He replaces Newcastle Falcons full-back Tom Catterick, who has gone under the knife to rectify a shoulder injury sustained in last week's warm-up game against Loughborough Students. Buchanan, 19, appeared at prop for England U18s last season and won his first U20 cap as a hooker in the 41-14 Six Nations victory over Wales in February.
He was a try-scorer in the U19 England Academies 37-34 win over France U19 last month and has been training with England U20s at their pre-tournament camp.
U20s head coach, Mark Mapletoft, said: “Rob has experience across the front row and he's been doing really well in his time with us so far.”
England are No.2 seeds for the tournament after reaching the 2008 and 2009 finals in Wales and Japan respectively.
Their campaign starts against hosts Argentina in Rosario on June 5 and they face further pool games against Ireland (June 9) and France (June 13) before the knock-out stages on June 17 and 21.
