, increase the impact toughness, molybdenum content
    1.3 molding hammer weight 64kg, the pattern specification hammer top A HRC50, B HRC37~42, the casting process is shown in Figure 1 is shown in Figure 1. Hammer casting process drawing according to actual conditions, using semi dry type clay sand process, sand ratio is: new 50%+ old 50%+ silica silica sand bentonite 8%+ refractory clay water 5%+ 5%. core sand for the carbon dioxide and water glass sand, silica sand ratio: the new 100%+ 2%+ bentonite water glass 7%+ sodium hydroxide 0.5%. core blowing carbon dioxide after drying, brushing the surface of zircon powder coating and drying. The diluted water glass shaped cavity surface spray layer, then hardening layer 5min and uniform drying burner. Coated zircon powder coating, continue to use the torch bake to dry layer 15~20mm, and then the cavity surface polished with emery cloth. Gating ring are using dry type. Before pouring the assembled at the baking circle to 200 DEG C immediately when pouring, pouring and sprinkle to take heavy Content is 2%, thermal insulating agent, take the feeding effect is very good. To prevent the cracks cutting risk should be carried out in the casting of glowing red (400 to 500 DEG C), cutting with hot sand cover and run and Taiwan height should be 5-8 mm to stay around, after quenching and tempering planing.
    1.4 heat treatment due to addition of various alloy elements, the critical point of the steel reduced. Select 860 Deg. C water quenching a period of 2 min and immediately transferred to the stage of oil quenching oil groove of quenching process and in 220 DEG C low-temperature tempering (air cooling) processing, adapted to the hammer head top and tail of different hardness gradient distribution is reasonable, but also maintains the castings with high strength and toughness. The test. Microstructure of acicular martensite, as shown in Figure 2.
    2 conclusions.
    For the chemical composition of the alloy high strength martensitic wear resistant steel. Steel heat treatment specification for 850~860 DEG C water quenching 2min after oil quenching +220 low temperature tempering (air cooling) heat treatment. Steel Metallurgical Group. Steel after quenching and tempering microstructure fabric for the tempered martensite.
    The mechanical properties. The steel for manufacturing at low stress, impact conditions easy wear parts, - times higher comprehensive mechanical properties of high manganese steel, instead of high manganese steel is to expand the application value of new wear-resistant material

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