Both have already achieved the ‘A’ qualifying standard, but with the places of Dai Greene and Jack Green – absent from the championships in Helsinki – already cemented, whoever performs best in Friday’s final will earn selection.
Wales’s Williams fell in the British Trials last weekend.
On Thursday he won his semi-final in 49.63 from Adrien Clemenceau of France, while Woodward had a nervous wait after finishing fourth in a faster first semi in 49.68 – but qualified as the second of two fastest losers.
The GB athletics team is named on July 3.
Briton Meghan Beesley was last in her 400m hurdles semi-final.
Hattie Dean was only 1.42s away from making the women’s 3000m steeplechase final despite finishing last in her quick semi while Sally Peake was 25cm short of the required height in the pole vault.
Larry Achike, 37, failed in his bid to reach the final of the triple jump – Phillips Idowu is absent – while Italian favourite Daniel Greco also bowed out.
Eden Francis did not qualify in the women’s shot while Mark Dry also fell short in the men's hammer.
Ashley Bryant is 17th in the 19 remaining competitors in the decathlon with the javelin and 1500m to come.
At the conclusion of the evening session, Harry Aikines-Aryeetey will line up in the men’s 100m final. Some time before, fellow British hopes Steph Twell, Helen Clitheroe and Julia Bleasdale will go in the women’s 5000m final.
Mukhtar Mohammed and Gareth Warburton contest the men’s 800m semis while Richard Buck – reinstated on appeal despite running out of lane while winning his heat – takes part in the 400 semis.
There are also three Britons in the ladies’ 800 – Jemma Simpson, Jenny Meadows and Lynsey Sharp - while Lee McConnell goes in the 400m semi-finals.