Zr foil probe redefines molten steel purification and online monitoring

    In the iron and steel metallurgy industry, the deoxidation process has always been the lifeline that determines steel products. Since then, the industry has been accustomed to the final deoxidation by adding aluminum or silicon at the end of the ladle refining furnace (LF furnace) or vacuum degassing (RH) process, and then using the oxygen determination probe (that is, what we usually call "oxygen concentration probe" or "rapid sample cup") to detect the activity oxygen to judge whether the deoxidation is in place.

    However, there is a huge logical pain point: the oxygen deter-mination probe can only "find the problem" and cannot "solve the problem". When the test shows that the oxygen content exceeds the standard, the operator often can only refeed the aluminum wire or silicon calcium wire. This kind of "measurement-calculation -addition" reaction not only has the problems of time lag and erra-tic yield, but also because the supplementary alloy is very easy to introduce new inclusions, falling into the vicious circle of "deoxida-tion-inclusion-redeoxidation".

    Recently, with the breakthrough of special alloy material techno-logy, a new molten steel detection and treatment technology call-ed "self-reactive zirconium foil deoxidization probe" is quietly em-erging in the high-end special metallurgical circle. This technology combines "detection" and "treatment" into one, and uses the uniq-ue ultra-high temperature thermodynamic characteristics of zirco-nium (Zr) element to achieve "in-situ precise deoxidation" at the moment of sampling.

    Technological innovation: "four or two sets of kilograms" of one gram of zirconium foil

    Although the aluminum deoxidization has high efficiency and low cost, the Al ₂ O ㎡ inclusions are easy to accumulate and nozzle Even if later calcium treatment modified it to low melting point 12CaO · 7 Al ₂ O ₂, it was still difficult to completely remove it.

So, why choose zirconium?

    According to the reporter of "Metallurgy Today" learned from the relevant materials laboratory that zirconium (Zr), as a rare metal of the IVB group, has a strong deoxidization ability. At 1600 ℃, the affinity of zirconium to oxygen is even higher than that of aluminum. But what really makes the "zirconium foil probe" stand out is not just "taking off quickly", but "taking off skillfully".

1. The miracle of "diffusion" of products

    After the deoxidizer (such as aluminum) is added to molten steel, the oxidation formed is often large and unevenly distributed. The new probe technology makes pure zirconium into extremely thin foil as the core component of the steel sample probe. When the probe is immersed in molten steel, the zirconium foil melts rapidly and releases evenly.

    Studies have shown that the ZrO ₂ particles produced by zirconium deoxidation are extremely fine. The simulation experiments of Northeastern University confirmed that the size of this fine Zr-O inclusion can be controlled between 0.2 ~ 1μm, and it presents a very high dispersion distribution state under a high-power microscope. This means that zirconium deoxidation not only removes oxygen, but also provides a heterogeneous nucleation core for subsequent grain refinement of steel by forming extremely fine oxide particles.

2. "Adsorption" rather than "reaction"

    Another uniqueness of zirconium is its morphological control of sulfides. During the solidification process of molten steel, MnS (manganese sulfide) is very easy to precipitate with these disper-sed ZrO ₂ as the core, forming ZrO ₂ · MnS composite inclusions. This structure not only avoids the formation of deleterious long strips of MnS, but also induces the formation of a large number of acicular ferrites due to the "manganese-poor region" formed on its surface.

    A technical director from a Nordic special steel plant commen-ted: "This is not a simple deoxidation, this is using the logic of" additives' to do "refining '. The layer of zirconium foil in the probe is actually for The final tissue of the steel is 'vaccinated'."

Application scenarios: from "Be wiser after the event" to "Be wiser before the event"

    In the independent station industry news, we often see static reports on steel performance, and the emergence of zirconium foil probes is subverting the on-site control logic of dynamic smelting.

Scenario 1: Solving the "dead zone" deoxidation of high alloy steel

    For stainless steel or heat-resistant steel with high chromium and nickel content, aluminum deoxidization is easy to fail due to the change of aluminum activity coefficient. The chemical affinity of zirconium to oxygen in molten steel is less disturbed by other alloy elements. At the moment of immersion of the probe, an extremely low oxygen partial pressure is formed in the local area of the molten steel surface, which effectively solves the deoxidation problem of high-alloy steel.

Scenario 2: End the "nozzle nodulation"

    For thin wire rods, cold heading steel and other steel grades that require extremely high purity, the nozzle nozzle nodulation caused by Al ₂ O ㎡ is a persistent problem in the industry. The melting point of the zirconium deoxidization product ZrO ₂ is extremely high (about 2700 °C), and the trend of being in a "liquid" or "semi-melted" state in molten steel is much lower than that of Al ₂ O ₂, and it is not easy to adhere to the nozzle wall, thus significantly prolonging the continuous casting furnace times.

Industry Perspective: Dialectical Unity of Economic Account and Performance Account

    Although the price of zirconium is much higher than that of aluminum and ferrosilicon, why is the industry willing to try this "expensive" probe in today's increasingly meager profits in high-end manufacturing?

The answer lies in "comprehensive cost".

    The process chain of "silk feeding + calcium treatment" is long, and the calcium recovery rate is extremely unstable. The zirconium foil probe actually adds the amount of deoxidizer accurately to "grams". Because the probe acts directly on the limited molten steel area, the excessive addition caused by the addition of alloys to the steel in the whole furnace is avoided.

    More importantly, by using zirconium treatment, the fatigue strength of the steel (especially the high cycle fatigue zone of the S-N curve) is significantly improved. For auto parts, wind power fasteners and high-speed rail spring steel manufacturers, this means higher product premiums and safety premiums.