Did they even go into SCRAM when nr.4 blew itself to bits?
Yes, the SCRAM (AZ-3 switch) actually blew it up. It was already out of control before, but unknown to the operators, the SCRAM in that situation increased the nuclear reaction rate for the first seconds at that low power level.
When the same happened during a SCRAM in 1977 at Leningrad, the reactor was operating already at a higher power level and the increase in reactivity was lower by higher coolant flow. Still it was noteworthy enough to write a report that the operators of Chernobyl never had the chance to see before the accident investigation.
The low power level of Chernobyl is important for understanding the accident - they had removed nearly all control rods, far below the safety limit of 20, to keep the reactor running at 200 MW despite strong Xenon poisoning.
Also, as workaround for some missing test conditions because of the accelerated preparation schedule, they reduced the inflow of coolant, which not only increased the coolant temperature and steam production, but also caused steam bubbles or voids in the lower core of the reactor, which, by design, increased reactivity since steam absorbs less neutrons as liquid water by volume.
Dyatlov documented this good in his own account of the accident, but he adamantly decided to not talk much about the circumstances that led to the steam voids in the lower reactor core.
The increased neutron production in the lower parts of the core quickly reduced the amount of Xenon poisoning there and made the power increase rapidly - large powerful steam bubbles formed in individual tubes, displaced water around them and caused water hammers, that made the 350 kg heavy concrete covers of the reactor tubes jump up and fall down again when the steam bubble collapsed. At this point, the reactor was already disintegrating and pressure tubes started to fail, deforming the graphite blocks around them and the neighboring control rod and instrumentation channels. Also power level increased rapidly and ran out of control, which made the operators decide to trigger a SCRAM of the reactor.
This meant, when they activated the SCRAM, many more graphite tips at the control rods acting as moderator entered the reactor at once (because they had been retracted), far more than considered safe by the engineers which designed those tips, and pushed a zone of very high reactivity downwards towards an already existing zone of high reactivity (by the steam voids).
Also, the control rods moved really slow because they had been lowered by gravity against the coolant flow (They just had been hanging on steel cables), having to displace water while moving the 7 m downwards. They fixed it in the 1990s for some reactors by putting special control rods into gas filled tubes that allowed to drop them in a much shorter time. This is also why the engineers tried to disconnect the clutches of the control rod drives when they stopped moving, they hoped they would fall by gravity into position, even if this means the reactor is damaged by the fall. They did not know and did not expect, that the control rods had been unable to move because the local steam bubbles are already forming deformed the core.
This all added up and caused a rapid, uncontrolled chain reaction and caused a massive steam explosion. Which lifted up the top cover of the reactor, opened the core and allowed the second larger and possibly nuclear explosion to happen. Its really easy to explain afterwards. Before, only very few people did know that a lower power level is more dangerous than a high power level for this reactor type.