The phrase "a challenging step" is correct and usable in written English.
You can use it when referring to a difficult or demanding action or decision that needs to be taken in a process or journey.
Example: "Starting a new business can be a challenging step, but it often leads to great rewards."
Alternatives: "a difficult step" or "a tough step".
Ihab Balh admitted that building the project had been a "challenging step", but that his work with these imams over the past decade had laid the groundwork to bring them into Amen and made it seem "more acceptable".
Puncture of the renal collecting system represents a challenging step in percutaneous nephrolithotomy (PCNL).
Functional genomic analysis is a challenging step in the so-called post-genomic field.
Well placement within a reservoir is a challenging step in the reservoir development process.
Drug target interaction (DTI) prediction is a challenging step in further drug repositioning, drug discovery and drug design.
A challenging step in this research field is to couple the cathodic process to that of the water oxidation reaction.
A particularly challenging step in modelling the latex bead phagosome system was to select a qualitatively correct set of equations that accurately represent the processes occurring in the system.
Calibrating watershed-scale hydrologic models remains a critical but challenging step in the modeling process.
Data-driven prediction of the system components and their component interplays that are responsible for the target system's phenotype is a key and challenging step in this endeavor.
Hypertension management at commune level was an important but challenging step in moving essential cardiac care services into primary health care sectors in Vietnam.
Knowledge about the etiological agent of pneumonia related critical illness is an important but challenging step in the management of pneumonia in such mass gatherings [ 9- 11].
