CN112011752B

CN112011752B - High-corrosion-resistance hot-formed steel part and manufacturing method thereof

Info

Publication number: CN112011752B
Application number: CN202010843220.6A
Authority: CN
Inventors: 李子涛; 计遥遥; 晋家春; 周世龙; 崔磊; 张军; 王伟峰; 刘东亚; 成昌晶
Original assignee: Maanshan Iron and Steel Co Ltd
Current assignee: Maanshan Iron and Steel Co Ltd
Priority date: 2020-08-20
Filing date: 2020-08-20
Publication date: 2022-06-21
Anticipated expiration: 2040-08-20
Also published as: CN112011752A

Abstract

The invention discloses a high-corrosion-resistance hot-formed steel part and a manufacturing method thereof, belonging to the technical field of metallurgy. The high-corrosion-resistance hot-formed steel part comprises a substrate and a plating layer, wherein the plating layer consists of a gamma-FeZn phase rich in zinc and an alpha-Fe (Zn) phase rich in Fe, and the volume percentage of the gamma-FeZn phase is 10-20%; the manufacturing method comprises the steps of cutting an alloyed galvanized hot-formed steel plate into blanks, transferring the blanks into a heating furnace to be heated to 880-900 ℃, preserving heat for 3-5 min, and then transferring the blanks into a hot-forming die to be subjected to hot forming, wherein the hot-forming temperature is as follows: more than or equal to 500 ℃; cooling rate: not less than 30 ℃/s. The hot formed coating has sacrificial anode protection effect on the steel matrix, and the corrosion rate is reduced.

Description

High-corrosion-resistance hot-formed steel part and manufacturing method thereof

Technical Field

The invention belongs to the technical field of metallurgy, and particularly relates to a high-corrosion-resistance hot-formed steel part and a manufacturing method thereof.

Background

In recent years, the requirements of laws and regulations of various countries around the world on the carbon emission of automobiles are more strict, and the light weight of the automobiles is one of effective ways for reducing energy consumption and carbon emission. In this process, high-strength parts such as hot forming are widely used in automobile body manufacturing, and the collision performance of the automobile body is ensured while the weight of the automobile body is reduced. Compared with the cold forming technology, the hot forming technology can avoid the rebound effect, fully ensure the precision of the part and simultaneously has high strength of the part. However, the steel sheet is heated during hot forming even if N is present₂Under the condition of atmosphere protection, an oxide layer still can be generated on the surface of the steel plate, and the hot forming part needs to be subjected to shot blasting or acid pickling treatment to ensure the subsequent coating quality. On the other hand, corrosion performance is one of important performance characteristics of automobile parts, and in recent years, corrosion of hot-formed steel parts as safety members deteriorates safety performance of vehicles, which is receiving more attention from consumers. Hot forming with coating layer on surface for above problemsThe shape steel plates were successively developed.

In the coating hot forming steel, the alloying galvanized hot forming steel can improve the melting point of a coating due to the diffusion of Fe into a Zn layer in the alloying process, reduce the risk of liquid induced cracking (LME), can be applied to direct hot forming, and has excellent corrosion resistance of a formed part.

It is well known that for coated products, it is desirable that the coating potential be low enough to provide sacrificial anodic protection to the steel substrate, while the coating can form corrosion products that can impede further corrosion from occurring. However, for galvanized hot formed steel, the situation is more complicated. It is known that increasing the heating time and temperature results in a decrease in the zinc content of the coating, an increase in the self-corrosion potential of the coating, and a decrease in the sacrificial anodic protection capability. However, the long-term corrosion weight loss is affected not only by the self-corrosion potential of the plating layer, but also by the thickening of the plating layer during heating and by the formation of corrosion products after the plating layer is corroded. However, these factors have conflicting beneficial effects, such as increased heating temperature or extended heating time leading to increased self-etching potential, which, although slowing the rate of corrosion of the coating, results in reduced sacrificial anodic protection and, at the same time, in increased thickness of the coating after hot forming, reduced corrosion inhibition by the corrosion products. Therefore, it is difficult to realize a galvanized hot formed steel that has a sacrificial anode protection effect and a low long-term corrosion rate (metal reduction rate) of the steel sheet.

