Experimental Study on Primary Scale Formation and Descalability on Steels Containing Ni and Ni+Si

Abstract

Nickel and silicon are attractive alloying elements for high-strength low-alloyed (HSLA) steel production. However, it is well known that the presence of Ni and Si in the steel can impair the surface quality, making it unsuitable for certain markets. The combined effects of Ni+Si on the oxide scale formation are still relatively unknown. Literature is dealing mostly with steels containing combinations of Ni and Si, with either traces of nickel (0.1%) or very high (8-16%) nickel levels. At Tata Steel we explored the effect of an optimum composition selected to achieve steel properties (0.15%Si and 1%Ni) on the formation of oxide in the reheating furnace and its descalability. Pilot hydraulic descaling trials were performed on blocks of three steel grades, applying reheating and hydraulic descaling in conditions closely resembling the industrial practice.The oxidation experiments show that synergistic effects occurring during the oxidation of alloys containing Ni (1.1%) are already obvious at relatively low levels of Si of 0.05%. This effect is even enhanced at higher Si levels of 0.15% and consists of increasing the adherence of oxide scale to the steel substrate by forming an entangled layer with oxidic pegs.In order to maximize descalability of (Ni,Si)-alloyed steels slabs, the metal/scale entanglement has to be minimised. In this respect, it was found that the slab surface temperature is the most important parameter. A gentle, smooth reheating process is required in which slab surface temperatures exceeding 1 300°C should be avoided.

The Effect of Boron and Titanium Microalloying on the Scale Formation of AISI 304 Austenitic Stainless Steel in Simulated Walking Beam Furnace Conditions

“…The largest differences were found between the inner oxidation zone metallic area compositions of the low to medium boron additions and the high boron addition. Based on previous study regarding scale entanglement with the metal substrate, it was observed that the presence of metal‐free fracture paths throughout the scale layer is favorable to descaling and the presence of oxide “pegs” protruding into the metal substrate at the scale‐metal substrate interface is detrimental to descaling, especially in alloys containing Ni and Si . Based on these results, the more metal‐free zones there are in the inner and intermediate oxidation zones, the easier it is to remove the scale layer.…”

“…Based on previous study regarding scale entanglement with the metal substrate, it was observed that the presence of metal-free fracture paths throughout the scale layer is favorable to descaling [13] and the presence of oxide "pegs" protruding into the metal substrate at the scale-metal substrate interface is detrimental to descaling, especially in alloys containing Ni and Si. [13][14][15] Based on these results, the more metal-free zones there are in the inner and intermediate oxidation zones, the easier it is to remove the Table 3. 1300 8C analysis point compositions of samples 1511L and 1513L in wt%, analysis point origins are denoted in Figure 6.…”

Time Change in Scale Microstructure of Fe-5 mass%Ni Alloy at 1200°C

“…However, removing an oxide scale formed during hot-rolling process on the Ni containing steel by high-pressure hydraulic descaling is known to be difficult. [1][2][3][4] Asai et al 3) evaluated the removability of scale in Ni containing steel. They reported that the scale becomes difficult to be removed if Ni concentration in the steel is as little as 0.05 mass%.…”

Crystallographic Texture Based Analysis of Fe₃O₄/<i>α</i>-Fe₂O₃ Scale Formed on a Hot-rolled Microalloyed Steel

“…2,3) Correspondingly, wustite (Fe1-xO, with 1-x ranging from 0.83 to 0.95) dominates at high temperatures (normally > 650°C for steels), whereas Fe3O4 prevails at low temperatures, and hematite (Fe2O3) remains low in either case. [17][18][19] The proportion of the three phases within oxide scale at high-temperature oxidation depends greatly on the equilibrium transformation of Fe1-xO or Fe3O4 precipitation which is related to heat treatment, atmospheric conditions and alloying elements in the steel.…”

“…[1][2][3][4] Specifically, oxide scale formed in hot strip rolling has posed a serious obstacle, and thereby causes the surface quality of final products to deteriorate. [5][6][7][8] In most cases, many different surface properties of metals and alloys can dominate surface characteristics of two solids in contact and thereby influence tribological performance.…”