This paper summarizes the application of ferrosilicon nitride in steelmaking through the production research of a small domestic steel plant.
The steel plant produces HRB400 with the content of Nb and V. High prices due to the tight supply of FeNb and FeV cause the high producing cost of HRB400. The V content of HRV400 is obviously reduced after adding ferrosilicon nitride.
This article introduces the ferrosilicon nitride used in the production of HRB400.
The Technological Process and Composition Control of Ferrosilicon Nitride Addition
The technological process of HRB400 production with ferrosilicon nitride: The molten iron – Converter smelting – Deoxidation – Bottom blowing refining — Continuous casting – Rolling.
Ferrosilicon nitride is a compound with high-smelting-point. The production of HRB400 first requires that the ferrosilicon nitride can be fully dissolved in molten steel. Therefore the order of addition is very important for the HRB400 production. The order of alloy addition is as below.
- Silicon Carbide (SiC): 4.6-5.4kg/t, add before tapping.
- Ferro Silicon Nitride (Si3N4): 0.65kg/t, add before tapping.
- Silico Manganese (SiMn): 21-22kg/t, add during tapping.
- Carbon (C): add during tapping.
- Ferro Vanadium (FeV): 0.5-0.55kg/t, add FeV after the silicon manganese additional.
- Ferro Silicon Aluminum (SiAlFe): add according to the endpoint.
The chemical composition of ferrosilicon nitride and ferrovanadium that are used in the
production of HRB400.
Table1: Chemical composition of ferrosilicon nitride
|Chemical Composition (%)||Si3N4||Si||N||Fe||Al+Ca|
Table2: Composition control of HRB400
|Chemical composition||C||Mn||Si||P, S||N||V|
Add micro-alloying elements in HRB335 for the production of HRB400. The micro-alloying elements include V, Nb, Ti, etc.
Mechanism of Ferrosilicon Nitride Used in Production of Vanadium-containing HRB400
When V micro-alloying is used, HRB400 threaded steel bars with qualified and stable performance can be obtained by the conventional rolling process. V easily dissolves into steel, and also easily separates out micro-alloying from the steel. V combines with carbon elements in the steel to form VC, without the addition of ferrosilicon nitride, which exists on the matrix and grain boundaries. The VC has the effect of strengthening precipitation and inhibiting grain growth. During the rolling process, the vanadium compound granule occurred, which prevents the growth of austenite grains, on the one hand, prevents or delays the recrystallization of austenite.
After adding ferrosilicon nitride, the steel contains more N elements. The affinity of V to N is greater than the affinity of V to C, and the VN occurred. The higher the concentration of N in the molten steel, the more V (C, N) is separated out during the rolling process. Without added ferrosilicon nitride or ferrosilicon nitride is insufficient, 56% of vanadium dissolves in the steel. A large amount of micro-alloying elements in steel does not play a role in precipitation strengthening and inhibiting grain growth. Added ferrosilicon nitride, on the contrary, more than 70% of vanadium separate out to form V(C, N), and with the precipitation strengthening and inhibiting grain growth.
The N element in the steel reduces the size of V(C, N), increases the amount of the precipitated phase of V(C, N), and improves the strength of Vanadium-containing steel bars.
It can be seen from the figure that after adding ferrosilicon nitride, the N content in the steel increases, which significantly refines the crystal and increases the volume fraction of pearlite, thereby greatly improving the toughness of the steel bar.
Economic Benefits of Adding Ferro Silicon Nitride
Added a certain amount of ferrosilicon nitride can increase the amount of precipitated V(C, N). Therefore, added ferrosilicon nitride, under the condition of guaranteed performance, reduces the amount of vanadium and reduces the production cost.
Take the conventional rolling V-containing HRB400 for example.
Adding 0.65kg of ferrosilicon nitride to produce one ton of steel can save 0.65kg of ferrovanadium. The cost savings are
The price of ferrovanadium is USD30/kg. The price of Ferrosilicon nitride is USD1.5/kg.
Cost savings per ton of HRB400=0.65*30-0.65*1.5=18.525usd/t
A steel mill with an HRB capacity of 1 million tons can save annual alloy costs: 1,000,000*18.525=18525000usd.
- Ferrosilicon nitride combined with ferrovanadium to take place of ferrovanadium only to produce HRB400 is available.
- Ferrosilicon nitride combined with ferrovanadium used in the production of HRB400 can enhance the mechanical properties of the steel.
- Ferrosilicon nitride combined with ferrovanadium used in the production of HRB400 reduces the amount of ferrovanadium and reduces the production cost.