For example, chinese patent application No. 201710294431.7, published as 2017, 9 and 1, discloses a niobium-titanium composite strengthened alloyed plated steel sheet for hot press forming and a method for manufacturing the same. The steel plate comprises the following chemical components in percentage by weight: c: 0.14 to 0.4%, Si: 0.1-0.4%, Mn: 0.8-2.0%, Cr: 0.1-0.8%, B: 0.002-0.01%, Ti: 0.01 to 0.1%, Nb: 0.01-0.05%, less than or equal to 0.08% of Al, less than or equal to 0.005% of N, and the balance of Fe and inevitable impurities; the plating layer comprises the following chemical components in percentage by weight: al: 0.1-0.2%, Fe: 5-14% of Zn and the balance of inevitable impurities. Hot pressing of the inventionThe niobium-titanium composite strengthening coated steel plate is characterized in that on the premise that the tensile strength after hot press forming is 1300-1500 MPa and the elongation after fracture is more than 5%, the coating is continuous and complete after high-temperature heating punch forming, and no crack is formed when the coating extends to a base body; two-phase structure gamma-Fe is formed in the alloy phase of the coating₄Zn₉(30Zn-70Fe) and alpha-Fe (Zn) (80Zn-20Fe), and the Zn content in the alloy phase is higher than 30 percent in whole. However, the solution of the patent does not reduce the long term corrosion rate of the hot formed parts. However, it is not recognized that the existence of a proper range of the proportion of gamma-FeZn and alpha-Fe (Zn) can play a role in reducing the long-term corrosion rate of the hot-formed parts, and a technical scheme for ensuring that the coating has a sacrificial anode and the long-term corrosion rate of the parts is reduced is not provided.

For another example, the applicant disclosed in 2018, 10/12, chinese patent with application number 201810472765.3 entitled plating solution for hot-forming steel sheet, hot-forming steel sheet and hot-forming part, the plating solution comprising the following chemical components in percentage by weight: al: 0.10-0.25%; mg: 0.01-0.20%; REM: 0.01-0.25%; the balance of zinc and inevitable impurities. The Zn-based coating of the hot-formed steel plate formed by the plating solution provided by the invention forms a layer of MgO and Al on the surface of the coating even under the condition of long-time heating at a high temperature of more than 900 ℃ in the hot-forming heating process₂O₃And GeO₂Or Y₂O₃The compact and continuous oxide layer can well prevent the volatilization and oxidation of zinc, and the Mg and rare earth elements added in the coating layer obviously improve the corrosion resistance of the hot-formed part. However, it is not described how to reduce the long-term corrosion rate of thermoformed parts while ensuring the sacrificial anodic effect.

For another example, a doctrine by kingdom, northeast university, 5/1 in 2014, discloses a research on the structure and performance of a coating of ultra-high strength hot-formed steel, which mainly studies the dip coating process of a coating of hot-formed steel, the structural change of the coating during heating, the rule of the influence of the heating process on the structure and performance of the coating, and the influence of hot forming on the performance of a coated hot-formed steel plate. Although it illustrates the problem of reduced Zn content in the coating that may lead to reduced sacrificial anode protection, it does not recognize that the presence of a suitable range of Γ -FeZn to α -fe (Zn) ratios may serve to reduce the long term corrosion rate of thermoformed parts.

In the scheme, the galvanized hot forming steel has no sacrificial anode protection effect, and the long-term corrosion rate (metal thinning rate) of the steel plate can be reduced.

Disclosure of Invention

1. Problems to be solved

In order to enhance the protection of a coating on a steel plate and reduce the long-term corrosion rate of the steel plate, the invention provides a high-corrosion-resistance hot forming steel part and a manufacturing method thereof.

