Thermal analysis after laser cutting

Dear All member,

I'm analysis thermal of part with 6061 Alloy material.

This part have cutting by laser source with temperature of laser is 3000 °C.

During laser cutting, the part is cooled with nitrogen gas with Convection Coefficie : 500W/m^2.K.

when I analyze the thermal problem with Transient option, heat source setting is 3000 , Convection Coefficien: 500W/m^2.K, analysis time is 266s.

The result obtained in shape1 has negative temperature in temperature result graph. Why is this happening, how to fix this error.

I have attach Description of the analysis problem and image setup, result of study.

Can anyone help me explain why i am getting this error and how to fix it.

Thanks!

Convection