An experimental investigation had been carried out for heating-only on samples of type 304 stainless steel with oxyacetylene gas flame set to neutral flame with temperature 2700°-3300°C. The flame effect on surface integrity was investigated in terms of hardness test and microstructural characterization. Substrates temperatures were raised to 355°C as well as 550°C while oxyacetylene flame travels at approximate of 74 mm/min along the span of the material. The experimental outcome revealed the microstructures from two examined conditions: Initial grain structures as well as grain structure when flame heated to 355°C has retained austenite crystal structure while flame heating to 5000-550°C revealed chromium carbide precipitates. Within the investigated temperature range of 500°-550°C, preheating was evidently proven to result to sensitization. © (2014) Trans Tech Publications, Switzerland.