2. Technical scheme

In order to solve the problems, the technical scheme adopted by the invention is as follows:

the high-corrosion-resistance hot-formed steel part comprises a base body and a plating layer, wherein the base body is a steel base body, the plating layer is composed of a gamma-FeZn phase rich in zinc and an alpha-Fe (Zn) phase rich in Fe, and the volume percentage of the gamma-FeZn phase is 10-20%. It should be noted that the coating structure here does not contain an oxide layer, which is loose and easily peeled off, and the parts also need to be removed for practical use in a vehicle body.

The manufacturing method of the high-corrosion-resistance hot forming steel part comprises the following steps:

(1) preparing an alloyed galvanized hot-formed steel plate: substrate → cleaning → hot dip coating process → alloying treatment → cooling → oiling; wherein the cleaning solution is an alkaline degreasing agent, and the oiling type is antirust oil RD550HN produced by Pakaxing.

(2) Preparing a hot forming steel part: cutting the alloyed galvanized hot-formed steel plate obtained in the step (1) into blanks, transferring the blanks to a heating furnace, heating to austenitizing temperature, namely heating to 880-900 ℃, preserving heat for 3-5 min, then transferring the blanks to a hot-forming die for hot forming, and cooling by introducing water, wherein the hot-forming temperature is as follows: more than or equal to 500 ℃; cooling rate: more than or equal to 30 ℃/s.

Further, the coating composition on the alloyed galvanized hot-formed steel sheet obtained in the step (1) is: the coating comprises 8-15 Wt% of Fe, 0.1-0.3 Wt% of Al, and the balance of Zn and inevitable impurities, wherein the thickness of the coating is 7-15 μm on one side.

Further, the substrate has a composition in weight percent as follows: c: 0.10-0.25, Si: 0.10-0.50, Mn: 0.50-1.80, P: less than or equal to 0.03, S: less than or equal to 0.03, Al: less than or equal to 0.10, Cr: 0.10-0.50, Mo: less than or equal to 0.03, B: 0.0004-0.01, N: not more than 0.01, Ti + Nb + V: 0.01-0.10, and the balance of Fe and inevitable impurities.

Further, in the hot dip coating process, the temperature of the plating solution entering the substrate is 440-490 ℃, the temperature of the hot dip coating solution is 440-480 ℃, and the hot dip coating time is 4-10 s. And after the hot dip coating process is finished, blowing by using an air knife to control the thickness of the coating.

Further, in the alloying treatment, the hot-dip coated strip steel enters an alloying furnace to be alloyed at the temperature of 480-520 ℃, the alloying treatment time is 3-10 s, and the alloying treatment mainly has the effect of preventing the liquid induced cracking phenomenon in hot forming.

Furthermore, the thickness of the alloying galvanized hot forming steel plate is t, wherein t is more than or equal to 1.2mm and less than 1.8 mm.

When t is more than or equal to 1.2mm and less than 1.4mm, the heating temperature is 880-890 ℃, the heating time is 3-4 min, and the thermoforming temperature is as follows: more than or equal to 500 ℃; cooling rate: not less than 30 ℃/s;

when t is more than or equal to 1.4mm and less than 1.6mm, the heating temperature is 890-895 ℃, the heating time is 4-5 min, and the thermoforming temperature is as follows: more than or equal to 500 ℃; cooling rate: not less than 30 ℃/s;

when t is more than or equal to 1.6mm and less than 1.8mm, the heating temperature is 895-900 ℃, the heating time is 4-5 min, and the thermoforming temperature is as follows: more than or equal to 500 ℃; cooling rate: not less than 30 ℃/s.

