Factors Affecting the Mechanical Properties of Ultra-high-strength Bainitic Steel Containing W and 0.33 mass% C

A novel ultra-high-strength bainitic steel was designed. The analysis of its mechanical properties by quasistatic testing showed that upper bainitic steel exhibited an ultimate tensile strength of 2260 MPa (engineering stress) and an ultimate compressive strength of more than 2700 MPa (true stress). The ultra-high strength of upper bainitic steel was mainly attributed to untempered martensite and upper bainite with a feather-like microstructure. Moreover, lower bainitic steel demonstrated an ultimate tensile strength of 1922 MPa (engineering stress) and an ultimate compressive strength of 2500 MPa (true stress). The ultra-high strength of lower bainitic steel was primarily due to untempered martensite and lower bainite with an acicular microstructure. The untempered martensite in the two kinds of bainitic steels was produced in different ways. The dynamic test results showed that the ultimate compressive strengths of the two bainitic steels were maintained at 1600 MPa (true stress) under high strain rates (1100 and 2200 s−1) at 600 °C, because of the added tungsten, confirming the satisfactory hot hardness property of the steel. Furthermore, lower bainitic steel showed better comprehensive mechanical properties than upper bainitic steel.