Cast-iron driving wheel centers became standard after their introduction in 1834. Because these tend to fracture after being subjected to numerous impacts (such as when the part of the wheel opposite the counterbalance strikes the rail), they were supplanted by wrought-iron wheel centers in about 1850. Cast-steel wheels were introduced with the great steel-making technology advances of the 1870s and—except for specific railroads and/or locomotives—were used until the end of steam power.