Further, when t is more than or equal to 1.2mm and less than 1.4mm, the heating temperature is 880 ℃, the heating time is 4min, and the thermoforming temperature is as follows: more than or equal to 500 ℃; cooling rate: not less than 30 ℃/s;

when t is more than or equal to 1.4mm and less than 1.6mm, the heating temperature is 890 ℃, the heating time is 4min, and the thermoforming temperature is as follows: more than or equal to 500 ℃; cooling rate: not less than 30 ℃/s;

when t is more than or equal to 1.6mm and less than 1.8mm, the heating temperature is 900 ℃, the heating time is 5min, and the thermoforming temperature is as follows: more than or equal to 500 ℃; cooling rate: not less than 30 ℃/s.

Furthermore, the hot forming die is heated by a box type furnace in a radiation heating or induction heating mode, and no reducing or inert gas protection is provided in the furnace.

3. Advantageous effects

Compared with the prior art, the invention has the beneficial effects that:

(1) according to the hot-formed steel part obtained by the invention, the coating has a sacrificial anode protection effect on a steel matrix, and meanwhile, the corrosion rate of the steel plate is reduced, because the coating contains a zinc-rich gamma-FeZn phase and a Fe-rich alpha-Fe (Zn) phase, the gamma-FeZn has the effect of enabling the overall electrochemical potential of the coating to be low enough to ensure the sacrificial anode protection effect, but the defect is that the coating is corroded quickly, so if the gamma-FeZn content is high, the sacrificial anode protection effect is strong, but the long-term corrosion rate of the part can be increased; the corrosion rate of alpha-Fe (Zn) is low, but the corrosion product has weaker effect on reducing the long-term corrosion rate compared with the corrosion product of the gamma-FeZn, and in addition, the thicker plating layer brought by the increase of the phase proportion of the alpha-Fe (Zn) in the plating layer has certain beneficial effect on reducing the long-term corrosion rate of the part, but the sacrificial anode has insufficient protection effect when the content of the alpha-Fe (Zn) is higher; the inventor finds a balance interval between the protection effect of the sacrificial anode and the long-term corrosion rate, strictly controls the phase proportion of the r-FeZn through the hot forming process, realizes the strong protection effect of the sacrificial anode on the plating layer, and simultaneously realizes the minimization of the long-term corrosion rate of the part; specifically, the volume percentage of the gamma-FeZn phase is 10-20%, less than 10% of the gamma-FeZn phase can cause insufficient protection effect of a sacrificial anode of a plating layer and increase long-term corrosion rate of a part, and more than 20% of the gamma-FeZn phase can cause too fast corrosion of the plating layer and increase long-term corrosion rate of the part;

(2) in the coating components on the alloyed galvanized hot-formed steel plate, Al is introduced during hot dipping and has the function of forming a restraining layer to improve the binding force between the coating and a substrate; fe is introduced into the coating by diffusion from the matrix Fe in the alloying step, and the main function of the Fe is to prevent the matrix cracking phenomenon (LME) caused by the infiltration of the zinc liquid along the austenite crystal boundary in the hot forming;

in addition, the thickness of the plating layer needs to be controlled to be 7-15 μm on one surface, the thickness of the plating layer below 7 μm can cause insufficient corrosion resistance, and the thickness of the plating layer above 15 μm can cause poor adhesion of the plating layer, thereby increasing the cost;

(4) different process parameters are designed according to the thickness of the steel plate, the strength after hot forming is ensured in order to ensure that the steel matrix is fully austenitized, and the plating layer structure requiring the volume ratio of the Gamma-FeZn phase can be achieved by adopting the process parameters corresponding to the thickness of the invention.

Drawings

FIG. 1 is a SEM photograph of a cross section of a hot formed coating of example 1;

FIG. 2 is a SEM photograph of a cross section of a hot formed coating of example 2;

FIG. 3 is a SEM photograph of a cross section of a hot formed coating of example 3;

FIG. 4 is a SEM photograph of a cross section of a hot formed coating of comparative example 1;

FIG. 5 is a SEM photograph of a cross section of a hot formed coating of comparative example 2;

FIG. 6 shows the cyclic corrosion process of JASO M610-1992;

FIG. 7 is a graph of corrosion potential and cyclic corrosion weight loss after thermoforming for each of the examples and comparative examples;

FIG. 8 is a plot of electrochemical polarization after thermoforming for each example and comparative example.

