seting parameter in simulink

[procionn]

Hi,
I want to use set_param funcion in a ´for´ loop , but value has to be set as a string instead of integer.
This just doesnt work

for k=0:50
set_param('transfer/Step','After',k);
end

I even tried this one, but it doesnt work as well

kstr={'0','1','2','3','4','5'};

for k=0:50
set_param('transfer/Step','After',kstr(k+1));
end

Any idea?