A method for reducing the adhesion of iron oxide scale from a steel containing ni

Abstract

The application discloses a method for reducing the adhesion of iron oxide scale of a Ni-containing steel, wherein the Ni-containing steel billet is heated and then dephosphorized; the heating process comprises the following steps: 1) the loading temperature of the steel is 600 DEG C; when the thickness h of the iron oxide scale is less than or equal to 2 mm, the heating speed is less than or equal to 100 DEG C / h at 950 DEG C or below; when the thickness h of the iron oxide scale is greater than 2 mm, the heating speed is less than or equal to 120 DEG C / h at 950 DEG C or below; 2) when the thickness h of the iron oxide scale is less than or equal to 4 mm, the billet is heated to 950 DEG C and kept for 2 hours; when the thickness h of the iron oxide scale is greater than 4 mm, the billet is heated to 950 DEG C and kept for 1.5 hours; 3) the billet is heated to 1220-1230 DEG C and kept for 3-4 hours; 4) the billet is heated to the soaking temperature of 1240-1250 DEG C, and the soaking time is calculated according to 8-9 min / cm billet thickness. The method can weaken the adhesion of the iron oxide scale by controlling the heating temperature, the heating time and the heating speed, so that the iron oxide scale can be completely peeled off during high-pressure water descaling, and the surface quality of the rolled material can be ensured to meet the requirements.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of continuous casting and rolling, in particular to a method for reducing the adhesion of iron oxide scale of Ni-containing steel. BACKGROUND

[0002] Iron oxide scale is generated due to chemical reactions occurring with air contact. During the heating process, various elements are oxidized on the surface of steel, and if not treated with foreign agents or pretreatment agents, the oxides will adhere to the metal surface to form iron oxide scale. In recent years, there are few methods for reducing the adhesion of iron oxide scale of Ni-containing steel; Patent Application No. CN105803173A provides a production method for removing the surface scale of Ni-containing steel to enable the steel plate after rolling to meet the flaw detection requirements, which includes a heating process, a rolling process and a tempering process, and the heating process uses a soaking furnace and a continuous furnace for heating. Patent No. CN103602925A proposes a method for heating and removing iron oxide scale of Ni-containing steel, which uses a pusher-type or walking beam-type heating furnace to control the temperature of each section, effectively solves the problems of excessive iron oxide scale of Ni-containing steel billets, high adhesion, and difficulty in removing with high-pressure water, etc., thereby ensuring the surface quality of finished steel plates. The above methods mostly heat and hold in a general temperature range, and cannot perform more accurate dynamic control. SUMMARY

[0003] The technical problem to be solved by the present application is to provide a method for reducing the adhesion of iron oxide scale of Ni-containing steel, which can completely strip the iron oxide scale.

[0004] To solve the above technical problems, the technical solution adopted by the present application is that the Ni-containing steel billet is heated after dephosphorization; the heating process is as follows: 1) the steel loading temperature is 600℃; when the thickness h of the iron oxide scale is ≤2mm, the heating rate is ≤100℃ / h at 950℃ and below; when the thickness h of the iron oxide scale is >2mm, the heating rate is ≤120℃ / h at 950℃ and below;

[0005] 2) when the thickness h of the iron oxide scale is ≤4mm, the billet is heated to 950℃ and held for 2 hours; when the thickness h of the iron oxide scale is >4mm, the billet is heated to 950℃ and held for 1.5 hours;

[0006] 3) the billet is heated to 1220-1230℃ and held for 3-4 hours;

[0007] 4) the billet is heated to the soaking temperature of 1240-1250℃, and the soaking time is calculated according to 8-9min / cm billet thickness.

[0008] Further, a digitalized regenerative step heating furnace is used for heating.

[0009] Further, the Ni content of the Ni-containing steel is 1.1-1.4%.

[0010] The beneficial effects produced by the above technical solution are that the present application weakens the adhesion of the oxide scale by controlling the heating temperature, heating time and heating rate, so that the oxide scale can be completely peeled off during high-pressure water descaling, thereby ensuring the surface quality of the rolled material to meet the requirements. BRIEF DESCRIPTION OF DRAWINGS

[0011] The present application will be further described in detail below in combination with the drawings and specific embodiments.

[0012] Figure 1 is the phosphorus removal effect diagram of the conventional process;

[0013] Figure 2 is the phosphorus removal effect diagram of the present process. DETAILED DESCRIPTION