Detailed Description

The invention is further described with reference to specific examples.

In order to further illustrate the present invention, the present invention will be described in detail with reference to examples.

The compositions of the substrates of the examples and comparative examples are shown in table 1.

Table 1 shows the chemical compositions and weight percentages (wt%) of the substrates in each example and comparative example

The alloyed galvanized hot-formed steel sheets obtained in each example and each comparative example were obtained after the processes of substrate → cleaning (cleaning liquid is alkaline degreasing agent) → hot dip plating process → air knife purge for controlling the thickness of the plated layer → alloying treatment → cooling to room temperature → oiling (oiling type is rust preventive oil of model RD550HN produced by paka). Table 2 shows the parameters relevant to the hot dip plating process, and table 3 shows the parameters relevant to the alloying treatment.

TABLE 2 Hot Dip coating Process and alloying Process

And then hot forming the hot formed steel parts by hot forming process, wherein the parameters of the hot forming process are shown in table 3.

TABLE 3 thermoforming Process

The structure of the plated layer after thermal forming is shown in FIGS. 1-5 (α -Fe (Zn) is gray and r-FeZn is white in BSE mode of SEM) and Table 4. Compared with comparative examples 1 and 2, the plating layers of the examples 1 to 3 are composed of a gamma-FeZn phase rich in zinc and an alpha-Fe (Zn) phase rich in Fe, wherein the volume percentage of the gamma-FeZn phase is 10 to 20 percent. The diffusion of Fe to the plating layer is reduced due to the low heating temperature or short heating time, and the formation of a Zn-rich gamma-FeZn phase is facilitated; while higher heating temperatures and relatively long heating times will cause Fe to diffuse into the coating and will result in higher alpha-Fe (zn) content.

TABLE 4 coating layer structure

Performance test

The corrosion test of the hot-formed test piece (test piece specification 150 mm. about.75 mm) was carried out with reference to JASO M610-1992, test method for cyclic corrosion of automobile parts. The single cycle includes: salt spray for 2 hours, drying for 4 hours, wet heating for 2 hours, and carrying out 480h corrosion test in total according to the specific experimental process shown in FIG. 6. After the circulation experiment is finished, the rust removal is carried out according to the method in GB/T19746-2005, namely removal of corrosion products on corrosion samples of metals and alloys, and the components of the rust removal liquid are as follows: 500ml of hydrochloric acid, 500ml of distilled water and 3.5g of hexamethylenetetramine. And after rust removal, washing by using deionized water, blow-drying and weighing, and taking the weight loss average value of 3 flat plate samples in each group as the final weight loss result. Electrochemical testing: the corrosion potential of the samples was measured using a three-electrode system with SCE standard electrodes and electrolyte as 5% Wt NaCl solution. The corrosion potential and weight loss by cyclic corrosion after thermoforming of each example and comparative example are shown in table 5 and fig. 7, and fig. 8 is an electrochemical polarization curve after thermoforming of each example and comparative example.

As shown in FIG. 7, the electrochemical potentials of the examples are all lower than that of the substrate (-0.591V) by more than 0.25V, and the sacrificial anode protection effect is realized on the substrate. Compared with the comparative example 2, in the examples 1 to 3, the electrochemical potential is more than 0.25V lower than that of the substrate sample, and the corrosion weight loss is reduced by 29 to 39 percent. Compared with comparative example 1, the corrosion weight loss of examples 1-3 is reduced by 15% -27%.

