0Cr18Ni9 stainless steel heat-resistant steel as the most widely used for food equipment, general chemical equipment, atomic energy with industrial equipment. Popular talk 0Cr18Ni9 stainless steel is 304 stainless steel, 0Cr18Ni9 stainless steel is 321, one is GB, one is American standard. 321 is not good because the original smelting technology can not only reduce the carbon content of research, and now due to increase smelting technology, ultra-low carbon steel smelting has been very common, so the 321 has a tendency to be eliminated. Currently, few production 321. Only some of the military is still in use. 0Cr18Ni9 steel (AISI304) austenitic stainless steel, is the basis of the evolution of the original invention 18-8 austenitic stainless steel on steel, the steel is a stainless steel body, with its output accounting for stainless steel production song 30% or more. 2 properties with good corrosion resistance, heat resistance, low temperature strength and mechanical properties, stamping bending and other thermal processing, and no heat hardening, non-magnetic. 3 uses household goods, cabinets, indoor pipes, water heaters, boilers, bathtubs, auto parts, medical equipment, building materials, chemical, food industry, agriculture, ship parts. 4 Chemical composition Carbon C: ≤0.07 Si Si: ≤1.00 Mn Mn: ≤2.00 sulfur S: ≤0.030 phosphorus P: ≤0.035 chromium Cr: 17.00 ~ 19.00 Ni Ni: 8.00 ~ 11.00 [2] 5 Mechanical Properties Tensile strength σb (MPa): ≥520 Conditions yield strength σ0.2 (MPa): ≥205 Elongation δ5 (%): ≥40 section shrinkage ψ (%): ≥60 Hardness: ≤187HBS; ≤90HRC; ≤200HV [3 ] 6 microstructure organization for the austenitic type. 7 Heat Treatment 1) solution treatment; The aim is to fully dissolve the carbides and retained austenite, thereby obtaining single-phase austenite at room temperature, at room temperature, the steel has the highest corrosion resistance. Heating the solution treatment temperature generally higher among 1050-1100C, the level of carbon content in accordance with appropriate adjustments. Due to poor thermal conductivity of 18-8 stainless steel, not only heated by preheating before quenching, and the holding time at the time of solution treatment (quenching) to be longer. When the solution treatment, pay special attention to prevent the increase of carbon. Will increase because of increased carbon steel 18-8 intergranular corrosion tendency. Cooling medium, generally use water. Tissue after solution treatment is generally single-phase austenite, but containing titanium, niobium, molybdenum, stainless steel, especially when the casting, also contain small amounts of ferrite. Hardness after solution treatment is generally about 135HBS. 2) stress-relief annealing; In order to eliminate the residual stress after cold working, the process proceeds at a lower temperature. Typically heated to 250-425C, often used is 300-350C. For steel containing no titanium or niobium should not exceed 450C, so as not to cause precipitation of chromium carbide and intergranular corrosion. In order to eliminate the residual stress after welding, eliminating susceptibility to stress corrosion of steel, the treatment is generally at a higher temperature. The heating temperature is not lower than 850C. Cooling method, for steel containing titanium or niobium can be cooled down in air; for steel not containing titanium or niobium should cooled to 500C and then cooled in air after. 3) stabilization treatment; after titanium and niobium in order to prevent the austenitic stainless steel welding or solution treatment, since the TiC and NbC reduced resistance to intergranular corrosion caused by reduced, this stainless steel needs to be heated to a certain temperature (the temperature to completely dissolve austenitic chromium carbide, TiC and NbC but only partially dissolved) followed by slow cooling. In the cooling process, the carbon in the steel is sufficiently compound with titanium and niobium, and the precipitated stable TiC NbC, without precipitation of chromium carbides, thereby eliminating inter-18-8 austenitic stainless steel corrosion tendency, this the process is called stabilization process.