DQ542MA Driver proper settings for NEMA 17 Stepper Motor
It is completely normal for a stepper motor to get hot. Taking this datasheet for example, specifies a 80 °C temperature rise. That is, in an room that is 25 °C ambient temperature, the motors would get up to 105 °C.

To prevent the motors from getting as hot you could further reduce the operating current, but likely the temperature they're running at is normal.