[0014] One of the significant features of the Ni-containing steel is that at high temperature, Ni reacts with S in the furnace gas to form a lower melting point NiS network structure, which melts and destroys the protective film formed at a lower temperature, thereby accelerating the diffusion of oxygen in the steel, intensifying oxidation and increasing the adhesion of the oxide scale. Ni is a difficult-to-oxidize alloy element, and during the oxidation of the steel, due to the preferential oxidation of Fe, Ni enrichment occurs in the inner layer of the oxide scale, forming Ni-rich metal particles and network filaments. This Ni-rich metal network filament tightly connects the oxide scale and the metal matrix, preventing the peeling of the oxide scale, and the effect of Ni is intensified with the increase of the heating temperature and the extension of the heating time. After heating, the oxide scale of the nickel-based steel has high viscosity, making it difficult to remove, and during rolling, it is pressed into the surface of the steel, resulting in uneven surface quality, concave-convex phenomenon, and even surface cracks of the steel, affecting the use of the user. Therefore, to minimize the adhesion of the oxide scale of the Ni-containing steel, a suitable heating process must be selected. In the preheating stage and the early stage of the heating stage, the temperature is low, the network filament of the Ni-rich phase just appears, the oxidation along the grain boundary is not serious, and the eutectic of fayalite has not yet been produced. In the late heating stage and the soaking stage, the eutectic and the Ni-rich metal particles and network filaments are produced, so a relatively low temperature should be controlled in the late heating stage and the soaking stage, and the heating time should not be too long, so that the eutectic and the Ni-rich metal particles and network filaments are relatively less, and thus the adhesion of the oxide scale is relatively weak. At the same time, the furnace pressure should be controlled to be stable, the atmosphere in the furnace should be kept reducing, and after the billet is discharged from the furnace, it is contacted with cold air, and the surface temperature is generally below 1200℃. When high-pressure water descaling is performed, the oxide scale can be completely peeled off, thereby ensuring the surface quality of the rolled material to meet the requirements.

[0015] The steel used in the method for reducing the adhesion of the oxide scale of the Ni-containing steel has the following composition (wt): C 0.3-0.4%, Si 0.2-0.3%, Mn 0.7-0.8%, P 0.01-0.015%, S 0.005-0.006%, Ni 1.1-1.4%, Cr 0.75-0.8%, Mo 0.17-0.19%, and the balance of Fe and inevitable impurities.

[0016] The process design of the method for reducing the adhesion of the oxide scale of the Ni-containing steel is as follows: (1) the route of large bar wire production is selected in the process design, because the large bar wire heating adopts the most advanced digitalized regenerative step-by-step heating furnace in the world, and because the heating is divided into more zones, the heating temperature of each zone can be accurately controlled. Specifically, it is divided into: preheating section, early heating section, late heating section and soaking section.

[0017] (2) The effect of heating temperature and time on the formation of the oxide scale Since the oxidation rate depends on diffusion and atomic movement, it increases with the increase of the temperature index. The relationship between the temperature of the steel and the oxidation rate is given by the Arrhenius equation, see formula (I) below:

[0018] (I);

[0019] In the formula, h is the thickness of the oxide scale, mm; Q is the activation energy, J; T is the heating temperature, K; and R is the gas constant.

[0020] However, since it is a diffusion-controlled process, its relationship with time can be described by a parabola, and the relationship between the thickness of the oxide scale and the heating time is shown in formula (II):

[0021] (II);

[0022] In the formula, t is the heating time, h.

[0023] As the thickness of the oxide scale increases, the diffusion distance becomes longer, and therefore the oxidation rate decreases.

[0024] (3) The oxidation at different temperatures, the oxide scale peeling rate is compared when high-pressure water descaling, so as to determine the best heating temperature and heating time.

[0025] (4) The heating process parameters obtained from the above process are as follows: 1) the steel charging temperature is 600°C when heated in the soaking furnace; the temperature rising speed is reduced, and when the thickness h of the oxide scale is ≤2 mm, the temperature rising speed is ≤100°C / h at 950°C and below, preferably 95°C≤temperature rising speed≤100°C / h; the Arrhenius model is used as an auxiliary tool, and when the thickness h of the oxide scale is >2 mm, the temperature rising speed is ≤120°C / h at 950°C and below, preferably 105°C≤temperature rising speed≤120°C / h; the generation of eutectic and Ni-rich metal particles and mesh wires is controlled, and the phenomenon of direct contact of the flame with the surface of the ingot is reduced or avoided.

[0026] The cast blank continues to be heated; when the thickness h of the oxide scale is ≤4 mm, the cast blank is heated to 950°C for 2 hours; and when the thickness h of the oxide scale is >4 mm, the cast blank is heated to 950°C for 1.5 hours, so as to reduce the temperature difference of the ingot cross section, prevent the generation of cracks, and reduce the generation and melting of NiS.

[0027] The cast blank continues to be heated; the cast blank is heated to 1220-1230°C for 3-4 hours, so as to reduce the formation of (FeO)2·SiO2 eutectic low-melting substance and the melting speed of NiS, shorten the soaking time during heating, and reduce the melting of (FeO)2·SiO2 eutectic low-melting substance and NiS.

[0028] The cast blank continues to be heated to the soaking temperature of 1240-1250°C, and the soaking time is calculated according to 8-9 min / cm of the thickness of the cast blank, so as to ensure the peeling rate of the oxide scale during high-pressure water descaling.

[0029] Example 1: The method for reducing the adhesion of the oxide scale of the Ni-containing steel is specifically as follows.

