Study About Effect Of Si Content On Structure And Properities Of Cold Work Die Steel Cr8Mo2SiV

Cr8-type cold die steel is widely used in and abroad because of high toughness and wear resistance.This kind of steel usually contains carbon 1%, chromium 8%, by adding Mo, V, Si and other alloying elements, their carbide small, evenly distributed,and toughness is much higher than Cr12 type steel, while the wear resistance is associated similar. Their hardness, flexural strength, fatigue strength and resistance to tempering stability are also higher than Cr12 mold steel, suitable for efficient, high-speed, high precision and automation of the direction of high-speed punching machine and multi-station press. Thus the research increasing the Cr8 steel is significative.Adjusting the chemical composition of steel and optimizing heat treatment process are the most effective ways to change the organization and structure of steel. In this paper, by optical microscopy, SEM, EDX, TEM, phase analysis, study the Si content (0.3-1.6mass%) and different heat treatment process on organization and mechanical properties of a new type cold-working die steel Cr8Mo2SiV. Thus determine suitable Si content with high wear resistance and high toughness, while optimizing its optimum heat treatment process. Which are Used to guide the actual production.In this paper, vacuum induction furnace smelting (25kg ingot)→annealing→forging useful person (Φ15)→steel annealing as experimental material, the main conclusions are as follows:(1)There are carbides M7C3, M23C6 and M6C primarily in the steel. Quenching heating, large numbers of carbides dissolution, carbides which do not melt exist at the austenite grain boundaries, preventing the austenite grain growth.(2) In the 1020-1040℃quenching and tempering at different temperatures, the three kinds of steel have a significant secondary hardening phenomenon; with the Si content increasing, the hardness of secondary hardening peak heightens.(3) In 1030℃quenching and tempering at different temperatures, with the Si content increased, the impact toughness increased by up to 25%; Flexural strength increased, especially when 520℃tempering, the flexural strength is about 500Mpa higher than 1#,2 # steel.(4) 1030℃quenching and 520℃tempering, with the Si content increased, the residual austenite content decreases.1030℃quenching, (-196℃) deep cryogenic treatment and tempering at different temperatures,1# steel secondary hardening peak disappears,2# steel, secondary hardening peak exists,3# steel, secondary hardening peak slightly increased, which indicate:with the Si content increased, secondary hardening mechanism of the three kinds of steel are the transformation of residual austenite→the transformation of residual austenite and carbide precipitation→carbide precipitation. After cryogenic treatment of the three kinds of steel, the impact toughness is lower than steel without the deep cryogenic treatment.