The invention belongs to the field of
metal materials, and relates to non-quenched and tempered steel containing Ti and N and applied to an automobile engine
crankshaft. The non-quenched and temperedsteel comprises chemical components in percentage by
mass as follows: 0.44%-0.48% of C, 0.25%-0.45% of Si, 0.82%-0.92% of Mn, 0.12%-0.21% of Cr, 0.07%-0.10% of V, 0.02%-0.03% of Ti, 0.010%-0.020% of N, smaller than or equal to 0.025% of P, 0.040%-0.060% of S and the balance of Fe and normal impurities. The microscopic structure of a large rolled bar (with
diameter being 110 mm) containing the components is
pearlite+ferrite, and the structure of the large rolled bar is thinner and has good uniformity;
austenite grain size in the position of 1 / 2
radius of the large rolled bar can reach level 8.0, and core-surface grain size range can be as low as level 0.5. The
crankshaft is made of the large rolled bar as a
raw material through die
forging, and the microscopic structure of the
crankshaft ispearlite+
grain boundary ferrite+intragranular ferrite; yield strength in the position of 1 / 2
radius of a main journal of the crankshaft can reach 500 MPa or higher, tensile strength can reach 800 MPaor higher, and room-temperature
impact energy KU2 can reach 20 J or higher;
hardness of a cross section of an output end of the crankshaft is 240-260 HB, which is suitable for drilling operation, andmachining cost can be reduced. Therefore, requirements for structure uniformity of the large rolled bar and comprehensive mechanical properties of the crankshaft can be met.