Method for direct use of chromite ore in the production of stainless steel

A method of producing stainless steel by smelting metal oxide insitu in a top-and bottom-blowing refining reactor, comprising the following stages:

• Stage 1--providing a carbon-containing iron/slag bath mixture in the reactor,
• the reactor including means for top-blowing of oxygen and means for bottom-stirring the iron bath, charging an oxygen-bound metal, a carbonaceous material and slagging agents into the reactor, passing oxygen gas through the blowing means,
• a portion of the oxygen gas being discharged above the iron bath to effect post-combustion of CO and H.sub.2 and the remainder of the oxygen gas being injected into the iron bath to effect decarburization of carbon in the iron bath to CO,
• injecting an oxygen-containing gas through the stirring means to effect decarburization in the iron bath and vigorous mixing of the iron bath, slag, and oxygen-bound metal thereby forming a chromium alloy bath,
• Stage 2--discontinuing passing the oxygen gas through the blowing means thereby ceasing post-combustion and decarburization, and reducing the carbon content of the alloy bath to its final carbon specification, and
• Stage 3--charging a metalloid reductant into the reactor and injecting a non-oxidizing gas through the stirring means to rinse the alloy bath until dynamic equilibrium is sustained and chromium yield is maximized.

A method of producing stainless steel by smelting metal oxide insitu in a refining reactor, comprising the steps of:

• providing an iron/slag bath mixture containing at least 0.5 wt. % C and having a temperature of at least 1500.degree. C. in the reactor,
• the reactor including means for top-blowing of oxygen and means for bottom-stirring the molten iron,
• charging chromite, a carbonaceous material and slagging agents into the iron bath,
• passing oxygen gas through the blowing means,
• a portion of the oxygen gas being discharged above the iron bath to effect post-combustion of CO and H.sub.2 wherein the post-combustion degree is less than 50% and injecting the remaining portion of the oxygen gas into the bath to effect decarburization in the iron bath to CO,
• injecting an oxygen-containing gas through the stirring means to effect decarburization in the iron bath and vigorous mixing of the iron bath, slag, and chromite to decarburize the bath thereby forming a chromium alloy bath containing no greater than 1.5 wt. % C, at least 2 wt. % Cr and having a temperature no greater than 1750.degree. C. at the end of post-combustion,
• discontinuing passing the oxygen gas through the blowing means thereby ceasing post-combustion and decarburization, and then decreasing the oxygen content of the stirring gas as the carbon content of alloy bath approaches its final carbon specification, and
• charging a metalloid reductant into the reactor and injecting a non-oxidizing gas through the stirring means to rinse the alloy bath until dynamic equilibrium is sustained and chromium yield is maximized.

A method of producing stainless steel by smelting metal oxide insitu in a refining reactor, comprising the steps of:

• providing an iron/slag bath mixture containing at least 0.5 wt. % C and having a temperature of at least 1500.degree. C. in the reactor,
• the reactor including a top lance and means for stirring the molten iron,
• charging a concentrate produced from a chromite ore, a solid carbonaceous reductant and slagging agents into the iron bath,
• the concentrate containing at least 25 wt. % Cr.sub.2 O.sub.3 and at least 7 wt. % FeO,
• the chromium oxide of the concentrate being at least 10% metallized and the iron oxide of the concentrate being at least 50% metallized,
• passing oxygen gas through the lance,
• the lance discharging a portion of the oxygen gas above the bath to effect post-combustion of CO and H.sub.2 wherein the post-combustion degree is less than 50% and the lance injecting the remaining portion of the oxygen gas into the bath to effect decarburization,
• injecting an oxygen-containing gas through the stirring means to effect decarburization in the iron bath and vigorous mixing of the iron bath, slag, and chromite concentrate to decarburize the bath thereby forming a chromium alloy bath containing 0.5-1.5 wt. % C, at least 5 wt. % Cr and having a temperature no greater than 1750.degree. C. after post-combustion,
• discontinuing passing the oxygen gas through the lance thereby ceasing post-combustion and decarburization via the lance, and then decreasing the oxygen content of the stirring gas as the carbon content of alloy bath approaches its final carbon specification,
• charging a metalloid reductant into the reactor and injecting a non-oxidizing gas through the stirring means to rinse the alloy bath until dynamic equilibrium is sustained wherein at least 50% of the chromium in the alloy bath is from the chromite concentrate.

A method of producing stainless steel by smelting metal oxide insitu in a refining reactor, comprising the steps of:

• providing an iron/slag bath mixture containing at least 0.5 wt. % C and having a temperature of at least 1500.degree. C. in the reactor,
• the reactor including a top lance and means for bottom-stirring the iron bath,
• charging an oxygen-bound metal, at least one of a solid carbonaceous or metalloid reductant and slagging agents into the iron bath,
• passing oxygen gas through the lance,
• the lance having a pair of gas passages,
• the lance discharging a portion of the oxygen gas through one of the passages above the bath to effect post-combustion of CO and H.sub.2 wherein the post-combustion degree is less than 30% and the lance injecting the remaining portion of the oxygen gas through the other of the passages into the bath to effect decarburization,
• injecting a gas through the stirring means to effect decarburization and vigorous mixing of the iron bath, slag, and oxygen-bound metal thereby forming a chromium alloy bath containing 0.5-1.5 wt. % C, at least 8 wt. % Cr and having a temperature no greater than 1750.degree. C. after post-combustion,
• the stirring gas being a mixture of oxygen and a non-oxidizing gas,
• the total specific flow of oxygen gas flowing through the lance and oxygen-containing gas flowing through the stirring means being 2 to 4 NM.sup.3 /min/MT,
• discontinuing passing the oxygen gas through the lance thereby ceasing post-combustion and decarburization via the lance, and then decreasing the oxygen content of the stirring gas as the carbon content of the alloy bath approaches its final carbon specification,
• the molar ratio of oxygen to non-oxidizing gas in the stirring gas being no greater than 4/1 during post-combustion,
• charging a metalloid reductant into the reactor, and
• injecting a non-oxidizing gas through the stirring means to rinse the alloy bath until dynamic equilibrium is sustained wherein the chromium yield of the oxygen-bound metal is at least 97% and at least 80% of the chromium in the alloy bath is from the chromite concentrate.