TABLE 5 Corrosion potential and Corrosion weight loss after thermoforming

Number of	E/V	Weight loss/g
			Example 1	-0.843	7.2951
Example 2	-0.841	8.3314
			Example 3	-0.845	8.5190
Comparative example 1	-0.861	10.0121
			Comparative example 2	-0.734	12.0791

The above embodiments have been described in detail to illustrate the object and practice of the invention, it should be understood that the above embodiments are only specific embodiments of the invention, and the invention is not limited by the above embodiments, and various modifications, equivalent substitutions, improvements and the like within the spirit and principle of the invention or by using the technical concept and technical scheme of the invention are within the protection scope of the invention.

Claims

1. A high corrosion resistant hot formed steel part characterized in that: the coating comprises a substrate and a coating, wherein the coating consists of a gamma-FeZn phase rich in zinc and an alpha-Fe (Zn) phase rich in Fe, and the volume percentage of the gamma-FeZn phase is 10-20%.

2. A method for manufacturing a highly corrosion-resistant hot-formed steel part according to claim 1, characterized in that: the method comprises the following steps:

(1) preparing an alloyed galvanized hot-formed steel plate: substrate → cleaning → hot dip plating process → alloying treatment → cooling → oiling;

(2) preparing a hot forming steel part: cutting the alloyed galvanized hot-formed steel plate obtained in the step (1) into blanks, transferring the blanks into a heating furnace, heating to 880-900 ℃, preserving heat for 3-5 min, and then transferring the blanks into a hot-forming die for hot forming, wherein the hot-forming temperature is as follows: more than or equal to 500 ℃; cooling rate: not less than 30 ℃/s.

3. The method for manufacturing a highly corrosion-resistant hot-formed steel part according to claim 2, wherein: the coating on the alloyed galvanized hot-formed steel plate obtained in the step (1) comprises the following components: the coating comprises 8-15 Wt% of Fe, 0.1-0.3 Wt% of Al and the balance of Zn and inevitable impurities, wherein the thickness of the coating is 7-15 mu m on one side.

4. A method for manufacturing a highly corrosion-resistant hot-formed steel part according to claim 3, characterized in that: the substrate has a composition in weight percent as follows: c: 0.10-0.25, Si: 0.10-0.50, Mn: 0.50-1.80, P: less than or equal to 0.03, S: less than or equal to 0.03, Al: less than or equal to 0.10, Cr: 0.10-0.50, Mo: less than or equal to 0.03, B: 0.0004-0.01, N: less than or equal to 0.01, Ti + Nb + V: 0.01-0.10, and the balance of Fe and inevitable impurities.

5. A method for manufacturing a highly corrosion-resistant hot-formed steel part according to claim 3, characterized in that: in the hot dip coating process, the temperature of the plating solution entering the substrate is 440-490 ℃, the temperature of the hot dip coating solution is 440-480 ℃, and the hot dip coating time is 4-10 s.

6. A method for manufacturing a highly corrosion-resistant hot-formed steel part according to claim 3, characterized in that: in the alloying treatment, the hot-dipped strip steel enters an alloying furnace to be alloyed at the temperature of 480-520 ℃, and the alloying treatment time is 3-10 s.

7. A method for manufacturing a highly corrosion-resistant hot-formed steel part according to claim 3, characterized in that: the thickness of the alloying galvanized hot forming steel plate is t, wherein t is more than or equal to 1.2mm and less than 1.8 mm.

8. The method for manufacturing a highly corrosion-resistant hot-formed steel part according to claim 7, wherein:

when t is more than or equal to 1.4mm and less than 1.6mm, the heating temperature is 890-895 ℃, the heating time is 4-5 min, and the thermoforming temperature is as follows: more than or equal to 500 ℃; cooling rate: more than or equal to 30 ℃/s;

when t is more than or equal to 1.6mm and less than 1.8mm, the heating temperature is 895-900 ℃, the heating time is 4-5 min, and the hot forming temperature is as follows: more than or equal to 500 ℃; cooling rate: not less than 30 ℃/s.

9. The method for manufacturing a highly corrosion-resistant hot-formed steel part according to any one of claims 2 to 8, wherein: the hot forming die is heated by a box furnace in a radiation heating or induction heating mode.