Study On Heat Treatment Process And Microstructure And Properties Of H13 Steel Smelted By New Smelting Process

H13 steel,domestically named 4Cr5MoSiV1,is one of the most widely applied hot work die steels in the world.It has excellent hardenability,thermal strength,red hardness,high toughness and good thermal fatigue resistance,and is widely applied in die casting molds,extrusion molds and hot forging molds.At present,there are great differences between domestic H13 steel and foreign high-quality steel.Its mechanical properties can't meet the requirements of high-performance special materials,and the purity,uniformity,grain size and other important indicators of the material can't reach the international advanced level.This paper takes the hot work die steel of H13(H13A,H13 R,JB11U,JB13U)produced by a domestic company as the test material,the microstructure,grain size and mechanical properties of different H13 die steels in annealed and tempered states were studied by direct reading spectrometer,metallographic microscope,scanning electron microscope,impact testing machine and other equipment,and compared with foreign H13 steel.The thermal fatigue properties of domestic H13 steel produced by the new smelting process and its microstructure changes during thermal fatigue are mainly studied.The research results are as follows:1.The contents of major alloying elements in the four kinds of test steels are well controlled.the contents of sulfur is lower than 10 ppm and the contents of phosphorus are lower than 130 ppm,which have reached the highest level in NADCA#207-97 standard of North American Die Casting Association.Sulfide inclusions were not found in 4 kinds of test steels under optical microscope and scanning electron microscope,and alumina inclusions were found,which were less than 5?m in size.H13 A steel show the best purity,less inclusions and small inclusion.2.There are band segregation and uneven distribution of alloy elements in annealed,quenched and tempered H13 A,H13R and JB13 U steels.The banded segregation of H13 A steel is the most obvious,which seriously affects the isotropy of steel properties,and its lateral impact strength is the lowest;H13A steel has the finest austenite grains,fine carbides,the highest hardness(48.7HRC),and the highest longitudinal impact energy(47.4J).The annealed microstructure,quenched microstructure and tempered microstructure of JB11 U steel have good uniformity,and there is no obvious band segregation.The ratio of impact energy value of JB11 U steel in longitudinal and transverse directions reaches 0.99.JB11 U steel has good isotropy of steel properties.The austenite grains of H13 R steel and JB13 U steel are relatively bigger,and there are primary insoluble eutectic carbide in annealed,quenched and tempered microstructure,and their mechanical properties such as impact strength are between H13 A and JB11 U steel.3.H13 A steel,H13 R steel,JB11 U steel and JB13 U steel all have secondary hardening phenomenon.The temperature range of their secondary hardening peak is 480~530?,and the secondary hardening phenomenon of H13 A steel is the most obvious.The temperature of the secondary hardening peak of JB11 U steel is about 490?,and the hardness decreases quickly when the tempering temperature is higher than the temperature of the secondary hardening peak.The peak hardening temperature of H13 A steel is about 520?,and the hardness decreases slowly when the tempering temperature is higher than the temperature of the secondary hardening peak.H13 A steel has the best thermal stability,its hardness always keeps the highest and its decline speed is slow at 620?tempering.After 30 hours of heat preservation,the hardness of H13 A steel is 36.5HRC,which is higher than that of imported H13 steel(34.3HRC).H13 A steel has excellent thermal stability.4.The thermal fatigue tests of 4 kinds of test steels were carried out by a self-developed full-automatic thermal fatigue tester.The upper limit temperature of the thermal fatigue test is 700?,and the lower limit temperature is room temperature.After 3000 cycles of cooling and heating,the H13 A test steel has fine thermal fatigue cracks and its thermal fatigue performance is the best.The thermal fatigue crack of JB11 U test steel is coarse,and the main cracks are distributed in parallel trend,and the crack depth is the deepest,exceeding 25.5?m,and its thermal fatigue performance is the worst.The purity of the test steel produced under the new smelting process is higher,and the grain size is greater than 8.5 grade.H13 A steel has the highest hardness(48.7HRC)and has the highest longitudinal impact energy(47.4J)after tempering at 610?.The secondary hardening phenomenon of quenched H13 A steel is the most obvious,and the secondary hardening peak temperature is about 510?;H13A steel has the best thermal stability and thermal fatigue properties.The comprehensive properties of H13 steel are the best.