[0030] The steel charging temperature is 600°C when heated in the soaking furnace; the thickness h of the oxide scale is 1.8 mm, and the temperature rising speed is 100°C / h at 950°C and below; the soaking time is 2 hours at 950°C; the soaking time is 3.5 hours at 1220°C; and the soaking time at the soaking temperature of 1240°C is calculated according to 8.5 min / cm of the thickness of the cast blank. The cast blank after the above heating process is subjected to high-pressure water descaling; Figure 1 is a phosphorus removal effect diagram of a conventional process, Figure 2 is a phosphorus removal effect diagram of the present embodiment, which is Figure 1 , Figure 2 It can be seen that the present method effectively improves the phosphorus removal effect.

[0031] Example 2: The method for reducing the adhesion of the oxide scale of the Ni-containing steel is specifically as follows.

[0032] The steel is heated in a soaking furnace at a temperature of 600°C; the thickness of the oxide scale h = 2.0 mm, the temperature rising speed at 950°C and below is 95°C / h; the temperature is kept at 950°C for 2 hours; the temperature is kept at 1220°C for 3 hours, and the soaking time at the soaking temperature of 1240°C is calculated as 8.5 min / cm thickness of the billet. Compared with the conventional process, the phosphorus removal effect is effectively improved in this embodiment.

[0033] Embodiment 3: The method for reducing the adhesion of the oxide scale of the Ni-containing steel is specifically as follows.

[0034] The steel is heated in a soaking furnace at a temperature of 600°C; the thickness of the oxide scale h = 1.5 mm, the temperature rising speed at 950°C and below is 98°C / h; the temperature is kept at 950°C for 2 hours; the temperature is kept at 1225°C for 4 hours, and the soaking time at the soaking temperature of 1250°C is calculated as 8 min / cm thickness of the billet. Compared with the conventional process, the phosphorus removal effect is effectively improved in this embodiment.

[0035] Embodiment 4: The method for reducing the adhesion of the oxide scale of the Ni-containing steel is specifically as follows.

[0036] The steel is heated in a soaking furnace at a temperature of 600°C; the thickness of the oxide scale h = 2.2 mm, the temperature rising speed at 950°C and below is 120°C / h; the temperature is kept at 950°C for 2 hours; the temperature is kept at 1220°C for 4 hours, and the soaking time at the soaking temperature of 1240°C is calculated as 9 min / cm thickness of the billet. Compared with the conventional process, the phosphorus removal effect is effectively improved in this embodiment.

[0037] Embodiment 5: The method for reducing the adhesion of the oxide scale of the Ni-containing steel is specifically as follows.

[0038] The steel is heated in a soaking furnace at a temperature of 600°C; the thickness of the oxide scale h = 3 mm, the temperature rising speed at 950°C and below is 105°C / h; the temperature is kept at 950°C for 2 hours; the temperature is kept at 1230°C for 3.5 hours, and the soaking time at the soaking temperature of 1250°C is calculated as 8.5 min / cm thickness of the billet. Compared with the conventional process, the phosphorus removal effect is effectively improved in this embodiment.

[0039] Embodiment 6: The method for reducing the adhesion of the oxide scale of the Ni-containing steel is specifically as follows.

[0040] The steel is heated in a soaking furnace at a temperature of 600°C; the thickness of the oxide scale h = 4 mm, the temperature rising speed at 950°C and below is 115°C / h; the temperature is kept at 950°C for 2 hours; the temperature is kept at 1225°C for 3 hours, and the soaking time at the soaking temperature of 1245°C is calculated as 8 min / cm thickness of the billet. Compared with the conventional process, the phosphorus removal effect is effectively improved in this embodiment.

[0041] Embodiment 7: The method for reducing the adhesion of the oxide scale of the Ni-containing steel is specifically as follows.

[0042] The steel is heated to 600°C in a soaking furnace; the thickness of the iron scale h = 4.1 mm, the temperature rising speed at 950°C and below is 110°C / h; the temperature is kept at 950°C for 1.5 hours; the temperature is kept at 1220°C for 3.5 hours, and the soaking time at the soaking temperature 1240°C is calculated according to 8.5 min / cm thickness of the billet. Compared with the conventional process, the phosphorus removal effect is effectively improved in this embodiment.

Claims

1. A method of reducing the adhesion of iron oxide scale from a Ni-containing steel, characterized by: The Ni-containing steel billet is heated and then dephosphorized; the heating process is as follows: 1) the loading temperature is 600℃; when the thickness h of the iron oxide scale is ≤2mm, the heating rate at 950℃ and below is ≤100℃ / h; when the thickness h of the iron oxide scale is >2mm, the heating rate at 950℃ and below is ≤120℃ / h; the Ni content of the Ni-containing steel is 1.1-1.4%; 2) when the thickness h of the iron oxide scale is ≤4mm, the billet is heated to 950℃ and kept for 2 hours; when the thickness h of the iron oxide scale is >4mm, the billet is heated to 950℃ and kept for 1.5 hours; 3) the billet is heated to 1220-1230℃ and kept for 3-4 hours; 4) the billet is heated to the soaking temperature of 1240-1250℃, and the soaking time is calculated according to 8-9min / cm billet thickness.

2. A method of reducing scale adhesion of a steel containing Ni according to claim 1, characterized in that: The digital regenerative step-heating furnace is used for heating.

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