Research On Heat Treatment Process And Microstructure And Properties Of Hot Work Die Steel

The mold is called the"mother of industry",and its material and process level have become the standard to measure the level of a country's manufacturing industry.With the increasing demand for high-performance die steel in manufacturing industries such as automobiles,home appliances,electronic equipment,and military industries,The development of high strength and long service life die steel is imminent.Compared with cold-worked die steel,hot-worked die steel is used in the harsh environment of high temperature,high pressure,rapid heating and quenching,which makes the influencing factors of its failure complex and changeable,and puts forward higher requirements on the performance of the material.In this thesis,the heat treatment and alloying elements of hot work die steel have important significance on its microstructure and thermal fatigue life.By studying the thermal fatigue damage of H13 steel and DIEVAR steels under different heat treatment processes and different cycles of thermal cycle tests,it is found that:The structure of H13 and DIEVAR steel quenched at 1030?and tempered at 520-580?is tempered martensite,and the structure tempered at 640?contains recovered or recrystallized ferrite and spherical cementite;In the tempering temperature range of520-640?,the hardness of H13 steel is higher than that of DIEVAR steel but the toughness is slightly lower than that of DIEVAR steel.The highest hardness value of H13 steel is54.1HRC;under different heat treatment processes,the thermal fatigue properties of DIEVAR steel are better than those of DIEVAR steel.H13 steel has the smallest thermal fatigue damage factor when tempered at 520?,and the worst thermal fatigue performance at 580?;The average par Ti(C,N)le size of carbides in H13 and DIEVAR steels both increased at 580?and the carbide par Ti(C,N)les were coarsened to the maximum,and the maximum par Ti(C,N)le size of H13 carbides was 0.75?m;The main carbides in H13 steel are a small amount of small spherical M₈C₇,cobblestone-shaped M₂C,nearly spherical M₂₃C₆ and more short rod-shaped M₇C₃,while DIEVAR steel is mainly small spherical M₈C₇and cobblestone-shaped M₂C;The structure of H13 steel after being quenched and tempered at 520?after 1000 times of 700?thermal fatigue is mainly lath martensite+acicular martensite+cementite+retained austenite.In the figure,the main structure formed at 580?is acicular martensite+cementite+retained austenite.The maximum width of lath martensite in the former is 3.82?m,and the maximum width of acicular martensite in the latter is 1.23?m.By exploring the thermal fatigue damage of two austeni Ti(C,N)heat-resistant steels(3Cr18Mn10Ni4 and 3Cr18Mn10Ni4Ti2.1B0.9 steels)under thermal cycle tests with different holding times,we found that:The Fe₃O₄peaks and Fe Cr₂O₃peaks in the X-ray diffraction pattern of 3Cr18Mn10Ni4Ti2.1B0.9 steel are significantly larger than those of3Cr18Mn10Ni4 steel,and 3Cr18Mn10Ni4Ti2.1B0.9 and 3Cr18Mn10Ni4 steels have an increase in the oxide layer with the increase of holding time in the thermal fatigue process,and 3Cr18Mn10 Ni4Ti2.1B0.9 steel oxide layer is greater than 3Cr18Mn10Ni4 steel.At room temperature,the elongation at break of 3Cr18Mn10Ni4Ti2.1B0.9 steel is 18.31%,and the elongation at break of 3Cr18Mn10Ni4 steel is 63.21%.3Cr18Mn10Ni4 and3Cr18Mn10Ni4Ti2.1B0.9 steel are ductile fracture.Through quantitative analysis of the surface and cross-section damage of the two steels,the total thermal fatigue damage factor was calculated.The thermal fatigue performance of 3Cr18Mn10Ni4Ti2.1B0.9 steel is better than that of 3Cr18Mn10Ni4 steel.3Cr18Mn10Ni4Ti2.1B0.9 steel contains Ti and B elements,and the generated Ti(C,N)and rod-shaped(Cr,Fe)₂B have a significant improvement in thermal fatigue performance.