45钢电子束相变硬化中温度场与组织场的双向耦合分析.pdfVIP

Abstract 1.6 x 103 K/s. During the cooling process of hardening area, martensite transformation occurs only. The minimum cooling rate is 860 K/s. After the process of transformation hardening, the volume fraction isoline of martensite is a parabolic. The hardening area can be divided into three parts according to the degree of the austenite. The three parts are complete phase transformation hardening area, incomplete phase transformation hardening area and the matrix. During the hardening process, the closer to the center of the beam, the greater of the rate of temperature rise, the temperature on which the austenitic began to change is higher and it can be as high as 1085~1300 K which is shapely higher than the average isothermal transition temperature which is 1000 K. The highest temperature of hardening area temperature field will low 32 K when the latent heat is considered during the heating, while the figure will bigger than 13 K in the process of cooling. During the process of electron beam phase transformation hardening of 45 steel, 1123 K can be taken as the critical temperature (Ac1 line) to easily confirming the hardening shapes and sizes of the hardening area. Hardness distribution contour shows a trend of parabola as a whole on the transverse cross section . The maximum of the hardness is not in the center of the beam scanning, but it is on the boundary of complete phase transformation hardening area and not complete phase transformation hardening area. The hardness gradient on the hardening boundary is big. In the condition of solid state phase change, the width and the depth of the hardening area nonlinearly decrease with the increase of the scanning