When the tempering
time was increased to 30 min,the mechanical properties were
nearly homogeneous along the thickness,and the yield strength,
tensile strength,and elongation of 1/2 thickness sample were
770 MPa,875 MPa,and 25.0%,respectively, and 772 MPa,880 MPa,
and 27.5%,respectively,of 1/4 thickness.The reduction in area and
yield ratiowere 65.4% and 0.88 for 1/2 thickness,and 63.6%and
0.88 for 1/4 thickness samples.